JP3338873B2 - Road-to-vehicle communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road-to-vehicle communication system for performing communication between a plurality of base stations installed along a road and vehicles running on the road, and more particularly to a ROF (Radio Radio) system.
on fiber: wireless transmission using an optical fiber).

[0002]

2. Description of the Related Art At present, a road-vehicle communication system using broadband wireless communication is being studied as a communication system for providing advanced information services. The road-to-vehicle communication system is a system for performing wireless communication between a road and a vehicle, that is, between base stations installed along the road and terminals mounted on vehicles running on the road.

[0003] By constructing a broadband road-to-vehicle communication system, for example, a CD-R conventionally installed in a vehicle is used.
A service such as receiving map information for navigation read from a recording medium by an OM drive device or a DVD-ROM drive device from the outside of the vehicle through communication can be realized. Among such road-vehicle communication systems, in particular, ROF (Radio on Fibe)
r: wireless transmission using optical fiber)
Since the base station can be used without obsolescence for a long period of time, it is considered to be promising as infrastructure on expressways and the like.

In general, in broadband communication, the transmission energy per bit is small due to the limitation of the total transmission power. Therefore, when a broadband road-vehicle communication system is to be constructed, the communication coverage area per base station becomes small. Would. This means that even in a system in which the same signal is transmitted from a plurality of adjacent base station groups (local base station groups), the communication coverage area (signals having the same local base station group) can be easily determined due to frequency utilization efficiency. Cannot be enlarged).

[0005] From such a background, in a road-vehicle communication system for performing wireless communication between a base station and a wireless terminal mounted on a vehicle moving at a high speed, the time required for the wireless terminal to pass through the communication coverage area of the base station. Becomes very short, and the frequency of handover increases. For this reason, in the case where it takes time for the handoff, the communication may be forcibly disconnected.

[0006]

As described above, in a road-vehicle communication system having a wide band, since a communication coverage area of a base station is small, a radio terminal moving at high speed together with a vehicle can instantaneously communicate with a different base station. Since the transition to the area occurs, handover control cannot be performed in time, and there is a possibility that forced disconnection of communication may occur. In order to realize stable and continuous communication, it is essential to make such handover control surely successful.

An object of the present invention is to provide a road-vehicle communication system capable of performing broadband communication and performing stable handover control to enable stable communication.

[0008]

In order to solve the above-mentioned problems, a road-to-vehicle communication system according to the present invention provides a road-to-vehicle communication system for performing wireless communication with a wireless terminal mounted on a vehicle running on a road and moving. A plurality of local base stations are installed at predetermined intervals along with a plurality of local base stations divided into a plurality of local base station groups, and provided for each of the local base station groups. A plurality of integrated base stations managed for each local base station group;
A plurality of transmission paths for transmitting signals between a local base station in the local base station group and an integrated base station corresponding to the local base station group; and communication coverage by the local base station. The areas overlap each other within the same local base station group and between adjacent local base station groups, and furthermore, how to move the wireless terminal in the overlapping area within the same local base station group of the communication coverage area.
Than the length in the direction, characterized in that it is set to satisfy the relationship a length greater in the direction of movement of the radio terminal of the overlap region between adjacent remote base station group.

More specifically, the transmission beam pattern of each local base station in the local base station group is determined based on the local base station located at the start and end of the wireless terminal moving in the communication coverage area by the local base station. The transmission beam pattern is set so as to have a wider relationship than the transmission beam pattern of the local base station located at the center.

As described above, a plurality of local base stations are made to correspond to one integrated base station to form a local base station group, and each of the integrated base stations forms a local base station of a corresponding local base station group. By transmitting the same optical modulation signal to each other, the communication coverage area of each local base station group is expanded, the handoff rate is reduced, and the length of the overlapping area of the communication coverage area of the adjacent local base station groups is reduced. By making the length longer than the length of the overlap area of the communication coverage area in the same local base station group, it is possible to perform a handoff determination with sufficient time, and handover control is performed while the wireless terminal passes through the former overlap area. It can be done easily.

According to a preferred embodiment, the present invention uses an optical fiber as a transmission line connecting the integrated base station and the local base station, and the integrated base station converts a radio modulation signal input from the outside into an optical modulation signal. The local base station is configured to convert the optical modulation signal input from the integrated base station via the optical fiber into a wireless modulation signal and transmitted by the antenna. .

In the present invention, it is desirable that the transmission power of each base station is non-uniform. The transmission power of each base station can be controlled by, for example, the optical power of the optical modulation signal input to each base station.

