JP2003124867A - On-vehicle unit for communication between vehicle and road - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable mutual communication by searching in a short time for a channel that a road station of a lane that one's own vehicle is to enter is using even when many communication channels are available. SOLUTION: The starting frequency of a local oscillation signal supplied to a mixer 4b to which one of a plurality of road station signals of mutually different frequencies is inputted is set to a frequency corresponding to a road station signal of an intermediate frequency among the plurality of road station signals and the 2nd and succeeding frequencies of the local oscillation signal supplied to the mixer 4b are switched to frequencies corresponding to road station signals in a group higher or lower than the intermediate frequency when the level of a signal of an intermediate frequency band supplied last is different.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to road-to-vehicle communication (hereinafter referred to as DSRC) used for an automatic toll collection system (hereinafter referred to as ETC), a parking lot, drive-through, etc.
For on-vehicle equipment.

[0002]

2. Description of the Related Art At present, ETC is put into practical use as one application of DSRC. Two channels are used for communication between the road station (transmission station installed for each lane) and the vehicle-mounted device in the tollgate, and the Down-Link signal (road) of one channel (first channel) is used. The frequency of the signal transmitted from the station to the vehicle-mounted device) is 5.795 GHz, and the frequency of the Up-Link signal (the signal transmitted from the vehicle-mounted device to the road station) is 4 than that.
It is 5.835 GHz, which is 0 MHz higher. Also, Down-L of another channel (referred to as the second channel)
The frequency of the ink signal is 5.805 GHz, Up-Lin
The frequency of the k signal is 5.845 GHz, which is 40 MHz higher. When there are a plurality of lanes at a tollgate, adjacent road stations use channels with different frequencies in order to avoid mutual interference.

FIG. 4 shows the configuration of the vehicle-mounted device that is currently in practical use.
, And the operation until the communication is established with the road station will be described. When the vehicle approaches the tollgate, the bandpass filter 22 connected to the antenna 21 is connected to the reception unit 24 by the antenna switching device 23, and the vehicle-mounted device is Down-Lin.
A standby state for receiving the k signal is set. Also, since the car is not sure which channel the lane it is going to enter is using, the local oscillator 25
The local oscillation signals (5.835 GHz and 5.845 GHz) having a frequency corresponding to the two Down-Link signals are alternately output. This frequency is set by the PLL circuit 27 controlled by the control unit 26. Then, the D amplified by the low noise amplifier 24a of the receiving unit 24
The down-link signal and the local oscillation signal are mixed by the mixer 24b.
Is input to the mixer 24b, and the mixer 24b outputs an intermediate frequency signal having a frequency difference converted.

The frequencies of the intermediate frequency signals are, for example, 40 MHz and 50 M if the road station is set to the first channel.
Alternately switching to Hz and 30 MHz and 40 MHz if set to the second channel.

The bandpass filter 24c provided at the next stage of the mixer 24b has a center frequency of 40 MHz and a bandwidth of about 5 MHz, so that the bandpass filter 24c outputs only the intermediate frequency signal frequency-converted to 40 MHz. And is detected by the reception detector 24d. The frequency of the local oscillation signal at the time of this detection output makes it possible to know which channel the road station is set to.
The detection output is a CD (carrier detection) signal as the control unit 26.
Entered in. When the detection output is input, the control unit 26 stops switching the local oscillation frequency and fixes the local oscillation frequency at that time. As a result, it becomes possible to receive the Down-Link signal from the road station of the lane which is about to enter. Then, the control unit 26 processes the ASK demodulated signal detected by the reception detector 24d.

On the other hand, the local oscillation signal whose frequency is fixed is input to the modulator 28a of the transmitter 28. Then, at the time of transmission, the ASK modulation signal is input from the control unit 26 to the modulator 28a, and the Up-Link signal is generated. At the same time, the transmitter 28 is connected to the bandpass filter 22 by the antenna switch 23, and the Up-Link signal is amplified by the power amplifier 28b and sent to the antenna 21.

[0007]

DISCLOSURE OF THE INVENTION Currently, D including ETC
A system study of the entire SRC is being conducted mainly by the Ministry of Internal Affairs and Communications, and five channels have been added to road-to-vehicle communication,
Seven channels will be allocated in addition to the conventional two channels. Since all of these channels are used only for road-to-vehicle communication, and a control channel for selecting a communication channel is not assigned, the vehicle-mounted device needs to search for a channel for communication by itself.

However, when the frequency of the local oscillation signal corresponding to each channel is changed to search one channel out of the seven channels as in the prior art, the number of frequency changes becomes 6 at worst, It takes a lot of time to complete the search. This does not meet the purpose of DSRC, which is one of the purposes of eliminating traffic congestion.

