Research On Relay Selection Methods In Wireless Cooperative System

Cooperative communication, which can obtain space diversity gain and increasesystem capacity as well as transmission performance by allowing multi-users to sharetheir antennas, has become a research hotspot in mobile communication area in recentyears. How to select one or more relay nodes from numerous relays according to thechannel state information and user’s quality of service is an important researchinterest.This thesis firstly discusses the fairness problem of single-user single-relaycooperative system. The idea of priority scheduling is utilized, and the priorities ofcandidate relays are adjusted in order to balance the selected probability of relays onthe premise that the quality of service is satisfied. Thus, the fairness of relay selectionis improved. Secondly, the relay selection method in the cooperative system whichemploys space-time codes is studied. The relay transmission model which combinesAlamouti space-time code is established. The expression equation of thesignal-to-noise ratio of the decision signal which is obtained by the decoding ofdestination is deduced. A relay selection method is proposed for such a system so thatits symbol error rate of transmission is decreased. Finally, aiming to the multi-usermulti-relay cooperative system, the relay selection problem which assigns one ormore relay nodes to each source node is discussed. A hybrid algorithm whichcombines simulated annealing and genetic algorithm is employed to search for theoptimal solution which may maximize the minimum received signal-to-noise ratio ofall transmission links. Simulation results show that the proposed method may significantly improve the received signal-to-noise ratio at the destination along withihe system throughput.