Radar device and method for operating a radar device

Abstract

The invention relates to a radar device having a transmitting device and a receiving device. The transmitting device is configured to generate and emit a radar transmission signal. The receiving device is configured to receive and analyze a radar reception signal, wherein the receiving device is further configured to perform an undersampling at a predefined sampling rate for the analysis of the radar reception signal. The transmitting device is further configured to use subcarriers for the generation of the radar transmission signal, wherein there are gaps in the frequency range between predefined subcarriers, wherein the sampling frequency and the gaps in the frequency range are chosen such that signal aliasing generated in the undersampling is substantially convolved onto the gaps at lower frequencies. The invention further relates to a method for operating a radar device.

Description

Technical Field

[0001] The present invention relates to a radar device and a method for operating the radar device. Background Technology

[0002] OFDM (Orthogonal Frequency-Division Multiplexing) radar systems are based on a modulation method that uses multiple orthogonal carriers for data transmission. An exemplary OFDM radar system is known from US 2016 / 356885A. The sampling rate of OFDM radar is typically higher than that of FMCW (Frequency-Modulated Continuous Wave) radar systems because the entire bandwidth must be sampled simultaneously, or, in the case of stepped-carrier OFDM radar systems, sub-bands must be sampled simultaneously.

[0003] Multiple subcarriers are used in OFDM. Therefore, determined subcarriers can be kept idle (freigelassen) to allow bandwidth to be divided among multiple participants, for example. Furthermore, this gap in the spectrum can be advantageous for compressed sensing methods. Here, undersampling is intentionally accepted during sampling, so that under normal conditions, information can no longer be fully reconstructed due to ambiguity (Mehrdeutigkeit). In compressed sensing methods, gaps exist in the sampled state space, which is called "sparseness." If the ambiguity arising from undersampling happens to fall into these unoccupied states, it can be directly reconstructed under ideal conditions. Compressed sensing methods can be used to account for non-ideal effects (e.g., Doppler shift). A method for correcting the Doppler effect is known from "A Novel Intercarrier-Interference Free Signal Processing Scheme for OFDM Radar" by Hakobyan et al. (IEEE Transactions on Vehicular Technology, Vol. 67, No. 6, pp. 5158-5167, 2018). Summary of the Invention

[0004] The present invention provides a radar device and a method for operating the radar device.

[0005] Preferred embodiments are described below.

[0006] According to a first aspect, the present invention therefore relates to a radar device having a transmitting device and a receiving device. The transmitting device is configured to generate and transmit radar transmitted signals. The receiving device is configured to receive and analyze radar received signals, wherein the receiving device is further configured to perform undersampling at a predetermined sampling rate for analyzing and processing the radar received signals. The transmitting device is further configured to use subcarriers for generating radar transmitted signals, wherein there are gaps in a frequency range between predetermined subcarriers, wherein the sampling frequency and the gaps in the frequency range are selected such that the signal aliasing generated in the undersampling is substantially convolved to the lower frequency gaps by means of aliasing.

[0007] According to a second aspect, the present invention therefore relates to a method for operating a radar device. The radar device generates and transmits radar signals. The radar device receives and analyzes radar signals, wherein, for the analysis and processing of the radar signals, undersampling is performed at a predetermined sampling rate. To generate the radar transmission signal, subcarriers are used, wherein gaps exist in a frequency range between predetermined subcarriers, wherein the sampling frequency and the gaps in the frequency range are selected such that the signal aliasing generated in the undersampling is substantially convolved to the lower frequency gaps by means of aliasing.

[0008] Advantages of the present invention

[0009] The radar signal transmitted on the transmitting side can be adjusted by dividing the phase code to create gaps in the frequency range, such as gaps between each subcarrier. By matching the sampling frequency and the gaps, the complete signal can be reconstructed.

[0010] The radar transmitted signal consists of subcarriers, preferably orthogonal subcarriers, and is therefore a subcarrier radar transmitted signal or preferably an OFDM radar transmitted signal. Correspondingly, the radar received signal consists of subcarriers, preferably orthogonal subcarriers, and is therefore a subcarrier radar received signal or preferably an OFDM radar received signal.

