EP1352263A2

EP1352263A2 - Radar device and method for suppressing interference in a radar device

Info

Publication number: EP1352263A2
Application number: EP01984725A
Authority: EP
Inventors: Thomas Brosche
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-01-08
Filing date: 2001-12-22
Publication date: 2003-10-15
Also published as: US20040090361A1; WO2002054101A2; DE10100414A1; US7158077B2; WO2002054101A8; WO2002054101A3

Abstract

Die Erfindung betrifft eine Radareinrichtung mit Mitteln (10) zum Erzeugen eines Trägersignals mit einer Trägerfrequenz f>T<, Mitteln (12, 13, 15, 17) zum Erzeugen von Pulsen mit einer Pulswiederholfrequenz f>PW<, Mitteln (16) zum Aufteilen des Trägersignals auf einen Sendezweig und einen Empfangszweig, Mitteln (18, 19, 21, 27, 29) zum Verzögern der Pulse, Mitteln (24) zum Mischen des Trägersignals in dem Empfangszweig mit einem Empfangssignal und Mitteln (26) zum Integrieren des gemischten Signals, wobei Mittel (20, 23) zum Modulieren des Trägersignals in dem Sendezweig mit den verzögerten Pulsen vorgesehen sind und Mittel zum Ändern der Verzögerung der Pulse entsprechend einem vorgegebenen Code vorgesehen sind. Die Erfindung betrifft ferner ein Verfahren zum Unterdrücken von Störungen einer Radareinrichtung.

Description

Radar device and method for suppressing interference from a radar device

The invention relates to a radar device with means for generating a carrier signal with a carrier frequency f _τ , means for generating pulses with a pulse repetition frequency f _PW , means for dividing the carrier signal into a transmitting branch and a receiving branch, means for delaying the pulses, means The invention further relates to a method for suppressing interference in a radar device, comprising the steps of generating a carrier signal with a carrier frequency f _τ , generating pulses with a pulse repetition frequency f _P Splitting the carrier signal into a transmission branch and a reception branch, delaying the pulses, mixing the carrier signal in the reception branch with a reception signal and integrating the mixed signal,

State of the art

Generic radar devices and methods are used, for example, for close-range sensors in motor vehicles. They serve, for example, to guarding or detecting objects in a blind spot of a motor vehicle.

Figure 1 shows schematically the basic structure of a radar device of the prior art. A carrier frequency f _{τ is} generated by a local oscillator (LO) 110. This carrier frequency is divided by a power divider 116 into a transmission branch and a reception branch. In addition to the carrier frequency f _τ , a pulse repetition frequency f _PW is provided by a pulse generator 112 for modulating the carrier frequency. This modulation takes place in the transmission branch with the switch 120, to which the carrier frequency is applied and which is switched with the pulse repetition frequency. The signal generated in this way is emitted by the transmission antenna 136. Modulation also takes place in the reception branch. However, for the purpose of this modulation, the pulses of the pulse repetition frequency are delayed by a delay device 118. With these delayed pulses, the carrier frequency f _τ is modulated by actuating the switch 122, to which the carrier frequency is also applied. In this way, a reference signal S _R is made available in the reception branch. This reference signal is mixed in a mixer 124 with a received signal received via the receiving antenna 134. The output signal of the mixer 124 is fed to an integration means 126, for example a low-pass filter and an amplifier. The signal generated in this way is fed to a signal evaluation and control 138, preferably after analog-digital conversion. The signal evaluation and control 138 now determines the delay of the delay device 118, these .DELTA.t between a value _m i _n and .DELTA.t _max is varied. For example, the delay can be varied by a microcontroller or a digital signal processor. It is also conceivable that special hardware is used for this. If the transit time of the radar pulses, which generally corresponds to twice the transit time between the target and the antenna, coincides with the delay, the amplitude of the output signal of the mixer 124 becomes maximum. A correlation receiver is thus available, in which the target distance and the radial speed between target and antenna can be inferred from the delay set by controller 138. FIG. 1 shows an example of only the formation of the in-phase (I) signal. The quadrature (Q) signal is formed in an analogous manner by mixing with the carrier frequency which is phase-shifted by 90 °.

In principle, it is desirable to suppress interference signals from a wide variety of causes. It has already been proposed to use an additional modulation of the microwave signal in order to separate the signal components reflected from the targets from interference signals. Such methods particularly suppress interference from other non-coded transmitters, for example radio transmitters, or noise.

However, ambiguities can arise when determining target distances outside the uniqueness range of a pulsed radar device. The ambiguity range lies with target distances r

c / (2f _PW ) <r <R _max with f _PW : pulse repetition frequency c: speed of light

Rm _ax ^ range of the radar.

The following target distances are measured in the ambiguity area:

r = r - nc / (2f _pw

with n = 1, 2, 3, ... and r> 0.

In addition, interference occurs due to several pulse radar sensors operating at the same time if the sensors operate within the range of another sensor. Disturbances or the detection of false targets can occur. A measured apparent signal delay or the corresponding distance to the apparent target depends on the position between the transmission and reception times of the respective sensors. If you consider sensors that are installed in different vehicles, for example, it can happen that the transmit and receive antennas of the different sensors face each other. In this case, the interference between the individual sensors can generally no longer be neglected.

Advantages of the invention

The invention builds on the generic radar device in that means for modulating the carrier Signals are provided in the transmission branch with the delayed pulses and that means for changing the delay of the pulses are provided in accordance with a predetermined code. In this way it is possible the measurement space, that is the period between the minimum delay .DELTA.t _m i _n and maximum delay .DELTA.t _max, non-monotonic increasing or decreasing sense but in a certain order of the code. Such sampling is comparable to a "random sampling" method. After the scanning, the measured values can be ordered according to ascending or descending values for the respective delays Δt, so that the measured values can subsequently be processed further in a conventional manner. This "irregular" scanning is advantageous since the mutually interfering radar sensors are usually put into operation at different times, so that they also record the measurement values for generally different scanning intervals at a particular time. Due to the modulation of the carrier signal in the transmission branch, the time intervals between the radar pulses transmitted by the various sensors change constantly. Therefore, the measured distances to the apparent targets, which result from the mutual interference of the radar sensors, also change. As a result, the signal energy of the apparent targets is distributed over the measuring room, so that the distinction between apparent and real targets can be improved. In other words, the signals are decoupled between different sensors. If different radar sensors are used for the modulation of the transmission time for different radar sensors and thus different sequences for the scanning inter- valle, a further reduction in interference is possible. Since the time intervals between the sampling intervals and the respective previously transmitted pulses also change during the switchover between the respective scans, the signal energy becomes ambiguous targets with a distance r from the transmitter

c / (2f _PW ) <r <R _max

scattered within the measuring room. Since this change in the time interval occurs only once per switchover, it is useful to switch over as often as possible. However, the maximum frequency of the switchover depends on the integration time required for a target discovery. A switchover for each transmitted radar pulse would be ideal. This is possible if the individual pulses have sufficient signal energy or an adequate signal-to-noise ratio for the individual pulse detection.

Means for modulating the carrier signal in the receiving branch with a constant delay are preferably provided. A constant delay can be sufficient, since the delay in the transmission branch allows a variation and thus a distance detection. It therefore only serves to ensure that the reference pulse is always delayed compared to the transmitted pulse.

The invention is particularly advantageous in that the means for generating a pulse repetition frequency f _{P have} a PN code generator ("pseudo noise") and that Means for delaying the pulses have means for code shifting. When using such a discrete shift of a PN code, the delay of the modulation in the reference signal can be omitted. Negative values for the "delay" (preview) of the modulation in the transmission signal can be calculated or set in advance using the discrete code shift. By using PN codes, it is possible to improve the S / N ratio, since PN codes with a suitable autocorrelation function can work with an increased pulse repetition frequency without reducing the maximum range of the radar.

It can be advantageous if means are provided for changing the transmission times and the reception times. In particular, if the delay is caused by code shifting, different modulation principles can be implemented in the transmitting branch and in the receiving branch, the modulation being able to take place with the differently shifted codes.

The carrier frequency fψ is preferably an integer multiple of the pulse repetition frequency f _P. Under these circumstances, modulation can be implemented by an integer or a half-number code shift.

It can be advantageous if means are provided for cyclically changing the code. This is a suitable way to vary the changed code and thus to have an advantageous effect on the interference signal suppression. It can be particularly advantageous that means are provided for generating ASK-modulated ("amplitude shift keying") or PSK-modulated ("phase shift keying") signals. Such means lead to a further suppression of interference effects.

For the same reason, it can also be advantageous if means are provided for polarizing the signals.

The invention is based on the generic method in that the carrier signal in the transmission branch is modulated with the delayed pulses and in that the delay in the pulses is changed in accordance with a predetermined code. In this way it is possible to scan the measuring space, ie the period between the minimum delay Δt _min and the maximum delay Δt _max , not monotonically increasing or decreasing but in a sequence determined by the code.

The carrier signal in the reception branch is preferably modulated with a constant delay. A constant delay can be sufficient, since the delay in the transmission branch allows a variation and thus a distance detection. It therefore only serves to ensure that the reference pulse is always delayed compared to the transmitted pulse.

It can also be useful if a PN code ("pseudo noise") is generated and if the pulses are delayed by code shifting. When using such a discrete shift of a PN code, the delay of the modulation in the reference signal can be omitted. Negative values for the "delay" (preview) of the modulation in the transmission signal can be calculated or set in advance using the discrete code shift. By using PN codes, it is possible to improve the S / N ratio, since PN codes with a suitable autocorrelation function can work with an increased pulse repetition frequency without reducing the maximum range of the radar.

It can be useful if the transmission times and the reception times are changed. In particular, if the delay is caused by code shifting, different modulation principles can be implemented in the transmission branch and in the reception branch, it being possible for the modulation to take place with the differently shifted codes.

The carrier frequency f _τ is preferably an integer multiple of the pulse repetition frequency f _Pw . Under these circumstances, modulation can be implemented by an integer or a half-number code shift.

It can also be advantageous if the code is changed cyclically. This is a suitable possibility to vary the changed code and thus to have an advantageous effect on the interference signal suppression.

It can be useful if ASK-modulated ("amplitude shift keying") or PSK-modulated ("phase shift keying") signals are generated. Such means lead to a further suppression of interference effects. For the same reason, it can be useful if the signals are polarized.

The invention is based on the surprising finding that suppression of interference by the transmission signals of other, in particular identical, radar sensors can be achieved by coding the transmission time on the transmitter side. Furthermore, the risk of overloading the I or Q channel can be reduced by the mutual interference of the radar sensors. Signals from targets with target distances in the ambiguity range can also be suppressed. The method can also be used advantageously in radar systems which already use coded transmission signals or reference signals which have been generated, for example, with the aid of PN coding by phase or amplitude modulation. It should also be emphasized that the length of the interval required for integration or averaging, for example in PN coding, is not influenced. The cut-off frequency of a low-pass filter used for the integration can thus remain unchanged or can be selected with regard to an optimal value for the signal-to-noise ratio.

drawings

The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments. It shows:

Figure 1 is a schematic representation of a radar device of the prior art;

Figure 2 is a schematic representation of a radar device according to the invention;

FIG. 3 shows a graphic representation of a signal amplitude to explain a sampling method;

Figure 4 is a schematic representation of a further radar device according to the invention;

FIG. 5 shows a schematic illustration of a further radar device according to the invention; and

Figure 6 is a schematic representation of a further radar device according to the invention.

Description of the embodiments

FIG. 2 shows a schematic illustration of a radar device according to the invention. A local oscillator 10 is connected to a power divider 16. This power divider 16 is connected to a transmission branch. Part of the power of the local oscillator 10 is coupled out of the power divider 16 into the receiving branch. A pulse generator 12 is also provided for generating the pulse repetition frequency fp _W. The output of the pulse generator is with an adjustable delay element 18 and connected to an adjustable or non-adjustable delay element 19. The output of the adjustable delay element 18 actuates a switch 20 in the transmission branch for modulating the carrier signal. The output signal of the adjustable or non-adjustable delay element 19 actuates a switch 22 in the receiving branch for modulating the carrier signal in the receiving branch and thus for providing a reference signal S _R. The signal modulated by the switch 20 in the transmission branch is emitted by the transmission antenna 36 and reflected on a target. This signal is received by a receiving antenna 34 and mixed in a mixer 24 with the reference signal S _R. The mixed signal is then fed to a means 26 for integration, for example a low pass and amplifier. The signal generated in this way is fed to a signal evaluation and control 38 on the input side, which controls the adjustable delay element 18 on the output side.

Consequently, with the radar device according to FIG. 2, the transmission times can be varied by the adjustable delay element 18. The delays are in a range Δt _s = 0 s ... Δt _max - t _m j ..., whereby it must be taken into account that the non-adjustable delay element 19 provides a delay Δt _E = Δt _max . This fixed delay is useful because the reference pulse must always be delayed compared to the transmitted pulse. The total _delay is thus Δt = Δt _E - Δt _s = Δt _πάn ... Δt _max . Figure 2 shows an example of only the formation of the in-phase (I) signal. The quadrature (Q) signal is formed by mixing with the Carrier frequency phase-shifted by 90 ° in an analog manner.

FIG. 3 shows how the measuring space .DELTA.t _min ... .DELTA.t _{max is} scanned in an exemplary manner, an amplitude A being plotted against the signal delay .DELTA.t. Parallel to the delay time axis, a distance axis is shown, which is a distance between the transmitter and the target in the range r _m j. _n ... r _max shows. The course of the amplitude A is divided into equidistant intervals, these being parameterized by way of example with the numbers 1 to 16. These digits indicate the order of the scan. The I and Q output signals of the sensor are recorded at all intervals. The sequence of the scanning and thus the value for the respectively set delay is determined by a suitable code. After the sampling, the measured values can be ordered according to ascending or descending values for Δt. As a result, the measured values can then be processed in a conventional manner.

The advantageous effect of a scan, as is shown by way of example in FIG. 3, can be explained by the fact that the various radar sensors are usually put into operation at different times. Therefore, at a certain point in time, they record the measured values for generally different sampling intervals. Since the time intervals between the radar pulses sent by the various sensors are constantly changing, the distances to the apparent targets are also changing. The signal energy of the apparent Targets are thus distributed over the measuring space Δt _m i _n ... Δt _max , so that there is an advantageous distinction between apparent and real targets. The signal energy is also scattered from ambiguous targets within the measuring room.

FIG. 4 shows a further radar device according to the invention. Elements which correspond to those from FIG. 2 are identified by identical reference symbols. The special feature of the embodiment according to FIG. 4 is that a PN code generator 13 is provided, the selection of the code being taken over by the signal evaluation and control 38. This code is supplied to a code delay 21 where that in certain of the controller 38 is delayed manner _max in an interval between delta T _m i _n and delta T. The code is then fed to a modulator 23 in the transmission branch. The non-delayed code is transmitted to a modulator 25 in the receiving branch, which delivers the reference signal S _R as an output signal. When using a discrete shift of the PN code, the delay of the modulation in the reference signal can be omitted, since negative values for the "delay" (preview) of the modulation in the transmission signal can be calculated or set in advance using the discrete shift. Again, only the formation of the in-phase (I) signal is shown in FIG. The quadrature (Q) signal is formed in an analogous manner by mixing with the carrier frequency which is phase-shifted by 90 °.

FIG. 5 shows a further embodiment of a radar device according to the invention. Elements which 2 or 4 correspond to the same reference numerals. The special feature of the radar device according to FIG. 5 is that the pulse repetition frequency f _{P is} generated with the aid of a noise generator 15. In order to suppress frequencies below the maximum Doppler frequency fma _x to be processed, the output signal of the noise generator 15 can be filtered via a high-pass filter 17. The result is a delay in both the transmission times and the reception times with a delay time Δt _mod . In the present case, the radar device is tuned with an adjustable delay element 27, which controls the modulation of the carrier signal to generate the reference signal S _R. The radar device according to FIG. 5 allows an improved suppression of ambiguous targets compared to the radar device according to FIG. 2, since the phase position of the pulse repetition frequency f _{PW is changed} from pulse to pulse. A further advantage of this radar device is that the remaining signal evaluation corresponds to the state of the art according to FIG. 1, so that only minor modifications to the hardware need be made. In FIG. 5 only the formation of the in-phase (I) signal is shown as an example. The quadrature (Q) signal is formed in an analogous manner by mixing with the carrier frequency which is phase-shifted by 90 °.

FIG. 6 shows a further embodiment of a radar device according to the invention. Here, in turn, a PN code generator 13 is provided, which supplies the pulse repetition frequency to a first means for code shifting 21 and a second means for code shifting 29. Both means 21, 29 for code shift are from the Control 38 set, which is also responsible for the selection of the PN code. The output signals of the means 21 for code shifting are fed to a modulator 23 in the transmission branch, so that the carrier signal is modulated in the transmission branch with a code shifted by Δt _s = Δt _m0 d. In the receiving branch, the carrier signal is modulated in a modulator 25 with a code which is delayed by Δt _E = Δt _m od + Δt _m i _n ... Δt _max , so that a delayed reference signal S _R is made available. If one assumes that the carrier frequency is an integer multiple of the pulse repetition frequency, then the modulation can be implemented, for example, by an integer or half-integer code shift. This can be changed, for example, for every period of the code used or for every measuring interval. 6, only the formation of the in-phase (I) signal is shown as an example. Again, the quadrature (Q) signal is formed by mixing with the carrier frequency, which is phase-shifted by 90 °, in an analogous manner.

The preceding description of the exemplary embodiments according to the present invention serves only for illustrative purposes and not for the purpose of restricting the invention. Various changes and modifications are possible within the scope of the invention without leaving the scope of the invention and its equivalents.

Claims

Expectations

1. Radar device with

Means (10) for generating a carrier signal with a carrier frequency f _τ , means (12, 13, 15, 17) for generating pulses with a pulse repetition frequency f _P ,

Means (16) for dividing the carrier signal into a transmitting branch and a receiving branch, means (18, 19, 21, 27, 29) for delaying the pulses, - means (24) for mixing the carrier signal in the receiving branch with a received signal and means ( 26) for integrating the mixed signal, characterized in that means (20, 23) are provided for modulating the carrier signal in the transmission branch with the delayed pulses, and in that means are provided for changing the delay of the pulses in accordance with a predetermined code.

2. Radar device according to claim 1, characterized in that means (22) for modulating the carrier signal in the receiving branch are provided with a constant delay.

3. Radar device according to claim 1 or 2, characterized in that the means for generating a pulse repetition frequency f _{PW have} a PN code generator (13) ("pseudo noise") and that the means for delaying the pulses have means (21, 29) for code shifting.

4. Radar device according to one of the preceding claims, characterized in that means are provided for changing the transmission times and the reception times.

5. Radar device according to one of the preceding claims, characterized in that the carrier frequency f _{τ is} an integer multiple of the pulse repetition frequency f _P.

6. Radar device according to one of the preceding claims, characterized in that means are provided for cyclically changing the code.

7. Radar device according to one of the preceding claims, characterized in that means are provided for generating ASK-modulated ("amplitude shift keying") or PSK-modulated ("phase shift keying") signals.

8. Radar device according to one of the preceding claims, characterized in that means for polarizing the signals are provided.

Method for suppressing interference from a radar device, comprising the steps Generating a carrier signal with a carrier frequency f _ϊ ,

Generation of pulses with a pulse repetition frequency

Splitting the carrier signal into a transmission branch and a reception branch,

Delaying the pulses,

Mixing the carrier signal in the reception branch with a reception signal and integrating the mixed signal, characterized in that the carrier signal in the transmission branch is modulated with the delayed pulses and that the delay of the pulses is changed in accordance with a predetermined code.

10. The method according to claim 9, characterized in that the carrier signal is modulated in the receiving branch with a constant delay.

11. The method according to claim 9 or 10, characterized in that a PN code ("pseudo noise") is generated and that the pulses are delayed by code shifting.

12. The method according to any one of claims 9 to 11, characterized in that the transmission times and the reception times are changed.

13. The method according to any one of claims 9 to 12, characterized in that means (15, 17) are provided with which is a simultaneous modulation in the transmitting and receiving branch by a phase or frequency modulation of the pulse repetition frequency.

14. The method according to any one of claims 9 to 13, characterized in that the carrier frequency f _{τ is} an integer multiple of the pulse repetition frequency f _PW .

15. The method according to any one of claims 9 to 14, characterized in that the code is changed cyclically.

16. The method according to any one of claims 9 to 15, characterized in that ASK-modulated ("amplitude shift keying") or PSK-modulated ("phase shift keying") signals are generated.

17. The method according to any one of claims 9 to 16, characterized in that the signals are polarized.