JP3230016B2 - FM-CW radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing interference by reducing interference.
FM-CW that can measure the relative distance and relative speed between
About radar.

[0002]

2. Description of the Related Art FIG . 11 shows a conventional general FM-CW laser.
Shows an example of a basic configuration of a triangular wave generator, 11 is a triangular wave generator, and 12 is
FM modulator, 13 is a transmitting antenna, 14 is a receiving antenna.
, 15 is a directional coupler, 16 is a mixer, and 17 is a signal processor.
A triangular wave signal from the triangular wave generator 11
The frequency of the carrier is frequency-modulated in the FM modulator 12 and
The modulated high-frequency signal from the transmitting antenna 13 via the coupler 15
Send the issue.

[0003] The receiving antenna 14 causes an obstacle or a preceding vehicle.
, And the received signal is
Mixes with the modulated high-frequency signal via the directional coupler 15
Input the beat frequency signal to the signal processor 17, and
Phase with the target according to the processing result
Distance and relative speed can be determined.

FIG . 12A shows the relative velocity between the target and the target.
In the case of 0, (b) shows the case of the relative velocity v with the target.
The transmission frequency, the reception frequency, the beat frequency, and the
FIG. Transmission signal (modulated high-frequency signal)
Is used to modulate the frequency of a carrier with a triangular wave.
The reception frequency changes in a triangular waveform at a predetermined cycle. FIG. 1
In the 2 (a), the beat frequency f _b = (4ΔΩf _m
It can be expressed as _R) / c = f _r. Also in (b)
Te, the beat frequency f _b = [(4ΔΩf _m R) / c] ±
[(2f ₀ ) / v]. Note that _fr is
Distance frequency corresponding to the distance to the target , f _d is the target
Speed frequency corresponding to the relative velocity between the object, f ₀ is transmitted
Signal center frequency, ΔΩ is FM modulation width, T is modulation repetition
F _m (= 1 / T) is the modulation repetition frequency, f _b
Is the transmission and reception beat frequency, c is the speed of light, _tr is the _distance to the obstacle
R is the distance to the obstacle, v is the obstacle
And relative speed.

[0005] Transmission from the transmission antenna 13 (see FIG. 11)
Modulated high-frequency signals traveling over fixed obstacles or ahead
The light is reflected from the preceding vehicle and received by the receiving antenna 14.
At that time, the time from transmission to reception is
The time delay _tr = 2R / c proportional to the distance at
Subject to Doppler frequency shift proportional to relative velocity
Becomes

[0006]As shown in FIG.
Frequency f _b Is the distance frequency f depending on the distance _r When,
Speed frequency f depending on relative speed _d Frequency of sum and difference
When the relative speed is 0, f _b = (4ΔΩf
_m R) / c. When the relative speed is v, f _b = (4
ΔΩf _m R) / c ± (2f ₀ ) / V. So this
Means for detecting these frequencies and information on the detected frequencies.
The relative distance R to the target and the relative velocity v
be able to.

In the conventional FM-CW radar shown in FIG .
In other words, the signal frequency-modulated by the triangular wave signal is continuously
And continuously receive and transmit reflected waves from the target.
The beat frequency signal of the frequency difference between the
The signal is output from the mixer 16 and the beat is
Calculate relative distance and relative speed based on frequency signal
However, if the calculation process in this case cannot keep up,
While discarding the information indicating the beat frequency from the mixer 16
Calculation of relative distance and relative speed in real time
Is what you do.

[0008]

SUMMARY OF THE INVENTION Conventional FM-CW lasers
The transmitter continuously transmits and receives the modulated high-frequency signal.
You. Therefore, vehicles equipped with the same type of FM-CW radar
When passing each other, the reflected wave together with the transmitted wave of the oncoming vehicle
Is often received by the receiving antenna. So
In the case of, a radio wave different from the reflected wave is received as an interference wave
Calculation errors in the relative distance and relative speed are large.
There is a problem.

As a method of reducing radar interference, for example,
For example, in aircraft surveillance radars and ship surveillance radars,
Detects interference waves and automatically adjusts transmission and reception frequencies without interference
A method of switching to a frequency has been considered. But,
This method requires the complexity and size of the system.
There is a point. Therefore, mounted on road vehicles such as automobiles
Applying to FM-CW radar for vehicles is space-saving
It is also difficult in terms of cost.

In addition, the polarization plane is made different to reduce interference.
Means, means for making the frequency different, and the like are conceivable. Only
To be applied to a large number of automobiles
Need to be different from each other. Therefore, practical application is difficult.
It is difficult. Also, the transmission beam from the transmission antenna is
By squeezing like a beam, interference with oncoming vehicles
It is conceivable to reduce it. But applied for automotive
Then, the preceding car running ahead approached the curve
Sometimes, the reflected wave from the preceding vehicle cannot be obtained.
The guardrail in front of the curve
There is a problem that there is a high possibility that the vehicle will be mistaken for the preceding vehicle.

Japanese Patent Application No. 3-22 by the same applicant as the present application.
No. 3397 (JP-A-5-40169).
The FM-AM based on the frequency characteristics of the voltage controlled oscillator.
A rectangle with a duty of about 50% to reduce conversion noise
The transmission wave is modulated by a wave and transmitted. This
When the transmission wave is AM-modulated with a square wave, the rectangular wave
The transmission level is lower at the bell, reducing interference during this time
Is done. However, when the relative distance from the target is large
In addition, since the delay time until the reflected wave can be received is large,
Find the frequency difference between the transmitted wave and the received wave, that is, the beat frequency.
Time is short, making it difficult to detect long-distance targets
There is a problem.

The present invention solves the above-mentioned conventional problems.
So, to calculate the distance to the target and the relative speed
A modulated wave signal is transmitted only for the required time,
The purpose is to reduce interference.

[0013]

SUMMARY OF THE INVENTION An FM-CW laser according to the present invention.
Referring to FIG. 1, the modulator generates a control voltage for modulation.
Generated modulation signal generating means 1 and the modulated signal generating means 1
Frequency modulated by the modulation control voltage from
FM wave generating means 2 for generating a signal;
Branching means 3 for branching the modulated high-frequency signal from stage 2;
One modulated high-frequency signal branched by the branching means 3
Switch to switch and transmit from transmitting antenna 5
Branching means 4 and a signal received by the receiving antenna 6
Mixing with the other modulated high-frequency signal branched by means 3
Mixing means 7 for outputting a baseband signal to
Based on the frequency component information of the baseband signal from the combining means 7.
To calculate the relative distance and relative speed to the target
Processing means 8, wherein the signal processing means 8 comprises a mixing means.
7 to measure the frequency of the baseband signal from
Measurement means and the frequency measurement means
The transmission control is performed by turning on the switching means 4 only for the time.
It has control means.

When the interference rate is large based on the interference rate information
Shortens the transmission time, and increases the transmission time when the interference rate is small.
A transmission time control unit to control the transmission time
A digitized configuration can be used. The transmission time control unit
When the relative distance to the target in the signal processing unit is short,
Increase the frequency of turning on the switching means, and
When the relative distance between
With a configuration that controls so that the frequency of
is there.

[0015]

The signal processing means 5 causes the switching means 4 to be turned off.
Control of the transmission and reception of the modulated high-frequency signal
Control the time to send from. The transmission time is
Switching only the time required for measurement processing by the measurement means
Turn on means 4 and off at other times
Do not transmit from the transmitting antenna 5 at all times
Control. This reduces the probability of interference
You.

