Low-complexity iteration-based interference cancellation in asynchronous physical-layer network coding

When two terminals exchange information through an intermediate relay, physical-layer network coding (PLNC) improves the spectrum efficiency by allowing cocurrent packet transmission. Synchronisation is one of the most important issues in distributed wireless communications systems. In time-domain (TD)-based PLNC, signals transmitted from user terminals may arrive the relay at different time. The fractional symbol level delay will introduces inter-symbol interference because of the use of practical pulse-shaping and matched-filter. Orthogonal-frequency division-multiplexing (OFDM) can be used to deal with time asynchrony. However, OFDM systems are very sensitive to carrier frequency offsets, which will introduce inter-carrier interference. In this study, a novel low-complexity symbol-based decoding iterative interference cancellation schemes are proposed for TD-based and OFDM-based PLNC. Signals from two sources are separately decoded, and interference is reconstructed and eliminated. Monte Carlo simulations show that the proposed scheme with over just one iteration can significantly improve the bit error rate performance.