JP2003273944A - Modulation system judging method, demodulation method using the same, modulation system judging device and demodulation device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulation system judging method capable of judging a modulation system of a digital signal of which the communication specification is unknown, a demodulation system using it, a modulation system judging device and a demodulation device using it. <P>SOLUTION: The modulation system judging device is constituted so as to multiply frequencies of a modulated digital signal by a multiplication part 10, to perform Fast Fourier Transformation to a signal obtained by multiplication by an FFT part 11 and to judge a modulation system by a threshold judging part 13 based on a power spectrum obtained by the Fast Fourier Transformation. In addition, the demodulation system and method are constituted so as to further perform demodulation by a demodulation part 21 according to judgment results of the threshold judging part in addition to the modulation system judging device. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation method determination method and a demodulation method using the same, a modulation method determination apparatus and a demodulation apparatus using the same, and particularly to a digital signal whose communication data are unknown. The present invention relates to a technique for automatically determining a modulation method.

[0002]

2. Description of the Related Art Conventionally, digital communication using various modulation methods has been performed. As one of such digital communications, a method of performing communications by a frequency-modulated digital signal is known. In this case, the receiving side determines the modulation method by calculating the bandwidth of the received modulated signal using the communication data known in advance, and the demodulation is performed according to the determined modulation method.

[0003]

By the way, in recent years, a radio called a software radio, which realizes various functions by software processing, has been developed. Since this software radio can realize various functions simply by changing the contents of software processing, it is desired to develop a radio that can support various modulation methods by utilizing this feature.

The present invention has been made in order to meet such a demand, and a modulation method determination method capable of determining a modulation method of a digital signal whose communication specifications are unknown, a demodulation method using the same, and a modulation method. It is to provide a determination device and a demodulation device using the same.

[0005]

In order to achieve the above-mentioned object, a modulation method determination method according to a first aspect of the present invention multiplies the frequency of a modulated digital signal and obtains the result by the multiplication. The signal is subjected to fast Fourier transform, and the modulation method is determined based on the power spectrum obtained by the fast Fourier transform.

According to this modulation method determination method, the modulation method is determined based on, for example, the shape of the power spectrum that depends on the modulation method. Therefore, even when a digital signal whose communication parameters are unknown is input. It is possible to determine which modulation method the digital signal is modulated with.

More specifically, in the modulation method determining method according to the first aspect, the first step of determining the modulation method is that the bandwidth before multiplication is increased when one peak appears in the power spectrum. It can be configured to judge that the digital signal is modulated by BPSK when the bandwidth after multiplication is narrower. In the second step of judging the modulation method, after the first step, when the power spectrum has one peak, the MSK modulation is performed when the level of the peak is larger than a predetermined value. It can be configured to determine that it is a digital signal. In the second step of determining the modulation method, after the first step, when the power spectrum has two or more peaks, when the level between the peaks is larger than a predetermined value, the modulation is performed by MSK. Can be configured to determine that it is a digital signal being made. Further, the third step of determining the modulation method is configured to determine that the digital signal is modulated by BFSK when two peaks appear in the power spectrum after the second step. it can. In addition, the third step of determining the modulation method is to determine that the digital signal is modulated by MFSK when three or more peaks appear in the power spectrum after the second step. Can be configured to.

Further, the demodulation method according to the second aspect of the present invention achieves the same object as described above by the first aspect of the present invention.
The modulation method determination method according to the aspect (1) further includes a step of demodulating the digital signal that has been modulated by using a demodulation method corresponding to the determined modulation method. Also in this case, the same effect as that of the modulation scheme determination method according to the first aspect can be obtained.

Further, in order to achieve the same problem as the above, the modulation method determination device according to the third aspect of the present invention is such that the modulation method determination device according to the third aspect of the present invention is modulated. A multiplying unit for multiplying the frequency of the digital signal, a fast Fourier transforming unit for fast Fourier transforming the signal multiplied by the multiplying unit, and a modulation based on the power spectrum obtained by the fast Fourier transform in the fast Fourier transforming unit. And a determination unit that determines the method. Also in this case, the same effect as that of the modulation scheme determination method according to the first aspect can be obtained.

