JP2000311290A - Communication system between vehicles and road - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a communication system between vehicles and road capable of using the same frequency for all cells installed along the road and preventing inter-carrier interference and inter-code interference thereby performing stable communication between road and vehicle. SOLUTION: In this system, an OFDM modulation system is adapted and a subcarrier is classified into plural kinds S1 and S2. When on-road transmission antenna devices arranged at adjacent cells Eb and Ec transmit data A and B different in contents by using one subcarrier S1, either data A of the data A or B is transmitted in common by using another subcarrier S2. Data can continuously be received without being interrupted by switching the subcarrier S1 to the subcarrier S2 when a vehicle passes through the boundary of adjacent cells. Then, even though cells are changed, the timewise continuity of data reception can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road-vehicle communication system in which a roadside antenna is arranged along a road and a series of cells are formed on the road to enable mobile communication with a vehicle-mounted device.

[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. The development of such a system will lead to an autonomous driving system that covers various sensors and cameras on both the road and the vehicle, and closely contacts and drives the road and the vehicle (for example, JP-A-8-2414
No. 95).

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, if the on-road antennas are installed at predetermined intervals at various places on the road for communication, a relatively wide cell can be secured with one on-road antenna. In this case, the on-road antennas are respectively coupled to base stations on the road manager side via optical fibers or the like.

[0005]

In the case of a system using the above-mentioned road antenna, communication is usually performed using radio waves having different frequencies for each cell in order to prevent inter-carrier interference and inter-symbol interference. . However, since an automobile moves at high speed and passes through a plurality of cells in a short time, it is necessary to switch the transmission / reception frequency of the vehicle-mounted communication device 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.

Therefore, it is desired to construct a system using the same frequency for all cells after taking measures to prevent inter-carrier interference and inter-symbol interference. Therefore, an object of the present invention is to provide the same frequency for all cells and to prevent inter-carrier interference and inter-symbol interference, thereby enabling stable communication between the road and the vehicle. A communication system is provided.

[0007]

According to a first aspect of the present invention, there is provided a road-to-vehicle communication system according to the first aspect of the present invention.
A control device for transmitting a signal modulated in, on the basis of the transmitted signal, on-road transmitting antenna device for radiating radio waves of the same frequency into the cell, and radiated from the on-road transmitting antenna device An in-vehicle receiving antenna for receiving incoming radio waves, and an in-vehicle device having an in-vehicle receiving means for receiving and demodulating by receiving the in-vehicle receiving antenna, the control device classifies the subcarrier into a plurality of types,
In the case of having transmission means for transmitting data to the plurality of types of subcarriers, and a roadside transmitting antenna device arranged in an adjacent cell transmits data having different contents from each other using one type of subcarrier. The on-road transmitting antenna devices arranged in these adjacent cells commonly transmit any one of the data having the different contents using another type of subcarrier.

[0008] In the present invention, from the on-road transmitting antenna device,
Radio waves of the same frequency are radiated based on the OFDM-modulated signal. Generally, when radio waves arrive at a vehicle from a plurality of directions, so-called multipath interference may occur. Specifically, a propagation delay time difference occurs between radio waves radiated from the on-road transmitting antenna devices, and intersymbol interference occurs. However, in the present invention, the OFDM method is adopted, and a guard time is provided for each symbol so that interfering codes can be prevented from overlapping. The resulting intersymbol interference can be avoided.

By the way, data transmitted from the on-road transmitting antenna apparatus using one type of subcarrier may have the same contents at all times between cells, or may have different contents. In the former case, the vehicle receives data of the same content from one type of subcarrier even when traveling across cells, and can receive the data without interruption. However, in the latter case, the vehicle will receive different data as it moves from cell to cell. In the latter case, even at the OFDM scheme, at the cell boundary,
Interference occurs between the codes.

Therefore, according to the present invention, when sub-carriers are classified into a plurality of types, and the on-road transmitting antenna devices arranged in adjacent cells transmit data having different contents from each other using one type of sub-carrier, On the other hand, the on-road transmitting antenna devices arranged in these adjacent cells commonly transmit any one of the data having the different contents using another type of subcarrier. This allows
When a vehicle passes the boundary between adjacent cells, by connecting the "one type of sub-carrier" to the "other type of sub-carrier", it is possible to continuously receive data without interruption. it can. Therefore, even if the cell changes, temporal continuity of data reception can be ensured.

