JPH0735849A - Collision prevention radar device - Google Patents

Abstract

PURPOSE:To detect distance with high resolution, high accuracy, and high speed while securing a high inhibition resistance and a wide measurement range. CONSTITUTION:When correlation detection result according to a correlation detection circuit 40 becomes high and exceeds a threshold in a threshold comparison circuit 42, the frequency-dividing ratio of a frequency-dividing circuit 24 is reduced by an operation control part 28 and the clock output from a PN clock generation circuit 20 is increased the frequency. The chip length of PN signals output from a PN generator 18 for transmission and a PN generator 36 for reception is reduced. Distance is detected with a relatively low resolution initially and then with a high resolution later.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a collision prevention radar device mounted on a vehicle or the like.

[0002]

2. Description of the Related Art In recent years, various collision prevention radar devices have been developed in order to ensure safe operation of vehicles and the like. This type of device transmits a radio wave in a predetermined direction, for example, a traveling direction of a vehicle, and an object to be detected in front (another vehicle, etc.)
It is a device that receives a reflected wave from a device and measures the distance and speed to the detected object.

When the collision prevention radar device is to be realized by using a so-called spread spectrum technique, particularly a direct spread system, the circuit structure has the following functions. First,
Pseudo Noise (P) having a predetermined chip length
N) A signal is generated, and the carrier wave is phase-modulated by using this PN signal as a PN signal for transmission. The phase-modulated carrier wave is transmitted in front of the vehicle, for example. An object to be detected existing in front of the vehicle, for example, a signal reflected by another vehicle is received, and a PN signal is demodulated from the received signal. On the other hand, a reception PN signal that is delayed in chip units with respect to the transmission PN signal is generated, and this is appropriately delayed. If there is a high correlation between the delayed reception PN signal and the PN signal demodulated from the reflected wave, the reception P for the transmission PN signal
It can be seen that the delay time of the N signal corresponds to the propagation time required for the radio waves to travel back and forth between the vehicle and the object to be detected. Therefore, the distance to the detected object can be obtained based on this delay time.

[0004]

When trying to measure the distance to the object to be detected by such a principle, the accuracy of distance measurement is defined by the chip speed. That is, the higher the chip speed, in other words, the shorter the chip length, the higher the accuracy and the higher resolution the distance to the object to be detected can be measured.

On the other hand, in order to improve the anti-jamming property, it is necessary to lengthen the epoch length. Further, in order to extend the maximum measurable distance, it is necessary to set the delay amount of the reception PN signal with respect to the transmission PN signal to a relatively large time, which also requires a long epoch length.
However, when the epoch length is set long, it is difficult to measure with high resolution, high accuracy and high speed.

The present invention has been made to solve the above-mentioned problems, and enables high-resolution, high-accuracy and high-speed distance measurement while ensuring a large maximum measurable distance. The purpose is to

[0007]

In order to achieve such an object, the present invention further shortens the chip length when a relatively high correlation is obtained as a result of correlation detection.
It is characterized in that the chip lengths of the transmission PN signal and the reception PN signal are set to be successively shortened.

[0008]

In the present invention, the chip length is set shorter when a relatively high correlation is obtained as a result of the correlation detection. Therefore, the distance detection is performed with a relatively coarse resolution at first and a higher resolution afterwards. As described above, in the present invention, since the chip length is shortened and updated, the distance can be detected with higher accuracy and higher resolution while maintaining the maximum measurable distance. Further, since the distance detection is performed at a relatively coarse resolution at first, the time required to finally obtain highly accurate distance information is shortened, which enables high-speed distance detection.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a collision prevention radar device according to an embodiment of the present invention. The apparatus shown in this figure includes a transmitting antenna 10 and a receiving antenna 12 as antennas. The transmitting antenna 10 and the receiving antenna 12 are antennas mounted on, for example, the front or rear of the vehicle. The transmitting antenna 10 transmits a signal to the front of the vehicle, and the receiving antenna 12 exists on the front of the vehicle. A reflected wave from a detection object (for example, another vehicle) is received.