Furthermore, the demodulator according to the fourth aspect of the present invention achieves the same object as described above by the third aspect of the present invention.
The modulation method determination device according to the aspect (1) further includes a demodulation unit that performs demodulation according to the determination result of the determination unit. Also in this case, the same effect as that of the modulation scheme determination method according to the first aspect can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

First, the modulation method to be judged in the present invention will be described. The modulation method to be judged is digital frequency modulation (FSK).
ying) and digital phase modulation (BPSK: Binary Phase S)
hift Keying). FSK is also BF
SK (Binary Frequency Shift Keying), MFSK (M
ultilevel Frequency Shift Keying) and MSK (Mini
mum Shift Keying).

(A) BFSK is different for each "1" (called "mark") and "0" (called "space") of the information signal (corresponding to the modulation signal), as shown in FIG. This is a modulation method in which frequencies are associated and sine waves of each frequency are assigned according to the level of an input digital signal.

This BFSK has a carrier frequency of f _c ,
When the shift width is Δf, it can be expressed by the following formula (1).

F (t) = a ₀ (t) * cos (2π (f _c −Δf) t) + a ₁ (t) * cos (2π (f _c + Δf) t) (1) This formula ( In 1), when the information signal is 0: a ₀ (t) = 1, a ₁ (t) = 0 [(n-1) T <t <= n
T, n = 0,1,2 ,,,] When the information signal is 1: a ₀ (t) = 0, a ₁ (t) = 1 [(m-1) T <t <= m
T, m ≠ n].

FIG. 4A shows "1011001 ...".
Represents an information signal having a bit string such as. Further, FIG. 4B shows a BFSK signal. For example, when the carrier frequency f _c is 500 Hz and the shift width Δf is 250 Hz, a sine wave of 250 Hz is assigned to the space and a sine wave of 750 Hz is assigned to the mark. It shows the situation.

FIG. 5 shows a 1-bit information signal. The mark or space length T shown in FIG. 5 is the reciprocal of the communication speed B (1
/ B). The modulation index M is represented by ΔfT = Δf / B. For example, if the communication speed B is set to “250”, the modulation index M of BFSK is Δf * (1 / B) =
500 × (1/250) = 2.

(B) MFSK is a modulation method in which different frequencies are associated with digital signals of three or more values, and sine waves of each frequency are assigned according to the value of the input digital signal.

In this MFSK, the shift width of each of the m kinds of multivalues with respect to the carrier frequency f _c is f ₀ , f ₁ ,.
···· F _m−1 , it can be expressed by the formula (2).

F (t) = a ₀ (t) * cos (2π (f _c + f ₀ ) t) + a ₁ (t) * cos (2π (f _c + f ₂ ) t) + ・ ・ ・ + a _{m- 1} (t) * cos (2π (f _c + f _m-1 ) t) (2) In this equation (2), when the information signal is “0”: a ₀ (t) = 1, a ₁ (t) = 0, ...
If _{· a m-1 (t)} = 0 information signal is _{"1": a 0 (t) = 0} , a 1 (t) = 1, ··
_{· A m-1 (t)} = 0 when the information signal is _{"m-1": a 0 (t) = 0} , a 1 (t) = 0,
... am _-1 (t) = 1.

For example, in the case of a four-valued digital signal, a value "00 (0)" is added to a sine wave of 250 Hz and a value "01".
(1) ”is a sine wave of 500 Hz, and the value“ 10 (2) ”is 7
Sine wave of 50Hz and value "11 (3)" 1000Hz
It can be configured to assign each of the sine waves of.

(C) MSK assigns sine waves of different frequencies to "1" and "0" of the digital signal, respectively.
It is a kind of SK, and the phase must be ±
This is a modulation method in which the smallest frequency difference is assigned so that it becomes 90 degrees. This MSK corresponds to FSK with a modulation index M of "0.5".

This MSK can be expressed by equation (3).

[0024] _{F (t) = u c (} t) * cos (πt / 2T) * cos (2πft) * cos (2πf c t) + u s (t) * sin (πt / 2T) * sin (2πft) * in _{sin (2πf c t) ... (} 3) this equation (3), if the information signal is _{0: (u c (t)} , u s (t)) = (- 1, -1), (- 1 ,
1) Information When the signal is _{1: (u c (t)} , u s (t)) = (1,1), a (1, -1).

