Multi-User MIMO with Limited Feedback Using Alternating Codebooks

Accurate channel information at the transmitter is crucial to multi-user MIMO performance. Unfortunately, the bandwidth of the control channel by which the feedback is conveyed is often limited. An important issue is how to improve multi-user MIMO performance with minimal feedback. Conventional feedback techniques focus on improving the quantized codebook performance using various quantization criteria. In this paper, instead of trying to optimize a single codebook, we apply multiple alternating codebooks to effectively reduce the multi-user MIMO quantization error in addition to the reduction provided by the single codebook optimization techniques. That is, we use an existing quantization codebook design methodology to create not one but multiple such similar codebooks. The codebooks are alternated at each feedback instance creating a larger virtual codebook with the same number of feedback bits as the single smaller codebook. Simulation results show that significant performance gain in multi-user MIMO systems is obtained via the alternating codebook scheme.