Optimum transmit beamforming in an interactive wireless relay system with network coding

Wireless relay is an essential technology to achieve a flexible network for ubiquitous communication. To improve throughput performance in the network, network coding (NC) has been proposed for a two-user relay node. NC is a concept encoding both users´ data into one packet and multicasting it simultaneously. However, if the relay node has two or more antenna elements, antenna pattern control is additionally required to send the packet efficiently to both users. In this paper, we formulate several transmit-beamforming techniques in the interactive wireless relay system and compare the performance with each other and with non-NC systems. Numerical analysis has shown that the method maximizing the total capacity in NC provides the best performance.