JP3008946B2 - Road-to-vehicle communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcell roadside-to-vehicle communication system in which a plurality of roadside antennas are arranged along a road and a series of cells are formed on the road to enable mobile communication with a vehicle-mounted device. . In particular, the present invention provides orthogonal frequency division multiplexing (OFDM) as a data modulation scheme.
The present invention relates to a road-to-vehicle communication system employing a system.

[0002]

2. Description of the Related Art The communication demand between a road manager and a vehicle is:
It is on the rise. Frequent exchanges of roadside information and vehicle information are required, especially on expressways, in order to realize road driving without burdening the driver of the vehicle and avoiding accidents with each other. There is. As such a system is developed, various sensors and cameras will be covered on both the road and the vehicle, leading to an automatic driving system in which the road and the vehicle are in close contact with each other and operate (for example, , Japanese Patent Application No. 7-4326
No. 0).

In consideration of future expansion to automatic driving, a driving support system for vehicles (hereinafter referred to as "road-vehicle communication system")
It is necessary to provide continuous cells on the road when building the Therefore, it is conceivable to lay a leaky coaxial cable along the road.However, the laying work becomes large and it is necessary to install the leaky coaxial cable relatively low from the ground. There is a disadvantage that the reach distance is short.

On the other hand, as shown in FIG. 12, if the road antennas 120 are installed at various positions on the road at predetermined intervals to perform communication, a relatively wide cell 121 can be secured by one road antenna 120. can do. in this case,
It goes without saying that the on-road antennas 120 are respectively coupled to base stations on the road manager side via optical fibers or the like.

When the on-road antenna 120 is installed, when a large vehicle approaches a small vehicle, the on-road antenna 12
You may not be able to see 0. FIG. 13 is a diagram illustrating a state in which a small car enters a radio wave shielding area 122 formed by a bus and communication becomes difficult. In particular, microwaves and millimeter waves having high frequencies have small diffraction angles and are easily shielded. For this reason, communication is interrupted between the road and the vehicle, and communication becomes impossible.

Therefore, in order to enable continuous communication between the road and the vehicle, a road transmitting antenna having a specific directivity is arranged along the road, and radio waves having the same contents are transmitted from each road transmitting antenna to the same cell. Proposals have been made for multi-station transmission that radiates within.

[0007]

However, if a road antenna is installed, a multipath delay wave is generated due to a structure near the road becoming a reflector or a plurality of vehicles existing in the cell. Therefore, it is normal that inter-carrier interference and inter-symbol interference occur. When intersymbol interference occurs, a so-called floor error occurs without improving the bit error rate even if the reception level of the received radio wave is high.

Particularly, in the case of multi-station transmission, since a plurality of radio waves are radiated at the same transmission power in the same cell, the above-mentioned inter-carrier interference and inter-symbol interference appear strongly. Required for construction. Generally, in a mobile communication system using a single carrier (single carrier), an equalizer having a characteristic opposite to that of a transmission line is provided in a receiver in order to avoid the influence of intersymbol interference due to multipath delay waves. Have been done.

However, since an automobile moves at high speed in a cell, the fluctuation of the received electric field per time is so large that the calculation speed of the equalizer cannot keep up, and signal transmission cannot be performed at a certain transmission error rate or less. . Further, the scale of hardware for realizing the equalizer increases, and the power consumption also increases. In road-to-vehicle communication that presupposes high-speed movement, communication is performed using radio waves of different frequencies for each cell. However, since the vehicle passes through multiple cells in a short time as the vehicle travels, the in-vehicle communication device It is necessary to switch the transmission / reception frequency of the data at high speed. For this reason, it is necessary to take measures such as providing an oscillator capable of high-speed pull-in or a plurality of oscillators, which hinders downsizing and cost reduction of the device.

Accordingly, an object of the present invention is to provide a road-vehicle communication system which solves the above-mentioned technical problems, can prevent inter-carrier interference and inter-symbol interference, and enables stable communication between a road and a vehicle. That is.

[0011]

According to a first aspect of the present invention, there is provided a road-to-vehicle communication system for transmitting a signal having the same content, which is OFDM-modulated, to a plurality of transmission lines. A transmitting device, arranged at different positions along the road, having a specific directivity, receiving a signal transmitted to the transmission line from the signal transmitting device, respectively,
A plurality of road transmitting antennas for radiating radio waves into the same cell based on the received signal, a vehicle-mounted receiving antenna for receiving radio waves radiated from the road transmitting antenna, and the vehicle-mounted receiving antenna And an in-vehicle device having a receiving means for receiving and demodulating the received data.

