Radar device and method for operating a radar device

Abstract

In a method for operating a radar device, a transmission signal is sent, the transmission signal comprising a plurality of temporally interleaved sequences of frequency ramps. Each frequency ramp is transmitted at a time grid point of an equidistant time grid. A received signal is received, and an evaluation signal is determined. A plurality of velocity hypotheses are determined using the evaluation signal. For each velocity hypothesis, a corresponding corrected evaluation signal is generated. For each velocity hypothesis, an angle estimation is performed based on the respective corrected evaluation signal. The object velocity is determined by evaluating the angle estimation.A time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to a number of grid points of the time grid corresponding to a code time interval.

Description

[0001] The present invention relates to a radar device and a method for operating a radar device. State of the art

[0002] Radar devices with multiple transmitters and multiple receivers (multiple input multiple output, MIMO) are used. A time division multiplexing (TDM) method can be used to modulate radar signals.

[0003] In TDM-MIMO radars, frequency ramps of different sequences are transmitted in a temporally interleaved manner. This reduces the uniqueness of the speed in the distance-speed-power matrix compared to radars with a single transmitter (single input multiple output, SIMO). In SIMO radars, the time intervals between consecutive frequency ramps are the same across the entire slow time dimension. The uniqueness of MIMO compared to SIMO, however, is reduced by a factor at least equal to the number of transmitters.

[0004] There are several approaches to increasing the unambiguity of speed. DE 10 2020 202 500 A1 discloses a MIMO radar system, in which only a single transmitting antenna is active in each time slot. DE 10 2014 212 284 A1 discloses a method for locating a radar target, in which ramps can be arranged at irregular temporal intervals. DE 10 2017 208 789 A1 relates to a method for determining a parameter of an object using radar, in which transmission intervals in a transmission grid are not equidistant in time.

[0005] Sometimes it is necessary to extend the unambiguousness of the speed beyond that of SIMO radar devices, for example in order to correctly determine the speed of particularly fast-moving cars. Disclosure of the invention

[0006] The invention provides a radar device and a method for operating a radar device having the features of the independent patent claims.

[0007] Preferred embodiments are the subject of the respective subclaims.

[0008] According to a first aspect, the invention accordingly relates to a method for operating a radar device. A transmission signal is transmitted by a plurality of transmission devices of the radar device, the transmission signal comprising a plurality of temporally interleaved sequences of frequency ramps, each sequence being assigned to a transmission device, each frequency ramp being transmitted at a time grid point of an equidistant time grid, the ramps within the respective sequence following one another with a predetermined code time interval, and the code time interval corresponding to a predetermined number of grid points of the time grid. A reception signal caused by reflections of the transmission signal is received by a plurality of reception devices of the radar device. An evaluation signal is determined by evaluating the reception signal.A plurality of velocity hypotheses are determined using the evaluation signal. For each velocity hypothesis, a respective corrected evaluation signal is generated by correcting the evaluation signal depending on the velocity hypothesis. For each velocity hypothesis, an angle estimate is performed based on the respective corrected evaluation signal. An object velocity is determined based on the velocity hypotheses by evaluating the angle estimate. The time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval.

[0009] According to a second aspect, the invention relates to a radar device having a plurality of transmitting devices configured to transmit a transmitted signal, each sequence being assigned to a transmitting device, the transmitted signal comprising a plurality of temporally interleaved sequences of frequency ramps, each frequency ramp being transmitted at a time grid point of an equidistant time grid, the ramps within the respective sequence following one another with a predetermined code time interval, and the code time interval corresponding to a predetermined number of grid points of the time grid. The radar device comprises a plurality of receiving devices configured to receive a received signal caused by reflections of the transmitted signal.The radar device further comprises an evaluation device configured to determine a plurality of speed hypotheses using the evaluation signal. The evaluation device is configured to generate a respective corrected evaluation signal for each speed hypothesis by correcting the evaluation signal as a function of the speed hypothesis. The evaluation device is configured to perform an angle estimate for each speed hypothesis based on the respective corrected evaluation signal. The evaluation device is configured to determine an object speed based on the speed hypotheses by evaluating the angle estimate. A time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval. Advantages of the invention

[0010] The method allows an extension of the velocity uniqueness (ie Doppler uniqueness) beyond that of SIMO radar devices.

[0011] A “speed” can be understood as a relative speed of an object that reflects the transmitted signal relative to the radar device.

