Top 5 Challenges for 5G New Radio Device Designers

WHITE PAPER Top 5 Challenges for 5G New Radio Device Designers 5G New Radio (NR) Release-15, introduced in December 2017, lays the foundation for ultra-fast download speeds, reliable low latency connections, and connectivity to billions of IoT devices coming online over the next few years. With scalable numerology, flexible waveforms, and new spectrum, 5G NR provides a robust framework to address the many different use cases envisioned by the 5G IMT-2020. The new physical layer standards define a flexible air interface to support the many use cases expected in 5G. Designs for devices like smartphones, tablets, laptops, and wearables will need to operate in new spectrum with new enabling technologies. The 5G NR Release-15 defines the specifications to support two of the three primary use cases: enhanced Mobile Broadband (embb) and Ultra- Reliable Low Latency Communications (URLLC). These use cases will enable high data throughput for streaming of high definition video and movies, and low latency for applications like remote controlled drones and virtual reality. Using new spectrum and the emerging 5G NR technologies means more complexity and greater challenges for design teams. The Top 5 Challenges for 5G NR Device Designers: 1. Leverage scalable numerology to optimize performance 2. Support higher throughput via carrier aggregation, mmwave frequencies, and wider bandwidths 3. Effectively deploy beam steering techniques at mmwave frequencies 4. Perform OTA test on 5G mmwave components and devices 5. Achieve peaceful coexistence with LTE and other wireless communications Page 1

Here are some key challenges product designers need to address before they implement 5G NR: new scalable numerology, higher frequency and wider bandwidths, MIMO (multiple input, multiple output) and beam steering, over-the air (OTA) testing, and 5G NR coexistence with other wireless communications systems. Companies that master these 5G NR complexities will accelerate their deployment and time to market. 1. Leverage scalable numerology to optimize performance Scalable numerology is a new 5G NR feature that offers flexible allocation of resources to support many different use cases and services that can be deployed across diverse frequency bands. Numerology is a function of waveform parameters including sub-carrier spacing and symbol time. Subcarrier spacing scales from 15 khz up to 120 khz, and as sub-carrier spacing gets wider, the slot length gets shorter, resulting in decreased slot duration times as shown in figure 1. The variable slot duration provides for better adaptation to channel characteristics like frequency range, phase noise, and delay spread. Scalable subcarrier spacing and slot duration in the frame structure enable different use cases like high throughput millimeter wave (mmwave) operation, highly reliable IoT services, and low-latency, no fail applications. In addition, using minislots (aka mapping type B ), 5G NR allows transmission to start anywhere within a slot, enabling quick delivery of ultra-low latency payloads. 1ms subframe aligned with LTE CP-OFDM symbol Subframe 15 khz 0 1 2 3 4 5 6 7 8 9 10 11 12 13 30 khz 500 µs slot Mini- Slot 60 khz 250 µs slot 120 khz 125 µs slot Figure 1. Scalable subcarrier spacing enables shorter slot duration Page 2

Scalable numerology increases the complexity of test. Many more permutations are required to test the many different use case scenarios. For example, consider the maximum throughput use case at 28 GHz. How the designer assigns resources in the frame impacts how and when the device transmits and receives, affecting overall device performance. Keysight s Protocol R&D Toolset enables you to model the allocation of resources and run scripts to test and optimize device performance under various conditions. Designers can model parameters such as the number of slots per frame, and the order and number of symbols assigned to downlink and uplink within the frame. Figure 2. Keysight s 5G Protocol R&D Toolset lets you model the allocation of resources and test performance results Page 3

2. Support higher throughput via carrier aggregation, mmwave frequencies, and wider bandwidths 5G NR introduces new ways to use spectrum in sub-6 GHz and mmwave frequencies. Sub-6 GHz will focus on coverage and support for many low data rate IoT applications and low latency applications such as digital control systems, security cameras, autonomous automobiles, and pacemakers. mmwave frequencies offer wider channel bandwidths to support embb use cases, enabling data-hungry applications like the streaming of ultra-high definition videos. 5G NR reallocates some of the existing LTE bands and adds new licensed spectrum in several bands: mmwave spectrum will enable 5G NR peak data rates of 20 Gbps in downlink (DL) and 10 Gbps in uplink (UL). 0.6 GHz I S M ISM ISM 2.5 GHz 3.3-4.2 GHz 4.4-5 GHz 5.7-5.8 24 GHz 24 GHz 28 GHz 39 GHz 64-71GHz 71-76GHz Frequency Range 1: 450 MHz to 6 GHz Frequency Range 2: 24.25 to 52.6 GHz Adds 1.5 GHz of new spectrum in frequency bands n77: 3.3 4.2 GHz n78: 3.3 3.8 GHz n79: 4.4 5 GHz Adds 8.25 GHz of new spectrum in frequency bands n257: 26.5-29.5 GHz n258: 24.25-27.5 GHz n260: 37 40 GHz Frequencies up to 90 GHz are currently being investigated for future releases Figure 3. New operating bands in 5G NR Release-15 Creating designs optimized for mmwave frequencies up to 52.6 GHz is one of the most challenging aspects of 5G NR. Signal impairments such as IQ impairments, phase noise, linear/non-linear compression, and frequency error increase with higher frequencies and wider bandwidths. These impairments can distort the modulated signal, making it difficult for the receiver to demodulate the signal accurately. Page 4

