The Studies On The Fair Relay Selection Technology In The Mobile Cooperative Communication Systems

The cooperative communication which uses relay nodes to assist source nodes in carrying data transmission is the solution to achieve high data rate and wide coverage in the future wireless communication systems. It provides the space diversity to cope with the deep fadings of wireless propagations and reduce the occurrences of outage events. Especially, compared with MIMO(Multiple Input Multiple Output) technologies, it can obtain diversity gain without increasing the number of transmitting and receiving antennas and provides a good feasibility in the practical applications of cooperative communication systems. In the cooperative process different relay links might have good or bad channel conditions, therefore relay selection is very important for the performance of cooperative communication systems in the presence of multiple possible relay nodes. The fair selection in relay nodes can improve the equilibrium configuration of resource utilizations and the user experience. Existing relay selection methods, however, usually lead to load imbalance at the relay nodes, which may cause unfair resource utilization and serious damage to the satisfaction degree of user experience. Therefore, this study aims to achieve fair relay selection methods in mobile cooperative communication systems. The main contributions are demonstrated in the following aspects:(1)The load imbalance at the relay nodes, caused by the best relay selection(BRS) method, is analyzed on the basis of the established relay network model. A method of hybrid relay selection(HRS) is proposed to cope with the problem of higher bit error rate(BER) in the low signal-to-noise ratio(SNR) area in the load balancing relay selection(LBRS) method, which utilizes fuzzy controls for load balancings. The simulation results show that the HRS method has significant advantages in balancing the service loads at the relay nodes and slightly inferior BER performance compared with the BRS method, which is optimal in the outage performance. On the whole, the HRS method is an excellent fair relay selection method.(2)By taking both the multi-antenna relay selection and the fair resource utilizations into considerations of the relay selection designs, a fair multi-antenna relay selection(FMRS) method is proposed. Two kinds of normalization functions for mapping the link SNR and service loading into real numbers between 0 and 1 are developed in the FMRS method. At the same time, the antenna selection and relay selection are effectively combined for the fixed multi-antenna relay nodes. Compared with known joint opportunistic relay-transmit antenna selection(Joint OR-TAS), the FMRS method is superior on the fairness and BER performance.