WO2013083269A2 - Empfängerarchitektur für orthogonale multiple-input-multiple-output radarsysteme - Google Patents

Empfängerarchitektur für orthogonale multiple-input-multiple-output radarsysteme Download PDF

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Publication number
WO2013083269A2
WO2013083269A2 PCT/EP2012/005016 EP2012005016W WO2013083269A2 WO 2013083269 A2 WO2013083269 A2 WO 2013083269A2 EP 2012005016 W EP2012005016 W EP 2012005016W WO 2013083269 A2 WO2013083269 A2 WO 2013083269A2
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WIPO (PCT)
Prior art keywords
signal
transmitter
radar
phase
unit
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PCT/EP2012/005016
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German (de)
English (en)
French (fr)
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WO2013083269A3 (de
Inventor
Viktor Krozer
Jochen Moll
Florian WIEGANDT
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Johann Wolfgang Goethe-Universität Frankfurt am Main
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Publication of WO2013083269A2 publication Critical patent/WO2013083269A2/de
Publication of WO2013083269A3 publication Critical patent/WO2013083269A3/de

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06Systems determining position data of a target
    • G01S13/08Systems for measuring distance only
    • G01S13/32Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S13/325Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of coded signals, e.g. P.S.K. signals
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/003Bistatic radar systems; Multistatic radar systems
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88Radar or analogous systems specially adapted for specific applications
    • G01S13/89Radar or analogous systems specially adapted for specific applications for mapping or imaging

Definitions

  • the invention relates to a radar system for detecting one or more target objects and to a receiving device of a radar system comprising at least one receiving unit. Further, the invention relates to a method of operating the receiver units in the radar system and an implementation of the method in computer readable instructions stored on a computer readable storage medium.
  • Fig. 1 shows a schematic representation of a simple radar system with a transmitter unit and a receiving unit.
  • radar signals are emitted in one direction by a transmitter unit and radar signals (echoes) reflected back from one or more target objects (targets) in the beam path are detected at a receiver unit.
  • the received radar signals are processed in the radar system and displayed.
  • Radar systems work with one or more transmitters and one or more receivers (so-called ⁇ radar systems).
  • the data is usually recorded by means of time or frequency multiplexing.
  • the channel diversity in time-division multiplexing is conventionally carried out by a sequential circuit of the transmitter, as illustrated in Fig. 2.
  • the time-division multiplexing requires switches whose use is accompanied by signal attenuation. Usually, the number of channels in the switches is limited in practice, so that often several switches are used in parallel and thereby add the losses. For a large number of channels must be at this Method high multiplex rates are used, which increase the sampling rate and thus the amount of data in the receiving units considerably. In addition, the time for data acquisition in the receiving units increases linearly with the number of transmitter units.
  • a second approach is in frequency division multiplexing, where multiple carrier frequencies are used to transmit the radar signals and achieve channel diversity.
  • a ⁇ -radar system utilizing frequency division multiplexing is described in J. Zhang and A. Papandreou-Suppappola, " ⁇ Radar with Frequency Diversity", in Proceedings of the International Conference on Waveform Diversity Design (WDD), Orlando, USA, 2009, pp. 208-212 known.
  • WCD Waveform Diversity Design
  • Fig. 3 the available bandwidth must be divided, as shown in Fig. 3 by way of example. This circumstance will limit or prevent scaling to high numbers of stations.
  • the transmitted and received frequencies change either by a moving object and by continuous or abrupt changes in transmission frequencies.
  • a commonly used approach is the FMCW (Frequency Modulated Continuous Wave) method, where frequency tends to change linearly with time.
  • the frequency can be incrementally increased in discrete steps with a given time T f . This is also referred to as a "stepped frequency" method, which is usually done linearly with time.
  • FIG. 5 illustrates the receiver structure of a receiver Ri in the frequency multiplexing method.
  • sufficient oscillators for the carrier frequencies would have to be present.
  • frequency multiplexing the use of multiple carrier frequencies results in a higher IF bandwidth, which adversely affects the required sampling rates.
  • oscillators are used, this means that with a larger number of transmitters, the number of oscillators also increases. At high transmitter numbers, many oscillators are used, all of which must be wired and take up space.
  • one of the objects of the invention is to propose an improved radar system that solves one or more of these disadvantages.
  • one of the objects of the invention is to propose a structure, which can also be scaled to large transmitter and receiver numbers, of a radar system transmitting in parallel on the same frequency band.
  • At least one of the objects is achieved by the subject matter of the independent patent claims.
  • Advantageous embodiments of the invention are the subject of the dependent claims.
  • One of the aspects of the invention is the use of orthogonal spreading codes (which consist of so-called chips) in a radar system having an M1MO (or MISO) structure.
  • M1MO or MISO
  • the radar signals radiated by the individual transmitter units are spread with a transmitter-specific spreading code.
