JP2017058324A - Target information measuring device and target information measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring device capable of separating a plurality of targets of a same speed using a narrow band RF signal and a BB signal to detect each target distance.SOLUTION: A target information measuring device detects a Doppler frequency contained in a reflection wave when a transmission wave of a prescribed frequency is radiated onto a plurality of targets to obtain a distance from the target, and sets the number M of frequency so that the number N (N is a positive integer of 1 or more) of frequency satisfies a relation N≥M+1 when the number of the target is M (M is a positive integer of 1 or more).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a target information measuring apparatus and a target information measuring method for measuring target information such as a distance to a target and a relative speed.

  The in-vehicle radar emits radio waves toward a target such as another vehicle or an obstacle, and receives a reflected wave reflected by the target. Then, the presence of the target, the distance to the target (target distance), and the relative speed of the target are measured by analyzing the received signal by the received wave. Hereinafter, the presence of the target, the target distance, and the relative speed of the target are collectively referred to as target information.

  Such an on-vehicle radar is used as a system for improving driving safety of an automobile such as a collision mitigation (brake) system or a preceding vehicle following system. At this time, it is important to improve the detection resolution of the target in order to improve reliability and driving safety.

  In general, the detection resolution in the distance direction is improved by broadening the RF signal and baseband signal (BB signal) used as the basis of the radiated radio wave. However, it is desirable to reduce the bandwidth of the RF signal and the baseband signal (BB signal) while improving the detection resolution. This is because by narrowing the signal bandwidth, circuit design with the required detection resolution can be facilitated, and the system cost can be reduced. Furthermore, if a desired detection resolution can be obtained with a narrow RF signal bandwidth, the number of channels that can be used increases, so there is an advantage that radio wave interference between in-vehicle radars is suppressed.

  As such an on-vehicle radar, FMCW (Frequency Modulated Continuous Wave) radar, pulse radar, and pulse compression radar are known. Also, a multi-frequency CW radar using a continuous wave (CW: Continuous Wave) that switches the frequency in time, or a multi-frequency ICW (Interrupted Continuous Wave) radar that combines a multi-frequency CW radar system and a pulse radar system (see Non-Patent Document 1). ) Has been proposed. Furthermore, a multi-frequency CPC (Complementary Phase Code) radar system (see Non-Patent Document 2) that combines a multi-frequency CW radar system and a pulse compression radar system has been proposed.

Here, the bandwidth of the RF signal and BB signal required in various vehicle-mounted radars will be examined. 5, by using the RF signal of frequency f _c is 60.5 [GHz], is a diagram summarizing the bandwidth of the RF signal and BB signal required in detecting the target at a predetermined detection resolution. The target is located in front of the on-vehicle radar, the target distance R is R = 50 [m], and the speed V is V = 30 [km / h]. The distance resolution ΔR is set to ΔR = 0.3 [m], and the speed resolution ΔV is set to ΔV = 0.3 [km / s].

  In FIG. 5, the signal bandwidth in each of the FM-CW method, the two-frequency CW method, the pulse method, and the pulse compression method was calculated from the formula (see Non-Patent Document 3) shown in the lower column of each method. In addition, the value of the signal bandwidth in the multi-frequency CPC method refers to the actual measurement value in Non-Patent Document 2. In the two-frequency CW method, the number of frequencies used in the multi-frequency CW method is two.

  From FIG. 5, it can be seen that the two-frequency CW method that can suppress both the bandwidth of the RF signal and the BB signal is effective in order to achieve the desired distance resolution ΔR.

  Note that both the FM-CW system and the pulse / pulse compression system require a wide RF signal bandwidth given by c / (2ΔR). Here, c is the speed of light, and ΔR is the distance resolution. In addition, the multi-frequency CPC method is a method in which the multi-frequency CW method and the pulse compression method are combined. However, the RF signal bandwidth of the same level as the pulse compression used for the combination is still required.

  The two-frequency CW method (or the multi-frequency CW method) has an advantage that both the bandwidth of the RF signal and the BB signal can be suppressed. However, when there are a plurality of targets having the same speed as the in-vehicle radar, there is a problem that each target cannot be individually recognized (target information corresponding to each target cannot be acquired).

  The problem in the two-frequency CW method will be described with reference to the block diagram of the on-vehicle radar in the two-frequency CW method shown in FIG. 6 (see Non-Patent Document 3).

