AN OVERVIEW OF LTE- NEXT GENERATION WIRELESS TECHNOLOGY

Transcription

1 AN OVERVIEW OF LTE- NEXT GENERATION WIRELESS TECHNOLOGY 1 Pallavi and 2 Paras Chawla 1 M. Tech. Research Scholar, Electronics & Communication Engg. Department, JMIT, Radaur, Kurukshetra University, Yamunanagar, Haryana, India pallavibaliyan920@gmail.com 2 Associate Professor, Electronics & Communication Engg. Department, JMIT, Radaur, Kurukshetra University, Yamunanagar, Haryana, India paras.chawla@jmit.ac.in Abstract Long Term Evolution (LTE) is the next step towards in the arena of 3G cellular wireless services. Expected in the 2008 time frame, it is a 3GPP standard which provides an uplink transmission rate of up to 50 megabits per second (Mbps) and a downlink transmission rate of up to 100 Mbps. LTE evolved from an early 3GPP wireless standard identified as Universal Mobile Telecommunication System (UMTS), which consecutively is evolved from the Global System For Communication (GSM). This review paper provides an framework of the LTE physical layer (LTE PHY), LTE Architecture, plus its features. Supplementary, it also gives an gestalt of future services including technologies that are new to cellular such as Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and Multiple Input Multiple Output (MIMO) data transmission. Keywords LTE, LTE PHY, OFDMA, SC-FDMA, MIMO, E-UTRAN 1. INTRODUCTION The LTE has provided a major development in the scenario of cellular technology. It is mainly designed to meet the carrier [1][2] requirements for media transport and high speed data as well as to improve the spectral efficiency in 3G networks, due to this carriers are able to provide more data and voice services over a given bandwidth. Along with this LTE is also capable to provide a significant increase in the spectrum efficiency as compared to 3rd generation (3G) systems, to provide a radio-network [8] delay of less than 5 ms one way and a simplify operated and reduced cost flat radio-network architecture. In the enhanced LTE version, which was released in the 2010 time frame that is LTE-Advanced [6], provided with a further increase in the transmission bandwidth. The transmission rate can reach up to 1Gbps if UEs (Mobile Equipment) are in low mobility status. Even if the UEs are in high mobility status, the transmission rate can still reach up to 100Mbps [13]. Here, the major concern of ours is the physical layer of LTE which is denoted as LTE PHY which is used to provide the data and control information particularly in an efficient manner between an base station and mobile user equipment (UE). Now days there are a number of advanced technologies that are new to cellular applications which are used by the physical layer of LTE. The technologies in particular include the two Multiplexing schemes, these are OFDM and MIMO data transmission. ` Figure 1: Basic SC-FDMA Transmitter/Receiver arrangement 63 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

2 In addition, for the downlink transmission (DL) OFDMA and for the uplink transmission (UL) SC-FDMA is used. OFDMA and SC-FDMA have the same basic transmitter and receiver architecture which therefore offers the same degree of multipath protection. The basic SC-FDMA transmitter/receiver architecture arrangement is provided in fig. 1. In the figure, blocks which are shaded are common to both OFDMA and SC-FDMA schemes, due to this there is a high [20] degree of functional block commonality between the uplink and downlink chains. Below, a brief description of the functional blocks is provided which belongs to the transmit chain: Constellation mapper: It converts the incoming set of the bit stream of data to single carrier symbols such as BPSK, QPSK, or 16QAM depending on the channel conditions. Serial/parallel converter: It formats the time domain SC symbols which are in the serial form into blocks for input to the FFTI. M-point DFT: It converts the time domain SC symbols arrived from the constellation mapper into M discrete tones. Subcarrier mapping: It maps the DFT discrete output tones to specified subcarriers for further transmission. Here, SC-FDMA systems can either make use of contiguous tones (localized) or uniformly spaced tones (distributed). N-point IDFT: It performs the reverse operation of the M-point DFT block which converts the mapped subcarriers back into the time domain for transmission. Cyclic prefix: Cyclic prefix is pre-pended behind the composite SC-FDMA symbols in order to provide multipath immunity as in the OFDM scheme. Pulse shaping: It is employed to prevent spectral regrowth of the bandwidth in the case of OFDM. RFE: It converts the digital signal to analog signal and up converts the signal to RF for further transmission over the channel. 2. OVERVIEW OF 3GPP LTE FEATURES The SC-FDMA transmitter/ receiver represented in this paper meets the physical layer requirement listed in table 1. TABLE 1. Downlink ofdm modulation parameters 64 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

