Turbo Multiuser Detection: Analysis, Optimization and Applications

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Wang, XiaodongColumbia UniversityObjectives and Significance: The turbo principle [27 ],namely,the strategy that exploits the iteratedexchange of soft information between di .erent blocks in a communication receiver,has grown to be a powerfultool in attacking a diverse set of problems in communications.In particular,the turbo multiuser detection(MUD)paradigm [59 ]has attracted signi .cant recent attention as an e .ective technique for joint decodingin multiuser communication systems.However to date the performance of various turbo MUD schemesis largely demonstrated via simulations,and the impact of turbo MUD on the network performance (e.g.,throughput and delay)has not been explored systematically.It also remains unclear at this time how theupper-layer functionalities (such as ARQ protocol,power control,and admission control)should be designedto exploit the physical-layer turbo MUD.The objective of the proposed project is to develop analytical tools toassess and optimize the performance of various turbo MUD methods,and to apply these esults to c oss-layerdesign in wireless networks.Recently a technique known as density evolution [66,67 ]has been developed in the coding community thatpermits analysis of iterative decoding algorithm for in .nite-length codewords.In this proposal,under thedensity evolution framework,we outline a research plan aimed at understanding of the design and analysis ofturbo multiuser detection for a variety of channel conditions and receiver structures,and the design of someupper-layer functionalities which takes into account the physical layer turbo MUD.While in this study wefocus on multiuser CDMA systems,the general principle is applicable to several systems,such as space-timecoding systems,OFDM systems,and intersymbol interference systems.