JPH0114946Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a radar signal processing device especially for automobiles.
The present invention relates to a signal processing device that reduces false alarms in a warning system using FM-CW radar.

The effectiveness of collision prevention systems using FM-CW radar is known as one of the safety devices for automobiles, but the most difficult technical issue in developing this type of collision prevention radar system is: The key is how to reduce the probability of false alarms occurring. Collision prevention radar provides an accurate warning to prevent the own vehicle (a vehicle equipped with the radar system) from colliding with a target that is at risk of collision (hereinafter referred to as a dangerous target), such as a vehicle in front. Although it emits
Because the radar beam does not search in front of the vehicle, it simply travels straight ahead and spreads out in a slightly conical shape, so false alarms can also be generated for targets on the side or above the road (hereinafter referred to as noise sources) that are not expected to collide. may be issued. Specific examples of noise sources include highway guardrails, road signs, overpasses, and tunnel entrances.

If a signal processing device could distinguish between effective reflected signals obtained from dangerous targets and unnecessary reflected signals (clutter) obtained from noise sources, the occurrence of false alarms could be significantly reduced, but there are few reports of this type of signal processing. In general, there are two methods: (1) limiting the maximum detection distance in proportion to the vehicle's steering angle to reduce the influence of unnecessary reflected signals from a distance, and (2) limiting the maximum detection distance in proportion to the vehicle's speed. Attempts have been made to reduce the occurrence of false alarms by constantly monitoring the minimum necessary area and reducing the influence of unnecessary reflected signals, but none of these solutions can be expected to have significant effects.

The present invention focuses on the strength of the radar reception signal level to significantly reduce the probability of false alarm occurrence. Figure 1 shows the reception level a of the FM-CW radar.
It shows the relationship between C and the distance L to the target, C ₁
is a characteristic curve with a small passenger car as the target, and C ₂ is due to reflection from the ground (earth surface). curve
As is clear from C ₁ , the higher the reception level a (a>a ₁ to _{a 3} ), the closer the target is and the higher the potential for danger. Therefore, in this case, it is required to determine whether or not it is dangerous within a short period of time.
Of course, if the reception level a is strong, the S/N is also good, so it can be expected that an alarm can be issued accurately even if only a short check is performed. On the other hand, if the target is far away, the reception level a will be low, so the S/
N deteriorates and errors are likely to occur when checking for a short time. However, if the target is far away, the potential for danger is low, so there is no problem even if it takes a little longer to determine whether or not it is dangerous. From this point of view, if the danger judgment time is changed according to the reception level,
The probability of issuing a false alarm for noise sources that are far away and are out of the range of the radar beam within a short time, such as road signs, overpasses, etc., is significantly reduced.

For example, as shown in FIG.
When the own vehicle 2 passes through m, the width of the radar beam 3 is
If the angle is 3 degrees, the reflected wave from beacon 1 will begin to be received from around 75m in front of it. However, the vehicle speed is 100
If it is about Km/H, the reflected wave will only last for about 10 ms, that is, the time the vehicle 2 travels several meters. Therefore, in this case, if the alarm judgment time is set to be longer than the duration of the reflected wave, and objects that do not continue for longer than the half-interruption time are not regarded as obstacles, false alarms will not be issued.
The present invention focuses on this point, which will be explained in detail below with reference to FIGS. 3 and 4.

Figure 3 shows FM-CW used in collision prevention devices.
In the schematic diagram of the radar, 4 is a target object such as a car.
When a transmission wave _T obtained by frequency modulating a carrier wave CW using a modulation signal MOD that changes in the shape of a triangular wave is emitted in front of the own vehicle, a reflected wave _R from the target object 4 is received. This reflected wave _R is mixed with the transmitted wave _T by a mixer MIX, and the difference signal is amplified by an amplifier AMP to obtain a beat signal BT. FIG. 4 shows a signal processing device according to the present invention, which processes the received beat signal BT and sends out an accurate alarm ALM. After the signal BT is amplified by an amplifier 5, its band is limited by a range cut filter 6. This is to limit the maximum detection distance of the radar to, for example, 80 m. Filter 6
The output is integrated by an integrator 7, and its DC component is determined. The DC component obtained by the integrator 7 indicates the level of the beat signal BT, and therefore the level of the received wave _R , so this is compared by multiple comparators (window comparators, etc.) 8a, . . . 8n with different reference values. . For example, if the first comparator 8a is a≧ in FIG.
An output is generated under an input condition corresponding to a ₁ (equivalent to within 20), and a second comparator (not shown) determines that a ₁ > a ≥ a ₂
(Equivalent to 20m to 40m) Set to generate output under input conditions. The same applies to the third comparator (not shown) that produces an output when a ₂ > a ≥ a ₃ and the outputs (reception level classification information) of all the comparators 8 a to 8 n are sent to the continuity determination circuit 9. be guided.