3 A. OFDMA and SC-FDMA Being significantly different from 3GPP WCDMA/HSPA standards which make use of the code division multiple access (CDMA), LTE here adopted OFDMA as the downlink access scheme for the downlink transmission and SC-FDMA as the uplink transmission scheme. The major difference between these two schemes is that the SC- FDMA introduces one extra Discrete Fourier Transform (DFT) to mitigate the peak-to average power ratio problem B. Multi-Antenna The LTE PHY is able to exploit multiple transceivers [3] at both the base-station and the mobile user equipment UE which enhances the link stoutness and increase data rates for the LTE downlink transmission. In particular, MIMO also known as Maximal Ratio Combining (MRC) enhances the link consistency in different propagating environment where the multipath conditions are challenging and the signal level is low. Basically, MIMO can also be used for the increase in the system data rates. Here the first figure 2.a shows a conservative single channel receiver with antenna diversity. This receiver assembly uses multiple antennas, but still is not capable of supporting MRC/MIMO. The basic receiver topology for both MRC and MIMO is shown in figure 2.b. Figure 2(a) Figure 2(b) Figure. 2: Types of receivers for single channel and MRC/MIMO configuration C. Multimedia Broadcast Multicast Services (MBMS) MBMS was proposed in order to support[15] multimedia services. It is well suited to enhance bandwidth efficiency of the wireless systems. MBMS in LTE is known as evolved MBMS (embms) which by means of multi-cell single frequency network (SFN) operation achieve better transmission efficiency and coverage. It also provides efficient mode of delivery for both broadcast and multicast services over the core network. 3. LTE ARCHITECTURE LTE network is based on [12] architecture called EPS (Evolved Packet Switched System) shown in Figure 3. EPS is poised of two main subsystems:\ 1. Radio Access Network: Evolved UTRAN (E-UTRAN) 2. Core Network: Evolved Packet Core (EPC) The main network elements E-UTRN are: UE: User Equipment, it is a terminal of end user. enb: evolved Node B, it is Radio Base Station of Mobile Network Operator (MNO) which used to deliver radio signals. 65 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

4 Figure. 3: LTE Architecture In addition to the E-UTRAN, the LTE system [14] supports non-3gpp access networks such as wireless local area networks (WLAN), WiMAX systems, and code division multiple access (CDMA) 2000 systems, that are connected to the EPC [9]. There are basically two types of non-3gpp access networks, the trusted non-3gpp access networks and untrusted non-3gpp access networks [10][11]. The main network elements of EPC are: MME: Mobility Management Entity, it is network node which is deputed to manage end user s attached procedures, mobility, handover and traffic balance operations. HSS: Home Subscriber Systems, it is used to verify end user subscription. S-GW: Serving PDN (Packet Data Network) Gateway, it is the transmission node linking E-UTRAN and EPC. P-GW: Proxy PDN (Packet Data Network) Gateway, this transmission node links the LTE Core Network (EPC) and other networks. PCRF: Policy and Charging Rules Function, it is network node which is able to define QoS (Quality of Service) policies of a particular service requested by user. A. Qos Architecture LTE architecture also [17] chains end-to-end quality of service with the help of hard Qos and guaranteed bit rate (GBR) for the radio bearers. Ethernet and internet use dissimilar types of QoS architecture, for example, LTE traffic uses different levels of Qos for different applications. Evolved Packet System (EPS) bearers provide support for Traffic Flow Templates and also provide one-to-one correspondence with PLC radio bearers. The EPS bearers can be classified into four categories: Non-GBR Bearer: no admission control for apportionment of resources GBR Bearer: It resources permanently assigned by admission control Default Bearer: Non GBR, catch-all for unassigned traffic Dedicated Bearer: It is allied with specific TFT (GBR or non-gbr) B. System requirements for LTE The LTE technology supports multiple transmission bandwidths in the range of 1.4 to 20 MHz. There is one of the most distinctive [4] feature of LTE i.e. it supports only packet-switching (PS) mode. Hence, all the traffic including real-time service with a rigid delay requirement flows in the form of packets for example, voice services are provided in a unified manner using the packet- switching mode. The object peak data rate is 50 Mbps in the uplink transmission and 100 mbps in the downlink transmission in the case of LTE. Table below summarizes the system requirements for LTE according to which using relevant techniques and quantified radio interface the targets and requirements of LTE can be achieved. 66 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

