Analysis of physical-layer network coding over asymmetric two-way relay channel with carrier frequency offset

The physical-layer network coding (PNC) can greatly improve the throughput of wireless network communications. However, critical synchronization in both time domain and frequency domain is required. Orthogonal frequency division multiplexing (OFDM) solves the problem of the synchronization in time domain while more critical synchronization in frequency domain is required. In this paper, we investigate the inter-channel interference (ICI) issue for OFDM-based physical-layer network coding (FPNC) over the two-way relay channel (TWRC). An approximate formula that calculates the ICI is derived. The compensation frequency, used by intermediate node to obtain minimal ICI power, has also been calculated. We find that average compensation is the optimal compensation method in the symmetric TWRC system while a different compensation method should be adopted in the asymmetric TWRC system. In addition, it is observed that bit error rate (BER) performance is not only decided by the power of the ICI but also by the distribution of it. At last, numerical results indicate that our approximate formula is accurate enough to calculate the ICI and can be applied to other OFDM systems.