Evolution of the 4 th Generation Mobile Communication Network: LTE- Advanced

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1 Evolution of the 4 th Generation Mobile Communication Network: LTE- Advanced Khondokar Fida Hasan Lecturer, Department of Information and Communication Technology Comilla University, Comilla, Bangladesh k.fidahasan@yahoo.com Md. Morshedul Islam Department of Computer Science and Engineering Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh morshed_cse_cu@yahoo.com ABSTRACT Mobile communication network experiences dramatic advances and changes over the last two decades. With the growing demand, the development of the design and optimization of radio access technologies and a further evolution of the existing system, the Third Generation Partnership Project (3GPP) had laid down the foundation of the future Long Term Evolution (LTE) advanced standards as the 3GPP candidates for 4G. This research work provides a high-level technical overview of LTE Release-10, also known as LTE-Advanced. This article covers a quick overview of LTE-Advanced technology and its predecessor technologies. It also describes all the technological enhancements introduced to LTE-Advanced. Thus, this paper can steer all those learners and researchers who desire to have a foundation for further research and study in the field of next generation mobile communication system. Keywords: LTE, LTE-Advanced, 4G network, Carrier Aggregation, Relaying, Spectrum Utilization. I. INTRODUCTION In recent years, the demand for mobile internet access has grown significantly. The number of pages viewed on the mobile Web browser Opera grew from 1.8 billion pages in January 2008 to 51.5 billion pages in February 2011 where 7.3 petabytes of operator data were compressed for 89.8 million Opera Mini users [1]. Nevertheless, the current technology is not widely successful to serve and to satisfy the users because of its low transmission rate and high service costs. Consequently, research is going and new concepts toward evolution are subjected to verify for implementation throughout the world. Based on the requirements of high speed mobile wireless access services, wireless systems can be broadly classified as into two groups; Cellular system based on IMT 2000 (WCDMA, HSDPA, HSUPA, HSPA+, LTE/LTE-Advanced by 3GPP, CDMA2000 1X) and Extension of fixed wireless systems incorporate mobile functions i.e. WiMAX (IEEE e) & IEEE m. The overall evolution of cellular technology is diagrammatically shown in Figure-1[2]. LTE Advanced is a broadband mobile communication standard. It is being standardized by the 3rd Generation Partnership Project (3GPP) as a major enhancement of the pre-4g 3GPP Long Term Evolution (LTE) standard, which verified to be insufficient to satisfy market s demand [3]. The 3GPP group has been working on different aspects to improve LTE performance, using for this purpose the framework provided by LTE Advanced, which includes some advanced features. Figure 2 shows a typical migration scenario toward LTE-Advanced. The horizontal axis explains the performance which includes capacity, throughput, latency and cost, etc. LTE (Release-8) area will be overlaid firstly with 3G area and expanded gradually according to the customer s demand. Since LTE-Advanced is based on the 1092

2 LTE Rel. 8 and supported with full backward compatibility with LTE Rel. 8, LTE-Advanced UE can be shared with LTE of previous release in the same frequency and area Thus, the migration from LTE toward LTE- Advanced is very smooth, e.g. support of CA with new frequency to improve the capacity and throughput. In other words, LTE operators can easily upgrade to the LTE-Advanced according to the market demands and new frequency allocation [4]. IEEE 3GPP 3GPP2 OFDMA based physical 2G 3G layer 4G GSM GPRS EDG UMT HSDPA HSUPA LTE IS95A cdma 1X b/g WiFi d WiMAX-e WiMAXm 1x EV-DO IS 956 DO Rev A DO Rev B Flash-OFDM Rev 0 & UMB IMT- Advanced Converged OFDMA based standard Figure: 1. Evolutionary path of cellular technology. In this research work, it has been presented a detail review on the LTE-Advanced mobile broad band communication systems and outlines some features that are still in progress. Figure: 2. Migration scenario toward LTE-Advanced. LTE-Advanced requirements: Based on the ITU requirements for IMT-Advanced systems, 3GPP created a technical report summarizing LTE-Advanced requirements in [3-5]. In wards the prime requirements are: A high degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner; Compatibility of services within IMT and with fixed networks; Capability of interworking with other radio access systems; High quality mobile services; User equipment suitable for worldwide use; User-friendly applications, services and equipment; Worldwide roaming capability; and Enhanced peak data rates to support advanced services and applications (100 Mbps for high and 1 Gbps for low mobility were established as targets for Research). 1093

