Coding and cooperation in multi-user multi-antenna communication systems

Prashant Udupa Sripathi, Purdue University


The utility of multi-antenna transceivers in single-user, point-to-point links is well understood. With multiple antennas on both ends of a point-to-point link, spectral efficiency may be improved by spatial multiplexing, and link reliability may be improved by utilizing spatial diversity. Similar benefits also apply to multi-antenna systems in a multi-user environment. However, the conditions under which the benefits may be obtained and the techniques to achieve them differ significantly from the single-user environment. In this dissertation, multi-antenna techniques for three canonical multi-user systems, namely, broadcast, multiple-access, and cooperative are proposed and analyzed. Firstly, a technique for optimizing linear zero-forcing precoders for broadcast channels is proposed. A computationally efficient algorithm based on (Gram-Schmidt) QR-factorization and QR-updates is then proposed to implement this optimization technique. The proposed technique is utilized to identify optimal subspaces for communicating at low data-rates over the multi-antenna broadcast channel. The technique is then extended to high-data-rate communication. A nonlinear precoder based on sequential Tomlinson-Harashima preceding is then developed. The performance of the proposed precoders in terms of uncoded bit-error rates and coded bit-error rates with turbo codes is then evaluated, and their merit is established. The application of these techniques to multi-access channels is then discussed. Next, a scaling law for achievable throughput in coherent ad-hoc multi-input multi-output (MIMO) networks is established and its relevance to cellular networks is discussed. Finally, the concept of efficient co-operative diversity systems is introduced in the cellular context, and both coherent and non-coherent relaying schemes are introduced and analyzed.




Lehnert, Purdue University.

Subject Area

Electrical engineering

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