Research On Light CSI Feedback Overhead In WLAN MU-MIMO Transmission

In wireless communications,Channel State Information(CSI)refers to known channel properties of a communication link.In Multi-User Multi-Input-Multi-Output(MU-MIMO)transmission under Wireless Local Area Network(WLAN),explicit CSI feedback is required to insure accuracy,which brings heavy overhead in the time domain.Meanwhile,selection of concurrent transmission users brings even more overhead.It is a critical problem of MU-MIMO transmission in WLAN that how to reduce CSI feedback overhead.This paper addresses these matters and discusses how to realize MU-MIMO transmission with light CSI feedback overhead?Firstly,we optimize the current CSI feedback and TXOP transmission mechanism combined with channel-based user selection,and propose the Group TXOP Sharing mechanism.It produces a User Group with orthogonal channels,and change the TXOP holder from AC/ACs to the User Group.Thus CSI feedback overhead is amortized to the multiple packets transmitted continuously.Group TXOP improves the system performance by reducing CSI feedback overhead and meanwhile optimizing the channel orthogonality between users.Secondly,we further improve the CSI utilization according to the variety of valid CSI time between users with different mobility,and propose Adaptive CSI Coherence Window Update mechanism.It calibrate channel and update valid CSI time adaptively and evaluate CSI effectiveness through the Coherence Window.Meanwhile,control frames exchanging procedure is designed to avoid coherence window expiration caused by mobility changing.Through Adaptive Window Update mehanism,CSI feedback frequency is further reduced and transmission efficiency is improved.