JP7590221B2 - Communication Systems - Google Patents

Description

The present invention relates to a communication system.

In fifth-generation and later wireless communication systems, high-frequency signals of quasi-millimeter waves or higher are used as radio signals. High-frequency signals are easily attenuated and are significantly affected by the vehicle body, etc. For this reason, radio signals may not reach terminals placed inside the vehicle.

To address this issue, technology is known that relays wireless signals within the vehicle (for example, see Patent Document 1).

According to Patent Document 1, an exterior antenna is provided on the outside of the vehicle, and an interior antenna is provided inside the vehicle. When the exterior antenna receives a wireless signal from an external communication target, it outputs the received wireless signal to the interior antenna. The interior antenna re-radiates the wireless signal inside the vehicle.

JP 2018-198383 A

However, if there is a vehicle window in the direction from which the wireless signal arrives, the wireless signal arriving from outside the vehicle will reach the inside of the vehicle without being attenuated near the window. In this case, there is a possibility that the wireless signal arriving from outside the vehicle will interfere with the wireless signal re-radiated from the antenna inside the vehicle.

When inside a vehicle, radio signals coming from outside the vehicle interfere with radio signals re-radiated from the antenna inside the vehicle, the quality of the received signal at the terminal can deteriorate, so there is room for further improvement.

The present invention has been made in consideration of the problems inherent in the conventional technology. The object of the present invention is to provide a communication system that can suppress deterioration in the quality of the received signal at the terminal inside the vehicle, even when the wireless signal is relayed inside the vehicle.

The communication system according to an aspect of the present invention is a communication system in a vehicle including a first window provided on one side in the longitudinal direction of the vehicle, and a second window provided on the other side in the longitudinal direction of the vehicle and facing the first window, and includes a first exterior antenna provided near the top of the first window in the upper part of the body of the vehicle and having directivity toward the side on which the first window faces the outside, at least one first interior antenna provided inside the vehicle at least either above the end of the vehicle on the other side in the longitudinal direction of the vehicle or below the end of the vehicle on one side in the longitudinal direction of the vehicle depending on the directivity of the first exterior antenna, and a communication system for transmitting a signal from the first exterior antenna to the vehicle. The vehicle includes a first relay device that receives a first electrical signal and relays the first electrical signal to at least one first interior antenna, a second exterior antenna that is provided near an upper portion of a second window in an upper portion of a vehicle body of the vehicle and has directivity toward a side where the second window faces the outside, at least one second interior antenna that is provided inside the vehicle at least one of above an end of the vehicle on one side in the longitudinal direction of the vehicle and below an end of the vehicle on the other side in the longitudinal direction of the vehicle depending on the directivity of the second exterior antenna, and a second relay device that receives a second electrical signal from the second exterior antenna and relays the second electrical signal to at least one second interior antenna. The at least one first interior antenna radiates a radio signal based on the first electrical signal relayed by the first relay device. The at least one second interior antenna radiates a radio signal based on the second electrical signal relayed by the second relay device. The first relay device includes a first electrical-optical converter that converts a first electrical signal output from a first exterior antenna into a first optical signal, a first optical fiber that transmits the first optical signal, and at least one first optical-electrical converter that converts a first optical signal received via the first optical fiber into a first electrical signal and outputs the first electrical signal to at least one first interior antenna. The second relay device includes a second electrical-optical converter that converts a second electrical signal output from a second exterior antenna into a second optical signal, a second optical fiber that transmits the second optical signal, and at least one second optical-electrical converter that converts a second optical signal received via the second optical fiber into the second electrical signal and outputs the second electrical signal to at least one second interior antenna.

The present invention provides a communication system that can suppress degradation of the quality of the received signal at the terminal inside the vehicle, even when the wireless signal is relayed inside the vehicle.

FIG. 1 is a diagram showing an overall schematic configuration of a communication system according to this embodiment. FIG. 2 is a side view of the vehicle according to this embodiment. FIG. 3 is a functional block diagram of the relay device according to the present embodiment. FIG. 4 is a block diagram showing an example of the configuration of an electro-optical conversion unit according to this embodiment. FIG. 5 is a block diagram showing an example of the configuration of a photoelectric conversion unit according to this embodiment. FIG. 6 is a diagram illustrating an example of the operation of the communication system according to the present embodiment. FIG. 7 is a diagram illustrating an example of the operation of the communication system according to the present embodiment. FIG. 8 is a side view illustrating a first modified example of an in-vehicle antenna arrangement in the vehicle according to this embodiment. FIG. 9 is a side view illustrating a second modified example of the in-vehicle antenna arrangement in the vehicle according to this embodiment. FIG. 10 is a diagram illustrating the operation of a communication system of the comparative example. FIG. 11 is a top view illustrating an arrangement of antennas inside a vehicle according to a first modified example of the present embodiment. FIG. 12 is a top view illustrating a first modified example of an in-vehicle antenna arrangement in a vehicle according to a first modified example of the present embodiment. FIG. 13 is a top view illustrating a second modified example of an in-vehicle antenna arrangement in a vehicle according to the first modified example of the present embodiment. FIG. 14 is a top view illustrating a third modified example of an in-vehicle antenna arrangement in a vehicle according to the first modified example of the present embodiment. FIG. 15 is a diagram illustrating the radiation direction of a wireless signal from an in-vehicle antenna in a vehicle according to a second modified example of this embodiment. FIG. 16 is a diagram for explaining the radiation direction of a radio signal from an in-vehicle antenna in a vehicle according to a third modified example of this embodiment. FIG. 17 is a side view illustrating the arrangement of an exterior antenna in a vehicle according to a fourth modified example of this embodiment. FIG. 18 is a top view illustrating the arrangement of an exterior antenna and an interior antenna in a vehicle according to a fifth modified example of this embodiment. FIG. 19 is a functional block diagram of a control device in a vehicle according to a sixth modified example of the present embodiment.

The communication system according to this embodiment will be described in detail below with reference to the drawings. Note that identical functions and configurations are denoted by the same or similar reference symbols, and descriptions thereof will be omitted as appropriate.

[Overall Schematic Configuration of Communication System]
1 is a schematic diagram of an entire configuration of a communication system 1. Note that the X direction, Y direction, and Z direction in the figure correspond to the length direction, width direction, and height direction of a vehicle 20, respectively.

The communication system 1 is, for example, a fifth generation mobile communication system (5G system), and uses high-frequency signals of quasi-millimeter waves or higher (approximately 20 GHz to 90 GHz) as wireless signals. As shown in FIG. 1, the communication system 1 includes a base station 10, a vehicle 20, and a terminal 100. The base station 10 is placed, for example, near a roadway on which the vehicle 20 moves. The base station 10 emits radio waves in a specific direction to transmit wireless signals with high directivity. Hereinafter, the term "wireless signal" may include radio waves. Note that the communication system 1 is not limited to a 5G system, and may be any system in which the base station 10 transmits wireless signals with high directivity.

The base station 10 uses radio signals to perform broadcast communication with the terminal 100. Information reported from the base station 10 includes, for example, traffic information, weather information, and local information. By transmitting identification information of the terminal 100 from the vehicle 20 to the base station 10, the base station 10 can perform unicast communication or multicast communication with the terminal 100 using radio signals. The base station 10 is also referred to as an external communication target.

The vehicle 20 is, for example, a large bus, and is located within a range where it can communicate with the base station 10. The vehicle 20 may be a small bus, a medium-sized bus, a general passenger car, a train, or other vehicle. The vehicle 20 has a vehicle front 20a (positive side in the X direction) and a vehicle rear 20b (negative side in the X direction) along the length of the vehicle 20. The vehicle 20 has a vehicle left 20c (positive side in the Y direction) and a vehicle right 20d (negative side in the Y direction) along the width of the vehicle 20. The vehicle front 20a is also referred to as one side in the length of the vehicle 20. The vehicle rear 20b is also referred to as the other side in the length of the vehicle 20. The vehicle left 20c is also referred to as one side in the width of the vehicle 20. The vehicle right 20d is also referred to as the other side in the width of the vehicle 20.

The vehicle 20 includes a front window 21a, a rear window 21b, side windows 21c1, 21c2, side windows 21d1, 21d2, side windows 21e1, 21e2, side windows 21f1, 21f2, side windows 21g1, 21g2, and an upper vehicle body 23. Note that the size and number of these windows are not limited to the dimensions and numbers shown in the drawings.

The front window 21a is provided on the body of the vehicle 20 along the width direction of the vehicle 20 at the front end of the vehicle front part 20a. The rear window 21b is provided on the body of the vehicle 20 along the width direction of the vehicle 20 at the rear end of the vehicle rear part 20b. The rear window 21b faces the front window 21a. The front window 21a is also called the first window. The rear window 21b is also called the second window.

The side windows 21c1, 21d1, 21e1, 21f1, and 21g1 are provided on the body of the vehicle 20 at the left end of the vehicle left section 20c, in the longitudinal direction of the vehicle 20, in order from the front side (+ side), with a predetermined interval between them. The side windows 21c2, 21d2, 21e2, 21f2, and 21g2 are provided on the body of the vehicle 20 at the right end of the vehicle right section 20d, in the longitudinal direction of the vehicle 20, in order from the front side (+ side), with a predetermined interval between them. The side windows 21c2, 21d2, 21e2, 21f2, and 21g2 face the side windows 21c1, 21d1, 21e1, 21f1, and 21g1, respectively. The side windows 21c1, 21d1, 21e1, 21f1, and 21g1 are also referred to as third windows. Side windows 21c2, 21d2, 21e2, 21f2, and 21g2 are also referred to as the fourth windows.

The upper vehicle body 23 is provided on the upper part of the body of the vehicle 20 and is exposed to the outside of the vehicle 20. Note that the term "outside of the vehicle 20" refers to the external space outside the body of the vehicle 20.

The terminal 100 is located inside the vehicle 20. The terminal 100 performs wireless communication (e.g., broadcast communication) with the base station 10 using a radio signal. In FIG. 1, the number of terminals 100 is one, but the number of terminals 100 may be two or more. Note that the term "inside the vehicle 20" refers to the internal space surrounded by the body of the vehicle 20.

Figure 2 is a side view of the vehicle 20. As shown in Figure 2, the vehicle 20 further includes exterior antennas 30a, 30b, interior antennas 40a, 40b, and relay devices 50a, 50b. The exterior antenna 30a is provided in the vehicle front 20a in the upper body 23. Specifically, the exterior antenna 30a is provided near the top of the front window 21a in the upper body 23. The exterior antenna 30a is inclined by an angle θ1 toward the vehicle rear 20b with respect to the longitudinal direction of the vehicle 20. The exterior antenna 30a is also referred to as the first exterior antenna.

