JP2008089505A - Radar device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive high-performance radar device capable of detecting surely reception of an interference wave. <P>SOLUTION: This radar device is equipped with a transmission means for performing pulse modulation of an electromagnetic wave and transmitting it, a reception means for receiving the electromagnetic wave reflected by a target object, and a distance/relative speed calculation means for measuring at least either of the distance and the relative speed of the target object based on the transmitted electromagnetic wave and the received electromagnetic wave. The radar device is also equipped with an interference wave detection means for detecting reception of an interference wave from another equipment by operating the reception means in a time zone just before performing pulse modulation of the electromagnetic wave and transmitting it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radar apparatus.

A radar device used in a system that controls the distance and relative speed with a target object to control the distance between vehicles, etc., amplifies the transmission pulse, transmits it as an electromagnetic wave from the antenna, and receives the electromagnetic wave reflected by the target object with the antenna. Amplify to obtain a received pulse. A distance gate is specified based on the beat signal obtained by mixing the transmission pulse and the reception pulse, and a Doppler shift accompanying the movement of the target object appears in the beat signal that detects the distance from the distance gate to the target object. The relative speed of the target object is detected from the Doppler shift.
Based on the distance to the target object and the relative speed detected by the radar device, the acceleration / deceleration of the host vehicle is calculated, and the throttle and brake are controlled. In the inter-vehicle distance warning system, the degree of danger is calculated from the distance of the target object, the relative speed, the own vehicle speed, etc., and a warning is generated as necessary.

However, when this radar apparatus receives an interference wave (hereinafter referred to as an interference wave) from another wireless device or another radar apparatus, the noise level increases due to the interference wave, so that the S / N ratio deteriorates and detection failure occurs. It may become.
In addition, a beat signal that should not exist originally appears due to the interference wave, which may cause erroneous detection. As a result, a problem occurs in the inter-vehicle distance control system and the inter-vehicle distance alarm system. For example, a detection failure may cause a collision with a preceding vehicle in the inter-vehicle distance control device. In addition, erroneous detection may cause deceleration control in the inter-vehicle distance control device even when there is no preceding vehicle.

  Therefore, interference is determined when a signal having a value larger than the amplitude or frequency of a received signal or beat signal due to reflection of a target object that is assumed to exist normally is detected (see, for example, Patent Document 1).

JP 2002-168947 A

  However, if the threshold value of the amplitude or frequency is set to be higher than the reception signal due to the reflection of the normal target object that can be assumed, the signal due to interference of amplitude and frequency below the threshold value cannot be detected.

  An object of the present invention is to obtain a high-performance and inexpensive radar apparatus that reliably detects that an interference wave has been received.

  A radar apparatus according to the present invention includes a transmitting unit that modulates and transmits an electromagnetic wave, a receiving unit that receives an electromagnetic wave reflected from the target object, and at least a distance or a relative speed of the target object based on the transmitted electromagnetic wave and the received electromagnetic wave. In a radar apparatus equipped with a distance / relative velocity calculating means for measuring any one of them, the receiving means is operated in a time zone immediately before the electromagnetic wave is pulse-modulated and transmitted to receive an interference wave from another device. Interference wave detection means for detecting was provided.

  The effect of the radar apparatus according to the present invention is that an interference wave detection gate is set in a time zone prior to transmission of a transmission pulse, a signal received by the interference wave detection gate is stored in the interference wave detection memory, and the interference wave is The data stored in the memory for detection is subjected to fast Fourier transform to obtain the frequency spectrum, and when the noise level of the frequency spectrum is equal to or higher than the noise level threshold, the reception of interference waves from other devices is detected. Interference waves that affect the detection performance of the apparatus can be reliably detected.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a radar apparatus according to Embodiment 1 of the present invention.
As shown in FIG. 1, a radar apparatus 1 according to Embodiment 1 of the present invention includes an oscillator 2, a power divider 3, a transmission amplifier 4, a transmission / reception selector switch 5, a transmission / reception shared antenna 6, a reception amplifier 7, a mixer 8, and a filter. 9, AGC amplifier 10, AD converter 11, signal processing device 12, distance gate memory 13 for storing data sampled by each distance gate, and interference wave detection memory 14 for storing data sampled by the interference wave detection gate Is provided.
The radar apparatus 1 measures the distance D of the target object 16 and the relative speed v of the target object 16, and sends the data of the distance D and the relative speed v to the inter-vehicle distance control apparatus 15.

