Wireless Two-way Relay System For Network Coding Research

Network coding, first proposed to achieve the max-flow bound of network multicast in the wire line networks, is an information exchange technology which combines coding and routing. By taking advantage of the broadcast nature of wireless networks, the application of network coding in wireless networks can improve the network throughput, ensure the optimization of utilization of wireless network resources and enhance network robustness, which is widely concerned in current literature.Wireless two-way relay system is a basic and practical topology model in wireless relay networks. Because of the two-way data transmission flows, application of network coding in two-way relay systems can obtain higher throughput compared to traditional relaying. So far, many researches on wireless network coding are developed in wireless two-way relay systems, including physical network coding, cooperative diversity, and joint channel coding and network coding.First, after introducing the concept of network coding briefly, the principles and design methods of four wireless network coding applications in two-way relay systems are analyzed in detail. Based on the direct network coding scheme in two-way relay system in which the links between the source nodes exist, an improved hybrid decode-forward and estimate-forward network coding scheme is proposed. Simulation results show that this proposed scheme can achieve the diversity and achieve better performance compared to the direct and adaptive network coding schemes。To further improve the performance of network coding in wireless relay networks, three joint network coding and channel coding design methods are analyzed. Combined with low density parity check (LDPC) channel code which not only have the simple description of coding and decoding procedure, but also has low error floor and near Shannon capacity performance, two joint network coding-LDPC decoding schemes——separate network coding and LDPC decoding scheme, and joint physical network coding and LDPC decoding scheme are proposed and the simulation of these two schemes are presented.Based on the linearity of LDPC code and network coding, to make full use of the information contained in the superposition of the electromagnetic wave signal received at relay node, a joint physical network coding and LDPC decoding scheme is proposed. Specifically, the belief propagation decoding algorithm of the LDPC code is redesigned to suit the scheme. Simulation results show that the proposed scheme outperforms the joint physical network coding and LDPC decoding scheme in terms of BER without adding computational complexity.