In such a configuration, the transmission power of the local base station in each local base station group is reduced by at least the moving direction end side of the wireless terminal in the communication coverage area of the local base station group (the wireless terminal leaves. The transmission power of one local base station located on the side (side) is set to have a smaller relationship than the transmission power of the other local base stations.

In this case, the electric field strength of the radio wave radiated from the base station located at the end of the radio terminal in the direction of movement of the radio terminal in the communication coverage area is weakened. By recognizing that the end of the coverage area in the moving direction has been approached, preparation for handover control can be started at an early stage, and handover control can be performed more reliably.

In the present invention, at least one local base station located at an end of a group of adjacent local base stations may be installed so that the communication coverage areas of the local base stations overlap each other in substantially the entire area. desirable.

According to this configuration, the overlapping area of the communication coverage area between adjacent local base station groups extends over a wide area. In this overlapping area, the radio terminal is connected to two different integrated base stations. Since the radio waves of the radio modulation signals from the two local base stations can be received, handover control can be easily realized even when the radio terminal passes through these overlapping areas at high speed.

Further, according to the present invention, the transmission power of the local base station in the overlapping area of the communication coverage area between adjacent local base station groups shows that the transmission power gradually decreases in the moving direction of the wireless terminal. By providing such a gradient, it is also possible to recognize that the wireless terminal has entered these overlapping areas and to prompt execution of handover control.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. [First Embodiment] FIG. 1 shows an outline of a road-vehicle communication system according to a first embodiment of the present invention. In this road-vehicle communication system, a plurality of wireless devices 1 and wireless devices 1
An integrated base station 2 provided one-to-one with a plurality of local base stations 3 and optical fibers 4 installed at intervals along the road are disposed on both sides of the road. Wireless communication is performed with the wireless terminal 6 installed in the wireless terminal 5. The wireless device 1 and the integrated base station 2 are installed in, for example, a building, and the local base station 3 is installed near a road with the transmission beam pattern directed to the road.

In the present invention, the content of the information service provided for communication is not particularly limited. For example, the wireless device 1 and the wireless terminal 6 are connected to a second generation cordless telephone system (ARIB STD).
-28). As another example, wireless LA
N, applications such as mobile phones (including PHS) and pagers are also conceivable.

Here, a plurality of local base stations 3 correspond to each of the integrated base stations 2, and the local base stations 3 connected to the same integrated base station 2 via the optical fiber 4 are: .. Respectively constitute local base station groups G1, G2,. In other words, the local base station 3 corresponds to each of the integrated base stations 2 and a plurality of local base station groups G1, G2,.
Are managed by the integrated base station 2 for each local base station group G1, G2,... .. Between the local base stations 3 in the local base station groups G1, G2,... And the integrated base stations 2 corresponding to the local base station groups G1, G2,. Transmission and reception of an optical modulation signal are performed.

The communication coverage area of the local base station 3 is the same as the local base station groups G1, G2,.
Are overlapped in the local base station groups G1, G2,... Adjacent to each other, and further, compared with the length of the overlapping area in the same local base station group G1, G2,. The length of the overlapping area between the adjacent local base station groups G1, G2,... Is set to be large.

Next, each part of FIG. 1 will be described in detail. (Regarding Wireless Device 1) The wireless device 1 converts a signal to be finally transmitted to the wireless terminal 6 into a wireless modulated signal and outputs the modulated signal to the corresponding integrated base station 2. , A wireless modulation signal input through the optical fiber 4 and the integrated base station 2.

(Regarding Integrated Base Station 2) Integrated Base Station 2
Is converted into a light-modulated signal from the wireless device 1 at the time of transmission (at the time of reception of the wireless terminal 6) and transmitted to the optical fiber 4, and is transmitted at the time of reception (at the time of transmission of the wireless terminal 6). The optical modulation signal input via the fiber 4 is converted into a wireless modulation signal and transmitted to the wireless device 1.

FIG. 2 shows the configuration of the transmission system of the integrated base station 2. The light sources 11-1 to 11-N are, for example, semiconductor lasers, and light emitted from these light sources 11-1 to 11-N is input to the optical modulators 12-1 to 12N. Optical modulator 1
2-1 to 12N intensity-modulate the light from the light sources 11-1 to 11-N with the same wireless modulation signal from the wireless device 1, and convert the resulting optical modulation signal into an optical fiber 4-1.
To 4-N. From the integrated base station 2 to the optical fiber 4-
The optical modulation signals transmitted to 1 to 4-N are transmitted to the local base stations 3 in the local base station group corresponding to the integrated base station 2 respectively.

