JP2008170323A - Radar equipment - Google Patents

Abstract

[PROBLEMS] A conventional radar mounted on a moving body may not be able to detect a target that should be originally detected due to radio wave attenuation when rain, snow, fog, and humidity are high, and unnecessary reflection echo from rain or snow. was there.
A reflected high-frequency signal from a target received by an antenna is frequency-converted to a baseband by a reception signal converter, converted to a digital signal by an A / D converter, and a digital reception signal is Fourier-transformed by a frequency analyzer. In the radar that detects the target from the frequency-analyzed signal in the target detection unit, the radar includes a detection unit that detects a condition in which the weather around the moving object adversely affects the signal-to-noise power ratio, and the frequency analyzer includes the detection unit The detection signal is input, and the integration time of the digital reception signal is adjusted according to the degree of adverse effect of the detection signal.
[Selection] Figure 1

Description

  The present invention relates to a radar device that is mounted on a moving body, particularly an automobile, and measures a distance from an obstacle in front and another automobile, and a relative speed with another automobile.

  In order to further improve the safety of automobiles, automatic driving control systems and driver assistance systems have been studied and some have been put into practical use. These systems are often equipped with a radar device that observes the situation around the vehicle in order to supplement the driver's perception and feeling. As such a radar system for on-vehicle use, pulse signals, pulse compression radars, FMCW (Frequency Modulated Continuous Wave) radars, multi-frequency CW (Continuous Wave) radars, FMCW radars and multi-frequency CW radars are used to pulse transmission signals. Various systems such as FMICW (Frequency Modulated Interrupted Continuous Wave) radar and multi-frequency ICW (Interrupted Continuous Wave) radar have been proposed.

  A radar that is installed in front of the vehicle and observes obstacles and other automobiles (hereinafter simply referred to as targets) at a distance of several tens of meters to a distance of about 100 to 200 m is a millimeter wave with a frequency of 76.5 GHz. Used. Laser radar may also be used.

  For example, in Japanese Patent Laid-Open No. 2004-230910, the amount of rainfall is detected by using a rainfall amount detecting means, and the detection distance performance due to rainfall is taken into account in an inter-vehicle distance alarm device or an ACC (Adaptive Cruise Control) device. In the inter-vehicle distance alarm device, an upper limit of the alarm generation speed is set and notified to the driver, and in the ACC device, an upper limit of the set speed is set and notified to the driver.

JP 2004-230910 A

In the above radar, radio waves may be attenuated or an unnecessary reflected echo from rain or snow may be received when it is raining, snowing, in a foggy state or when the humidity is high. In such a case, there is a problem that a target that should be detected may not be detected.
In addition, the technique disclosed in Japanese Patent Application Laid-Open No. 2004-230910 is configured to notify the driver by setting the upper limit of the alarm generation speed of the inter-vehicle distance alarm device and the upper limit of the set speed of the ACC device in consideration of the amount of rainfall. It does not increase the ability to detect the target.

  The present invention has been made to solve such a problem, and when it is raining, snowing, when there is fog, or when the humidity is high, the accumulated time of the radar reception signal is set when it is not raining or snowing. The goal is to improve the target detection capability by taking longer and increasing the signal to noise power ratio (SNR).

The radar device of the present invention is mounted on a moving body,
The transmission signal generated by the signal generator is converted to a high-frequency signal by the transmission signal converter, radiated as a transmission wave in the air by the antenna, and the reflected high-frequency signal from the target received by the antenna is baseband by the reception signal converter. The frequency converted signal is digitized by an A / D converter and converted into a digital signal, and the converted digital received signal is subjected to frequency analysis by Fourier transform using a frequency analyzer. In the target detection with
Comprising detection means for detecting conditions in which the weather around the moving object adversely affects the signal-to-noise power ratio;
The frequency analyzer is configured to receive the detection signal from the detection means and adjust the integration time of the digital reception signal in accordance with the degree of adverse effect of the detection signal.

According to the radar apparatus of the present invention, the detection unit detects a condition in which the weather around the moving body adversely affects the signal-to-noise power ratio, and the frequency analyzer according to the degree of adverse influence of the detection signal of the detection unit. In the configuration, the integration time of the digital reception signal is adjusted.
The number of transform points of the Fourier transform performed by the frequency analyzer corresponds to the number of integrated received signals. Generally, the greater the number, the greater the signal-to-noise power ratio. A large number of integrations is equivalent to a long integration time. In this invention, since the frequency analyzer adjusts the integration time of the digital reception signal in accordance with the degree of the adverse effect of the detection signal from the detection means, the condition that adversely affects the signal-to-noise power ratio during raining or snowing The target detection capability of the radar will be improved even underneath, preventing the target to be detected from becoming undetectable.

Embodiment 1 FIG.
FIG. 1 is a block diagram of a radar apparatus according to Embodiment 1 of the present invention. 1 is a radar apparatus of the present invention, 2 is a target, 3 is a transmission wave from the radar apparatus 1, and 4 is a target reflected wave with respect to the transmission wave 3.

  11 is a signal generator that generates a transmission signal from the radar apparatus 1, 12 is a transmission signal converter that converts the signal generated by the signal generator 11 into a high-frequency signal, and 13 is a high-frequency signal output from the transmission signal converter 12. A pulsator for pulsing, a transmission / reception switch 14 for switching between transmission and reception, and 15 an antenna for radiating a high-frequency signal as a transmission wave 3 into the air and receiving a target reflected wave 4 as a high-frequency signal. Here, the antenna is used for both transmission and reception, but the transmission and reception antennas may be separated. The same applies to the second embodiment.

16 is a received signal converter that amplifies a high-frequency signal received by the antenna as necessary and converts the frequency to baseband, and 17 is a time-discretized (sampled) signal converted to baseband and converted to a digital signal. A / D converter 18, a frequency analyzer 18 that performs frequency analysis of the sampled digital received signal by discrete or fast Fourier transform, and the like 19 detects a target from the frequency-analyzed signal, and reaches the observed target A target detection unit 20 for outputting the distance and relative speed 20 is a wiper operation monitoring unit that monitors the operation of the driver's wiper and outputs the result to a signal integrating unit provided in the frequency analyzer 18.
The wiper operation monitor unit 20 forms detection means for detecting conditions in which the weather around the moving object adversely affects the signal-to-noise power ratio.

  The operation of the radar apparatus according to the present embodiment will be described with reference to FIGS. As an example, a case will be described in which the signal to be transmitted is a multi-frequency ICW system in which a continuous wave (multi-frequency CW) whose frequency increases stepwise is pulsed. FIG. 2 is a diagram schematically showing a multi-frequency ICW transmission signal.

In the signal generator 11, the frequency is stepwise N types increased in equidistant Delta] f (call this period modulation period represents a period in T _P) to generate a multi-frequency CW signal of a base band repeating the. If the duration of one frequency is T _PRI , the modulation period T _P = N · T _PRI . The baseband multi-frequency CW signal is converted into a high-frequency signal by the transmission signal converter 12. As shown in FIG. 2, the frequencies are f ₁ , f ₂ ,. . . , F _N. The frequency f _n (n = 1, 2,..., N) is expressed as f _n = f _c + (n−1) Δf. f _c is the minimum carrier frequency. The section corresponding to the signal of frequency f _n is called the nth step. The m-th modulation period is referred to as the m-th modulation process.

The multi-frequency CW signal converted to a high frequency is pulsed by the pulse generator 13. The solid line in FIG. 2A schematically represents a transmitted pulse, and the vertical axis represents frequency. The pulsed multi-frequency CW signal is radiated into the air as the transmission wave 3 through the transmission / reception switch 14 and the antenna 15. The transmission wave contacting the target 2 is reflected from the target 2 to become a reflected wave 4, is received via the antenna 15 and the transmission / reception switch 14, and is sent to the reception signal converter 16. In the reception signal converter 16, the reflected wave is mixed with a high-frequency multi-frequency CW signal that is the output of the transmission signal converter 12, converted into a baseband reception signal, and output to the A / D converter 17. The baseband received signal is converted into a digital signal is sampled at a sampling interval T _s by the A / D converter 17. T _s is a time shorter than the pulse width.

