Robust MMSE Transceiver Design for Nonregenerative Multicasting MIMO Relay Systems

Abstract

In this paper, we investigate the transceiver design for nonregenerative multicasting multiple-input multiple-output (MIMO) relay systems, where one transmitter broadcasts common message to multiple receivers with the aid of a relay node. The transmitter, relay, and receivers are all equipped with multiple antennas. We assume that the true (unknown) channel matrices have Gaussian distribution, with the estimated channels as the mean value, and the channel estimation errors follow the well-known Kronecker model. We first develop an iterative robust algorithm to jointly design the transmitter, relay, and receiver matrices to minimize the maximal mean-squared error (MSE) of the signal waveform estimation among all receivers. Then, we derive the optimal structure of the relay precoding matrix and show that the MSE at each receiver can be decomposed into the sum of the MSEs of the first-hop and second-hop channels. Based on this MSE decomposition, we develop a simplified transceiver design algorithm with a low computational complexity. Numerical simulations demonstrate the improved robustness of the proposed transceiver design algorithms against the mismatch between the true and estimated channels. Interestingly, compared with the iterative algorithm, the simplified transceiver design has only negligible performance loss with significantly reduced computational complexity.