JPH07107128A - Digital modulating/demodulating method and digital modulator - Google Patents

Abstract

PURPOSE:To provide a digital modulating/demodulating method which dispenses with frequency synchronization and generates no deterioration of a transmission characteristic to a frequency deviation, even if the frequency deviation and a frequency fluctuation exist in a receiving signal. CONSTITUTION:Input data partitioned at every (m) bits by a serial-parallel converting circuit 1 is converted into a frequency displacement amount (df) corresponding to combination of (m) bits by a frequency displacement amount determining circuit 2. A frequency modulating circuit 3 modulates and outputs it by a frequency obtained by adding the frequency displacement amount (df) to a frequency of an immediately previous symbol period. A frequency discriminator 4 of a demodulator side decides a frequency of every symbol period of a receiving signal. A frequency displacement amount deciding circuit 5 derives a displacement amount of a frequency decided value of every symbol period, based on the frequency decided value. A data deciding circuit 6 derives the combination of (m) bits by an operation reverse to an operation of the frequency displacement amount determining circuit 2, and outputs it as demodulation data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital modulation / demodulation method and a digital demodulation device, and more particularly to a digital land mobile communication system such as a digital car telephone system, a digital portable telephone system, a digital cordless telephone system, a digital radio calling system or a digital mobile unit. The present invention relates to a digital modulation / demodulation method and a digital demodulation device used in a satellite communication system or a local wireless communication system such as a wireless LAN.

[0002]

2. Description of the Related Art There is an FSK modulation / asynchronous detection method as a digital modulation / demodulation method which does not require phase synchronization on the receiving side. FIG. 9 is a block diagram showing a configuration example of this conventional method.

According to this conventional method, on the transmitting side,
The serial-parallel conversion circuit 1 divides the input data into blocks by dividing it into a fixed number of bits. The frequency determination circuit 20
For each block, the frequencies of the modulated signals are made to correspond one-to-one according to the combination of bits in the block. The frequency modulation circuit 30 performs FSK modulation according to the determined frequency.

On the other hand, on the receiving side, the frequency discriminator 4
Discriminates the frequency of the received signal, and the data discriminating circuit 6 associates the discriminated frequency with a block consisting of a fixed number of bits in a one-to-one correspondence and outputs the bits in the block as demodulated data. The received signal is demodulated.

The operation of the conventional system having the above configuration is as follows. Now, if there is input data b1, b2, b3, ... As shown in FIG. 10, the serial-parallel conversion circuit 1 divides this input data into m blocks. Then, each block is associated with the modulation frequencies Fi, Fi + 1, ... In accordance with the correspondence table between the bits in the block and the modulation frequency included in the frequency determining circuit 20. Next, as shown in FIG. 11, the frequency modulation circuit 30 performs FSK modulation of the symbol period T according to the modulation frequencies Fi, Fi + 1, ... And outputs it.

On the receiving side, the FSK modulated signal as shown in FIG. 12 is received, and the frequency discriminator 4 discriminates the frequency of the received signal. When the frequency of the received signal is determined,
The data determination circuit 6 performs inverse conversion using the correspondence table between the bits in the block of FIG. 10 and the modulation frequency. As a result, the received signal is demodulated.

[0007]

In the above-mentioned conventional techniques, correct demodulation cannot be performed if the received signal has frequency deviation or frequency fluctuation. Therefore, a circuit for frequency compensation with respect to the frequency deviation and frequency fluctuation of the received signal is required, and there is a drawback that the device scale increases and it takes a long time to initially capture the frequency.

For example, in an environment where a frequency shift occurs due to a transmission line or frequency conversion, AF on the transmission side
C (Automatic Frequency Control) or reception frequency synchronization on the receiving side is required.

AFC is a method of detecting the frequency deviation of a received signal by some method and controlling the transmission frequency so that the frequency deviation of the received signal is eliminated. When performing AFC, on the receiving side, means for detecting the amount of frequency deviation,
A means for transmitting the detected shift amount to the transmitting side is required. Further, the transmitting side needs a means for controlling the transmission frequency according to the frequency shift amount transmitted from the receiving side, and it is considered that a complicated control circuit is required to realize these means. Furthermore, when the amount of frequency deviation fluctuates, it is necessary to set the AFC control parameter according to the fluctuation speed, but it is not always possible to set the optimum parameter, and the transmission characteristics are also adversely affected. become.

