Keysight Technologies LTE-Advanced: Technology and Test Challenges

Transcription

1 Keysight Technologies LTE-Advanced: Technology and Test Challenges 3GPP Releases 10, 11, 12 and Beyond Application Note

2 Introduction LTE-Advanced is the evolved version of the Long Term Evolution (LTE) standard developed by 3GPP to meet or exceed the requirements of the International Telecommunication Union (ITU) for a true fourth generation (4G) radio communication standard known as IMT-Advanced. LTE-Advanced is defined in 3GPP Release 10 and in subsequent 3GPP releases. The LTE-Advanced specifications are focused mainly on achieving higher capacity with increased peak data rates, higher spectral efficiency, ability to handle a greater number of simultaneously active subscribers, and improved performance at cell edges. This application note gives an overview of the following topics: LTE and LTE-Advanced, including summaries of LTE Release 8/9 features, ITU requirements for 4G, and 3GPP requirements for LTE evolution Release 10 and LTE-Advanced Release 11 LTE-Advanced enhancements Release 12 radio evolution Release 13 update LTE-Advanced product design and testing challenges The focus here is on the LTE-Advanced air interface, although the 3GPP specifications also cover the core network standards and services. This application note assumes that the reader is familiar with LTE basic concepts and features. You can read a detailed explanation of LTE technology in the book LTE and the Evolution to 4G Wireless: Design and Measurement Challenges, Second Edition (ISBN ); information is found at You can also download a Keysight Technologies, Inc. application note, 3GPP Long Term Evolution: System Overview, Product Development, and Test Challenges (literature number EN), at Click on the link for Long Term Evolution LTE Resources. This document covers 3GPP LTE in Releases 8 and 9.

3 03 Keysight LTE Advanced: Technology and Test Challenges Application Note Contents 1 Overview of LTE and LTE-Advanced 1.1 Evolution of wireless communication standards 1.2 Summary of Release 8 LTE features 1.3 Release 9 enhancements with implications for LTE-Advanced 1.4 Requirements for 4G and LTE-Advanced 2 Release 10 LTE-Advanced 2.1 Release 10 LTE enhancements Carrier aggregation for wider bandwidths Uplink transmission scheme Downlink transmission scheme Relaying 2.2 Other Release 10 enhancements Enhanced inter-cell interference coordination (eicic) Minimization of drive test Machine-type communications (MTC) New frequency bands New UE categories 3 Release 11 LTE-Advanced enhancements 3.1 New frequency bands 3.2 Release 11 features for LTE and UTRA Further self-optimizing network (SON) enhancements Enhancement of minimization of drive test (MDT) for E-UTRAN and UTRAN Network energy saving for E-UTRAN RF requirements for multi-band and multi-standard radio Further enhancements to H(e)NB mobility 3.3 Release 11 features for LTE Network-based positioning support in LTE Service continuity improvements for MBMS for LTE Further enhanced non CA-based ICIC for LTE LTE RAN enhancements for diverse data applications Relays for LTE Signaling and procedure for interference avoidance for in-device coexistence Coordinated multi-point transmission (CoMP) Enhanced downlink control channels for LTE-Advanced Public safety broadband high power UE for Band 14, Region 2 Improved minimum performance requirements for E-UTRA: interference rejection Additional special subframe configuration for LTE TDD Release 11 carrier aggregation

4 04 Keysight LTE Advanced: Technology and Test Challenges Application Note 4 Release 12 radio evolution 4.1 New frequency bands 4.2 Carrier aggregation scenarios 4.3 Release 12 work items Dual connectivity for LTE Further enhancements for H(e)NB Mobility Part 3 RF and EMC requirements for active antenna systems (AAS) Machine-type communications (MTC) WLAN/3GPP radio interworking LTE TDD-FDD joint operation including carrier aggregation Further MBMS operations support for E-UTRAN E-UTRA small cell enhancements physical layer aspects Inter-eNB CoMP for LTE LTE device-to-device proximity services Network-assisted interference cancellation and suppression for LTE Verification of radiated multi-antenna reception performance of UEs in LTE/UMTS Performance requirements of 8 Rx antennas for LTE uplink 4.4 Release 12 study items Study on mobile relay for E-UTRA Study on 3D-channel model for elevation beamforming/fd-mimo studies for LTE Study on group communication for LTE Verification of radiated multi-antenna reception performance of UEs: MIMO OTA 5 Release 13 and beyond 5.1 Selected topics New frequency bands Study on multi-rat joint coordination Summary of WLAN aspects Evolution of carrier aggregation Progression of cellular/wifi integration LTE operation in unlicensed bands (LTE-U) 5.2 New focus on end users 6 Challenges for LTE-Advanced product developers 6.1 Carrier aggregation 6.2 Interference mitigation 6.3 Power efficiency and battery life 6.4 Product development strategy 7 Design and test tools for LTE-Advanced developers 8 References 9 Acronyms

5 05 Keysight LTE Advanced: Technology and Test Challenges Application Note 1 Overview of LTE and LTE-Advanced Fourth generation wireless technology has been long and eagerly awaited. To better understand the evolutionary changes that are occurring with the implementation of 4G and LTE-Advanced, it is helpful to summarize what came before. 1.1 Evolution of wireless communication standards Wireless communications have evolved from the so-called second generation (2G) systems of the early 1990s, which first introduced digital cellular technology, through third generation (3G) systems with higher speed data networks, to the much-anticipated fourth generation (4G) technology being developed and deployed today. This evolution is illustrated in Figure 1, which shows that fewer standards were proposed for 4G than in previous generations, with only two 4G candidates having been actively developed: 3GPP LTE-Advanced and IEEE m, which is the evolution of the WiMAX standard known as Wireless MAN-Advanced. Figure 1.Evolution of wireless communication standards from 1990 to the present Early 3G systems, of which there were five, did not immediately meet the ITU s peak data rate target of 2 Mbps in practical deployment, although the systems did so in theory. However, improvements to the standards later brought deployed systems closer to and well beyond the original 3G targets.

6 06 Keysight LTE Advanced: Technology and Test Challenges Application Note Figure 2 shows the evolution of 3GPP s Universal Mobile Telecommunication System (UMTS), the original wideband code division multiple access (CDMA) technology, starting from its initial release in 1999/2000. There have been a number of different releases of UMTS, and the addition of high speed downlink packet access (HSDPA) in Release 5 ushered in the informally named 3.5G. The subsequent addition of the enhanced dedicated channel (E-DCH), better known as high speed uplink packet access (HSUPA), completed 3.5G. LTE arrived with the publication of the Release 8 specification in 2008, and LTE-Advanced was introduced in Release 10. The LTE-Advanced radio access network (RAN) was functionally frozen in December 2010 (excluding the ASN.1 definitions) and the core specifications were completed in March Enhancements to LTE-Advanced were added in Release 11, whose core specifications were completed in September 2012, and in Release 12, on which work began in December As of March 2014, considerable activity continues on Release 12, including 219 work items (which will result in written specifications) and 34 study items (areas of further investigation that could be incorporated into the specs).the completion date for Release 12 is September 2014, and work has begun on Release 13. It s important to note that 3GPP continues to develop the HSDPA and HSUPA standards along with LTE/LTE-Advanced in these releases, although discussion of the high speed packet access technologies is beyond the scope of this application note. Figure 2. Evolution of UMTS specifications

7 07 Keysight LTE Advanced: Technology and Test Challenges Application Note 1.2 Summary of Release 8 LTE features The Long Term Evolution project was initiated in The motivation for LTE included the desire to reduce the network operator s cost per bit, to add lower cost services with better user experience, to use both new and existing frequency bands in flexible ways, to simplify and lower the cost of the network via open interfaces, and to reduce terminal complexity with an allowance for reasonable power consumption. The baseline LTE radio access network (RAN) and the evolved packet core (EPC) network defined in 3GPP Release 8 and evolved in subsequent releases has provided the world with a comprehensive and highly capable new cellular communication standard. According to a June 2014 Global Suppliers Association ( report, LTE has been launched successfully in 300 commercial networks in 107 countries, with more than 350 LTE commercial networks forecast to be operating by the end of As of June 2014,1563 LTE user devices had already been announced. With these impressive statistics, LTE has become the fastest growing cellular technology ever. The main attributes that differentiate LTE from previous generations are: Single-channel peak data rates of up to 300 Mbps in the downlink and 75 Mbps in the uplink Improved spectral efficiency over legacy systems, particularly for the uplink Full integration of frequency division duplex (FDD) and time division duplex (TDD) access modes Packet-based EPC network to eliminate cost and complexity associated with legacy circuit-switched networks. Some key technologies introduced in Release 8 that enabled the new capabilities are: Adoption of orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) for the downlink and uplink air interfaces to enable narrowband scheduling and efficient support of spatial multiplexing Support for six channel bandwidths from 1.4 MHz to 20 MHz to enable high data rates and also efficient spectrum re-farming for narrowband legacy systems Baseline support for multiple input multiple output (MIMO) spatial multiplexing of up to four layers on the downlink Faster physical layer control mechanisms leading to lower latency. Speed is probably the feature most associated with LTE. Examples of downlink and uplink peak data rates for a 20 MHz channel bandwidth are shown in Table 1. Downlink figures are shown for single input single output (SISO) and MIMO antenna configurations at a fixed 64 quadrature amplitude modulation (QAM) depth, while the uplink figures are for SISO but at different modulation depths. These figures represent the physical limitation of the LTE FDD radio access mode in ideal radio conditions with allowance for signaling overheads. Lower rates are specified for specific user equipment (UE) categories, and performance requirements under non-ideal radio conditions have also been developed. Figures for LTE s TDD radio access mode are comparable, scaled by the variable uplink and downlink ratios.

8 08 Keysight LTE Advanced: Technology and Test Challenges Application Note Table 1. Peak data rates for LTE Downlink peak data rates (64 QAM) Antenna configuration SISO 2x2 MIMO 4x4 MIMO Peak data rate Mbps Uplink peak data rates (single antenna) Modulation QPSK 16 QAM 64 QAM Peak data rate Mbps Unlike previous systems, LTE was designed from the beginning to use MIMO technology, resulting in a more integrated approach to this advanced antenna technology than the addition of MIMO to legacy 3G systems. In terms of mobility, LTE is aimed primarily at low mobility applications in the 0 k/m/h to 15 km/h range, where the highest performance can be seen. However, the system is capable of working at higher speeds and is supported with high performance from 15 km/h to 120 km/h and functional support from 120 to 350 km/h. Despite the substantial capabilities of LTE in Release 8, the 3GPP standard has continued to evolve. Release 9 completed and enhanced basic LTE, while Release 10, Release 11, and now Release 12 have defined and enhanced the specifications for LTE-Advanced.

9 09 Keysight LTE Advanced: Technology and Test Challenges Application Note 1.3 Release 9 enhancements with implications for LTE-Advanced Release 9 is considered a short release between the major effort required to finish Release 8 and the definition of LTE-Advanced in Release 10. Some items in Release 9 are carryovers from Release 8 that were not yet complete; others are new items not in the original Release 8 definition. At a formal level, Release 9 includes more than 80 identifiable features. Several of the key items that pertain to the radio aspects are briefly described here. These features are further developed in Release 10 LTE-Advanced. New frequency bands Each release of the 3GPP specification adds new frequency bands. Release 9 introduced four new FDD bands shown in Table 2. Bands 18 and 19 are referred to as the extended LTE 800 bands and were specified for use in Japan. Band 20 was added for the so-called digital dividend spectrum in Europe that was made available through the switchover to digital television. Note that the uplink and downlink frequencies in this band are reversed from the usual arrangement. The final band added in Release 9 is the extended LTE 1500 band in Japan. Table 2. Frequency bands added during Release 9 Band number Uplink Downlink Low High Low High Bandwidth Duplex spacing FDD FDD FDD FDD Gap Duplex mode Femtocells and the home base station Work on femtocell inclusion in UMTS was ongoing during Release 8 and continued in Release 9 for the home base station (home BS), also known as the home evolved node B (HeNB) or femtocell. The femtocell concept is not unique to LTE or LTE-Advanced, but there was an opportunity for LTE to incorporate the technology from the start rather than retrospectively designing it into legacy systems such as UMTS and GSM. From a radio perspective the femtocell operates over a small area within a larger cell. The radio channel can be the same as that of the larger cell (known as co-channel deployment) or a dedicated channel. The femtocell concept is fundamentally different from relaying since the femtocell connects back into the core network via a local, existing DSL internet connection rather than back to the macrocell using over the air transmission. Most femtocell deployments will be indoors, which helps provide isolation between the femtocell and the macrocell. A femtocell can be located outside the macrocell s coverage area; for example, as a way to provide local cellular coverage in rural areas where digital subscriber line (DSL) exists but there is no cellular coverage provided by an operator. This is shown in Figure 3. Femtocells may be operated for the benefit of a closed subscriber group (CSG) or for open public access.

10 10 Keysight LTE Advanced: Technology and Test Challenges Application Note Figure 3. Home base stations (femtocells) Studies have shown that increased average data rates and 100 times greater capacity are possible with femtocells than can be achieved from the macro network alone. However, femtocells do not provide the mobility of a macrocellular or even microcellular system, and differences exist in their use models as shown in Table 3. For these reasons, femtocellular deployments should be considered as complementary rather than competitive with the macrocellular and microcellular systems. Table 3. Comparison of macro- and microcellular with femtocellular use models Macro-/microcellular Ubiquitous mobile data and voice Mobility and continuous coverage Ability to control QoS Limited capacity and data rates High costs, acceptable for high value traffic User is often outdoors and moving Femtocellular Opportunistic nomadic data Hotspot coverage Limited QoS for lower value data Distributed cost (not low cost) Free or charged User is sitting down indoors Work regarding the femtocell-based home BS in Release 9 had two objectives: first, to complete the RF specifications for the introduction of the home BS class, and second, to introduce features in the home BS and network that enable control of the home BS output power, in order to mitigate interference to the macro network or to other home BS. A number of relaxations to the RF specifications were introduced, not least in importance the maximum output power, which is limited to 20 dbm and lower in some scenarios. The expected low UE speeds in home BS deployments enabled a five times looser requirement for frequency error and there are various other relaxations for spurious emissions. However, to enable effective interference mitigation, the home BS must be able to measure the signal strength of other base stations in the neighborhood. Downlink measurement is not an issue for TDD, but for FDD a downlink measurement function is required in the home BS although some measurements may also be gathered from the connected UEs.

11 11 Keysight LTE Advanced: Technology and Test Challenges Application Note The need for interference mitigation is most important when the home BS is deployed in a co-channel closed subscriber group. In this mode the home BS is deployed on the same frequency as the macro network. When close to this home BS, UEs that are part of the CSG would hand over to the home BS. However, UEs that are not part of the closed subscriber group would likely experience a loss of coverage. For this reason it is important to limit the potential for the home BS to interfere with the macro network when the home BS is operated in a co-channel CSG mode. The general term applied to this form of interference mitigation is inter-cell interference coordination (ICIC). Interference mitigation work continued in Release 10 with enhanced ICIC (eicic) and in Release 11 with further enhanced ICIC (FeICIC), covered later in this application note. Multimedia broadcast multicast service (MBMS) The MBMS television service was specified at the physical layer in Release 8 but was not functionally complete until Release 9. The features in Release 9 provide a basic MBMS service carried over an MBMS single frequency network (MBSFN). In Release 9 only the guaranteed bit rate (GBR) bearers were specified, which means that the maximum bit rate (MBR) is always equal to the GBR. This is not good for variable bit rate services which, by exploiting statistical multiplexing, would otherwise allow the MBR to exceed the GBR. The Release 9 definition also lacks a feedback mechanism from the UEs to the network to determine whether sufficient UEs are present in the target area to justify turning on the MBSFN locally. Further MBMS enhancements were added in Release 11 for service continuity including support on multiple frequencies, reception during RRC idle and RRC connected states, and support to take UE positioning into account for further optimization of the received services. Positioning support Positioning support work in Release 9 included specifications for support of the Assisted Global Navigation Satellite System (AGNSS), which incorporates the following satellite positioning systems: Galileo Global Positioning System (GPS) and modernized GPS GLObal naya NAvigatsionnaya Sputnikovaya Sistema (GLONASS) Quazi-Zenith Satellite System Space Based Augmentation System (SBAS). The LTE physical layer was augmented to support the observed time difference of arrival (OTDOA) positioning scheme with the introduction of the positioning reference signal (PRS). Network-based positioning for LTE was added in Release 11 with a further study item in Release 12 on positioning based on RF pattern matching. Multi-standard radio (MSR) Release 9 introduced the concept of MSR in recognition of evolved base station technology that allows more than one carrier from the same or different radio access technologies (RATs) to be operated from a single BS using a wideband receiver. Although MSR did not add new radio requirements for LTE, it changed the way in which existing radio requirements are interpreted for conformance testing. Thus a new MSR conformance test specification was created. In Release 11 the MSR concept was extended for non-contiguous (inter-band) cases; that is, cases in which different RATs are located in different bands. New base station classes for medium-range and local area MSR were also added.

12 12 Keysight LTE Advanced: Technology and Test Challenges Application Note RF requirements for local base stations The local area BS (picocell) is another important introduction to the LTE specifications in Release 9 along with the home BS (femtocell). The local area BS enables the deployment of a heterogeneous network comprising macrocells (wide area), picocells, and femtocells. The RF requirements for local area base stations are based on a reduced UE-to-BS coupling loss of 45 db compared to the 70 db used for macrocells. This allows for a lower maximum output power requirement of 24 dbm and other relaxations such as those for frequency error and unwanted emissions consistent with small cell deployment. Enhanced dual-layer transmission Release 8 specified seven downlink transmission modes (TMs). Transmission mode 7 (TM7) introduced the concept of UE-specific reference symbols (RS) that enable non-codebook precoding of the physical downlink shared channel (PDSCH) for single layer transmission. Release 9 extended the UE-specific RS to support two spatial layers with the addition of TM 8. Self-organizing networks (SON) Today s cellular systems are very much centrally planned and the addition of new nodes to the network involves expensive and time-consuming work, including site visits for optimization. A number of use cases were identified by 3GPP in which SON could be applied to reduce the burden: Automation of neighbor relation lists in the E-UTRAN and UTRAN and between different 3GPP radio access technologies Self-establishment of a new enb in the network Self-configuration and self-healing of the BS Automated coverage and capacity optimization Optimization of parameters affected by troubleshooting Continuous optimization to accommodate dynamic changes in the network Automated handover optimization Optimization of quality-of-service (QoS) related radio parameters. Release 8 introduced a basic version of SON that included automatic neighbor relations (ANR) list management and self-establishment of new base stations. In Release 9 SON was extended to include new operation and maintenance features for load balancing and handover parameter optimization. The SON work was continued in Release 10 with specification of the management aspects for interference control, capacity and coverage optimization, and random access channel (RACH) optimization. The concept of self-healing was also developed in Release 10. This feature involves the detection and, analysis of network faults and identification of the corrective action required of the network to respond to disruptive events with minimal manual intervention. Additional enhancements were added in Release 11 to address inter- RAT mobility issues and HetNet deployments.

13 13 Keysight LTE Advanced: Technology and Test Challenges Application Note 1.4 Requirements for 4G and LTE-Advanced The most significant changes to the 3GPP standard occur in Release 10 for the support of LTE-Advanced, 3GPP s submission to the ITU Radio-communication sector (ITU-R) IMT-Advanced program. The IMT-Advanced program is often referred to as 4G although the term is not formally defined by the ITU or any other official body. Because of the ITU involvement in setting the requirements for Release 10, the specification process was more complicated than any previous or subsequent release to date: ITU-R defined the requirements for IMT-Advanced 3GPP defined the requirements for LTE-Advanced 3GPP undertook a feasibility study that proposes LTE-Advanced as an IMT-Advanced candidate technology 3GPP created work items to develop the many-detailed specification in Release 10 to define LTE-Advanced. In the feasibility study for LTE-Advanced, 3GPP determined that the existing Release 8 LTE could meet most of the IMT-Advanced requirements apart from uplink spectral efficiency and the peak data rates. These higher requirements could be addressed with the addition of the following LTE-Advanced features in Release 10: Wider bandwidths, enabled by carrier aggregation Higher efficiency, enabled by enhanced uplink multiple access and enhanced multiple antenna transmission (advanced MIMO techniques). Other performance enhancements that were being considered for LTE-Advanced in Release 10 and beyond for example, coordinated multipoint transmission and reception (CoMP), support for heterogeneous networks, SON enhancements, and home enhanced node B (HeNB) mobility enhancements were not critical to meeting the ITU s IMT- Advanced requirements. In October 2009, 3GPP formally submitted LTE-Advanced as a candidate for IMT- Advanced. Another candidate submitted in this timeframe was an enhanced version of the IEEE e standard known as Wireless Mobile Area Network Advanced (Wireless MAN- Advanced). After considering the merits of both technologies, the ITU in January 2012 formally approved both as meeting the requirements of their program. It is worth pointing out that both technologies approved for IMT-Advanced are based heavily on pre-existing standards and the modifications that were required of these technologies to meet IMT- Advanced requirements are not considered major. Figure 4 shows the initial timeline of the ITU-R for IMT-Advanced along with the parallel 3GPP activities for LTE-Advanced. Figure 4.Historical timeline for IMT-Advanced and LTE-Advanced

14 14 Keysight LTE Advanced: Technology and Test Challenges Application Note The high level requirements for IMT-Advanced defined by the ITU-R are the following: A high degree of common functionality worldwide while retaining the flexibility to support a wide range of local services and applications in a cost-efficient manner Compatibility of services within IMT and with fixed networks Capability for interworking with other radio systems High quality mobile services User equipment suitable for worldwide useser-friendly applications, services, and equipment Worldwide roaming capability Enhanced peak data rates to support advanced mobile services and applications (100 Mbps for high mobility and 1 Gbps for low mobility were established as targets for research). The first seven of the eight requirements are rather general goals already being pursued by the industry. The eighth requirement, for 100 Mbps high mobility and 1 Gbps low mobility, is somewhat different and has fundamental repercussions on system design. The 1 Gbps peak target for IMT-Advanced is similar to the 2 Mbps target for its predecessor, IMT-2000, set some ten years earlier. Like its predecessor, the 1 Gbps peak figure is not without qualification since it applies only for low mobility in excellent radio conditions and could require up to 100 MHz of spectrum. The work by 3GPP to define a 4G candidate radio interface technology started in Release 9 with the study phase for LTE-Advanced. The requirements for LTE-Advanced were captured in 3GPP Technical Report (TR) , Requirements for Further Advancements for E-UTRA (LTE-Advanced) [1]. These requirements were defined based on the ITU-R requirements for IMT-Advanced and on 3GPP operators own requirements for advancing LTE: Continual improvement to the LTE radio technology and architecture Scenarios and performance requirements for interworking with legacy radio access technologies Backward compatibility of LTE-Advanced with LTE (an LTE terminal should be able to work in an LTE-Advanced network and vice versa; any exceptions will be considered by 3GPP) Account taken of recent World Radio-communication Conference (WRC-07) decisions regarding new IMT spectrum as well as existing frequency bands to ensure that LTE- Advanced geographically accommodates available spectrum for channel allocations above 20 MHz. Also, requirements must recognize those parts of the world in which wideband channels are not available.

