Wireless MIMO Switching with Imperfect Channel State Information

This paper investigates the transceiver design in a wireless multiple-input multiple-output (MIMO) switching network in which multiple users exchange messages via a multi-antenna relay. Previous work assumed that perfect channel state information (CSI) is known at the relay, which is intractable in practice. Regarding different types of CSI imperfection of uplink and downlink transmission, a statistical and a norm- bounded uncertainty model are adopted to characterize the imperfect CSI of uplink and downlink respectively for the transceiver design. An optimization problem is formulated by minimizing the worst-case mean square error (MSE) with respect to channel uncertainty in the constraint of the maximum transmit power of the relay. Since the problem is non-convex and difficult to solve, we divide the original problem into two subproblems in which the channel uncertainty of uplink and downlink are treated individually. For the uplink subproblem, we propose an iterative approach to determine a closed- form solution of the robust transceiver. In addition, a Sylvester equation is formulated which closed-form solution is provided explicitly for the downlink channel uncertainty subproblem. An overall iterative algorithm is proposed by combining the two algorithms for the subproblems, which can solve the original problem efficiently in a low complexity. Simulation results show that the proposed iterative algorithm reduces the sum MSE significantly in the channel uncertain scenarios.