Impact of channel side information availability at the source node on the capacity of multi-hop MIMO relay networks

In this paper, we investigate the impact of channel side information (CSI) availability at the source node on the capacity of multi-hop fading relay channels where the nodes are all equipped with multiple antennas. We consider both Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying strategies. We study a system where the source node multiplexes the information into a number of parallel streams. When the source node has CSI of the source to relay links, we propose a transmission scheme where each stream is matched to a different relay node based on the conventional eigen-mode transmission. When no CSI is available at the source node, all cooperating relays are assumed to get involved in forwarding all data streams. We derive ergodic capacity expressions for all scenarios considered and observe that CSI availability at the source node provides significant gains over the case where no CSI is available. It should be noted that the CSI availability at the source node assumed in this paper is a limited one, in that, no CSI for the relay to destination links are assumed.