Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
  • G01S7/4004—Means for monitoring or calibrating of parts of a radar system
  • G01S7/4008—Means for monitoring or calibrating of parts of a radar system of transmitters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S13/00—Systems 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
  • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
  • G01S13/06—Systems determining position data of a target
  • G01S13/08—Systems for measuring distance only
  • G01S13/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
  • G01S13/34—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
  • G01S13/343—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal using sawtooth modulation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S13/00—Systems 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
  • G01S13/88—Radar or analogous systems specially adapted for specific applications
  • G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
  • G01S13/931—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of land vehicles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/35—Details of non-pulse systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/35—Details of non-pulse systems
  • G01S7/352—Receivers
  • G01S7/354—Extracting wanted echo-signals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S13/00—Systems 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
  • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
  • G01S13/06—Systems determining position data of a target
  • G01S13/42—Simultaneous measurement of distance and other co-ordinates
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO 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
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/35—Details of non-pulse systems
  • G01S7/352—Receivers
  • G01S7/356—Receivers involving particularities of FFT processing

Definitions

• the invention relates to a radar system for use in driver assistance systems in motor vehicles.
• the radar system according to the invention has means and methods for analyzing and monitoring its frequency modulation via a series of similar transmission signals. If the frequency modulation deviates too much from its desired course, either corrective measures are used or the driver assistance system is partially or completely deactivated.
• Motor vehicles are increasingly being equipped with driver assistance systems which detect the surroundings with the aid of sensor systems and derive automatic reactions of the vehicle from the traffic situation thus recognized and / or instruct the driver, in particular warn him. A distinction is made between comfort and safety functions.
• FSRA Frell Speed Range Adaptive Cruise Control
• Safety functions are now available in a variety of forms.
• a group form functions to reduce the braking or stopping distance in emergency situations;
• the spectrum of the corresponding driver assistance functions ranges from an automatic pre-fill of the brake to the reduction of the brake latency (Prefill), an improved brake assist (BAS +) up to the autonomous emergency braking.
• Another group are lane change functions: they warn the driver or intervene in the steering if the driver wants to make a dangerous lane change, ie if a vehicle in the secondary lane is either in the blind spot (is called BSD - "Blind Spot Detection"). - called) or approaching quickly from behind (LCA - "Lane Change Assist"). In the foreseeable future, however, the driver will no longer be assisted, but the driver's task will increasingly be done autonomously by the vehicle itself, ie the driver will increasingly be replaced; one speaks of autonomous driving.
• radar sensors are used, often also in fusion with sensors of other technology such as e.g. Camera sensors.
• Radar sensors have the advantage that they can work reliably even in bad weather conditions and, in addition to the distance between objects, they can also directly measure their radial relative speed via the Doppler effect.
• the transmission frequencies are 24GHz, 77GHz and 79GHz.
• the radar image must correspond to reality, i. that the object sizes, in particular distance, relative speed and angle must be correct, that no objects are overlooked and that no so-called ghost objects, which in reality do not exist, may be reported.
• the central element of radar sensors is the modulation of the transmission frequency in order to measure distance and relative speed.
• the most common type of modulation is the frequency modulation, in particular a linear change of the frequency, often a series of similar linearly modulated transmission signals is used.
• an erroneous frequency modulation for example, by failure or malfunction of individual circuit parts
• the errors described above may occur, ie erroneously measured object sizes, undetected objects and ghost objects.
• the driver assistance function implemented with the radar system could have a faulty functioning; in an emergency brake assistant, e.g. An unauthorized emergency braking can be activated by ghost objects, which could lead to a rear-end collision of a subsequent vehicle with serious consequences to deaths.
• the object of the invention is to propose for a radar system arrangements and methods for analyzing the frequency modulation via a series of similar transmission signals, which differ from the approach set out in DE 10 2016 214 808 and can be more advantageous due to technological constraints and implementation aspects ,
• methods are to be proposed which can either work with large frequency divider factors or have no reinitialization of counters.