In the present invention, radio waves are radiated from a plurality of road transmitting antennas based on a signal that has been OFDM-modulated with the same data. In this case, since each on-road transmitting antenna has a unique directivity (including non-directionality), radio waves radiated from each on-road transmitting antenna arrive at vehicles traveling on the road from different directions. Therefore, even if the radio wave from one of the vehicles is shielded by a large vehicle, the in-vehicle device increases the reception level of the radio wave from the other of the vehicles. Therefore, communication between the road transmitting antenna and the vehicle-mounted device becomes possible.

[0013] Further, since radio waves arriving from different directions with respect to a vehicle traveling on a road are received, there is an environment in which multipath is likely to occur. In the present invention, an OFDM system which is strong against multipath is preferably employed. A transmission system for transmitting a signal to the transmission line may be an optical fiber wireless transmission system (claim 2).

According to the present invention, since a high-frequency signal is fed from the signal transmitting device to the road transmitting antenna through the optical fiber, it is not necessary to provide a signal transmitting device for each road transmitting antenna. Therefore, the configuration of the road transmitting antenna can be simplified. The on-vehicle device further includes an on-vehicle transmission antenna for emitting an OFDM-modulated radio wave based on vehicle data, is disposed at a different position along a road, has a specific directivity, and emits from the on-vehicle transmission antenna. And a plurality of road receiving antennas for transmitting signals corresponding to the received radio waves to predetermined transmission lines, respectively, and signals transmitted from the plurality of road receiving antennas to the transmission line. And a road receiving means for performing demodulation on the basis of the above.

In the present invention, vehicle data is provided from the vehicle side to the roadside. In this case, in the in-vehicle apparatus, a radio wave is radiated from the in-vehicle transmission antenna, and the reception level at each road receiving antenna is affected by multipath and depends on the directivity. Therefore, by receiving signals at so-called multiple stations, radio waves can be reliably received on the roadside, and vehicle data can be restored without errors.

The transmission system for transmitting a signal to the transmission line may be an optical fiber wireless transmission system. According to the present invention, a received signal received by a roadside receiving antenna can be transmitted to a transmission line at a high frequency,
In the signal selection device, the reception level of each reception signal can be easily compared with the high frequency level. Therefore, the configurations of the road receiving antenna and the signal selection device can be simplified.

Further, an orthogonal frequency division multiplexing (OFDM) system in which a guard time is provided for each symbol can be employed as an OFDM modulation system for data.
Claim 6). Generally, when radio waves arrive at a vehicle from a plurality of directions, so-called multipath interference may occur. Specifically, due to the difference in the distance from the on-road transmitting antenna depending on the position of the vehicle, a propagation delay time difference of radio waves radiated from each on-road transmitting antenna occurs,
Intersymbol interference occurs.

However, in the present invention, a guard time is provided for each symbol so that interfering codes can be prevented from overlapping, so that intersymbol interference due to multipath delay can be avoided. When transmission is performed from a plurality of road transmitting antennas to the same cell, there is a possibility that a slight difference in carrier frequency may occur between stations.
It is known that transmission quality deterioration due to differences in carrier frequencies is inferior to other transmission methods. To solve this problem, the optical fiber wireless transmission system according to claim 2 or 5 is an extremely effective and economical solution, whereby the carrier frequency of each station can be completely matched.

According to a seventh aspect of the present invention, in the road-vehicle communication system, the plurality of on-road transmitting antennas form a plurality of sub-areas obtained by dividing one cell. According to the present invention, since the radio waves OFDM-modulated by the road traffic data having the same contents are radiated to the respective sub-areas, each time the sub-area changes, the arrival direction of the radio waves changes. Therefore, even if the radio wave is shielded in a certain sub area, the radio wave can be received when it reaches the next sub area. Therefore, communication between the vehicle side and the roadside is not interrupted in the same cell, and continuous communication becomes possible.

Further, since the subarea of each roadside transmitting antenna is obtained by dividing one cell, the transmission power of the roadside transmitting antenna can be small. Therefore, it is possible to reduce the cost of the on-road transmitting antenna. According to the road-vehicle communication system of the eighth aspect, communication is performed over a plurality of continuous cells with the same frequency and the same content.

For example, since the downlink signal from the on-road transmitting antenna to the on-vehicle antenna has the same content and the same carrier frequency even when the vehicle moves to an adjacent cell, there is no need to switch the oscillator of the on-vehicle communication device. Such a configuration,
OFD that is not in general communication system that is strong against multipath
It becomes possible only by adopting M.

