Traffic-Aware Distributed Resource Unit Selection for Uplink OFDMA Random Access in IEEE 802.11ax WLANs

IEEE 802.11ax adopts Orthogonal Frequency Division Multiple Access (OFDMA), which divides a wireless channel into multiple Resource Units (RUs) with different sizes and transmission rates. Most existing studies on uplink random access assume that all stations contend for RUs of the same size and mainly improve channel access by adjusting contention parameters, such as the OFDMA backoff mechanism. As a result, the transmission requirements of stations are not sufficiently considered, leading to inefficient RU utilization. Stations with heavy traffic may not obtain adequate transmission resources, whereas stations with light traffic may occupy unnecessarily large RUs. To address this limitation, this paper proposes a Traffic-Aware Distributed Selection (TADS) scheme for IEEE 802.11ax uplink random access with different RU sizes. Each station estimates its traffic demand based on the mean data rate, delay bound, and buffer status. It also estimates the expected service capacity of each RU size using the transmission capacity and collision probability. The station selects the smallest RU size whose expected service capacity satisfies its traffic demand. If no RU size can satisfy the demand, the RU size with the highest ratio of expected service capacity to traffic demand is selected. When multiple RUs of the selected size are available, the station randomly selects one of them. In TADS, each station determines its RU independently without additional scheduling by the access point. Simulation results show that TADS achieves higher network throughput than conventional random RU selection under data, real-time, and mixed traffic scenarios. The results also show that the performance gain depends on the available RU configuration, with greater benefits when different RU sizes are available.