CA2854620C - Detection system with simultaneous multiple transmissions and detection method - Google Patents
Detection system with simultaneous multiple transmissions and detection method Download PDFInfo
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- CA2854620C CA2854620C CA2854620A CA2854620A CA2854620C CA 2854620 C CA2854620 C CA 2854620C CA 2854620 A CA2854620 A CA 2854620A CA 2854620 A CA2854620 A CA 2854620A CA 2854620 C CA2854620 C CA 2854620C
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
- G01S7/414—Discriminating targets with respect to background clutter
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/42—Simultaneous measurement of distance and other co-ordinates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/46—Indirect determination of position data
- G01S13/48—Indirect determination of position data using multiple beams at emission or reception
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/50—Systems of measurement based on relative movement of target
- G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
- G01S13/583—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets
- G01S13/584—Velocity or trajectory determination systems; Sense-of-movement determination systems using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves and based upon the Doppler effect resulting from movement of targets adapted for simultaneous range and velocity measurements
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- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
The system includes an antenna composed of transmission sub-arrays (A1, ... A Q) illuminating one and the same zone of the space and at least one reception sub-array (A R), each sub-array having a given position in said array, each transmission sub-array transmitting a signal having a specific characteristic, the set of characteristics specific to each sub-array forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different transmission codes, echoes being detected in the main lobe and in the sidelobes, the system: - transmits different codes (67) from among at least two bursts, - detects the signals (68) originating from each direction; - carries out the aggregation (69) of the different signals (70) detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes detected by said sidelobes.
Description
DETECTION SYSTEM WITH SIMULTANEOUS MULTIPLE
TRANSMISSIONS AND DETECTION METHOD
The present invention concerns a detection system with simultaneous multiple transmissions. It also relates to a detection method using the simultaneous multiple transmissions.
The invention notably applies to the field of radars with simultaneous multiple transmissions, also known as MIMO ("Multiple Input Multiple Output") radars or MISO ("Multiple Input Single Output") radars. These can be terrestrial, naval, airborne or space radars. The invention can also apply to active sonars.
Among the various functions of a radar, one function is to detect slow objects of low reflectivity, such as drones notably. To detect slow objects in the presence of clutter, it is necessary to have good Doppler resolution and therefore a long coherent processing interval. To preserve good angular accuracy, one solution consists in employing a widened transmission beam and a cluster of reception beams that covers the whole of the transmission beam. In a conventional solution the beam is widened by a phase law.
However, this solution does not make it possible to obtain the necessary isolation between the desired low-reflectivity and low-speed target, for example a drone, and vehicles on the ground, of the same speed and of much higher reflectivity. Another solution consists in widening the beam by simultaneous multiple transmissions; this solution is described below. It will be seen that it only meets the need to a certain extent; indeed, certain sidelobes can be reduced but they still remain too high or too numerous.
Simultaneous multiple transmission, also called coloured transmission, consists in transmitting different signals as a function of the sub-arrays of the transmission antenna, and in thus producing a spatio-temporal coding of the space. These signals combine in space according to phase groups or delays that depend on the targeted direction. This results in an overall signal that differs from one direction to another. At reception, to detect a signal originating from a given direction, the processing involves filtering matched to the signal associated with this direction. This filter is not matched to the signals originating from the other directions since the signal is no longer the same in these other directions. However, the signals from different directions all originate from the same elementary signals. This results in a correlation that means that the filter matched to one direction does not produce a perfect
TRANSMISSIONS AND DETECTION METHOD
The present invention concerns a detection system with simultaneous multiple transmissions. It also relates to a detection method using the simultaneous multiple transmissions.
The invention notably applies to the field of radars with simultaneous multiple transmissions, also known as MIMO ("Multiple Input Multiple Output") radars or MISO ("Multiple Input Single Output") radars. These can be terrestrial, naval, airborne or space radars. The invention can also apply to active sonars.
Among the various functions of a radar, one function is to detect slow objects of low reflectivity, such as drones notably. To detect slow objects in the presence of clutter, it is necessary to have good Doppler resolution and therefore a long coherent processing interval. To preserve good angular accuracy, one solution consists in employing a widened transmission beam and a cluster of reception beams that covers the whole of the transmission beam. In a conventional solution the beam is widened by a phase law.
However, this solution does not make it possible to obtain the necessary isolation between the desired low-reflectivity and low-speed target, for example a drone, and vehicles on the ground, of the same speed and of much higher reflectivity. Another solution consists in widening the beam by simultaneous multiple transmissions; this solution is described below. It will be seen that it only meets the need to a certain extent; indeed, certain sidelobes can be reduced but they still remain too high or too numerous.
Simultaneous multiple transmission, also called coloured transmission, consists in transmitting different signals as a function of the sub-arrays of the transmission antenna, and in thus producing a spatio-temporal coding of the space. These signals combine in space according to phase groups or delays that depend on the targeted direction. This results in an overall signal that differs from one direction to another. At reception, to detect a signal originating from a given direction, the processing involves filtering matched to the signal associated with this direction. This filter is not matched to the signals originating from the other directions since the signal is no longer the same in these other directions. However, the signals from different directions all originate from the same elementary signals. This results in a correlation that means that the filter matched to one direction does not produce a perfect
2 zero when it receives a signal originating from another direction. This level corresponds to a sidelobe of the ambiguity function.
Analyses carried out over a wide variety of codes show that most of the analysed codes produce sidelobes, the level of which exceeds the desired level in certain zones of the angle-distance-Doppler space. The rare codes that almost reach the level reduction objective significantly widen the main lobe, which in the long run means they are of little use due to the lack of discrimination this incurs. In conclusion, none of the simultaneous multiple transmission codes analysed satisfy the operational requirements.
One problem to be solved for radars of MIMO or MISO type is therefore the reduction of the sidelobes of the angle-distance-Doppler ambiguity function.
A document US 6 977 610 B2 notably having the aim of increasing radar detection sensitivity presents a solution using a combination of two radars that simultaneously transmit towards one and the same target and both receive the echoes originating from the two transmissions and aggregate them. The solution does not indicate how to remove the unwanted echoes originating from the sidelobes.
A document EP 2 434 310 Al describes reception processing, by computational beamforming, aiming to make optimal use of various antenna sub-arrays. The document specifies that this process can be combined with simultaneous multiple transmission or coloured transmission. However, the solution described in this document does not deal with the reduction of the sidelobes of the angle-distance-Doppler ambiguity function.
