Method for synchronizing U-APSD trigger frames

摘要

A wireless LAN is comprised of a number of wired infrastructure devices, including at least one access point able to support a number of wireless communication devices configured to operate in the U-APSD mode. The wireless communications devices periodically contending for the wireless medium to transmit trigger messages to the access point and the access point responding by transmitting at least one frame of information. The wireless communications devices operate to synchronize the transmission of their trigger messages such that the possibility that the messages collide with one another is minimized.

主权项

1. A method for synchronizing the transmission of trigger messages through a wireless medium from a plurality of wireless communications devices associated with an access point, the method comprising:
transitioning, by a first wireless communications device, to a higher powered state and detecting an ending time of a first unscheduled service period between a second wireless communication device and the access point; storing, by the first wireless communication device, the ending time of the first unscheduled service period in non-transitory memory in communication with the first wireless communication device; when the wireless medium to the access point is idle for a predetermined minimum period of time after storing the detected ending time:
initiating, by the first wireless communication device, a back off timer from a randomly selected value;after waiting a specified interframe time, determining, by the first wireless communication device, whether the back off timer is equal to zero;when the back off timer is not equal to zero, decrementing, by the first wireless communication device, the back off timer until the back off timer is equal to zero;when the back off timer is equal to zero, transmitting a first trigger message from the first wireless communication device to the access point;receiving one or more buffered frames from the access point; andtransitioning, by the first wireless communication device, to a lower powered state after transmitting the first trigger message and receiving any buffered frames in response; at the time of a desired next service period, transitioning, by the first wireless communications device, to the higher powered state and detecting an ending time of a next unscheduled service period between the second wireless communication device and the access point; storing, by the first wireless communication device, the ending time of the next unscheduled service period in the non-transitory memory; comparing, by the first wireless communication device, the ending times of the first and next unscheduled service periods of the second wireless communication device; and when the ending times of the first and next unscheduled service periods are the same with respect to a predetermined interval, transmitting a second trigger message from the first wireless communication device to the access point without sensing if the wireless medium to the access point is free for the predetermined minimum period of time after detecting the ending time of the next unscheduled service period, without re-initiating the back off timer, without waiting the specified interframe time and in less than a specified minimum time from when the ending time of the next unscheduled service period is detected, the specified minimum time corresponding to a time for any other wireless communication device to access the access point through the wireless medium.