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Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Mode Switching for the Multi-Antenna Broadcast Channel Based on Delay and Channel Quantization | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2009 Article ID 802548 15 pages doi 10.1155 2009 802548 Research Article Mode Switching for the Multi-Antenna Broadcast Channel Based on Delay and Channel Quantization Jun Zhang Robert W. Heath Jr. Marios Kountouris and Jeffrey G. Andrews Wireless Networking and Communications Group Department of Electrical and Computer Engineering The University of Texas at Austin 1 University Station C0803 Austin TX 78712-0240 USA Correspondence should be addressed to Jun Zhang jzhang06@mail.utexas.edu Received 16 December 2008 Revised 12 March 2009 Accepted 23 April 2009 Recommended by Markus Rupp Imperfect channel state information degrades the performance of multiple-input multiple-output MIMO communications its effects on single-user SU and multiuser MU MIMO transmissions are quite different. In particular MU-MIMO suffers from residual interuser interference due to imperfect channel state information while SU-MIMO only suffers from a power loss. This paper compares the throughput loss of both SU and MU-MIMO in the broadcast channel due to delay and channel quantization. Accurate closed-form approximations are derived for achievable rates for both SU and MU-MIMO. It is shown that SU-MIMO is relatively robust to delayed and quantized channel information while MU-MIMO with zero-forcing precoding loses its spatial multiplexing gain with a fixed delay or fixed codebook size. Based on derived achievable rates a mode switching algorithm is proposed which switches between SU and MU-MIMO modes to improve the spectral efficiency based on average signal-to-noise ratio SNR normalized Doppler frequency and the channel quantization codebook size. The operating regions for SU and MU modes with different delays and codebook sizes are determined and they can be used to select the preferred mode. It is shown that the MU mode is active only when the normalized Doppler frequency is very small and the codebook