First, the calculation principle of the target distance will be described. FIG. 6 is a block diagram of a two-frequency CW in-vehicle radar. This in-vehicle radar includes at least an antenna 101, an isolator 102, a mixer 103, a low-pass filter (LPF) 104, an oscillator 105, an analog-digital (A / D) converter 106, a Fourier transform unit 107, a calculator 109, and a controller 110. It is configured to include. Incidentally, the Fourier transform unit 107 is provided with two of Fourier transformer 108 ₁ and Fourier transformer 108 _2.

Then, as shown in FIG. 7, the oscillator 105 switches the RF signals (transmission signals) of the two transmission frequencies f ₁ and f ₂ in accordance with instructions from the controller 110 and outputs them to the isolator 102 and the mixer 103. In FIG. 7, Tc is a period.

  The RF signal output from the oscillator 105 to the isolator 102 is output as a transmission wave Wt via the antenna 101. This transmission wave Wt is reflected by the target T and received by the antenna 101 as a reception wave Wr.

The frequency of the reception wave Wr is subjected to the Doppler effect by the target T having the relative velocity V, and is shifted by the Doppler frequency f _d (= 2V / λ, λ is the wavelength of the transmission wave Wt) with respect to the frequency of the transmission wave Wt (Doppler). shift.

The received wave Wr received by the antenna 101 is input to the mixer 103 via the isolator 102. The mixer 103 mixes the transmission signals of the transmission frequencies f ₁ and f ₂ and the reception signals of the reception frequencies f ₁ + f _d and f ₂ + f _d from the oscillator 105, and sends them to the A / D converter 106 via the BPF 104. Output. A signal input to the A / D converter 106 is referred to as a beat signal. The frequency of the beat signal is, the Doppler frequency f _d.

When the beat signal when the transmission frequency of the RF signal output from the oscillator 105 is f ₁ and f ₂ is S _f1 (t) and S _f2 (t) and the indefinite constant of the in-vehicle radar is φ ₀ , the beat signal S _f1 (t) and S _f2 (t) are
S _f1 (t) ∝cos [2πf _d t−4πf ₁ R / c + φ ₀ ] (1)
S _f2 (t) ∝cos [2πf _d t−4πf ₂ R / c + φ ₀ ] (2)
Are given by Equations 1 and 2.

  The beat signal is converted into a digital signal by the A / D converter 106 and input to the Fourier transform unit 107, and the spectrum phase is obtained by the Fourier transform unit 107.

When the frequency of the transmission wave Wt is f ₁ , the Fourier transformer 108 ₁ calculates the spectrum phase φ ₁ (= φ ₀ −4πf ₁ R / c) of the reception wave Wr. Further, when the frequency of the transmission wave Wt is f ₂ , the spectrum phase φ ₂ (= φ ₀ −4πf ₂ R / c) of the reception wave Wr is calculated by the Fourier transformer 108 ₂ .

The Fourier transformers 108 ₁ and 108 ₂ used for the calculation of the spectrum phase are selected in synchronization with the frequency switching timing signal of the RF signal (transmitted wave Wt) output from the controller 110 to the oscillator 105, and the Fourier transform unit. This is performed based on the instruction output to 107.

The computing unit 19 calculates the difference Δφ between the spectrum phases φ ₁ and φ ₂ of the beat signals S _f1 (t) and S _f2 (t) as follows:
Δφ = φ ₁ −φ ₂
Therefore, using this, the target distance R is
R = cΔφ / 4π (f ₂ −f ₁ ) (3)
It calculates with the formula 3 of.

Next, based on such a target distance calculation principle, consider a case where _two targets T ₁ and T ₂ are detected simultaneously as shown in FIG. At this time, the relative speeds of the _two targets T ₁ and T ₂ are set to V ₁ and V ₂ , respectively.

The beat signal output from the BPF 104 is a superposition of the beat signal S _{1 from the} target T ₁ included in the received wave Wrni and the beat signal S _{2 from the} target T ₂ (S = S ₁ + S ₂ ). The frequencies of the beat signals S ₁ and S ₂ are Doppler frequencies f _d1 = 2V ₁ / λ and f _d2 = 2V ₂ / λ, respectively. That is, when the targets T ₁ and T ₂ are detected at the same time, the spectrum of the beat signal is in a state in which two spectra consisting of the beat signals S ₁ and S ₂ stand as shown in FIG.

