Adaptive Network Coding in Two-Way Relaying MIMO Systems

We investigate physical-layer network coding for two-way relaying systems which employ multiple-input multiple-output (MIMO) techniques. For single-antenna cases, it has been previously verified that adaptive network coding, whose mapping rule is dependent on channel state information (CSI), can offer good performance for two-stage relaying protocols. In this paper, we evaluate gains achieved by adaptive network coding over the conventional network coding in MIMO channels. We consider several different scenarios: any CSI is not available, only local CSI is available, and global CSI is available at transmitters. Optimal precoding is derived for each scenario to minimize pairwise error probability. We confirm that the adaptive network coding still outperforms the fixed network coding even for MIMO communications.