Further, as a frequency synchronization method on the receiving side, for example, the document "FSK demodulation method for satellite communication using spectrogram" (Tsuchida, Hara, Morinaga, IEICE Technical Report, RCS92-86, November 1992) There is a method shown in. This method uses a fast FFT (Fourier Fourier Transform) to convert the received signal over multiple symbols to the binary FSK modulated signal.
The frequency spectrum is converted into a frequency spectrum and the two peaks corresponding to the two types of frequencies of the binary FSK signal are detected to obtain the center frequency of the reception signal, which is used to correct the reception frequency.

This method also requires a means for detecting the reception frequency in addition to the means for demodulation, which leads to an increase in the circuit scale and requires a long time for the initial acquisition of the frequency. Further, when such a frequency synchronization method is applied to a multi-level FSK signal, it becomes difficult to distinguish between a frequency shift due to modulation and a frequency shift due to Doppler, so that more complicated processing is required and the circuit scale becomes large. It is considered that the initial acquisition time is further increased by further increasing it.

In addition to the above-mentioned problems, when multi-valued FSK is used, there is a problem that the larger the number of multi-valued data, the larger the transmission bandwidth required in comparison with the transmission speed and the worse the frequency utilization efficiency becomes.

The present invention solves the above-mentioned problems of the prior art, and does not require frequency synchronization and phase synchronization even if the received signal has a frequency deviation and a frequency fluctuation, and thus can cope with the frequency deviation. An object of the present invention is to provide a digital modulation / demodulation method and a digital demodulation device which do not cause deterioration of transmission characteristics.

It is another object of the present invention to provide a digital modulation / demodulation method and a digital demodulation device in which the same frequency band is shared and the frequency utilization efficiency is improved when multi-valued FSK is used.

[0015]

The first feature of the present invention is to:
On the transmitting side, a signal subjected to differential multilevel FSK modulation is transmitted,
On the receiving side, the frequency discriminator determines the frequency of each symbol of the received signal, or the received signal is transformed into a frequency spectrum by Fast Fourier Transform (FFT) for each symbol, and the frequency of the component with the maximum power in the frequency spectrum. Or obtain the frequency of the received signal by interpolating the observed frequency by the fast Fourier transform based on the component with the maximum power and the adjacent component, and calculate the frequency from the frequency obtained for the symbol one symbol before. The amount of displacement is calculated, a block consisting of a combination of a fixed number of bits is uniquely associated with the amount of frequency displacement, and the bits in the block are output as demodulation data to demodulate the received signal. Especially.

A second feature of the present invention is that, on the transmitting side, the differential multilevel FSK modulated signal is multiplied by a code signal that periodically repeats a fixed pattern to perform secondary modulation by direct spreading, and on the receiving side. The despreading of the received signal is performed by multiplying the received signal by a signal that periodically repeats a fixed pattern.

[0017]

Even if the received signal has a large frequency deviation, it is considered that the frequency deviation amounts of consecutive symbols of the signal multi-valued differentially FSK-modulated on the transmitting side according to the present invention are substantially equal, so that between consecutive symbols. The frequency difference of is not affected by the frequency shift amount. On the other hand, on the receiving side, a frequency discriminator or F
Since the frequency of each symbol is detected by FT and the data is demodulated from the frequency difference between consecutive symbols, it is not necessary to perform frequency synchronization or phase synchronization for the frequency deviation, and moreover, it is detected as described above. The frequency difference is not affected by the frequency shift, so that the demodulation characteristic does not deteriorate due to the frequency shift.

In addition, by multiplying a multi-level FSK signal by a signal that periodically repeats a fixed pattern on the transmitting side to perform spread spectrum, a plurality of signals can share the same frequency band, and the multi-level signal can be shared. The frequency utilization efficiency can be greatly improved as compared with the case where the FSK signal is used without spectrum spreading.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a digital modulation / demodulation method and a digital demodulation device according to the present invention. In the figure, 1 is a serial-parallel conversion circuit, 2 is a frequency displacement amount determination circuit, 3 is a frequency modulation circuit, 4 is a frequency discriminator,
Reference numeral 5 is a frequency displacement amount determination circuit, and 6 is a data determination circuit.

