Frequency modulation radar apparatus for vehicle use background of the invention

• US 20080122679A1
• Filed: 01/22/2007
• Published: 05/29/2008
• Est. Priority Date: 09/20/2006
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Noda, Shinsaku
• Granted Patent: US 7,432,849 B2
• Time in Patent Office: Days
• US Class Current: 342/104
• CPC Class Codes: G01S 13/34 using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
• CPC Class Codes: G01S 13/345 using triangular modulation
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/9325 for inter-vehicle distance regulation, e.g. navigating in platoons
• CPC Class Codes: G01S 7/354 Extracting wanted echo-signals Doppler systems G01S13/50
• CPC Class Codes: G01S 7/356 involving particularities of FFT processing

Abstract

A frequency modulation radar apparatus for vehicle use can suppress the influence of noise to avoid incorrect estimation due to noise thereby to provide a beat frequency with high accuracy and at high speed without increasing the frequency resolution of the beat frequency that causes an increase in an observation time. The apparatus includes a frequency correction section that calculates a corrected frequency (f_n+δ) by adding an amount of frequency correction (δ) to the frequency (f_n) of a peak signal, and a CPU that calculates a distance or a relative speed to a target object based on the corrected frequency (f_n+δ). In an FFT calculation section, the frequency (f_t) of the true peak signal is calculated based on the characteristic of a window function, and if the frequency (f_t) thus calculated is determined as an incorrect estimation, the frequency of the true peak signal is further corrected.

Claims

1. A frequency modulation radar apparatus for vehicle use which sends a transmission signal the frequency of which is frequency modulated so as to linearly rise or fall in accordance with the elapse of time, receives the signal reflected by a target object, samples a beat signal that is obtained by mixing the reception signal thus received with said transmission signal, performs a discrete frequency analysis by using a predetermined window function, extracts a peak signal from a spectrum of said beat signal obtained, and calculates a distance or a relative speed to said target object based on a frequency (f_n) of said peak signal,

said apparatus comprising:

a frequency correction section that adds an amount of frequency correction (δ

) to said frequency (f_n) of said peak signal thereby to calculate a corrected frequency (f_n+δ

); and

a CPU that calculates the distance or relative speed to said target object based on said corrected frequency (f_n+δ

);

wherein by using a strength (a_n) of said peak signal, a strength (a<sub>n−

1</sub>) of a signal of which a discrete frequency is smaller by one than that of said peak signal, a strength (a_n+1) of a signal of which a discrete frequency is larger by one than that of said peak signal, and a strength (a_max) of one of said strength (a<sub>n−

1</sub>) and said strength (a_n+1) which is not smaller than the other, said frequency correction section calculates said amount of frequency correction (δ

) based on the strength (a_n) of said peak signal, said strength (a_max) and a characteristic of said window function; and

when said strength (a<sub>n−

1</sub>) is larger than said strength (a_n+1) and said amount of frequency correction (δ

) is positive, or when said strength (a<sub>n−

1</sub>) is less than or equal to said strength (a_n+1) and said amount of frequency correction (δ

) is negative, said frequency correction section correctively sets said amount of frequency correction (δ

) to zero (δ

=0).

2. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hanning window;

and

said frequency correction section calculates said amount of frequency correction (δ

) by the following expression (1).

$\begin{array}{cc}\mathrm{\delta <br><br>}=\{\begin{array}{cc}\frac{2<br><br>a_{n+1}-a_n}{a_{n+1}+a_n}& \left(\mathrm{when}<br><br><br><br>a_{n-1}\le <br><br>a_{n+1}\right)\\ -\frac{2<br><br>a_{n-1}-a_n}{a_{n-1}+a_n}& \left(\mathrm{when}<br><br><br><br>a_{n-1}><br><br>a_{n+1}\right)\end{array}& \left(1\right)\end{array}$

3. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hamming window;

and

said frequency correction section calculates said amount of frequency correction (δ

) by the following expression (2).