• a method for a radar system for detecting the surroundings of a motor vehicle and realizing a function for driver assistance and / or for autonomous driving maneuvers comprises the steps of generating a frequency modulation by means of a controllable oscillator, generating a sequence of Ko (Ko> 1) in the transmission frequency modulated transmit signals, each having the same nominal frequency course, if appropriate, apart from a variation of the frequency ge, so in particular a variation of the beginning and thus have the same center frequency, emitting of transmission signals by means of transmission, receiving reflected on objects transmission signals by receiving means, analyzing the frequency response of the transmission signals and evaluating the received signals, in particular for the detection of objects by means of signal processing means , Wherein an actual course of the transmission frequency within the transmission signals or a deviation of the actual course of the desired frequency characteristic absolute or relative, ie to an indeterminate constant proportion is determined, thereby atsftfindet for accurate determination of particular similar gradients or deviations over the Ko transmission signals , wherein a time-discrete signal
• a parameter of the frequency modulation of the individual transmission signals in particular the frequency position and / or a parameter of the frequency response of the oscillator between the transmission signals, can be varied in order to change the phase of the oscillator at the start of the oscillator over the individual transmission signals To ensure transmission signal to prevent similar errors in the averaging.
• the averaging over the Ko transmission signals to an accurate determination of the actual course of the transmission frequency or its deviation from the desired course is sattfindet that for analysis Signal is used, which is compared to the transmission signal by frequency division by the factor T> 1 and / or reduced by mixing in the frequency, these are scanned via the transmission signals resulting low-frequency signals, if necessary, after filtering, this optionally on the transmitted signals resulting sampled signals
• at least approximately phase-normalized that is to say phase-shifted to at least approximately the same phase position, these phase-normalized signals are then added and the actual frequency profile is determined from the phase characteristic of this accumulated and optionally previously filtered signal.
• the phase normalization for the case that the low-frequency sampled signals are real be realized that the low-frequency sampled real-valued signals at least approximately in their analytical signal, ie the complex-valued signal only be converted to the positive or negative frequency components, preferably to a
• Hilbert filter first degree with the zero point at about the negative or positive of the center frequency of the frequency-modulated signals is used, from these analytical signals in each case a value is determined in the same way, e.g. the conjugate complex of the first signal value or the signal value at the time when the desired frequency characteristic assumes the average frequency, and the analytical signals are multiplied by this value.
• the signal accumulated via the transmission signals or a signal derived therefrom can be converted into its analytical signal with high precision by Hilbert filtering.
• the frequency of the radiated transmission signals are linearly modulated, the signals received by reflection of the transmission signals to objects by mixing with a signal whose frequency corresponds to the current transmission frequency or differs from it by a constant factor the low-frequency range are transferred, the low-frequency received signals are sampled in an equidistant grid NA times and on these NA samples a first spectral analysis is formed in particular in the form of a discrete Fourier transformation in order to be able to realize in particular a distance measurement of the objects and a separation for the simultaneous detection of multiple objects.
• the difference between instantaneous and delayed by the time At measured Istfrequenzverlauf within the transmission signals are formed, a signal is calculated whose frequency response corresponds to this difference, via this signal a spectral analysis in particular in shape a discrete Fourier transform is performed, which results in a spectrum, and the resulting spectrum or its amount is used directly for deriving a quality measure of the frequency modulation and / or from the deviation of the spectrum from the expected in the desired frequency response spectrum of an object in the time At corresponding Distance is derived from a measure of merit, wherein for both spectral analyzes the same window function is used and the resulting spectra are related to the comparison to an equal level.
• the factor may be proportional to an assumed object distance or may include a sine function whose argument is proportional to the object distance and proportional to the respective frequency reference point of the spectral analysis.
• the method for a radar system it can be derived from a determined quality standard whether a detection by or due to a deviation of the actual frequency characteristic from the desired frequency profile has occurred or could be, and this detection is then possibly completely rejected or identified as a potential false detection.
• the average frequency slope of the actual frequency curve or their Deviation from the nominal frequency slope and used to calculate the distance of objects.
• the center frequency of the actual frequency curve or its deviation from the desired center frequency can be determined and used for the calculation of the relative speed and / or the angular position of objects.
• a radar system is set up to carry out a method according to a preceding preferred embodiment.
