Object detection with multiple frequency chirps
A system and method are disclosed for the generation and processing of waveforms utilized to modulate the carrier frequency of a microwave sensor employed, to determine the range and velocity of an object of interest. The system and method result in improved performance in environments with high levels of interference.
1. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
the method further comprising
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope.
2. The method according to claim 1 , further comprising
determining beat frequencies between the transmitted signal and the received signal,
wherein
the determination of the range and/or the velocity of the object is performed for the measured beat frequencies and the corresponding normalized slopes within a portion, respectively.
3. The method according to claim 2 , wherein
the determination of the range and/or the velocity of the object is performed on the basis of parameters calculated on the basis of the measured beat frequencies and the corresponding normalized slopes within a portion, respectively.
4. The method according to claim 3 , wherein
the determination of the range and/or the velocity of the object is performed including the determination of a round-trip delay and a Doppler frequency of reflected signals from the object, respectively.
5. The method according to claim 1 , wherein the normalized slopes satisfy predetermined conditions.
6. The method according to claim 1 , wherein
the portions exist in pairs such that for each portion with a normalized slope S k there is a portion with normalized slope −S k .
7. The method according to claim 1 , wherein
the portions exist in pairs such that for each portion with a normalized slope S k there is a portion with normalized slope 1/S k .
8. A method of detecting an object according to claim 1 wherein
the portions exist in quadruples such that for each portion with a normalized slope S k there are portions with normalized slope 1/S k , −1/S k and −S k .
9. The method according to claim 8 , wherein
the ratio of maximum desired magnitude of slope to the minimum desired magnitude of slope is Z,
and the normalized slopes S k of a quadruple are
−√{square root over ( Z )},−1 /√{square root over (Z)}, 1 /√{square root over (Z)},√{square root over (Z)}.
10. The method according to claim 1 , wherein
the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope to calculate the geometric mean or the arithmetic mean of the slopes, and dividing each slope by the mean slope.
11. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
the method further comprising
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope;
determining beat frequencies between the transmitted signal and the received signal, wherein the determination of the range and/or the velocity of the object is performed for the measured beat frequencies and the corresponding normalized slopes within a portion, respectively
wherein the determination of the range and/or the velocity of the object is performed on the basis of parameters calculated on the basis of the measured beat frequencies and the corresponding normalized slopes within a portion, respectively and
wherein parameters G K , H K , and P K are calculated which are obtainable by:
G
K
=
∑
k
=
1
K
S
k
2
1
+
S
k
2
,
H
K
=
∑
k
=
1
K
1
1
+
S
k
2
,
P
K
=
∑
k
=
1
K
S
k
1
+
S
k
2
,
where,
S k is a normalized slope within a portion k, 4≦k≦K, and K is the total number of signal portions.
12. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
the method further comprising
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope;
determining beat frequencies between the transmitted signal and the received signal, wherein the determination of the range and/or the velocity of the object is performed for the measured beat frequencies and the corresponding normalized slopes within a portion, respectively
wherein the determination of the range and/or the velocity of the object is performed on the basis of parameters calculated on the basis of the measured beat frequencies and the corresponding normalized slopes within a portion, respectively wherein parameters G K , H K , and P K are calculated which are obtainable by:
G
K
=
∑
k
=
1
K
S
k
2
1
+
S
k
2
,
H
K
=
∑
k
=
1
K
1
1
+
S
k
2
,
P
K
=
∑
k
=
1
K
S
k
1
+
S
k
2
,
where,
S k is a normalized slope within a portion k, 4≦k≦K, and K is the total number of signal portions and, wherein the determination of the range and/or the velocity of the object is performed including the determination of a round-trip delay and a Doppler frequency of reflected signals from the object as {tilde over (τ)} 0 and {tilde over (f)} V0 , respectively, where {tilde over (τ)} 0 and {tilde over (f)} V0 are obtainable by:
τ
~
0
=
H
K
·
I
K
+
P
K
·
Q
K
G
K
·
H
K
-
P
K
2
,
f
~
V
0
=
G
K
·
Q
K
+
P
K
·
I
K
G
K
·
H
K
-
P
K
2
,
wherein I K and Q K are obtainable by:
I
K
=
-
∑
k
=
1
K
f
Bk
·
S
k
1
+
S
k
2
,
Q
K
=
∑
k
=
1
K
f
Bk
1
+
S
k
2
,
where,
S k is a normalized slope within a portion k and,
f Bk is a measured beat frequency.
13. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
the method further comprising
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope, wherein the normalized slopes satisfy predetermined conditions
wherein a predetermined condition is:
P
K
=
∑
k
=
1
K
S
k
1
+
S
k
2
=
0
,
where, S k is a normalized slope within a portion k, 4≦k≦K and
K is the total number of portions.
14. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
the method further comprising
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope,
wherein there exist a minimum magnitude of normalized slope |S| min and a maximum magnitude normalized slope |S| max that define the angular intervals
(tan −1 |S| min ,tan −1 |S| max )and
(−tan −1 |S| max ,−tan −1 |S| min )
wherein,
the angles defined by the normalized slopes are equally spaced within these said angular intervals.
15. An apparatus for detecting an object, comprising
a transmitter operable to transmit a varying-frequency signal of finite duration,
a receiver operable to receive a reflection of the transmitted signal from an object,
a signal generator operable to provide the varying-frequency signal such that the transmitted signal comprises a sequence of at least four adjacent portions, such that the frequency of the signal varies linearly with time within each of the said portions and such that the linear frequency variation has a different slope within each of the portions, and
a signal processor operable to determine a range and/or a velocity of the object on the basis of normalized slopes for each portion obtained by dividing each slope by a mean slope, where the mean slope is the average of the absolute values of each slope.
16. An apparatus according to claim 15 , further comprising
a beat frequency detector operable to detect beat frequencies between the transmitted signal and the received signal,
and wherein the signal processor is arranged to perform the determination of the range and/or the velocity of the object for the measured beat frequencies and the corresponding normalized slopes within a portion, respectively.
17. An apparatus according to claim 16 , wherein
the signal processor is arranged to perform the determination of the range and/or the velocity of the object on the basis of parameters calculated on the basis of the measured beat frequencies and the corresponding normalized slopes within a portion, respectively.
18. An apparatus according to claim 15 , wherein the signal generator further comprises
a memory for storing predefined sets of normalized slopes; and
a selector operable to randomly select one of the predefined sets of normalized slopes.
19. An apparatus for detecting an object, comprising
a transmitter operable to transmit a varying-frequency signal of finite duration,
a receiver operable to receive a reflection of the transmitted signal from an object,
a signal generator operable to provide the varying-frequency signal such that the transmitted signal comprises a sequence of at least four adjacent portions, such that the frequency of the signal varies linearly with time within each of the said portions and such that the linear frequency variation has a different slope within each of the portions, and
a signal processor operable to determine a range and/or a velocity of the object on the basis of normalized slopes for each portion obtained by dividing each slope by a mean slope, where the mean slope is the average of the absolute values of each slope;
a beat frequency detector operable to detect beat frequencies between the transmitted signal and the received signal,
wherein the signal processor is arranged to perform the determination of the range and/or the velocity of the object for the measured beat frequencies and the corresponding normalized slopes within a portion, respectively,
wherein the signal processor is arranged to perform the determination of the range and/or the velocity of the object on the basis of parameters calculated on the basis of the measured beat frequencies and the corresponding normalized slopes within a portion, respectively, and
wherein the signal processor is arranged to calculate parameters G K , H K , and P K which are obtainable by:
G
K
=
∑
k
=
1
K
S
k
2
1
+
S
k
2
,
H
K
=
∑
k
=
1
K
1
1
+
S
k
2
,
P
K
=
∑
k
=
1
K
S
k
1
+
S
k
2
,
where,
S k is a normalized slope within a portion k, 4≦k≦K and
K is the total number of portions.
20. A method of detecting an object, the method comprising
transmitting a varying-frequency signal of finite duration, and
receiving a reflection of the transmitted signal from the object,
wherein
the transmitted signal comprises a sequence of at least four adjacent portions,
the frequency of the signal varies linearly with time within each of the said portions, and
the linear frequency variation has a different slope within each of the portions,
determining the range and/or the velocity of the object on the basis of normalized slopes for each portion, wherein the normalization is performed by obtaining a mean slope by averaging the absolute value of each slope and dividing each slope by the mean slope;
determining beat frequencies between the transmitted signal and the received signal,
wherein,
the frequency of the signal varies linear, and
the portions of the transmitted signal exist in K/2 pairs of opposite and/or inverse normalized slopes,
and further comprising
calculating a range and/or velocity of the object from the beat frequencies and their respective normalized slopes K/2 times, each time with one of the pairs excluded from the calculation process,
determining if a calculation with a pair generates a result located outside of a cluster formed by the results of the other pairs, and
outputting the range and/or velocity given by the result.