  The signal processing device 12 samples the beat signal input from the AD converter 11 at each distance gate and the interference wave detection gate, respectively, and stores the sampled values in the distance gate memory 13 and the interference wave detection memory 14, respectively. The storage means 21, the distance / relative speed calculation means 22 for obtaining the distance D and the relative speed v of the target object 16 from the data sampled at each distance gate, and the fact that the interference wave has been received from the data sampled by the interference wave detection gate. Interference wave detection means 23 for detection is provided.

  The signal processing device 12, the distance gate memory 13 and the interference wave detection memory 14 are constituted by a computer including a CPU, a ROM, a RAM, and an interface circuit. The data storage means 21, the distance / relative speed calculation means 22 and the interference wave detection means 23 have their processing contents stored as programs in the ROM.

Next, an electromagnetic wave transmission operation in the radar apparatus 1 according to the first embodiment will be described.
The signal processing device 12 controls the oscillator 2 to oscillate transmission pulses at a predetermined pulse repetition period. Since the maximum measurement distance is set to 1000 m in consideration of a distance margin that does not allow reception of the electromagnetic wave transmitted immediately before, the predetermined pulse repetition period is set to 6.67 μs. From the oscillator 2, for example, a transmission pulse with a transmission frequency f ₀ = 76.5 GHz is output. The transmission pulse passes through the power divider 3 and is amplified by the transmission amplifier 4. When transmitting electromagnetic waves, the transmission / reception change-over switch 5 connects the transmission amplifier 4 and the transmission / reception common antenna 6, so that the transmission pulse amplified by the transmission amplifier 4 passes through the transmission / reception change-over switch 5 and is transmitted from the transmission / reception common antenna 6. It is transmitted to space as electromagnetic waves.

Next, an electromagnetic wave receiving operation in the radar apparatus 1 according to the first embodiment will be described. When a pulse time width t _g , for example, 33.3 ns (time required for the transmitted electromagnetic wave to be reflected by the target object 16 at a distance of 5 m and returned to the transmission / reception antenna 6) has elapsed since the electromagnetic wave transmission start time, The changeover switch 5 is switched to the reception side, and the transmission / reception shared antenna 6 and the reception amplifier 7 are connected.
On the other hand, the transmission electromagnetic wave transmitted to the space from the transmission / reception shared antenna 6 is reflected by the target object 16 existing at a position separated by the distance D, and the delay time corresponding to the distance D with respect to the transmission electromagnetic wave as shown in FIG. It is received as a reception electromagnetic wave by the transmission / reception shared antenna 6 with a delay of Δt.
When the target object 16 is moving at the relative speed v, the frequency of the received electromagnetic wave is Doppler shifted by the Doppler shift frequency f _{b with} respect to the frequency f _{0 of the} transmitted electromagnetic wave.

Receiving electromagnetic wave received by the transceiving antenna 6 is amplified by the receiving amplifier 7, are LO electromagnetic wave and mixing from the power divider 3 by the mixer 8, is output as a beat signal corresponding to the Doppler shift frequency f _b.
The obtained beat signal passes through the filter 9 having a cutoff frequency of 30 MHz, is amplified by the AGC amplifier 10, is converted into a digital beat signal by the AD converter 11, and the digital beat signal is input to the signal processing device 12. The

In the radar apparatus 1 according to the first embodiment, the speed resolution Δv in the measurement of the relative speed v is 1 km / h. Since the speed resolution Δv has the relationship of the frequency resolution Δf and the expression (1), the frequency resolution Δf is 141.64 Hz.
The data storage means 21 samples a digital beat signal for a measurement time of 7.06 ms so as to satisfy the frequency resolution Δf and stores it as a group of data. Note that λ is the wavelength of the transmission electromagnetic wave.

Data storage means 21 sets range gate at equal intervals in the transmission start time of origin and the time pulse in the direction of traveling of the time duration t _g of the transmitted pulse. In order to specify this distance gate, serial numbers from 1 are assigned from the origin side. Then, as shown in FIG. 3, the amplitude of the beat signal is sampled for each distance gate and stored in the area of the distance gate memory 13 corresponding to the distance gate for each distance gate.
The data storage means 21 sets the interference wave detection gate timing predated from the origin by the time t _inf transmission start time in the direction of returning the time in the time with the origin of the transmitted pulse. Then, the amplitude of the beat signal is sampled by the interference wave detection gate and stored in the interference wave detection memory 14.

The distance / relative speed calculation means 22 obtains 1024 beat signals stored in the area corresponding to each distance gate of the distance gate memory 13 as shown in FIG. 4 in order to obtain a speed resolution of 1 km / h. The amplitude is read, and the frequency spectrum is obtained by performing frequency analysis, for example, fast Fourier transform, on the beat signal data for each distance gate. As shown in FIG. 5, the frequency spectrum of the distance gate corresponding to the distance D of the target object 16 is shifted from the transmission frequency f ₀ by the Doppler shift frequency f _b , and a beat signal having an amplitude M is obtained.

