DSSS radar, method implemented by radar and computer-readable storage medium

• US 20080316090A1
• Filed: 03/13/2008
• Published: 12/25/2008
• Est. Priority Date: 03/16/2007
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Shirakawa, Kazuo
• Granted Patent: US 7,812,761 B2
• Time in Patent Office: Days
• US Class Current: 342/195
• CPC Class Codes: G01S 13/325 using transmission of coded signals, e.g. P.S.K. signals
• CPC Class Codes: G01S 13/584 adapted for simultaneous range and velocity measurements
• CPC Class Codes: G01S 7/352 Receivers
• CPC Class Codes: G01S 7/356 involving particularities of FFT processing
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A DSSS (Direct Sequence Spectrum Spreading) radar has a transmitting part to transmit a transmitting signal, including a predetermined code sequence, to one or a plurality of targets, a receiving part to receive a received signal corresponding to the transmitting signal which has been reflected from the one or a plurality of targets, and a computing part. The computing part computes a sum signal and a difference signal of received signals received by the receiving part at different points in time, and obtains a Doppler frequency of the one or a plurality of targets based on a phase difference between the sum signal and the difference signal.

Claims

1. A DSSS (Direct Sequence Spectrum Spreading) radar comprising:

a transmitting part configured to transmit a transmitting signal, including a predetermined code sequence, to one or a plurality of targets;

a receiving part configured to receive a received signal corresponding to the transmitting signal which has been reflected from said one or a plurality of targets; and

a computing part configured to compute a sum signal and a difference signal of received signals received by the receiving part at different points in time, and to estimate a Doppler frequency of said one or plurality of targets based on a phase difference between the sum signal and the difference signal.

2. The DSSS radar as claimed in claim 1, wherein the different points in time are separated by a time amounting to one or more period of the predetermined code sequence.

3. The DSSS radar as claimed in claim 1, wherein the computing part estimates the Doppler frequency by setting an imaginary part of a value, which is obtained by dividing the difference signal by the sum signal, to an argument of an arctangent function.

4. The DSSS radar as claimed in claim 1, wherein the computing part estimates the Doppler frequency by setting an imaginary part of a value, which is obtained by dividing the sum signal by the difference signal, to an argument of an arccotangent function.

5. The DSSS radar as claimed in claim 1, wherein the computing part estimates the Doppler frequency by a linear combination of an arctangent function having an argument set to an imaginary part of a value, which is obtained by dividing the difference signal by the sum signal, and an arccotangent function having an argument set to an imaginary part of a value, which is obtained by dividing the sum signal by the difference signal.

6. The DSSS radar as claimed in claim 1, wherein each of the received signals received at the different points in time is derived by averaging a plurality of reception samples.

7. The DSSS radar as claimed in claim 1, further comprising:

a deriving part configured to compute a correlation between the received signal and the predetermined code sequence, and to derive a synchronization timing for each of said one or plurality of targets.

8. The DSSS radar as claimed in claim 7, wherein the computing part computes the sum signal and the difference signal of received signals received by the receiving part at different points in time, with respect to each of said one or plurality of targets, and estimates a Doppler frequency of each of said one or plurality of targets based on the phase difference between the sum signal and the difference signal.

9. The DSSS radar as claimed in claim 3, wherein the computing part estimates the Doppler frequency by computing an inverse trigonometric function, having an argument set to an imaginary part of a value which is obtained by dividing the difference signal by the sum signal or, by dividing the sum signal by the difference signal, by means of Pade expansion.

10. The DSSS radar as claimed in claim 1, wherein the computing part comprises:

a first computing part configured to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N))^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing part configured to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>; and

a third computing part configured to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using (RR^H)<sup>−

1</sup>.

11. The DSSS radar as claimed in claim 1, wherein the computing part comprises:

a first computing part configured to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N))^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing part configured to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>;

a third computing part configured to estimate a number N_S of arriving signals;

a fourth computing part configured to form a projection matrix Q from, the pseudo-covariance matrix R depending on the number N_S;

a fifth computing part configured to compute a scale matrix S from a partial matrix of the pseudo-covariance matrix R; and

a sixth computing part configured to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using a matrix which is generated from an arbitrary combination of the projection matrix Q and the scale matrix S, including QS<sup>−

1</sup>Q^H.

