Efficient interference mitigating strategies for two-way relay channels

Hierarchical wireless networks have the potential to provide the needed capacity to a large number of mobile stations (MSs). According to this system architecture, the MSs are served by a dense network of fixed relay nodes (RNs) fed by a small number of large hub base stations (HBSs). In such deployment, high spectral efficiencies can be achieved if the RNs act as two-way relays; however this gives rise to co-channel interference (CCI) which needs to be mitigated. In order to gain insights on the impact of CCI to this scenario we consider an HBS with two highly directional antennas communicating with two MSs via two interfering two-way RNs. We investigate the average maximum sum-rate of two cooperative strategies. The first is based on Decode-and-Forward (DF) and network coding and acts as a baseline. The second strategy is based on Amplify-and-Forward (AF) and Network MIMO processing over both the backhaul and access channels. Furthermore we devise some cooperative protocols that utilize two, three or four time slots. It is shown that the 2-slot schemes perform generally better and that the DF strategy achieves superior performance when CCI is low while AF with Network MIMO is superior when CCI is high.