[0011] According to one embodiment of the radar equipment, the receiving and transmitting devices are configured to use symbols with variable duration and sampling rate in order to generate and analyze vacancies.

[0012] According to one embodiment of the radar equipment, the receiving device also includes an analog-to-digital converter (ADC) configured to digitize the received radar signal. By matching the sampling rate of the ADC to the resulting vacancies, the entire received radar signal can be sampled using a single ADC capable of operating below the Nyquist rate. This results in a lower data stream, and the ADC can operate at a lower sampling frequency without reducing the modulation bandwidth. The maximum uniquely allocatable range is reduced due to the additional vacancies. However, the range resolution remains unchanged. This allows for a significantly lower system cost for memory and the ADC with a slightly lower maximum effective range, which is particularly advantageous for radar sensors at short or medium ranges, where the cost share for the ADC and digital memory is very large.

[0013] Furthermore, the receiving device includes an anti-aliasing filter configured to filter the radar received signal, wherein the bandwidth of the anti-aliasing filter is greater than a pre-defined sampling rate. For example, in the receiving device, the sampling rate of the analog-to-digital converter of the radar equipment is appropriately selected to be lower than the Nyquist rate (F...). ADC (2B) During the sampling process, the radar received signal can be convolved such that unused subcarriers are occupied by subcarriers with frequencies higher than the sampling frequency. Therefore, the analog-to-digital converter (ADC) only needs to sample a portion of the entire bandwidth, while the entire channel information remains on the subcarriers. This allows the ADC to operate more slowly and reduces the data rate.

[0014] According to one embodiment of a radar device, the receiving device is configured to determine and analyze the interference effects between subcarriers when analyzing and processing the received radar signal, in order to identify and compensate for errors in clock synchronization between the transmitting and receiving devices. Therefore, erroneous convolution of the subcarriers can be detected. For example, when using estimation methods, clock recovery can thus be achieved. Consequently, the accuracy of the radar device is improved.

[0015] According to one embodiment of a radar device, a transmitting device includes a first local oscillator configured to generate a first local oscillator frequency, and a receiving device includes a second local oscillator configured to generate a second local oscillator frequency. The transmitting device is configured to generate a radar transmitted signal using the first local oscillator frequency, and the receiving device is configured to analyze and process a radar received signal using the second local oscillator frequency. The receiving device is configured to analyze and process the signal-to-noise ratio (SNR) when analyzing and processing the radar received signal to identify and compensate for the difference between the first local oscillator frequency and the second local oscillator frequency. Therefore, estimation and compensation of frequency offset can be achieved.

[0016] According to one embodiment of the radar equipment, the receiving device is configured to modulate multiple frequency levels onto the radar received signal and analyze the signal-to-noise ratio while taking into account the multiple frequency levels. The frequency levels can here be approximated as FMCW signals.

[0017] According to one embodiment of the radar equipment, the receiving device is configured to modulate an FMCW signal onto a radar received signal and analyze and process the signal-to-noise ratio while taking the FMCW signal into account.

[0018] According to one embodiment of a method for operating radar equipment, the radar received signal is digitized using an analog-to-digital converter, wherein the radar received signal is filtered using an anti-aliasing filter, wherein the bandwidth of the anti-aliasing filter is greater than a pre-given sampling rate. Due to the large bandwidth, aliasing effects may still exist to some extent. However, due to gaps in the frequency range, complete signal reconstruction is still possible.

[0019] According to one embodiment of a method for operating radar equipment, interference effects between subcarriers are determined and analyzed when analyzing and processing radar received signals in order to identify and compensate for errors in clock synchronization when transmitting radar transmitted signals and receiving radar received signals.

[0020] According to one embodiment of a method for operating radar equipment, a first local oscillator generates a first local oscillator frequency, and a second local oscillator generates a second local oscillator frequency. A radar transmitted signal is generated using the first local oscillator frequency, and a radar received signal is analyzed and processed using the second local oscillator frequency. During the analysis and processing of the radar received signal, the signal-to-noise ratio is analyzed and processed to identify and compensate for the difference between the first and second local oscillator frequencies. Attached Figure Description

[0021] The attached diagram shows:

[0022] Figure 1 A schematic block diagram of a radar device according to an embodiment of the present invention is shown;

[0023] Figure 2a , 2b The subcarrier structure of the OFDM radar signal transmission is shown.

