The trigger frame can be implemented in a new frame format, or in a new information element (IE) of MAC to carry the SOFDMA related information. If SOFDMA information is carried in IE, it could be transmitted in a beacon frame, control frame or management frame.

The trigger frame (or attached to control frame, management frame, beacon frame with trigger information) could be used by SOFDMA capable stations to perform timing synchronization to the timing reference of AP.

In order to provide fairness of access to the medium for legacy CSMA/CA stations and SOFDMA stations, the SOFDMA capable AP can adjust the number of CA slots in a given period of time according to the ratio of the number of legacy CSMA/CA stations to the number of SOFDMA stations, or other ratio of access time between legacy and SOFDMA stations based on the operation policy such as access network loading. In this way, it would give fair opportunity and time of occupancy to both legacy stations and SOFDMA stations.

FIG. 4 illustrates an example of AP's SOFDMA channel access procedure 400.

401. The SOFDMA AP determines whether or not the next transmission time is for SOFDMA channel access based on the traffic load of legacy stations and HE stations, or ratio of legacy and HE stations or other fairness policy. The AP broadcasts the target trigger transmission time in the beacon frame to notify the HE stations for the coming MU CA-TXOP so that stations would be prepared for listening to the trigger frame.

402. If the upcoming transmission time is for SOFDMA channel access, the AP resets the CA counter to 0 and transmits the trigger frame to indicate commencing the SOFDMA channel access, and include MU RA parameters in the trigger frame, such as: