OFDM radar sensor with multiple transmission channels and step-by-step calculation of time signals

Abstract

An OFDM radar sensor having a plurality of transmission channels (10) and at least one reception channel (12) and a method for operating such an OFDM radar sensor, wherein, at least for a first transmission channel (10.1), for each transmission channel (10.1), a signal waveform of a signal to be transmitted is calculated stepwise and in parts, the signal waveform comprising a relevant sequence of OFDM symbols (82), wherein a plurality of buffer memories (18; 20) are used alternately to store the calculated parts of the signal waveform and to read out previously calculated and stored preceding parts of the signal waveform, the preceding parts being digital / analog converted and transmitted, wherein the corresponding part of the signal waveform is calculated and stored in one of the buffer memories (20), while the preceding part of the signal waveform has already been read out from another of the buffer memories (18) and converted digital / analog and transmitted on the relevant transmission channel (10.1).

Description

Technical Field

[0001] The invention relates to an OFDM radar sensor having a plurality of transmission channels and having at least one reception channel. The invention further relates to a method for operating such an OFDM radar sensor. Background Art

[0002] The orthogonal frequency division multiplexing (OFDM) method is a digital modulation method with multiple carrier frequencies. In the future, the OFDM method for radar systems will gain importance. In the OFDM method, the frequency band is divided into orthogonal sub-bands of multiple subcarriers or subcarriers, and OFDM symbols (OFDM-Symbole) are sent in sequence. The transmitted signal of the OFDM symbol consists of subcarrier signals (subcarrier signals) modulated according to the modulation mode of the symbol and orthogonal to each other, and the subcarrier signals are sent simultaneously within the OFDM symbol period. For this purpose, the subcarrier frequency is selected so that in the spectrum, the maximum value of the subcarrier is located at the zero crossing point of the other subcarriers.

[0003] In the received signal, the distance of the radar object can be estimated based on the propagation time of the OFDM symbol, and the speed can be estimated based on the phase change curve caused by the Doppler effect with respect to the sequence of OFDM symbols. Multiple radar objects lead to the sum of delayed and Doppler-shifted echoes of the transmitted OFDM signal. The cyclic data header (pilot header) before the symbol period makes it possible to separate the superimposed radar echoes with different propagation times from the radar echoes of the subsequent OFDM symbols.

[0004] US2016 / 0356885 A1 and DE 10 2015 210 454 A1 describe a method for operating a radar device with at least two transmitting antennas, in which OFDM subcarriers are not superimposed and are essentially unequally distributed to a transmission spectrum, which is simultaneously transmitted by the transmitting antenna, wherein each transmission spectrum has at least two directly adjacent OFDM subcarriers. The transmission spectrum is generated by complex modulation of orthogonal OFDM subcarriers that are equidistant from each other. A reception spectrum is generated for each transmission spectrum from a received signal, wherein the allocation of OFDM subcarriers is performed corresponding to its allocation in the transmission spectrum. The transmitted signal waveform of the transmission spectrum is eliminated from the reception spectrum, and a radar image is generated for each reception spectrum, wherein the radar image is analyzed in the spacing dimension and in the speed dimension. In one example, 256 equidistant frequency lines are pseudo-randomly distributed to two non-equidistant partial spectra corresponding to the OFDM subcarriers.

[0005] B. Schweizer, C. Knill, D. Schindler, C. Waldschmidt, "Stepped Carrier OFDM Radar Processing Mode for Retrieving High-Resolution Range-Velocity Curves at Low Sampling Rates" (IEEE Transactions on Microwave Theory and Techniques, Vol. 66, No. 3, March 2018, pp. 1610-1618) describes a processing method for stepped OFDM radar signals. Each OFDM symbol is divided into sub-symbols, which are sent at a carrier frequency that is increased by one step in order to reduce the baseband bandwidth. The phase correction of the received signal that is necessary due to the stepwise transmitted sub-symbols is integrated into the modified Digital Fourier Transformation (DFT). Summary of the invention

[0006] The object of the present invention is to provide an OFDM radar sensor and a method for operating such an OFDM radar sensor, in which the memory and / or computing complexity for generating signals for a plurality of transmission channels is reduced or the number of transmission channels can be increased without increasing the memory complexity to the same extent.

[0007] In conventional OFDM radar methods, the corresponding time signals of the individual transmission channels are generated by inverse Fourier transformation, especially inverse fast Fourier transformation (IFFT), of the OFDM subcarriers of the corresponding OFDM symbols modulated with complex amplitudes. Therefore, the memory required for the time signal increases with the number of transmission channels.

[0008] According to the invention, this object is achieved by an OFDM radar sensor having a plurality of transmission channels and at least one reception channel, the OFDM radar sensor having a control and evaluation device, which is designed for an operating mode in which the plurality of transmission channels transmit corresponding signals, wherein the signals of the corresponding transmission channels comprise a sequence of OFDM symbols, wherein the signals of the plurality of transmission channels are transmitted simultaneously,

[0009] The OFDM symbols transmitted on the corresponding transmission channels respectively have OFDM subcarriers, and the OFDM subcarriers are orthogonal to the OFDM subcarriers of the OFDM symbols transmitted on other transmission channels in the multiple transmission channels at the same time.

