CSI feedback reduction by checking its validity period

Abstract

Multi-user MIMO (MU-MIMO) is proposed in 802.11ac to achieve more than 3x faster than 802.11n. In the real world no-one gets close to theoretical speeds. The primary reason for this anomaly are the various overheads of channel access and channel state information (CSI) feedback. In order to achieve concurrent data transmission, (CSI) feedback from users is required. However, this overhead can easily overwhelm the actual channel time spent on data transmission in large-scale network. Moreover, due to spontaneous uplink traffic, which makes the problem even more challenging. In this paper, we propose a smart CSI feedback protocol called Gabriel. Firstly, Gabriel achieves alterable CSI feedback by evaluating its validity period to eliminate the unnecessary CSI feedback operation. Secondly, we introduce a new concept named 'large time slice' to solve fairness problem. Software-radio based implementation and testbed experimentation show that Gabriel significantly outperforms state-of-the-art CSI feedback reduction methods under various traffic patterns and node mobility.