TIMING RE-SYNCHRONIZATION WITH REDUCED COMMUNICATION ENERGY IN FREQUENCY HOPPING COMMUNICATION NETWORKS

• US 20140064172A1
• Filed: 11/20/2013
• Published: 03/06/2014
• Est. Priority Date: 07/12/2011
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Hui, Jonathan W., Woo, Lik Chuen Alec, Hong, Wei
• Granted Patent: US 8,964,762 B2
• Time in Patent Office: Days
• US Class Current: 370/311
• CPC Class Codes: H04B 1/7156 Arrangements for sequence synchronisation
• CPC Class Codes: H04W 52/0209 in terminal devices terminal devices per se H04W88/02
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

In one embodiment, a battery-operated communication device “quick-samples” a frequency hopping sequence at a periodic rate corresponding to a substantially low duty cycle, and is discovered by (e.g., attached to) a main-powered communication device. During a scheduled sample, the main-powered communication device transmits a control packet to be received by the battery-operated communication device, the control packet containing timing information and transmitted to account for worst-case clock drift error between the two devices. The battery-operated communication device responds to the control packet with a link-layer acknowledgment containing timing information from the battery-operated communication device. Accordingly, the two devices may re-synchronize their timing based on the timing information in the control packet and acknowledgment, respectively.

Claims

1. A method, comprising:

sampling a frequency hopping sequence in a communication network by a battery-operated communication device at a periodic rate corresponding to a substantially low duty cycle;

receiving, during at least one sample of the sampling, a control packet at the battery-operated communication device transmitted from a main-powered communication device, the control packet containing timing information to account for timing errors between the battery operated device and the main-powered device;

responding to the control packet with an acknowledgment to the main-powered communication device, the acknowledgment containing timing information from the battery-operated communication device; and

re-synchronizing timing between the battery-operated communication device and the main-powered communication device at the battery-operated communication device based on the timing information in the control packet.

2. The method as in claim 1, further comprising:

discovering, by the battery-operated communication device, one or more main-powered communication devices; and

establishing an attachment between the battery-operated communication device and one or more particular main-powered communication devices, wherein the battery-operated communication device re-synchronizes timing with the one or more particular main-powered communication devices.

3. The method as in claim 1, wherein the main-powered communication device is a parent node for the battery-operated communication device in a directed acyclic graph (DAG).

4. The method as in claim 1, wherein the acknowledgment contains an indication of enqueued data, the method further comprising:

transmitting the enqueued data from the battery-operated communication device to the main-powered communication device following the acknowledgment.

5. The method as in claim 1, further comprising:

determining that the battery-operated communication device has critical data for transmission; and

in response, transmitting the critical data without waiting for a subsequent control packet from the main-powered communication device, the transmitting accounting for worst-case clock drift error between the battery-operated communication device and the main-powered communication device.

6. The method as in claim 1, wherein the duty cycle is less than 0.1%.

7. The method as in claim 6, wherein the duty cycle is less than 0.01%.

8. A method, comprising:

discovering, by a main-powered communication device, a low duty cycle, periodic, sample schedule of a battery-operated communication device within a frequency hopping sequence in a communication network;

transmitting, during a scheduled sample, a control packet from the main-powered communication device to the battery-operated communication device, the control packet containing timing information to account for timing errors between the battery operated device and the main-powered device;

receiving, in response to the control packet, an acknowledgment at the main-powered communication device, the acknowledgment containing timing information from the battery-operated communication device; and

re-synchronizing timing between the battery-operated communication device and the main-powered communication device at the main-powered communication device based on the timing information in the acknowledgment.

9. The method as in claim 8, wherein the battery-operated communication device is a child node of the main-powered communication device in a directed acyclic graph (DAG).

10. The method as in claim 8, further comprising:

sampling all of the frequency hopping sequence by the main-powered communication device.

11. The method as in claim 10, further comprising:

receiving critical data from the battery-operated communication device at the main-powered communication device during the frequency hopping sequence and not in response to the control packet.

12. The method as in claim 8, further comprising:

receiving enqueued data from the battery-operated communication device at the main-powered communication device following the acknowledgment in response to the control packet.

13. The method as in claim 8, wherein the control packet is transmitted at a periodic rate to ensure that the worst-case clock drift is not more than can be accounted for in an allowed transmission time based on a corresponding communication protocol.

14. The method as in claim 13, wherein a preamble and data portion of control packet is transmitted in less than 0.4 seconds.

15. The method as in claim 13, further comprising:

determining a clock drift estimation; and

extending the periodic rate for transmitting the control packet based on the clock drift estimation.

16. The method as in claim 15, further comprising:

determining a temperature compensation for the clock drift estimation; and

extending the periodic rate for transmitting the control packet based on the clock drift estimation with the temperature compensation.

17. An apparatus, comprising:

a processor;

a battery power supply;

a transceiver configured to communicate in a communication network according to a frequency hopping sequence; and

a memory configured to store a process executable by the processor, the process when executed by the processor operable to;

sample the frequency hopping sequence at a periodic rate corresponding to a substantially low duty cycle;

receive, during at least one sample, a control packet transmitted from a main-powered communication device, the control packet containing timing information to account for timing errors between the battery operated device and the main-powered device;

respond to the control packet with an acknowledgment to the main-powered communication device, the acknowledgment containing timing information from the apparatus; and

re-synchronize timing between the apparatus and the main-powered communication device based on the timing information in the control packet.

18. The apparatus as in claim 17, wherein the process when executed is further operable to:

discover one or more main-powered communication devices; and

establish an attachment between the apparatus and one or more particular main-powered communication devices, wherein the process re-synchronizes timing with the one or more particular main-powered communication devices.

19. The apparatus as in claim 17, wherein the acknowledgment contains an indication of enqueued data, and wherein the process when executed is further operable to:

transmit the enqueued data to the main-powered communication device following the acknowledgment.

20. The apparatus as in claim 17, wherein the process when executed is further operable to:

determine that the apparatus has critical data for transmission; and

in response, transmit the critical data without waiting for a subsequent control packet from the main-powered communication device, the transmitting accounting for worst-case clock drift error between the apparatus and the main-powered communication device.

21. An apparatus, comprising:

a processor;

a main-power power supply;

a transceiver configured to communicate in a communication network according to a frequency hopping sequence; and

a memory configured to store a process executable by the processor, the process when executed by the processor operable to;

discover a low duty cycle, periodic, sample schedule of a battery-operated communication device;

transmit, during a scheduled sample, a control packet to the battery-operated communication device, the control packet containing timing information to account for timing errors between the battery operated device and the main-powered device;

receive, in response to the control packet, an acknowledgment containing timing information from the battery-operated communication device; and

re-synchronize timing between the battery-operated communication device and the apparatus based on the timing information in the acknowledgment.

22. The apparatus as in claim 21, wherein the process when executed is further operable to:

sample all of the frequency hopping sequence; and

receive critical data from the battery-operated communication device during the frequency hopping sequence and not in response to the control packet.

23. The apparatus as in claim 21, wherein the process when executed is further operable to:

receive enqueued data from the battery-operated communication device following the acknowledgment in response to the control packet.

24. The apparatus as in claim 21, wherein the control packet is transmitted at a periodic rate to ensure that the worst-case clock drift is not more than can be accounted for in an allowed transmission time based on a corresponding communication protocol.

25. The apparatus as in claim 24, wherein the process when executed is further operable to:

determine a clock drift estimation and a temperature compensation for the clock drift estimation; and

extend the periodic rate for transmitting the control packet based on the clock drift estimation with the temperature compensation.