The exterior antenna 30b is provided in the upper vehicle body 23, at the rear of the vehicle 20b. Specifically, the exterior antenna 30b is provided in the upper vehicle body 23, near the top of the rear window 21b. The exterior antenna 30b is inclined at an angle θ1 toward the front of the vehicle 20a with respect to the longitudinal direction of the vehicle 20. The exterior antennas 30a and 30b may be inclined at different angles. The exterior antenna 30b is also referred to as the second exterior antenna. In this way, the exterior antenna 30b is positioned so as to face in a different direction from the exterior antenna 30a.

Each of the exterior antennas 30a and 30b has directivity in a different direction. Therefore, each of the exterior antennas 30a and 30b receives radio signals arriving from different directions.

Specifically, the exterior antenna 30a has directivity on the side of the front window 21a facing the outside. In this embodiment, the exterior antenna 30a has directivity in a first direction DR1 that intersects with the height direction of the vehicle 20 at an angle θ1 on the side of the front window 21a facing the outside. Therefore, the exterior antenna 30a receives radio signals arriving from the first direction DR1. In this embodiment, the directivity of the exterior antenna 30a is adjusted by the inclination of the exterior antenna 30a with respect to the longitudinal direction of the vehicle 20.

The exterior antenna 30b has directivity on the side of the rear window 21b facing the outside. In this embodiment, the exterior antenna 30b has directivity in a second direction DR2 that intersects with the height direction of the vehicle 20 at an angle θ1 on the side of the rear window 21b facing the outside. Therefore, the exterior antenna 30b receives radio signals arriving from the second direction DR2. In this embodiment, the directivity of the exterior antenna 30b is adjusted by the inclination of the exterior antenna 30b with respect to the longitudinal direction of the vehicle 20.

The directivity of the exterior antennas 30a, 30b is not limited to being adjusted by the inclination of the exterior antennas 30a, 30b relative to the longitudinal direction of the vehicle 20. For example, each of the exterior antennas 30a, 30b may be configured as an array antenna in which multiple antenna elements are arranged, and the directivity of the exterior antennas 30a, 30b may be adjusted by controlling the weighting of each antenna element.

The interior antenna 40a is provided inside the vehicle 20, above the rear end 20b1 of the vehicle rear 20b. The interior antenna 40b is provided inside the vehicle 20, above the front end 20a1 of the vehicle front 20a. Thus, each of the interior antennas 40a, 40b is disposed inside the vehicle 20 on the opposite side to the direction in which the corresponding exterior antenna faces. The interior antenna 40a is also referred to as the first interior antenna. The interior antenna 40b is also referred to as the second interior antenna. The rear end 20b1 of the vehicle rear 20b is also referred to as the vehicle end on the other side in the vehicle length direction. The front end 20a1 of the vehicle front 20a is also referred to as the vehicle end on one side in the vehicle length direction.

The relay devices 50a, 50b are connected to the exterior antennas 30a, 30b and the interior antennas 40a, 40b inside the vehicle 20. When the exterior antennas 30a, 30b receive a wireless signal outside the vehicle 20, they output an electrical signal based on the received wireless signal to the relay devices 50a, 50b. When the relay devices 50a, 50b receive an electrical signal from the exterior antennas 30a, 30b, they relay the received electrical signal to the interior antennas 40a, 40b. When the interior antennas 40a, 40b receive an electrical signal from the relay devices 50a, 50b, they radiate a wireless signal based on the received electrical signal into the interior of the vehicle 20.

The relay device 50a includes an electro-optical conversion unit 51a, a multimode optical fiber 53a, and an optical-electrical conversion unit 55a. The relay device 50b includes an electro-optical conversion unit 51b, a multimode optical fiber 53b, and an optical-electrical conversion unit 55b. Here, the relay device 50a is also referred to as the first relay device. The relay device 50b is also referred to as the second relay device. The electro-optical conversion unit 51a, the multimode optical fiber 53a, and the optical-electrical conversion unit 55a are also referred to as the first electro-optical conversion unit, the first optical fiber, and the first optical-electrical conversion unit, respectively. The electro-optical conversion unit 51b, the multimode optical fiber 53b, and the optical-electrical conversion unit 55b are also referred to as the second electro-optical conversion unit, the second optical fiber, and the second optical-electrical conversion unit.

The configurations of the electro-optical conversion unit 51a, multimode optical fiber 53a, and photoelectric conversion unit 55a in the relay device 50a will be described using Figures 3 to 5. Note that the configurations of the electro-optical conversion unit 51b, multimode optical fiber 53b, and photoelectric conversion unit 55b in the relay device 50b are the same as the configurations of the electro-optical conversion unit 51a, multimode optical fiber 53a, and photoelectric conversion unit 55a, respectively, so descriptions of these will be omitted.

Figure 3 is a functional block diagram of relay device 50a. As shown in Figure 3, electro-optical conversion unit 51a is a circuit that converts an electrical signal into an optical signal, and is connected to exterior antenna 30a. Photoelectric conversion unit 55a is a circuit that converts an optical signal into an electrical signal, and is connected to interior antenna 40a. Multimode optical fiber 53a is a transmission path that transmits optical signals, and is connected to electro-optical conversion unit 51a and photoelectric conversion unit 55a.

When the exterior antenna 30a receives a radio signal, it outputs an electrical signal based on the received radio signal to the electrical-to-optical converter 51a. When the electrical-to-optical converter 51a receives an electrical signal from the exterior antenna 30a, it converts the received electrical signal into an optical signal. The electrical-to-optical converter 51a transmits the optical signal to the optical-to-electrical converter 55a via the multimode optical fiber 53a.

Figure 4 is a block diagram showing an example of the configuration of the electro-optical conversion unit 51a. As shown in Figure 4, the electro-optical conversion unit 51a includes a signal power adjustment circuit 511a, a bias Tee 513a, and a surface emitting laser 515a. The signal power adjustment circuit 511a is a circuit that adjusts the power of an electrical signal, and is connected to the exterior antenna 30a. When the signal power adjustment circuit 511a receives an electrical signal from the exterior antenna 30a, it amplifies the received electrical signal. The signal power adjustment circuit 511a outputs the amplified electrical signal to the bias Tee 513a.

If necessary, a bandpass filter, an analog-digital converter, an intermediate frequency converter, etc. may be provided in front of the signal power adjustment circuit 511a. The analog-digital converter is provided, for example, for digital RoF (Radio-over-Fiber) transmission, and converts a high-frequency signal (RF signal) into a digital signal. The intermediate frequency converter is provided, for example, for IFoF (IF-over-Fiber) transmission, and converts a high-frequency signal (RF signal) into a signal in the intermediate frequency band.

The bias Tee 513a is a circuit that adds a DC component and is connected to the signal power adjustment circuit 511a. When the bias Tee 513a receives the amplified electrical signal from the signal power adjustment circuit 511a, it adds a DC component to the received electrical signal. The bias Tee 513a outputs the electrical signal with the DC component added to the surface emitting laser 515a.

The surface-emitting laser 515a is a semiconductor laser that converts an electrical signal into an optical signal, and is connected to the bias-Tee 513a. When the surface-emitting laser 515a receives an electrical signal to which a DC component has been added from the bias-Tee 513a, it converts the received electrical signal into an optical signal. The surface-emitting laser 515a outputs the optical signal to the multimode optical fiber 53a.

Returning to FIG. 3, the optical axis of the multimode optical fiber 53a is adjusted and connected to the electrical-to-optical conversion unit 51a and the optical-to-electrical conversion unit 55a. The multimode optical fiber 53a is made of glass or resin. The multimode optical fiber 53a has a core layer through which an optical signal propagates, and a cladding layer that covers the periphery of the core layer. In the multimode optical fiber 53a, the optical signal propagates within the core layer by being reflected at a predetermined angle at the boundary surface between the core layer and the cladding layer.

When the photoelectric conversion unit 55a receives an optical signal from the electrical-to-optical conversion unit 51a via the multimode optical fiber 53a, it converts the received optical signal into an electrical signal. The photoelectric conversion unit 55a outputs the electrical signal to the in-vehicle antenna 40a.

Figure 5 is a block diagram showing an example of the configuration of the photoelectric conversion unit 55a. As shown in Figure 5, the photoelectric conversion unit 55a includes a light receiving element 551a and a signal power adjustment circuit 553a. The light receiving element 551a is, for example, a photodiode that converts an optical signal into an electrical signal, and is connected to the multimode optical fiber 53a. When the light receiving element 551a receives an optical signal from the multimode optical fiber 53a, it converts the received optical signal into an electrical signal. The light receiving element 551a outputs the electrical signal to the signal power adjustment circuit 553a.

The signal power adjustment circuit 553a is a circuit that adjusts the power of an electrical signal and is connected to the light receiving element 551a. When the signal power adjustment circuit 553a receives an electrical signal from the light receiving element 551a, it amplifies the received electrical signal. The signal power adjustment circuit 553a outputs the amplified electrical signal to the in-vehicle antenna 40a.

If necessary, a bandpass filter, digital-to-analog converter, intermediate frequency converter, etc. may be provided downstream of the signal power adjustment circuit 553a. The digital-to-analog converter is provided, for example, for digital RoF (Radio-over-Fiber) transmission, and converts a digital signal into a high-frequency signal (RF signal). The intermediate frequency converter is provided, for example, for IFoF (IF-over-Fiber) transmission, and converts an intermediate frequency band signal into a high-frequency signal (RF signal).

When the in-vehicle antenna 40a receives an electrical signal, it radiates a radio signal based on the received electrical signal into the interior of the vehicle 20.

The electrical signal relayed from the exterior antenna 30a to the interior antenna 40a is also referred to as the first electrical signal. The optical signal converted from the electrical signal during relay from the exterior antenna 30a to the interior antenna 40a is also referred to as the first optical signal. The electrical signal relayed from the exterior antenna 30b to the interior antenna 40b is also referred to as the second electrical signal. The optical signal converted from the electrical signal during relay from the exterior antenna 30b to the interior antenna 40b is also referred to as the second optical signal.

[Example of operation of communication system]
Next, an operation example of the communication system 1 will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a diagram for explaining an operation example of the communication system 1 in a state where the base station 10 (not shown) is located in front of the vehicle 20. As shown in Fig. 6, in this operation example, the range in which the radio signal emitted from the base station 10 reaches the inside of the vehicle 20 through the front window 21a is a range excluding the vicinity of the rear end 20b1 of the vehicle rear part 20b.

Specifically, in this operation example, the angle θ1 shown in FIG. 2 has a value near the minimum value in the possible range. Thus, in this operation example, since the elevation angle of the exterior antenna 30a is large, the directivity of the exterior antenna 30a is oriented in a direction close to the height direction (vertical direction) of the vehicle 20 on the side where the front window 21a faces the outside. Accordingly, the wireless signal received by the exterior antenna 30a arrives from a direction close to the height direction (vertical direction) of the vehicle 20 on the side where the front window 21a faces the outside. Therefore, the wireless signal arriving from the first direction DR1 enters the inside of the vehicle 20 with a large incident angle with respect to the front window 21a, and is unlikely to reach the vicinity of the rear end 20b1 of the vehicle rear part 20b. Note that the term "incident angle" refers to the angle between the incident direction of the wireless signal and the normal direction of the surface of the front window 21a.

