Transmit beamforming and diversity techniques in multicast systems with a single relay

In this work, we study the impact of the addition of a single antenna relay in a multicasting system with transmit beamforming. We propose the division of the problem into relaying and precoding problems and use this decoupling to apply precoding algorithms available in the literature to the problem of maximizing the minimum user SNR in the relayed system without algorithm specific changes. Next, we study three different relaying schemes representing: the classic setup without using the relay, a combination of the signal from the direct and relayed paths using Maximal Ratio Combining (MRC) and an iterative algorithm that performs precoding and MRC in sequence. Finally, the results show that the proposed schemes are able to increase the system throughput even at the expense of an additional transmission phase. In addition, the performance of the proposed iterative scheme was shown not to depend significantly on the underlying precoding algorithms, which leads to the conclusion that the relaying problem solution has a higher impact on the overall performance than the precoding problem.