On-vehicle radio station, ground radio station, train radio system, handover determination method, and handover position management method

Abstract

An on-vehicle radio station (20) mounted on a train comprises: a reception level measurement unit (21) that measures a reception level when a signal transmitted from a first ground radio station is received; a handover determination unit (23) that, on the basis of a handover position serving as a reference for handover from the first ground radio station to a second ground radio station, train position information indicating the position of the train, and the reception level, all of which are received from the first ground radio station, determines that handover from the first ground radio station to the second ground radio station is being performed in cases where the reception level after the train arrives at the handover position is equal to or less than a stipulated reception level threshold value, and outputs a handover instruction for instructing handover from the first ground radio station to the second ground radio station; and a radio control unit (24) that performs handover from the first ground radio station to the second ground radio station on the basis of the handover instruction.

Description

On-board radio station, ground radio station, train radio system, handover determination method, and handover position management method

[0001] The present disclosure relates to an on-board radio station used in a train, a ground radio station, a train radio system, a handover determination method, and a handover position management method.

[0002] Conventionally, a radio device mounted on a train transmits and receives various control information by wireless communication with a ground base station installed along the track. Since the position of the radio device mounted on the train changes as the train moves, a handover is performed to switch the ground radio base station to communicate with, thereby enabling continuous wireless communication with the ground base station installed along the track. For example, Patent Literature 1 discloses a technology in a train control device in which the ground control device stores a handover position and reserves a radio channel when the train approaches the handover position, thereby preventing communication interruptions and deterioration of communication quality during the actual handover.

[0003] Patent No. 3451543

[0004] A radio train control system that controls train operation by radio communication between the train and a ground system requires train position information. However, because the train measures its position using a tachometer generator or the like, errors in the train position can occur due to wheel slippage, skidding, and other factors. The radio train control system performs control that takes into account errors in train position caused by the tachometer generator or the like by extending the length of the train according to the train's traveling distance. However, because the control is performed by extending the length of the train, a discrepancy occurs between the actual train position and the controlled train position. Therefore, when a system that controls the timing of handover based on the train position, as in Patent Document 1, is applied to a radio train control system, there is a problem that handover may not be performed at the appropriate time.

[0005] The present disclosure has been made in view of the above, and aims to provide an on-board radio station that can perform handover at an appropriate train position.

[0006] In order to solve the above-mentioned problems and achieve the object, the present disclosure provides an on-board radio station mounted on a train, the on-board radio station including: a reception level measurement unit that measures a reception level when receiving a signal transmitted from a first terrestrial radio station; a handover determination unit that determines to perform a handover from the first terrestrial radio station to the second terrestrial radio station based on a handover position that is a reference position for handover from the first terrestrial radio station to the second terrestrial radio station, train position information that indicates the position of the train, and the reception level received from the first terrestrial radio station, if the reception level becomes equal to or lower than a specified reception level threshold after the train reaches the handover position, and outputs a handover instruction that instructs the handover from the first terrestrial radio station to the second terrestrial radio station; and a radio control unit that performs a handover from the first terrestrial radio station to the second terrestrial radio station based on the handover instruction.

[0007] The on-board radio station of the present disclosure has the effect of being able to perform handover at an appropriate train position.

[0008] FIG. 1 shows an example of the configuration of a train radio system according to embodiment 1. FIG. 1 shows an example of the configuration of an on-board radio station according to embodiment 1. FIG. 2 shows a state in which a ground radio station transmits a handover position to an on-board radio station in the train radio system according to embodiment 1. FIG. 3 shows a state in which an on-board radio station reaches a handover position in the train radio system according to embodiment 1. FIG. 4 shows a state in which an on-board radio station passes a handover position in the train radio system according to embodiment 1. FIG. 5 shows a state when an on-board radio station determines to perform a handover in the train radio system according to embodiment 1. Flowchart showing the operation of a ground radio station according to embodiment 1. Flowchart showing the operation of an on-board radio station according to embodiment 1. FIG. 6 shows an example in which a processing circuit realizing an on-board radio station according to embodiment 1 is configured with a processor and a memory. FIG. 7 shows an example in which a processing circuit realizing an on-board radio station according to embodiment 1 is configured with dedicated hardware.