First, in the modulator, the input binary data is divided into m bits by the serial / parallel conversion circuit 1 and is input to the frequency displacement amount determination circuit 2 collectively for m bits.

The frequency displacement amount determining circuit 2 is M (= 2 m).
The amount of frequency displacement is made to correspond one-to-one with each combination of m bits. To achieve this, for example,
A correspondence table of combinations of m bits and frequency displacement amounts may be prepared in advance, and a corresponding frequency displacement amount may be obtained by referring to the table for each input. The obtained frequency displacement amount is input to the frequency modulation circuit 3.

That is, as shown in FIG. 2, the serial-parallel conversion circuit 1 divides the input data into m bits. A block composed of delimited m-bit data is converted into a frequency displacement amount dFi by the frequency displacement amount determining circuit 2 and sent to the frequency modulation circuit 3 in accordance with, for example, a correspondence table shown in the figure.

A function f (b1, b2, ..., Bm) for calculating the frequency displacement amount for the m-bit inputs b1, b2 ,. Alternatively, the frequency displacement amount dFi may be calculated by calculating the function for each m-bit input data.

The frequency modulation circuit 3 shifts the modulation frequency for each symbol period according to the input frequency shift amount and outputs an FSK modulation signal. Here, the modulation frequency of the immediately preceding symbol is f0, and the input frequency displacement amount is d.
f, where f is the frequency of the new symbol, the frequency f
Can be expressed by the following equation (1). f = f0 + df (1) At this time, the conditions of the following expressions (2) to (4) may be added so that the modulation frequency does not go out of a certain frequency band. When fmin <f0 + df <fmax, f = f0 + df (2) When f0 + df> fmax, f = fmin + f0 + df-fmax (3) When f0 + df <fmin, f = fmax + f0 + df-fmin (4) Here, fmin and fmax are the lower limit frequency and the upper limit frequency of the modulation frequency band, respectively. In order for f to correspond one-to-one, the upper and lower limits of the frequency displacement amount dfmin
, Dfmax, the condition of the following equation (5) must be satisfied.

Fmax−fmin ≧ dfmax−dfmin (5) With respect to the frequency f determined in this way, a modulation signal represented by the following equation is output for one symbol period. X (t) = COS (2πft + θ) (nT ≦ t <(n + 1) T, T:
Symbol period) Here, the phase θ of the modulation signal may be an arbitrary value.

In this manner, the FSK-modulated signal is appropriately frequency-converted and then transmitted. In addition, in the configuration example described in FIG. 1 and the following, both the modulator and the demodulator are
Circuits for frequency conversion, amplification, etc. are omitted.

Next, the operation of demodulating the signal transmitted from the modulator with respect to the signal received via the transmission path will be described. In the demodulator, the frequency discriminator 4 first determines the frequency of each symbol period of the received signal. The frequency determination value is input to the frequency displacement amount determination circuit 5.

The frequency displacement amount determination circuit 5 determines the displacement amount of the frequency determination value for each symbol period based on the input frequency determination value. Here, if the frequency determination value of the immediately preceding symbol is fd0, the frequency determination value of a new symbol is fd, and the frequency displacement amount determination value is dfd, the frequency displacement amount determination value is expressed by equation (6). You can dfd = fd−fd0 (6) At this time, in order to prevent the frequency displacement amount judgment value dfd from being out of the range of the frequency displacement amount set by the modulator, equation (7)-
The condition of (9) may be added. When dfmin <fd-fd0 <dfmax, dfd = fd-fd0 (7) fd-fd0> dfmax, dfd = fmin + fd-fd0-fmax (8) fd-fd0 <dfmin, dfd = fmax + Fd-fd0-fmin (9) Here, dfmin and dfmax are the lower limit and the upper limit of the frequency displacement amount, respectively.

When the transmission frequency of the modulated signal transmitted from the modulator can be correctly determined, the following equation (10) is established, so that the frequency displacement amount given by the modulator can be correctly determined. fd−fd0 = f−f0 (10) For example, when the modulator determines the modulation frequency according to the equation (1), the demodulator can determine the frequency displacement amount according to the equation (6). dfd = fd-fd0 = f-f0 = df, and the frequency displacement amount df set by the modulator is correctly determined.