At this time, when the speeds V ₁ and V ₂ are different between the _two targets T ₁ and T ₂ (V ₁ ≠ V ₂ ), the Doppler frequencies f _d1 = 2V ₁ / λ and f _d2 = of the beat signals S ₁ and S ₂ 2V ₂ / λ is also a different value (f _d1 ≠ f _d2 ). Therefore, as shown in FIG. 9, the spectrums of the beat signals S ₁ and S ₂ are observed as spectra having different frequencies, so that the spectrum phases of the beat signals S ₁ and S ₂ can be obtained separately. Therefore, the target distances of the targets T ₁ and T ₂ can be calculated individually from the detected spectral phase and Equation 3.

On the other hand, when the speeds V ₁ and V _{2 of} the targets T ₁ and T ₂ are the same (V ₁ = V ₂ ), the frequencies f _d1 = 2V ₁ / λ and f _d2 = 2V ₂ / λ of the beat signals S ₁ and S ₂ Also have the same value (f _d1 = f _d2 ). Therefore, as shown in FIG. 10, the spectrums of the beat signals S ₁ and S ₂ have the same frequency, and the spectrum phases of the beat signals S ₁ and S ₂ cannot be detected separately. Therefore, there arises a problem that the target distances of the targets T ₁ and T ₂ cannot be calculated individually.

  As a method for solving such problems of the two-frequency CW method, Patent Document 1 proposes a method combining the multi-frequency CW method and the pulse method (equivalent to the multi-frequency CPC method).

JP 2009-244136 A Japanese Patent Laid-Open No. 2003-167048 JP 2009-42061 A

Takayuki Inaba, “Multi-target separation method by multi-frequency step ICW radar”, IEICE Transactions B, Vol. J89-B, no. 3, pp. 373-383, 2006 Masato Watanabe, Manabu Akita, Takayuki Inaba, “Millimeter Wave Radar using Stepped Frequency Complementary Phase Code Modulation”, TOS WOR G Tetsuro Kirimoto, “Fundamentals of Automotive Radar” MWE 2007 Digest, 2007

  However, in the configuration according to Patent Document 1 described above, since the RF signal and the BB signal have a wide band by using the pulse signal, there is a problem that the circuit design becomes difficult and the system cost increases.

  Further, Patent Document 2 uses a normal two-frequency CW waveform as a transmission wave to mix a reception wave and a high-speed sawtooth wave, thereby separately detecting a plurality of targets having the same speed. Wave) has the advantage that it can be narrow. However, since the bandwidth of the BB signal becomes wide due to the influence of the sawtooth wave, there is a problem that circuit design becomes difficult and system cost increases.

  In Patent Document 3, the transmission frequency of the transmission radio wave is switched at a timing synchronized with the sample frequency of A / D conversion. However, even in this method, there is a problem that the RF signal has a wide band. In Patent Document 3, the bandwidth of the RF signal is 1 [GHz].

  Therefore, a main object of the present invention is to provide a target information measuring apparatus and a target information measuring method capable of separately detecting a plurality of targets having the same speed using narrow band RF signals and BB signals.

To solve the above problem,
The invention according to the target information measuring apparatus for detecting the Doppler frequency included in the reflected wave when a plurality of targets are irradiated with a transmission wave having a predetermined frequency and determining the distance to the target is provided with the number of targets M (M is 1). The number M of frequencies is set so that the number N of frequencies (N is a positive integer greater than or equal to 1) satisfies the relationship N ≧ M + 1. .

  Further, the invention relating to the target information measuring method for detecting the Doppler frequency included in the reflected wave when a plurality of targets are irradiated with the transmission wave of the predetermined frequency and obtaining the distance to the target is provided with M (M Is a positive integer greater than or equal to 1), the number of frequencies M is set so that the number N of frequencies (N is a positive integer greater than or equal to 1) satisfies the relationship N ≧ M + 1. And

According to the present invention, it is possible to separately detect target distances of a plurality of targets having the same speed by using narrow-band RF signals and BB signals at low cost without performing complicated circuit design.

It is a block diagram of the target information measuring device concerning an embodiment. It is the figure which illustrated the oscillation frequency in an oscillator. It is the flowchart which showed the procedure which calculates | requires the actual number of targets in hypothetical target number reduction mode. It is the flowchart which showed the procedure which calculates | requires the actual number of targets in the assumption target number increase mode. It is the figure which put together the bandwidth of RF signal and BB signal which are required when detecting the target applied to description of related technology with predetermined detection resolution. It is a block diagram of the vehicle-mounted radar in a 2 frequency CW system applied to description of related technology. It is the figure which illustrated RF signal of two oscillation frequencies applied to explanation of related technology. It is a block diagram of the vehicle-mounted radar in the case of detecting simultaneously two targets applied to description of related technology. It is the figure which illustrated two spectra of a different frequency applied to description of related technology. It is the figure which illustrated two spectra of the same frequency applied to description of related technology.