15 15 Keysight LTE Advanced: Technology and Test Challenges Application Note System performance requirements When the ITU-R defined IMT-2000, the only requirements were for peak data rates. No targets were proposed for latency or, more importantly, for the average or cell-edge performance that defines the typical user experience. Fortunately, this requirement gap is eliminated with IMT-Advanced, which specifies a much broader range of performance. The IMT-Advanced performance requirements along with operator requirements were used by 3GPP to develop TR , which defines LTE-Advanced performance requirements in the following areas: Peak data rates: 1 Gbps downlink, 500 Mbps uplink Latency Control plane: idle to connected < 50 ms, un-sync to in-sync < 10 ms (see Figure 5) User plane: Improvements over Release 8 for with and without scheduling assignment Spectral efficiency Peak spectral efficiency see Table 4 Average spectral efficiency see Table 4 Cell-edge user data throughput see Table 4 VoIP capacity Mobility Support for up to 350 km/h and for some frequency bands 500 km/h Enhanced performance for 0 10 km/h over Release 8 with no degradation and preferred enhancement for higher speeds Further enhancements to MBMS: Improved requirements for spectrum efficiency over Release 8. Figure 5. Requirements for state transitions (TR [1] Figure 7.1) Table 4 compares selected performance targets for LTE, LTE-Advanced, and IMT- Advanced. The cell and cell-edge spectral efficiency figures are given for an inter-site distance (ISD) of 500 m. Note that the peak efficiency targets for LTE-Advanced are substantially higher than the requirements for IMT-Advanced thus the desire to drive up peak performance is maintained despite the average targets and requirements being very similar. However, TR [1] states: The target for average spectrum efficiency and the cell edge user throughput efficiency should be given a higher priority than the target for peak spectrum efficiency and VoIP capacity. Note also that with the exception of uplink spectral efficiency, LTE Release 8 meets the requirements for IMT-Advanced.

16 16 Keysight LTE Advanced: Technology and Test Challenges Application Note Table 4 compares selected performance targets for LTE, LTE-Advanced, and IMT-Advanced. The cell and cell-edge spectral efficiency figures are given for an inter-site distance (ISD) of 500 m. Note that the peak efficiency targets for LTE-Advanced are substantially higher than the requirements for IMT-Advanced thus the desire to drive up peak performance is maintained despite the average targets and requirements being very similar. However, TR [1] states: The target for average spectrum efficiency and the cell edge user throughput efficiency should be given a higher priority than the target for peak spectrum efficiency and VoIP capacity. Note also that with the exception of uplink spectral efficiency, LTE Release 8 meets the requirements for IMT-Advanced. Table 4.Spectral efficiency performance targets for LTE, Advanced-LTE, and IMT-Advanced Item Sub-category LTE (Release 8) target LTE-Advanced target Peak spectral efficiency (b/s/hz) Downlink cell spectral efficiency b/s/hz/user Microcellular 3 km/h, 500 m ISD Uplink cell spectral efficiency b/s/hz/user Microcellular 3 km/h, 500 m ISD IMT-Advanced requirement Downlink 16.3 (4x4 MIMO) 30 (8x8 MIMO or less) 15 (4x4 MIMO) Uplink 4.32 (64QAM SISO) 15 (4x4 MIMO or less) 6.75 (2x4 MIMO) (2x2 MIMO) (4x2 MIMO) (4x4 MIMO) (1x2 MIMO) 1.2 (2x4 MIMO) Downlink cell-edge user spectral efficiency (b/s/ Hz/user), (5 percentile, 10 users), 500m ISD Uplink cell-edge user spectral efficiency (b/s/ Hz/user), (5 percentile, 10 users), 500m ISD (2x2 MIMO) (4x2 MIMO) (4x4 MIMO) (1x2 MIMO) 0.04 (2x4 MIMO) *Note: ISD = Inter-site distance

17 17 Keysight LTE Advanced: Technology and Test Challenges Application Note 2 Release 10 LTE-Advanced The submission to ITU-R in TR , Feasibility study for Further Advancements for E-UTRA (LTE-Advanced) [2], outlines the features identified for development in Release 10 relevant for the IMT-Advanced requirements. This subset of Release 10 was the original meaning of the term LTE-Advanced but now LTE-Advanced is used to refer to all developments from Release 10 onwards. The following sections outline the key LTE-Advanced proposals, which cover the following areas: Support of wider bandwidths Uplink transmission scheme Downlink transmission scheme Coordinated multi point transmission and reception (CoMP) Relaying Not all the above were essential to meet the IMT-Advanced requirements and not all aspects were subsequently developed in Release 10 (for example, CoMP, which is a work item in Release 11 and is covered later in this application note). There were other areas for development also identified in TR for which details were not elaborated. These included mobility enhancements, radio resource management enhancements, MBMS enhancements, and further work on SON. The study concludes with a self-evaluation that reports how LTE-Advanced meets or exceeds the ITU-R IMT-Advanced requirements. The following sections outline the main functional areas that were developed in Release 10 specifically for LTE-Advanced. These sections are followed by other work items in Release 10 that were not part of the ITU-R submission. 2.1 Release 10 LTE enhancements Carrier aggregation for support of wider bandwidths Support of wider bandwidths is primarily aimed at addressing the IMT-Advanced requirements for peak single user data rates up to 1 Gbps, although there are additional systemlevel benefits in terms of deployment flexibility and associated trunking gains that come from the availability of a wider instantaneous transmission bandwidth. Today s spectrum allocations (frequency bands) offer almost no opportunity for finding 100 MHz of contiguous spectrum needed for 1 Gbps peak data rates. Some new IMT spectrum was identified at the World Radio Conference in 2007 (WRC-07), but there are still only a few places where continuous blocks of 100 MHz might be found (for example, at 2.6 GHz or 3.5 GHz). One possible way of increasing available bandwidths would be to encourage network sharing, which reduces fragmentation caused by splitting one band between several operators. However, sharing the spectrum, as opposed to just the sites and towers, is a considerable step up in difficulty. The ITU-R recognized the challenge that wide-bandwidth channels present and so expected that the required 100 MHz would be created by the aggregation of non-contiguous channels from different bands in a multi-transceiver mobile device. The beginnings of such aggregation techniques have already shown up in established technologies first with EDGE Evolution, for which standards have been written to aggregate two non-adjacent 200 khz channels, potentially to double the single-user data rates that are possible with standard EDGE. Along similar lines, there are 3GPP specifications for dual-carrier HSDPA that try to close the bandwidth gap between 5 MHz UMTS and 20 MHz LTE. Contiguous multi-carrier cdma2000 (3xRTT) has also been defined, which avoids the need for multiple transceivers. Carrier aggregation is clearly not a new idea; however, the proposal to extend aggregation up to 100 MHz in multiple bands presents numerous design challenges, particularly for the UE in terms of additional cost and complexity. At each of the layers in the radio protocol, from the physical layer up through radio resource control (RRC), changes are required for carrier aggregation. An overview of these can be found in [2] Section 5.

18 18 Keysight LTE Advanced: Technology and Test Challenges Application Note Carrier aggregation in Release 10 Carrier aggregation for LTE-Advanced is first defined in 3GPP Release 10 although it continues to evolve in subsequent releases. To preserve LTE backward compatibility, carrier aggregation is based on the component carriers first defined in Release 8. This definition allows existing LTE devices to continue operating properly but enables new devices to support the higher data throughput that carrier aggregation makes possible. LTE-Advanced networks can support carrier aggregation in just the downlink or in both the downlink and the uplink. Initial deployments are implementing the technology in the downlink only as this configuration is a good match to typical internet packet-data traffic. The Release 8 component carriers (CCs) can use any of the 3GPP-defined LTE bandwidths 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz. The Release 10 standard allows aggregation of up to five component carriers; thus, combining five 20 MHz CCs would yield a theoretical maximum of 100 MHz of instantaneous bandwidth. If each 20 MHz CC could achieve the downlink maximum throughput of 150 Mbps, the result would be a throughput potential of 750 Mbps. This scenario is unlikely, however, since most operators lack the spectrum to support 20 MHz wide channels and will primarily use 5 or 10 MHz modulation bandwidths for carrier aggregation. In LTE FDD-based systems, the number of CCs aggregated in the downlink can differ from the number in the uplink, but the number of uplink CCs must be always be less than or equal to the number of downlink CCs. Also, the bandwidths of the component carriers can vary for example, a 5 MHz carrier can be combined with a 10 MHz carrier as this is a common scenario to be fielded by operators. For LTE TDD-based systems, the number of CCs and the bandwidth of each CC must be the same for the downlink and the uplink, since both the downlink and the uplink share the same channel. This definition changes in Release 11 of the 3GPP standard (discussed later), which introduces TDD to support for different uplink and downlink configurations in each frequency band. Two types of component carriers have been defined. There is a single primary component carrier, which is the carrier signal to which the UE is connected. This carrier handles the RRC and non-access stratum (NAS) procedures, including authentication and security; measurement reporting; and mobility procedures. All of the physical channels are mandatory in this primary cell, including the physical uplink shared channel (PUSCH). Secondary component carriers are optional LTE carriers used opportunistically to increase the number of radio resources that are available in order to increase the data rates. Secondary CCs are configured using RRC signaling procedures. Not all of the physical channels are mandatory in this case; for example, the PUSCH is optional and thus allows asymmetric carrier aggregation.

19 19 Keysight LTE Advanced: Technology and Test Challenges Application Note Types of carrier aggregation As defined in the Release 10 standard, aggregated CCs may occupy channels within a single LTE frequency band, called intra-band carrier aggregation. These channels may be contiguous (adjacent), non-contiguous, or both if more than three CCs are used (Figure 6). Figure 6. Downlink intra-band carrier aggregation Intra-band carrier aggregation can be implemented in UEs with a single receiver and transmitter, which helps to minimize the cost and complexity of adding this new feature. A UE designer can fairly easily create a receiver that has a bandwidth wide enough to capture the component carriers in the receiver s intermediate frequency (IF). The baseband chipset can then demodulate the CCs individually and assemble the multiple data streams into a single packet data stream. Likewise, the UE transmitter can be given sufficient bandwidth to modulate the combined bandwidths of the CCs. For those operators who have sufficient spectrum to operate multiple LTE carriers within a single band, intra-band carrier aggregation is an attractive method for increasing throughput while maintaining backward compatibility with existing LTE user equipment that does not support CA. The Release 10 standard also defines inter-band carrier aggregation, which allows the combining of CCs located in different frequency bands (Figure 7). Operators with blocks of spectrum in different bands can use this approach to achieve the performance and throughput of 20 MHz or wider LTE systems. Figure 7. Downlink inter-band carrier aggregation For example, many operators in North America hold spectrum in the 700 MHz band and the 1900 MHz band. Existing 3G networks heavily occupy the 800 MHz cellular bands and cannot accommodate LTE. In the 700 MHz band, operators may have sufficient spectrum for one or two 5 MHz LTE channels. At this bandwidth, LTE offers no real improvement over 3G systems. However, more spectrum is available at 1900 MHz and many operators have one 10 MHz LTE channel in this band. The solution to offering the performance gains of 20 MHz LTE for these operators is to combine their 700 MHz spectrum and 1900 MHz spectrum using LTE advanced inter-band carrier aggregation. If the operator has two 5 MHz LTE channels in the 700 MHz band and one 10 MHz LTE channel in the 1900 MHz band, using inter-band carrier aggregation results in an LTE Advanced system that matches the performance of a 20 MHz LTE channel. Further, by operating in the inter-band carrier aggregation mode, additional frequency diversity as well as cell loading diversity is gained to further enhance system performance.

20 20 Keysight LTE Advanced: Technology and Test Challenges Application Note One limitation of inter-band carrier aggregation is that the UE must have at least two receivers and possibly two transceivers if the operator intends to support inter-band aggregation in the uplink. This clearly increases UE cost. Moreover, inter-band carrier aggregation is considerably more complicated than intra-band. An enormous number of carrier aggregation scenarios are possible, and each combination of bands must be studied in order to identify the combination of requirements necessary to ensure commercially viable deployment. Frequency band combinations The Release 10 standard defined the first three carrier aggregation frequency band combinations. These limited the aggregation to two component carriers with a maximum aggregated bandwidth of 40 MHz. For FDD intra-band carrier aggregation, the Release 8 band 1 (IMT-2000 band) is defined as carrier aggregation band CA_1 For TDD intra-band carrier aggregation, Band 40 (2300 MHz TDD band) is defined as carrier aggregation band CA_40 For inter-band non-contiguous carrier aggregation, Release 8 bands 1 (IMT-2000 band) and 5 (US cellular 800 MHz band) are defined by a single carrier aggregation band CA_1-5. In practice, operators will likely want to perform carrier aggregation with any spectrum that they hold, so many more combinations are being defined. At the time of this writing, a total of 132 combinations have been defined through the beginning work on Release 13, and that number will rise as Release 13 is further developed. Fortunately the standard is self-limiting, covering only those scenarios considered relevant to specific geographical areas or potential deployments. Unfortunately, every combination has the potential to require a new UE design to handle filter and power amplifier requirements. Release 12 introduced aggregation of three carriers and aggregation of four carriers is likely in release 13. Inter-site carrier aggregation is being specified in Release 13 as dual connectivity for LTE. However, currently the practical considerations of UE power dissipation, weight, battery life, and transceiver cost limit the number of bands that can be supported to two or three. Of the first generation UEs supporting CA, most support twocarrier downlink carrier aggregation only. Uplink transmission scheme Several enhancements were introduced to the uplink for LTE-Advanced: Spatial multiplexing of up to four layers Transmit diversity Clustered SC-FDMA Simultaneous PUCCH/PUSCH. Spatial multiplexing and transmit diversity The introduction of spatial multiplexing and transmit diversity to the uplink makes a significant departure from the UE architecture of Release 8 since both enhancements require the support of more than one uplink transmitter. This has implications for cost, space, power handling, and many new spurious emission scenarios that need to be studied and will require new designs. The benefits of spatial multiplexing provide the improvements in spectral efficiency over Release 8 that are needed in LTE-Advanced to meet the IMT- Advanced requirements.

21 21 Keysight LTE Advanced: Technology and Test Challenges Application Note Clustered SC-FDMA The Release 8 LTE uplink is based on single-carrier frequency division multiple access (SC- FDMA), a powerful technology that combines many of the flexible aspects of orthogonal frequency division multiplexing (OFDM) with the low peak to average power ratio (PAPR) of a single carrier system. However, SC-FDMA requires carrier allocation across a contiguous block of spectrum and this prevents some of the scheduling flexibility inherent in pure OFDM. Release 10 enhances the uplink multiple access scheme by adopting clustered SC-FDMA, also known as discrete Fourier transform spread OFDM (DFT-S-OFDM). This scheme is similar to SC-FDMA but has the advantage that it allows non-contiguous (clustered) groups of subcarriers to be allocated for transmission by a single UE, thus enabling uplink frequency-selective scheduling and better link performance. Clustered SC-FDMA was chosen in preference to pure OFDM to avoid a significant increase in PAPR. SC-FDMA will help satisfy the requirement for increased uplink spectral efficiency while maintaining backward-compatibility with LTE. For Release 10 the number of clustered groups is restricted to two. Table 5 shows the impact this has on the PAPR as calculated by the cubic metric. Table 5. Comparing SC-FDMA and two-cluster SC-FDMA Modulation depth Cubic metric SC-FDMA QPSK QAM QAM Two-cluster SC-FDMA It can be seen that two-cluster SC-FDMA adds just over 1 db to the PAPR of single-cluster SC-FDMA. If the number of clusters goes beyond six, the PAPR begins to look like that of OFDMA. The cost in terms of implementation is that slightly more power amplifier back-off is required and there are further issues with in-channel intermodulation products cause by the presence of two discrete carriers within the channel. Simultaneous PUCCH/PUSCH transmission In Release 8 the user data carried on the physical uplink shared channel (PUSCH) and the control data carried on the physical uplink control channel (PUCCH) are time-multiplexed. It is also possible to multiplex control data with user data on the PUSCH. LTE-Advanced introduces a new mechanism for simultaneous transmission of control and data by allowing the PUSCH and the PUCCH to be transmitted simultaneously. This mechanism has some latency and scheduling advantages over time-multiplexed approaches although it does generate a multi-carrier signal within one component carrier of the uplink. Simultaneous PUCCH/PUSCH transmission should not be confused with carrier aggregation, which involves more than one component carrier. Simultaneous PUCCH/ PUSCH transmission is known to increase PAPR, which makes it more likely that the power amplifier will create unwanted intermodulation products. This effect is similar to the one described for clustered SC-FDMA. Some examples of complementary cumulative distribution function (CCDF) power measurements for a 10 MHz LTE-Advanced uplink signal are given in Figure 8. The modulation formats of the PUSCH are QPSK and each PUSCH cluster consists of three RBs. There are five curves in the measurement graph on the left. From left to right they are (1) nonclustered PUSCH with SC-FDMA precoding, which is the baseline Release 8 format; (2) multi-clustered PUSCH with SC-FDMA precoding; (3) simultaneously transmitted PUCCH and non-clustered PUSCH; (4) simultaneously transmitted PUCCH and multi-clustered PUSCH; and finally (5) the additive white Gaussian noise (AWGN) reference curve.

22 22 Keysight LTE Advanced: Technology and Test Challenges Application Note Figure 8. CCDF and spectrum measurements of various LTE-Advanced uplink signals. Downlink transmission scheme 3GPP included improvements in Release 10 for higher order MIMO techniques. The enhancements to the downlink include the following: Extension of spatial multiplexing from four to eight layers Enhancements to downlink reference signals. Eight-layer spatial multiplexing A number of enhancements were introduced in Release 10 to accommodate spatial multiplexing up to eight layers on the downlink. This increase may appear to be a symbolic extension to the standard, since performance requirements through Release 11 exist only for two-layer transmission to a single UE, even though four-layer transmission has been defined since Release 8. The main drawback to the implementation of eight-layer single user spatial multiplexing (SU-MIMO) is not so much at the base station end, where eightantenna systems already exist, but at the UE receiver, which would require implementation of eight receive antennas per carrier. This proposition is not practical today due mainly to space constraints. The potential for eight spatial layers does open up, however, new possibilities for multiuser spatial multiplexing (MU-MIMO), offering new combinations for the simultaneous support of more than one user sharing the eight layers. Release 10 enhancements include a new transmission mode, TM 9, which adds UE-specific reference signals (RS) for eight layers. TM 9 is flexible, supporting different combinations of SU-MIMO and MU-MIMO up to the eight-layer maximum. Additionally, the potential for eight transmitters at the base station opens up the potential for enhanced transmission using beamforming; for example, in an 8x2 configuration. Downlink reference signals Release 10 includes a number of elaborations to the reference signal structure, one of which is a new channel state information reference signal (CSI-RS). This reference signal performs the same basic function as a cell reference signal (CRS); that is, it provides a known amplitude and phase reference to the UE. However, the CSI-RS has two distinct differences from the CRS. First, the CSI-RS can be scheduled as required rather than being present in every frame. Second, the CSI-RS is used only for reporting of channel state information by the UE on the uplink and (unlike the CRS) is not used for demodulation. The use of the CSI-RS is limited to channel state information reporting of the channel quality indicator (CQI), precoding matrix indicator (PMI), and rank indication (RI). The CSI-RS is not used in support of PDSCH demodulation, which is the task of the precoded UE-specific RS and the non-precoded CRS.