One aim of the invention is notably to reduce as much as possible the sidelobes of the ambiguity function, notably of a radar with simultaneous multiple transmissions. With this aim, the subject of the invention is a detection system with simultaneous multiple transmissions including an antenna composed of transmission sub-arrays illuminating one and the same zone of the space and at least one reception sub-array, each sub-array having a given position in said array, each transmission sub-array transmitting a signal having a specific characteristic, the set of characteristics specific to each sub-array forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different
Analyses carried out over a wide variety of codes show that most of the analysed codes produce sidelobes, the level of which exceeds the desired level in certain zones of the angle-distance-Doppler space. The rare codes that almost reach the level reduction objective significantly widen the main lobe, which in the long run means they are of little use due to the lack of discrimination this incurs. In conclusion, none of the simultaneous multiple transmission codes analysed satisfy the operational requirements.
One problem to be solved for radars of MIMO or MISO type is therefore the reduction of the sidelobes of the angle-distance-Doppler ambiguity function.
A document US 6 977 610 B2 notably having the aim of increasing radar detection sensitivity presents a solution using a combination of two radars that simultaneously transmit towards one and the same target and both receive the echoes originating from the two transmissions and aggregate them. The solution does not indicate how to remove the unwanted echoes originating from the sidelobes.
A document EP 2 434 310 Al describes reception processing, by computational beamforming, aiming to make optimal use of various antenna sub-arrays. The document specifies that this process can be combined with simultaneous multiple transmission or coloured transmission. However, the solution described in this document does not deal with the reduction of the sidelobes of the angle-distance-Doppler ambiguity function.
One aim of the invention is notably to reduce as much as possible the sidelobes of the ambiguity function, notably of a radar with simultaneous multiple transmissions. With this aim, the subject of the invention is a detection system with simultaneous multiple transmissions including an antenna composed of transmission sub-arrays illuminating one and the same zone of the space and at least one reception sub-array, each sub-array having a given position in said array, each transmission sub-array transmitting a signal having a specific characteristic, the set of characteristics specific to each sub-array forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different
3 transmission codes, echoes being present in the main lobe and in the sidelobes of the ambiguity function, said system:
- transmitting different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
- detecting the signals originating from each direction;
- carrying out the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes, variable from burst to burst, of the ambiguity function.
In a particular embodiment, said at least two transmission codes are consecutive. Said at least two codes are for example repeated within said series of bursts.
Since the transmission includes N different codes, one per burst, the aggregation is for example performed according to a "2 of N" criterion or according to a "K of N" criterion, K being greater than 2.
The aggregation is made for example according to processing of the "Compressed Sensing" type or according to a process of the maximum likelihood type.
A simultaneous multiple transmission code is for example produced by attributing a frequency sub-band to each transmission sub-array.
In one possible embodiment, the phase centres of said transmission sub-arrays are aligned on an axis.
Said system including several reception sub-arrays, said sub-arrays are not co-located, each reception sub-array receiving the signals originating from the different transmissions produced by said transmission sub-arrays.
Another subject of the invention is a detection method with simultaneous multiple transmissions using an antenna composed of transmission sub-arrays illuminating one and the same zone of the space and at least one reception sub-array, each sub-array having a given position in said array, a method in which:
- to each transmission sub-array is attributed a transmission signal having a specific characteristic, the set of characteristics specific to each sub-array =
- transmitting different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
- detecting the signals originating from each direction;
- carrying out the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes, variable from burst to burst, of the ambiguity function.
In a particular embodiment, said at least two transmission codes are consecutive. Said at least two codes are for example repeated within said series of bursts.
Since the transmission includes N different codes, one per burst, the aggregation is for example performed according to a "2 of N" criterion or according to a "K of N" criterion, K being greater than 2.
The aggregation is made for example according to processing of the "Compressed Sensing" type or according to a process of the maximum likelihood type.
A simultaneous multiple transmission code is for example produced by attributing a frequency sub-band to each transmission sub-array.
In one possible embodiment, the phase centres of said transmission sub-arrays are aligned on an axis.
Said system including several reception sub-arrays, said sub-arrays are not co-located, each reception sub-array receiving the signals originating from the different transmissions produced by said transmission sub-arrays.
Another subject of the invention is a detection method with simultaneous multiple transmissions using an antenna composed of transmission sub-arrays illuminating one and the same zone of the space and at least one reception sub-array, each sub-array having a given position in said array, a method in which:
- to each transmission sub-array is attributed a transmission signal having a specific characteristic, the set of characteristics specific to each sub-array =
4 forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different transmission codes, echoes being present in the main lobe and in the sidelobes of the ambiguity function, - different codes are transmitted from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting the sidelobes of said ambiguity function in different directions from burst to burst;
- the signals originating from each direction are detected;
- the aggregation is made of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in the sidelobes, variable from burst to burst, of the ambiguity function.
Other characteristics and advantages of the invention will become apparent thanks to the following description, made with reference to the appended drawings, which represent:
- Figure 1, an illustration of the ambiguity sidelobes of a radar with simultaneous multiple transmission;
- Figure 2, an example of a main lobe and sidelobes corresponding to a simultaneous multiple transmission code;
- Figure 3, an example of a main lobe and sidelobes corresponding to a simultaneous multiple transmission code allowing the sidelobes to be reduced;
- Figures 4a to 4d, an illustration of the principle of the invention;
- Figures 5a to 5c, an illustration of a result obtained by the invention;
- Figure 6, a possible exemplary embodiment of a radar according to the invention;
- Figures 7a to 7b, examples of simultaneous multiple transmission coding that can be implemented by the invention.
Figure 1 illustrates the ambiguity sidelobes of a radar with simultaneous multiple transmissions. As a general rule, the term "ambiguity function" is associated with a function depending on at least two variables, distance and Doppler for example. Figure 1 only describes one variable. In other words, Figure 1 describes the phenomenon in relation to angle. Figure 2 will hereinafter provide a more complete description of the phenomenon, which in reality involves both angle and distance.
- the signals originating from each direction are detected;
- the aggregation is made of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in the sidelobes, variable from burst to burst, of the ambiguity function.
