Linear precoding and finite rate feedback design for V-BLAST architecture

Linear precoding is a simple method to improve the performance of V-BLAST architecture. However, it requires perfect channel state information at the transmitter, which necessitates a great amount of feedback. In this paper, we propose a linear precoding scheme for the V-BLAST architecture with an MMSE-SIC receiver. The whole scheme includes the design of an unquantized precoder and its finite rate feedback. The unquantized precoder, consisting of a beamforming matrix and a power allocation matrix, is designed by maximizing the minimum post-detection SINR of the MMSE-SIC receiver. In addition to the optimal precoder, we give a suboptimal solution which is shown to be asymptotically optimal at low SNR. The advantage of this suboptimal solution is that its extension to finite rate feedback is straightforward. Specifically, beamforming vectors are selected sequentially from a predetermined codebook and the indices are fed back. Besides, elements of the power allocation matrix are scalar quantized and fed back. Theoretical analysis reveals that the unquantized beamforming vectors are uniformly distributed on the unit sphere, leading to a very natural codebook design criterion - the Grassmannian criterion. Moreover, the proposed scheme is flexible enough to allow for a change in the number of data streams without redesigning the codebook. Simulation results are presented to demonstrate the effectiveness of the proposed scheme.