WIRELESS COMMUNICATION NETWORK SYSTEM SYNCHRONIZATION METHOD

• US 20140211782A1
• Filed: 03/27/2014
• Published: 07/31/2014
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Nippon Signal Company Limited
• Original Assignee: Nippon Signal Company Limited
• Inventors: YAMAGUCHI, Terufumi, OTSUKA, Yuhei, SHIRAI, Toshihito, SAITO, Hiroki
• Granted Patent: US 9,319,163 B2
• Time in Patent Office: Days
• US Class Current: 370/350
• CPC Class Codes: B61L 15/0027 Radio-based, e.g. using GSM-R
• CPC Class Codes: B61L 27/70 Details of trackside communication
• CPC Class Codes: H04B 7/026 Co-operative diversity, e.g. using fixed or mobile stations as relays
• CPC Class Codes: H04J 3/06 Synchronising arrangements for television systems H04N5/04; bit-synchronisation H04L7/00
• 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 56/0025 synchronizing potentially movable access points

Abstract

Mobile radio sets are installed on front and rear parts of a mobile body, one of fixed radio sets is set as a synchronization base station, and the other radio sets including the mobile radio sets are set as synchronization packet relay stations. Each of the relay stations in a synchronization acquiring mode makes a transition to a ground synchronization maintaining mode higher in synchronization accuracy when receiving a synchronization packet without the intervention of the mobile radio sets, or makes a transition to an on-vehicle synchronization maintaining mode lower in synchronization accuracy when receiving a synchronization packet with the intervention of the mobile radio sets, and the relay station in the on-vehicle synchronization maintaining mode makes a transition to the ground synchronization maintaining mode when receiving a synchronization packet from a relay station in the ground synchronization maintaining mode.

Claims

1. A synchronization method for a wireless communication network system provided with mobile radio sets that are mounted on a mobile body moving along a predetermined route, and a plurality of fixed radio sets that is spatially separated and installed along the route in such a manner that adjacent fixed radio sets perform wireless communication with each other to transmit information while relaying the information from a transmission source to a terminal fixed radio set, wherein the mobile radio sets and the fixed radio sets are time-synchronized in a communicable manner to perform communication,

wherein the mobile radio sets are installed on front and rear parts of the mobile body in a manner to be communicable with each other, and when the mobile body exists between fixed radio sets, synchronization information between the fixed radio sets can be relayed by the two mobile radio sets mounted on the mobile body.

2. The synchronization method for the wireless communication network system, according to claim 1, wherein at least one of the fixed radio sets is set as a base station for transmitting a synchronization packet as the synchronization information, and the other fixed radio sets and the two mobile radio sets are set as relay stations for relaying the synchronization packet transmitted from the base station, wherein these relay stations do not adopt a synchronization packet relayed with intervention of the mobile radio sets while a synchronization packet relayed without intervention of the mobile radio sets is being received and adopted periodically.

3. The synchronization method for the wireless communication network system, according to claim 2, wherein after making a transition to a synchronization acquiring mode that is a state of waiting for reception of a synchronization packet in response to application of power,

when receiving a synchronization packet relayed without intervention of the mobile radio sets, each of the relay stations in the synchronization acquiring mode makes a transition to a ground synchronization maintaining mode indicating that synchronization accuracy is high, so that the relay station can transmit the synchronization packet during a preset own synchronization packet transmission allocation period,

when receiving a synchronization packet relayed with intervention of the mobile radio sets, each of the relay station in the synchronization acquiring mode makes a transition to on-vehicle synchronization maintaining mode indicating that synchronization accuracy is lower than the ground synchronization maintaining mode, so that the relay station can transmit the synchronization packet during the preset own synchronization packet transmission allocation period, and

when the relay station in the on-vehicle synchronization maintaining mode receives a synchronization packet from another relay station in the ground synchronization maintaining mode, the relay station makes a transition to the ground synchronization maintaining mode.

4. The synchronization method for the wireless communication network system, according to claim 3, wherein when the relay station in the ground synchronization maintaining mode or the on-vehicle synchronization maintaining mode receives a synchronization packet, the relay station compares master time information, which is included in the synchronization packet and indicative of a synchronization packet transmission time of the base station, with own master time information stored and held by the relay station, and then, when the own master time information is newer, the relay station determines that the synchronization packet has been received, and stores and holds the master time information in the synchronization packet as own master time information.