Further , the transmission is performed so that the interference rate becomes a predetermined value or less.
Transmission time of the modulated high-frequency signal transmitted from the transmission antenna 5
Control. The frequency at which the switching means 4 is turned on is
The control is performed according to the relative distance from the target.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
Will be described. In FIG. 2, 11 is a triangular wave generator, 13
Is a transmitting antenna, 14 is a receiving antenna, 15 is a directional connection.
A mixer, 16 is a mixer, 21 is a voltage controlled oscillator, and 22 is a switch.
The switching unit 23 indicates a pulse counter, which corresponds to FIG.
Corresponding functional parts are indicated by numbers in parentheses.

The triangular wave signal from the triangular wave generator 11 is shown in FIG.
To the voltage controlled oscillator 21 corresponding to the FM wave generating means 2 of FIG.
Output a modulated high-frequency signal frequency-modulated by a triangular wave
And corresponds to the branching means 3 and the switching means 4 in FIG.
Via the directional coupler 15 and the switching unit 22.
The transmission antenna 13 transmits the modulated high-frequency signal. or
The received signal received by the receiving antenna 14 is
The signal partially branched by the combiner 15 is input to the mixer 16
And mix the frequency difference, that is, the beat frequency component.
Input to the counter 23. This pulse counter 23
Is one of the frequency measuring means in the signal processing means 8 of FIG.
Calculate the relative distance and relative speed to the target by showing an example
And the switching unit 22 and the triangular wave generator 11
Are not shown in the figure. Note that these
The means can be easily realized.

When the switching section 22 is turned on, the modulation
The transmission time for transmitting the wave signal from the transmission antenna 13 is
Baseband signal from beater 16 (beat frequency component)
Measurement such as pulse counter 23 for measuring the frequency of
The reciprocal of the measurement frequency resolution of the means
can do. In this case, at least the signal processing means
Pulse counter and the relative distance and relative speed
Transmit so that the signal of the time required for the measurement process can be received
You can set the time. Also, relative distance and relative speed
Generates a triangular wave according to one or both measurement result conditions
Of the frequency of the switch 11 and turning on of the switching unit 22
Time control and the like can be performed. And switchon
Transmission from the transmission antenna 13 only when the
And do not transmit from the transmitting antenna 13 at other times
Things.

FIG . 3 shows a directional coupler 1 as a branching means.
5 between the transmitting antenna 13 and the switching unit 22
The same reference numerals as those in FIG. 2 denote the same parts.
Show. Therefore, the pulse counter 23 as a signal processing unit
Of the switching unit 22 controlled by
And a part of the modulated high-frequency signal is branched and input to the mixer 16.
Is what you do. In this case, consider the delay time of the reflected wave.
To set the transmission time.

FIG . 4A shows that the frequency f ₀ is represented by a triangular wave.
Provides an overview of the frequency change of the modulated high-frequency signal.
(B) and (c) show the outline of the switching waveform and the transmission signal.
It is important. Let T (transmission interval) be a predetermined cycle,
The switching unit 22 (see FIGS. 2 and 3)
) Is turned on to transmit the modulated high-frequency signal to the transmitting antenna 13.
Send from. (B) shows the relative distance to the target and
(C) shows a case where relative speed is measured.
This shows the case where only measurement is performed.

The beat frequency component of the mixer 16 is
Input to the counter 23 to measure the beat frequency.
The relative distance and relative speed calculation means (not shown)
The relative distance to the target and the relative speed
You. The pulse counter 23 measures the beat frequency.
The measurement time for measurement is at least one round of the triangular wave.
Beat frequency in rising and falling part of period
Will be used. And the relative distance and relative speed
During the calculation period, the beat frequency data
Can not be processed.
And

FIG . 5 shows the switching means 4 of FIG.
3 shows the main part of the switching unit 22 of FIG.
A high frequency element such as AsMESFET or HEMT, 32 is
3 shows a switching transistor. Switching
The transistor 32 and the high-frequency element 31 are connected in series with the power supply.
And the switching transistor 32 is switched
When turned on by the control signal shown as the
The high frequency element 32 such as a frequency transistor is turned on,
A modulated high-frequency signal, indicated as RF, is transmitted. Therefore,
The switching transistor 32 is used as the signal processing means described above.
Therefore, only the transmission time is turned on and the modulated high-frequency signal is transmitted.
It can be transmitted from an antenna.

