JP2014062804A - Fmcw radar apparatus, and signal processing method for fmcw radar - Google Patents

Fmcw radar apparatus, and signal processing method for fmcw radar Download PDF

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JP2014062804A
JP2014062804A JP2012207855A JP2012207855A JP2014062804A JP 2014062804 A JP2014062804 A JP 2014062804A JP 2012207855 A JP2012207855 A JP 2012207855A JP 2012207855 A JP2012207855 A JP 2012207855A JP 2014062804 A JP2014062804 A JP 2014062804A
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target
frequency
chirp period
up
distance
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JP5554384B2 (en
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Masa Mitsumoto
雅 三本
Kentaro Isoda
健太郎 磯田
Teruyuki Hara
照幸 原
Tadashi Oshima
正資 大島
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Mitsubishi Electric Corp
三菱電機株式会社
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Abstract

PROBLEM TO BE SOLVED: To provide an FMCW radar apparatus capable of correctly measuring a distance up to a target and a relative speed to the target even when a beat signal to be observed comprises only in-phase components, and to provide a signal processing method for the FMCW radar.SOLUTION: A FMCW radar apparatus includes: a frequency bin extraction part for extracting only a complex spectrum of a frequency bin in a predetermined range from a frequency complex spectrum of a beat signal in an up-chirp period after FFT and a frequency complex spectrum of a beat signal in a down-chirp period; and a target measurement part for measuring a distance up to a target and a relative speed to the target from the frequency bin of the target in the up-chirp period and a frequency bin of the target in the down-chirp period.

Description

  The present invention relates to an FMCW (Frequency Modulated Continuous Wave) radar apparatus and an FMCW radar signal processing method for measuring a distance to a target object (hereinafter referred to as a “target”) and a relative speed with respect to the target.

  In recent years, FMCW radar devices (hereinafter also simply referred to as “FMCW radars”) that are compatible with targets with a distance of several hundred meters or less have been used with a cheaper and simpler configuration than pulse radars and the like. The FMCW radar radiates (transmits) a specific modulated transmission signal as an electromagnetic wave, receives the electromagnetic wave reflected by the target, receives the received electromagnetic wave as a reception signal, and uses the transmission signal and the reception signal as a beat. Generate a signal.

  Here, the beat signal is converted into digital data by an AD converter (ADC: Analog-to-Digital Converter), and then input to a CPU (Central Processing Unit) or the like, and the distance to the target by signal processing at the CPU. And the relative speed to the target and the target angle are measured.

  Note that the beat frequency of the beat signal in the FMCW radar can take either a positive (> 0) or negative (<0) value depending on the combination of the distance to the target and the relative speed with respect to the target.

  As such FMCW radar, the first transmission means detects two types of beat frequencies (U, D), the second transmission means detects two types of beat frequencies (u, d), and the four types of beat frequencies. (U, D, u, d) An on-vehicle radar device that performs target detection processing by determining the sign of a beat frequency or the like based on all appearance states is known (see, for example, Patent Document 1).

JP-A-10-170641

However, the prior art has the following problems.
That is, for example, an FMCW radar apparatus mounted on a vehicle and used for vehicle speed / interval control (ACC: Adaptive Cruise Control), collision damage reduction, or collision prevention is required to be reduced in size from the viewpoint of mountability. .

  Here, regarding the reception circuit of the FMCW radar, when an ideal circuit for observing both the in-phase component and the quadrature component, that is, the real part and the imaginary part in the complex signal, a complicated two-system circuit is required. Become. On the other hand, when only the in-phase component, that is, only the real part in the complex signal is observed, a simple single circuit is sufficient, and the apparatus can be downsized.

  However, in an FMCW radar that observes only the in-phase component, if the beat signal is converted into a frequency power spectrum by Fast Fourier Transform (FFT) or the like, the beat frequency has a positive (> 0) range and a negative (> 0) range. The power peak (maximum value) appears symmetrically in the range <0).

  Therefore, for example, when the beat frequency corresponding to the target is detected as a power peak, it is always detected at both positive and negative frequencies. Therefore, in order to correctly measure the distance to the target and the relative velocity with respect to the target, It is necessary to obtain the corresponding correct beat frequency.

  Here, the in-vehicle radar device disclosed in Patent Document 1 does not assume a state in which the beat frequency is always detected at both positive and negative frequencies. For this reason, when the beat frequency of the correct code corresponding to the target cannot be obtained, there is a problem that the distance to the target and the relative speed with respect to the target cannot be measured correctly.

  The present invention has been made to solve the above-described problems. Even if the beat signal to be observed is only an in-phase component, by obtaining the beat frequency of the correct code corresponding to the target, An object of the present invention is to obtain an FMCW radar apparatus and a signal processing method for an FMCW radar capable of correctly measuring the distance and the relative velocity with respect to the target.

  The FMCW radar device according to the present invention transmits a transmission signal as an electromagnetic wave, receives an electromagnetic wave reflected by a target as a reception signal, mixes the transmission signal and the reception signal, generates a beat signal, and generates a beat signal. FMCW radar apparatus for measuring the distance to the target and the relative velocity with respect to the target based on the frequency complex spectrum of the beat signal in the up-chirp period after FFT and the frequency complex spectrum of the beat signal in the down-chirp period, The frequency bin extraction unit that extracts only the complex spectrum of frequency bins in a predetermined range, the target frequency bin in the up-chirp period, and the target frequency bin in the down-chirp period, the distance to the target and the relative speed to the target It is obtained by a target measurement unit for constant.

  The FMCW radar signal processing method according to the present invention transmits a transmission signal as an electromagnetic wave, receives an electromagnetic wave reflected by a target as a reception signal, mixes the transmission signal and the reception signal, and generates a beat signal. A signal processing method for FMCW radar executed by an FMCW radar apparatus that measures a distance to a target and a relative velocity with respect to the target based on the beat signal, and a frequency complex spectrum of the beat signal in an up-chirp period after FFT, And a frequency bin extraction step for extracting only the complex spectrum of the frequency bin in a predetermined range from the frequency complex spectrum of the beat signal in the down chirp period, the target frequency bin in the up chirp period, and the target frequency bin in the down chirp period And from It is obtained by a target measurement step of measuring a relative speed with respect to distance and the target to the target.

