JP2010050761A - Time synchronization mode and time synchronization method of radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately execute time synchronization between multiple master and slave stations without imposing large burden on traffics. <P>SOLUTION: Time synchronization is executed between master stations 1 and 2 via a LAN, each of the master stations adds a time stamp (clock) to a vender IE of a beacon frame and regularly transmits the time stamp, an interruption signal as beacon reception timing (beacon reception interval) is generated in a host CPU in radio devices of slave stations (terminals) 3A-3N, and the host CPU corrects the time of the clock, based on the reception timing and the time stamp (vender IE). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless communication system that performs information transmission between a master station (access point) and a slave station (terminal) using a wireless LAN, and more particularly to a time synchronization method and a time synchronization method between a master station and a slave station.

  As existing wireless equipment, wireless LAN (wireless equipment conforming to IEEE802.11 a / b / g) devices are frequently used. The IEEE 802.11 standard as a wireless LAN standard is mainly composed of a physical layer standard and a MAC layer standard, and a single MAC layer standard can support a plurality of physical layer standards. As the physical layer, there are three types of spread spectrum: frequency hopping (FHSS), direct spreading (DSSS), and infrared, which are defined by IEEE802.11a, IEEE802.11b, and IEEE802.11g. Each has different standards in the physical layer. For the MAC layer, a CSMA / CA (Carrier Sense Multiple Access with Collision Aidance) method is used.

  When constructing a monitoring control system for a large-scale facility such as a power system as a wireless communication system in which the above-described wireless LAN device is mounted on each of the master station and the slave station, the system voltage and the Although current is measured and wireless LAN transmission is performed mutually, time synchronization in which the measurement times at the master station and the slave station are matched is required for the protective relay function of the power system.

In the time synchronization described above, there is a method in which time information is acquired by the clock management server (master station), the time is set, and the time is corrected for all terminals by accessing the server individually to the terminals (slave stations). (For example, refer to Patent Document 1).
JP 2005-099886 A

  The IEEE 802.11 standard does not have a function for time synchronization. Therefore, in order to synchronize the time between the server and the terminal, there is only a means for developing a communication protocol for time synchronization from the upper application and performing synchronization using the time stamp information from the upper application.

  When time synchronization is performed in a host application, a delay due to processing time between the physical layer and the MAC layer, a delay due to communication time between the host and the device, a processing time such as TCP / IP from the WLAN driver processing time, and a delay due to OS management time Due to various factors, time synchronization with high resolution cannot be realized.

  In addition, since time correction must be performed frequently in order to obtain high time synchronization accuracy, such as periodically performing time correction, a heavy load is imposed on the traffic of the wireless network. This significantly reduces network throughput.

  In a large-scale network covering 1000 or more terminals, when time synchronization of all terminals is performed, the time acquisition operation is performed from each terminal to the time management server, so that air packet collisions frequently occur between the terminals. As a result, it is possible to predict such a situation that communication is not possible, retransmissions occur frequently, or very old time data is returned. For this reason, a delay time occurs between terminals, and stable time management cannot be performed.

  As an existing technology, when access to the time management server is executed individually, access of more than 1000 terminals periodically performs time correction via the wireless network, so air packet collisions and retransmissions occur frequently, and throughput decreases. Etc. occur frequently and communication quality deteriorates.

  An object of the present invention is to provide a time synchronization method and a time synchronization method for a wireless communication system capable of performing time synchronization with high accuracy without imposing a heavy load on traffic for time synchronization between a large number of master stations and slave stations. There is.

  In order to solve the above-mentioned problem, the present invention performs time synchronization between the master stations via the LAN, and each master station periodically adds a “time stamp” (clock) to the vendor IE of the beacon frame. Then, in the wireless device of the slave station terminal, an interrupt signal serving as a beacon reception timing (beacon reception interval) is generated in the host CPU, and the host CPU performs time correction of the clock from the reception timing and the time stamp (Vender IE). It is characterized by the following methods and methods.

(1) A system in which information transmission between a plurality of master stations and a plurality of slave stations is performed by a wireless LAN, and information acquisition times in each master station and each slave station are synchronized by a clock mounted on each master station and each slave station. There,
Each parent station performs time synchronization of the clock between the parent stations via the LAN, and periodically sends a signal called a beacon from each parent station to the child station. A means for adding time stamp information to be a clock is provided,
Each slave station receives the beacon at the timing determined as the master station, determines the operation based on the internal information of the beacon, and includes the “Vender IE” included in the beacon with the time stamp information from the master station. A means for correcting the time of the clock in the slave station is provided.