3 Another important requirement for LTE-Advanced is to reduce the cost in the radio interface network. As LTE advanced (Release-10 and beyond) is the next phase of LTE (Release-8), it has been shown a brief comparison of the performance target of LTE and LTE-Advanced technological demands in Table-1 [3], [5], [6]. II. TECHNOLOGY COMPONENTS OF LTE-ADVANCED To satisfy the requirements for the next generation broadband wireless technology, LTE-Advanced focused on five technical topics also called technology components. Which are: wider bandwidths with carrier aggregation, uplink transmission scheme including spatial multiplexing, MIMO (Multiple Input Multiple Output) enhancements, coordinated multiple point transmission and reception (CoMP) and relaying functionality. Features LTE LTE-Advanced Uplink Downlink Uplink Downlink Peak Spectrum usage efficiency (b/s/cell) >2.5 > With respect to antenna configuration. 1ˣ2 2ˣ4 2ˣ2 4ˣ4 1ˣ2 2ˣ4 2ˣ2 4ˣ4 Average spectrum usage efficiency (b/s/cell) Cell-edge spectrum usage efficiency (b/s/user) Operating bandwidth (MHz) Up to 100 User Plane delay (Unidirectional) (ms) <5 <5 Connection setup delay (ms) <100 <50 Mobility Optimized for low speeds(<15km/hr) High performance at speed up to 120km/hr Same as that in LTE Maintain links at speeds up to 350km/hr Coverage Full performance up to 5km a) Same as LTE requirements. b) Should be optimized or deployments in local areas/micro cell environments Capacity 200 active users per cell in 5 MHz 3 times higher than that in LTE Table: 1. Comparison of the performance target of LTE and LTE-Advanced. 1. BAND AGGREGATION FOR WIDEBAND TRANSMISSION AND SPECTRUM UTILIZATION One of the salient targets of LTE-Advanced is to evolve technology that will support to significantly increase the pick data rate up to 1Gbits/s in the downlink and 500Mbits/s in the uplink [7]. An effective and slim strategy to reach high data rates requirements is to aggregate multiple LTE carriers. Two or more component carriers are aggregated in order to support wider transmission bandwidths up to 100MHz [8]. 100 Figure: 3. Carrier aggregation of five contiguous carriers. 1094

