JPH05297122A - Fm radar system - Google Patents

Abstract

PURPOSE:To provide an FM radar device which presents high measuring accuracy and quick response when interference between devices is taken into account. CONSTITUTION:An FM radar device concerned is equipped with a means consisting of a gate circuit 20 and pseudo-random pulse device 21 to release FM signals in conformity to the rule or one of the rules which is/are set about whether at least one release of FM signal takes place in each releasable period upon setting as the cyclic period that period of time which is longer than the cyclic period of FM signal modulating where a certain number of releasable periods appear successively. This is further equipped with an inspecting means such as a microprocessor 18 which inspects the sensing results of the frequency of beat signals or the distance based thereupon over the latest updated number of pieces as specified, assumes peculiar data pieces contained therein as a false sensing result produced due to interference with any other radar device, etc., and removes such pieces eventually from the sensing results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM radar device used for a vehicle collision prevention warning system.

[0002]

2. Description of the Related Art An on-vehicle radar device mounted on a vehicle such as a passenger car and used as a warning device for a rear-end collision or collision prevention requires a very high resolution because it can detect a close range of several tens of cm. From this point, the form of the FM radar is preferable to the form of the pulse radar. In addition, since the farthest measurement range to the target such as the preceding vehicle is several hundred meters at most, it is possible to avoid interference with existing communication facilities in the microwave band, and to reduce the size of the antenna. ,
Use of the millimeter wave band is preferable.

Regarding a pulse radar device using sound waves and the like, a method for avoiding interference between the radar devices mounted on each vehicle is disclosed in Japanese Patent Laid-Open No. 61-79177. According to this method, each radar device radiates a pulse signal in a random pattern and receives a reflected wave, and collates the pattern of the radiated pulse with the pattern of the received pulse. There is disclosed a technical idea of determining the distance and the distance to the obstacle when it is determined that there is an obstacle.

[0004]

In the FM radar device,
Since the beat frequency is detected by the FFT, the beat signal needs to be generated for at least one cycle, but the period of this one cycle becomes considerably long as the beat frequency decreases as the obstacle approaches. As a result, the minimum emission period of the pulse radar, that is, the minimum emission period of the FM signal is considerably longer than the emission pulse width. In order to randomize the radiation timing, it is necessary to disperse the radiation timing over tens of times the minimum radiation period. However, if such randomization is aimed at in the FM radar device, the measurement result will be long-term. There is a possibility that it may not be obtained, and there arises a problem that the responsiveness is lowered. That is, regarding the FM radar device,
There is a problem in directly following the method of the pulse radar device.

Further, in the above conventional pulse radar device,
Since the random pulse pattern is generated by controlling the random number table and the timer by software, there is also a problem that the load of the microprocessor executing this software becomes excessive.

[0006]

In the FM radar device of the present invention, a period longer than the modulation period of the FM signal is set as the radiable period, and a period in which this radiable period is continuous for a predetermined number is set as the repeating period. , At least one rule relating to whether or not to radiate the FM signal at least once for each radiable period, means for radiating the FM signal according to one of the set rules, and the frequency of the beat signal or Inspection means for inspecting the latest distance detection results based on this, and excludes from the detection results by considering the special ones included in these as false detection results caused by interference with other radar devices Is equipped with.

[0007]

That is, the FM radar device of the present invention sets a period in which a predetermined number of consecutive radiable periods longer than the modulation period of the FM signal are set as a repeating period, and the FM signal is transmitted at least once for each radiable period. By setting at least one rule regarding whether to radiate or not, and by providing a means for radiating an FM signal according to one of the set rules, it is possible to have a constant repetition period rather than aiming at more complete randomization. Adopting a pseudo-randomization configuration to avoid deterioration of responsiveness. Then, in order to ensure a certain measurement accuracy under the interference between the devices that occurs at a considerable frequency with this pseudo-randomization, the detection results are inspected over the latest predetermined number, and the special It is provided with an inspection means which regards an object as a false detection result caused by interference with another radar device and excludes it from the detection result.

[0008]

1 is a block diagram showing the configuration of an FM radar apparatus according to an embodiment of the present invention, in which 11 is an FM oscillator and 1 is an FM oscillator.
2 is a modulation signal generator, 13 is a directional coupler, 14 is a transmitting antenna, 15 is a receiving antenna, 16 is a mixer, 17 is an FFT processing unit, 18 is a microprocessor, 19 is a display unit, 20 is a gate circuit, 21 is a pseudo random pulse generator.

The FM oscillator 11 receives a triangular waveform voltage output from the modulation signal generator 12, and generates a millimeter wave band FM signal whose frequency is linearly increased and decreased in proportion to the voltage. The FM signal output from the FM oscillator 11 passes through the gate circuit 20 which is opened and closed by the gate pulse GP of the pseudo random pattern output from the pseudo random pulse generator 21, and passes through the directional coupler 13 to transmit the antenna 14 Is emitted to the outside.

The reflected wave from the object received by the receiving antenna 15 is supplied to one input terminal of the mixer 16, and is mixed with the FM signal supplied from the directional coupler 13 to the other input terminal to obtain a frequency. Generates a beat signal that changes according to the distance to the object. This beat signal is supplied to the FFT processing unit 17, and its frequency is detected. The detected frequency is supplied as a digital signal to the microprocessor 18, where it becomes an average value of the latest plurality of detection results and is displayed on the display unit 19.

The pseudo random pulse generator 21 shown in FIG.
It is composed of a shift register having a feedback loop with an exclusive OR gate. The number of stages of the shift register is preferably about 8 or more, but here, for convenience of explanation, when the number of stages of the shift register is set to 4, as shown in FIG. Shift register 21 in which a plurality of flip-flops a, b, c, d are connected in cascade
0 and a feedback loop by the exclusive OR gate 211,
And an output terminal 212. In this pseudo random pulse generator 21, by changing the feedback loop variously, for example, by changing as shown in FIG. 2 (B),
Different patterns of pseudo-random pulses can be generated.

These pseudo-random patterns are used to divide mass-produced FM radar devices into groups and to allocate the groups. Therefore, the F mounted on the adjacent vehicle group in which mutual interference is a problem
The M radar device groups may have different pseudo random patterns, or may have the same pseudo random pattern.

The binary signal held in the flip-flop of each stage of the pseudo random pulse generator 21 is sequentially shifted to the subsequent stage in synchronization with the rising edge of the clock signal CK. FIG. 3 illustrates a gate pulse GP ₁₁ output from the pseudo random pulse generator 21 having the configuration of FIG. 2A when the initial value of the flip-flop is set to “1” only in the frontmost stage. The F output from the FM oscillator 11 over a minimum of one clock cycle in which this gate pulse changes to "1".
The M signal passes through the gate circuit 20, and the waveform FMS _{1 of} FIG.
The discrete FM signal illustrated in FIG.

The minimum width of the gate pulse GP determined by the clock period is set to 5 times the FM signal modulation period, and the frequency of the FM signal radiated from the transmitting antenna is shown in FIG.
The increase / decrease is repeated according to the triangular modulation signal M shown in FIG.
Of the FM signals radiated over the modulation cycle of 5 cycles, the beat frequency is detected for an appropriate 1 cycle, for example, the FM signal of the final 5th cycle. Within the period of the preceding 4 cycles, it is used for training such as sensitivity adjustment of each circuit in this radar device. For details of the configuration of assigning the preceding several cycles to training such as sensitivity adjustment, if necessary, the specification of the patent application entitled “Frequency Multiplier Circuit” filed by the present applicant on March 24, 1992. Please refer to the book.

The waveform GP _{12 in} FIG. 3 is the gate pulse GP ₁₁
Other gate pulses output at a timing shifted by twice the minimum gate pulse width under the same pseudo-random pattern as in FIG. When the FM radar devices operating under the gate pulses GP ₁₁ and GP ₁₂ come close to each other, there is a risk of interference in the emission period of the FM signal shaded with diagonal lines, but there is a possibility of interference in the other emission periods. There is no

The gate pulse GP ₂₁ shown in FIG. 3 corresponds to that shown in FIG.
The pseudo-random pulse generators of different configurations shown in FIG. 8 happen to be output at the same timing as the gate pulse GP ₁₁ . When the FM radar devices operating under the gate pulses GP ₁₁ and GP ₂₁ come close to each other, there is a risk of interference in the emission period of the FM signal shaded with diagonal lines, but there is a possibility of interference in the other emission periods. There is no

In order to further reduce the risk of interference between FM radars, a circuit for preventing continuation of "1" is added between the flip-flop 210 and the output terminal 212.
Each of the gate pulses GP ₁₁ and GP ₂₁ shown in FIG.
GP ₁₁ ′ and GP ₂₁ ′ are obtained, and the radiation period with the possibility of mutual interference hatched is further reduced. Such a "1"
As shown in FIG. 3C, the continuous prevention circuit includes a delay circuit 213 for a minimum emission period and a logic state inverting circuit 215.
And AND gate 214 can easily realize.

