TIME SYNCHRONIZATION METHOD, COMMUNICATION APPARATUS, AND NODE USED FOR THE METHOD

• US 20090122783A1
• Filed: 11/01/2006
• Published: 05/14/2009
• Est. Priority Date: 11/04/2005
• Status: Abandoned Application

• Current Assignee: National Universit Corporation The University of Electro-Communications
• Original Assignee: National Universit Corporation The University of Electro-Communications
• Inventors: Ohta, Daisuke, Tanaka, Hisaaki
• Application Number:
  US12/092,420
• Publication Number:
  US 20090122783A1
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: G04G 7/02 by radio
• CPC Class Codes: H04B 7/2696 Over the air autonomous synchronisation, e.g. by monitoring network activity H04B7/2693 takes precedence
• CPC Class Codes: H04J 3/0658 Clock or time synchronisation among packet nodes
• CPC Class Codes: H04W 56/002 Mutual synchronization
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

A time synchronization method performed by each node in an ad hoc network in which a plurality of nodes are connected with each other by radio and time synchronization of each node is performed by transmitting and receiving a beacon including time information in a beacon period is provided. The time synchronization method includes: a generation step of generating a slot number using a random number every one beacon period; a determination step of determining whether to cancel beacon transmission based on the slot number when the node does not receive a beacon from another node by beacon transmission time corresponding to the slot number; and a step of canceling beacon transmission when determining to cancel beacon transmission in the determination step, and transmitting a beacon including time information of the own node at the beacon transmission time when determining not to cancel beacon transmission.

Claims

1. A time synchronization method performed by each node in an ad hoc network in which a plurality of nodes are connected with each other by radio and time synchronization of each node is performed by transmitting and receiving a beacon including time information in a beacon period, comprising:

a generation step of generating a slot number using a random number every one beacon period;

a determination step of determining whether to cancel beacon transmission based on the slot number when the node does not receive a beacon from another node by beacon transmission time corresponding to the slot number; and

a step of canceling beacon transmission when determining to cancel beacon transmission in the determination step, and transmitting a beacon including time information of the own node at the beacon transmission time when determining not to cancel beacon transmission.

2. The time synchronization method as claimed in claim 1, comprising:

a step of putting the own node in an active mode for one beacon period after canceling beacon transmission based on the result of the determination in the determination step.

3. The time synchronization method as claimed in claim 1, comprising:

a step of putting the own node in an active mode or in a power save mode for one beacon period with an arbitrary probability after canceling beacon transmission based on the result of the determination in the determination step.

4. The time synchronization method as claimed in claim 1, comprising:

a step of putting the own node in an active mode or in a power save mode for one beacon period with a probability based on the slot number after canceling beacon transmission based on the result of the determination in the determination step.

5. The time synchronization method as claimed in any one of claims 1-4, comprising:

a step of putting the own node in an active mode for one beacon period if a time of the own node corresponds to a predetermined time when beacon transmission is canceled.

6. A communication apparatus that forms a node in an ad hoc network in which a plurality of nodes are connected with each other by radio and time synchronization of each node is performed by transmitting and receiving a beacon including time information in a beacon period, comprising:

slot number generation means configured to generate a slot number using a random number every one beacon period;

determination means configured to determine whether to cancel beacon transmission based on the slot number when the communication apparatus does not receive a beacon from another node by beacon transmission time corresponding to the slot number; and

beacon transmission control means configured to cancel beacon transmission when the determination means determines to cancel beacon transmission, and to transmit a beacon including time information of the communication apparatus at the beacon transmission time when the determination means determines not to cancel beacon transmission.

7. The communication apparatus as claimed in claim 6, comprising:

active mode setting means configured to put the communication apparatus in an active mode for one beacon period if a time of the communication apparatus corresponds to a predetermined time when beacon transmission is canceled.

8. A node comprising the communication apparatus as claimed in claim 6 or 7.

9. A program causing a computer, that forms a node in an ad hoc network in which a plurality of nodes are connected with each other by radio and time synchronization of each node is performed by transmitting and receiving a beacon including time information with a beacon period, to function as:

slot number generation means configured to generate a slot number using a random number every one beacon period;

determination means configured to determine whether to cancel beacon transmission based on the slot number when the computer does not receive a beacon from another node by beacon transmission time corresponding to the slot number; and

beacon transmission control means configured to cancel beacon transmission when the determination means determines to cancel beacon transmission, and to transmit a beacon including time information of the computer at the beacon transmission time when the determination means determines not to cancel beacon transmission.

10. The program as claimed in claim 9, further causing the computer to function as:

active mode setting means configured to put the computer in an active mode for one beacon period if a time of the computer corresponds to a predetermined time when beacon transmission is canceled.

11. A computer readable recording medium storing the program as claimed in claim 9 or 10.