• Fig. 1 the exemplary embodiment of a radar system is shown.
• Fig. 2 shows the frequency of the transmission and the reception signals, which consists of so-called frequency ramps, as well as the respectively used antenna combinations consisting of transmitting and receiving antennas.
• Fig. 3 shows a sampled signal in the presence of two objects before the first DFT (left) and after the first DFT (right).
• FIG. 5 schematically shows the two-dimensional complex-valued spectrum e (j, l, m) after the second DFT for an antenna combination m.
• FIG. 6 shows the different path lengths between the individual antennas and a distant object relative to the sensor at an azimuth angle C (Az ⁇ 0.
• Fig. 7a shows an antenna arrangement with a transmitting and 8 receiving antennas, which is equivalent to the antenna arrangement according to Fig. 1 with 2 transmitting and 4 receiving antennas; in Fig. 7b are shown for this equivalent arrangement, the different path lengths between the individual antennas and a distant relatively relative to the sensor object.
• FIG. 8a shows the complex spectral value rotating in the distance-relative-speed gate over the antenna combinations (9,0), in which exactly one object (resting relative to the sensor) is located; in FIG. 8b, the associated spectrum according to the third DFT is shown in terms of magnitude.
• FIG. 11 shows the frequency error fE (n) for an actual frequency characteristic which is slightly curved with respect to the nominal frequency characteristic and additionally has a periodic interference, wherein the center frequency and the average frequency gradient correspond to their nominal values.
• FIG. 12b shows the relative difference between these two range spectra.
• Fig. 13 shows the values of the frequency counter read out every 25ns and normalized to the ramp start via a transmission signal (plotted dots); shown in dashed lines is the expected desired course.
• the radar system has 2 transmission antennas TXO and TX1 for emitting transmission signals and 4 reception antennas RX0-RX3 for receiving transmission signals reflected on objects;
• the antennas are implemented on a planar board 1 .1 in planar technology as patch antennas, this board with respect to horizontal and vertical direction in the vehicle as shown in the image is oriented. All antennas (transmit and receive antennas) have the same beam characteristic in elevation and in azimuth.
• One of the two transmitting antennas and one of the four receiving antennas can be selected via the multiplexers 1 .3 and 1 .4.
• the transmitted on the respectively selected transmitting antenna transmission signals are obtained from the high-frequency oscillator 1 .2 in the 24GHz range, which can be changed in its frequency via a control voltage v control.
• the control voltage is generated in the control means 1 .9, these control means e.g. a phase locked loop or a digital-to-analog converter, which are controlled so that the frequency response of the oscillator of the desired frequency modulation at least approximately corresponds.
• the signals received by the respectively selected receiving antenna are also down-converted in the real-valued mixer 1 .5 to the signal of the oscillator 1 .2 in the low-frequency range.
• the received signals then pass through a bandpass filter 1 .6 with the transmission function shown, an amplifier 1 .7 and an analog / digital converter 1 .8; then they are further processed in the digital signal processing unit 1 .10.
• the frequency of the high-frequency oscillator and thus of the transmission signals is changed very rapidly linearly (in 8 s by 187.5 MHz, the center frequency being 24.15 GHz), as shown in FIG. 2; one speaks of a frequency ramp.
• the frequency ramps are repeated periodically (every 10 s); In total, there are 2048 frequency ramps, all of which have the same nominal frequency response.
• the 8 combinations of the 2 transmit and 4 receive antennas are in the order TX0 / RX0, TX0 / RX1, TX0 / RX2, TX0 / RX3, TX1 / RX0, TX1 / RX1, TX1 / RX2 and TX1 / RX3 is repeated periodically, with the next combination being selected before each frequency ramp.
• the received signal is mixed real-valued with the oscillator and thus transmission frequency, results after the mixer a sinusoidal oscillation with the frequency Af.
• This frequency is in the MHz range and is still shifted at a non-vanishing radial relative speed by the Doppler frequency, which is only in the kHz range and therefore approximately negligible compared to the frequency component by the object distance. If there are several objects, the received signal is a superimposition of several sinusoidal oscillations of different frequency.
