Coherent MIMO Radar Processing Method Using DDMA Waveform

Abstract

The present invention relates to a coherent MIMO radar processing method using a DDMA waveform. The radar processes the DDMA waveform and includes NT X transmitters and NR X receivers, and the method includes the steps of: a) generating waveforms on up to NT X transmitters, the waveforms being the same for each transmitter, having a pulse repetition frequency of F R and within a phase ramp specific to each transmitter; b) for at least one receiver, generating a range-Doppler representation of the echoes of the transmitted waveforms, for each receiver, the echoes of the transmitters on a plurality of range cells occupy at least one frequency cell called a signal band in the Doppler spectrum, each signal band being specific to one of the transmitters, determining the position of the signal band in the Doppler spectrum according to the phase ramp applied to each transmitter, and the waveform being generated such that a part of the Doppler spectrum between two signal bands is unoccupied; c) identifying the transmitters corresponding to each signal band according to the range-Doppler representation of the echoes of the transmitted waveforms.

Description

Field of the Invention

[0001] The field of the invention is MIMO ("Multiple Input Multiple Output") radar with a DDMA (Doppler Diversity Multiple Access) waveform. The invention is particularly applicable to millimeter-wave radar, especially radar operating in the W band (frequencies between 75 GHz and 110 GHz). Without limitation, the invention can be applied to airborne radar, especially for landing assistance. Background Art

[0002] MIMO radar specifically enables improved radar detection performance in a number of applications (especially airborne radar) by providing better angular resolution and better Doppler resolution. MIMO radar consists of multiple receivers and multiple transmitters. MIMO radar is generally divided into two types: bistatic MIMO radar and coherent MIMO radar. In bistatic MIMO radar, not all transmitters and / or receivers are located in the same area or on the same vehicle. In coherent MIMO radar, the transmitters and receivers are co-located on the vehicle: hence the name coherent MIMO radar. In the present invention, the radar is assumed to be coherent.

[0003] The DDMA waveform used in MIMO radar is particularly advantageous because the DDMA waveform exhibits good orthogonality between channels and thus has good isolation. Specifically, the signals transmitted on each transmit antenna are the same, except that the center frequencies of the signals transmitted by the respective transmit antennas are slightly offset from each other such that these signals can be separated in the Doppler domain. Thus, the respective waveforms are generated by applying different phase modulations between each transmit channel.

[0004] Next, the received signals are processed by a set of matched filters, each filter matching the waveform and isolating each transmit channel.

[0005] Figure 1 A representation of the signals received on a particular receiver is shown, where each signal band (vertical in the direction of the figure) corresponds to the echo of a fixed or moving target of each transmitter after Doppler processing. In Figure 1 , the radar includes NT X = 8 transmitters, each transmitter offset by F Figure 1 in R / NT X where F R is the pulse repetition frequency.

[0006] Next, the signals received by all receivers are combined with the signals transmitted by all transmitters in order to perform DBF (Digital Beamforming) processing. Recall that, in order to perform DBF processing, by allocating power on the transmit antennas to obtain the maximum energy in a given direction, an optimization of the transmit / receive relationship is sought on each transmit path / receive path pair.

[0007] However, in order to perform DBF processing, it is necessary to identify the transmitter corresponding to each received signal band. The differences between the bands of the received signals are known because this difference is related to the phase law of the DDMA waveform, but the absolute positioning of these bands (i.e., the transmitter corresponding to at least one of the received signal bands) remains to be determined. Then, the other transmitters can be deduced by knowing the phase shift of each transmitter.

[0008] Taking the transmitter with a zero phase ramp as a reference, the received signal bands are centered at the Doppler frequency related to the aiming direction and speed of the radar. Therefore, this Doppler frequency must be known with sufficient accuracy so as not to confuse the bands.

[0009] Figure 2 Show the vector representing the movement of the vehicle / radar and the aiming axis of the radar in the direction of target C.