According to the FMCW radar apparatus and the FMCW radar signal processing method according to the present invention, the frequency bin extraction unit (step) includes the frequency complex spectrum of the beat signal in the up chirp period after the FFT and the frequency of the beat signal in the down chirp period. Only the complex spectrum of the frequency bin in a predetermined range is extracted from the complex spectrum, and the target measurement unit (step) detects the target frequency bin in the up-chirp period and the target frequency bin in the down-chirp period to the target. Measure distance and speed relative to target.
Therefore, even if the observed beat signal is only the in-phase component, the distance to the target and the relative speed with respect to the target can be correctly measured by obtaining the beat frequency with the correct code corresponding to the target.

It is a block block diagram which shows the FMCW radar apparatus which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the relationship between the time in the observation period of the FMCW radar apparatus based on Embodiment 1 of this invention, and a modulation voltage. It is explanatory drawing which shows the relationship between the time in the observation period of the FMCW radar apparatus which concerns on Embodiment 1 of this invention, and a transmission signal frequency. (A), (b) is explanatory drawing which showed the beat frequency of the target in the up-chirp period of the FMCW radar apparatus which concerns on Embodiment 1 of this invention on the distance-relative velocity plane. (A), (b) is explanatory drawing which showed the beat frequency of the target in the down chirp period of the FMCW radar apparatus which concerns on Embodiment 1 of this invention on the distance-relative velocity plane. It is a block block diagram which shows the FMCW radar apparatus which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows the relationship between the time in the observation period of the FMCW radar apparatus which concerns on Embodiment 2 of this invention, and a modulation voltage. It is explanatory drawing which shows the relationship between the time in the observation period of the FMCW radar apparatus which concerns on Embodiment 2 of this invention, and a transmission signal frequency. It is explanatory drawing which shows the relationship between the time in the observation period of the FMCW radar apparatus which concerns on Embodiment 2 of this invention, and a transmission signal frequency. (A)-(c) is explanatory drawing which shows the measurable area | region on the distance-relative velocity plane in the FMCW radar apparatus which concerns on Embodiment 2 of this invention. (A), (b) is explanatory drawing which shows the measurable area | region on the distance-relative velocity plane in the FMCW radar apparatus which concerns on Embodiment 2 of this invention. (A), (b) is explanatory drawing which shows the measurable area | region on the distance-relative velocity plane in the FMCW radar apparatus which concerns on Embodiment 2 of this invention.

  Hereinafter, preferred embodiments of an FMCW radar apparatus and an FMCW radar signal processing method according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals. To do.

  In the following embodiments, a case where the FMCW radar apparatus according to the present invention is mounted on an automobile and performs target detection processing will be described as an example. However, the present invention is not limited to this, and it goes without saying that the same effect can be obtained even when the FMCW radar apparatus according to the present invention is applied to other moving bodies other than automobiles such as ships and airplanes. .

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an FMCW radar apparatus 1 according to Embodiment 1 of the present invention.

  In FIG. 1, an FMCW radar apparatus 1 includes a control unit 11, a modulation voltage generation unit 12, a voltage controlled oscillator (hereinafter referred to as “VCO: Voltage Controlled Oscillator”) 13, a distribution circuit 14, a high frequency amplifier circuit 15, and a transmission antenna. 16, receiving antennas 17a and 17b, mixers 18a and 18b, filter circuits 19a and 19b, amplifier circuits 20a and 20b, ADCs 21a and 21b, a memory 22, an FFT processing unit 23, a frequency bin extraction unit 24, and a detection / angle measurement processing unit 25, a pairing processing unit 26 and a target measurement unit 27 are provided.

Next, the operation of each part of the FMCW radar apparatus 1 will be described.
The control unit 11 is configured by, for example, a dedicated logic circuit, a general-purpose CPU, a program in a DSP (Digital Signal Processor), or a combination thereof, and controls the operation timing of each component of the FMCW radar apparatus 1.

  The modulation voltage generator 12 generates a FMCW modulation voltage as shown in FIG. 2 under the control of the controller 11. FIG. 2 is an explanatory diagram showing the relationship between time and modulation voltage within the observation period of the FMCW radar apparatus 1 according to Embodiment 1 of the present invention.

  In FIG. 2, the modulation voltage has an up-chirp period in which the applied voltage increases with time and a down-chirp period in which the applied voltage decreases with time, within a preset fixed observation period. The generator 12 generates a preset modulation voltage for FMCW for each period.

  The VCO 13 generates a transmission signal whose frequency changes with time as shown in FIG. 3 according to the voltage applied from the modulation voltage generator 12. FIG. 3 is an explanatory diagram showing the relationship between time and transmission signal frequency in the observation period of the FMCW radar apparatus 1 according to Embodiment 1 of the present invention.

  In FIG. 3, the transmission signal, like the modulation voltage, is an up-chirp period in which the frequency of the transmission signal increases over time and a down frequency in which the frequency of the transmission signal decreases over time within a predetermined observation period. The VCO 13 generates a transmission signal whose frequency changes over time for each period.

  Hereinafter, after the transmission signal generated by the VCO 13 is divided into an up-chirp period and a down-chirp period, the operation from the VCO 13 to the detection / angle measurement processing unit 25 will be described for each period.

First, the operation in the up chirp period will be described.
The VCO 13 generates an up-chirp period transmission signal having a modulation frequency width of B [Hz] and a modulation time width of T [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to a target (not shown), and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target.

  The receiving antenna 17a receives the electromagnetic wave reflected by the target, and outputs the received electromagnetic wave as a received signal to the mixer 18a. The mixer 18a mixes the transmission signal from the distribution circuit 14 and the reception signal from the reception antenna 17a, generates a beat signal, and outputs the beat signal to the filter circuit 19a.

  The filter circuit 19a outputs to the amplifier circuit 20a a beat signal in which unnecessary frequency components are suppressed (a signal in a desired band is extracted) with respect to the beat signal from the mixer 18a. The amplifier circuit 20a amplifies the voltage of the beat signal to a preset magnitude and outputs it to the ADC 21a. The ADC 21a converts the voltage value of the beat signal into digital data and stores it in the memory 22 as the up-chirp period beat signal # 1.

