Joint Orthogonal Coding and Modulation Scheme for Soft Information in Bi-Directional Networks

In this paper, the authors propose a confidence- based joint orthogonal coding and modulation algorithm for soft information cooperation in the time-division broadcast bi-directional relaying networks. We first compute the log-likelihood ratio (LLR) of the received signals at relay nodes in the first two time slots, then derive the probability distribution of the scaled LLR. Inspired by the space-time coding, the quadrature components of the orthogonal coded signal is composed by the soft information from two terminals. Later, to reduce the computation complexity of the traditional cluster partition, we quantize the orthogonal coded signal to the lattice points, and propose a confidence-based cluster partition algorithm which is adaptive to the modulation scheme and bandwidth limitation. Moreover, we derive the bit error rate (BER) expression for the proposed algorithm. From the simulation results, it is shown that with multiple relays assisting the transmission, the proposed scheme is outperforms AF, DF and CF strategies in BER metric; while for single relay case, the BER performance of the proposed scheme is comparable with AF, DF and CF strategies.