[0022]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. -First Embodiment- FIG. 1 is a conceptual diagram showing a configuration of a road-vehicle communication system according to a first embodiment of the present invention. This road-vehicle communication system is for performing communication between a ground station 1 and an in-vehicle device 3 mounted on a vehicle 2.

In the ground station 1, a plurality of cells E along the road
Are continuously formed. Near the boundary in the longitudinal direction of the road of each cell E, a first on-road antenna 4a and a second on-road antenna 4b having directivity toward the inside of cell E, respectively.
Is installed. From the first road antenna 4a and the second road antenna 4b, the same frequency (for example, 6 (GHz))
Band) is radiated into the cell E.
Specifically, radio waves are radiated from the first roadside antenna 4a in the direction indicated by the white arrow, and the second roadside antenna 4a
Radio waves are radiated from b in the direction indicated by the black arrow. Therefore, at each point in the cell E, radio waves of the same frequency arrive from the front-back direction with respect to the longitudinal direction of the road. Therefore, when the vehicle 2 passes through the inside of the cell E, a radio wave is received from the front and rear direction of the vehicle 2.

The height h of the on-road antenna 4 from the ground is h.
Is, for example, 10 (m), and the length r of the cell E in the longitudinal direction of the road is, for example, 100 (m). Each road antenna 4a, 4b is connected to one base station 6 via an optical fiber 5a, 5b, respectively. Each optical fiber 5
a and 5b are each composed of two optical fibers for up / down. As a result, signal attenuation can be suppressed lower than in a case where a coaxial cable or the like is used as a transmission line, and deterioration in communication quality can be prevented.

The base station 6 applies OFDM-modulated signals of road traffic data including driving support information such as road shape information ahead to each of the on-road antennas 4a, 5b via optical fibers 5a, 5b.
4b. Thereby, each road antenna 4a, 4b
The radio waves radiated from the vehicle include the same road traffic data. In addition, the vehicle data (including vehicle ID and data related to the road surface state detected by various sensors (not shown)) received from the on-vehicle device 3 is acquired from each of the on-road antennas 4a and 4b, and an appropriate process is performed.

The carrier frequency of the OFDM-modulated radio wave radiated from the base station 6 is the same between adjacent base stations 6, and the content of data to be communicated is also the same. By transmitting signals of the same content using carrier waves of the same frequency in this way, when the vehicle moves to an adjacent cell, it is not necessary to change the frequency of the on-board oscillator, so expensive high-speed pull-in to the on-board device There is no need to provide a possible oscillator or a plurality of oscillators, and the cost and size of the device can be reduced.

FIG. 2 is a conceptual diagram showing the configuration of the vehicle-mounted device 3. The vehicle-mounted device 3 has a vehicle-mounted communication unit 11 and a vehicle-mounted antenna unit 12. The in-vehicle communication unit 11 radiates radio waves including vehicle data from the in-vehicle antenna unit 12. Further, the on-vehicle communication unit 11 acquires road traffic data included in the radiated radio waves from the on-road antennas 4a and 4b received by the on-vehicle antenna unit 12, and notifies the acquired road traffic data to, for example, a driver.

FIG. 3 is a block diagram showing an electrical configuration of the ground station 1. As shown in FIG. The base station 6 includes a transmission device 21 for providing road traffic data to the road antenna 4. The transmission device 21 divides data and multiplexes the data using a plurality of orthogonal carrier waves.
Division Multiplex) The modulation method is adopted. The transmission device 21 includes an error correction coding circuit (Forward Error Correction
ion Encoder) 130, an interleave circuit 131,
Differential encoding circuit 132 and inverse Fourier transform circuit 133
And an up-converter 134 and the like.

The error correction coding circuit 130 is a circuit for performing error correction such as block coding or convolutional coding. Since the strength of the electric field strength (standing wave) is generated on the road and irregular changes (fading) in the amplitude and phase of the received signal appear in the traveling vehicle, this error correction is an effective means. The interleaving circuit 131 is a circuit that performs time interleaving and frequency interleaving employed in digital audio broadcasting DAB (Digital Audio Broadcasting) and the like.

The differential encoding circuit 132 is a circuit that performs encoding to enable demodulation by taking a difference from a previous signal. Even if the transmission line becomes unstable,
By taking this difference, the effect can be canceled. The inverse Fourier transform circuit 133 performs serial-to-parallel conversion on the serial information, performs an inverse Fourier transform, converts the inverse Fourier transform to parallel / serial again, and returns to serial.
This circuit implements various functions of setting the guard time by time-compressing the serially returned symbol sequence and bringing the subsequent symbol to the front.