Other characteristics and advantages of the invention will become apparent thanks to the following description, made with reference to the appended drawings, which represent:
- Figure 1, an illustration of the ambiguity sidelobes of a radar with simultaneous multiple transmission;
- Figure 2, an example of a main lobe and sidelobes corresponding to a simultaneous multiple transmission code;
- Figure 3, an example of a main lobe and sidelobes corresponding to a simultaneous multiple transmission code allowing the sidelobes to be reduced;
- Figures 4a to 4d, an illustration of the principle of the invention;
- Figures 5a to 5c, an illustration of a result obtained by the invention;
- Figure 6, a possible exemplary embodiment of a radar according to the invention;
- Figures 7a to 7b, examples of simultaneous multiple transmission coding that can be implemented by the invention.
Figure 1 illustrates the ambiguity sidelobes of a radar with simultaneous multiple transmissions. As a general rule, the term "ambiguity function" is associated with a function depending on at least two variables, distance and Doppler for example. Figure 1 only describes one variable. In other words, Figure 1 describes the phenomenon in relation to angle. Figure 2 will hereinafter provide a more complete description of the phenomenon, which in reality involves both angle and distance.
5 In a structure of the prior art, several transmission elements each transmit a characteristic signal. One or more reception elements carry out processing that makes use of the knowledge of the radiated signal as a function of direction, and therefore of the coding of the space.
More particularly, Figure 1 shows the amplitude of the transmission beam Tx corresponding to an antenna sub-array, as a function of the angle O. The beamwidth, a function of the dimension of the antenna sub-array, exhibits a given width.
Figure 1 also shows a reception beam Rx in a direction defined by an angle GO, which is narrower. As indicated previously, simultaneous multiple transmission consists in transmitting different signals, one signal being associated with each sub-array that transmits from a given position in the antenna. These signals combine in space to supply an overall signal that differs from one direction to another. The signal in a given direction results from a combination of the signals originating from the different sub-arrays.
The signal in another direction results from another combination of the same signals originating from the different sub-arrays.
At reception, to detect a signal originating from a given direction GO, the processing carries out a filtering matched to the signal associated with this direction. However, the signals of the other directions all originate from the same elementary signals. By an effect of correlation, the filter matched to the direction eo does not produce a perfect zero when it receives a signal in another direction. This level of reception corresponds to a sidelobe 1, 2, 3, 4.
Figure 1 moreover illustrates the drawbacks of these sidelobes. Indeed, a target 11 of large equivalent radar cross section (RCS), present in a sidelobe, can be detected as a target 10 of low RCS present in the main reception lobe.
Figure 2 presents, for a simultaneous multiple transmission code, the main lobe 20 at reception flanked by two sidelobes 201, 202 in the angle-distance domain, the abscissae representing the distance to the target and the
More particularly, Figure 1 shows the amplitude of the transmission beam Tx corresponding to an antenna sub-array, as a function of the angle O. The beamwidth, a function of the dimension of the antenna sub-array, exhibits a given width.
Figure 1 also shows a reception beam Rx in a direction defined by an angle GO, which is narrower. As indicated previously, simultaneous multiple transmission consists in transmitting different signals, one signal being associated with each sub-array that transmits from a given position in the antenna. These signals combine in space to supply an overall signal that differs from one direction to another. The signal in a given direction results from a combination of the signals originating from the different sub-arrays.
The signal in another direction results from another combination of the same signals originating from the different sub-arrays.
At reception, to detect a signal originating from a given direction GO, the processing carries out a filtering matched to the signal associated with this direction. However, the signals of the other directions all originate from the same elementary signals. By an effect of correlation, the filter matched to the direction eo does not produce a perfect zero when it receives a signal in another direction. This level of reception corresponds to a sidelobe 1, 2, 3, 4.
Figure 1 moreover illustrates the drawbacks of these sidelobes. Indeed, a target 11 of large equivalent radar cross section (RCS), present in a sidelobe, can be detected as a target 10 of low RCS present in the main reception lobe.
Figure 2 presents, for a simultaneous multiple transmission code, the main lobe 20 at reception flanked by two sidelobes 201, 202 in the angle-distance domain, the abscissae representing the distance to the target and the
6 ordinates representing the angle of reception, i.e. the direction. The coding, used to come as close as possible to the objective of eliminating or at least greatly reducing the sidelobes, does however allow excessively high sidelobes to appear in certain (angle-direction) zones 203, 204, 205.
Figure 3 illustrates a case corresponding to a few codes that make it possible to approach the constraints on the sidelobes but at the cost of a greatly widened, and therefore undiscriminating, main lobe 300. Figures 1 to 3 illustrate the limits of the simultaneous multiple transmissions of the prior art.
Figures 4a to 4d illustrate the principle of the invention using a particular, simple case. The solution according to the invention consists in transmitting not one single multiple transmission code but different codes successively, from one burst to another, and in combining the responses obtained using non-linear processing. It is possible to ensure that the code does not vary between two successive bursts but among more than 2 bursts, not necessarily successive.
Figure 4a presents an antenna array 41 including, for example, eight antenna sub-arrays 42. An antenna sub-array can be made up of a single antenna or several elementary antennas or antenna elements, radiating elements for example. The latter can be aligned.
Each sub-array transmits according to a code. One code is assigned to each sub-array 42. Each code is assigned to one sub-array and one only. Figure 4a illustrates the coding of the transmission for a burst of order M. A first sub-array Ai transmits according to a code Ci, a second sub-array A2 transmits according to a code C2 and so on until the last sub-array A8 which transmits according to a code C8. In the example in Figure 4a, a code Ci corresponds to the allocation of a frequency sub-band 43, to a sub-array.
Figure 4b shows the ambiguity function of the received signals corresponding to the transmission in Figure 4, represented in the angle-distance domain.
The main lobe 44 is situated at the origin of the axes. The sidelobes 45 are aligned on each side of this main lobe 44 at a distance that increases in a linear manner as a function of the angle A.
Figure 4c illustrates the coding of the transmission on the following burst, M+1, for the same network as that in Figure 4a. In this example, the
Figure 3 illustrates a case corresponding to a few codes that make it possible to approach the constraints on the sidelobes but at the cost of a greatly widened, and therefore undiscriminating, main lobe 300. Figures 1 to 3 illustrate the limits of the simultaneous multiple transmissions of the prior art.
