HePNC: Design of physical layer network coding with heterogeneous modulations

Physical layer network coding (PNC) has been proposed for the two-way-relay scenario. The existing PNC solutions typically use the same modulation for the source nodes´ signals which may not be desirable for practical situations when the amount of data exchanged between the two source nodes are un-equal and their links to the relay node are heterogeneous. In this paper, physical layer network coding with heterogeneous modulations (HePNC) has been proposed to further improve the spectrum and energy efficiency considering the above mentioned heterogeneity. Similar to the existing PNC, HePNC also includes two stages: the multiple access (MA) stage for two source nodes to transmit data to the relay and the broadcast (BC) stage for the relay to broadcast data to both source nodes. The main difference is that at the MA stage, HePNC can select heterogeneous modulation methods according to the channel conditions and the ratio of data to be exchanged. We present two sample designs of HePNC, including QPSK-BPSK and 8PSK-BPSK, and obtain the mapping rules for the relay´s de-noising and forwarding based on the neighbor clustering algorithm. In addition, we discuss the end-to-end bit-error-rate, energy efficiency and optimal relay location selection when HePNC is used. Extensive simulations demonstrated that the proposed HePNC can substantially enhance the end-to-end throughput and the energy efficiency compared to the homogeneous PNC, and thus it is a promising technology for future green communication systems.