23 23 Keysight LTE Advanced: Technology and Test Challenges Application Note Relaying The concept of relaying is not new but the level of sophistication continues to grow. The most basic relay method is the use of a repeater, which receives, amplifies, and then retransmits the downlink and uplink signals to overcome areas of poor coverage. The repeater could be located at the cell edge or in some other area of poor coverage. Repeaters are relatively simple devices operating purely at the RF level. Typically they receive and retransmit an entire frequency band; therefore, care is needed when repeaters are sited. In general repeaters can improve coverage but do not substantially increase capacity. More advanced relays can in principle decode transmissions before retransmitting them. This gives the ability to selectively forward traffic to and from the UE local to the relay station thus minimizing interference. Depending on the level at which the protocol stack is terminated in the relay node (RN), such types of relay may require the development of relay-specific standards. This can be largely avoided by extending the protocol stack of the RN up to Layer 3 to create a wireless router that operates in the same way as a normal enb, using standard air interface protocols and performing its own resource allocation and scheduling. The distinguishing feature of such relays compared to normal enbs is that the backhaul connecting the relays to the other enbs operates as an in-band LTE radio link to the donor enb (DeNB). This link, called the Un interface, can be on the same frequency as the RN-to-UE link (in-band) or on a different frequency (out-of-band). The concept of the relay station can also be applied in low density deployments where a lack of suitable backhaul would otherwise preclude use of a cellular network. The use of in-band or in-channel backhaul can be optimized using narrow point-to-point connections to avoid creating unnecessary interference in the rest of the network. Multi-hop relaying is also possible as shown in Figure 9. Figure 9.Multi-hop relaying

24 24 Keysight LTE Advanced: Technology and Test Challenges Application Note Since the RN cannot simultaneously receive from the donor enb and transmit to a local UE at the same time and frequency, downlink transmission gaps during which the enb communicates with the RN can be created by configuring MBSFN subframes at the RN. This principle is shown in Figure 10. Figure 10. Relay-to-UE communication using normal subframes (left) and enb-to-relay communication using MBSFN subframes (right). (TR [2] Figure 9.1) The essential functionality to enable relaying is specified in Release 10, but the radio requirements for the RN transmitter and receiver performance are specified in Release 11. A study item in Release 12 is investigating mobile relaying as a solution for improving performance on high speed trains. Currently, the handover success rate from high speed trains is problematic due to the large number of UEs attempting to handover at the same time. By using a mobile relay, possibly equipped with a group handover mechanism, the signaling load on the macro network could be substantially reduced. The physical layer aspects of relaying are captured in a technical specification, TS [3]. The overall network architecture of relaying is captured in Figure 11 from TS [4]. Figure 11. Network architecture for relaying (TS [4] Figure 4.-1) Not all of the core work was completed in Release 10, in particular security aspects, and the remaining work was moved to Release 11 along with the radio performance aspects that led to a new conformance test specification, TS [5]. This specification is a hybrid of enb tests for the access link and UE tests for the backhaul radio link to the DeNB.

25 25 Keysight LTE Advanced: Technology and Test Challenges Application Note 2.2 Other Release 10 enhancements The following sections describe further Release 10 work items that were not originally identified to meet the ITU-R requirements for IMT-Advanced in [2]. Enhanced inter-cell interference coordination (eicic) Basic support for inter-cell interference coordination started in Release 8 and is enhanced in Release 10 with the eicic work item. Before discussing eicic it is worth reviewing the attributes of the CDMA and OFDM air interfaces to see how they behave with regard to inter-cell interference and the techniques that can be applied to mitigate it. In the CDMA systems that dominate 3G, cell-edge interference is now a well-understood phenomenon and techniques for dealing with it continue to advance. This was not always the case and early CDMA systems were dogged with unexpected issues such as cell breathing in which the cell boundary moves as a result of power-control problems and excessive soft handover activity. Cell breathing can now be used with care as a tool for inter-cell load balancing. UMTS Release 7 introduced the HSDPA Type 3i receiver, which incorporated diversity reception, an equalizer, and dual-input interference cancellation capability. Due to the use of cell-specific scrambling codes and the presence of patterns within the signal caused by frequency selective fading, a cell-edge interferer in a CDMA system has considerably more structure than AWGN. This structure can be used by an interference-cancelling receiver to remove significant portions of the co-channel interference. The introduction of OFDMA to cellular systems starting with e and continuing with LTE has significantly changed the nature of cell-edge interference. In CDMA systems all the transmissions occupy the entire channel and are summed to create a signal with relatively stable dynamics. In OFDMA the potential for frequency-selective scheduling within the channel opens up new possibilities for optimizing intra-cell performance but also creates dynamic conditions in which inter-cell co-channel interference may occur. Work continues in 3GPP to better understand the effect of this interference on operational performance. In particular it has been noted that the narrowband and statistical (temporal) nature of the downlink interference can influence the behavior of sub-band CQI and PMI reporting. While the presence of interference in CDMA systems is largely consistent across the channel bandwidth, the presence of interference in OFDMA systems using frequencyselective scheduling can change rapidly from the time of CQI reporting to its impact on the next scheduled transmission. However, the use of a scheduled uplink for LTE is an advantage compared to the approach used in CDMA whose capacity was limited by noise rise at the base station. The downlink interference protection between CDMA cells offered by the use of scrambling codes is not available in narrowband OFDMA transmissions, which leaves the narrowband signals vulnerable to narrowband interference. However, the ability of cells to coordinate their narrowband scheduling offers some potential for interference avoidance. Support for coordination of resource block (RB) allocation between cells in the downlink was introduced in Release 8 with the inclusion of the relative narrowband transmit power (RNTP) indicator. This support feature is a bitmap that can be shared between base stations over the X2 interface. It represents those RBs for which the base station intends to limit its output power to a configurable upper limit for some period of agreed-upon time. This feature allows schedulers to agree on how cell-edge RB will be used so that, for instance, cell-edge users who cause the most interference can be restricted to certain parts of the channel. This coordination could be implemented using a semi-static agreement for partial frequency reuse at the cell edge or might involve more dynamic scheduling based on realtime network loading.

26 26 Keysight LTE Advanced: Technology and Test Challenges Application Note Two interference coordination mechanisms based on RB bitmaps are available for the uplink. The first is a bitmap called the overload indicator (OI), which can be provided by a base station to neighbor base stations indicating the level of uplink power plus noise as being low, medium, or high. The second is more proactive and is the high interference indicator (HII). This is communicated to neighbor base stations prior to the UE being scheduled, giving other base stations the chance to avoid the identified RB rather than allowing interference to occur and then having to deal with the consequences. These basic frequency domain approaches to ICIC are elaborated in Release 10 with the additional ability to coordinate inter-cell scheduling in the time domain. Heterogeneous networks The original cellular deployment scenario in Release 8 was the traditional cellular pattern of adjacent cells sharing the same frequency. By Release 10 a variety of new base station types have been introduced including the local area BS (picocell), home BS (femtocell), and relay node. The inter-cell coexistence techniques that might be employed in a Release 8 network comprising wide area base stations are well understood; however, the introduction of the new base station types creates new coexistence scenarios. The issue is not that a network incorporating only one base station type might be deployed in which case existing techniques might suffice but that the network might include a mixture of different base station types, all occupying the same frequency. This scenario has been termed the heterogeneous network or HetNet for short. In the HetNet environment new co-channel interference scenarios arise that require new inter-cell interference coordination solutions. There are two forms of co-channel heterogeneous deployment, each requiring a different approach to interference avoidance. The first is the open subscriber group (OSG), a type of deployment that might be used by an operator with a macro network providing broad coverage overlaid with local area base stations in areas where coverage issues exist or where higher capacity is needed for example, in a shopping mall. In this scenario a user is free to roam between the macro network and any local area BS deployed by the operator on the same frequency. For OSG deployment, the local area BS is located in the center of the area in the network where the increased capacity is required. At the perimeter of this area the strengths of the wide area and local area base stations are similar and performance may be significantly degraded. Closer to the local area BS the interference becomes less problematic. It is also possible to have an OSG scenario with a home BS, provided that the home BS is configured to be open to all users of that operator. The second form of co-channel deployment is the closed subscriber group (CSG). This type of deployment is essentially limited to a home BS scenario in which access to the home BS is limited to a fixed group of subscribers; for example, the occupants of a dwelling or employees of an enterprise. The deployment provides good service for the closed subscriber group but creates a much more difficult interference situation for all other users since the problem area is no longer limited to a ring around the local area BS or home BS but extends to the entire coverage area of the home BS. Such a situation could be acceptable in low density rural areas but is likely to cause severe difficulties for macro network coverage in more densely populated areas. The obvious solution to home BS CSG is to assign different channels to the home BS and the macro network, thus restricting the interference to that which exists between adjacent home BS. Unfortunately this approach is not available to operators with only a single channel. Some form of partial frequency reuse is also possible although this does not solve interference in the control channels, which always occupy the central 1.08 MHz of the channel. Given the difficulty of CSG, the initial work on eicic in heterogeneous networks has been focused on the OSG case.

27 27 Keysight LTE Advanced: Technology and Test Challenges Application Note Almost blank subframes The frequency domain ICIC techniques available in Release 8 and Release 9 are effective in managing the interference caused by data traffic, but these techniques are not suited to minimizing interference between the control channels, which always occupy the same central 1.08 MHz of the channel regardless of channel bandwidth. To deal better with control channel interference issues, Release 10 introduces the almost blank subframe (ABS) as the primary mechanism for eicic. In this time-domain approach, the macro network chooses to minimize scheduled transmissions on certain subframes so that they can be used by the local area BS with minimal degradation of performance. These subframes are considered almost blank since minimal control traffic on the PDCCH may still be present in order to schedule macro uplink traffic and maintain HARQ ACK/NACK feedback to the macro UE. Backward compatibility to Release 8 and Release 9 UEs must also be maintained, which requires that the base station downlink still be measurable by legacy UEs. To do this, the downlink subframe must contain the cell RS, synchronization signals, and the paging channel. If the downlink subframe is designated as an MBSFN subframe, then fewer signals will be required. As with the RNTP indicator introduced for frequency-domain ICIC, the use of ABS by the macro BS is indicated by an ABS pattern bitmap, but in this case we are not dealing with frequency domain RBs but with the time-domain subframe. There is also a secondary indicator known as the measurement subset, which indicates to the victim BS those subframes that the UE connected to the victim BS should use to assess the interference from the macro network when ABS is not configured. There is a great deal of flexibility in how ABS can be used and as such the standards specify the mechanisms for use in proprietary implementations but does not mandate specific solutions. Further enhanced ICIC Some of the work on eicic was not completed in Release 10 and so the further enhanced ICIC (FeICIC) work item was created for Release 11. This includes specification of system performance requirements for scenarios involving a dominant downlink interferer. Carrier-based HetNet ICIC The ICIC requirements developed through Release 10 are all based on co-channel (intrafrequency) scenarios. It was originally planned to develop ICIC further in Release 11 to take advantage of network-based carrier selection and this work was carried over to Release 12 but subsequently terminated early due to overlap with other work on small cell enhancements. Minimization of drive test Drive testing has long been used to facilitate the planning and operational optimization of networks. While drive testing is a powerful technique, it is time-consuming and expensive to carry out. To alleviate some of the cost associated with drive testing, a new set of UE measurement capabilities are introduced in Release 10 under the minimization of drive test (MDT) work item. The Release 10 work was focused on coverage and Release 11 added QoS verification. The MDT technical report is in TR [6]. Machine-type communications (MTC) For most of the history of cellular communications the goal has been to provide services between people. However, since the advent of data services there has been an increasing desire to support cellular communication between machines. These could be vending machines communicating with a corporate server to indicate sales activity and the need for restocking, or perhaps machines providing remote meter reading. The types and frequency of traffic in such scenarios are quite different from those for which LTE was originally developed. Machine-type communications often involve small amounts of data sent infrequently, preferably using very low cost infrastructure.

28 28 Keysight LTE Advanced: Technology and Test Challenges Application Note These attributes are well-served by legacy systems such as GSM but are not well-suited to the footprint provided by LTE Release 8, whose lowest UE category mandates support for at least 10 Mbps in the downlink with two receivers and 5 Mbps in the uplink. The purpose of the MTC work item is therefore to develop additional UE categories more suited to the lower requirements of MTC. The work on MTC started in Release 10 continued in Releases 11 and 12. The scope has been clarified to indicate a target improvement in coverage over legacy systems of some 20 db (later reduced to 15 db) for very small data packets on the order of 100 bytes per message in the uplink and 20 bytes per message in the downlink. This may be achieved through drastically reduced latency of up to 10 seconds in the downlink and one hour in the uplink. High overall system efficiency can then be delivered through scheduling during quiet times. The MTC technical report is in TR [7]. For a summary of the further enhancements, see page 50. New frequency bands New frequency bands were added in Release 10 as shown in Table 6. The number has continued to grow with each release of the 3GPP specification. To help maintain some degree of simplicity in the specification, LTE-Advanced frequency bands are therefore release independent, which means that a band defined in a later release can be applied to an earlier release. A list of all frequency bands specified to date is found on page 47. Table 6. Frequency bands added during Release 10 Band number Uplink Downlink Low High Low High Bandwidth Duplex spacing FDD FDD FDD FDD TDD TDD TDD Gap Duplex mode

29 29 Keysight LTE Advanced: Technology and Test Challenges Application Note New UE categories LTE-Advanced introduces technology to support higher data rates and higher order MIMO capabilities. For practical reasons, performance levels below the maximum theoretically possible are necessary to enable a range of implementation choices for system development. These are handled through the different UE categories specified for LTE and LTE-Advanced. Release 8/9 LTE supports five categories, with the maximum category able to reach approximately 300 Mbps in the downlink and 75 Mbps in the uplink. Release 10 adds three new categories to support LTE-Advanced features, as shown in Table 7. More categories were added in Releases 11 and 12. Table 7. Peak data rates and layers supported by UE categories specified in Release 10 Introduced in Release 8/9 LTE Introduced in Release 10 LTE-Advanced UE category Date rate DL/UL (Mbps) Downlink Uplink Max number of Max number of Support layers layers for 64QAM 1 10/5 1 1 No 2 50/ No 3 100/ No 4 150/ No 5 300/ Yes 6 300/50 2 or 4 1 or 2 No 7 300/100 2 or 4 1 or 2 No / Yes Comparing categories 5 and 6 shows that both can reach 300 Mbps in the downlink. The main difference is in the MIMO capabilities that the UE must support to reach the maximum. In a category 5 device, MIMO 4x4 is required to reach 300 Mbps. However, a category 6 device can reach that maximum using just 2x2 MIMO. The reason is that category 6 supports carrier aggregation, and with this feature the transmission bandwidth can be increased thus increasing the IP data rates available without requiring the very complex higher order MIMO techniques. The highest category supported by LTE-Advanced is category 8, which represents the maximum theoretical values provided by this technology: 3 Gbps in the downlink and 1.5 Gbps in the uplink. As Table 8 shows, there is a large gap between what can be supported by a category 7 and a category 8 device. Currently 3GPP is evaluating the creation of new UE categories to reduce this performance gap.

30 30 Keysight LTE Advanced: Technology and Test Challenges Application Note 3 Release 11 LTE-Advanced Enhancements Release 11 continues the work of Release 10 with enhancements to LTE-Advanced along with new frequency bands and new band combinations for carrier aggregation. Work continued on a number of items started in earlier releases, including carrier aggregation, home base stations (HeNB), SON, minimization of drive test, machine-type communication, and MBMS service enhancements. New features were also introduced in Release 11, including coordinated multi-point (CoMP) operation for LTE, further enhanced inter-cell interference coordination (FeICIC) for devices with interference cancellation, and an enhanced physical downlink control channel (EPDCCH) for LTE-Advanced. A complete list of all Release 11 features is found in the Overview of 3GPP Release 11 [8]. Work on Release 11 for RAN started in December 2010 and the core work was completed in September 2012 with test aspects following on later. 3.1 New frequency bands The new frequency bands added in Release 11 are shown in Table 8. Table 8. Frequency bands added during Release 11 Band number Uplink Downlink Low High Low High Bandwidth Duplex spacing FDD FDD FDD 29* FDD TDD *Band 29 is a supplemental downlink only band intended for use in carrier aggregation scenarios. 3.2 Release 11 features for UTRA and LTE Gap Duplex mode The following enhancements in Release 11 apply to the high speed packet access (HSPA) UTRA as well as the LTE/LTE-Advanced E-UTRA. Further self-optimizing network (SON) enhancements Mobility robustness optimization (MRO) enhancements were completed in Release 10 with appropriate support for LTE. However, although the need for an inter-rat solution was identified, there was no time to complete the work at that time and the inter-rat MRO enhancement topic was postponed. Release 11 enhancements for inter-rat MRO provide mechanisms for detecting and enabling correction of connection failures due to inter-rat mobility and inter-rat ping pong. Solutions may involve handover optimization techniques, analysis of statistics collected by the responsible node, and coverage verification. To that end, support has been added for retrieving information for problem analysis from both the enb and the network. Several inter-rat ping-pong scenarios were identified to be brought to the specification stage: (1) inter-rat failure issues related to deployment of LTE over broader 2G/3G coverage; (2) connection failure resolution support for HetNet deployments in case of certain handover problems occurring between macro and pico cells; and (3) inter-rat ping pong event resolution. See [8] [4].

31 31 Keysight LTE Advanced: Technology and Test Challenges Application Note Enhancement of MDT for E-UTRAN and UTRAN E-UTRAN measurement and reporting solutions are enhanced for immediate MDT that is, measurement results are reported immediately to the enb when the UE is in the connected state (RRC_CONNECTED). The enb can request detailed location information from the UE, and it is desired that the UE provide fresh location information with each immediate MDT measurement report. However, the means by which this is achieved is up to the specific UE implementation. The MDT data reported from UEs and the RAN may be used to verify QoS, assess user experience from the RAN perspective, and assist network capacity extension. Release 11 adds the first quality of service (QoS) use cases, which address traffic location in a cell and for user QoS experience. It also adds new coverage use cases for cell boundary mapping and coverage mapping. See [6]. Network energy saving for E-UTRAN With the growth in network capacity there is an increasing need to consider the energy costs of operating the network. In particular, opportunities exist to dynamically dimension the network based on traffic loading. The stage 2 definition of network energy saving is defined in TS [4] Section The basic mechanism is that an enb containing one or more capacity booster cells in addition to the basic coverage cells may choose to deactivate the booster cells based on a drop in the network load. This deactivation may require communication with peer enbs over the X2 interface to indicate that the booster cell is going to be deactivated. Also, it may be necessary to offload users from the booster cell to the coverage cells by means of handover. A study item in Release 11 evaluated three energy saving use cases and the feasibility of solutions and enhancements. Solutions for intra-enb energy savings use cases are implementation-based and are already supported in the specification. However, for inter-enb and inter-rat use cases further specification work is needed. For inter-enb energy savings when the cells are overlapping, it may be necessary to add enhancements on top of the Release 9 solution. For inter-rat energy savings, an OAM or signaling-based solution is feasible. The results of the study are found in TR [9]. See also [8] [4]. RF requirements for multi-band and multi-standard radio Prior to Release 11, the RF requirements for multi-band, multi-standard radio (MB-MSR) base stations had not yet been defined. Existing MSR RF requirements based on the single-band scenario could not necessarily be reused directly for an MB-MSR base station. Therefore, both core and test requirements needed to be updated based on identified multi-band application scenarios. A work item was created in Release 11 to define the RF requirements for macro-cell deployment scenarios (scenarios based on micro- or pico-cell deployments will be developed in a later stage).both FDD and TDD deployment scenarios and band combinations were identified for development, and the MB-MSR BS is based on a common transmitter or receiver RF chain for the multiple bands. The specification work included creation of the core RF requirements (transmitter and receiver characteristics) and the test configuration and test requirements derived from the RF requirements. A complete description of the work item is found in TR [10].

32 32 Keysight LTE Advanced: Technology and Test Challenges Application Note Further enhancements to H(e)NB mobility A number of mobility-related enhancements for UMTS HNBs and LTE HeNBs were evaluated and the results are captured in TR For LTE, Release 11 defines the requirements to support and update specifications for enhanced mobility between the macro to open HeNB, macro to hybrid HeNB, open HeNB to hybrid HeNB, hybrid HeNB to hybrid HeNB (inter-closed subscriber group (CSG)), CSG HeNB to macro CSG, and HeNB to hybrid HeNB. Closed subscriber group membership verification is performed using a method defined in TR for mobility towards hybrid-mode HeNBs. Release 11 also introduces an optional X2 gateway in support of HeNB to HeNB mobility. See [8]. 3.3 Release 11 features for LTE A number of LTE-only enhancements were added in Release 11 to support LTE-Advanced. In addition to new frequency bands and carrier aggregation combinations, the following features were defined. Network-based positioning support in LTE As noted earlier, positioning support was added to LTE in Release 9 based on methods such as AGNSS and downlink observed time difference of arrival (OTDOA). Network-based positioning support is added in Release 11; specifically, uplink time difference of arrival (UTDOA) positioning is specified based on the sounding reference signals (SRS) being used for uplink measurements. The UTDOA method is widely deployed and proven in the US and it was determined that this method could support emergency service calls requiring a high degree of accuracy. Further, UTDOA can be used in areas with insufficient satellite coverage to support AGNSS or where downlink OTDOA is not supported. The core specifications for network-based positioning support of LTE include the following: Stage 2 specification of UE positioning architecture, protocol, interface, and procedures for UTDOA. Specification of SRS measurement definition, SRS measurement requirements (mea surement period and accuracy requirements) and RF requirements based on SRS only. Specification of the interface and signaling support between UTDOA measurement units and between UTDOA measurement units and the evolved serving mobile location center (E-SMLC).The location measurement units (LMUs) that support UTDOA measurements are located at the enb. A new interface called the SLm is specified at the boundary between the LMUs and the E-SMLC. It is described in new TS [11]. Specification of procedures for UTDOA measurement triggering, measurement configuration, assistance data transfer, and measurement report transfer. Completion of the performance specifications which include the RF measurement definitions, reports, and measurement time and accuracy requirements based on SRS was moved from Release 11 to Release 12. The performance specifications are detailed in TS [12] and the conformance test specifications are in TS [13].