The FFT processing unit 17 of FIG. 1 receives the beat signal supplied from the mixer 16 in synchronization with the gate pulse GP, and performs FFT processing to detect the beat frequency. FF
When the beat frequency detection is completed, the T processing unit 17 transfers the beat frequency to the output port and requests the microprocessor 18 for an interrupt. The microprocessor 18 uses this FM
It is shared not only by the radar device but also by various controls inside the vehicle. Only when the FFT processing unit 17 receives an interrupt, F
Responsible for part of the functions of the M radar device.

Upon receipt of the interrupt request from the FFT processor 17, the microprocessor 18 starts the processing of the beat frequency shown in the flowchart of FIG. The microprocessor 18 receives the newly detected beat frequency from the FFT processing unit 17, converts it into the distance to the object that has caused the reflected wave (step 31), and averages the new detected value and the past detected value. The absolute value of the difference from the value is calculated (step 32). Next, the microprocessor 18
It is determined whether the calculated absolute value of the difference is less than or equal to a predetermined threshold value (step 33), and if it is less than or equal to the threshold value, a new average value is calculated by averaging the latest detected value and the past average value. Calculation is performed (step 34), and the calculated average value is output to the display unit 19 (step 35). Finally, the microprocessor 18 reduces the current threshold value by an appropriate constant scaling factor, for example, 10% (step 36), and ends the process.

Microprocessor 18 proceeds to step 32.
When it is determined in step 33 that the absolute value of the difference calculated in step 3 is larger than the threshold value, this threshold value is increased by an appropriate constant scaling factor, for example, 10% (step 37), and the process is terminated. In other words, if the newly detected distance is a certain distance away from the past average value, the new detected value is considered to be an erroneous detected value caused by interference with another FM radar device or the like. Will be discarded.

The above has exemplified the configuration in which the minimum gate pulse width is set to 5 times the modulation period of the FM signal and the FM signal is radiated five times within the period of the minimum gate pulse width. However, from the viewpoint of emphasizing avoidance of interference with other FM devices, the FM signal may be emitted only once within the period of the minimum gate pulse width.

[0022]

As described in detail above, the F of the present invention
Since the M radar device adopts a pseudo-randomization configuration at the radiation stage, it is provided with an inspection means for eliminating false measurement results due to the interference between the devices which occurs relatively frequently as a result. The effect of achieving high responsiveness and high measurement accuracy is achieved.

Further, according to the embodiment of the present invention, since the radiation timing is randomized by using the pseudo-random pulse generator, compared to the conventional configuration in which the random number table and the timer are controlled by software. As a result, the burden on the microprocessor can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an FM radar device according to an embodiment of the present invention.

2 is a circuit diagram showing an example of a configuration of a pseudo random pulse generator 21 of FIG.

3 is a waveform diagram illustrating a gate pulse GP of a pseudo random pattern output from the pseudo random pulse generator 21 of FIGS.

FIG. 4 is a flowchart showing an example of averaging processing of detection results by the microprocessor 18 of FIG.

[Explanation of symbols]

 11 FM oscillator 14 Transmitting antenna 15 Receiving antenna 16 Mixer 17 FFT processing unit 18 Microprocessor 20 Gate circuit 21 Pseudo random pulse generator

Claims (4)

[Claims] 1. An FM signal whose frequency linearly increases and decreases is radiated to receive a reflected wave of the FM signal, and the reflected wave and the radiated FM signal are mixed to generate a beat signal. In the FM radar device for detecting the distance to the object that has generated the reflected wave, a period longer than the modulation cycle of the FM signal is set as the radiable period, and the radiable period is repeated for a predetermined number of consecutive periods. Means for setting as a cycle, setting at least one rule regarding whether or not to radiate the FM signal at least once for each radiable period, and selectively radiating the FM signal according to one of the set rules And the detection result of the frequency of the beat signal or the distance detection based on it, over the latest predetermined number, and a special one included in these is used as another radar device. Further comprising an inspection means excluded from the detection result regarded to detect false results caused by interference FM radar system according to claim. 2. The FM radar according to claim 1, wherein the means for selectively radiating the FM signal comprises a pseudo random pulse generator and an FM signal gate circuit opened / closed by the output. apparatus. 3. The inspection means according to claim 1, wherein the inspection means averages the distance detection results over a latest predetermined number, and creates an average value, and the average value and the next detection result. If the difference is greater than or equal to a predetermined value, the next detection result is regarded as the false detection result and is excluded from the averaging process.
M radar device. 4. The range detection result according to claim 1, wherein the distance detection result is obtained from the last radiated one of the FM signals radiated a plurality of times consecutively within the radiable period. FM radar device.