[0012] The speed is determined by the fact that the time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval. This results in a speed-dependent phase difference during signal analysis, which can be determined as clearly as if sampling were carried out at a time interval of two consecutive time grid points.

[0013] If the time interval between two consecutive time grid points is smaller than the duration of a frequency ramp, the speed uniqueness can be extended beyond that of SIMO radar devices.

[0014] The calculation of the velocity within the extended uniqueness of the velocity and the angle estimation to the target can take place simultaneously, meaning they do not have to be performed sequentially. This has the advantage of a comparatively robust calculation of these variables in scenarios where a particularly large number of targets are separated by their angle.

[0015] According to one embodiment of the method, the number of grid points of the time grid corresponding to the code time interval is a prime number. This makes it possible to ensure that the time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval.

[0016] According to one embodiment of the method, the velocity hypothesis is selected for which the power occurring during the angle estimation is maximum. The object velocity is determined as the velocity corresponding to the velocity hypothesis. Due to coprimity, the power is maximized and enables an exact determination of the velocity in the extended uniqueness range.

[0017] According to one embodiment of the method, an object angle is determined as the angle at which the power occurring during the angle estimation is maximum for the selected velocity hypothesis. In addition to the velocity, at least one angle, ie, the azimuth and / or elevation angle, can also be determined.

[0018] According to one embodiment of the method, a number of speed hypotheses is equal to the number of grid points of the time grid corresponding to the code time interval.

[0019] According to one embodiment of the method, no frequency ramp is transmitted between at least two grid points of the time grid. Gaps in the transmission grid can therefore occur. This is the case, for example, if the conditions of coprimality are met for two ramps and, at the same time, the ramps are longer than one time grid.

[0020] According to one embodiment of the method, exactly one frequency ramp is transmitted for each sequence within a code time interval. By eliminating the need to transmit multiple times with the same transmitter, an increased integration gain is achieved for a given measurement duration, since more data can be coherently integrated along the slow time dimension.

[0021] According to one embodiment of the method, a time interval between two consecutive time grid points of the equidistant time grid corresponds to a Nyquist time.

[0022] According to one embodiment of the method, the evaluation signal comprises a distance-speed-power matrix calculated using the received signal. The plurality of speed hypotheses are determined using the distance-speed-power matrix.

[0023] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing. Short description of the drawings

[0024] They show: Fig. 1 is a schematic block diagram of a radar device according to an embodiment of the invention; Fig. 2 shows an exemplary transmission scheme used by the radar device; Fig. 3 shows an exemplary location signal associated with a virtual antenna array; Fig. 4 an exemplary amplitude spectrum for determining a speed; and Fig. 5 is a flowchart of a method for operating a radar device according to an embodiment of the invention.

[0025] In all figures, identical or functionally equivalent elements and devices are provided with the same reference numerals. The numbering of process steps serves the purpose of clarity and is generally not intended to imply a specific chronological order. In particular, several process steps can be performed simultaneously. Description of the embodiments

[0026] Fig. 1 shows a schematic block diagram of a radar device 1 with a plurality of transmitting devices 21 to 2n and a plurality of receiving devices 31 to 3m, as well as an evaluation device 4.

[0027] The invention is not limited to a specific number n of the transmitting devices 21 to 2n or a specific number m of the receiving devices 31 to 3m.

[0028] The transmitting devices 21 to 2n and the receiving devices 31 to 3m can each be transmitting antennas or receiving antennas of a transmitting array or receiving array.

[0029] The transmitting devices 21 to 2n transmit a transmitted signal. The transmitted signal comprises a plurality of temporally interleaved sequences of frequency ramps, with each frequency ramp being transmitted at a time grid point of an equidistant time grid. Each transmitting device 21 to 2n transmits a corresponding sequence.

[0030] The receiver devices 31 to 3m receive a reception signal caused by reflections of the transmission signal.

[0031] The evaluation device 4 evaluates the received signal and generates an evaluation signal, which may in particular comprise a distance-speed-power matrix (or amplitude matrix).

[0032] The evaluation device 4 determines a plurality of speed hypotheses using the received evaluation signal. The evaluation device 4 generates a respective evaluation signal for each speed hypothesis by correcting the evaluation signal depending on the speed hypothesis.

[0033] A “corrected evaluation signal” can be understood, for example, as a distance-speed-power matrix modified depending on the speed hypothesis.