Figures 4a to 4d illustrate the principle of the invention using a particular, simple case. The solution according to the invention consists in transmitting not one single multiple transmission code but different codes successively, from one burst to another, and in combining the responses obtained using non-linear processing. It is possible to ensure that the code does not vary between two successive bursts but among more than 2 bursts, not necessarily successive.
Figure 4a presents an antenna array 41 including, for example, eight antenna sub-arrays 42. An antenna sub-array can be made up of a single antenna or several elementary antennas or antenna elements, radiating elements for example. The latter can be aligned.
Each sub-array transmits according to a code. One code is assigned to each sub-array 42. Each code is assigned to one sub-array and one only. Figure 4a illustrates the coding of the transmission for a burst of order M. A first sub-array Ai transmits according to a code Ci, a second sub-array A2 transmits according to a code C2 and so on until the last sub-array A8 which transmits according to a code C8. In the example in Figure 4a, a code Ci corresponds to the allocation of a frequency sub-band 43, to a sub-array.
Figure 4b shows the ambiguity function of the received signals corresponding to the transmission in Figure 4, represented in the angle-distance domain.
The main lobe 44 is situated at the origin of the axes. The sidelobes 45 are aligned on each side of this main lobe 44 at a distance that increases in a linear manner as a function of the angle A.
Figure 4c illustrates the coding of the transmission on the following burst, M+1, for the same network as that in Figure 4a. In this example, the
7 assignment of the codes Ci, i.e. of the sub-bands 43, is reversed with respect to the position of the sub-arrays. Consequently, the first sub-array Ai transmits according to the code C8, the second sub-array A2 according to the code C7 and so on, the eighth sub-array As transmitting according to the code Ci.
Figure 4d shows the ambiguity function of the received signals corresponding to the transmission in Figure 4c in the same angle-distance domain as that of Figure 4b. There is still a main lobe 46 at the origin of the axes and sidelobes are still aligned on each side of this main lobe. However, the alignment is oriented differently, it is symmetrical to the preceding alignment about the angle axis.
Using a suitable process it is then possible to remove the sidelobes 45, 47 that are not positioned at the same places from one burst to another and only preserve the main lobe 44, 46. In a case of an embodiment where the changes of codes occur from one burst to another, the code of the burst M+2 is the same as for the burst M, the code of the burst M+3 being the same as that of the burst M+1 and so on.
Advantageously, the invention uses a principle similar to that used for suppressing distance-Doppler ambiguities. In the latter case, the transmission of several bursts with different ambiguities is carried out, then the aggregation of the signals of the different bursts is carried out by a non-linear process. The simplest and most commonly used process requires detection in one and the same distance-Doppler cell, over at least two bursts.
In the case of successive multiple transmissions according to the invention, the simplest process requires the detection in one and the same angle-distance-Doppler cell over at least two bursts.
The succession of different multiple transmissions exhibits the advantage of combining very well with the variation of distance and Doppler ambiguities from burst to burst. The latter relies on a variation, from burst to burst, of the repetition period and where applicable of the transmission frequency. The solution proposed by the invention consists in varying, in addition, the multiple simultaneous transmission code as illustrated by the simple case in Figures 4a to 4d. The process of aggregating these bursts, with the aim of removing the sidelobes, can remain unchanged once the filters have been matched to the codes transmitted by each burst. This process implies the
Figure 4d shows the ambiguity function of the received signals corresponding to the transmission in Figure 4c in the same angle-distance domain as that of Figure 4b. There is still a main lobe 46 at the origin of the axes and sidelobes are still aligned on each side of this main lobe. However, the alignment is oriented differently, it is symmetrical to the preceding alignment about the angle axis.
Using a suitable process it is then possible to remove the sidelobes 45, 47 that are not positioned at the same places from one burst to another and only preserve the main lobe 44, 46. In a case of an embodiment where the changes of codes occur from one burst to another, the code of the burst M+2 is the same as for the burst M, the code of the burst M+3 being the same as that of the burst M+1 and so on.
Advantageously, the invention uses a principle similar to that used for suppressing distance-Doppler ambiguities. In the latter case, the transmission of several bursts with different ambiguities is carried out, then the aggregation of the signals of the different bursts is carried out by a non-linear process. The simplest and most commonly used process requires detection in one and the same distance-Doppler cell, over at least two bursts.
In the case of successive multiple transmissions according to the invention, the simplest process requires the detection in one and the same angle-distance-Doppler cell over at least two bursts.
The succession of different multiple transmissions exhibits the advantage of combining very well with the variation of distance and Doppler ambiguities from burst to burst. The latter relies on a variation, from burst to burst, of the repetition period and where applicable of the transmission frequency. The solution proposed by the invention consists in varying, in addition, the multiple simultaneous transmission code as illustrated by the simple case in Figures 4a to 4d. The process of aggregating these bursts, with the aim of removing the sidelobes, can remain unchanged once the filters have been matched to the codes transmitted by each burst. This process implies the
8 detection of at least two bursts in one and the same angle-distance-Doppler cell. It is of course possible to envisage other processes than that based on the detection of at least two bursts (2 of N criterion). For the detection of slow objects, a priori situated in the first distance-Doppler ambiguity, no burst is obscured by the ambiguities and the "2 of N" criterion can be replaced by a "K of N" criterion where K is greater than 2. For a sufficient value of N, it is more effective, notably because it allows a better probability of detection, for one and the same probability of false alarm and a better probability of rejection of strong multiple echoes.
The example illustrated by Figures 4a to 4d is a simple case where there are two codes produced in two successive bursts, the detection being carried out on the basis of these two bursts. Cases can be proposed where the two successive codes can be repeated several times, over N bursts. In these cases where more successive bursts are processed, while transmitting only two codes, the criterion is of 1+N/2 of N. For example with N=6, a well-placed target responds on the 6 bursts, a badly-placed target responds on 3 bursts since the code that is suited to it is present three times. To discriminate this badly-placed target, a criterion of 4 of 6, or 5 of 6, or 6 of 6, and not 2 of 6 is necessary. More generally, in the case where the codes repeat in the series of transmitted bursts, the 2 of N process is not the most suitable. Other processes can advantageously be used.
It is thus possible to use processing of the "compressed sensing" algorithm type. These "compressed sensing" type algorithms make it possible to construct a signal from a small number of measurements. When applied to the present aggregation, the signal for detecting a target is constructed from the measurements carried out in each direction, for the successive multiple transmission codes.
These processes applied to the proposed waveforms make it possible to obtain performances superior to those of the 2 of N criterion or even the K of N criterion. They optimize the simultaneous detection of a set of targets.
Examples of processing of the "compressed sensing" type are notably described in the document "Compressed Sensing", by David L. Donoho, Department of Statistics, Stanford University, September 2004, or in the document "Compressed sensing radar", by Matthew Herman et al, Department of Mathematics, University of California, 2008 IEEE.
The example illustrated by Figures 4a to 4d is a simple case where there are two codes produced in two successive bursts, the detection being carried out on the basis of these two bursts. Cases can be proposed where the two successive codes can be repeated several times, over N bursts. In these cases where more successive bursts are processed, while transmitting only two codes, the criterion is of 1+N/2 of N. For example with N=6, a well-placed target responds on the 6 bursts, a badly-placed target responds on 3 bursts since the code that is suited to it is present three times. To discriminate this badly-placed target, a criterion of 4 of 6, or 5 of 6, or 6 of 6, and not 2 of 6 is necessary. More generally, in the case where the codes repeat in the series of transmitted bursts, the 2 of N process is not the most suitable. Other processes can advantageously be used.
It is thus possible to use processing of the "compressed sensing" algorithm type. These "compressed sensing" type algorithms make it possible to construct a signal from a small number of measurements. When applied to the present aggregation, the signal for detecting a target is constructed from the measurements carried out in each direction, for the successive multiple transmission codes.
These processes applied to the proposed waveforms make it possible to obtain performances superior to those of the 2 of N criterion or even the K of N criterion. They optimize the simultaneous detection of a set of targets.
Examples of processing of the "compressed sensing" type are notably described in the document "Compressed Sensing", by David L. Donoho, Department of Statistics, Stanford University, September 2004, or in the document "Compressed sensing radar", by Matthew Herman et al, Department of Mathematics, University of California, 2008 IEEE.
9 It is also possible to envisage adaptive processes, for example of the Capon or maximum likelihood type.
The invention therefore notably performs, in a radar with simultaneous multiple transmissions, the transmission of different codes from burst to burst and carries out the aggregation of various bursts by non-linear processing, for example of the "2 of N", "K of N", "compressed sensing", Capon or Maximum Likelihood type.
Figures 5a, 5b and 5c illustrate a result obtained by the implementation of the invention. According to the invention, several transmission elements each transmit several codes successively, therefore obtaining a succession of simultaneous multiple transmissions according to different codes. In the example in these figures, the succession of the codes is established over two bursts.
Figure 5a illustrates the ambiguity functions for a first code transmitted in the burst of order M and Figure 5b illustrates the ambiguity functions for a second code transmitted in the burst of order M+1. These ambiguity functions corresponding to sidelobes are represented in the angle-distance domain. Figure 5a exhibits a main lobe 51 and two first sidelobes 52, 53 as well as a multitude of sidelobes along three lines 54 passing through the preceding lobes and oriented in one and the same direction. Figure 5b exhibits the main lobe 51 and the two first sidelobes 52, 53 as well as a multitude of sidelobes along three lines 55 passing through these three lobes 51, 52, 53 and oriented in another direction.
At reception, one or more reception elements carry out:
- a process that makes use of the knowledge of the radiated signal as a function of the direction for each simultaneous multiple transmission, by means of a matched filter. This process can be carried out at the output of the Computational Beamforming function (with one matched filter per beam, the coefficients of which are associated with the direction of the beam), or be carried out before the Computational Beamforming (with a set of matched filters, each being associated with one of the directions of the beams that the Computational Beamforming produces);
- then a process that aggregates the responses originating from successive transmissions, this process being for example of "2 of N", "K of N", "compressed sensing", "Capon" or "Maximum Likelihood"
type.
5 The example in Figures 5a and 5b corresponds to the transmission of two successive codes. During the aggregation processing, a "2 of 2" criterion is equivalent to taking, at each point, the 2nd strongest signal from among the 2 available signals, i.e. to taking the minimum signal.
The ambiguity function resulting from this aggregation is illustrated by Figure
The invention therefore notably performs, in a radar with simultaneous multiple transmissions, the transmission of different codes from burst to burst and carries out the aggregation of various bursts by non-linear processing, for example of the "2 of N", "K of N", "compressed sensing", Capon or Maximum Likelihood type.
Figures 5a, 5b and 5c illustrate a result obtained by the implementation of the invention. According to the invention, several transmission elements each transmit several codes successively, therefore obtaining a succession of simultaneous multiple transmissions according to different codes. In the example in these figures, the succession of the codes is established over two bursts.
Figure 5a illustrates the ambiguity functions for a first code transmitted in the burst of order M and Figure 5b illustrates the ambiguity functions for a second code transmitted in the burst of order M+1. These ambiguity functions corresponding to sidelobes are represented in the angle-distance domain. Figure 5a exhibits a main lobe 51 and two first sidelobes 52, 53 as well as a multitude of sidelobes along three lines 54 passing through the preceding lobes and oriented in one and the same direction. Figure 5b exhibits the main lobe 51 and the two first sidelobes 52, 53 as well as a multitude of sidelobes along three lines 55 passing through these three lobes 51, 52, 53 and oriented in another direction.
At reception, one or more reception elements carry out:
- a process that makes use of the knowledge of the radiated signal as a function of the direction for each simultaneous multiple transmission, by means of a matched filter. This process can be carried out at the output of the Computational Beamforming function (with one matched filter per beam, the coefficients of which are associated with the direction of the beam), or be carried out before the Computational Beamforming (with a set of matched filters, each being associated with one of the directions of the beams that the Computational Beamforming produces);
- then a process that aggregates the responses originating from successive transmissions, this process being for example of "2 of N", "K of N", "compressed sensing", "Capon" or "Maximum Likelihood"
type.
5 The example in Figures 5a and 5b corresponds to the transmission of two successive codes. During the aggregation processing, a "2 of 2" criterion is equivalent to taking, at each point, the 2nd strongest signal from among the 2 available signals, i.e. to taking the minimum signal.
The ambiguity function resulting from this aggregation is illustrated by Figure
10 5c. There now remains only the main lobe 51 and the two first sidelobes 52, 53 and the sidelobes 57 on the distance axis.