On the other hand, the beat signal BT is also guided to the relative speed calculator 10 and the relative distance calculator 11, so that the relative speed V _r (m/sec) and relative distance R (m) to the target object 4 are calculated. Calculated. In other words, the beat signal BT has an upbeat frequency _b1 when the frequency _of the modulation signal MOD increases and _{a downbeat frequency b2 when} the frequency decreases, but these are expressed as: _b1 = _r − _d ... (1) There is the relationship _b2 = _r + _d ...(2). Therefore, the computing unit 10 calculates the relative velocity V _r using _d obtained from equations (1) and (2), and similarly the computing unit 11 calculates the relative distance R using the obtained _r . The alarm calculator 12 takes into account the information V _r , R, the vehicle speed V ₀ (m/sec), human reaction time (sec), etc., and calculates the information in a fixed cycle, for example, in a 50 ms cycle.
In this example, it is repeatedly determined whether or not it is dangerous using the well-known formula below.

R≦K{V ₀ ² −(V ₀ −V _r ) ² }T _R・V ₀ …(3) In equation (3), K=1/(2μ×9.8), μ is the reduction during braking. It's speed.

If the calculation result of the alarm calculator 12 satisfies equation (3), it means that there is a danger, but the alarm ALM is not immediately sent out at that point.
That is, the output of the arithmetic unit 12 (information on whether or not each arithmetic cycle is dangerous) is temporarily stored in the register 13, and its continuity is determined by the determination circuit 9. For example, if the reception level is a>a ₁ , the echo signal ALM is sent out when the output of the arithmetic unit 12 occurs three times in a row. In this case, the target is close and the danger level is high, so it is necessary to send out a warning within a short time (150 ms in this example). On the other hand, if the reception level is a ₁ ≧a ₂ , a ₂ ≧a
>a ₃ , the alarm ALM
The number of consecutive outputs of the arithmetic unit 12 as a condition for sending out is increased as 4 times (200 ms), 5 times (250 ms), and so on. In other words, as the reception level a decreases, there is a possibility that it is a reflected wave from a distant target, especially a noise source, so the determination time becomes longer. In this way, for example, sign 2 in Figure 2, which is in the range of a ₂ ≧ a > a ₃ , will not continue to exist in beam 3 for more than 250 ms, so a false alarm will not be issued. .

Note that the number of reception level classifications and the number of continuity determinations described above are merely examples, and are not limited thereto.
Moreover, if a microcomputer is used for these signal processing, it will be easier to realize this. Further, the signal processing can be performed in an analog manner, and in this case, the time during which the output of the arithmetic unit 12 continues is monitored by the outputs of the systems 5 to 8. Further, in the embodiment, a road sign is used as a noise source, but it is effective for all types of targets on the road side and above that stay within the laser beam for a short time. Note that the reflected waves from the ground surface are continuous, but this can be eliminated by setting the reference level to the comparator 8, and guardrails on straight roads can be dealt with by strengthening the beam directionality. In this way, by combining the means of the present invention with other known means,
False alarms can be further reduced.

As described above, according to the signal processing device of the present invention, false alarms of the FM-CW radar for noise sources are greatly reduced, and accurate alarms for dangerous targets are reliably sent. This has the advantage of further increasing the effectiveness of automobile collision prevention systems that use the system.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the relationship between the reception level of the FM-CW radar and the distance to the target, Figure 2 is an explanatory diagram showing the relationship between the radar beam and the noise source, and Figure 3 is
FIG. 4 is a schematic diagram of an FM-CW radar, and is a block diagram showing an embodiment of the present invention. In the figure, 8a to 8n are comparators (level detection units);
9 is a continuity determination circuit, and 12 is an alarm calculator.

Claims (1)

[Scope of utility model registration request] A level production unit that detects the level of the beat signal based on the difference between the transmitted wave and the received wave obtained by the FM-CW radar, calculates relative speed information and relative distance information from the beat signal, and further calculates this information and the own vehicle speed. Corresponding to the level information from the warning calculation unit that calculates and outputs a warning signal for collision from information etc. and the level detection unit, if the level is high, the warning signal is short;
and a continuity determination section that sends out an alarm output when the arithmetic section continuously sends out alarm signals for a predetermined period of time, such as a long time when the alarm signal is low. Signal processing device.