Reducing Duration of the MU-MIMO CSI Acquisition Procedure in Wi-Fi Networks With OFDMA

A common way to increase throughput in Wi-Fi networks with multiple devices is to use Multi-User Multiple Input Multiple Output (MU-MIMO). Downlink MU-MIMO requires the access point to know the exact channel conditions between itself and the associated stations. For that, it performs channel sounding and collects channel state information (CSI), which is a time-consuming procedure, especially for future Wi-Fi networks with an increased number of antennas and multiple clients. Thus, the long duration of this procedure may adversely reduce network performance. In 802.11ax networks, this procedure can be shortened thanks to the uplink Orthogonal Frequency Division Multiple Access. For that, the access point needs to schedule various Resource Units to the stations sending CSI reports. The paper emphasizes how the problem of resource allocation for CSI differs from the common resource allocation problem and proposes an algorithm that assigns resource units taking into account the frequency selectivity of the channel. It is shown that the proposed algorithm can significantly shorten the procedure duration compared to the known solutions from the literature.