FIG . 6 shows a PIN diode or a Schottky
High frequency switching element 33 such as a barrier diode
The switching means 4 of FIG. 1 and the switches of FIGS.
3 shows a main part of the notching portion 22. This high frequency switch
High level shown as a switching control waveform on the
When the control signal of
33 is turned on and the modulated high frequency signal shown as RF input
Is bypassed, so that the switching means 4 or the switch
The chin 22 is equivalent to the off state. Also low level
Is applied, the high frequency switching element 3
3 is off and RF input is sent out as RF output
Therefore, the switching means 4 or the switching unit 22 is off.
State is equivalent to

FIG . 7 shows a 90 ° hybrid 34 and a high frequency type.
Using switching elements 35 and 36 and resistors 37 and 38
Switching means 4 of FIG. 1 and switches of FIGS. 2 and 3
2 shows a main part of the ringing section 22. High frequency switching element 3
5, 36 are PIN diodes or short-circuits as described above.
Devices that can use a key-barrier diode
And 90 ° hybrid in parallel with resistors 37 and 38, respectively.
Connected to the terminal of the pad 34 as a switching control waveform.
The control signal shown in FIG.
Apply.

In this case, the resistors 37 and 38 are used as terminating resistors.
Low-level control by setting a resistance value that satisfies the matching conditions
A signal is applied to the high frequency switching elements 35 and 36,
The high frequency switching elements 35 and 36 were turned off.
At the time, RF input due to termination matching of 90 ° hybrid 34
Is terminated and not output. Therefore, the switching means
4 or the switching unit 22 is turned off. Also high
The level control signal is supplied to the high frequency switching elements 35 and 3.
6, the high-frequency switching elements 35, 3
When the 6 is turned on, the 90 ° hybrid 34
Grounded, the RF input is reflected to the RF output. Follow
Therefore, the switching means 4 or the switching unit 22 is turned on.
State.

FIG . 8 shows a circulator 39 and a high frequency switch.
1 using the switching element 40 and the resistor 41
Of the switching means 4 and the switching unit 22 of FIGS. 2 and 3
Is shown. The high-frequency switching element 40 is, as described above,
In addition, PIN diode or Schottky barrier diode
The resistor can be used in parallel with the resistor 41.
Connect to the terminal of the calculator 39. This circular
To the terminal of the high frequency switching element 40.
Is off, the resistor 41 is in conformity with the condition of non-reflective termination.
And the high-frequency switching element 40 is turned off.
In the case of switching on,
If the control signal shown as the control waveform is low,
Since the wave switching element 40 is turned off, the RF input
Is terminated from the terminal of the circulator 39. Therefore,
The switching means 4 or the switching unit 22 is in the off state.
State. When the control signal is at high level,
The switching element 40 is turned on and the RF input is
The light is reflected at the terminal of the oscillator 39 and becomes an RF output. Follow
Therefore, the switching means 4 or the switching unit 22 is turned on.
State.

FIG . 9 shows an AD converter 42 and an FFT (high-speed format ) .
Required for frequency measurement means using the Rie transform) processing circuit 43
Output of the mixer 16 (see FIG. 2 or FIG. 3).
The signal of the force beat frequency component is decoded by the AD converter 42.
Digital signal, and the FFT processing circuit 43
Measure the carrier frequency. In this case, when importing data
Is the reciprocal of the triangular wave frequency at which the required measurement accuracy is obtained.
Time, that is, at least one cycle of the triangular wave is sufficient.
You. In this case, the beat frequency is
Excellent noise immunity compared to the configuration that determines the wave number
There are many advantages.