(D) BPSK of digital phase modulation is a modulation method that modulates so as to represent "0" or "1" depending on whether or not the phase is shifted by 180 degrees, and is expressed by the formula (4).
It is represented by.

[0026] _{F (t) = a 0 (} t) * cos (2πf c t + 0) + a 1 (t) * cos (2πf c t + π) = a 0 (t) * cos (2πf c t + 0) + (- 1) * in _{a 1 (t) * cos (} 2πf c t + π) ... (4) the equation (4), if the information signal is 0: a _{0 (t)} = 1, a ₁ (t) = 0 [(n-1) T <t <= n
T, n = 0,1,2 ,,,] When the information signal is 1: a ₀ (t) = 0, a ₁ (t) = 1 [(m-1) T <t <= m
T, m ≠ n].

(First Embodiment) Next, the first embodiment of the present invention will be described.
A modulation method determination device and a modulation method determination method according to the embodiment will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a modulation system determination device according to the first embodiment of the present invention. This modulation method determination device includes a multiplication unit 10 and a fast Fourier transform (F
The FT) unit 11, the power calculation unit 12, and the threshold value determination unit 13 are included. Each of these units can be realized by processing of a CPU (not shown).

The multiplication unit 10 multiplies the frequency of the input signal by two by performing a complex operation. The multiplication calculation is generally performed as follows by complex multiplication. First, assuming that the input signal is a sine wave, this signal is expressed by equation (5).

E (j * 2πft) = I (t) + j * Q (t) (5) where Q (t) is the in-phase component and I (t) is the quadrature component. If the frequency of the signal of equation (5) is multiplied by 2, equation (6)
Is obtained.

E (j * 2πft) * e (j * 2πft) = e (j * 4πft) (6) From the result of squaring the complex number on the right side of Expression (5) and the value on the right side of Expression (6). Equations (7) and (8) are obtained. Re represents a real number component, and Im represents an imaginary number component.

Re (e (j * 4πf)) = I (t) * I (t) -Q (t) * Q (t) ... (7) Im (e (j * 4πf)) = I (t) * Q (t) + I (t) * Q (t) (8) (a) First, in the case of BFSK, f _{c is set} to “0” for simplicity.
Then, equations (9) and (10) are obtained.

Re (BFSK (t)) = a ₀ (t) * cos (2πf ₁ t) + a ₁ (t) * cos (2πf ₁ t) ... (9) Im (BFSK (t)) = a ₀ (t) * sin (2πf ₁ t) + a ₁ (t) * sin (2πf ₁ t) (10) Equations (11) and (12) are obtained by the multiplication operation.

I2 (t) = cos (4πf ₁ t) ... (11) Q2 (t) = sin (4πf ₁ t) ... (12) This means that only the shift width is doubled. The reason for doubling this frequency will be described later.

[0035] (b) For MFSK, when the _{f c} for simplicity to "0", the formula (13), equation (14) is obtained.

Re (MFSK (t)) = a ₀ (t) * cos (2πf ₀ t) + a ₁ (t) * cos (2πf ₂ t) + ... + a _m−1 (t) * cos (2πf _m-1 t) ... (13) Im (MFSK (t)) = a ₀ (t) * sin (2πf ₀ t) + a ₁ (t) * sin (2πf ₁ t) + ... + a _m−1 (t) * sin (2πf _m−1 t) (14) Equations (15) and (16) are obtained by the multiplication operation.

I2 (t) = cos (4πf ₀ t) + cos (4πf ₁ t) + ... + cos (4πf _m-1 t) (15) Q2 (t) = sin (4πf ₀ t) + sin ( 4πf ₁ t) + ... + sin (4πf _m-1 t) (16) In this case also, only the shift width is doubled.

(C) In the case of MSK, if f _{c is set} to “0” for the sake of simplicity, equations (17) and (18) are obtained.

[0039] Re (MFSK (t)) = u c (t) * cos (πt / 2T) ... (17) Im (MFSK (t)) = u s (t) * sin (πt / 2T) ... (18 ) Equation (19) and Equation (20) are obtained by the doubling operation.

