Gaining an mu-TXOP for transmitting packet using OFDMA

A method of performing OFDMA transmission with aggregation from multiple access categories to improve channel utilization of a wireless channel is proposed. In one novel aspect, data from multiple access categories are allowed to be aggregated and transmitted in the same packet to utilize idle time efficiently. In downlink OFDMA, AP can send different AC data to different STAs so that AP can better arrange the transmission resource block. If the resource for one STA has long enough idle time, AP can aggregate more data that is different to the current AC for the same STA to better utilize the resource. In UL OFDMA, different STAs can send different AC data to AP. If the resource for one STA has long enough idle time, the STA can aggregate more data that is different to the current AC to better utilize the resource.