[0010] As is well known, the Doppler frequency f D has a value of:

[0011]

[0012] where V is the speed of the radar, S and G are the elevation angle and azimuth angle of aiming respectively, λ is the wavelength of the radar, V R is the relative radial velocity of the radar with respect to the target, which corresponds to the projection of the speed of the radar on the aiming axis.

[0013] Therefore, the selection of the samples associated with the transmitter having a zero phase ramp depends on knowing that the accuracy improves with the frequency resolution c F of the pulse and the reduction of the wavelength of V R . Due to aliasing in the Doppler domain, it is more important to know V R when the speed of the radar is not clear.

[0014] For example, if the value of the frequency resolution is c F = 10 Hz, the frequency of the radar is F E = 3 GHz (S band, λ = 0.1 m); in order to know the positioning of the signal within the cell, the accuracy of V R is λ / 2 * c F= 0.5 m / s, which is achievable using conventional inertial measurement units or GPS relatively.

[0015] Under the same conditions, for an X-band radar (F E = 10 GHz, λ = 3 cm), the accuracy of V R becomes λ / 2 * c F = 0.15 m / s = 15 cm / s, which requires a high-quality inertial measurement unit.

[0016] However, under the same conditions, for a millimeter-wave radar (W-band between 75 GHz and 110 GHz), the accuracy of V R is about 1 cm / s, which requires a very high-precision inertial measurement unit, and this is not always compatible with low-cost systems.

[0017] The article "Airborne GMTI using MIMO techniques" (J. Kantor & S. K. Davis, 2011, Technical Report 1150, Lincoln Laboratory) describes a MIMO system with a DDMA waveform. In this article, no method for selecting samples from each transmitter is mentioned, but since the radar used is the S-band radar as described above, the required accuracy of the carrier velocity is not a problem. Summary of the Invention

[0018] The object of the present invention is to propose a system that not only does not require high-precision knowledge of the relative radial velocity of the radar with respect to the target, but can also completely dispense with it.

[0019] Therefore, one subject of the present invention is a coherent MIMO radar processing method, the coherent MIMO radar processing a DDMA waveform and including NT X transmitters and NR X receivers, and the method includes the following steps:

[0020] a) Generate waveforms on at most NT X transmitters, the waveforms being the same modulo the pulse repetition frequency F R from one transmitter to the next and within a phase ramp specific to each transmitter;

[0021] b) For at least one receiver, generate a range-Doppler representation of the echoes of the transmitted waveform, wherein, for each receiver, the echoes of the transmitter over a plurality of range cells occupy at least one frequency cell, called a signal band, in the Doppler spectrum, each signal band being specific to one of the transmitters, and the position of the signal band in the Doppler spectrum is determined according to the phase ramp applied to each transmitter, and the waveform is generated such that a portion of the Doppler spectrum between two signal bands is unoccupied;

[0022] c) Identify the transmitters corresponding to each signal band according to the range-Doppler representation of the echoes of the transmitted waveform.

[0023] Advantageously, step c) includes the following sub-steps:

[0024] - Calculate a signal called the echo signal, which is obtained by summing the powers of the echoes of each signal band over all range cells;

[0025] - Generate a signal called the pattern signal on the same number of frequency cells as the range-Doppler representation of the echoes of the transmitted waveform, and the transmitters are numbered in ascending order according to the phase ramp applied to the transmitters. The pattern signal is generated such that the transmitters are sorted in ascending order, taking into account the unoccupied portion of the Doppler spectrum;

[0026] - Calculate the cross-correlation signal between the echo signal and the pattern signal;

[0027] - Identify the transmitters corresponding to each signal band according to the maximum value of the cross-correlation signal.

[0028] Advantageously, in the identification step, the position of the maximum value of the cross-correlation signal corresponds to the echo of the first transmitter in the Doppler spectrum, and the first transmitter is defined as the transmitter with a phase ramp of zero.

