Capacity evaluation with limited feedback for amplify-and-forward MIMO relay channels in urban environment

The combination of multiple-input multiple-output (MIMO) and relay technology promises to increase coverage and system capacity, while the actual performance of MIMO relay system highly depends on the practical channel conditions. Based on the propagation measurement data in urban environment, we deal with the capacity evaluation for a two-hop amplify-and-forward MIMO relay channel in this paper. Since achieving the theoretic capacity requires the channel state information of both hops at the relay node, a limited feedback scheme is introduced. Distinguished from the conventional schemes, both precoding matrix and channel eigenvalues are quantized and fed back, and a novel codebook design method for the eigenvalues is proposed. Adopting the presented scheme, the values of ergodic capacity for various antenna configurations, precoding codebooks, feedback quantities and power allocation strategies are finally evaluated by real channel responses. The numerical results indicate that the proposed scheme outperforms the existing ones and the channel eigenvalues are essential for feedback.