[0024] Figure 3a , 3b The filter characteristics of the anti-aliasing filter are shown;

[0025] Figure 4a , 4b The subcarrier division within the frequency range and the resulting sampled signals are shown.

[0026] Figure 5a , 5b The diagram shows the subcarrier division and the resulting sampled signal within the frequency range under frequency offset conditions.

[0027] Figure 6 A schematic block diagram of a radar device according to another embodiment of the present invention is shown;

[0028] Figure 7a , 7b The sampling frequency points under the synchronization method are shown;

[0029] Figure 8 The phase reference and the resulting sampled signal are shown in the absence of synchronization error;

[0030] Figure 9 The phase reference and the resulting sampled signal are shown with synchronization error.

[0031] Figure 10 The sub-symbol spectrum of a receiving device with convolved subcarriers is shown;

[0032] Figure 11 The distance-symbol plot after Fourier transform is shown;

[0033] Figure 12 A flowchart illustrating a method for operating a radar device according to an embodiment of the present invention is shown.

[0034] In all the accompanying drawings, identical or functionally equivalent elements and devices are given the same reference numerals. The numbering of method steps is for clarity and should not generally imply any definite chronological order. In particular, it is possible to perform multiple method steps simultaneously. Detailed Implementation

[0035] The invention is described in more detail below with reference to OFDM subcarriers. The invention is applicable if the OFDM subcarriers are not perfectly perpendicular to each other.

[0036] Figure 1 A schematic block diagram of radar device 100 is shown. Radar device 100 includes a transmitting device 1a that generates and transmits OFDM radar signals.

[0037] Radar device 100 also includes a receiving unit 2a for receiving and analyzing OFDM radar received signals. The OFDM radar received signals correspond to OFDM radar transmitted signals reflected from objects in the radar channel. To analyze and process the OFDM radar received signals, the receiving unit 2a operates at a pre-defined sampling rate F. S Undersampling is performed. The receiving device 2a analyzes and processes the OFDM radar received signal in order to detect the distance, velocity, and angle of the object relative to the radar device 100.

[0038] The transmitting device 1a uses OFDM subcarriers with vacancies in a pre-defined frequency range between OFDM subcarriers to generate an OFDM radar transmission signal. This selection of the sampling frequency and the vacancies in the frequency range ensures that the signal aliasing generated in undersampling is essentially convolved to the lower-frequency vacancies by means of aliasing.

[0039] The transmitting device 1a includes a digital-to-analog converter 13, a first mixer 12, and an antenna element 11 for transmitting OFDM radar signals. The receiving device 2a includes an antenna element 21 for receiving OFDM radar signals, a second mixer 22, an anti-aliasing filter 23, and an analog-to-digital converter 24. The first and second mixers 12 and 22 are coupled to a common local oscillator 3.

[0040] Figure 2a The diagram illustrates the subcarrier structure of an OFDM radar signal transmission. For different frequencies f, there are occupied positions 201 (or subcarriers) and empty positions 202. More than 1000 independent subcarriers can exist. If multiple transmission channels of the transmitting device 1a need to be active simultaneously, multiplexing can be achieved by distributing the transmission channels across different subcarriers.

[0041] To generate a signal with subcarriers, for example in the case of eight transmission channels, each individual transmission signal is generated using the Inverse Discrete Fourier Transform (IDFT), and preferably using the Inverse Fast Fourier Transform (IFFT). The input values ​​of the IDFT or IFFT are the amplitude and phase of the corresponding subcarrier. For all disabled subcarriers, the input amplitude of the IDFT or IFFT is equal to zero. As a result of the IDFT or IFFT, a time signal is obtained that contains the frequency components of all active carrier frequencies. For orthogonal subcarriers, the IFFT can be used, characterized by its speed. For non-orthogonal subcarriers, the IDFT can be used.

[0042] The time signal is converted into an analog signal by each channel of the transmitting device 1a using its own digital-to-analog converter 13. The digital-to-analog converter 13 is clock-driven at least at the Nyquist rate in this step. In the receiving device 2a, the analog-to-digital converter 24 is used to convert the signal at a sampling rate F. S The signal is sampled and analyzed.