For simplicity, the target is single, the distance at time t = 0 is R, and the relative speed in the line-of-sight direction with the radar apparatus 1 is v. The digitized baseband received signal x (n, m), which is the target reflected signal, corresponding to the nth step of the mth modulation process is expressed by Equation (1). In formula (1), a is the received signal amplitude, c is the speed of light, lambda is the wavelength for f _c, phi is the phase. Strictly speaking, the wavelength differs for each transmission frequency f _n , but in the range used by the automotive radar, it can be regarded as being equal. Expression (1) is a signal at the range bin number corresponding to the target distance. As shown in FIG. 2B, the range bin number is a sample point number when the received signal is sampled at the sampling interval T _s within the duration T _PRI of one frequency equal to the pulse repetition period. In FIG. 2B, the sampling interval T _s is equal to the pulse width, and the number of range bins is L.

  The received signal of Expression (1) is frequency analyzed by the frequency analyzer 18 by a method such as fast Fourier transform. For example, the frequency analysis is performed by discrete Fourier transform (or fast Fourier transform) represented by the following equation (2) for the nth step (n = 1, 2,..., N). k = 1, 2,. . . , M are frequency numbers. The discrete Fourier transform score M will be described later.

The target detection unit 19 calculates the relative speed and distance from the target from Expression (2) that is the frequency analysis result in the frequency analyzer 18. For this purpose, the amount of equation (3) is calculated, and the maximum value is detected. Usually, detection is performed by detecting an object that exceeds a predetermined threshold value. The frequency giving the maximum value is the Doppler frequency due to the difference in speed relative to the target. The relative speed with the target can be measured from the Doppler frequency. Here, since it is assumed that the target is single, in this case, the maximum value of Equation (3) is detected. The right side of Equation (3) is the sum of absolute values of X _k (n), but this may be the sum of powers of 2 or more of the absolute values of X _k (n).

When the frequency number k which gives the maximum value of the formula (3) and k _peak, frequency f _peak corresponding to k _peak is the Doppler frequency to be measured. Accordingly, the measured relative speed v is expressed by Equation (4).

The distance R is obtained from the phase difference of the received signal with respect to any two transmission frequencies in the frequency number k _peak and the target existence range bin. Or the distance R is calculated | required from the phase gradient between N frequency and the average of the phase difference between several sets of 2 frequency of Formula (5). In the equation (5), arg [•] means a complex argument. The relative velocity v and the distance R thus determined are the output of the target detection unit 19.

  In practice, since it is not known where the target is, the processing described above is performed for all L range bins.

The discrete Fourier transform score M performed by the frequency analyzer 18 is equal to the cumulative number of received signals. Generally, the greater the score, the greater the signal-to-noise power ratio. A large number of integrations is equivalent to a long integration time. The number of discrete Fourier transform points M is increased according to the driver's wiper operation. The wiper operation of the driver is monitored by the wiper operation monitor unit 20 and the operation state of the wiper is output to the frequency analyzer 18. The accumulated number at the time of the wiper non-operating S _1, the cumulative number at the time of the wiper operation and S _w. w is an integer of 2 or more, and the number of types of wiper intermittent time and wiping time is the maximum value. However, the time when the wiper is not operated is defined as w = 1, and the number of types W includes the time when the wiper is not operated. When w is larger as the intermittent wiper time and the wiper time are shorter, that is, as the wiper operates in response to a larger amount of rain, S ₁ <S ₂ ≦. . . And ≦ _{S W.} Then, M in Expression (2) is set as S _w (w = 1, 2,..., W). As the rain and snow are more intense, the driver shortens the wiper's intermittent time and wiping time. Therefore, the shorter the intermittent time and the wiping time, the greater the number of integration. On the other hand, since the signal to noise power ratio (SNR) of the received signal decreases as rain or snow gets more severe, it is necessary to increase the signal number to increase the signal to noise power ratio for target detection. Since the number of integrated signals is increased by the driver's wiper operation, the target detection capability of the radar is naturally improved even when it is raining or snowing.

Cumulative number of S _w at the time of the wiper operation may be changed depending on the range bin number. For example, for the same w, the S _w in the range bin corresponding to the far distance may be larger than the S _w in the range bin corresponding to the near distance. As a result, it is possible to secure the detection performance for a distant target that is disadvantageous in detection in terms of SNR.

  Although the multi-frequency ICW radar has been described above, the same applies to a radar that pulsates and transmits a continuous wave such as the FMICW system.

  Note that the wiper operation monitoring unit 20 may monitor the wiper operation duration, and increase the signal integration number when the wiper operates for a certain period or longer. Further, the wiper operation is not performed by a driver's operation, and may be automatically operated by sensing rain or snow. In addition, it is desirable not to change the signal integration number during window washer. Furthermore, not only the wiper operation by the driver, but also the wiper that operates automatically based on a raindrop sensor or the like can be similarly applied.

  Further, it is not always necessary to use only the wiper to provide a trigger for extending the integration time of the radar reception signal. For example, a fog lamp used in fog may be turned on. By increasing the integration time of the radar reception signal when the fog lamp is turned on, the radar target detection performance can be improved even in fog. If the vehicle is equipped with a sensor that measures the humidity at the outer periphery, the accumulated time of the radar reception signal may be increased when the measured humidity is higher than a certain value. Thus, the integration time may be lengthened. Furthermore, the signal integration number may be increased from weather information obtained from the outside, such as television / radio, local road information, or information from the Internet.

Embodiment 2. FIG.
A radar apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. In the present embodiment, a case where the modulated wave to be transmitted is FMCW will be described. The signal generator 11 generates a baseband FMCW signal in which the frequency linearly increases and then decreases (this period is referred to as a modulation period), is converted into a high-frequency signal by the transmission signal converter 12, and is transmitted and received. The transmitted wave 3 is radiated into the air via the switch 14 and the antenna 15. The transmission wave contacting the target 2 is reflected from the target 2 to become a reflected wave 4, is received via the antenna 15 and the transmission / reception switch 14, and is sent to the reception signal converter 16. In the reception signal converter 16, the reflected wave is mixed with the FMCW high-frequency signal that is the output of the transmission signal converter 12, converted into a beat signal that is a baseband signal, and the beat signal is output to the A / D converter 17. . The beat signal is sampled by the A / D converter 17 and converted into a digital signal.

A digitized beat signal (hereinafter simply referred to as a beat signal) is subjected to frequency analysis by the frequency analyzer 18b by a method such as fast Fourier transform. The unit of the period for performing the frequency analysis is approximately half of the modulation period. That is, it is a period during which the frequency of the FMCW signal increases and a period during which it decreases, and frequency analysis is performed individually.
In FIG. 3 showing the present embodiment, a signal integration function provided in the frequency analyzer is separately drawn and illustrated as a signal integration unit 30.

  The signal integration unit 30 as signal integration means performs integration by taking the amplitude (or square of amplitude) of a plurality of frequency analysis results. Alternatively, the frequency analysis results as complex numbers may be integrated by matching the phases and the like. In this case, the absolute value of the complex number or the square of the absolute value is taken after integration. Integration is performed individually for each of a plurality of frequency increase periods and a plurality of frequency decrease periods. The target detection unit 19b detects peaks corresponding to the respective periods. Based on the well-known FMCW radar principle (for example, “Radar Technology”, pages 287-289, supervised by Takashi Yoshida, edited by the Institute of Electronics, Information and Communication Engineers, 1984) Find the distance. This is the radar output. Usually, peak detection is performed by detecting a peak exceeding a predetermined threshold value.

Regarding the number of integrations performed by the signal integration unit 30, a large integration number is equivalent to a long integration time. As in the first embodiment, the cumulative number is increased according to the driver's wiper operation. The wiper operation of the driver is monitored by the wiper operation monitor unit 20, and the operation state of the wiper is output to the signal integration unit 30. The accumulated number at the time of the wiper non-operating S _1, the cumulative number at the time of the wiper operation and S _w. w is an integer of 2 or more, and the number of types of wiper intermittent time and wiping time is the maximum value. However, the time when the wiper is not operated is defined as w = 1, and the number of types W includes the time when the wiper is not operated. When w is larger as the intermittent wiper time and the wiper time are shorter, that is, as the wiper operates in response to a larger amount of rain, S ₁ <S ₂ ≦. . . And ≦ _{S W.} As the rain and snow are more intense, the driver shortens the wiper's intermittent time and wiping time. Therefore, the shorter the intermittent time and the wiping time, the greater the number of integration. On the other hand, since the SNR of the received signal decreases as the rain or snow gets more severe, it is necessary to increase the SNR by increasing the integrated number of signals for target detection. Since the number of integrated signals is increased by the driver's wiper operation, the target detection capability of the radar is naturally improved even when it is raining or snowing.