[0009] Hereinafter, an on-board radio station, a ground radio station, a train radio system, a handover determination method, and a handover position management method according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0010] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a train radio system 30 according to a first embodiment. The train radio system 30 includes an on-board radio station 20 mounted on a train (not shown) and ground radio stations 10a and 10b installed on the ground. In the following description, the ground radio stations 10a and 10b will be referred to as the ground radio station 10 when there is no need to distinguish between them. The train radio system 30 is a system used in, for example, CBTC (Communications Based Train Control). Although the illustration in Fig. 1 is simplified, the train radio system 30 actually includes a plurality of ground radio stations 10 and a plurality of on-board radio stations 20.

[0011] FIG. 1 illustrates a situation in which an onboard radio station 20 mounted on a train moves from left to right as the train moves, immediately before switching the connected terrestrial radio station 10 from terrestrial radio station 10a to terrestrial radio station 10b through handover. The upper reception level diagram in FIG. 1 shows the measurement results of the reception level of the signal from terrestrial radio station 10a measured by the onboard radio station 20 as the onboard radio station 20 moves from left to right in FIG. 1, with the left-hand peak representing the measurement results of the reception level of the signal from terrestrial radio station 10b measured by the onboard radio station 20. As described below, the onboard radio station 20 is equipped with a directional antenna that is directional in the direction of train travel. Therefore, when the train passes the terrestrial radio station 10, the reception level of the signal from the terrestrial radio station 10 that the train has passed drops sharply. The reception level threshold is a threshold used in the operation of the onboard radio station 20, as described below. This also applies to subsequent similar figures.

[0012] First, the configuration and operation of the terrestrial radio station 10 will be described. Fig. 2 is a diagram showing an example of the configuration of the terrestrial radio station 10 according to the first embodiment. The terrestrial radio station 10 includes a handover position management unit 11, a handover position storage unit 12, a transmitter 13, and a terrestrial radio station antenna 14. In the examples shown in Figs. 1 and 2, the terrestrial radio station antenna 14 is located outside the terrestrial radio station 10, but it is assumed that the terrestrial radio station antenna 14 is also included in the terrestrial radio station 10. For convenience of explanation, the terrestrial radio station 10 shown in Fig. 2 is assumed to be the first terrestrial radio station, which is the terrestrial radio station 10a shown in Fig. 1. Furthermore, the terrestrial radio station 10b shown in Fig. 1 is assumed to be the second terrestrial radio station.

[0013] The handover position storage unit 12 stores handover positions that are reference positions at which the onboard radio station 20 mounted on the train performs handover from the terrestrial radio station 10a to the terrestrial radio station 10b. The handover positions stored in the handover position storage unit 12 are adjusted by the handover position management unit 11, as will be described later. The initial values ​​of the handover positions stored in the handover position storage unit 12 are stored in the handover position storage unit 12, for example, by a person in charge of the railway operator that operates the train.

[0014] The transmitter 13 reads the handover position from the handover position storage unit 12 and transmits the handover position to the on-board radio station 20. The transmitter 13 also transmits to the on-board radio station 20 train control information, which is control information for the train obtained from a control center of the ground system (not shown) or the like.

[0015] The handover position management unit 11 adjusts the handover position stored in the handover position storage unit 12 based on the handover position fed back from the on-board radio station 20. Here, the handover position management unit 11 may directly feed back, i.e., receive, the handover position fed back from the on-board radio station 20, or may indirectly feed back, i.e., receive, the handover position fed back from the on-board radio station 20 via the terrestrial radio station 10b. This is because the on-board radio station 20 feeds back the handover position to the terrestrial radio station 10a or the terrestrial radio station 10b. Since both the terrestrial radio stations 10a and 10b are connected to the control center of the above-mentioned ground system, the terrestrial radio station 10a can also indirectly receive feedback of the handover position via the terrestrial radio station 10b. Therefore, the handover position management unit 11 can adjust the handover position stored in the handover position storage unit 12 based on the handover position fed back directly from the on-board radio station 20 or the handover position fed back via the terrestrial radio station 10b.

[0016] The ground radio station antenna 14 is an antenna used when the handover position management unit 11 receives feedback of the handover position from the on-board radio station 20, and when the transmitter 13 transmits the handover position, train control information, etc. to the on-board radio station 20.