The up-converter 134 is a circuit for converting the frequency to a radio frequency, similarly to the mixer section 23 described above. The transmission signal for wireless transmission converted by the up-converter 134 is converted into an optical signal in an electric / optical converter (E / O) 26, distributed via an optical coupler 59, and used for two optical fibers for upstream. 5a and 5b. The optical signals transmitted to the optical fibers 5a and 5b are converted into optical / electrical conversion units (O / E) attached to the roadside antennas 4a and 4b, respectively.
After being converted into an electric signal by 27a, 27b, it is radiated from each road antenna 4a, 4b as a radio wave. As the configuration of the optical coupler 59, a known configuration can be used (for example, C-NS series manufactured by Fiber Optic Communications).

FIG. 4 shows the symbol transmission by OFDM on a frequency axis f and a time axis t. The effective symbol length is represented by TS, and the guard time is represented by Δt. The time compression ratio is represented by (TS + Δt) / TS. In the present embodiment, the guard time Δt is longer than the delay time due to multipath. This allows
Even if there is a long propagation delay time, demodulation can be performed on the receiving side ignoring symbol overlap.

The delay time due to multipath is actually
It can be obtained by actual measurement in the cell. Also,
It may be empirically determined from the cell size. Specifically, if the cell size is 100 m, it is expected to be about 500 nsec. As shown in FIG. 3, the base station 6 includes a receiving device 28 for acquiring vehicle data from the road antennas 4a and 4b. When a radio wave radiated from the vehicle-mounted antenna 12 is received by each of the road antennas 4a and 4b, a reception signal corresponding to the received radio wave is
The optical / optical converters (E / O) 29a and 29b convert the optical signals into optical signals as they are, and then convert them into two optical fibers 5 for downlink.
a and 5b, respectively, and received by the receiving device 28 of the base station 6.
Given to.

The receiving device 28 has two optical / electrical conversion units (O
/ E) 30a and 30b, and the two optical / electrical converters 30a and 30b convert the respective optical signals into the original received signals. Each of the received signals is transmitted to the high-frequency amplifiers 31a and 31b.
, And then applied to a switch section 32 composed of a semiconductor switch or the like. The amplified received signal is also supplied to the level comparing section 33. The level comparison unit 33 compares the reception levels of the respective reception signals,
Check which reception level is higher. Then, the switch unit 32 is controlled so that the reception signal having the maximum reception level is passed. The received signal that has passed through the switch unit 32 is mixed with a frequency conversion carrier oscillated from a local oscillation unit 35 in a mixer unit 34, is frequency-converted, and is provided to a detection unit 36. And the detection unit 3
After the synchronous detection by the demodulation carrier is performed in 6,
It is provided to decoding section 37 and converted into a reception code corresponding to the vehicle data.

Although the two signals are switched by the switch unit 32 in the block diagram of FIG. 3, a configuration may be adopted in which the two signals are combined with a predetermined weight. In this case, the “predetermined weight” is determined based on the reception levels of the respective reception signals compared by the level comparison unit 33. In the block diagram of FIG. 3, the switch unit 32 switches the high-frequency signals amplified by the high-frequency amplifier units 31a and 31b, respectively. However, a configuration may be adopted in which data detected by the detection unit 36 is switched or combined, or a configuration in which code data decoded by the decoding unit 37 is switched or combined.

FIG. 5 shows a configuration in which a switch section 32 is arranged at a stage subsequent to the detection section and a received signal to be passed after synchronous detection is selected. More specifically, each high-frequency amplifier 31
a, the received signal amplified in 31b is
4a and 34b, respectively, are frequency-converted, synchronously detected by detectors 36a and 36b, and then supplied to the switch unit 32. On the other hand, the level comparison unit 33 controls the switch unit 32 so as to pass the reception signal having the maximum reception level among the reception signals amplified by the high-frequency amplification units 31a and 31b.

As described above, if the process of selecting the received signal is performed after the detection, there is an advantage that noise is hardly included in the received signal, and deterioration of the signal quality can be prevented. In the above configuration, a so-called optical fiber wireless transmission method (for example, AJCooper, "FIBER / RADIO 'FOR THE PROVI") is used as a transmission method for transmitting an optical signal to the optical fibers 5a and 5b.
SION OF CORDLESS / MOBILE TELEPHONY SERVICES IN THE
ACCESSNETWORK ", Electron.Lett., Vol.26, No.24 (Nov.199
0)).