  Note that the wiper operation monitoring unit 20 may monitor the wiper operation duration, and increase the signal integration number when the wiper operates for a certain period or longer. Further, the wiper operation is not performed by a driver's operation, and may be automatically operated by sensing rain or snow. In addition, it is desirable not to change the signal integration number during window washer. Furthermore, not only the wiper operation by the driver, but also the wiper that operates automatically based on a raindrop sensor or the like can be similarly applied.

  Further, it is not always necessary to use only the wiper to provide a trigger for extending the integration time of the radar reception signal. For example, a fog lamp used in fog may be turned on. By increasing the integration time of the radar reception signal when the fog lamp is turned on, the radar target detection performance can be improved even in fog. In addition, if the vehicle is provided with a sensor for measuring the humidity at the outer periphery, the accumulated time of the radar reception signal may be increased when the measured humidity is higher than a certain value, or the humidity value may be increased. Accordingly, the integration time may be lengthened. Furthermore, the signal integration number may be increased from weather information obtained from the outside, such as television / radio, local road information, or information from the Internet.

As described above, the multi-frequency ICW method and the FMCW method have been described as examples of the received signal integration, but the present invention is not necessarily limited to these methods. Needless to say, the above two methods are also applicable to other integration methods.
This invention does not ask | require antenna form. For example, an aperture antenna may be used, or a digital beam forming antenna using an array antenna may be used.

  The radar apparatus according to the present invention can improve the target detection capability when it is raining, snowing, when there is fog, or when the humidity is high. .

It is a block diagram of the radar apparatus by Embodiment 1 of this invention. 3 is a schematic diagram of a multi-frequency ICW transmission signal of the radar apparatus according to Embodiment 1. FIG. It is a block diagram of the radar apparatus which concerns on Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1; Radar apparatus, 2; Target, 3; Transmission wave, 4; Reflected wave, 11; Signal generator, 12: Transmission signal converter, 13: Pulse generator, 14; Transmission / reception switch, 15; Antenna, 16; Received signal converter, 17; A / D converter, 18, 18b; Frequency analyzer, 19, 19b; Target detection unit, 20; Wiper operation monitoring unit, 30;

Claims (7)

A signal generator for generating a transmission signal;
A transmission signal converter for converting the transmission signal generated by the signal generator into a high-frequency signal;
An antenna that radiates a high-frequency signal into the air as a transmission wave and receives a reflected wave from the target as a high-frequency signal;
A reception signal converter that converts a high-frequency signal received by an antenna into a baseband; and
An A / D converter for converting a signal frequency-converted to baseband into a digital signal;
A frequency analyzer for analyzing the frequency of digital received signals by Fourier transform;
In a radar apparatus equipped with a target detection unit that detects a target from a frequency-analyzed signal and is mounted on a moving body,
Detecting means for detecting that the weather around the moving object is a condition that adversely affects the signal-to-noise power ratio;
The radar apparatus according to claim 1, wherein the frequency analyzer is configured to input a detection signal from the detection means and adjust an integration time of the digital reception signal in accordance with a degree of adverse influence of the detection signal.   2. The radar apparatus according to claim 1, wherein the detection means is a wiper operation monitor unit that detects the operation of the wiper.   3. The radar apparatus according to claim 2, wherein the frequency analyzer makes the integration time of the radar reception signal longer when the wiper operation duration exceeds a predetermined time than when the wiper is not operating.   The frequency analyzer includes a signal integration unit that increases an integration time of a signal of a range bin corresponding to a reception signal according to a distance to be measured when the transmission wave and the reception wave are pulses. Item 4. The radar device according to Item 2 or 3.   2. The radar apparatus according to claim 1, wherein the detecting means is means for detecting lighting of a fog lamp.   2. The radar apparatus according to claim 1, wherein the detecting means is means for measuring humidity around the moving body.   2. The radar apparatus according to claim 1, wherein the detecting means is means for detecting a condition that adversely affects the signal-to-noise power ratio from weather information transmitted from an external engine.

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