[0029] Advantageously, the unoccupied portion of the Doppler spectrum is obtained by turning off one of the NT X transmitters. For each frequency cell k*F R / NT X , the pattern signal is non-zero, where k = {0,..., NT X - 1}, and in other frequency cells, the pattern signal is zero.

[0030] Advantageously, the unoccupied portion of the Doppler spectrum is obtained by determining the phase ramp such that the signal bands are separated by F R / NT X2 frequency cells in the Doppler spectrum, where NT X2 is an integer such that NT X2 > NT X and for each frequency cell k*FR / NT X2 where the pattern signal is non-zero, where k = {0, …, NT X -1}, and in other frequency units, the pattern signal is zero.

[0031] Advantageously, the range-Doppler representation of the echo is obtained by performing a fast Fourier transform (FFT) on multiple sampling points. If NT X is not a power of 2, the number of sampling points is supplemented by adding zeros to obtain a total of N FFT points, and N FFT is determined to be an integer multiple of the number of transmit paths NT X .

[0032] Advantageously, the range-Doppler representation of the echo is obtained by performing a fast Fourier transform (FFT) on a pulse sequence encoded over a coherent processing interval (CPI), and the number of pulses per coherent processing interval (CPI) is adjusted to be a multiple of the number of transmitters.

[0033] Another subject of the present invention is a coherent MIMO radar processing method. The coherent MIMO radar utilizes a DDMA waveform and includes NT X transmitters and NR X receivers. The method includes the following steps:

[0034] a) Generate waveforms on up to NT X transmitters, the waveforms being modulo the pulse repetition frequency F R and being the same from one transmitter to the next within the phase ramp specific to each transmitter;

[0035] b) For at least one receiver, generate a range-Doppler representation of the echo of the transmitted waveform. For each receiver, the echo of the transmitters on multiple range cells occupies at least one frequency unit called the signal band in the Doppler spectrum. Each signal band is specific to one of the transmitters, and the position of the signal band in the Doppler spectrum is determined according to the phase ramp applied to each transmitter. The waveform is generated such that the interval between at least two consecutive signal bands is different from the interval between other consecutive signal bands;

[0036] c) Identify the transmitter corresponding to each signal band according to the range-Doppler representation of the echo of the transmitted waveform.

[0037] Advantageously, the intervals between two consecutive signal bands are all different.

[0038] Advantageously, the signal bands are separated according to a predetermined interval rule.

[0039] Advantageously, the spacing between each signal band is determined such that the average value of the spacing is equal to F R / NT X .

[0040] Advantageously, the range-Doppler representation of the echo is obtained by performing a fast Fourier transform (FFT) on a plurality of sampling points, and the number of sampling points is supplemented by adding zeros to obtain a total of N FFT points, N FFT is determined such that the spacing between two consecutive frequency bands is F R / N FFT times an integer of.

[0041] Advantageously, the range-Doppler representation of the echo is obtained by performing a fast Fourier transform (FFT) on a pulse sequence encoded over a coherent processing interval (CPI), and the number of pulses N REC for each coherent processing interval (CPI) is determined such that the spacing between two consecutive frequency bands is F R / N REC times an integer of.

[0042] Advantageously, the method includes an additional step of digital shaping processing, wherein the waveforms are combined with the echoes from different receivers in a weighted manner.

[0043] Another subject of the present invention is a MIMO radar capable of implementing the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other features, details and advantages of the present invention will become apparent by reading the description given with reference to the accompanying drawings, which are given by way of example and in which:[[]]END]]

[0045] The above-described Figure 1 shows a DDMA waveform according to the prior art;

[0046] The above-described Figure 2 shows the carrier vector of the radar relative to the target;

[0047] Figure 3 shows a schematic diagram of a MIMO radar processing method according to a first embodiment of the present invention, wherein one of the transmitters is turned off;

[0048] Figure 4 shows a schematic diagram of a MIMO radar processing method according to a second embodiment of the present invention, wherein the spacing between the frequency bands is modified;

[0049] Figure 5 shows a schematic diagram of a MIMO radar processing method according to a third embodiment of the present invention, wherein the spacing between the frequency bands is non-uniform. Detailed implementation manners

[0050] According to the first and second embodiments of the present invention, the method includes three steps.