  • the spreading codes also serve the individual receiving units to determine the transit time of the radar signal of the respective transmitter unit scattered on a target object for each transmitter unit (and in the detection of more than one target object, additionally for each target object) and also the absolute Determine the amplitude of the received in the respective receiving unit radar signal of the respective transmitter unit. From the transit time of the radar signal of the respective transmitter unit scattered at a target object, the respective receiver unit can subsequently determine the absolute distance of the target object. The absolute amplitude determined by each receiving unit (for each target object) with the associated distance (running time) of the target object has an ideal resolution in the path range.
  • the echo signals can be described with a time-discrete unit pulse weighted with the respective amplitude, which, given an identical processing (processing) of the echo signals in the receiving unit (and / or evaluation unit), leads to an increase in performance in the evaluation, for example in the form of higher-resolution images leads in imaging systems.
  • the individual radar signals radiated by the transmitter units can all be transmitted on a carrier frequency.
  • the processing of the received signal mixture in a receiving unit can be done in one embodiment of the invention by means of a method which operates similar to a control loop.
  • such a method can be based on the principle of successive interference elimination: For each transmitter unit (and in the detection of more than one target object, for each target object) determines the transit time and the absolute amplitude, formed a reconstruction of the received radar signal and before Processing the signal mixture for the next transmitter unit subtracted from the signal mixture or the previously determined difference signal, so that the further processing, the next (s) transmitter unit (s) based on a difference signal.
  • the structure of the receiving unit (s) made possible by successive Interference elimination, the determination of absolute amplitude values, which greatly simplifies and possibly eliminates the need for elaborate calibration routines.
  • the successive processing of the received signal mixture which is simplified in each pass, makes it possible to realize a comparatively higher number of transmitters and receivers in the radar system, so that it is also possible to scale to large numbers of transmitter units and receiver units.
  • the radar system can be easily scaled to a large number of receiver units.
  • the use of mutually orthogonal or quasi-orthogonal spreading codes as the "identifier" of the transmitter units also makes it possible to easily scale the number of transmitter units, since the complexity of processing the signal mixture of radar signals in each receiver unit increases linearly with the number of transmitter units Also, an adjustment through the use of longer spreading codes (ie codes with a larger number of chips) is easily feasible to allow a sufficient number of "identifiers" for the number of transmitter units.
  • Orthogonal or quasi-orthogonal codes can be e.g. Generate easily using arbitrary generator polynomials.
  • the signal mixture received by a receiving unit which includes the individual radar signals of the transmitter units scattered / reflected at the detected target objects, is processed by each receiving unit for each transmitter unit.
  • This processing in one embodiment of the invention, for each transmitter unit comprises demodulation of a signal range of the received signal mixture corresponding to the length of the modulated transmitter-specific spreading codes, a chip-wise integration (ie integration over a period of time, the temporal extent of a single chip the spreading sequence corresponds) of the demodulated signal range and then a multiplication of this integration result with the transmitter-specific spreading sequence.
  • the signal thus obtained can then be integrated over the time period corresponding to the signal range in order to determine the absolute amplitude of the radar signal received by the respective transmitter unit.
  • a radar system for detecting one or more target objects.
  • the radar system is made as mentioned a plurality of transmitter units, each comprising a transmitter antenna and a transmitter.
  • Each transmitter is designed to spread a signal with a transmitter-specific spreading code and to perform a phase modulation of the spread signal.
  • each of the transmitter units is adapted to transmit the phase-modulated and spread signal as a radar signal via the transmitting antenna of the respective transmitter unit.
  • the transmitter-specific spreading codes of the transmitters are mutually orthogonal or at least quasi-orthogonal.
  • the radar system of the presently described embodiment of the invention is capable of receiving radar signals of the type described above.
  • the radar system has at least one receiving unit, the receiving unit - and in the event that there are multiple receiving units, each receiving unit - a receiving antenna for receiving a signal mixture consisting of the emitted radar signals of the transmitter units, their amplitude and phase by a reflection on a target object changed.
  • Each receiving unit further has a receiver adapted by means of a matched filter of the received signal mixture from the transmitted radar signals of the transmitter units and using the transmitter-specific spreading codes for each transmitter unit, the transit time of the radar signal received by the respective transmitter unit
  • the receiver of each receiving unit is adapted to determine the absolute amplitude for each radar signal received by the transmitter units.
  • the term of the radar signals is determined, which in contrast to the processing of the phase information has no ambiguity, since it has no periodicity .
  • the transit time can be determined by means of a technically easy to implement signal-matched filtering, so that, for example, a so-called "phase unwrapping", as it occurs in many based on time or frequency multiplex radar systems, is not necessary.
  • the receiver of each receiving unit is further adapted for each transmitter to demodulate a signal range of the received signal mixture corresponding to the length of the modulated transmitter-specific spreading codes.
  • each receiver unit is further adapted to chip-wise integrate the demodulated signal range and then to multiply with the transmitter-specific spreading sequence and integrate the signal thus obtained over the time corresponding to the signal range, so as to obtain the absolute amplitude of the received from the respective transmitter Radar signal to determine.
