Feedback budget allocation optimization for P-VQ in downlink beamforming

In this paper, we analyze the performance of a downlink beamforming system with partitioned vector quantization (P-VQ). A multiuser multiple-input single-output (MU-MISO) downlink beamforming system with accurate channel state information (CSI) at user terminals is considered. The optimization of feedback bits allocation to different partitions and channel direction indicator (CDI), channel quality indicator (CQI) corresponding to each partition has been performed exploiting quantization mean square error (MSE). The impacts of equal and unequal partitioning, and the number of partitions on codebook memory and overall system capacity have also been investigated and depicted through simulation results. We have found that with optimized CQI and CDI bits allocations, the amount of bits allotted to equal and unequal partitions are proportional to the size ratios of the respective partitioned sub-vectors. It has also been observed that for small-sized partitions, the optimal ratio of CDI to CQI is much smaller than that of large-sized partitions.