Research On Cooperative Network Coding Based On Physical Layer Technologies

Cooperative communication has received significant attention in research community since it can extend the communication range of wireless network and mitigate the fading effect of wireless channels. However, due to the half-duplex constraint in practical communication system, cooperative communication suffers from loss in spectrum efficiency. Network coding has been regarded as one promising solution to solve this problem. Using the broadcast nature of wireless media, physical layer network coding (PNC) in wireless cooperative network can effectively improve the transmission rate and spectrum efficiency. In general, the existing PNC can be grouped into three schemes, which are decode-and-forward (DF), amplify-and-forward (AF) and denoise-and-forward (DNF). Compared with other two schemes, DNF provides better performance when the transmissions are symmetric. However, when the transmissions are asymmetric, its performance degrades severely. The paper contributes to the research on the improvement of DNF when the transmissions are asymmetric and the application of DNF in two-way opportunistic relay system.To overcome the constraint of asymmetry in DNF scheme, a novel PNC scheme called joint superposition and DNF physical layer network coding (JS-DNF PNC) is proposed. For the proposed JS-DNF PNC scheme, the theoretical analysis of the normalized throughput and rate is presented as well as the numerical analysis. The analysis results show that JS-DNF PNC not only overcomes the defect of asymmetric traffic of DNF scheme, but also achieves better performance. For the application of DNF in two-way opportunistic relay (TW-DNF-OR) system, the effect of modulation scheme is investigated. Based on the features of TW-DNF-OR system, some modifications are made on the conventional max-min criterion (C-max-min) and a novel max-min criterion jointed with modulation scheme (JM-max-min) is proposed. The comprehensive comparison between two TW-DNF-OR systems in which C-max-min and JM-max-min is employed respectively is performed. The comparison result shows that the proposed JM-max-min criterion exploits perfectly the modulation schemes employed at both sources and system performance is improved.