Figure 5c moreover illustrates the effectiveness of the invention. It can indeed be seen that the invention greatly reduces the angle-distance domain in which a strong echo can disturb the detection of a weak echo. In the example in Figure 5c, it appears that the residual lobes 57 are nearly all on the distance axis. It is possible to resolve these sidelobes according to the prior art.
The basic process of removal of the sidelobes from one burst to the next is of "K of N" type. The value K = 2 is usually used for fast targets whereas a higher value is better suited to the detection of slow targets with low reflectivity, being first and foremost distance and speed, they are not obscured by the distance and speed eclipses, and are therefore visible over the N bursts. It is possible to implement two channels for aggregating the signals, one for the detection of fast targets, with K = 2, and the other for the detection of slow targets, with K> 2.
Several families of simultaneous multiple transmission codes can be used.
Preferably, code families are used that make it possible to easily obtain the operational objective. It is thus possible to choose a constraint that imposes sidelobes that are few in number or localized, such as for example the sidelobes 54 and 55 in Figures 5a and 5b, while accepting that they are relatively high. Being fewer in number and localized, their removal by a K of N criterion is effective and barely affects the detection of other targets.
The codes satisfying this constraint are numerous and easy to synthesize. Some examples will be given in the following text.
Figure 5c moreover illustrates the effectiveness of the invention. It can indeed be seen that the invention greatly reduces the angle-distance domain in which a strong echo can disturb the detection of a weak echo. In the example in Figure 5c, it appears that the residual lobes 57 are nearly all on the distance axis. It is possible to resolve these sidelobes according to the prior art.
The basic process of removal of the sidelobes from one burst to the next is of "K of N" type. The value K = 2 is usually used for fast targets whereas a higher value is better suited to the detection of slow targets with low reflectivity, being first and foremost distance and speed, they are not obscured by the distance and speed eclipses, and are therefore visible over the N bursts. It is possible to implement two channels for aggregating the signals, one for the detection of fast targets, with K = 2, and the other for the detection of slow targets, with K> 2.
Several families of simultaneous multiple transmission codes can be used.
Preferably, code families are used that make it possible to easily obtain the operational objective. It is thus possible to choose a constraint that imposes sidelobes that are few in number or localized, such as for example the sidelobes 54 and 55 in Figures 5a and 5b, while accepting that they are relatively high. Being fewer in number and localized, their removal by a K of N criterion is effective and barely affects the detection of other targets.
The codes satisfying this constraint are numerous and easy to synthesize. Some examples will be given in the following text.
11 The figures that follow present possible embodiments for the generation of signals and the digital processing of echoes originating from the successive simultaneous transmissions.
Figure 6 illustrates a possible exemplary embodiment of a radar according to the invention. The hardware necessary to transmit different multiple transmissions from one burst to another is essentially the same as for a single multiple transmission code. It is notably necessary to also provide the digital storage of the codes and their commands in a memory, which is simple to implement. In the example in Figure 6, the radar includes an antenna composed of Q transmission sub-arrays Ai, A2 AQ. Each sub-array possesses a signal generator 611, 612 ...61Q, programmable for example, capable of transmitting a different transmission characteristic from burst to burst. An amplifier 621, 622, 62Q amplifies the signals originating from the generators 611, 612 ...61Q before their passage through the sub-arrays. A local oscillator 10 supplies a base frequency to the frequency generators. The signal generators are commanded by command means 63, storing in a memory the various codes assigned to each sub-array AQ
for each burst. These means for storing codes in a memory and commanding codes are for example incorporated into the radar processing means. In the example in Figure 6, the transmission includes three successive codings 67, instead of two in the example in Figures 5a to 5d. The storage means 63 must therefore store at least 3xQ different codes in the memory.
The antenna thus transmits a succession of simultaneous multiple signals, in a period of three bursts.
Based on this succession of signals of simultaneous multiple transmissions, the radar receives a succession 68 of responses from targets. For a first target 60 a signal 681 is received corresponding to the coding of the burst M, a signal 682 corresponding to the coding of the burst M+1 and a signal 683 corresponding to the coding of the burst M+2. For a second target 60', another series of signals 681', 682', 683' is received.
At reception, the radar includes at least one antenna AR as well as reception means 64, 65 comprising at least one low-noise amplifier 64 and one digital receiver per antenna sub-array.
Figure 6 illustrates a possible exemplary embodiment of a radar according to the invention. The hardware necessary to transmit different multiple transmissions from one burst to another is essentially the same as for a single multiple transmission code. It is notably necessary to also provide the digital storage of the codes and their commands in a memory, which is simple to implement. In the example in Figure 6, the radar includes an antenna composed of Q transmission sub-arrays Ai, A2 AQ. Each sub-array possesses a signal generator 611, 612 ...61Q, programmable for example, capable of transmitting a different transmission characteristic from burst to burst. An amplifier 621, 622, 62Q amplifies the signals originating from the generators 611, 612 ...61Q before their passage through the sub-arrays. A local oscillator 10 supplies a base frequency to the frequency generators. The signal generators are commanded by command means 63, storing in a memory the various codes assigned to each sub-array AQ
for each burst. These means for storing codes in a memory and commanding codes are for example incorporated into the radar processing means. In the example in Figure 6, the transmission includes three successive codings 67, instead of two in the example in Figures 5a to 5d. The storage means 63 must therefore store at least 3xQ different codes in the memory.
The antenna thus transmits a succession of simultaneous multiple signals, in a period of three bursts.
Based on this succession of signals of simultaneous multiple transmissions, the radar receives a succession 68 of responses from targets. For a first target 60 a signal 681 is received corresponding to the coding of the burst M, a signal 682 corresponding to the coding of the burst M+1 and a signal 683 corresponding to the coding of the burst M+2. For a second target 60', another series of signals 681', 682', 683' is received.
At reception, the radar includes at least one antenna AR as well as reception means 64, 65 comprising at least one low-noise amplifier 64 and one digital receiver per antenna sub-array.