  An embodiment of the present invention will be described. FIG. 1 is a block diagram of a target information measuring apparatus 2 according to the embodiment. The target information measuring device 2 includes at least an antenna 11, an isolator 12, a mixer unit 13, an oscillator 15, a Fourier transform unit 17, a calculator 19, and a controller 20. The mixer unit 13 includes a mixer 13a, a bandpass filter (BPF) 13b, and an analog-digital (A / D) converter 13c.

The target T is composed of M targets T _{1 to} T _M , and each target T is moving at the same speed. In FIG. 1, the target T is also illustrated, but it is added that the target T does not constitute the target information measuring device 2.

  Then, the target information measuring device 2 identifies a plurality of targets T and acquires target information for each target. The target information is a term that collectively refers to the presence of the target, the target distance, and the relative speed of the target.

Thus, in order to acquire the target information of the plurality of targets T, the Fourier transform unit 17 is configured by _N Fourier transformers 18 ₁ to 18 _N. In the following, each of the Fourier transformers 18 ₁ to 18 _N is different only in the frequency of the signal to be processed, and therefore the common description may be described as the Fourier transformer 18 or the Fourier transformer 18 _i .

The oscillator 15 outputs RF signals (transmission signals) G3 having _N transmission frequencies f _{1 to} f _N. FIG. 2 is a diagram illustrating transmission frequencies f _{1 to} f _N in the oscillator 15. Again, there may be described the oscillation frequency _f 1 ~f _N and oscillation frequency f or transmission frequency _{f i.}

  The number M of the targets T, the number N of the Fourier transformers 18 and the number N of the frequencies of the transmission frequency f are positive integers of 1 or more, and it is required to satisfy the relationship of N ≧ M + 1 as will be described later. Is done.

The controller 20 outputs a frequency switching command G1 to the oscillator 15, and outputs an FET switching command G2 to the Fourier transform unit 17 in synchronization with the frequency switching command G1. As a result, the oscillator 15 outputs the transmission signal G3 having the transmission frequencies f _{1 to} f _N specified by the frequency switching command G ₁ to the isolator 12 and the mixer unit 13. Further, the Fourier transform unit 17, selects the Fourier transformer ₁₈ 1 ~ 18 _N corresponding to the oscillation frequency _f 1 ~f _N specified in the FET switching command G2, the selected the Fourier transformer ₁₈ 1 ~ 18 _N Performs the FFT conversion process.

  The target information measuring apparatus 2 having such a schematic configuration operates as follows. First, the transmission signal G3 output from the oscillator 15 to the isolator 12 is irradiated from the antenna 11 toward the target T as the transmission wave Wt. The irradiated transmission wave Wt is reflected by the target T and received by the antenna 11 as a reception wave Wr.

When the transmission wave Wt is reflected by the target T, it is modulated by the Doppler effect. That is, the target _T 1 through T _M of the speed _V 1 ~V _M, oscillation frequency of the received wave Wr is the Doppler frequency _f d1 with respect to the frequency of the transmission wave _{Wt (= 2V 1 / λ)} ~ff dM (= 2V _The frequency is Doppler shifted by _M / λ).

  The received wave Wr is received by the antenna 11 and input to the mixer unit 13 via the isolator 12 as a received signal. The mixer unit 13 mixes the reception signal and the transmission signal, and outputs the result to the A / D converter 13c as a beat signal via the BPF 104.

When the frequency of the transmission signal G3 is f _i (i = 1 to N), the beat signal S _M (t, f _i ) is
S _M (t, f _i ) = ΣB _j (4)
Given in. Note that Σ means the sum between 1 and M for j. Where B _j is
B _j = A _j · sin [2πf _dj t + φ ₀ -4πf _i R _j / c]
It is. B _j is a beat signal of the received signal by the received wave Wr reflected by each target T _j . That is, the beat signal S _M (t, f _i ) in Expression 4 is the sum of the beat signals based on the received signals from the respective targets T. R _j is the target distance of each target T _j , A _j is the amplitude of the beat signal obtained from the received signal from the target T _j , and φ ₀ is an indefinite constant.