  On the other hand, the receiving antenna 17b receives the electromagnetic wave reflected by the target, and outputs the received electromagnetic wave as a received signal to the mixer 18b. The mixer 18b mixes the transmission signal from the distribution circuit 14 and the reception signal from the reception antenna 17b, generates a beat signal, and outputs the beat signal to the filter circuit 19b.

  The filter circuit 19b outputs, to the amplifier circuit 20b, a beat signal in which unnecessary frequency components are suppressed (a signal in a desired band is extracted) with respect to the beat signal from the mixer 18b. The amplifier circuit 20b amplifies the voltage of the beat signal to a preset magnitude and outputs it to the ADC 21b. The ADC 21b converts the voltage value of the beat signal into digital data and stores it in the memory 22 as the up-chirp period beat signal # 2.

  Here, the FFT processing unit 23, the frequency bin extraction unit 24, the detection / angle measurement processing unit 25, the pairing processing unit 26, and the target measurement unit 27 are, for example, a dedicated logic circuit, a general-purpose CPU, a program in the DSP, Alternatively, the following operations are performed under the control of the control unit 11.

  The FFT processing unit 23 reads the up chirp period beat signal # 1 from the memory 22, converts the up chirp period beat signal # 1 into the up chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. In the following description, the frequency minimum discrete unit after FFT is a frequency bin. That is, when the time width of the input data to the FFT processing unit 23 is equal to the modulation time width T [s], the width of the frequency bin that is the minimum frequency discrete width is 1 / T [Hz].

  The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the up-chirp period beat signal # 2 from the memory 22, converts it into an up-chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 from the memory 22 and obtains a power spectrum from each complex spectrum, for example, for the same frequency bin Both power values are added to obtain a new power value.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique. At this time, an angle error occurs in a frequency bin whose sign is opposite to that of a true frequency bin.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many up-chirp period detection data sets as the detected number. 22 to save.

Next, the operation in the down chirp period will be described.
The VCO 13 generates a down-chirp period transmission signal having a modulation frequency width of B [Hz] and a modulation time width of T [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to the target, and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target, respectively.

  The receiving antennas 17a and 17b respectively receive the electromagnetic waves reflected by the target, and output the received electromagnetic waves to the mixers 18a and 18b as received signals. The mixers 18a and 18b respectively mix the transmission signal from the distribution circuit 14 and the reception signals from the receiving antennas 17a and 17b, generate beat signals, and output the beat signals to the filter circuits 19a and 19b.

  The filter circuits 19a and 19b output beat signals obtained by suppressing unnecessary frequency components (taken out signals in a desired band) to the beat signals from the mixers 18a and 18b, respectively, to the amplifier circuits 20a and 20b.

  The amplifier circuits 20a and 20b amplify the voltage of the beat signal to a preset level and output the amplified signals to the ADCs 21a and 21b. The ADCs 21a and 21b convert the voltage value of the beat signal into digital data, respectively, and store them in the memory 22 as the down chirp period beat signal # 1 and the down chirp period beat signal # 2.

  The FFT processing unit 23 reads the down chirp period beat signal # 1 from the memory 22, converts it into a down chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the down chirp period beat signal # 2 from the memory 22, converts the down chirp period beat signal # 2 into the down chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extracting unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extracted frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads out the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 from the memory 22, obtains a power spectrum from each complex spectrum, and is the same as the up-chirp period. A new power value is calculated by the method.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique. At this time, an angle error occurs in a frequency bin whose sign is opposite to that of a true frequency bin.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many down-chirp period detection data sets as the detected number. 22 to save.

  The pairing processing unit 26 reads the up-chirp period detection data set and the down-chirp period detection data set from the memory 22 and performs, for example, a small difference in power value or a difference in angle by a pairing process that is a known technique. Based on a determination index such as “low”, a pair of a detection frequency bin in the up-chirp period and a detection frequency bin in the down-chirp period is generated and output to the target measurement unit 27. At this time, there can be a plurality of pairs.

  When the detection frequency bin in the up-chirp period is U bin and the detection frequency bin in the down chirp period is D bin, the target measurement unit 27 sets the modulation center frequency of the transmission signal to Fc [Hz] and sets the velocity of electromagnetic waves to C. As [m / s], based on the principle of FMCW radar, the distance R [m] to the target and the relative velocity V [m / s] to the target (defined as a negative value when approaching) Obtained by (1) and (2).

  R = {C / (4 × B)} × (DU) (1)

  V = − {C / (4 × Fc × T)} × (U + D) (2)

  Further, the target measuring unit 27 extracts the target angles from the up-chirp period detection data set and the down-chirp period detection data set, for example, the average value thereof is set as the final target angle, and the target angle, The distance and the relative speed with respect to the target are set and stored in the memory 22 or output to the outside.

  Here, with reference to FIGS. 4 and 5, the frequency bin extraction unit 24 extracts the distance to the target and the relative speed with respect to the target by using the in-phase components only by the above formulas (1) and (2). A method for setting the frequency bin range will be described.

  FIGS. 4A and 4B are explanatory diagrams showing the beat frequency of the target in the up-chirp period of the FMCW radar apparatus 1 according to Embodiment 1 of the present invention on the distance-relative velocity plane. 5 (a) and 5 (b) are explanatory diagrams showing the beat frequency of the target in the down-chirp period of the FMCW radar apparatus 1 according to Embodiment 1 of the present invention on the distance-relative velocity plane.

  First, in the up-chirp period and the down-chirp period, the modulation time width is T [s], the modulation frequency width is B [Hz], the modulation center frequency of the transmission signal is Fc [Hz], The speed is C [m / s], the distance to the target is R [m], and the relative speed with respect to the target is V [m / s].

  At this time, based on the principle of FMCW radar, the beat frequency Fu of the target observed in the up-chirp period is expressed by the following equation (3), and the beat frequency Fd of the target observed in the down-chirp period is expressed by the following equation ( 4).

  Fu = − {(2 × B) / (C × T)} × R − {(2 × Fc) / C} × V (3)

  Fd = {(2 × B) / (C × T)} × R − {(2 × Fc) / C} × V (4)

  Here, in the distance-relative velocity plane shown in FIG. 4A, the combination of the distance to the target where the beat frequency of the target has the same value and the relative velocity with respect to the target is represented as a straight line. A set of points at which the target beat frequency Fu is 0 [Hz] in the up-chirp period is a straight line passing through the origin represented by the following equation (5).