[0051] In the first step, a radar including NT X transmitters generates waveforms on at most NT X transmitters. According to the first embodiment described in detail below, one of the NT X transmitters is turned off. According to the second embodiment also described in detail below, all transmitters are activated. As described above, the principle of the DDMA waveform is to transmit radar pulses that are the same within the phase ramp specific to each transmitter from one transmitter to the next at each pulse repetition interval. The phase ramp is created by a phase shifter, which is a relatively easy-to-integrate component. Next, each received echo is processed by a bank of matched filters (i.e., one filter for each waveform).

[0052] The processing method according to the present invention can be implemented at one, multiple, or even all receivers in the receiver. Applying to digital beamforming particularly requires associating all receivers with the transmitters, but this application is non-limiting. Generally, the method according to the present invention enables, in the MIMO context, even for one receiver, associating each signal band with one of the transmitters.

[0053] For this purpose, in the second step b), a range-Doppler representation of the echoes of the transmitted waveforms is generated. As shown in the above description Figure 1 , the range-Doppler representation includes frequency cells (or FFT (Fast Fourier Transform) points) on the abscissa and range cells on the ordinate. Each signal band is concentrated on the frequency cell of the Doppler shift of each transmitter. Therefore, the signal bands are separated by F R / NT X , where F R is the pulse repetition frequency (the reciprocal of the pulse repetition interval).

[0054] Due to the nature of the DDMA waveform, which introduces a phase shift for each transmitter, this phase shift can be found in the Doppler spectrum and in the separation of the signal bands. Each received echo is processed by a bank of matched filters (i.e., one filter for each waveform). At reception, the processor of the MIMO radar removes the phase shift applied during transmission.

[0055] The method according to the invention is characterized in that the waveform is generated such that a portion of the Doppler spectrum between two signal bands is not occupied. For the prior art DDMA MIMO radar, the applied phase shifts are determined such that the signal bands are evenly distributed in the Doppler spectrum. However, by leaving a portion of the spectrum unoccupied, it is facilitated to identify the transmitters corresponding to each signal band, as shown below (step c) of the method).

[0056] Advantageously, step c) of the processing method comprises a first sub-step of calculating a signal called the echo signal. The echo signal is obtained by summing the echo powers for each signal band over all range cells. Thus, a signal representing the energy of each signal band is obtained. Thus, the echo signal is obtained directly and easily (i.e., without computational complexity) from the range-Doppler representation.

[0057] Next, in a second sub-step, a signal called the pattern signal is generated on the same number of frequency cells as the range-Doppler representation of the echo of the transmit waveform. The pattern signal is an ordered representation of the offsets caused by the phase ramps applied to each transmitter. Thus, in a MIMO radar, the applied phase ramps are associated with each transmitter. Next, numbers are assigned to the transmitters: No. 1 for the transmitter with zero phase ramp, No. 2 for the first phase ramp, and so on. Thus, numbers from 1 to NT X are assigned to each transmitter. The pattern signal is a binary signal, and for each frequency cell corresponding to the offsets caused by the ramps with various phase laws, the value of the pattern signal is 1 (or any other value other than zero, as long as the value is the same for all transmitters), otherwise it is 0. Additionally, in the unoccupied portion of the Doppler spectrum, the pattern signal is also set to 0.

[0058] Then the cross-correlation signal between the echo signal and the pattern signal is calculated. The cross-correlation signal corresponds to the cross-correlation function between the echo signal and the pattern signal. Each of these two signals can be considered as a "comb" signal. When the two "comb" signals meet, the cross-correlation signal is at its maximum.

[0059] The position of the maximum of the cross-correlation signal indicates the position of the first transmitter in the Doppler spectrum. The positions of the other transmitters are derived by offsetting according to the theoretical separation between the signal bands, modulo the pulse repetition frequency or modulo the number of FFT points.