When data is transmitted to a plurality of types of subcarriers, a plurality of types of subcarriers are often distributed according to the purpose of the data. In this case, the data commonly transmitted using the other type of subcarrier is data requiring continuity (claim 3). Data that does not require continuity need not be transmitted in common using the other types of subcarriers. The switching between the data of the one type of subcarrier and the data of the other type of subcarrier is performed by the on-vehicle receiving means. Although the timing of switching becomes a problem, it is desirable to switch when the reception state is stable. Therefore, the following measures (a) or (b) can be considered.

(A) A marker is provided on a road, and switching is performed when the vehicle passes through the marker. (b) A subcarrier switching instruction signal is inserted in the data. There are various ways of classifying the plurality of types of subcarriers. A method of dividing a subcarrier into a plurality of segments on the frequency axis (Claim 5) and a method of arranging subcarriers of the same type every K lines on the frequency axis (Claim 6) is there. The method according to claim 5,
In this method, a plurality of subcarriers are divided into a plurality of groups on the frequency axis and transmitted. In the method according to claim 6,
Subcarriers transmitting data of the same content are arranged every K lines. For example, when dividing into two types of sub-carriers, the sub-carriers are alternately arranged one by one.

(2) The road-vehicle communication system according to claim 7, wherein the data to be transmitted is classified into a plurality of types, and the classified data is arranged in a fixed pattern in the frequency axis direction and the time axis direction. When the on-road transmitting antenna devices arranged in adjacent cells transmit data having different contents using one pattern, the on-road transmitting antenna devices arranged in these adjacent cells have The antenna device transmits one of the data having different contents in common by using another pattern.

According to the present invention, data to be transmitted is classified into a plurality of types, and the classified data is transmitted by arranging them in a fixed pattern in the frequency axis direction and the time axis direction. As a result, the classified data is arranged along the frequency axis direction, so that the subcarriers are classified. However, in addition to this, in the present invention, the classified data is also arranged along the time axis direction. Therefore, as a result, it can be said that the manner of classification or the manner of classification of the subcarriers changes over time.

Thus, by arranging the classified data in a fixed pattern in the frequency axis direction and the time axis direction, each type of data is switched in the frequency axis direction and the time axis direction. For this reason, the effects of frequency diversity and time diversity appear synergistically. In mobile communication, fading always occurs, but the effect of the fading can be reduced by the effects of the frequency diversity and the time diversity.

The control device includes a plurality of types of patterns,
Each data may be allocated according to the use of the data (claim 8). In this case, data that is commonly transmitted using the other type of pattern is data that requires continuity between cells. (Claim 9). It is preferable that the on-vehicle receiving means includes switching means for switching between the data of the one type of pattern and the data of the other type of pattern (claim 10).

The above-mentioned "arranged data is arranged in a fixed pattern in the frequency axis direction and the time axis direction, respectively".
As a method, after the data including the classified data is temporally rearranged, the data is transmitted by performing an inverse Fourier transform process, and on the vehicle side, the data subjected to the Fourier transform is subjected to the inverse rearrangement process, thereby performing classification. There is a method of obtaining various types of data (claim 11).

[0018]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a conceptual diagram showing a configuration of a road-vehicle communication system according to an embodiment of the present invention. This road-to-vehicle communication system is for performing communication between a ground station 1 and a vehicle-mounted communication device mounted on the vehicle 2. In the ground station 1, a plurality of cells E
Are continuously formed. Each cell E has a cell E
A road antenna 4 having directivity directed inward is installed. A predetermined frequency (for example, 6 GHz) is output from the road antenna 4.
(z band) radio waves are radiated into the cell E.

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). When the vehicle 2 passes through the cell E, radio waves are received from the front or the rear of the vehicle 2 or from above when the vehicle 2 is passing directly below the on-road antenna 4. Road antenna 4
Are connected via the coaxial cable 5 to the control devices 6a, 6b,.
(Hereinafter, collectively referred to as "control device 6"). The coaxial cable 5 is composed of two up / down coaxial cables. Note that an optical fiber can be used as the transmission line instead of the coaxial cable. In this case, as a transmission method for transmitting an optical signal to an optical fiber, a so-called optical fiber wireless transmission method (for example,
AJCooper, "FIBER / RADIO FOR THE PROVISION OF COR
DLESS / MOBILE ELEPHONY SERVICES IN THE ACCESS NETW
ORK ", Electron. Lett., Vol. 26, No. 24 (Nov. 1990)).