5 TABLE 2. Major Requirements 4. TRANSMISSION SCHEMES OF LTE The transmission schemes of LTE can be classified into two categories: LTE downlink transmission scheme (OFDMA) LTE uplink transmission scheme (SC-FDMA) A.. LTE downlink transmission schemes This scheme for TDD and FDD modes of E-UTRA is based on predictable OFDM. Here the sub-carriers which are formed by dividing the available spectrum into multiple carriers, are orthogonal to each other. Here each of these sub-carriers are independently modulated by a low data rate stream. OFDM has several benefits over other multiplexing schemes including efficient receiver architecture and stoutness against multipath fading. Figure 4 shows a representation of an OFDM signal with 5 MHz bandwidth, but the principle of OFDM signal is same for the other E-UTRA bandwidths. Here, Data symbols are transmitted over a high number of closely spaced orthogonal sub-carriers by first modulating them. In order to combat inter-ofdm-symbol-interference a guard interval is added in the time domain due to channel delay spread. This is called a cyclic prefix in the case of E- UTRA which is inserted prior to each OFDM symbol. Smart antenna technologies are also supported by OFDM, because the antenna weights can be elevated on a persubcarrier or block of subcarriers basis that is provided due to the flat faded nature of the subcarrier. In addition, OFDM also enables broadcast services with applicable cyclic prefix design on a single frequency network, due to this there is a momentous increase in the received signal power as here the different cells combine over the air and results in sustainable data rates for broadcast services. Figure.4: Representation of OFDM signal 67 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

6 B. LTE uplink transmission schemes Due to the fragile peak-to-average power ratio (PAPR) properties the OFDMA scheme which results in worse uplink coverage it is less favourable for the uplink transmission. Thus, the LTE uplink transmission scheme for TDD and FDD mode uses SC-FDMA. The main reason for selecting SCFDMA as LTE uplink access scheme is that it has better PAPR properties than OFDMA signal. The PAPR characteristics play an important role for cost-effective design of Mobile User Equipment (UE) power amplifiers. The parametrization of uplink and downlink can be synchronised as the signal processing of the OFDMA and SC-FDMA are very much similar. Here, the SC-FDMA uses cyclic prefix for low-complexity receiver execution and high performance in the enodeb. To uphold the single-carrier properties in the frequency domain the terminal is allotted with contiguous spectrum blocks and thus ensure power-efficient transmission. This type of approach is referred as localized or blocked SC-FDMA. Below is a figure is provided which [5] shows the comparison of OFDMA and SC-FDMA. 5. LTE FUTURE SERVICES Figure 5: Comparison of OFDMA and SC-FDMA Some of the services which have provided with a true test [16] of the success of these technologies can be enumerated as follows: (i) Premium MOD(Music On Demand)/ VOD(Video On Demand) Services: With distinguished QoS services and high data rates operators can provide superior multimedia based services such as music - on-demand and video-on-demand, high definition movie downloads, high quality video downloads to subscribers who wish to reward such services. (ii) Fixed broadband services, PDA s and Laptops: These are interrelated to all the fixed wired DSL services which are the most intuitive set of services that can be provided. Also, these technologies with strong Qos support, can help the operators plan business strategies for various sectors based on the middling throughputs of that sector. (iii) Consumer Electronics: Today, customers require the same broadband experience or services they get at their office or at home, regardless of their locations. The high data rates combined with flexibility of LTE shall also increase the growth in development of fresher and better consumer electronic goods. Better gaming consoles, vehicular entertainment systems, portable [19] multimedia players, digital cameras with network capabilities shall add value to the technology. 68 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

