Research On The Technologies Of Analog Network-coding Relay In Wireless Communication Systems

Relay-assisted cooperative transmission offers significant benefits such asthroughput enhancement and coverage extension for wireless communicationsystems. Therefore, relay technique becomes one of the most importantresearch areas for both academia and industry. As a key technology ofphysical layer, it will be utilized in4G and the next generation wirelesscommunication systems. By applying multiple antennas in each node,multi-input multi-output (MIMO) technique, such as diversity andmultiplexing, can further improve the system performance. Network coding isutilized in cases that multiple sources transmit signal simultaneously. Analognetwork coding (ANC) is a signal processing strategy where relay nodeamplifies the superimposed message and then broadcasts it. Due to itssimplicity and efficiency, ANC is very attractive and widely used.In this paper, we firstly give a brief introduction to the relay technology inwireless communication. In the ANC relay system, some traditional precodingand antenna selection schemes are analyzed. Our emphasis is the two-wayrelay system where frequency spectrum efficiency is higher than traditionalrelay protocols.In traditional two-way relay research, model in which two user exchangedata via one relay node is considered. We extend this model to the multi-usermulti-relay two-way multi-input multi-output relay systems with analognetwork coding. We address the problem of joint design of user precoders andreceivers as well as the relay precoder based on the minimummean-squared-error (MMSE) criterion. We decouple the original non-convexproblem into three sub-problem and proposed an iterative precoding scheme. This precoding scheme supports multi-pair user communication and hashigher spectrum efficiency than one-way relay protocol. Simulation resultsshow that the proposed scheme obtains better bit error rate (BER) and meansquared error (MSE) performance.In addition, we consider the robust precoding design of multi-usermulti-relay two-way relay systems. In practical system, channel stateinformation (CSI) is obtained by channel estimator at the receiver. Due to thereceiver noise, CSI estimate error exists. Our robust precoding schemeconsidering CSI error is designed to overcome the channel error modeling byGaussian random error model. Simulation results illustrate that the proposedrobust precoding scheme can reduce the performance impact of the channelestimate error.In wireless communication systems, antenna selection technique isadopted to select suitable antenna to transmit and receive signal to get betterperformance. In this paper, antenna selection scheme based on greedyalgorithm in two-way relay systems is proposed to maximize the achievablesystem sum rate. The computational complexity reduces significantly whilesystem achieves very close sum rate performance with exhaustive antennaselection scheme. Simulation results show that the proposed scheme maintainthe performance with the growth of user antenna number.Finally, we summarize the main innovational research results of this paperand show some of further research aspects of relay technology, such as robustprecoding design with other channel error model; the simplified precodingdesign in two-way relay system; the precoding scheme considering fairness intwo-way relay systems.