[0043] In the transmitting device 1a, the OFDM radar transmit signal can be defined in the frequency range by the occupancy of phase codes. Here, vacant slots 202 are inserted between occupied subcarriers 2021, which have been used, for example, for simultaneous multiplexing of multiple transmitters (e.g., for multiple-input multiple-output (MIMO)).

[0044] The regular unoccupiedness of subcarriers leads to a reduction in the maximum uniquely allocatable range during subsequent radar signal analysis and processing. Therefore, it is possible to configure the vacancy distribution to be random to prevent this situation.

[0045] The receiving device 2a and the transmitting device 1a can be configured to use symbols with variable duration and sampling rate in order to generate and analyze vacancies. The subcarrier spacing f in OFDM... c Depends on the duration T of a single signal S =1 / f c This means that, with a longer signal duration, other subcarriers can be inserted. This results in a reduction in the maximum uniquely and definitively allocable velocity in radar signal analysis and processing, thanks to the Doppler effect. The trade-off of empty subcarrier positions can thus be made not only in the range dimension but also in the velocity dimension, and can be selected accordingly depending on the application.

[0046] Unlike in the MIMO case (where empty subcarriers are occupied by other transmitters), the empty spaces are used in the current case to: reduce the bandwidth to be sampled in the OFDM radar transmitted signal by appropriately selecting the sampling frequency of the analog-to-digital converter 24 of the receiving device 2a, without losing important and relevant channel information. However, it can also be used simultaneously with MIMO.

[0047] This reduces the sampling frequency of the analog-to-digital converter 24 of the receiving device 2a to below the Nyquist frequency, i.e., F. ADC <2 B Therefore, aliasing effects are generated in a targeted manner.

[0048] As in Figure 2b As shown, the resulting signal aliasing position 204 can be adjusted by the sampling frequency so that the resulting convolved OFDM signal is located at the empty position 203. For this purpose, an anti-aliasing filter 23 must be matched compared to conventional applications.

[0049] Figure 3a Therefore, the filter characteristics A of a conventional anti-aliasing filter are shown, where the bandwidth of filter 301 is less than the sampling rate F. S On the contrary, in Figure 3b The filter characteristics of the anti-aliasing filter according to the present invention are shown, wherein the bandwidth of the filter 302 is greater than the sampling rate F.S .

[0050] The position of subcarrier 201 in the spectrum is known through prior dimensional determination in transmitting device 1a. Since channel information is stored in subcarrier 201, the entire signal bandwidth is available for range resolution, although only at a significantly lower sampling frequency F. ADC <2B is sampled.

[0051] Figure 4a This shows the subcarrier division within the frequency range. Sampling frequency F S Corresponding to bandwidth B plus frequency offset:

[0052] F S =B+Δf c .

[0053] Curve 403 corresponds to the original frequency change process, and curve 404 corresponds to signal aliasing. Curve 402 corresponds to the frequency characteristics of the anti-aliasing filter with filter region 401.

[0054] Figure 4b The resulting sampled signal is shown. Due to aliasing during signal sampling, frequency ranges 4, 5, and 6 are convolved between frequency ranges 1 and 2, between 2 and 3, or after frequency range 3.

[0055] Figure 5a This illustrates the subcarrier partitioning within the frequency range under frequency offset conditions. Figure 5b The corresponding sampled signal is shown. Frequency offset occurs when the transmit and receive carrier frequencies are not perfectly aligned. A second grid (Grid) 501 is generated through aliasing, thereby causing the subcarriers to no longer be orthogonal to each other and become blurred.

[0056] Figure 6 A schematic block diagram of another radar device 200 is shown for this purpose, in which this effect may occur. (Compared to...) Figure 1 The radar device 100 shown is different, with the transmitting device 1b and the receiving device 2b each having their own local oscillators 31 and 32.

[0057] Furthermore, the transmitting device 1b and the receiving device 2b each have reference oscillators 41 and 42, such as quartz oscillators, which pre-determine the clocks for the corresponding local oscillators 31 and 32, as well as the analog-to-digital converter 24 or digital-to-analog converter. Because the reference oscillators 41 and 42 are different, the first local oscillator frequency of the first local oscillator 31 on the transmitting side, the second local oscillator frequency of the second local oscillator 32 on the receiving side, and the frequencies of the digital-to-analog converter 14 and the analog-to-digital converter 24 are also different.