The control device 6 gives a signal modulated by image data such as road traffic data and road information ahead to the road antenna 4 via the coaxial cable 5. Further, the vehicle data (including the vehicle ID and data relating to the road surface state detected by various sensors (not shown)) received from the vehicle 2 is acquired from the on-road antenna 4. The carrier frequencies of the radio waves radiated from the control devices 6 are the same between the adjacent control devices 6. By transmitting a signal using a carrier having the same frequency in this manner, it is not necessary to change the frequency of the vehicle-mounted oscillator when the vehicle moves to an adjacent cell. For this reason, it is not necessary to equip the in-vehicle device 8 with an expensive high-speed pull-in oscillator, or with a plurality of oscillators, so that the cost and size of the device can be reduced.

First Embodiment FIG. 2 is a block diagram showing an electric configuration of the ground station 1. As shown in FIG. The ground station 1 includes a control device 6, a coaxial cable 5, a road antenna 4, and the like. The control device 6 includes a transmission device 7 for providing road traffic data and the like to the road antenna 4. The transmission device 7 divides data and multiplexes the data using a plurality of orthogonal carrier waves.
nal Frequency Division Multiplex) modulation scheme is adopted.

The transmitting device 7 includes an inverse Fourier transform circuit 71,
A QPSK modulation circuit 73, an up-converter 74 and the like are provided. In addition, an error correction coding circuit, an interleaving circuit for performing time interleaving and frequency interleaving, a differential coding circuit, and the like may be provided. The inverse Fourier transform circuit 71 performs an inverse Fourier transform on the parallel information, performs parallel-serial conversion on the inverse Fourier transform, returns the serial to serial, time-compresses the serialized symbol sequence, and processes the subsequent symbol. It is a circuit that realizes various functions of setting a guard time by bringing it in advance. In the present embodiment, the parallel signals S1 and S2 respectively corresponding to the two subcarrier segments on the frequency axis are input and inverse Fourier transformed.

The QPSK modulation circuit 73 performs D / A conversion on the signals corresponding to the phases 0 ° and 180 ° and the signals corresponding to the phases 90 ° and 270 ° output from the inverse Fourier transform circuit 71 to obtain a sine wave, This is a circuit for performing QPSK modulation by adding a cos wave. In this embodiment, QPSK modulation is performed, but other modulation schemes, for example, QAM, BPSK, 8PSK, etc., may be adopted. However, the following description will be given on the assumption that QPSK modulation is performed unless otherwise specified.

The up-converter 74 is a circuit for converting the frequency to a radio frequency. The accuracy of the local oscillator 74a included in the upconverter 74 is determined by taking into account the Doppler effect that occurs between the ground and the traveling vehicle.
A speed on the order of (vehicle speed) / (propagation speed of radio waves) is necessary, but a commercially available oscillator can sufficiently secure such accuracy. The output signal of the up-converter 74 is radiated as radio waves from the road antenna 4 through the coaxial cable 5.

When the above-mentioned optical fiber wireless transmission system is adopted, an electric / optical conversion unit (E / O) for converting the output signal of the up-converter 74 into an optical signal is required. An optical / electrical converter (O / E) for converting an optical signal into an electric signal is required. FIG. 3 shows a state of 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 (TS + Δt)
/ TS. Assuming that the number of subcarriers is n and the transmission rate is m (Mbps), TS = 2n / m (μse
It is represented by c).

In the present embodiment, the guard time Δt is longer than the delay time due to multipath. As a result, 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 the multipath can be actually measured and obtained in the cell. Alternatively, it may be empirically determined from the size of the cell. In particular,
If the cell size is 100 m, it is expected to be about 500 nsec.