[0040] _{I2 (t) = u c 2} (t) * cos 2 (πt / 2T) -u s 2 (t) * sin 2 (πt / 2T) = cos 2 (πt / 2T) -sin 2 (πt / 2T) = cos (πt / T) ... (19) Q2 (t) = 2 * u _c (t) * us _s (t) * cos (πt / 2T) * sin (πt / 2T) = sin (πt / T) (20) The complex signal doubled by the multiplying unit 10 as described above is sent to the fast Fourier transform unit 11.

The fast Fourier transform unit 11 fast Fourier transforms the complex signal from the multiplication unit 10. In this fast Fourier transform, conversion from the time domain to the frequency domain is performed. The signal obtained by performing the fast Fourier transform in the fast Fourier transform unit 11 is sent to the power calculation unit 12. The power calculator 12 calculates the power spectrum based on the signal from the fast Fourier transform unit 11.

(A) First, consider the spectrum waveform of the BFSK signal. For simplicity, considering the case of f _c = 0, the BFSK signal is expressed by equation (21).

BFSK (t)) = a ₀ (t) * e (-j * 2πΔft) + a ₁ (t) * e (j * 2πΔft) (21) At this time, a ₀ (t) (or a The power spectrum (PSD) of the rectangular wave representing ₁ (t) is represented by Expression (22). FIG. 6 shows a spectrum waveform of a rectangular wave.

PSD (f) = 1 / B ² * sinc ² {2πf / (2B)} (22) The BFSK signal represented by the equation (21) is expressed by Δ in the equation (22).
The frequency is shifted by f (or -Δf), and the power spectrum waveform of the BFSK signal is as shown in FIG. 7.

The shift width and the communication speed are 2Δf = M * B
The relationship of (M: modulation index) is established. At this time, when the value of the modulation speed M, that is, the shift width is changed with the communication speed kept constant, the relationship between the line spectra in FIG.
As shown in FIGS. 8A to 8D.

The spectrum waveform shown in FIG. 8A is a waveform when the modulation index is 2. The spectrum waveform shown in FIG. 8B is a waveform when the modulation index is 4. The spectrum waveform shown in FIG. 8C is a waveform when the modulation index is 1. The spectrum waveform shown in FIG. 8D is a waveform when the modulation index is 0.5. As can be seen from FIG. 8, according to the value of the modulation index,
The peaks are separated, approached, or overlapped.

(B) Next, consider the spectrum waveform of the MFSK signal. The spectrum waveform of the MFSK signal is B
Multi-valued spectrum peak of FSK signal (2 or more)
Minutes exist, as shown in FIG. MF
Similarly to the BFSK signal, the shift width between the adjacent spectra in the case of the SK signal depends on the modulation index.
(A), changes as shown in FIG. (C) Next, the spectrum waveform of the MSK signal corresponds to the case where the modulation index of the BFSK signal is 0.5, and the spectrum waveform matches the waveform shown in FIG. 8 (d). For example,
When the spectrum waveforms of BFSK and MSK are compared, as shown in FIG. 11, their center levels are greatly different. Therefore, it is possible to distinguish between BFSK and MSK by measuring the center level and then performing threshold determination.

When comparing BFSK and MSK having a modulation index of 1 as shown in FIG. 8C, they cannot be discriminated from each other even if the center level is judged by a threshold value. However, the BFSK shown in FIG. 8C is obtained by performing the double processing.
Changes as shown in FIG. 8A, and the MSK shown in FIG. 8D changes as shown in FIG.
A level difference occurs in the central spectrum, and this change can be used to distinguish between BFSK and MSK.

Next, the power spectrum calculated in this way is sent to the threshold value judging section 13. The threshold determination unit 13 obtains the peak of the power spectrum sent from the power calculation unit 12, calculates the level of the frequency component near the center of the signal having one peak, and determines the level of two or more peaks. For the signal, the level of the frequency component near the center between the peaks is calculated.

If the calculated level is larger than a predetermined value, it is determined to be MSK. If not, the number of peaks is calculated, and if the number of peaks is 3 or more, MF is determined.
If it is determined to be SK and the number of peaks is 2, BFSK
It is determined that Then, a signal representing this determination result is sent to the outside as an output of the modulation method determination device.

(D) In the case of BPSK, BPS
The K signal is expressed by equation (23).