Therefore, in the present invention, even if there are many communication channels, the channel used by the road station of the lane where the vehicle is about to enter can be searched for in a short time and communicate with each other. The purpose is to

[0010]

In order to solve the above problems, according to the present invention, a mixer to which one of a plurality of road station signals having different frequencies is input and an intermediate frequency band for each of the road station signals. , A local oscillator controlled to sequentially switch the local oscillation signal for conversion to a predetermined frequency in the mixer, a low-pass filter and a high-pass filter having the same amount of attenuation at the predetermined frequency, and Comparing each level of the signal in the intermediate frequency band that has passed through a low-pass filter and the signal in the intermediate frequency band that has passed through the high-pass filter, a control unit that controls the frequency switching of the local oscillation signal,
The first frequency of the local oscillation signal supplied to the mixer is set to a frequency corresponding to a road station signal having an intermediate frequency in the plurality of road station signals, and the second or subsequent times of the local oscillation signal supplied to the mixer. When the level of the signal in the intermediate frequency band when supplied last time is different, the frequency is switched to the frequency corresponding to the road station signal in the group higher or lower than the intermediate frequency.

Further, the second and subsequent frequencies of the local oscillation signal supplied to the mixer are switched to a frequency corresponding to the intermediate frequency of the road station signal in the high group or the frequency of the road station signal in the low group. .

When the levels of the signals in the intermediate frequency band are equal, the frequency of the local oscillation signal supplied to the mixer at that time is not switched.

Further, the attenuation characteristics of the low-pass filter and the high-pass filter are set to be symmetric with respect to the predetermined frequency.

A bandpass filter is provided between the mixer and the lowpass filter and the highpass filter, the center frequency of the bandpass filter is the predetermined frequency, and the pass band is the maximum frequency of the road station signal. The difference from the lowest frequency was used.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An on-vehicle device for road-to-vehicle communication according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration in which a bandpass filter 2 is connected to the antenna 1 and an antenna switch 3 is connected to the bandpass filter 2. The receiving unit 4 is connected to the output terminal of the antenna switching unit 3. The receiving unit 4 includes a low noise amplifier 4a connected to the antenna switching unit 3 and a mixer 4 provided in the next stage.
b and the bandpass filter 4c provided in the next stage
And a receiving wave detector 4d provided in the subsequent stage and an amplifier 4e provided in the next stage. The local oscillation signal output from the local oscillator 5 is input to the mixer 4b. The center frequency of the bandpass filter 4c is 40 MH
z, the bandwidth is approximately 5 MHz.

Further, Down-L is provided at the subsequent stage of the mixer 4b.
A channel search circuit 6 for searching the channel of the ink signal is connected. The channel search circuit 6 includes a bandpass filter 6a, a lowpass filter 6b and a highpass filter 6c arranged in parallel at the subsequent stage, and a first detector 6d provided at the next stage of the lowpass filter 6b.
And a second detector 6e and the like provided in the next stage of the high-pass filter 6c. The center frequency of the bandpass filter 6a is 40 MHz, and the bandwidth is approximately 35 MHz. Further, as shown in FIG. 2, the characteristics of the low-pass filter 6b and the high-pass filter 6c are such that their cutoff frequencies are set to about 20 MHz and 60 MHz, respectively.
It has a slope of 6 dB per octave so as to be vertically symmetrical about 0 MHz. By the way, the amount of attenuation at 40 MHz is about 4 dB.

The receiving detector 4d of the receiving section 4, the amplifier 4e, and the two detectors 6 of the channel search circuit 6 are provided.
d and 6 e are connected to a control unit (referred to as CPU) 7.
Further, the PLL circuit 8 is controlled by the CPU 7,
The oscillation frequency of the local oscillator 5 is set by the L circuit 8.

The transmitting unit 9 connected to the input terminal of the antenna switching unit 3 has a modulator 9a, a power amplifier 9b, etc., and the modulator 9a receives the ASK modulation signal from the CPU 7 and the local oscillator 5 as well. A local oscillation signal is input. The power amplifier connected to the next stage of the modulator 9a is connected to the antenna switching unit 3.

Between the on-vehicle device for road-to-vehicle communication (hereinafter referred to as on-vehicle device) of the present invention having the above configuration and the road station (transmission station installed for each lane) provided in the entrance lane of the tollgate One of seven channels is used for communication. Signal transmitted from the road station to the on-board device (Down
Seven (−Link signal) frequencies are arranged at 0.05 GHz intervals, and the frequency of a signal transmitted from the vehicle-mounted device to the road station (referred to as Up-Link signal) is 40 MHz higher than those. Dow for each channel
Table 1 shows the frequency of the n-Link signal and the frequency of the Up-Link signal.