Therefore, it is not necessary to provide a transmitting / receiving device for each of the on-road antennas 4a and 4b, and the transmitting / receiving device can be collectively installed in the base station 6, so that the configuration of the on-road antennas 4a and 4b can be simplified. Further, the base station 6 can process the received signals given from the on-road antennas 4a and 4b with high frequency. Therefore, the level comparison section 33 can easily compare the high-frequency reception levels of the respective reception signals. Therefore, the configuration of the receiving device 28 can be simplified.

Further, the transmitting device 21 performs the OFD
M (Orthogonal Frequency Division Multiplex) modulation scheme is adopted. In OFDM, the frequencies of the carrier waves are arranged at narrow intervals, so that if there is a deviation in the frequency, interference occurs between the carrier waves, and the communication quality is significantly degraded. Thus, as described above, if the fiber wireless transmission method of distributing by the optical coupler 59 is adopted, the frequencies of the carrier waves radiated from the roadside antennas 4a and 4b are in principle the same, so there is no such inconvenience. Therefore, the advantage of OFDM, which is strong against multipath interference, can be fully demonstrated in the road-to-vehicle communication system.

FIG. 6 is a block diagram showing a configuration of a receiving device for receiving radio waves radiated from road antennas 4a and 4b in vehicle-mounted antenna 12. In FIG. The receiving device includes a down converter 140, a Fourier transform circuit 141,
Differential decoding circuit 142 and deinterleave circuit 143
And an error correction decoding circuit 146.

The Fourier transform circuit 141 performs a process reverse to that of the inverse Fourier transform circuit 133 on the transmission side, and obtains a decoded signal by performing Fourier transform with a window length of the effective symbol length TS. The differential decoding circuit 142 and the deinterleave circuit 143
2. A circuit that performs processing opposite to that of the interleave circuit 131.

The error correction decoding circuit 146 is a circuit that performs a process reverse to that of the error correction encoding circuit 130. FIG. 7 is a conceptual diagram of a road viewed from the sky for explaining shielding of radio waves radiated from the road antennas 4a and 4b. When the length r of the cell E in the longitudinal direction of the road is 100 (m) and the height of the on-road antenna 4 is 10 (m), for example, as shown in FIG. ), Vehicle width of about 3 (m) 2
It is assumed that the two trucks 161 and 162 are traveling near the center of the cell E.

In this case, the area 163 where the radio wave radiated from the first road antenna 4a is shielded by the tracks 161 and 162 appears on the front side with respect to the traveling direction of the tracks 161 and 162. The maximum length of the radio wave shielding area 163 along the longitudinal direction of the road is about 12 (m).
On the other hand, an area 164 where radio waves radiated from the second roadside antenna 4b are shielded by the tracks 161 and 162.
Appears on the rear side with respect to the traveling direction of the tracks 161 and 162. Also in this case, the radio wave shielding area 164
The maximum length of the road along the longitudinal direction is about 12 (m).

The front of the truck 161 and the truck 16
Behind 2, as is clear from FIG.
The two radio wave shielding areas 163 and 164 do not overlap. Therefore, when the vehicle 2 is traveling in this section, the in-vehicle device 3 can receive the radio wave radiated from one of the road antennas 4a and 4b. for that reason,
In the same cell E, communication between the vehicle-mounted device 3 and the road antenna 4 is not interrupted.

On the other hand, in a section sandwiched between the two trucks 161 and 162, depending on the distance between the two trucks 161 and 162, two radio shielding areas 163 and 164 are provided.
Overlap area 165 appears. Specifically, 2
When the inter-vehicle distance between the two trucks 161 and 162 is less than 20 (m), an overlapping area 165 appears. However, the distance between the two trucks 161 and 162 during normal traveling is
It is rare for the vehicle to be less than 20 (m), and it is even more rare for the vehicle to travel between the two trucks 161 and 162. Therefore, in normal running, the overlapping area 16
You can safely assume that 5 does not appear. Therefore, even in this case, communication between the vehicle-mounted device 3 and the road antenna 4 is not interrupted.

However, it is conceivable that the vehicle travels between two trucks 161 and 162 traveling at a distance of less than 20 (m) during a traffic jam. However, as approaching the edge of the area of the cell E, that is, the second roadside antenna 4b, the radio wave shielding area 1 by the truck 161 running in front of the cell E is approached.
Since 64 becomes shorter, two radio wave shielding areas 16
3, 164 overlap area 165 becomes narrower, and communication becomes possible. In this case, since the vehicle is traveling near the edge of the area of the cell E, there is a possibility that the vehicle will exit the cell E in a short time after the communication becomes possible. Communication can be performed.