The transmission power control section 13 reads a transmission power setting pattern which is preset according to the average moving speed of the wireless terminal 6 and is stored in a memory (not shown), and a desired communication coverage area is statically formed in advance. Like
The switches 14-1 to 14-N inserted on the wireless modulation signal input sides of the optical modulators 12-1 to 12N are switching-controlled. The method of selecting the transmission power setting pattern in the transmission power control unit 13 is not particularly limited, and the switches 14-1 to 14-N are used to select the transmission power control.
Was used, but the method is not limited to this method.

Further, the transmission power control unit 13 controls the optical output of the light sources 12-1 to 12N, or changes the attenuation of an optical attenuator (not shown) or the amplification factor of an optical amplifier, for example. It also has a function of controlling the transmission power of the local base station 3 by changing the optical power of the optical modulation signal obtained at -1 to 12N. By controlling the optical power of the optical modulation signal in this way, the transmission power of the local base station 3 that receives the optical modulation signal transmitted by the optical fibers 4-1 to 4-N can be controlled.

(About Local Base Station 2) Local Base Station 3
When transmitting (when receiving the wireless terminal 6), the optical modulation signal transmitted from the integrated base station 2 via the optical fiber 4 is converted into a wireless modulation signal, transmitted to the wireless terminal 6, and received. At the time (at the time of transmission by the wireless terminal 6), the radio wave transmitted from the wireless terminal 6 is converted into an optical modulation signal and transmitted to the optical fiber 4. The wireless communication frequency between the integrated base station 2 and the local base station 3 is, for example, a frequency such as 5.8 GHz or 30 GHz. The number of local base stations 3 corresponding to one integrated base station 2 is, for example, about 3 to 10 when the communication frequency is the former, and about several tens when the latter is the latter.

FIG. 3 shows the configuration of the transmission system of the local base station 3. The optical modulation signal input from the optical fiber 4 is converted into a wireless modulation signal by a photodetector 21 such as a photodiode, then power-amplified by an amplifier 22 and supplied to an antenna 23. Thereby, the wireless modulation signal is radiated to the space as a radio wave from the antenna 23 and received by the wireless terminal 6. When the transmission system of the local base station 3 is configured as described above, the transmission power from the antenna 23 can be controlled by the optical power of the optical modulation signal input from the optical fiber 4.

(Regarding Transmission Power Control Unit 13) On the other hand, the transmission power control unit 13 described with reference to FIG. 2 is not limited to this, but uses, for example, a personal computer 31 as shown in FIG. In this configuration, various transmission power setting patterns stored in the switch 32 are read out, and the switches 14-1 to 14-N shown in FIG. 2 are turned on / off.

Next, a communication coverage area and a transmission beam pattern by the local base station in this embodiment will be described with reference to FIG. In FIG. 5, three integrated base stations 2-1 to 2-2 and 2-3 are shown.
In practice, more integrated base stations are installed. The local base stations 3-1 to 3-9 are each integrated base station 2- in this example.
The mobile station is divided into local base station groups each including three local base stations corresponding to 1, 2, and 2-3. That is,
The integrated base station 2-1 includes the local base station 3 of the local base station group G1.
-1, 3-2, 3-3, the integrated base station 2-2, the local base stations 3-4, 3-5, 3-6 of the local base station group G2, and the integrated base station 2-3. The local base station 3-7 of the local base station group G3,
3-8 and 3-9 are connected via the optical fiber 4, respectively.

The local base stations 3-1 to 3-9 have communication coverage areas A1 to A9, respectively, and the communication coverage areas A1 to A9 are adjacent to each other in the moving direction of the wireless terminal 6. ３−3-9 partially overlap each other. That is, the communication coverage areas A1 to A
9 is B1 and B in the local base station group G1, G2, G3.
2, B3 and B4, overlapping in the area of B5 and B6, between adjacent local base station groups (between G1 and G2, between G2 and G3)
Also in the areas C1 and C2.

Here, the communication coverage areas A1 to A9
Area B1 in each local base station group G1, G2, G3
The point is that the lengths of the overlapping areas C1 and C2 between adjacent local base station groups are made longer than the lengths of B6 to B6. Such overlapping areas B1 to B6 and C1, C2
Can be realized by adjusting the transmission beam patterns of the local base stations 3-1 to 3-9.