  • each receiving unit of the radar system further has an analog-to-digital converter, which converts the signal mixture received by the antenna with the radar signals into a time-discrete signal mixture with the radar signals.
  • the receiver of each receiving unit is designed to process the time-discrete signal mixture.
  • each receiving unit of the radar system is designed to determine the respective transit times of the radar signals received by the respective transmitter units and their respective absolute amplitude using a successive interference elimination.
  • the received radar signals can be processed in the time domain. This avoids uniqueness problems typically encountered in frequency modulated continuous wave radar systems (e.g., FMCW radar). In addition, it seems possible to use a radar system according to the invention without elaborate calibration.
  • FMCW radar frequency modulated continuous wave radar systems
  • the receiver of each receiving unit is advantageously designed to process the signal mixture with the receiving radar signals of the transmitters successively, transmitter by transmitter, and before processing the signal mixture for a next transmitter, to subtract a receiver-side reconstruction of the received radar signals of the already processed transmitter with the determined for the respective transmitter absolute amplitude and delay of the signal mixture to form a difference signal.
  • the receiver of each receiving unit uses this difference signal to determine the transit time and absolute amplitude for the next transmitter.
  • the receiver or the receiver as dedicated hardware, such as FPGA or ASIC or in the form of another dedicated semiconductor circuit.
  • the transmitter units and the at least one receiver unit can be phase-coupled or not phase-coupled.
  • each receiver in the radar system is adapted to determine, by means of matched filtering and using the transmitter-specific spreading codes for each transmitter unit, the relative transit time of the radar signal received by the respective transmitter unit, and then from the relative transit times of the received radar signals of the transmitter units and based on the positions the transmitter units and the at least one receiver unit, for example by triangulation, to determine the absolute distance of the target object.
  • each receiver is adapted to determine by means of a matched filtering and using the transmitter-specific spreading codes for each transmitter unit, the absolute duration of the radar signal received by the respective transmitter unit, and then from the absolute terms of the received radar signals of the transmitter units, the absolute distance of the target object directly to determine.
  • each transmitter is designed to frequency-multiply the phase-modulated and spread signal in order to obtain the radar signal.
  • a frequency division is to be made accordingly.
  • each receiver is adapted to frequency-divide the signal mixture with the received radar signals before processing the signal mixture with the receiving radar signals.
  • a frequency multiplication / frequency division can be realized with the aid of oscillators.
  • the transmitter of the transmitter units can therefore use a common oscillator or multiple oscillators for frequency multiplication. Accordingly, it is likewise possible for the receivers of the at least one frequency division receiving unit to use a common oscillator or a plurality of oscillators.
  • radar signals of the desired frequency (s) can also be generated without oscillators.
  • the transmitters of the transmitter units may, for example, comprise means for direct digital signal synthesis (for example in the form of corresponding DDS components).
  • the transmitter-side signal has a predetermined, fixed signal value (eg the discrete value +1 or -1) and the transmitters of the transmitter units are adapted to periodically adjust the signal value with the respective transmitter-specific spreading code, that of the respective transmitter Sender unit is assigned to spread.
  • a predetermined, fixed signal value eg the discrete value +1 or -1
  • the transmitters of the transmitter units are adapted to periodically adjust the signal value with the respective transmitter-specific spreading code, that of the respective transmitter Sender unit is assigned to spread.
  • the receiver of each receiving unit is adapted to the matched filtering using the transmitter-specific spreading codes for each transmitter unit, the runtime by calculating a cross-correlation function between the phase-modulated, the respective transmitter unit associated transmitter-specific spreading code and the signal mixture and to determine the duration of the radar signal of each transmitter based on the absolute maximum of the cross-correlation function. If the radar system is to or can detect several target objects, it is possible for the receiver of each receiver unit to determine a number of detected target objects on the basis of the number of maxima in the cross-correlation function. In this case, the absolute amplitude and the transit time are determined for each target object.
  • a successive interference elimination can also be used in the detection of multiple target objects by the radar system, in which case the signal mixture received by the receiving unit is processed by the respective receiving unit per transmitter unit and for each target object.
  • the receiver of each receiving unit is formed, the signal mixture with the received radar signals of the transmitter successively, transmitter for transmitter to process and before processing the signal mixture for a next transmitter to subtract a receiver-side reconstruction of the received radar signals of the already processed transmitter with the determined for the respective transmitter absolute amplitudes and transit times of the detected target objects of the signal mixture to form a difference signal
  • the receiver of each receiving unit is further configured to determine the transit times and absolute amplitudes for the detected target objects for the next transmitter based on the difference signal.
  • the radar system further comprises an evaluation device which receives and processes from each receiving unit and for each detected target object the absolute amplitude and transit time of the received radar signals determined by the respective receiving unit.
  • the evaluation device is set up to generate a visual representation of the detected target objects from the determined absolute amplitudes and propagation times of the received radar signals and to display them on a screen.
