JP2005311646A - High-speed handover method in radio lan, and radio lan system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably execute handover even during high-speed movement. <P>SOLUTION: A mobile body transmits a request signal for acquiring radio link information of base stations, to which handover is scheduled, to a base station before starting high-speed movement. The base station transfers the request signal and specific information of the mobile body transmitting it to a management station. The management station manages the radio link information of a plurality of the base stations. When receiving the request signal including the specific information of the mobile body, the management station collectively transmits the radio link information of each base station, to which handover is scheduled, along the route of the mobile body to the mobile station via the base station with which the mobile body executes communication. The base station transfers the radio link information of each base station, to which handover is scheduled, to the mobile body. The mobile body stores the radio link information of each base station to which handover is scheduled. When confirming the opportunity of the handover, the mobile body executes the handover processing by acquiring the radio link information of the base station, to which the handover is executed, from among the stored information. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless LAN that performs high-speed handover between a mobile body and a base station in a system that implements a wireless LAN such as IEEE802.11 with a mobile body (for example, a train) that moves at a high speed along a predetermined route. The present invention relates to a high-speed handover method and a wireless LAN system.

  In a wireless LAN system, when a handover is required between a mobile object moving at high speed and a base station, the ratio of the time required for the handover to the time required for the mobile object to pass through the wireless zone of the base station increases. The problem is that the body communication speed (communication bandwidth) decreases.

  The time ratio of handover in this wireless LAN system will be described with reference to FIG. In FIG. 3 (1), it is assumed that base stations 31 and 32 form wireless zones 33 and 34, respectively, and a moving body 35 moves from the wireless zone 33 toward the wireless zone 34. The speed of the moving body 35 is v, the range of the wireless zones 33 and 34 (linear distance in the moving direction) is L, and the time T (= L / v) when the moving body 35 passes through the wireless zones 33 and 34 is Let Y (= t / T) be the ratio of the handover time t for changing the radio link of the mobile unit 35 from the base station 31 to the base station 32. The handover time t is a parameter for determining the average communication band if the radio link is broken.

  Here, with respect to the relationship between Y, v and t (Y = (v / L) t) when L = 50 m, v = 300 km / h (when traveling by train) and v = 3 km / h (when walking) This case is shown in Fig. 3 (2). Considering the case where the communication band is fixed, if Y is set to 10%, 6s can be secured for the handover time when walking, but only 1/100 of 60 ms can be secured when traveling by train. This indicates that it is important to shorten the handover time in order to secure a certain communication band when the moving body moves at a high speed.

  There is "Techniques to reduce IEEE802.11b MAC Layer handover time" as research related to wireless LAN handover time (Non-patent Document 1). In this document, the time required for each stage using a commercially available device is divided into three stages of “detection”, “search”, and “execution” as the handover time of the wireless LAN system. Measurement and time-saving methods are proposed. Here, the three stages are outlined, and the main stages for determining the length of the handover time are described.

  First, the first “detection” is a stage in which a mobile unit recognizes a trigger for handover in a radio link. If the mobile cannot receive a packet from the base station several times, the mobile determines that it should switch to another base station. As described above, when the mobile body uses the arrival of a packet from the base station as a trigger for the handover, a detection time of 1000 ms is required. However, according to Non-Patent Document 1, the time required for this stage can be shortened by using physical layer parameters such as the reception level as a trigger for the handover.

  “Execution” is a stage for establishing a belonging relationship after the mobile station moves to the radio zone of the new base station, and exchanges packets over the radio link. According to Non-Patent Document 1, the time required for this stage is about 2 to 3 ms, and the time occupying the entire handover is very small. Therefore, this stage is not the main factor that determines the handover time.

  “Search” is a step of searching for a new base station to which the mobile body can belong after recognizing the trigger of the handover through the “detection” step. As an active base station search method, the wireless LAN defined by IEEE802.11 broadcasts a request packet at an arbitrary frequency and receives a response packet from the corresponding base station. Specifies how to obtain radio link information. In this method, since the mobile unit does not know the radio link information of the base station to which it belongs, the frequency is changed until the corresponding base station is found, and the search is repeated. It will search. According to Non-Patent Document 1, it has been reported that the time of “Search” ranges from several tens to several hundreds ms in proportion to the number of channels to be searched, and “Execution” It is longer than the time required (2 to 3 ms). From the above, it is understood that “Search” is the main stage for determining the handover time, and how to shorten the “Search” time is important for reducing the handover time.