5. The synchronization method for the wireless communication network system, according to claim 3, wherein when the relay station in the ground synchronization maintaining mode or the on-vehicle synchronization maintaining mode receives a synchronization packet, the relay station compares clock level information, which is included in the synchronization packet and indicative of the number of relay stations, through which the synchronization packet goes from the base station until reception, with own clock level information stored and held by the relay station, and then, when an own clock level value is smaller, the relay station determines that the synchronization packet has been received, adds one to a clock level value of the synchronization packet, and stores and holds the obtained clock level value as own clock level information, while the base station prestores clock level information indicative of a transmission source of the synchronization packet, and the relay station in the synchronization acquiring mode prestores, as clock level information, a value larger than an estimated maximum number of relay stations through which the synchronization packet is expected to go from the base station until reception.

6. The synchronization method for the wireless communication network system, according to claim 3, wherein when the relay station in the ground synchronization maintaining mode or the on-vehicle synchronization maintaining mode receives a synchronization packet, the relay station compares master time information, which is included in the synchronization packet and indicative of a synchronization packet transmission time of the base station, and clock level information, which is indicative of the number of relay stations, through which the synchronization packet goes from the base station until reception, with own master time information and own clock level information stored and held by the relay station, respectively, and then, when the master time information in the received synchronization packet is newer, or when an own clock level value is smaller if both pieces of master time information are identical, the relay station determines that the synchronization packet has been received, stores and holds the master time information in the synchronization packet as own master time information, adds one to a clock level value of the synchronization packet, and stores and holds the obtained clock level value as own clock level information, while the base station prestores clock level information indicative of a transmission source of the synchronization packet, and the relay station in the synchronization acquiring mode prestores, as clock level information, a value larger than an estimated maximum number of relay stations through which the synchronization packet is expected to go from the base station until reception.

7. The synchronization method for the wireless communication network system, according to claim 3, wherein the relay station in the on-vehicle synchronization maintaining mode makes a transition to the synchronization acquiring mode when a state without reception of any synchronization packet exceeds a preset limited time of synchronization information update.

8. The synchronization method for the wireless communication network system, according to claim 5, wherein the relay station in the on-vehicle synchronization maintaining mode increments the clock level value by a constant value every period shorter than the limited time of synchronization information update until receiving a synchronization packet before making a transition to the synchronization acquiring mode.

9. The synchronization method for the wireless communication network system, according to claim 2, wherein when receiving a reference time signal within a preset limited time of reference time signal reception, the base station can transmit a synchronization packet as a base station, while when receiving no reference time signal within the limited time of reference time signal reception, the base station operates as the relay station.

10. The synchronization method for the wireless communication network system, according to claim 9, wherein after making a transition to a reference time signal acquiring mode that is a state of waiting for reception of a reference time signal in response to application of power,

when receiving a reference time signal within the limited time of reference time signal reception, the base station in the reference time signal acquiring mode makes a transition to a base station synchronization maintaining mode indicating that synchronization accuracy is higher than the ground synchronization maintaining mode, so that the base station can transmit a synchronization packet during a preset own synchronization packet transmission allocation period,

the base station in the reference time signal acquiring mode or the base station synchronization maintaining mode makes a transition to the synchronization acquiring mode when receiving no reference time signal within the limited time of reference time signal reception,

the base station in the synchronization acquiring mode makes a transition to the ground synchronization maintaining mode when receiving a synchronization packet from the relay station in the ground synchronization maintaining mode or makes a transition to the on-vehicle synchronization maintaining mode when receiving a synchronization packet from the relay station in the on-vehicle synchronization maintaining mode,

the base station in the ground synchronization maintaining mode makes a transition to the base station synchronization maintaining mode when receiving the reference time signal, while when receiving no synchronization packet within a preset limited time of synchronization information update, the base station makes a transition to the on-vehicle synchronization maintaining mode, and

the base station in the on-vehicle synchronization maintaining mode makes a transition to the reference time signal acquiring mode when receiving no synchronization packet within the limited time of synchronization information update.

