Abstract
In Multi-user MIMO (MU-MIMO) downlink system, suitable user selection schemes can improve spatial diversity gain. In most of previous studies, it is always assumed that the base station (BS) knows full channel state information (CSI) of each user, which does not consider the reality. However, there are only limited feedback bits in real system. Besides, user fairness is often ignored in most of current user selection schemes. To discuss the user fairness and limited feedback, in this paper, the user selection scheme with limited feedback bits is proposed. The BS utilizes codebook precoding transmitting strategy with LTE codebook. Furthermore, this paper analyzes the influence of the number of feedback bits and the number of users on user fairness and system sum capacity. Simulation results show that in order to achieve better user fairness, we can use fewer bits for feedback CSI when the number of user is small, and more feedback bits when the number of users is large.
Highlights
In Multi-user MIMO downlink system, the base station (BS) can independently transmit data streams to different user utilizing the same time-frequency resources
In most of previous studies, it is always assumed that the base station (BS) knows full channel state information (CSI) of each user, which does not consider the reality
The two PFS schemes have a crosspoint. It signifies that the system sum capacity of 2 bit feedback PFS scheme is higher than 4 bit when the user number is small, but at the same time, the user fairness will be lower
Summary
In Multi-user MIMO downlink system, the BS can independently transmit data streams to different user utilizing the same time-frequency resources. It is called space division multiple access (SDMA), which can bring more throughput due to multi-user division gain. Some suboptimal schemes are studied, in which the Zero-forcing beamforming (ZFBF) is a classic scheme It is shown in [3] that in the condition of large number of users, the capacity of ZFBF approaches to DPC. Feedback the codeword index, which achieves the maximum SINR and the corresponding SINR value, the BS schedules users with the max system sum capacity among the sub-codebooks. Using LTE codebook and PFS, we consider the user fairness with different number of feedback bits on the condition of different number of users
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