Although not shown, the control device 6 includes a receiving device for acquiring data from the vehicle 2 from the road antenna 4. In the receiving apparatus, the received signal is down-converted, detected, and decoded. As the detection method, the modulation method is QPSK, BPSK, 8PS.
In the case of a phase modulation method such as K, delay detection is performed by multiplying the current signal by one bit before using a delay circuit. QA
In the case of M, synchronous detection is performed using the demodulation carrier.
In the case of delay detection, transmission data needs to be differentially encoded.

FIG. 4 is a conceptual diagram showing the configuration of the vehicle-mounted device 8. The vehicle-mounted device 8 includes a vehicle-mounted receiver 9 and a vehicle-mounted antenna 10.
And The on-vehicle receiving unit 9 is for acquiring road traffic data and the like included in radio waves radiated from the on-road antenna 4 received by the on-vehicle antenna 10, and includes a down converter 91, a QPSK demodulation circuit 92, and a Fourier transform circuit 93. , A changeover switch circuit 94, and a changeover control circuit 95.

In addition, an error correction decoding circuit, a deinterleave circuit, and a differential decoding circuit corresponding to the above-described error correction encoding circuit, interleave circuit, and differential encoding circuit, respectively, may be provided. The Fourier transform circuit 93
A circuit that performs a process reverse to that of the inverse Fourier transform circuit 71 on the transmission side, Fourier transforms the down-converted and QPSK demodulated signal with the window length of the effective symbol length TS to convert the two decoded signals S1 and S2. It is a circuit to get.

The changeover switch circuit 94 is a circuit for switching the arrangement of the two decoded signals S1 and S2, and uses a semiconductor switch or the like. The switching control of the switching switch circuit 94 is performed by the switching control circuit 95.
For example, it is performed as in the following (1) or (2). (1) A marker is provided on the road, and the vehicle is switched when the vehicle passes the marker. In this case, a road marker including a magnet for notifying the position on the road, a colored reflector, a light-emitting body, and the like is set at a predetermined position in the cell E. Specifically, the location of the road marker is desirably around the center of the cell E where stable reception of radio waves is possible, but is not limited to the center of the road. On the other hand, the in-vehicle device 8 is provided with a marker detection unit including a magnetic sensor for detecting a road marker, a light receiving element, and the like.

(2) A subcarrier switching command signal is put in the data. FIGS. 5 and 6 show the control devices 6a,
FIG. 6 is a diagram for explaining signals transmitted from 6b, 6c, and #, and a reception state of the vehicle-mounted device 8. In the description of FIGS. 5 and 6, the number of subcarriers is set to 2 for convenience, but it is needless to say that the number is not actually limited to 2. FIG.
It is a figure which shows the comparative example of this invention in which the data contained in the subcarrier S1 and the data contained in the subcarrier S2 change independently and time-dependently.

The signal a transmitted from the control device 6a includes data A that changes temporally to A1, A2, A3,... In the subcarrier S1, and C1, C2, C3,. And changing data C. The signal b sent from the adjacent control device 6b is also the signal a
Similarly, the data A includes data A that temporally changes to A1, A2, A3, ‥, and data C that temporally changes to C1, C2, C3, ‥. The signal c transmitted from the adjacent control device 6c includes data B temporally changing to B1, B2, B3, ‥, and data C temporally changing to C1, C2, C3, ‥. I have. The signal d sent from the control device 6d also includes data B temporally changing to B1, B2, B3, ‥, and data C temporally changing to C1, C2, C3, ‥.

The data A and the data B are data to be received continuously (for example, still image data to be provided to a vehicle, the image content of which is changed as the vehicle travels through a cell), and the data C is data It is assumed that the data does not necessarily need to be continuously received by the vehicle (for example, road traffic data such as weather, regulated speed, construction work, accidents, and traffic jams). As described above, the data C of the sub-carrier S2 is unchanged, but the contents of the signal b and the signal c change from A to B when focusing on the sub-carrier S1. Therefore, when the vehicle passes through the overlapping portion Y between the cell Eb from which the signal b is sent and the cell Ec from which the signal c is sent, intersymbol interference occurs between the data A and the data B, and the data cannot be decoded. Disappears. On the other hand, since the content of the data C is unchanged, the vehicle can receive the data C stably.