The distance / relative speed calculating means 22 uses the distance gate number n and the Doppler shift frequency f _b where the beat signal appears in the frequency spectrum, and calculates the distance D and the relative speed v from the expressions (2) and (3). calculate. Here, c is the speed of electromagnetic waves.

  Next, the interference wave detection gate will be described. Considering that the amplitude of the beat signal is sampled (i−1) times by the interference wave detection gate, since the i-th transmission pulse has not yet been oscillated, the target object 16 of the i-th transmission electromagnetic wave The reflected received electromagnetic wave is not sampled by the interference wave detection gate. If the beat signal related to the received electromagnetic wave obtained by the reflection of the (i-1) th transmission pulse to the target object 16 can be sampled by the interference wave detection gate, the distance to the target object 16 is a pulse repetition. The value is close to a distance of 1000 m corresponding to the period. Since the electromagnetic wave from the radar apparatus 1 attenuates while propagating a distance of about 150 m, it is designed so that the target object 16 existing at a distance of 150 m or more cannot be detected. The beat signal related to the received electromagnetic wave due to the reflection of 16 is not sampled by the interference wave detection gate.

  Therefore, if a beat signal related to any electromagnetic wave is sampled by the interference wave detection gate, it can be considered that the interference wave is incident on the radar apparatus 1 and detected. If no interference wave is incident, only a noise with a low noise level is observed in the frequency spectrum obtained by the fast Fourier transform at the interference wave detection gate, as shown in FIG. On the other hand, when an interference wave is incident, the noise level of the frequency spectrum increases as shown in FIG. 7, or a peak occurs in the frequency spectrum as shown in FIG. The difference between whether the noise level rises or a peak occurs depends on the frequency of the incident interference wave and the modulation method.

FIG. 9 is a flowchart showing the procedure of the interference wave detection processing routine according to the first embodiment of the present invention.
Next, the interference wave detection processing routine according to the first embodiment of the present invention will be described with reference to FIG. This interference wave detection processing routine is started every predetermined period. Further, the initial value of the interference wave detection threshold value is stored, and the initial value is read as the noise level threshold value at the start of measurement immediately after the radar apparatus 1 is turned on.
In step S1, the distance D and the relative speed v of the target object 16 are calculated using the data of each distance gate, and the process proceeds to step S2.
In step S2, fast Fourier transform is not performed on the data stored in the interference wave detection memory 14, the frequency spectrum is obtained, and the process proceeds to step S3.
In step S3, the noise level of the frequency spectrum is calculated, and the process proceeds to step S4. As a method for calculating the noise level, since the peak is not originally detected by the interference wave detection gate, it is possible to simply take an average value of all data, or a more accurate calculation method may be used.

In step S4, it is determined whether or not the noise level is equal to or higher than the noise level threshold value. When the noise level is equal to or higher than the noise level threshold value, the process proceeds to step S5 and the noise level is lower than the noise level threshold value. If there is, the process proceeds to step S6.
In step S5, the interference wave detection flag is turned on, and the process proceeds to step S9.
In step S6, the interference wave detection flag is turned OFF and the process proceeds to step S7.
In step S7, the current noise level is stored and the process proceeds to step S8.

  In step S8, the noise level threshold value is updated from the noise level data stored this time and in the past, and the process proceeds to step S9. Since the noise level in each measurement may vary to some extent, an average value within a predetermined time is calculated, and a value that is a predetermined multiple of the calculated average value is used as the noise level threshold value.

  In step S9, the distance D of the target object 16, the relative speed v, and the state of the interference wave detection flag obtained in the processes from step S1 to step S6 are output, and the interference wave detection processing routine is terminated. In the vehicle control system using the radar device 1, when the interference wave detection flag is ON, the control can be stopped or a warning message can be displayed to notify the driver of the interference wave detection.

  The radar apparatus 1 according to the first embodiment of the present invention sets an interference wave detection gate in a time zone immediately before transmission of a transmission pulse, and the data sampled by the interference wave detection gate is stored in the interference wave detection memory 14. The frequency spectrum is obtained by fast Fourier transforming the data stored in the interference wave detection memory 14, and when the noise level of the frequency spectrum is equal to or higher than the noise level threshold, the interference wave is transmitted by the transmitting / receiving antenna 6. Since it detects that it received, it can detect that the interference wave was received reliably.