• the receive signal at the A / D converter is sampled 256 times at intervals of 25 ns (ie 40 MHz) (see FIG. 2), the sampling always commencing at the same time relative to the start of the ramp.
• signal sampling only makes sense in the time range where received signals arrive from objects in the range of interest - after ramp start, at least the corresponding maximum transit time must be awaited (this corresponds to a maximum interest of 99m) 0.66 s); It should be noted that here and below by distance always the radial distance is understood.
• a discrete Fourier transform is formed in the form of a fast Fourier transform (FFT).
• FFT fast Fourier transform
• the range gates where there are objects, power peaks occur in the DFT. Since the sampled received signals are real-valued (no additional information in the upper half of the DFT, since symmetric) and the upper transition region of the analog bandpass filter 1 .6 of FIG.
• the filter 1 .6 attenuates small frequencies and thus the received signals from nearby objects in order to avoid an overdriving of the amplifier 1 .7 and the A / D converter 1 .8 (the signals received at the antennas become stronger with decreasing object distance) ,
• Several objects with different radial relative velocity in the same distance Gate are separated by calculating a second DFT for each antenna combination and each range gate via the complex spectral values occurring in the 256 frequency ramps.
• a two-dimensional complex-valued spectrum v (j, l, m) results for each antenna combination m, wherein the individual cells can be referred to as distance-relative-velocity gates and through objects power peaks at the respectively associated distance-relative velocity Tor occur (see Fig. 5).
• the information from the 8 antenna combinations is then fused.
• the waves originating from the two transmitting antennas and reflected at a single point-like object arrive at the four receiving antennas with different phase positions relative to each other, depending on the azimuth angle CIAZ, since the distances between object and transmitting and receiving antennas are slightly different. This will now be explained in more detail, wherein the observed object should first rest relative to the sensor, ie, it has the relative speed zero.
• the quantity (2a + d / 2 + md) represents the horizontal distance of the so-called relative phase center of the antenna combination m to the reference point RP and is the sum of the horizontal distance of the associated transmitting and receiving antenna to the reference point (the relative phase center of a combination of transmitting and transmitting antennas). and a receive antenna is defined here as the sum of the two vectors from a reference point to the phase centers of the transmit and receive antennas).
• the arrangement presented here according to FIG. 1 has the advantage that it has almost only half the horizontal extent in comparison to the conventional arrangement according to FIG. 7a, as a result of which the sensor size can be significantly reduced.
• the summation described above is realized by a 16-point DFT, where the 8 values of the 8 antenna combinations are supplemented by 8 zeros.
• Fig. 8b the magnitude w (j, l, n) of the spectrum of the third DFT for the ratios of Fig.
• the power peaks By determining the power peaks, one can therefore detect objects and determine their distance, relative velocity (apart from any ambiguities, see above) and azimuth angle (for each ambiguity hypothesis the relative velocity corresponds to a value, see FIG. 9). Since power peaks due to the DFT windowings also have levels in neighboring cells, the object dimensions can be determined much more accurately than the gate widths by interpolation as a function of these levels. It should be noted that the window functions of the three DFTs are chosen so that, on the one hand, the power spikes do not become too wide (for sufficient object separation), but On the other hand, the side lobes of the window spectra do not become too high (in order to be able to recognize even weakly reflecting objects in the presence of strongly reflecting objects).
• From the height of the power peaks can be estimated as the fourth object measure nor its reflection cross-section, which indicates how much the object reflects the radar waves. Due to the noise present in each system (eg due to thermal noise), after the three-dimensional DFT, even without received object reflections, a certain level of performance results; this noise level, which varies to some extent by statistical effects, represents the lower physical limit of the detection capability.
• the detection threshold above which power peaks are formed into objects is placed about 12 dB above the average noise.
• the described detection of objects and the determination of the associated object dimensions represent a measurement cycle and provide an instantaneous image of the environment; this is cyclically repeated approximately every 40ms.
• the instantaneous images are tracked, filtered and evaluated over successive cycles;
• Reasons are in particular:
• Some sizes can not be determined directly in a cycle, but only from the change over successive cycles (eg longitudinal acceleration and lateral velocity),
• Tracing and filtering object detections over consecutive cycles is also referred to as tracking.