The beat signal is converted into a digital signal by the A / D converter 13c, and an FFT conversion process is performed by the Fourier transform unit 17 to calculate a spectrum phase. At this time, controller 20, when instructed to output the oscillation frequency f _i the frequency switching command G1 relative to oscillator 15, the Fourier transform corresponding to the oscillation frequency f _i for the Fourier transform unit 17 The unit 18 _i is instructed to perform the FFT conversion process.

The computing unit 19 calculates the target distance R _i using the spectral phase calculated by the Fourier transformer 18 _i .

Next, the procedure for calculating the target distance will be described. For simplicity of explanation, two targets T ₁ and T ₂ having the same speed are considered.

In this case, the Doppler frequencies by the targets T ₁ and T ₂ are f _d1 and f _d2 , and these are f _d1 = f _d2 (≡f _d ). Therefore, the beat signal S _M (t, f _i ) shown in Equation 4 is
S ₂ (t, f _i ) = B ₁ + B ₂ (5)
Is given by Equation 5. Where B ₁ and B ₂ are
B ₁ = A ₁ · sin [2πf _d t + φ ₀ -4πf _i R ₁ / c]
B ₂ = A ₂ · sin [2πf _d t + φ ₀ -4πf _i R ₂ / c]
It is.

When this beat signal S ₂ (t) is transformed,
S ₂ (t, f _i ) = A ₁₂ (f _i ) · sin [2πf _d t + Φ ₁₂ (f _i )] (6)
It becomes. Where {A ₁₂ (f _i )} ² and Φ ₁₂ (f _i ) are
^{_{{A 12 (f i)}}} 2 = A 1 2 + A 2 2 + 2A 1 A 2 cos [K · f i (R 2 -R 1)] ... (7)
_{Φ 12 (f i) ≡φ 0} -K · f i · R 1 + tan -1 [X (A 1, A 2, R 1, R 2, f i)] ... (8)
It is.

K is a constant,
K≡4π / c (9)
And the function X (A ₁ , A ₂ , R ₁ , R ₂ , f _i ) is
X (A ₁ , A ₂ , R ₁ , R ₂ , f _i ) ≡A ₂ · sin (K · f _i (R ₂ −R ₁ )) / [A ₁ + A ₂ · cos (K · f _i (R _{2 -R 1))] ... (} 10)
Given in.

If each target T ₁ , T ₂ has the same speed, from Equation 6, the beat signal S ₂ (t, f _i ) will contain only a single Doppler frequency f _d .

The amplitude A ₁₂ (f _i ) and the phase Φ ₁₂ (f _i ) of the beat signal expressed by the equations 6 to 8 are values based on the observation result, and the transmission frequency f _{i of the} transmission signal G 3 output from the oscillator 15. When changing, each takes a different value.

In the case of _N transmission frequencies f _{1 to} f _N , Expressions 7 and 8 each have N expressions. Therefore, the total number of expressions is 2N. The unknowns contained in Equations 7 and _{8, A 1, A 2, φ} 0, R 1, a total of five _{R 2.} Therefore, if the number of frequencies N is one more than the number of targets M (= 2) (N ≧ M + 1), the number of equations (= 2N ≧ 2 (M + 1) = 6) will be greater than the number of unknowns. The unknowns A ₁ , A ₂ , φ ₀ , R ₁ , R ₂ included in Equations 7 and 8 can be determined (ie, simultaneous equations of Equations 7 and 8 can be solved).

As a result, the target distances R ₁ and R ₂ of the _two targets T ₁ and T ₂ that move at the same speed can be separated (identified) and calculated.

  Next, a case where there are a plurality of targets having the same speed will be described.

When the targets T _{1 to} T _M have the same speed, the Doppler frequencies included in the beat signal shown in Expression 4 are all equal (f _d1 = f _d2 =... = F _dM ≡f _d ).

That is, the beat signal of Equation 4 is the sum of M components having the same Doppler frequency f _d ,
S _M (t, f _i ) = A _{12... M} (f _i ) · sin [2πf _d t + Φ _{12... M} (f _i )] (11)
Given in.

Also, the beat signal of Equation 4 is
S _M (t, f _i ) = S _(M−1) (t, f _i ) + A _M · sin [2πf _d t + φ ₀ −4πf _i R _M / c] (12)
S _(M-1) (t, f _i ) = A _{12 (M−1)} (f _i ) · sin [2πf _d t + Φ _{12 (M−1)} (f _i )] (13)
Can be expressed inductively.

