System clock synchronization in an ad hoc and infrastructure wireless networks

• US 7,239,626 B2
• Filed: 06/30/2004
• Issued: 07/03/2007
• Est. Priority Date: 06/30/2004
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Kandala, Srinivas, Bennett, Richard Thomas, Kowalski, John Michael
• Primary Examiner(s): Gary; Erika A.
• Application Number:
  US10/882,918
• Publication Number:
  US 20050169233A1
• Time in Patent Office: 1,098 Days
• Field of Search: None
• US Class Current: 370/349
• CPC Class Codes: H04B 1/7183 Synchronisation
• CPC Class Codes: H04J 3/0664 unidirectional timestamps
• CPC Class Codes: H04J 3/067 Details of the timestamp structure
• CPC Class Codes: H04J 3/0676 Mutual
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04W 56/001 Synchronization between nodes
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A method of synchronizing clocks in the stations of ad hoc and infrastructure networks includes providing a time stamp field in a header; reading the header by all stations in a network; extracting the time stamp information from the header by each station in the network as time information; sending extracted time information to a station clock; and adjusting the station clock as a function of the extracted time information. A system for synchronizing clocks in the stations of ad hoc and infrastructure networks includes a DLL having a comparator for receiving the time stamp information and a low-pass filter having a long time-constant for adjusting the station clock in a gradual manner; a time stamp field in a header; and time information extracted from the time stamp information of the header by each station in the network.

Claims

1. A method of synchronizing clocks in the stations of ad hoc and infrastructure networks comprising:

providing a time stamp field in a header;

reading the header by all stations in a network;

extracting time stamp information from the header by each station in the network as time information;

sending extracted time information to a station clock;

adjusting the station clock as a function of the extracted time information; and

providing a Delay Locked Loop (DLL) having a comparator for receiving the time stamp information and a low-pass filter having a long time-constant for adjusting the station clock in a gradual manner.

2. The method of claim 1 wherein the time stamp field is located in a MAC header.

3. The method of claim 1 wherein the time stamp field is located in a PHY header.

4. The method of claim 1 wherein the time stamp field is an eight-octet field containing the time of day and an accuracy parameter.

5. The method of claim 1 which includes providing a switch after the low-pass filter to control transmission of the time information to the station clock.

6. The method of claim 1 which includes providing a gain element for adjusting a weight value applied to the time information.

7. The method of claim 1 which includes providing an interpolator for providing periodic input to the comparator.

8. A system for synchronizing clocks in the stations of ad hoc and infrastructure networks comprising:

a Delay Locked Loop (DLL) having a comparator for receiving time stamp information and a low-pass filter having a long time-constant for adjusting the station clocks in a gradual manner;

a time stamp field in a header; and

time information extracted from the time stamp information of the header by each station in a network.

9. The system of claim 8 which includes a switch after the low-pass filter to control the transmission of the time information to the station clocks.

10. The system of claim 8 which includes a gain element for adjusting a weight value applied to the time information.

11. The system of claim 8 which includes an interpolator for providing periodic input to the comparator.

12. The system of claim 8 wherein the time stamp field is located in a MAC header.

13. The system of claim 8 wherein the time stamp field is located in a PHY header.

14. The system of claim 8 wherein the time stamp field is an eight-octet field containing the time of day and an accuracy parameter.