JP4632883B2 - Train radio system - Google Patents

Description

  The present invention relates to an improvement in inter-base station movement (IP handover) technology of a train radio system.

In the case of a telephone system in which a radio is mounted on a moving body, such as a train radio, it communicates with base stations (access points) that are scattered in various locations in advance and connected one after another as they move. continue. If the terminal does not move and stays in one place, it may be connected to a specific access point, but the range that can be covered by one access point is limited in distance, so as the terminal moves It is necessary to switch the connection to another access point during communication. This access point switching operation is called handover.
There are two types of handover methods, the make after break method and the make before break method, depending on the connection state of the link before and after switching. The present invention relates to the method of the make after break method.
For example, Patent Literature 1 discloses the configuration of a conventional train radio system, and describes an operation at the time of handover. Patent Document 2 describes not only a train radio system but also a handover of a mobile phone or the like.
In order to help understanding of the operation of the present invention, a conventional radio handover operation disclosed in Patent Document 2 will be described.

The plurality of base stations are connected to a communication line (generally wired) via a home agent (referred to as HA). A radio of one base station is connected to a home agent and is a foreign agent (hereinafter referred to as FA) that exchanges communication data (generally a plurality of communications), and a radio that is connected to the FA and performs communication data transmission and other control. A radio (for example, a leaky coaxial cable radio, hereinafter referred to as an LCX radio) that transmits and receives signals between the adapter and the radio adapter and communicates with a radio (car station) mounted on the train. Including.
That is, base station = FA + wireless adapter + LCX wireless device.
On the other hand, the on-board station is a mobile router (hereinafter referred to as MR) that exchanges communication data with one or more telephone terminal devices installed on the train, and a radio that is connected to the MR and performs signal transmission and other control. It includes an adapter and a radio that exchanges signals with the wireless adapter and performs wireless communication with the base station.
That is, on-board station = MR + wireless adapter + wireless device.
The radio wave transmitted from the base station radio includes a color code which is different for each base station and is information for identifying the base station. When a train (terminal radio, hereinafter referred to as onboard station) moves from a communicable zone covered by one base station to a communicable zone covered by another base station, the onboard station changes the received color code. Detects that the communicable zone has changed (hereinafter referred to as inter-base station movement). Then, handover is executed according to the following procedure.

Conventional handover procedure (explained by taking data transmission from onboard station to base station as an example).
1) The change in the color code included in the signal received from the base station is detected by the on-board station radio, and the movement between the base stations is detected.
2) The on-board station radio that detects the movement between the base stations notifies the MR of the switching. The MR stops transmitting the data that was being transmitted and accumulates the data in the buffer. The wireless adapter makes a slot request to the wireless adapter of the base station and prompts the FA of the base station for router advertisement.
3) The FA of the base station makes a router advertisement to the MR of the onboard station.
4) The MR of the on-board station that has received the router advertisement transmits location registration information to the FA of the base station.
5) When the location registration is completed, the base station FA responds to the on-board station MR.
6) The MR of the on-board station notifies the FA on the base station side of the traffic volume of the data stored in the buffer.
7) The FA of the base station assigns a slot corresponding to the traffic volume and performs slot allocation. The on-board MR starts transmitting the stored data to the new base station, and finally communication between the new base station and the on-board station is resumed.
The above switching sequences 1) to 7) are performed in a time of about 0.5 to 2 seconds. Although this time is short, the data in the meantime is accumulated in the buffer and is interrupted. Therefore, there is a problem that when the time is interrupted, the caller is uncomfortable.

There are also the following problems. That is, data transmission from the base station side to the on-board station is executed in the same procedure (of course, FA and MR are interchanged) from 1) to 6) above. Of course, there is no data accumulation. (Data that has not been transmitted is stored in the buffer of the base station before switching that has been communicated until then). Therefore, at the time of starting communication with a new base station, a base station that newly communicates must newly take in data to be transmitted via the home agent (HA). Therefore, there is a problem that time loss occurs.
JP 2000-165312 A JP2003-179616

In the conventional train radio system, when the onboard station moves between base stations due to the movement of the train, switching from the communication state in the original base station zone to the completion of allocation of the radio band in the new base station zone As described above, the transmission / reception of the control signal must be performed at least six times. During that time, the original contents of communication cannot be transmitted, so that the state of communication interruption apparently continues for a long time. This is because, for example, when a train moves like a bullet train and many users move simultaneously at a high speed (ie, a large amount of data), the line congestion for retransmitting delayed data due to communication interruption during movement between zones The packet delay not only gives the user an unpleasant feeling, but also has a problem that sometimes it is difficult to connect the telephone.
In addition, the new base station after switching has to take transmission data from the communication line after completion of the handover, resulting in a problem of time loss.