Next, as shown in FIG. 7 (b), the case where one truck 161 is running near the second road antenna 4b will be considered. In this case, the area 163 for shielding the radio wave radiated from the second road antenna 4b by the truck 161 is about 2 (m) behind the truck 161. In this case, even if the track 162 is the track 161
And the overlapping area of the radio wave shielding areas 163 and 164 is formed, the maximum length of the overlapping area is 2 (m).
It is. On the other hand, since the front and rear length of the vehicle 2 on which the on-vehicle device 3 is mounted is usually about 5 (m), communication is not interrupted even if an overlapping area is formed.

The radio wave shielding areas 163 and 164 are
As described above, it appears not only before and after the trucks 161 and 162, but also in the lane crossing direction of the trucks 161 and 162. The extent to which the radio wave shielding areas 163 and 164 protrude from the lane changes depending on the extent to which the on-road antenna 4 projects from the road side. Specifically, when the on-street antenna 4 is positioned near the boundary between the road side and the lane 166 adjacent to the road side, the radio wave shielding areas 163 and 164 are separated from the tracks 161 and 162 as shown in FIG. Reaches only the vicinity of the center of the lane 168 adjacent to the lane 167 where the vehicle is traveling. Further, as shown in FIG. 7C, if the on-street antenna 4 is extended to the vicinity of the center of the lane 166 adjacent to the road side, the radio wave shielding area formed in the lane crossing direction is further shortened. Therefore, for example, in the example shown in FIG. 7, if the on-vehicle antenna 12 is installed on the right side of the vehicle 2, there is no problem in the radio wave shielding area formed in the lane crossing direction.

As described above, according to the first embodiment,
Since the propagation path of the radio wave radiated from the road antenna 4 in one cell E is two, even if the vehicle 2 is running near a large vehicle such as a truck, shielding of the radio wave can be avoided. In addition, since the OFDM method is adopted and a guard time is set to avoid interference between symbols, the influence of multipath interference can be avoided. Therefore, continuous communication between the on-vehicle device 3 and the road antenna 4 can be favorably performed.

In the above description, a pair of road antennas 4a and 4b forming one cell E are installed at the end of each area of the cell E in the longitudinal direction of the road. But,
The installation positions of the roadside antennas 4a and 4b are not limited to the edge of the area. For example, as shown in FIG. 8, the antennas may be installed at a position closer to the center of the cell E than the edge of the area. In the above description, the pair of road antennas 4
Although one cell E is formed by a and 4b, one cell E may be formed by three or more road antennas. That is, regardless of the installation position of the on-road antenna 4 and the number of on-road antennas 4, the point is that it is only necessary that the vehicle 2 can receive radio waves from different directions.

In the above description, the on-road antenna 4
Reference numerals a and 4b use an optical fiber wireless transmission system and convert the frequency of a received signal into an optical signal without converting it. However, for example, the frequency of the received signal may be converted to a lower frequency in the road antennas 4a and 4b, and then converted to an optical signal and transmitted to the optical fibers 5a and 5b. According to this configuration, since a laser diode generally used as a light source of an optical signal can be inexpensive, the cost can be reduced.

In this case, if a method of transmitting a local oscillation signal from the base station 6 to the on-road antennas 4a and 4b (for example, see Japanese Patent Application Laid-Open No. 6-141361) is adopted, the signals are converted by the on-road antennas 4a and 4b. The frequency of the received signal after the reception can be almost completely matched. Second Embodiment FIG. 9 is a conceptual diagram illustrating a configuration of a road-vehicle communication system according to a second embodiment of the present invention. In FIG. 9, the same reference numerals are used for the same functional parts as in FIG.

In the first embodiment, radio wave shielding is avoided by forming one cell E by a pair of road antennas 4a and 4b, whereas in the second embodiment, a plurality of road antennas are 71 is installed in the cell E from which radio waves of the same frequency are radiated, and the cell E is divided into a plurality of sub-areas Es to avoid radio wave shielding.

More specifically, one base station 6 includes:
The four road antennas 71a, 71b, 71c, 71d are connected via optical fibers 72a, 72b, 72c, 72d (hereinafter referred to as "optical fiber 72" when collectively referred to). Each of the on-road antennas 71a to 71d radiates radio waves of the same frequency, which are OFDM-modulated by the same road traffic data, toward the sub-area Es.

In this case, for example, when the vehicle is in the sub area E
When traveling on the downstream side of the approximate center of s and a truck traveling on an adjacent lane is positioned diagonally behind the vehicle 2, the truck may shield radio waves. However, when the vehicle arrives at the next sub-area Es as it is, the direction of arrival of the radio wave changes and the radio wave arrives from the front of the vehicle 2. The radio wave radiated to the next sub area Es can be received. That is, the in-vehicle device 3 can receive the radio wave radiated from any of the road antennas 71 while passing through the four sub-areas Es.