[0052] _{F (t) = a 0 (} t) * e (j * 2πf c t + 0) + (- 1) * a 1 (t) * e (j * 2πf c t) ... (23) BPSK signal The time waveform of is represented by the sum of the waveform shown in FIG. 12 (a) and the waveform shown in FIG. 12 (b). For this reason,
By overlapping the spectra, only the DC (direct current) component in FIG. 12 is canceled out, and the spectrum is as shown in FIG.

When the BSPK signal is multiplied by 2, the equation (24) is obtained.

F _{× 2} (t) = {a ₀ (t) * e (j * 2πft + 0) + a ₁ (t) * e (j * 2πft + π)} ² = a ₀ ² (t) * e (j * 4πft) + a ₁ ² (t) * e (j * 4πft + 2π) + 2a ₀ (t) a ₁ (t) * e (j * 2πft + 0) * e (j * 2πft + π )… (24) At this time, since 2 * θ (t) = 0 (or 2π), F _{× 2} (t) = {a ₀ ² (t) + a ₁ ² (t)} * e (j * 4πft + 2π) = e (4πft) ... (25) This spectrum is shown in FIG. 14
As is apparent from the above, the phase of the BPSK signal is degenerated by the doubling process, and only the carrier signal is obtained. Therefore, B
The bandwidth of FSK, MSK, and MFSK increases due to the multiplication process, whereas the bandwidth of BPSK decreases. Therefore, it is possible to determine the modulation method including BPSK.

Next, the operation of the above configuration will be described with reference to the flow chart shown in FIG.

First, a doubling process for doubling the frequency of the input signal is performed (step S8a). The multiplication processing is performed in the multiplication unit 10. Next, this 2
The FFT process of performing the fast Fourier transform on the multiplied signal is performed, and the power spectrum is calculated (step S1).
0a). The process of step S10a is performed by the FFT unit 11
And the power calculation unit 12. Next, the number of peaks on the power spectrum is calculated (step S11a). FIG. 3 shows the power spectrum before and after the multiplication in each modulation method.

FIG. 3A shows the power spectrum of MFSK. In this example, for example, 250, 500, 75
A power spectrum having four peaks can be obtained by subjecting a four-value digital signal of 0 and 1000 Hz to fast Fourier transform. In the case of this MFSK, if the modulation index is "1" or more, the modulation index becomes "2" or more by doubling, so that the power spectrum shape has a level of the frequency component near the center between the peaks. .

FIG. 3B shows the power spectrum of BPSK. Since BPSK is modulated so that the phase is shifted by 180 degrees, a signal with a phase shift of 0 degrees remains unchanged even if it is multiplied by 2, and a signal with a phase shift of 180 degrees is multiplied by 2. The shift is 360 degrees, that is, 0 degrees. Therefore, when multiplied by 2, all phases are aligned,
A power spectrum having one frequency component is obtained.

FIG. 3C shows the power spectrum of MSK. In the case of MSK, since the modulation index becomes “1” by doubling, the position of the frequency component changes, but in the power spectrum shape, the level of the frequency component near the center hardly changes.

FIG. 3D shows the power spectrum of BFSK. In this example, for example 250 and 750 Hz
By performing a fast Fourier transform on such a binary digital signal, a power spectrum having two peaks can be obtained. In the case of this BFSK, if the modulation index is "1" or more, the modulation index becomes "2" or more by doubling, so that the shape of the power spectrum drops in the level of the frequency component near the center.

When the above FFT processing is completed, it is next determined whether or not the bandwidth is below a predetermined value (step S12). That is, the threshold determination unit 13 checks the bandwidth of the frequency component having the peak of the power spectrum. If the bandwidth is less than or equal to the predetermined value, the BPS
The digital signal modulated by K is recognized, and a signal indicating that is output (step S13).

If it is determined in step S12 that the bandwidth is not less than the predetermined value, then it is determined whether the level of the frequency component near the center between the peaks is not less than the predetermined level (step S14). .

Here, in the case of MFSK and BFSK,
As shown in FIGS. 3A and 3D, the peaks discretely appear at frequency intervals according to the modulation index M. The threshold determination unit 13 compares the level of the frequency component near the center of the peak with a predetermined threshold level.
If a frequency component of a predetermined level or higher exists near the center of the peak, the digital signal is recognized as a digital signal modulated by MSK, and a signal indicating that fact is output (step S15).

