Time synchronization method in wireless sensor network

• US 20070177574A1
• Filed: 01/09/2007
• Published: 08/02/2007
• Est. Priority Date: 01/09/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Park, Jong-hun, Park, Woo-jong, Jeong, Min-seop, Kim, Min-Q, Kim, Dae-young, Kim, Hyun-hak
• Granted Patent: US 7,817,616 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 56/0005 synchronizing of arrival of multiple uplinks
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A time synchronization method in a wireless sensor network, has an upper node that provides back-off scheduling to lower nodes in the wireless sensor network of a hierarchical structure. Each of the lower nodes synchronizes time according to the back-off scheduling based on its local clock. The time synchronous method also allows the number of packets required for synchronization in the wireless sensor network to sharply decrease, and the life time of the network to increase. Additionally, the time synchronous method provides a response packet from a lower node in response to a synchronization packet from an upper node, which is used as a synchronization start packet for secondary lower nodes, so that synchronization in the entire network is rapidly processed.

Claims

1. A time synchronization method in a wireless sensor network, the method comprising:

receiving synchronization packet data containing time information broadcasted from an upper node;

starting synchronization by receiving the synchronization packet data;

generating response packet data by calculating back-off time using a local clock; and

broadcasting the response packet data to the upper node.

2. The method of claim 1, wherein the time information comprises time stamp1 information based on transmission time of the broadcasted synchronization packet data, response duration (RD) information on response time, and a response limit seed (RLS) information on a node to perform synchronization.

3. The method of claim 1, wherein the back-off time is calculated as below:

backofftime=(RLS/|T1−

Tint|)*RD,

where Tint is the time when the synchronization packet data are transmitted, T1 is the time when the synchronization packet data are received, and RD is the response duration time.

4. The method of claim 1, wherein in the broadcasting the response packet, the broadcasted response packet data are transmitted to a secondary lower node.

5. The method of claim 1, wherein in the broadcasting the response packet, the response packet data contains information on a time stamp1, a time stamp2, a time stamp3, a response duration (RD) information, a response limit seed (RLS) information and a reference.

6. The method of claim 5, wherein the time stamp1 corresponds to the time when the synchronization packet data are transmitted, the time stamp2 corresponds to the time when the broadcasted synchronization packet data are received, the time stamp3 corresponds to the time when the response packet data are transmitted, the response duration (RD) information corresponds to the response duration time, and the reference is an identification (ID) of a broadcast transmission node.

7. The method of claim 6, wherein the upper node collects the response packet data from each of the lower nodes during the response duration time, calculates each offset, and broadcasts at least one packet data containing the time stamp1, the time stamp2 and the offset to each of the lower nodes.

8. The method of claim 1, wherein in the broadcasting the response packet, if the response packet data cause a collision during transmission to the upper node and result in synchronization failure, a message overhearing is performed.

9. The method of claim 8, wherein the message overhearing confirms if there is an adjacent node whose time stamp1, which indicates time when the synchronization packet data are transmitted, is similar to a time stamp1 of a node that receives the synchronization packet data.

10. The method of claim 9, wherein the synchronization is performed by recognizing response packet data of an adjacent node whose time stamp1 is similar to the possessing time stamp1 as a user'"'"'s own synchronization start packet data.