More specifically, as shown in FIGS. 5 and 6, the starting point of the moving direction of the wireless terminal 6 in the communication coverage area by each of the local base station groups G1, G2, G3 (the wireless terminal 6).
Base station 3-1 or 3 located at the end on the side where
-4, 3-7, and the local base stations 3-3, 3-6, 3 located at the rear end of the communication coverage area in the moving direction of the wireless terminal 6 (the end on the side from which the wireless terminal 6 leaves). The transmission beam pattern of −9 is set to the local base station 3- located at the center of the local base station groups G1, G2, and G3 (the center of the communication coverage area by each of the local base station groups G1, G2, and G3).
What is necessary is just to widen from the transmission beam patterns of 2, 3-5 and 3-8.

The difference between such transmission beam patterns is as follows.
For example, the directivity of the antenna 23 in FIG. 3 used in the local base stations 3-1 to 3-9 is determined by using the local base stations 3-1 to 3-7.
And 3-3, 3-6, 3-9 and local base stations 3-2, 3-
5, 3-8, or the local base station 3- located at the beginning of the movement direction of the wireless terminal 6 in the communication coverage area of each of the local base station groups G1, G2, G3.
1, 3-4, 3-7, and a local base station 3- located at the rear end in the moving direction of the wireless terminal 6 in these communication coverage areas.
The transmission power of 3,3-6,3-9 is transmitted to the local base station groups G1, G
2, a local base station 3-2, 3- located at the center of G3
This can be realized by making the transmission power larger than 5, 3-8.

As described above, the adjacent local base station groups G1, G
Overlap area C of communication coverage area between G2 and G3
1 and C2, that is, by increasing the length in the moving direction of the wireless terminal 6, the wireless terminal 6
Handover control can be easily performed with a margin while passing through C2.

Further, in the present embodiment, as shown in FIG. 6, the local base station 3 located at the end of the wireless terminal 6 in the moving direction of the communication coverage area of each of the local base station groups G1, G2, G3. -3, 3-6, 3-9, the transmission power of other local base stations 3-1, 3-2, 3-4, 3-
5, 3-7, and 3-8. However, in FIG. 6, the transmission power is represented by the electric field strength. As described above, such transmission power control is performed by the integrated base station 2-
Local base station groups G1, G2, G3 from 1, 2, 2-3
By controlling the optical power of the optical modulation signal transmitted to the local base station.

In this manner, the base stations 3-3, 3--3 located at the end of the radio terminal 6 in the movement direction in the communication coverage area.
By weakening the electric field strength of the radio wave radiated from 6, 3-9, the wireless terminal 6 recognizes that the end of the communication coverage has been approached from the decrease in the received electric field strength, and starts preparing for the handover control early. Therefore, the possibility of successful handover control can be increased.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG. The road-to-vehicle communication system according to the present embodiment includes, in the same basic configuration as that of the first embodiment, at least one local base station that exists at each end of the adjacent local base station groups G1, G2, and G3. The communication coverage areas of the respective devices are installed so as to overlap almost all areas.

That is, in this embodiment, as shown in FIG. 7, the local base station group G1 includes the local base stations 3-1, 3-2, 3-3, 3 corresponding to the integrated base station 2-1. -4, the local base station group G2 includes the local base stations 3-5, 3-6, 3-7, 3-8, 3-9 connected to the integrated base station 2-2, and the local base station group G3. Is a local base station 3- connected to the integrated base station 2-3.
9, 3-10, 3-11, and 3-12.

Then, the second local base station 3-3 from the right end of the local base station group G1 and the local base station 3-5 at the left end of the local base station group G2 are installed in substantially the same place, Similarly, the local base station 3-4 at the right end of the local base station group G1, the second local base station 3-6 from the left end of the local base station group G2, and the second local base station 3-6 from the right end of the local base station group G2. Of the local base station 3-8 and the local base station group G3 at the left end of the local base station group G3.
2 and a second local base station 3-11 from the left end of the local base station group G3 are installed at substantially the same location.

In this way, the communication coverage area of the local base stations at the ends located at substantially the same location in the local base station groups G1, G2, and G3,
That is, the communication coverage area by the local base stations 3-3 and 3-5, the communication coverage area by the local base stations 3-4 and 3-6, the communication coverage area by the local base stations 3-8 and 3-10, and the station. The communication coverage areas of the base stations 3-9 and 3-11 substantially overlap each other.
Therefore, the overlapping area of the communication coverage area between the adjacent local base station groups G1, G2, and G3 extends to a very wide area corresponding to the communication coverage area of the two local base stations in this example. Become.