[0034] The evaluation device 4 performs an angle estimation for each velocity hypothesis based on the respective corrected evaluation signal. The evaluation device determines an object velocity based on the velocity hypotheses by evaluating the angle estimate.

[0035] Fig. Figure 2 shows an exemplary transmission pattern used by radar device 1. The invention will be explained in more detail below using this exemplary transmission pattern.

[0036] In Fig. 2, the number n of transmitting devices 21 to 2n is four and there are four sequences, each sequence being assigned to a transmitting device 21 to 2n, ie being transmitted by it.

[0037] The ramps follow within the respective sequence with a predetermined code time interval T rep,slow The code time interval corresponds to a predetermined number N TN at grid points of the time grid, with respective distance predetermined code time interval T Nyquist . In the Fig. In the example shown in Figure 2, the number is 17. This gives the following for the predetermined code time interval: Trep,slow=NTNTNyquist=17⋅TNyquist.

[0038] The code time interval corresponds to a code time dimension, i.e., a slow time dimension. Shown are a first repetition A and a second repetition B, corresponding to two "ramps" along the slow time dimension. The individual frequency ramps correspond to the fast time dimension. The frequency ramps of the individual transmitting devices Tx 1 to Tx 4 repeat several times along the slow time dimension.

[0039] The time interval between two consecutive time grid points of the equidistant time grid corresponds to a Nyquist time T Nyquist This grid spacing is smaller than a frequency ramp. Each frequency ramp begins at one of the time grid points. The duration T rep,chirp of a respective frequency ramp corresponds to four times the Nyquist time T Nyquist , i.e. Trep,chirp=4⋅TNyquist.

[0040] The invention is not limited to this, in particular the duration of a frequency ramp does not have to be an integer multiple of the Nyquist time T Nyquist are equivalent to.

[0041] In the transmission scheme shown, two frequency ramps of different sequences usually follow one another directly, so that the time interval between two (for example consecutive) frequency ramps of different sequences corresponds to a predetermined (integer) number of grid points of the time grid, which is a multiple of 4. Only between the fourth frequency ramp and the first frequency ramp is there a pause of a Nyquist time T Nyquist , meaning no frequency ramp is transmitted, so the time interval corresponds to five grid points of the time grid. The transmission pattern thus has a gap in which no transmission occurs. The invention is not limited to this. Multiple gaps may also occur with other transmission patterns.

[0042] These numbers 4 and 5 are coprime to the number of grid points of the time grid corresponding to the code time interval, namely 17. In general, this applies to two frequency ramps each, ie to any two frequency ramps.

[0043] For example, the distance between the frequency ramp to the second transmitting antenna Tx2 and the frequency ramp to the fourth transmitting antenna Tx4 is: dTx2Tx4TNyquist, with dTx2Tx4=s4−s2=12−4=8. where s4 and s2 denote the grid points of the beginning of the respective ramps.

[0044] This results in a phase difference φ(dTx2Tx4,m,vsmall).

[0045] More generally, within the code time dimension between two frequency ramps with the grid spacing k ∈ {1,2,...,N TN -1} a speed-dependent phase difference, φk,m=m⋅360°NTN⋅k, where the speed within a speed range m ∈ {0,1,...,N TN -1} occurs, which is understood to be a certain spectral repetition of the distance-speed-power matrix along the speed dimension.

[0046] From the speed range and the ambiguous speed v determined from the distance-speed-power matrix small The evaluation device 4 calculates the speed hypotheses in the extended uniqueness range as follows: v=vsmall+m⋅2|vTDM|

[0047] For each value of m, a velocity hypothesis results.

[0048] V describes TDM the speed uniqueness in the distance-speed-power matrix, which results from the wavelength and duration of the code time dimension T rep,slow can be derived: vTDM=±λ4Trep,slow.

[0049] The maximum reconstructable speed uniqueness is: Trep,chirpTNyquist⋅(±vSIMO)=Trep,chirpTNyquist⋅(±λ4Trep,chirp).

[0050] Here, λ denotes the mean wavelength of the signal and v SIMO the speed uniqueness of a SIMO radar device. This uniqueness range corresponds to the uniqueness range that can be achieved when scanning with the time interval between two consecutive grid points T Nyquist receives.

