Transmit strategies for the mimo two-way amplify-forward channel with multiple relays and mmse receiver

Two-way multi-antenna relaying with multiple relays offers great potential to increase the reliability and performance of bidirectional data transmission in relay networks. The optimal transmit strategies at the relay and at the nodes are known for the decode and forward strategy at one relay. However, for multiple linear amplify and forward relays the optimal strategy is not known. We compare three different recent proposals, DFT relaying, dual channel matching, and ANOMAX with optimal transmit strategies at the nodes under average power constraints at the relays and with linear MMSE receivers. It turns out that for a few relays DFT relaying performs reasonably whereas for more relays channel aware relaying gains significantly in performance. For large number of relays in rich multi-path fading it is more important to adapt the relay strategy than the node strategies to the current channel state.