[0017] Next, the configuration and operation of the on-board radio station 20 will be described. Fig. 3 is a diagram showing an example of the configuration of the on-board radio station 20 according to the first embodiment. The on-board radio station 20 includes a reception level measuring unit 21, a handover position storage unit 22, a handover determining unit 23, a radio control unit 24, and an on-board radio station antenna 25. In the examples of Figs. 1 and 3, the on-board radio station antenna 25 is located outside the on-board radio station 20, but it is assumed that the on-board radio station antenna 25 is also included in the on-board radio station 20.

[0018] The reception level measurement unit 21 measures the reception level of a signal transmitted from the terrestrial radio station 10a before handover from the terrestrial radio station 10a to the terrestrial radio station 10b. The reception level is, for example, a received signal strength indicator (RSSI). The onboard radio station 20 may use other parameters instead of the reception level as long as it can grasp the state of wireless communication between the onboard radio station 20 and the terrestrial radio stations 10a and 10b. The reception level measurement unit 21 measures the reception level of a signal transmitted from the terrestrial radio station 10b after handover from the terrestrial radio station 10a to the terrestrial radio station 10b. In this way, the reception level measurement unit 21 switches the terrestrial radio station 10 that is the source of the signal for which the reception level is to be measured each time the onboard radio station 20 performs a handover. The reception level measurement unit 21 stores the handover position of the signal received from the terrestrial radio station 10a in the handover position storage unit 22 and outputs train control information to a control device of a train integrated management system (not shown) that controls the running of the train. Furthermore, the reception level measuring unit 21 outputs the measured reception level to the handover determining unit 23. The reception level measuring unit 21 may output the measured reception level to the handover determining unit 23 when requested by the handover determining unit 23.

[0019] The handover position storage unit 22 stores the handover position from the terrestrial radio station 10a to the terrestrial radio station 10b, received from the terrestrial radio station 10a, before a handover from the terrestrial radio station 10a to the terrestrial radio station 10b. After a handover from the terrestrial radio station 10a to the terrestrial radio station 10b, the handover position storage unit 22 stores the handover position from the terrestrial radio station 10b to the next terrestrial radio station 10 (not shown), received from the terrestrial radio station 10b. In this way, the handover position storage unit 22 changes the stored handover position every time the on-board radio station 20 performs a handover.

[0020] The handover determination unit 23 determines whether to perform a handover based on the handover position, which is a reference position for handover from the terrestrial radio station 10a to the terrestrial radio station 10b, received from the terrestrial radio station 10a, train position information indicating the position of the train, and the reception level. The handover determination unit 23 reads and acquires the handover position from the handover position storage unit 22, acquires train position information from the control device of the above-mentioned train integrated management system, etc., and acquires the reception level from the reception level measurement unit 21. If the reception level becomes equal to or lower than a specified reception level threshold after the train reaches the handover position, the handover determination unit 23 determines to perform a handover from the terrestrial radio station 10a to the terrestrial radio station 10b, and outputs a handover instruction to the radio control unit 24 to instruct a handover from the terrestrial radio station 10a to the terrestrial radio station 10b. The reception level threshold is set to a value greater than the reception level at which the onboard radio station 20 cannot communicate wirelessly with the terrestrial radio station 10. The handover determination unit 23 also outputs the train position information together with the handover instruction to the radio control unit 24. When the handover determination unit 23 determines that a handover will not be performed, it may output a notification indicating that a handover will not be performed to the radio control unit 24. Furthermore, the handover determination unit 23 may request the reception level measurement unit 21 to acquire the reception level from the reception level measurement unit 21 after determining that the train has reached the handover position, and may acquire the reception level from the reception level measurement unit 21.

