MAC controller and clock synchronizing method for use with the same

• US 7,330,459 B2
• Filed: 09/25/2003
• Issued: 02/12/2008
• Est. Priority Date: 10/22/2002
• Status: Active Grant

• Current Assignee: VIA Technologies Incorporated (VIA Technologies)
• Original Assignee: VIA Technologies
• Inventors: Kang, Celine, Chen, Lyndon
• Primary Examiner(s): Ngo; Ricky Q.
• Assistant Examiner(s): SINKANTARAKORN, PAWARIS
• Application Number:
  US10/671,277
• Publication Number:
  US 20040076186A1
• Time in Patent Office: 1,601 Days
• Field of Search: 370/350, 370/503, 375/354, 375/358, 375/359
• US Class Current: 370/350
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 56/0075 based on arrival time vs. expected arrival time
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

In a wireless local area network media access controller (MAC) disposed in a first node of a wireless local area network, a method is performed to synchronize the clock of the first node with the clock of a second node in the wireless local area network. When a request signal is asserted from the first node to the second node, a responsive signal packet containing a time stamp is asserted from the second node to the first node in response to the request signal. Then, the MAC tags a local time value to the responsive signal packet at the first node, and operates the time stamp and the local time value according to a control program to obtain a difference T, which is stored in a register of the MAC. Afterwards, at least one of the clocks of the first and the second nodes is adjusted to synchronize the clocks of the first and the second nodes according to the difference T.

Claims

1. A method for synchronizing clocks of a station and an access point in a wireless local area network, comprising steps of:

asserting a request signal from a station to an access point;

asserting a responsive signal packet containing a time stamp in response to said request signal from said access point to said station;

tagging a local time value to said responsive signal packet at said station;

operating said time stamp and said local time value at said station according to a control program to obtain a difference T; and

determining switching timing between a working and a sleeping modes of said station after said clocks of said station and said access point are synchronized, which comprises sub-steps of;

obtaining next target beacon transmission time by operating a beacon interval and said adjusted local time value; and

determining said switching timing between said working and said sleeping modes of said station according to said local time value, said difference T and said next target beacon transmission time.

2. The method according to claim 1 wherein said request signal is a probe-request signal asserted by said station.

3. The method according to claim 1 wherein said responsive signal packet is a probe-response signal packet asserted by said access point.

4. The method according to claim 1 wherein said time stamp is a counting value C1 of a remote counter in said access point, which is generated when said responsive signal packet is asserted by said access point.

5. The method according to claim 4 wherein said local time value is a counting value C2 of a local counter in said station, which is generated when said responsive signal packet is received by said station.

6. The method according to claim 5 wherein said difference T is equal to C1-C2, and stored in a difference register in said station.

7. The method according to claim 6 wherein said clock of said station is synchronized with said clock of said access point by adding said difference T to a new counting value of said local counter.

8. A wireless local area network media access controller, disposed in a first node of a wireless local area network. comprising:

a local time tagger tagging a local time value to a responsive signal packet received from a second node of said wireless local area network in response to a request signal asserted by said first node to said second node; and

a difference register storing therein a difference T between said local time value and a time stamp, said difference T being referred to adjust at least one of clocks of said first and said second nodes to synchronize said clocks of said first and said second nodes;

a register for storing a next target beacon transmission time, a next target beacon transmission time being obtained by operating a beacon interval and said local time value adjusted with said difference T, and referred to determine switching timing between a working and a sleeping modes of said first node along with said local time value and said difference T.

9. The wireless local area network media access controller according to claim 8 wherein said first and said second nodes are a first and a second station, respectively.

10. The wireless local area network media access controller according to claim 8 wherein said first and second nodes are a station and an access point, respectively.

11. The wireless local area network media access controller according to claim 10 wherein said clock of said station is adjusted to synchronize with said clock of said access point according to said difference T.

12. The wireless local area network media access controller according to claim 11 wherein said request signal is a probe-request signal asserted by said station, and wherein said responsive signal packet is a probe-response signal packet asserted by said access point.

13. The wireless local area network media access controller according to claim 12 wherein said time stamp is a counting value C1 of a remote counter in said access point, which is generated when said responsive signal packet is asserted by said access point.

14. The wireless local area network media access controller according to claim 13 wherein said local time value is a counting value C2 of a local counter in said station, which is generated when said responsive signal packet is received by said station.

15. The wireless local area network media access controller according to claim 14 wherein said clock of said station is adjusted by adding said difference T to a new counting value of said local counter.