  By the way, a handover procedure that can omit the “Search” stage has been proposed (Patent Document 1). In this handover procedure, information necessary for establishing a radio link with an adjacent base station to be handed over is exchanged while the mobile unit (terminal in Patent Document 1) is in the radio zone of the current base station. This eliminates the need to go through the procedure for searching for a handover destination base station after the mobile recognizes the trigger of the handover, so that the mobile can skip the “Search” stage and smoothly perform handover. It can be done.

  The handover procedure described in Patent Document 1 will be described with reference to FIG. 4 and FIG. In FIG. 4, base stations 41, 42, and 43 form wireless zones 44, 45, and 46, respectively, and a moving body 47 belonging to the base station 41 moves from the wireless zone 44 toward the wireless zone 45. To do. The base stations 41, 42, and 43 are connected to the router device 48 by wire or wirelessly, and a server 50 is connected to the router device 48 via the Internet 49. Hereinafter, a case where the moving body 47 moves from the wireless zone 44 to the wireless zone 45 will be described as an example.

  The base stations 41, 42, and 43 transmit the respective radio link information to the adjacent radio stations via the router device 48. In FIG. 5, the radio link information of the base station 42 adjacent to the base station 41 is transmitted to the router. Received via the device 48 (S51). The wireless link information here refers to a signal called beacon information in Patent Document 1. The base station 41 transmits the radio link information of the adjacent base station 42 together with the radio link information of the own station to the mobile unit 47 (S52). Upon obtaining the radio link information of the handover destination base station 42 from the base station 41, the mobile unit 47 transmits a radio link establishment request for requesting a radio link connection with the base station 42 to the base station 41 (S53). . The base station 41 transfers a wireless link establishment request not addressed to itself to the base station 42 via the router device 48 (S54). The base station 42 transmits a wireless link establishment response to this wireless link establishment request to the mobile unit 47 via the router device 48 and the base station 41 (S55, S56). The mobile unit 47 receives this radio link establishment response, confirms that it is ready to establish a radio link with the base station 42, and notifies the router device 48 via the base station 41 of the fact. The registration signal to be transmitted is transmitted (S57, S58). As described above, preparation for handover to the adjacent base station 42 is completed.

  Next, when the mobile unit 47 is exchanging user data with the server 50 via the base station 41 and the router device 48, the mobile unit 47 moves to the boundary between the wireless zone 44 and the wireless zone 45, and the base station 42. When the reception level from the mobile terminal 47 reaches a certain value or more and recognizes the trigger of handover, the mobile unit 47 transmits a data transmission signal to the router device 48 via the base station 41 (S59, S60). When receiving this data transmission signal, the router device 48 multicasts the user data from the server 50 to the base stations 41 and 42 (S61, S62, S63, S64). At this point, user data between the mobile unit 47 and the server 50 is transmitted / received via the base station 41 (S61, S62, S63).

  Further, the router device 48 transmits a simultaneous transmission signal for informing the mobile unit 47 that multicasting is performed to the base stations 41 and 42 (S65, S66). By receiving this simultaneous transmission signal, the mobile unit 47 determines that the service can be received in both the wireless zones 54 and 55, and switches from the base station 41 to the base station 42. A transmission stop signal is transmitted to the router device 48 (S67, S68). When receiving the transmission stop signal from the mobile unit 47, the router device 48 confirms that the mobile unit 47 has completed switching to the base station 42 and stops transmitting user data to the base station 41. Thereby, transmission / reception of user data between the mobile unit 47 and the server 50 is performed via the router device 48 and the base station 42 (S69, S70, S71).

