System and method for performing clock synchronization of nodes connected via a wireless local area network

1. In a communication system including a plurality of non-master nodes being communicatively coupled via a network, each of said plurality of non-master nodes having a local time base, one of said plurality of non-master nodes being designated as a master node having a master time base which serves as a master clock against which said non-master node's local time bases are synchronized, a clock synchronization method for adjusting the local time bases, the method comprising the steps of:

in an ith iteration cycle, at said master node:

(1) transmitting a synchronization frame, F i , including an i−1th iteration cycle master node time value, a(n i−1 ), and an i−1th iteration cycle sequence number, n i−1 ;

(2) detecting, during transmission from said master node, a predefined symbol position associated with said transmitted synchronization frame, F i ;

(3) saving an ith iteration cycle master node time value, a(n i ), corresponding to a time of detection of said predefined symbol position; and

(4) saving an ith iteration cycle sequence number, n i , corresponding to said synchronization frame, F i ;

at each of said non master nodes:

(a) receiving said synchronization frame, F i ;

(b) detecting, during reception of said synchronization frame, F i , said predefined symbol position;

(c) saving an ith iteration cycle non-master node cycle time value, b(n i ), corresponding to a time of detection of said predefined symbol position;

(d) saving said ith iteration cycle sequence number, n i corresponding to said synchronization frame, F i ;

(e) computing a cycle time difference value as, a(n i−1 )−b(n i−1 ),

wherein b(n i−1 ) is an i−1th iteration cycle non-master node time value; and

(f) adjusting said non-master node's local time base in accordance with said computed cycle time difference value.

2. The method of claim 1 , wherein in an i+1th iteration cycle, a(n i ) and b(n i ), stored in said ith iteration cycle, are used to compute said cycle time difference value.

3. The method according to claim 2 , wherein a(n i ) and n i , are transmitted in a next synchronization frame, F i+1 .

4. The method of claim 1 , wherein said network is one of a wired and a wireless network.

5. The method of claim 2 , wherein said wireless network operates in accordance with the IEEE 802.11 wireless standard.

6. The method of claim 1 , wherein said synchronization frame F i and said next synchronization frame, F i+1 are transmitted at near-periodic intervals.

7. The method of claim 1 , further comprising the step of correcting the saved cycle time value, a(n i ), at the master node, by subtracting an offset value prior to said step (3), said corrected cycle time value computed as:

a ( n i ) corrected =cycle_time (at observed PHY-TXEND.confirm) −offset

where:

offset=a delay associated with a time difference between the observation of the said symbol position of said synchronization frame F i and said next synchronization frame, F i+1 at a higher layer of the hierarchy and the time of detection at the physical layer; and;

PHY-TXEND.confirm=a time that the physical layer confirms the detection of said symbol position.

8. The method of claim 1 , further comprising the step of correcting the saved cycle time value, b(n i ), at each of said non-master nodes, by subtracting an offset value prior to step (iv), computed as:

b ( n i ) corrected =cycle_time (at observed PHY-RXEND.indication) −offset

where:

offset=a delay associated with a time difference between the observation of said symbol position of said synchronization frame F i and said next synchronization frame, F i+1 at a higher layer of the non-master node hierarchy and the time of detection at the physical layer; and

PHY-RXEND.indication=a time that the physical layer confirms the detection of said symbol position.

9. The method of claim 1 , wherein the sequence number, n i of the synchronization frame F i and the sequence number n i+1 of the next synchronization frame, F i+1 , corresponds to a 2-octet sequence control field of the synchronization frame.

10. The method of claim 1 , wherein the synchronization frame F i and said next synchronization frame, F i+1 are medium access control (MAC) frames.

11. The method of claim 1 , wherein the synchronization frame F i and said next synchronization frame, F i+1 are identified at each of said non master nodes by a source address and a destination address.

12. The method of claim 11 , wherein the destination address is a reserved multicast medium access control (MAC) address, reserved for transmitting clock synchronization information.

13. In a communication system including a plurality of non-master nodes said plurality of non-master nodes being communicatively coupled via a network, each of said plurality of non-master nodes having a local time base, one of said plurality of non-master nodes designated as a master node having a master time base which serves as a master clock against which said non-master local time bases are synchronized, a clock synchronization method for adjusting the local time bases, the method comprising the steps of:

(a) transmitting an ith synchronization frame F i from said master node over said network to said plurality of non-master nodes;

(b) saving a cycle time value, a(n i ), corresponding to a time of detection of a symbol position of the ith synchronization frame F i and a sequence number n i associated with said ith synchronization frame F i ;

at said plurality of non-master nodes:

(c) receiving said ith synchronization frame F i ;

(d) detecting the symbol position of said ith synchronization frame F i ;

(d) saving a cycle time value, b(n i ), associated with a time of detection of the symbol position and said sequence number n i associated with said ith synchronization frame F i ;

(e) computing a cycle time difference value as:

a(n i−1 )−b(n i−1 ); and

(f) adjusting said local time bases in accordance with said computed cycle time difference value.

14. The communication system of claim 13 , further comprising the step of transmitting an i+1th synchronization frame, F i+1 , from said master node in a next iteration of said clock synchronization method, said next synchronization frame, F i+1 , including said cycle time value, a(n i ), and said sequence number n i saved at the ith iteration cycle at said step (b).

15. In a communication system including a plurality of non-master nodes said plurality of non-master nodes being communicatively coupled via wireless a network, each of said plurality of non-master nodes having a local time base, one of said plurality of non-master nodes designated as a master node having a master time base which serves as a master clock against which said non-master local time bases are synchronized, a clock synchronization method for adjusting the local time bases, the system comprising:

means for transmitting a current synchronization frame, F i ;

means for detecting a symbol position during on air transmission of the current synchronization frame, F i over said wireless network;

means for saving a cycle time value associated with a time of detection of the detected symbol position during said transmission, and a sequence number of said current synchronization frame;

means for receiving said transmitted current synchronization frame;

means for detecting the symbol position during on air reception of the received current synchronization frame over said network;

means for saving a cycle time value associated with a time of detection of the symbol position of the reception of said current synchronization frame and a sequence number n of said current synchronization frame;

means for transmitting a next synchronization frame including the saved symbol position and sequence number corresponding to said current synchronization frame;

means for computing a cycle time value difference; and

means for adjusting said local time base in accordance with said computed time difference.