The Gaussian parallel relay network with multiple antennas

Abstract

We consider a cooperative relaying network with a source, a destination, and two relays. Some previous results on a similar network are extended to incorporate the effect of having multi-antenna nodes. With multiple antennas at the source and at the destination, fundamental characteristics of the channel becomes considerably different from those of single antenna cases in the sense that both the first and second hops are vector-input vector-output channels. The first hop becomes a non-degraded broadcast channel (BC) where the quality of source-to-relay links cannot be ordered, and, in the second hop, having relay signals fully correlated is not optimal in general. We propose a new Decode-and-Forward (DF) scheme by cascading some achievable schemes for multiple-input single-output broadcast channel (MISO BC) and single-input multiple-output multiple access channel (SIMO MAC), where both have common information. It turns out that common information signaling is essential to achieve the capacity under a certain condition. An Amplify-and-Forward (AF) scheme is also considered, compared with DF, and shown to be asymptotically optimal in the high relay power limit.