An adaptive rate compress-and-forward cooperation for virtual-MIMO systems

A practical virtual multiple-input multiple-output (MIMO) system that implements compress-and-forward (CF) cooperation is proposed in this paper. Bit-interleaved coded modulation (BICM) technique is implemented here to provide forward error correction and improve the system performance. A closed-form union bound for the system error probability is derived, based on which we prove that the smallest singular value of the cooperative channel matrix dominates the system error performance. Accordingly, an adaptive rate CF scheme is proposed, which uses the smallest singular value as the switching criterion. Depending on the instantaneous channel conditions, the relay could therefore choose various quantization rates. It is shown that the adaptive rate CF scheme eliminates unnecessary complexity for the quantization at the relay, and enables the virtual-MIMO system to achieve almost MIMO performance.