MIMO Multipair Two-Way Relaying With Distributed Relays: Joint Signal Alignment and Interference Neutralization

摘要

We study the degrees of freedom (DoFs) of the multiple input multiple output (MIMO) multipair two-way distributed relay channel (mTDRC), where pairs of users, each equipped with antennas, exchange messages in a pairwise manner with the help of two geographically separated relay nodes, each with antennas. We establish a general framework for the DoF analysis by combining the ideas of signal space alignment and interference neutralization. The proposed framework involves a joint design of user transmit beamformers, relay precoders, and user receive beamformers. Novel signal alignment techniques are proposed to reduce the number of linearly independent constraints for interference neutralization. Based on that, the original joint transceiver and relay design problem boils down to a problem solely on the design of the relay precoders. This problem is then solved utilizing recent development on the solvability of linear matrix equations. As a result, we derive an achievable DoF for the MIMO mTDRC with an arbitrary configuration of . For , the optimal DoF of the considered network is derived for by showing that the obtained achievable DoF meets a DoF upper bound. This result beats the state of the art by establishing the optimal DoF of the considered network in an extra range of . In addition, the achievable DoF obtained for . Furthermore, we show that the optimal DoF of the considered network with is derived for .