Probability Complementary Transmission Scheme for Uplink OFDMA-based Random Access in 802.11ax WLAN

The next generation of wireless local area network (WLAN) adopts IEEE 802.11ax standard to be published in 2019, which provides the orthogonal frequency division multiple access (OFDMA) mechanism. The Uplink OFDMA-based Random Access (UORA) in the 802.11ax standard enables multiple users to randomly pick resource units (RUs) to transmit uplink data simultaneously. Under the UORA, access point (AP) dynamically announces some eligible random access RUs in the trigger frame so that the associated mobile stations (STAs) can contend for these RUs. Only when the picked OFDMA-based random access backoff (OBO) counter is no more than the number of eligible random access RUs, can a STA randomly select a RU to transmit. An unsuccessful transmission forces the STA to double its OFDMA contention window (OCW) size, which causes the STA to endure a longer delay for retransmission(s). In this paper, we propose the probability complementary transmission scheme (PCTS) to mitigate the delay for retransmissions. We define the complementary probability for the PCTS, with which the STA performs complementary transmission without backoff. In addition, we formulate the optimization problem that maximizes the throughput. The solution of the optimization problem is applied in the design of the PCTS so that the maximal throughput is gained. Simulation results show that the PCTS outperforms the existing schemes in terms of throughput and packet delay.