Enhanced Dual Carrier Sensing With Transmission Time Control for Fair Spatial Reuse in Heterogeneous and Dense WLANs

In this paper, we focus on fairness and spatial reuse in heterogeneous and dense wireless local area networks (WLANs) where stations (STAs) have different capabilities of carrier sensing and basic service sets (BSSs) are densely deployed. First, we show a serious problem of unfairness arising when STAs with different carrier sensing threshold (CSTH) coexist and compete for channel access. To cope with this problem, a dual carrier sensing mechanism has been proposed in the on-going IEEE 802.11ax standardization. This mechanism uses two differentiated CSTHs: a conservative CSTH for fairness among intra-BSS STAs and an aggressive CSTH for spatial reuse by inter-BSS STAs. This dual carrier sensing mechanism may be effective in improving fairness. However, we show that its gain is marginal in terms of spatial reuse because an acknowledgment (ACK) frame is liable to be corrupted due to interference from a data frame transmitted by an inter-BSS STA. In order to avoid ACK corruption, we enhanced the dual carrier sensing mechanism by controlling the transmission time of the data frame. Depending on the receiving signal strength of data frame transmitted by an inter-BSS STA, the proposed mechanism selectively adjusts the concurrent transmission time of the data frame so that ACK frames can be successfully delivered. Results from simulation confirmed the outstanding performance of the proposed mechanism in heterogeneous and dense WLANs; compared with conventional mechanisms, the total throughput was considerably increased by more than two-fold while the fairness among the STAs was improved.