On the other hand, if it is determined in step S14 that there is no frequency component above the predetermined level near the center of the peak, it is recognized that the signal is a digital signal modulated by BFSK or MFSK.

If the calculated number of peaks is "3" or more, the threshold judgment unit 13 recognizes that it is a digital signal modulated by MFSK, and outputs a signal to that effect (step S17). . On the other hand, if the number of peaks is "2", it is recognized that the signal is a digital signal modulated by BFSK, and a signal indicating that is output (step S1).
8). Then, the modulation method is determined (step S1
9).

If the multiplication process is not performed, the FFT
The process is performed (step S10b), the number of peaks is calculated (step S11b), and then the process proceeds to step S12.

As described above, according to the modulation system determination device of the first embodiment of the present invention, even if a digital signal whose communication specifications are unknown is input, the digital signal is BFSK, MFSK, MSK and BPSK
It is possible to determine which of the modulation methods is used for modulation.

Further, it is difficult to judge the MSK and the BFSK having the modulation index “1” which are conventionally difficult to determine without communication specifications.
By multiplying, it becomes possible to make a determination without communication specifications.

(Second Embodiment) A second embodiment of the present invention is a demodulation device using the modulation system determination device according to the first embodiment described above.

As shown in FIG. 15, this demodulation device is composed of a modulation system determination section 20, a demodulation section 21, and a decoding processing section 22. As the modulation method determination unit 20, the modulation method determination device according to the above-described first embodiment is used. Therefore, in this modulation method determination device 20, the modulation method of the input digital signal is BFSK, MFSK, MS.
It is determined which is K or BPSK, and the determination result is sent to the demodulation unit 21.

The demodulation unit 21 demodulates the input signal according to the modulation system indicated by the determination result from the modulation system determination device 20, and outputs the demodulated signal to the decoding processing unit 22. Demodulation unit 21
Is an MSK demodulation processing unit 201 that performs MSK demodulation processing on an input signal when the modulation scheme is determined to be MSK, and a BPSK demodulation processing that performs BPSK demodulation processing on the input signal when the modulation scheme is determined to be BPSK. A unit 202, an MFSK demodulation processing unit 203 for performing MFSK demodulation processing on an input signal when the modulation scheme is determined to be MFSK, and a BFSK demodulation processing for an input signal when the modulation scheme is determined to be BFSK. It has a demodulation processing unit 204.

Next, the operation of the demodulating apparatus according to the second embodiment of the present invention having the above configuration will be described with reference to the flowchart shown in FIG.

In this demodulation device, first, a modulation method determination process is performed (step S20). This modulation method determination processing is the same as the processing in the first embodiment described with reference to the flowchart in FIG. By this modulation method determination processing, the modulation method determination device 20 outputs a signal indicating which of BFSK, MFSK, MSK and BPSK the input signal is modulated.

Next, the demodulation section 21 uses the BPSK modulation method.
Is determined (step S21). Here, when it is determined that the BPSK is BPSK, the BPSK demodulation processing unit 202 uses the BPSK demodulation method.
Demodulation processing is performed and a binarized signal is output (step S22).

When it is determined in step S21 that the modulation method is not BPSK, the demodulation unit 21 then determines whether the modulation method is MSK (step S23). here,
If it is determined to be MSK, the MSK demodulation processing unit 2
01, the MSK demodulation process using the MSK demodulation method is performed, and the binarized signal is output (step S2).
4).

If it is determined in step S23 that it is not MSK, then the demodulation unit 21 determines whether the modulation method is BFSK (step S25). here,
If it is determined to be BFSK, the BFSK demodulation processing unit 204 performs BFSK demodulation processing using the BFSK demodulation method, and outputs a binarized signal (step S26).

On the other hand, when it is determined that the signal is not BFSK, the MFSK demodulation processing unit 203 performs MFSK demodulation processing using the MFSK demodulation method, and outputs a binarized signal (step S27). By the above processing,
The demodulation operation is completed.

As described above, according to the demodulation device of the second embodiment of the present invention, even when a digital signal whose communication data is unknown is input, the digital signal is BFSK, It is automatically determined which one of MFSK, MSK and BPSK modulation method is used for modulation, and demodulation is performed according to the determination result. It can be used as a multi-demodulation device capable of demodulating the generated signal.