The present invention was made to reduce the communication interruption time during IP handover and to eliminate the discomfort given to the user. It is possible to perform IP handover between the train station and the base station in a shorter time. Is to provide a train radio system.
It is another object of the present invention to provide a train radio system that can perform data transmission from a base station to an onboard station after completion of handover in a shorter time.

The train radio system according to the present invention uses an IP address between an on-board station mounted on a train traveling on a railroad track and any one of a plurality of base stations arranged along the railroad track. A train radio system for communication,
A server connected to a communication line and communicating using an IP address, a first router connected to the server,
An integrated second router that is connected to the first router and includes a wireless adapter function for controlling the transmission and reception of communication data, and the railway connected to the integrated second router and the railway A plurality of base stations having a leaky coaxial cable radio connected to a leaky coaxial cable installed along the track,
A wireless device mounted on the train that moves between the plurality of base stations and communicating with the leaky coaxial cable wireless device, and a wireless adapter function connected to the wireless device to exchange communication data and perform other controls An integrated mobile router, and an on-board station that switches between base station zones of each of the plurality of base stations by handover,
The integrated second router and the integrated mobile router both perform a radio layer slot assignment request and an IP layer location registration at the time of the handover in one data communication .

Since the train radio system of the present invention shortens the communication disconnection time at the time of handover, it can eliminate the discomfort given to the user.
In addition, after the handover is completed, data transmission from the base station to the on-board station can be performed in a shorter time for data whose transmission is delayed during the handover.

Embodiment 1 FIG.
A train radio system according to Embodiment 1 of the present invention will be described below with reference to FIG. In FIG. 1, a server 8 connected to a general telephone line (not shown) (generally in a broad sense, including not only a telephone dedicated line but also an Internet line), and a home agent connected to the server 8 ( (Hereinafter referred to as HA) 7 is provided. HA7 is connected to a plurality of base stations including base station 1 and base station 4 (only two 1 and 4 are shown in the figure) and is in communication with moving onboard station 9 I will explain it. The white arrow indicates the movement of the onboard station 9.

Home Agent (H A) 7 is in the present invention is referred to as a first router. A home agent (HA) is used for a mobile IP (in-vehicle station in the present invention) that moves between a plurality of base stations, and is a mobile connected to an unspecified network by connecting the networks to each other. A router that controls the transfer of packets with IP, and forwards packets transmitted to the original address of Mobile IP to the destination address of the current Mobile IP.

The base station 1 includes an integrated foreign agent (hereinafter referred to as integrated FA) 2 and a leaky coaxial cable radio (hereinafter referred to as LCX radio) 3. The integrated FA 2 has a wireless adapter function for controlling transmission and reception of communication data, and has a function for centrally managing the wireless layer and the IP layer.
Since the base station 4 and a plurality of other base stations (not shown) have the same configuration, detailed description thereof is omitted.
Specific functions of the integrated FA 2 are a routing function, traffic control, location management, slot allocation management, and radio status monitoring.

  The integrated foreign agents (FA) 2 and 5 are also called integrated second routers in the present invention. A foreign agent (FA) is used for a mobile IP (in-vehicle station in the present invention) that moves between a plurality of base stations, and is a mobile connected to an unspecified network by connecting the networks to each other. A router that controls the transfer of packets with IP, and forwards packets transmitted to the original address of Mobile IP to the destination address of the current Mobile IP. The function of the device is almost the same as the above-mentioned home agent, but it is called a foreign agent (FA) depending on the position of the network used.

  The onboard station 9 has a configuration including an integrated mobile router (hereinafter referred to as an integrated MR) 11 and a radio 10 (a radio having a function capable of transmitting and receiving between the LCX radio 3). It has a wireless adapter function for controlling transmission / reception of communication data, and a function for centrally managing the wireless layer and the IP layer.

  Specific functions of the integrated MR 11 are a routing function, traffic control, location management, slot allocation management, and radio status monitoring.

The time chart of FIG. 2 shows the procedure of the handover operation when the communication performed between the onboard station 9 and the base station 4 in FIG. 1 is switched to the communication between the onboard station 9 and the base station 1. This will be described with reference to the flowchart of FIG. In FIG. 2, the vertical axis indicates the passage of time from the top to the bottom, and each vertical axis indicates each related unit.
That is, the auxiliary line 200 communicates with the base station 4, the auxiliary line 201 indicates the state of the integrated FA2, the auxiliary line 202 indicates the state of the LCX radio 3, the auxiliary line 203 indicates the state of the radio 10, and the auxiliary line Reference numeral 204 denotes the state of the integrated MR.

