Method and apparatus of link adaptation in wireless local area network

A device for a wireless local area network, the device comprising:

• a transceiver configured to receive and transmit radio signals;
• and
• a processor operatively coupled with the transceiver and configured to:
• instruct the transceiver to receive a Multi User-Physical layer Protocol Data Unit (MU-PPDU) from a requesting station, the MU PPDU including a plurality of data frames destined for a plurality of receiving stations including the device,
• wherein one data frame of the plurality of data frames includes a Quality of Service (QoS) Null frame that includes an ACK policy field that identifies an ACK policy for the responding station, and
• wherein the QoS Null frame indicates that the device will firstly send an acknowledgement (ACK) frame among the plurality of receiving stations,
• wherein the QoS Null frame does not include any user data for the device,
• wherein the ACK policy field is set to a value indicating that the ACK policy is an immediate ACK response to request a transmission of the ACK frame after a Short Interframe Space (SIFS), and
• wherein the QoS Null frame further includes a Modulation and Coding Scheme Feedback Request (MRQ) field that indicates whether the device requested to send a Modulation and Coding Scheme Feedback (MFB);
• and
• instruct the transceiver to transmit the ACK frame to the requesting station based on the ACK policy,
• wherein only when the MRQ field indicates that the device is requested to send the MFB does the ACK frame include a MCS estimate that is estimated by the device based on the MU-PPDU.