Thereafter, handover from the base station 42 to the base station 43 is performed in the same manner, and in particular, the sequence of S51 to S58 is repeated every time handover is performed. As a result, the mobile unit 47 acquires the radio link information with the adjacent base station to be handed over via the current base station. The handover can be executed immediately without the “Search” step.
JP 2002-171558 A H.Velayos et al., TRITA-IMIT-LCN R 03:02 ISSN 1651-7717 ISRN KTH / IMIT / LCN / R-03 / 02 SE, Laboratory for Communication networks, Department Microelectronics Information Technology (IMIT) KTH, royal Institute of Technology Stockholm, Sweden

  In the conventional handover procedure, as described in Non-Patent Document 1, since the mobile unit searches for a new base station after entering the radio zone of the handover destination base station, the search time is indispensable. It was.

  On the other hand, the handover procedure described in Patent Document 1 has the following problems, although there is an advantage that there is no need to search for a handover destination base station, which is indispensable in the conventional handover procedure. That is, as shown in the sequence of S51 to S58 in FIG. 5, every time handover is performed, the radio link information of the adjacent base station must be acquired via the router device. On the other hand, when the moving speed of the moving body becomes high, the number of base stations through which the moving body passes per unit time increases, so the frequency of acquiring the radio link information of adjacent base stations also increases. Therefore, when the mobile body moves at a high speed, the resources of the wireless and wired networks are greatly consumed to acquire the wireless link information of the adjacent base station.

  Further, when the time required for the sequence (S51 to S58) for acquiring the radio link information of the adjacent base station becomes longer than the radio zone passing time of the mobile body, the mobile body establishes the radio link of the adjacent base station. I can't do that. In general, since the time for passing through the radio zone of each base station is shortened in proportion to the moving speed of the moving body, there is a limit to the moving speed of the moving body in order to enable the handover procedure of Patent Document 1.

  The present invention eliminates the need to search for a base station in a handover procedure, and does not consume radio and wired network resources for acquiring radio link information of neighboring base stations, and is stable even during high-speed movement. It is an object of the present invention to provide a high-speed handover method and a wireless LAN system in a wireless LAN that can execute handover.

  The invention according to claim 1 is a wireless LAN system including a mobile body that moves at a high speed along a predetermined route, wherein a plurality of base stations form wireless zones in which communication is possible, and the mobile body moves in the wireless zone. In a high-speed handover method in a wireless LAN that switches base stations that communicate with each other, a mobile unit is scheduled to perform handover along a route to a base station that is currently connected via a wireless link before starting high-speed movement. When the base station receives the request signal, the base station transfers the request signal and the specific information of the transmitted mobile unit to the management station for management. A station is connected to a plurality of base stations by wire or wirelessly, manages radio link information of a plurality of base stations, and receives a request signal including mobile unit specific information, and then routes the mobile unit Radio link information of each base station scheduled to be handed over to the mobile unit via the base station with which the mobile unit is communicating, and the base station transmits the radio link information of each base station scheduled to be handed over The mobile unit accumulates the radio link information of each base station scheduled for handover, and acquires the radio link information of the base station to be handed over from the stored information when confirming the trigger of the handover. To perform handover processing.

  The invention according to claim 2 includes a mobile body that moves at high speed on a predetermined route, forms a wireless zone in which a plurality of base stations can communicate with each other, and the mobile body communicates with the movement of the wireless zone In a wireless LAN system for performing handover for switching stations, a mobile station is provided with a management station that is connected to a plurality of base stations by wire or wirelessly and manages radio link information of the plurality of base stations. A request signal for acquiring radio link information of a base station that is scheduled to be handed over along a route is transmitted to a base station that is currently connected via a radio link, and a handover schedule that is transmitted from the management station Means for storing the radio link information of each base station of the base station, and when the handover trigger is confirmed, the radio link information of the base station to be handed over from the stored information is confirmed. When the base station receives the request signal, the base station transfers the request signal and the specific information of the transmitted mobile unit to the management station and is transmitted from the management station. The configuration is such that the radio link information of each base station scheduled for handover is transferred to the mobile unit, and the management station receives each request signal from the mobile unit received via the base station for each handover planned along the route of the mobile unit. In this configuration, the radio link information of the base station is transmitted to the mobile unit in a lump.