Embodiment 2. FIG.
FIG. 10 is a configuration diagram of a radar apparatus according to Embodiment 2 of the present invention.
As shown in FIG. 10, the radar apparatus 1B according to the second embodiment of the present invention is different from the radar apparatus 1 according to the first embodiment in that the interference wave detecting means 23B is the same. Are denoted by the same reference numerals and description thereof is omitted.
The interference wave detecting means 23B according to the second embodiment reads the amplitude data of the beat signal sampled by the interference wave detection gate during the measurement time, obtains the frequency spectrum by performing fast Fourier transform on the data, and obtains the frequency spectrum. It is detected that an interference wave has been received based on the number of peaks appearing at.

Next, an interference wave detection processing routine according to the second embodiment of the present invention will be described with reference to FIG. FIG. 11 is a flowchart showing a procedure of an interference wave detection processing routine according to the second embodiment of the present invention. This interference wave detection processing routine is started every predetermined period.
In step S11, the distance to the target object 16 and the relative speed are calculated based on normal distance gate data, and the process proceeds to step S12.
In step S12, fast Fourier transform is performed using the data stored in the interference wave detection memory 14, the frequency spectrum is obtained, and the process proceeds to step S13.
In step S13, the noise level of the frequency spectrum is obtained, a predetermined multiple of the noise level is set as a peak detection threshold, and a frequency at which the maximum value of the spectrum amplitude is greater than or equal to the peak detection threshold is detected as a peak. move on.

In step S14, the number of detected peaks is counted and the process proceeds to step S15.
In step S15, it is determined whether or not the counted number of peaks is greater than or equal to a predetermined number. If the number of peaks is greater than or equal to the predetermined number, the process proceeds to step S16, and if the number of peaks is less than the predetermined number, the process proceeds to step S17.
In step S16, the interference wave detection flag is turned on and the process proceeds to step S20.

In step S17, the interference wave detection flag is turned OFF and the process proceeds to step S18.
In step S18, the average value of the amplitudes of all peaks detected in step S13 is obtained and stored, and the process proceeds to step S19. In principle, if there is no interference wave reception, the number of peaks is considered to be zero at all times, but in reality there may be peaks due to other noises, etc., in order to prevent false detection of interference. The past peak detection state in the interference wave non-detection state is stored.

  In step S19, the peak detection threshold is updated from the average value of the peak amplitudes stored this time and in the past. Since the average value of the peak amplitude in each measurement varies to some extent, the average value within a predetermined time is calculated, and a value that is a predetermined multiple of the calculated average value is used as the peak detection threshold value.

In step S20, the distance D of the target object 16, the relative speed v, and the state of the interference wave detection flag obtained in the processing from step S11 to step S17 are output, and the interference wave detection processing routine is terminated.
When the interference wave detection flag is ON, the vehicle control system that uses the radar device 1B may stop the control or display a warning message to notify the driver of the interference wave detection. it can.

  In the radar apparatus 1B according to the second embodiment of the present invention, when an interference wave is received in the frequency spectrum of the data sampled by the interference wave detection gate, the peak is increased, and the possibility of detection failure or erroneous detection is obtained. When there is, the state can be detected.

  In the second embodiment, only the number of peaks is described. However, when the average value of the amplitudes of the peaks existing in the frequency spectrum is equal to or greater than a predetermined average value threshold value, interference waves from other devices are used. May be determined to have been received.

If a certain frequency noise is generated, the frequency may be stored, and the peak of the stored frequency may be excluded from the interference wave detection process.
Further, when the amplitude of the peak due to other noise or the like is sufficiently lower than the amplitude of the peak due to reception of the interference wave, a peak smaller than a predetermined amplitude value may be excluded from the interference wave detection.

In addition, when the noise level of the frequency spectrum rises above a predetermined noise level threshold and the number of peaks present in the frequency spectrum is greater than or equal to a predetermined number, it is determined that an interference wave from another device has been received. Also good. Thus, by making a determination regarding the noise level and the number of peaks, it is possible to prevent erroneous detection of interference wave reception.
In addition, when the noise level of the frequency spectrum rises above a predetermined noise level threshold and the average value of the amplitudes of the peaks present in the frequency spectrum is above the predetermined average value threshold, It may be determined that an interference wave has been received. Thus, by making a determination regarding the average value of the noise level and the peak amplitude, erroneous detection of interference wave reception can be prevented.

  Also, when the number of peaks present in the frequency spectrum is greater than or equal to a predetermined number and the average amplitude of peaks present in the frequency spectrum is greater than or equal to a predetermined average value threshold, interference waves from other devices are received. You may judge that you did. By making a determination regarding the average number of peaks and peak amplitude in this way, erroneous detection of reception of interference waves can be prevented.