$\begin{array}{cc}\mathrm{\delta <br><br>}=\{\begin{array}{cc}\frac{\left(50/29\right)<br><br>a_{n+1}-\left(21/29\right)<br><br>a_n}{a_{n+1}+a_n}& \left(\mathrm{when}<br><br><br><br>a_{n-1}\le <br><br>a_{n+1}\right)\\ -\frac{\left(50/29\right)<br><br>a_{n-1}-\left(21/29\right)<br><br>a_n}{a_{n-1}+a_n}& \left(\mathrm{when}<br><br><br><br>a_{n-1}><br><br>a_{n+1}\right)\end{array}& \left(2\right)\end{array}$

4. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hanning window;

and

said frequency correction section uses a strength (a_t) obtained by the following expression (3) as a strength of a true peak signal.

$\begin{array}{cc}{a}_t=\frac{3<br><br>\mathrm{\pi <br><br>}<br><br><br><br>a_{\max }<br><br>\left(2<br><br>a_{\max }-a_n\right)<br><br>\left(2<br><br>a_n-a_{\max }\right)}{{\left(a_{\max }+a_n\right)}^3<br><br>\sin <br><br>\left(\frac{2<br><br>a_{\max }-a_n}{a_{\max }+a_n}<br><br>\mathrm{\pi <br><br>}\right)}\times <br><br>a_n& \left(3\right)\end{array}$

5. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hanning window;

and

said frequency correction section uses a strength (a_t) obtained by the following expression (4) as a strength of a true peak signal.

a_t=0.81a_n++0.35a_max  

 

(4)

6. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hamming window;

and

said frequency correction section uses a strength (a_t) obtained by the following expression (5) as a strength of a true peak signal.

$\begin{array}{cc}{a}_t=\frac{\begin{array}{c}\left(25/29\right)<br><br>\mathrm{\pi <br><br>}<br><br>\left(79<br><br>a_{\max }+8<br><br>a_n\right)\\ \left(50<br><br>a_{\max }-21<br><br>a_n\right)<br><br>\left(50<br><br>a_n-21<br><br>a_{\max }\right)\end{array}}{\begin{array}{c}\left(a_{\max }+a_n\right)<br><br>\left(45<br><br>a_{\max }+187<br><br>a_n\right)<br><br>\left(245<br><br>a_{\max }+103<br><br>a_n\right)\\ \sin <br><br>\left\{\frac{\left(50/29\right)<br><br>a_{\max }-\left(21/29\right)<br><br>a_n}{a_{\max }+a_n}<br><br>\mathrm{\pi <br><br>}\right\}\end{array}}\times <br><br>a_n& \left(5\right)\end{array}$

7. The frequency modulation radar apparatus for vehicle use as set forth in claim 1, wherein

said window function is a Hamming window;

and

said frequency correction section uses a strength (a_t) obtained by the following approximate expression (6) as a strength of a true peak signal.

a_t=0.82a_n+0.38a_max  

 

(6)

8. A frequency modulation radar apparatus for vehicle use which sends a transmission signal the frequency of which is frequency modulated so as to linearly rise or fall in accordance with the elapse of time, receives the signal reflected by a target object, samples a beat signal that is obtained by mixing the reception signal thus received with said transmission signal, performs a discrete frequency analysis by using a predetermined window function, extracts a peak signal from a spectrum of said beat signal obtained, and calculates a distance or a relative speed to said target object based on a frequency (f_n) of said peak signal,

said apparatus comprising:

a frequency correction section that calculates a frequency (f_t) of a true peak signal; and

a CPU that calculates a distance or a relative speed to said target object based on the frequency (f_t) of said true peak signal;

wherein by using a strength (a_n) of said peak signal, a strength (a<sub>n−

1</sub>) of a signal of which a discrete frequency is smaller by one than that of said peak signal, a strength (a_n+1) of a signal of which a discrete frequency is larger by one than that of said peak signal, the frequency (f_n) of said peak signal, a frequency (f<sub>n−

1</sub>) of said signal of which the discrete frequency is smaller by one than that of said peak signal, a frequency (f_n+1) of said signal of which a discrete frequency is larger by one than that of said peak signal, a strength (a_max) of one of said strength (a<sub>n−

