JPH03183218A - Woodpecker radio interference removal system - Google Patents

Abstract

PURPOSE:To improve speech quality by removing the input waveform of time width corresponding to woodpecker radio interference when the peak level of the input waveform appears plural times within a definite period determined beforehand and this is decided to be the woodpecker radio interference by a decision part. CONSTITUTION:A pulse generation circuit 1 generates a pulse when it detects the peak level of the input waveform exceeding a variable threshold level generated in this circuit. A woodpecker radio interference detection circuit 2 decides the presence of the woodpecker radio interference when a pulse period generated from the pulse generation circuit 1 appears more than the prescribed number of times at every time width determined beforehand. This information is sent respectively to a clock regeneration circuit 3, a control pulse generation circuit 4, and control circuits 6, 7. A radio interference removal.interpolation part 102 removes the input waveform of 30ms and interpolates the waveform of each 15ms before and after the removed input waveform by changing switches 16 and 17 on the basis of control pulses P1 and P2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to shortwave radio lines, and particularly relates to a method for eliminating woodpecker interference, which is a noise similar to the sound of a woodpecker pecking at a tree. It is something.

(Prior Art) Shortwave wireless lines that perform long-distance communication by utilizing the reflection of radio waves on the electric M layer have been used for a long time because they have a simple device configuration and are capable of long-distance communication. Even today, it is widely used as a communication means for mobile communications such as ship communications and amateur radio. However, because shortwave wireless lines utilize so-called ionospheric propagation, various types of interference from various parts of the world are added, leading to deterioration of voice quality. In particular, in recent years, interference called false signals has been occurring frequently and deteriorating voice quality, so the cause of this has been investigated. According to the survey results, Woodpecker interference is 197
It has been occurring since around 1995, and is called "Landbelaka interference" because the noise is similar to the sound of a "woodpecker" pecking at a tree, and the source is said to be an over-horizon (OTH) radar in the Siberian direction. . Furthermore, Woodpecker interference is noise that spans a band of several hundred KHz, has a pulse width of about 10 to 50 ms, and a period of about Looms.

Currently, there is a method for removing Woodpecker interference that utilizes a noise blanker that removes short pulses of several hundred microseconds or less.

FIG. 6 is a block diagram of a conventional noise blanker.
The peak detection circuit 61 detects the signal in the intermediate frequency band from F-AMP etc. using a predetermined darkness value (threshold level).
The control pulse generating circuit 63 generates a control pulse for each detected peak level. When the control pulse is input, the input waveform removal circuit 64 removes the input waveform by adjusting the bias current of the amplifier or the forward voltage of the diode for a predetermined time width. Noise blankers are used because short pulses of several hundred microseconds or less, which cause interference, enter at a higher level than the audio level.
It is configured to determine that an input signal exceeding a predetermined darkness value is interference, and to remove the input waveform only during that period (several hundred microseconds or less). When removing Woodpecker interference using this noise blanker, the threshold value of the peak detection circuit 61 is manually set via the dark value control circuit 62 so that only the Woodpecker interference is removed as much as possible without removing the voice. At the same time, the control pulse generation circuit 6 changes the removal time width of the input waveform from several hundred microseconds or more to several ms or less via the removal time switching circuit 65.
Control is performed to change the pulse width of 3.

(Problem to be Solved by the Invention) However, in the conventional noise blanker, when receiving Woodpecker interference, it is necessary to manually adjust the dark value control circuit 62 and the removal time switching circuit 65, which is extremely inconvenient. there were. Additionally, Woodpecker interference is generally higher than the audio signal level, but in rare cases it may be lower than the propagation state, so conventional noise blankers sometimes mistakenly remove audio signals. Furthermore, as mentioned above, Woodpecker interference has a pulse width of 10 to 50 ms, so
- Even if several milliseconds of noise were removed, the quality of the call could become extremely poor.

The present invention has been made to solve the problems of the prior art described above, and an object of the present invention is to provide a Woodpecker interference removal method that can automatically remove Woodpecker interference.

(Means for Solving the Problems) The first feature of the present invention is to detect a peak level of an input waveform that exceeds a variable threshold level in an interference removal method that removes interference that interferes with shortwave wireless line communication. and a peak level detection unit that sets the variable threshold level to a predetermined level value or the peak of the detected input waveform when it is detected that the peak level of the input waveform exceeds the variable threshold level. Variable threshold level control that controls the variable threshold level so that the peak level of the input waveform is set to a level value and decreases over time until it is next detected that the peak level of the input waveform exceeds the variable threshold level. a determination unit that determines that there is Woodbenker interference when a peak level of the input waveform exceeding the variable threshold level appears multiple times in a predetermined period; The present invention is characterized in that it includes a removal section that removes an input waveform having a predetermined time width or a time width corresponding to the Woodbenker interference when it is determined that it is interference.

A second feature of the present invention is that it further includes a signal interpolation section that inserts a predetermined portion of the input waveform into the input waveform portion removed by the removal section.

The present invention will be described in detail below using the drawings.

(Embodiment 1) FIG. 1 is a first embodiment of the present invention, and is a block diagram of a Woodbenker interference removal device. In the figure, 1 is a pulse generation circuit that generates a pulse when it detects a peak level of an input waveform that exceeds a variable threshold level created within this circuit, and 2 is a pulse generation circuit that generates a pulse with a pulse period generated from pulse generation circuit 1. Predetermined time width (100ms±5
%; 95, O ~ 105.0 m s)), which determines that there is Woodpecker interference when it appears more than a specified number of times. 3 is the pulse period when it is determined that Woodpecker interference exists. A clock regeneration circuit 4 constantly generates a clock, and reference numeral 4 indicates a predetermined time width (15 to 3) based on the clock of the clock regeneration circuit 3.
5 is an input waveform removal circuit that removes the input waveform by adjusting the bias current of the amplifier and diode as in the conventional case. A removal device 10 is configured.

FIG. 2(a) shows a specific example of the pulse generating circuit 1 used in the present invention, and FIG. 2(b) shows each point (A) of the pulse generating circuit 1.
It is a waveform diagram in ~(G).

As shown in the figure, the pulse generation circuit 1 is composed of a peak hold circuit 31 which extracts and holds the voltage at the peak portion from the input waveform, and is configured to reduce the held voltage a by about 20% after about 100 ms. peak voltage a
and comparators 32 and 33 that compare b, which is equivalent to 1/2 of a, with the input waveform, one-shot multivibrators 34 and 35 that extend the pulse width to 50 ms when there is a pulse in the output of the comparators 32 and 33, and one-shot One-shot multivibrator 3 that converts the output pulse of multivibrator 35 into a 1ms short pulse
6. One Shigontoma! It consists of an OR circuit 37 that ORs the output of the reciprocator 34 and the output of the one-shot multivibrator 36, and a one-shot multivibrator 38 that converts the output of the OR circuit 37 into a 50ms pulse.

Note that the pulse generation circuit 1 generates a pulse when the input waveform receives Woodbenker interference, but in the present invention, the Woodbenker interference is two short pulses, and the former is at a lower level. Consists of pulses ((A) in the figure)
Two comparators with different darkness values are used so that even when the previous pulse is at a higher level, the trigger is generated at the peak of the previous pulse. Further, the variable threshold level used in the pulse generation circuit 1 is charged to a predetermined level value or the peak value of the detected input waveform when a certain peak value is detected, and is discharged by about 20% after about 100 ms. 20 if Woodbenker interference does not continue.
It is designed to gradually decrease by %.

(A) in FIG. 2B is an output waveform diagram of the peak hold circuit 31 when two different levels of Woodbenker interference are received as input waveforms.

(B) of the same figure is an output waveform diagram of the comparator 32, in which a pulse with a short pulse width is generated at the peak portion by comparing the peak voltage a with the input waveform.

(C) in FIG. 3B is an output waveform diagram of the comparator 33, in which the peak voltage is compared with the input waveform, and a plurality of short pulses are generated at portions larger than the peak voltage.

(D) in FIG. 3B is an output waveform diagram of the one-shot multi-by-break 34, in which the pulse at point (B) is expanded to 50 ms by the one-shot multi-by-break 34.

Similarly, (E) of the figure (b) is an output waveform diagram of the one-shot multi-by-break 35, which is expanded to 50 ms by the one-shot multi-by-break 34 for each pulse group at point (C), and the final pulse As a result, the pulse width becomes 50 ms or more. Therefore, even if a plurality of Woodpecker interferences exist during this pulse width, the first one can be detected.

(F) of the same figure (b) is an output waveform diagram of the one-shot multivibrator 36, in which the pulse at point (E) is converted into a short pulse of 1 ms.

(G) of the figure (b) is an output waveform diagram of the one-shot multi-by-break 38, in which the peak voltage
Or, if there is a pulse generated at either the peak voltage, a 50 ms pulse is generated.

As mentioned above, the pulse generating circuit 1 used in the present invention is configured to be able to generate one accurate pulse within 50 ms even if Woodpecker interference changes the waveform or phase of two different levels. .

As described above, the present invention generates a pulse for each peak of the input waveform that exceeds a variable threshold level, and only detects Woodpecker interference when the pulse period is within a certain period (100 ms ± 5%). It is determined that there is. Therefore, compared to conventional noise blankers that remove input waveforms when the peak level exceeds a variable threshold level, the present invention dramatically reduces the number of cases in which audio signals are mistakenly removed, and also automatically can effectively eliminate Woodpecker interference.

(Embodiment 2) FIG. 3 is a block diagram of a Woodpecker interference removal/interpolation device according to the present invention. It is roughly divided into an interference removal/interpolation section 102 that removes the Pecker interference portion and interpolates other signals. The major difference from the first embodiment is that another signal is interpolated in the audio frequency band to the removed input waveform portion. In the following, points different from the first embodiment will be mainly explained.

In the figure, 11 is an input terminal for the audio frequency band, 12 is a line for allowing the input waveform to pass through without going through the Woodpecker interference removal/interpolation unit W100 when there is no Woodpecker interference, 13 is an output terminal, and 18 is an input waveform. 1 and 2 respectively show switches for selecting whether to pass or not pass through the Woodpecker interference removal/interpolation device 100. In addition, the control circuit 6 of the interference determination unit 101 uses a timer (here, it is set to 5 seconds) to determine the timing at which the Woodpecker interference removal/interpolation device 100 is not allowed to pass when the Woodpecker interference is eliminated. (can be set from 3 to 10 seconds), and the control circuit 7 uses a timer (set to 1 second here, but from 0.3 to
(can be set up to 3.0 seconds).

On the other hand, the interference removal/interpolation unit 102, which is a feature of this embodiment, uses a delay element 14 that gives a 15 ms delay to the input waveform, a delay element 15 that gives a 30 ms delay to the input waveform, and the output waveforms of the delay elements 14 and 15. It is comprised of a switch 16 that selects based on the control pulse P1, and a switch 17 that selects whether to give a delay or pass through the input waveform based on the control pulse P2.

Next, the operation of the Woodbenker interference removal/interpolation device 100 according to the present invention will be explained.

FIG. 4 is a state transition diagram for explaining the operation outline of the Woodbenker interference removal/interpolation device 100 according to the present invention. It is roughly divided into four processing states.

■ Through (cold standby) condition: There is no wood bender interference at all. At this time, the Woodbenker interference removal/interpolation device 100 is not inserted.
The input waveform from input terminal 11 is taken out from output terminal 13 via input 12 and switch 18 . Note that in the through state, in order to avoid false detection, the interference determination unit 101
specified number of times (approximately 1 to 4 times; 4 times is used here)
This state is maintained until continuous wood bender interference is detected.

■ Interference cancellation/interpolation state This is a state in which Woodbenker interference is continuously detected. In this state, the portion of the input waveform that has received Woodbenker interference has a predetermined time width (approximately 10 to 50 ms;
(here, 30 ms), and another predetermined signal is interpolated to the deleted waveform portion. The interpolation method is performed by controlling the switches 16 and 17 using control pulses P1 and P2 for signals of 15 ms before and after the deleted input waveform.

■ Removal/interpolation holding (self-running) state This is the state from immediately after Woodbenker interference is no longer detected in the interference removal/interpolation state until a specified time (here, set to 1 second by the control circuit 7). The reason why Woodbender interference is no longer detected is that in addition to completely eliminating Woodbender interference, if the phase of Woodbaker interference changes due to a change in the source of Woodbender interference, A case may be considered in which a voice or the like stronger than car interference enters within a 100 ms cycle. In such a case, Woodbenker interference will no longer be detected, but since there is a high probability that interference still exists near the position of lOOms period, 15ms of input waveform deletion and 15ms before the deleted input waveform are performed. The signal is interpolated. When Woodbenker interference cannot be detected for a specified period of time (about 0.3 to 3 seconds; in this case, 1 second), the state shifts to an unprocessed state.

■ Unprocessed (hot standby) state Similar to the through state, interference cancellation and signal interpolation are not performed, but if Woodbenker interference is detected even once, interference cancellation and signal interpolation are not performed.
This is a hot standby state that transitions to interpolation state ■. That is, the input waveform is output as a 15 ms delayed waveform via the delay element 14, switch 16, switch 17, and switch 18. When Woodbenker interference cannot be detected for a specified period of time (approximately 3 to 10 seconds; here, 5 seconds), the state shifts to the through state. Woodbenker interference may reappear after a few seconds of cessation, or if the audio signal is stronger, it may reappear when the audio signal disappears. This is a standby state so that interference cancellation can be started immediately in such a case.

Although the explanation has been made using four states, the present invention does not necessarily require the removal/interpolation holding state and the unprocessed state, and it is sufficient to have at least the through state (2) and the interference removal/interpolation state (2).

Next, a specific circuit operation when the input waveform receives Woodbenker interference will be explained using FIG. here,
Let us take as an example the case of transitioning to the through state or interference removal/interpolation state.

(1) The input waveform subjected to Wood-Benker interference enters the pulse generation circuit 1 of the Wood-Benker interference removal/interpolation device 100 from the input terminal 11.

(2) The pulse generating circuit 1 outputs a pulse when there is Woodbenker interference.

(3) The Woodbenker interference detection circuit 2 measures whether the period from the rise of the pulse to the rise of the next pulse is a predetermined period (approximately 95 ms to 105 ms), and continuously When the number of times is exceeded, it is determined that there is Woodbenker interference. In other words, it enters the interference removal/interpolation state. The information is sent to the clock regeneration circuit 3, control pulse generation circuit 4 and control circuit 6.7, respectively.

(4) On the other hand, the other output of the pulse generation circuit 1 is input to the clock regeneration circuit 3, and the clock is regenerated at the cycle when the previous Woodbaker interference was present even if the Woodbender interference is eliminated. .

(5) A control pulse P0 with a pulse width of 15 ms is created in the control pulse creation circuit 4 based on the clock in the clock regeneration circuit 3, and a control pulse PI that is delayed by 15 ms and a control pulse that is delayed by 30 ms from the control pulse P. Create P2 respectively.

(6) Control pulse P created by control pulse creation circuit 4
1 and P2 are sent to the interference removal/interpolation section 102.

(7) The interference removal/interpolation unit 102 removes the 30 ms input waveform and interpolates the 15 ms waveform before and after the removed input waveform portion by switching switches 6 and 17 based on the control pulses P1 and P2. .

The details of the interference removal/interpolation unit 102 when changing from the through state (state B where there is no Woodbenker interference) to the removal/interpolation state (state where Woodbenker interference is detected four times in a row) are described below. An example of the operation is shown in Figure 5 (a).
This will be explained using (h).

FIG. 5(a) shows a specific configuration example of the interference removal/interpolation section 102 of the present invention, where switches 16a and 17b are inverting switches, and A-D indicates each point, respectively. Figure 5(b) shows the input waveform passing through point A (no delay), and for the sake of simplicity, the time width of Woodbenker interference is 30rn.
This is the case where the period is exactly 100 ms. Note that the subscripts A and ~A38 above the input waveform are numbers given to the input waveform at every 5 ms interval. Also,
Woodbenker interference of A, ~A1□ is detected by the interference determination unit 101.
It is assumed that the interference removal/interpolation state starts from the fourth time that Woodbenker interference is continuously determined to be present. FIGS. 5(b) and 5(C) are waveform diagrams passing through points B and C, and the waveforms are delayed by 15 ms and 30 ms, respectively, from the waveforms to the points due to delay elements 14 and 15.

FIG. 5(e) shows the period of Woodbenker interference (100 m here) due to the pulse generation circuit 1 and clock regeneration circuit 3.
A pulse P with a pulse width of 15 ms is synchronized with s),
It is created by the control pulse creation circuit 4. Same figure (
f) and (g) are respectively 15ms and 30ms from pulse P.
The pulses P, , P, are delayed by ms. This pulse P...
The switches 16 and 17 are controlled by
One of the input waveforms shown in ) to (d) is selected, and Woodbenker interference is removed and the waveform is interpolated.

FIG. 5(h) is an output waveform diagram at the point where Wood-Benker interference has been removed and the signals before and after the removed portion have been interpolated. In addition, when removing Woodbenker interference from A7 to AI2, which is the first stage of transitioning from the through state to the interference removal/interpolation state, 15
In order to use the ms-delayed waveform (waveform at point B) as a reference, the input waveforms A4 to A6 are output in one batch, but
This will disappear in the second and subsequent removal/interpolation parts.

That is, in this embodiment, the waveform before interference is interpolated into the 30 ms portion from which Woodbenker interference has been removed, and the waveform before interference is interpolated into the first 15 ms, and the waveform after interference is eliminated is interpolated into the latter 15 ms. It is composed.

In addition, in FIG. 3, the pulse generation circuit l is placed in the intermediate frequency band (IF band) as in the first embodiment, and the other circuits in FIG. (AF
If the configuration is placed in the AF band, it is possible to remove Wood-Baker interference before the AGC, and interpolation processing is performed in the simple AF band, so interference removal and interpolation with a good S/N ratio can be performed. I can do it.

The removal time (30ms) for Woodbenker interference is approximately 1
Although the time width was different in the range of 0 to 50 ms, the time width with the highest probability of occurrence was used here. Therefore, the removal time may be changed depending on the situation of Woodbenker interference. In addition, as an interpolation method, an example was described in which 15 ms were inserted before and after interference cancellation in consideration of the pitch period of the voice, etc., but the method is not limited to this method.
Various combinations can be used, such as 0 ms, or 10 ms before and 20 ms after.

In the present invention, when Woodpecker interference is no longer detected, the state shifts from the interference removal/interpolation state to the removal/interpolation holding state. This is because if the Woodpecker interference level temporarily decreases depending on the propagation condition, or conversely, if the audio level increases, the pulse period generated from the pulse generation circuit will deviate from the predetermined period, and there will be no Woodpecker interference. It is determined that However, in reality, Woodpecker interference exists, albeit weakly, in continuous periods of 100 ms, so this interference is removed by 15 ms before interpolation. Note that the control circuit 7 allows the removal/interpolation holding state to last only one second during which the interference removal/interpolation state transitions to the unprocessed state. Therefore, the time for this removal/interpolation holding state may be extremely short, or it may not be provided at all.

According to the observation results so far, the phase changes two to three times after a certain period of time has passed since Woodpecker interference occurred. This phase is considered to be caused by switching the radar transmission base.

In such a case, in the removal interpolation hold state, when the phase changes, the input waveform other than the part receiving Woodpecker interference will be removed, but the pulse generation circuit 1 will remove the pulse in the new synchronized state. Therefore, the waveform of the interference portion can be removed from the second time onwards.

In the above description, Woodpecker interference was used as an example of periodic pulse noise, but the present invention can be applied to other noises as long as they are periodic pulse noise.

(Effects of the Invention) As explained in detail above, the present invention detects the peak level of the input waveform and automatically determines that there is Woodpecker interference when the peak level appears multiple times at a predetermined period. It becomes possible to remove it.

By inserting a predetermined portion of the input waveform into the removed input waveform portion, speech quality can be significantly improved.

By determining that it is Woodpecker interference when the peak level appears at a period of about 100 ms, it becomes possible to distinguish it from voice.

By removing 30 ms of the input waveform, Woodpecker interference can be efficiently removed.

By interpolating input waveforms of 15 ms before and after the removed input waveform, extremely good call quality can be obtained.

Therefore, since the present invention can automatically remove periodic pulse noise, it is extremely effective in improving the call quality of shortwave radio lines such as ship communications and amateur radio communications.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of a Woodpecker interference removal device according to the present invention, and FIGS. 2 (a) and (b) are diagrams of the configuration of the pulse generation circuit according to the present invention and waveform diagrams at each point.
FIG. 3 is a block diagram showing a configuration example of the Woodpecker interference removal/interpolation device according to the present invention, FIG. 4 is a state transition diagram for explaining the operation of the Woodpecker interference removal/interpolation device according to the invention, and FIG. 5 (a) to (h) are block diagrams and waveform diagrams at each point of the interference removal/interpolation unit according to the present invention;
The figure is a block diagram of a conventional Woodpecker interference removal device. 1... Pulse generation circuit, 2... Woodpecker interference detection circuit, 3... Clock regeneration circuit, 463... Control pulse creation circuit, 5, 64... Input waveform removal circuit,
6.7... Control circuit, 10... Woodpecker interference remover, 11... Input terminal, 12... Line, 1
3... Output terminal, 14.15... Delay element, 16,
17°18...Switch, 31...Peak hold, 32°33...Comparator, 34,35,36.
38...One shot multi pie break, 37...
・OR circuit, 61...Peak detection circuit, 62...Dark value control circuit, 65...Removal time switching circuit, 100...
・Woodpecker interference removal/interpolation device, 101...Interference determination unit, '102...Interference removal/interpolation unit.

Claims (5)

[Claims] (1) In an interference removal method for removing interference that interferes with communication on a shortwave wireless line, a peak level detection section detects a peak level of an input waveform that exceeds a variable threshold level, and a peak level detection section that detects a peak level of an input waveform that exceeds a variable threshold level; When it is detected that the threshold level has been exceeded, the variable threshold level is set to a predetermined level value or the peak level value of the detected input waveform, and the peak level of the input waveform is set to the variable threshold level. a variable threshold level control unit that controls the variable threshold level to decrease over time until the next detection that the threshold level has been exceeded; and a peak of the input waveform that exceeds the variable threshold level. a determination unit that determines that there is woodpecker interference when the level appears multiple times in a predetermined period; and a determination unit that determines that there is woodpecker interference when the determination unit determines that there is woodpecker interference, and a predetermined time period or the woodpecker interference. 1. A Woodpecker interference removal method, comprising: a removal section that removes an input waveform having a time width corresponding to the time width of the Woodpecker interference removal method. (2) The Woodpecker interference removal method according to claim 1, further comprising a signal interpolation section that inserts a predetermined portion of the input waveform into the input waveform portion removed by the removal section. . (3) According to claim 1 or 2, the determining unit is configured to determine that Woodpecker interference occurs when the peak level appears at a cycle of approximately 100 ms. Woodpecker interference removal method described. (4) The Woodpecker interference cancellation method according to claim 1 or 2, wherein the removal section is configured to remove 30 ms of the input waveform. (5) Woodpecker interference removal according to claim 2, wherein the signal interpolation unit is configured to interpolate input waveforms 15 ms before and after the input waveform removed by the removal unit. method.