33 33 Keysight LTE Advanced: Technology and Test Challenges Application Note Service continuity improvements for MBMS for LTE Release 11 evolved MBMS for LTE to make the feature set more competitive. As defined in Release 9, MBMS services are broadcast over an entire multi-broadcast single frequency network (MBSFN) area, even though some services may be relevant only to certain parts of the area. A UE could potentially minimize battery consumption if it can determine which MBMS services are relevant to its current location and, based on that information, decide which services to receive and decode. Further, mobility procedures do not account for MBMS reception in Release 9 and Release 10. Making the network aware of the services that the UE is receiving or is interested in receiving via MBMS could facilitate proper action by the network, such as handover to a target cell or reconfiguration of secondary cells to facilitate the continuity of unicast services and desired MBMS services. The Release 11 MBMS enhancements specify the mechanisms for enabling the network to provide continuity of the services provided by an MBSFN in deployment scenarios involving one or more frequencies. These mechanisms include cell selection and reselection that allow the UE to receive the desired MBMS services in RRC Idle mode, and the signaling mechanisms for providing continuity of the desired MBMS services in RRC Connected mode. The related multi-cell/multicast coordination entity (MCE) functionality for these mechanisms is also specified. Mobility procedures are enhanced for MBMS reception, allowing the UE to start or continue receiving MBMS services via MBSFN when changing cells. The E-UTRAN procedures provide support for service continuity with respect to mobility within the same MBSFN area. Within the same geographic area, MBMS services can be provided on more than one frequency, and the frequencies used to provide MBMS services may change from one geographic area to another within a public land mobile network (PLMN). See [4] [8]. Further enhanced non CA-based ICIC for LTE Efforts to reduce interference in co-channel deployments of heterogeneous networks were begun in Release 10 with the specification of eicic. Release 11 continues this work, defining further enhancements to ICIC (FeICIC) which do not rely on carrier aggregation. Updates to UE performance requirements and signaling are specified (1) to improve detection of physical cell identifier (PCI) and critical system information in the presence of dominant interferers and different network configurations, and (2) to improve downlink control and data detection and UE measurement and reporting in the presence of dominant interferers including colliding and non-colliding reference signals as well as almost blank subframe (ABS) configurations. These enhancements are all dependent on the UE receiver configuration. See [8]. Without a receiver capable of interference cancellation, a heterogeneous network s eicic can work effectively only for non-colliding cell-specific reference signal (CRS) cases. Release 11 enables the network to signal assistance information to the UE for CRS interference cancellation that involves signaling of neighbor macrocell information. To better detect system information, the network uses dedicated signaling of the broadcast system information block type 1 (SIB-1) [14].

34 34 Keysight LTE Advanced: Technology and Test Challenges Application Note LTE RAN enhancements for diverse data applications The diverse range of mobile data applications available to consumers is now very extensive and includes short message service (SMS), instant messaging, web browsing, social networking, and a variety of push services. Modern devices such as tablets and smartphones will often activate some or all of these services in parallel, putting considerable strain on the radio network not just due to the volume of data but also the substantial signaling overhead created by the chatty nature of many applications. In addition, the user expectation of an always-on mobile broadband experience puts great demands on battery consumption since the device may be prevented from reaching the idle state. Moreover, most modern applications were not developed with the unique characteristics of cellular networks in mind and so the use of network resources is often inefficient. How to balance the demands of user experience with battery consumption and network efficiency will depend on the characteristics of individual applications that may vary over time. The outcome of the RAN enhancement work item is captured in TR [15]. It has resulted in the specification of a power preference feature that allows the UE to signal the network its preference for a configuration that reduces power consumption. The details of how the UE sets the preference indicator mechanism are left to UE implementation. Relays for LTE Support for relays was specified in Release 10, and Release 11 defines the RF core requirements needed for full relay specification support. Specifically, these are transmitter and receiver requirements for access and backhaul, and they are captured in a technical specification, TS [16]. Transmitter characteristics are defined for output power and output power dynamics, transmitted signal quality, unwanted emissions, and intermodulation. Receiver characteristics are defined for reference sensitivity, dynamic range, in-channel selectivity, adjacent channel selectivity and blocking requirements, receiver spurious emissions, and receiver intermodulation. Another new technical specification, TS [5] defines the RF test methods and conformance test requirements for E-UTRA relay derived from the specifications defined in TS Signaling and procedure for interference avoidance for in-device coexistence So that users can access various networks and services wherever they are, an increasing number of UEs are equipped with multiple radio transceivers for LTE, Wi-Fi, Bluetooth, GNSS, etc. As a result, UEs are challenged to avoid coexistence interference between those co-located radio transceivers. The studies done for the work item that led to this feature showed that existing radio resource management (RRM) mechanisms in some cases were not effective enough to handle the coexistence issues, and some enhanced signaling and other procedures would be necessary to avoid or mitigate the coexistence interference in the identified usage scenarios. As a result of this work a new in-device coexistence (IDC) indication message was defined in TS [17]. This message enables the UE to alert the network of an interference issue and provide information regarding the direction and nature of the interference, which may be identified in either the time or frequency domain. Upon receipt of the IDC message, the network will take appropriate steps to alleviate the problem by reallocating radio resources.

35 35 Keysight LTE Advanced: Technology and Test Challenges Application Note Coordinated multi-point transmission (CoMP) Coordinated multi-point (CoMP) sometimes called cooperative MIMO or network MIMO has long been under consideration for LTE and in Release 11 is at last defined. The goal of CoMP is to improve the coverage of high data rates and cell-edge throughput, and also to increase system throughput. Figure 12 compares standard MIMO with CoMP. The primary difference between standard MIMO and CoMP is that for the latter, the transmitters are not physically co-located. In the case of downlink CoMP, however, there is the possibility of linking the transmitters at baseband (shown as the link between the transmitters on the right half of Figure 8 to enable sharing of payload data for the purposes of coordinated precoding. This sharing is not physically possible for the uplink, which limits the options for uplink CoMP. For the standard network topology in which the enbs are physically distributed, provision of a high capacity, low latency baseband link is challenging and would probably require augmentation of the X2 inter-enb interface using fiber. However, a cost-effective solution for inter-enb connectivity is offered by the move towards a network architecture in which the baseband and RF transceivers are located at a central site with distribution of the RF to the remote radio heads via fiber. The physical layer framework for CoMP is described in the Release 11 feasibility study in [18]. Figure 12. Standard MIMO versus coordinated multi-point CoMP deployment scenarios Four downlink scenarios were defined for the feasibility study: Scenario 1 (Figure 13) is a homogeneous network (all cells have the same coverage area) with intra-site CoMP. This is the least complex form of CoMP and is limited to enbs sharing the same site. Figure 13. Scenario 1 Homogeneous network with intra-site CoMP ( [18], Figure A.1-1)

36 36 Keysight LTE Advanced: Technology and Test Challenges Application Note Scenario 2 (Figure 14) is also a homogeneous network but with high Tx-power remote radio heads (RRHs). This is an extension of scenario 1 in which the six sites adjacent to the central site are connected via fiber optic links to enable baseband cooperation across a wider area than is possible with scenario 1. Figure 14. Scenario 2 Homogeneous network with high Tx power RRHs [( [18], Figure A.1-2)] Figure 15. Reference CoMP coordination cell layout for Scenario 2 [( [18], Figure A.1-3)]

37 37 Keysight LTE Advanced: Technology and Test Challenges Application Note Scenarios 3 and 4 (Figure 16) are heterogeneous networks in which low power RRHs with limited coverage are located within the macrocell coverage area. In scenario 3 the transmission/reception points created by the RRHs have different cell identifications than does the macro cell and for scenario 4 the cell identifications are the same as that of the macro cell. Figure 16. Scenario 3/4 - Network with low power RRHs within the macrocell coverage area [( [18], Figure A.1-4)] CoMP categories The introduction of CoMP enables several new categories of network operation. Downlink CoMP categories are defined as follows. Joint processing (JP): Data for a UE is available at more than one point in the CoMP cooperating set for the same time-frequency resource. Joint transmission (JT): This is a form of spatial multiplexing that takes advantage of de-correlated transmission from more than one point within the cooperating set. Data to a UE is simultaneously transmitted from multiple points; e.g., to coherently or noncoherently improve the received signal quality or data throughput. Dynamic point selection (DPS)/muting: The UE data is available at all points in the cooperating set but is only transmitted from one point based on dynamic selection in time and frequency. The DPS includes dynamic cell selection (DCS). DPS may be combined with JT, in which case multiple points can be selected for data transmission in the time-frequency resource. Coordinated scheduling and beamforming (CS/CB): Data for a UE is only available at and transmitted from one point in the CoMP cooperating set but user scheduling and beamforming decisions are made across all points in the cooperating set. Semi-static point selection (SSPS) is used to make the transmission decisions. Dynamic or semi-static muting may be applied to both JP and CS/CB. Hybrid JP and CS/CB: Data for a UE may be available in a subset of points in the CoMP cooperating set for a time frequency resource but user scheduling and beamforming decisions are made with coordination among points corresponding to the CoMP cooperating set. For example, some points in the cooperating set may transmit data to the target UE according to JP while other points in the cooperating set may perform CS/CB. New categories in the uplink are the following. Joint reception (JR): The PUSCH transmitted by the UE is simultaneously (jointly) received at some or all of the points in the cooperating set. This simultaneous reception can be used with inter-point processing to improve the received signal quality. Coordinated scheduling and beamforming (CS/CB): User scheduling and precoding selection decisions are made with coordination among points corresponding to the cooperating set. Data is intended for one point only.

38 38 Keysight LTE Advanced: Technology and Test Challenges Application Note CoMP sets Various sets of enbs are identified for downlink CoMP purposes. CoMP cooperating set: The set of enb points within a geographic area that are directly or indirectly participating in data transmission to a UE. The UE may or may not know about this set. The direct participation points are those actually transmitting data and the indirect points are those involved in cooperative decision making for user scheduling and beamforming in the time and frequency domains. CoMP transmission point(s): The point or set of points transmitting data to a UE. CoMP transmission points are a subset of the CoMP cooperating set. For JT, CoMP transmission points may include multiple points in the CoMP cooperating set at each subframe for a certain frequency resource. For CS/CB, DPS, and SSPS, a single point in the CoMP cooperating set is the CoMP transmission point at each subframe for a given frequency resource. For SSPS, the CoMP transmission point can change semi-statically within the CoMP cooperating set. CoMP measurement set: The set of points about which channel state and statistical information related to the UE radio link is measured and reported. RRM measurement set: The set of cells for which Release 8 radio resource management (RRM) measurements are performed. Additional RRM measurement methods may be developed; e.g., in order to separate different points belonging to the same logical cell entity or in order to select the CoMP measurement set. For the uplink, the following sets are identified. CoMP reception point(s): The point or set of points that is a subset of the cooperating set receiving data from a UE. For JR, CoMP reception points may include multiple points in the CoMP cooperating set at each subframe for a certain frequency resource. For CS/CB, a single point in the CoMP cooperating set is the CoMP reception point at each subframe for a certain frequency resource. Radio interface aspects To enable CoMP operation, changes to the radio interface will likely be needed in the areas of channel state information (CSI) feedback from the UE, preprocessing schemes for coordination of joint transmission, and possibly new reference signal designs and new control signaling mechanisms. Reuse of existing Release 8 CSI measurements extended for CoMP, called explicit feedback, is expected. Channel parameters (per point) include the channel matrix H, the transmit covariance matrix R, and possibly inter-point properties such as the inter-point phase relationship required for JT. Noise and interference parameters are also required. To take full advantage of CoMP, more advanced implicit feedback will be required based on UE hypotheses about different CoMP transmission and reception processing. The potential for CoMP becomes greater for TDD operation since UE transmission of the sounding reference signal (SRS) can be used by the enb to precisely determine the downlink channel conditions on the assumption of TDD channel reciprocity.

39 39 Keysight LTE Advanced: Technology and Test Challenges Application Note Simulation results Extensive simulation of CoMP performance has been performed by multiple companies for the four deployment scenarios identified for uplink and downlink FDD and TDD. Both 3GPP and ITU channel models were used, and the impact of cell loading and inter-cell communication latency and bandwidth was also studied. Although the simulation criteria were specified, the results showed variations in performance that may be due to different assumptions being made for the channel estimation error modeling, channel reciprocity modeling, feedback and SRS mechanisms, the scheduler, and the receiver. The impact of CoMP on legacy UEs is not considered. The results of the simulations show that CoMP gains vary widely depending on the specific scenario and whether the focus is on average cell performance, mean user performance, or improving the performance of the worst 5% of users in the cell. Some scenarios provide no gain at all and others, particularly TDD with its channel reciprocity advantage, show gains of up to 80%. Typical gains fall in the range of 10% to 30%. As a result, a work item to progress CoMP was defined in Release 11 with the intention of developing the following aspects: Joint transmission Dynamic point selection, including dynamic point blanking Coordinated scheduling and beamforming, including dynamic point blanking. In support of downlink CoMP, a new PDSCH transmission scheme, TM 10, was introduced in Release 11. This includes a new feedback mechanism that supports CS/CB and DPS. Work on CoMP is ongoing. Enhanced downlink control channels for LTE-Advanced In LTE-Advanced, the continued introduction of features such as carrier aggregation, CoMP, and enhanced downlink MIMO has resulted in the need to enhance the capabilities of the physical downlink control channel (PDCCH). As defined in the Release 11 core specification, the enhanced PDCCH (EPDCCH) will be compatible with legacy carriers, provide more signaling capacity, support frequency domain ICIC, improve the spatial reuse of the control channel, support beamforming and diversity schemes, and operate in MBSFN subframes. (The ability to also operate in non-mbsfn subframes is assumed.) Frequency-selective scheduling for the EPDCCH is also desirable as is mitigation of intercell interference. The common search space for enhanced downlink control channels is not included in this definition.

40 40 Keysight LTE Advanced: Technology and Test Challenges Application Note Public safety broadband high power UE for Band 14, Region 2 The US Federal Communications Commission Public Safety and Homeland Security Bureau has selected LTE as the technology for public safety services in the 700 MHz public safety band (3GPP Band 14; see page 46 table). Due to the coverage and uplink performance requirements for public safety broadband (PSBB) systems, the existing 23 dbm UE power class (class 3) is not considered sufficient. Public safety first responders will rely on handheld UEs as well as vehicular mobile applications that have fewer constraints on size, weight, and power consumption than handheld UEs. A vehicular mobile application also has the possibility of incorporating very efficient vehicle-mounted antennas. Unlike commercial cellular systems, which often generally have a 95 % population coverage target, PSBB systems target 99% coverage. Although this change may seem insignificant, to reach the additional 4% of the US population requires a 60% increase in the coverage area. Providing such coverage using base stations alone would be very expensive, so a higher power UE (HPUE) power class 1 has been specified in band 14 for a vehicular mobile form factor with vehicular-mounted antennas. The provisional requirements are captured in TS [19] and the RF specifications in TS [20]. In order to optimize reuse of the existing LTE UE ecosystem, the new requirements minimize change that might impact the design of the baseband and lower-power RF components of the UE. The bulk of the design changes are in the RF front end containing the power amplifier (PA), filtering, and signal-combining components. The headline parameter driving the HPUE specification is the 8 db increase of maximum output power to 31 dbm. Although few other transmitter and receiver requirements will be changed from those defined for the existing power class 3 UE (23 dbm), this increased maximum power has considerable design implications for both the transmitter and the receiver. For instance, the dynamic range of the transmitter increases 8 db and all fixed-level unwanted emissions become 8 db harder to meet. For the receiver to maintain the existing RF sensitivity the duplex filter has to provide 8 db more isolation from the transmitter. The tighter filtering requirements represent probably the biggest design change for the HPUE because existing miniature surface acoustic wave (SAW) filters measuring perhaps 5 mm3 cannot handle the higher output power or provide the necessary filtering performance. Alternative technologies will be required for example, ceramic or cavity filters, which are substantially larger at around 8000 mm3. Fortunately, the form factor of the vehicular mobile has more relaxed constraints on size and power than does the standard handheld UE. Studies have shown that to maintain the existing co-existence performance of power class 3 UE, the HPUE will need to have better ACLR and so one of the few performance requirements to change for the HPUE was the ACLR requirement which has been tightened from 30 db to 37 db. In summary, the increase in maximum output power along with the potential for vehicularmounted antennas means that the power class 1 HPUE will offer substantially better performance in areas of poor reception than was possible with the power class 3 UE. It s expected that the increased cost of the HPUE will be offset by substantial savings in the number of base stations needed to achieve 99% population coverage.

41 41 Keysight LTE Advanced: Technology and Test Challenges Application Note Improved minimum performance requirements for E-UTRA: interference rejection Existing LTE UE demodulation requirements are based on the assumption of a linear minimum mean squared error (LMMSE) dual receiver. This is a powerful receiver architecture capable of suppressing both inter-cell and intra-cell interference. However, existing demodulation requirements are based on additive white Gaussian noise (AWGN), which is de-correlated between the antennas. This simplified method of modeling interference has been widely used for many years and is suitable for measuring the performance of receivers without interference cancellation capabilities. However, to exploit the full potential an LMMSE receiver with interference rejection combining (IRC) capabilities and achieve a performance gain over standard receivers, it is necessary to more accurately model the interference. Studies carried out in Release 10 showed that enhanced receivers capable of RS-based interference covariance estimation to mitigate spatial domain interference could provide significant throughput gains in the high interference conditions of a heavily loaded network. The scope of the Release 11 work included a variety of deployment scenarios that take into account the number of interfering sources, their structure (including transmission rank and precoding), and their power ratio relative to the total interference from other cells. This ratio is known as the dominant interferer proportion (DIP) ratio. Both synchronized and asynchronous cases were considered since they can have a major impact on interference susceptibility. Also within the scope of Release 11 were definitions of cell RS and UEspecific RS in anticipation of future network deployment scenarios. In TS [20], enhanced performance requirements are specified for interferenceaware receivers based on LMMSE IRC. Two aspects were considered: demodulation performance and receiver type verification, with the goal of ensuring that the LMMSE-IRC receiver structure is used for both demodulation and channel state information reporting. Corresponding updates to UE conformance test specifications along with a new technical report on the derivation of test tolerances for UE radio reception conformance tests, TR [21], are expected in September Additional special subframe configuration for LTE TDD The operation of TDD networks requires careful coordination between systems deployed on adjacent channels. Co-existence of LTE TDD with legacy UMTS TD-SCDMA systems is required and for this case, special subframe configuration number 5 is chosen for the normal cyclic prefix case and configuration number 4 for the extended cyclic prefix case. The special subframe lasts for one ms and always comes between the transition from downlink transmission to uplink transmission, although it is not required from the uplink back to the downlink. The special subframe comprises the downlink pilot timeslot (DwPTS), a gap period (GP), and an uplink pilot timeslot (UpPTS). The ratio between the DwPTS, GP, and UpPTS is configurable, and for TD-SCDMA co-existence, configuration 5 uses a ratio of 3:9:2 and configuration 4 uses 3:7:2. Although these configurations provide the necessary protection when LTE TDD and TD-SCDMA systems are in adjacent channels, the use of a relatively large GP in these configurations is seen as inefficient since no data can be transmitted during the gap period. To address this shortcoming, two new special subframe configurations have been specified in Release 11. For the extended cyclic prefix case, a new option for special configuration number 7 has been defined for a ratio of 5:5:2, which provides an additional two symbols for data communication per special subframe. For the normal cyclic prefix case a new special subframe configuration number 9 provides a ratio of 6:6:2, which is three extra useful symbols per special subframe. The signaling and procedure to support the use of the special subframe configurations are also specified.

42 42 Keysight LTE Advanced: Technology and Test Challenges Application Note Release 11 carrier aggregation One of the most significant air interface enhancements to the LTE specifications was the introduction of carrier aggregation in Release 10.Through Release 11, the specification of minimum air interface performance requirements is limited to dual-carrier CA, and the maximum aggregated bandwidth is still 40 MHz. Each carrier scenario needs to be studied in order to identify the combination of requirements necessary to ensure commercially viable deployment. Most of the carrier aggregation tradeoffs are made on the UE side since the UE has limited power and space to implement a multi-carrier transceiver. Release 11 introduces new carrier aggregation capabilities such as the ability to support multiple timing advances. Some uplink CA scenarios require the ability to define different timing advances for each carrier; for instance, in an inter-band case that uses repeaters for one band but not the other. To deal with the situation, the UE is allowed to adjust the timing advance of the two carriers independently such that the time orthogonality of the uplink in the cell is preserved. Another new CA feature introduced in Release 11 is the ability for TDD to support different uplink and downlink configurations for each band. This provides more flexibility than was possible in Release 10, which required that the format of each carrier be the same. As part of the Release 11 work on LTE carrier aggregation, TR [22] was created to summarize the radio requirements for the base station and UE radio transmission and reception. This report contains information related to the general framework for carrier aggregation enhancements covering the UE and base station aspects and intra-band noncontiguous spectrum. It specifies the support for use of multiple timing advances in case of LTE uplink carrier aggregation as well as the base station and UE characteristics for intra-band non-contiguous CA. TR also acts as a skeleton report to other Release 11 TRs that cover new CAspecific intra-band combinations, including contiguous scenarios for bands 7, 38, and 41 and non-contiguous scenarios for bands 3 and 25. The non-contiguous scenarios are more complicated in terms of their impact on device architecture and requirements. The inter-band carrier aggregation scenarios in Release 11 are studied in TR [23]. Inter-band CA is considerably more complicated than intra-band CA, so for the purposes of characterizing the different combinations, five inter-band CA classes have been identified. Class A1, low-high band combination without harmonic relation between bands Class A2, low-high band combination with harmonic relation between bands Class A3, low-low or high-high band combination without intermodulation problem (low order IM) Class A4, low-low or high-high band combination with intermodulation problem (low order IM) Class A5, combination except for A1 to A4 (similar to mid band combinations). The classes A2 and A4 require special study and may require alternative UE architectures.

