Baseband Codebook Design with Long-term Information for Hybrid Beamforming Systems

In this paper, we propose a codebook for the baseband of hybrid beamforming systems to reduce the feedback bits. The baseband codebook is designed with the long-term information, so that the space distribution of codewords in proposed codebook is same as the equivalent channel between baseband and users. Then we analyze the performance of the proposed baseband codebook. We provide the rate gap between the ideal case with the perfect equivalent channel and the practical case with quantized equivalent channel from the proposed baseband codebook. Finally, a lower bound of the required number of feedback bits is derived to limit the rate gap within a constant value.