IEEE 802.11 standards (g, a, n, ac) delivered WiFi performance improvements out of the box. They focused on progressively increasing the data rate over the wireless link. All that was needed to take advantage of any new standard, was a radio chipset that incorporated the new radio and MAC enhancements.

The situation is different for the upcoming 802.11ax standard. The focus of 802.11ax is not on increasing the data rate but on improving the overall wireless network performance. This introduces significant new radio and MAC enhancements such as OFDMA and BSS colouring.

Ranking high among the issues is a transmission-scheduling mechanism. The downlink transmission scheduling in WiFi has been a simple FIFO (First In First Out) system. 802.11e introduced a small variation regarding the maintenance of multiple transmission queues for different priority classes.

However, 802.11ax introduces significant complexity in wireless transmission scheduling due to its OFDMA and MU-MIMO enhancements.

•  With MU-MIMO, there is now an option to transmit a single wireless frame to a single client or concurrently transmit different wireless frames to multiple clients using multi-user beamforming.
• With OFDMA, there is now an option to transmit a single wireless frame to single client using traditional OFDM or concurrently transmit different wireless frames to multiple clients using subsets of channel width.
• 802.11ax introduces multi-user transmission in uplink direction too. The AP needs to schedule multiple clients for concurrent uplink transmissions according to their requirements.

These methods need to take into account service requirements of traffic flows, radio conditions on the channel, client capabilities and client state feedbacks. It is no easy feat to come up with scheduling mechanisms that will work in most practical scenarios with relative ease of configuration and fine tuning.