Based on the baseline EDCA medium access rules, AP and non-AP STAs have roughly equal probability of gaining medium contention. In IEEE 802.11ax, AP has higher frequency of accessing the medium. In addition to AP accessing the medium for SU and MU downlink traffic, AP also transmits trigger frames to start the uplink MU traffic, which includes aggregation of uplink resource units from multiple non-AP station in frequency domain (e.g., OFDMA) or uplink spatial streams from multiple non-AP stations. In a dense environment, medium access become difficult due to increased medium traffic and larger number of contending nodes, leading to AP starvation issue. This can significantly penalize 802.11ax network, affecting both downlink and uplink traffic.

If 802.11ax APs employ prioritized EDCA parameters to increase their probability of gaining medium contention, it raises the issues of fairness to the co-existing legacy APs/STAs that operate without prioritized EDCA parameters. As a result, it aggregates the AP starvation issue in the legacy networks when co-exist with 802.11ax networks. Another issue is secondary channel underutilization during uplink access, when STA transmits in narrow channel, or when STA detects secondary channel busy (but AP does not detect secondary channel busy).

A solution is sought.