[0058] By identifying the difference between the first local oscillator frequency of the first local oscillator 31 and the second local oscillator frequency of the second local oscillator 32, the transmitting device 1b and the receiving device 2b can synchronize with each other, for example, through offset frequency estimation and clock recovery. Furthermore, deviations in signal shape can be detected.

[0059] Figure 7a The diagram illustrates a subcarrier structure with overlapping subcarriers 701 in a synchronization method under ideal conditions without synchronization errors. Figure 7b The diagram shows the subcarrier structure in the synchronization method with synchronization errors, which results in superposition 702.

[0060] Possible offset frequency estimation can be performed using a controllable phase reference of the subcarrier's phase code. The subcarrier is generated in transmitting device 1b such that, after analog-to-digital conversion in receiving device 2b, a frequency is generated based on... Figure 7a , 7b The structure is as follows. Here, the determined subcarriers can be exactly superimposed on each other, or empty or unoccupied subcarrier positions can be explicitly inserted between the used subcarriers.

[0061] Figure 8 The diagram shows the phase reference (left) and the resulting sampled signal (right) without synchronization error.

[0062] Figure 9 The diagram shows the phase reference (left) and the resulting sampled signal (right) with synchronization error.

[0063] The sampled subcarrier information 801 consists of at least two overlapping subcarriers (e.g., in...). Figure 8 In the case of subcarriers 1 and 6), the phase references of these overlapping subcarriers are superimposed. Since the phase references of these overlapping subcarriers are known in the transmitting device 1b through OFDM phase coding, these phase references can be fully utilized. Figure 8 and Figure 9 In this process, destructive interference from phase codes via carrier 1+6 (0° / 180°) and 3+4 (180° / 0°) is minimized because these carriers ideally cancel each other out. The carriers 2+5 are in phase (0° / 0°) and their sum forms the maximum value. Since the phase code can be freely defined in the transmitting device 1b, any phase reference for the overlapping subcarriers can be generated to, for example, show partial cancellation. Here, only the relative phase references of the phase codes with respect to each other are important.

[0064] Due to non-ideal effects, such as synchronization errors in the sampling frequency between transmitting device 1b and receiving device 2b, the subcarriers are no longer sampled at their ideal positions because the convolved subcarriers no longer overlap each other, as from Figure 7b As can be seen from the above. This effect is similar to the frequency shift of OFDM subcarriers, for example, due to the Doppler effect. Therefore, the subcarrier information (intercarrier-interference, ICI) between adjacent subcarrier positions becomes blurred as a function of sin(x) / x. Since the received signal is discretized by the analog-to-digital converter 24, only the superposition of blurred subcarriers remains at the expected frequency position. Figure 7b (702) In the superposition of the subcarriers. Therefore, the phase information of the overlapping subcarriers depends on the offset from the ideal sampling position. Now, instead of the superposition of the subcarriers φ(2)+φ(5), Figure 8 and Figure 9 The second occupied subcarrier position φ(2) occupies the additional component of the adjacent subcarrier, which is additionally attenuated or phase-modulated:

[0065] φ ges (2)=φ(2)+αφ(5)+βφ(6)+…

[0066] Therefore, perfect constructive or destructive intervention is no longer possible, thus... Figure 9 The received subcarrier mode shown on the upper right of the image is similar to that in... Figure 8 The expected subcarrier patterns shown on the right are inconsistent. For Figure 9 In the example, the destructively superimposed subcarriers do not completely cancel each other out, the constructive subcarrier 902 has a lower amplitude, and the actual empty spaces occupy subcarrier information 901, 903. The synchronization error can be determined, for example, by adjusting the sampling frequency and re-measuring, by comparing it with the expected pattern.

[0067] Figure 10 This illustrates a simulation of this error without additional phase modulation. The depicted spectrum is the sub-symbol spectrum of receiver 2b with convolved subcarriers, having 256 subcarriers B and 256 symbols C. Periodicity 1001 is shown.