[0010] In this case, a spectral separation of the signal components of the receive signal is carried out for a receive signal received by at least one receive channel, wherein an allocation of the OFDM subcarriers to the signal components is carried out in an OFDM symbol transmitted simultaneously on the transmit channel in a manner corresponding to the allocation of the OFDM subcarriers to the transmit channel and an evaluation of the signal components is carried out,

[0011] The OFDM radar sensor comprises, at least for a first transmission channel of the plurality of transmission channels, a plurality of buffer memories for each first transmission channel for parts of the signal waveform of the signal to be transmitted of the transmission channel,

[0012] wherein in the operating mode mentioned, at least for the first transmission channel for each transmission channel, a signal waveform of the signal to be transmitted, which signal waveform comprises a relevant sequence of OFDM symbols, is calculated step by step in sections, wherein a plurality of buffer memories are used alternately in order to store the calculated sections of the signal waveform and in order to read out previously calculated and stored preceding sections of the signal waveform, which are converted digitally / analog and transmitted,

[0013] In this case, the corresponding part of the signal waveform is calculated and stored in one of the buffer memories, while the preceding part of the signal waveform is already read out of the other of the buffer memories and converted digitally / analog and transmitted on the relevant transmission channel.

[0014] In this way, symbols can be used for the corresponding transmission channels, the subcarriers of the symbols are orthogonal to the subcarriers of the symbols of other transmission channels, and at least for the first transmission channel only a buffer memory for a portion of the signal waveform of the complete sequence of OFDM symbols is required. The number of first transmission channels is at least 1 (one). The number of first transmission channels can be, for example, smaller than the number of transmission channels.

[0015] The signal waveform can be understood as a time signal, i.e. a signal waveform that reproduces the temporal variation curve of the signal or a part thereof (e.g. an OFDM symbol). The step-by-step calculation of the signal waveform of the signal to be transmitted can be understood as the step-by-step sequential generation (segment-by-segment) of a time signal, i.e. a part of the signal waveform, which reproduces the temporal variation curve of the signal. Each part preferably includes one or more OFDM symbols of a sequence of OFDM symbols of the signal of the transmission channel. Each buffer memory preferably has a quantity corresponding to a portion, preferably a quantity corresponding to one or two OFDM symbols.

[0016] Therefore, in order to gradually save and read out the digital / analog conversion of the signal waveform of the transmission signal, the corresponding buffer memory is repeatedly used for saving and reading out the digital / analog conversion. For example, two buffer memories can be used alternately, or more than two buffer memories can be used cyclically.

[0017] By calculating step by step in parts, it is not necessary to provide a corresponding memory for the complete signal waveform for the complete sequence of OFDM symbols of the first transmission channel. Therefore, the number of first transmission channels can be increased without the required memory increasing significantly. At least two buffer memories are used for each transmission channel, the digital / analog converter can access the buffer memory to read out and directly convert it into an analog signal, while other buffer memories can be used to write data to the next part of the signal seamlessly. Multiple buffer memories can be corresponding memory areas of the memory.

[0018] Therefore, the OFDM symbols included in the signal waveform are particularly understood as signal waveforms of time periods of a sequence of OFDM symbols, and the signal waveform includes the symbol spectrum of the OFDM symbol transformed into the time domain. The symbol spectrum is defined by the occupied OFDM subcarriers and their corresponding complex phases. For the corresponding OFDM symbol, the corresponding signal segment of the signal can be calculated, for example, based on the phase code of the OFDM symbol. Here, the corresponding symbol spectrum is generated by complex modulation with complex phase codes of OFDM subcarriers that are orthogonal to each other. The corresponding symbol spectrum is transformed into the time domain, for example by means of IFFT transformation, thereby obtaining the corresponding segment of the signal waveform. Therefore, the corresponding part of the signal waveform includes one or more of these segments, each of which corresponds to an OFDM symbol.

[0019] The digital / analog conversion performed by the DA converter (digital / analog converter) can be performed directly from the buffer memory to be read out. Alternatively, the DA converter can have its own buffer memory, which is filled from the buffer memory to be read out.

[0020] In order to transmit the signal of the corresponding transmission channel, the digital / analog converted signal is modulated at high frequency, in particular with the radar frequency of a local oscillator. The HF modulated signal is transmitted via the corresponding transmission antenna of the transmission channel.

[0021] In the receiving channel, the received receive signal is demodulated and digitized, i.e., an analog / digital conversion is performed. Due to the described structure of the transmit signal of the corresponding transmit channel, in which the OFDM subcarriers of the OFDM symbols transmitted simultaneously are assigned to the transmit channels, in the received signal reflected by the radar object, an assignment is made for each OFDM subcarrier frequency to the relevant transmit channel from which the signal came. Accordingly, a spectral separation of the signal components of the receive signal is performed, wherein the assignment of the OFDM subcarriers to the signal components is performed in the transmitted signal in a manner corresponding to their assignment to the transmit channels.

[0022] For each of the signal components, the corresponding OFDM symbol sent is eliminated, in particular by dividing the received signal components by the complex spectrum of the OFDM symbol sent. This can also be referred to as normalization of the received signal components. The channel information obtained by eliminating the sent OFDM symbols then includes information about the propagation time and possible phase shifts of the signal and can be further analyzed to obtain spacing information and speed information as well as angle information.

[0023] Preferred embodiments and developments of the invention are apparent from the dependent claims.

[0024] According to a first embodiment of the invention, the OFDM radar sensor has, for each of the plurality of transmission channels, a plurality of buffer memories for parts of the signal waveform of the signal to be transmitted of the transmission channel.

[0025] wherein in the aforementioned operating mode, for each of a plurality of transmission channels, a signal waveform of a signal to be transmitted, including a relevant sequence of OFDM symbols, is calculated step by step in parts, wherein a plurality of buffer memories are used alternately in order to store the calculated parts of the signal waveform and in order to read out previously calculated and stored preceding parts of the signal waveform, which were converted digitally / analog and transmitted,

[0026] wherein the corresponding part of the signal waveform is calculated based on a phase code, wherein the phase code corresponds to a corresponding OFDM subcarrier through a corresponding OFDM symbol of a sequence of OFDM symbols of the signal,

[0027] In this case, the corresponding part of the signal waveform is calculated and stored in one of the buffer memories, while the preceding part of the signal waveform is already read out of the other buffer memory and converted digitally / analog and transmitted on the relevant transmission channel.

