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This paper addresses the problem of transceiver design for an amplify-and-forward relay network with multiple sources, multiple relays and multiple destinations. Each node in the network is assumed to be equipped with multiple antennas. A general iterative algorithm is proposed based on convex quadratic optimization theory to minimize mean-square-error of the recovered signals at the destinations. Its convergence and extensions to other scenarios are also discussed. Finally, the effectiveness of the proposed iterative algorithm is demonstrated by computer simulations.

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Abstract-In this paper, pilot-aided in-phase and quadraturephase (IQ) imbalance compensation for orthogonal frequency division multiplexing (OFDM) systems operating over doubly selective channels is addressed. Based on a reformulated system model and the least squares (LS) criterion, a joint IQ imbalance and channel estimation method is developed, and the corresponding compensation scheme is also proposed. Moreover, to further enhance the compensation performance, an iterative compensation algorithm is derived via an expectation-maximization (EM) algorithm. Simulation results show that the iterative compensation algorithm initialized by the proposed LS compensation scheme converges in a few iterations and its performance after convergence is close to the ideal case with perfect IQ imbalance and channel state information.Index Terms-Channel estimation, doubly selective channel (DSC), in-phase and quadrature-phase (IQ) imbalance, intercarrier interference (ICI), orthogonal frequency division multiplexing (OFDM).

In this paper, robust joint design of linear relay precoders and destination equalizers for amplify-and-forward (AF) MIMO relay systems under Gaussian channel uncertainties is investigated. After incorporating the channel uncertainties into the robust design based on the Bayesian framework, a closedform solution is derived to minimize the mean-square-error (MSE) of the received signal at the destination. The effectiveness of the proposed robust transceiver is verified by simulations. This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2010 proceedings.