When the exterior antenna 30a receives a radio signal arriving from the first direction DR1, it outputs an electrical signal based on the received radio signal to the interior antenna 40a using the relay device 50a. When the interior antenna 40a receives an electrical signal from the relay device 50a, it radiates a wireless signal based on the received electrical signal into the interior of the vehicle 20.

As shown in FIG. 6, the in-vehicle antenna 40a is provided inside the vehicle 20 above the rear end 20b1 of the vehicle rear 20b, and therefore radiates wireless signals downward from the rear end 20b1. This reduces the possibility that the area F1 inside the vehicle 20, where wireless signals arriving from outside the vehicle 20 arrive, overlaps with the area F2 where wireless signals radiated from the in-vehicle antenna 40a arrive. With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in either area F1 or F2.

Figure 7 is a diagram illustrating an example of the operation of the communication system 1 when the base station 10 (not shown) is located at the rear of the vehicle 20. As shown in Figure 7, in this example of operation, the range in which the radio signal emitted from the base station 10 reaches the inside of the vehicle 20 through the rear window 21b is a range excluding the vicinity of the front end 20a1 of the vehicle front 20a.

Specifically, in this operation example, the angle θ1 shown in FIG. 2 has a value near the minimum value in the possible range. Thus, in this operation example, since the elevation angle of the exterior antenna 30b is large, the directivity of the exterior antenna 30b is oriented in a direction close to the height direction (vertical direction) of the vehicle 20 on the side where the rear window 21b faces the outside. Accordingly, the wireless signal received by the exterior antenna 30b arrives from a direction close to the height direction (vertical direction) of the vehicle 20 on the side where the rear window 21b faces the outside. Therefore, the wireless signal arriving from the second direction DR2 enters the inside of the vehicle 20 with a large incident angle with respect to the rear window 21b, and is unlikely to reach the vicinity of the front end 20a1 of the front part 20a of the vehicle. Note that the term "incident angle" refers to the angle between the incident direction of the wireless signal and the normal direction of the surface of the rear window 21b.

When the exterior antenna 30b receives a radio signal arriving from the second direction DR2, it outputs an electrical signal based on the received radio signal to the interior antenna 40b using the relay device 50b. When the interior antenna 40b receives an electrical signal from the relay device 50b, it radiates a wireless signal based on the received electrical signal into the interior of the vehicle 20.

As shown in FIG. 7, the in-vehicle antenna 40b is provided inside the vehicle 20 above the front end 20a1 of the vehicle front 20a, and therefore radiates wireless signals downward from the front end 20a1. This reduces the possibility that the area B1 inside the vehicle 20, where wireless signals arriving from outside the vehicle 20 reach, overlaps with the area B2 where wireless signals radiated from the in-vehicle antenna 40b reach. With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in either area B1 or B2.

[First modified example of interior antenna arrangement]
Next, a first modified example of the in-vehicle antenna arrangement will be described with reference to Fig. 8. Fig. 8 is a diagram illustrating the first modified example of the in-vehicle antenna arrangement. As shown in Fig. 8, the in-vehicle antenna 40a is provided inside the vehicle 20 below the front end 20a1 of the vehicle front part 20a. The in-vehicle antenna 40b is provided inside the vehicle 20 below the rear end 20b1 of the vehicle rear part 20b. In this way, each of the in-vehicle antennas 40a, 40b is provided at the bottom inside the vehicle 20 on the same side as the direction in which the corresponding exterior antenna faces.

This arrangement is effective when the range in which the radio signal emitted from the base station 10 reaches the inside of the vehicle 20 through the front window 21a is a range that excludes the lower vicinity of the front end 20a1 of the vehicle front part 20a. Specifically, when the angle θ1 shown in FIG. 2 has a value close to the maximum value among the possible ranges, the elevation angle of the exterior antenna 30a is small, so that the directivity of the exterior antenna 30a is oriented in a direction close to the length direction (horizontal direction) of the vehicle 20 on the side where the front window 21a faces the outside. Accordingly, the radio signal received by the exterior antenna 30a arrives from a direction close to the length direction (horizontal direction) of the vehicle 20 on the side where the front window 21a faces the outside. Therefore, the radio signal arriving from the first direction DR1 enters the inside of the vehicle 20 with a small incident angle with respect to the front window 21a, and is unlikely to reach the lower vicinity of the front end 20a1 of the vehicle front part 20a.

When the exterior antenna 30a receives a radio signal arriving from the first direction DR1, it outputs an electrical signal based on the received radio signal to the interior antenna 40a using the relay device 50a. When the interior antenna 40a receives an electrical signal from the relay device 50a, it radiates a wireless signal based on the received electrical signal into the interior of the vehicle 20.

As shown in FIG. 8, the in-vehicle antenna 40a is provided below the front end 20a1 of the vehicle front 20a inside the vehicle 20, and therefore radiates wireless signals below the front end 20a1. This reduces the possibility that the area F3 inside the vehicle 20, where wireless signals arriving from outside the vehicle 20 arrive, overlaps with the area F4 where wireless signals radiated from the in-vehicle antenna 40a arrive. With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in either area F3 or F4.

Similarly, this modified example is also effective when the range in which the radio signal emitted from the base station 10 reaches the interior of the vehicle 20 through the rear window 21b is a range excluding the area below the rear end 20b1 of the vehicle rear 20b.

[Second modified example of interior antenna arrangement]
Next, a second variation of the interior antenna arrangement will be described with reference to Fig. 9. Fig. 9 is a diagram illustrating the second variation of the interior antenna arrangement. As shown in Fig. 9, two interior antennas are arranged inside the vehicle 20 for one exterior antenna.

Specifically, the exterior antenna 30a is connected to the interior antennas 40a1 and 40a2 via a relay device 50a1. The interior antenna 40a1 is provided inside the vehicle 20, above the rear end 20b1 of the vehicle rear section 20b. The interior antenna 40a2 is provided inside the vehicle 20, below the front end 20a1 of the vehicle front section 20a. The interior antennas 40a1 and 40a2 have the same functions as the interior antenna 40a.

The relay device 50a1 includes an electro-optical conversion unit 51a, multimode optical fibers 53a, 53a1, and 53a2, photoelectric conversion units 55a1 and 55a2, and an optical coupler 60a. The electro-optical conversion unit 51a is connected to the exterior antenna 30a. The photoelectric conversion unit 55a1 has the same function as the photoelectric conversion unit 55a, and is connected to the interior antenna 40a1. The photoelectric conversion unit 55a2 has the same function as the photoelectric conversion unit 55a, and is connected to the interior antenna 40a2.

The multimode optical fiber 53a has one end connected to the electro-optical conversion unit 51a and the other end connected to the optical coupler 60a. The multimode optical fibers 53a1 and 53a2 have the same function as the multimode optical fiber 53a. The multimode optical fiber 53a1 has one end connected to the photoelectric conversion unit 55a1 and the other end connected to the optical coupler 60a. The multimode optical fiber 53a2 has one end connected to the photoelectric conversion unit 55a2 and the other end connected to the optical coupler 60a.

The multimode optical fiber 53a is branched by the optical coupler 60a into the transmission paths of the multimode optical fibers 53a1 and 53a2. Note that the optical coupler 60a may be omitted and the multimode optical fibers 53a1 and 53a2 may be directly connected to the electrical-to-optical converter 51a.

Similarly, the exterior antenna 30b is connected to interior antennas 40b1 and 40b2 via a relay device 50b1. The interior antenna 40b1 is provided inside the vehicle 20, above the front end 20a1 of the vehicle front 20a. The interior antenna 40b2 is provided inside the vehicle 20, below the rear end 20b1 of the vehicle rear 20b. The interior antennas 40b1 and 40b2 have the same functions as the interior antenna 40b.

The relay device 50b1 includes an electro-optical conversion unit 51b, multimode optical fibers 53b, 53b1, and 53b2, photoelectric conversion units 55b1 and 55b2, and an optical coupler 60b. The electro-optical conversion unit 51b is connected to the exterior antenna 30b. The photoelectric conversion unit 55b1 has the same function as the photoelectric conversion unit 55b, and is connected to the interior antenna 40b1. The photoelectric conversion unit 55b2 has the same function as the photoelectric conversion unit 55b, and is connected to the interior antenna 40b2.

The multimode optical fiber 53b has one end connected to the electro-optical conversion unit 51b and the other end connected to the optical coupler 60b. The multimode optical fibers 53b1 and 53b2 have the same function as the multimode optical fiber 53b. The multimode optical fiber 53b1 has one end connected to the photoelectric conversion unit 55b1 and the other end connected to the optical coupler 60b. The multimode optical fiber 53b2 has one end connected to the photoelectric conversion unit 55b2 and the other end connected to the optical coupler 60b.

The multimode optical fiber 53b is branched into multimode optical fibers 53b1 and 53b2 by the optical coupler 60b. Note that the optical coupler 60b may be omitted and the multimode optical fibers 53b1 and 53b2 may be directly connected to the electrical-to-optical converter 51b.

In this way, the two interior antennas are each positioned inside the vehicle 20 on the opposite side of the direction in which the corresponding exterior antenna faces, and are positioned at the bottom inside the vehicle 20 on the same side of the direction in which the corresponding exterior antenna faces.

Such an arrangement is effective when the range in which the radio signal emitted from the base station 10 arrives inside the vehicle 20 through the front window 21a is a range excluding the lower vicinity of the front end 20a1 of the front part 20a of the vehicle and the vicinity of the rear end 20b1 of the vehicle rear part 20b. Specifically, when the angle θ1 shown in FIG. 2 has an intermediate value among the possible ranges, the elevation angle of the exterior antenna 30a is gentle. Therefore, the directivity of the exterior antenna 30a is directed in a direction that is approximately the same distance from the length direction and height direction (horizontal and vertical directions) of the vehicle 20 on the side where the front window 21a faces the outside. Accordingly, the radio signal received by the exterior antenna 30a arrives from a direction that is approximately the same distance from the length direction and height direction (horizontal and vertical directions) of the vehicle 20 on the side where the front window 21a faces the outside. For this reason, the radio signal coming from the first direction DR1 enters the interior of the vehicle 20 at a gentle angle of incidence with respect to the front window 21a, and is therefore unlikely to reach the lower area near the front end 20a1 of the vehicle front 20a, or the rear end 20b1 of the vehicle rear 20b.

When the exterior antenna 30a receives a radio signal arriving from the first direction DR1, it outputs an electrical signal based on the received radio signal to the interior antennas 40a1 and 40a2 using the relay device 50a1. When the interior antennas 40a1 and 40a2 receive an electrical signal from the relay device 50a1, they radiate a wireless signal based on the received electrical signal into the interior of the vehicle 20.

