Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2003-03-26
2004-02-17
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S130000, C342S134000, C342S135000, C342S145000, C342S201000, C342S202000
Reexamination Certificate
active
06693582
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radar system having means for producing a code, means for modulating a transmission signal in a transmit branch using the code, means for delaying the code, means for modulating a signal in a receive branch using the delayed code, and means for mixing a reference signal with a receiving signal. The present invention also relates to a method for coding a radar system having the steps: generating a code, modulating a transmission signal in a transmit branch using the code, delaying the code, modulating a signal in a receive branch using the delayed code, and mixing a reference signal with a receiving signal.
BACKGROUND INFORMATION
There are numerous applications for radar systems in the most varied fields of technology. For instance, it is possible to install radar sensors in motor vehicles for very short range sensor systems.
In radar systems, in principle, electromagnetic waves are radiated by a transmission antenna. If these electromagnetic waves hit an obstacle, they are reflected, and after the reflection they are received by another or by the same antenna. Thereafter, the received signals are supplied to a signal processing and a signal evaluation.
For example, in motor vehicles, radar sensors are installed for measuring the distance to targets and/or the relative speed with respect to such destinations outside the motor vehicle. As targets, for example, preceding or parking motor vehicles come into consideration.
FIG. 1
shows a schematic representation of a radar system having a correlation receiver representing the state of the art. A transmitter
300
is induced by pulse generation
302
to radiate a transmission signal
306
from an antenna
304
. The transmission signal
306
hits a target object
308
, where it is reflected. The receiving signal
310
is received by antenna
312
. This antenna
312
may be identical to antenna
304
. After receiving signal
310
is received by antenna
312
, this is communicated to receiver
314
, and subsequently, via a unit
316
having a lowpass filter and an analog-digital converter, is supplied to a signal evaluation
318
. The specialty about the correlation receiver is that receiver
314
receives a reference signal
320
from pulse generation
302
. Receiving signals
310
received by receiver
314
are mixed in the receiver
314
with reference signal
320
. Because of the correlation, conclusions may be drawn, for instance, as to the distance of a target object, on the basis of the temporal delay between the transmitting and receiving of the radar impulses.
In principle, it is desirable to separate interference signals, which may, for instance, originate from other transmission antennas, from portions of the signal reflected from the targets. Interferences are produced, for example, by other radar sensors, transmitters, consumers on the vehicle electrical system of the motor vehicle, cellular phones or by noise. Methods are already known which use an additional modulation of signals to separate interference signals from signal portions reflected from the targets. Likewise, it has already been proposed to use pseudo-noise coding (PN coding) for suppressing interference signals. By this coding it is supposed to be achieved that such interferences are minimized, in particular, the signal
oise (S/N) ratio in the output signal of the radar system being supposed to be increased. By such an increase in the S/N ratio it is made possible either to detect targets having a lower reflecting cross section or to decrease the pulse peak performance at constant S/N. The advantages of detecting targets having a lower reflecting cross section are, for instance, that a motor vehicle not only detects a preceding motor vehicle, but also, with great probability, pedestrians and bicyclists. The decrease in pulse peak performance has the result that lesser interferences from other systems, such as from directional radio systems, are brought about; in this connection, the decrease in pulse peak performance simplifies the approval of sensors by the appropriate regulating authorities.
SUMMARY OF THE INVENTION
According to a first specific embodiment, the present invention builds up on the radar system of the related art in that the modulation of one of the signals is carried out by an amplitude modulation (ASK; “Amplitude Shift Keying”), and the modulation of the other signal is carried out by a phase modulation (PSK; “Phase Shift Keying”). In this manner, an improvement in the S/N ratio is achieved. Thereby targets having a clearly lower reflection cross section may be detected, than used to be possible with radar systems of the related art having pure BPSK (“Binary Phase Shift Keying”) or amplitude modulation. It is also possible to lower the pulse peak performance at a constant S/N ratio.
In the first specific embodiment it is particularly advantageous if the code is a pseudo-noise code (PN code). The use of PN codes for interference signal suppression has been discussed comprehensively in the literature, so that the present invention, in using PN codes, can be especially well implemented.
Preferably, the modulation of transmitting signals in the first specific embodiment is carried out by amplitude modulation, and the modulation of the signal in the receive branch is done by phase modulation. By using an amplitude modulation ASK in the transmit branch, this results in an improvement of the S/N ratio as opposed to using pure phase modulation PSK. The average transmitting power drops off by ca 3 dB as opposed to a phase modulation PSK in the transmit branch.
Likewise, it may be preferred in the first specific embodiment that the modulation of the transmitting signal is done by phase modulation, and that the modulation of the signal in the receive branch is done by amplitude modulation.
The first specific embodiment is advantageous when the means for mixing the reference signal with the received signal emit an output signal at a lowpass filter. The output signal is integrated using the lowpass filter, so that a suitable signal for further processing is available.
In the first specific embodiment, digital means for controlling the delay are preferably provided. Such digital means, such as a microcontroller or a digital signal processor are in a position to delay both the pulse repetition rate and the P/N code in a suitable manner, so that the signals in the receive branch experience the required correlation.
But in the first specific embodiment it may also be advantageous if circuitry means are provided for controlling the delay. Besides controlling the delay using digital means, it is also possible to install hardware for implementing the delay.
In the first specific embodiment, preferably, the means for producing and delaying an n-bit PN code are implemented as n-bit counters having combinatorial linkage of the counter outputs. An n-bit shift register makes several outputs available, the same PN code being made available at each output having in each case different temporal delays. Thus it is possible, in a simple way, to make available any desired code delays by a corresponding combinatorial linkage of the weighted outputs.
In the first specific embodiment it may also be of advantage if the receive branch is subdivided into several channels which use several PN codes for modulating, and if several lowpass filters are provided for further processing of the modulated signals. Because of this, the radar system may be broadened to include the evaluation of other signals transmitted by other radar sensors and modulated using other PN codes.
In the first specific embodiment it is particularly advantageous if means for blanking of phase transitions are provided. Since the transition of the phase relation in the actual setup does not occur instantaneously, errors occur after the integration of the signal. However, if the phase-modulated signal is blanked during the transition time between the various phase relations, these errors may be minimized. In the case of a combination, according to the p
Brosche Thomas
Steinlechner Siegbert
Kenyon & Kenyon
Robert & Bosch GmbH
Sotomayor John B.
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