[0068] The sampling frequencies of the transmitting and receiving sides differ by 4.7 kHz. (k-1) times of convolutional subcarrier overlap (ICI) occurs, resulting in periodic, destructive interference within the subcarriers. This interference is observed to have a periodicity of 1 / N. dICI (For example, using FFT), the frequency error of digital-to-analog converter 13 or analog-to-digital converter 24 can be obtained:

[0069]

[0070] In this example, N dICI =4,T meas =M·T s ≈0.85ms, therefore the difference in sampling frequencies ΔF is obtained. ADC =4.7kHz.

[0071] If, in addition to the difference in frequencies between the digital-to-analog converter 13 and the analog-to-digital converter 24, a difference in the local oscillator frequency also occurs, this can also be estimated. Frequency errors cause ICI, and if this error is not too large (i.e., approximately less than a fraction of the subcarrier spacing), the noise level increases in signal analysis processing, that is, the signal-to-noise ratio decreases. To find the frequency spacing, one can additionally either modulate multiple frequency levels or an FMCW signal onto the received signal, more precisely, either digitally or analogically. Here, the frequency levels approximate the FMCW signal, thus the procedures in the analysis processing are similar for both methods. Instead of a slope, a quantized slope can be assumed for this frequency level:

[0072] K Stufe =Δf Stufe / T Stufe .

[0073] If the slope K = B / T of FMCW modulation satisfies the following relationship:

[0074]

[0075] Furthermore, since the transmitted and received local oscillator signals overlap during the ramp, it is possible to analyze and process at least one single symbol without significant frequency-dependent interference. The signal-to-noise ratio then varies from symbol to symbol until an optimal value (position m) is reached, in which the frequency of the first local oscillator on the transmitting side coincides with the frequency of the second local oscillator on the receiving side, and then deteriorates again.

[0076] Figure 11 The simulation of this analysis is shown. What is depicted is the distance-symbol graph after the one-dimensional Fourier transform.

[0077] Due to the initial frequency, FMCW ramp slope K, and symbol duration T S It is known, therefore it can be used with the help of

[0078] Δf off =KT S m

[0079] To estimate frequency offset. The estimation of FMCW-type interference (e.g., local oscillator frequency drift) works similarly to the described estimation, such as estimation based on frequency offset.

[0080] If the gradient of the signal-to-noise ratio per symbol can be seen without additional desired FMCW modulation, it is proportional to the existing FMCW ramp frequency, for example due to the drift of the local oscillator frequency, and can be corrected digitally or analogously.

[0081] Since this method operates based on the signal-to-noise ratio of each individual symbol, thus omitting the integration gain in the symbol direction, it is advantageous if strong targets are present in the radar channel. If K is sufficiently small, it is also conceivable to integrate over multiple symbols, thereby making T... s The virtual size increases in order to improve the integral gain. Here, the accuracy of the estimate decreases proportionally to the number of symbols combined, because T... S It becomes larger in the virtual world.

[0082] exist Figure 11 The signal-to-noise ratio 1101 shown varies depending on the symbol C. The symbol m with the maximum signal-to-noise ratio 1101 (here, at 120) is determined by the known symbol duration T. S The slope K of the frequency ramp provides the frequency offset as K·T S ·m.

[0083] Figure 12 A flowchart illustrating a method for operating a radar device according to an embodiment of the present invention is shown. This method can be performed using one of the radar devices 100 and 200 described above.

[0084] In the first method step S1, the OFDM radar transmits signals through radar devices 100 and 200.

[0085] In the second method step S2, the OFDM radar received signal is received by radar devices 100 and 200. To analyze and process the OFDM radar received signal, undersampling is performed at a predetermined sampling rate. To generate the OFDM radar transmitted signal, OFDM subcarriers are used, wherein gaps exist within a predetermined frequency range between the OFDM subcarriers. The sampling frequency and the gaps within the frequency range are selected such that the signal aliasing generated in the undersampling is substantially convolved to the lower frequency gaps by means of aliasing.

[0086] As described above, it is possible to additionally determine and analyze the interference effects between OFDM subcarriers in order to identify and compensate for errors in clock synchronization when transmitting and receiving OFDM radar signals.

[0087] As described above, the difference between the first local oscillator frequency of the first local oscillator 31 on the transmitting side and the second local oscillator frequency of the second local oscillator 32 on the receiving side can also be further determined and compensated.