[Table 1]

When there are a plurality of lanes at the toll gate, adjacent road stations use different channels to avoid mutual interference, and the Down-Link signal is transmitted to a car entering with sharp directivity. It

The operation until the vehicle approaches the lane in which the vehicle is approaching and communication is established with the road station will be described with reference to the flowchart of FIG. First, in step 1, the CPU 7 controls the antenna switching unit 3 to connect the bandpass filter 3 to the receiving unit 4, and the local oscillator 5 is the U of the fourth channel which is just the middle channel.
By controlling the PLL circuit 8 to oscillate at the oscillation frequency (5.830 GHz) of the p-Link signal, the standby state of the fourth channel is set.

In this state, Down-Link from the road station
Receive the signal. The received Down-Link signal is converted into an intermediate frequency signal by the mixer 4b and input to the band pass filters 4c and 6a. Bandpass filter 6
The intermediate frequency signal input to a is a low pass filter 6b,
It is detected by the first detector 6d and the second detector 6e through the high-pass filter 6c, and each detection output level is C
Down-Link received by being compared by PU7
It is determined whether the signal is for the fourth channel (step 2). If the detected output levels are equal to each other, it can be seen that the frequency of the intermediate frequency signal is 40 MHz and the received Down-Link signal is of the fourth channel. At that time, the CPU 7 operates the local oscillator 5
The oscillation frequency is maintained as it is in the standby state of the fourth channel (step 3).

When the detected output levels are not equal to each other in step 2, it is compared whether the Down-Link signal is higher or lower than the frequency of the fourth channel (step 4). In this case, the first detector 6
The detection output level of d (low-pass filter 6d side) is the detection power level of the second detector 6e (high-pass filter 6e).
The frequency of the intermediate frequency signal is 40 MH
This is the case of z or less, and the case where the received Down-Link signal is higher than the frequency of the fourth channel. On the contrary, if the detection output level of the first detector 6d (low-pass filter 6d side) is lower than the detection power level of the second detector 6e (high-pass filter 6e side), the frequency of the intermediate frequency signal is 40 MHz or more. And received Dow
This is the case where the n-Link signal is lower than the frequency of the fourth channel.

When the received Down-Link signal is higher than the frequency of the fourth channel, the CPU
Reference numeral 7 controls the PLL circuit 8 so that the local oscillator 5 is up-Li of the sixth channel which is the middle of the fifth to seventh channels.
The sixth channel is set to the standby state by oscillating at the frequency of the nk signal (5.840 GHz) (step 5). Then, it is again compared whether or not the detection output levels are equal (step 6). Here, if the detected output levels are equal to each other, the Down-Link signal is for the sixth channel, so the CPU 7 maintains the oscillation frequency of the local oscillator 5 as it is in the standby state for the sixth channel (step 7).

If the detected output levels compared in step 6 are not equal to each other, it is compared whether the Down-Link signal is higher or lower than the frequency of the sixth channel (step 8). Similarly, when the frequency is high, the CPU 7 controls the PLL circuit 8 so that the local oscillator 5 causes the frequency (5.8) of the Up-Link signal of the seventh channel.
Switching to oscillate at 45 GHz (step 9). On the other hand, if it is low, the CPU 7 controls the PLL circuit 8 so that the local oscillator 5 causes the fifth channel Up-Link.
Switching to oscillate at the signal frequency (5.835 GHz) (step 10).

On the other hand, in step 2, the received Do
When the wn-Link signal is lower than the frequency of the fourth channel, the CPU 7 controls the PLL circuit 8 so that the local oscillator 5 has the frequency of the Up-Link signal of the second channel (the middle of the first to third channels) ( 5.820GH
The second channel is set to the standby state by oscillating in step z) (step 11). Then, it is again compared whether or not the detection output levels are equal (step 12).
Here, if the detection output levels are equal to each other, Down-
Since the Link signal is for the second channel, CP
U7 maintains the oscillation frequency of the local oscillator 5 as it is in the standby state of the second channel (step 13).

If the detected output levels compared in step 12 are not equal to each other, it is compared whether the Down-Link signal is higher or lower than the frequency of the second channel (step 14). Similarly, when it is high, the CPU 7 controls the PLL circuit 8 to switch the local oscillator 5 to oscillate at the frequency (5.825 GHz) of the Up-Link signal of the third channel (step 15). On the other hand, when the value is low, the CPU 7 controls the PLL circuit 8 so that the local oscillator 5 is up for the first position channel.
-Switch to oscillate at the frequency of the Link signal (5.815 GHz) (step 16).

As described above, the local oscillator 5 transmits the Up-Link signal of any one of the first to seventh channels so that the Down-Link signal transmitted from the road station of the lane finally entering can be received. Since it is controlled to oscillate at the frequency, communication with the road station becomes possible thereafter, the received Down-Link signal is ASK demodulated by the reception detector 4d, and the demodulated signal is processed by the CPU.
Repaired at 7. Also, during transmission, the local oscillation signal input to the modulator 9a is modulated by the ASK modulation signal from the CPU 7, and the modulated Up-Link signal is amplified by the power amplifier 9b and sent to the antenna 1. It goes without saying that the antenna switching unit 3 is connected to the receiving unit 4 and the transmitting unit 9 during reception and transmission, respectively.