11. A synchronization method for a wireless communication network system provided with mobile radio sets that are mounted on a mobile body moving along a predetermined route, and a plurality of fixed radio sets that is spatially separated and installed along the route in such a manner that adjacent fixed radio sets perform wireless communication with each other to transmit information while relaying the information from a transmission source to a terminal fixed radio set, wherein the mobile radio sets and the fixed radio sets are time-synchronized in a communicable manner to perform communication,

wherein at least one of the fixed radio sets is set as a base station for transmitting a synchronization packet as synchronization information, and the other fixed radio sets are set as relay stations for relaying the synchronization packet transmitted from the base station,

wherein each of these relay stations makes a transition to a synchronization acquiring mode that is a state of waiting for reception of a synchronization packet in response to application of power, the relay station that made the transition to the synchronization acquiring mode makes a transition to a synchronization maintaining mode when receiving a synchronization packet, so that the relay station can transmit the synchronization packet during a preset own synchronization packet transmission allocation period, and the relay station in the synchronization maintaining mode makes a transition to the synchronization acquiring mode when a state without reception of any synchronization packet exceeds a preset limited time of synchronization information update.

12. The synchronization method for the wireless communication network system, according to claim 11, wherein when receiving a synchronization packet, the relay station in the synchronization maintaining mode compares master time information, which is included in the synchronization packet and indicative of a synchronization packet transmission time of the base station, with own master time information stored and held by the relay station, and then, when the own master time information is newer, the relay station determines that the synchronization packet has been received, and stores and holds the master time information in the synchronization packet as own master time information.

13. The synchronization method for the wireless communication network system, according to claim 11, wherein when receiving a synchronization packet, the relay station in the synchronization maintaining mode compares clock level information, which is included in the synchronization packet and indicative of the number of relay stations, through which the synchronization packet goes from the base station until reception, with own clock level information stored and held by the relay station, and then, when an own clock level value is smaller, the relay station determines that the synchronization packet has been received, adds one to a clock level value of the synchronization packet, and stores and holds the obtained clock level value as own clock level information, while the base station prestores clock level information indicative of a transmission source of the synchronization packet, and the relay station in the synchronization acquiring mode prestores, as clock level information, a value larger than an estimated maximum number of relay stations through which the synchronization packet is expected to go from the base station until reception.

14. The synchronization method for the wireless communication network system, according to claim 11, wherein when receiving a synchronization packet, the relay station in the synchronization maintaining mode compares master time information, which is included in the synchronization packet and indicative of a synchronization packet transmission time of the base station, and clock level information, which is indicative of the number of relay stations, through which the synchronization packet goes from the base station until reception, with own master time information and own clock level information stored and held by the relay station, respectively, and then, when the master time information in the received synchronization packet is newer, or when an own clock level value is smaller if both pieces of master time information are identical, the relay station determines that the synchronization packet has been received, stores and holds the master time information in the synchronization packet as own master time information, adds one to a clock level value of the synchronization packet, and stores and holds the obtained clock level value as own clock level information, while the base station prestores clock level information indicative of a transmission source of the synchronization packet, and the relay station in the synchronization acquiring mode prestores, as clock level information, a value larger than an estimated maximum number of relay stations through which the synchronization packet is expected to go from the base station until reception.

15. The synchronization method for the wireless communication network system, according to claim 13, wherein the relay station in the synchronization maintaining mode increments the clock level value by a constant value every period shorter than the limited time of synchronization information update until receiving a synchronization packet before making a transition to the synchronization acquiring mode.

16. The synchronization method for the wireless communication network system, according to claim 11, wherein after making a transition to a reference time signal acquiring mode that is a state of waiting for reception of a reference time signal in response to application of power,

when receiving a reference time signal within a preset limited time of reference time signal reception, the base station makes a transition to a base station synchronization maintaining mode indicating that synchronization accuracy is higher than the synchronization maintaining mode, so that the base station can transmit a synchronization packet during a preset own synchronization packet transmission allocation period,

the base station in the reference time signal acquiring mode or the base station synchronization maintaining mode makes a transition to the synchronization acquiring mode when receiving no reference time signal within the limited time of reference time signal reception,

the base station in the synchronization acquiring mode makes a transition to the synchronization maintaining mode when receiving a synchronization packet, and

the base station in the synchronization maintaining mode makes a transition to the base station synchronization maintaining mode when receiving the reference time signal, while when receiving no synchronization packet within a preset limited time of synchronization information update, the base station makes a transition to the reference time signal acquiring mode.

17. The synchronization method for the wireless communication network system, according to claim 11, wherein at least two of the fixed radio sets are set as base stations for transmitting a synchronization packet.