7 (iv) Exchange services and Multimedia upload: LTE provides with high data rates for the uplink transmission which allows for interchange services such as file sharing, social networking, mobile blogging etc. and multimedia upload at a faster rate. (v) Business Solicitations for Vertical Markets: LTE shall allow business operators to provide services to markets through business compliances like video surveillance services to homes, video conferencing to enterprise customers etc. 6. CONCLUSIONS We have given a brief overview of the LTE technology, LTE features and LTE architecture. The paper is concluded with the transmission modes used for the downlink and uplink and showing the LTE future services is well aligned with expectations. 7. ACKNOWLEDGMENT The author gratefully acknowledge the contributions of Professor Dr. Rajesh Khanna (ECE Department, Thapar University) for his important contributions on final version of this document. 8. REFERENCES [1] E. Dahlman, S. Parkvall, J. Sköld, P. Beming, 3G Evolution: HSPA and LTE for Mobile Broadband, Academic Press, Oxford, UK, second edition, [2] D. Astély, E. Dahlman, A. Furuskär, Y. Jading, M. Lindström, S. Parkvall, LTE: The evolution of mobile broadband, IEEE Communications Magazine, April [3] Di Wu, Johan Eilert, Dake Liu, Andres Nilsson, Eric Tell, Erik Alfredsson System Architecture for 3GPP LTE modem using a Programmable Baseband Processor, International Symposium on System On Chip [4] Sadayuki Abeta Toward LTE Commercial Launch and Future Plan for LTE Enhancements (LTE- Advanced) IEEE [5] ITU/BDT Arab Regional Workshop on 4G Wireless Systems January [6] 3rd Generation Partnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Further advancements for E-UTRA physical layer aspects (Rel 9), 3GPP TR V9.0.0 March [7] 3GPP TS , Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Rel. 10, v10.2.0, Dec [8] Stefan Parkvall, Eva Englund, Anders Furuskär, Erik Dahlman, Tomas Jönsson, Anthony Paravati LTE Evolution towards IMT-Advanced and Commercial Network Performance, IEEE International Conference on Communication System,2010. [9] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Service requirements for the Evolved Packet System (EPS) (Rel 12), 3GPP TS V June [10] 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Access to the 3GPP Evolved Packet Core (EPC) via non-3gpp access networks (Rel 11), 3GPP TS V Sep [11] 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Security aspects of Machine-Type Communications (Rel 12), 3GPP TR V0.10.0, Sep [12] Sonia Forconi, Alessandra Vizzarri Review of studies on End- to End Qos in LTE networks AEIT Annual Conference, [13] Yi-Ting Mai and Jeng-Yueng Chen IP Multimedia Relay Architectures with Multi-RAT Support in LTE- Advanced Wireless Network 7th Asia Modelling Symposium [14] Jin Cao, Maode Ma, Senior Member, IEEE Hui Li, Member, IEEE, Yueyu Zhang, and Zhenxing Luo A Survey on Security Aspects for LTE and LTE-A Networks IEEE COMMUNICATIONS SURVEYS & TUTORIALS, VOL. 16, NO. 1, FIRST QUARTER [15] Pallvi Chawla, Bhasker Gupta BER Analysis of Single/Multi-User LTE and LTE- A Systems IEEE International Advance Computing Conference (IACC), P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12

8 [16] Subharthi Paul, Prof. Raj Jain Long term Evolution (LTE) and Ultra- Mobile Broadband (UMB) Technologies for Broadband Wireless Access. ADDITIONAL READING [1] LTE Quick Guide /lte_quick_guide.htm, Copyright tutorials point.com [2] UMTS Long Term Evolution (LTE) Technology Introduction, karriere.rohde-schwarz.de/fileadmin/customer [3] LTE: The Future of Mobile Broadband Technology, innovation.verizon.com [4] Overview of the 3GPP Long Term Evolution Physical Layer, 70 P a g e IJRREST h t t p : / / i j r r e s t. o r g / i s s u e s /? p a g e _ i d = 12