JPH035097B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a technique for determining the presence of a signal,
Especially noise generated by the receiver itself (system noise)
The present invention relates to a signal determination method that eliminates erroneous determination due to

(Prior art) A system that emits pulsed radio waves toward a target, receives reflected waves from the target, detects the presence of the target, or calculates the distance to the target from the reception time of the reflected waves. is known as pulse radar.

In such a system, the output of the receiver that receives the reflected waves includes, in addition to the regular signal from the reception of the reflected waves, external noise that enters the antenna along with the reflected waves, and noise generated by the receiver itself (hereinafter referred to as system noise). ) is included.

In order to distinguish between a normal signal and noise, conventionally, a comparator is used to compare the level of the receiver output with a reference level, and any output that exceeds the reference level is determined to be a normal received signal. It is true.

(Problems to be Solved by the Invention) Of the noises mentioned above, system noise constantly fluctuates due to changes in the environment, particularly changes in temperature. Therefore, when the system noise has an extreme fluctuation range, or when the reference level is set low to improve signal reception sensitivity, the noise level may become higher than the reference level. A situation arises in which noise is erroneously determined as a regular signal. Although such inconveniences can be avoided to some extent by setting the reference level high, this poses a problem in that the signal receiving sensitivity becomes low.

The present invention is proposed to solve the above problems.
The purpose of this invention is to effectively remove noise components due to system noise from the receiver output and to obtain a signal determination method that does not cause false determinations.

(Means for Solving the Problems) For the above purpose, the present invention stores the system noise level by detecting the output level of the receiver during the signal non-reception period, and stores the system noise level during the signal reception period. The noise component due to system noise is removed from the receiver output by subtracting the system noise level from the receiver output level at
Based on the output thus obtained, signal reception is determined.

(Configuration of Embodiment) FIG. 1 is a block diagram of an embodiment in which the present invention is implemented in a radar system.

As shown in FIG. 1, the system according to the embodiment includes a transmitter 1 that outputs a transmission signal (pulse signal), a duplexer 2 that switches the transmission path of the transmission signal and reception signal, and a transmission signal from the transmitter 1. Antenna 3 receives the reflected signal of the radiated signal from the target object, a switch 4 blocks the transmission of the received signal during the transmission period of the transmitter 1 (so-called TX blanking), and a switch 4 A receiver 5 receives the reflected signal, and a noise gate 6 transmits only the system noise component to the next stage by passing the output of the receiver 5 during the non-receiving period of the receiver 5. The system noise level is stored by detecting and holding the output levels of the signal gate 7 and the noise gate 6, which pass the output during the reception period of the receiver 5 and transmit the received signal containing noise components to the next stage. a noise level detector 8 that detects and holds the output level of the signal gate 7; a subtracter 10 that subtracts the output level of the noise level detector 8 from the output level of the signal level detector 9; and a determiner 11 that determines the presence of a signal (the reflected signal) based on the output from the subtracter 10, the transmission timing of the transmission signal from the transmitter 1, and the on/off of the switch 4, noise gate 6, and signal gate 7. It is comprised of a timing pulse generator 12 and the like that generates pulses that define control timing.

In each of the above parts, the noise level detector 8 and the signal level detector 9 have internal sample and hold circuits, and are configured to hold the input signal level by sample and hold, respectively.
Their output signals will be at the maintained level.

(Operation of the embodiment) FIG. 2 is a time chart for explaining the operation of the embodiment shown in FIG. .

The timing pulse generator 12 has a period T at point (A).
, a TX blanking pulse (negative pulse) with a pulse width t ₁ including the sending time of the transmit pulse at point (B), and a TX blanking pulse (negative pulse) with a pulse width of t 1 including the transmission time of the transmission pulse at point (C), at the same timing and the same as the above TX blanking pulse at point (C). A signal gate pulse with a polarity is outputted at point (d), and a noise gate pulse with a pulse width t ₂ that rises simultaneously with the fall of the TX blanking pulse and falls immediately before the rise of the transmit pulse is output, respectively.

