Rate enhancement and multi-relay selection schemes for application in wireless cooperative networks
2012-11-20T13:34:59Z (GMT) by
In this thesis new methods are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve transmission rate, mitigate asynchronous transmission and maximise end-to-end signal-to-noise ratio are described. An offset transmission scheme with full interference cancellation for a two-hop synchronous network with frequency flat links and four relays is introduced. This approach can asymptotically, as the symbol block size increases, achieve maximum transmission rate together with full cooperative diversity provided the destination node has multiple antennas. A novel full inter-relay interference cancellation method that also achieves asymptotically maximum rate and full cooperative diversity is then designed which only requires a single antenna at the destination node. Extension to asynchronous networks is then considered through the use of orthogonal frequency division multiplexing (OFDM) type transmission with a cyclic prefix, and interference cancellation techniques are designed for situations when synchronization errors are present in only the second hop or both the first and second hop. End-to-end bit error rate evaluations, with and without outer coding, are used to assess the performance of the various offset transmission schemes. Multi-relay selection methods for cooperative amplify and forward type networks are then studied in order to overcome the degradation of end-to-end bit error rate performance in single-relay selection networks when there are feedback errors in the destination to relay node links. Outage probability analysis for two and four relay selection is performed to show the advantage of multi-relay selection when no interference occurs and when adjacent cell interference is present both at the relay nodes and the destination node. Simulation studies are included which support the theoretical expressions. Finally, outage probability analysis of a cognitive amplify and forward type relay network with cooperation between certain secondary users, chosen by single and multi-relay (two and four) selection is presented. The cognitive relays are assumed to exploit an underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection is performed either with a max-min strategy or one based on maximising exact end-to-end signal-to-noise ratio. The analyses are again confirmed by numerical evaluations.