  In addition, when it is considered that the reliability is low only by detecting the reception of one interference wave, when the reception of the interference wave is detected continuously for a predetermined time, the interference of electromagnetic waves by other devices has occurred. You may judge. Thus, since it is determined that interference of electromagnetic waves from other devices has occurred only when reception of interference waves is detected for a predetermined time, the reliability of detection of reception of interference waves can be improved. .

It is a block diagram of the radar apparatus concerning Embodiment 1 of this invention. 6 is an explanatory diagram showing sampling timing of an interference wave detection gate of the radar apparatus according to Embodiment 1. FIG. It is a figure which shows a mode that the amplitude of a beat signal is sampled by arbitrary distance gates over measurement time. It is the figure which showed the data sampled by the arbitrary distance gates in time series. It is a frequency spectrum obtained by fast Fourier transform of data sampled by a distance gate corresponding to the distance of the target object. It is a frequency spectrum obtained by fast Fourier transform of data sampled by the interference wave detection gate when there is no interference wave. It is a frequency spectrum obtained by fast Fourier transform of data sampled by an interference wave detection gate when an interference wave exists. This is a frequency spectrum obtained by fast Fourier transform of data sampled by an interference wave detection gate when another type of interference wave exists. It is a flowchart which shows the procedure of the interference wave detection process routine of Embodiment 1 of this invention. It is a block diagram of the radar apparatus concerning Embodiment 2 of this invention. It is a flowchart which shows the procedure of the interference wave detection process routine of Embodiment 2 of this invention.

Explanation of symbols

  1, 1B radar device, 2 oscillator, 3 power divider, 4 transmission amplifier, 5 transmission / reception changeover switch, 6 transmission / reception antenna, 7 reception amplifier, 8 mixer, 9 filter, 10 AGC amplifier, 11 AD converter, 12 signal processing device , 13 Distance gate memory, 14 Interference wave detection memory, 15 Inter-vehicle distance control device, 16 Target object, 21 Data storage means, 22 Distance / relative speed calculation means, 23, 23B Interference wave detection means.

Claims (7)

Transmission means for pulse-modulating and transmitting electromagnetic waves, reception means for receiving electromagnetic waves reflected by the target object, and distance for measuring at least one of the distance or relative velocity of the target object based on the transmitted electromagnetic waves and the received electromagnetic waves -In a radar apparatus equipped with a relative speed calculation means,
A radar apparatus comprising interference wave detection means for operating the reception means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave to detect reception of an interference wave from another device.   The radar apparatus according to claim 1, wherein when the reception of interference waves from other devices is continuously detected for a predetermined time, it is determined that interference of electromagnetic waves by other devices has occurred.   The interference wave detection means performs frequency analysis on data over a measurement time acquired by operating the reception means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave, and the noise level of the obtained frequency spectrum is 3. The radar apparatus according to claim 1, wherein reception of an interference wave from another device is detected when the noise level is equal to or greater than a predetermined noise level threshold value.   The interference wave detecting means performs frequency analysis on data over a measurement time acquired by operating the receiving means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave, and a peak existing in the obtained frequency spectrum. The radar apparatus according to claim 1, wherein reception of an interference wave from another device is detected when the number of signals is a predetermined number or more.   The interference wave detecting means performs frequency analysis on data over a measurement time acquired by operating the receiving means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave, and a peak existing in the obtained frequency spectrum. 3. The radar device according to claim 1, wherein reception of an interference wave from another device is detected when an average value of the amplitudes of the first and second amplitudes is equal to or greater than a predetermined average value threshold value.   The interference wave detection means performs frequency analysis on data over a measurement time acquired by operating the reception means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave, and the noise level of the obtained frequency spectrum is When the number of peaks present in the obtained frequency spectrum is equal to or greater than a predetermined noise level threshold value, or when the average value of the amplitudes of the peaks present in the obtained frequency spectrum is a predetermined average The radar apparatus according to claim 1, wherein reception of an interference wave from another device is detected when the value is equal to or greater than a value threshold value.   The interference wave detecting means performs frequency analysis on data over a measurement time acquired by operating the receiving means in a time zone immediately before pulse-modulating and transmitting an electromagnetic wave, and a peak existing in the obtained frequency spectrum. Detecting the reception of interference waves from other devices when the average value of the peak amplitudes present in the obtained frequency spectrum is equal to or greater than a predetermined threshold value. The radar apparatus according to claim 1, wherein the radar apparatus is characterized.

Images