Claims

1. A radar device (100; 200), said radar device comprising: Transmitting device (1a; 1b), the transmitting device being configured to generate and transmit radar signals; Receiving devices (2a; 2b), said receiving devices are configured to receive and analyze radar received signals, wherein, The receiving devices (2a; 2b) are also configured to, in order to analyze and process the radar received signals, perform sampling at a predetermined sampling rate F. S Perform undersampling; The transmitting device (1a; 1b) is further configured to use subcarriers to generate the radar transmission signal, wherein there are gaps in a frequency range between pre-given subcarriers, wherein the sampling rate and the gaps in the frequency range are selected such that the signal aliasing generated in the undersampling is substantially convolved to the lower frequency gaps by means of aliasing.

2. The radar device (100; 200) according to claim 1, wherein, The receiving device (2a; 2b) and the transmitting device (1a; 1b) are configured to use symbols with variable duration and sampling rate in order to generate and analyze the vacancy.

3. The radar device (100; 200) according to claim 1 or 2, wherein, The receiving device (2a; 2b) further comprises: Analog-to-digital converter (24), the analog-to-digital converter being configured to digitize the radar received signal; An anti-aliasing filter (23) is configured to filter the radar received signal, wherein the bandwidth of the anti-aliasing filter (23) is greater than the pre-given sampling rate F. S .

4. The radar device (100; 200) according to claim 1 or 2, wherein, The receiving devices (2a; 2b) are configured to determine and analyze the interference effects between subcarriers when analyzing and processing the radar received signals, so as to identify and compensate for errors in the clock synchronization of the transmitting devices (1a; 1b) and the receiving devices (2a; 2b).

5. The radar device (100; 200) according to claim 1 or 2, wherein, The transmitting device (1a; 1b) includes a first local oscillator (31) configured to generate a first local oscillator frequency, and the receiving device (2a; 2b) includes a second local oscillator (32) configured to generate a second local oscillator frequency. The transmitting device (1a; 1b) is configured to generate the radar transmitting signal using the first local oscillator frequency, and the receiving device (2a; 2b) is configured to analyze and process the radar receiving signal using the second local oscillator frequency. The receiving devices (2a; 2b) are configured to analyze and process the signal-to-noise ratio when analyzing and processing the radar received signal in order to identify and compensate for the difference between the frequency of the first local oscillator and the frequency of the second local oscillator.

6. The radar device (100; 200) according to claim 5, wherein, The receiving devices (2a; 2b) are configured to modulate multiple frequency levels onto the radar received signal and analyze and process the signal-to-noise ratio in consideration of the multiple frequency levels.

7. The radar device (100; 200) according to claim 5, wherein, The receiving devices (2a; 2b) are configured to modulate the FMCW signal onto the radar received signal and analyze and process the signal-to-noise ratio while taking the FMCW signal into account.

8. A method for operating radar equipment (100; 200), the method comprising the following steps: The radar equipment (100; 200) generates and transmits radar signals; The radar equipment (100; 200) receives and analyzes the radar received signals, wherein... In order to analyze and process the radar received signal, at a pre-given sampling rate F S Undersampling is performed; In order to generate the radar transmit signal, subcarriers are used, wherein there are gaps in the frequency range between pre-given subcarriers, wherein the sampling rate and the gaps in the frequency range are selected such that the signal aliasing generated in undersampling is substantially convolved to the lower frequency gaps by means of aliasing.

9. The method according to claim 8, wherein, The radar received signal is digitized using an analog-to-digital converter (24), wherein the radar received signal is filtered using an anti-aliasing filter, wherein the bandwidth of the anti-aliasing filter is greater than the pre-given sampling rate F. S .

10. The method according to claim 8 or 9, wherein, The first local oscillator (31) generates the first local oscillator frequency, and the second local oscillator (32) generates the second local oscillator frequency; The radar transmit signal is generated using the first local oscillator frequency, and the radar receive signal is analyzed and processed using the second local oscillator frequency. Specifically, when analyzing and processing the radar received signal, the signal-to-noise ratio is analyzed and processed in order to identify and compensate for the difference between the frequency of the first local oscillator and the frequency of the second local oscillator.

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