WIRELESS SENSOR NODE AND METHOD

• US 20130038358A1
• Filed: 08/10/2011
• Published: 02/14/2013
• Est. Priority Date: 08/10/2011
• Status: Abandoned Application

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Cook, David M., Van Brocklin, Andrew L.
• Application Number:
  US13/206,754
• Publication Number:
  US 20130038358A1
• Time in Patent Office: Days
• US Class Current: 327/141
• CPC Class Codes: G01V 1/26 Reference-signal-transmitting devices, e.g. indicating moment of firing of shot
• CPC Class Codes: G01V 2200/12 Clock synchronization-related issues
• CPC Class Codes: G04R 20/06 Decoding time data; Circuits therefor
• CPC Class Codes: G04R 20/30 Decoding time data; Circuits therefor

Abstract

Determining time latency at a sensor node in a mesh network. A beacon time is received at the sensor node from an upstream node, the beacon time offset from global time by the latency. The latency, the global time, and a corresponding local time are determined at the sensor node.

Claims

1. A method of time-synchronizing a wireless sensor node of a mesh network, comprising:

wirelessly receiving at the node, intermittently from an upstream node in the network, a plurality of beacon times each offset from a global time by a latency;

using a power-consuming resource of the node, determining the global time associated with a selected one of the beacon times;

computing the latency using the selected beacon time and the global time;

using the latency and without using the power-consuming resource, computing the global time corresponding to at least some of the beacon times; and

for each beacon time, recording the global time and a local time corresponding to that beacon time.

2. The method of claim 1, wherein the latency includes an aggregate latency of a wireless transmitter in the upstream node and a wireless receiver in the sensor node.

3. The method of claim 1, wherein the power-consuming resource is a GPS receiver.

4. The method of claim 1, wherein the sensor node does not transmit any time value to the upstream node.

5. The method of claim 1, comprising:

transmitting the global time from the sensor node to a downstream node in the mesh.

6. The method of claim 1, wherein the determining the global time is repeated after multiple beacon times have been wirelessly received.

7. The method of claim 1, wherein the determining the global time is repeated after the upstream node in the mesh is replaced by a different upstream node.

8. The method of claim 1, comprising:

measuring seismic data using a sensor in the node; and

recording the seismic data together with the local clock value corresponding to the seismic data measurement.

9. The method of claim 1, wherein the computing the latency comprises:

calculating a difference between the selected beacon time and the global time.

10. The method of claim 9, wherein the computing the latency comprises:

calculating a delta time between a first time corresponding to receiving the selected beacon time and a second time corresponding to determining the associated global time; and

offsetting the latency by the delta time.

11. A wireless sensor node, comprising:

a wireless transceiver configured to intermittently receive beacon times from another node in a mesh network, each beacon time offset from a corresponding global time by a latency;

a wireless receiver configured to receive the global time without the latency;

a clock configured to provide a local ti and

a controller configured to

operate the wireless receiver to obtain the global time associated with a first beacon time,

compute the latency using the first beacon time and the corresponding global time,

using the latency, computing the global time corresponding to each of a set of subsequent beacon times without operating the wireless receiver, and

record, for each beacon time, a timestamp of the global time and the corresponding local time.

12. The sensor node of claim 11, comprising:

a sensor configured to measure seismic energy incident to the sensor, the controller configured to record the measured seismic energy together with local time corresponding to the seismic energy measurement.

13. The sensor node of claim 12, wherein the controller records the measured seismic energy asynchronously from the recording of the timestamp.

14. The sensor node of claim 11, wherein the sensor node does not transmit any time value to the another node.

15. The sensor node of claim 11, wherein the clock of the sensor node is not synchronized to a clock of the another node.

16. The node of claim 11, wherein the controller is further configured to compute the latency by:

calculating a delta time between the receipt of the first beacon time and the obtaining of the global time associated with the first beacon time; and

calculating the latency according to the formula;

latency=global time−

beacon time+delta time.

17. The node of claim 11, wherein the recorded seismic energy measurements and the recorded timestamps are processed external to the sensor node in order to correlate the energy measurements to global time.

18. A method of time-synchronizing data from wireless sensor nodes in a mesh network, comprising:

providing an upstream node with an upstream local time not synchronized to a downstream local time of a downstream node;

correlating, at the upstream node, the upstream local time to a global time;

wirelessly transmitting a beacon time equal to the global time from the upstream node to the downstream node;

wirelessly receiving the beacon time at the downstream node, the received beacon time value from the global time by a latency of the transmitting and the receiving;

determining the latency at the downstream node; and

at the downstream node, using the global time and the latency to correlate the downstream local time to the global time.

19. The method of claim 18, wherein the upstream and downstream local times are not synchronized.

20. The method of claim 18, wherein the downstream node does not transmit any time to the upstream node.