(2) A method in which information transmission between a plurality of master stations and a plurality of slave stations is performed by a wireless LAN, and information acquisition times in each master station and each slave station are synchronized by a clock mounted on each master station and each slave station. There,
Each parent station performs time synchronization of the clock between the parent stations via the LAN, and periodically sends a signal called a beacon from each parent station to the child station. Add time stamp information to be a clock,
Each slave station receives the beacon at the timing determined as the master station, determines the operation based on the internal information of the beacon, and includes the “Vender IE” included in the beacon with the time stamp information from the master station. A time correction of a clock in the slave station is performed.

  As described above, according to the present invention, time synchronization is performed between the master stations via the LAN, and each master station periodically sends a “time stamp” (clock) to the vendor IE of the beacon frame, In the wireless device of the slave station terminal, an interrupt signal serving as a beacon reception timing (beacon reception interval) is generated in the host CPU, and the host CPU performs time correction of the clock from the reception timing and the time stamp (Vender IE). It has the following effects.

  (1) It is possible to avoid a decrease in throughput due to collision of air packets or retransmission of air frames, and time synchronization can be performed without placing a heavy load on existing traffic.

  (2) By receiving beacon frames transmitted at a fixed period, time synchronization with a resolution of 1TU = 1.024 msec becomes possible, and accuracy is improved.

  (3) Since the beacon is transmitted by broadcast, the time stamp can be transferred to a plurality of terminals at a time, so that the delay time between the terminals can be made as close to zero as possible.

  (4) By performing time synchronization between a plurality of master stations on the LAN side, time synchronization among a large number of terminals having different master stations becomes possible.

  FIG. 1 is a network configuration diagram showing an embodiment of the present invention, and assumes a network environment in which a Beacon frame is periodically transmitted from a master station (AP) to a slave station (terminal) based on a Beacon Interval setting.

  Time synchronization between the master stations is performed via the LAN from the master station (AP) 1 serving as a master to another master station (AP) 2. This enables synchronization between wireless terminals having different master stations, for example, time synchronization among 1000 or more terminals.

  The slave stations 3A to 3N receive the Beacon frame from the master station at the Listen Interval period set by the local station. As shown in FIG. 2, the Beacon frame transmitted from the master station is transmitted by adding “Vender Information Element (IE)” to the MAC control frame defined by the IEEE802.11 MAC protocol. Here, the master station clock data is notified to the slave station by adding time stamp information serving as a base clock of the master station to “Vender Information Element (IE)” added to the Beacon frame.

  When the slave stations 3A to 3N receive the Beacon frame by the wireless device 4 as shown in FIG. 3 and the time synchronization timing chart in FIG. 3 and FIG. 4, respectively, the Beacon reception event interrupt INTR is sent to the host CPU 5. Is generated. When the beacon reception event interrupt INTR is generated, the slave stations 3A to 3N are notified to the host 5 of the clock data (TIME STUMP) of the master station in the “Vender IE information” in the Beacon frame. By this event, the time of the clock managed by the host 5 is corrected.

  The time accuracy at this time has a resolution of 1 TU = 1.024 msec (the minimum unit of Beacon interval).

The network block diagram which shows embodiment of this invention. Beacon frame format. The principal part block diagram of the internal circuit block of slave station 3A-3N. Time synchronization timing chart.

Explanation of symbols

1, 2 Master station 3A-3N Slave station 4 Wireless device 5 Host CPU

Claims (2)

A method of performing information transmission between a plurality of master stations and a plurality of slave stations by a wireless LAN, and synchronizing information acquisition times in each master station and each slave station by a clock mounted in each master station and each slave station,
Each parent station performs time synchronization of the clock between the parent stations via the LAN, and periodically sends a signal called a beacon from each parent station to the child station. A means for adding time stamp information to be a clock is provided,
Each slave station receives the beacon at the timing determined as the master station, determines the operation based on the internal information of the beacon, and includes the “Vender IE” included in the beacon with the time stamp information from the master station. A time synchronization system between a master station and a slave station, comprising means for correcting the time of a clock in the slave station. A method of performing information transmission between a plurality of master stations and a plurality of slave stations by a wireless LAN, and synchronizing information acquisition times at each master station and each slave station by a clock mounted on each master station and each slave station,
Each parent station performs time synchronization of the clock between the parent stations via the LAN, and periodically sends a signal called a beacon from each parent station to the child station. Add time stamp information to be a clock,
Each slave station receives the beacon at the timing determined as the master station, determines the operation based on the internal information of the beacon, and includes the “Vender IE” included in the beacon with the time stamp information from the master station. A time synchronization method between a master station and a slave station, wherein time correction of a clock in the slave station is performed.

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