Joint Hierarchical Modulation and Network Coding for Two Way Relay Networks

The performance of a joint Hierarchical Modulation (HM) and Network Coding (NC) scheme for two way relay networks is introduced and evaluated in this paper. The proposed scheme uses selective relaying based on a signal-to-noise (SNR) threshold at the relay. In particular, a two way cooperative network with two sources and one relay is considered. Two different protection classes are modulated by a hierarchical 4/16-Quadrature Amplitude Modulation (QAM) constellation at the source. Based on the instantaneous received SNR at the relay, the relay decides to retransmit both classes by using a hierarchical 4/16-QAM constellation, the more- protection class by using a Quadrature Phase Shift Keying (QPSK) constellation, or remains silent. These thresholds at the relay give rise to multiple transmission scenarios in a two way cooperative network. Simulation results verify our analysis and efficacy of the scheme.