Performance analysis for Physical-Layer Network Coding with Hierarchical Modulation

In practice, channel state is complicated and changing in the mobile communication environment. For the downlink asymmetric Two-Way Relay Channels (TWRC), we presented a joint Hierarchical Modulation and Physical-Layer Network Coding (HM-PNC) scheme. Firstly, a two-way relay communication system model consisting of the source and relay nodes using 2/4-QAM hierarchical modulation is constructed. Secondly, the Physical layer Network Coding (PNC) demodulation and mapping rules at the relay node is presented, the formula for calculating the end-to-end Bit Error Rate (BER) under the Additive White Gaussian Noise (AWGN) is derived as well. Finally, the simulation results are presented which verify the theoretical analysis results. Compared with PNC using the traditional 4QAM modulation technique, the advantage of the hierarchical modulation is made use of to ensure a higher data rate in the better link and to take into account the reliability of worse link.