METHOD FOR SWITCHING BETWEEN MIMO RADAR OPERATING MODES

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a method for switching between different operating modes of a MIMO radar system ("multiple-input multiple-output") and a correspondingly configured MIMO radar system. TECHNICAL BACKGROUND

[0002] Conventional radar systems are based on the concept of coherent signal processing in the radar system's transmit / receive antenna arrays, i.e., the processing of received signals while maintaining signal coherence. Such radar systems operate on the principle of a phased array, according to which phased transmit antenna arrays achieve a directivity effect by focusing the radiated energy from individually controllable antennas. This directivity is often implemented electronically via a corresponding control mechanism.

[0003] MIMO (multiple-input multiple-output) radar systems are systems with a large number of transmitting and receiving antennas, where each transmitting antenna can independently radiate any signal. The reflections of these signals can be received by any receiving antenna, digitized, and subjected to common radar signal processing. The antenna system, or antenna array, consists, for example—without limiting generality—of M transmitting antennas and N receiving antennas. Computationally, these antenna arrays result in a virtual antenna field consisting of M*N virtual antenna elements and a correspondingly enlarged virtual aperture.

[0004] By virtualizing the aperture magnification, the spatial resolution of MIMO radar systems can be significantly improved, and their susceptibility to interference, scatter radiation, or noise can be considerably reduced. This, in turn, leads to an improvement in the signal-to-noise ratio (SNR), which can substantially enhance the radar system's performance in target acquisition and tracking.

[0005] In the antenna arrays of a MIMO radar system, the number and spatial arrangement of the M transmitting and N receiving antennas are typically constant. Various operating modes of the MIMO radar system can be defined, differing in the degree of orthogonality of the transmitted signals. Between full orthogonality of all transmitted signals and no orthogonality of the transmitted signals, hybrid forms are also possible, in which a number of K radar antenna groups of the same or different sizes are formed, within which the transmitted signals are not orthogonal to each other, but there is orthogonality across the groups. The control of the antenna arrays of a MIMO radar system can be electronic, i.e., as a software-defined radar (SDR).

[0006] Document US 2022 / 026524 A1 discloses a radar device for detecting a target object and an antenna device used in the radar device that can operate in two modes. Document US 2018 / 0252809 A1 discloses a digitally programmable radar system with multiple switchable operating modes. The document A. Hassanien, S.A. Vorobyov: Phased-MIMO Radar, A Tradeoff Between Phased Array and MIMO Radars; IEEE Transactions on Signal Processing, Vol. 68, No. 6, June 2010; pp. 3137–3151 discloses fundamental principles for the operation of MIMO radar systems. SUMMARY OF THE INVENTION

[0007] One of the objectives of the invention is therefore to find solutions for the design of MIMO radar systems so that dynamically changing and potentially competing requirements for radar range, search area size and bearing accuracy can be optimally taken into account.

[0008] These and other tasks are solved by the items with the features of the independent claims.

[0009] According to a first aspect of the invention, a method for switching between different operating modes of a MIMO radar system comprises the steps of calculating a coding matrix specifying the coding / decoding scheme of an antenna array of the MIMO radar system, a set of group centers of a number of desired transmit antenna groups of the antenna array, and an antenna position matrix of a desired virtual receive antenna array within the antenna array by means of a configuration device of a radar functional unit of the MIMO radar system; calculating beamforming transmit antenna signals as a function of the calculated set of group centers by means of a signal processing device of the radar functional unit of the MIMO radar system; and encoding the beamforming transmit antenna signals as a function of the calculated coding matrix by means of the signal processing device.The control of the antenna array of the MIMO radar system based on the coded and beamforming transmit antenna signals; the decoding of receive antenna signals divided into receive antenna groups according to the calculated coding matrix using the signal processing unit; and the calculation of beamforming receive antenna signals according to the calculated antenna position matrix using the signal processing unit. The configuration unit and the signal processing unit are designed as logically separate modules of the radar functional unit of the MIMO radar system.

