STS Adaptation for Beamforming Training of Asymmetric Links in IEEE 802.11ay-based Dense Networks

IEEE 802.11ay introduced Beamforming (BF) for asymmetric links in its D0.3 release. The BF for asymmetric links aims to increase the BF Training (BFT) success probability for Stations (STAs) with insufficient link budget to communicate with an Access-Point (AP). For the BFT of asymmetric links, the AP schedules BFT allocations that use directional reception instead of quasi-omni reception to yield extra-gain on the AP's side. Each BFT allocation consists of a number of Space-time Slots (STSs) and each STA randomly selects a STS to perform its BFT. In dense environments, a large number of STAs contends for a limited number of STSs, leading to collisions. The level of collision directly depends on the number of STSs. However, there is no specification on how to adjust the number of STSs of each BFT allocation depending on network conditions. In this paper, we propose a COllision-aware STS Adaptation (COSA) scheme for IEEE 802.11ay dense environments that allows the AP to assign the optimal number of STSs for each BFT allocation based on the observed STS status. Simulation results show that COSA achieves better performance than the traditional BFT for asymmetric links in terms of BFT success ratio and BFT time while decreasing the overhead generated by the BFT allocations.