43 43 Keysight LTE Advanced: Technology and Test Challenges Application Note A consequence of carrier aggregation in terms of the RF requirements is that many single-band requirements have to be modified to take into account what is practical to implement. There are also some new definitions and measurements required. For the base station, CA can be seen as a special case of multi-standard radio, and for that purpose additions have been made to TS [24] in support of non-contiguous intra-band CA: Introduction of definition of sub-block bandwidth for intra-band non-contiguous spectrum Clarification on requirements for contiguous and non-contiguous spectrum Introduction of time-alignment error requirement for intra-band non-contiguous operation Clarification of occupied bandwidth and adjacent channel leakage ratio (ACLR) requirements for non-contiguous spectrum Introduction of cumulative ACLR (CACLR) requirement for intra-band non-contiguous operation Clarification of operating band unwanted emissions and transmitter intermodulation requirements for noncontiguous spectrum Clarification of adjacent channel selectivity (ACS), narrowband blocking, blocking, and receiver intermodulation requirements for non-contiguous spectrum. For the UE, the introduction of CA has implications on most of the transmitter and receiver requirements in TS [20] Sections 6 and 7, including maximum output power and output power dynamics, transmit signal quality, spectrum emission mask (SEM), ACLR, spurious emissions, reference sensitivity, and many of the other receiver requirements. In general for the transmitter the existing requirements still apply per carrier although there are some exceptions. For example, the in-band emission requirements for transmit signal quality are specified for the intra-band contiguous CA case to take into account the different ways in which the UE is designed. The UE can implement intra-band CA either by aggregating two separate transmitters or by using a single wideband transmitter. The interaction between the carriers and the resulting spurious products are different in each case. The in-band emission requirements have been written with this in mind and are specified for both carriers active but only one carrier allocated. There are also differences in the number of exceptions for the IQ image and carrier leakage requirements. Additionally there are special cases in which network signaling requirements interact with carrier aggregation. An example for CA class 1C contiguous allocation is given in Table 9. Table 9. Contiguous allocation A-MPR for CA_NS_01 (TS [20] Table 6.2.4A.1-1 CA_1C RB Start L CRB [RBs] RB Start + L CRB [RBs] 100 RB/100 RB 75 RB/75 RB 0 30 and > 0 N/A [ 10] >80 N/A [ 5] N/A >70 [ 3] 0 13 and >0 N/A [ 10] >55 N/A [ 6] N/A >137 [ 2] A-MPR for QPSK and QAM [db]

44 44 Keysight LTE Advanced: Technology and Test Challenges Application Note Some of the specification relaxations are quite substantial (up to 10 db) indicating the considerable strain that certain combinations of carrier aggregation put on the UE design. Operating the UE under such conditions is therefore limited to small cell deployments in which maximum power handling is not critical. There are also implications from CA for many of the base station radio requirements including the new concept of CACLR, which defines the ACLR requirements as the addition of emissions from multi-carrier signals on either side of a gap between the carriers. In anticipation of the specification of three-carrier aggregation in Release 12, two new UE categories have been introduced in TS [25] Release 11. Category 9. Downlink is 450 Mbps paired with the uplink processing requirement as defined for uplink Category 6. Category 10. Downlink is 450 Mbps paired with the uplink processing requirement as defined for uplink Category 7. See Table 10. Table 10. Downlink physical layer parameter values set by the field UE category (TS [25] Table 4.1 1) UE category Maximum number of DL-SCH transport block bits received within a TTI (see Note) Maximum number of bits of a DL-SCH transport block received within a TTI Total number of soft channel bits Category Category Category Category Category Category Category (4 layers) (2 layers) (4 layers) (2 layers) or or 4 Category Category (4 layers) or 4 Category (4 layers) (2 layers) or 4 Maximum number of supported layers for spatial multiplexing in downlink NOTE: In carrier aggregation operation, the DL-SCH processing capability can be shared by the UE with that of MCH received from a serving cell. If the total enb scheduling for DL-SCH and an MCH in one serving cell at a given TTI is larger than the defined processing capability, the prioritization between DL-SCH and MCH is left up to UE implementation.

45 45 Keysight LTE Advanced: Technology and Test Challenges Application Note 4 Release 12 Radio Evolution Release 12 of the 3GPP specifications is a major upgrade that comes at a time when the amount of network traffic is exploding and shows no signs of slowing down. Although Release 12 is much anticipated, work is still in progress at the time of this writing. The completion of the stage 3 core specifications, originally scheduled for June 2014, is now expected in September Work on Release 12 began shortly after a June 2012 workshop to consider proposals. At that time the broad areas identified for future radio evolution were energy saving, cost efficiency, support for diverse application and traffic types, and backhaul enhancements. Although 3GPP focused largely on spectrum issues in earlier versions of the LTE/LTE- Advanced standard, with Release 12 there is a new emphasis on support for small cell and heterogeneous networks. Other areas that are prominent in the new Release concern advanced multiple antenna techniques (MIMO and beamforming) as well as procedures for supporting diverse traffic types. Important studies evaluate solutions for integration with wireless LAN, device-to-device communication, machine-type communication, and mobile relays. Table 11 lists 26 non-spectrum core work items for LTE in Release12, 15 of which have corresponding performance work items. Three core work items were deleted before their completion: New BS specification structure, Carrier-based HetNet ICIC for LTE, and New carrier type for LTE, the last of which is complemented by the work on E-UTRA small cell enhancements. Table 12 lists the two LTE RAN Release 12 performance work items based on core requirements defined in earlier releases and table 13 lists a few of the 27 study items in Release 12 that are likely to affect work in Release 13. The items in Tables 11, 12, and 13 marked with an asterisk will be further described. Table 11. Release12 LTE RAN core work items, non-spectrum Core work items Rel-12 LTE carrier aggregation* Further enhancements for H(e)NB mobility-part 3* RAN aspects for SIPTO at the local network Support for BeiDou Navigation Satellite System (BDS) for LTE LTE UE TRP and TRS and UTRA Hand Phantom related UE TRP and TRS requirements Base station RF requirements for Active Antenna System (AAS)* RAN enhancements for machine-type and other mobile data applications communications* WLAN/3GPP radio interworking* Increasing the minimum number of carriers for UE monitoring in UTRA and E-UTRA Further downlink MIMO enhancement for LTE-Advanced Further enhancements to LTE TDD for DL-UL interference management and traffic adaptation* HetNet mobility enhancements for LTE Further enhancements for HeNB mobility-x2-gw Public Warning System - Reset/Failure/Restart in warning message delivery in LTE LTE coverage enhancements Low cost and enhanced coverage MTC UE for LTE* LTE TDD-FDD joint operation including carrier aggregation* LTE-HRPD (high rate packet data in 3GPP2) inter-rat SON Further MBMS operations support for E-UTRAN* E-UTRA small cell enhancements - Physical layer aspects* Dual connectivity for LTE* Inter-eNB CoMP for LTE* LTE device to device proximity services* Network-assisted interference cancellation and suppression for LTE* Smart congestion mitigation in E-UTRAN Positioning enhancements for RF pattern matching in E-UTRA

46 46 Keysight LTE Advanced: Technology and Test Challenges Application Note Table 12. Release 12 LTE RAN performance work items deriving from core requirements in earlier releases Performance work items Verification of radiated multi-antenna reception performance of UEs in LTE/UMTS* Performance requirements of 8 Rx antennas for LTE UL* Table 13. Subset of Release 12 study items Study items Study on mobile relay for E-UTRA* Study on 3D-channel model of elevation beamforming and FD-MIMO studies for LTE* Study on group communication for LTE* 4.1 New frequency bands Release 12 added three new frequency bands (30, 31, and 32) for the LTE E-UTRA, shown in Table 14. As in prior releases, these frequency bands are considered releaseindependent, meaning that any band defined in a later release can be applied to an earlier release, considerably simplifying the specifications. Table 14. Release 12 new frequency bands E-UTRA operating band Uplink Downlink Duplex mode MHz 2315 MHz 2350 MHz 2360 MHz FDD MHz MHz MHz MHz FDD 32 N/A 1452 MHz 1496 MHz FDD* *Restricted to E-UTRA operation when carrier aggregation is configured. The downlink operating band is paired with the uplink operating band (external) of the carrier aggregation configuration that is supporting the configured Pcell. Table 15 shows all E-UTRA operating bands as of September It s worth noting that there is overlap between bands in some cases to accommodate regional differences. The duplex space varies from 30 MHz to 799 MHz and the gap between downlink and uplink varies from 5 MHz to 680 MHz. The narrow duplex spacing and gaps make it hard to design filters to prevent the transmitter spectral regrowth leaking into the receiver (known as self-blocking). Also notice that bands 13, 14, 20, and 24 have reversed uplink downlink frequencies and Bands 15 and 16 are specified by the European Telecommunication Standards Institute (ETSI) only for use in Europe. Bands 29 and 32 are defined as supplemental downlink only for use with carrier aggregation and as such have no uplink frequencies assigned.

47 47 Keysight LTE Advanced: Technology and Test Challenges Application Note Table 15. E-UTRA operating bands through Release 12 [3GPP TS V ( )] E-UTRA operating band Uplink (UL) operating band BS receive UE transmit F UL_low F UL_high Downlink (DL) operating band BS transmit UE receive F DL_low F DL_high Duplex mode MHz 1980 MHz 2110 MHz 2170 MHz FDD MHz 1910 MHz 1930 MHz 1990 MHz FDD MHz 1785 MHz 1805 MHz 1880 MHz FDD MHz 1755 MHz 2110 MHz 2155 MHz FDD MHz 849 MHz 869 MHz 894MHz FDD MHz 840 MHz 875 MHz 885 MHz FDD MHz 2570 MHz 2620 MHz 2690 MHz FDD MHz 915 MHz 925 MHz 960 MHz FDD MHz MHz MHz MHz FDD MHz 1770 MHz 2110 MHz 2170 MHz FDD MHz MHz MHz MHz FDD MHz 716 MHz 729 MHz 746 MHz FDD MHz 787 MHz 746 MHz 756 MHz FDD MHz 798 MHz 758 MHz 768 MHz FDD 15 Reserved Reserved FDD 16 Reserved Reserved FDD MHz 716 MHz 734 MHz 746 MHz FDD MHz 830 MHz 860 MHz 875 MHz FDD MHz 845 MHz 875 MHz 890 MHz FDD MHz 862 MHz 791 MHz 821 MHz FDD MHz MHz MHz MHz FDD MHz 3490 MHz 3510 MHz 3590 MHz FDD MHz 2020 MHz 2180 MHz 2200 MHz FDD MHz MHz 1525 MHz 1559 MHz FDD MHz 1915 MHz 1930 MHz 1995 MHz FDD MHz 849 MHz 859 MHz 894 MHz FDD MHz 824 MHz 852 MHz 869 MHz FDD MHz 748 MHz 758 MHz 803 MHz FDD 29 N/A 717 MHz 728 MHz FDD MHz 2315 MHz 2350 MHz 2360 MHz FDD MHz MHz MHz MHz FDD 32 N/A 1452 MHz 1496 MHz FDD MHz 1920 MHz 1900 MHz 1920 MHz TDD MHz 2025 MHz 2010 MHz 2025 MHz TDD MHz 1910 MHz 1850 MHz 1910 MHz TDD MHz 1990 MHz 1930 MHz 1990 MHz TDD MHz 1930 MHz 1910 MHz 1930 MHz TDD MHz 2620 MHz 2570 MHz 2620 MHz TDD MHz 1920 MHz 1880 MHz 1920 MHz TDD MHz 2400 MHz 2300 MHz 2400 MHz TDD MHz 2690 MHz 2496 MHz 2690 MHz TDD MHz 3600 MHz 3400 MHz 3600 MHz TDD MHz 3800 MHz 3600 MHz 3800 MHz TDD MHz 803 MHz 703 MHz 803 MHz TDD NOTE 1: Band 6 is not applicable NOTE 2: Restricted to E-UTRA operation when carrier aggregation is configured. The downlink operating band is paired with the uplink operating band (external) of the carrier aggregation configuration that is supporting the configured Pcell.

48 48 Keysight LTE Advanced: Technology and Test Challenges Application Note 4.2 Carrier aggregation scenarios There are now 143 carrier aggregation combinations defined for LTE-Advanced in the E-UTRA operating bands. Each new release of the 3GPP specification adds to the number, which indicates the fragmented nature of operator frequency allocations. And with Release 12, several carrier aggregation combinations for 3 carriers have been introduced. Rel-10, 3 new CA combinations Rel-11, 25 new CA combinations Rel-12, 87 new CA combinations, including aggregation of 3 downlink frequencies Rel-13, 28 new CA combinations so far. For equipment designers, this growing number poses a challenge, as every combination has the potential to require a new UE design to handle the filtering and power amplifier requirements. In Release 12 and beyond, carrier aggregation will evolve to include inter-site aggregation (dual connectivity for LTE; see next entry) and macrocell-assisted small cells. The goal is to enable the UE to remain connected at all times to the macro network on one carrier, which is likely to be at a lower (< 1 GHz) frequency for coverage reasons, while opportunistically connecting to the macro network on a second carrier provided by a small cell (probably not co-located) to provide higher capacity. The advantage of doing this using carrier aggregation rather than handover is that CA should provide much faster adaptation to the network conditions than handover-based approaches. Also under investigation are opportunities to exploit inter-site carrier aggregation with other radio systems such as UMTS and Wi-Fi to optimize overall performance. 4.3 Release 12 features and studies The following subset of Release 12 radio-related features and studies introduce new concepts to LTE or add important enhancements to existing capability. Dual connectivity for LTE As part of the Release 12 Study on Small Cell Enhancements from higher layer aspects, TR [26], it was concluded there was value in enabling a UE to be simultaneously connected to at least two different network points, the master enb (MeNB) and secondary enb (SeNB), with non-ideal backhaul. This inter-node radio resource aggregation is also known as dual connectivity. Dual connectivity can be across different locations and different frequencies, and potentially even different radio access technologies (for example, wireless LAN) at some time in the future. Many architectural options were considered by 3GPP and the work item takes forward scenarios 1A and 3C from the technical report. See Figures 17 and 18. Dual connectivity scenario 1A Benefits: No need for MeNB to buffer or process packets for an evolved packet system (EPS) bearer transmitted by SeNB Little or no impact to PDCP/RLC and GTP-U/UDP/IP No need to route all traffic to MeNB; low requirements on the backhaul link between MeNB and SeNB and no flow control needed between the two Support of local break-out and content caching at SeNB is easy for dual-connectivity UEs.

49 49 Keysight LTE Advanced: Technology and Test Challenges Application Note Drawbacks: SeNB mobility visible to CN Offloading needs to be performed by the mobility management entity (MME) and cannot be very dynamic Security impacts due to ciphering being required in both MeNB and SeNB Use of radio resources across MeNB and SeNB for the same bearer is not possible For the bearers handled by SeNB, handover-like interruptions at SeNB change with forwarding between SeNBs In the uplink, logical channel prioritization impacts the transmission of uplink data (radio resource allocation is restricted to the enb where the radio bearer terminates). Figure 17. Alternative 1A from TR [26], Figure Dual connectivity scenario 3C Benefits: SeNB mobility hidden to CN No security impacts with ciphering being required in MeNB only No data forwarding between SeNBs required at SeNB change Offloads RLC processing of SeNB traffic from MeNB to SeNB Little or no impacts to RLC Use of radio resources across MeNB and SeNB for the same bearer possible Relaxed requirements for SeNB mobility (MeNB can be used in the meantime). Drawbacks: Need to route, process and buffer all dual connectivity traffic in MeNB PDCP to become responsible for routing PDCP PDUs towards enbs for transmission and reordering them for reception Flow control required between MeNB and SeNB In the uplink, logical channel prioritization impacts for handling RLC retransmissions and RLC Status PDUs (restricted to the enb where the corresponding RLC entity resides) No support of local break-out and content caching at SeNB for dual connectivity UEs. Figure 18. Alternative 3C from TR [26], Figure

50 50 Keysight LTE Advanced: Technology and Test Challenges Application Note Further enhancements for H(e)NB mobility part 3 Following a Release 11 study item, this work item was introduced in Release 12 to further enhance the mobility between home (e)nbs, and from the home (e)nb to a wide-area enb. Both UMTS and LTE are considered. The aspects relevant to LTE focus on RAN sharing supported on the macro network, specifically for the following scenario: First, the UE reports the subset of the broadcast PLMN identities that can be accessed and can pass a closed subscriber group membership check. The home enb then verifies the access check, selecting just one PLMN identity if more than one pass the check. Finally the MME/SGSN verifies the CSG membership check for the PLMN selected by the home enb. RF and EMC requirements for active antenna system (AAS) The multiple antenna base station techniques that have been deployed to date are largely proprietary in nature and have no formal specifications or performance requirements. With the increasing sophistication of multiple antenna techniques it has become apparent that the largely omni-directional assumptions about base station RF and EMC performance are becoming less representative of actual system performance. The current reference point for base station requirements is the antenna connector and excludes the antenna behavior and any multi-antenna array affects such as beamforming. This work item will define the conducted and radiated performance requirements for AAS, independent of implementation, that will better represent the true spatial performance of the base station. The work item output is being captured in TR [27]. In order to progress the work the concept of an AAS has been defined as a base station system that combines an antenna array with an active transceiver unit array. An AAS may also include a radio distribution network (RDN), which is a passive network that physically separates the active transceiver unit array form the antenna array. Figure 19 shows the general AAS architecture. The Release 12 work will be limited to arrays of up to eight elements, with higher order arrays, possibly incorporating massive MIMO, being handled in later releases. Figure19. General AAS radio architecture (TR [27] Figure 4.3-1)

51 51 Keysight LTE Advanced: Technology and Test Challenges Application Note Machine type communications Providing machine-type communications (MTC) via the cellular network has become a significant opportunity for mobile operators to generate new revenue. Because most MTCrelated traffic is tolerant of delays and low throughput, MTC devices today operate mainly on GSM/GPRS networks, allowing the devices to be developed at a low cost knowing there is already broad coverage in legacy networks. Given that the market for MTC is growing, this situation perpetuates reliance on 2G networks at the cost of LTE. The study item Study on provision of low-cost Machine-Type Communications (MTC) User Equipment (UEs) based on LTE (Release 12) published in TR [7] looked at the feasibility of specifying and building cost-competitive LTE MTC devices, thus facilitating the migration of MTC traffic from 2G to LTE networks. The study also evaluated whether LTE coverage can be improved for MTC devices, with a target coverage improvement of up to 20 db that would address existing use cases in which MTC devices are deployed deep inside buildings. The study concluded that it is possible to specify an LTE MTC device with a material cost comparable to that of an EGPRS modem by combining various cost reduction techniques. The solutions considered in the study are applicable to both FDD and TDD. The study also concluded that a coverage improvement of 20 db in comparison to the normal LTE footprint is achievable for both FDD and TDD. However, TR recommended a coverage improvement target of 15 db for FDD in consideration of the additional UE power consumption, spectrum efficiency, specification impact, and standardization effort required. This coverage improvement may be further reduced in the downlink depending on which cost-reduction techniques are adopted in the design of the device. An additional study item, Study on Enhancements to Machine-Type Communications (MTC) and other Mobile Data Applications; Radio Access Network (RAN) aspects (Release 12), [29)], evaluates the impact on the RAN of the proposed solutions for implementing MTC and other mobile data communications. The study identifies and assesses possible mechanisms for enhancing the ability of the RAN to handle traffic profiles comprising small data transfers generated by both machine-type and non-machine-type devices and applications. The results of this study are captured in TR [28)]. Based on the study reports in and , a work item RAN enhancements for Machine-Type and other mobile data applications Communications was started in Release 12 to enhance the RAN for MTC. There are two objectives: Optimize UE power consumption by introducing a new power saving state in the UE controlled by the non-access stratum. In the power saving state the UE remains at tached; however, all access stratum functions are stopped. Reduce signaling overhead by introducing assistance information about the UE and its traffic type or pattern, with the goal of helping the RAN nodes to configure the RRC connection accordingly. In addition to changes in the RAN, a work item Low cost and enhanced coverage MTC UE for LTE was started to define a new UE category 0 that will have lower requirements than UE category 1 defined in Release 8. The main changes are deletion of the requirements for receive diversity and MIMO, thus enabling a simpler single receiver design. There are also limitations at baseband for data channels to 1.4 MHz (with maximum transport block size limited to 1000 bits) but the RF channels remain as in Release 8. A half-duplex mode that enables use of a single oscillator is also being defined. The work to define the core requirements for these changes will conclude in September 2014 with the UE performance requirements to follow in March 2015.

52 52 Keysight LTE Advanced: Technology and Test Challenges Application Note WLAN/3GPP radio interworking User equipment operating on WLANs owned by cellular operators often make sub-optimal decisions regarding offload to and from the WLAN, resulting in a poor end-user experience and inefficient use of the operator s network resources. As part of a study in Release 12 on WLAN and 3GPP radio interworking, 3GPP identified a set of requirements, assumptions, scenarios, and use cases that need to be addressed. Three solutions were identified to improve access network selection and traffic steering to and from the WLAN. These solutions are intended to support deployments both with and without the access network discovery and selection function (ANDSF) to satisfy different operator needs. Following the study item, a work item WLAN/3GPP Radio Interworking was created in Release 12 to specify mechanisms for WLAN/3GPP access network selection and traffic steering. For the access network selection part, selected RAN assistance parameters will be transferred via system broadcast or dedicated signaling, in which case specified RAN rules will apply when enhanced ANDSF is not deployed in the network or not supported by the UE. In such cases, RAN assistance information may be enhanced with WLAN identifiers. When enhanced ANDSF is deployed in the network and supported by the UE, ANDSF policies will prevail. For traffic routing, selected RAN assistance parameters will be transferred via system broadcast or dedicated signaling in a similar manner. RAN assistance information may be enhanced with traffic routing information (e.g., offload granularity) when ANDSF is not deployed or not supported by the UE. The following RAN assistance parameters will be signaled by radio resource control (RRC): LTE RSRP/UMTS CPICH RSCP threshold (for FDD)/UMTS PCCPCH RSCP threshold (for TDD) LTE RSRQ/UMTS CPICH Ec/No threshold (for FDD) WLAN channel utilization in the BSS load IE (MaximumBSSLoadValue defined in TS [38]) threshold Available WLAN DL and UL backhaul data rate (MinBackhaulThreshold defined in TS [38]) Offload preference indicator (OPI) List of WLAN identifiers (SSIDs, BSSIDs, or HESSIDs). Parameters may be signaled using broadcast or dedicated RRC signaling. WLAN identifiers (SSID, BSSID, or HESSIDs) may be broadcast in a new system information block (SIB). Additionally, in the RAN sharing environment, the RAN should support the signaling of different values of assistance parameters (e.g., WLAN identifiers) for different PLMNs. Also, it has been determined that the RAN solution without ANDSF supports only APN level offload granularity, therefore two signaling alternatives RRC vs. NAS are being analyzed.