[0010] According to a second aspect of the invention, a MIMO radar system comprises an antenna array and a radar functional unit, which includes a configuration device and a signal processing device coupled to the configuration device as logically separate modules. The configuration device is designed to calculate a coding matrix specifying the encoding / decoding scheme of the antenna array, a set of group centers for a number of desired transmit antenna groups of the antenna array, and an antenna position matrix for a desired virtual receive antenna array within the antenna array.The signal processing device is designed to calculate beam-shaped transmitting antenna signals depending on the calculated set of group centers, to encode the beam-shaped transmitting antenna signals depending on the calculated coding matrix, to drive the antenna array based on the encoded and beam-shaped transmitting antenna signals, to decode received antenna signals divided according to receive antenna groups depending on the calculated coding matrix, and to calculate beam-shaped received antenna signals depending on the calculated antenna position matrix.

[0011] A key aspect of the invention is to implement a logical separation between a signal processing unit and a configuration unit within a radar functional unit of a MIMO radar system. This ensures that the signal processing unit can always operate according to the same signal processing algorithms, regardless of the configured settings. This allows for flexible, rapid switching between different operating modes of the MIMO radar system without significant adjustment effort. The adaptation of the various processing steps required for the different operating modes is performed exclusively in the configuration unit, which calculates appropriately formatted configuration parameter sets and provides them to the signal processing unit as input parameters.

[0012] Depending on the selected operating mode, the degree of grouping of the transmitted signals into non-orthogonal group signals correlates with the processing gain, advantageously resulting in a greater radar range and / or an improved signal-to-noise ratio (SNR) for a given area. Conversely, the degree of beam shaping decreases with the degree of grouping of the transmitted signals into non-orthogonal group signals. While this does not degrade the main beam, it does impair the beams required for bearing acquisition and / or the parallel search beams during the acquisition phase.

[0013] The flexible adjustability of the operating modes of the MIMO radar system allows for advantageous responses to changing requirement profiles regarding range, bandwidth, detection accuracy and / or detection speed, depending on the operating situation.

[0014] Advantageous designs and further developments result from the additional sub-claims as well as from the description with reference to the figures.

[0015] According to some embodiments of the method and the MIMO radar system, the configuration device and the signal processing device can be designed as software modules within the radar functional unit of the MIMO radar system.

[0016] According to the invention, the configuration device calculates the coding matrix, the set of group centers of the number of desired transmitting antenna groups of the antenna array, and the antenna position matrix as a function of a number of different mutually orthogonal signal shapes entered as input parameters into the configuration device.

[0017] The number of different mutually orthogonal signal shapes characterizes the operating mode of the MIMO radar system.

[0018] The above embodiments and further developments can be combined with one another as appropriate. Further possible embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention. BRIEF SUMMARY OF THE CHARACTERS

[0019] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures. These figures show: Fig. 1 a schematic block diagram of a MIMO radar system according to an embodiment of the invention; and Fig. 2 a schematic block diagram of details of a radar functional unit for a MIMO radar system according to a further embodiment of the invention.

[0020] The accompanying figures are intended to provide a further understanding of the embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain the principles and concepts of the invention. Other embodiments and many of the aforementioned advantages become apparent with reference to the drawings. The elements of the drawings are not necessarily shown to scale. Directional terminology such as "above," "below," "left," "right," "over," "below," "horizontal," "vertical," "front," "back," and similar terms are used for explanatory purposes only and are not intended to limit the general public to specific embodiments as shown in the figures.

[0021] In the figures of the drawing, identical, functionally equivalent and equally effective elements, features and components - unless otherwise stated - are each provided with the same reference symbols. DESCRIPTION OF EXAMPLES OF EXECUTION

[0022] MIMO radar systems, without loss of generality, have T transmitting antennas and R receiving antennas. These T transmitting and R receiving antennas can be operated in different modes via an SDR, each differing in the number of orthogonal transmitted signals. The following disclosure describes various techniques that enable the MIMO radar system to switch between these different operating modes, depending on the application or radar deployment phase. For each of the different operating modes, a specific set of parameters is calculated, which serves as the configuration basis for the signal processing algorithm that is fundamentally the same in all operating modes.

[0023] Fig. 1 Figure 10 shows an exemplary schematic representation of a MIMO radar system in which the antenna elements are arranged in a row and a column. In principle, the individual antennas can be implemented in any suitable design or with any desired radiation pattern, such as horn antennas or structurally integrated antennas. In principle, however, any type of antenna is suitable for the MIMO radar system.

