JP4465235B2 - MSK canceller device - Google Patents

Description

  The present invention relates to a technique for muting an MSK signal used in MCA radio on the receiving side.

  Conventionally, in the MCA radio using an MSK signal for control, when the MSK signal is detected and outputted from a speaker as a low frequency signal on the receiving side, it becomes an annoying sound, so the MSK signal is muted or cut off. Things were going on. (For example, see Patent Document 1)

Japanese Utility Model Publication No. 4-76734 (Japanese Utility Model Application No.2-121412)

However, the above-described removal circuit disclosed in Patent Document 1 uses a band-pass filter and a detector for detecting a 1200 Hz signal and a 1800 Hz signal for detecting an MSK signal. A band pass filter, a detector, a logic circuit, and a timer circuit are required. Since these circuits are constituted by hardware analog circuits, there is a problem that they are easily affected by the environmental temperature and the characteristics are not stable.
Moreover, since frequency components other than 1200 Hz and 1800 Hz are not analyzed, there is a problem that it is difficult to distinguish from white noise. For this reason, there is a problem that adjustment is required frequently and is difficult to use.

Note that it is also possible to perform the same processing as described above by digital processing using a high-performance DSP or CPU.
In that case, it is necessary to sample the received signal at a predetermined interval, and to perform processing such as generation of a fundamental wave, correlation processing, integration processing, and spectrum calculation processing at high speed for 1200 Hz and 1800 Hz, respectively.
For example, the configuration shown in FIG. 6 can be realized. In such a configuration, the input analog signal is sampled by the A / D conversion means via a low-pass filter as an anti-aliasing filter, the influence of the DC component is eliminated by the differentiation process, and the influence of the amplitude by the encoding process. Eliminate and output.
Then, the output is subjected to correlation calculation between the generated 1200 Hz data and 1800 Hz data, and the correlation value is integrated to obtain the amplitude of the frequency component. Here, it is assumed that a = cos component and b = sin component.
Since the cos component and the sin component have a phase difference of 90 degrees, a vector v (= √ (a ² + b ² ), root mean square of a and b)) is obtained. The absolute value of the vector v is an amplitude spectrum, and the square of the absolute value is a power spectrum.
When these amplitude spectra exceed a predetermined threshold value, it is determined that there is any frequency component.
Based on this determination result, the audio signal is blocked or muted.

  And it is necessary to perform such a series of processes at high speed. For this purpose, a high-function (that is, expensive) DSP or CPU is essential, and a low-function (that is, low-cost) CPU or the like has a problem that the digital processing cannot be realized because the processing capability is not in time.

  Therefore, the present invention has been made for the purpose of stably detecting and canceling an MSK signal by digital processing using a low-function (ie low-cost) CPU or the like.

In the MSK canceller apparatus according to claim 1 of the present invention,
An MSK canceller device for muting the audio output when an MSK signal is detected, wherein all combinations of binary code for a predetermined number of bits and whether each pattern signal includes an MSK signal component A reference table storing judgment elements;
Storage means for sequentially storing the binary-encoded input signal for the predetermined number of bits;
A reference means for outputting a determination element corresponding to a matched pattern by comparing the stored input signal with the pattern of the reference table;
Determination means for determining whether or not an MSK signal is included based on a determination element output from the reference means and outputting a determination result;
The present invention is characterized in that the MSK signal is detected based on the determination result output from the determination means and the audio output is muted.
In the invention of claim 2,
The reference table is characterized in that output values corresponding to the difference between the first frequency component and the second frequency component included in the signal of each pattern are stored as determination elements for every combination pattern.
In the invention of claim 3,
The determination element corresponding to the matched pattern by the stored input signal and the pattern of the reference table comparing a predetermined number of times to output the predetermined number of times accumulated and,
In the determination means,
The determination element accumulated for the predetermined number of times is compared with a predetermined threshold value,
It is characterized in that a determination result as to whether or not an MSK signal is included is output depending on whether or not the determination element accumulated for the predetermined number of times exceeds a predetermined threshold value.