53 53 Keysight LTE Advanced: Technology and Test Challenges Application Note LTE TDD-FDD joint operation including carrier aggregation The E-UTRA supports both FDD and TDD duplex modes. Prior to Release 12, the interworking mechanisms between E-UTRA FDD and TDD had been specified; however, the behavior of terminals simultaneously connected to the network on two or more bands with different duplex modes had not. For operators with both FDD and TDD spectrum, it has become crucial to identify efficient mechanisms so that both spectrum resources can be fully utilized to improve system performance and user experience. Moreover, in future LTE FDD TDD carrier aggregation deployment scenarios, it is possible that either a TDD or FDD cell could be specified as the PCell. In such cases, support for generic LTE FDD TDD CA would be needed. Work in Release 12 is ongoing to define a joint LTE TDD FDD operation with an LTE TDD FDD carrier aggregation feature. Other TDD FDD joint operation solutions may be identified based on the outcome of the initial phase of the work item, which is evaluating deployment scenarios and network/ue support requirements. 3GPP is using 8+40, 3+40, 1+41, and 1+42 as the example band combinations in the Release 12 TDD FDD joint operation including carrier aggregation work item. Further MBMS operations support for E-UTRAN The LTE multicast broadcast multimedia services (MBMS) feature uses multicast-broadcast single frequency network (MBSFN) transmission in which signals from several antennas originating from one or more base stations are combined in the UE. This combining makes MBSFN transmission different from unicast transmissions, and so it is difficult to use unicast transmission to verify the MBSFN transmission performance. Because MBSFN transmissions are unacknowledged and the RAN thus lacks a feedback mechanism (such as a HARQ or RLC acknowledgement), the RAN does not know whether transmissions have been received successfully or not. Hence, it is difficult for an operator to understand the MBMS quality of service being delivered. The only way for operators to verify and optimize MBSFN radio transmission has been with manual drive tests. Unfortunately, using manual drive tests to optimize a network is costly and limits measurement to locations along a drive route. These generally are not the places where customers consume MBMS. It is therefore desirable to have automated solutions that allow operators to gather information such as the radio measurements associated with customer UEs and use this information to assist network operation and optimization. Release 12 builds on work in earlier releases to define solutions for minimization of drive test (MDT) aimed at reducing the need for manual drive tests for MBMS. The Release 12 MBMS work item introduces a collection of MBSFN UE measurements with UE geographical location, with the purpose of supporting the verification of MBSFN signal reception and the planning and reconfiguration of MBSFN areas and MBMS operation parameter selections. The specifications for this feature include new MBMS physical layer measurements; Layer 2 and 3 protocol aspects using the MDT functionality; definition of the backhaul signaling and configuration for new UE enhanced MBMS (embms) measurements in the existing MDT framework (e.g., extension to the trace activation over S1); and definition of the parameter range and quantization and the performance requirements for the UE embms measurements.

54 54 Keysight LTE Advanced: Technology and Test Challenges Application Note E-UTRA small cell enhancements physical layer aspects Various features in support of small cells have been incorporated into the LTE specifications since Release 8, including the definition of the home area base station class and the ongoing work on such topics as ICIC and mobility in heterogeneous networks. Further enhancements for indoor and outdoor scenarios using low-power nodes were identified by 3GPP as one of the most important topics for Release 12 and onward. Accordingly, scenarios and requirements for small cell enhancements were studied and captured in TR [29]. Taking into account these scenarios and requirements, potential technologies for the physical-layer aspects of small cell enhancements were studied and captured in TR [30]. To enhance small cell spectrum efficiency, multiple improvement mechanisms have been thoroughly evaluated, including downlink higher-order modulation, overhead reduction, and enhanced control signaling. Different benefits were observed for each of these mechanisms in some scenarios, and ultimately downlink 256QAM was given top priority for spectrum efficiency improvement. It was found that downlink higher order modulation (256QAM) was beneficial in evaluated indoor sparse small cell scenarios with low mobility, and this higher order modulation has become the recommended solution. To enhance small cell operational efficiency, small cell on/off with discovery enhancement and radio-interface based synchronization have been investigated. A benefit was observed in reducing the small cell on/off transition time depending on the detailed scheme, and an increase in the gain was observed with the decreasing transition time. To support an enhanced transition time reduction requires a discovery procedure and signals. A new discovery mechanism defined for small cell on/off could be used for other purposes without further optimization. Although cells with reduced small cell on/off times will most likely not be able to serve legacy UEs without performance loss, there is no problem in mixing legacy UEs and small cell on/off in the same carrier. In addition, the cells with legacy UEs not operating with reduced time scale of small cell on/off may obtain performance gain by cells with reduced time scale of small cell on/off. Support for radio interface based inter-cell synchronization was found to benefit cases in which other methods such as GNSS or synchronization over backhaul were not available. Network listening solutions also have been considered and evaluated. For the deployment among the cells of different TDD operators deployed in the same band and same region, mechanisms to facilitate inter-operator synchronization should be considered. Taking into account the findings documented in the technical reports, the work in Release 12 is specifying the mechanisms for small cell enhancements in the physical layer to improve the spectrum efficiency for UEs experiencing high geometry or low frequency-selective and time-selective fading channel, and to ensure the efficient operation of networks with small cell layers composed of small cell clusters. As recommended for small cell spectrum efficiency enhancement, higher order modulation of 256QAM is being introduced in the downlink transmission while keeping the existing size of CQI feedback field and MCS indication. Work is also progressing to specify efficient operation with reduced transition time of small cell on/off in single-carrier or multi-carrier operation with enhanced discovery of small cells. It s worth noting that as a result of the small cell on/off work, 3GPP cancelled the new carrier type (NCT) feature, which had targeted a similar use case. Finally, efficient radio-interface-based inter-cell synchronization (network listening) for single-carrier and multi-carrier operation is being defined for small cells, as are the corresponding UE and enb core requirements for all of the Release 12 small cell enhancement mechanisms and features. Although the focus on small cells is now well-established in the specification, the work of defining these enhancements is very detailed and much remains to be done.

55 55 Keysight LTE Advanced: Technology and Test Challenges Application Note Inter-eNB CoMP for LTE Coordinated multi-point (CoMP) transmission and reception was introduced in Release 11 to improve the coverage of high data rates and the cell-edge throughput, and to increase the overall system throughput. However, Release 11 CoMP did not specify a network interface for CoMP involving multiple enbs with non-ideal backhaul. As a result of this limitation, affected operators may not be able to take advantage of performance benefits from inter-enb CoMP operation. The study item Study on CoMP for LTE with Non-Ideal Backhaul has identified cases for which CoMP can provide performance enhancements and for which enhancements to the network interface and signaling messages should be specified to allow implementation of both centralized and distributed coordination focused on macro-to-pico heterogeneous networks but also considering macro-to-macro homogeneous networks. Potential throughput gains were evaluated while taking into account estimation errors, downlink overhead, complexity, feedback overhead, backwards compatibility, and practicality of UE implementation. It was noted that allowing implementation of centralized coordination does not necessarily call for the introduction of a new node. LTE device-to-device proximity services Proximity-based applications and services are part of an emerging trend in social-networking and direct-communication technology. Introducing a Proximity Services (ProSe) feature in LTE taps into this developing market while at the same time addressing the needs of various public safety communities for location-based services. A 3GPP study in Release 12, LTE Device to Device Proximity Services, published in TR [31], concluded that adding device-to-device (D2D) discovery and broadcast communication techniques is compatible with LTE given the current status of work on the standard. Proceeding from the TR findings, the work item LTE Device to Device Proximity Services was begun in Release 12 to enable D2D discovery and communication in intra-cell and inter-cell network coverage, in partial network coverage, and in coverage outside the network. The communication part of this work is targeted for application to public safety use only, as are the partial network coverage and out-of-network coverage scenarios. Specifically, the ProSe feature defines the following: Physical signals and channels and related UE behaviors for D2D discovery and broadcast communication Resource allocation mechanisms for D2D discovery and broadcast communication Resource allocation mechanisms for synchronization signals and, if supported, synchronization channels for D2D discovery and broadcast communication Synchronization procedures for inter-cell, in partial network coverage, and outside network coverage Higher layer (access stratum) protocols for D2D discovery and communication Physical layer and higher layer techniques to enable the LTE network to manage, and continuously control D2D discovery and communication Solutions related to lawful interception for D2D discovery and communication defined by SA3-LI, if they impact the RAN specification Co-existence between D2D enabled LTE-network and victim network operating in adjacent carrier frequencies Tx and Rx RF requirements for the UE RRM core requirements. In accordance with the recommendations of D2D proximity services study, the impact of the feature on cellular traffic, spectrum, and the quality of other services from the same operator is being studied and minimized.

56 56 Keysight LTE Advanced: Technology and Test Challenges Application Note Network-assisted interference cancellation and suppression for LTE With the goal of achieving higher network capacity under co-channel interference, 3GPP approved the study item Network Assisted Interference Cancellation and Suppression (NAICS). The study looks at advanced interference cancellation (IC) and interference suppression (IS) receivers with and without network assistance, evaluating each for the tradeoffs between performance and complexity, and studying potential system level gain and impact on the specification. Several candidate NAICS receivers were assessed as being able to achieve noticeable performance gains over the Release 11 LMMSE-IRC receiver in most scenarios, depending on the interference profile. Additionally, the study concluded that when some network assistance or coordination is provided, it can reduce receiver complexity compared to requiring the UE to blindly detect all the interference parameters. Nevertheless, blind detection of some parameters was found acceptable in certain cases (e.g., under certain interference conditions), and further study of this issue is needed. For Release 12, the scope of the study was limited to a total of up to three layers (serving + interfering) and cancellation of one interferer. The study also found that higher-layer signaling of parameters related to interference PDSCH could help reduce the blind detection complexity or performance degradation. Candidate parameters for higher-layer signaling were identified for further study, as were parameters desirable to reduce scheduling restriction and signaling overhead in blind detection. The study also concluded that further investigation of CSI enhancement is needed to help ensure that NAICS receivers can achieve a user throughput gain. Based on the study conclusions, work began on the NAICS feature to enable receiver gains in commercial deployments as quickly as possible. The goal of the first phase was to decide on the signaling parameters from among the candidates identified and then to specify the necessary signaling. Specification of the appropriate receiver performance will follow, with a target date of June The parameters initially identified as desirable for blind detection are as follows: Presence or absence of interference Transmission modes (TM) For DMRS-based TMs: DMRS ports, modulation order, Virtual cell ID, nscid, Cell ID, CRS ports, and MBSFN pattern For CRS-based TMs: PMI, RI, modulation order, Cell ID, CRS ports, and MBSFN pattern, ρa Control format indicator (CFI), if not coordinated and required by receiver implementation. Work is ongoing to specify the final higher-layer signaling parameters, including any subset restrictions. Investigation also continues to determine what, if any, CSI enhancements for NAICS receivers will be required. Based on the core definitions of the interference signaling parameters and any further agreements on blind detection, the demodulation and CSI feedback performance requirements will be specified. 3GPP intends to target a unified performance requirement for the NAICS receivers, including requirements covering both DMRS and CRS. The specification must ensure that no performance is lost compared to LMMSE-IRC receivers in all interference PDSCH scenarios in a wide range of typical network deployment conditions (including 4Tx) for both CRS-based and DMRS-based transmission modes.

57 57 Keysight LTE Advanced: Technology and Test Challenges Application Note Performance requirements of 8 Rx antennas for LTE uplink The performance bottleneck for LTE has historically been the uplink, due to the limitations on the uplink transmitter power and the overall cost of user equipment. When uplink traffic is low, this problem is not so severe. However, with widespread use of intelligent terminals and new applications such as social networking, the gap between downlink and uplink traffic loads is shrinking. Therefore, the need to improve uplink performance has become very important to operators deploying LTE. Deployment of eight Rx antennas at the enb is an efficient way to improve the LTE uplink performance in terms of capacity, coverage, and reduced transmitter power needs. Optimization techniques such as the use of cross-polarized antennas and higher carrier frequencies could lead to the development of more compact antennas, which could help ease the challenges of deploying eight uplink receiver antennas. However, demodulation performance requirements for eight Rx antennas at the enb are still lacking; therefore, 3GPP has specified demodulation performance requirements for eight Rx antennas at the LTE uplink. Work on the performance requirements was concluded with specification of the following in TS [24] and TS [33]: Channel model for eight uplink Rx antennas Demodulation performance requirements of eight Rx antennas for uplink channels Conformance tests of eight Rx antennas for uplink channels. 4.4 Release 12 study items Study on mobile relay for E-UTRA Mobile users want to receive their services even while they are traveling on high speed vehicles. Providing LTE in a high speed environment is challenging for a number of reasons. In a high speed environment, handovers occur much more frequently. When many UEs attempt to handover at the same time for example, on a high speed public train the handover success rate is reduced, in part because the signaling overhead required is excessive and the tracking area update (TAU) is provided in a very short time period. Moreover, UE measurements in high speed environments are typically less accurate than in low speed environments. A second problem is degraded throughput due to high Doppler effects. Impairments caused by high Doppler include frequency estimation errors and channel estimation errors, and they can significantly limit the achievable throughput. Specific enb and UE implementations to combat these impairments are possible but add to the equipment cost. Dedicated network planning may help alleviate these problems, but the quality of service for UEs on high speed vehicles remains to be improved. One solution approach is the use of mobile relays that is, relays mounted on a vehicle that connect wirelessly to the macro cells. In essence, the mobile relay becomes a base station mounted in a moving vehicle to which the onboard UEs can connect. The mobile relay must provide at a minimum the following key functions: Wireless connectivity service to end users inside the vehicle Wireless backhaul connection to a landline network Capability to perform group mobility Capability to allow different air interface technologies on the backhaul and the access link.

58 58 Keysight LTE Advanced: Technology and Test Challenges Application Note Handover success rate can be improved with mobile relays. For example, excessive handover signaling can be avoided by performing a group mobility procedure instead of individual procedures for each UE. Mobile relays can also improve spectrum efficiency by exploiting more advanced antenna arrays and signal processing algorithms than are available to standard UEs. In addition, separate antennas for communication on backhaul and access links can be used to effectively eliminate the penetration loss through the vehicle. When a UE connects to a nearby mobile relay node, the transmit power required of the UE is much less, saving a significant amount of UE power and increasing UE battery life. By effectively addressing all of these problems with the use of mobile relays, operators can make better use of their radio resources. And with mobile relays, only one radio access system is required on the backhaul link, which may reduce the number of radio access systems required at macro NBs along the vehicle path. Using an L1 repeater mounted on a vehicle is an alternative technique in fast-moving environments. L1 repeaters amplify and forward signals of a certain frequency band. Since repeaters do not regenerate the received signal, they are useful when deployed at positions with advantageous SINR. Repeaters with an indoor and an outdoor antenna will have good channel conditions towards the UEs for improved uplink transmissions and towards the network for improved downlink transmissions. In addition the repeaters overcome the wall or window penetration loss. Being connected through an L1 repeater, UEs can reduce their transmit power, which increases UE battery life. L1 repeaters are transparent and do not have an impact on radio interface standards. Since Release 10 of the 3GPP standard specified only stationary relay nodes, a study item on mobile relay was started in Release 11 but its completion was moved to Release 12. The object of the study was to investigate the backhaul design of mobile relays, first by identifying the target deployment scenarios, and then by evaluating suitable mobile system relay architectures and procedures, considering both the PHY and higher layer effects. The L1 work begun in Release 11 is taken into account. Although the benefits of mobile relay are evident, the work has not been treated with high priority and has been put on hold for nearly two years, with plans to continue in September 2014.

59 59 Keysight LTE Advanced: Technology and Test Challenges Application Note Study on 3D channel model for elevation beamforming and full dimension MIMO studies for LTE Release 8 MIMO and subsequent MIMO enhancements in Release 10 and Release 11 were designed to support antenna configurations at the enb that are capable of adaptation in azimuth only. Recently there has been a significant interest in enhancing system performance through the use of antenna systems with a two-dimensional array structure that provides adaptive control over both the elevation dimension and the azimuth dimension. This additional control enables a variety of strategies such as sector-specific elevation beamforming (e.g., adaptive control over the vertical pattern beam width and down-tilt), advanced sectorization in the vertical domain, and user-specific elevation beamforming. Vertical sectorization can improve average system performance through the higher gain of the vertical sector patterns, but the technique generally does not need additional standardization support. UE-specific elevation beamforming promises to increase the SINR statistics seen by the UEs by pointing the vertical antenna pattern in the direction of the UE while spraying less interference to adjacent sectors by virtue of being able to steer the transmitted energy in elevation. To specify further methods of enhancing performance using 3D-beamforming or fulldimension MIMO (FD-MIMO), a new channel model is needed that will enable modeling in both the vertical and horizontal dimensions of the environment as well as at user locations in the network. To accelerate the process of defining this channel, work done outside 3GPP specifically, WINNERII/WINNER+ (channel modeling documentation available in public domain) is being leveraged. The Release 12 study is focused on identifying typical usage scenarios for UE-specific elevation beamforming and FD-MIMO, and then to identify the modifications to 3GPP evaluation methodology needed to support proper modeling and performance evaluation of these scenarios. This work includes modeling a 2D array structure at the enb with possible modifications to the antenna patterns and modeling a 3D channel with multipath characteristics in both elevation and azimuth. The study assesses the need to define a new way of modeling the location of outdoor and indoor UEs within a sector in both the horizontal and vertical domains, and the need to define a new way of modeling the mobility of UEs outdoors in both the horizontal and vertical domains. The results of the study are published in TR , Study on 3D channel model for LTE (Release 12) [34], which presents the scenarios for UE-specific elevation beamforming and FD-MIMO, the 3GPP evaluation methodology needed for elevation beamforming and FD- MIMO evaluation, and the simulation results.

60 60 Keysight LTE Advanced: Technology and Test Challenges Application Note Study on group communication for LTE Group communication is a key functionality of land mobile radio (LMR), private mobile radio, and public safety systems. It is most familiar today as the push to talk functionality in existing LMR platforms. To position LTE as technology for critical communications such as public safety, a group communication service is needed. An LTE-based service is intended to allow flexible modes of operation supporting voice, video, and general data communications. It should also allow users to communicate with several groups in parallel; for example, using voice with one group while sending streams of video or data to other groups. Group Communication System Enablers for LTE, TS [35], defines the Stage 1 requirements to develop enablers ; that is, modular functions and open interfaces that can be used to design group communication services. Such enablers will allow the service to accommodate the different operational requirements expected for different user groups and different regions or countries. The specification covers the high level functional requirements, performance, service continuity, resource efficiency, scalability, and security of group communications. It also defines group handling and group communication service requirements, as well as how the service will interact with other related services and functions such as e911 emergency and ProSe functions. With completion of the GCSE Stage 1 requirements, work shifted to defining the architecture for this functionality, and the description of a system level solution is captured in Study on architecture enhancements to support Group Communication System Enablers for LTE (GCSE_LTE), TR [36]. It was important that this solution meet agreed-upon public safety requirements, and consideration was given to a number of important aspects of group communication including the impact of user mobility on group communications; the need for high availability of the radio connection for public safety related group communications; the scalability of the solution; support for various media beyond voice; performance aspects such as end-to-end setup time, service joining and acquisition time, and end-to-end delay time for media transport. The study concluded that the group communication requirements can be fulfilled using unicast and MBMS bearers with certain assumptions on network configuration and with the following exceptions: Even though there are UE implementation options which could be used for service continuity while leaving MBSFN area, there is no currently specified UE behavior in place. When using MBMS for media delivery the required end-to-end delay for media transport may exceed the requirement of 150ms by 10ms. A separate Study on group communication for E-UTRA, TR [37], evaluates existing E-UTRA procedures to support group communication based on the requirements put forth in TS The study provides further detailed analysis of the use of the unicast and MBMS bearers. It also suggests areas within the E-UTRA specifications that could be further enhanced to better support group communications in parallel.

61 61 Keysight LTE Advanced: Technology and Test Challenges Application Note Verification of radiated multi-antenna reception performance of UEs: MIMO OTA Work has been ongoing on MIMO over-the-air (OTA) performance verification methods since March The initial work concluded in December Four test methods were approved in TR [32]: Multi-probe anechoic Reverberation Reverberation plus channel emulator Two stage. Table 16 compares these methodologies. Table 16. Test methods for verifying MIMO OTA Methods Pros Cons Multi-probe anechoic Can handle dynamic antenna patterns Highest cost $2M $5M (but falling) 3D extension very expensive Cheaper option has limitations on device size (tablet or bigger) Reverberation Two-stage Low cost Inherently 3D Low cost (can reuse SISO chamber) Arbitrary 3D channels and interferers at no extra cost No limits on device size Can t create realistic spatial channels or interference Can t test polarized devices (e.g., laptops) Not applicable to active antennas UE test mode required Not currently applicable to active antennas Although MIMO OTA was a Release 12 work item, the output is limited to the technical report, TR [32], and no radiated UE performance requirements were specified. The work to complete UE performance requirements has been moved to Release 13 and will start again in September During this next phase of work the accuracy of the test methods approved in TR will be further defined along with the detailed testing conditions to be used for specifying UE performance requirements.

