Adaptive transmit antenna selection in MIMO amplify-and-forward relay channels

Obtaining the most from multiple-antenna relay systems requires adapting the number of substreams based on channel conditions. In this paper, we develop algorithms for selecting dynamically the number of data streams and the transmit antenna subsets at both the source and relay to minimize the vector symbol error rate at a fixed overall rate. An antenna selection mode of operation is defined by the number of transmit antennas and the substream-to-antenna mapping at the source and relay. We propose three suboptimal multimode algorithms that aim to select the best mode based on the knowledge of channel conditions. The algorithms are shown by Monte Carlo simulations to achieve the full diversity order and to provide considerable gains over the existing designs.