[0021] The radio control unit 24 performs handover from the terrestrial radio station 10a to the terrestrial radio station 10b based on the handover instruction acquired from the handover determination unit 23. The method of handover from the terrestrial radio station 10a to the terrestrial radio station 10b in the radio control unit 24 may be a general handover method and is not particularly limited. The radio control unit 24 feeds back the train position information acquired from the handover determination unit 23 to the terrestrial radio station 10a or the terrestrial radio station 10b as the handover position where the handover from the terrestrial radio station 10a to the terrestrial radio station 10b actually took place. After the handover from the terrestrial radio station 10a to the terrestrial radio station 10b is performed, the radio control unit 24 does not communicate with the terrestrial radio station 10a, but is still communicating with the terrestrial radio station 10a at the stage when the train position information is acquired from the handover determination unit 23. Therefore, the radio control unit 24 may feed back the handover position to the terrestrial radio station 10a before the handover is completed, or may feed back the handover position to the terrestrial radio station 10b after the handover is completed.

[0022] The on-board radio station antenna 25 is a directional antenna having directivity and used for wireless communication with the terrestrial radio station 10a and the terrestrial radio station 10b. In the example of Fig. 1 etc., the on-board radio station antenna 25 has directivity in the direction of train travel. The on-board radio station antenna 25 is used when the reception level measuring unit 21 receives a handover position, train control information, etc. from the terrestrial radio station 10a, and when the radio control unit 24 feeds back the handover position to the terrestrial radio station 10a or the terrestrial radio station 10b.

[0023] Next, the operation of the on-board radio station 20 when it performs a handover from the terrestrial radio station 10a to the terrestrial radio station 10b will be described. Fig. 4 is a diagram showing a state in which the terrestrial radio station 10a has transmitted a handover position to the on-board radio station 20 in the train radio system 30 according to the first embodiment. As explained above in the section on the operations of the terrestrial radio station 10a and the on-board radio station 20, the transmitter 13 of the terrestrial radio station 10a transmits the handover position to the on-board radio station 20. The handover position shown in Fig. 4 is indicated by the handover position transmitted from the transmitter 13 of the terrestrial radio station 10a to the on-board radio station 20. The on-board radio station 20 stores the received handover position in the handover position storage unit 22.

[0024] 5 is a diagram showing a state in which the on-board radio station 20 has reached the handover position in the train radio system 30 according to embodiment 1. The handover determination unit 23 of the on-board radio station 20 determines that the train position indicated by the train position information has reached the handover position, but the reception level of the signal from the terrestrial radio station 10a measured by the reception level measurement unit 21 is higher than the reception level threshold, so that handover from the terrestrial radio station 10a to the terrestrial radio station 10b should not be performed.

[0025] 6 is a diagram showing a state in which the on-board radio station 20 has passed the handover position in the train radio system 30 according to embodiment 1. The handover determination unit 23 of the on-board radio station 20 determines that the train position indicated by the train position information has passed the handover position, but the reception level of the signal from the terrestrial radio station 10a measured by the reception level measurement unit 21 is higher than the reception level threshold, so that handover from the terrestrial radio station 10a to the terrestrial radio station 10b should not be performed.

[0026] 7 is a diagram showing a state when the onboard radio station 20 determines to perform a handover in the train radio system 30 according to the first embodiment. After the train position indicated by the train position information reaches the handover position, the reception level of the signal from the terrestrial radio station 10a measured by the reception level measuring unit 21 falls below the reception level threshold, and therefore the handover determination unit 23 of the onboard radio station 20 determines to perform a handover from the terrestrial radio station 10a to the terrestrial radio station 10b. In this way, even when the train position indicated by the train position information reaches the handover position, if the reception level of the signal from the terrestrial radio station 10a is sufficiently high, i.e., greater than the reception level threshold, the reception level is stable, and so the handover determination unit 23 of the onboard radio station 20 does not dare to perform a handover, but determines to perform a handover after the reception level of the signal from the terrestrial radio station 10a falls below the reception level threshold.

[0027] 8 is a flowchart showing the operation of the terrestrial radio station 10 according to the first embodiment. In the terrestrial radio station 10, the transmitter 13 reads out a handover position from the handover position storage unit 12 and transmits it to the on-board radio station 20 (step S101). The handover position manager 11 receives feedback on the handover position from the on-board radio station 20 (step S102). The handover position manager 11 adjusts the handover position stored in the handover position storage unit 12 based on the received feedback on the handover position (step S103).