In the present invention, instead of the high-speed calculation processing necessary for detecting the MSK signal, all combinations of binary codes for a predetermined number of bits, and whether or not the signal of each pattern includes an MSK signal component And a reference table storing
The binary coded input signal is sequentially accumulated for the predetermined number of bits and compared with the pattern of the reference table to determine the presence / absence of the MSK signal based on the determination element corresponding to the matched pattern. Since the signal is detected, a low-function (that is, low-cost) CPU, for example, a CPU used to control the reception function can be shared. Accordingly, since the configuration of the entire receiving device can be simplified, the cost of the entire receiving device can be suppressed.
In addition, by comparing the accumulated input signal with the pattern of the reference table for a predetermined number of times, the determination element corresponding to the matched pattern is accumulated and output for the predetermined number of times, and the determination element accumulated for the predetermined number of times Is compared with a predetermined threshold, and a determination result as to whether or not an MSK signal is included is output depending on whether or not the determination element accumulated for the predetermined number of times exceeds a predetermined threshold. Thus, a more accurate MSK canceller circuit can be obtained.

Hereinafter, an MSK canceller apparatus according to the present invention will be described in detail with reference to the drawings showing embodiments thereof.
FIG. 1 is a block diagram of a receiving apparatus including an MSK signal cancel circuit (MSK canceller circuit) as an embodiment of an MSK canceller apparatus according to the present invention.
In FIG.
Reference numeral 1 denotes an MCA radio receiving apparatus, which includes a receiving circuit 2, a switch circuit 3, a speaker 4, and an MSK signal detection circuit 5. The switch circuit 3 and the MSK signal detection circuit 5 constitute an MSK signal cancel circuit 6.

The internal configuration of the MSK signal detection circuit 5 is shown in FIG.
In FIG.
Reference numeral 51 denotes a low-pass filter, which is configured as an anti-aliasing filter that cuts off a high-frequency component that is ½ or more of the sampling frequency in order to eliminate an alias error in the A / D conversion at the subsequent stage.
Reference numeral 52 denotes A / D conversion means, which samples an input analog signal at the sampling frequency and converts it into a digital signal. The sampling frequency is 4800 Hz.
53 is a differential processing means for performing differential processing on the digital signal converted to the digital signal to eliminate the influence of the DC component and to output it.
An encoding unit 54 converts the signal output by the differentiation process into a binary code of +1 and −1 and outputs it. By converting to a binary code, the influence of amplitude is eliminated.
Reference numeral 55 denotes a buffer, which stores the binary code output by the encoding means 54 sequentially for 8 bits. At this time, +1 is actually stored as 0 and -1 as 1.
Reference numeral 56 denotes a reference means, which compares the stored 8-bit digital data with the reference data in the ROM table and outputs a spectrum value corresponding to the matched reference data as a determination element.
57 is a determination means, which compares the spectrum value of the determination element output from the reference means 56 with a predetermined threshold value. When the threshold value is exceeded, the 1200 Hz component of the first frequency component or the second frequency component It is determined that there is a 1800 Hz component of the frequency component, and a control signal is output.
The first frequency component is not limited to the 1200 Hz component, and the second frequency component is not limited to the 1800 Hz component.

As shown in FIG. 4A, when the spectrum value of the 1800 Hz component exceeds the threshold value, a control signal is output, and as shown in FIG. 4B, the spectrum value of the 1200 Hz component. A control signal is also output when the value exceeds the threshold. As shown in (c) of FIG. 4, no control signal is output when the spectrum value of any component does not exceed the threshold value.
The switch circuit 3 is controlled by the control signal determined and output in this way, and cancels (blocks or mutes) the audio signal.

The structure of the ROM table is shown in FIG.
In FIG. 3, in the ROM table, a pattern P corresponding to digital data of 8 bits of 256 patterns from 00 _{(16) to} FF ₍₁₆₎ is recorded as reference data, and 1200 Hz of each pattern P is recorded. The spectral value S1 (corresponding to the amplitude) in the case and the spectral value S2 (corresponding to the amplitude) in the case of 1800 Hz are recorded in advance as determination elements. Each spectral value is a root mean square value.
In the reference means 56, the bit pattern of the accumulated digital data for 8 bits is compared with the pattern P of the ROM table, and when they match, the spectral value S1 and the 1800 Hz component of the 1200 Hz component corresponding to the pattern P are matched. Is output as a determination element.

With the above configuration, since the audio signal is canceled when the MSK signal is detected, the low frequency signal obtained by detecting the MSK signal is not output from the speaker 4. Therefore, since the annoying sound obtained by detecting the MSK signal is eliminated, it is possible to use it comfortably.
When the MSK signal is not detected, the control signal is not output, and the audio signal is not canceled. Therefore, the speaker 4 outputs a low frequency signal obtained by detecting a normal reception signal. In this way, by using the reference table, it is possible to share a low-function (that is, low-cost) CPU, for example, a CPU used to control the reception function. Accordingly, since the configuration of the entire receiving device can be simplified, the cost of the entire receiving device can be suppressed.

