Interference alignment using a MIMO relay and partially-adapted transmit/receive filters

Interference alignment is proposed for achieving the maximum degrees of freedom in interference channels. In the present paper, a scenario consisting of several pairs of multiple antenna nodes and a single MIMO relay helping the interference alignment is considered. The interference alignment is performed in two subsequent transmission phases assuming a time-invariant channel during the two transmission phases. Firstly, the relay and the destination nodes receive the signals from all the source nodes, i.e., also the direct links between the communicating node pairs are exploited. In the second transmission phase, both the source nodes and the relay retransmit the signals to the destination nodes. By adapting the relay´s linear signal processing and partially adapting both the transmit and receive filters to the channel, a closed form solution for interference alignment is obtained. The performance of the proposed scheme is investigated by simulations. The results show that the proposed scheme achieves the maximum degrees of freedom and outperforms conventional relaying schemes at high SNRs.