These adjacent local base station groups G1, G2,
In the overlapping area of the communication coverage area between G3, the wireless terminal 6 has two different integrated base stations 2-1 and 2-2, 2
-2 and 2-3, the radio waves of the radio modulation signals from the two local base stations respectively connected thereto can be received. Therefore, even if the radio terminal 6 passes through these overlapping areas at high speed, a handover with a high success rate is possible. Control can be realized.

In this case, the wireless terminal 6 is located in these overlapping areas.
Requires a control signal to prompt the execution of handover control when entering, but this control signal is substituted by a reception signal from the local base station of the handover destination, and when this reception signal is detected, handover is performed. It is also possible to prompt the execution of the control.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIG. The road-to-vehicle communication system according to the present embodiment uses the functions of the transmission power control unit 13 in the integrated base station 2 described in FIGS. 9 is a system in which the transmission power control of No. 9 is combined with the configuration of the second embodiment.

In this embodiment, as shown in FIG. 8, similarly to FIG. 7, the local base station group G1 includes local base stations 3-1 to 3-2 corresponding to the integrated base station 2-1. 3, 3-4, the local base station group G2 includes local base stations 3-5, 3-6, 3-7, 3-8, 3-9 connected to the integrated base station 2-2.
In FIG. 8, the integrated base station 2-3 shown in FIG. 7 and the local base station group G3 (local base stations 3-9, 3
-10, 3-11, 3-12) are omitted.

Further, the second local base station 3-3 from the right end of the local base station group G1 and the local base station 3-5 on the left end of the local base station group G2 are installed in substantially the same place. The point that the local base station 3-4 at the right end of the local base station group G1 and the second local base station 3-6 from the left end of the local base station group G2 are installed at substantially the same place is also shown in FIG. Same as 7.

In a road-vehicle communication system using ROF,
As described above, the transmission power control of the local base stations 3-1 to 3-9 is transmitted from the integrated base stations 2-1 to 2-2 to the local base stations 3-1 to 3-9 via the optical fiber 4. This can be easily performed by controlling the optical power of the modulated optical signal.

By utilizing this function, in the present embodiment, FIG.
The transmission power distribution of remote base stations in the communication coverage area overlap region by G2 and remote base station group G1 as shown in, such that the transmission power with respect to the direction of movement of the wireless terminal 6 is gradually Tsuyokara weak By providing a decreasing gradient, it is also possible to recognize that the wireless terminal 6 has entered these communication coverage area overlapping areas and to prompt execution of handover control.

That is, when the radio terminal 6 is in the local base station group G
1, passing through the communication coverage area overlapping area between G2,
The local base station group G from which the wireless terminal 6 was receiving until then
When a handover from 1 to a neighboring local base station group G2 is expected, the local base station group G1 of the handover source is located at the local base station 3-3, 3 near the local base station group G2 of the handover destination. Communication is performed with transmission power as weak as -4. As a result, the reception power from the local base station of the handover source decreases, and the handover control is executed due to the deterioration of the transmission quality.

[Other Embodiments] As another embodiment of the present invention, in a communication coverage area of each local base station group, a local base station on the terminal side in the moving direction of the wireless terminal (destination end side of the wireless terminal). The transmission power of the local base station at the center of the communication coverage area and at the beginning of the moving direction of the wireless terminal (the entrance end of the wireless terminal) is fixedly increased. Accordingly, it is possible to secure a preparation time for the handover control between the local base station groups, and to avoid a forced disconnection due to a sudden decrease in reception power.

In the above embodiment, each integrated base station and each corresponding base station in the local base station group are individually connected by an optical fiber, but the integrated base station and the local base station are connected individually. The station groups may be connected by one optical fiber, and the optical signal on one optical fiber may be distributed to each local base station using, for example, an optical tap in the local base station group. In this case, in order to make transmission power non-uniform between the local base stations, for example, the power of the optical signal distributed from the optical tap in each local base station may be adjusted.

[0052]

As described above, according to the present invention, the preparation time for the handover control can be reduced by increasing the overlapping area of the communication coverage area by the adjacent local base stations connected to different integrated base stations. Since sufficient security is ensured, reliable handover control can be realized even for a wireless terminal mounted on a vehicle and moving at a high speed. Therefore, stable and continuous communication can be performed without disconnection of communication in road-to-vehicle communication.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a road-to-vehicle communication system according to a first embodiment of the present invention;

FIG. 2 is a block diagram showing a configuration of a transmission system of the integrated base station according to the first embodiment.

