Sounding Node Set and Sounding Interval Determination for IEEE 802.11ac MU-MIMO

In this paper, we propose a sounding control scheme for IEEE 802.11ac multiuser multiple-input multiple-output (MU-MIMO). The proposed scheme comprehensively considers the long-term characteristics of a network environment, including the downlink traffic loads and channel coherence times of wireless links, and jointly determines the sounding node set and sounding interval to maximize the long-term expected MU-MIMO throughput gain in consideration of sounding overhead. To this end, we analytically formulate an MU-MIMO throughput gain maximization problem, considering the network environment and sounding overhead. We conduct MIMO channel measurement in practical wireless local area network (WLAN) environments and evaluate the performance of the proposed scheme by employing the real channel data traces. Simulation results verify that the proposed scheme adaptively determines the sounding node set and sounding interval, according to the network environment, and outperforms the existing scheme, which considers the channel coherence times only.