Limited Feedback of Precoder and Bit Loading for MIMO Systems: A Joint Design

This paper jointly considers limited feedback of bit loading and precoder. In the past when both precoder and bit loading are fed back to the transmitter, the feedback rate is often allocated between the two using an ad hoc approach and codebooks are designed separately rather than jointly. In this paper we allocate feedback rate in a systematic manner by analyzing the effect of quantization on transmission power. The analysis allows us to obtain the rate allocation that minimizes the power penalty due to limited feedback. As both precoder and bit loading are fed back to the transmitter, the information embedded in one can be exploited for the design of the other. To take advantage of bit loading feedback, which carries valuable information on the importance of individual subchannels, we employ multiple precoder codebooks, each tailored to a bit loading vector in the bit loading codebook. The multi-codebook scheme enjoys significant gain over the single-codebook case that does not take bit loading feedback into consideration. Simulations are given to demonstrate that the proposed system can achieve a very good performance due to carefully designed feedback rate allocation and joint codebook designs.