[0051] In order to enable the maximum reconstructable uniqueness range, the number of grids N TN and the integer grid spacing k of any two frequency ramps is relatively prime or the greatest common divisor of these two numbers is equal to 1.

[0052] In general, the reconstructable uniqueness range is: vNyquist=±1ggT(NTN,k)⋅Trep,chirpTNyquistvSIMO.

[0053] The uniqueness range is particularly maximized when the number of grids N in the transmission scheme TN is a prime number and the frequency ramps are an integer number of grids long, since k is less than N TN In this case, there are necessarily different time intervals between the frequency ramps within the code time dimension.

[0054] The evaluation device 4 performs a MIMO angle estimation using the position signal based on a virtual antenna array. The position signal elements associated with the virtual antenna elements have been corrected by a phase depending on their respective transmitting antennas, which results from the respective velocity hypothesis in the extended uniqueness range. The velocity v = v(m) depends on the velocity range m.

[0055] In Fig. Figure 3 illustrates an exemplary location signal associated with a virtual antenna array. Four virtual antenna elements or location signal elements belong to each transmitting device Tx1 to Tx3, with the three transmitting devices Tx1 to Tx3 being active at different times within the code time dimension. As a result, phase differences are formed. φk1,v(m),φk2,v(m) which depend on both the speed v and the grid spacing k between the individual transmitting devices Tx1 to Tx3 and must be corrected as part of the MIMO angle estimation.

[0056] Because the speed range var is an element of the set {0, 1, ..., N TN -1}, consequently N TN such MIMO angle estimations are carried out. gcd(NTN,k)=1 for any grid spacing k between two frequency ramps, and the virtual antenna array allows a unique MIMO angle estimation, one of the N TN Amplitude spectra of the MIMO angle estimates show a global maximum.

[0057] The velocity hypothesis associated with this angular spectrum is correct, meaning that the corresponding velocity is determined by the evaluation device 4 as the correct velocity v within the extended uniqueness range. Furthermore, the correct angle of the object is determined.

[0058] Fig. Figure 4 shows an example amplitude spectrum for determining speed. The amplitude spectra A are plotted in a logarithmic representation horizontally for each possible speed range m. The global maximum in this two-dimensional matrix reveals the speed and angle α of the target. In the example shown, m = 8 and the angle α corresponds to 0°.

[0059] This results in a relatively small sidelobe spacing along the speed range dimension. This sidelobe spacing tends to be better the more pairs of frequency ramps within the code time dimension satisfy the condition gcd(NTN,k)=1 for different k. According to one embodiment, a simulation series can be performed in which, for a given number of grids N TNand for given durations of the frequency ramps for all possible transmission schemes where at least for one pair of frequency ramps the condition gcd(N TN , k) = 1 is met, the sidelobe spacing is calculated. The result reveals the transmission pattern with the largest sidelobe spacing.

[0060] Fig. 5 shows a flowchart of a method for operating a radar device, in particular the radar device 1 described above.

[0061] In a first method step S1, a transmission signal is transmitted by a plurality of transmission devices 21 to 2n of the radar device 1, wherein the transmission signal has a plurality of temporally interleaved sequences of frequency ramps, wherein each frequency ramp is transmitted at a time grid point of an equidistant time grid, wherein the ramps follow one another within the respective sequence with a predetermined code time interval, and wherein the code time interval corresponds to a predetermined number of grid points of the time grid.

[0062] In a second method step S1, a reception signal caused by reflections of the transmission signal is determined by a plurality of receiver devices 31 to 3m of the radar device 1.

[0063] In a third method step S3, an evaluation signal is determined by evaluating the received signal, in particular a distance-speed-power matrix which indicates the transmission power at certain distance-speed bins.

[0064] In a fourth method step S4, a plurality of speed hypotheses are determined using the received signal. The number of speed hypotheses can be equal to the number of grid points of the time grid corresponding to the code time interval.

[0065] In a fifth method step S5, a respective corrected evaluation signal is generated for each speed hypothesis by correcting the received signal depending on the speed hypothesis.

[0066] In a sixth process step S6, an angle estimation is carried out for each speed hypothesis based on the respective corrected evaluation signal.

[0067] In a seventh method step S7, an object speed is determined based on the speed hypotheses by evaluating the angle estimate. For this purpose, the speed hypothesis can first be selected for which the power occurring during the angle estimation is maximum, whereby the object speed is determined as the speed corresponding to the speed hypothesis.

[0068] Furthermore, an object angle can be determined as the angle at which the power occurring in the angle estimation is maximum for the selected velocity hypothesis.

[0069] A time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval. The number of grid points of the time grid corresponding to the code time interval can, in particular, be a prime number.

[0070] In certain embodiments, no frequency ramp can be transmitted between at least two grid points of the time grid.

[0071] Furthermore, exactly one frequency ramp can be transmitted for each sequence within a code time interval.

[0072] A time interval between two consecutive time grid points of the equidistant time grid can be assigned to a Nyquist time T Nyquist are equivalent to. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 202 500 A1

[0004] DE 10 2014 212 284 A1

[0004] DE 10 2017 208 789 A1

[0004]

Claims

[1] Method for operating a radar device (1), comprising the steps: Emission (S1) of a transmission signal by a plurality of transmission devices (21-2n) of the radar device (1), wherein the transmission signal has a plurality of temporally interleaved sequences of frequency ramps, wherein each sequence is assigned to a transmission device (21 to 2n), wherein each frequency ramp is transmitted at a time grid point of an equidistant time grid, wherein the ramps within the respective sequence follow one another with a predetermined code time interval (T_rep, slow), and wherein the code time interval (T_rep, slow) corresponds to a predetermined number (N_TN) of grid points of the time grid; Receiving (S2) a received signal caused by reflections of the transmitted signal by a plurality of receiver devices (31-3m) of the radar device (1); Determining (S3) an evaluation signal by evaluating the received signal; Determining (S4) a plurality of speed hypotheses using the evaluation signal; Generating (S5) a respective corrected evaluation signal for each speed hypothesis by correcting the evaluation signal as a function of the speed hypothesis; Carrying out (S6) an angle estimation for each velocity hypothesis based on the respective corrected evaluation signal; and Determining (S7) an object speed based on the speed hypotheses by evaluating the angle estimate; wherein a time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval. [2] Method according to claim 1, wherein the number of grid points of the time grid corresponding to the code time interval (T_rep, slow) is a prime number. [3] Method according to claim 1 or 2, wherein the speed hypothesis is selected at which a power occurring in the angle estimation is maximum, and wherein the object speed is determined as the speed corresponding to the speed hypothesis. [4] Method according to one of the preceding claims, wherein an object angle is determined as the angle at which the power occurring in the angle estimation is maximum for the selected velocity hypothesis. [5] Method according to one of the preceding claims, wherein a number of the speed hypotheses is equal to the number of grid points of the time grid corresponding to the code time interval (T_rep, slow). [6] Method according to one of the preceding claims, wherein no frequency ramp is transmitted between at least two grid points of the time grid. [7] Method according to one of the preceding claims, wherein exactly one frequency ramp is transmitted for each sequence within a code time interval (T_rep, slow). [8] Method according to one of the preceding claims, wherein a time interval between two consecutive time grid points of the equidistant time grid corresponds to a Nyquist time (T_Nyquist). [9] Radar device (1), with: a plurality of transmitting devices (21-2n) which are designed to transmit a transmitted signal, wherein the transmitted signal has a plurality of temporally interleaved sequences of frequency ramps, wherein each sequence is assigned to a transmitting device (21 to 2n), wherein each frequency ramp is transmitted at a time grid point of an equidistant time grid, wherein the ramps follow one another within the respective sequence with a predetermined code time interval (T_rep, slow), and wherein the code time interval (T_rep, slow) corresponds to a predetermined number (N_TN) of grid points of the time grid; a plurality of receiver devices (31-3m) which are designed to detect a received signal caused by reflections of the transmitted signal; and an evaluation device (4) which is designed to: - to determine an evaluation signal based on the received signal, - to determine a variety of speed hypotheses using the evaluation signal, - to generate a respective corrected evaluation signal for each speed hypothesis by correcting the evaluation signal depending on the speed hypothesis, - to carry out an angle estimation for each velocity hypothesis based on the respective corrected evaluation signal, and - to determine an object speed based on the speed hypotheses by evaluating the angle estimate; wherein a time interval between two frequency ramps of different sequences corresponds to a predetermined number of grid points of the time grid, which is coprime to the number of grid points of the time grid corresponding to the code time interval. [10] Radar device (1) according to claim 9, wherein the number of grid points of the time grid corresponding to the code time interval (T_rep, slow) is a prime number.

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