As shown in FIG. 9, the in-vehicle antenna 40a1 is provided inside the vehicle 20 above the rear end 20b1 of the vehicle rear 20b, and so radiates wireless signals downward from the rear end 20b1. This reduces the possibility that the area F5 inside the vehicle 20, where wireless signals arriving from outside the vehicle 20 arrive, overlaps with the area F6, where wireless signals radiated from the in-vehicle antenna 40a1 arrive.

The in-vehicle antenna 40a2 is provided below the front end 20a1 of the vehicle front 20a inside the vehicle 20, and therefore radiates wireless signals below the front end 20a1. This reduces the possibility that the area F5 inside the vehicle 20, where wireless signals arriving from outside the vehicle 20 arrive, overlaps with the area F7, where wireless signals radiated from the in-vehicle antenna 40a2 arrive.

With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives a wireless signal in one of areas F5, F6, or F7.

Similarly, this modified example is also effective when the range in which the radio signal emitted from the base station 10 reaches the interior of the vehicle 20 through the rear window 21b is a range excluding the vicinity of the front end 20a1 of the vehicle front part 20a and the vicinity below the rear end 20b1 of the vehicle rear part 20b.

[Action and Effects]
According to this embodiment, the vehicle 20 includes a windshield 21a provided in a vehicle front portion 20a. The exterior antenna 30a is provided in the upper portion 23 of the vehicle body of the vehicle 20 near above the windshield 21a, and has directivity toward the side of the windshield 21a facing the outside.

With this configuration, when the exterior antenna 30a receives a wireless signal from the base station 10, the exterior antenna 30a is located near the top of the front window 21a in the upper part 23 of the vehicle body, so the front window 21a is in the first direction DR1 from which the wireless signal arrives. Therefore, near the front window 21a inside the vehicle 20, the wireless signal reaches the inside of the vehicle 20 without being attenuated.

However, the interior antenna 40a (or the interior antennas 40a1, 40a2) is provided at least one of above the rear end 20b1 of the rear part 20b of the vehicle and below the front end 20a1 of the front part 20a of the vehicle, depending on the directivity of the exterior antenna 30a.

Specifically, when the directivity of the exterior antenna 30a causes the angle of incidence of a wireless signal coming from outside the vehicle 20 to the front window 21a to be large, the wireless signal coming from outside the vehicle 20 has difficulty reaching the rear end 20b1 of the vehicle rear 20b. In this case, the interior antenna 40a is provided above the rear end 20b1 of the vehicle rear 20b.

When the directivity of the exterior antenna 30a causes the angle of incidence of the wireless signal coming from outside the vehicle 20 to the front window 21a to be small, the wireless signal coming from outside the vehicle 20 is unlikely to reach below the front end 20a1 of the vehicle front 20a. In this case, the interior antenna 40a is provided below the front end 20a1 of the vehicle front 20a.

In cases other than the above two, radio signals arriving from outside the vehicle 20 are unlikely to reach the lower part of the front end 20a1 of the vehicle front 20a and the rear end 20b1 of the vehicle rear 20b. In these cases, the in-vehicle antennas 40a1 and 40a2 are provided above the rear end 20b1 of the vehicle rear 20b and below the front end 20a1 of the vehicle front 20a, respectively.

This reduces the possibility that the radio signal radiated from the base station 10 and arriving inside the vehicle 20 will interfere with the radio signal re-radiated from the in-vehicle antenna 40a or the in-vehicle antennas 40a1 and 40a2. This reduces the degradation of the quality of the received signal at the terminal 100 placed inside the vehicle 20.

The above-mentioned features also apply to the combination of the exterior antenna 30b and the interior antenna 40b, and to the combination of the exterior antenna 30b and the interior antennas 40b1 and 40b2.

Figure 10 is a diagram explaining the operation of the communication system of the comparative example. As shown in Figure 10, in the vehicle 220 in the communication system of the comparative example, when an exterior antenna 230 provided on the upper part 223 of the vehicle body receives a wireless signal, it relays an electrical signal based on the received wireless signal to the interior antenna 240 via the relay device 250. When the interior antenna 240 receives an electrical signal, it radiates a wireless signal based on the received electrical signal throughout the interior of the vehicle 220.

Therefore, within the vehicle 220, the area F9 where the wireless signal arriving from outside the vehicle 220 through the front window 221a reaches is highly likely to overlap with the area F8 where the wireless signal radiated from the in-vehicle antenna 240 reaches.

According to this embodiment, the exterior antenna 30a has directivity toward the side of the front window 21a facing the outside, and the exterior antenna 30b has directivity toward the side of the rear window 21b facing the outside. With this configuration, the exterior antennas 30a and 30b have directivity in opposite directions.

Therefore, for example, when the exterior antenna 30a is receiving a wireless signal from the front of the vehicle 20, if the vehicle 20 moves and passes the base station 10, the exterior antenna 30a will no longer be able to receive the wireless signal. However, even in this case, the exterior antenna 30b can receive a wireless signal from the rear of the vehicle 20. This reduces the possibility that the terminal 100 placed inside the vehicle 20 will be unable to receive a wireless signal as the vehicle 20 moves, and can further suppress deterioration in the quality of the received signal at the terminal 100.

According to this embodiment, a multimode optical fiber is used to relay signals from the exterior antenna 30a (or the exterior antenna 30b) to the interior antenna 40a (or the interior antenna 40b). Similarly, a multimode optical fiber is used to relay signals from the exterior antenna 30a (or the exterior antenna 30b) to the interior antennas 40a1, 40a2 (or the interior antennas 40b1, 40b2).

This configuration makes it possible to suppress signal attenuation during signal relay. Therefore, it is possible to further suppress deterioration in the quality of the received signal at the terminal 100 placed inside the vehicle 20.

Therefore, according to this embodiment, it is possible to provide a communication system 1 that can suppress deterioration in the quality of the received signal at the terminal 100 even when the wireless signal is relayed inside the vehicle 20.

According to this embodiment, the in-vehicle antennas 40a1 and 40a2 are provided above the rear end 20b1 of the vehicle rear 20b and below the front end 20a1 of the vehicle front 20a, respectively. In this case, the multimode optical fiber 53a of the relay device 50a1 is branched into multimode optical fibers 53a1 and 53a2 by the optical coupler 60a. The photoelectric conversion units 55a1 and 55a2 convert the optical signals transmitted by the multimode optical fibers 53a1 and 53a2 into electrical signals and output them to the in-vehicle antennas 40a1 and 40a2.

This simple configuration allows two interior antennas to be arranged in relation to one exterior antenna inside the vehicle 20. The above-mentioned features also apply to the combination of the exterior antenna 30b and the interior antennas 40b1 and 40b2.

[First Modification]
In the above-described embodiment, the combination of the exterior antenna and the interior antenna is provided on the upper body 23 of the vehicle 20 along the length direction of the vehicle 20, but is not limited to this. In the vehicle 20 of the first modified example of this embodiment, the combination of the exterior antenna and the interior antenna is also provided on the upper body 23 of the vehicle 20 along the width direction of the vehicle 20.

In the following explanation, the description of the exterior antennas 30a, 30b, interior antennas 40a, 40b, and relay devices 50a, 50b provided on the upper body 23 of the vehicle 20 along the length of the vehicle 20 will be omitted as appropriate. Similarly, the description of the exterior antennas 30a, 30b, interior antennas 40a1, 40a2, 40b1, 40b2, and relay devices 50a1, 50b1 provided on the upper body 23 of the vehicle 20 along the length of the vehicle 20 will be omitted as appropriate.

Figure 11 is a top view illustrating the arrangement of interior antennas in vehicle 20 of the first modified example. As shown in Figure 11, vehicle 20 includes exterior antennas 30a, 30b, 30c, 30d, 30e, and 30f, interior antennas 40a, 40b, 40c, 40d, 40e, and 40f, and relay devices 50a, 50b, 50c, 50d, 50e, and 50f.

The exterior antenna 30c is provided on the vehicle front 20a side of the vehicle left portion 20c in the upper body 23. Specifically, the exterior antenna 30c is provided near the top of the side window 21d1 in the upper body 23. The exterior antenna 30c has directivity toward the side of the side window 21d1 facing the outside. The exterior antenna 30c is also referred to as the third exterior antenna. The exterior antenna 30c is positioned so as to face in a different direction from the exterior antennas 30a and 30b.

The exterior antenna 30d is provided on the vehicle rear 20b side of the vehicle left 20c in the upper body 23. Specifically, the exterior antenna 30d is provided near the top of the side window 21f1 in the upper body 23. The exterior antenna 30d has directivity toward the side of the side window 21f1 facing the outside. The exterior antenna 30d is also called the third exterior antenna. The exterior antenna 30d is positioned so as to face in a different direction from the exterior antennas 30a, 30b, and 30c.

Exterior antenna 30e is provided on the vehicle front 20a side of the vehicle right 20d in the upper body 23. Specifically, exterior antenna 30e is provided near the top of the side window 21d2 in the upper body 23. Exterior antenna 30e has directivity toward the side of side window 21d2 facing the outside. Exterior antenna 30e is also referred to as the fourth exterior antenna. In this way, exterior antenna 30e is positioned to face in a different direction from exterior antennas 30a, 30b, 30c, and 30d.

Exterior antenna 30f is provided on the vehicle rear 20b side of the vehicle right 20d in the upper body 23. Specifically, exterior antenna 30f is provided near the top of the side window 21f2 in the upper body 23. Exterior antenna 30f has directivity toward the side of side window 21f2 facing the outside. Exterior antenna 30f is also referred to as the fourth exterior antenna. In this way, exterior antenna 30f is positioned so as to face in a different direction from exterior antennas 30a, 30b, 30c, 30d, and 30e.

The in-vehicle antenna 40c is provided inside the vehicle 20, above the right end 20d1 of the vehicle right side 20d on the vehicle front 20a side. The in-vehicle antenna 40d is provided inside the vehicle 20, above the right end 20d1 of the vehicle rear 20b side on the vehicle right side 20d. The in-vehicle antenna 40e is provided inside the vehicle 20, above the left end 20c1 of the vehicle left side 20c on the vehicle front 20a side. The in-vehicle antenna 40d is provided inside the vehicle 20, above the left end 20c1 of the vehicle left side 20c on the vehicle rear 20b side.

The interior antennas 40c and 40d are also referred to as the third interior antenna. The interior antennas 40e and 40f are also referred to as the fourth interior antenna. The right end 20d1 of the vehicle right part 20d on the vehicle front part 20a or vehicle rear part 20b side is also referred to as the vehicle end on the other side in the vehicle width direction. The left end 20c1 of the vehicle left part 20c on the vehicle front part 20a or vehicle rear part 20b side is also referred to as the vehicle end on one side in the vehicle width direction.