FIG. 3 is a block diagram showing a configuration of a transmission system of a local base station according to the first embodiment;

FIG. 4 is a block diagram showing a configuration of a transmission power control unit according to the first embodiment.

FIG. 5 is a diagram illustrating a communication coverage area and a transmission beam pattern by each local base station in the first embodiment.

FIG. 6 is a diagram for explaining a difference in transmission power between local base stations in the first embodiment.

FIG. 7 is a diagram showing a configuration of a road-to-vehicle communication system according to a second embodiment of the present invention and a communication coverage area of each local base station;

FIG. 8 is a diagram showing a configuration of a road-to-vehicle communication system according to a third embodiment of the present invention and a communication coverage area of each local base station.

FIG. 9 is a diagram showing a transmission power distribution of a local base station in an overlapping area of a communication coverage area between adjacent local base stations in the third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wireless apparatus 2, 2-1 to 2-3 ... Integrated base station 3, 3-1 to 3-13 ... Local base station 4 ... Optical fiber 5 ... Vehicle 6 ... Wireless terminal G1 to G3 ... Local base station Groups A1 to A9: Communication coverage area by local base station B1 to B6: Communication coverage area overlapping area within local base station group C1 to C2: Communication coverage area overlapping area by adjacent local base station group 11 -1 to 11-N light source 12-1 to 12-N optical modulator 13 transmission power control unit 14-1 to 14-N switch 21 photodetector 22 amplifier 23 antenna 31 personal computer 32 …Storage device

Continuing on the front page (72) Inventor Fumihide Kojima 3-4 Hikarinooka, Yokosuka City, Kanagawa Prefecture Inside the Communications Research Laboratory Yokosuka Radio Communication Research Center of the Ministry of Posts and Telecommunications (72) Inventor Shigeru Oshima Toshiba-cho, Komukai-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Toshiba Research and Development Center Co., Ltd. (72) Inventor Manabu Mukai No. 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Research and Development Center Co., Ltd. JP-A-5-300077 (JP, A) JP-A-11-178052 (JP, A) JP-A-11-261478 (JP, A) JP-A-50-105001 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 H04Q ⁷ /00-7/36

Claims (6)

(57) [Claims] An apparatus is provided at predetermined intervals along a road so as to perform wireless communication with a wireless terminal mounted on a vehicle running on a road and moving, and is divided into a plurality of local base station groups. A plurality of local base stations; a plurality of integrated base stations that are provided corresponding to each of the local base station groups and manage the plurality of local base stations for each of the local base station groups; A transmission path for transmitting a signal between a local base station in the local base station group and an integrated base station corresponding to the local base station group, and a communication coverage area by the local base station is In the same local base station group and between adjacent local base station groups, and in the moving direction of the wireless terminal in the overlapping area within the same local base station group in the communication coverage area .
Kicking than the length, the road-vehicle communication system, wherein a length in the moving direction of the radio terminal is set to a larger relationship of the overlap region between adjacent remote base station group. 2. The transmission beam pattern of each local base station in the local base station group is determined based on the local base stations located at the start and end of the wireless terminal in the direction of movement of the wireless terminal in the communication coverage area of the local base station. 2. The road-vehicle communication system according to claim 1, wherein the transmission beam pattern is set to have a wider relationship than the transmission beam pattern of the local base station located at the center. 3. The transmission line is an optical fiber, wherein the integrated base station is configured to convert a radio modulation signal input from the outside into an optical modulation signal and send the signal to the optical fiber. 3. The road-vehicle communication system according to claim 1, wherein the base station converts the optical modulation signal input from the integrated base station via the optical fiber into a radio modulation signal and transmits the radio modulation signal by an antenna. . 4. The road-vehicle communication system according to claim 1, wherein the transmission power of the local base station is not uniform. 5. The transmission power of a local base station in each of the local base station groups is one local base station located at least in the moving direction end side of the wireless terminal in the communication coverage area of the local base station group. The road-vehicle communication system according to any one of claims 1 to 4, wherein the transmission power of the station is set to have a smaller relationship than the transmission power of the other local base stations. . 6. The at least one local base station located at an end of a group of adjacent local base stations is installed such that the communication coverage areas of the at least one local base station overlap each other substantially over the entire area, and further, the communication coverage The transmission power distribution of the local base station in an overlapping area of an area has a gradient such that transmission power gradually decreases in a moving direction of the wireless terminal . road-vehicle communication system of one of claims <br/> described.