Fairness-constrained uplink OFDMA optimization under saturated traffic in mixed IEEE 802.11ac/ax WLANs
Anh Tuan Giang, Hoang Ha Nguyen, Nhat Quang Doan, Van Loi Le, Huu Ton Le, Anthony Busson · Computer Networks · 2026
In this paper, we study uplink resource management in mixed IEEE 802.11ac/ax WLANs under saturated traffic and formulate it as a constrained optimization problem. We consider two practical access point (AP) control parameters: the aggressiveness of UL OFDMA opportunity and the AP contention window configuration. A population-aware throughput and fairness model is developed to capture the dependence of uplink performance on the number of HE and legacy stations, and a legacy-protection constraint is enforced using Jain’s fairness index between the two groups. Using extensive ns-3.46 simulations across multiple population mixes and parameter settings, we reveal non-trivial throughput–fairness tradeoffs induced by UL OFDMA operation. The results show the existence of fairness cliffs, where enforcing a mild fairness constraint leads to a disproportionate throughput loss, as well as regimes in which the fairness constraint becomes infeasible under aggressive UL OFDMA opportunity. To complement the simulation study, we validate the proposed model against simulation outcomes and demonstrate that it accurately predicts throughput trends, fairness behavior, and the optimal parameter selection under the imposed constraints. This study intentionally focuses on saturated homogeneous uplink traffic as a stress-test regime in which coexistence effects are most visible; therefore, the reported optimal configurations and infeasibility thresholds should be interpreted as saturated-load design guidelines rather than universal predictions for bursty, heterogeneous, or delay-constrained WLAN traffic. The findings highlight that UL OFDMA gains in mixed WLANs are highly context-dependent and that population-aware, fairness-constrained tuning is essential for robust deployment. The proposed framework provides analytical insight and practical guidance for AP-side configuration under saturated-load IEEE 802.11ax coexistence scenarios.