  • the signal mixture processed by each receiving unit can be described with a few amplitude and delay values, so that a strong reduction of the data rates exchanged between the receiving units and downstream units of the radar system (eg an evaluation unit and / or imaging unit) leads. Also, the scaling of the radar system in turn allows for very high transmitter and receiver numbers.
  • the invention relates to a method for detecting one or more target objects in a radar system having a plurality of transmitter units and at least one receiver unit.
  • the method comprises the step of a) receiving a signal mixture with radar signals emitted by the transmitter units in each receiver unit, the amplitude and phase of the radar signals emitted by the transmitter units being changed by reflection on at least one target object.
  • each receiving unit for each of the transmitter units, the following steps are carried out: b) performing a matched filtering of the received signal mixture with the transmitted radar signals of the transmitter units using a transmitter-specific spreading code by each receiving unit to determine from the signal mixture for the transmitter-specific spreading code associated transmitter unit, the duration of the radar signal received from the respective transmitter unit wherein the transmitter-specific spreading codes are mutually orthogonal or at least quasi-orthogonal, c) determining the absolute distance of a target object in each receiving unit based on the transit times of the radar signals received by the transmitter units, and d) determining the absolute amplitude for each radar signal received by the transmitter units through each receiving unit.
  • the method further comprises spreading a signal with a respective transmitter-specific spreading code assigned to each transmitter unit in each transmitter unit, performing a phase modulation of the spread signal by each transmitter unit, and transmitting the phase-modulated and spread signal as a radar signal via one Transmission antenna of the respective transmitter unit.
  • the determination of the absolute amplitude of the radar signal received by the respective transmitter unit can be a demodulation of a signal range of the received signal mixture for the respective transmitter unit, the signal range corresponding to the length of the modulated transmitter-specific spread code, a chip-wise integration of demodulated signal range, a multiplication of the chip-wise integrated signal range with the transmitter-specific spreading sequence, and an integration of the signal thus obtained over the signal range corresponding time period include.
  • the method according to another embodiment provides that, for each transmitter unit, steps b) to d) are carried out for each target object detected by the radar system, for each tuple of transmitter unit and detected target object, the absolute amplitude and the transit time of the detected by Target object modified radar signal to capture in each receiving unit.
  • the matched filtering using the transmitter-specific spreading code for each transmitter unit comprises the steps of calculating a cross-correlation function between the phase-modulated transmitter-specific spreading code of the respective transmitter unit and the signal mixture of received radar signals and determining the transit time of the radar signal of each transmitter based on the absolute maximum of the cross-correlation function.
  • the number of detected targets increases based on the number of maxima in the cross-correlation function.
  • each receiving unit successively processes the signal mixture with the receiving radar signals, transmitter unit transmitter unit, and the method further comprises, for example: e) before processing the signal mixture for each next transmitter unit, reconstruction of the received radar signals of the already processed transmitter units in one F) forming a difference signal by subtracting the reconstruction of the received radar signals from the received signal mixture, each receiving unit for the next transmitter unit comprising steps b) to d) based on the Performs difference signal.
  • the invention further relates to a computer-readable medium storing instructions which, when executed by a processor unit of a radar receiver, cause the radar receiver to perform the step of: a) receiving a signal mixture having radar signals transmitted from a plurality of transmitter units in each receiving unit of the radar receiver, the amplitude and phase of the radar signals emitted by the transmitter units being changed by reflection on at least one target object,
  • the execution of the commands by the processor unit of the radar receiver also causes each receiving unit of the radar receiver to perform the following steps for each of the transmitter units: b) performing matched filtering of the received signal mixture with the transmitted radar signals of the transmitter units using a transmitter-specific spreading code by each receiving unit for determining from the signal mixture for the transmitter unit associated with the transmitter-specific spreading code the transit time of the radar signal received by the respective transmitter unit, the transmitter-specific spreading codes being mutually orthogonal or at least quasi-orthogonal, c) determining the absolute distance of a target object in each receiver unit d) determining the absolute amplitude for each radar signal received
  • the computer-readable medium further stores, in accordance with another embodiment, instructions that, when executed by the processor unit of the radar receiver, cause the radar receiver to further include the steps of a method of detecting one or more target objects in a radar system according to one of the embodiments of the invention perform.
  • DDS Direct Digital Synthesis
  • direct digital signal synthesis first generates a digital sawtooth signal from a digital frequency information (eg, a frequency word) indicative of the desired signal frequency by corresponding one of the frequency information with a corresponding predetermined clock (ie, clock frequency) Count added continuously.
  • the individual intermediate results of the addition can be temporarily stored in a memory, eg a register. If the digital sum value exceeds a threshold value (corresponds to the "peak" of the sawtooth), the digital intermediate result is reset to zero and the addition begins again.
  • DAC digital-to-analog conversion
  • the spreading code for the respective transmitter unit may for example already be stored in the amplitude values for the radar signal, i. the amplitude values in the memory already correspond to the phase-modulated (BSPK) signal form of the radar signal with the spreading code.