[0028] In this way, the time signals of the transmission channels can be calculated completely "on the spot", so that the memory requirements are minimized.

[0029] According to a further development of the invention, the control and evaluation device is designed to calculate, for the first transmission channel in the mentioned operating mode, the corresponding part of the signal waveform of the signal to be transmitted of the transmission channel from the corresponding part of the signal waveform of the generic signal or from the corresponding part of the signal waveform of the signal to be transmitted of a second transmission channel of at least one second transmission channel of the plurality of transmission channels by multiplication with a periodic oscillation having a frequency (which corresponds to n times the OFDM subcarrier spacing, wherein n is an integer not equal to zero and wherein different n is used for different first transmission channels). The (minimum) OFDM subcarrier spacing is predetermined by the OFDM mode used.

[0030] In this way, the respective parts of the signal waveform of the first transmission channel to be calculated can be calculated in a particularly simple and efficient manner from the corresponding parts of the signal waveform of the second transmission channel or from a part of the signal waveform of the common signal, in particular from the common signal waveform. Here, in an advantageous manner, it is fully utilized that the selection of the phase code of the OFDM symbol of the corresponding transmission channel can be freely selected. In other words, the phase code modulated onto the OFDM subcarrier can be selected arbitrarily. Therefore, if a part of the signal waveform of the first transmission channel is calculated from the corresponding part of the signal waveform of the second transmission channel or the common signal by multiplication with the mentioned periodic oscillation, then by the appropriate selection of the frequency of the oscillation (that is, by the appropriate selection of n), it is ensured that the OFDM symbol of the first transmission channel calculated in this way is orthogonal to the OFDM symbol of the second transmission channel or other first transmission channels that is transmitted simultaneously, in the sense that their corresponding subcarriers are orthogonal to the subcarriers of other OFDM symbols that are transmitted simultaneously.

[0031] The simple execution of the multiplication with the periodic oscillation means a considerable saving in computational effort compared to the separate calculation of the signal waveform by complex modulation of the OFDM subcarriers and the transformation into the time domain. In addition, due to the partial step-by-step calculation, memory is saved to a large extent. Thus, for each first transmission channel, for the calculation of a portion of the signal waveform, the corresponding portion of the signal waveform of the second transmission channel or of the common signal is read out from a memory (for example from a corresponding buffer memory for a portion of the signal waveform of the signal of the second transmission channel); the read portion is multiplied in the time domain with the mentioned periodic oscillation and is stored in a corresponding buffer memory as the calculated portion of the signal waveform of the signal of the relevant first transmission channel.

[0032] Preferably, the periodic oscillation (with which the periodic oscillation is multiplied) is a harmonic oscillation. Here, a harmonic oscillation is understood to be a real sinusoidal oscillation (including a linear combination of sines and cosines with corresponding amplitudes) or a complex-valued oscillation with a real part of a sinusoid and an imaginary part of a sinusoid (for example according to the notation Z exp(iωt), where Z is the complex amplitude and ω is the circular frequency, where ω=2πf).

[0033] According to one embodiment, the OFDM radar sensor has a memory in which at least one signal waveform of at least one OFDM symbol is stored.

[0034] Wherein, in the mentioned operation mode, for at least one second transmission channel of the plurality of transmission channels, the signal waveform of the signal of the corresponding second transmission channel includes a plurality of parts, each of the plurality of parts includes at least one OFDM symbol, and,

[0035] wherein the part is provided and converted digitally / analog and transmitted on an associated second transmission channel,

[0036] Therein, in order to provide each of the mentioned parts of the signal waveform of the signal of the associated second transmission channel, at least one signal waveform stored in a memory is accessed. In this case, the mentioned parts of the signal sequence are provided for digital / analog conversion and transmission.

[0037] Here, preferably, for the first transmitting channel, a corresponding part of the signal waveform of the signal to be sent of the corresponding transmitting channel is calculated from a corresponding part of the signal waveform of the signal to be sent of a second transmitting channel of at least one second transmitting channel of the multiple transmitting channels by means of multiplication with a periodic oscillation having a frequency (the frequency corresponds to n times the OFDM subcarrier spacing, wherein n is an integer not equal to 0, and wherein different n is used for different first transmitting channels).

[0038] In this way, a memory for the signal waveforms of the OFDM symbols used in the sequence of OFDM symbols or for the signal waveforms corresponding to the complete sequence of OFDM symbols is required only for one or more second transmission channels. In this way, the required computing power can be minimized, while the memory requirement for the first transmission channel can nevertheless be minimized by calculating the parts of the transmission signal of the first transmission channel from the corresponding parts of the transmission signal of the second transmission channel. For example, during the digital / analog conversion and transmission of all parts of the signal waveform of the relevant second transmission channel, at least one signal waveform of the OFDM symbol stored in the memory remains in the memory.

[0039] For example, the signal waveform of the sequence of OFDM symbols of the signal of the second transmission channel can be stored in the memory in its entirety. However, the signal waveform of the signal of the second transmission channel can also be collected from at least one signal waveform of the OFDM symbol stored in the memory. Therefore, during the provision and transmission of the signal waveform of the signal of the second transmission channel, the storage content does not need to be changed.

[0040] The memory can be, for example, a read-only memory. Alternatively, in the aforementioned operating mode, the signal waveform of the complete signal of the second transmission channel, for example, is calculated and stored in the memory, wherein the signal waveform is calculated for the corresponding OFDM symbol based on a phase code, which is associated with the corresponding OFDM subcarrier via the corresponding OFDM symbol.