FIG . 10 shows a transmission time system according to the embodiment shown in FIG.
The same reference numerals as those in FIG.
Show a part. Input interference rate information to transmission time controller 44
And the interference rate information is already known
It can be obtained using various means. example
If it is determined that interference has occurred, it is determined that interference has occurred
In addition, the interference rate can be calculated based on the number of occurrences within a predetermined time.
Noh. And if this interference rate is larger than the set value
Has a lot of interference, so the measurement time is shortened.
If less, increase the measurement time. Also with signal processing device
Japanese Patent Application No. 3-22339 filed by the same applicant as the present application.
No. 6 (see JP-A-5-40168).
It is also possible to apply a multiple target detection method.

In the modulated high-frequency signal modulated by the triangular wave
Heart frequency f ₀ [Hz] and maximum frequency deviation ΔΩ [Hz]
Can be set to the following values, for example. f ₀ = 75 × 10 ⁹ ΔΩ = 150 × 10 ^{6 When} radar A with period T and transmission time τ is mounted
The probability of occurrence of the interference is τ / T. Oncoming vehicles are the same type
Probability of interference when equipped with a similar type of radar
Is a 2τ / T.

In the FM-CW radar, for example, FF
When measuring relative distance and relative speed using T, send
The time τ is made smaller than the reciprocal of the resolution of the speed frequency. This
The resolution of the speed frequency is half the frequency of the triangular wave.
Since that, the frequency f _m of the triangular wave 1 × 10 ³ [Hz]
When, the transmission time tau, the _{τ = 1 / 2f m = 0.5} × 10 -3. That is, it becomes 0.5 [ms]. Next send
Imming is performed until the distance corresponding to the distance resolution changes
, And the distance resolution is, for example, 1 [m].
Assuming that the speed is 50 [m / s], the transmission cycle T is T = 1/50 = 20 × 10 ⁻³ . That is, the transmission cycle T = 20 [ms], the transmission time τ
= 0.5 [ms]. Probability of interference in this case
p is: p = 2τ / T = 2 × 0.5 × 10 ⁻³ / 20 × 10 ⁻³ =
0.05, that is, the probability p of interference is 5%.

When the target is at a short distance, the transmitting antenna
Most of the power radiated from the
The possibility of interference is reduced. Also between the target
Are not the same, but in the direction approaching each other,
Risk of collision if the relative distance is gradually reduced
The frequency of transmission to increase the frequency of distance detection
Will be. Conversely, if the target is far away,
The power radiated from the antenna is blocked by the target
, The possibility of interference increases. Danger of collision
Due to the low ruggedness, the transmission frequency is increased and the relative distance is frequently measured.
No measurement is required. That is, the relative distance to the target is
According to the measurement result, the transmission time τ and the transmission period T
Can be controlled. For example, when measuring only distance
In this case, the frequency of the triangular wave is increased. In that case,
At a speed frequency (50 [m / s], for example, 25 × 10 ³ [H
z]) to separate the distance frequency from the triangular wave frequency f
_{If m} is 25 × 10 ³ [Hz], the transmission time τ is opposite
Probability experiencing interference from the car p becomes _{τ = 1 / 2f m = 20} × 10 -6 p = 2 × 20 × 10 -6 / 20 × 10 -3 = 2 × 10 -3. That is, the transmission time τ = 20 [μa],
Probability p = 0.2 [%]. In fact, the
The probability of interference is not 1
p becomes even lower.

[0033]

As described above, the present invention provides a modulated signal.
Signal generating means 1, FM wave generating means 2, branching means 3, switch
Ching means 4, transmitting antenna 5, receiving antenna 6, mixed
Means 7 and a signal processing means 8
The processing means 8 controls the frequency of the baseband signal from the mixing means 7.
Frequency measuring means for measuring a wave number, and this frequency measuring means
Switching means only for the time required for measurement processing by
And control means for performing transmission control by turning on 4
Yes, and continuously transmits a modulated high-frequency signal from the transmitting antenna 5.
Not interfere with other radars.
There are advantages that can be reduced.

