JP2008107158A - On-vehicle radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein, in an on-vehicle radar device for transmitting a radio wave from a transmission part toward a target, receiving the radio wave reflected by the target by a reception part, and measuring the distance to the target from a time from transmission of the radio wave until reception thereof, a domain wherein a reception signal is lowered by multipath caused by reflection from the road surface is generated, and thereby stable detection of the target becomes impossible. <P>SOLUTION: This device includes a variable gain amplifier 7 for adjusting a gain of the reception signal, and a gain control means 10 for controlling so that a gain amount of the variable gain amplifier is enlarged in the distance to the target wherein the reception signal is lowered by an influence of the multipath caused by the road surface reflection of the radio wave, to thereby enable stable detection of target information. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an in-vehicle radar device that is mounted on an automobile and measures an inter-vehicle distance, a relative speed, and the like with a vehicle target that travels in the forward direction of the host vehicle, and is used in an inter-vehicle distance control system, a collision prevention device, and the like. is there.

The in-vehicle radar device transmits a radio wave from a transmission unit to a target, receives a radio wave reflected from the target by a reception unit, and measures a distance from the transmission to reception of the radio wave to the target. .
In such an in-vehicle radar device, when the level of the radar signal received by the radar device is high, the level of the radar signal transmitted from the radar device is reduced and the level of the radar signal received by the radar device is low. There is an in-vehicle radar system in which transmission power is controlled so as to increase the level of a radar signal transmitted from a radar apparatus. (See Patent Document 1)

Also, since the received signal at the radar device is inversely proportional to the fourth power of the distance to the target, the target received signal is high at a short distance, and the target received signal is low at a long distance.
There is an on-vehicle radar device in which an amplifier capable of adjusting the gain according to the received power of the radio wave reflected by the target is provided to adjust the gain of the received signal. (See Patent Document 2)
JP 2002-22826 A JP2003-130944A (FIG. 6, paragraph number 0002)

  In a radar that detects a target on a road surface like an in-vehicle radar device, in addition to a direct wave from the target, an influence of a road surface reflected wave reflected on the road surface is superimposed on the direct wave. When the direct wave and the road surface reflected wave are in phase, the received signal is high. On the contrary, when the phase of the direct wave and the road surface reflected wave is opposite, the direct wave and the road surface reflected wave cancel each other, and the received signal decreases. When the received signal decreases, the baseband signal after gain adjustment falls below the threshold level and cannot be detected. The conventional in-vehicle radar device does not take any measures regarding the reduction of the received signal due to multipath due to reflection on the road surface, and cannot detect the target stably at a certain inter-vehicle distance. There was a point.

  The present invention has been made to solve such a problem, and an object thereof is to obtain an on-vehicle radar device capable of stably detecting a target even in a multipath region.

  The present invention relates to an in-vehicle radar device that transmits a radio wave from a transmission unit to a target, receives a radio wave reflected by the target by a reception unit, and measures a distance from the transmission to reception of the radio wave to the target. A variable gain amplifier that is provided in the receiver and adjusts the gain of the received signal, and controls to increase the gain amount of the variable gain amplifier at the distance to the target where the received signal decreases due to the multipath effect due to the road surface reflection of radio waves Gain control means is provided.

  According to the present invention, gain adjustment based on multipath becomes possible, and the level of a signal after gain adjustment in the multipath region can be made larger than the threshold level, so that a received signal cannot be detected. Therefore, stable target detection is possible.

Embodiment 1 FIG.
An in-vehicle radar device according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a block configuration diagram according to Embodiment 1 of the present invention, FIG. 2 is a diagram showing a multipath state in a radar apparatus, and FIG. 3 is a diagram showing received signals and baseband signals when there is no gain control means. 4 is a diagram showing a gain amount and a received signal when gain control is performed according to the present invention, and FIG. 5 is a diagram showing a gain amount according to the distance to the target.

In the block configuration diagram of FIG. 1, a transmission unit of a radar apparatus includes an oscillator 1 that outputs an electromagnetic wave for radiating a radio wave to a target such as a vehicle, a directional coupler 2 that distributes the power of the electromagnetic wave, and a transmission on / off function. The switch 3 includes a circulator 4 that distributes power to be transmitted and received power, and a transmission / reception antenna 5. The receiving unit of the radar apparatus includes a transmission / reception antenna 5, a circulator 4, a mixer 6 that mixes received power and electromagnetic waves distributed by the directional coupler 2, a variable gain amplifier 7 that adjusts the gain of the received signal, and an analog signal that is digital. It comprises an A / D converter 8 that converts to a signal, a signal processing device 9, and a gain control means 10 that controls the gain of the variable gain amplifier 7. The gain control means 10 includes a memory 11 and a D / A converter 12 that converts a digital signal into an analog signal. The memory 11 stores a gain amount based on multipath in advance.
A signal is sent from the timing control circuit 13 to the transmission on / off switch 3 and the gain control means 10, and the timing control circuit 13 sets the timing for transmitting the radio wave from the transmission section and the timing for adjusting the gain amount by the gain control means 10. Synchronize.

  FIG. 2 is a diagram showing a multipath state when a vehicle or the like target is detected using the on-vehicle radar device according to the present invention. The positional relationship between the radar device 101 and the target 102 on the road surface is as shown in FIG. Then, the on-vehicle radar device 101 receives the superposed effect of the road surface reflected wave 104 reflected on the road surface in addition to the direct wave 103 from the target 102. Thus, the on-vehicle radar device 101 is affected by the multipath of the road surface reflected wave 104 reflected on the road surface in addition to the direct wave 103.

Next, the operation of measuring the distance to the target using the radar apparatus according to the present invention will be described. First, in order to understand the present invention, the operation when the gain control means 10 is not provided will be described.
The on-vehicle radar device 101 is a radar device that operates according to a general pulse system, and an oscillator 1 generates an electromagnetic wave transmission signal. The transmission signal is transmitted to the transmission / reception antenna 5 via the circulator 4 and radiated as a radio wave via the directional coupler 2, which is divided into a predetermined on time and off time by the transmission on / off switch 3. .
Thereafter, the radio wave reflected by the target 102 such as a vehicle traveling in front of the host vehicle is received by the antenna 5 and input to the mixer 6 via the circulator 4 as a received signal. In the mixer 6, the received signal is mixed with the signal for transmission, and a baseband signal is generated. Thereafter, the baseband signal is subjected to gain adjustment set by a slope function in accordance with the distance to the target 102 by the variable gain amplifier 7.
The gain-adjusted baseband signal is sampled by the A / D converter 8, and then R = c · Td based on the delay time Td until the signal processor 9 transmits the radio wave and reflects it to the target for reception. The target distance R is calculated from the relationship of / 2 (c is the speed of light).

The relationship between the received signal and baseband signal received by the radar apparatus 101 at this time and the distance R to the target is shown in FIG.
FIG. 3A is a diagram showing a received signal with respect to the distance R from the radar apparatus to the target in the position state of the radar apparatus 101 and the target 102 shown in FIG. 2, where the dotted line indicates that there is no multipath, and the solid line indicates the multipath. When there is. FIG. 3B is a diagram illustrating a baseband signal after gain adjustment with respect to the distance R from the radar apparatus 101 to the target 102.

  As shown in FIG. 3, due to the phase relationship between the direct wave 103 and the road surface reflected wave 104, the received signal becomes high when the phase of the direct wave 103 and the road surface reflected wave 104 is in phase. On the other hand, when the phase of the direct wave 103 and the road surface reflected wave 104 is opposite, the direct wave 103 and the road surface reflection 104 cancel each other, and the received signal decreases. As shown in FIG. 3B, when the received signal is lowered, the baseband signal after gain adjustment is below the threshold level, and the received signal cannot be detected. This is called a dead zone. An area that includes this dead zone and in which the received signal decreases due to multipath is called a multipath area.