  {(2 × B) / (C × T)} × R = − {(2 × Fc) / C} × V (5)

  In FIG. 4A, the beat frequency of the target in the up-chirp period is divided into a positive (> 0) region and a negative (<0) region, with the straight line represented by Equation (5) as a boundary. . 4A, considering the actual distance range (> 0), the target beat frequency in the up-chirp period is wider in the negative (<0) region.

  In addition, when the range of the relative velocity to be observed is (−Vmax) [m / s] to (+ Vmax) [m / s], the distance R = 0 [m] to the target shown in FIG. The straight line passing through the target relative velocity V = (− Vmax) [m / s] is a positive (> 0) region of the target beat frequency observed in the up-chirp period, and has a magnitude (absolute value). ) Corresponds to the maximum beat frequency (+ Fumax) expressed by the following equation (6).

(+ Fumax)
=-{(2 * B) / (C * T)} * (0)-{(2 * Fc) / C} * (-Vmax)
= − {(2 × Fc) / C} × (−Vmax) (6)

  At this time, the fact that (+ Fumax) is observed means that a positive / negative sign determination is required for the frequency detected in the range of (−Fumax) to (+ Fumax). On the other hand, if the beat frequency is negative (<0) smaller than (−Fumax) expressed by the following equation (6), the positive / negative sign determination is unnecessary.

  (−Fumax) = {(2 × Fc) / C} × (−Vmax) (7)

  When the observation period is T [s], the frequency bin width after FFT is 1 / T [Hz], so the frequency bin (−Umax) as an integer value smaller than (−Fumax) is Is represented by the following equation (8).

(-Umax)
= RoundUp [(-Fumax) / (1 / T)]
= −RoundUp [(+ Fumax) × T]
= −RoundUp [− {(2 × Fc) / C} × (−Vmax) × T]
= −RoundUp [{(2 × Fc × T) / C} × (Vmax)] (8)
However, RoundUp [] is a function that rounds up after the decimal point.

  Therefore, the frequency bin extracting unit 24 may extract a negative (<0) frequency bin equal to or less than (−Umax) for the up chirp period.

  Similarly, in the distance-relative velocity plane shown in FIG. 5A, the set of points at which the beat frequency Fd of the target in the down chirp period becomes 0 [Hz] is the origin represented by the following equation (9). It becomes a straight line that passes.

  {(2 × B) / (C × T)} × R = {(2 × Fc) / C} × V (9)

  In FIG. 5 (a), the beat frequency of the target in the down chirp period is divided into a positive (> 0) region and a negative (<0) region, with the straight line represented by Expression (9) as a boundary. . From FIG. 5A, in consideration of the actual distance range (> 0), the target beat frequency in the down chirp period is wider in the positive (> 0) region.

  Further, when the range of the relative velocity to be observed is (−Vmax) [m / s] to (+ Vmax) [m / s], the distance R = 0 [m] to the target shown in FIG. The straight line passing through the target relative velocity V = (+ Vmax) [m / s] is a negative (<0) region of the target beat frequency observed in the down-chirp period, and has a magnitude (absolute value). Corresponds to the beat frequency (−Fdmax) represented by the following equation (10).

(-Fdmax)
= {(2 * B) / (C * T)} * (0)-{(2 * Fc) / C} * (+ Vmax)
= − {(2 × Fc) / C} × (+ Vmax) (10)

  At this time, the fact that (−Fdmax) is observed means that a positive / negative sign determination is required for the frequency detected in the range of (−Fdmax) to (+ Fdmax). In contrast, if the beat frequency is positive (> 0) greater than (+ Fdmax) expressed by the following equation (11), the positive / negative sign determination is not necessary.

  (+ Fdmax) = {(2 × Fc) / C} × (+ Vmax) (11)

  When the observation period is T [s], the frequency bin width after FFT is 1 / T [Hz], and therefore the frequency bin (+ Dmax) as an integer value larger than (+ Fdmax) is It is represented by Formula (12).

(+ Dmax)
= RoundUp [(+ Fdmax) / (1 / T)]
= RoundUp [(+ Fdmax) × T]
RoundUp [{(2 × Fc) / C} × (+ Vmax) × T]
= RoundUp [{(2 × Fc × T) / C} × (Vmax)] (12)
However, RoundUp [] is a function that rounds up after the decimal point.

  Therefore, the frequency bin extracting unit 24 may extract positive (> 0) frequency bins greater than (+ Dmax) for the down chirp period.

  As described above, by setting the frequency bin range extracted by the frequency bin extraction unit 24 according to the up-chirp period and the down-chirp period as described above, even if the observed beat signal is only the in-phase component. From the equations (1) and (2), the distance to the target and the relative velocity with respect to the target can be obtained.

As described above, according to the first embodiment, the frequency bin extraction unit (step) determines a predetermined frequency from the frequency complex spectrum of the beat signal in the up-chirp period after FFT and the frequency complex spectrum of the beat signal in the down-chirp period. The target measurement unit (step) extracts only the complex spectrum of the frequency bin in the range of, and the target frequency bin in the up chirp period and the target frequency bin in the down chirp period, and the distance to the target and relative to the target Measure speed.
Therefore, even if the observed beat signal is only the in-phase component, the distance to the target and the relative speed with respect to the target can be correctly measured by obtaining the beat frequency with the correct code corresponding to the target.
Therefore, the receiving circuit can be simplified and the device size can be reduced.

Embodiment 2. FIG.
FIG. 6 is a block diagram showing an FMCW radar apparatus 1A according to Embodiment 2 of the present invention.

  In FIG. 6, the FMCW radar apparatus 1 </ b> A includes a distance range modulation voltage generation unit 31 and a distance range target measurement unit 32 instead of the modulation voltage generation unit 12 and the target measurement unit 27 illustrated in FIG. 1. Other configurations are the same as those of the first embodiment described above, and thus description thereof is omitted.

Next, the operation of the FMCW radar apparatus 1A that is different from that of the first embodiment will be described.
The control unit 11 is configured by, for example, a dedicated logic circuit, a general-purpose CPU, a program in the DSP, or a combination thereof, and controls the operation timing of each component of the FMCW radar apparatus 1A.

  The modulation voltage generator 31 for each distance range generates a modulation voltage for FMCW for each of the distance ranges # 1 to #M as shown in FIG. FIG. 7 is an explanatory diagram showing the relationship between time and modulation voltage in the observation period of the FMCW radar apparatus 1A according to Embodiment 2 of the present invention.

  In FIG. 7, the modulation voltage has a period for observing the distance range # 1 to the distance range #M in a predetermined fixed observation period, and for each distance range period, as time elapses. The modulation voltage generator 31 for each distance range has an up-chirp period in which the applied voltage is increased and a down-chirp period in which the applied voltage is decreased as time elapses. Is generated.

  The VCO 13 generates a transmission signal whose frequency changes with time for each distance range, as shown in FIG. 8, according to the voltage applied from the modulation voltage generator 31 for each distance range. FIG. 8 is an explanatory diagram showing the relationship between time and transmission signal frequency in the observation period of the FMCW radar apparatus 1A according to Embodiment 2 of the present invention.

  In FIG. 8, the transmission signal has a period for observing the distance range # 1 to the distance range #M within a predetermined fixed total observation period, like the modulation voltage, and the period of each distance range. Every time, the VCO 13 has an up-chirp period in which the frequency of the transmission signal increases as time elapses and a down-chirp period in which the frequency of the transmission signal decreases as time elapses. A changing transmission signal is generated.

  Hereinafter, as shown in FIG. 9, taking the case where the distance range is two (M = 2) as an example, the transmission signal generated by the VCO 13 is divided into an up-chirp period and a down-chirp period. The operation from the VCO 13 to the detection / angle measurement processing unit 25 will be described for each period.

First, the operation in the up-chirp period of distance range # 1 will be described.
For the distance range # 1, the VCO 13 generates an up-chirp period transmission signal having a modulation frequency width of B_1 [Hz] and a modulation time width of T_1 [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to the target, and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target, respectively.

  The receiving antennas 17a and 17b respectively receive the electromagnetic waves reflected by the target, and output the received electromagnetic waves to the mixers 18a and 18b as received signals. The mixers 18a and 18b respectively mix the transmission signal from the distribution circuit 14 and the reception signals from the receiving antennas 17a and 17b, generate beat signals, and output the beat signals to the filter circuits 19a and 19b.

  The filter circuits 19a and 19b output beat signals obtained by suppressing unnecessary frequency components (taken out signals in a desired band) to the beat signals from the mixers 18a and 18b, respectively, to the amplifier circuits 20a and 20b.

  The amplifier circuits 20a and 20b amplify the voltage of the beat signal to a preset level and output the amplified signals to the ADCs 21a and 21b. The ADCs 21a and 21b convert the voltage values of the beat signals into digital data, respectively, and store them in the memory 22 as up-chirp period beat signals # 1 and up-chirp period beat signals # 2.

  The FFT processing unit 23 reads the up chirp period beat signal # 1 from the memory 22, converts the up chirp period beat signal # 1 into the up chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the up-chirp period beat signal # 2 from the memory 22, converts it into an up-chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 from the memory 22, obtains a power spectrum from each complex spectrum, and is the same as the up-chirp period. A new power value is calculated by the method.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many up-chirp period detection data sets as the detected number. 22 to save.

Subsequently, an operation in the down chirp period of the distance range # 1 will be described.
For the distance range # 1, the VCO 13 generates a down-chirp period transmission signal having a modulation frequency width of B_1 [Hz] and a modulation time width of T_1 [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to the target, and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target, respectively.

  The receiving antennas 17a and 17b respectively receive the electromagnetic waves reflected by the target, and output the received electromagnetic waves to the mixers 18a and 18b as received signals. The mixers 18a and 18b respectively mix the transmission signal from the distribution circuit 14 and the reception signals from the receiving antennas 17a and 17b, generate beat signals, and output the beat signals to the filter circuits 19a and 19b.

  The filter circuits 19a and 19b output beat signals obtained by suppressing unnecessary frequency components (taken out signals in a desired band) to the beat signals from the mixers 18a and 18b, respectively, to the amplifier circuits 20a and 20b.

  The amplifier circuits 20a and 20b amplify the voltage of the beat signal to a preset level and output the amplified signals to the ADCs 21a and 21b. The ADCs 21a and 21b convert the voltage value of the beat signal into digital data, respectively, and store them in the memory 22 as the down chirp period beat signal # 1 and the down chirp period beat signal # 2.

  The FFT processing unit 23 reads the down chirp period beat signal # 1 from the memory 22, converts it into a down chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the down chirp period beat signal # 2 from the memory 22, converts the down chirp period beat signal # 2 into the down chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extracting unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extracted frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 from the memory 22, obtains a power spectrum from each complex spectrum, and is the same as the down-chirp period. A new power value is calculated by the method.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many down-chirp period detection data sets as the detected number. 22 to save.

  The pairing processing unit 26 reads the up-chirp period detection data set and the down-chirp period detection data set from the memory 22 and performs, for example, a small difference in power value or a difference in angle by a pairing process that is a known technique. Based on a determination index such as “small”, a pair of a detection frequency bin in the up-chirp period and a detection frequency bin in the down-chirp period is generated and output to the target measurement unit 32 for each distance range.

  When the target measurement unit 32 for each distance range receives the fact that the processing target is the distance range # 1 from the control unit 11, the detection frequency bin in the up chirp period is the U_1 bin, and the detection frequency bin in the down chirp period is the D_1 bin. Further, assuming that the modulation center frequency of the transmission signal is Fc [Hz], the velocity of the electromagnetic wave is C [m / s], and based on the principle of FMCW radar, the distance R [m] to the target and the relative velocity V [ m / s] is obtained by the following equations (13) and (14).

R = {C / (4 × B_1)} × (D_1−U_1) (13)
V = − {C / (4 × Fc × T_1)} × (U_1 + D_1) (14)

  Further, the target measurement unit 32 for each distance range extracts the target angle from each of the up-chirp period detection data set and the down-chirp period detection data set, for example, the average value thereof is set as the final target angle, and the target angle, The distance to the target and the relative speed with respect to the target are set, and the result in the distance range # 1 is stored in the memory 22 or output to the outside.

Next, the operation in the up chirp period of the distance range # 2 will be described.
For the distance range # 2, the VCO 13 generates an up-chirp period transmission signal with a modulation frequency width of B_2 [Hz] and a modulation time width of T_2 [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to the target, and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target, respectively.