FIG. 6 shows a case where different data A and B having different contents are transmitted using the subcarrier S1 according to the present invention. FIG. 3 is a diagram showing a form in which one of data A is transmitted in common. Signal a transmitted from control device 6a includes data A and data C. The subcarrier S1 of the signal b transmitted from the adjacent control device 6b includes data A as in the signal a, but the subcarrier S2 is data A. In the signal c sent from the control device 6c, the subcarrier S1 changes to data B, and the subcarrier S2 remains data A. Signal d sent from control device 6d
Includes data B and data C.

The vehicle is connected to a cell Ea from which the signal a is transmitted,
When the signal b passes through the overlapping portion X with the cell Eb from which the signal b is transmitted, the data A of the subcarrier S1 is invariable and can be continuously received. In addition, when passing through the overlapping portion Y of the cell Eb from which the signal b is transmitted and the cell Ec from which the signal c is transmitted, focusing on the subcarrier S1, the signal b
And the content of signal c has changed from data A to data B, but the content of subcarrier S2 remains unchanged at data A. Therefore, even if the contents of the data A of the subcarrier S1 cannot be decoded, the contents of the data A of the subcarrier S2 can be decoded.

Therefore, the on-vehicle receiving unit 9 changes the arrangement of the received data into the sub-carrier S1
And the subcarrier S2 are exchanged. As a means for setting the switching timing, (1) or (2) can be adopted as described above. Although the data C originally associated with the subcarrier S2 is interrupted, there is no problem because the data C is allocated as data C that can be interrupted.

When the vehicle passes through the cell boundary Y in a state where the arrangement of the received data is switched, the data B of the subcarrier S1 and the data A of the subcarrier S2 can be both received. At this time, the changeover switch circuit 94
It is necessary to restore the array of received data. As the return timing, the above (1) or (2) can also be employed. When the vehicle comes to the next boundary Z, the contents of the data B of the subcarrier S1 can be decoded, but the contents of the data C of the subcarrier S2 cannot be decoded. However, as described above, there is no problem because data for use that may be interrupted as data C is assigned.

As described above, the in-vehicle receiving unit 9 can continuously acquire the data A and B while passing through a series of cells. FIG. 7 is a diagram showing a mode in which the number of subcarriers is set to 5 and more data A to D are continuously switched. In this example, there is no data that may be interrupted and all data is received continuously between cells. FIG. 7A shows data transmitted from each of the on-road antennas 4a to 4h for each sub-carrier. For example,
The leftmost roadside antenna 4a receives data A from subcarrier S1, data A from S2, data A from S3,
, And data D from S5. The next on-road antenna 4b changes the data D into the data A and transmits the data A in the subcarrier S4. Further, the next roadside antenna 4c changes the data D into the data A in the subcarrier S5, and changes the data A into the data B in the subcarrier S1, and transmits the data. N indicates a data repetition unit (N = 4 in this example).

FIG. 7B is a diagram showing a receiving state in the vehicle-mounted receiving section 9. The hatching indicates that the data cannot be decoded. For example, when passing through the boundary between the cell of the on-road antenna 4a and the cell of 4b, the data D and the data A are mixed in the sub-carrier S4 and cannot be decoded. Therefore, in FIG.
In the middle between the cell a and the cell 4b, the subcarrier S4
Is hatched.

Referring to FIG. 7B, at the cell boundary, 1
One or two subcarriers cannot be decoded, but the other three
The data for one to four sub-carriers can be decoded without interference. In the diagram showing the reception state at the cell boundary as shown in FIG. 7 (b), assuming that the number of hatched cells is m and the number of all cells is M in the data repetition unit N, the frequency band utilization efficiency η becomes η = 1-m / M. If the number of subcarriers is k, M = kN, m = k
Holds, η = 1−1 / N, and the use efficiency η of the frequency band is a function of the data repetition unit N. The use efficiency η deteriorates as the frequency of switching data between cells increases, and the use efficiency η improves as the data repetition unit N increases. For example, assuming a condition N = 2 that data is switched every time one cell passes, the utilization efficiency η is η = 1-1 / 2 = 50%.

In the example of FIG. 7B, since the data repetition unit N = 4, the utilization efficiency η is η = 1-７５ = 75%. The rate of frequency bands that cannot be used due to data switching remains at 25%. In the embodiment of the present invention described above, the subcarrier is divided into two segments on the frequency axis. However, in addition to this dividing method, the following dividing method can be given.