62 62 Keysight LTE Advanced: Technology and Test Challenges Application Note 5 Release 13 and beyond The work to date for Release 13 prior to the September 2014 RAN plenary meeting was mainly limited to spectrum aspects. At this time only a few Release 13 study and work items have been approved (Table 17) in order that Release 12 can be completed. It is expected that many more Release 13 work items will be started in September Table 17. Study items and work items currently approved for Release 13 Items Not Related to Carrier Aggregation RP RP RP RP RP RP RP RP Core part: LTE in the MHz Band for US Core part: Enhanced Signaling for Inter-eNB Coordinated Multi-Point (CoMP) Core part: 2GHz FDD LTE in Region 1 ( MHz and MHz Bands) Performance part: Performance requirements of interference cancellation and suppression receiver for SU-MIMO Study on Multi-RAT joint coordination Study on Advanced Wireless Services (AWS) - Extension band for LTE Study on MIMO OTA antenna test function for LTE Study on Indoor Positioning Enhancements for UTRA and LTE Items Related to Carrier Aggregation RP Core part: LTE Advanced intra-band contiguous Carrier Aggregation in Band 42 RP Core part: LTE Advanced intra-band contiguous Carrier Aggregation in Band 40 for 3DL RP Core part: LTE Advanced inter-band Carrier Aggregation of Band 7 and Band 22 RP Core part: LTE Advanced inter-band Carrier Aggregation of Band 5 and Band 13 RP Core part: Additional bandwidth combination set for LTE Advanced inter-band Carrier Aggregation of Band 4 and Band 12 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 4, Band 4, and Band 12 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 2, Band 4, and Band 4 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 2, Band 2 and Band 5 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 4, Band 4 and Band 5 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 2, Band 5 and Band 13 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 4, Band 5 and Band 13 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 1, Band 3 and Band 26 RP Core part: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 1, Band 18 and Band 28 RP New WID: Additional bandwidth combination set for LTE Advanced inter-band Carrier Aggregation of Band 2 and Band 5 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 1, Band 41 and Band 41 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 26, Band 41 and Band 41 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) for Band 2, Band 2 and Band 12 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 4, Band 7 and Band 12 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 4, Band 4 and Band 7 RP New WID: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 3, Band 3 and Band 8 RP New WID Proposal: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 39, Band 41 and Band 41 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 1, Band 3 and Band 19 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 19, Band 42 and Band 42 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 3, Band 42 and Band 42 RP New WI: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) of Band 1, Band 42 and Band 42 RP New WID: LTE Advanced 3 Band Carrier Aggregation (3DL/1UL) for Band 41, Band 42 and Band 42 RP New WI proposal: Additional bandwidth combination set for LTE Advanced intra-band contiguous Carrier Aggregation in Band 40 for 3DL RP New WID proposal: E-UTRA UE flexible CA performance requirements

63 63 Keysight LTE Advanced: Technology and Test Challenges Application Note 5.1 Selected topics New frequency bands There are currently 43 frequency bands defined by 3GPP for LTE with three more work items approved so far in Release 13, as shown in Table 18. Table 18. Frequency bands as of June GPP specification FDD TDD Release (excl. 15, 16*) Release Release Release Release Release MHz & MHz Region 1, MHz Band for US, AWS (Band 4) extension (study) * Bands 15 and 16 are specified by ETSI only for use in Europe Study on multi-rat joint coordination This study item looks at multi-rat coordination from the RAN perspective of the following: Service-aware UE steering between different RATs to provide consistent user experience and user satisfaction; e.g., by connecting to multi-rats (e.g. WiFi and LTE) Traffic steering between WAN and WLAN (e.g., LTE and WiFi) Multi RAT joint radio resource coordination for an operator, especially between LTE and GSM, to provide an operator a smooth transition from GSM to LTE while still keeping basic GSM coverage for services such as voice or GSM M2M. Similar migration and spectrum sharing scenarios may also exist for UMTS/CDMA and LTE Reducing core network impact caused by addition of a new RAT due to inter-rat communication. Summary of WLAN aspects The integration of WLAN into 3GPP specifications has been ongoing since Release 8. The ETSI Mobile Competence Centre (MCC) created Document RP to summarize all work items on WLAN interworking with a 3GPP system (I-WLAN) across 3GPP Releases and TSGs. The most recent addition is the Release 13 Study on Multi-RAT joint coordination found in RP This new overview document provides a concise summary of everything that has been going on since Release 7 and in aggregate indicates how crucial interworking with WLAN will be in the future.

64 64 Keysight LTE Advanced: Technology and Test Challenges Application Note Evolution of carrier aggregation Work is expected to focus on the evolution of carrier aggregation from co-located channels to inter-site CA. The original goal of CA was to increase the spectrum and hence the peak data rate available from one cell site. However, when the second carrier is at a very different frequency from the primary carrier, the benefit of CA is limited to the center of the cell, which is not ideal. See Figure 20. Figure 20. Limitations of co-located carrier aggregation By allowing CA between sites it is possible to provide continuous CA coverage using a low frequency macro (umbrella) cell and local capacity using a higher frequency small cell. The separation of the sites means that enhancements are required at the physical layer including multiple timing advances. See Figure 21. Figure 21. Continuous CA coverage with a macro (umbrella) cell The ultimate flexibility is then achieved if CA is performed across radio access technologies (RATs) and in particular with today s dominant small cell technology: Wi-Fi. This level of integration will require solutions for authentication and billing issues that limit the potential of Wi-Fi today. See Figure 22. Figure 22. Carrier aggregation across different radio access technologies

65 65 Keysight LTE Advanced: Technology and Test Challenges Application Note Progression of cellular/wifi integration Carrier aggregation was intended to create wider cellular channels, but cellular spectrum is limited as discussed previously. Inter-site CA has the potential to make possible effective use of higher frequency cellular spectrum. However, the ultimate benefit of inter-site inter- RAT CA is the potential for cellular to become fully integrated with: 80 MHz of ISM spectrum at 2.4 GHz 160 MHz of ISM spectrum at 5.8 GHz 8.4 GHz of ISM spectrum at 60 GHZ 4.2 GHz available worldwide. Compared to the cost, design, and roaming issues inherent in dealing with today s 44 bands of LTE spectrum, full cellular integration with evolving Wi-Fi appears very attractive. LTE operation in unlicensed bands (LTE-U) There has been considerable recent interest at 3GPP in the operation of LTE in unlicensed bands in particular the 5 GHz ISM band used for WLAN although LTE-U is not yet formally part of Release 12 or 13. This feature could enable operators to offload traffic to LTE femtocells without having to implement WLAN. Proposals are controversial, however, since standard LTE interferes with WLAN. And although LTE has been shown to be more efficient, WLAN was first to operate in this spectrum. To make co-existence of LTE with WLAN more tolerable, modifications to the LTE air interface such as Listen Before Talk (LBT) are being proposed. LTE-U is likely to become the single biggest increase of cellular spectrum (up to 680 MHz in the 5 GHz band) since the allocations made by the World Radio Conference in New focus on end users The evolution of LTE since Release 8 shows no sign of slowing, as evidenced by the rapid acceptance of LTE-Advanced. Many of the most important innovations are based on the recognition of the importance of changing network topology as a means of improving end-user performance, rather than the traditional focus on spectral efficiency and peak channel bandwidth. Several areas of cellular evolution will continue to make a difference to end users over the long term: Heterogeneous networks (integration of macro and small cells) Dual connectivity to extend carrier aggregation for inter-site Extension of dual connectivity to include Wi-Fi, especially as the industry shows a renewed interest in network operator-grade Wi-Fi provision as a cost-effective solution to the capacity crunch Radiated performance testing that includes the quality of device and base station antennas, especially for MIMO.

66 66 Keysight LTE Advanced: Technology and Test Challenges Application Note 6 Challenges for LTE-Advanced Product Developers As an evolution of LTE, LTE-Advanced poses many challenges to engineers. The LTE standard itself is still relatively new and quite complex, with multiple channel bandwidths, different transmission schemes for the downlink and uplink, both frequency and time domain duplexing (FDD and TDD) transmission modes, and use of MIMO antenna techniques. LTE and LTE-Advanced have to co-exist with older cellular systems for some time, so interworking necessities and potential interference remain important issues. In typically difficult radio environments, LTE sets the bar for performance targets very high, and LTE-Advanced raises it even higher. Despite these challenges, many cellular operators now view the speed and capacity improvements of LTE-Advanced as necessary for delivering a reliable, consistent end-user experience as traffic loads continue to grow. The first implementations involve carrier aggregation (CA), which allows operators to make use of their available spectrum to achieve significantly higher data rates. Other LTE-Advanced features on the horizon include techniques for managing interference among large and small cells in heterogeneous networks (HetNets), and incorporation of higher order MIMO antenna systems for higher data rates and better connections. As shown throughout this application note, the complexity of the wireless environment means that developers of RF components and systems are dealing continuously with new or enhanced architectures for carrier aggregation, 8x8 MIMO, and the other LTE-Advanced options. The technology has to work on multiple frequency bands and alongside other communication formats, delivering more capability and higher data throughput while maintaining or even improving the power efficiency of the previous generation of equipment. The remainder of this application note considers several challenging areas of design and test confronting developers of LTE-Advanced products, and introduces the newest measurement solutions to help make this development work a success. Figure 23. LTE-Advanced adds more complexity to an already-challenging cellular environment

67 67 Keysight LTE Advanced: Technology and Test Challenges Application Note 6.1 Carrier aggregation Carrier aggregation poses some difficulties for the UE, which must handle multiple simultaneous transceivers. The addition of simultaneous non-contiguous trans mitters creates a highly challenging radio environment in terms of spur management and self-blocking. Simultaneous transmit or receive with mandatory MIMO support will add significantly to the challenge of antenna design. Creating carrier aggregation signals To illustrate the concepts of carrier aggregation some examples are provided here using Keysight s SystemVue design software. Various options exist for implementing CA in the transmitter architecture depending primarily upon the frequency separation, which heavily influences where the component carriers are combined: At digital baseband In analog waveforms before the RF mixer After the RF mixer but before the power amplifier (PA) After the PA. Figure 24 shows some of these possible transmitter architectures for the UE. Figure 24. Possible UE transmitter architectures for various carrier aggregation scenarios (TR [2] Fig )

68 68 Keysight LTE Advanced: Technology and Test Challenges Application Note All of the transmitter architectures illustrated in Figure 24 can be implemented easily in Keysight SystemVue software. Figure 25 shows a quick implementation of LTE Advanced sources with carrier aggregation. Figure 25. Example of intra-band carrier aggregation in Keysight SystemVue Figure 25 is an example of intra-band contiguous carrier aggregation. The structure assumes that each component carrier is processed by an independent signal chain. This structure could also be applied to non-contiguous carrier aggregation for both intra-band and inter-band. Figure 26 shows the spectrum of two 20 MHz component carriers chosen from Band 7 (2600 MHz), which are aggregated with the center frequency spacing set to 20.1 MHz (a multiple of the required 300 khz). Figure 26. Carrier aggregation spectrum of two adjacent component carriers

69 69 Keysight LTE Advanced: Technology and Test Challenges Application Note Figure 27 shows the constellation of the physical channels and physical signals in the first component carrier (2630 MHz). Figure 27. Constellation of the first component carrier In Figure 28, four adjacent 20 MHz component carriers chosen from 3.5 GHz are aggregated with the adjacent center frequency spacing set to 20.1 MHz. Figure 28. Carrier aggregation spectrum of four component carriers

70 70 Keysight LTE Advanced: Technology and Test Challenges Application Note Impact of carrier aggregation on the UE design As Figure 29 suggests, carrier aggregation involves mainly the physical and MAC layers and is essentially transparent for layers RLP, PDCP, and above. However, there are some changes that need to occur at these higher layers. Since carrier aggregation enables higher data rates, the user plane must be enhanced to support this feature. As a result, higher processing power will be required in the chip as well as larger buffers to support the higher data rates. Figure 29. Impact of carrier aggregation on UE design The biggest challenges come at the physical layer and the MAC. In the case of the physical layer, each component carrier will have its own PHY, which provides the mechanisms for channel coding, modulation, resource mapping, etc. Changes are required at this layer in the control information to support scheduling of multiple carriers and multiple HARQ acknowledgements coming from different cells. The data aggregation occurs at the MAC layer, which acts as a multiplexer collecting data coming from all the cells and delivering the data as a single stream to the upper layers. This can be supported in the traditional LTE manner whereby the radio resource is scheduled in the same cell in which the grant has been sent, or the cross-carrier scheduling may be used. In the latter case the secondary cell does not have a PDCCH configured and the grant for scheduling resources is done via the primary component carrier.

71 71 Keysight LTE Advanced: Technology and Test Challenges Application Note It is important to stress again that the addition of carrier aggregation to the UE leads to very complex transceiver designs. This is especially true in the case of non-contiguous aggregation, whether inter-band or intra-band. Non-contiguous aggregation always requires multiple receiver chains working simultaneously, which creates a highly challenging radio environment in terms of spurs and self-blocking, as previously noted. There are numerous multi-band combinations already defined in the specifications and more are on the way, so the UE front ends must be designed to support as many of these frequency band combinations as possible. Moreover, if MIMO capabilities are added to this multi-transceiver chain, the antenna design will also be more challenging. In such cases the test setups can become quite complex. A typical scenario might require a couple of base station emulators to generate the signal for transmission. A realistic scenario calls for RF impairments such as fading and noise, which requires channel emulators. Finally, cables, combiners, RF connectors, etc., are needed to connect to the UE. The number of boxes, interconnections, and calibration routines to do all this can become quite complicated. An integrated one-box test set such as the Keysight UXM can combine all these elements internally to greatly simplify this setup, as shown in Figure 30. For more on the UXM, see page 80. Figure 30. Keysight UXM simplifies complex carrier aggregation test setups

72 72 Keysight LTE Advanced: Technology and Test Challenges Application Note 6.2 Interference mitigation Advanced radio access techniques such as MIMO require nearly ideal signal environments with high signal-to-noise ratio and power. These conditions are usually found close to the base station; however, as mobile devices get farther away and approach the cell edge, performance goes down. Adding more traditional base stations (macrocells) to improve coverage is expensive for many reasons: the difficulty of finding suitable locations, initial cost of the hardware, power requirements, and the installation and maintenance costs. For these same reasons adding macrocells is not a good solution to increase capacity in an overloaded network. Therefore, as noted earlier, LTE-Advanced supports the use of relay nodes and small cells, which are much less expensive to acquire and operate and relatively easy to deploy. Small cells in HetNets are full-fledged local base stations with their own backhaul. Although the term includes microcells, picocells, and femtocells, it is femtocells that are most often associated with the home base station defined in the LTE and LTE-Advanced specifications. These small cells can be applied effectively in many situations from personal hotspots to the metrocells that enhance coverage in dense urban areas and indoor campuses. Elements of a HET-NET may encompass many radio access technologies from cellular to WiFi. The network also may include remote radio heads (RRH) and distributed antenna systems (DAS), as shown in Figure 31. Figure 31. A heterogeneous network supports the deployment of small cells and relay nodes, each optimized for different user demands.

73 73 Keysight LTE Advanced: Technology and Test Challenges Application Note As HetNets are deployed, one of the most significant challenges will be handling the interference generated by the interactions of multiple layers of cells and other RF-emitting devices that occupy the same frequency. Contributing to the interference will be the multiple new transceivers that are required for LTE-Advanced enhancements such as MIMO and dual-layer beamforming. A significant amount of work in the specifications has focused on advanced interference mitigation solutions such as eicic and FeICIC. (See pages 25 and 32.) Additionally, as discussed earlier, there are different types of co-channel heterogeneous deployment and each requires its own approach to interference avoidance. The open subscriber group (OSG) allows users to roam between the macro network and any local area BS deployed by the operator on the same frequency. In the area of the network where the strengths of the wide area and local area base stations are similar typically a ring around the local area BS interference is greatest and performance may be significantly degraded. Closer to the local area BS the interference becomes less problematic. The closed subscriber group (CSG) limits local base station access to a fixed group of subscribers such as the occupants of a dwelling or employees of an enterprise. In the local BS coverage area, service for the CSG is good but all other users experience significant interference. This situation could be a major problem for macro network coverage in densely populated areas. The obvious solution is to assign different channels to the local BS and the macrocell. However, the solution is not available to operators with only a single channel. Some form of partial frequency reuse is also possible although there will still be interference in the control channels. Given the difficulty of CSG, it is the focus of the initial LTE-Advanced standards work on enhanced interference mitigation in heterogeneous networks. Meticulous design of network devices and rigorous interference testing from design through deployment will be key to keeping this problem under control.

74 74 Keysight LTE Advanced: Technology and Test Challenges Application Note 6.3 Power efficiency and battery life Battery life is critical in a high end mobile device, yet product developers do not have the option of making batteries larger to power the extra transceivers required by higher order MIMO and other LTE-Advanced features. Also, base stations and small cells need to operate as efficiently as possible, for both economical and ecological reasons. Therefore new techniques are necessary to optimize power efficiency in RF, baseband, and system-level designs. Power amplifiers (PAs) account for a significant portion of both the energy consumed and heat generated by the RF front end. PAs are an essential component affecting the overall performance and throughput of wireless systems and are inherently non-linear. Techniques to enable PAs to operate near saturation, where they are most efficient but also more nonlinear, are becoming more widely adopted. Crest factor reduction (CFR) and digital pre-distortion (DPD) are two techniques that, particularly when used together, improve the linearity of a PA so that it may be operated at its high power-added efficiency (PAE) region, near saturation, without significant signal distortion. CFR pre-conditions a signal, reducing its high peak-to-average power ratio (PAPR) without causing significant additional distortion. DPD is a method of determining a PA s distortion characteristics, then applying the opposite effect to the baseband signal via a pre-distortion algorithm to improve linearity at the PA output. Both CFR and DPD are techniques used by product developers today. Average power tracking (APT) and envelope tracking (ET) are newer techniques to improve PA performance and efficiency. Both involve the control of the PA supply voltage as a function of the signal amplitude, and these techniques can now be used with modern PAs that offer switched high- and low-power operation. Thus, for example, envelope tracking can dynamically adjust the PA s supply voltage to track the magnitude of the envelope of the RF input signal. When the input signal envelope is low, the supply voltage can be reduced so the amplifier operates closer to its optimal efficiency point. See Figure 32. Figure 32. Envelope tracking is a technique that improves power amplifier performance by dynamically adjusting the supply voltage to track the magnitude of the RF input signal envelope.

75 75 Keysight LTE Advanced: Technology and Test Challenges Application Note In LTE and LTE-Advanced devices, power is required not just for the primary radio but also for multiband multi-rat support, receive diversity, MIMO, interference cancellation, high data rates, and a host of user features including Wi-Fi, Bluetooth, FM radio, MP3/4, GPS, larger and higher definition displays, and many more. Indeed, it was primarily concern with battery performance that led 3GPP to define SC-FDMA for the LTE uplink rather than the more power-hungry OFDMA used for the downlink. Even so, these features are a constant drain on the battery as any mobile device user well knows. Since battery life must be increased but not battery size, product developers are increasingly focused on designing, measuring, optimizing, and verifying UE current consumption in an ever wider set of use cases. Fortunately advanced battery-current drain measurement solutions are available for analyzing current drain and validating and optimizing UE run times. Advanced tools such as Keysight DC source/measurement units are designed specifically for wireless device current drain testing. These sources can be used as battery emulators or in a special zero voltage configuration to measure the performance of the mobile device battery, commonly called battery run down testing. A typical setup is shown in Figure 33. The DC sources are used in conjunction with the Keysight battery drain analysis software, enabling developers to carry out advanced current drain analysis either manually or with full automation at all stages of the product design lifecycle. Figure 33. Typical UE (device under test) battery drain measurement setup

76 76 Keysight LTE Advanced: Technology and Test Challenges Application Note 6.4 Product development strategy The schedule for LTE-Advanced deployment is aggressive, yet the standards are still being defined and are open to change and interpretation. New techniques are adding substantial complexity the use of carrier aggregation and multiple antenna configurations, for example, with up to 8x8 MIMO currently supported in LTE-Advanced. The real-world behavior of these new enhancements is only now becoming understood and products optimized accordingly. Multiple channel bandwidths, while increasing the flexibility and capability of the cellular system, add to the overall complexity. Since LTE-Advanced products must handle LTE and UMTS operating modes along with other wireless formats, the ability to interwork seamlessly with other technologies is critical. Certain aspects of LTE-Advanced such as MIMO over-the-air (OTA) performance require entirely new test approaches, which are still being defined in the 3GPP specifications. With the integration of TD-SCDMA into the 3GPP specifications, TD-LTE is emerging as a popular option. New components in the network architecture such as small cells/femtocells further complicate the picture. Along with development challenges specific to LTE and LTE-Advanced are those generally associated with designing products for emerging wireless systems. Product designs tend to be mixed-signal in nature, consisting of baseband and RF sections. Overall system performance depends on the performance of the whole, yet each component type is associated with particular impairments for example, non-linearity and effective noise figure in an RF up-converter or down-converter; phase and amplitude distortion from a power amplifier; channel impairments such as multi-path and fading; and impairments associated with the fixed bit-width of baseband hardware. With performance targets for LTE-Advanced set exceptionally high, developers have to allocate resources to cover each critical part of the transmit and receive chain. Astute decisions regarding system performance budgets are key to meeting system-level specifications as well as time-to-market goals. Managing the effort required in the design and verification process is a major challenge for developers at every step of the product development lifecycle. Keysight is actively involved in developing design and measurement tools to efficiently turn LTE-Advanced concepts into deployed and operational systems. Although the process of developing the radio equipment for a new standard is complex and no one model captures everything, Figure 34 is an attempt to define the product development lifecycle. Figure 34. Development lifecycle example

77 77 Keysight LTE Advanced: Technology and Test Challenges Application Note Design simulation tools can address LTE-Advanced development challenges and verify their interpretations of the standard. Models simulated at various levels of abstraction can support the progression from product concept through detailed design. Performance of both baseband and RF sections can be evaluated individually and together to minimize the problems and surprises encountered during system integration and other phases of the development cycle. Then, during the transition to hardware testing, a means of moving smoothly back and forth between design simulation and testing will ensure that engineers are not forced to redesign the product on the bench to get it to work. Integration of design and test provides even greater power and flexibility for hardware testing. For example, using signal creation and analysis software in simulation along with logic analyzers, digital oscilloscopes, and RF signal analyzers provides a common test methodology with a consistent user interface to help diagnose issues along the mixed-signal, RF transmitter and receiver chain (baseband, analog IQ, IF, and RF). See Figure 35. This powerful capability can be used to identify potential issues earlier in the cycle, when they are easiest and least costly to fix. Figure 35. Combining simulation and test facilitates measurement and troubleshooting at various stages along the RF and mixed signal transmitter and receiver chain of a product design.

78 78 Keysight LTE Advanced: Technology and Test Challenges Application Note The core specifications are required to design a cellular product, while conformance tests provide the methods of measuring that product s compliance to the core specs. The 3GPP conformance tests cover RF, radio resource management (RRM), and signaling (protocol) conformance. They are used by test labs in the process of certifying devices for the market, under the auspices of the GCF (Global Certification Forum) representing GSM and UMTS operators and the PTCRB (PCS Type Certification Review Board) in North America. In the case of LTE-Advanced, the core specifications are being published at a rapid pace while the conformance tests definitions have tended to lag behind. This is in part due to the fact that the large number of specified frequency bands, along with the option for FDD or TDD systems and the use of multiple subcarriers and multiple bandwidths, creates a seemingly endless number of possible test configurations. The specifications thus far are limited in the number of test scenarios available and of those, the certification groups have chosen a limited set of tests. Thus developers may find that the tests for a desired configuration do not yet exist or that the tests change during the course of product development as new test scenarios are defined. Test equipment vendors who provide standards-compliant test platforms can be of help ahead of validated conformance testing by providing knowledge of the most important types of test and acceptable test procedures.

79 79 Keysight LTE Advanced: Technology and Test Challenges Application Note 7 Design and Test Tools for LTE-Advanced Developers Keysight s design and verification test products address the areas of greatest concern to LTE-Advanced product developers. Baseband design and verification Keysight s SystemVue design and modeling system facilitates system-level architecture design, baseband algorithm and hardware implementation, and RF/baseband co-verification with test equipment. RF design and verification Keysight s 3GPP LTE wireless library provides signal processing models and preconfigured simulation setups for Keysight s Advanced Design System (ADS) EDA software. The LTE wireless library enables you to create spectrally correct test waveforms that comply with 3GPP requirements, saving valuable design and verification time. Design and measurement challenges of LTE transmitters The simpler RF measurements can be made with general purpose analog signal analysis techniques, while a variety of measurements based on digital demodulation are necessary to fully analyze the highly complex and flexible signals that make up the LTE air interface. With the introduction of digital interfaces, transmitter development now involves mixed signal analysis with a digital interface on the input to the transmitter module and an RF interface on the output. Figure 36. Keysight s Signal Studio signal generation software showing a 5 component carrier configuration Design and measurement challenges of LTE receivers The basic RF characteristics of the receiver include blocking, selectivity, spurious emissions, and reference sensitivity. Receiver performance testing, which is performed under faded RF channel conditions, includes the most complex of receiver performance verification challenges. For example, closed-loop analysis of a MIMO receiver in a faded channel requires real time feedback of the channel conditions to enable adaptive modulation control and frequency-selective scheduling, in addition to the use of incremental redundancy for damaged packets and retransmission for lost packets. Methods for analyzing receiver performance at the application layer include throughput testing as well as channel state information (CSI) testing for the channel quality indicator (CQI), precoding matrix indicator (PMI), and rank indication (RI).

80 80 Keysight LTE Advanced: Technology and Test Challenges Application Note Gain clarity at crucial handoffs The Keysight E7515A UXM wireless test set is a highly integrated one-box signaling test set created for functional and RF design validation in the 4G era and beyond. The UXM tests the newest designs, delivering LTE-Advanced category 6 now and handling increasingly complex requirements in the future. Its extensible architecture can evolve as technology changes: the UXM has upgradable processors, multiple expansion slots, and high-speed interconnects. Two independent 100 MHz RF transceivers allow testing of multiple cells, carrier aggregation, 4 2 MIMO, and integrated fading. The UXM also has built-in servers for extensive functional test applications. The ability to build on these features makes the UXM a future-ready platform that will handle multiple formats and the next advances in antenna techniques, component carriers, and data rates. Figure 37. Validating true category 4/6/7 performance with the Keysight UXM s stable, bidirectional data throughput With the UXM s integrated capabilities, engineers can emulate a wide range of complex operations and dive ever more deeply into functional testing. For example, a single UXM with two independent cells built in can check LTE handover behavior. The UXM also supports two active cells at the same time for testing LTE-to-LTE intra- and inter-frequency handovers. Connecting UXM to a Keysight 8960 wireless test set allows verification of inter-radio access technology (IRAT) handover scenarios such as those between LTE/LTE-Advanced and 2G or 3G. The inclusion of Wireshark-based logging software enables thorough analysis of protocol messaging. The UXM also ensures greater confidence in RF performance with flexible automated testing and industry-proven Keysight X-Series measurement science. The UXM s integrated capabilities and flexible automation software combined with Keysight s Wireless Test Manager (WTM) make it easy to step through the full range of 3GPP channel configurations for a device-under-test. To support the development process from early design to finished product, the UXM offers signaling and non-signaling (i.e., test mode) operation. This lets engineers focus on characterization of RF performance: the UXM pushes aside the protocol barriers and enables the engineer to just connect to the device under test.

81 81 Keysight LTE Advanced: Technology and Test Challenges Application Note Open and closed-loop behaviors of the physical layer For this lower level testing, the demodulation capabilities of the Keysight VSA software provide essential insight into whether the UE is correctly responding to the dynamic radio environment, which might otherwise be missed by higher level tests such as end-toend throughput. Figure 38. Keysight VSA software enables in-depth analysis of LTE-Advanced signals Improving power amplifier efficiency Modern mobile communication devices use wider bandwidths, multi-input multi-output technology, and higher order orthogonal frequency division multiplexing (OFDM) modulation, which place added demands on power consumption in wireless components. One of the most power-hungry and nonlinear components in a mobile terminal is the power amplifier. Technologies such as crest factor reduction (CFR), envelope tracking (ET), and digital pre-distortion (DPD) are often used to minimize PA power consumption and reduce nonlinearity. Figure 39. Keysight Signal Studio for Power Amplifier Test software is an all-in-one, general-purpose test suite for improving PA efficiency using CFR, ET, and DPD technologies

82 82 Keysight LTE Advanced: Technology and Test Challenges Application Note RF challenges of multi-antenna systems including MIMO The theoretical gains possible from such systems are well documented; however, the practical gains that will be seen in realistic conditions are influenced by many factors that involve new methods for analyzing antenna design, the channel propagation conditions, and the received signals. Figure 40. Keysight VSA software fully characterizes LTE-Advanced 8x8 MIMO signals and measures EVM, frequency response, amplitude, phase, time offset between each layer, more MIMO beamforming from the perspective of the enb Beamforming is a very powerful technique, but for it to work effectively requires precise knowledge of the transmit phase of each of the enb antenna ports. Keysight offers a test solution for verifying the beamforming performance of up to an eight-antenna system. Figure 41. Verify and visualize TD-LTE beamforming signals with the Keysight N7109A Multi-Channel Signal Analyzer and VSA software

83 83 Keysight LTE Advanced: Technology and Test Challenges Application Note RF power measurement New requirements for multi-channel RF power measurement have been defined in the ETSI EN v1.8.1 test standard that enable characterization of devices using MIMO and beamforming. The power measurement must be fully time-synchronized and in compliance with the standard for up to four channels and have up to 4 million data samples of detection power of the burst signal. The power measurement rate must be greater than 1 MSa/s and, for non-frequency hopping spread spectrum (FHSS) devices, must support at least a 1 s measurement time. The Keysight U2020X-Series USB peak power sensor and U2531A 2 MSa/s USB modular data acquisition unit can be used during the design and development stages to verify that products meet the new certification requirements. Signaling protocol development and testing Integrated systems can facilitate the different phases from early development through conformance testing to interoperability and acceptance testing. UE functional testing Achieving a user-centric view of UE functionality requires the network elements and servers necessary to test the UE in an environment as close as possible to a real, operational network. Tests include voice functionality and inter-rat handover performance as well as end-to-end throughput testing at the application layer. New test solutions are making these challenges easier. For example, the UXM test application (TA) and lab application (LA) software customize the UXM wireless test set to meet specific testing needs. The test application software provides the network emulation, receiver, and transmitter test functionality required to validate the latest RF designs. The lab application software also includes capabilities to validate UE and chipset functional performance, such as data throughput, complex handover scenarios, and protocol logging. Figure 42. Go deeper in functional testing by emulating a wide range of complex network operations

84 84 Keysight LTE Advanced: Technology and Test Challenges Application Note Battery drain testing With the ever-increasing demands being put on high-end mobile devices, power consumption is often a limiting factor. The right tools can help developers measure and optimize battery current drain. Figure 43. Keysight mobile communications power supplies provide DC sourcing, current sinking, and measurement capabilities to address the unique challenges of simulating batteries and battery packs and measuring the current drawn by LTE-Advanced devices. Conformance testing for RF and signaling Numerous test cases have been developed for LTE-Advanced and a continuous stream of new cases is flowing into the pipeline. Keysight s automated test systems support all the 3GPP conformance test specifications for LTE RF, RRM, and protocol testing, along with carrier acceptance test plans. The test platform can also be used for RF parametric and design verification, and has been validated by the Global Certification Forum (GCF) and PCS Type Certification Review Board (PTCRB) Figure 44. Keysight T4010S automated test systems include LTE and LTE-Advanced carrier aggregation RF solutions for design verification and conformance testing of LTE UEs.

85 85 Keysight LTE Advanced: Technology and Test Challenges Application Note Manufacturing problems solved Historically UE manufacturing tests were a subset of the conformance tests executed using signaling with a base station emulator. However, the demands for high speed testing have caused the use of signaling to be dropped in favor of non-signaling approaches. Such approaches offer significant time savings but present new challenges in the area of DUT control, which is now based on proprietary mechanisms closely associated with the chipset chosen for the UE design. Finding efficient and effective manufacturing test methods is difficult given today s competitive environment and multi-format, multi-band devices. The Keysight E6640A EXM wireless test set builds on the non-signaling and sequencing capabilities of previous generations and offers a new architecture with expanded parallel testing and scalability to match changing production needs. The EXM provides the fastest testing of the newest chipsets it delivers the speed, accuracy, and port density needed to ramp up and optimize full-volume manufacturing of multi-format devices that use LTE-Advanced carrier aggregation, MIMO, and more. At the new product introduction (NPI) stage, the EXM provides chipset compatibility and validated test capabilities that directly control chipset functionality. This includes the fastest, most reliable calibration and verification functions offered in each vendor s chipset. The EXM s broad multi-format, multi-port flexibility handles the complex chipsets while allowing easy upgradability for tomorrow s features. For greater scalability, the EXM can be configured with up to four independent transmit/receive channels, each of which is a complete vector signal generator, vector signal analyzer, and RF I/O section. To further extend port density, the EXM can be customized to connect up to 32 DUTs through multi-port adapter (MPA) technology.additionally, the EXM helps maximize throughput and yield with fast and accurate parallel testing of multiple devices. This comes from ultra-fast data processing and transfers, advanced sequencing, and single-acquisition/multi-measurement (SAMM) capability built into the EXM.

86 86 Keysight LTE Advanced: Technology and Test Challenges Application Note As production needs change, each unit can be expanded with up to four TRX modules, and these can be upgraded with higher frequency coverage and wider analysis bandwidth. For maximum reliability and uptime, the EXM has been tested to survive the rigors of the factory floor. When calibration or repair service is needed, Keysight s global presence ensures fast turnaround times. The EXM is designed, built, and supported to ensure success in manufacturing. Figure 45. Keysight E6640A EXM parallel-tests multi-format wireless devices, as shown here testing 2G, 3G, and 4G devices and wireless connectivity The right solution for any LTE-Advanced measurement challenge Keysight offers a full range of LTE-Advanced design and test products that includes powerful simulation and design verification software, baseband emulators, signal analyzers, sources, base station emulators, power meters and sensors, logic analyzers, scopes, signal creation software, integrated one-box test sets, RF and protocol compliance test systems, and much more. For more information, visit

87 87 Keysight LTE Advanced: Technology and Test Challenges Application Note References [1] 3GPP TR V ( ) [2] 3GPP TR V ( ) [3] 3GPP TS V ( ) [4] 3GPP TS V ( ) [5] 3GPP TS V ( ) [6] 3GPP TR V ( ) [7] 3GPP TR V ( ) [8] Overview of 3GPP Release 11, V0.1.8 ( ) [9] 3GPP TR V ( ) [10] 3GPP TR V ( ) [11] 3GPP TS V ( ) [12] 3GPP TS V ( ) [13] 3GPP TS V ( ) [14] 4G Americas, 4G Mobile Broadband Evolution: Release 11, Release 12 and Beyond, February 2014, [15] 3GPP TR V ( ) [16] 3GPP TS V ( ) [17] 3GPP TS V ( ) [18] 3GPP TR V ( ) [19] 3GPP TS V ( ) [20] 3GPP TS V ( ) [21] 3GPP TR V ( ) [22] 3GPP TR V ( ) [23] 3GPP TR V ( ) [24] 3GPP TS V ( ) [25] 3GPP TS V ( [26] 3GPP TR V ( ) [27] 3GPP TR (3gpp.org/ftp/specs/archive/37_series/37.842) [28] 3GPP TR V ( ) [29] 3GPP TR V ( ) [30] 3GPP TR V ( ) [31] 3GPP TR V ( ) [32] 3GPP TR V ( ) [33] 3GPP TS V ( ) [34] 3GPP TR V ( ) [35] 3GPP TS V ( ) [36] 3GPP TR V ( ) [37] 3GPP TR V ( ) [38] 3GPP TS V ( ) All 3GPP technical reports and specifications can be found at

88 88 Keysight LTE Advanced: Technology and Test Challenges Application Note Acronyms 2G 3G 3GPP 4G AAS ABS ACK ACK/NACK ACLR ACS AGNSS ANDSF APT AWGN BS CA CACLR CC CCDF CDMA CFI CFR CoMP CPICH CQI CRS CS/CB CSG CSI CSI-RS D2D DeNB DFT DFT-S-OFDM DIP DL-MIMO DL-SCH DMRS DPS DSL DwPTS E-DCH EDGE EDPCCH eicic embms enb EPC EPS E-SMLC ETSI E-UTRA E-UTRAN FDD FD-MIMO 2nd Generation 3rd Generation 3rd Generation Partnership Project 4th Generation Active Antenna System Almost Blank Subframe Acknowledgement Acknowledgement/Negative Acknowledgement Adjacent Channel Leakage Ratio Adjacent Channel Selectivity Assisted Global Navigation Satellite System Access Network Discovery and Selection Function Average Power Tracking Additive White Gaussian Nose Base Station Carrier Aggregation Cumulative Adjacent Channel Leakage Ratio Component Carrier Complementary Cumulative Distribution Function Code Division Multiple Access Control Format Indicator Crest Factor Reduction Coordinated Multi-Point Common Pilot Channel Channel Quality Indicator Cell Reference Symbol Coordinated Scheduling and Cooperative Beamforming Closed Subscriber Group Channel State Information Channel State Information Reference Signal Device-to-Device Donor Evolved Node B Discrete Fourier Transform Discrete Fourier Transform Spread OFDM Dominant Interferer Proportion Downlink Multiple Input Multiple Output Downlink Shared Channel Demodulation Reference Signal Dynamic Point Selection Digital Subscriber Line Downlink Pilot Time Slot Enhanced Dedicated Channel Enhanced Data rates for GSM Evolution Enhanced Downlink Physical Control Channel Enhanced Inter-cell Interference Coordination Enhanced Multimedia Broadcast and Multicast Service Evolved Node B Evolved Packet Core Evolved Packet System Evolved Serving Mobile Location Center European Telecommunications Standards Institute Evolved Universal Terrestrial Radio Access Evolved Universal Terrestrial Radio Access Network Frequency Division Duplex Full Dimension Multiple Input Multiple Output

89 89 Keysight LTE Advanced: Technology and Test Challenges Application Note FeICIC FHSS GBR GCF GPRS GPS GSM GTP GTP-U HARQ HeNB HII HPUE HSDPA HSPA HSUPA ICIC IDC IF IMT IMT-Advanced IMT-2000 IP ISD ITU ITU-R JP JR JT LAN LCR-TDD LMMSE LTE LTE-A MAC MB-MSR MBMS MBR MBSFN MDT MeNB MIMO MME MRO MSR MTC MU-MIMO NAICS NAS OFDM OFDMA OI OSG OTA OTDOA PA PAG Further Enhanced Inter-cell Interference Coordination Frequency Hopping Spread Spectrum Guaranteed Bit Rate Global Certification Forum General Packet Radio System Global Positioning System Global System for Mobile Communication GPRS Tunneling Protocol GTP User Hybrid Automatic Repeat Request Home enb High Interference Indicator Higher Power User Equipment High Speed Downlink Packet Access High Speed Packet Access High Speed Uplink Packet Access Inter-Cell Interference Coordination In-Device Coexistence Intermediate Frequency International Mobile Telecommunications International Mobile Telecommunications-Advanced (4G) International Mobile Telecommunications 2000 project (3G) Internet Protocol Inter-Site Distance International Telecommunications Union International Telecommunications Union Radiocommunication Sector Joint Processing Joint Reception Joint Transmission Local Area Network Low Chip Rate Time Division Duplex Linear Minimum Mean Square Error Long Term Evolution LTE-Advanced Medium Access Control Multi-Band Multi-Service Radio Multimedia Broadcast Multicast Service Maximum Bit Rate Multimedia Broadcast Single Frequency Network Minimization of Drive Test Master enb Multiple Input Multiple Output Mobility Management Entity Mobility Robustness Optimization Multi-Standard Radio Machine-Type Communication Multi-User MIMO Network Assisted Interference Cancellation and Suppression Non-Access Stratum Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiple Access Overload Indicator Open Subscriber Group Over The Air Observed Time Difference of Arrival Power Amplifier Performance Agreement Group

90 90 Keysight LTE Advanced: Technology and Test Challenges Application Note PAPR PBCH PCFICH PCI PDCCH PDCP PDS PDSCH PHICH PHY PMI ProSe PSBB PTCRB PUCCH PUSCH QAM QoS QPSK RACH RAN RAT RB RDN RF RI RLC RLP RN RNTP RRC RRH RRM RS RSRP RSRQ RX SAE SBAS SC-FDMA SeNB SEM SISO SMS SON SSPS SU-MIMO TAU TB TDD TDMA TD-SCDMA TM TR TS TTI TX Peak-to-Average Power Ratio Physical Broadcast Channel Physical Control Format Indicator Channel Physical Cell Identity Physical Downlink Control Channel Packet Data Control Plane Packet Data System Physical Downlink Shared Channel Physical Hybrid ARQ Indicator Channel Physical Layer Precoding Matrix Indicator Proxy Server Public Security BroadBand PCS Type Certification Review Board Physical Uplink Control Channel Physical Uplink Shared Channel Quadrature Amplitude Modulation Quality of Service Quadrature Phase-Shift Keying Random Access Channel Radio Access Network Radio Access Technology Resource Block Radio Distribution Network Radio Frequency Rank Indication Radio Link Control Radio Link Protocol Relay Node Relative Narrowband Transfer Power Radio Resource Control Remote Radio Head Radio Resource Management Reference Signal Reference Signal Received Power Reference Signal Received Quality Receiver System Architecture Evolution Space Based Augmentation System Single Carrier Frequency Division Multiple Access Secondary enb Spectrum Emission Mask Single Input Single Output Short Message Service Self Optimizing Network Semi Static Point Selection Single User MIMO Tracking Area Update Transport Block Time Division Duplex Time Division Multiple Access Time Domain Synchronous Code Division Multiple Access Transmission Mode Technical Report Technical Specification Transmission Time Interval Transmitter

91 91 Keysight LTE Advanced: Technology and Test Challenges Application Note UCI UDP UE UL UL-MIMO UL-SCH UM UMTS UpPTS UTDOA UTRA UTRAN VoIP VSA VSG W-CDMA WI WLAN WRC Uplink Control Information User Datagram Protocol User Equipment Uplink (subscriber to base station transmission) Uplink Multiple Input Multiple Output Uplink Shared Channel Unacknowledged Mode Universal Mobile Telecommunications System Uplink Pilot Time Slot Uplink Time Difference of Arrival Universal Terrestrial Radio Access Universal Terrestrial Radio Access Network Voice over Internet Protocol Vector Signal Analyzer Vector Signal Generator Wideband Code Division Multiple Access Work Item Wireless Local Area Network World Radio Conference

92 92 Keysight LTE Advanced: Technology and Test Challenges Application Note Evolving Since 1939 Our unique combination of hardware, software, services, and people can help you reach your next breakthrough. We are unlocking the future of technology. From Hewlett-Packard to Agilent to Keysight. For more information on Keysight Technologies products, applications or services, please contact your local Keysight office. The complete list is available at: Americas Canada (877) Brazil Mexico United States (800) mykeysight A personalized view into the information most relevant to you. Register your products to get up-to-date product information and find warranty information. Keysight Services Keysight Services can help from acquisition to renewal across your instrument s lifecycle. Our comprehensive service offerings onestop calibration, repair, asset management, technology refresh, consulting, training and more helps you improve product quality and lower costs. Keysight Assurance Plans Up to ten years of protection and no budgetary surprises to ensure your instruments are operating to specification, so you can rely on accurate measurements. Keysight Channel Partners Get the best of both worlds: Keysight s measurement expertise and product breadth, combined with channel partner convenience. Asia Pacific Australia China Hong Kong India Japan 0120 (421) 345 Korea Malaysia Singapore Taiwan Other AP Countries (65) Europe & Middle East Austria Belgium Finland France Germany Ireland Israel Italy Luxembourg Netherlands Russia Spain Sweden Switzerland Opt. 1 (DE) Opt. 2 (FR) Opt. 3 (IT) United Kingdom For other unlisted countries: (BP ) DEKRA Certified ISO9001 Quality Management System Keysight Technologies, Inc. DEKRA Certified ISO 9001:2015 Quality Management System This information is subject to change without notice. Keysight Technologies, 2017 Published in USA, December 1, EN