Analysis and design of synchronous/asynchronous cooperative communication systems

The main objective of this thesis is to analyze and develop practical cooperative communication schemes considering synchronization issue. The initial research is on distributed application of turbo and multilevel codes via user cooperation. For distributed turbo coded cooperative scheme an upper bound on bit error rate is expressed for fading channels incorporating the erroneous inter-user transmission in the analysis. For multilevel coded cooperative scheme, orthogonal signaling is employed in order to embed the data of both users in single symbol and detect independently at the destination. The multilevel coded cooperative system is shown to attain the performance of non-cooperative counterpart employing two transmit antennas.The second research direction is on low density parity check coded cooperative communication over wireless relay channel. The performance of decode-and-forward (DF) protocol is compared with both detect-and-forward (DetF) and amplify-and-forward (AF) protocols for fading channels. Finally, asynchronism is introduced on relay channel by assuming a time delay and phase offset between source and relay transmission. Information theoretical analysis is realized initially and a receiver, employing maximum a posteriori probability type detector, is proposed. The asynchronous system employing the proposed receiver is shown to even outperform synchronous system for additive white Gaussian noise channel. However a small performance loss, which even vanishes for small relative delay values, is observed for fading channel. As an alternative to complex MAP type detector, a reduced complexity minimum mean square error type of detector is proposed.