FIG. 8 is a block diagram showing an electrical configuration of the ground station 1 according to the second embodiment. The difference from the block diagram of FIG. 2 is that two types of subcarrier signals S1 and S2 input to the inverse Fourier transform circuit 71 are alternately arranged. As a result, in the frequency spectrum of the transmitted radio wave, the subcarriers of data A and the subcarriers of data B are alternately arranged on the frequency axis f, as shown in FIG. When the data to be received is A, the subcarrier indicated by the solid line is used, and the subcarrier indicated by the broken line is not used. Therefore, the detuning frequency Δf between the sub-carriers is substantially doubled as shown in FIG.

In a transmission system using multicarriers such as OFDM, the characteristics deteriorate when the frequency synchronization of each carrier is not completely achieved. In particular, when applied to high-speed mobile communication, Doppler shift occurs, making it difficult to synchronize carriers. Therefore, an AFC circuit for correcting the shifted frequency is required. If the detuning frequency Δf between adjacent subcarriers is narrow, it is necessary to determine whether the frequency of the subcarrier captured by the AFC circuit is that of the upper frequency or that of the lower frequency, which complicates the AFC circuit. Become. If the AFC circuit is not to be complicated, the detuning frequency Δf must be widened, and therefore a band wider than the band required for data to be transmitted must be secured.

Therefore, by alternately interleaving the subcarriers as in this embodiment, the detuning frequency Δf
, The determination process of the AFC circuit becomes easy, and it is not necessary to widen the band, so that the device can be simplified and the frequency can be effectively used. Further, according to the present embodiment, it is possible to provide a system that is resistant to frequency selective fading. FIG. 10 is a diagram in which amplitude fluctuation U for frequency selective fading is written on the frequency axis. FIG. 10B shows a case where the subcarrier is divided into a plurality of segments on the frequency axis as in the first embodiment.
FIG. 10A shows a case where subcarriers are alternately arranged in an interleaved manner as in the present embodiment.

As shown in FIG. 10 (b), when frequency selective fading U occurs where the subcarriers of data A are dense, most of the subcarriers used for communication are affected. , Fail. However, FIG.
As shown in, by arranging the subcarriers alternately, only a part of the subcarriers used for communication is affected,
Communication failure is less likely to occur, and the system is resistant to fading. In the present embodiment, the subcarriers are classified and arranged not only on the frequency axis but also on the time axis.

In order to realize such an arrangement, data is temporally rearranged before performing the inverse Fourier transform processing. FIG. 11 is an image diagram of a buffer used when performing interleaving used for error correction coding. One cell in the figure has a predetermined number (for example, 8, 16, 32, etc.)
Represents one unit of data composed of bits. When writing data to the buffer, the data is written in the horizontal direction in the order of 1, 2, 3,..., And at this time, check bits used for error correction are also written. Reading is performed in the vertical direction by 1,11,21,31,
行 う, 2, 12, 22, ‥‥.

The number of data to be subjected to one inverse Fourier transform or Fourier transform used in OFDM is represented by "FFT
Unit. " The FFT unit may be one unit of data, but is usually composed of several units of data. In FIG.
4 units are shown. In this case, subcarriers are allocated to every four units of data read in the vertical direction. At this time, one subcarrier is not allocated to one data unit, but one subcarrier is allocated to each bit constituting one unit of data. However, the number of bits allocated per subcarrier varies depending on the modulation scheme. For example, in the case of the QPSK method, two bits are assigned to one wave.

Therefore, the data 1, 2, 3,... Which were continuous at the time of writing can be dispersed in time and frequency, so that even if data is lost over a certain time range or a certain frequency is lost. Even if data is lost over the range, the original data can be easily reproduced on the receiving side. The above is a description of general interleaving. In the embodiment of the present invention, there are two types of data A and B to be transmitted. Therefore, when the data A is represented by oblique lines and the data B is represented by white, as shown in FIG. 12, two types of data A and B are dispersedly arranged in a buffer image diagram. The algorithm of this distributed arrangement may be arbitrary, but must be agreed between the transmitting side and the receiving side.

