Channel and traffic status aware relay selection and traffic queue analysis in wireless user-relaying networks

User relaying is a very effective technique to achieve cooperative diversity in wireless networks. In this paper, a new relay selection scheme is proposed jointly considering the channel conditions and traffic status of relay nodes. We introduce traffic model with MMPP (two-state Markov Modulated Poisson Process) for all users, and then jointly taking into account the different QoS (quality of service) requirements and the channel conditions for each user; according to the proposed relay selection scheme, adopt a direct transfer mode, or a user-relaying transfer mode by using AF (amplify-and-forward) strategy, in order to reduce the outage probability of source node and minimize the effects on collaborative users as well. Finally, from queuing theory point of view, according to the system equilibrium equation, we analyze traffic queue performances of source and relay nodes and evaluate the proposed relay selection scheme compared with traditional schemes. Simulation results show that the proposed relay selection scheme can significantly improve the transmission performance of the source node, while reduce queue length of the relay nodes by more than 30% when average SNR is small, and achieve a better cooperative diversity gain.