US 7,120,092 B2Granted

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

AssigneeKoninklijke Philips Electronics N. V.

InventorsJavier del Prado Pavon, Sai Shankar Nandagopalan, Sunghyun Choi, Takashi Sato, Jeff Bennet

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Abstract

A clock synchronization method and apparatus is disclosed for use in a communication system including a plurality of wireless nodes communicatively coupled via a wireless network, each of the plurality of wireless nodes having a local time base, and one of the plurality of wireless nodes being designated as a master node having a master time base which serves as a master clock against which the local time bases are synchronized. The clock synchronization method includes the steps of periodically transmitting synchronization frames to the plurality of non-master nodes so as to adjust the slave clocks associated with the respective non-master nodes. The synchronization frames are distributed from the master node at near-periodic intervals and includes a cycle time value that corresponds to the end of the previously transmitted synchronization frame. The slave clocks (i.e., non-master nodes) receiving the synchronization frame determine the cycle time value at the point of reception of the synchronization frame and adjusts their clocks by calculating a difference value between the received cycle time and a previously saved local cycle time value.

Claims15

Dependent claims

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, Fi, including an i−1th iteration cycle master node time value, a(ni−1), and an i−1th iteration cycle sequence number, ni−1;
(2) detecting, during transmission from said master node, a predefined symbol position associated with said transmitted synchronization frame, Fi;
(3) saving an ith iteration cycle master node time value, a(ni), corresponding to a time of detection of said predefined symbol position;
and
(4) saving an ith iteration cycle sequence number, ni, corresponding to said synchronization frame, Fi;
at each of said non master nodes:
(a) receiving said synchronization frame, Fi;
(b) detecting, during reception of said synchronization frame, Fi, said predefined symbol position;
(c) saving an ith iteration cycle non-master node cycle time value, b(ni), corresponding to a time of detection of said predefined symbol position;
(d) saving said ith iteration cycle sequence number, ni corresponding to said synchronization frame, Fi;
(e) computing a cycle time difference value as, a(ni−1)−b(ni−1),
wherein b(ni−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.

12 more elements

Dependencies are inferred from the claim text.