4 Here several smaller contiguous and noncontiguous carriers can be aggregated while maintaining the backward compatibility with the legacy user. Five 20MHz component carriers can be aggregated to form 100 MHz system as shown in Figure-3. Initially, LTE- Advanced (3GPP Release 10) deployments will likely be limited to the use of maximum two component carrier, i.e. the maximum DL/UL bandwidth will be 40MHz for FDD. This will not preclude higher number of aggregated carriers been specified in 3GPP Release 11 and/or higher [8]. Considering frequency location of component carriers, carrier aggregation can be represented into three categories (as shown in figure: 4); intra-band aggregation with contiguous carriers (e.g., aggregation of #2 and #3 in Fig. 2), inter-band aggregation (#1and #4), and intraband aggregation with non-contiguous carriers (#1 and #2) [9]. Together MIMO and OFDMA (Orthogonal Frequency Division Multiple Access) improves the spectral efficiency and capacity of the wireless network, and proves a very valuable asset in maximizing usage of scarce spectrum typically controlled by regulatory bodies. Thus MIMO (Multiple Input Multiple Output) is probably the most important feature of LTE-Advanced for improving the data bit rates and the spectral efficiency [10]. LTE-Advanced extends the MIMO capabilities and now supporting eight downlink antennas and four uplink antennas where as LTE support maximum four downlink antennas and one uplink antennas. In order to support downlink peak spectrum efficiency of 30bps/Hz and uplink peak spectrum efficiency of 15 bps/hz according to LTE-Advanced requirement [13], the spatial multiplexing with antenna configuration of 8 8 for downlink transmission and 4 4 for uplink transmission is being investigated. Here N N denotes a configuration of N transmit antennas and N receive antennas. In addition to meeting the peak spectrum efficiency, further improvement of the average cell throughput as well as the cell edge performance is also an important aspect of the LTEadvanced study [8]. 3. ENHANCED UPLINK TRANSMISSION SCHEME Figure: 4. Carrier Aggregation in LTE-Advanced (Release-10) 2. ENHANCED MULTIPLE ANTENNA TECHNOLOGIES Multiple Input/Multiple Output (MIMO) increases peak throughput by transmitting and receiving multiple streams of information within the same spectrum. The uplink transmission scheme of LTE-Advanced is based on SC-FDMA, a powerful technology that combines many parts of OFDM with the low peak to average power ratio of a single carrier system. SC-FDMA is a discrete Fourier transformed (DFT) pre-coded orthogonal frequency division multiple access scheme [3]. Figure-5 shows a block diagram for the enhanced uplink multiple access (clustered SC-FDMA) process. It has one transport block and one hybrid ARQ entity per scheduled component carrier. Each transport block is mapped to a single component carrier, and a UE may be scheduled over multiple component carriers simultaneously using carrier aggregation, as described in the previous section. 1095

5 scenario. An example scheme is to form a beam to the scheduled UE by using the transmit antennas of the cells 1, 2, and 3, where each cell transmits the same data to the scheduled UE and the UE-specific reference signal is used for support of demodulation at the UE. Figure: 5. Block diagram of clustered SC-FDMA in uplink LTE-Advanced. 4. CO-ORDINATE MULTIPLE POINT TRANSMISSION AND RECEPTION Coordinated multi-point (CoMP) transmission/reception is a candidate technology considered for LTE-Advanced as a tool to improve the coverage of high data rates, the cell-edge throughput and to increase system throughput [6]. It has been demonstrated that Spectrum efficiency can be improved with multiple antenna technologies (4 or more antennas) using spatial interference coordination methods. Thus the multiple access schemes, enhanced multiple-input multiple-output (MIMO) channel transmission techniques and widespread coordination among multiple cell sites called coordinated multipoint (CoMP) transmission/reception were accepted as the key techniques for LTE Advanced at the Technical Specification Group- Radio Access Network (TSG-RAN) Working Group 1 (WG1) meeting in the 3GPP [11]. CoMP improves the received signal of the user terminal. Both the serving and the neighbor cells are used in a way that the co-channel interference from neighboring cells is reduced. It implies dynamic coordination between geographically separated transmission points in the downlink and reception at separated points in the uplink. This mechanism will improve the coverage of high data rates and will increase the system bit rate [12]. The application of coordinated multipoint transmission is illustrated in Figure-6 for a downlink transmission Figure: 6. Coordinate multipoint transmission in the downlink For the cells 1, 2, and 3 to jointly form the transmit signal matching to the composite channel experienced by the UE, it may be necessary to provide feedback representing the downlink spatial channel of each cell without any presumption on operation at the enodeb transmitter and the UE receiver. The feedback for explicit representation of the spatial channel of each cell may naturally require much larger overhead than the feedback defined in LTE. 5. RELAYING In the evolution process of next generation mobile communication system, relaying is a technological milestone to improve the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. With relaying, the mobile terminal communicates with the network via a relay node that is wirelessly connected to the rest of the part of the radio-access network. The relay node (RN) is wirelessly connected to a donor cell of a donor enb via the Un interface, and UEs connect to the RN via the Uu interface as shown in figure: 7 [14] 1096

