Abstract
Imperfect channel state information degrades the performance of multiple-input multiple-output (MIMO) communications; its effect on single-user (SU) and multi-user (MU) MIMO transmissions are quite different. In particular, MU-MIMO suffers from residual inter-user 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 on the downlink due to delay and channel quantization. Accurate closed-form approximations are derived for the 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 spatial multiplexing gain with a fixed delay or fixed codebook size. Based on derived achievable rates, a mode switching algorithm is proposed that switches between SU and MU MIMO modes to improve the spectral efficiency, based on the average signal-to-noise ratio (SNR), the 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, which 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 size is large.
Highlights
Over the last decade, the point-to-point multiple-input multiple-output (MIMO) link (SU-MIMO) has been extensively researched and has transited from a theoretical concept to a practical technique [1, 2]
We assume that the transmitter knows perfectly the actual received signal-to-interference-plusnoise ratio (SINR) at each active user, and so there will be no outage in the transmission
It is shown that the MU mode is only possible to be active in the medium signal-to-noise ratio (SNR) regime, with a small normalized Doppler frequency and a large codebook size
Summary
The point-to-point multiple-input multiple-output (MIMO) link (SU-MIMO) has been extensively researched and has transited from a theoretical concept to a practical technique [1, 2]. We compare SU and MUMIMO transmissions in the multiantenna broadcast channel with CSI delay and channel quantization, and propose to switch between SU and MU-MIMO modes based on the EURASIP Journal on Advances in Signal Processing achievable rate of each technique with practical receiver assumptions. Previous studies show that the spatial multiplexing gain of MU-MIMO can be achieved with limited feedback, it requires the codebook size to increase with SNR and the number of transmit antennas Even if such a requirement is satisfied, there is an inevitable rate loss due to quantization error, plus other CSIT imperfections such as estimation error and delay. An SU/MU mode switching algorithm is proposed based on the ergodic sum rate as a function of average SNR, normalized Doppler frequency, and the quantization codebook size This transmission technique only requires a small number of users to feed-back instantaneous channel information.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
