Physical-Layer Network Coding with High-Order Modulations

Physical-Layer Network Coding (PNC) can double the throughput of a Two-Way Relay Network (TWRN) by reducing packet exchanging timeslots. In a multi-user wireless communication system, time domain phase shift can inevitably lead to deterioration of PNC performance. In previous studies, there have been many studies result to enhance the performance of some low-order modulation techniques such as BPSK and QPSK, but fewer studies are designed for high-order modulation such as 16-QAM. It is known that high-order modulation is the only way to improve the spectrum utilization rate. This paper uses simulation to explain that the time domain phase shift will greatly affect the performance of 16-QAM PNC, and its’ performance couldn’t be improved even polar code is used. To address this phase penalty problem, we propose a half-symbol asynchronous algorithm to introduce correlations using belief propagation (BP). Simulation results show that the time domain phase shift problem of 16-QAM modulated PNC systems can be solved effectively using our proposed half-symbol asynchronous BP algorithm.