Finite-SNR Precoder Designs for the Interference Relay Channel Without CSI at the Transmitters

Recently, a transmission strategy was designed for the K-user interference channel (IC) without CSI at the transmitters (CSIT) but aided by a relay which knows the global CSI, where it was shown that K - 1 relay antennas are required to attain the maximum network DoF. In this paper, we derive general IA feasibility conditions for a single relay-aided IC with CSI at both the relay and the transmitters. Our result shows that except for the special case of K = 3 users, providing CSI to the transmitters still requires K - 1 relay antennas to achieve the maximum network DoF. Next, we design the minimum-sum-mean-square-error (MSMSE) and weighted-sum-rate (WSR) maximizing pre-coders for the relay-aided IC network without CSIT which show higher sum-rate in the finite-SNR region compared to the IA pre-coding. Further, a so-called scaled-IA initialization is proposed for the MSMSE and the WSR algorithms which not only preserves the network DoF but also saves the power at the relay considerably compared to the MSMSE and the WSR schemes with random initializations. Extensive simulation results in both symmetric and asymmetric networks show that the MSMSE precoder shows better BER performance than both the IA and the WSR algorithms for low-to-moderate data rates.