Research On Full-Rate Cooperative Communication In Distributed Multi-Relay Network

Cooperative communication, as a new technology, by utilizing the spatial diversity principle, enables single-antenna nodes in a multi-user environment to share their antennas and cooperate with each other to generate a virtual multiple antenna array that allows them to achieve diversity gain. Not only against the deep-fading channel, but also it solves inconvenience of carrying multi-antenna in one mobile node, not only can the cooperative communication enhance the reliability, but also it can optimize the network throughput. However, in the traditional cooperative scheme one time slot has to be wasted in order to achieve the diversity gain which means the data rate between source and destination is halved. So the full-rate cooperative communication has been widely proposed, how to improve the transmission rate and reduce the time of transmitting a symbol without losing any reliability has been a popular topic. This paper is based on the distributed multi-relay networks which are the common scene in wireless cooperative communication nowadays.The strategies of full-rate cooperative communication in distributed multi-relay network are the main research contents in this paper. A full-rate wireless transmission scheme based on multiple half-duplex relays is proposed. To the best of our knowledge, we are the first to adopt DF mode into relay decoding strategy in this topic. Our motivation is that DF mode can reduce the noise among source and relay nodes effectively. We use prevailing linear constellation precoding process at the source node but design coding strategy with DSTC at each relay node. Thus the"Short Broad Effect"caused by the imbalance of error performance between odd time slot and even time slot can be solved. Two precoding matrixes are given out, which occupies low complexity. Meanwhile, the design principle of an easy operated DSTC matrix which matches the precoding matrix is proposed. The analysis on all possible situation of decoding is presented, which proves that full diversity gain can be achieved through easy operated matrixes compared to previous work. Analysis and simulation results also indicate that the scheme proposed obtains lower BER than the multi-relay NAF (NAF, Non-orthogonal AF) scheme in the SNR range of the real system.Based on the first full-rate cooperative communication strategy, a limited feedback full-rate cooperative communication scheme in distributed multi-relay network is proposed. This strategy continues using the method in the first strategy: using prevailing linear constellation precoding process at the source node but design coding strategy with DSTC at each relay node. By utilizing sliding window algorithm, the average channel capacity is achieved, and then the optimization of the average channel capacity by using limited feedback mechanism to change the DSTC structure. Finally a higher transmission rate and more stable transmission quality are obtained. The main factors affecting the performance of the full-rate cooperative communication system are given out. Compared with the none-feedback communication strategy, the feedback communication strategy get a certain degree of ascension both in BER performance and channel capacity according to the simulation results.