The amplitude and phase of the beat signal S _M (t, f _i ) when there are M targets T, and the beat signal S _(M−1) (t, f) when there are (M−1) targets T. The relationship between the amplitude and phase of f _i ) is
{A _{12... M} (f _i )} ² = {A _{12... (M−1)} (f _i )} ² +
A _M ² + 2A _{12 (M−1)} (f _i ) · A _M cos [α (Φ _{12 (M−1)} (f _i ), R _M , f _i , φ ₀ )] (14)
Φ _{12... M} (f _i ) = Φ _{12... (M−1)} (f _i ) + tan ⁻¹ [β (A _{12... (M−1)} (f _i ), A _M , R _M , f _i , φ ₀ )] ... (15)
Given in.

here,
α (Φ _{12... (M−1)} (f _i ), R _M , f _i , φ ₀ ) = φ ₀ −4π f _i R _M / c + Φ _{12 (M−1)} (f _i ) (16)
β (A _{12... (M−1)} (f _i ), A _M , R _M , f _i , φ ₀ ) = A _M · sin (α (Φ _{12... (M−1)} (f _i ), R _{M , f i, φ 0))} / [A 12 ... (M-1) (f i) + A M · cos (α (Φ 12 ... (M-1) (f i), R M, f i, φ 0 ))] ... (17)
It is.

By applying an induction method for the number of targets M to the equations 14 to 17, the amplitudes A _{12... M} (f _i ) and the phases Φ _{12... M} (f _i ) of the beat signal are amplitudes A _{1 to} A _M. , Phase φ ₀ , and simultaneous equations expressed by target distances R _{1 to} R _M.

Here, the amplitudes A _{12... M} (f _i ) and the phases Φ _{12... M} (f _i ) of the beat signal are known variables obtained by measurement. In addition, the amplitudes A _{1 to} A _M , the phase φ ₀ , and the target distances R _{1 to} R _M are unknown variables.

When the number of transmission frequencies f _i is N, the amplitudes A _{12... M} (f _i ) and the phases Φ _{12... M} (f _i ) of the beat signal have amplitudes A _{1 to} A _M , phase φ ₀ , and target. The total number of equations expressed by the distances R _{1 to} R _M is 2N.

On the other hand, unknown variables are amplitudes A _{1 to} A _M , phase φ ₀ , target distances R _{1 to} R _M , and the total number is 2M + 1.

Therefore, if the number N of transmission frequencies is set to M + 1 or more (M is the number of targets), 2N simultaneous equations can be solved and desired target distances R _{1 to} R _M can be calculated.

  Thus, the number N of transmission frequencies to be used for measurement depends on the number M of targets. Therefore, it is necessary to determine the number of targets.

As a method of determining the target number M, was measured on assuming the target number M in advance, a method may be mentioned that the measurement is repeated by changing the target number M _A which is assumed according to the measurement results.

Specifically, as equations for calculating the target distance, Expressions 14 to 17 are used, and 2M _A +1 unknown variables [amplitude A _{1 to} A _MA , phase φ ₀ , target distance R _{1 to} R _MA ] are assumed. Establish the equation.

In order to solve this equation, the amplitude A _{12... M} (f _i ) and the phase Φ _{12... M} (f _i ) of the beat signal at N = M _A +1 transmission frequencies f _i (i = 1 to N). To calculate the target distances R _{1 to} R _MA .

In this case, it assumed target number M _A is, if the actual larger than the target number M is, shall take the same value among the calculated target distance R ₁ to R _MA appear at least two. That is, since the target distance is calculated based on a larger number of equations than the actual number of targets, there are cases where a plurality of equations are solved for the same target, and the solution (target distance) of this duplicated equation has the same value. It is to become.

In this way, it cannot be determined whether or not the assumed number of targets matches the actual number of targets.
That is, there are two cases of (a) N _assum ≤ N _real and (b) N _assum ≥ N _{real in} the assumed target number N _assum and the actual target number N _real .

Therefore, “when two or more of the calculated target distances R _{1 to} R _MA that have the same value do not appear, a process of determining that the assumed target number N _assum indicates the actual target number N _real is performed. (Appropriate target number judgment process).

  3 and 4 are flowcharts showing the appropriate target number determination processing. The appropriate target number determination process is performed by the operator 19, but may be performed by a system control unit (not shown).

The main flow of the appropriate target number determination process assumes an assumed target number N _assum and performs a calculation cycle for calculating the target distance of each target at that time. Then, the calculation cycle is repeated by changing the assumed target number N _assum until there is no target distance of the same value. The assumed target number N _assum obtained in this way is set as the actual target number N _real .