The relay devices 50c, 50d, 50e, and 50f are connected to the exterior antennas 30c, 30d, 30e, and 30f and the interior antennas 40c, 40d, 40e, and 40f inside the vehicle 20. When the exterior antennas 30c, 30d, 30e, and 30f receive a wireless signal outside the vehicle 20, they output an electrical signal based on the received wireless signal to the relay devices 50c, 50d, 50e, and 50f. When the relay devices 50c, 50d, 50e, and 50f receive an electrical signal from the exterior antennas 30c, 30d, 30e, and 30f, they relay the received electrical signal to the interior antennas 40c, 40d, 40e, and 40f. When the in-vehicle antennas 40c, 40d, 40e, and 40f receive electrical signals from the relay devices 50c, 50d, 50e, and 50f, they radiate wireless signals based on the received electrical signals into the interior of the vehicle 20.

The relay devices 50c, 50d, 50e, and 50f include electro-optical conversion units 51c, 51d, 51e, and 51f, multimode optical fibers 53c, 53d, 53e, and 53f, and photoelectric conversion units 55c, 55d, 55e, and 55f. The electro-optical conversion units 51c, 51d, 51e, and 51f have the same configuration as the electro-optical conversion unit 51a. The multimode optical fibers 53c, 53d, 53e, and 53f have the same configuration as the multimode optical fiber 53a. The photoelectric conversion units 55c, 55d, 55e, and 55f have the same configuration as the photoelectric conversion unit 55a.

The relay devices 50c and 50d are also referred to as the third relay devices. The relay devices 50e and 50f are also referred to as the fourth relay devices. The electro-optical conversion units 51c and 51d, the multimode optical fibers 53c and 53d, and the photoelectric conversion units 55c and 55d are also referred to as the third electro-optical conversion unit, the third optical fiber, and the third photoelectric conversion unit, respectively. The electro-optical conversion units 51e and 51f, the multimode optical fibers 53e and 53f, and the photoelectric conversion units 55e and 55f are also referred to as the fourth electro-optical conversion unit, the fourth optical fiber, and the fourth photoelectric conversion unit.

The electrical signal relayed from the exterior antenna 30c, 30d to the interior antenna 40c, 40d is also referred to as the third electrical signal. The optical signal converted from the electrical signal during relay from the exterior antenna 30c, 30d to the interior antenna 40c, 40d is also referred to as the third optical signal. The electrical signal relayed from the exterior antenna 30e, 30f to the interior antenna 40e, 40f is also referred to as the fourth electrical signal. The optical signal converted from the electrical signal during relay from the exterior antenna 30e, 30f to the interior antenna 40e, 40f is also referred to as the fourth optical signal.

This arrangement is effective, for example, when the range in which the radio signal emitted from the base station 10 reaches the interior of the vehicle 20 through the side window 21d1 excludes the area near the right end 20d1 of the vehicle right section 20d. Specifically, when the directivity of the exterior antenna 30c is oriented in a direction close to the height direction (vertical direction) of the vehicle 20 on the side where the side window 21d1 faces the outside, the radio signal enters the interior of the vehicle 20 with a large angle of incidence with respect to the side window 21d1. For this reason, it is difficult for the radio signal to reach the area near the right end 20d1 of the vehicle right section 20d.

Here, the in-vehicle antenna 40c is provided inside the vehicle 20 above the right end 20d1 of the vehicle right section 20d, and therefore radiates wireless signals downward from the right end 20d1. This reduces the possibility that the area inside the vehicle 20 where wireless signals arriving from outside the vehicle 20 reach overlaps with the area where wireless signals radiated from the in-vehicle antenna 40c reach. With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in either of the two areas described above.

Similar features also apply to the combination of exterior antenna 30d and interior antenna 40d, the combination of exterior antenna 30e and interior antenna 40e, and the combination of exterior antenna 30f and interior antenna 40f.

[First modified example of interior antenna arrangement]
Next, a first modified example of the interior antenna arrangement in the vehicle 20 of the first modified example will be described with reference to Fig. 12. Fig. 12 is a top view illustrating the first modified example of the interior antenna arrangement. As shown in Fig. 12, the vehicle 20 includes exterior antennas 30a, 30b, 30g, and 30h, interior antennas 40a, 40b, 40g1, 40g2, 40h1, and 40h2, and relay devices 50a, 50b, 50g, and 50h.

Exterior antenna 30g is provided in upper vehicle body 23, on vehicle left side 20c. Specifically, exterior antenna 30g is provided in the upper vehicle body 23, near the top of side window 21e1. Exterior antenna 30g has directivity toward the side of side window 21e1 facing the outside. Exterior antenna 30g is also referred to as the third exterior antenna. Exterior antenna 30g is positioned so as to face in a different direction from exterior antennas 30a and 30b.

The exterior antenna 30h is provided in the upper vehicle body 23, on the right vehicle part 20d. Specifically, the exterior antenna 30h is provided in the upper vehicle body 23, near the upper part of the side window 21e2. The exterior antenna 30h has directivity toward the side of the side window 21e2 facing the outside. The exterior antenna 30h is also called the fourth exterior antenna. The exterior antenna 30e is positioned so as to face in a different direction from the exterior antennas 30a, 30b, and 30g.

The interior antenna 40g1 is provided inside the vehicle 20, above the right end 20d1 of the vehicle right side 20d on the vehicle front 20a side. The interior antenna 40g2 is provided inside the vehicle 20, above the right end 20d1 of the vehicle rear 20b side on the vehicle right side 20d. The interior antenna 40h1 is provided inside the vehicle 20, above the left end 20c1 of the vehicle left side 20c on the vehicle front 20a side. The interior antenna 40h2 is provided inside the vehicle 20, above the left end 20c1 of the vehicle left side 20c on the vehicle rear 20b side. The interior antennas 40g1 and 40g2 are also referred to as the third interior antenna. The interior antennas 40h1 and 40h2 are also referred to as the fourth interior antenna.

The relay device 50g includes an electrical-optical conversion unit 51g, multimode optical fibers 53g, 53g1, and 53g2, photoelectric conversion units 55g1 and 55g2, and an optical coupler 60g. The relay device 50h includes an electrical-optical conversion unit 51h, multimode optical fibers 53h, 53h1, and 53h2, photoelectric conversion units 55h1 and 55h2, and an optical coupler 60h.

The electro-optical conversion units 51g and 51h have the same configuration as the electro-optical conversion unit 51a. The multimode optical fibers 53g and 53h have the same configuration as the multimode optical fiber 53a. The multimode optical fibers 53g1 and 53h1 have the same configuration as the multimode optical fiber 53a1 (see FIG. 9). The multimode optical fibers 53g2 and 53h2 have the same configuration as the multimode optical fiber 53a2 (see FIG. 9). The photoelectric conversion units 55g1 and 55h1 have the same configuration as the photoelectric conversion unit 55a1 (see FIG. 9). The photoelectric conversion units 55g2 and 55h2 have the same configuration as the photoelectric conversion unit 55a2 (see FIG. 9). The optical couplers 60g and 60h have the same configuration as the optical coupler 60a (see FIG. 9).

Relay device 50g is also referred to as the third relay device. Relay device 50h is also referred to as the fourth relay device. The electro-optical conversion unit 51g, the multimode optical fibers 53g, 53g1, 53g2, and the photoelectric conversion units 55g1, 55g2 are also referred to as the third electro-optical conversion unit, the third multimode optical fiber, and the third photoelectric conversion unit, respectively. The electro-optical conversion unit 51h, the multimode optical fibers 53h, 53h1, 53h2, and the photoelectric conversion units 55h1, 55h2 are also referred to as the fourth electro-optical conversion unit, the fourth multimode optical fiber, and the fourth photoelectric conversion unit.

The multimode optical fiber 53g is branched into multimode optical fibers 53g1 and 53g2 by the optical coupler 60g. The photoelectric conversion units 55g1 and 55g2 convert the optical signals transmitted by the multimode optical fibers 53g1 and 53g2 into electrical signals and output them to the in-vehicle antennas 40g1 and 40g2.

The multimode optical fiber 53h is branched into multimode optical fibers 53h1 and 53h2 by the optical coupler 60h. The photoelectric conversion units 55h1 and 55h2 convert the optical signals transmitted by the multimode optical fibers 53h1 and 53h2 into electrical signals and output them to the in-vehicle antennas 40h1 and 40h2.

This simple configuration allows two interior antennas to be arranged for one exterior antenna inside the vehicle 20.

[Second modified example of interior antenna arrangement]
Next, a second modified example of the in-vehicle antenna arrangement in the vehicle 20 of the first modified example will be described with reference to Fig. 13. Fig. 13 is a diagram illustrating the second modified example of the in-vehicle antenna arrangement. As shown in Fig. 13, the in-vehicle antenna 40c is provided inside the vehicle 20 below the left end 20c1 of the vehicle left part 20c on the vehicle front part 20a side.

The interior antenna 40d is provided inside the vehicle 20, below the left end 20c1 of the vehicle left section 20c on the vehicle rear 20b side. The interior antenna 40e is provided inside the vehicle 20, below the right end 20d1 of the vehicle right section 20d on the vehicle front 20a side. The interior antenna 40f is provided inside the vehicle 20, below the right end 20d1 of the vehicle right section 20d on the vehicle rear 20b side.

This arrangement is effective, for example, when the range in which the radio signal emitted from the base station 10 reaches the interior of the vehicle 20 through the side window 21d1 excludes the area below the left end 20c1 of the left vehicle section 20c. Specifically, when the directivity of the exterior antenna 30c is oriented in a direction close to the width direction (horizontal direction) of the vehicle 20 on the side where the side window 21d1 faces the outside, the radio signal enters the interior of the vehicle 20 with a small angle of incidence with respect to the side window 21d1. For this reason, it is difficult for the radio signal to reach the area below the left end 20c1 of the left vehicle section 20c.

Here, the in-vehicle antenna 40c is provided below the left end 20c1 of the vehicle left section 20c inside the vehicle 20, and therefore radiates wireless signals below the left end 20c1. This reduces the possibility that the area inside the vehicle 20 where wireless signals arriving from outside the vehicle 20 reach overlaps with the area where wireless signals radiated from the in-vehicle antenna 40c reach. With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in either of the two areas described above.

Similar features also apply to the combination of exterior antenna 30d and interior antenna 40d, the combination of exterior antenna 30e and interior antenna 40e, and the combination of exterior antenna 30f and interior antenna 40f.

[Third modified example of interior antenna arrangement]
Next, a third modified example of the interior antenna arrangement in the vehicle 20 of the first modified example will be described with reference to Fig. 14. Fig. 14 is a diagram for explaining the third modified example of the interior antenna arrangement. As shown in Fig. 14, two interior antennas are arranged inside the vehicle 20 for one exterior antenna.

