In multiple input multiple output (MIMO) downlink systems, if all users send their channel state information (CSI) to the base station, the base station can schedule users whose channels are good and send them information to obtain high system throughout However, when the number of users in the systems grows quickly, large quantity of feedback information will lead the overflow of the feedback channel. In this paper, we propose a limited feedback strategy based on user rank. In this strategy, only those users whose signal interference and noise ratio (SINR) above a predetermined threshold will send their channel direction information (CDI) and their user ranks to the base station and other users will send nothing to the base station, resulting in the greatly reduced feedback load. Theoretical analysis and computer simulation show the feedback load can be greatly reduced by this method and MMO downlink systems can achieve multiplexing and multiuser diversity gain at the same time.%在MIMO下链路通信系统中,如果每个用户将它们的信道状态信息反馈回基站,则基站可以根据用户信道状态信息,调度信道条件好的用户传输数据,从而获得很高的系统容量.该文针对当系统中用户个数显著增加,大量的反馈信息导致反馈信道溢出的状况,提出一种基于用户分级的减少反馈信息总量的策略,该策略要求只有当用户的信扰噪比高于某个门限,用户才反馈其信道方向信息和用户级别信息；否则不反馈任何信息,理论分析和计算机仿真结果证明了该策略能有效地减少反馈的信息总量并且可获得复用增益和多用户分集增益.
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