[0041] According to one embodiment, the OFDM radar sensor has, for at least one second transmission channel of the plurality of transmission channels, a plurality of buffer memories for each second transmission channel for parts of the signal waveform of the signal to be transmitted of the transmission channel,

[0042] wherein in the operating mode mentioned, for at least one second transmission channel, for each transmission channel, a signal waveform of the signal to be transmitted (the signal waveform comprises a relevant sequence of OFDM symbols) is calculated step by step in parts, wherein a plurality of buffer memories are used alternately to store the calculated parts of the signal waveform and to read out a previously calculated and stored preceding part of the signal waveform, the preceding part being converted digitally / analog and transmitted,

[0043] In this case, the corresponding part of the signal waveform is calculated and stored in one of the buffer memories, while the preceding part of the signal waveform is already read out of the other buffer memory and converted digitally / analog and transmitted on the relevant transmission channel,

[0044] The corresponding part of the signal waveform is calculated based on a phase code, and the phase code corresponds to the corresponding OFDM subcarrier through the corresponding OFDM symbol of the sequence of OFDM symbols of the signal.

[0045] Here, preferably, for the first transmitting channel, a corresponding part of the signal waveform of the signal to be sent of the corresponding transmitting channel is calculated from a corresponding part of the signal waveform of the signal to be sent of a second transmitting channel of at least one second transmitting channel of the multiple transmitting channels by means of multiplication with a periodic oscillation having a frequency (the frequency corresponds to n times the OFDM subcarrier spacing, wherein n is an integer not equal to 0, and wherein different n is used for different first transmitting channels).

[0046] In this way, only a memory in the form of a buffer memory is required for the time signal for one or more second transmission channels. The corresponding part of the signal waveform of the associated first transmission channel can be generated from the corresponding part of the signal waveform of the second transmission channel by multiplication with the mentioned periodic oscillation.

[0047] According to one or more specific embodiments, the control and evaluation device is preferably designed to determine the amplitude value of the corresponding periodic oscillation in the mentioned operating mode by reading the amplitude value from the table according to a table index, the table index being determined according to a phase angle, which increases for temporally subsequent amplitude values ​​of the oscillation, wherein for oscillations of different frequencies, different phase increments are used for reading the amplitude value from the same table. An increasing table index corresponds to an increasing phase angle.

[0048] In this way, the values ​​required for the periodic oscillations can be simply read from the table, thereby saving calculation time. In particular, the same table can be used for the different frequencies of the periodic oscillations used for the corresponding first transmission channel. Therefore, only one table is needed for the minimum frequency used.

[0049] The phase angle is thus increased with the phase increment and the table index is calculated from the new value of the phase angle. Preferably, the variation curve of the phase angle periodically has a period corresponding to 360°. For example, the increase can include a modulo operation.

[0050] Particularly preferably, the table includes only one quarter of the period of a periodic oscillation, wherein, in order to read out the amplitude value of the second half of the first or second half-period of the periodic oscillation, the table is accessed in the reverse order of the table index, and wherein, when reading out the amplitude value of the second half-period of the periodic oscillation, the sign of the read amplitude value is reversed.

[0051] In this way, the range of the table can be reduced to one quarter relative to the memory of the profile of a full period of the oscillation. The amplitude value of the first half of the first half-cycle of the periodic oscillation is read out directly from the table.

[0052] Preferably, the multiplication is calculated as a multiplication with a complex-valued harmonic oscillation. For example, if, in the case of a number N of transmission channels, the OFDM symbol of the second transmission channel contains N-1 unoccupied subcarriers between two occupied subcarriers, then orthogonal symbols can be generated with the number N-1 first transmission channels by a simple multiplication in the time domain with a complex harmonic oscillation having a frequency corresponding to the subcarrier spacing multiplied by n=1, ..., N-1.

[0053] Preferably, the OFDM radar sensor has a single sideband mixer for each of a plurality of transmission channels, wherein the digital / analog conversion of a portion of the signal waveform comprises a digital / analog conversion of a real part of the portion of the signal waveform and a digital / analog conversion of an imaginary part of the portion of the signal waveform, and wherein the transmission of the portion of the signal waveform comprises mixing the real part and the imaginary part of the portion of the signal waveform with a radar signal (radar frequency) of a local oscillator by means of the single sideband mixer of the transmission channel.

[0054] In this way, a true frequency shift of the relevant part of the signal waveform can be achieved by multiplication with a complex harmonic oscillation, without any second sidebands being generated in the HF-modulated transmit signal.

[0055] Preferably, in the aforementioned operating mode, the respective OFDM symbols of the signals of the respective transmission channels of the plurality of transmission channels have unoccupied OFDM subcarriers, wherein the OFDM subcarriers occupied in the respective OFDM symbols of the signals of the respective transmission channels in the transmission channels are arranged in an OFDM subcarrier spectrum in an alternating manner with the occupied OFDM subcarriers of the OFDM symbols of the signals of the respective other transmission channels that are transmitted simultaneously. The alternating arrangement means, in particular, that the OFDM subcarriers occupied in the respective OFDM symbols of the signals of the respective transmission channels of the transmission channels are unoccupied in the OFDM symbols of the signals of the respective other transmission channels that are transmitted simultaneously.

[0056] In this way, different transmission channels use corresponding overlapping complete frequency regions, wherein the frequencies of the corresponding transmission channels are arranged in the frequency gaps of other transmission channels. In particular, the signals of all transmission channels have a comparable, spectral distribution of the occupied OFDM subcarriers of the OFDM symbols transmitted simultaneously, so that the radar signal characteristics are highly similar. At the same time, in this way, the signal for the first transmission channel can be calculated in a simple and efficient manner from the signal of the second transmission channel by the mentioned multiplication with the periodic oscillation.

