Quantized multi-rank beamforming for MIMO systems

We consider the sum-rate maximization via linear precoding in downlink MIMO systems with quantized feedback. We address the precoding codebook design based on the capacity measure by introducing a new distance metric. We propose a codebook structure and its associated design algorithm that allows for significant reduction in the memory requirement and computational complexity. We then provide a system design approach comprising of a multi-rank beamforming (MRBF) scheme, an efficient CQI-based precoder selection algorithm, reduced feedback strategies and novel channel quality indicator (CQI) combining. Our simulation results show that the proposed MRBF scheme can approach the precoding upper bounds with relatively small feedback bits. Moreover, with the same number of bits, the proposed scheme simultaneously achieves higher throughput and lower computational complexity in comparison to the other existing precoding schemes.