  The present invention stores the radio link information of each base station to which the mobile unit performs handover before high-speed movement, and confirms the trigger of the handover, and the radio link information of the next base station to be handed over from the stored information And execute handover to the base station. This eliminates the need for the “search” process of the handover procedure, and shortens the time required for the handover. In addition, since the time required for reading the stored information is extremely short, it is possible to acquire the radio link information of the base station to be handed over reliably even when the mobile is moving at high speed, and execute the handover.

  In addition, since the radio link information of each base station to which the mobile unit is handed over is a configuration in which the mobile unit is collectively transferred and accumulated from the management station during a period when the mobile unit is not moving at high speed, and is read out at the time of handover. Unlike the method described in Patent Document 1, network resources are not consumed by communicating with the management station at every handover.

  FIG. 1 shows an embodiment of a wireless LAN system of the present invention. In the figure, base stations 11, 12, and 13 form wireless zones 14, 15, and 16, respectively, and a mobile unit 17 belonging to the base station 11 moves from the wireless zone 14 to the wireless zone 15. . The base stations 11, 12, and 13 are connected to the management station 18 by wire or wireless, and a server 20 is connected to the management station 18 via the Internet 19.

  Note that the moving body 17 is assumed to be a train, for example, and it is assumed that the management station 18 knows base stations (herein, 12 and 13) scheduled to be handed over with movement. In the mobile unit 17, for example, a wireless terminal in the vehicle is connected to a base station outside the vehicle via the access point installed in the vehicle, and further, the Internet 19, and a broadband wireless LAN communication service can be provided. To do.

  The management station 18 manages radio link information of a plurality of base stations including the base stations 11, 12, and 13, and the request signal from the mobile body 17 causes the mobile station 17 to be handed over from now on. Wireless link information is transmitted to the mobile unit 17 in a batch.

  Before starting high-speed movement, the mobile unit 17 transmits a request signal for acquiring radio link information of each base station scheduled for handover to the base station 11 currently connected via the radio link, It includes storage means 21 for storing the radio link information of each base station scheduled for handover transmitted from the management station 18, and obtains the radio link information of the base station scheduled for handover from the storage means 21 when the trigger for handover is confirmed. Then, the handover process is performed.

  When the base station 11 receives the request signal transmitted from the mobile unit 17, the base station 11 transfers the request signal and the specific information of the transmitted mobile unit 17 to the management station 18, and schedules the handover schedule transmitted from the management station 18. The radio link information of each base station 12, 13 is transferred to the mobile unit 17.

  FIG. 2 shows a processing procedure example of the fast handover method in the wireless LAN of the present invention. Here, it is assumed that the mobile body 17 is in the wireless zone 14 and is in communication with the base station 11 and moves sequentially from the wireless zone 14 to the wireless zones 15 and 16.

  Before starting communication with the server 20, the mobile unit 17 obtains radio link information of a base station that is scheduled to be handed over to the base station 11 that is currently connected via the radio link. An information request signal is transmitted (S11). When receiving the radio link information request signal, the base station 11 includes the specific information of the mobile unit 17 in the radio link information request signal and transfers it to the management station 18 (S12). When the management station 18 receives the radio link information request signal including the specific information of the mobile unit 17, the management station 18 confirms the route of the mobile unit 17 from the specific information, and the base station scheduled to be handed over as the mobile unit 17 moves The stations 12 and 13 are grasped, and the radio link information of the base stations 12 and 13 is collectively transmitted to the mobile unit 17 via the base station 11 (S13). The base station 11 transfers the radio link information of the base stations 12 and 13 scheduled for handover transmitted from the management station 18 to the mobile unit 17 (S14). The mobile unit 17 stores the radio link information of the base stations 12 and 13 to be handed over transmitted from the management station 18 in the storage device 21, and receives a storage completion notification from the storage device 21 (S15, S16).

  The above sequence is executed before the mobile body 17 starts moving or during a period during which the mobile body 17 is moving at a low speed, that is, during a period in which the mobile station 17 stays in the radio zone 14 of the base station 11 for a sufficiently long time. When the sequence of S11 to S16 is completed, user data can be transmitted and received between the mobile unit 17 and the server 20 via the base station 11 and the management station 18 (S17, S18, S19).

