Cooperative communication becomes a practical alternative to multiple-input multiple-output (MIMO) systems when MIMO cannot be implemented due to size, cost or hardware limitations. The diversity provided by cooperative communication techniques can effectively combat the deleterious effect of fading, thus cooperative diversity is believed as a powerful approach to facilitate high-speed and high-quality wireless communications. Low-Density Parity-Check LDPC) codes were largely ignored until Mackay and Neal rediscovered in 1995. Nowadays owing to its sparse graph structure and low complexity iterative decoding methods, LDPC codes have not only been successful in the field of coding theory but are also being used in a variety of practical applications. This thesis explores practical decoding schemes of LDPC codes for cooperative communication. We start with the Gaussian multiple access channel (MAC) since the MAC could be seen as one component in a multi-user cooperative communication system. In this part, we investigate the performance of LDPC codes with soft iterative successive interference cancellation (SIC) and decoding scheme using BPSK modulation. Next, we propose a cooperative diversity scheme for the communication model of two sources sharing a single relay under two scenarios. The scheme uses algebraic code superposition relating in a frequency division mode or in the multiple access fading channel to create spatial diversity under the constraint of limited communication resources. We also describe in detail a novel, computationally efficient message passing algorithm at the destinations decoder which can extract the substantial spatial diversity contained in the code and signal superposition. The decoder is based on a sliding window structure where certain a posteriori soft values are retained to form a priori soft values for the next decoding. We show that despite the simplicity of the proposed scheme, diversity gains are efficiently leveraged by the simple combination of channel coding at the sources and network coding at the relay.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:664080 |
| Date | January 2009 |
| Creators | Xu, Xiaoyan |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11627 |
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