• values for the next cycle are predicted from the tracked object dimensions of the current cycle for each object. These predictions are compared with the objects detected in the next cycle as snapshots and their object dimensions in order to assign them to each other. Then the predicated and measured object measures belonging to the same object are fused, resulting in the actual tracked object measures, which thus represent values filtered over successive cycles. If certain object dimensions can not be determined unambiguously in one cycle, the different hypotheses must be taken into account in tracking. From the tracked objects and the associated tracked object measures, the environment situation for the respective driver assistance function is analyzed and interpreted, in order to derive the corresponding actions.
• Such an imperfect frequency modulation means that even with punctiform objects, the power peaks in the distance dimension are blurred or frayed, which can lead to erroneously measured removal, obscuring smaller objects by larger objects and generation of ghost objects.
• the driver assistance function implemented with the radar system could have a faulty functioning; in an emergency brake assistant, e.g. An unauthorized emergency braking can be activated by ghost objects, which could lead to a rear-end collision of a subsequent vehicle with serious consequences to deaths.
• the output of a divider has a rectangular shape; in Fig. 10 a section is shown (solid curve).
• the resulting sinusoidal signal is also shown in FIG. 10 (dashed curve).
• the phase profile (pT (t, k, m) of this sinusoidal signal ST (t, k, m) is obtained by integration of the divided-down frequency fT (t, k, m), so that
• STA (n, k, m) A S COS (2TT- [frs / fA-n + bi / 2 / fA 2 -n 2 ] + ⁇ po (k, m))
• the real signal STA (n, k, m) also carries a noise component r (n, k, m) which is e.g. caused by phase noise of the oscillator and quantization effects in the A D conversion.
• r e.g. caused by phase noise of the oscillator and quantization effects in the A D conversion.
• STA (n, k, m) A s -cos (2n- [fTs / fA-n + br / 2 / fA 2 -n 2 ] + (po (k, m) + ⁇ ( ⁇ )) + r ( n, k, m), where 0 ⁇ n ⁇ 8Ms fA, ie 0 ⁇ n ⁇ 320.
• the noise component r (n, k, m) is much smaller than the useful component with the amplitude A s , but i. Gen. but so large that it is not possible to determine from the signal STA (n, k, m) of a single frequency ramp the phase error ⁇ ( ⁇ ) and thus the frequency error fE (n) with sufficient accuracy. Therefore, an averaging over many frequency ramps is necessary so that the noise component can be sufficiently well determined.
• the averaging only brings about a positive effect if an at least partially in-phase accumulation of the signals STA (n, k, m) is carried out, that is to say the signals are first to be normalized in phase, ie to be shifted to the same phase position.
• the real-valued signals STA (n, k, m) are first to be converted into their corresponding complex-valued signal, that is, into their analytic signal STAc (n, k, m):
• STAc (n, k, m) A s -exp i- (2n- [fTs / fA -n + br / 2 / fA 2 -n 2 ] + (po (k, m) + ⁇ ( ⁇ ))) + rc (n, k, m), where rc (n, k, m) is the analytic signal of noise r (n, k, m) and has a much smaller amplitude than the useful portion of the signal having amplitude A s ; denotes the imaginary unit.
• An analytic signal is produced by complex-valued filtering with a so-called ideal Hilbert filter, which suppresses all negative frequencies and cancels all positive frequencies with constant transmission.
• This measurement error can be further reduced by extending the averaging over several cycles. For this one can either mittein the measured frequency errors resulting per cycle, or one extends the averaging of the phase-normalized signals over several cycles.
• the phase noise cp r (n) (eg generated by quantization noise from the A / D converter) has an effect on the measurement error amplified by the divider factor T, which is why a high divider factor tor is disadvantageous; when the oscillator signal is reduced by mixing, this problem does not arise; however, generating a second signal in the 24 GHz range is expensive; therefore, a combination of division and mixture can also be implemented; for example, the oscillator signal may first be divided by a factor of 64 to the range of about 377MHz and then downconverted to a fixed frequency of 367MHz,
• the coefficients of the Hilbert filtering can also be chosen variably, that is, adapted to the respective setpoint frequency course; For example, with a Hilbert filter of the first degree, you can change the coefficients within a frequency ramp so that the zero point always lies at the negative of the respective nominal frequency.