  The receiving antennas 17a and 17b respectively receive the electromagnetic waves reflected by the target, and output the received electromagnetic waves to the mixers 18a and 18b as received signals. The mixers 18a and 18b respectively mix the transmission signal from the distribution circuit 14 and the reception signals from the receiving antennas 17a and 17b, generate beat signals, and output the beat signals to the filter circuits 19a and 19b.

  The filter circuits 19a and 19b output beat signals obtained by suppressing unnecessary frequency components (taken out signals in a desired band) to the beat signals from the mixers 18a and 18b, respectively, to the amplifier circuits 20a and 20b.

  The amplifier circuits 20a and 20b amplify the voltage of the beat signal to a preset level and output the amplified signals to the ADCs 21a and 21b. The ADCs 21a and 21b convert the voltage values of the beat signals into digital data, respectively, and store them in the memory 22 as up-chirp period beat signals # 1 and up-chirp period beat signals # 2.

  The FFT processing unit 23 reads the up chirp period beat signal # 1 from the memory 22, converts the up chirp period beat signal # 1 into the up chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the up-chirp period beat signal # 2 from the memory 22, converts it into an up-chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the up-chirp period, and stores it in the memory 22 as an up-chirp period extraction frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 from the memory 22, obtains a power spectrum from each complex spectrum, and is the same as the up-chirp period. A new power value is calculated by the method.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the up-chirp period extracted frequency complex spectrum # 1 and the up-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many up-chirp period detection data sets as the detected number. 22 to save.

Next, the operation during the down chirp period in the distance range # 2 will be described.
For the distance range # 2, the VCO 13 generates a down-chirp period transmission signal having a modulation frequency width of B_2 [Hz] and a modulation time width of T_2 [s] as shown in FIG. The distribution circuit 14 outputs a part of the transmission signal generated by the VCO 13 to the high frequency amplifier circuit 15 and outputs the remainder of the transmission signal to the mixers 18a and 18b.

  The high frequency amplifier circuit 15 amplifies the power of the transmission signal from the distribution circuit 14 to a preset magnitude and outputs the amplified signal to the transmission antenna 16. The transmission antenna 16 radiates (transmits) the transmission signal amplified by the high-frequency amplifier circuit 15 into space as an electromagnetic wave. The transmitted electromagnetic waves are applied to the target, and the receiving antennas 17a and 17b receive the electromagnetic waves reflected by the target, respectively.

  The receiving antennas 17a and 17b respectively receive the electromagnetic waves reflected by the target, and output the received electromagnetic waves to the mixers 18a and 18b as received signals. The mixers 18a and 18b respectively mix the transmission signal from the distribution circuit 14 and the reception signals from the receiving antennas 17a and 17b, generate beat signals, and output the beat signals to the filter circuits 19a and 19b.

  The filter circuits 19a and 19b output beat signals obtained by suppressing unnecessary frequency components (taken out signals in a desired band) to the beat signals from the mixers 18a and 18b, respectively, to the amplifier circuits 20a and 20b.

  The amplifier circuits 20a and 20b amplify the voltage of the beat signal to a preset level and output the amplified signals to the ADCs 21a and 21b. The ADCs 21a and 21b convert the voltage value of the beat signal into digital data, respectively, and store them in the memory 22 as the down chirp period beat signal # 1 and the down chirp period beat signal # 2.

  The FFT processing unit 23 reads the down chirp period beat signal # 1 from the memory 22, converts it into a down chirp period frequency complex spectrum # 1 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extraction unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extraction frequency complex spectrum # 1.

  Subsequently, the FFT processing unit 23 reads the down chirp period beat signal # 2 from the memory 22, converts the down chirp period beat signal # 2 into the down chirp period frequency complex spectrum # 2 by FFT processing, and outputs it to the frequency bin extraction unit 24. The frequency bin extracting unit 24 extracts a complex spectrum of frequency bins in a range set in advance for the down chirp period, and stores it in the memory 22 as a down chirp period extracted frequency complex spectrum # 2.

  The detection / angle measurement processing unit 25 reads the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 from the memory 22, obtains a power spectrum from each complex spectrum, and is the same as the down-chirp period. A new power value is calculated by the method.

  Further, the detection / angle measurement processing unit 25 has, for example, a power value equal to or higher than a preset threshold value for the power value in each of the frequency bins, that is, from the power value of the adjacent frequency bin. Detect frequency bins with large power values.

  Further, the detection / angle measurement processing unit 25 calculates a phase difference from the down-chirp period extracted frequency complex spectrum # 1 and the down-chirp period extracted frequency complex spectrum # 2 of the detected frequency bin, and if necessary, After performing the phase correction, the angle is converted into the target angle according to the principle of phase monopulse angle measurement which is a known technique.

  The detection / angle measurement processing unit 25 sets the detected frequency bin obtained in this way, the power value in the frequency bin and the angle of the target as a set, and stores as many down-chirp period detection data sets as the detected number. 22 to save.

  The pairing processing unit 26 reads the up-chirp period detection data set and the down-chirp period detection data set from the memory 22 and performs, for example, a small difference in power value or a difference in angle by a pairing process that is a known technique. Based on a determination index such as “small”, a pair of a detection frequency bin in the up-chirp period and a detection frequency bin in the down-chirp period is generated and output to the target measurement unit 32 for each distance range.

  When the target measurement unit 32 for each distance range receives the fact that the processing target is the distance range # 2 from the control unit 11, the detection frequency bin in the up chirp period is the U_2 bin, and the detection frequency bin in the down chirp period is the D_2 bin Further, assuming that the modulation center frequency of the transmission signal is Fc [Hz], the velocity of the electromagnetic wave is C [m / s], and based on the principle of FMCW radar, the distance R [m] to the target and the relative velocity V [ m / s] is obtained by the following equations (15) and (16).

R = {C / (4 × B_2)} × (D_2−U_2) (15)
V = − {C / (4 × Fc × T_2)} × (U_2 + D_2) (16)

  Further, the target measurement unit 32 for each distance range extracts the target angle from each of the up-chirp period detection data set and the down-chirp period detection data set, for example, the average value thereof is set as the final target angle, and the target angle, The distance to the target and the relative speed with respect to the target are set, and the result in the distance range # 2 is stored in the memory 22 or output to the outside.

