An optimized LDPC product network coding scheme in multiple access relay system

An optimized LDPC-product network coding scheme is proposed for a multiple-access relay system with two users, one relay station (RS) and one base station (BS). In the first stage, these two users broadcast their LDPC-coded data packets in turn to the RS and the BS. In the second stage, the RS uses LDPC product code to combine the decoded packets from these two users and generate extra redundancy instead of employing XOR-based network coding, and then the RS forwards the redundancy packet to the BS. In the third stage, the BS decodes the packets from the users and the RS jointly by the iterative decoding (ID) manner. In this scheme, based on the extrinsic information transfer (EXIT) charts, an optimization algorithm of irregular LDPC product code is also put forward in order to further improve the performance of the system. Simulation results confirm that the proposed scheme significantly outperforms the regular LDPC-product networking coding scheme and the conventional XOR-based network coding scheme on both AWGN and fading channels.