When the vehicle is traveling near the boundary of the sub-area Es, radio waves of the same frequency arrive from the front and rear directions. Therefore, there is no particular problem. FIG. 10 is a block diagram showing an electrical configuration of the base station 6. As shown in FIG. The transmitting device 81 provided in the base station 6
The OFDM modulator 82 creates a transmission signal including road traffic data. The transmission signal is provided to up-converter 83,
It is converted to a transmission signal for wireless transmission in the (GHz) band. The transmission signal for wireless transmission is converted into an optical signal in an electrical / optical converter (E / O) 84, then divided into four by an optical coupler 59, and sent out to upstream optical fibers 72a to 72d.

Receiving device 85 provided in base station 6
Are electrical / optical converters (E / O) 86a, 86b, 86 for converting optical signals sent from the on-road antennas 71a to 71d to the down optical fibers 72a to 72d, respectively, into received signals.
c, 86d. Each received signal is received by the reception IF unit 8
7a, 87b, 87c, and 87d are mixed with a carrier for frequency conversion and frequency-converted, and then detected by a detector 88a,
88b, 88c, and 88d, where OFDM demodulation is performed. After that, it is given to the switch unit 89. Also,
Each received signal is also provided to the level comparing section 90. The level comparing section 90 compares the reception levels of the respective reception signals and checks which reception level is higher. Then, the switch unit 89 is controlled so that the reception signal having the maximum reception level is passed. The received signal that has passed through the switch unit 89 is decoded by the decoding unit 91, and a code corresponding to the vehicle data is created.

Although a plurality of signals are switched by the switch unit 89 in the block diagram of FIG. 10, a configuration may be adopted in which a plurality of signals are synthesized using a predetermined weight vector. In this case, the “predetermined weight vector” is
It is determined based on the reception levels of the respective reception signals compared by the level comparison section 90. Further, in the block diagram of FIG. 10, the switch unit 89 switches the signals detected by the detectors 88a to 88d. However, the electrical / optical converter (E
/ O) A configuration for switching or synthesizing the high-frequency output signals 86a to 86d may be adopted, and a configuration for switching or synthesizing the code data decoded by the decoding unit 91 may be adopted.

FIG. 11 is a block diagram showing the electrical configuration of the road antenna 71. The antenna communication device 100 is attached to the road antenna 71. The antenna communication device 100 includes a transmission unit 101. Transmission unit 1
Reference numeral 01 includes an optical / electrical conversion unit (O / E) 102 for converting an optical signal transmitted from the base station 6 to the optical fiber 72 into a transmission signal and a carrier generation reference signal. The output of the optical / electrical converter 102 is provided to the transmission IF unit 103 via a band-pass filter (not shown). As a result, the transmission IF
Unit 103 receives only the transmission signal. After the transmission signal is amplified in the transmission IF section 103, it is further provided to the transmission mixer section 104. The output of the optical / electrical converter 102 is provided to a local oscillator 105 via a low-pass filter (not shown). As a result, only the carrier generation reference signal is provided to local oscillation section 105. Local oscillating section 105 oscillates a carrier based on the carrier signal and provides the carrier to transmission mixer 104. Transmission mixer section 104
Creates a transmission signal for wireless transmission by mixing a transmission signal and a carrier wave. The transmission signal for wireless transmission is subjected to high-frequency amplification in the high-frequency amplifier 106, and then the circulator 1
07 and is radiated from the road antenna 71 as radio waves.

The antenna communication device 100 also includes a receiving unit 108. The receiving unit 108 includes the on-road antenna 7
1 and a high-frequency amplifier 109 for high-frequency amplification of a received signal passing through the circulator 107
It has. The amplified reception signal is supplied to the reception mixer 11
0, the signal is mixed with the carrier wave oscillated from the local oscillation unit 105, amplified, and then further received by the reception IF unit 111.
After the frequency conversion in the E / O conversion unit (E / O) 1
At 12, the signal is converted into an optical signal and transmitted to the optical fiber 72.

As described above, according to the second embodiment,
Radio waves of the same frequency, which have been OFDM-modulated with the same contents of road traffic data, are divided and emitted into a plurality of sub-areas Es, so that the in-vehicle device 3 can receive the radiated radio waves in any of the sub-areas Es. Therefore, the in-vehicle device 3 and the on-road antenna 7
Communication with the device 1 is not interrupted, and continuous communication becomes possible.

