An efficient carrier estimation algorithm for two-way relay systems with physical-layer network coding

A key issue in physical-layer network coding (PLNC) is how to recover the network-coded packet by the relay from the superimposed signals transmitted simultaneously by multiple transmitters. In order to decode correctly, the asynchrony between signals must be perfectly dealt with. That is, symbols transmitted by different transmitters could arrive at the receiver with relative carrier frequency offset (CFO), relative carrier phase offset and different channel fading. In this paper, we propose an algorithm to estimate the relative carrier offset from the PLNC signals, and investigate two decoding schemes, JCNC and M-JCNC, to construct the XORed packet. As shown in the simulation results, the algorithm can efficiently estimate the relative carrier offsets and significantly reduce the SNR penalty due to asynchrony.