[0028] It should be noted that the handover location management unit 11 does not need to adjust the handover location to the actual handover location indicated in the handover location feedback. The handover location management unit 11 adjusts the handover location stored in the handover location storage unit 12, for example, by slightly shifting it forward or backward, based on the comparison result between the handover location indicated in the handover location feedback received at the previous handover and the handover location indicated in the handover location feedback received this time.

[0029] 9 is a flowchart showing the operation of the on-board radio station 20 according to the first embodiment. In the on-board radio station 20, when the reception level measurement unit 21 receives a handover position from the terrestrial radio station 10, it stores the handover position in the handover position storage unit 22. The handover determination unit 23 acquires the handover position from the handover position storage unit 22 (step S201). The handover determination unit 23 acquires train position information from a control device of the train integrated management system or the like (step S202). The handover determination unit 23 determines whether the train has reached the handover position based on the train position information and the handover position (step S203). If the train has not reached the handover position (step S203: No), the handover determination unit 23 returns to step S202.

[0030] When the train reaches the handover position (step S203: Yes), the handover determination unit 23 acquires the reception level from the reception level measurement unit 21 and confirms the reception level (step S204). When the reception level is greater than the reception level threshold (step S205: No), the handover determination unit 23 returns to step S204. When the reception level is equal to or less than the reception level threshold (step S205: Yes), the handover determination unit 23 outputs a handover instruction to the radio control unit 24. As a result, the radio control unit 24 performs the handover (step S206). The radio control unit 24 feeds back the handover position where the handover was actually performed to the terrestrial radio station 10 (step S207).

[0031] Next, the hardware configuration of the on-board radio station 20 will be described. In the on-board radio station 20, the handover position storage unit 22 is a memory. The on-board radio station antenna 25 is an antenna element. The reception level measurement unit 21, the handover determination unit 23, and the radio control unit 24 are realized by processing circuits. The processing circuit may be a processor and memory that executes a program stored in memory, or may be dedicated hardware.

[0032] 10 is a diagram showing an example in which a processing circuit 90 that realizes the on-board radio station 20 according to the first embodiment is configured with a processor 91 and a memory 92. When the processing circuit 90 is configured with the processor 91 and the memory 92, each function of the processing circuit 90 of the on-board radio station 20 is realized by software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the memory 92. The processing circuit 90 realizes each function by having the processor 91 read and execute the program stored in the memory 92. That is, the processing circuit 90 includes the memory 92 for storing a program that results in the processing of the on-board radio station 20 being executed. It can also be said that these programs cause a computer to execute the procedures and methods of the on-board radio station 20.

[0033] The above program can also be said to be a program that causes the on-board radio station 20 to execute the following steps: a first step in which the reception level measuring unit 21 measures the reception level when receiving a signal transmitted from the terrestrial radio station 10a; a second step in which the handover determination unit 23 determines, based on the handover position that is a reference position for handover from the terrestrial radio station 10a to the terrestrial radio station 10b, train position information that indicates the position of the train, and the reception level received from the terrestrial radio station 10a, that a handover should be performed from the terrestrial radio station 10a to the terrestrial radio station 10b if the reception level becomes equal to or lower than a specified reception level threshold after the train has reached the handover position, and outputs a handover instruction instructing a handover from the terrestrial radio station 10a to the terrestrial radio station 10b; and a third step in which the radio control unit 24 performs a handover from the terrestrial radio station 10a to the terrestrial radio station 10b based on the handover instruction.

[0034] Here, the processor 91 may be a CPU (Central Processing Unit), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor), etc. The memory 92 may be, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, or a DVD (Digital Versatile Disc).

[0035] Fig. 11 is a diagram showing an example in which the processing circuit 93 that realizes the on-board radio station 20 according to embodiment 1 is configured with dedicated hardware. When the processing circuit 93 is configured with dedicated hardware, the processing circuit 93 shown in Fig. 11 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Each function of the on-board radio station 20 may be realized by the processing circuit 93 separately for each function, or all functions may be realized by the processing circuit 93 together.

[0036] It is also possible to realize some of the functions of the on-board radio station 20 with dedicated hardware and some with software or firmware. In this way, the processing circuit can realize each of the above-mentioned functions with dedicated hardware, software, firmware, or a combination of these.