Specifically, the exterior antenna 30c is connected to the interior antennas 40c1 and 40c2 via a relay device 50c1. The interior antenna 40c1 is provided inside the vehicle 20, above the right end 20d1 of the vehicle right section 20d on the vehicle front 20a side. The interior antenna 40c2 is provided inside the vehicle 20, below the left end 20c1 of the vehicle left section 20c on the vehicle front 20a side. The interior antennas 40c1 and 40c2 have the same function as the interior antenna 40a.

The relay device 50c1 includes an electro-optical conversion unit 51c, multimode optical fibers 53c, 53c1, and 53c2, photoelectric conversion units 55c1 and 55c2, and an optical coupler 60c. The electro-optical conversion unit 51c is connected to the exterior antenna 30c. The photoelectric conversion unit 55c1 has the same function as the photoelectric conversion unit 55c, and is connected to the interior antenna 40c1. The photoelectric conversion unit 55c2 has the same function as the photoelectric conversion unit 55c, and is connected to the interior antenna 40c2.

The multimode optical fiber 53c has one end connected to the electro-optical conversion unit 51c and the other end connected to the optical coupler 60c. The multimode optical fibers 53c1 and 53c2 have the same function as the multimode optical fiber 53c. The multimode optical fiber 53c1 has one end connected to the photoelectric conversion unit 55c1 and the other end connected to the optical coupler 60c. The multimode optical fiber 53c2 has one end connected to the photoelectric conversion unit 55c2 and the other end connected to the optical coupler 60c.

The multimode optical fiber 53c is branched into multimode optical fibers 53c1 and 53c2 by the optical coupler 60c. Note that the optical coupler 60c may be omitted and the multimode optical fibers 53a1 and 53a2 may be directly connected to the electrical-to-optical converter 51a.

External antennas 30d, 30e, 30f, internal antennas 40d1, 40d2, 40e1, 40e2, 40f1, 40f2, and relay devices 50d1, 50e1, 50f1 have the same configuration. Electrical-to-optical converters 51d, 51e, 51f, multimode optical fibers 53d, 53d1, 53d2, 53e, 53e1, 53e2, 53f, 53f1, 53f2, and optical-to-electrical converters 55d1, 55d2, 55e1, 55e2, 55f1, 55f2 also have the same configuration.

This arrangement is effective, for example, when the range in which the radio signal emitted from the base station 10 reaches the inside of the vehicle 20 through the side window 21d1 is a range excluding the area below the left end 20c1 of the left part 20c of the vehicle and the right end 20d1 of the right part 20d of the vehicle. Specifically, when the directivity of the exterior antenna 30c is oriented in a direction that is approximately the same distance away from the width and height directions (horizontal and vertical directions) of the vehicle 20 on the side where the side window 21d1 faces the outside, the incident angle of the radio signal to the side window 21d1 becomes gentle. In this way, the radio signal enters the inside of the vehicle 20 at a gentle angle of incidence to the side window 21d1, and therefore is unlikely to reach the area below the left end 20c1 of the left part 20c of the vehicle and the right end 20d1 of the right part 20d of the vehicle.

The in-vehicle antenna 40c1 is provided inside the vehicle 20 above the right end 20d1 of the vehicle right section 20d, and so radiates wireless signals downward from the right end 20d1. This reduces the possibility that the area inside the vehicle 20 where wireless signals arriving from outside the vehicle 20 reach overlaps with the area where wireless signals radiated from the in-vehicle antenna 40c1 reach.

The in-vehicle antenna 40c2 is provided below the left end 20c1 of the vehicle left section 20c inside the vehicle 20, and so radiates wireless signals below the left end 20c1. This reduces the possibility that the area inside the vehicle 20 where wireless signals arriving from outside the vehicle 20 reach overlaps with the area where wireless signals radiated from the in-vehicle antenna 40c2 reach.

With this configuration, the terminal 100 (not shown) placed inside the vehicle 20 receives wireless signals in any of the three areas described above.

Similar features also apply to the combination of exterior antenna 30d and interior antennas 40d1, 40d2, the combination of exterior antenna 30e and interior antennas 40e1, 40e2, and the combination of exterior antenna 30f and interior antennas 40f1, 40f2.

According to the first modification of this embodiment, the interior antenna is provided at least one of above the right end 20d1 of the vehicle right section 20d and below the left end 20c1 of the vehicle left section 20c, depending on the directivity of the exterior antenna 30a.

This reduces the possibility that the radio signal radiated from the base station 10 and arriving inside the vehicle 20 will interfere with the radio signal re-radiated from the in-vehicle antenna 40c or the in-vehicle antennas 40c1 and 40c2. This reduces the degradation of the quality of the received signal at the terminal 100 placed inside the vehicle 20.

The above-mentioned features also apply to the combination of the exterior antenna 30d and the interior antenna 40d (or the interior antennas 40d1 and 40d2), and to the combination of the exterior antenna 30e and the interior antenna 40e (or the interior antennas 40e1 and 40e2). Similarly, the above-mentioned features also apply to the combination of the exterior antenna 30f and the interior antenna 40f (or the interior antennas 40f1 and 40f2).

According to the first modification of this embodiment, the exterior antennas 30a to 30f have directivity in different directions. For this reason, for example, when the exterior antenna 30a is receiving a wireless signal from the base station 10 from the front, and the vehicle 20 moves past the base station 10, the exterior antenna 30a will no longer be able to receive the wireless signal. However, even in this case, the exterior antennas 30c and 30d (or the exterior antennas 30e and 30f) can receive wireless signals in sequence from the sides of the vehicle 20.

In addition, when the vehicle 20 passes the base station 10, the exterior antenna 30d (or exterior antenna 30f) is no longer able to receive wireless signals. However, even in this case, the exterior antenna 30b can still receive wireless signals from the rear of the vehicle 20. This further reduces the possibility that the terminal 100 placed inside the vehicle 20 will be unable to receive wireless signals as the vehicle 20 moves, thereby further suppressing deterioration in the quality of the received signal at the terminal 100.

Therefore, according to the first variant of this embodiment, it is possible to provide a communication system 1 that can suppress deterioration in the quality of the received signal at the terminal 100 even when the wireless signal is relayed inside the vehicle 20.

[Second Modification]
In the above-described embodiment, the radiation direction of the wireless signal from the in-vehicle antenna 40a is oriented vertically downwardly to the rear end portion 20b1 of the vehicle rear portion 20b, but the present invention is not limited to this.

Figure 15 is a diagram illustrating the radiation direction of wireless signals from the interior antennas 40a, 40b in the vehicle 20 of the second modified example of this embodiment. As shown in Figure 15, in the vehicle 20 of the second modified example, the interior antenna 40a is provided inside the vehicle 20, above the rear end 20b1 of the vehicle rear 20b, on the side farther from the rear window 21b. The radiation direction of wireless signals from the interior antenna 40a is toward the side closer to the rear window 21b, below the rear end 20b1 of the vehicle rear 20b. In this way, in the interior antenna 40a, the radiation direction P1 of the wireless signal is tilted so that the wireless signal is re-radiated in the opposite direction to the direction in which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the interior antenna 40a1 (see Figure 9).

In the above-described embodiment, the direction of radiation of the wireless signal from the in-vehicle antenna 40b was vertically downward toward the front end 20a1 of the front part 20a of the vehicle, but this is not limited thereto.

As shown in FIG. 15, in the second modified vehicle 20, the in-vehicle antenna 40b is provided inside the vehicle 20, above the front end 20a1 of the vehicle front 20a, on the side farther from the windshield 21a. The radiation direction of the wireless signal from the in-vehicle antenna 40b is directed toward the side closer to the windshield 21a, below the front end 20a1 of the vehicle front 20a. Thus, in the in-vehicle antenna 40b, the radiation direction P2 of the wireless signal is tilted so that the wireless signal is re-radiated in the opposite direction to the direction in which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the in-vehicle antenna 40b1 (see FIG. 9).

Similarly, in the vehicle 20 of the second modified example, the interior antennas 40c, 40d are provided inside the vehicle 20, above the right end 20d1 of the vehicle right section 20d, on the side farther from the side windows 21d2, 21f2. The radiation direction of the wireless signal from the interior antennas 40c, 40d is directed toward the side closer to the side windows 21d2, 21f2, below the right end 20d1 of the vehicle right section 20d. In this way, the radiation direction of the wireless signal from the interior antennas 40c, 40d is tilted so that the wireless signal is re-radiated in the opposite direction to the direction in which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the interior antennas 40c1, 40d1.

In the vehicle 20 of the second modified example, the interior antennas 40e, 40f are provided inside the vehicle 20, above the left end 20c1 of the vehicle left section 20c, on the side farther from the side windows 21d1, 21f1. The radiation direction of the wireless signal from the interior antennas 40e, 40f faces the side closer to the side windows 21d1, 21f1, below the left end 20c1 of the vehicle left section 20c. In this way, the radiation direction of the wireless signal from the interior antennas 40e, 40f is tilted so that the wireless signal is re-radiated in the opposite direction to the direction in which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the interior antennas 40e1, 40f1.

This configuration also reduces the possibility that the radio signal radiated from the base station 10 and arriving inside the vehicle 20 will interfere with the radio signal re-radiated from the in-vehicle antenna 40a, 40b, 40c, 40d, 40e, or 40f.

[Third Modification]
In the first modified example of the interior antenna arrangement of the embodiment described above, the radiation direction of the wireless signal from the interior antenna 40a is oriented vertically downwardly to the front end portion 20a1 of the vehicle front portion 20a, but this is not limited thereto.

Figure 16 is a diagram illustrating the radiation direction of wireless signals by the in-vehicle antennas 40a and 40b in a vehicle 20 according to a third modified example of this embodiment. As shown in Figure 16, in the vehicle 20 according to the third modified example, the in-vehicle antenna 40a is provided inside the vehicle 20, below the front end 20a1 of the vehicle front 20a, on the side farther from the front window 21a. The radiation direction P3 of the wireless signal in the in-vehicle antenna 40a faces the side closer to the front window 21a, below the front end 20a1 of the vehicle front 20a. In this way, in the in-vehicle antenna 40a, the radiation direction P3 of the wireless signal is tilted so that the wireless signal is re-radiated toward the direction from which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the in-vehicle antenna 40a2 (see Figure 9).

In the first modified example of the interior antenna arrangement of the embodiment described above, the direction of radio signal radiation from the interior antenna 40b is oriented vertically downward at the rear end 20b1 of the vehicle rear 20b, but this is not limited thereto.

As shown in FIG. 16, in the vehicle 20 of the second modified example, the in-vehicle antenna 40b is provided inside the vehicle 20, below the rear end 20b1 of the vehicle rear 20b, on the side farther from the rear window 21b. The radiation direction P4 of the wireless signal in the in-vehicle antenna 40b is oriented toward the side closer to the rear window 21b, below the rear end 20b1 of the vehicle rear 20b. In this way, in the in-vehicle antenna 40b, the radiation direction P4 of the wireless signal is tilted so that the wireless signal is re-radiated toward the direction from which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the in-vehicle antenna 40b1.

