REDUCED POWER TIME SYNCHRONIZATION IN WIRELESS COMMUNICATION

• US 20070014264A1
• Filed: 07/14/2005
• Published: 01/18/2007
• Est. Priority Date: 07/14/2005
• Status: Active Grant

• Current Assignee: Ademco Inc. (Resideo Technologies, Inc.)
• Original Assignee: Honeywell International Inc.
• Inventors: Davis, Keith
• Granted Patent: US 7,394,782 B2
• Time in Patent Office: Days
• US Class Current: 370/336
• 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: Y02D 30/70 in wireless communication networks

Abstract

Methods, devices, and systems for wireless communication in which one or more devices are scheduled to awake from a low power sleep state at a scheduled time for data transmission. An illustrative embodiment addresses difficulties that may arise as a result of clock errors that can occur when a device enters a sleep mode for a period of time with a scheduled wake-up time. The device that enters sleep mode may be a remote device in a system including a master device that devises a schedule for the remote device to enter and exit sleep and active communication modes. In one embodiment, the active window for a remote device is extended for a period of time related to the period between a reference time and the remote device transmission time. In another embodiment, a master device is adapted to schedule active time periods for remote devices by including an adjustment for time uncertainty caused by clock errors, the adjustment being related to the period between a reference time and the remote device transmission time. The methods may be adaptive to individual remote devices.

Claims

1. A method for wirelessly communicating between a first unit and a second unit, the method comprising:

identifying a desired communication time at a selected time in the future; and

identifying a time uncertainty that is dependent on the selected time in the future; and

identifying a communication window at or near the desired communication time, the communication window taking into account the time uncertainty.

2. The method of claim 1 further comprising:

communicating between the first unit and the second unit sometime during the communication window.

3. The method of claim 2 wherein the first unit operates in a sleep mode for at least a first time period prior to the communication time, the first unit activating to a non-sleep mode during the communication window.

4. The method of claim 1 wherein the time uncertainty is adaptive to the second unit.

5. A building monitoring system comprising:

a master unit having wireless communication functionality; and

a first remote unit having wireless communication functionality;

the master unit scheduled to communicate with the first remote unit during a communication period at or near a desired communication time in the future;

wherein a time uncertainty is generated and associated with the first remote unit, the time uncertainty being related to a duration of time between a reference time and the scheduled communication time.

6. The system of claim 5 wherein the time uncertainty is generated by the first remote unit.

7. The system of claim 5 wherein the time uncertainty is generated by the master unit.

8. The system of claim 7 wherein the time uncertainty is communicated to the first remote unit.

9. The system of claim 5 further comprising a second remote unit having wireless communication functionality, wherein the master unit uses the time uncertainty in spacing scheduled transmissions from the remote units.

10. The system of claim 5 wherein the first remote unit is configured to have at least a low-power state and an active state, the low-power state being a state in which the first remote unit does not transmit or receive wireless signals, and the active state being a state in which the first remote unit may transmit and/or receive wireless signals.

11. The system of claim 10 wherein the first remote unit is configured to switch to the active state at a time associated by the time uncertainty with the communications time.

12. The system of claim 5 wherein the time uncertainty is generated using an adaptive method which takes into account previous timing errors of the first remote unit.

13. A method of operating a building monitoring system having at least a master device and a remote device both adapted for wireless communication, the method comprising:

generating a schedule in which the remote device is configured to execute a low power sleep mode during a first time period and an active mode during a second time period, the remote device capable of communicating wirelessly with the master device while in the active mode, the second time period following the first time period;

defining a time uncertainty that is related to the duration of the first time period; and

identifying a communication window that overlaps with the second time period, the communications window having a duration, wherein the duration of the communication window is dependent upon the time uncertainty.

14. The method of claim 13 wherein the remote devices comprise building monitoring sensors.

15. The method of claim 13 wherein the time uncertainty is calculated by the master device and used by the master device to set the schedule.

16. The method of claim 15 wherein the master device communicates data from the schedule to the remote device to indicate when the remote device is to transmit data.

17. The method of claim 15 wherein the time uncertainty is used to space out remote device communications in the schedule.

18. The method of claim 13 wherein the time uncertainty is calculated by the remote device.

19. The method of claim 13 further comprising observing an environmental condition with the remote device and communicating data related to the environmental condition to the master device during the communication window.

20. A method of operating a building monitoring system comprising first and second peer devices communicating with a base station, the method comprising:

generating a schedule in which the first and second peer devices communicate with the base station at first and second times that are exclusive of one another, the first and second times occurring first and second durations after a reference time;

wherein;

the first peer device is active during a first time period prior to the first time;

the second peer device is active during a second time period prior to the second time; and

;

if the first duration is longer than the second duration, the first time period is longer than the second time period; and

if the first duration is shorter than the second duration, the second time period is longer than the first time period.