[0060] The described processing is systematically performed for each burst of radar signals.

[0061] Figure 3Shows a first embodiment of a processing method according to the present invention. According to the first embodiment, an unoccupied portion in the spectrum is generated by turning off one of the transmitters. Specifically, MIMO radars typically have a number of transmitters, for example around 10, and in the case where the radar includes 10 transmitters, turning off one transmitter only has an impact of around 10% on the radar image.

[0062] In Figure 3 the example of X NT = 6 transmitters, and the fifth transmitter is turned off.

[0063] One of the transmitters can be turned off in various ways. For example, amplitude control used in radar active antennas for amplitude and phase control can apply zero amplitude to the transmitter to be turned off. The advantage of this solution is that it can be reconfigured during the mission by modifying the amplitude control command. Another option is that the output of the transmitter to be achieved in the power transmitter is not connected, which constitutes a permanent solution and can only be modified between two missions. Another possibility is to add a controlled switch upstream of each power transmitter.

[0064] When the number of transmitters to be turned off is known, the selection of the transmitter to be turned off can be completely random. The choice of path has no effect on the result of the process.

[0065] The echo signal is obtained by summing the power of each range cell for each signal band. In the Doppler spectrum, all echoes of the transmitters are separated by F R / NT X , except for the frequency band where the transmitter is turned off by definition. In Figure 3 , echoes are received at 120 FFT points, and this value does not limit the scope of the present invention.

[0066] The mode signal is represented on the same number of frequency cells as the Doppler spectrum of the received echo. For each frequency cell k*F R / NT X , where k = {0,..., NT X - 1}, the mode signals are non-zero (e.g., having a value of 1) except for the signal band of the turned-off transmitter. The mode signals of other frequency cells are also zero. In Figure 3 the example of R the fifth (out of six transmitters) transmitter is turned off. Therefore, the mode signal is a comb with non-zero values in the 0, F R / 6, 2*F R / 6, 3*F R / 6, and 5*F

[0067] Finally, the cross-correlation signal between the echo signal and the pattern signal is calculated. In Figure 3 , the cross-correlation signal read in combination with the Doppler spectrum of the received echo should be maximum at a position in the Doppler spectrum corresponding to the signal band of the first transmitter (i.e., Figure 3 in the example, the second signal band on the right side of the spectrum). Therefore, the second signal band on the right corresponds to the echo from the first transmitter. Next, the positions of the other transmitters can be derived by simply shifting cyclically from left to right with respect to the phase ramp. In Figure 3 's example, the first signal band on the right corresponds to the echo of the second transmitter, and the first band on the left corresponds to the echo of the third transmitter, and so on.

[0068] Therefore, the signals from each transmitter are associated in the Doppler spectrum without using the information about the radial velocity of the carrier, which corresponds to the projection of the velocity of the carrier on the aiming axis.

[0069] The first embodiment described above is particularly suitable for a DDM A MIMO radar having a large number of transmitters (e.g., around 10). Therefore, turning off one transmitter has little impact on the radar efficiency.

[0070] However, when the MIMO radar has fewer transmitters, from the perspective of radar efficiency, turning off one of them may prove to be disadvantageous. For example, if the MIMO radar only contains four transmitters, turning off one of them will affect the radar image by about 25%, which does not represent the optimal use of the radar.

[0071] The second embodiment of the processing method according to the present invention also enables the association of transmitters with each signal band. To this end, the phase ramp is generated such that the signal bands are separated in the Doppler spectrum by F R / NT X2 frequency units, where NT X2 is an integer such that NT X2 >NT X . For example, NT X2 =NT X +1. In Figure 4 's example, NT X2 =NT X +2, NT X =6, NT X2 =8.

[0072] The intervals generated in this way also create blank spaces in the Doppler space, as in the first embodiment. Figure 4 The Doppler spectrum shown shows six signal bands separated by F R / 8 in the range-Doppler representation of the echo of the transmitted waveform.

[0073] As in the first embodiment, an echo signal is created. In the second embodiment, the value of the echo signal is the sum of the powers of the echoes received on all range cells of the signal band. Thus, at N FFT frequency units, the echo signal has NT R / NT X2 positive values separated by X .

[0074] In addition, for each frequency unit k*F R / NT X2 , where k = {0, …, NT X - 1}, the pattern signal is non-zero (e.g., has a value of 1) and zero in other frequency units. The pattern signal is represented on the same number of frequency units as the Doppler spectrum of the received echo. In the Figure 4 example, the pattern signal takes the value "1" at 0 on the abscissa and for each frequency unit separated by F R / NT X2 , and "0" in other frequency units.

[0075] The cross-correlation signal corresponds to the cross-correlation function between the echo signal and the pattern signal. The maximum value of the cross-correlation signal indicates the first transmitter, i.e., the transmitter for which the phase ramp applied during transmission is zero.

[0076] In the Figure 4 example, by superimposing the cross-correlation signal on the Doppler spectrum, it can be seen that the maximum value of the cross-correlation signal corresponds to the leftmost signal band in the Doppler spectrum. The second band from the left corresponds to the second transmitter path, and so on. As in the first embodiment, the blank spaces created in the Doppler spectrum enable the relative position of the signals to be identified without knowing the radial velocity of the carrier relative to the target, i.e., which transmitter the signal is from.

[0077] Although the spacing between the DDMA signal bands is uniform (having a value of F R / NT X or F R / NT X2 according to the first or second embodiment), it is not always equal to an integer of the frequency unit. If NT X or NT X2(According to the second embodiment), this occurs when the number of points for performing the FFT is not a power of 2, while it is typically a power of 2. In this case, one option is to take the nearest frequency bin, but the same echo from different transmitters will be sampled differently from one signal frequency band to the next, which will result in unwanted amplitude modulation and thus worse DBF results. Another solution is to interpolate the signal so that the signal is placed on the sampling grid shared by each DDMA channel, or equivalently perform the inverse Fourier transform, numerically apply a phase ramp opposite to the phase ramp used during transmission, and then perform the direct Fourier transform again to select the samples around the zero frequency bin. All these operations can obtain defect-free DBF, but at the cost of high computational complexity.

[0078] To overcome this, it is proposed to supplement the number of sampling points by adding zeros in the time domain ("zero-padding" technique) until the FFT number of points N FFT is an integer multiple of the number of transmitters NT X .

[0079] For example, if there are NT X = 12 transmitters and it is initially envisioned to perform the FFT on N REC = 512 points (recall that T E = 1 / c F = N REC / F R ), then an FFT of N FFT = 540 points must be performed, which is a multiple of NT X = 12.

[0080] As an alternative, adjust the number of pulses per coherent processing interval (CPI) so that it is a multiple of the number of transmitters.

[0081] For example, when NT X = 12, N REC = 480 or N REC = 540 will be used instead of N REC = 512, which allows performing the FFT without zero-padding while maintaining a multiple of NT X .

[0082] Figure 5 Figure 3 shows the third embodiment of the present invention.

[0083] Step a) of the method according to the third embodiment of the present invention is the same as step a) of the first two embodiments.

[0084] In step b), a range-Doppler representation of the echoes of the transmitted waveform is generated for at least one receiving path. For each receiver, the echoes of the transmitter on multiple range cells occupy at least one frequency cell in the Doppler spectrum (signal band). Each signal band is specific to one of the transmitters. The position of the signal band in the Doppler spectrum is determined according to the phase ramp applied to each transmitter. A more specific feature of the third embodiment is the spacing between each signal band: the spacing between each signal band is non-uniform: the spacing between at least two signal bands (between these two bands) is different from the spacing between other signal bands. In particular, all the spacings between two consecutive signal bands are different, but this is not a necessary condition. This non-uniform spacing enables the transmitter corresponding to the echo to be easily identified without turning off one of the transmitters. Therefore, this embodiment does not affect the radar efficiency.