  Whether or not to perform the calculation cycle is determined based on whether or not a target distance having the same value exists. However, the target distance of the same value is not exactly the same value, and is the same value within the range of distance resolution.

At this time, the processing is different between (A) N _assum ≧ N _real (assumed target number decrease mode) and (B) N _assum ≦ N _real (assumed target number increase mode). Figure 3 shows the procedure for obtaining the actual target number N _real in assuming the target number reducing mode, Figure 4 shows a procedure for determining the actual target number N _real in assuming the target number increasing mode.

(A) When N _assum ≥ N _real (assumed target number reduction mode)
Steps SA1 and SA2: First, the number of targets is assumed, and this is set as the assumed number of targets N _assum . Thereafter, each target distance is calculated according to the above-described equation using the set assumed target number N _assum .

  Step SA3: Next, it is determined whether or not the calculated target distances have the same value. If there is a target distance having the same value, the process proceeds to step SA4, and if there is no target distance having the same value, the process proceeds to step SA5.

Step SA4: If the calculated target distances have the same value, the calculation cycle is repeated while reducing the assumed target number N _assum by “1”.
Step SA5: By repeating the calculation cycle, the assumed target number N _assum may become equal to the actual target number N _real . Therefore, the assumed target number N _assum at this time is set as the actual target number N _real .

(B) When N _assum ≦ N _real (assumed target number increase mode)
Steps SB1, SB2: First, the number of targets is assumed, and this is set as the assumed number of targets N _assum . Thereafter, each target distance is calculated according to the above-described equation using the set assumed target number N _assum .

  Step SB3: Next, it is determined whether or not the calculated target distances have the same value. If the target distance has the same value, the process proceeds to step SB4. If the target distance has the same value, the process proceeds to step SB5.

Step SB4: If the calculated target distances do not have the same value, the calculation cycle is repeated while increasing the assumed target number N _assum by “1”.

Step SB5: By repeating the calculation cycle, there is a case where the calculated target distances have the same value. Since the assumed target number N _{assum in} this case is “1” more than the actual target number N _real , the assumed target number N _assum −1 is set as the actual target number N _real .

  With the configuration described above, when N oscillation frequencies are used, the bandwidth of the transmission wave Wt is N times that in the case of the two-frequency CW method in the known technology, and the number of targets is approximately several.

  In contrast to the conventional two-frequency CW transmission signal G3 bandwidth (1.4 MHz) shown in FIG. 5, in the method according to this embodiment, the bandwidth of the transmission wave Wt is estimated to be about several MHz. The signal bandwidth is also estimated to be about several MHz.

On the other hand, in the methods according to Patent Documents 1 to 3, the bandwidth of the transmission signal G3 and the bandwidth of the baseband signal are wide.
For example, when a multi-frequency CW method and a pulse method are combined in Patent Document 1, a method using a time waveform for a radar (equivalent to the multi-frequency CPC method), the band of a transmission signal or baseband signal as shown in FIG. The width is as wide as several hundred MHz.
Further, the method according to Patent Document 2 uses a normal two-frequency CW waveform for the transmission wave, and the reception unit mixes the reception wave and the high-speed sawtooth wave. Therefore, the bandwidth of the BB signal (reception unit) is a sawtooth wave. It becomes a wide band by the influence of.

  Furthermore, in the method according to Patent Document 3, since the transmission frequency of the transmission radio wave is switched at a timing synchronized with the sample frequency of A / D conversion, the bandwidth of the transmission signal is as wide as 1 GHz.

  Therefore, in the method according to the present embodiment, a plurality of targets having the same speed can be separated and detected with a narrow band transmission signal and a base signal as compared with the known method described above.

As a result, circuit design becomes easier and system cost can be reduced compared with the known method, and the problem of the decrease in spectrum efficiency and the interference caused by the wider bandwidth of the transmission signal, which was a problem with the known method, is avoided. You can enjoy the effect that you can.