  Here, referring to FIGS. 10 to 12, a method for setting the modulation frequency width B_1 and the modulation time width T_1 for the distance range # 1, and the modulation frequency width B_2 and the modulation time width T_2 for the distance range # 2. explain.

  10 (a) to 10 (c), 11 (a), 11 (b), 12 (a), and 12 (b) are distance-relative velocity planes in the FMCW radar apparatus 1A according to the second embodiment of the present invention. It is explanatory drawing which shows the upper measurable area | region.

  First, in the up-chirp period of the distance range # 1, the frequency bin (−U — 1max) expressed by the following equation (17) is extracted by the frequency bin extraction unit 24 as in the first embodiment. Is the upper limit of the range.

(-U_1max)
= −RoundUp [{(2 × Fc × T_1) / C} × (Vmax)] (17)
However, RoundUp [] is a function that rounds up after the decimal point.

  Further, the upper limit of the frequency bin range is a straight line represented by the following equation (18) on the distance-relative velocity plane of FIG.

(−U_1max) × (1 / T_1)
=-{(2 * B_1) / (C * T_1)} * R-{(2 * Fc) / C} * V (18)

  In the up-chirp period of distance range # 1, 2 × (N_1) (where N_1 is an integer that is a power of 2) is sampled by ADCs 21a and 21b, and FFT is performed on all the data. In this case, the lower limit of the frequency bin range is (1-N_1), and on the distance-relative velocity plane in FIG. 10A, the line is represented by the following equation (19).

(1-N_1) × (1 / T_1)
=-{(2 * B_1) / (C * T_1)} * R-{(2 * Fc) / C} * V (19)

  That is, in the up-chirp period of the distance range # 1, with respect to the frequency bins extracted by the frequency bin extraction unit 24, the distance to the target and the relative to the target only within the region having the dotted line in FIG. You can get speed.

  On the other hand, in the down chirp period of distance range # 1, the frequency bin (+ D_1max) expressed by the following equation (20) is the frequency bin extracted by the frequency bin extraction unit 24, as in the first embodiment. The lower limit of the range.

(+ D_1max)
= RoundUp [{(2 * Fc * T_1) / C} * (Vmax)] (20)
However, RoundUp [] is a function that rounds up after the decimal point.

  Further, the lower limit of the frequency bin range is a straight line represented by the following equation (21) on the distance-relative velocity plane of FIG.

(+ D_1max) × (1 / T_1)
= {(2 * B_1) / (C * T_1)} * R-{(2 * Fc) / C} * V (21)

  Further, in the down-chirp period of distance range # 1, the same 2 × (N_1) data as in the up-chirp period is sampled by the ADCs 21a and 21b, and FFT is performed on all the data. The upper limit of the bin range is (N — 1-1), and on the distance-relative velocity plane in FIG. 10B, the upper limit of the bin range is a straight line represented by the following equation (22).

(N_1- 1) × (1 / T_1)
= {(2 * B_1) / (C * T_1)} * R-{(2 * Fc) / C} * V (22)

  That is, in the down chirp period of the distance range # 1, the frequency bins extracted by the frequency bin extracting unit 24 are the distance to the target and the target with respect to the target only within the region having the one-dot chain line in FIG. Relative speed can be obtained.

  Here, since the target measuring unit 32 for each distance range can deal only with the common part of the dotted line area and the one-dot chain line area, in the distance range # 1, the target is measured only within the hatched area of FIG. Distance and relative speed with respect to the target.

  In the distance range # 2, as in the case of the distance range # 1, the upper limit of the frequency bin range in the up-chirp period is a straight line represented by the following equation (23) on the distance-relative velocity plane. Become.

(−U_2max) × (1 / T_2)
=-{(2 * B_2) / (C * T_2)} * R-{(2 * Fc) / C} * V (23)

  Note that the following equation (24) is established for the equation (23).

(-U_2max)
= −RoundUp [{(2 × Fc × T_2) / C} × (Vmax)] (24)
However, RoundUp [] is a function that rounds up after the decimal point.

  In addition, the lower limit of the frequency bin range in the up-chirp period is a straight line represented by the following equation (25) on the distance-relative velocity plane.

(1-N_2) × (1 / T_2)
=-{(2 * B_2) / (C * T_2)} * R-{(2 * Fc) / C} * V (25)

  In addition, the lower limit of the frequency bin range in the down chirp period is a straight line represented by the following equation (26) on the distance-relative velocity plane.

(+ D_2max) × (1 / T_2)
= {(2 * B_2) / (C * T_2)} * R-{(2 * Fc) / C} * V (26)

  Note that the following equation (27) holds for the equation (26).

(+ D_2max)
= RoundUp [{(2 × Fc × T_2) / C} × (Vmax)] (27)
However, RoundUp [] is a function that rounds up after the decimal point.

  In addition, the upper limit of the frequency bin range in the down chirp period is a straight line represented by the following expression (28) on the distance-relative velocity plane.

(N — 2-1) × (1 / T — 2)
= {(2 * B_2) / (C * T_2)} * R-{(2 * Fc) / C} * V (28)

  At this time, the outer edge position is different due to the difference between the modulation frequency widths B_1 and B_2 and the difference between the modulation time widths T_1 and T_2. The distance to the target and the relative speed with respect to the target can be obtained only in the area similar to the hatching area of ().

  Here, in the distance range # 1, when the value of the modulation frequency width B_1 is fixed and the value of the modulation time width T_1 is changed, the value of the modulation time width T_1 is determined from FIGS. 11A and 11B. It can be seen that the area where the distance to the target and the relative speed with respect to the target can be measured (hatched area in FIG. 11) changes.

  Specifically, the target measuring unit 32 for each distance range can measure up to a closer distance when the value of T_1 is small than when the value of T_1 is large, and when the value of T_1 is large, It is possible to measure up to a far distance than when the value of T_1 is small.

  Therefore, in order to realize the distance range # 1 in which a distance closer to the distance range # 2 can be measured and the distance range # 2 in which a distance farther than the distance range # 1 can be measured, T_1 < What is necessary is just to set the modulation | alteration time width | variety used as T_2.