[0085] The third embodiment includes a third step c): identifying the transmitter corresponding to each signal band according to the range-Doppler representation of the echoes of the transmitted waveform. This step is the same as step c) of the first two embodiments.

[0086] Figure 5 The Doppler spectrum shown displays six signal bands, and the spacing between the six signal bands in the range-Doppler representation of the echoes of the transmitted waveform is non-uniform. In Figure 5 it, the spacing varies from F R / 8 to F R / 6; these values are given only as examples.

[0087] In the third embodiment, the value of the echo signal is the sum of the powers of the echoes received on all range cells of the signal band. Therefore, the echo signal has N T X positive values.

[0088] In addition, for each frequency cell f(k)*F R / N T X , where k = {0,..., N T X -1}, the pattern signal is non-zero (for example, has a value of 1), and in other frequency cells, the pattern signal is zero, and f() is a function representing the non-uniform spacing. Therefore, the function f() can define the spacing rule. For example, the spacing rule can be linear or logarithmic. The pattern signal is represented on the same number of frequency cells as the Doppler spectrum of the received echo.

[0089] Advantageously, the spacing between each signal band is determined such that the average value of the spacing is equal to F R / N T X .

[0090] The cross-correlation signal corresponds to the cross-correlation function between the echo signal and the pattern signal. The maximum value of the cross-correlation signal indicates the first transmitter, i.e., the transmitter for which the phase ramp applied during transmission is zero.

[0091] In Figure 5 the example, by superimposing the cross-correlation signal on the Doppler spectrum, it can be seen that the maximum value of the cross-correlation signal corresponds to the leftmost signal band in the Doppler spectrum. The second band from the left corresponds to the second transmitter, and so on.

[0092] As in the first two embodiments, the number of FFT samples can also be supplemented by adding zeros (“zero-padding”) to N FFT points, or by adjusting the number of pulses N REC for each coherent processing interval (CPI). In the third embodiment with non-uniform spacing, the number of FFT points N FFT , or correspondingly, the number of pulses N REC should be such that the frequency difference between two consecutive bands related to the phase ramp of the DDMA modulation is an integer multiple of the frequency unit, i.e., F R / N FFT or F R / N REC respectively.

[0093] The method according to the invention is particularly suitable for the millimeter-wave band (W-band) for automotive radar applications or airborne radar applications on aircraft or drones, for detecting targets fixed or moving relative to the carrier.

Claims

1. A coherent MIMO radar processing method, the coherent MIMO radar processing DDMA waveforms and including NT X transmitters and NR X receivers, the method comprising the steps of: -a) Generate waveforms on at most NT X transmitters, the waveforms being modulo the pulse repetition frequency F R and being the same from one transmitter to the next, within a phase ramp specific to each transmitter; -b) For at least one receiver, generate a range-Doppler representation of the echoes of the transmitted waveform, wherein, for each receiver, the echoes of the transmitter on multiple range cells occupy at least one frequency cell called a signal band in the Doppler spectrum, each signal band being specific to one of the transmitters, and the position of the signal band in the Doppler spectrum is determined according to the phase ramp applied to each transmitter, and the waveform is generated such that a portion of the Doppler spectrum between two signal bands is unoccupied; -c) Identify the transmitter corresponding to each signal band according to the range-Doppler representation of the echoes of the transmitted waveform.

2. The method according to claim 1, wherein Step c) includes the following sub-steps: - Calculate a signal called the echo signal, which is obtained by summing the powers of the echoes of each signal band over all range cells; - Generate a signal called the pattern signal on the same number of frequency cells as the range-Doppler representation of the echoes of the transmitted waveform, and the transmitters are numbered in ascending order according to the phase ramp applied to the transmitters, and the pattern signal is generated such that the transmitters are sorted in ascending order, taking into account the unoccupied portion of the Doppler spectrum; - Calculate the cross-correlation signal between the echo signal and the pattern signal; - Identify the transmitter corresponding to each signal band according to the maximum value of the cross-correlation signal.