When the interference rate is large based on the interference rate information
Shortens the transmission time τ, and when the interference rate is small, the transmission time τ
Transmission time control to control the transmission time τ so that
Measurement of relative distance and relative speed
It is possible to reduce interference as well as actually. Also target
When the relative distance between the switching means 4 and the
More frequently, and the relative distance to the target is longer
Sometimes, the frequency of turning on the switching means 4 is reduced.
Controls when collisions are likely to occur.
Increase the frequency of distance measurement, improve the accuracy of distance measurement,
It is also possible to perform collision prevention in cooperation with collision prevention means.
You. The switching means 4 is already known.
Various high frequency switching means can be applied.
Wear. Also, the signal processing means 8 has various known structures.
Can be applied.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing an embodiment (1) of the present invention.

FIG. 3 is a diagram showing an embodiment (2) of the present invention.

FIG. 4 is a diagram showing signal transmission timing in the present invention.

FIG. 5 is a diagram showing an embodiment (3) of the present invention.

FIG. 6 is a diagram showing an embodiment (4) of the present invention.

FIG. 7 is a diagram showing an embodiment (5) of the present invention.

FIG. 8 is a diagram showing an embodiment (6) of the present invention.

FIG. 9 is a diagram showing an embodiment (7) of the present invention.

FIG. 10 is a diagram showing an embodiment (8) of the present invention.

FIG. 11 is a diagram illustrating a basic configuration example of an FM-CW radar.

FIG. 12 is a diagram illustrating an operation principle of the FM-CW radar.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 modulation signal generating means 2 FM wave generating means 3 branching means 4 switching means 5 transmitting antenna 6 receiving antenna 7 mixing means 8 signal processing means 23 pulse counter 31 high frequency element 33 high frequency switching element 34 hybrid 35 high frequency switching element 36 high frequency Switching element 37 Resistance 38 Resistance 39 Circulator 40 High frequency switching element 41 Resistance 43 FFT processing circuit 44 Transmission time control unit

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Tamio Saito 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Osamu Isa 1-2-28, Goshodori, Hyogo-ku, Kobe-shi, Hyogo Fujitsu Inside Ten Co., Ltd. (72) Inventor Kazuhiko Kobayashi 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Toshihiro Shimura 1015 Uedanaka, Nakahara-ku, Nakazaki-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (56) Reference Document JP-A-59-79175 (JP, A) JP-A-3-54494 (JP, A) JP-A-4-259874 (JP, A) JP-A-64-57187 (JP, A) 240947 (JP, A) JP-B-57-20592 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95

Claims (3)

(57) [Claims] 1. A modulation signal generating means for generating a modulation control voltage, frequency by the modulation control voltage from the modulating signal generator
Graphics and FM wave generating means, a branching unit for branching the modulated high-frequency signal from said FM wave generating means, one modulation frequency signal branched by said branching means for generating a number modulated high-frequency signal
Switching means for switching from the transmitting antenna for transmission, a signal received by the receiving antenna , and branching by the branching means.
And mixing means for outputting a baseband signal by mixing the other of the modulation high-frequency signal, the frequency component information of the baseband signal from the mixing means
And signal processing means for calculating the relative distance and relative velocity between the target based on, the signal processing means, the baseband signal from the mixing means
Frequency measurement means for measuring the frequency of the signal, and the frequency measurement
Switch for the time required for the measurement process by means
FM-CW radar comprising: a control unit that controls transmission by turning on a switching unit . 2. When the interference rate is large based on the interference rate information.
Shortens the transmission time, and when the interference rate is low,
Transmission time for controlling the transmission time so as to lengthen the time
The FM- according to claim 1, further comprising a control unit.
CW radar. 3. The signal processing unit according to claim 2 , wherein
When the relative distance to the target in
Increasing the frequency of turning on the switching means,
When the relative distance to the object is long, the switching means
Has a configuration to control so that the frequency of turning on
The FM-CW radar according to claim 1 or 2, wherein: