Research On The Physical Layer Network Coding In Wireless Relay Cooperative System

Since proposed in 2000, the concept of network coding has been considered as one of the major breakthrough in the field of telecommunications. It incorporates the ideas of coding and routing that intermediate nodes in a network are allowed not only to route but also to combine incoming data from different links with coding operations. Thus, network performance can achieve capacity limit of maximum-flow transmission. In addition, network coding has many advantages, such as save bandwidth resources, balance link payload, improve throughput, and reduce energy consumption. In order not to make big changes of software and hardware equipment as well as corresponding protocols, network coding is usually viewed as an upper layer technique and separated from other lower-layer processes. However, in the wireless cooperative communication system, broadcast nature of the wireless medium facilitates the operation of network coding in physical layer. Physical layer network coding provides a new horizon for making further improvement on the performance of wireless network.In order to effectively improve transmission performance of wireless relay-based cooperative system, we design physical layer network coding combined with other key technologies in physical layer, such as channel coding, interleaving and so on. With the aim to exploit potential coding gain in the network code for a better error protection, we propose more effective relay-forwarding solutions. In this paper, the major work and contributions include the following aspects:Firstly, typical cooperative protocols are reviewed in detail. In terms of the upper bound method, theoretical error performance of different cooperative techniques is analyzed, and the numerical simulation is implemented to testify the analysis results. Moreover, we proposed a new coded cooperative scheme. In this enhanced distributed turbo code scheme with soft systematic bit repeating, it not only can mitigate the effect of error propagation, but also achieve extra signal-to-noise gain.Secondly, on the basis of introduction on basic idea and method of network coding, we proposes a new physical layer network coding scheme for two-way relay channel model based on a belief propagation approach. Then we make performance analysis through numerical simulation.Thirdly, for multiple access relay channel model, we propose multi-user network coding scheme based on Turbo code and product code, respectively. Our scheme can effectively solve the problem of network coding operations for many users access to network. Meanwhile joint processing of network coding and channel coding can obtain additional coding gain to further improve the reliability of system.