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The performance targets for the long term evolution (LTE) of the Universal Mobile Telecommunication System (UMTS) into a 4th generation system have been chosen to be very ambitious. While all of these targets may not be achievable in practice, they have served to motivate the decisions for a particular LTE design. Specifically, we discuss the choice of the multiple access scheme for LTE, provide details on the uplink and downlink transmission formats, analyze the benefits of multiple input multiple output (MIMO), and outline approaches for intercell interference mitigation. The trade-off between usage of MIMO spatial multiplexing and beamforming is shown for a practical system. The required signaling overhead is weighed against the performance improvements available from the additional information. Finally, some examples for the achievable physical layer performance are given. © 2007 Alcatel-Lucent.(HSDPA) using orthogonal frequency division multiple access (OFDMA) transmission in a second 5 MHz downlink carrier using and maintaining the same channel structure as wideband code division multiple access (W-CDMA) HSDPA. The study concluded in June 2004 that there were some questions on the performance advantage of OFDMA over W-CDMA in a 5 MHz bandwidth under certain simulation assumptions [1], although it was feasible to introduce OFDMA in UMTS terrestrial radio access networks (UTRANs) in the downlink. Nevertheless, the need for conducting a wider feasibility study for evolution for both uplink (UL) and downlink (DL) in bandwidths below and beyond 5 MHz (from 1.25 MHz up to 20 MHz) was emphasized.

The work on the future evolution of 3G systems is taking momentum in the wireless research community. The UMTS system was standardised in 1999 and contained basic capabilities such as but is not limited to, UTRA FDD and TDD modes, GSM based evolved core network, AMR speech codec, Multimedia Messaging Service (MMS), Location services, a broad range of supplementary services, Open Service Architecture (OSA) and telecommunication management [ 11. The need for improved spectral efficiency, network optimizations and new services has motivated continued enhancements of 3G.The first phase of evolution to the UMTS system started immediately in the form of enhancements on these topics. The UMTS Release 5 system contained some of these enhanced better service capabilities like the initial phase o f the IP Multimedia Subsystem (IMS), Wideband AMR, OSA enhancement, Global Text Telephony, Location Services enhancements, etc. features for higher utilisation of spectral efficiency like High Speed Downlink Packet Access (HSDPA), Intelligent Antenna (IA), network optimization features like IP transport in the UTRAN (IP-RAN), connection of RAN to multiple Core Networks (Iu-flex), etc. HSDPA enabled the UMTS system to achieve higher throughput and high peak data rate up to 14Mbps [2]. IMS allowed rich set of multimedia services defined in the TETF like shared White Boards to be used over UMTS.With the first commercial launch of UMTS, as new application areas for UMTS are realized and network limitations better understood, additional enhancements are found necessary. The second phase of evolution is a continuation of the first phase with emphasise on service enablers as well as UL spectral efficiency. Multimedia multicast services (MBMS) is looking at defining point to multipoint bearers to send multimedia services such as football replays to several users in a cell over one radio bearer [3]. Enhancements to the Uplink Dedicated channel are being studied to improve spectral efficiency and reduce delays [4]. Multiple Input Multiple Output is another technique being considered for higher spectral efficiency [5]. IP based services and transport networks are expected to be increasingly adopted in the enhanced 3G networks [ 6 ] . Distributed UTRAN Architecture aims to exploit the IP transport network to improve system performance [7]. Service enhancements' like Optimised Voice over IP, Push to Talk over Cellular and OSA enhancements are all candidates for the next phase. Network sharing enhancements will allow Service providers to offer innovative services without having to own a radio access network or spectrum.In addition, a parallel approach to enhanced spectral efficiency using OFDM access is being studied. Enhanced OFDM access scheme combined with enhanced IP architecture makes a very attractive and powerful system that may lead to become a candidate for the next 4G system. However, it is not yet clear what shape 4G will take except that it will not be a one thing, Air Interface or Network; nor it seems it will converge to one Globa...

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