Vehicle radar system
A vehicle radar system including at least one transceiver arrangement ( 52 ) that is arranged to generate and transmit a least one FMCW chirp signal ( 4 a, 4 b ). Each chirp signal ( 4 a, 4 b ) includes a corresponding plurality of frequency ramps (r 1 , r 2 ). The vehicle radar system ( 3 ) is arranged to receive reflected signals ( 5 a, 5 b ) and to mix the received signals ( 5 a, 5 b ) with the respective transmitted chirp signal ( 4 a, 4 b ) to obtain at least one IF signal ( 14 ). The vehicle radar system ( 3 ) is further arranged to produce a periodically updated dwell list ( 34 ), and to collect and process data in dependence of the present dwell list ( 34 ). The present dwell list includes information where the probability of presence of objects exceeds a certain threshold.
1. A vehicle radar system comprising:
at least one transceiver arrangement, the at least one transceiver arrangement being configured to generate and transmit a Frequency Modulated Continuous Wave (FMCW) chirp signal, where the chirp signal includes a corresponding plurality of frequency ramps, where the vehicle radar system is configured to receive reflected signals and to mix the received reflected signals with the respective transmitted chirp signal to obtain at least one Intermediate Frequency (IF) signal;
wherein the vehicle radar system is configured to produce a periodically-updated dwell list and to collect and process data in dependence of the periodically-updated dwell list, where the periodically-updated dwell list includes information where the probability of presence of one or more objects exceeds a certain threshold;
wherein the at least one transceiver arrangement is further configured to:
convert the IF signals to digital signals,
convert the digital signals to a range domain by use of a first Fast Fourier Transform (FFT),
combine the results from a successive of the chirp signal into the Doppler domain by use of a second FFT to obtain a plurality of Range-Doppler matrices, and
feed a two-dimensional spectrum of a Range-Doppler matrix of the plurality of Range-Doppler matrices into a first processing path and a second processing path, where the first processing path is configured to produce the periodically-updated dwell list by determining elements of the Range-Doppler matrix which are most likely to contain energy of radar targets using a log-likelihood function (LLF), and where the second processing path is configured to collect and process data to detect targets from the Range-Doppler matrix in dependence of the periodically-updated dwell list,
wherein the log-likelihood function (LLF) computes a natural log of a ratio of a first probability distribution function to a second probability distribution function, with the first probability distribution function representing a probability that an object is present at a specified signal magnitude, and with the second probability distribution function representing a probability that no object is present at the specified signal magnitude.
2. The vehicle radar system according to claim 1 , wherein the log-likelihood function is computed as
r
(
m
,
σ
)
=
2
σ
e
D
m
σ
D
2
/
2
2
π
m
.
3. The vehicle radar system according to claim 1 , wherein the second probability distribution function follows a Rayleigh distribution.
4. The vehicle radar system according to claim 3 , wherein the second probability distribution function is computed as:
f
1
(
c
)
=
m
σ
2
·
exp
(
-
m
2
2
·
σ
2
)
.
5. The vehicle radar system according to claim 1 , wherein the first probability distribution function follows a Rice distribution.
6. The vehicle radar system according to claim 5 , wherein the first probability distribution function is approximated by a Gaussian distribution.
7. The vehicle radar system according to claim 5 , wherein the first probability distribution function is computed as:
f
0
(
m
)
=
1
σ
·
√
(
2
·
π
)
,
exp
(
-
(
m
-
m
T
)
2
2
·
σ
2
)
.
8. The vehicle radar system according to claim 1 , wherein the first processing path comprises a search module and a dwell computation module, with the search module configured to find the elements of the Range-Doppler matrix which are most likely to contain energy of radar targets, and with the dwell computation module configured to select range-velocity combinations that are most likely to contain energy of radar targets.
9. The vehicle radar system according to claim 8 , wherein the search module includes a noise estimation module, where the noise estimation module is configured to estimate a noise floor for all ranges in the Doppler dimension within the Range-Doppler matrix using a median function.
10. The vehicle radar system according to claim 8 , wherein the search module includes an LLF matrix alignment module configured to generate an LLF matrix based upon the Range-Doppler matrix by determining a range-rate of energy within a given element of the Range-Doppler matrix using a matrix element index in the Doppler dimension.
11. The vehicle radar system according to claim 8 , wherein the search module includes a probability ratio computation module configured to perform sequential detection using a sequential probability ratio test (SPRT) algorithm.
12. The vehicle radar system according to claim 11 , wherein the target detection module includes a dwell data transformation module, where the dwell data transformation module is configured to transfer a dwell signal from the dwell buffer into the frequency domain.
13. The vehicle radar system according to claim 12 , wherein the parameter estimation module is configured to apply a 3-point interpolation to the plurality of orthogonal neighboring matrix elements of the target in three-dimensional signal space.
14. The vehicle radar system according to claim 12 , wherein the parameter estimation module is configured to calculate a target distance to the target using the equation
R
RES
=
N
S
-
1
N
S
·
C
0
2
·
BW
.
15. The vehicle radar system according to claim 12 , wherein the parameter estimation module is configured to calculate a target speed of the target using the equation
V
RES
=
C
0
N
R
·
7
N
R
·
T
R
·
(
f
start
-
f
stop
)
.
16. The vehicle radar system according to claim 11 , wherein the target detection module includes a peak detection module, where the peak detection module includes a detection algorithm configured to identify targets by:
creating a magnitude signal from an output of a complex FFT,
estimating a noise floor for the dwell signal,
calculating a detection threshold, and
designating a local maxima that exceeds the detection threshold as a target.
17. The vehicle radar system according to claim 11 , wherein the target detection module includes a parameter estimation module configured to calculate the parameters of the target using a plurality of orthogonal neighboring matrix elements of the target in a three-dimensional signal space.
18. The vehicle radar system according to claim 8 , wherein the search module includes an LLF matrix updating module configured to detect an actual target signal by comparing the ratio of the first probability distribution function to the second probability distribution function with one or more threshold values.
19. The vehicle radar system according to claim 8 , wherein the dwell computation module includes a Range-Doppler (RD) matrix element identification module and a dwell position calculation module, where the RD matrix element identification module is configured to determine whether a given element of the LLF matrix exceeds a first threshold value, and where the dwell position calculation module is configured to compute a dwell position using a range index value and a Doppler index value of the given element of the LLF matrix.
20. The vehicle radar system according to claim 1 , wherein the second processing path comprises a dwelling module and a target detection module, where the dwelling module is configured to store data in a dwell buffer using the Range-Doppler matrix in dependence of the present dwell list, and where the target detection module is configured to evaluate the data stored in the dwell buffer to calculate parameters of a target, the parameters of the target including a range parameter, a Doppler parameter, and a bearing parameter.