  • BSPK phase-modulated
  • a phase control signal can subject the stored amplitude values in the memory according to the spreading code of the transmitter unit of a phase modulation.
  • the phase control signal can cause a cyclic shift of the amplitude values assigned to the individual digital values of the sawtooth signal, so that a skilful shift of the assignment can achieve a phase modulation according to the spreading code.
  • phase-modulated (digital) radar signals it is provided to provide a constant phase shift of the phase-modulated (digital) radar signals so as to ensure that the phase jumps occurring at the transitions between the chips of the spreading code occur at the zero crossing of the waveform.
  • Fig. 2 shows the structure of a transmitter in an MDVIO radar system that a
  • Time multiplexing used to achieve channel diversity
  • Fig. 3 shows the structure of a transmitter in a ⁇ radar system that a
  • Frequency division multiplexing used to achieve channel diversity 4 shows three frequency steps of the "stepped frequency" method
  • Fig. 5 shows the structure of a receiver in a MEMO radar system that a
  • Fig. 6 shows the components of a radar system according to an embodiment of the
  • FIG. 7 shows the structure of a receiving unit of a radar system according to FIG.
  • Fig. 8 explains the processing steps performed by a receiving unit of a ⁇
  • FIG. 9 shows the structure of the transmitter units of a radar system according to FIG.
  • FIG. 11 illustrates (a) the superposition of radar waves at the receiver forming a signal mixture of radar signals from different transmitter units (shown here for three transmitters and a relatively short spreading code), (b) signal reconstruction by means of successive interference elimination, and (c) 12 shows the structure of the transmitter units of a radar system according to a further embodiment of the invention, wherein the transmitter units use a direct digital signal synthesis,
  • Fig. 13 shows the structure of a direct digital synthesizer (DDS) according to a
  • FIG. 14 shows another construction of a direct digital synthesizer (DDS) according to an embodiment of the invention.
  • DDS direct digital synthesizer
  • the invention relates to ⁇ or MISO radar systems that achieve channel diversity using orthogonal or quasi-orthogonal spreading codes.
  • the invention is described below by way of example with reference to a radar system of this type, the invention is not limited to radar systems.
  • imaging applications eg in ultrasound systems, systems for microwave-based breast cancer detection
  • these applications being able to differ in the frequency ranges for the carrier wave of the emitted "radar signals" in addition to the optionally application-dependent imaging ,
  • Sequences of chips which have orthogonal or quasi-orthogonal properties and are used according to the invention as spreading codes can be generated for example by means of generator polynomials of any desired length and thus adapted to the desired number of transmitter units in the radar system.
  • generator polynomials for example, gold codes, Walsh codes, etc. can be used as spreading codes.
  • the radiated radar signals are each spread with a transmitter-specific spreading code.
  • the use of the spreading codes serve to achieve channel diversity, which in turn allows the individual receiving units, for each transmitter unit (and when detecting more than one target object, additionally for each target object) the propagation time of the radar signal scattered at a target object to determine respective transmitter unit and further to determine the absolute amplitude of the received radar signal in the respective receiving unit of the respective transmitter unit. From the transit time of the radar signal of the respective transmitter unit scattered at a target object, the respective receiver unit can subsequently determine the absolute distance of the target object.
  • the transmitter units and the at least one receiver unit are not phase-coupled, can the relative transit time can be determined by the signal-matched filtering of the received signal mixture (or of the difference signal), from which the absolute transit time to the target object can then be determined by triangulation taking into account the position information of the respective transmitter unit and receiving unit. From the absolute transit time, the distance to the detected target object can then be determined in the receiving unit or an evaluation unit of the radar system.
  • each receiving unit in the matched filtering calculates a cross-correlation function between the received signal mixture and a respective phase-modulated, transmitter-specific spreading code.
  • the absolute maximum of the cross-correlation function then corresponds to the absolute or relative transit time of the radar signal of the transmitter unit, which is assigned to the transmitter-specific spreading code.
  • the cross-correlation function contains several maxima whose number corresponds to the detected target objects.
  • the respective receiving unit for each maximum and thus for each target object that was detected by the radar beam of the transmitter unit, which is associated with the transmitter-specific spreading code determine the transit time, from which then the respective distance of the target object can be determined.
  • the individual radar signals radiated by the transmitter units can be transmitted on a single carrier frequency and with the same bandwidth.
  • different carrier frequencies for example if the frequency dependence of the changes of phase (transit time) and amplitude of the reflected "radar signals" is of interest for the subsequent evaluation and / or imaging
  • the individual receiving units on the carrier frequency each receive a signal mixture of radar signals of the transmitter units scattered / reflected at the detected target objects and evaluate this transmitter unit for transmitter units
  • the carrier frequencies are typically in the range of 1 GHz and several
  • radar systems operating in the THz range are also under development, but the invention is not limited to carrier frequencies, but rather the choice of suitable carrier frequency (s) is for an invention ndes system depending on the particular application of the invention, or predetermined.
  • the processing of the received signal mixture in a receiving unit can be carried out, for example, with the aid of successive interference elimination.