The signal transmitted by the transmitting antenna 10 is a signal phase-modulated by the transmitting PN signal. That is, the phase modulation unit 14 phase-modulates the carrier wave generated by the carrier wave oscillator 16 with the transmission PN signal generated by the transmission PN generator 18 (direct spread modulation), and outputs the resulting signal for transmission. Aerial 1
Supply to 0. The transmitting antenna 10 transmits this signal as a transmitted wave to the front of the vehicle or the like.

The epoch of the transmission PN signal is composed of a plurality of (generally N) chips. The chip length Δt of the transmission PN signal is determined by the speed of the clock supplied from the PN clock generation circuit 20.

The PN clock generating circuit 20 supplies the signal generated by the reference oscillator 22 and frequency-divided by the frequency dividing circuit 24 to the transmitting PN generator 18 according to the transmission trigger supplied from the transmission trigger circuit 26. Circuit.
Therefore, the chip length of the transmission PN signal is determined by the frequency division ratio of the frequency dividing circuit 24. This frequency division ratio is calculated by the arithmetic control unit 28.
Set by.

On the other hand, the receiving antenna 12 receives a reflected wave from an object to be detected existing in front of the vehicle or the like and supplies it to the frequency conversion circuit 30. The frequency conversion circuit 30 receives the reflected wave (received wave) received by the receiving antenna 12.
And the local signal generated by the local signal generating circuit 32, and the resulting signal is supplied to the multiplier 34. The multiplier 34 multiplies the output of the frequency conversion circuit 30 by the reception PN signal. The receiving PN signal is the receiving PN
Generated by generator 36. PN generator for reception 36
Like the transmission PN generator 18, generates a reception PN signal having the same configuration as the transmission PN signal according to the clock supplied from the PN clock generation circuit 20. Delay circuit 38 provided after the PN generator 36 for reception
Is the chip length Δ of the receiving PN signal and the transmitting PN signal.
t, that is, the chip length Δt of the PN signal for reception is delayed as a unit and supplied to the multiplier 34. Therefore, the multiplier 3
What is multiplied by the output of the frequency conversion circuit 30 by 4 is a signal obtained by delaying the transmission PN signal with the chip length Δt as a unit.

The output of the multiplier 34 is supplied to the correlation detection circuit 40. The correlation detection circuit 40, based on the output of the multiplier 34, receives the PN signal related to the received wave and the delayed reception PN.
Detect the correlation with the signal. That is, if the output of the multiplier 34 has a substantially single frequency, it can be considered that the correlation between the PN signal related to the received wave and the receiving PN signal is relatively high. The correlation detection circuit 40 outputs a signal indicating the degree of correlation between the two to the arithmetic control unit 28 and the threshold value comparison circuit 42.

The threshold comparison circuit 42 is a correlation detection circuit 4
The signal indicating the degree of correlation output from 0 is compared with a predetermined threshold value. If the result of this comparison shows that the degree of correlation is higher than the threshold value, the threshold value comparison circuit 42
Notifies the arithmetic and control unit 28 of that fact. Arithmetic control unit 28
When the threshold comparison circuit 42 notifies that, the frequency division ratio of the frequency division circuit 24 is set to a small value, and the transmission P
The chip lengths of the N signal and the receiving PN signal are shortened, for example, from Δt ₁ to Δt ₂ . The distance counter 44 includes the delay circuit 3
The delay amount of 8 is counted according to the transmission trigger supplied from the transmission trigger circuit 26, and the result is output to the arithmetic control unit 28. The arithmetic control unit 28 outputs the count value of the distance counter 44 as the distance between the own vehicle and the detected object when the correlation is detected by the correlation detection circuit 40 in the state where the chip length is Δt ₂ .

FIG. 2 shows the contents of the operation according to the features of this embodiment.