It is important to evaluate the signal modulation properties by viewing the IQ constellation and identifying potential waveform distortion errors. Designers can evaluate signal performance by measuring overall error vector magnitude (EVM), EVM per symbol, and EVM per subcarrier. Degraded EVM is an indicator of poor performance and could result in signal lock issues. The denser modulation expected in 5G NR is reflected in tighter EVM requirements in 3GPP specification: Modulation scheme for PDSCH Required EVM QPSK 17.5% 16QAM 12.5% 64QAM 8% 256QAM 3.5% Table 1: 3GPP TS 38.101-1 EVM requirements for user equipment (UE) EVM for 256 QAM is much more difficult to achieve in designs, so test solutions need to have higher levels of fidelity to measure, validate, and troubleshoot devices using denser modulation schemes. An additional measure of signal performance is wideband spectrum performance, measured with occupied bandwidth (OBW), adjacent channel power ratio (ACPR), spectrum emissions masks (SEM), and spurious emissions mask. These measurements can provide some insight into overall power and signal quality outside the signal bandwidth. Figure 4. Analysis of a 5G NR 256 QAM signal viewing EVM and spectrum Page 5

3. Effectively deploy beam steering techniques at mmwave frequencies Use of mmwave frequencies with wider channel bandwidth can enable higher data throughput. Signals at mmwave frequencies, however, experience signal propagation issues such as increased path loss and reduced penetration through walls and windows. Beam steering and beamforming combine multiple antenna elements to create high-gain, directional beams, which can be steered to specific users. In 5G NR mmwave designs, the base station and the mobile device will use narrower beams configured through beam steering. One of the biggest challenges with the use of narrow beams is establishing and maintaining the communications link between the base station and the UE device. When using narrower beams, neither the base station nor the mobile device knows the other s position, especially during initial access to the network. New initial access and attach procedures in 5G NR include finding beams, initiating access, and switching beams as a device travels through the network. The base station will use beam sweeping to broadcast signals from the base station to find the UE. The UE devices will find and select the strongest beam and establish a communication link. Synchronization and gnb broadcast signals gnb Beam acquisition for UE (beam sweeping) Uplink Beam Downlink Beam UE UE Figure 5. Next generation NodeB (gnb) beam sweeping and initial access and attach procedures Testing is required at multiple stages during the design of 5G NR devices. Early in the design phase, designers validate the protocol procedures to ensure the device can connect to the network. This includes testing initial access and beam management tasks as the device travels through the network. A network emulator simulates network commands during testing and captures the resulting actions from the device. Page 6

Designers must also validate the RF performance of their devices during simulation and with hardware prototypes. In both models, designers should measure and optimize RF characteristics such as EVM and ACPR. It is also important to understand and maximize the radiated signal efficiency by measuring the antenna s 3D beam performance with antenna gain, side lobes, and null depth measurements. Designers should perform these measurements to understand how the beam characteristics change with movement. A calibrated OTA test method with a 5G NR compliant waveform and 3D analysis tools is an ideal solution to measure 3D beam performance. 4. Perform OTA test on 5G mmwave components and devices Currently, designers perform most sub-6 GHz RF performance tests using cabled connections. Moving to 5G, low frequency tests will remain similar to 4G, but for mmwave, the following will require over-the-air test solutions: RF performance minimum level of signal quality Demodulation data throughput performance Radio resource management (RRM) initial access, handover, and mobility Signaling upper layer signaling procedures Beam Antenna Beam Antenna Beam Antenna Figure 6. Prototype 5G NR smartphone with antenna arrays located around the perimeter of the enclosure Page 7