  • a reconstruction of the radar signal received at the receiving unit by the respective transmitter unit is formed for each transmitter unit for which the signal mixture has already been "processed" by the receiver unit (ie runtime and amplitude information is available) and before the signal is processed.
  • the mixture is subtracted from the signal mixture so that the further processing will be based on a difference signal for the next transmitter unit (s) Ideally, the difference signal would only contain measurement noise after "processing" the last transmitter unit.
  • Another aspect of the invention is the processing of the signal mixture for the individual transmitter units.
  • the signal mixture received by the antenna of the receiving unit which includes the individual radar signals of the transmitter units scattered / reflected at the detected target objects, is processed for each transmitter unit by each receiving unit.
  • This processing comprises in one embodiment of the invention for each transmitter unit - after signal-matched filtering to determine the transit time per target object - a demodulation of a signal range of the received signal mixture corresponding to the length of the modulated transmitter-specific spreading codes, a chip-wise integration (ie integration over a time period corresponding to the time extent of a single chip of the spreading sequence) of the demodulated signal range, and then multiplying this integration result by the transmitter-specific spreading sequence.
  • the signal thus obtained can then be integrated over the time period corresponding to the signal range in order to determine the absolute amplitude of the radar signal received by the respective transmitter unit.
  • the processing of the signal mixture takes place at least partially discretely. Accordingly, the signal mixture may be e.g. be converted into discrete values even before the matched filtering in the receiving unit.
  • Fig. 6 shows a radar system according to an embodiment of the invention.
  • the radar system is capable of detecting one or more target objects.
  • the radar system consists of several transmitter units (total Ns transmitter units), each comprising a transmitting antenna and a transmitter.
  • Each transmitter is designed to provide a signal with a fixed discrete value (shown here by way of example as +1), with a transmitter-specific value Spreading code c, to spread and make a phase modulation of the spread signal.
  • each of the transmitter units is adapted to transmit the phase-modulated and spread signal as a radar signal via the transmitting antenna of the respective transmitter unit.
  • the transmitter-specific spreading codes of the transmitters are mutually orthogonal or at least quasi-orthogonal. In the example shown in Fig.
  • the modulation symbols of the spread signal are multiplied by a higher frequency oscillation given by an oscillator VCO and then supplied to a frequency multiplier.
  • the resulting radar signal is then amplified in an amplifier and transmitted via the antenna of the transmitter unit.
  • a common oscillator is used for modulation to a higher carrier frequency.
  • the transmission signals-as will be described in more detail below-can also be generated directly from the phase-modulated chip sequence of the respective spreading sequences by a direct digital signal synthesis.
  • semiconductor devices DDS are available that require no separate oscillator, but usually a downstream frequency multiplier.
  • the radar system of the presently described embodiment of the invention is capable of receiving radar signals of the prescribed type.
  • the radar system has at least one receiving unit, the receiving unit - and in the event that there are several receiving units, each receiving unit - a receiving antenna for receiving a signal mixture consisting of the emitted radar signals of the transmitter units whose amplitude and phase by a reflection on a target object changed.
  • FIG. 6 shows by way of example NE receiving units which receive a mixture of radar signals of the respective transmitter units scattered at the target object.
  • Fig. 11 (a) exemplifies a sum signal of the radar signals r- (i) as received from a receiving unit j of the radar system.
  • the sum signal (signal Mixture) is formed from the superposition of the coded and BPSK modulated radar signals from three transmitter units positioned at different distances to a detected target object. Due to the different transit times, the individual radar signals of the three transmitter units on the receiver unit occur at different times, or by multiplication with the speed of light c at different locations in the path range.
  • FIG. 11 (b) illustrates the signal reconstructions s (t-T t ) of the individual received radar signals of the three transmitter units determined with the aid of the successive interference elimination.
  • Fig. 7 shows a receiving unit j according to an embodiment of the invention.
  • the operation of the receiving unit j according to an embodiment of the invention is shown in FIG.
  • the sum signal r ()) of the radar signals of the transmitter units is received 801 by an antenna of the receiving unit j and down-converted to an intermediate frequency 802 (LO with fo).
  • Step 800 in Figure 8 is merely an optional step that initializes a count variable i for the transmitter units.
  • the signal mixture r y (f) is then converted into time-discrete values 803, which can be done for example by means of an AD converter (ADC). From the signal mixture r j (t) and a reconstruction of the received radar signals for the already processed
  • Transmitter units becomes a difference signal D; is formed (812) that is further processed in the receiving unit j.
  • the processing of the received radar signal of the first transmitter unit i 0 (with the spreading code Co) corresponds to the difference signal Z ) _, the sum signal r- (r) -
  • Each receiving unit also has a correlator, which is provided by means of a matched filter of the difference signal D l and using the one for the
  • Transmitter unit s transmitter-specific spreading code c t for each transmitter unit, the transit time T, of the radar signal received from the respective transmitter unit i 804.
  • the correlator calculates a cross-correlation function between the difference signal D M and the modulated chip sequence of the spreading c c. which corresponds to the signal s t (t) (see also Fig. 9).
  • the correlator recognizes a known pattern (the modulated spreading code c 1) emitted by the transmitter unit i.
  • the time difference relative to the beginning of the known pattern in which the absolute maximum of the cross-correlation function occurs corresponds to the transit time T i of the radar signal, from which the radar system determines the absolute distance of the target object.
  • synchronization takes place 805 with regard to the modulated chip sequence of the spreading code c i (signal s ⁇ t)), the transit time r, for determining its expected time position in the difference signal £> ._, is used.
  • a signal part s t (t) can be extracted from the difference signal fl M , which contains the expected signal s t (t).
  • the signal part s ( (t) is then demodulated 806, whereby a certain number of discrete-time values are obtained for the individual chips of the expected spreading code v, depending on the sampling rate V.
  • a receiving unit shown in Fig.
  • the orthogonal or quasi-orthogonal properties of the spreading sequences result in a sequence g t (t) based on which the amplitude k i is subsequently determined the received sequence g. (t) is determined to be 809. This is done, for example, by integration of the time-discrete values of the sequence g ; (t) or - optionally - by averaging.
  • the amplitude k t of the received sequence gi (t) can be calculated as follows: where T B represents the duration of the transmitted bit which is just the product of chip length x chip duration.
  • steps 805 through 809 are performed for each of the maxima (ie, for each of the detected target objects) in the cross-correlation function, taking into account the respective delay ⁇ , m for each maximum / target object m.
  • steps 805 to 809 an amplitude k in of the received radar signal from the transmitter unit i and its transit time T tm can be determined for each of the detected target objects m.
  • the individual receiving units j operate during the processing of the signal mixture r. (f) the individual transmitter units / or their
  • FIGS. 7 and 8 illustrate the use of successive interference elimination, in which, after successful determination of the amplitudes k t and k, respectively, in the received signal
  • step 810 If it is determined in block 810 that there is still another transmitter unit (s) to be processed, it is optionally also possible to jump directly to step 813, in which case the entire processing of the signal mixture r (i) on the signal mixture r ; (i) itself and not based on a difference signal £ ) ._,. If all transmitter units have been processed (step 810: no), the processing of the signal mixture r. (F) is complete and the individual amplitudes k t and k in the received radar signals (for each target object) from the transmitter units i and their transit times r ; or r im can be transmitted to a unit that recorded the
  • the amount of data to be transmitted between the receiving units j and the evaluation unit is very small and depends on the individual amplitudes k t and k in the received radar signals (for each target object) from the transmitter units i and their transit times T i and T im confined, from which then - for example - with the help of a
  • Graphics processor a visual representation of the detected target objects relative to the position of the radar system can be generated and displayed on a screen.
  • the received data must be transmitted at the data rate of the ADC, which increases very rapidly especially in frequency division multiplexed signals.
  • steps 800 and 804 through 813 in FIG. 8 may be implemented in dedicated hardware (eg, an FPGA or ASIC) of the receiving unit.
  • the radar system uses a frequency range / carrier frequency for all radar signals of the transmitter units, it is possible to temporally vary the frequency of the carrier signal at the transmitter side.
  • the frequency change in the carrier frequency is not used to determine the absolute amplitude and transit time of the carrier Radar signals used; Rather, the frequency changes are used to determine a (frequency-dependent) absolute amplitude and duration of the respective radar signals for the respective carrier frequencies in each case per transmitter unit and per detected target object.
  • the transmission signals can also be generated directly from the phase-modulated chip sequence of the respective spreading sequences by a direct digital signal synthesis.
  • a direct digital synthesizer DDS
  • the output signal generated by the DDS can be supplied to a frequency multiplier. If the DDS can already generate output signals at the desired frequency, a frequency multiplier is not necessary and can be dispensed with.
  • the radar signal obtained can also be amplified in an amplifier and is transmitted via the antenna of the transmitter unit.
  • DDS devices often offer higher bandwidth than oscillators, which can improve the resolution and image quality of the radar system.
  • a DDS device may be designed to cover a frequency range between 0 Hz and 1.5 GHz or more.
  • the frequency of the DDS components is digitally adjustable, so that the DDS components are less susceptible to fluctuations in the control voltages compared to oscillators.
  • DDS typically have low phase noise, which is very important in radar applications.
  • Fig. 13 shows the construction of a DDS 1300 according to an embodiment of the invention.
  • the shown DDS 1300 may be used, for example, in the transmitter units of the radar system as shown in FIG.
  • the respective radar signal which contains the transmitter-specific spreading code, by means of a direct digital signal synthesis. obtained by the DDS 1300.
  • a logic module such as the FPGA 1301 shown by way of example, controls the frequency of the sawtooth signal, which is generated with the aid of the adder 1302 and the register 1303 from the clock (Clock) with a control signal, the frequency word shown by way of example.
  • the frequency word shown by way of example.
