SYSTEM AND METHOD FOR SYNCHRONIZING WIRELESS DEVICES WITHOUT SENDING TIMESTAMP DATA

• US 20130336205A1
• Filed: 06/13/2012
• Published: 12/19/2013
• Est. Priority Date: 06/13/2012
• Status: Active Grant

• Current Assignee: Simmonds Precision Products, Inc. (Rtx Corporation)
• Original Assignee: Goodrich Corporation (Rtx Corporation)
• Inventors: Zakrzewski, Radoslaw R., Lynch, Michael A., Hicks, Brandon, Rittenhouse, Garret Edward
• Granted Patent: US 9,154,249 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04Q 9/04 Arrangements for synchronous operation
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A sensor network includes a plurality of sensors and a base station for sending a series of data acquisition requests to the sensors. Each data acquisition request has an index. Each sensor has a synchronization calculation module and an internal clock. The sensors are adapted and configured to receive the series of data acquisition requests and record a timestamp of receipt for each data acquisition request. The sensors also store a predefined time interval related to the plurality of data acquisition requests so that the sensor can calculate a time to start collecting data based upon the series of data acquisition requests, the timestamps, the indices, and the predefined time interval. In an alternative embodiment, the base station only sends a general request for data acquisition and a synchronization sensor module receives the general request and, in turn, sends the series of data acquisition requests to the sensors.

Claims

1. A method for synchronizing a plurality of wireless devices without exchanging timestamp information, wherein each wireless device has a clock, the method comprising the steps of:

receiving, at the plurality of wireless devices, a series of data acquisition requests having a predefined time interval between the data acquisition requests, wherein each data acquisition request includes an index;

recording timestamps for each received request according to the clock of each wireless device;

determining a clock value to start data acquisition for each timestamp at each wireless device based on the timestamps, the respective index, and the predefined time interval; and

selecting a minimum clock value for each wireless device from the respective clock values as an instant to start data acquisition for the respective wireless device.

2. A method as recited in claim 1, wherein a series of clock values t_j^(k) is processed to determine the clock values t_aj^(k) using a formula t_aj^(k)=t_j^(k)+(M−

j)Δ

+δ

, where t_j^(k) denotes the timestamps, “

k”

denotes a particular wireless device, “

j”

denotes a number of messages sent in the series, “

δ

”

denotes a time delay, “

Δ

”

denotes the predefined time interval, and “

M”

denotes a number of messages in the series.

3. A method as recited in claim 1, wherein a series of clock values t_j^(k) is processed to determine the clock values t_aj^(k) using a formula t_aj^(k)=t_j^(k)+iΔ

+δ

, where t_j^(k) denotes the timestamps, “

k”

denotes a particular wireless device, “

i”

denotes a number of messages left in the series as the index, “

δ

”

denotes a time delay, and “

Δ

”

denotes the predefined time interval.

4. A method as recited in claim 1, further comprising the step of using a base station to send at least one data acquisition request.

5. A method as recited in claim 4, further comprising the step of using a synchronization node to receive the at least one data acquisition request and, in turn, send the series of data acquisition requests.

6. A method as recited in claim 1, wherein the wireless devices are sensors and the sensors begin collecting data at the minimum clock value calculated even if the complete series has not been received.

7. A method for synchronizing a plurality of sensors without timestamp information, wherein each sensor has a clock, the method comprising the steps of:

receiving, at the plurality of sensors, a series of data acquisition requests having a predefined time interval Δ

between the data acquisition requests, wherein each data acquisition request includes an index “

j”

;

recording timestamps t_j^(k) for each received request according to the clock of each sensor, wherein “

k”

denotes the number of sensors; and

calculating a clock value t_a^(k) for starting data acquisition at each sensor for each timestamp t_j^(k) based upon the predefined time interval Δ

, the index “

j” and

the timestamps (k).

8. A method as recited in claim 7, further comprising the step of determining a time to start the data acquisition by selecting a smallest calculated clock value t_a^(k) for each sensor as the time to start the data acquisition for each sensor.

9. A method as recited in claim 7, wherein a smallest of the clock values t_a^(k) is used to reset the sensors clocks to a predefined value.

10. A method as recited in claim 7, further comprising the step of calculating a mean value of the clock values t_a^(k) and using the mean value to determine a time to start the data acquisition for the respective sensor.

11. A method as recited in claim 7, further comprising the step of calculating a median value of the estimated clock values t_a^(k) and using the median value to determine a time to start the data acquisition for the respective sensor.

12. A method as recited in claim 7, further comprising the step of using a base station to send at least one data acquisition request.

13. A method as recited in claim 12, wherein the base station sends the series of data acquisition requests.

14. A method as recited in claim 12, further comprising the step of using a synchronization node to receive the at least one data acquisition request and, in turn, send the series of data acquisition requests.

15. A sensor network comprising:

a plurality of sensors, each sensor having an internal clock, wherein the sensors are adapted and configured to;

receive a series of data acquisition requests, wherein each data acquisition request has an index;

record a timestamp of receipt for each data acquisition request;

store a predefined time interval related to the plurality of data acquisition requests; and

calculate a time to start collecting data based upon the series of data acquisition requests, the timestamps, the indices, and the predefined time interval.

16. A sensor network as recited in claim 15, wherein the time is equal to the index times the predefined time interval plus the respective timestamp and an offset.

17. A sensor network as recited in claim 16, wherein the offset is approximately equal to the predefined time interval.

18. A sensor network as recited in claim 15, further comprising a base station for sending the series.

19. A sensor network as recited in claim 18, wherein once the sensors acquire data, transmission to the base station is controlled relative to the time to avoid energy waste from sensor radio components waiting to transmit acquired data.

20. A sensor network as recited in claim 15, further comprising a base station for sending a general request for data acquisition and a synchronization sensor module for receiving the general request and, in turn, sending the series.