Downlink MU-MIMO LTE-LAA for Coexistence With Asymmetric Hidden Wi-Fi APs

To maximize the spectral efficiency while satisfying the increasing mobile traffic demand, LTE can offload downlink traffics to unlicensed UNII bands at 5GHz via the standardized technology LTE-LAA (Licensed Assisted Access). In the scenario where LTE-LAA inevitably coexists with already pervasive WiFi devices which were designed without the consideration of LTE-LAA, recent studies have reported that the asymmetric hidden terminal (AHT) problem, caused by the difference in the listen-before-talk clear-channel-assessment (CCA) thresholds of WiFi and LTE-LAA, severely degrades the throughput and delay performance of both LTE-LAA and WiFi. As a remedy to the AHT problem, we propose a multi-antenna multi-user transmit precoding and power control techniques for LTE-LAA base stations to make neighboring Wi-Fi APs defer their new transmissions, thereby peacefully coexisting with them. The proposed scheme does not require any technical amendment or extra work on the conventional Wi-Fi. Based on our realistic simulator with essential MAC and PHY functions implemented, it is confirmed that the proposed scheme improves the throughput and delay performance of LTE-LAA while maintaining or even improving that of Wi-Fi.