The handover procedure in the train radio system of the present invention.
11) Different color codes are transmitted from the LCX radio 3 of the base station 1 and the LCX radio 6 of the base station 4, and the radio 10 of the onboard station 9 first receives the color code of the base station 4. ing. (Reference numeral 100 in FIG. 2, step S01 in FIG. 3)
12) When the onboard station 9 moves and crosses between zones of the base station (called zone shift), the integrated MR 11 changes the received color code from that of the base station 4 to that of the base station 1. Detect changes. (Reference numeral 101 in FIG. 2, step S02 in FIG. 3).
13) This detects that the onboard station 9 has moved between the communication zones of the two base stations. (Step S03 in FIG. 3)
14) The integrated MR 11 stops transmitting data that has been transmitted until then, and starts accumulating data in a buffer (not shown) (reference numeral 102 in FIG. 2, step S04 in FIG. 3).
15) The MR 11 simultaneously performs location registration, slot request for the wireless section, and traffic notification to the integrated FA 2 of the base station 1 (reference numeral 103 in FIG. 2, step S05 in FIG. 3). The term “simultaneously” means that all of these are communicated in one data communication.

16) The integrated FA 2 performs location registration, assigns slots according to the traffic volume (reference numeral 104), and sends a response of completion of location registration to the integrated MR 11 (reference numeral 105 in FIG. 2, step S06 in FIG. 3). . This response is also performed in one communication.
17) The integrated MR 11 of the on-board station 9 starts transmitting the data stored in the buffer (reference numeral 106 in FIG. 2, step S07 in FIG. 3). That is, communication after zone switching is started with the base station after switching.

  In the above procedures 11) to 17), since the integrated MR 11 is used, slot request, location registration, and traffic notification can be executed in one communication, and control signals are transmitted and received twice (one way three times) Since it is simplified as compared with the prior art, the time until the IP handover is completed in the new zone is shortened. That is, it is about half of the time.

Embodiment 2. FIG.
With the train radio system described in the first embodiment, the handover time is shortened. In the first embodiment, the example in which data is transmitted from the onboard station 9 side to the base station side has been described. In the example of the first embodiment, there is no particular inconvenience for transmitting the data accumulated by the onboard station 9 during the handover after the handover is completed. However, when data is transmitted from the base station side to the on-board station side, as described in the background art section, the new base station does not store data, so after the handover is completed, data must be taken in from HA7 again. There is a problem that must be done. This causes a delay in packet transmission. This is referred to as packet delay for the convenience of the following description.

FIG. 4 illustrates an operation for reducing the packet delay after the handover according to the second embodiment. The vertical axis in FIG. 4 indicates the passage of time, and each vertical axis indicates each related unit. Also, all of # 1, # 2, # 3, and # 4 indicate packet numbers to be transmitted from the HA 7 to the onboard station 9.
The auxiliary line 401 shows the state of HA7, the auxiliary line 402 shows the state of the base station 1, the auxiliary line 403 shows the state of the base station 4, and the auxiliary line 404 shows the state of the onboard station 9. In order to help understanding, the flow of FIG. 4 is shown in a flowchart in FIG.

  Similar to the first embodiment, the case where the on-board station 9 enters the zone of the base station 1 from the zone of the base station 4 will be described. In the first place, base stations are arranged along the track in the train radio system. In addition, as described above, the current position of the train (position information indicating the current base station area, not the exact position) can be determined from the color code of the base station received by the onboard station. Can be grasped by returning to the base station side. The direction of travel is naturally known, and since the arrangement of base stations is known in advance, the next base station to be switched is also known.

21) The HA 7 estimates that the next handover is near, for example, from the passage of time after the completion of the previous handover.
22) When the next handover is approaching, the HA 7 has previously registered with the FA 5 of the base station 4 while registering with the base station 4 while the onboard station 9 is still communicating with the base station 4. The MR 11 position information (here, the position information refers to information indicating the address number to which data is to be transmitted) is changed to the base station (FA2 of the base station 1 in the example of FIG. 4) to be switched next. ) And register. (Reference numeral 411 in FIG. 4)
23) Thereby, after the notification, the HA 7 transmits the data transmission destination not only to the FA 5 of the base station 4 but also to the FA 2 of the base station 1, that is, the data to which the sequence number is assigned to the two base stations. Broadcast transmission starts. (Reference numeral 412 in FIG. 4)
24) In principle, the timing for starting broadcast communication should be started immediately before the handover is started (for example, several seconds before), but the timing of whether or not it is just before the handover is the speed of the train. It may be affected by fluctuations and cannot always be accurately grasped. For example, after entering a certain zone, it may be started after a predetermined time has elapsed. The predetermined time here is different depending on whether the next base station zone to enter is near or far, so it is preferable to set a different value for each base station based on such a difference in physical distance. Of course, the broadcast communication may be started immediately after the handover is completed regardless of the distance. (Reference numeral 411 in FIG. 4)