  The mobile unit 17 detects a decrease in the reception level from the base station 11 in the wireless zone 14, or detects an increase in the reception level from the base station 12, or from the management station 18 that the base station 11 relays. When a handover command (S20, S21) or the like is received, it is recognized as a trigger for handover. The mobile unit 17 transmits a signal for obtaining the radio link information of the base station 12 to be handed over next to the storage device 21 (S22). The storage device 21 searches the radio link information of the base station 12 to be handed over next from the stored radio link information of the base station scheduled to be handed over, and notifies the mobile unit 17 (S23). The radio link information here refers to a frequency used by the base station, a MAC address, a modulation method, a supported radio modulation rate, and the like.

  Similar to the conventional “Execution” procedure, the mobile unit 17 sets its own radio transceiver in accordance with the frequency of the base station 12, and sends a connection request signal for linking with the base station 12. Transmit to the base station 12 (S24). Upon receiving this connection request signal, the base station 12 returns a connection response signal to the mobile unit 17 and transmits a registration signal to the management station 18 to register the mobile unit 17 (S25, S26). When this registration is completed, user data can be transmitted and received between the mobile unit 17 and the server 20 via the base station 12 and the management station 18 (S27, S28, S29).

  Next, when the mobile unit 17 similarly recognizes the opportunity of handover in the wireless zone 15, the radio link information of the base station 13 to be handed over next is stored from the storage device 21 through the processing procedures S30 to S36 similar to S20 to S26. Acquire and execute handover to the base station 13.

The figure which shows embodiment of the wireless LAN of this invention. The figure which shows the example of a process sequence of the high-speed handover method in wireless LAN of this invention. The figure explaining the time ratio of the hand-over in a wireless LAN system. The figure which shows the structure of the conventional mobile communication system. The figure which shows the process sequence of the hand-over in the conventional mobile communication system.

Explanation of symbols

11, 12, 13 Base station 14, 15, 16 Wireless zone 17 Mobile 18 Management station 19 Internet 20 Server 21 Storage device

Claims (2)

A wireless LAN system including a mobile body that moves at high speed along a predetermined route, wherein a plurality of base stations form wireless zones in which communication is possible, and the mobile body switches base stations with which the wireless zone communicates In a fast handover method in a wireless LAN,
Before the mobile unit starts high-speed movement, a request signal for acquiring radio link information of a base station scheduled to be handed over along the route to a base station currently connected via a radio link Send
When the base station receives the request signal, it transfers the request signal and the specific information of the transmitted mobile unit to the management station,
The management station is connected to the plurality of base stations in a wired or wireless manner, manages radio link information of the plurality of base stations, and receives the request signal including the specific information of the mobile body. The radio link information of each base station scheduled to be handed over along the route of the mobile station is sent to the mobile body in batch via the base station with which the mobile body is communicating,
The base station forwards radio link information of each base station scheduled for handover to the mobile unit, and the mobile unit accumulates radio link information of each base station scheduled for handover and confirms the trigger of the handover. A method of fast handover in a wireless LAN, characterized in that radio link information of a base station to be handed over is acquired from stored information and a handover process is performed. A wireless LAN system that includes a mobile body that moves at a high speed along a predetermined route, forms a wireless zone in which a plurality of base stations can communicate with each other, and performs handover for switching the base station with which the mobile body communicates as the wireless zone moves In
A management station that is connected to the plurality of base stations by wire or wirelessly and manages radio link information of the plurality of base stations;
Before the mobile unit starts high-speed movement, a request signal for acquiring radio link information of a base station scheduled to be handed over along the route to a base station currently connected via a radio link And means for accumulating radio link information of each base station scheduled for handover transmitted from the management station, and when confirming the trigger of the handover, the radio of the base station to be handed over from the accumulated information It is a configuration that acquires link information and performs handover processing,
When the base station receives the request signal, the base station transfers the request signal and the specific information of the transmitted mobile unit to the management station, and transmits the radio link information of each base station scheduled for handover transmitted from the management station. It is configured to transfer to the mobile body,
The management station collectively transmits radio link information of each base station scheduled for handover along the route of the mobile unit to the mobile unit in response to a request signal from the mobile unit received via the base station. A wireless LAN system, characterized in that

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