Communications: directive radio wave systems and devices (e.g. – Determining distance – With frequency modulation
Reexamination Certificate
2002-11-08
2004-11-23
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
With frequency modulation
C342S145000, C342S189000, C342S136000
Reexamination Certificate
active
06822605
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radar device having means for generating a first code, means for modulating a transmission signal in a transmitting branch using the first code, means for delaying the first code, means for modulating a signal in a receiving branch using the delayed first code, and means for mixing a reference signal with a reception signal. The present invention further relates to a method of coding a radar device having the following steps: generating a first code, modulating a transmission signal in a transmitting branch using the first code, delaying the first code, modulating a signal in a receiving branch using the delayed first code, and mixing a reference signal with a reception signal.
BACKGROUND INFORMATION
There are numerous applications for radar devices in greatly varying fields of technology. For example, it is possible to use radar sensors for local range sensor systems in motor vehicles.
Electromagnetic waves are emitted from a transmission antenna in radar devices. If these electromagnetic waves encounter a barrier, they are reflected and, after the reflection, received again by another antenna or the same antenna. Subsequently, the signals received are fed to a signal processing and signal analysis system.
In motor vehicles, radar sensors are used for measuring the distance to targets and/or the relative speed in relation to such targets outside the motor vehicle. Vehicles which are traveling ahead or parking are considered targets, for example.
FIG. 1
shows a schematic illustration of a radar device having a correlation receiver according to the related art. A transmitter
300
is caused by a pulse generator
302
to emit a transmission signal
306
via an antenna
304
. Transmission signal
306
encounters a target object
308
, where it is reflected. Reception signal
310
is received by antenna
312
. This antenna
312
may be identical to antenna
304
. After reception signal
310
is received by antenna
312
, the signal is transferred to receiver
314
and subsequently fed via a unit
3
having a low-pass filter and an analog/digital converter, to a signal analysis system
318
. The special feature of the correlation receiver is that receiver
314
obtains a reference signal
320
from pulse generator
302
. Reception signals
310
received by receiver
314
are mixed in receiver
314
with reference signal
320
. Receiver
314
may contain an inphase/quadrature (I/Q) demodulator. Through the correlation, the distance to a target object, for example, may be determined on the basis of the time delay from transmission to reception of the radar pulse.
It is desirable to separate interference signals, which arise, for example, from other transmitter antennas, from signal components reflected on the targets. Interference is generated, for example, by other radar sensors, transmitters, consumers on the vehicle electrical system of the motor vehicle, mobile telephones, or by noise. Conventional methods use additional modulation of signals in order to separate interference signals from signal components reflected on targets. Using pseudo-noise coding (PN coding) for interference signal suppression has also already been suggested. Minimizing this type of interference is to be achieved through coding, with the signal-to-noise ratio (S/N) in the output signal of the radar device possibly enhanced. Through such an enhancement of the S/N ratio, either detecting targets having smaller retroreflection cross-sections or reducing the peak pulse power at constant S/N is made possible. The advantage of detecting targets having smaller retroreflection cross-sections is, for example, that not only motor vehicles traveling ahead, but also pedestrians or bicyclists, are detected by a motor vehicle with greater probability. The reduction of the peak pulse power has the consequence that less interference is caused in other systems, for example, radio relay systems; in this connection, the reduction of the peak pulse power makes approval of the sensors by the relevant regulating authorities easier.
Furthermore, when multiple radar sensors are used, the aim is to receive and analyze the transmission signals of the respective other sensors. Therefore, one wishes to be able to differentiate between the signals of other radar sensors.
SUMMARY
The present invention is based on the radar device provided with multiple receiving channels. The receiving channels have means for generating additional codes, means for demodulating using the respective additional codes, and means for modulating the transmission signal using at least one of the additional codes. In this way, it is possible to differentiate between the signals of multiple radar sensors. Therefore, an improvement of the interference signal suppression and/or an enhancement of the S/N ratio occurs through the modulation of the signals with a decoupling of various radar sensors by using different codes. In this manner, the detection of apparent targets may be suppressed, and the target geometry may be determined more precisely.
One of the signals is preferably modulated using the first code through amplitude modulation (ASK; “amplitude shift keying”) and the other signal is modulated using the first code through phase modulation (PSK; “phase shift keying”). It is also possible to combine amplitude modulation with phase modulation, so that different types of modulation are usable in the scope of an exemplary embodiment of the present invention. It is also possible to use frequency modulation (FSK; “frequency shift keying”).
In the present invention, the transmission signal may be modulated using the first code through phase modulation (PSK) and the signal is modulated in the receiving branch using the first code through amplitude modulation (ASK) or frequency modulation (FSK). If types of modulation other than phase modulation (PSK) are used in the receiving branch, then phase modulation (PSK) may be used in the transmitting branch in the scope of an exemplary embodiment of the present invention.
However, it may also be advantageous for the transmission signal to be modulated using the first code through amplitude modulation (ASK), frequency modulation (FSK) or phase modulation (PSK), and for the signal to be modulated in the receiving branch using the first code through phase modulation (PSK). Therefore, if there is phase modulation (PSK) in the receiving branch, then greatly varying types of modulation are usable in the transmitting branch.
The radar device is particularly advantageously refined if one of the combinations of types of modulation cited is used for the additional codes independently of the types of modulation used for the first code.
A low-pass filter is preferably provided for filtering the signals before demodulation. In this manner, it is possible to use a low clock frequency for the additional codings. This particularly may have the advantage that the coding in the receiving channels does not have to be delayed. Implementation of a very large number of channels with only a low additional outlay for components is possible, these components being clocked using relatively low frequencies. On the high-frequency domain, only one additional modulation must be provided, possibly through an additional modulator. The implementation of the receiving channels on the low-frequency domain also has the advantage that there is no worsening of the S/N ratio.
It may be advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been extensively described in the literature, so that an exemplary embodiment of the present invention may be realized particularly well using PN codes.
The generation of the additional codes and the modulation are preferably performed using a clock frequency which is a whole-number fraction of the pulse repetition frequency for generating the first code. In this way, the code generations a to one another with regard to the various codes.
It is preferable for k receiving channels to be provided, for k m
Lobo Ian J.
Robert & Bosch GmbH
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