Cooperative Relaying with Multi-Antenna System in Fading Channel

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In this thesis, performance of cooperative relaying with multi-antenna system in Rayleigh/Nakagami-m fading channels has been investigated. The relay is assumed to operate in adaptive decode and forward mode and perform threshold based decoding. Installation of multiple receiving antennas on infrastructure based fixed relay is feasible thereby increasing the probability of relay participation and hence diversity order may be increased for systems which contain such relays. Such systems in different configurations have been analyzed in various path-loss conditions, severity of fading, relay placement at different locations and antennas installed on it. It has been found that for some locations of relay placement, performance of system depends only marginally on the number of antennas installed on relay and combining schemes at relay and destination. System performance can be improved significantly by appropriately positioning the relay. For such positioning, system performance depends to a considerable extent on number of antennas on the relay and the combining schemes at relay and destination. Performance of a system in which two cooperative single antenna user nodes communicate with multi-antenna destination has been analyzed and compared with the performance of a conventional single input multiple output (SIMO) system. System performance has been analyzed in various path-loss conditions, severity of fading and different number of antennas installed on destination. At higher path-loss condition, communication through intermediate relay node has been found to be superior to SIMO system because relay intermediately boost the signal. In such scenario, performance of cooperative relay network is equivalent or may even outperform SIMO system of same diversity order. Due to half duplex nature of relay operation, spectral efficiency suffers with the increase in number of relays. Opportunistic relaying with multiple relays addresses this issue and the same has been studied in this thesis. However, in such system model, a lot of control signal exchange may be required if channel is rapidly changing which reduces the actual throughput. Cooperative relay system in which signals received from all potential relays are coherently combined at the destination has also been studied. In this case, less number of relay cooperation is better at lower SNR because most of time relay will not decode the message and unnecessary wastage of spectrum efficiency will take place. At higher SNR, more number of relay assisted transmission is superior because probability of relay participation increases. The investigations reported in this thesis are expected to be useful in design of cooperative relaying schemes with multi-antenna systems....
Supervisor: R. Bhattacharjee