  When the values of the modulation time widths T_1 and T_2 and the modulation frequency width B_2 satisfying T_1 <T_2 are fixed and the value of the modulation frequency width B_1 is changed, the modulation is performed according to FIGS. 12A and 12B. It can be seen that the larger the frequency width B_1, the closer the distance can be measured. It can also be seen that the far side boundary distance of the distance range # 1 is shorter when the value of the modulation frequency width B_1 is larger.

  This is equivalent to the fact that the distance corresponding to one frequency bin is shortened considering that the value of the modulation time width T_1 is fixed and has the same number of FFT points. It means that the distance to can be measured.

  In addition, since this is suitable for measuring the distance to a target at a short distance, B_1 ≧ B_2 is set in the realization of the distance range # 1 capable of measuring a distance closer to the distance range # 2. Better.

  That is, in order to realize the distance range # 1 capable of measuring a distance closer to the distance range # 2 and the distance range # 2 capable of measuring a distance farther than the distance range # 1, T_1 <T_2. And a modulation frequency width such that B_1 ≧ B_2 may be set.

  When specific values of the modulation time widths T_1 and T_2 and the modulation frequency widths B_1 and B_2 are set, a measurable region is drawn for each distance range as shown in FIG. The distance and relative velocity measurement ranges are all covered by both areas so that no areas are missing.

As described above, according to the second embodiment, as in the first embodiment, the frequency bin extracting unit (step) performs the frequency complex spectrum of the beat signal in the up-chirp period after FFT and the beat in the down-chirp period. From the frequency complex spectrum of the signal, only the complex spectrum of the frequency bin in a predetermined range is extracted, and the target measurement unit (step), from the target frequency bin in the up chirp period and the target frequency bin in the down chirp period, Measure the distance to the target and the relative speed to the target.
Therefore, even if the observed beat signal is only the in-phase component, the distance to the target and the relative speed with respect to the target can be correctly measured by obtaining the beat frequency with the correct code corresponding to the target.
Therefore, the receiving circuit can be simplified and the device size can be reduced.

  In the second embodiment, the case where there are two distance ranges (M = 2) has been described as an example. However, even if the distance range is three or more (M ≧ 3), the same applies. By this method, the same effect as in the second embodiment can be obtained.

  For example, when there are three distance ranges (M = 3), a distance range # 1 that can measure a distance closer to the distance range # 2 and a distance farther than the distance range # 1 can be measured, and In order to realize the distance range # 2 capable of measuring a distance closer to the distance range # 3 and the distance range # 3 capable of measuring a distance farther than the distance range # 2, T_1 <T_2 <T_3 And a modulation frequency width that satisfies B_1 ≧ B_2 ≧ B_3 may be set.

  1, 1A FMCW radar device, 11 control unit, 12 modulation voltage generation unit, 13 VCO, 14 distribution circuit, 15 high-frequency amplifier circuit, 16 transmission antenna, 17a, 17b reception antenna, 18a, 18b mixer, 19a, 19b filter Circuit, 20a, 20b Amplifier circuit, 21 ADC, 22 Memory, 23 FFT processing unit, 24 Frequency bin extraction unit, 25 Detection / angle measurement processing unit, 26 Pairing processing unit, 27 Target measurement unit, 31 Modulation voltage per distance range Generating unit, 32 Target measuring unit for each distance range.

Claims (6)

  1. Transmitting the transmission signal as an electromagnetic wave, receiving the electromagnetic wave reflected by the target as a reception signal, generating the beat signal by mixing the transmission signal and the reception signal, based on the beat signal, An FMCW radar device for measuring a distance to a target and a relative velocity with respect to the target,
    A frequency bin extraction unit that extracts only a complex spectrum of frequency bins in a predetermined range from a frequency complex spectrum of the beat signal in an up-chirp period after FFT and a frequency complex spectrum of the beat signal in a down-chirp period;
    A target measurement unit for measuring a distance to the target and a relative velocity with respect to the target from the frequency bin of the target in the up-chirp period and the frequency bin of the target in the down-chirp period;
    An FMCW radar apparatus comprising:
  2. 2. The FMCW radar apparatus according to claim 1, wherein the predetermined range is a negative (<0) frequency in the up-chirp period and a positive (> 0) frequency in the down-chirp period.
  3. In the up-chirp period and the down-chirp period, the modulation time width is both T [s], the modulation center frequency of the transmission signal is Fc [Hz], and the speed of the electromagnetic wave is C [m / s]. Yes, when the relative velocity range to be observed is (−Vmax) [m / s] to (+ Vmax) [m / s],
    As the predetermined range,
    In the up-chirp period, the upper limit of the negative (<0) frequency is
    -RoundUp [{(2 × Fc × T) / C} × (Vmax)]
    However, RoundUp [] is a function that rounds up after the decimal point.
    In the down chirp period, the lower limit of the positive (> 0) frequency is
    RoundUp [{(2 × Fc × T) / C} × (Vmax)]
    The FMCW radar apparatus according to claim 2, wherein:
  4. A modulation voltage generator for each distance range that generates transmission modulation having a different modulation time width for each of the plurality of observation periods so that the distance range that can be measured for each of the plurality of observation periods changes,
    Instead of the target measurement unit,
    For each of the plurality of observation periods, for each distance range for measuring the distance to the target and the relative velocity with respect to the target from the frequency bin of the target in the up-chirp period and the frequency bin of the target in the down-chirp period The FMCW radar device according to any one of claims 1 to 3, further comprising a target measurement unit.
  5. The target measurement unit for each distance range measures the distance to the target by increasing the modulation frequency width of the transmission signal as the measurable distance range is closer in the plurality of observation periods. The FMCW radar apparatus according to claim 4.
  6. Transmitting the transmission signal as an electromagnetic wave, receiving the electromagnetic wave reflected by the target as a reception signal, generating the beat signal by mixing the transmission signal and the reception signal, based on the beat signal, An FMCW radar signal processing method executed by an FMCW radar apparatus for measuring a distance to a target and a relative velocity with respect to the target,
    A frequency bin extraction step of extracting only the complex spectrum of the frequency bin in a predetermined range from the frequency complex spectrum of the beat signal in the up-chirp period after FFT and the frequency complex spectrum of the beat signal in the down-chirp period;
    A target measurement step of measuring a distance to the target and a relative velocity with respect to the target from the frequency bin of the target in the up-chirp period and the frequency bin of the target in the down-chirp period;
    A signal processing method for FMCW radar, comprising:
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