In the present embodiment, first, the arithmetic control unit 2
By setting the frequency division ratio in the frequency dividing circuit 24 by 8, the chip lengths of the transmission PN signal and the reception PN signal are relatively long Δ.
set to t ₁ . The delay time of the delay circuit 38 is
With the chip length Δt ₁ as a unit, for example, the arithmetic control unit 2
In response to the command from 8, the receiving PN signal is delayed.

Now, the delay time t of the received wave for transmission is t
_{Let d} have a value close to 2Δt ₁ . When the delay time of the delay circuit 38 is Δt ₁ , the correlation between the PN signal related to the received wave and the delayed receiving PN signal does not have a high value. However, the delay time of the delay circuit 38 is 2Δt.
_When it reaches ₁ , the correlation between the two becomes relatively high. The threshold comparison circuit 42 is a circuit that detects that the correlation between the two has become relatively high in this way.

After the output of the correlation detection circuit 40 exceeds the threshold value of the threshold value comparison circuit 42, in the present embodiment,
The frequency division ratio of the frequency dividing circuit 24 is set to be relatively small by the arithmetic control unit 28. That is, the PN clock generation circuit 2
The frequency of the clock generated by 0 is set high, whereby the chip length Δt is shortened to Δt ₂ which is shorter than Δt ₁ . The delay time of the delay circuit 38 is
It is updated in units of Δt ₂ .

Therefore, according to this embodiment, the distance detection is performed with a relatively long chip length Δt ₁ immediately after the start of the distance detection, that is, with a relatively coarse resolution, and then with a relatively short chip length Δt ₂ . That is, the distance detection is performed with a relatively fine resolution. As a result, the epoch length can be increased initially, so that it is possible to secure the interference resistance and the maximum measurable distance.
Furthermore, since the chip length Δt ₁ is shortened to Δt ₂ after the comparison in the threshold value comparison circuit 42 is established, the distance can be detected with high accuracy and high resolution. Further, since the distance detection is first performed with the coarse resolution, the time required to measure the distance of the detected object can be shortened, and the distance data can be updated by the arithmetic and control unit 28 at a higher speed. Becomes

[0022]

As described above, according to the present invention,
Correlation detection results in relatively high correlation.The chip length was set to be shorter, so high resolution, high accuracy, and high-speed distance detection can be performed while ensuring high resistance to interference and a wide measurement range. Is possible. As a result, a radar device having a higher collision prevention effect can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a collision prevention radar device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of this embodiment.

[Explanation of symbols]

10 Antenna for Transmission 12 Antenna for Reception 14 Phase Modulator 16 Carrier Oscillator 18 PN Generator for Transmission 20 PN Clock Generation Circuit 22 Reference Oscillator 24 Dividing Circuit 26 Transmission Trigger Circuit 28 Operation Control Unit 30 Frequency Converter Circuit 32 Local Signal Generation Circuit 34 Multiplier 36 Reception PN Generator 38 Delay Circuit 40 Correlation Detection Circuit 42 Threshold Value Comparison Circuit 44 Distance Counter Δt ₁ , Δt ₂ Chip Length

Claims (1)

[Claims] 1. A means for generating a pseudo noise signal for transmission, which comprises one epoch from a plurality of chips, while sequentially generating a pseudo noise signal for reception delayed by a chip unit, and a transmission wave. Means for modulating with a pseudo noise signal for transmission and transmitting in a predetermined direction, means for receiving a reflected wave when this transmitted wave is reflected by a detected object such as a vehicle, and pseudo noise included in the received reflected wave Means for detecting the correlation between the signal and the receiving pseudo noise signal, and when a relatively high correlation is obtained as a result of the correlation detection, based on the delay time of the receiving pseudo noise signal with respect to the transmitting pseudo noise signal, In a collision prevention radar device equipped with a means for detecting a distance, the chip length is further shortened if a relatively high correlation is obtained as a result of correlation detection. Collision prevention radar apparatus characterized in that it comprises means for sequentially reduced set the chip length of the fine reception pseudo noise signal.