[0024] The MIMO radar system 10 further comprises a radar functional unit 2, which in principle includes a signal processing unit 3 and a configuration unit 4 coupled to the signal processing unit 3. The configuration unit 4 can, for example, configure a (in Fig. 1 (not explicitly shown) configuration data storage. The signal processing unit 3 is used to control the transmitting antennas and to process the signals received via the receiving antennas.

[0025] Other components of the MIMO radar system 10 – such as filters, transmit / receive switches, modulators, clock generators, phase shifters, display devices and similar functional components common to radar equipment – ​​are shown below for clarity. Fig. 1 not explicitly shown. The in Fig. 1 The components of the MIMO radar system 10 shown are only examples and further components can be implemented in connection with the MIMO radar system 10.

[0026] Fig. 2 shows a schematic block diagram of a radar functional unit, such as radar functional unit 2 of the Fig. 1 , for a MIMO radar system 10 in greater detail. The radar function unit 2 can, for example, implement a method for switching between different operating modes of a MIMO radar system, such as the MIMO radar system 10 of the Fig. 1 , implement.

[0027] The configuration unit 4 is configured to perform the functions necessary to calculate and provide to the signal processing unit 3 configuration parameters that depend on the desired operating mode of the MIMO radar system 10. The signal processing unit 3, in turn, is configured to perform the functions necessary to control the transmitting antenna elements of the antenna array 1 according to the configuration parameters calculated by the configuration unit 4, and to process the signals received by the receiving antennas of the antenna array 1.

[0028] The different operating modes of the MIMO radar system 10 differ primarily in the number of different mutually orthogonal signal waveforms (nO). Beamforming in the signal processing unit 3 is performed in principle in two stages: transmit signal beamforming and receive signal beamforming. Depending on the number of different mutually orthogonal signal waveforms (nO), three sets of configuration parameters are calculated by the configuration unit 4: the encoding / decoding scheme in an encoding matrix CM (with order TxT, where T denotes the number of transmit antenna groups), the group centers GC of the T transmit antenna groups, and the antenna position matrix RA (with order TxR, where R denotes the number of receive antenna groups) of the virtual receive antenna array.These three configuration parameter sets, calculated by the configuration unit 4 and standardized in terms of structure and size, are forwarded to the signal processing unit 3, which controls the transmitting antennas of the antenna array 1 according to the configuration parameter sets and processes the signals received via the receiving antennas of the antenna array 1 according to the configuration parameter sets.

[0029] By using standardized configuration parameter sets and logically separating the software modules between configuration unit 4 and signal processing unit 3, the signal processing unit 3 can operate in the same way in every operating mode of the MIMO radar system 10. Switching between operating modes of the MIMO radar system 10 is accomplished via configuration unit 4 and the corresponding input of the desired number of different mutually orthogonal signal waveforms (nO).

[0030] Configuration unit 4 includes a first calculation module 41 for calculating the group centers GC of the transmitting antenna groups. Calculation module 41 receives the number nO of transmitting antenna groups and the position vectors xT of the transmitting antennas as input. The number nO of transmitting antenna groups is also fed to a selection module 42, which is designed to select the encoding / decoding scheme depending on the selected operating mode. For this purpose, selection module 42 accesses predefined encoding matrices CM of order TxT stored in a configuration data memory 43 and selects one of the corresponding encoding matrices CM, which is then output to the signal processing unit 3.

[0031] The first calculation module 41 calculates the group centers GC of the transmitting antenna groups and outputs the calculated group centers GC to the signal processing unit 3 on the one hand, and to the selection module 42 and a second calculation module 44 of the configuration unit 4 on the other. The second calculation module 44 is used to calculate the antenna position matrix RA of order TxR of the virtual receiving antenna array based on the calculated group centers GC and the position vectors xR of the receiving antennas. The second calculation module 44 outputs the calculated antenna position matrix RA to the signal processing unit 3.

[0032] The signal processing unit 3 includes a transmit beamforming module 31, which calculates the transmit antenna signals TS based on the position vectors xT of the transmitting antennas, the normalized vector v of the intended beam orientation (defined by azimuth ψ and elevation angle θ), the calculated group centers GC, and the coding matrix CM. The transmit antenna signals TS are converted via a digital-to-analog converter (DAC), step-up-converted, and amplified (in Fig. 1 und 2 (not explicitly shown), before being passed to the antenna array 1 to control the antenna elements 5 acting as transmitting antennas.

[0033] The signal processing unit 3 further comprises a signal divider 32, which receives the receiving antenna signals RS from the antenna elements of the antenna array 1, which function as receiving antennas 6, and divides them into the receiving antenna groups nR. Each of the divided receiving antenna signals RS is forwarded to a decoding module 33, which processes and decodes the received receiving antenna signals RS based on the coding matrix CM. The decoded receiving antenna signals RS are then output to a receiving beamforming module 34, which calculates the antenna beam signals BS based on the normalized vector v of the intended beam orientation and the antenna position matrix RA, and outputs them externally as the output signal BS of the MIMO radar system 10.

[0034] In full MIMO operating mode, i.e., when all transmitted signals are orthogonal to each other, beamforming is performed using the respective position vectors xT and xR of the transmitting and receiving antennas, respectively. The position V(k,j) of the respective virtual array element with respect to the transmitting antenna k and the receiving antenna j is defined as V(k,j) = xT(k) + xR(j). For beamforming in a specific beam direction, the position V(k,j) is weighted for all nT transmitting antennas and all nR receiving antennas by the factor exp(-2πiλ - 1 < v*V(k,j)), where λ is the wavelength of the radar signal and v is the normalized vector of the intended beam orientation (defined by azimuth ψ and elevation angle θ).

[0035] In partial MIMO operating mode, i.e., when certain transmitting antennas are grouped together in which the transmitted signals are not orthogonal to each other, the beamforming is divided into transmit beamforming and receive beamforming. Each transmitting antenna group has its own assigned group center. For beam shaping in a specific beam direction, the position V(k,j) for all nT transmitting antennas and all nR receiving antennas is weighted by the factor exp(-2πiλ -1< v*(xT(k)-GCk))*exp((-2πiλ -1< v*RA(k,j)), where λ is the wavelength of the radar signal, v is the normalized vector of the intended beam orientation (defined by azimuth ψ and elevation angle θ), xT(k) is the position of the transmitting antenna k, GC(k) is the group center of the respective antenna group belonging to the transmitting antenna k, and RA is the antenna position matrix of the virtual receiving antennas.

[0036] The overall weighting factor for transmitting antenna k and receiving antenna j is the same in both cases, regardless of whether transmit and receive beamforming are performed in one step or in two separate steps. This advantageously allows group centers to be calculated even for the full operating mode, enabling signal processing to always be performed in two separate steps with transmit and receive beamforming, irrespective of the operating mode. This allows the signal processing device 3 to be built and implemented identically in all operating modes.

[0037] The coding matrices CM can follow a Hadamard coding scheme, i.e., matrices with entries of ±1 whose rows are pairwise orthogonal to each other. The rows of the Hadamard coding matrices CM correspond to the different transmitted signals, which are weighted by the different row elements. Orthogonal coding can be applied within a single transmitted signal pulse or over a sequence of transmitted signal pulses. For completely orthogonal transmitted signals, full Hadamard coding matrices can be used, whereas for groups of mutually non-orthogonal transmitted signals, Hadamard coding matrices with correspondingly correlated rows or Hadamard coding matrices with a reduced number of columns can be used. Depending on the type of Hadamard coding matrices used, the algorithm structure of the receiver decoding in the signal processing unit 3 can be adapted.Advantageously, with Hadamard coding matrices of the same order, neither the algorithm structure of the receiver decoding nor the coherent processing interval (CPI) nor the pulse modulation needs to be adapted for each of the MIMO operating modes.

[0038] The first calculation module 41 calculates the group centers GC of the transmitting antenna groups as GC(k)=nO*Σ j=1 T / nO< xT(j) / nT. The transmitting antenna groups can be in physical proximity to each other or arbitrarily grouped, since the calculation algorithm for the group centers GC is independent of the actual spatial arrangement of the individual transmitting antennas relative to each other.

[0039] The antenna position matrix RA of the virtual receiving antennas is calculated in the second calculation module 44 from the sum of the group center assigned to the respective transmitting antenna and the position of the respective receiving antenna as RA(k,j) =GC(k)+ xR(j).

[0040] The transmit beamforming module 31 weights the transmitted signals with the factor exp(-2πiλ -1< v*(xT(k)-GCk)) and applies the coding matrix CM from the selection module 42 to modulate the weighted transmitted signals.