Although the spectrum value is recorded as a determination element in the reference table, as will be described later in the first embodiment, the spectrum value S1 (corresponding to the amplitude) at 1200 Hz and 1800 Hz for each pattern P from 00 to FF. In this case, an output value D (see FIG. 3) obtained by multiplying the difference from the spectrum value S2 (equivalent to amplitude) by 20 is calculated in advance, and information indicating whether or not a predetermined threshold value is exceeded, that is, the MSK signal is Up to the determination result of whether or not it can be determined may be recorded in advance. In this case, the determination unit is included in the reference unit.

In the first embodiment, for each pattern P from 00 to FF, the reference table 20 times the difference between the spectral value S1 (equivalent to amplitude) at 1200 Hz and the spectral value S2 (equivalent to amplitude) at 1800 Hz. The output value D (see FIG. 3) was calculated in advance and recorded as a determination element.
In this case, since it determines based on the difference of both spectrum values, more exact determination is attained. Since the difference between the two spectral values is multiplied by 20, processing becomes easy.
In this case, the reference means 56 compares the accumulated bit pattern of the digital data for 8 bits with the pattern P of the ROM table, and if it matches, outputs the output value D corresponding to the pattern P. .
Instead of comparing bit patterns, they can be converted into numerical values and compared.

As shown in FIGS. 5A and 5B, when there is an MSK signal, the difference between the spectral values of both frequency components appears sufficiently. However, as shown in FIG. 5C, when there is no MSK signal, the difference between the spectral values of both frequency components hardly appears.
Accordingly, as shown in the output value D of FIG. 3, by obtaining the difference between the spectral values of both frequency components, it is only necessary to compare the output value D with a threshold value, so that the processing is simplified. When the output value D exceeds the threshold value, it is determined that there is an MSK signal, and when it is less, it is determined that there is no MSK signal.
Further, when the output value D is accumulated a predetermined number of times and the accumulated value is compared with a threshold value, the accuracy is further improved.

According to the first embodiment, the reference table is provided with a value obtained by multiplying the difference between the two spectral values by 20 as a determination element, so that the MSK signal can be canceled with high accuracy with simple processing. Therefore, it is possible to share a low-function (that is, low-cost) CPU, for example, a CPU used for controlling the reception function. Therefore, an accurate MSK canceller circuit can be realized even if the configuration of the entire receiving apparatus is simplified.

  The present invention can be widely used for MCA radio such as taxi radio using an MSK signal.

It is the block diagram which showed the structure of embodiment of the MSK canceller apparatus concerning this invention. It is a block diagram of the principal part of FIG. It is explanatory drawing explaining the structure of a reference table. It is explanatory drawing explaining the relationship between a threshold value and a spectrum value. It is explanatory drawing explaining the relationship between the threshold value in the case of Example 1, and the difference of a spectrum value. It is a block diagram of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Receiver apparatus for MCA radio | wireless 2 Reception circuit 3 Switch circuit 4 Speaker 5 MSK signal detection circuit 51 Low pass filter 52 A / D conversion means 53 Differentiation processing means 54 Encoding means 55 Buffer 56 Reference means 57 Determination means 6 MSK signal cancellation circuit , MSK canceller circuit

Claims (3)

An MSK canceller device for muting the audio output when an MSK signal is detected, wherein all combinations of binary code for a predetermined number of bits and whether each pattern signal includes an MSK signal component A reference table storing judgment elements;
Storage means for sequentially storing the binary-encoded input signal for the predetermined number of bits;
A reference means for outputting a determination element corresponding to a matched pattern by comparing the stored input signal with the pattern of the reference table;
Determination means for determining whether or not an MSK signal is included based on a determination element output from the reference means and outputting a determination result;
An MSK canceller apparatus configured to detect an MSK signal based on a determination result output from the determination means and mute the audio output. The output value corresponding to the difference between the first frequency component and the second frequency component included in the signal of each pattern is stored in the reference table as a determination element for every combination pattern. Item 2. The MSK canceller device according to Item 1. In the reference means,
The determination element corresponding to the matched pattern by the stored input signal and the pattern of the reference table comparing a predetermined number of times to output the predetermined number of times accumulated and,
In the determination means,
The determination element accumulated for the predetermined number of times is compared with a predetermined threshold value,
The configuration according to claim 2 , wherein a determination result as to whether or not an MSK signal is included is output depending on whether or not the determination element accumulated for the predetermined number of times exceeds a predetermined threshold value. MSK canceller device.

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