12. The DSSS radar as claimed in claim 1, wherein the computing part comprises:

a first computing part configured to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N))^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing part configured to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>;

a third computing part configured to form a projection matrix Q from the pseudo-covariance matrix R depending on a number N_S of arriving signals which is set in advance;

a fourth computing part configured to compute a scale matrix S from a partial matrix of the pseudo-covariance matrix R; and

a fifth computing part configured to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using a matrix which is generated from an arbitrary combination of the projection matrix Q and the scale matrix S, including QS<sup>−

1</sup>Q^H.

13. The DSSS radar as claimed in claim 1, further comprising:

an estimating part configured to estimate a distance from the DSSS radar to said one or a plurality of targets,

wherein the computing part computes the Doppler frequency based on a priority order of estimating the distance, which is determined from a relative relationship between the DSSS radar and said one or a plurality of targets.

14. A method implemented in a DSSS (Direct Sequence Spectrum Spreading) radar, comprising the steps of:

transmitting a transmitting signal, including a predetermined code sequence, to one or a plurality of targets;

receiving a received signal corresponding to the transmitting signal which has been reflected from said one or a plurality of targets; and

computing a sum signal and a difference signal of received signals obtained in the receiving step at different points in time, and estimating a Doppler frequency of said one or a plurality of targets based on a phase difference between the sum signal and the difference signal.

15. The method as claimed in claim 14, wherein the different points in time are separated by a time amounting to one or more period of the predetermined code sequence.

16. A computer-readable storage medium which stores a program for causing a computer to function as a DSSS (Direct Sequence Spectrum Spreading) radar, said program comprising:

a transmitting procedure causing the computer to transmit a transmitting signal, including a predetermined code sequence, to one or a plurality of targets;

a receiving procedure causing the computer to receive a received signal corresponding to the transmitting signal which has been reflected from said one or a plurality of targets; and

a computing procedure causing the computer to compute a sum signal and a difference signal of received signals obtained by the receiving procedure at different points in time, and estimating a Doppler frequency of said one or a plurality of targets based on a phase difference between the sum signal and the difference signal.

17. The computer-readable storage medium as claimed in claim 16, wherein the different points in time are separated by a time amounting to one or more period of the predetermined code sequence.

18. The computer-readable storage medium as claimed in claim 16, wherein the computing procedure includes:

a first computing procedure causing the computer to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N)^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing procedure causing the computer to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>; and

a third computing procedure causing the computer to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using (RR^H)<sup>−

1</sup>.

19. The computer-readable storage medium as claimed in claim 16, wherein the computing procedure includes:

a first computing procedure causing the computer to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N))^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing procedure causing the computer to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>;

a third computing procedure causing the computer to estimate a number N_S of arriving signals;

a fourth computing procedure causing the computer to form a projection matrix Q from the pseudo-covariance matrix R depending on the number N_S;

a fifth computing procedure causing the computer to compute a scale matrix S from a partial matrix of the pseudo-covariance matrix R; and

a sixth computing procedure causing the computer to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using a matrix which is generated from an arbitrary combination of the projection matrix Q and the scale matrix S, including QS<sup>−

1</sup>Q^H.

20. The computer-readable storage medium as claimed in claim 16, wherein the computing procedure includes:

a first computing procedure causing the computer to compute correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub> from a vector ν

=(ν

(t₁), . . . , ν

(t_N))^T which is formed from samples of received signals at mutually different times t₁, . . . , t_N and the received signals at the mutually different times t₁, . . . , t_N;

a second computing procedure causing the computer to form a pseudo-covariance matrix R applied with a spatial average by combining the correlation vectors r<sub>ν

1</sub> and r<sub>ν

2</sub>;

a third computing procedure causing the computer to form a projection matrix Q from the pseudo-covariance matrix R depending on a number N_S of arriving signals which is set in advance;

a fourth computing procedure causing the computer to compute a scale matrix S from a partial matrix of the pseudo-covariance matrix R; and

a fifth computing procedure causing the computer to compute the Doppler frequency from an algebraic equation or a pseudo-spectrum using a matrix which is generated from an arbitrary combination of the projection matrix Q and the scale matrix S, including QS<sup>−

1</sup>Q^H.