[0057] Preferably, each OFDM symbol has a number of unoccupied OFDM subcarriers between adjacent groups of occupied OFDM subcarriers, which number corresponds to the number of remaining transmission channels multiplied by the group size. For example, in the case of three transmission channels, groups of 2 occupied OFDM subcarriers may alternate with gaps of 4 unoccupied OFDM subcarriers (two remaining transmission channels multiplied by the group size of 2).

[0058] Preferably, the digital / analog conversion and / or the reading out of a part of the signal waveform of the signal for the digital / analog conversion is controlled by a clock signal that is different from the clock signal that controls the calculation or provision of the corresponding signal waveform of the signal of the transmission channel by the control and analysis device. Particularly preferably, the digital / analog conversion and / or the reading out of a part of the signal waveform of the signal for the digital / analog conversion is controlled by a clock signal that is different from the clock signal that controls the calculation of the corresponding signal waveform of the signal of the first transmission channel by the control and analysis device. That is, the clock signal of the digital / analog converter is different from the clock signal that controls the operation of the control and analysis device, in particular when calculating the corresponding signal waveform of the first transmission channel. This is achieved by a buffer memory.

[0059] Furthermore, the object is achieved by a method according to claim 11. Preferably, the method is a method for operating an OFDM radar sensor as described or specified in one of the other claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The following is a more detailed explanation of the embodiment based on the drawings. The drawings show:

[0061] Figure 1 A schematic diagram showing an OFDM radar sensor;

[0062] Figure 2 A schematic diagram showing a method of calculating a signal waveform;

[0063] Figure 3 A schematic diagram showing a variation of the calculation of a signal waveform;

[0064] Figure 4 The schematic diagram shows a further variant of the calculation of the signal waveform.

[0065] Figure 5 A schematic diagram showing occupied subcarriers in OFDM symbols of multiple transmission channels; and

[0066] Figures 6.1 to 6.3 A schematic diagram showing amplitude values ​​of a stored table. DETAILED DESCRIPTION

[0067] Figure 1The schematic diagram of an OFDM radar sensor having, for example, four transmission channels 10 and, for example, one reception channel 12 is shown. The transmission channels 10 each include a transmission antenna 14. A first device 16 of the control and evaluation device, which is controlled by a clock signal 17, calculates the corresponding signal waveform of the transmission signal for each transmission channel 10. The signal waveform is calculated step by step in parts, for example. For each transmission channel 10, two or more buffer memories 18, 20 are provided for the calculated parts of the signal waveform, and the parts of the signal waveform of the transmission signal calculated alternately by the first device 16 are stored in the two or more buffer memories.

[0068] The digital / analog converter 22, which is controlled by the clock signal 23, alternately accesses the buffer memories 18, 20 and generates an analog signal from the relevant read-out parts of the signal waveform. The analog signal is modulated at high frequency by the modulator 24 and transmitted by the transmission antenna 14. The transmitted transmission signal, which is reflected by one or more radar objects 26, is received by the receiving antenna 28, modulated at high frequency by the modulator 30 and digitized in the receiving channel 12 by the analog / digital converter 32.

[0069] The transmission signals of each transmission channel 10 each have a signal waveform that corresponds to a sequence of OFDM symbols. Here, for OFDM symbols transmitted simultaneously on different transmission channels 10, the occupied OFDM subcarriers of the OFDM symbols of the transmission channel are orthogonal to the occupied OFDM subcarriers in the OFDM symbols transmitted simultaneously on other transmission channels.

[0070] In the receiving channel 12, a transformation into the frequency domain is then performed by a transformation device 34, for example by means of FFT. In the frequency domain, the frequencies contained in the obtained spectrum, which correspond to the frequencies of the OFDM subcarriers of the transmitting channel 10, are assigned to the receiving branches 36 in accordance with the assignment of the contained OFDM subcarrier frequencies to the occupied OFDM subcarriers in the corresponding transmitting channel 10. Therefore, the signal components reprocessed in the corresponding receiving branch 36 correspond to the corresponding ones in the transmitting channel 10.

[0071] In each reception branch 36, OFDM demodulation of the signal components is performed by an OFDM demodulator 38. The channel information thus obtained is further evaluated by a corresponding detection device 40 of the control and evaluation unit, by detecting, for example, the speed and / or the distance of radar object 26. A further device 42 of the control and evaluation device evaluates the object detections obtained by the detection device 40 for the individual reception branches 36.

[0072] Figure 2A first variant of the calculation of the signal waveform of the transmission signal of the transmission channel 10 is shown, as it can be performed by the first device 16 of the control and analysis device, for example, in one embodiment of the present invention. In this example, the first device 16 includes a phase code memory 50 for each transmission channel 10. The phase code memory 50 of the transmission channel 10 stores, for example, a phase code for each OFDM subcarrier to be occupied for the OFDM symbol of the transmission channel. As the phase code, a 2-bit Quadrature Phase Shift Keying (QPSK) code can be used, for example. For example, the number of occupied OFDM subcarriers of the OFDM symbol can be 512. Therefore, for each OFDM symbol of the transmission channel, the phase code memory 50 includes 512×2 bits.

[0073] When performing a transformation of the OFDM symbols into the time domain, for example by means of an IFFT 52, the signal waveforms of the OFDM symbols to be transmitted simultaneously for different transmission channels 10 are calculated in parallel for the transmission channels by complex modulation of the corresponding transmission channels for the OFDM subcarriers to be occupied with the stored phase code. The respectively calculated signal waveforms of the OFDM symbols are stored, for example, in one of the intermediate memories 18, 20, while the previously calculated signal waveforms of the preceding OFDM symbols are read out and converted by the digital / analog converter 22 from the other of the intermediate memories 18, 20. Figure 2 In FIG. 5 , operations performed in the frequency domain 54 and operations performed in the time domain 56 are indicated by the regions 54 , 56 shown in dashed lines.

[0074] The calculations shown can be implemented, for example, in a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). They are characterized by a particularly low memory requirement, since the calculations described here are performed during ongoing operation based on the stored phase code for the OFDM symbols.

[0075] Figure 3 A second variant of the calculation of the signal waveform of the signal to be transmitted is shown, as it can be performed, for example, by the first device 16 of the control and evaluation device in one embodiment. In this example, the OFDM radar sensor includes a time signal memory 60, in which the time signal (signal waveform) corresponding to one or more OFDM symbols is stored. The time signal memory 60 can contain a number of 2048 samples with a resolution of 16 bits, for example, for OFDM.

[0076] For the first transmission channel 10.1, the corresponding part of the transmission signal is thus generated by multiplication with the complex harmonic oscillation exp(i2πnΔft). In this case, in the simplest case, Δf is the spacing between the subcarriers of the OFDM code used, n is the number of the corresponding first transmission channel (n=1, ..., 3), and t is the time. In the first transmission channel 10.1, the multiplication is respectively performed by a digital mixer 62. The actual frequency shift can be realized in a computationally simple manner by using a complex signal waveform and a digital / analog converter 22 which converts the real part and the imaginary part separately (corresponding to the conversion of the I / Q components).

[0077] For the second transmission channel 10 . 2 , the time signal read out from the time signal memory 60 is directly provided as the time signal, ie without multiplication by the mixer 62 .

[0078] This embodiment has the advantage that only a small amount of computing power is required. The calculation based on the signal stored in the time signal memory 60 takes place in the time domain 66, e.g. Figure 3 As shown by the dotted line in FIG.

[0079] Figure 4 A third variant of the calculation is shown, as it can be performed, for example, in one embodiment in the first device 16 of the control and evaluation device. In this example, the OFDM radar sensor includes a phase code memory 70, which stores phase codes for one or more OFDM symbols. This can be a general OFDM symbol or an OFDM symbol for the second transmission channel 10.2. For example, corresponding to Figure 2 In a variant of , the time signal for the second transmission channel 10.2 is calculated by the transformation unit 72 from the phase code stored in the phase code memory 70 of the OFDM symbol with phase modulation according to the phase code by means of transformation of the OFDM subcarriers. This corresponds to Figure 2 Calculation of a variant of the sending channel.

[0080] For the first transmission channel 10.1, by Figure 3 The multiplication in the variant of is correspondingly multiplied by the complex harmonic oscillation by the mixer 74 to calculate the corresponding time signal. In this case, a complex harmonic oscillation with a frequency nΔf is used for the nth first transmission channel 10.1. Figure 4 , it is again indicated which part of the calculation is carried out in the frequency domain 76 and which part is carried out in the time domain 78 .

[0081] In this example, the calculation methods of the first and second variants are therefore combined in an advantageous manner, so that the desired design of the transmission unit and the evaluation unit can be optimized with regard to their computing power and required memory.

[0082] Figure 5 An example of the occupation of OFDM symbols 80, 82, 84 for simultaneous transmission of OFDM subcarriers on different transmission channels 10 is schematically shown, as this can be provided in the above-described embodiment. To simplify the diagram, an example with one second transmission channel 10.2 and two first transmission channels 10.1 (for n=1, n=2) is shown. Different OFDM symbols 80, 82, 84 of different transmission channels 10.2, 10.1 are Figure 5 80. The second transmission channel 10.2 has occupied OFDM subcarriers 90 in the OFDM symbol 80, between which a plurality of OFDM subcarriers (OFDM subcarrier frequencies) are respectively unoccupied. The first transmission channel 10.1 has occupied OFDM subcarriers 92 or 94 in its OFDM symbols 82, 84, wherein for each transmission channel 10.1, between the occupied OFDM subcarriers 92 or 94 a plurality of OFDM subcarriers are respectively unoccupied. The occupied OFDM subcarriers 90, 92, 94 are shown by solid boxes at the frequency f. In the example shown, each OFDM symbol 80, 82, 84 occupies a certain number of unoccupied OFDM subcarriers between adjacent and occupied OFDM subcarriers, which number corresponds to the number of the remaining transmission channels.

[0083] As mentioned above Figure 3 and Figure 4 As explained in the example of , a time signal of the corresponding first transmission channel 10.1 orthogonal thereto can be generated from the time signal of the second transmission channel 10.2 by simple multiplication with a harmonic oscillation in the time domain. Therefore, in this example, the occupied OFDM subcarriers of the corresponding transmission channels 10.1, 10.2 are arranged in an alternating manner with the occupied OFDM subcarriers of the respective other transmission channels 10 in the OFDM subcarrier spectrum.

[0084] In practice, a bandwidth of, for example, 1 GHz may be used for 3000 OFDM subcarriers with a subcarrier spacing Δf of 333 KHz.

[0085] FIG. 6 schematically shows amplitude values ​​A of a periodic oscillation contained in a stored table of an OFDM radar sensor, as for example in Figure 3 , 4 In one of the examples of and 5, it can be used to multiply the complex-valued harmonic oscillation. The amplitude value A is shown at table index I.

[0086] Since in the example described, the frequency of the harmonic oscillation (for the first transmission channel 10.1, the corresponding multiplication is carried out together with the harmonic oscillation) is a multiple of the smallest such frequency Δf, it is sufficient that the table only includes amplitude values ​​for a quarter of the period of the harmonic oscillation, wherein, based on the phase shift between sine and cosine, for example, a quarter of a real sine wave is sufficient.

