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In multiple-antenna broadcast channels, if the transmitter has no perfect channel state information (CSI), feedbacks are usually needed from the receivers. When the number of receivers is small, fixed feedback will lead to a sum rate ceiling as the SNR increases. In this paper, we analyze the methods to increase the throughput in codebook based feedback in MIMO broadcast channels. Three codebooks are used for comparison and the results show that, using finer codebook and regularized zero-forcing can increase the system's throughput. However, the sum rate ceiling still exists as long as fixed feedback is used. Feedback bits increase along with SNR seems to be the only way to solve this problem.
Date of Conference: 26-28 Dec. 2009