Method and device for time-synchronization in ad hoc network

• US 9,585,113 B2
• Filed: 09/26/2013
• Issued: 02/28/2017
• Est. Priority Date: 03/29/2011
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Okamasu, Takayuki D, Nomura, Yayoi, Kurogi, Yasuhiro, Inao, Yuichi, Yamada, Kenji, Koga, Syunsuke
• Primary Examiner(s): Choudhury, Faisal
• Application Number:
  US14/038,416
• Publication Number:
  US 20140029603A1
• Time in Patent Office: 1,251 Days
• Field of Search: 370/350
• US Class Current: 1/1
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• 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 method and a device perform time-synchronization with an ad hoc network configured by a plurality of nodes. The method includes: transmitting a time-synchronization request frame including an address of one of the plurality of nodes which belong to the ad hoc network to one of the plurality of nodes having a function of receiving the time-synchronization request frame and transmitting a time-synchronization reply frame including time-synchronization information; receiving the time-synchronization reply frame including the time-synchronization information from one of the plurality of nodes which receive the time-synchronization request frame; and performing time-synchronization with one of the plurality of nodes using the time-synchronization information included in the time-synchronization reply frame.

Claims

1. A method for time synchronization between a network time of an ad hoc network which is configured by a plurality of time-synchronized nodes and a new node internal clock time, the method comprising:

receiving, by a new node, a message including an address of one of the plurality of time-synchronized nodes which belong to the ad hoc network from the one of the plurality of time-synchronized nodes having a function of receiving a time-synchronization request frame and a function of transmitting a time-synchronization reply frame including time-synchronization information for synchronizing the new node internal clock time to a synchronized internal clock time of the one of the plurality of time-synchronized nodes;

transmitting, by the new node, the time-synchronization request frame including, as a destination of the time-synchronization request frame, the address included in the message, after a specified transmission wait time has passed from a time when the message is received by the new node;

receiving the time-synchronization reply frame including the time-synchronization information transmitted from the destination of the time-synchronization request frame in response to reception of the time-synchronization request frame transmitted by the new node; and

performing, by the new node, time-synchronization between the new node internal clock time and the synchronized internal clock time of the one of the plurality of time-synchronized nodes using the time-synchronization information included in the time-synchronization reply frame received from the destination of the time-synchronization request frame.

2. The method according to claim 1, wherein a node to which the message is transmitted transmits to the one of the plurality of time-synchronized nodes the time-synchronization request frame when signal intensity of the message is equal to or exceeds a specified threshold.

3. The method according to claim 1, wherein the time-synchronization request frame is transmitted when the message is received a specified number of times or more continuously within a specified time period.

4. A device for time synchronization between a network time of an ad hoc network which is configured by a plurality of time-synchronized nodes and a new node internal clock time, the device comprising:

a memory, and

a processor in a new node configured to read instructions from the memory to execute a process including

receiving a message including an address of one of the plurality of time-synchronized nodes which belong to the ad hoc network from the one of the plurality of time-synchronized nodes having a function of receiving a time-synchronization request frame and a function of transmitting a time-synchronization reply frame including time-synchronization information for synchronizing the new node internal clock time to a synchronized internal clock time of the one of the plurality of time-synchronized nodes;

transmitting the time-synchronization request frame including, as a destination of the time-synchronization request frame, the address included in the message received by the new node, after a specified transmission wait time has passed from a time when the message is received by the new node;

receiving the time-synchronization reply frame including the time-synchronization information transmitted from the destination of the time-synchronization request frame in response to reception of the time-synchronization request frame transmitted by the new node; and

performing time-synchronization between the new node internal clock time and the synchronized internal clock time of the one of the plurality of time-synchronized nodes using the time-synchronization information included in the time-synchronization reply frame received from the destination of the time-synchronization request frame.

5. The device according to claim 4, further comprising a node selector which controls the time-synchronization request frame transmitter so that the time-synchronization request frame is transmitted to the one of the plurality of time-synchronized nodes when signal intensity of the message is equal to or exceeds a specified threshold.

6. The device according to claim 4, wherein the time-synchronization request frame transmitter transmits the time-synchronization request frame when the message is received a specified number of times or more continuously within a specified time period.

7. A method for allowing a new node to enter an ad hoc network which is configured by a plurality of time-synchronized nodes, the method comprising:

receiving, by the new node, a message including an address of one of the plurality of time-synchronized nodes which belong to the ad hoc network from the one of the plurality of time-synchronized nodes having a function of receiving a time-synchronization request frame and a function of transmitting a time-synchronization reply frame including time-synchronization information for synchronizing a new node internal clock time to a synchronized internal clock time of the one of the plurality of time-synchronized nodes;

transmitting, by the new node, the time-synchronization request frame including, as a destination of the time-synchronization request frame, the address included in the message after a specified transmission wait time has passed from a time when the message is received by the new node;

receiving the time-synchronization reply frame including the time-synchronization information transmitted from the destination of the time-synchronization request frame in response to reception of the time-synchronization request frame transmitted by the new node; and

performing, by the new node, time-synchronization between the new node internal clock time and the synchronized internal clock time of the one of the plurality of time-synchronized nodes using the time-synchronization information included in the time-synchronization reply frame received from the destination of the time-synchronization request frame, thereby entering the ad hoc network.

8. A network, comprising:

a first node which belongs to an ad hoc network configured by a plurality of time-synchronized nodes, having a first processor programmed to execute a process including

transmitting a message including an address of the first node,

receiving a time-synchronization request frame including, as a destination of the time-synchronization request frame, the address of the first node included in the message, and

transmitting a time-synchronization reply frame, including time-synchronization information for synchronizing a first internal clock time to a second internal clock time, in response to receiving the time-synchronization request frame; and

a second node, having the second internal clock time and a second processor programmed to execute a process including

receiving, from the first node, the message including the address of the first node,

transmitting the time-synchronization request frame to the address of the first node after a specified transmission wait time has passed from a time when the message is received by the second node,

receiving the time-synchronization reply frame including time-synchronization information transmitted from the first node which received the time-synchronization request frame, and

performing time-synchronization, between the first internal clock time of the first node and the second internal clock time of the second node, using the time-synchronization information included in the time-synchronization reply frame.