It is not always necessary to perform the distributed arrangement for each data unit as shown in FIG. For example, they may be finely distributed in bit units. Data distributed and arranged as shown in FIG. 12 is read out in units of four in the vertical direction and subcarriers are allocated. FIG. 13 is an arrangement diagram of data allocated on the frequency axis and the time axis after the inverse Fourier transform. Looking at a certain time, data A and B
Are arranged in a fixed pattern on the frequency axis, and when viewed at a certain frequency, the data A and B are arranged in a fixed pattern on the time axis.

With such an arrangement, the data A and B are switched in the time axis direction and the frequency axis direction, and the effects of time diversity and frequency diversity appear synergistically. When receiving the above data, the data is subjected to Fourier transform by the Fourier transform circuit 93, and then deinterleaving and reverse rearrangement of the data are performed. FIG. 14 is an image diagram of a buffer for allocating received data. The data reading direction and the writing direction are switched as compared with those in FIG. In-vehicle device 8 on the receiving side
Applies the algorithm of the inverse distribution arrangement to the read data string to separate the two types of data A and B. Then, a necessary type of data is selected and read out by the changeover switch circuit 94.

As described above, in the embodiment of the present invention, the classified data A and B are arranged in a fixed pattern in the frequency axis direction and the time axis direction, respectively, so that the frequency diversity and the time diversity are simultaneously performed. At the same time, the correction capability of the error correction code can be used more effectively, and high-quality data communication can be realized. Here, it will be described that if a predetermined algorithm is adopted as the distributed arrangement algorithm, it can be divided into two subcarrier segments on the frequency axis as described in the first embodiment.

FIG. 15 shows a state in which two types of data A and B are rearranged in a buffer image diagram by a predetermined algorithm. In this algorithm, 2
The distribution repetition period of the types of data A and B is matched to the FFT unit. Therefore, the arrangement of the data after the inverse Fourier transform is divided into two subcarrier segments on the frequency axis as shown in FIG. 16, and the manner of division is time-invariant. Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various design changes can be made within the scope of the present invention.

For example, the number of data classifications is not limited to two, but may be any integer greater than one. In the description of FIG. 1, one on-road antenna 4 forming one cell E is installed at the center of the cell E. But,
As shown in FIG. 17, the cell E may be divided into a plurality of sub-areas, and road antennas 41, 42, and 43 may be installed to supply the same signal. Since the subarea is relatively small, the transmission power of the roadside antenna can be small.

[0054]

According to the present invention, even when a vehicle passes a boundary between adjacent cells, data of the same content can be continuously obtained without being affected by intersymbol interference. Therefore, stable and continuous communication between the road and the vehicle can be performed without causing an instantaneous interruption of communication. Therefore,
For example, when this 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 an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an electrical configuration of a ground station.

FIG. 3 is a graph illustrating a state of symbol transmission by OFDM on a frequency axis f and a time axis t.

FIG. 4 is a conceptual diagram illustrating a configuration of an in-vehicle device.

FIG. 5 is a conceptual diagram illustrating a comparative example for describing a signal transmitted from each road antenna by a frequency axis f and a time axis t, and explaining a reception state of the vehicle-mounted device 8;

FIG. 6 is a conceptual diagram of the present invention for describing a signal transmitted from each road antenna by a frequency axis f and a time axis t, and explaining a reception state of the vehicle-mounted device 8;

FIG. 7 shows a case where the number of subcarriers is 5, and more data A
FIG. 7 is a diagram showing a mode in which the setting is continuously switched from to D.
(a) is a diagram showing data transmitted from each of the on-road antennas 4a to 4h for each subcarrier, and (b) is a diagram showing a reception state in the on-vehicle receiving unit 9.

FIG. 8 is a block diagram illustrating an electrical configuration of a ground station according to the second embodiment.

FIG. 9 is a frequency spectrum diagram showing a state in which subcarriers of data A and subcarriers of data B are alternately arranged on a frequency axis f.

FIG. 10 is a diagram in which amplitude fluctuation U for frequency selective fading is written on a frequency axis. (a), if the sub-carriers are interleaved alternately, (b)
Shows a case where the subcarrier is divided into a plurality of segments on the frequency axis.

FIG. 11 is an image diagram of a buffer used when performing interleaving used for error correction coding.

FIG. 12 is an image diagram showing a state where two types of data A and B are distributed and arranged in a buffer;

FIG. 13 is a layout diagram of data allocated on the frequency axis and the time axis after the inverse Fourier transform.