25) As the onboard station 9 exits the zone of the base station 4, the handover is started and data is accumulated in the base station 4. In the example of FIG. 4, data is stored as # 3, # 4. On the other hand, for the base station 1 that has received the broadcast communication, the previous data is also stored without being transmitted, and is rewritten and updated in order from the old data according to the buffer capacity. For example, in the example of FIG. 4, the base station 1 stores data # 1, # 2, # 3, # 4,. (Reference numeral 413 in FIG. 4)
26) When the handover is completed (handover is executed according to the procedure described in the first embodiment), the base station 1 tries to discharge the accumulated data sequentially, but the data of # 1 # 2 is already on the vehicle Station 9 has already been received and it is useless to retransmit.
27) Therefore, in the present invention, when the handover is completed (handover is performed according to the procedure described in the first embodiment), the integrated MR 11 notifies the FA 2 of the sequence number of the received data before the start of the handover. . That is, in the example of FIG. 4, it is notified that # 2 has been received, and it is only necessary to receive from # 3. (Reference numeral 414 in FIG. 4)
28) From the notified sequence number, FA2 selects data to be transmitted next without transmission, that is, data # 3 in the example of FIG. 4, and transmits it to MR11. (Reference numeral 415 in FIG. 4)

The above flow is shown again in FIG.
In step S51 of FIG. 5, the HA 7 detects that the next handover is imminent.
In step S52, location registration is also performed for the next base station to be switched.
In step S53, broadcast transmission is started from HA7 to two base stations. Data is accumulated in the base station used after switching.
In step S54, handover is started.
In step S55, handover is completed and the onboard station notifies the received data number.
In step S56, the new base station selects untransmitted data from the stored data and transmits it.
According to the procedures 21) to 28), in the past, when the sequence number to be transmitted was found, the packet data had to be newly collected from the HA 7 to the base station 1 in advance. Since the data is stored in the new base station, there is no need to take it in again, and the time is reduced accordingly.
With the method of the second embodiment, efficient data communication can be performed without excess or deficiency before and after IP handover, and packet delay can be reduced.

The handover procedure used in the train radio system of the present invention is not limited to train radio, but is used for communication between a plurality of base stations and mobile terminals such as mobile phones, automobile phones, and ship / aviation public radio phones. Can be used.

It is a figure which shows schematic structure of the train radio system of Embodiment 1 of this invention. It is a time chart which shows the handover procedure in the train radio system of FIG. It is a flowchart explaining the operation | movement of FIG. It is a time chart which shows the procedure of the packet delay reduction of this invention. It is a flowchart explaining the operation | movement of FIG.

Explanation of symbols

1 base station, 2 integrated FA (Foregin Agent),
3 LCX radios, 4 base stations,
5 Integrated FA (Foregin Agent),
6 LCX radios, 7 HA (Home Agent), 8 servers,
9 on-board stations, 10 radios,
11 Integrated MR (Mobile Router),
12 base stations, 13 FA (Foregin Agent),
14 wireless adapter,
15 LCX radio, 16 on-board station, 17 radio, 18 wireless adapter,
19 MR (Mobile Router).

Claims (5)

A train radio system that communicates between an on-board station mounted on a train traveling on a railroad track and any one of a plurality of base stations arranged along the railroad track using an IP address,
A server connected to a communication line and communicating using an IP address, a first router connected to the server,
An integrated second router that is connected to the first router and includes a wireless adapter function for controlling the transmission and reception of communication data, and the railway connected to the integrated second router and the railway A plurality of base stations having a leaky coaxial cable radio connected to a leaky coaxial cable installed along the track,
A wireless device mounted on the train that moves between the plurality of base stations and communicating with the leaky coaxial cable wireless device, and a wireless adapter function connected to the wireless device to exchange communication data and perform other controls An integrated mobile router, and an on-board station that switches between base station zones of each of the plurality of base stations by handover,
The integrated second router and the integrated mobile router both perform a radio layer slot allocation request and an IP layer location registration at the time of the handover in one data communication. Wireless system. The first router performs location registration separately from the location registration prior to the start of the handover with respect to a base station in a base station zone where the train enters next, and the onboard station actually exists. The train radio system according to claim 1, wherein data is broadcasted to a base station in a base station zone and a base station in a base station zone to which the onboard station enters next. 3. The location registration performed by the first router prior to the start of handover with respect to the base station is started after a predetermined time elapses after completion of the previous handover. Train radio system as described in.   The train radio system according to claim 3, wherein the predetermined time is set to a different value for each base station zone that enters next.   The first router assigns a sequence number to the data to be transmitted to the integrated second router of the base station and transmits the data, and the onboard station enters a new base station zone to complete the handover. Then, the integrated mobile router notifies the integrated second router of the sequence number received before that time, and the integrated second router performs the integration based on the notified sequence number. The train radio system according to claim 2, wherein a sequence number of data to be transmitted to the mobile router is determined.

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