Limited feedback MIMO precoding via alternating multiple differential codebooks

Differential codebook precoding is known as a capacity-achieving precoding scheme when the channel variation is slow. However, at medium to high channel variation speeds the differential codebook optimized for low channel variation speeds performs poorly compared to other precoding schemes, thereby limiting its application to practical systems. In this paper, we apply an alternating codebook technique to differential precoding to improve its robustness to high channel variability. The basic idea is creating multiple (instead of single) differential codebooks optimized for various channel variation speeds, and alternating these codebooks over time providing a virtually larger differential codebook, containing various precoding matrices optimized for different speeds, without the need for additional feedback overhead. Simulation results show that the proposed alternating differential codebook scheme not only retains the superior performance of differential precoding at low channel variation rate but, at the same time, reduces the sensitivity to high speed channel variations, resulting in a more practical precoding scheme.