FIG. 14 is an image diagram showing a state in which two types of received data A and B are distributed and arranged in a buffer.

FIG. 15 is a diagram showing a buffer indicating a state in which two types of data A and B are rearranged by an algorithm in which the distribution repetition period matches the FFT unit.

FIG. 16 is a diagram showing an arrangement of data after inverse Fourier transform on a frequency axis and a time axis.

FIG. 17 is a conceptual diagram showing a configuration of a road-vehicle communication system according to another embodiment of the present invention.

[Description of Signs] 1 Ground station 2 Vehicle 4 Roadside antenna 5 Coaxial cable 6 Control device 7 Transmitting device 8 In-vehicle device 9 In-vehicle receiving unit 10 In-vehicle antenna E cell A, B Classified data

Claims (11)

[Claims] A road-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 an on-vehicle device, an orthogonal frequency division multiplexing system (OFDM) ; Orthogonal Frequ
a control device for transmitting a signal modulated by the ency division multiplex, a road transmitting antenna device for radiating radio waves of the same frequency into the cell based on the transmitted signal, and the road transmitting antenna device An in-vehicle receiving antenna for receiving a radio wave radiated from the vehicle, and an in-vehicle device having an in-vehicle receiving means for receiving and demodulating by receiving the in-vehicle receiving antenna, the control device classifies the subcarrier into a plurality of types. And transmission means for transmitting data to the plurality of types of sub-carriers, respectively.
When transmitting data having different contents using two types of sub-carriers, the roadside transmitting antenna devices arranged in these adjacent cells use the other types of sub-carriers to transmit the data having different contents. A road-to-vehicle communication system characterized in that any one of the data is transmitted in common. 2. The control device according to claim 1, wherein the plurality of types of subcarriers are:
2. The road-to-vehicle communication system according to claim 1, wherein each data is assigned according to a use of the data. 3. The road-vehicle communication system according to claim 2, wherein the data commonly transmitted using the other type of subcarrier is data requiring continuity between cells. 4. The on-vehicle receiving means includes switching means for switching between the data of the one type of sub-carrier and the data of the other type of sub-carrier.
The road-to-vehicle communication system according to claim 1. 5. The road-vehicle communication system according to claim 1, wherein the classification into the plurality of types of subcarriers is performed by dividing the subcarrier into a plurality of segments on a frequency axis. 6. The classification into a plurality of types of subcarriers is performed by dividing the same type of subcarriers by K (K is a constant natural number) on a frequency axis.
2. The road-vehicle communication system according to claim 1, wherein the communication is performed by arranging every other book. 7. A road-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. ; Orthogonal Frequ
a control device for transmitting a signal modulated by the ency division multiplex, a road transmitting antenna device for radiating radio waves of the same frequency into the cell based on the transmitted signal, and the road transmitting antenna device An in-vehicle receiving antenna for receiving a radio wave radiated from the vehicle, and an in-vehicle device having an in-vehicle receiving means for receiving and demodulating by the in-vehicle receiving antenna, wherein the control device classifies the data to be transmitted into a plurality of types. And
It has transmission means for transmitting the classified data by arranging them in a fixed pattern in the frequency axis direction and the time axis direction, respectively. The on-road transmitting antenna device arranged in the adjacent cell has 1
When transmitting data having different contents using one pattern, the road transmitting antenna apparatus arranged in these adjacent cells uses one of the data having different contents using another pattern. A road-to-vehicle communication system characterized by transmitting data in common. 8. The control device according to claim 1, wherein the plurality of types of patterns are:
8. The road-vehicle communication system according to claim 7, wherein each data is allocated according to a use of the data. 9. The road-vehicle communication system according to claim 8, wherein the data commonly transmitted using the other type of pattern is data requiring continuity between cells. 10. The road-vehicle communication system according to claim 7, wherein said on-vehicle receiving means has switching means for switching between the data of the one type of pattern and the data of the other type of pattern. 11. The transmission means transmits the data by temporally rearranging the data including the classified data of each type and then performing an inverse Fourier transform process. 8. The road-vehicle communication system according to claim 7, wherein the classified data is subjected to a reverse recombination process to obtain classified data of each type.