• the sampling of the received signals is carried out during the rear 6.4 s of the frequency ramp; the front 1 .6 s are required for transient effects (in particular by filters in frequency generation and reception path) and for the propagation time corresponding to the maximum distance of interest (0.66 s at a maximum interest of 99m).
• the first e.g. 20 values i.e., the first 0.5 s
• the preferred approach is to compensate for these frequency errors.
• One approach to this is to change the drive signal to generate the frequency modulation (in the case of direct generation of the oscillator control voltage via a digital-to-analog converter whose drive values or in the case of a PLL the signal for the control default), which can also be done in an iterative manner.
• Another approach is to consider the frequency errors fE (n) in the evaluation of the received signals.
• an (average) gradient b of the frequency ramps deviating from the target specification has an altered length of the range gates (see further below) and can be correspondingly taken into account in the distance determination; a calculation of the real slope of the frequency ramps can be done, for example, by a linear regression over the actual frequency fist (n). A deviation of the center frequency of the frequency ramps from their nominal value changes the mean wavelength and thus has an effect on the calculated relative velocity and Angular position of objects (see derivations above); By using the real center frequency full of the desired center frequency errors can be avoided.
• frequency errors fE (n) can not be compensated, it must be judged whether their influence on the detection quality is still acceptable, ie that there are no unacceptable functional limitations; otherwise the affected driver assistance functions and / or autonomous driving maneuvers should be restricted or deactivated.
• s (i) sin (2n sum (fist (n) - fist (n-12 ), 65.65 + i) / fA) for 0 ⁇ i ⁇ 255, where sum (g (n), u, o) means that the sequence g (n) is summed over u ⁇ n ⁇ o.
• the spectrum e (j) of this signal is given by a DFT; if a window function w (i) is used in the normal data evaluation for environment detection, the same window is to be used here (ie the signal s (i) multiplied by w (i) before application of the DFT).
• the resulting distance spectrum e (j) is shown in absolute terms in FIG. 12a (solid line, logarithmic representation, ie in dB), the index j representing the distance represents.
• FIG. 12a also shows the range spectrum which results in the desired frequency characteristic for a target at the same distance, with the same amplitude 1 and when using the same window function (dashed curve).
• the distance spectrum e (j) calculated for the actual frequency curve for the amount of a limit curve
• Fig. 12b the magnitude of the difference of the range spectra for the example is shown above, normalized to the maximum of the range spectrum to the desired frequency response and plotted in dB; By normalizing to the maximum of the range spectrum to the desired frequency response is also called the relative difference.
• Checking for a limit curve represents a binary measure of quality (that is, with the two result states, good or bad);
• an analogue quality measure can also be defined, e.g. the maximum relative difference between the distance spectra and the actual frequency response.
• the relative difference between the distance spectra and the actual frequency response can be approximated using the error function
• E (j) 20-logio [
• This error function E (j) can now be checked again for a limit curve or determine its maximum value as an absolute measure of quality; In this case, one can either only consider an object distance r, that is, a transit time ⁇ t (for example, the maximum), or one considers all the transit times ⁇ t relevant for the driver assistance function. Due to the factor At, the maximum runtime tends to be the most critical, but depending on the form of the DFT FE (J), higher values of the error function E (j) could also occur with smaller run times.
• additional smaller power peaks occur around the actual object, which can lead to ghost objects with the same relative speed as the real object. If it is known from an analysis of the actual frequency profile how high such interference lines are or can be (eg by an upper estimation as explained above), then one can check for each detection whether it originated from a faulty frequency modulation from another detection of the same relative velocity or ., and then possibly reject this detection altogether or mark it as a potential false detection.
• the frequency modulation was monitored during the actual transmission signals (ie for the transmission signals whose associated receive signals are evaluated for environment detection).
• a / D converter for digitizing the divided-down oscillator signal
• the monitoring of the frequency modulation could not be done in parallel with the surroundings detection; So one would introduce another sequence of transmission signals with the same frequency response alone to monitor the frequency modulation - monitoring the frequency modulation and environment detection would then be at different frequency ramps, either in two sequentially successive blocks or by nesting are arranged one inside the other. With the ramps used to monitor the frequency modulation, one could also turn off the transmit power (to save power and if this does not affect the frequency modulation error).
• an A / D converter is used for digitizing the frequency-down-converted oscillator signal;
• a counter instead of the circuit block 1 .12 of FIG. 1, a counter will be used.
• the counter increments its value by 1 on each positive edge of the divided rectangular signal; it counts the number of periods of the divided signal.
• the counter is not reinitialized at the start of each frequency ramp, but simply counts on and on, even between the frequency ramps - so you can speak of a free-running counter, which does not need any Eiseninitialmaschineen.
• FIG. 13 shows the course of the normalized counter value ZN (n, k, m) for a frequency ramp k and an antenna combination m.
• Dashed line shows the expected desired course, which represents a parabolic section by the linear frequency modulation (normalized counter value is proportional to the signal phase, which results from the beginning of the ramp start integration over the linear signal frequency and thus has a quadratic component); It should be noted that the curvature of the desired course is exaggerated in the picture.
• the dots in Fig. 13 represent the measured normalized counter values ZN (n, k, m).
• the (exaggerated in Fig. 13) deviation from the desired course is mainly due to the fact that the counter virtually rounds to an integer number of periods - he counts only the positive edges of the divided down rectangular signal.
• the normalized counter value will either have the value 1210 or 121 1, depending on whether there has been more or less than half a period between ramp start and next positive edge.
• the error is thus plus or minus half a period, with a probability of 50% each; the standard deviation is then half a period.
• there are only 1210.25 periods between the start time of the counter and a read-out time n then with a probability of 75% 1210 periods are measured, with a probability of 25% 121 1 periods; the standard deviation then results in 0.43 periods. If the start time and the read-out second point are exactly 1210 periods apart, the correct value is always measured and the standard deviation is 0.
• the error of the measurement thus extends to a maximum of plus or minus one period; seen over different signal frequencies, the distribution is triangular with the maximum at error 0, so that the standard deviation is the 1 / V6-th part of a period.
• the normalized counter value ZN (n, k, m) for every n is accumulated over all 2048 frequency ramps and thus receives the accumulated normalized counter values ⁇ ( ⁇ ).
• the phases of the divided down signal must vary from ramp to ramp during ramp start. If phase noise or other effects are not sufficient, you can do this, for example by forcing one or more parameters of the oscillator frequency between the actual transmit signals; eg by varying the time of the frequency return (ie ramp end is slightly varied).
• the accuracy of the measurement decreases as the divider ratio T increases.
• the less the frequency is divided down the faster the meter is, the faster the counter is, but it is expensive to implement and requires a lot of power.
• Frequency mixing can circumvent this problem because it does not affect the accuracy of the measurement; however, generating a second signal in the 24 GHz range is expensive. Therefore, a combination of division and mixing can also be implemented.
• the oscillator signal first divided by a factor of 4 to the range of about 6.04GHz and then down-mixed with a fixed frequency of 5.8GHz, so that the counter only has to work in the range of well 200MHz.
• Another approach to reducing the divisor factor T is a counter that counts both the positive and negative edges of the divided down signal.
• the advantages and disadvantages of the two methods presented above for digitizing the frequency-stepped oscillator signal will be briefly discussed.
• the A / D conversion has the advantage that it can work with larger frequency divider factors, because in principle it can measure frequencies or phases more precisely (with the same frequencies of the input signals).
• an A / D converter but i. Gen.
• To realize more complex than a counter with the same frequencies of the input signals
• the evaluation of the A D converter values is more complex than that of the counter values.
• the considerations and embodiments according to the invention shown in the above examples can be applied to general dimensions and parameter interpretations, ie they can also be applied to other numerical values.
• the approaches according to the invention can also be applied to a radar in the 77 GHz range.

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