  While the present invention has been described with reference to the embodiments (and examples), the present invention is not limited to the above embodiments (and examples). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

2 Target Information Measuring Device 11 Antenna 12 Isolator 13 Mixer Unit 13a Mixer 13c Digital A / D Converter 15 Oscillator 17 Fourier Transform Unit 18 (18 ₁ to 18 _N ) Fourier Transformer 19 Arithmetic Unit 20 Controller

Claims (10)

A target information measuring device for detecting a Doppler frequency included in a reflected wave when a plurality of targets are irradiated with a transmission wave of a predetermined frequency and obtaining a distance from the target,
When the number of targets is M (M is a positive integer greater than or equal to 1), the frequency of the transmission wave is such that the number N of frequencies (N is a positive integer greater than or equal to 1) satisfies the relationship N ≧ M + 1. The target information measuring device characterized in that the number M is set. The target information measuring device according to claim 1,
An oscillator that receives a frequency switching command, oscillates a signal of a frequency specified by the frequency switching command, and outputs the signal as a transmission wave signal;
An antenna that irradiates the transmission wave by the transmission wave signal to the target, receives a reflected wave from the target, and uses this as a reception signal;
A mixer for mixing the transmission signal and the reception signal to output a digital beat signal;
A Fourier transform unit that includes M Fourier transformers, receives an FFT switching command, selects the Fourier transformer corresponding to the frequency indicated by the FFT switching command, and obtains the spectral phase of the beat signal;
An arithmetic unit that calculates at least a relative distance to the target using the spectral phase from the Fourier transform unit;
A controller that outputs the frequency switching command to the oscillator and outputs the FFT switching command to the Fourier transform unit in synchronization with the frequency switching command;
A target information measuring device comprising: The target information measuring device according to claim 2,
The computing unit performs a calculation cycle that calculates the distance to each target as a target distance, assuming the number of targets as an assumed target number,
When the target distance of the same value exists in the target distance calculated at that time, the calculation cycle is performed while reducing the number of assumed targets by one until the target distance of the same value does not exist,
The target information measuring apparatus characterized in that the assumed target number when the target distance having the same value as the target distance no longer exists is the actual number of the targets. The target information measuring device according to claim 2,
The computing unit performs a calculation cycle that calculates the distance to each target as a target distance, assuming the number of targets as an assumed target number,
When the target distance having the same value does not exist in the target distance calculated at that time, the calculation cycle is performed while increasing the number of assumed targets by one until the target distance having the same value exists. And
A target information measuring apparatus characterized in that a value obtained by subtracting one from the assumed target number when the target distance having the same value as the target distance no longer exists is used as the actual target number. The target information measuring device according to claim 2,
The arithmetic unit takes in image data obtained by photographing the target, analyzes the image data, counts the number of targets, and calculates the number of targets. A target information measuring method for detecting a Doppler frequency included in a reflected wave when a plurality of targets are irradiated with a transmission wave of a predetermined frequency and obtaining a distance from the target,
When the number of targets is M (M is a positive integer greater than or equal to 1), the frequency of the transmission wave is such that the number N of frequencies (N is a positive integer greater than or equal to 1) satisfies the relationship N ≧ M + 1. A target information measuring method characterized in that the number M is set. The target information measuring method according to claim 6,
Receives the frequency switching command, oscillates the signal of the frequency specified by the frequency switching command, outputs this as a transmission wave signal,
While irradiating the target with the transmission wave according to the transmission wave signal, receiving a reflected wave from the target, this as a reception signal,
Mixing the transmission signal and the reception signal to output a digital beat signal,
Including M Fourier transformers, receiving an FFT switching command, selecting the Fourier transformer corresponding to the frequency indicated by the FFT switching command to determine the spectral phase of the beat signal,
Using the spectral phase, calculate at least the relative distance to the target,
Outputting the frequency switching command and outputting the FFT switching command in synchronization with the frequency switching command;
A method for measuring target information. The target information measuring method according to claim 7,
Assuming the number of targets as the assumed target number, performing a calculation cycle to calculate the distance to each target as the target distance,
When the target distance of the same value exists in the target distance calculated at that time, the calculation cycle is performed while reducing the number of assumed targets by one until the target distance of the same value does not exist,
The target information measurement method, wherein the number of assumed targets when the target distance having the same value as the target distance no longer exists is set as the actual number of targets. The target information measuring method according to claim 7,
Assuming the number of targets as the assumed target number, performing a calculation cycle to calculate the distance to each target as the target distance,
When the target distance having the same value does not exist in the target distance calculated at that time, the calculation cycle is performed while increasing the number of assumed targets by one until the target distance having the same value exists. And
A target information measuring method, wherein a value obtained by subtracting one from the assumed target number when the target distance having the same value as the target distance no longer exists is used as the actual target number. The target information measuring method according to claim 7,
A method for measuring target information, comprising: capturing image data obtained by photographing the target, analyzing the image data, counting the number of targets, and calculating the number of targets.

Images