Method for synchronizing U-APSD trigger frames

• US 20080225756A1
• Filed: 03/13/2007
• Published: 09/18/2008
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: Spectralink Corporation (Mobile Devices Holdings LLC)
• Original Assignee: Spectralink Corporation (Mobile Devices Holdings LLC)
• Inventors: Hamilton, Mark A., Krahn, Oliver J., Amann, Keith R.
• Granted Patent: US 9,020,547 B2
• Time in Patent Office: Days
• US Class Current: 370/260
• CPC Class Codes: H04W 52/0216 using a pre-established activity schedule, e.g. traffic indication frame
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 74/0891 for synchronized access
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

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.

Claims

1. In a wireless LAN, a plurality of wireless communication devices are associated with an access point that buffers at least one frame of information for delivery to one or more of the wireless communication devices, a method for synchronizing the transmission of trigger messages between first and second ones of the plural wireless communications devices comprising the steps of:

the first wireless communications device transitioning to a higher powered state and detecting the ending time of a first unscheduled service period associated with the second wireless communication device and storing the detected time;

the first wireless communication device determining that the wireless medium is free for a predetermined minimum period of time after the detected and stored ending time, waiting a specified interframe time, transmitting a trigger message and then transitioning to a lower powered state;

the first wireless communication device transitioning to a higher powered state and detecting and storing an ending time of a next unscheduled service period associated with the second wireless communications device and determining that it is the same as the stored ending time for the first unscheduled service period associated with the second wireless communications device, and;

the first wireless communication device successfully transmitting a trigger message to the access point, subsequent to the detected ending time of the next unscheduled service period associated with the second wireless communications device, after waiting less than the time interval specified for any other wireless communications device associated with the access point to begin arbitrating for the wireless medium.

2. The at least one buffered frame of information in claim 1 is one of a null frame and a data frame.

3. The wireless communications device of claim 1 is a mobile phone.

4. The specified interframe time in claim 1 is determined by a EDCA backoff procedure.

5. The time interval of claim 1 that is less than the time interval specified for any other wireless communications device associated with the access point to begin arbitrating for the wireless medium is a SIFS time.

6. The predetermined minimum period of time in claim 1 is a period of time selected to determine that the medium is free long enough for another wireless device to successfully contend for the medium without having to change its backoff timer setting.

7. The ending time of the first unscheduled service period of claim 1 is detected by sensing the wireless medium for both the transmission of a frame of information from the access point to the second wireless communications device followed by the second wireless communications device transmitting an ACK to the access point.

11. The wireless communications device of claim 6 is a mobile phone.

12. The predetermined minimum period of time in claim 6 is a period of time selected to determine that the medium is free long enough for another wireless device to successfully contend for the medium without having to change its backoff timer setting.

13. The ending time of the first unscheduled service period of claim 6 is detected by sensing the wireless medium for both the transmission of a frame of information from the access point to the second wireless communications device followed by the second wireless communications device transmitting an ACK to the access point.

8. In a wireless LAN, a plurality of wireless communication devices are associated with an access point that buffers at least one frame of information for delivery to one or more of the wireless communication devices, a method for minimizing the time between unscheduled service periods among first and second ones of the plural wireless communication devices comprising the steps of:

the first wireless communication device transitioning to a higher powered state at a first transition time and storing this first transition time, contending for the wireless medium to transmit a trigger message, gaining access to the wireless medium, transmitting the trigger message, receiving an ACK and buffered frames from the access point and transitioning to a lower powered state;

the first wireless communications device decrementing the stored first transition time by a pre-selected period of time and storing this time as the next transition time;

the first wireless communications device transitioning to a higher powered state at the stored next higher powered state transition time, detecting the ending time of an unscheduled service period associated with the second wireless communications device; and

the first wireless communication device successfully transmitting a trigger message after waiting less than the time interval specified for any other wireless communications device associated with the access point to begin arbitrating for the wireless medium.

9. The at least one buffered frame of information in claim 8 is one of a null frame and a data frame.

10. The method of claim 8 wherein the step of decrementing the stored first transition time by a pre-selected period of time consists of decrementing the time by one quarter of the duration of an unscheduled service period.

14. In a wireless LAN, a plurality of wireless communication devices are associated with an access point that buffers at least one frame of information for delivery to one or more of the wireless communication devices, a method for synchronizing between first and second ones of the plural wireless communications devices the transmission of trigger messages to the access point comprising:

the first wireless communications device transitioning to a higher powered state and starting to contend for the wireless medium;

the first wireless communication device gaining access to the wireless medium, successfully transmitting a trigger message and storing the trigger message transmission time and transitioning to a lower powered state;

the first wireless communication device transitioning to a higher powered state, transmitting a trigger message at the stored trigger message transmission time, and receiving an ACK and at least one frame of buffered information from the access point; and

the first wireless communication device transitioning to a lowered powered state.

15. The at least one buffered frame of information in claim 14 is one of a null frame and a data frame.

16. The wireless communications device of claim 14 is a mobile phone.

17. The trigger message of claim 14 is a trigger frame.