Now, the received signal based only on the direct wave 103 is Pro, the received signal at the radar apparatus 101 is Pr, the installation height of the radar apparatus 101 is h1, the height of the target 102 is h2, the antenna gain for transmission and reception is G, and the target 102 When the scattering cross section is σ, the transmission power of the radar is Pt, the wavelength of the transmission signal is λ, and the distance from the radar device 101 to the target 102 is R, the received signal Pr at the radar device 101 is expressed by equation (1). Is well known.

  The multipath region is a distance before and after Pr becomes a minimum with respect to the distance R to the target 102 in Expression (1). When the gain control means 10 is not provided, the gain is set by the slope function by the variable gain amplifier 7 alone. Therefore, the received signal is lowered from the equation (1), and the baseband signal after gain adjustment is lower than the threshold level. There is a case where a dead zone region that is a low level occurs, and the target cannot be stably detected at a certain inter-vehicle distance.

Next, the operation when the gain control means 10 controls the gain of the variable gain amplifier 7 will be described.
In the on-vehicle radar device of the present invention, the operation from the generation of the transmission signal by the oscillator 1 to the generation of the reception signal of the baseband is the same as described above, so the description is omitted here.
The gain adjustment of the baseband signal generated from the received signal is performed by controlling the gain of the variable gain amplifier 7 by the gain control means 10. An example of information stored in the memory 11 in the gain control means 10 will be described with reference to FIG. 4A shows the amount of gain adjusted by the variable gain amplifier 7, and FIG. 4B shows the received signal after gain adjustment.

As described above, since the received signal at the radar device is inversely proportional to the fourth power of the distance to the target, the received signal at the target is high at a short distance, and the received signal at the target is low at a long distance. As indicated by the dotted line gain amount G1 in 4 (a), the gain amount of the variable gain amplifier 7 is reduced during the time corresponding to the short distance, and the gain amount of the variable gain amplifier 7 is increased during the time corresponding to the long distance. . The setting of the gain amount G1 will be described later.
Next, in addition to such a gain amount G1, there is a distance in which the level of the baseband signal decreases in the multipath region, so it is necessary to increase the baseband signal in that region. Adjust the timing by adding the amount of gain in the form of a pitch so that the gain increases at the same time as the distance that decreases. In this way, the gain amount corresponding to the multipath is added to the gain amount G1 corresponding to the distance, and as a result, the gain amount G2 indicated by the solid line is stored in the memory 11 as information.

  The digital signal read from the memory 11 is converted into an analog signal by the D / A converter 12, and the variable gain amplifier 7 is controlled based on the analog signal to amplify the baseband signal. After that, the method for calculating the distance from the amplified baseband signal to the target is the same as described above, and will be omitted.

  In the multipath region, the distance to the target at which the level of the baseband signal (reception signal) decreases is the distance before and after the reception signal Pr at the radar device of the above formula (1) is minimized, and is obtained from this. It is done. The distance R to the target can be calculated from the relationship R = c · Td / 2 (c is the speed of light) based on the delay time Td until the radio wave is transmitted, reflected by the target and received. Therefore, since the distance R can be known if the time Td from when the pulse is transmitted until it is received is known, the gain is adjusted to increase in a mountain-like manner according to that time. For this purpose, the timing control circuit 13 synchronizes the timing for turning on the transmission on / off switch 3 and transmitting the radio wave from the transmission unit and the timing for increasing the gain amount by the gain control means 10 to synchronize the timing. Is possible.