12 The reception means 65 notably carry out the following functions:
- Computational beamforming, capable of forming a cluster of beams covering the whole of the transmission pattern Tx;
- Pulse compression carrying out, in each formed beam, a filter 66 matched to the signal radiated in the direction of the beam;
- Doppler filtering producing a set of narrow filters;
- Regulation of false alarms combining CFAR (Constant False Alarm Rate, estimated on the distance and Doppler axes) and clutter map (estimated from scan to scan in each angle-distance cell, at low Doppler);
- Detection by comparison with a threshold;
- Distance-Doppler unfolding;
- Aggregation 69 of the signals 70 detected at the output of the filters 66 for the three bursts, for example in two types of aggregation:
- According to a "2 of N" criterion for the purpose of detecting fast targets;
- According to a "K of N" criterion for the purpose of detecting slow targets;
it being possible to use other criteria, with only the echo or echoes 600 of targets present in the direction of the matched filters subsisting at the output of the aggregation;
- Extraction of the data associated with each aggregation by:
- Grouping of neighbouring detections into a cluster of detections - Computation of the average position of each cluster - Grouping of the information into a pip - Optionally, a tracking performing:
- A chaining of the pips in sequence;
- A computation of the trajectory parameters.
It is possible to modify the order of the two first functions above which then become:
- Pulse compression adapted to the directions covering the whole of the transmission pattern Tx;
- Computational beamforming, capable of forming a cluster of beams covering the whole of the transmission pattern Tx;
- Pulse compression carrying out, in each formed beam, a filter 66 matched to the signal radiated in the direction of the beam;
- Doppler filtering producing a set of narrow filters;
- Regulation of false alarms combining CFAR (Constant False Alarm Rate, estimated on the distance and Doppler axes) and clutter map (estimated from scan to scan in each angle-distance cell, at low Doppler);
- Detection by comparison with a threshold;
- Distance-Doppler unfolding;
- Aggregation 69 of the signals 70 detected at the output of the filters 66 for the three bursts, for example in two types of aggregation:
- According to a "2 of N" criterion for the purpose of detecting fast targets;
- According to a "K of N" criterion for the purpose of detecting slow targets;
it being possible to use other criteria, with only the echo or echoes 600 of targets present in the direction of the matched filters subsisting at the output of the aggregation;
- Extraction of the data associated with each aggregation by:
- Grouping of neighbouring detections into a cluster of detections - Computation of the average position of each cluster - Grouping of the information into a pip - Optionally, a tracking performing:
- A chaining of the pips in sequence;
- A computation of the trajectory parameters.
It is possible to modify the order of the two first functions above which then become:
- Pulse compression adapted to the directions covering the whole of the transmission pattern Tx;
13 - Computational beamforming forming, for each pulse compression output, the beam associated with the direction.
A few variant embodiments can be implemented; in particular, an exemplary embodiment may be proposed including one or more of the following characteristics:
- The transmission antenna includes one generator per radiating element; this is equivalent to each transmission sub-array being a single antenna element;
- The transmission antenna possesses sub-arrays the centres of which are aligned on a single axis, for example in the form of vertical cantilevers spaced on the horizontal axis or horizontal cantilevers spaced on the vertical axis;
- The sub-arrays of reception antennas are not localized in the same place and each reception sub-array receives echoes originating from different transmissions, the process that brings together the signals originating from the remote sub-arrays being then achievable coherently or non-coherently; the example in Figure 6 exhibits a single reception sub-array but it is of course possible to provide several;
- The cluster of reception beams includes beams the separation of which is reduced for example by a root 2 factor on each axis to anticipate the gain in angular resolution contributed by the simultaneous multiple transmission;
- The reception antenna includes one receiver per radiating element, this being equivalent to each reception sub-array being a single antenna element;
- The pulse compression provides several parallel filters, each matched to a range of radial velocities. This is notably useful when the codes are sensitive to Doppler, which codes can be made beneficial for the purpose of the proposed solution;
- Doppler filtering may not be performed, for a transmission in bursts including a single pulse, or may include poorly resolving filters, for bursts including a small number of pulses;
- The false alarm regulating member carries out its estimate by relying on the properties of each transmitted code, for example by an estimate on a distance-angle diagonal;
=
A few variant embodiments can be implemented; in particular, an exemplary embodiment may be proposed including one or more of the following characteristics:
- The transmission antenna includes one generator per radiating element; this is equivalent to each transmission sub-array being a single antenna element;
- The transmission antenna possesses sub-arrays the centres of which are aligned on a single axis, for example in the form of vertical cantilevers spaced on the horizontal axis or horizontal cantilevers spaced on the vertical axis;
- The sub-arrays of reception antennas are not localized in the same place and each reception sub-array receives echoes originating from different transmissions, the process that brings together the signals originating from the remote sub-arrays being then achievable coherently or non-coherently; the example in Figure 6 exhibits a single reception sub-array but it is of course possible to provide several;
- The cluster of reception beams includes beams the separation of which is reduced for example by a root 2 factor on each axis to anticipate the gain in angular resolution contributed by the simultaneous multiple transmission;
- The reception antenna includes one receiver per radiating element, this being equivalent to each reception sub-array being a single antenna element;
- The pulse compression provides several parallel filters, each matched to a range of radial velocities. This is notably useful when the codes are sensitive to Doppler, which codes can be made beneficial for the purpose of the proposed solution;
- Doppler filtering may not be performed, for a transmission in bursts including a single pulse, or may include poorly resolving filters, for bursts including a small number of pulses;
- The false alarm regulating member carries out its estimate by relying on the properties of each transmitted code, for example by an estimate on a distance-angle diagonal;
=
14 - The aggregation of the bursts is carried out using a "Compressed sensing" process, a single aggregation process can then be suitable both to slow targets and to fast targets;
- The aggregation of the bursts is carried out using an adaptive type process, for example a least squares, Capon or else maximum likelihood method.
Figures 7a to 7d illustrate examples of coding of the space, by simultaneous multiple transmissions, by examples of allocation of frequency to the antenna sub-arrays distributed on a single axis. The frequency sub-bands allocated are represented as a function of the position of the sub-arrays. More particularly, the allocated frequencies are represented by squares 71, 72, 73, 74. The dimensions of each square represent the frequency sub-band along the ordinate axis and the dimension of the sub-array along the abscissa axis.
These squares form elements of a matrix including a single element per row and per column.
Figure 7a corresponds to an coding analogous to that in Figure 4a. In this example, the frequencies increase linearly with the position of the sub-arrays.
The squares 72 in Figure 7b are aligned regularly along three upward slopes shifted in frequency. In Figure 7c, the squares 73 are aligned regularly along three downward slopes shifted in frequency. In Figure 7d, the squares 74 are grouped into pairs, the pairs being themselves aligned regularly along downward slopes. One pair is composed of two contiguous squares according to one of their diagonals. Many other configurations of the squares, and therefore other codings by frequency allocation by sub-array, are of course possible.