1</sub>) and said strength (a_n+1) which is not smaller than the other, and a frequency (f_max) corresponding to said strength (a_max), said frequency correction section calculates the frequency (f_t) of said true peak signal based on a linear combination of the frequency (f_n) of said peak signal and said frequency (f_max); and

when said strength (a<sub>n−

1</sub>) is larger than said strength (a_n+1) and the frequency (f_t) of said true peak signal is larger than the frequency (f_n) of said peak signal, or when said strength (a<sub>n−

1</sub>) is less than or equal to said strength (a_n+1) and the frequency (f_t) of said true peak signal is smaller than the frequency (f_n) of said peak signal, said frequency correction section correctively sets the frequency (f_t) of said true peak signal to the frequency (f_n) of said peak signal (f_t=f_n); and

a combination coefficient of said linear combination is determined from the strength (a_n) of said peak signal and said strength (a_max) based on a characteristic of said window function.

9. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hanning window;

and

said frequency correction section calculates the frequency (f_t) of said true peak signal by the following expression (7).

$\begin{array}{cc}{f}_t=\frac{\left(2<br><br>a_n-a_{\max }\right)<br><br>f_n+\left(2<br><br>a_{\max }-a_n\right)<br><br>f_{\max }}{a_n+a_{\max }}& \left(7\right)\end{array}$

10. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hamming window;

and

said frequency correction section calculates the frequency (f_t) of said true peak signal by the following expression (8).

$\begin{array}{cc}{f}_t=\frac{\begin{array}{c}\left\{\left(50/29\right)<br><br>a_n-\left(21/29\right)<br><br>a_{\max }\right\}<br><br>f_n+\\ \left\{\left(50/29\right)<br><br>a_{\max }-\left(21/29\right)<br><br>a_n\right\}<br><br>f_{\max }\end{array}}{a_n+a_{\max }}& \left(8\right)\end{array}$

11. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hanning window;

and

said frequency correction section uses a strength (a_t) obtained by the following expression (3) as a strength of said true peak signal.

$\begin{array}{cc}{a}_t=\frac{3<br><br>\mathrm{\pi <br><br>}<br><br><br><br>a_{\max }<br><br>\left(2<br><br>a_{\max }-a_n\right)<br><br>\left(2<br><br>a_n-a_{\max }\right)}{{\left(a_{\max }+a_n\right)}^3<br><br>\sin <br><br>\left(\frac{2<br><br>a_{\max }-a_n}{a_{\max }+a_n}<br><br>\mathrm{\pi <br><br>}\right)}\times <br><br>a_n& \left(3\right)\end{array}$

12. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hanning window;

and

said frequency correction section uses a strength (a_t) obtained by the following approximate expression (4) as a strength of said true peak signal.

a_t=0.81a_n+0.35a_max  

 

(4)

13. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hamming window;

and

said frequency correction section uses a strength (a_t) obtained by the following expression (5) as a strength of said true peak signal.

$\begin{array}{cc}{a}_t=\frac{\begin{array}{c}\left(25/29\right)<br><br>\mathrm{\pi <br><br>}<br><br>\left(79<br><br>a_{\max }+8<br><br>a_n\right)\\ \left(50<br><br>a_{\max }-21<br><br>a_n\right)<br><br>\left(50<br><br>a_n-21<br><br>a_{\max }\right)\end{array}}{\begin{array}{c}\left(a_{\max }+a_n\right)<br><br>\left(45<br><br>a_{\max }+187<br><br>a_n\right)<br><br>\left(245<br><br>a_{\max }+103<br><br>a_n\right)\\ \sin <br><br>\left\{\frac{\left(50/29\right)<br><br>a_{\max }-\left(21/29\right)<br><br>a_n}{a_{\max }+a_n}<br><br>\mathrm{\pi <br><br>}\right\}\end{array}}\times <br><br>a_n& \left(5\right)\end{array}$

14. The frequency modulation radar apparatus for vehicle use as set forth in claim 8, wherein

said window function is a Hamming window;

and

said frequency correction section uses a strength (a_t) obtained by the following approximate expression (6) as a strength of said true peak signal.

a_t=0.82a_n+0.38a_max  

 

(6)