[0037] The hardware configuration of the on-board radio station 20 has been described above, but the hardware configuration of the terrestrial radio station 10 is also similar. In the terrestrial radio station 10, the handover position storage unit 12 is a memory. The terrestrial radio station antenna 14 is an antenna element. The handover position management unit 11 and the transmission unit 13 are realized by processing circuits. The processing circuit may be a processor and memory that executes a program stored in a memory, or may be dedicated hardware.

[0038] As described above, according to this embodiment, the onboard radio station 20 mounted on a train acquires a handover position, which is a reference position for handover, from the terrestrial radio station 10, and performs handover when the reception level of the signal from the terrestrial radio station 10 falls below a reception level threshold after the train reaches the handover position. As a result, even in cases where the exact position of the train cannot be determined because the train's running is controlled while extending its length in a radio-based train control system, the onboard radio station 20 can perform handover while avoiding communication interruptions and deterioration in communication quality by taking into account the reception level state. The onboard radio station 20 can perform handover at an appropriate train position even without information on the exact train position.

[0039] Furthermore, after performing a handover, the onboard radio station 20 feeds back the handover position where the handover actually took place to the terrestrial radio station 10. This allows the terrestrial radio station 10 to optimize the stored handover position using the fed-back handover position. Furthermore, by capturing changes in the handover position stored in the terrestrial radio station 10, personnel at the railway operator operating the train can capture changes in the radio wave environment along the line where the train is running, malfunctions of the train, and the like, and use this information for maintenance.

[0040] Embodiment 2 In the first embodiment, the handover determination unit 23 of the on-board radio station 20 determines to perform a handover when the reception level falls below the reception level threshold after the train reaches the handover position. However, in a radio communication state in which the reception level does not fluctuate gradually but fluctuates violently up and down without being stable, even if the conditions for performing a handover are temporarily met and a handover is performed, there is a possibility that the radio communication between the on-board radio station 20 and the terrestrial radio station 10b that is the handover destination will not be stable.

[0041] Therefore, the handover determination unit 23 may determine to perform handover from the terrestrial radio station 10a to the terrestrial radio station 10b when the number of times the reception level has fallen below the reception level threshold exceeds a specified number of times threshold. Alternatively, the handover determination unit 23 may determine to perform handover from the terrestrial radio station 10a to the terrestrial radio station 10b when the cumulative period during which the reception level has fallen below the reception level threshold exceeds a specified cumulative period threshold. The handover determination unit 23 may also use these two determination methods in combination. That is, the handover determination unit 23 may determine to perform handover from the terrestrial radio station 10a to the terrestrial radio station 10b when at least one of the following occurs: the number of times the reception level has fallen below the reception level threshold exceeds a specified number of times threshold; and the cumulative period during which the reception level has fallen below the reception level threshold exceeds a specified cumulative period threshold. This allows the on-board radio station 20 to perform handover in a more stable state.

[0042] The handover determination unit 23 may further operate in such a way that it appropriately changes the reception level threshold, the number threshold, the cumulative period threshold, etc. depending on the weather and other conditions on the day the train is operating.

[0043] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0044] 10, 10a, 10b terrestrial radio stations, 11 handover position management unit, 12, 22 handover position storage unit, 13 transmission unit, 14 terrestrial radio station antenna, 20 on-board radio station, 21 reception level measurement unit, 23 handover determination unit, 24 radio control unit, 25 on-board radio station antenna, 30 train radio system, 90, 93 processing circuit, 91 processor, 92 memory.

Claims

1. An on-vehicle radio station mounted on a train, comprising: a reception level measurement unit that measures a reception level when receiving a signal transmitted from a first ground radio station; a handover determination unit that determines, based on a handover position that is a position serving as a reference for handover from the first ground radio station to a second ground radio station, train position information indicating the position of the train, and the reception level, that when the reception level becomes equal to or lower than a specified reception level threshold after the train reaches the handover position, a handover is to be performed from the first ground radio station to the second ground radio station, and outputs a handover instruction for instructing the handover from the first ground radio station to the second ground radio station; a radio control unit that performs a handover from the first ground radio station to the second ground radio station based on the handover instruction; wherein the handover determination unit outputs the train position information to the radio control unit together with the handover instruction; the radio control unit feeds back the train position information acquired from the handover determination unit to the first ground radio station or the second ground radio station as a handover position where the handover from the first ground radio station to the second ground radio station has actually been performed; An on-vehicle radio station characterized by the above.