[0087] The sampling values ​​(samples) of the time signal for the first transmission channel 10.1 are multiplied element-wise with the corresponding amplitude values ​​A of the oscillation with the mentioned minimum frequency, as in Figure 6.1 As shown in , successive amplitude values ​​from the table are considered. For higher frequencies of the harmonic oscillation (which should be multiplied), at the same scanning rate, every nth value from the table is considered for element-by-element multiplication, as in Figure 6.2 As is shown in FIG. 1 for n=2 using the implemented signs for the corresponding amplitude values. Figure 6.3 A corresponding diagram is shown for n=3, in which only every third value from the table is taken into account for the element-by-element multiplication.

[0088] By multiplication with −1 and by mirroring the sequence of the specified values, a complete period of the harmonic oscillation can be generated, so that the memory required for the table can be further minimized.

Claims

1. An OFDM radar sensor, the OFDM radar sensor having a plurality of transmission channels (10) and at least one reception channel (12), the OFDM radar sensor having a control and analysis device (16, 34, 38, 40, 42), the control and analysis device being designed for the following operating mode: in the operating mode, the plurality of transmission channels (10) transmit corresponding signals, wherein: The signals of the corresponding transmission channels (10) include a sequence of OFDM symbols (80), wherein the signals of the plurality of transmission channels (10) are transmitted simultaneously, The OFDM symbols (80) transmitted on the corresponding transmission channels (10) respectively have OFDM subcarriers (90), and the OFDM subcarriers are orthogonal to the OFDM subcarriers (92, 94) of the OFDM symbols (82, 84) transmitted on other transmission channels in the plurality of transmission channels (10) at the same time. wherein, for a received signal received by the at least one receiving channel (12), a spectral separation of the signal components of the received signal is performed, wherein an allocation of OFDM subcarriers to the signal components is performed in OFDM symbols (80, 82, 84) transmitted simultaneously on the transmitting channel (10) in a manner corresponding to the allocation of the OFDM subcarriers on the transmitting channel (10), and an evaluation of the signal components is performed, The OFDM radar sensor comprises, at least for a first transmission channel (10.1) of the plurality of transmission channels, a plurality of buffer memories (18; 20) for parts of the signal waveform of the signal to be transmitted of the transmission channel (10.1) for each first transmission channel (10.1), wherein in the operating mode mentioned, at least for the first transmission channel (10.1), for each transmission channel (10.1), a signal waveform of the signal to be transmitted is calculated step by step in parts, the signal waveform comprising a related sequence of OFDM symbols (82), wherein the plurality of buffer memories (18; 20) are used alternately to store the calculated parts of the signal waveform and to read out previously calculated and stored preceding parts of the signal waveform, the preceding parts being converted digitally / analog and transmitted, In this case, the corresponding parts of the signal waveform are calculated and stored in one of the buffer memories (20), while the previous parts of the signal waveform are read out from the other buffer memory in the buffer memory (18) and converted digitally / analog and transmitted on the relevant transmission channel (10.1).

2. The OFDM radar sensor according to claim 1 , wherein the OFDM radar sensor has, for each of the plurality of transmission channels (10), a plurality of buffer memories (18; 20) for parts of the signal waveform of the signal to be transmitted of the transmission channel (10), in, In the operating mode mentioned, for each of the plurality of transmission channels (10), a signal waveform of the signal to be transmitted is calculated step by step in parts, the signal waveform comprising a related sequence of OFDM symbols (80), wherein the plurality of buffer memories (18; 20) are used alternately to store the calculated parts of the signal waveform and to read out previously calculated and stored preceding parts of the signal waveform, the preceding parts being converted digitally / analog and transmitted, wherein the corresponding portion of the signal waveform is calculated based on a phase code, the phase code being associated with a corresponding OFDM subcarrier (90) via a corresponding OFDM symbol (80) of a sequence of OFDM symbols (80) of the signal, The corresponding parts of the signal waveform are calculated and stored in one of the buffer memories (20), while the previous parts of the signal waveform are read out from the other of the buffer memories (18) and converted digitally / analog and transmitted on the relevant transmission channel (10).

3. The OFDM radar sensor according to claim 1, wherein: The control and analysis device (16, 34, 38, 40, 42) is designed to calculate, for the first transmission channel (10.1) in the mentioned operating mode, corresponding parts of the signal waveform of the signal to be transmitted of the transmission channel (10.1) from corresponding parts of the signal waveform of a common signal or from corresponding parts of the signal waveform of a signal to be transmitted of a second transmission channel (10.2) of at least one second transmission channel (10.2) of the plurality of transmission channels (10) by multiplication with a periodic oscillation having a frequency corresponding to n times the OFDM subcarrier spacing (Δf), wherein n is an integer not equal to zero, wherein different n is used for different first transmission channels (10.1).

4. The OFDM radar sensor according to claim 3, wherein: The OFDM radar sensor has a memory (60) in which at least one signal waveform of at least one OFDM symbol (80) is stored. Wherein, in the aforementioned operating mode, for at least one second transmission channel (10.2) of the plurality of transmission channels (10), a signal waveform of a signal of the corresponding second transmission channel (10.2) comprises a plurality of parts, each of the plurality of parts comprises at least one OFDM symbol (80), and, wherein the part is provided and converted digitally / analog and transmitted on the associated second transmission channel (10.2), wherein, in order to provide each of the mentioned parts of the signal waveform of the signal of the associated second transmission channel (10.2), the at least one signal waveform stored in the memory (60) is accessed, Wherein, for the first transmission channel (10.1), the corresponding part of the signal waveform of the signal to be transmitted of the corresponding transmission channel (10.1) is calculated from the corresponding part of the signal waveform of the signal to be transmitted of one second transmission channel (10.2) of at least one second transmission channel (10.2) of the plurality of transmission channels (10) by means of multiplication with a periodic oscillation having the following frequency: the frequency corresponds to n times the OFDM subcarrier spacing (Δf), wherein n is an integer not equal to 0, wherein different n is used for different first transmission channels (10.1).

