Research On Distributed Unitary Space-time Codes For Cooperative Communication

With the rapid development of wireless communication, high transmissionrate of the mobile communication network is becoming more and more pursuit bymodern people. The technology of MIMO uses time diversity and space diversity toimprove system capacity and reliability. However，how to set the antennas is a bigproblem in MIMO system, so the cooperative communication appears to solve theproblem. The most important job we need to do currently is to guarantee the datareliability in high speed transmission. The orthogonal structure characteristic ofunitary matrix makes it easy to achieve correct decoding without channel estimation,and save the cost of time and power. The main work of this paper is to combinethe technology of cooperative communication and the unitary codes, andpropose two classes of distributed unitary space time codes.Firstly, we review the overview of the unitary space-time codes. In thispaper,we introduce the unitary space-time modulation and the maximum likelihooddecoding algorithm under two different circumstances, and analyze the pairwise errorprobability and chernoff boundary. In the end, we also introduce the structure of thefour traditional unitary space-time codes.Secondly, a non-differential distributed unitary space time code based oncycle unitary matrix group is introduced in this thesis, and we analyze thecoding and decoding performance in two hop multiple relays in cooperativecommunication. Otherwise, we propose a low-complexity decoding algorithmaccording to the character of the code and analyze the performance of thedecoding with different parameter matrix. According to the simulation resultswe can see that there is a big influence on decoding performance withdifferent parameter matrix. And we also prove that the non-differentialcoding is3dB better than the differential one.Then, take the long distance transmission and the weak signal intoconsideration，a distributed cycle unitary group code for partial coherent multi-hop multi-relay network is proposed. In this paper, we analyze themulti-hop model and the coding and decoding performance detailedly. Andcompare it with two-hop model，we can see in the result that in the low SNR,the performance of two-hop is better than the multi-hop, but not much.However, in high SNR situation, multi-hop is much better. So, in the longdistance transmission we can increase relay nodes to guarantee the quality ofcommunicationFinally, a low-diversity distributed unitary space time code based ontrigonometric function is proposed for multi-source multi-relay cooperativecommunication. The special matrix structure of the code is introduced in thispaper, and just need one node to work, the other node can cooperate withothers, so the system can use the resources of channels and nodes reasonably.Then, we analyze the coding and decoding process with AF and DF. In theend, the low-complexity decoding is detailedly introduced in this paper, andget the decoding computation. Compared with the other three unitaryspace-time codes, the performance is worse than the others, but thecomplexity of computation is lower. Otherwise，compared two decodingalgorithms of this paper and maximum likelihood, the performance of both isalmost the same, but the complexity of the algorithm proposed in this paperis much lower.