Design of Channel Coded Heterogeneous Modulation Physical Layer Network Coding

Abstract

In a two-way relay channel network (TWRC), the integration of channel coding into symmetric physical layer network coding (PNC) has been well studied, where both sources use exactly the same channel coding and modulation schemes and the relay decodes and reencodes the codewords obtained from the superimposed signals. How to integrate the channel coding into heterogeneous modulation PNC (HePNC), where the sources apply different modulations, is an open issue. In this paper, we propose a channel coded HePNC (CoHePNC) scheme under asymmetric TWRC. For repeat-accumulate (RA) codes applied at the sources, a full-state sum-product decoding algorithm is proposed which enables the relay to decode the superimposed signals from the sources to the raw decoding results firstly, and then re-encode and obtain the network-coded codewords by mapping the raw decoding results according to the proposed bit-level mapping functions. We further optimized the bit-level mapping functions according to the two source-relay channel conditions. Extensive simulation results demonstrated that the proposed CoHePNC outperforms the existing channel coded PNC schemes in terms of the relay decoding error rate and the end-to-end bit error rate under asymmetric TWRC scenarios.