5. The OFDM radar sensor according to claim 3, wherein the OFDM radar sensor has, for at least one second transmission channel (10.2) of the plurality of transmission channels (10), a plurality of buffer memories (18; 20) for each second transmission channel (10.2) for parts of the signal waveform of the signal to be transmitted of the transmission channel (10.2), in, In the operating mode mentioned, for the at least one second transmission channel (10.2), for each transmission channel, a signal waveform of the signal to be transmitted is calculated step by step in parts, the signal waveform comprising a related sequence of OFDM symbols (80), wherein the plurality of buffer memories (18; 20) are used alternately to store the calculated parts of the signal waveform and to read out a previously calculated and stored preceding part of the signal waveform, the preceding part being converted digitally / analog and transmitted, wherein the corresponding part of the signal waveform is calculated and stored in one of the buffer memories (20), while a preceding part of the signal waveform has been read out of another of the buffer memories (18) and converted digitally / analog and transmitted on the associated transmission channel (10.2), wherein the corresponding portion of the signal waveform is calculated based on a phase code, the phase code being associated with a corresponding OFDM subcarrier (90) via a corresponding OFDM symbol (80) of a sequence of OFDM symbols (80) of the signal, and Wherein, for the first transmission channel (10.1), the corresponding part of the signal waveform of the signal to be transmitted of the corresponding transmission channel is calculated from the corresponding part of the signal waveform of the signal to be transmitted of a second transmission channel (10.2) of at least one second transmission channel of the multiple transmission channels by means of multiplication with a periodic oscillation having the following frequency: the frequency corresponds to n times the OFDM subcarrier spacing (Δf), wherein n is an integer not equal to 0, wherein different n is used for different first transmission channels (10.1).

6. The OFDM radar sensor according to any one of claims 3 to 5, in which the control and analysis device (16, 34, 38, 40, 42) is designed to determine the amplitude value (A) of the corresponding periodic oscillation in the mentioned operating mode by reading the amplitude value (A) from the table according to the table index (I), the table index being determined according to the phase angle (s), the phase angle increasing for the amplitude value (A) of the oscillation that follows in time, wherein For oscillations of different frequencies, different phase increments (Δs) are used for reading the amplitude value (A) from the same table.

7. The OFDM radar sensor according to claim 6, wherein the table includes only one quarter of the period of the periodic oscillation, wherein: In order to read out the amplitude value (A) of the second half of the first or second half cycle of the periodic oscillation, the table is accessed in the reverse order of the table index (I), wherein when reading out the amplitude value (A) of the second half cycle of the periodic oscillation, the sign of the read amplitude value (A) is reversed. 8 . The OFDM radar sensor according to claim 3 , in which the multiplication is calculated as a multiplication with a complex-valued harmonic oscillation.

9. An OFDM radar sensor according to any one of the preceding claims, wherein: In the aforementioned operating mode, a respective OFDM symbol (80) of a signal of a respective transmit channel (10) of the plurality of transmit channels has an unoccupied OFDM subcarrier, In this case, the OFDM subcarriers (90) occupied in a corresponding OFDM symbol (80) of a signal of a corresponding one of the transmission channels are arranged in an OFDM subcarrier spectrum in an alternating manner with the occupied OFDM subcarriers (92, 94) of a simultaneously transmitted OFDM symbol (82; 84) of a signal of each of the other transmission channels (10).

10. An OFDM radar sensor according to any one of the preceding claims, in which the digital / analog conversion and / or the reading out of a part of the signal waveform of a signal for digital / analog conversion is controlled by a clock signal (23) that is different from a clock signal that controls the calculation or provision of a corresponding signal waveform of a signal of a transmission channel by the control and analysis device (16, 34, 38, 40, 42).

11. A method for operating an OFDM radar sensor having a plurality of transmission channels (10) and at least one reception channel (12), wherein: The OFDM radar sensor comprises, at least for a first transmission channel (10.1) of the plurality of transmission channels, a plurality of buffer memories (18; 20) for each first transmission channel (10.1) for parts of the signal waveform of the signal to be transmitted of the transmission channel (10.1), wherein the method comprises: Sending corresponding signals on the multiple transmission channels (10), wherein the signals of the corresponding transmission channels (10) include a sequence of OFDM symbols (80), wherein the signals of the multiple transmission channels (10) are sent simultaneously, wherein the OFDM symbols (80) sent on the corresponding transmission channels (10) respectively have the following OFDM subcarriers (90): the OFDM subcarriers are orthogonal to the OFDM subcarriers (92; 94) of the OFDM symbols (82, 84) sent simultaneously on other transmission channels of the multiple transmission channels (10); Receiving a receive signal on the at least one receive channel (12); The signal components of the received signal are spectrally separated, wherein the allocation of OFDM subcarriers to the signal components is carried out in the OFDM symbols (80; 82; 84) transmitted simultaneously on the transmission channel (10) in a manner corresponding to the allocation of the OFDM subcarriers on the transmission channel (10); and Analyzing and processing the signal components, wherein, at least for the first transmission channel (10.1), for each transmission channel, a signal waveform of the signal to be transmitted is calculated stepwise in parts, the signal waveform comprising a related sequence of OFDM symbols (82), wherein the plurality of buffer memories (18; 20) are used alternately to store the calculated parts of the signal waveform and to read out previously calculated and stored preceding parts of the signal waveform, the preceding parts being converted digitally / analog and transmitted, In this case, the corresponding parts of the signal waveform are calculated and stored in one of the buffer memories (20), while the previous parts of the signal waveform are read out of the other of the buffer memories (18) and converted digitally / analog and transmitted on the relevant transmission channel (10.1).

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