Further, the gain amount G1 that is adjusted so that the gain amount of the variable gain amplifier 7 is reduced during the time corresponding to the short distance and the gain amount of the variable gain amplifier 7 is increased during the time corresponding to the long distance is the conventional (“radar”). This can be easily realized by using a function of STC (Sensitivity Time Control) circuit known from “Technology” edited by the Institute of Electronics, Information and Communication Engineers, p.189-191, 1984, Corona.
In the STC circuit, since the received signal at the radar device is inversely proportional to the fourth power of the distance to the target, the received signal at the target is high at a short distance, and the baseband signal after gain adjustment is not saturated by the A / D converter 8. In order to prevent the target received signal from being low and the baseband signal after gain adjustment from being lower than the threshold level at a long distance, the gain is reduced at a short distance and the gain is increased at a long distance. It is.
The STC circuit converts a certain gain control signal into a signal having a certain time constant as shown in FIG. 5 by an integrating circuit, and stores these gain amounts in the memory 11.

As described above, it is possible to compensate for the baseband signal degradation caused by the multipath effect and adjust the short-range and long-range baseband signals, so that the target information can be stably obtained even in the multipath region. Can be detected, the saturation of the baseband signal in the A / D converter 8 at a short distance can be prevented, and the decrease in the baseband signal at a long distance can be compensated.
In addition, since the gain adjustment amount of the variable gain amplifier 7 of the receiving unit can be controlled by a signal from the memory 11, it is possible to adjust the gain based on more accurate multipath.

Embodiment 2. FIG.
Next, an in-vehicle radar device according to Embodiment 2 of the present invention will be described with reference to FIGS. FIG. 6 is a block diagram showing the second embodiment of the present invention, and FIG. 7 is a diagram showing beat frequency signals detected by the radar apparatus.
In the block configuration diagram of the second embodiment shown in FIG. 6, a modulation signal generator 14 is connected to the oscillator 1. The modulation signal generator 14 outputs a signal whose frequency increases or decreases with time, and is input to the oscillator 1 as a modulation signal, like a general FMCW (Frequency Modulation Continuous Wave) radar device. . From the oscillator 1, a frequency-modulated transmission signal is output in accordance with the modulation signal modulated by the modulation signal generator 14. The timing control circuit 13 turns on the transmission on / off switch 3 to transmit radio waves from the transmission unit, increases the gain amount by the gain control means 10, and increases or decreases the frequency by the modulation signal generation unit 14. The timing to do is synchronized. In other configurations, the same components as those in the first embodiment and corresponding components are denoted by the same reference numerals, and description thereof is omitted.

Next, the operation in the second embodiment will be described. Since the transmission signal is generated from the oscillator 1 and the baseband signal obtained by signal processing of the reception signal is amplified, the process is exactly the same as in the first embodiment, and thus detailed description is omitted here.
The beat frequency of the baseband signal is extracted by the signal processing device 9 using FFT (Fast Fourier Transform). After that, frequency analysis is performed for each of the section where the frequency rises (UP side) and the section where the frequency falls (DOWN side) in the frequency modulation of the transmission signal in the same manner as a general FMCW radar, and the distance to the target , And calculations related to speed.

As shown in FIG. 7, at each frequency on the UP side and the DOWN side, the beat frequencies are detected as Fbu and Fbd, respectively, and the distance R to the target and the speed V are expressed by Equations (3) and (4). It is known that it is calculated by
R = α · (Fbu + Fbd) (3)
V = β · (Fbu−Fbd) (4)
Here, R is the distance to the target, V is the speed of the target, and α and β are constants determined by the frequency modulation width, frequency modulation time, center frequency, etc. of the transmission signal, respectively.
Next, distance resolution will be described. When τ is a pulse width for transmitting, the distance resolution ΔDp of the pulse radar is determined by the equation (5).
ΔDp> c · τ / 2 (5)
On the other hand, if the frequency modulation width is B, the distance resolution ΔDf of the FMCW radar is determined by equation (6).
ΔDf> c / (2 · B) (6)

In the pulse system, for example, a pulse width necessary for obtaining a distance resolution of 1 m is about 6.6 ns, and an in-vehicle pulse radar device that transmits and receives a very narrow pulse such as a pulse width of 6.6 ns and samples it. In order to realize it, the cost of H / W becomes high, which is not realistic. For this reason, there is a limit to narrowing the pulse width, and in-vehicle radar that measures a short distance of about a few tens of meters has a rough distance resolution.
In the FMCW system, the modulation width necessary for obtaining a distance resolution of 1 m is 150 MHz. Some of such oscillators are commercially available. Since the H / W can be realized at a low cost, the FMCW method can make the distance resolution finer than the pulse method.

