JP3641870B2 - Random modulation radar equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a random modulation radar device that transmits an electromagnetic wave of a random pulse, receives a reflected signal from the target of the electromagnetic wave, and measures a distance to the target by a propagation delay time from the transmission of the electromagnetic wave to the reception of the reflected signal About.
[0002]
[Prior art]
A radar apparatus that detects a preceding vehicle or the like existing in front of a vehicle has been developed that uses a correlation technique as means for detecting a reflected signal from the preceding vehicle. A radar apparatus using such a correlation technique is, for example, “Precision Machinery”, Vol. 33, No. 7 (1967), pages 482 to 489, or “Laser Research”, Vol. 11, No. 10, (1983), “Ambient”. It is described in “Pseudo random modulation CW rider for contamination measurement”.
[0003]
[Problems to be solved by the invention]
However, in such a conventional random modulation radar apparatus, the statistical processing time is increased in order to take advantage of the reduction in the output of the laser diode, the cost reduction, the cost reduction and simplification of the drive circuit. Since the maximum detection distance is increased by increasing the S / N ratio by increasing the number of correlation processing repetitions, it is necessary to improve the S / N ratio because the detected target exists at a short distance. Even if the statistical processing time may be short, the transmission and statistical processing are performed as many times as necessary for the maximum sensing distance, so efficiency is increased by consuming more power and time than necessary. There was a problem of being bad.
[0004]
The present invention has been made to solve the above-described problems of the prior art, and provides an efficient random modulation radar apparatus that can save power and time by eliminating wasteful processing. Objective.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as described in the claims. That is, in the present invention, by providing a determination means for determining whether the transmission operation of the transmission means is to be continued or completed based on the maximum value of the calculated correlation value, the detection target can be detected up to the target. When the S / N ratio sufficient for detecting the distance is obtained, the transmission operation and the correlation processing are terminated at that time. That is, in the present invention, when a sufficient S / N ratio is obtained, control is performed so that the number of repetitions of random pulse transmission required for one distance measurement operation is reduced.
Therefore, when the S / N ratio is good, such as when the target is close, the power consumption is low and the distance is measured in a short time. When the S / N ratio is bad, sufficient statistical processing is performed. It is possible to perform an effective distance measurement in which distance measurement is performed after obtaining an improvement in the N ratio, and statistical processing is terminated when there is no detected target.
[0006]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a random modulation radar apparatus that can save power and time and perform efficient measurement without reducing measurement accuracy.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention, and shows a vehicle random modulation radar apparatus using a correlation technique.
In FIG. 1, an M-sequence generator 1 includes an exclusive OR circuit 2 and a four-stage shift register 3, and operates according to a clock signal from a clock signal generator 11 to generate an M-sequence pulse signal. The M-sequence pulse signal generated from the M-sequence generator 1 is supplied to a light transmitter 6 composed of a laser diode or the like via a drive circuit 5 constituting the transmitter 4 and directed from the light transmitter 6 toward the front of the vehicle. The laser beam is output. A transmitter that transmits radio waves may be used instead of the light transmitter 6.
[0008]
The laser light output from the light transmitter 6 is reflected and returned to a preceding vehicle or the like existing ahead, and this reflected laser light is received by a light receiver 8 (the light transmitter 6 is a radio wave) constituting the receiver 7. In the case of the transmitter, the light is received by the receiver), amplified by the amplifier 9, and then sent to the comparator 10. The comparator 10 compares it with the reference signal V _th and converts it into a binary signal, which is supplied to one input of the exclusive OR circuit 13.
[0009]
On the other hand, the M-sequence pulse signal output from the M-sequence generator 1 is also supplied to the phase shifter 12. In response to the clock signal from the clock signal generator 11, the phase shifter 12 is an integral multiple of the period τ of the clock signal, that is, an integral multiple of one pulse width τ of the M-sequence pulse signal (0, τ, 2τ, 3τ, ...) M-sequence pulse signals whose phases are delayed are output. When this phase delay time is converted into distance, for example, a 0 m phase delay signal, a 10 m phase delay signal, a 20 m phase delay signal,..., A 100 m phase delay signal are sequentially output. The M-sequence pulse signal with the delayed phase is supplied to the other input of the exclusive OR circuit 13. In this case, the increment 10 m of the value that changes from 0 m, 10 m, 20 m to 100 m represents the distance measurement resolution, and the maximum 100 m represents the maximum distance.
[0010]
The exclusive OR circuit 13 is low when the M-sequence pulse signal delayed in each phase and the reflected signal binarized by the comparator 10 are at the same level, that is, when both signals are at a high level or a low level. A signal of a level is output, and when the level is different, that is, when one of the signals is at a high level and the other signal is at a low level, a high level signal is output.
[0011]
The output of the exclusive OR circuit 13 is supplied to the counter 14. The counter 14 counts up when the output signal of the exclusive OR circuit 13 is low, and counts down when it is high. The counting operation of the counter 14 is continued for each phase lag amount, that is, for each phase lag signal for a predetermined time t ₀ (eg, t ₀ = 1 msec). The correlation value is transferred to the RAM 15 and stored in correspondence with each phase delay signal. That is, in this operation, for each phase delay signal of 0 m, 10 m, 20 m,..., 100 m output from the phase shifter 12, the predetermined period t ₀ for each phase delay signal and the received reflected signal, respectively. The count value is stored in the RAM 15 as a correlation value corresponding to each phase delay signal. Thus, the exclusive OR circuit 13, the counter 14, and the RAM 15 constitute a correlator 16 that obtains a correlation value between each phase delay signal and the received signal as a count value.
[0012]
As described above, since the correlation value between each phase delay signal and the received signal is stored in the RAM 15, each count result is read out by the arithmetic unit 17, and the phase delay signal corresponding to the maximum value among them is read. The distance from the phase delay time to the preceding vehicle as a reflector can be calculated.
[0013]
Further, the determination unit 18 determines whether or not to continue the transmission (laser emission) from the transmitter 4 and the correlation process according to the value read from the RAM 15, and according to the result, The operation of the correlator 16 is controlled. The details of the determiner 18 will be described later based on the flowchart of FIG.
[0014]
In FIG. 1, each component is shown as an independent circuit or device, but portions other than the transmitter 4 and the receiver 7 can be configured by an arithmetic processing device such as a computer.
[0015]
Next, FIG. 2 is a signal waveform diagram when a reflective object exists in front of 60 m of the vehicle as an example, a transmission signal transmitted from the light transmitter 6, each phase delay signal of 0 m to 100 m, and the vehicle 6 shows the waveform of the received signal reflected from the preceding vehicle existing 60 m ahead of and the count value of the counter 14 for each phase delay signal and each received signal.
[0016]
In FIG. 2, the waveform shown in (m) is a received signal from a preceding vehicle existing ahead of 60 m, and exclusive OR of this received signal and each phase delay signal shown in (a) to (k) is excluded. When the output is taken by the logical OR circuit 13 and this output is counted by the counter 14 as described above, the count value is as shown in the rightmost table of FIG. This count value is a count value in one cycle of the M-sequence pulse signal, but the count value for the 60 m phase lag signal of (i) is the largest at 15, and the count values for the other phase lag signals are all -1. It has become. From this counting result, it can be accurately understood that a preceding vehicle exists 60 m ahead of the vehicle.
[0017]
Further, when noise is mixed in the received signal, the probability that the noise level and the random pulse signal level are different is ½, and the probability that they are the same is also ½. If the noise level and the random pulse signal level are different, the counter 14 is counted down, and if it is the same, the counter 14 is counted up, so that the probability of counting up due to noise is the same as the probability of counting down. That is, noise does not affect the counter 14. By utilizing this feature, the time required for correlation (statistical processing time) is lengthened even when noise is mixed in the received signal, that is, one period of the M sequence in FIG. By repeatedly performing correlation processing, the S / N ratio can be improved.
[0018]
FIG. 4 is a flowchart showing an example of conventional distance detection logic.
In the processing flow of FIG. 4, one cycle (corresponding to one cycle in FIG. 2) of M-sequence pulse transmission and correlation processing is performed for a predetermined number of repetitions (predetermined cycle number), and correlation is performed when all of them are completed. The distance is determined from the maximum value of. That is, the transmission of the M-sequence random pulse and the end of the correlation process are determined by outputting a predetermined cycle of an M-sequence random pulse in order to obtain an S / N ratio necessary for the maximum detection distance.
[0019]
Such a vehicle random modulation radar apparatus has an improved S / N ratio in accordance with the statistical processing time (the number of repetitions of correlation processing), as compared with the known giant pulse modulation laser radar system, so that the noise margin is greatly increased. There is an excellent feature that the laser diode can be reduced in output and cost, and the laser diode drive circuit can be reduced in cost and simplified. However, in the above-described conventional distance detection logic, as described in the above-mentioned section “Problems to be solved by the invention”, the statistical processing time is increased (the number of repetitions of the correlation processing is increased) in order to take advantage of the above-described advantages. Since the S / N ratio is improved and the maximum detection distance is increased, the detection target exists at a short distance and there is no need to improve the S / N ratio, that is, the statistical processing time. Even when the length may be shorter, transmission and statistical processing are performed as much as necessary for the maximum detection distance, so that there is a problem that power and time are consumed more than necessary and the efficiency is poor.
[0020]
Next, FIG. 3 is a flowchart showing the distance detection logic of the present invention.