The invention has been described for radars with simultaneous multiple transmissions. The invention can also advantageously be applied to active sonars operating according to the same principle of multiple transmissions.
- The aggregation of the bursts is carried out using an adaptive type process, for example a least squares, Capon or else maximum likelihood method.
Figures 7a to 7d illustrate examples of coding of the space, by simultaneous multiple transmissions, by examples of allocation of frequency to the antenna sub-arrays distributed on a single axis. The frequency sub-bands allocated are represented as a function of the position of the sub-arrays. More particularly, the allocated frequencies are represented by squares 71, 72, 73, 74. The dimensions of each square represent the frequency sub-band along the ordinate axis and the dimension of the sub-array along the abscissa axis.
These squares form elements of a matrix including a single element per row and per column.
Figure 7a corresponds to an coding analogous to that in Figure 4a. In this example, the frequencies increase linearly with the position of the sub-arrays.
The squares 72 in Figure 7b are aligned regularly along three upward slopes shifted in frequency. In Figure 7c, the squares 73 are aligned regularly along three downward slopes shifted in frequency. In Figure 7d, the squares 74 are grouped into pairs, the pairs being themselves aligned regularly along downward slopes. One pair is composed of two contiguous squares according to one of their diagonals. Many other configurations of the squares, and therefore other codings by frequency allocation by sub-array, are of course possible.
The invention has been described for radars with simultaneous multiple transmissions. The invention can also advantageously be applied to active sonars operating according to the same principle of multiple transmissions.
Claims (19)
1. Detection system with simultaneous multiple transmissions including an antenna composed of transmission sub-arrays (Ai, ... A()) illuminating one and the same zone of the space and at least one reception sub-array (AR), each sub-array having a given position in said array, each transmission sub-array transmitting a signal having a specific characteristic, the set of characteristics specific to each sub-array forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different transmission codes, echoes being present in the main lobe and in the sidelobes of the ambiguity function, said system being configured to:
transmit different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
detect the signals originating from each direction;
carry out the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes of the ambiguity function.
transmit different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
detect the signals originating from each direction;
carry out the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes of the ambiguity function.
2. Detection system according to claim 1, wherein said at least two transmission codes are consecutive.
3. Detection system according to claim 1 or 2, wherein said at least two codes are repeated within said series of bursts.
4. Detection system according to any one of claims 1 to 3, wherein, since the transmission includes N different codes, one per burst, the aggregation is performed according to a "2 of N" criterion.
5. Detection system according to any one of claims 1 to 3, wherein since the transmission includes N different codes, one per burst, the aggregation is performed according to a "K of N" criterion, K being greater than 2.
Date Recue/Date Received 2020-10-15
Date Recue/Date Received 2020-10-15
6. Detection system according to claim 1 or 2, wherein the aggregation is made according to processing of the "Compressed Sensing" type.
7. Detection system according to any one of claims 1 to 6, wherein the aggregation is made according to processing of the maximum likelihood type.
8. Detection system according to any one of claims 1 to 7, wherein a simultaneous multiple transmission code is produced by attributing a frequency sub-band to each transmission sub-array.
9. Detection system according to any one of claims 1 to 8, wherein the phase centres of said transmission sub-arrays (Ai, ... A()) are aligned on an axis.
10. Detection system according to any one of claims 1 to 9, wherein including several reception sub-arrays (AR), said sub-arrays are not co-located, each reception sub-array receiving the signals originating from the different transmissions produced by said transmission sub-arrays.
11. Detection system according to any one of claims 1 to 10, wherein the detection system is a radar.
12. Detection method with simultaneous multiple transmissions using an antenna composed of transmission sub-arrays (Ai, ... A()) illuminating one and the same zone of the space and at least one reception sub-array (AR), each sub-array having a given position in said array, a method in which to each transmission sub-array is attributed a transmission signal having a specific characteristic, the set of characteristics specific to each sub-array forming the simultaneous multiple transmission code, the detection of targets being performed by the transmission of a series of bursts of multiple transmissions, said series including at least two different transmission codes, echoes being present in the main lobe and in the sidelobes of the ambiguity function, the method comprising:
Date Recue/Date Received 2020-10-15 transmitting different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
detecting the signals originating from each direction;
making the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes of the ambiguity function.
Date Recue/Date Received 2020-10-15 transmitting different codes from among at least two bursts, said transmission preserving the main lobe of the ambiguity function but orienting said sidelobes of said ambiguity function in different directions from burst to burst;
detecting the signals originating from each direction;
making the aggregation of the different signals detected in each direction for said at least two bursts, said aggregation reducing the level of the echoes present in said sidelobes of the ambiguity function.
13. Detection method according to claim 12, wherein said at least two transmission codes are consecutive.
14. Detection method according to claim 12 or 13, wherein said at least two codes are repeated within said series of bursts.
15. Detection method according to any one of claims 12 to 14, wherein, since the transmission includes N different codes, one per burst, the aggregation is performed according to a "2 of N" criterion.
16. Detection method according to any one of claims 12 to 14, wherein since the transmission includes N different codes, one per burst, the aggregation is performed according to a "K of N" criterion, K being greater than 2.
17. Detection method according to any one of claims 12 and 13, wherein the aggregation is made according to processing of "Compressed Sensing" type.
18. Detection method according to any one of claims 12 to 17, wherein the aggregation is made according to processing of maximum likelihood type.
19. Method according to any one of claims 12 to 18, wherein a simultaneous multiple transmission code is performed by attributing a frequency sub-band (43) to each sub-array (Ai, AQ).
Date Recue/Date Received 2020-10-15
Date Recue/Date Received 2020-10-15
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| FR1301453A FR3007585B1 (en) | 2013-06-21 | 2013-06-21 | SIMULTANEOUS MULTI-EMISSION DETECTION SYSTEM AND DETECTION METHOD |
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| FR3125888B1 (en) | 2021-07-30 | 2023-07-07 | Thales Sa | METHOD FOR OPTIMIZING THE DETERMINATION OF THE DISTANCE OF A TARGET IN RELATION TO A PHASE ENCODED RADAR IN PULSE MODE |
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| EP2816369A1 (en) | 2014-12-24 |
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