3. The method according to claim 2, wherein In the identification step, the position of the maximum value of the cross-correlation signal corresponds to the echo of the first transmitter in the Doppler spectrum, and the first transmitter is defined as the transmitter with a phase ramp of zero.

4. The method according to any one of claims 2 and 3, wherein, The unoccupied part of the Doppler spectrum is obtained by turning off one of the NT X transmitters. For each frequency unit k*F R / NT X , the pattern signal is non-zero, and in other frequency units, the pattern signal is zero, where k = {0, …, NT X -1}.

5. The method according to any one of claims 2 and 3, wherein, The unoccupied portion of the Doppler spectrum is obtained by determining a phase ramp such that the signal band is separated in the Doppler spectrum by F R / NT X2 frequency units, where NT X2 is an integer such that NT X2 >NT X For each frequency unit k*F R / NT X2 the pattern signal is non-zero, and in the other frequency units the pattern signal is zero, where k = {0, …, NT X - 1}.

6. The method according to any one of claims 1 to 3, wherein The range-Doppler representation of the echo is obtained by performing a Fast Fourier Transform (FFT) on multiple sampling points. If NT X is not a power of two, the number of sampling points is padded with zeros to obtain a total of N FFT points, where N FFT is determined to be an integer multiple of the number of transmitters NT X .

7. The method according to any one of claims 1 to 3, wherein The range-Doppler representation of the echoes is obtained by performing a fast Fourier transform (FFT) on a pulse sequence encoded over a coherent processing interval (CPI), and the number of pulses in each coherent processing interval (CPI) is adjusted to be a multiple of the number of transmitters.

8. A coherent MIMO radar processing method, the coherent MIMO radar processing DDMA waveforms and including NT X transmitters and NR X receivers, the method comprising the steps of: -a) Generate waveforms on at most NT X transmitters, the waveforms being modulo the pulse repetition frequency F R and being the same from one transmitter to the next within a phase ramp specific to each transmitter; -b) For at least one receiver, generate a range-Doppler representation of the echoes of the transmitted waveform, wherein, for each receiver, the echoes of the transmitter on multiple range cells occupy at least one frequency cell called a signal band in the Doppler spectrum, each signal band being specific to one of the transmitters, and the position of the signal band in the Doppler spectrum is determined according to the phase ramp applied to each transmitter, and the waveform is generated such that the interval between at least two consecutive signal bands is different from the intervals between other consecutive signal bands; -c) Identify the transmitter corresponding to each signal band according to the range-Doppler representation of the echoes of the transmitted waveform.

9. The method according to claim 8, wherein, The intervals between two consecutive signal bands are all different.

10. The method according to any one of claims 8 and 9, wherein The signal bands are separated according to a predetermined interval rule.

11. The method according to any one of claims 8 to 9, wherein The interval between each signal band is determined such that the average value of the intervals is equal to F R / NT X .

12. The method according to any one of claims 8 to 9, wherein, The range-Doppler representation of the echo is obtained by performing a Fast Fourier Transform (FFT) on multiple sampling points. The number of sampling points is supplemented by adding zeros to obtain a total of N FFT points, where N FFT is determined such that the interval between two consecutive frequency bands is an integer multiple of F R / N FFT of the integer times.

13. The method according to any one of claims 8 to 9, wherein The range-Doppler representation of the echo is obtained by performing a fast Fourier transform (FFT) on a pulse sequence encoded over a coherent processing interval (CPI), where the number of pulses N in each CPI REC is determined such that the interval between two consecutive frequency bands is F R / N REC and is an integer multiple of that value.

14. The method according to any one of claims 8 to 9, including an additional step of digital shaping processing, wherein, The waveform is combined with the echoes from different receivers in a weighted manner.

15. A MIMO radar, characterized in that, It is capable of implementing the method according to any one of claims 1 to 14.

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