  • a clock frequency of 3GHz and a 32-bit frequency word a frequency resolution in steps of approximately 0.7 Hz can be achieved, which is sufficient for radar application.
  • the register 1303 supplies the intermediate result of the last clock (n-1) to the adder 1302.
  • the individual intermediate results (Z ( . (N)) of the addition are stored in a memory, eg a register
  • Counter is indicated by a pulse at the C out output of the adder 1302 and supplied to the FPGA 1301 so that it can control the phase modulation according to the transmitter-specific spreading code by means of the phase word in synchronism with this signal at the C out output of the adder 1302.
  • a preferably non-volatile memory 1305 eg an EEPROM, EPROM or ROM.
  • the memory 1305 stores the information corresponding to the individual counter values Z ; (n) corresponding amplitude values A of the digital radar signal s t (n), which are output from the memory according to and with the same clock as the summation of the count value and medium digital-to-analog conversion (DAC 1306) in an analog radar signal s t (t) be converted.
  • the following table shows purely by way of example one
  • Signal form of the radar signal represents a sine wave (of course, other signal forms, such as cosine function, sinc function, cosine rolloff, etc. are also conceivable): ⁇ ,. ( ⁇ ) AZ, (n) A
  • each waveform of a radar signal corresponding to a sawtooth is phase-modulated according to a chip of the spreading code.
  • each chip corresponds to a phase modulated waveform in the radar signal.
  • the division factor of the frequency divider 1304 is N> 1, then N successive waveforms of the radar signal would be phase-modulated according to one chip of the spreading code. In this case, a chip of the spreading code N would correspond successively to the following signal forms in the radar signal.
  • the FPGA 1301 may (in synchronization with the individual saw teeth) phase-modulate the stored amplitude values A in accordance with the spreading code.
  • the phase control signal may cause a cyclic shift of the amplitude values assigned to the individual digital values of the sawtooth signal, so that a skilful shift of the assignment can achieve a phase modulation according to the individual chips of the spreading code.
  • the spreading code c i 11 10100 from the seven
  • the FPGA 1301 may also supply the phase control signal (phase word) to the adder 1302 instead of the memory 1305.
  • the adder 1302 may achieve the phase modulation thereby .
  • the spreading code c for example, for the respective transmitter unit already in the amplitude values A for the radar signal s, (n) be deposited.
  • the components of the DDS shown in FIG. 13 can be implemented on an integrated circuit (IC).
  • the phase modulation of the digital radar signals generated by the (EP) ROM 1305, which contains the transmitter-specific spreading code is likewise integrated in the DDS.
  • the allocation table which converts the count values Z t ⁇ n) output by the register 1303 into corresponding amplitude values of the digital radar signal may already contain the correct phase-modulated values for the spreading code.
  • the (EP) ROM 1305 may also be replaced or supplemented with logic that implements the phase modulation of the waveform in accordance with the spreading code. This is shown by way of example in FIG. 14. There the logic 1401 is integrated in the DDS 1400 and can according to the C out
  • a constant phase shift is provided in the phase modulation to ensure that the phase jumps in the transitions between the individual chips of the spreading code c i in a zero crossing of the waveform for the
  • Figs. 13 and 14 also show a phase word having a plurality of bits (eg, 11 bits) capable of phase shifting by cyclically shifting the allocation of counts Z ; (n) and amplitude values A and a
  • Phase rotation by 180 ° can be realized for the individual chips.
  • BPSK Phase rotation by 180 °
  • an FMCW-based ⁇ / MISO radar can also be implemented (compare FIG. 4) by the frequency word being changed in a corresponding stepwise manner.
  • a code-based ⁇ MISO radar can be implemented using the DDS 1300, 1400 as just described.
  • a frequency division multiplex based ⁇ / MISO radar see Figures 3 and 5) in which the individual transmitter units transmit their radar signals at different carrier frequencies and a mixture of a frequency division multiplex based MEVIO / MISO radar and the one described Code-based MEVIO / MISO radar.
  • the transmitter units of the radar system would be divided into groups, the transmitter units of each group transmitting their respective radar signal on a carrier frequency.
  • the individual transmitter units of a group are to be distinguished from each other by corresponding spreading codes in the radar signal, as described previously with reference to FIG. 9, for example.
  • Each group is assigned a carrier frequency.
  • the individual groups can use the same set of spreading codes for transmitter separation. Of course, it is also possible that only some groups use the same set of spreading codes or the individual groups use different spreading codes to distinguish the transmitting units.
  • the individual groups of transmitter units can be separated from one another by means of corresponding (digital or analog) bandpass filters, and subsequently and the resulting band-filtered signal mixture, as described previously with reference to FIGS. 7 and 8, in each transmitter unit be further processed.
  • the user could determine or change the operating mode of the radar system via a user interface.
PCT/EP2012/005016 2011-12-05 2012-12-05 Empfängerarchitektur für orthogonale multiple-input-multiple-output radarsysteme WO2013083269A2 (de)

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