Similarly, in the vehicle 20 of the third modified example, the interior antennas 40c, 40d are provided inside the vehicle 20, below the left end 20c1 of the vehicle left section 20c, on the side farther from the side windows 21d1, 21f1. The radiation direction of the wireless signal from the interior antennas 40c, 40d is oriented toward the side closer to the side windows 21d1, 21f1, below the left end 20c1 of the vehicle left section 20c. In this way, the radiation direction of the wireless signal from the interior antennas 40c, 40d is tilted so that the wireless signal is re-radiated toward the direction from which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the interior antennas 40c2, 40d2 (see FIG. 14).

In the second modified vehicle 20, the interior antennas 40e and 40f are provided inside the vehicle 20, below the right end 20d1 of the vehicle right section 20d, on the side farther from the side windows 21d2 and 21f2. The radiation direction of the wireless signal from the interior antennas 40e and 40f faces the side closer to the side windows 21d2 and 21f2, below the right end 20d1 of the vehicle right section 20d. In this way, the radiation direction of the wireless signal from the interior antennas 40e and 40f is tilted so that the wireless signal is re-radiated toward the direction from which the wireless signal arrives from outside the vehicle 20. The above configuration can also be applied to the interior antennas 40e2 and 40f2 (see FIG. 14).

This configuration also reduces the possibility that a radio signal radiated from the base station 10 and arriving inside the vehicle 20 will interfere with a radio signal re-radiated from the in-vehicle antenna 40a, 40b, 40c, 40d, 40e, or 40f.

[Fourth Modification]
In the above-described embodiment, the exterior antennas 30a, 30b are provided separately on the upper body 23 of the vehicle 20, but this is not limited thereto. Fig. 17 is a side view illustrating the exterior antenna arrangement in the vehicle 20 of the fourth modified example of this embodiment. As shown in Fig. 17, in the vehicle 20 of the fourth modified example, the exterior antennas 30a, 30b are provided together in one location. With this configuration, the exterior antennas 30a, 30b can be easily arranged. The above configuration can also be applied to the exterior antennas 30c, 30d, 30e, 30f in the vehicle 20 of the first modified example.

[Fifth Modification]
In the above-described embodiment, the exterior antenna 30a is provided parallel to the surface of the front window 21a so that the exterior antenna 30a has directivity toward the side of the front window 21a facing the outside. However, the present invention is not limited to this.

Figure 18 is a top view illustrating the arrangement of exterior antennas 30i, 30j, 30k, 30l and interior antennas 40i, 40j, 40k, 40l in a vehicle 20 according to a fifth modified example of this embodiment. As shown in Figure 18, in the vehicle 20 according to the fifth modified example, the exterior antenna 30i is provided in the left corner of the front end of the vehicle 20 in the upper body 23 so as to have directivity toward the side where the front window 21a faces the outside and the side where the side window 21c1 faces the outside. The interior antenna 40i is provided inside the vehicle 20, above the right end of the rear end 20b1 of the vehicle rear part 20b. The relay device 50i is connected to the exterior antenna 30i and the interior antenna 40i inside the vehicle 20.

The exterior antenna 30j is provided in the upper body 23 at the right corner of the front end of the vehicle 20 so as to have directivity toward the side where the front window 21a faces the outside and toward the side where the side window 21c2 faces the outside. The interior antenna 40j is provided inside the vehicle 20, above the left end of the rear end 20b1 of the vehicle rear part 20b. The relay device 50j is connected to the exterior antenna 30j and the interior antenna 40j inside the vehicle 20.

In addition, in the above-described embodiment, the exterior antenna 30b is arranged parallel to the surface of the rear window 21b so that the antenna has directivity toward the side of the rear window 21b facing the outside, but this is not limited to this.

As shown in FIG. 18, the exterior antenna 30k is provided in the upper body 23 at the left corner of the rear end of the vehicle 20 so as to have directivity toward the side where the rear window 21b faces the outside and toward the side where the side window 21g1 faces the outside. The interior antenna 40k is provided inside the vehicle 20, above the right end of the front end 20a1 of the vehicle front 20a. The relay device 50k is connected to the exterior antenna 30k and the interior antenna 40k inside the vehicle 20.

The exterior antenna 30l is provided in the right corner of the rear end of the vehicle 20 in the upper body 23 so as to have directivity toward the side where the rear window 21l faces the outside and toward the side where the side window 21g2 faces the outside. The interior antenna 40l is provided inside the vehicle 20, above the left end of the front end 20a1 of the vehicle front 20a. The relay device 50l is connected to the exterior antenna 30l and the interior antenna 40l inside the vehicle 20.

With this configuration, the exterior antenna 30i has directivity toward the side where the front window 21a faces the outside and toward the side where the side window 21c1 faces the outside. The exterior antenna 30j has directivity toward the side where the front window 21a faces the outside and toward the side where the side window 21c2 faces the outside. The exterior antenna 30k has directivity toward the side where the rear window 21b faces the outside and toward the side where the side window 21g1 faces the outside. The exterior antenna 30l has directivity toward the side where the rear window 21b faces the outside and toward the side where the side window 21g2 faces the outside. In this way, the exterior antennas 30i, 30j, 30k, and 30l have directivity in different directions.

In this way, the exterior antennas 30i and 30j have directivity on the side where the side windows 21c1 and 21c2 face the outside, so compared to the exterior antenna 30a, the timing at which the wireless signal cannot be received when the vehicle 20 passes the base station 10 can be delayed. Similarly, the exterior antennas 30k and 30l have directivity on the side where the side windows 21g1 and 21g2 face the outside, so compared to the exterior antenna 30b, the timing at which the wireless signal can be received when the vehicle 20 passes the base station 10 can be advanced. Therefore, even if there are four exterior antennas, the possibility that the terminal 100 placed inside the vehicle 20 will be unable to receive a wireless signal as the vehicle 20 moves can be further reduced. Therefore, it is possible to further suppress the deterioration of the quality of the received signal at the terminal 100 while suppressing an increase in the number of exterior antennas.

[Sixth Modification]
In the above-described embodiment, the in-vehicle antenna that radiates wireless signals to the inside of the vehicle 20 is fixed, but this is not limiting. When a change in the directivity of the exterior antenna is detected using the control device, the in-vehicle antenna that radiates wireless signals to the inside of the vehicle 20 may be switched according to the directivity of the exterior antenna.

The control device 300 is provided inside the vehicle 20 shown in FIG. 9. When the control device 300 detects a change in the directivity of the exterior antenna 30a, it instructs the relay device 50a1 to relay the electrical signal to at least one of the interior antennas 40a1 and 40a2 in accordance with the changed directivity of the exterior antenna 30a. Similarly, when the control device 300 detects a change in the directivity of the exterior antenna 30b, it instructs the relay device 50b1 to relay the electrical signal to at least one of the interior antennas 40b1 and 40b2 in accordance with the changed directivity of the exterior antenna 30b.

In the vehicle 20 of the sixth modified example, the multimode optical fibers 53a1 and 53a2 are directly connected to the electro-optical conversion unit 51a. Similarly, the multimode optical fibers 53b1 and 53b2 are directly connected to the electro-optical conversion unit 51b.

Figure 19 is a functional block diagram of the control device 300 in the vehicle 20 of the sixth modified example of this embodiment. As shown in Figure 19, it includes a detection unit 301, a control unit 303, and a switching unit 305. The detection unit 301 detects a change in the directivity of the exterior antennas 30a and 30b.

For example, the detection unit 301 calculates the tilt of the exterior antennas 30a, 30b as the directivity of the exterior antennas 30a, 30b at regular intervals. When the detection unit 301 detects a change in the tilt of at least one of the exterior antennas 30a, 30b based on the calculated tilt of the exterior antennas 30a, 30b, it transmits a detection signal including information indicating the tilt of the exterior antenna to the control unit 303.

When the control unit 303 receives a detection signal from the detection unit 301, it selects an interior antenna that radiates a wireless signal inside the vehicle 20 based on the inclination of the exterior antenna indicated by the information contained in the detection signal.

For example, when the control unit 303 receives a detection signal including information indicating the inclination of the exterior antenna 30a, the operation flow of the control unit 303 is as follows. If the control unit 303 determines that the inclination of the exterior antenna 30a is large, the wireless signal arriving from outside the vehicle 20 is unlikely to reach the rear end 20b1 of the vehicle rear 20b, so the control unit 303 selects the interior antenna 40a1. If the control unit 303 determines that the inclination of the exterior antenna 30a is small, the wireless signal arriving from outside the vehicle 20 is unlikely to reach the lower part of the front end 20a1 of the vehicle front 20a, so the control unit 303 selects the interior antenna 40a2. If the control unit 303 determines that the inclination of the exterior antenna 30a is gentle, the wireless signal arriving from outside the vehicle 20 is unlikely to reach the rear end 20b1 of the vehicle rear 20b and the lower part of the front end 20a1 of the vehicle front 20a, so the control unit 303 selects the interior antennas 40a1 and 40a2.

The control unit 303 transmits a selection signal including information indicating the selected interior antenna to the switching unit 305. Upon receiving the selection signal, the switching unit 305 switches the interior antenna based on the interior antenna indicated by the information included in the selection signal.

For example, when the switching unit 305 receives a selection signal including information indicating the in-vehicle antenna 40a1, it instructs the electrical-optical conversion unit 51a to output an optical signal only to the multimode optical fiber 53a1. When the switching unit 305 receives a selection signal including information indicating the in-vehicle antenna 40a2, it instructs the electrical-optical conversion unit 51a to output an optical signal only to the multimode optical fiber 53a2. When the switching unit 305 receives a selection signal including information indicating the in-vehicle antennas 40a1 and 40a2, it instructs the electrical-optical conversion unit 51a to output an optical signal to both the multimode optical fibers 53a1 and 53a2.

With this configuration, the in-vehicle antenna that radiates wireless signals to the inside of the vehicle 20 can be appropriately switched in response to a change in the directivity of the exterior antenna. This allows for flexible response even if the directivity of the exterior antenna is changed and the area within the vehicle 20 in which wireless signals arriving from outside the vehicle 20 reach changes. The control device 300 may be provided inside the vehicle 20 shown in FIG. 14. In this case, the control device 300 may switch the in-vehicle antenna in response to a change in the directivity of each of the exterior antennas 30a, 30b, 30c, 30d, 30e, and 30f. The control device 300 may also be located outside the vehicle 20 and switch the in-vehicle antenna by remote instruction.