2. a handover position storage unit that stores the handover position received from the first ground radio station; The on-vehicle radio station according to claim 1, further comprising the above.

3. a directional antenna used for wireless communication with the first ground radio station and the second ground radio station; The on-vehicle radio station according to claim 1, further comprising the above.

4. The handover determination unit determines that a handover is to be performed from the first ground radio station to the second ground radio station when at least one of the following conditions is met: the number of times the reception level has become equal to or lower than the reception level threshold exceeds a specified number-of-times threshold, and the cumulative period during which the reception level has become equal to or lower than the reception level threshold exceeds a specified cumulative-period threshold. The on-vehicle radio station according to any one of claims 1 to 3, characterized by the above.

5. A ground radio station that is a first ground radio station, A handover position storage unit that stores a handover position, which is a position serving as a criterion for a on-vehicle radio station mounted on a train to perform handover from the first ground radio station to the second ground radio station; A transmission unit that transmits the handover position to the on-vehicle radio station; A handover position management unit that adjusts the handover position stored in the handover position storage unit based on the handover position feedback from the on-vehicle radio station; A ground radio station characterized by comprising the above.

6. The handover position management unit adjusts the handover position stored in the handover position storage unit based on the handover position directly feedback from the on-vehicle radio station or the handover position feedback via the second ground radio station. The ground radio station according to claim 5, characterized by the above.

7. Comprising the on-vehicle radio station according to claim 1 and the ground radio station according to claim 5, or comprising the on-vehicle radio station according to claim 1 and the ground radio station according to claim 6; A train radio system characterized by the above.

8. A handover determination method for an on-vehicle radio station mounted on a train, comprising: A first step in which a reception level measurement unit measures the reception level when receiving a signal transmitted from a first ground radio station; A second step in which a handover determination unit determines to perform handover from the first ground radio station to the second ground radio station and outputs a handover instruction for instructing the handover from the first ground radio station to the second ground radio station based on a handover position, which is a position serving as a criterion for handover from the first ground radio station to the second ground radio station received from the first ground radio station, train position information indicating the position of the train, and the reception level, when the reception level becomes equal to or lower than a specified reception level threshold after the train reaches the handover position; A third step in which a radio control unit performs handover from the first ground radio station to the second ground radio station based on the handover instruction; Including; In the second step, the handover determination unit outputs the train position information to the radio control unit together with the handover instruction. In the third step, the wireless control unit feeds back the train position information obtained from the handover determination unit to the first ground radio station or the second ground radio station as the handover position where the handover from the first ground radio station to the second ground radio station has actually been performed. A handover determination method characterized by the above.

9. The on-vehicle radio station includes a handover position storage unit that stores the handover position received from the first ground radio station. The handover determination method according to claim 8, characterized by the above.

10. The on-vehicle radio station includes a directional antenna used for wireless communication with the first ground radio station and the second ground radio station. The handover determination method according to claim 8, characterized by the above.

11. In the second step, when the number of times the reception level becomes equal to or lower than the reception level threshold exceeds a specified number threshold, and when at least one of the cumulative periods during which the reception level becomes equal to or lower than the reception level threshold exceeds a specified cumulative period threshold, the handover determination unit determines that a handover is to be performed from the first ground radio station to the second ground radio station. The handover determination method according to any one of claims 8 to 10, characterized by the above.

12. A handover position management method for a ground radio station that is a first ground radio station, comprising: The ground radio station: A handover position storage unit that stores a handover position, which is a position serving as a reference for a handover from a first ground radio station to a second ground radio station by an on-vehicle radio station mounted on a train; Comprising: A first step in which a transmission unit transmits the handover position to the on-vehicle radio station; A second step in which a handover position management unit adjusts the handover position stored in the handover position storage unit based on the handover position fed back from the on-vehicle radio station; A handover position management method characterized by including the above.

13. In the second step, the handover position management unit adjusts the handover position stored in the handover position storage unit based on the handover position directly fed back from the on-vehicle radio station or the handover position fed back via the second ground radio station. The handover position management method according to claim 12, characterized by the above.