Smart Retransmission for CSI Recovery in Uplink Multi-user MIMO Networks

Ambient noise not only influences the data transmission but also causes incorrect CSI. To overcome the low SNR problem, traditional methods usually retransmit the same packet for enough times to increase the SNR. Unfortunately, recently works only focus on the failed data retransmission, yet totally overlook the incorrect channel estimation, which are not efficient for multi-user MIMO WLAN. As long as there is an incorrect CSI, all the concurrent transmitted data will be miscalculated. Meanwhile, our realworld experiments show that there are nearly average 76% data errors caused by incorrect CSI, when using commodity network interface cards. To efficiently recover from failures for MU-MIMO, we propose a smart retransmission scheme based on partial packet recovery, called SMR, where the receiver determines whether the failures are data errors or incorrect CSI estimation, and then adopts the corresponding retransmission scheme. SMR reduces the retransmission rate and makes minimum amendments to integrate into current 802.11ac WLAN framework. We conduct extensive experiments to evaluate its efficacy. Experiment results demonstrate that SMR can substantially improve the throughput for MU-MIMO WLAN.