[0041] In addition to area processing independent of the MIMO operating mode (and therefore not explained further), the decoding module 33 performs decoding using the coding matrix CM received by the selection module 42. Here, the rows of the Hadamard coding matrix CM are assigned to the respective receive channels divided by the signal divider 32.

[0042] The processing algorithms of signal processing unit 3 are identical for all MIMO operating modes due to the uniform size and structure of the configuration parameter sets, which facilitates switching between different MIMO operating modes. The disadvantage is that some computational steps within the processing algorithms are redundant. Particularly with software-implemented processing modules 31, 32, 33, and 34, i.e., avoiding hardware logic devices such as FPGAs, these redundant computational steps can lead to an increased resource load.

[0043] To avoid redundancy, the following measures, for example, should be taken: The coding matrices CM are to be designed so that they do not have redundant forms in the receive path. The received signals are to be divided into only nO receive channels instead of nR receive channels in the signal divider 32. The antenna position matrix is ​​to be reduced by the number of redundant (i.e., identical) group centers GC.

Claims

1. Method for switching between different operating modes of a MIMO radar system (10), comprising the steps of: calculating a coding matrix (CM) specifying the coding / decoding scheme of an antenna array (1) of the MIMO radar system (10), a set of group centres (GC) of a number of desired transmitting antenna groups of the antenna array (1) and an antenna position matrix (RA) of a desired virtual receiving antenna array within the antenna array (1) using a configuration device (4) of a radar functional unit (2) of the MIMO radar system (10); calculating beamformed transmitting antenna signals (TS) as a function of the calculated set of group centres (GC) using a signal processing device (3) of the radar functional unit (2) of the MIMO radar system (10); encoding the beamformed transmitting antenna signals (TS) as a function of the calculated coding matrix (CM) using the signal processing device (3); decoding receiving antenna signals (RS), divided up by receiving antenna groups, as a function of the calculated coding matrix (CM) using the signal processing device (3); and calculating beamformed receiving antenna signals (RS) as a function of the calculated antenna position matrix (RA) using the signal processing device (3), wherein the configuration device (4) and the signal processing device (3) are configured as logically separate modules of the radar functional unit (2) of the MIMO radar system (10), wherein the configuration device (4) calculates the coding matrix (CM), the set of group centres (GC) of the number of desired transmitting antenna groups of the antenna array (1) and the antenna position matrix (RA) as a function of the number of different mutually orthogonal signal shapes (nO) which is inputted to the configuration device (4) as an input parameter, and wherein the number of different mutually orthogonal signal shapes (nO) characterises the different operating modes of the MIMO radar system (10).

2. Method according to claim 1, wherein the configuration device (4) and the signal processing device (3) are configured as software modules within the radar functional unit (2) of the MIMO radar system (10).

3. MIMO radar system (10) capable of switching between different operating modes, comprising: an antenna array (1); and a radar functional unit (2) comprising a configuration device (4) and a signal processing device (3) coupled to the configuration device (4) as logically separate modules, wherein the configuration device (4) is configured to calculate a coding matrix (CM) specifying the coding / decoding scheme of the antenna array (1), a set of group centres (GC) of a number of desired transmitting antenna groups of the antenna array (1) and an antenna position matrix (RA) of a desired virtual receiving antenna array within the antenna array (1), and wherein the signal processing device (3) is configured to calculate beamformed transmitting antenna signals (TS) as a function of the calculated set of group centres (GC), to encode the beamformed transmitting antenna signals (TS) as a function of the calculated coding matrix (CM), to actuate the antenna array (1) on the basis of the encoded and beamformed transmitting antenna signals (TS), to decode receiving antenna signals (RS), divided up by receiving antenna groups, as a function of the calculated coding matrix (CM) and to calculate beamformed receiving antenna signals (RS) as a function of the calculated antenna position matrix (RA), wherein the configuration device (4) is configured to calculate the coding matrix (CM), the set of group centres (GC) of the number of desired transmitting antenna groups of the antenna array (1) and the antenna position matrix (RA) as a function of the number of different mutually orthogonal signal shapes (nO) which is inputted to the configuration device (4) as an input parameter, and wherein the number of different mutually orthogonal signal shapes (nO) characterises the different operating modes of a MIMO radar system (10).

4. MIMO radar system (10) according to claim 3, wherein the configuration device (4) and the signal processing device (3) are configured as software modules within the radar functional unit (2) of the MIMO radar system (10).