As described above, the second embodiment can detect the distance and speed information to the target stably even in the multipath region in the same manner as the first embodiment, and can be further improved by combining general frequency modulation. The distance to the target can be accurately measured.
Therefore, by using the on-vehicle radar device of the present invention, the distance to the target can be measured with higher accuracy, and the target can be detected without being lost. Therefore, smooth and comfortable inter-vehicle distance control and high accuracy, and It is possible to realize a collision damage reduction operation without interruption.

It is a block block diagram of the vehicle-mounted radar apparatus which shows Embodiment 1 of this invention. It is a figure which shows the state of the multipath in a radar apparatus. It is a figure which shows a received signal and a baseband signal when there is no gain control means. It is a figure which shows the gain amount in the case of gain control by Embodiment 1 of this invention, and a received signal. It is a figure which shows the gain amount according to the distance to the target used for Embodiment 1 of this invention. It is a block block diagram of the vehicle-mounted radar apparatus which shows Embodiment 2 of this invention. It is the figure which showed the beat frequency detected by Embodiment 2 of this invention.

Explanation of symbols

1 oscillator, 2 directional coupler,
3 switches, 4 circulators,
5 Transmit / Receive antenna, 6 Mixer,
7 Variable gain amplifier, 8 A / D converter,
9 signal processing device, 10 gain control means,
11 memory, 12 D / A converter,
13 timing control circuit, 14 modulation signal generator,
101 radar device, 102 target,
103 Direct wave, 104 Road surface reflected wave

Claims (6)

  In the in-vehicle radar device that transmits a radio wave from the transmission unit to the target, receives a radio wave reflected by the target by the reception unit, and measures a distance from the transmission to reception of the radio wave to the target. A variable gain amplifier provided in the receiving unit for adjusting the gain of the received signal, and a gain amount of the variable gain amplifier is increased at a distance to the target where the received signal is lowered due to the multipath effect due to the road surface reflection of the radio wave. A vehicle-mounted radar device comprising a gain control means for controlling the vehicle.   The in-vehicle radar device according to claim 1, further comprising a timing control circuit that synchronizes a timing of transmitting a radio wave from the transmission unit and a timing of increasing a gain amount by a gain control unit. The in-vehicle use according to claim 1 or 2, wherein the distance to the target where the received signal decreases due to the influence of multipath due to road surface reflection is a distance before and after the received signal Pr in the radar apparatus of the following formula is minimized. Radar device.

Where h1 is the installation height of the radar device, h2 is the target height, and λ is the wavelength of the transmission signal
R is the distance to the target, Pro is the received signal by direct wave only

Where G is the antenna gain for transmission and reception, Pt is the transmission power, σ is the scattering cross section of the target   The gain control means performs gain control according to the distance to the target so that the gain amount is small when it corresponds to a short distance, and the gain amount is large when it corresponds to a long distance. Or the vehicle-mounted radar apparatus of Claim 2.   The gain control means has a memory and a D / A converter, the memory stores a gain adjustment amount in advance, converts a digital signal from the memory into an analog signal by the D / A converter, and uses the analog signal The on-vehicle radar device according to any one of claims 1 to 4, wherein a gain amount of the variable gain amplifier is controlled.   The frequency modulation means for changing the transmission signal so that the frequency increases or decreases with time is provided, and the distance to the target and the relative velocity are measured by analyzing the frequency from the beat signal of the reception signal. The in-vehicle radar device according to claim 5.

Images