[0079]

As described in detail above, according to the present invention,
A modulation method determination method capable of determining a modulation method of a digital signal whose communication specifications are unknown, a demodulation method using the same, a modulation method determination apparatus, and a demodulation apparatus using the same can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a modulation scheme determination device according to a first embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the modulation scheme determination device according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the processing operation of the modulation scheme determination device according to the first embodiment of the present invention for each modulation scheme.

FIG. 4 is a diagram for explaining a modulated signal that is a determination target in the modulation scheme determination device according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a 1-bit information signal.

FIG. 6 is a diagram showing a spectrum waveform of a rectangular wave.

FIG. 7 is a diagram showing a spectrum waveform of BFSK.

FIG. 8 is a diagram showing a spectrum waveform of BFSK when a modulation index is changed.

FIG. 9 is a diagram showing a spectrum waveform of MFSK.

FIG. 10 is a diagram showing a spectrum waveform of MFSK when a modulation index is changed.

FIG. 11 is a diagram showing a comparison of spectrum waveforms of BFSK and MSK.

FIG. 12 is a diagram showing a time waveform of a BPSK signal.

FIG. 13 is a diagram showing a spectrum waveform of BPSK.

FIG. 14 is a diagram showing a spectrum waveform of PSK after being doubled.

FIG. 15 is a block diagram showing a configuration of a demodulation device according to a second embodiment of the present invention.

FIG. 16 is a flowchart for explaining the operation of the demodulation device according to the second embodiment of the present invention.

[Explanation of symbols]

10 multiplier 11 FFT section 12 Power calculator 13 Threshold judgment unit 20 Modulation method determination unit 21 Demodulator 22 Decryption processing unit 201 MSK demodulation processing unit 202 BPSK demodulation processing unit 203 MFSK demodulation processing unit 204 BFSK demodulation processing unit

Claims (9)

[Claims] 1. A frequency of a modulated digital signal is multiplied, a signal obtained by the multiplication is subjected to fast Fourier transform, and a modulation method is determined based on a power spectrum obtained by the fast Fourier transform. A method for determining a modulation method, characterized by: 2. The first step of determining the modulation method is, when one peak appears in the power spectrum, when the bandwidth after multiplication is narrower than the bandwidth before multiplication, B
2. The modulation method determination method according to claim 1, wherein it is determined that the digital signal is modulated by PSK. 3. The second step of judging the modulation method is, after the first step, when the power spectrum has one peak, when the level of the peak is larger than a predetermined value, the modulation is performed by MSK. The modulation method determination method according to claim 2, wherein it is determined that the modulation method is a digital signal that is being performed. 4. The second step of judging the modulation method is, after the first step, when the power spectrum has two or more peaks, when the level between the peaks is larger than a predetermined value, the MSK is performed. 3. The modulation method determination method according to claim 2, wherein it is determined that the digital signal has been modulated by. 5. The third step of determining the modulation method determines that the digital signal is modulated by BFSK when two peaks appear in the power spectrum after the second step. The modulation method determination method according to claim 3 or 4, characterized in that. 6. The third step of determining the modulation method is a digital signal modulated by MFSK when three or more peaks appear in the power spectrum after the second step. The modulation method determination method according to claim 3 or 4, wherein the determination is performed. 7. A frequency of a modulated digital signal is multiplied, a signal obtained by the multiplication is fast Fourier transformed, and a modulation method is determined based on a power spectrum obtained by the fast Fourier transform, A demodulation method for demodulating a digital signal that has been modulated using a demodulation method corresponding to the determined modulation method. 8. A multiplication unit for multiplying the frequency of a modulated digital signal, a fast Fourier transform unit for fast Fourier transforming the signal multiplied by the multiplying unit, and a fast Fourier transform in the fast Fourier transform unit. A modulation method determination device, comprising: a determination section that determines a modulation method based on the obtained power spectrum. 9. A multiplication unit for multiplying the frequency of a modulated digital signal, a fast Fourier transform unit for fast Fourier transforming the signal multiplied by the multiplying unit, and a fast Fourier transform in the fast Fourier transform unit. A demodulation device comprising: a determination unit that determines a modulation scheme based on the obtained power spectrum; and a demodulation unit that performs demodulation according to the determination result of the determination unit.