Research On Adaptive Cooperative Mode Selection For Asynchronous Full-Rate Cooperative Underwater Acoustic Communication

Multi-path interference is one of the main factors affecting the underwater acoustic communication rate. Compared to terrestrial electromagnetic channel, multi-path effect of underwater acoustic channel is characterized by large propagation delay and random varying in time-space-frequency domain. Diversity is an effective technique to resist multipath fading, but the traditional diversity techniques(time diversity, frequency diversity and space diversity) is not applicable for underwater acoustic networks(UANs). Cooperative communication as a new diversity technique can effectively improve communication performance. So to research underwater cooperative communication has a very important significance.Existing underwater cooperative communication is synchronous, the source node transmits data only in the first stage, reducing the transmission rate; relay node requires synchronization mechanism which is difficult in UANs. In order to increase the transmission rate, people propose a full-rate cooperative communication in the terrestrial networks, but these methods are still synchronized.In this paper, we introduce an asynchronous full-rate underwater cooperative communication method. In addition, according to the drawback of fixed cooperative mode, we propose an adaptive cooperative mode. The main work of this paper is as follows:First, Give a detailed analysis and description to important characteristics of underwater acoustic channel, and then on this basis, introduce two typical shallow underwater acoustic channel modes.Second, give a brief introduction to the traditional diversity and receivers combined technique, and then study some kinds of cooperative strategies and use MATLAB to simulate two major strategies (AF, DF) and analyses its performance.Third, we propose an asynchronous full-rate cooperative communication while uses a full-rate way to improve the transmission rate and uses the asynchronous mechanism to reduce the propagation delay. Then use MATLAB to simulate the method and analyses its performance. The simulation result show, compared with existing underwater cooperative communication and synchronous full-rate cooperative communication, the method in this paper has better communication performance.Fourth, On the basis of asynchronous full-rate cooperative communication, we propose an adaptive cooperative mode. The simulation result show, compared with the best single-relay cooperative mode and non-cooperative mode, the adaptive cooperative mode in this paper has better system performance.