Turbo Coding For Two-way Relay Channel

Cooperative communications in relay networks, which can provide additional space diversity gain, have attracted extensive attentions. Physical network coding can effectively improve the transmission rate and throughput of cooperative communication without loss of diversity gain. In order to improve the BER performance of the two-way relay channel, the joint turbo-physical network code is designed in this paper.We first construct the model of turbo code and physical network coding in two way relay channel. A virtual turbo encoder is constructed, based on which the maximum a posteriori decoding algorithm is derived. Simulation shows this algorithm has 0.6dB gain than the minimum mean-squared error network coding.To decrease the decoding complexity, we propose the concept of symmetrical states and simplify trellis states for virtual turbo encoder by merging the symmetrical states. Simulation shows relay decoding based on simplified trellis has almost no performance degradation.We discuss the selection rules of sources'encoder in AWGN channel by some simulations and the conclusions are: two sources use same Turbo encoder and feedback polynomial of turbo component code is primitive polynomial.For high-order modulation models, we first discuss a general physical network coding de-mapping criterion. Then, the mapping scheme of QPSK modulation and corresponding joint decoding-demodulation algorithm in relay node are designed. Simulation shows QPSK modulation based on Gray mapping has much better performance than based on general mapping.