Since the sub-area Es is relatively small, the transmission power of the road antenna 71 can be small. Therefore, the cost of the road antenna 71 can be reduced. Although the description of the embodiment of the present invention is as described above, the present invention is not limited to the above two embodiments, and various design changes can be made within the scope of the present invention. .

[0063]

According to the present invention, since radio waves are made to arrive at a vehicle from a plurality of directions, continuous communication between the road and the vehicle in the same cell is not interrupted. Therefore, road traffic data can be provided to the vehicle without omission. Further, by employing OFDM as a modulation method, it is possible to perform code transmission with a low error rate.

For example, when the road-vehicle communication system is applied to an automatic driving system, the automatic driving of the vehicle can be appropriately performed.

[Brief description of the drawings]

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

FIG. 2 is a conceptual diagram illustrating a configuration of an in-vehicle device.

FIG. 3 is a block diagram illustrating an electrical configuration of a ground station.

FIG. 4 is a graph illustrating a state of symbol transmission by OFDM on a frequency axis f and a time axis t.

FIG. 5 is a block diagram showing another embodiment of the electrical configuration of the receiving device in the base station.

FIG. 6 is a block diagram illustrating an electrical configuration of the vehicle-mounted device.

FIG. 7 is a view of a road viewed from the sky for explaining shielding of radio waves.

FIG. 8 is a diagram illustrating another form of the installation position of the on-street antenna.

FIG. 9 is a conceptual diagram showing a configuration of a road-vehicle communication system according to a second embodiment of the present invention.

FIG. 10 is a block diagram illustrating an electrical configuration of a receiving device in an in-vehicle device according to a second embodiment.

FIG. 11 is a block diagram illustrating an electrical configuration of a road antenna.

FIG. 12 is a conceptual diagram showing a configuration of a conventional road-vehicle communication system.

FIG. 13 is a diagram for explaining radio wave shielding in a conventional road-vehicle communication system.

[Explanation of symbols]

 Reference Signs List 1 ground station 3 on-vehicle device 4a first on-road antenna 4b second on-road antenna 5a, 5b optical fiber 11 on-vehicle communication unit 12 on-vehicle antenna 21 transmitting device 71, 71a, 71b, 71c, 71d on-road antenna 72, 72a, 72b, 72c, 72d Optical fiber 100 Antenna communication device 133 Inverse Fourier transform circuit 141 Fourier transform circuit E cell Es Subarea

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-241495 (JP, A) JP-A-6-141361 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/24-7/26 102 H04Q 7/00-7/38 H04J 11/00

Claims (8)

(57) [Claims] 1. Orthogonal frequency division multiplexing (OFDM)
al Frequency Division Multiplex) A signal transmission device for transmitting the same modulated signal to a plurality of transmission lines, and a signal transmission device arranged at different positions along a road, having a specific directivity, and Each of the signals transmitted to the transmission line is received, and based on the received signals, a plurality of road transmitting antennas for radiating radio waves into the same cell, and radio waves radiated from the road transmitting antenna A road-to-vehicle communication system, comprising: an on-vehicle receiving antenna for receiving; and an on-vehicle device having a receiving unit for receiving and demodulating by the on-vehicle receiving antenna. 2. The road-vehicle communication system according to claim 1, wherein a transmission system for transmitting a signal to the transmission line is an optical fiber wireless transmission system. 3. The road-vehicle communication system according to claim 1, wherein an OFDM system in which a guard time is provided for each symbol is adopted as an OFDM modulation system for data. 4. An on-vehicle device according to claim 1, wherein said on-vehicle device is OFD
Further comprising an on-vehicle transmission antenna for emitting M-modulated radio waves, arranged at different positions along the road, having a specific directivity, receiving radio waves radiated from the on-vehicle transmission antenna, A plurality of road receiving antennas for transmitting signals corresponding to the received radio waves to predetermined transmission lines; and a road receiving antenna for demodulating based on signals transmitted from the plurality of road receiving antennas to the transmission line. The road-to-vehicle communication system according to claim 1, further comprising: 5. The road-vehicle communication system according to claim 4, wherein a transmission system for transmitting a signal to the transmission line is an optical fiber wireless transmission system. 6. The road-vehicle communication system according to claim 4, wherein an OFDM system in which a guard time is provided for each symbol is adopted as an OFDM modulation system for data in the vehicle-mounted device. 7. The road-to-vehicle communication device according to claim 1, wherein the plurality of on-road transmitting antennas form a plurality of sub-areas obtained by dividing one cell. Communications system. 8. The road-vehicle communication system according to claim 1, wherein communication is performed over a plurality of continuous cells by using signals having the same frequency and the same contents.