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We focus on imperfect channel state information (ICSI) in closed-loop multiple-input multiple-output (MIMO) amplify-andforward (AF) relaying systems. First, near-optimal closed-form solutions for transceiver designs are provided for the source-torelay-to-destination link with ICSI at all nodes. Next, considering a nonnegligible direct link with ICSI available only at the relay and destination and no CSI or ICSI at the source, near-optimal designs are proposed. e Wiener or minimum mean square error (MMSE) filter is employed at the destination to estimate the transmitted signal. e effect of CSI mismatch on the performance of the proposed scheme is then shown through simulations.

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