As described above, by providing the channel search circuit 6 and changing the channel in the standby state, the number of times the local oscillation frequency is switched can be reduced to a maximum of 3 times,
Time to communication connection is shortened.

[0030]

As described above, the first frequency of the local oscillation signal supplied to the mixer to which one of the plurality of road station signals having different frequencies is input is set to the intermediate frequency of the plurality of road station signals. When the frequency of the local oscillation signal supplied to the mixer after the second time is the frequency corresponding to the frequency of the local station signal and the level of the signal in the intermediate frequency band when it was supplied last time is different, Since the frequency is switched to the frequency corresponding to the road station signal of the high group or the low group, the number of times of switching the local oscillation frequency is reduced and the time until the communication connection is shortened.

Since the frequency of the second and subsequent local oscillation signals supplied to the mixer is switched to the frequency corresponding to the intermediate frequency road station signal in the high group or the low station road station signal, the local oscillation frequency is changed. The number of times of switching is reduced to 3 at maximum.

When the levels of the signals in the intermediate frequency band are equal, the frequency of the local oscillation signal supplied to the mixer at that time is not switched, so that communication can be performed at the initially set local oscillation frequency. Become.

Further, since the attenuation characteristics of the low-pass filter and the high-pass filter are set to be symmetric with respect to a predetermined frequency, it becomes easy to compare the height of the road station signal.

Further, a bandpass filter is provided between the mixer and the lowpass filter and the highpass filter, the center frequency of the bandpass filter is set to a predetermined frequency, and the pass band is the difference between the highest frequency and the lowest frequency of the road station signal. As a result, it is possible to eliminate interfering signals other than road station signals.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a vehicle-mounted device for road-to-vehicle communication of the present invention.

FIG. 2 is a characteristic diagram of a low-pass filter and a high-pass filter used in the vehicle-mounted device for road-to-vehicle communication of the present invention.

FIG. 3 is a flowchart for explaining the operation of the vehicle-mounted device for road-to-vehicle communication of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional vehicle-mounted device for road-to-vehicle communication.

[Explanation of symbols]

1 antenna 2 band pass filter 3 antenna switch 4 Receiver 4a Low noise amplifier 4b mixer 4c bandpass filter 4d receiver detector 4e amplifier 5 Local oscillator 6 channel search circuit 6a bandpass filter 6b low pass filter 6c high pass filter 6d First detector 6e Second detector 7 control unit 8 PLL circuit 9 Transmitter 9a modulator 9b power amplifier

Claims (5)

[Claims] 1. A mixer to which one of a plurality of road station signals having different frequencies is input, and a local oscillation signal for sequentially converting each of the road station signals into a predetermined frequency in an intermediate frequency band. A local oscillator controlled to be supplied to the mixer, a low-pass filter and a high-pass filter having the same amount of attenuation at the predetermined frequency, a signal in the intermediate frequency band that has passed through the low-pass filter, and the high-pass filter. Comparing each level with the signal of the intermediate frequency band that has passed, and comprising a control unit for controlling the frequency switching of the local oscillation signal, the first frequency of the local oscillation signal supplied to the mixer, A frequency corresponding to an intermediate frequency road station signal in the plurality of road station signals, and the second or more times of the local oscillation signal supplied to the mixer. The descending frequency is switched to a frequency corresponding to the road station signal in a group higher or lower than the intermediate frequency when the level of the signal in the intermediate frequency band when supplied last time is different. An on-vehicle device for road-to-vehicle communication. 2. The frequency of the second and subsequent frequencies of the local oscillation signal supplied to the mixer is switched to a frequency corresponding to the intermediate frequency of the road station signal in the high group or the frequency of the road station signal in the low group. The vehicle-mounted device for road-to-vehicle communication according to claim 1. 3. The frequency of the local oscillation signal supplied to the mixer at that time when the levels of the signals in the intermediate frequency band are equal to each other is not switched. The vehicle-mounted device for road-to-vehicle communication described. 4. The on-vehicle device for road-to-vehicle communication according to claim 1, wherein attenuation characteristics of the low-pass filter and the high-pass filter are set to be symmetric with respect to the predetermined frequency. 5. A bandpass filter is provided between the mixer and the lowpass filter and highpass filter,
The road-vehicle distance according to any one of claims 1 to 4, wherein the center frequency of the band-pass filter is the predetermined frequency, and the pass band is a difference between the highest frequency and the lowest frequency of the road station signal. Onboard equipment for communication.