[0021]
In FIG. 3, in step S1, an M-sequence pulse repetition counter S is initialized, and in step S2, one cycle of M-sequence pulse emission (transmission) and correlation processing is set. Next, in step S3, the maximum value among the correlation values between each phase delay signal and the binarized reception signal is compared with a predetermined correlation value A required for specifying the distance. When the maximum value among the correlation values becomes A or more, the process goes to step S4, and the distance is calculated from the phase delay signal having the maximum correlation. In other words, when the maximum of the correlation values is equal to or greater than the predetermined value A and a sufficient S / N ratio is obtained, the transmission and correlation processing cycles are not repeated any more, and one time at that time. The distance measuring operation is terminated.
Here, the value of A is a correlation value necessary for calculating the distance to the reflector by the phase lag signal having the maximum correlation value in the calculator 17 of FIG. 1, and the S / N ratio required for the distance calculation. In other words, the minimum correlation value for obtaining
[0022]
On the other hand, if the maximum value among the correlation values is less than A in step S3, the process goes to step S5, where the M-sequence pulse repetition counter S is compared with the M-sequence pulse repetition number B for determining the absence of the detection target. If the value is greater than or equal to the determination value B, it is determined in step S6 that there is no detected target. If the M-sequence repetition counter S does not exceed the determination value B, the value of S is incremented by 1 in step S7. After that, the process returns to step S2, and M-sequence pulse transmission and correlation processing are performed again.
[0023]
If the detected target is close and the S / N ratio is good as a result of the M-sequence random pulse transmission and the correlation processing end determination in steps S3 and S5 to S7, the M-sequence is immediately performed when the distance calculation is possible. Random pulse transmission and correlation processing can be completed. When the detected target is far away and the S / N ratio is poor, the M-sequence random pulse transmission and correlation processing are repeated a sufficient number of times to obtain the S / N ratio. It is possible to improve the distance calculation.
[0024]
In step S1, the M-sequence repetition counter S is initialized. In step S7, the M-sequence repetition counter S is counted up to count how many times the M-sequence pulse transmission and correlation processing are performed.
[0025]
The M-sequence repetition number B for detecting the absence of the detection target is the statistical processing time required for obtaining the S / N ratio with respect to the target maximum detection distance, that is, the repetition number of M-sequence pulse transmission and correlation processing. It is. When the detected target is not within the maximum detection distance in step S6 for determining the absence of the detected target, the M-sequence pulse transmission and the correlation process can be terminated to determine the absence of the detected target. When the target is within the maximum detection distance, the distance calculation is performed by performing the M-sequence random pulse transmission and the correlation process necessary for the distance calculation together with the M-sequence random pulse transmission and the correlation process end determination in step S3. it can.
[0026]
In FIG. 3, the portions surrounded by broken lines (steps S3, S5, S6, S7) correspond to the determination unit 18 of FIG. In general, when the arithmetic processing portion in the apparatus of FIG. 1 is configured by a computer, the ranging operation as described above can be performed by configuring the processing flow as shown in FIG.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a signal waveform diagram in the apparatus of FIG. 1;
FIG. 3 is a flowchart showing calculation processing of the present invention.
FIG. 4 is a flowchart showing conventional calculation processing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... M series generator 10 ... Comparator 2 ... Exclusive OR circuit 11 ... Clock signal generator 3 ... Shift register 12 ... Phaser 4 ... Transmitter 13 ... Exclusive OR circuit 5 ... Drive circuit 14 ... Counter 6 ... Transmitter 15 ... RAM
DESCRIPTION OF SYMBOLS 7 ... Receiver 16 ... Correlator 8 ... Light receiver 17 ... Operation unit 9 ... Amplifier 18 ... Judgment device

Claims (3)

In a random modulation radar device that transmits an electromagnetic wave of random pulses, receives a reflected signal from the reflector of this electromagnetic wave, and measures the distance to the reflector by the propagation delay time from the transmission of the electromagnetic wave to the reception of the reflected signal,
Random pulse generating means for generating a random pulse signal;
Transmitting means for transmitting electromagnetic waves in response to the random pulse signal;
Receiving means for receiving a reflection signal of the electromagnetic wave transmitted by the transmitting means; and phase means for outputting a plurality of phase delay signals that are shifted in phase by a predetermined phase by sequentially shifting the random pulse signal;
Binarizing means for binarizing the reflected signal received by the receiving means;
Correlation means for obtaining a correlation value between the reflected signal binarized by the binarization means and each phase delay signal phase-shifted by the phase means;
An arithmetic means for calculating the distance to the reflector based on the phase lag value of the phase lag signal where the correlation value is the maximum value;
Determining means for determining whether to continue the transmission operation and correlation processing based on the maximum correlation value;
A random modulation radar apparatus comprising: The determination means compares the maximum value among the correlation values between the respective phase lag signals and the binarized reception signal with a predetermined correlation value required for specifying the distance, The random modulation radar apparatus according to claim 1, wherein when the maximum value is equal to or greater than the predetermined correlation value, it is determined that the transmission of the random pulse and the correlation process are terminated. The random modulation radar apparatus according to claim 1, wherein the random pulse signal is an M-sequence random pulse signal.

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