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Computer Science Colloquia

Friday, June 28, 2013
Chenguang Xu
Advisor: Stephen G. Wilson
Attending Faculty: Toby Berger (Chair), Alfredo Garcia, Alfred C. Weaver, and Malathi Veeraraghavan

10:00 AM, Thornton Hall, C-310

Ph.D. Dissertation Defense
Two-way Data Exchange in Satellite Communication


We focus on data exchange between two terminals, with primary motivations from satellite communication. The abstract communication model of the problem is a special case of the two-way relay channel (TWRC). The main work of this thesis consists of two parts, corresponding to two different channel settings: linear channel and nonlinear channel.

The first part considers a linear satellite channel, i.e. we assume a linear transponder. We first summarize previously proposed protocols: AF, MAC-NC, MAC-BSI, MAC-XOR, and NLC, and compare their performance in terms of achievable rate regions, maximum sum rates in both symmetric and asymmetric scenarios, and required system complexities. Within these protocols, AF is flexible on signal synchronization, has minimum code knowledge requirements on each terminal, and is compatible with legacy satellites. In addition, it can achieve good performance for all scenarios considered, so we fix on the AF protocol for later study in this thesis. Then, we consider the AF protocol from a different view that given information rate requirements and resource constraints (transponder bandwidth and power) , how to minimize the satellite transponder cost for the AF protocol over a two-way relay satellite channel? A solution to this problem is presented that determines the most efficient bandwidth and power resources requests to reduce the transponder cost, which also leads directly to proper choice for modulation and coding. Finally, we work on the extension to a three-terminal hub-remote data exchange. Two application scenarios including three information flows and four information flows are studied. By analyzing and comparing between different decoding schemes for each case, we try to fully exploit the advantage of non-orthogonal signalling.

The second part considers a nonlinear satellite channel (NGC). We first consider the uncoded transmission with the AF protocol over NGC. We find that large input backoff at the amplifier and incorporation of memory in the receiver are essential to the performance of symbol detection for the AF protocol. Then we study the achievable information rates for NGC. We consider both single-user and two-user (AF) cases. These studies can tell us what is the maximum allowed information rate or minimum required SNR for a reliable transmission over NGC, and help us predict the best possible performance of channel coding. Finally, we study the channel coding performance over NGC in the context of DVB-S2 modulation and coding. Both single-user and two-user (AF) scenarios are studied. For the single-user case, adjusting input backoff and ring ratio of 16APSK can significantly improve the decoding performance, while for the two-user case, a much larger backoff is preferred (-6 dB). In addition, the proposed memory-2 decoder works well, with only a tiny performance gap between it and the ideal memory-2 decoder.