Designers typically perform radiated testing on their devices in the near-field or far-field region from the device. Far-field test methods are traditionally the most comprehensive but pose some issues at mmwave frequencies. As the operating frequency goes higher and the size of the radiated antenna increases, the far-field distance increases, resulting in higher path loss which makes it more difficult to achieve accurate radiated measurements. For example, a 15-cm radiating antenna, operating at 28 GHz, results in a far-field distance of 4.2 meters and a path loss of 73 db. Due to the higher operating frequency, a traditional far-field test method results in an excessively large far-field test chamber with path loss that is too great to make accurate and repeatable OTA measurements. Size D (cm) 2 GHz Distance (m) Path Loss (db) 28 GHz Distance (m) Path Loss (db) 43 GHz Distance (m) Path Loss (db) 10 0.13 m 21 db 1.87 m 66 db 2.87 m 74 db 15 0.30 m 28 db 4.2 m 73 db 6.4 m 81 db 20 0.53 m 33 db 7.4 m 78 db 11.4 m 86 db Table 2: Far-field test distance and resulting path loss for OTA measurements Test vendors and 3GPP are studying direct far-field (DFF), indirect far-field (IFF), and near-field to far-field transformation (NFTF) test methods to determine suitable OTA test methods for device and base station conformance tests. Recently approved by 3GPP for device RF performance test is the compact antenna test range (CATR). This OTA test method can perform measurements such as transmitted power, transmit signal quality, and spurious emissions for a radiated transmitter with much less path loss than a traditional far-field test chamber. As 5G NR evolves, designers should regularly review 3GPP approved OTA test methods and test vendor solutions to help reduce their development time and decrease the risk of costly rework. 5. Achieve peaceful coexistence with LTE and other wireless communications To fulfill the promises of 5G NR, devices need to operate in many different frequency bands and with many different operating models. 5G NR will need to operate in adjacent cellular bands and sometimes within the same spectrum as other wireless communications systems such as Wi-Fi, Citizens Broadband Radio Service (CBRS), military, and satellite services. Page 8

Shared spectrum can extend the performance and throughput of a device by using channel aggregation with unlicensed spectrum. LTE unlicensed (LTE-U), licensedassisted access (LAA), and MulteFire allow LTE operation with unlicensed spectrum. LAA uses the 4G network as an anchor and implements listen-before-talk to ensure no other operation is taking place before using a secondary channel to transmit data. LAA requires careful coexistence design and test with many different permutations due to the many different protocols used in the same frequency bands. 5G NR operating in mid-band frequencies (3.3 to 4.2 GHz, 3.3 to 3.8 GHz, and 4.4 to 5 GHz) can also cause interference with adjacent IEEE 802.11ac and 802.11ax Wi-Fi networks at 2.4 GHz and 5 GHz and other IMS (industrial, scientific and medical) bands. Without proper filtering for each band, emissions from harmonics, intermodulation spurs and spectral regrowth can impact the radio transmissions in these bands. A constellation diagram simultaneously displays phase and amplitude information. Measuring a signal with a vector signal analyzer and viewing the results in a constellation diagram can reveal signal interference and distortion issues. The EVM of the demodulated signal and the EVM per subcarrier can predict good or poor coexistence in a congested spectrum. Viewing wideband spectrum measurements such as ACLR and SEM can provide insight into the signal s interference possibilities. Figure 7. Wideband signal generators and signal analyzers with demodulation software perform 5G NR/4G LTE coexistence scenarios for device validation 5G NR not only needs to coexist with existing commercial wireless infrastructure, but also with military, non-military radar, and satellite signals. 5G NR mmwave operating bands in frequency range 2 (FR2) overlap with Fixed-Satellite Services (FSS) earth station uplinks from 27.5 to 29.5 GHz and FSS downlinks between 37.5 to 40 GHz. In these situations, the incumbent may have priority in the frequency band. 5G NR devices will need to sense the environment and modify behavior based on the policy for its location. Page 9

Conclusion New spectrum and emerging technologies introduced with 5G NR will require new design and test procedures. These new technologies bring new test challenges in processing and validating wider bandwidths, testing and validating beam steering performance, over-the air (OTA) testing methodologies, and 5G NR coexistence with other wireless communications systems. Keysight Technologies can help you innovate processes to keep up with 5G NR s accelerating pace and complexity. Our portfolio of 5G NR solutions provides the tools to address these challenges with solutions to emulate, measure, and validate 5G NR RF and protocol signals so you can innovate, transform, and win in 5G. Visit the Keysight 5G NR Resource Center to stay up-to-date on emerging standards, techniques, and best practices. Download tutorials, application notes, case studies, and more. Learn more at: www.keysight.com For more information on Keysight Technologies products, applications or services, please contact your local Keysight office. The complete list is available at: www.keysight.com/find/contactus This information is subject to change without notice. Keysight Technologies, 2018, Published in USA, October 29, 2018, 5992-3417EN Page 10