In response to the transmission pulse from the timing pulse generator 12, the transmitter 1 repeatedly outputs a transmission signal at a period T to point (e). The transmission signal outputted to this point (e) passes through a duplexer 2 and is radiated from an antenna 3 toward a target object.

On the other hand, since the timing pulse generator 12 sends out the TX blanking pulse before and after the above-mentioned sending signal is output, the switch 4 is turned off during this period, and the connection between the receiver 5 and the antenna 3 is cut off. That is, the period _t1 during which the TX blanking pulse is output is a signal non-receiving period. The output of the receiver 5 during the signal non-receiving period is only system noise, as shown by a in FIG. 2. Also, at this time, the timing pulse generator 12 outputs the signal gate pulse and the noise gate pulse at the above-mentioned timing, so the system noise passes only through the noise gate 6 during the pulse width _t2 of the noise gate pulse, and the noise It is input to the level detector 8. The noise level detector 8 samples and holds the system noise, and holds the system noise level e ₁ after the noise gate pulse disappears until the next noise gate pulse is output. Furthermore, this maintained system noise level e ₁
is reset at the leading edge of the next noise gate pulse, and when the next noise gate pulse is output, the system noise level at that time is maintained in the same manner as above. Therefore, each time a transmission pulse is output, the level of system noise at that time is stored.

Period during which TX blanking pulse is sent
During t ₁ , the signal gate 7 is activated by the signal gate pulse.
is off, and no signal including noise is input to the signal level detector 9. When this period t ₁ ends (i.e. the period of reception of the signal t ₃
When the TX blanking pulse and the signal gate pulse disappear, the switch 4 and the signal gate 7 are turned on, and the signal incident on the antenna 3 is input to the signal level detector 9.

When the reflected signal of the transmitted signal from the target is incident on the antenna 4 during the signal reception period _t3 ,
By the above operation, the received signal as a reflected signal is input to the signal level detector 9, and the signal level detector 9
samples and holds the level _e2 of the received signal and stores it.

Through the above operation, the signal level detection output output from the signal level detector 9 and the noise level detection output output from the noise level detector 8 are input to the subtracter 10, where the latter is subtracted from the former. A subtraction process is performed, and the subtraction output shown in FIG. The determiner 11 compares the subtraction output with the reference level e _S to determine reception, and outputs a reception determination output, that is, a signal indicating the presence of a target object to point (O). At this time, the presence of the target is determined by the rising edge (leading edge) of the determination output.

In the above operation, each time a reflected signal is received, the determination of a legitimate signal is made based on the output from which the system noise component at that time has been removed. Therefore, the judgment output does not change.

Note that the present invention can be implemented even in a reception-only system without a signal transmission function by providing a non-reception period.

(Effects of the Invention) As described above in detail, the present invention detects and stores the level of system noise at each signal non-receiving period, and calculates the level of the receiver output from the level of the receiver output for each signal receiving period. The received signal is judged based on the output after subtracting the level of the system noise, so even if the system noise fluctuates, the received signal will not be erroneously judged.
The present invention has various advantages, such as being able to set the receiving sensitivity independently of the fluctuation width of the system noise, so there is no need to lower the receiving sensitivity in consideration of the system noise, and therefore it is possible to detect signals with high sensitivity. The effect is extremely remarkable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a time chart showing the operation of the embodiment shown in FIG. (Main symbols), 4...Switch, 5...Receiver,
6...Noise gate, 7...Signal gate, 8...
noise level detector, 9...signal level detector,
10...Subtractor, 12...Timing pulse generator.

Claims (1)

[Claims] 1 The level of noise caused by the receiver itself is stored by detecting and holding the output level of the receiver during the signal non-receiving period, and the above-mentioned storage is performed based on the receiver output level during the signal receiving period. A signal determination method that determines the presence of a signal based on the output obtained by subtracting the noise level.