| In this thesis, we investigate relay assignment for cooperative networks comprising multiple relay nodes and multiple simultaneously transmitting users. The users are grouped in pairs where the nodes comprising each pair are assumed to communicate information between themselves. Such arrangement is normally referred to as a two-way relay channel. The relay nodes are assumed to be able to use network coding when they are selected to help in relaying.;In the first part of the thesis, we assume that the relays do not use network coding. We also assume that each pair is helped by one relay. We examine the bit error rate performance of the proposed relay schemes for both relaying protocols: Amplify-and-forward (AF) relaying and decode-and-forward (DF) relaying. For AF relaying, we derive an upper bound on the E2E bit error rate performance. For DF relaying, we derive closed-form expressions for the E2E bit error rate performance of ideal relaying. It is shown that the full diversity is maintained in all cases, which equals the number of relays. In addition, for DF relaying, we adopt log-likelihood (LLR)-threshold relaying to control error propagation at the relay and give the corresponding performance analysis.;In the second part of the thesis, we consider relay assignment for cooperative systems with multiple two-way relay channels. The relays are assumed to use network coding to simultaneously transmit the signals corresponding to the pairs they are assigned to. We consider the cases when a relay is assigned to a single pair and the case when a relay is assigned (simultaneously) to multiple pairs. To achieve the latter, we use higher order modulation schemes at the relay nodes. We analyze the performance of these schemes over symmetric and asymmetric independent Rayleigh fading channels, and derive closed-form expressions for the end-to-end bit error rate performance. We show that, for all cases, the full diversity is achieved, which equals the number of relays. We present several examples to verify the theoretical results.;We propose two relay assignment schemes, one that considers all possible permutations of relay assignments and picks the one that results in the best end-to-end (E2E) bit error rate performance. The other one is based on a subset of the available permutations and picks the one that gives the best performance. The latter scheme is devised to make the analysis more tractable and to reduce the computational complexity in finding the best permutation. |