6 Figure: 8. Inband-Outband Relaying Figure: 7. Relays The doner-cell/relay link is based on the LTE radiointerface technology and may operate on the same frequency as the relay/terminal link ( inband relaying ) or on a different frequency ( outband relaying ) as shown in figure: 8. Relay stations can be classified into different ways. Based on the amount of protocol knowledge a relay station may be distinguished into three layers. The first layer is the simplest one, Layer 1 relay station (repeater), which simply receives the donor enodeb signal and amplifies it into its own coverage area. A Layer 2 relay station will have medium access control (MAC) layer functionality. A layer 3 relay station would include functionality like mobility management, session set-up and handover and as such acts as a full service (sub-) enodeb. Relay Station Protocol Based Transparency Layer-1 Layer-2 Layer-3 Type-1 Type-2 Table: 2. Classification of Relays Another important classification is used in 3GPP standardization and distinguishes between Type 1 and Type 2 relay stations. A Type 1 relay effectively creates its own cell, i.e. transmits its own identity number (Cell_ID) and own synchronization and reference signals. The UE receives scheduling information and HARQ feedback directly from and sends its own control channels to the relay station. From an UE perspective this Type1 relay station looks like a enodeb. On the other hand, a Type 2 relay station will not have its own Cell_ID and thus would not create any new cell(s). Consequently the UE will not be able to distinguish between transmitted signals form the enodeb and the relay station. In such a scenario it would be possible to transmit control information from the enodeb and data via the relay station. [8], [14]. III. CONCLUSION The performance requirements of LTE-Advanced are set by ITU-R for IMT-Advanced and it is an evolution of existing LTE standard. This paper addressed all the LTE- Advanced features comparing with existing LTE network, as the commercial launch for LTE single mode has already been piloted in Northern Europe. Therefore this paper covers all the new concepts to power LTE- Advanced, towards next generation networks. 1097

7 REFERENCE [1] State of the Mobile Web, February Opera tech report, < [2]. Matti Kiiski, LTE-Advanced: The Mainstream in Mobile Broadband Evolution. European Wireless Conference, Nokia Siemens Networks Oulu, Finland, [3]. Introducing LTE advanced, An application note by Agilent Technologies. [4]. S. Abeta, Towards LTE Commercial Launch and Future Plan for LTE Enhancements (LTE- Advanced), NTT DOCOMO, INC. IEEE, 2010 [5]. Jolly Parikh, Anuradha Basau, LTE Advanced: The 4G Mobile Broadband Technology International Journal of Computer Applications ( ), Volume 13- No. 5, [6]. A. Kumar, Y. Liu, A. Wason,, LTE-Advanced: The Roadmap to 4G mobile wireless networks. Global journal of Computer Science and Technolgy, vol. 10 no. 4, Ver. 1.0, pp , [7]. D.M.Sacristan, Jose F.Monserrat. J.Penuelas, et al, On the way towards forth-generation mobile: 3GPP, LTE and LTE-Advanced. EURASIP Journal on Wireless Communications and Networking, [8]. LTE-Advanced Technology Introduction Rohde & Schwarz GmbH & Co. KG Mühldorfstraße 15 D München [9]. S. Parkvall, A. Furuskar, et al., Evolution of LTE toward IMT-Advanced. IEEE Communication Magazine, [10]. Juho Lee, Jin-Kyu Han, and Jianzhong (Charlie) Zhang, MIMO Technologies in 3GPP LTE and LTE-Advanced. EURASIP Journal on Wireless Communications and Networking, Volume 2009 (2009), Article ID [11]. 3GPP TR , V9.0.0, 2010, Further Advancements for E-UTRA Physical Layer Aspects [12]. LTE-Advanced, Release-10, last visited: 24 th June [13]. 3GPP, TR , Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8). [14]. Technical Specification Group Radio Access network; Feasibility study for futher advancements for E-UTRA(LTE-Advanced), Release 9; 3GPP TR V9.1.0,