[Seventh Modification]
In the above embodiment, the exterior antenna 30a is provided on the upper body 23 of the vehicle 20, but may be provided on one side of the body along the width direction of the vehicle 20 that forms the outer front end of the vehicle 20 in the upper body 23. The exterior antenna 30a may be provided on one side of the body along the height direction of the vehicle 20 that forms the right corner or left corner of the outer front end of the vehicle 20. Similarly, in the above embodiment, the exterior antenna 30b is provided on the upper body 23 of the vehicle 20, but may be provided on one side of the body along the width direction of the vehicle 20 that forms the outer rear end of the vehicle 20 in the upper body 23. The exterior antenna 30b may be provided on one side of the body along the height direction of the vehicle 20 that forms the right corner or left corner of the outer rear end of the vehicle 20. The above configuration is also applicable to the exterior antennas 30c, 30d, 30e, and 30f in the vehicle 20 of the first modified example.

Although the present embodiment has been described above, the present embodiment is not limited to these, and various modifications are possible within the scope of the gist of the present embodiment. In addition, a combination of multiple modifications from the first modification to the seventh modification described above may be applied to the present embodiment.

REFERENCE SIGNS LIST 1 Communication system 10 Base station 20 Vehicle 20a Vehicle front 20a1 Front end 20b Vehicle rear 20b1 Rear end 21a Front window 21a
21b Rear window 21b
23 Upper part of vehicle body 30a, 30b External antenna 40a, 40a1, 40a2, 40b, 40b1, 40b2 Internal antenna 50a, 50a1, 50b, 50b1 Relay device 51a, 51b Electrical-optical conversion unit 53a, 53a1, 53a2, 53b, 53b1, 53b2 Multimode optical fiber 55a, 55a1, 55a2, 55b, 55b1, 55b2 Optical-electrical conversion unit 100 Terminal F1, F2, B1, B2 Area θ1 Angle DR1 First direction DR2 Second direction

Claims (10)

A communication system for a vehicle including a first window provided on one side in a longitudinal direction of the vehicle, and a second window provided on the other side in the longitudinal direction of the vehicle and facing the first window,
a first exterior antenna provided in an upper portion of a body of the vehicle near an upper portion of the vehicle and having directivity toward a side of the first window facing the outside;
at least one first interior antenna provided inside the vehicle, at least one of above the vehicle end on the other side in the longitudinal direction of the vehicle and below the vehicle end on the one side in the longitudinal direction of the vehicle, depending on the directivity of the first exterior antenna;
a first relay device that receives a first electrical signal from the first exterior antenna and relays the first electrical signal to at least one of the first interior antennas;
a second exterior antenna provided in an upper portion of a body of the vehicle near an upper portion of the second window and having directivity toward a side of the second window facing the outside;
at least one second interior antenna provided inside the vehicle, at least one of above the vehicle end on the one side in the longitudinal direction of the vehicle and below the vehicle end on the other side in the longitudinal direction of the vehicle, depending on the directivity of the second exterior antenna;
a second relay device that receives a second electrical signal from the second exterior antenna and relays the second electrical signal to at least one of the second interior antennas;
Equipped with
At least one of the first interior antennas emits a radio signal based on the first electrical signal relayed by the first relay device;
At least one of the second interior antennas emits a radio signal based on the second electrical signal relayed by the second relay device;
The first relay device is
a first electric-to-optical converter that converts the first electric signal output from the first exterior antenna into a first optical signal;
a first optical fiber for transmitting the first optical signal;
at least one first photoelectric conversion unit that converts the first optical signal received via the first optical fiber into the first electrical signal and outputs the first electrical signal to at least one of the first interior antennas;
Including,
The second relay device is
a second electric-to-optical converter that converts the second electric signal output from the second exterior antenna into a second optical signal;
a second optical fiber for transmitting the second optical signal;
at least one second photoelectric conversion unit that converts the second optical signal received via the second optical fiber into the second electrical signal and outputs the second electrical signal to at least one second in-vehicle antenna;
A communication system comprising: The two first interior antennas are provided above the vehicle end on the other side in the longitudinal direction of the vehicle and below the vehicle end on the one side in the longitudinal direction of the vehicle,
the first optical fiber is branched by a first optical coupler and transmits the first optical signal to two of the first opto-electrical conversion units;
the two first photoelectric conversion units convert the first optical signal received via the first optical fiber into the first electrical signal, and output the first electrical signal to the two first in-vehicle antennas;
The two second interior antennas are provided above the vehicle end on the one side in the longitudinal direction of the vehicle and below the vehicle end on the other side in the longitudinal direction of the vehicle,
the second optical fiber is branched by a second optical coupler and transmits the second optical signal to two of the second opto-electrical conversion units;
The communication system according to claim 1 , wherein the two second photoelectric conversion units convert the second optical signal received via the second optical fiber into the second electrical signal and output the second electrical signal to the two second in-vehicle antennas. the first interior antenna is provided above the other vehicle end in a longitudinal direction of the vehicle, on a side farther from the second window,
a radiation direction of a radio signal from the first interior antenna is directed toward a side closer to the second window below the other vehicle end in the longitudinal direction of the vehicle,
the second interior antenna is provided above the one vehicle end in the longitudinal direction of the vehicle, on a side farther from the first window,
2. The communication system according to claim 1, wherein the radiation direction of the radio signal from the second interior antenna is directed toward a side closer to the first window below the vehicle end on the one side in the longitudinal direction of the vehicle. the first interior antenna is provided below the vehicle end on the one side in a longitudinal direction of the vehicle, on a side farther from the first window,
a radiation direction of a radio signal from the first interior antenna is directed toward a side closer to the first window below the one vehicle end in the longitudinal direction of the vehicle,
the second interior antenna is provided below the other vehicle end in the longitudinal direction of the vehicle, on a side farther from the second window,
The communication system according to claim 1 , wherein the radiation direction of the radio signal from the second interior antenna is directed toward a side closer to the second window below the other end of the vehicle in the longitudinal direction of the vehicle. the first exterior antenna has directivity toward a side of the first window facing the outside and toward a side of a window provided in a width direction of the vehicle facing the outside,
The communication system according to claim 1 , wherein the second exterior antenna has directivity toward a side of the second window facing the outside and toward a side of a window provided in a width direction of the vehicle facing the outside. A control device is further provided,
The two first interior antennas are provided above the vehicle end on the other side in the longitudinal direction of the vehicle and below the vehicle end on the one side in the longitudinal direction of the vehicle,
When the control device detects a change in the directivity of the first exterior antenna, the control device instructs the first relay device to relay the first electrical signal to at least one of the two first interior antennas in accordance with the changed directivity of the first exterior antenna;
The two second interior antennas are provided above the vehicle end on the one side in the longitudinal direction of the vehicle and below the vehicle end on the other side in the longitudinal direction of the vehicle,
The communication system described in claim 1, wherein when the control device detects a change in directivity of the second exterior antenna, the control device instructs the second relay device to relay the second electrical signal to at least one of the two second interior antennas in accordance with the changed directivity of the second exterior antenna. the vehicle includes a third window provided on one side in a width direction of the vehicle, and a fourth window provided on the other side in the width direction of the vehicle and facing the third window,
The communication system includes:
a third exterior antenna provided in an upper portion of a vehicle body of the vehicle near an upper portion of the vehicle body and having directivity toward a side of the third window facing the outside;
at least one third interior antenna provided inside the vehicle, at least one of above the vehicle end on the other side in the width direction of the vehicle and below the vehicle end on the one side in the width direction of the vehicle, depending on the directivity of the third exterior antenna;
a third relay device that receives a third electrical signal from the third exterior antenna and relays the third electrical signal to at least one of the third interior antennas;
a fourth exterior antenna provided in an upper portion of a body of the vehicle near an upper portion of the vehicle and having directivity toward a side of the fourth window facing the outside;
at least one fourth interior antenna provided inside the vehicle, at least one of above the vehicle end on the one side in the width direction of the vehicle and below the vehicle end on the other side in the width direction of the vehicle, depending on the directivity of the fourth exterior antenna;
a fourth relay device that receives a fourth electrical signal from the fourth exterior antenna and relays the fourth electrical signal to at least one of the fourth interior antennas;
Further equipped with
At least one of the third interior antennas emits a radio signal based on the third electrical signal relayed by the third relay device;
At least one of the fourth interior antennas emits a radio signal based on the fourth electrical signal relayed by the fourth relay device;
The third relay device is
a third electric-to-optical converter that converts the third electric signal output from the third exterior antenna into a third optical signal;
a third optical fiber for transmitting the third optical signal;
at least one third photoelectric conversion unit that converts the third optical signal received via the third optical fiber into the third electrical signal and outputs the third electrical signal to at least one third in-vehicle antenna;
Including,
The fourth relay device is
a fourth electric-to-optical converter that converts the fourth electric signal output from the fourth exterior antenna into a fourth optical signal;
a fourth optical fiber for transmitting the fourth optical signal;
at least one fourth opto-electrical converter that converts the fourth optical signal received via the fourth optical fiber into the fourth electrical signal and outputs the fourth electrical signal to at least one fourth in-vehicle antenna;
A communication system according to any one of claims 1 to 6, comprising: the two third interior antennas are provided above the vehicle end on the other side in the width direction of the vehicle and below the vehicle end on the one side in the width direction of the vehicle,
the third optical fiber is branched by a third optical coupler and transmits the third optical signal to two of the third opto-electrical conversion units;
the two third photoelectric conversion units convert the third optical signal received via the third optical fiber into the third electrical signal, and output the third electrical signal to the two third in-vehicle antennas;
the two fourth interior antennas are provided above the vehicle end on the one side in a width direction of the vehicle and below the vehicle end on the other side in the width direction of the vehicle,
the fourth optical fiber is branched by a fourth optical coupler and transmits the fourth optical signal to two of the fourth opto-electrical conversion units;
The communication system according to claim 7 , wherein the two fourth photoelectric conversion units convert the fourth optical signal received via the fourth optical fiber into the fourth electrical signal and output the fourth electrical signal to the two fourth in-vehicle antennas. the third interior antenna is provided above the vehicle end on the other side in a width direction of the vehicle, on a side farther from the fourth window,
a radiation direction of a radio signal from the third interior antenna is directed toward a side closer to the fourth window below the vehicle end on the other side in a width direction of the vehicle,
the fourth interior antenna is provided above the vehicle end on the one side in a width direction of the vehicle, on a side farther from the third window,
The communication system according to claim 7 , wherein a radiation direction of a radio signal from the fourth interior antenna is oriented toward a side closer to the third window below the vehicle end on the one side in the width direction of the vehicle. the third interior antenna is provided below the vehicle end on the one side in a width direction of the vehicle and on a side farther from the third window,
a radiation direction of a radio signal from the third interior antenna is directed toward a side closer to the third window below the vehicle end on the one side in a width direction of the vehicle,
the fourth interior antenna is provided below the vehicle end on the other side in a width direction of the vehicle, on a side farther from the fourth window,
The communication system according to claim 7 , wherein a radiation direction of a radio signal from the fourth interior antenna is oriented toward a side closer to the fourth window below the vehicle end on the other side in the width direction of the vehicle.

Images