Further, when the frequency displacement amount is determined in accordance with the equations (2) to (4) in the modulator, the frequency displacement amount may be determined in the demodulator according to the equations (7) to (9).

When fmin <f0 + df <fmax, the equation is
Since the modulation frequency is determined according to (2), f = f0 + df, and in the demodulator, fd-fd0 = f-f0 = df, and dfmin <df <dfmax.
As a result, dfd = fd−fd0 = df, and the amount of frequency displacement given by the modulator can be correctly determined.

When f0 + df> fmax, the modulation frequency is determined according to the equation (3), and therefore f = fmin + f0 + df-fmax. On the other hand, in the demodulator, from the relation of the equation (5), fd -Fd0 = f-f0 = df + fmin-fmax≤df-
(Dfmax-dfmin)) = dfmin + (df-dfmax)
) <Dfmin, dfd = fmax + fd−fd0−fmin = fmax + (df + fmin−fmax) −fmin = df is obtained from the equation (9), and the frequency displacement amount given by the modulator is correctly determined. You can

Next, when f0 + df <fmin, the expression
Since the modulation frequency is determined according to (4), f = fmax + f0 + df−fmin, and in the demodulator, from the relation of equation (5), fd−fd0 = f−f0 = df + fmax−fmin ≧ df +
(Dfmax-dfmin) = dfmax + (df-dfmin
)> Dfmax, so dfd = fmin + fd−fd0−fmax = fmin + (df + fmax−fmin) −fmax = df is obtained from the equation (8), and the frequency displacement given by the modulator is also correctly determined. You can

Even in the case where the modulator and demodulator perform frequency conversion on the signal after modulation and before demodulation,
Since the frequency difference is kept constant, the frequency displacement amount can be correctly determined in the same manner.

The frequency displacement amount determination value thus obtained is input to the data determination circuit 6. The data determination circuit 6 associates M (= 2 ^m ) combinations of m bits with the frequency displacement amount determination value. In order to realize this, for example, a correspondence table (see FIG. 2) of the same m-bit combinations and frequency displacement amounts that are used in the modulator is prepared in advance, and the frequency displacement amount determination value is set in reverse to the modulator. The corresponding m-bit combination may be obtained by referring to the table for each input of. At this time, when the input frequency displacement amount determination value does not match any of the frequency displacement amounts shown in the correspondence table, m corresponding to the frequency displacement amount closest to the determination value among the frequency displacement amounts shown in the correspondence table. You may ask for a combination of bits.

In the modulator, an m-bit input b1,
Function f for calculating the amount of frequency displacement for b2, ..., bm
When the frequency displacement amount is calculated using (b1, b2, ..., Bm), the inverse function f ⁻¹ of the function f is used to calculate the frequency displacement amount of the m-bit with respect to the input frequency displacement amount determination value. The combination may be calculated. The obtained combination of m bits is output as demodulation data.

Next, a second embodiment of the present invention will be described. In this embodiment, as shown in FIG. 3, a fast Fourier transform circuit 40 and a frequency determination circuit 41 are used instead of the frequency discriminator 4 of FIG. 1 to determine the frequency of a received signal for each symbol. Is.

In FIG. 3, the operation of the modulator is the same as the operation of the modulator in FIG. In the demodulator, the fast Fourier transform circuit 40 obtains the power spectrum of the received signal for each symbol. It should be noted that the frequency band to be observed may be wider than the modulation frequency band by the amount of frequency shift that is assumed to occur in the transmission path. That is, when the maximum frequency shift amount dF is assumed for the modulation frequency band of fmin to fmax,
The band from fmin-dF to fmax + dF may be observed.

The frequency judging circuit 41 judges the frequency of the received signal by using the obtained power spectrum as an input. The frequency determination value can be obtained as follows.

For example, the observed frequency by the Fast Fourier Transform (FFT) is i · fstep (fmin−dF <i · fstep
<Fmax + dF), if the modulation frequency f matches one of the observed frequencies as shown in FIG. 4A, that is, if f = k · fstep, then the observed frequency is The modulation frequency can be accurately determined by taking the peak value of the spectrum component of k · fstep and simply setting the frequency of the spectrum component having the maximum power as the frequency determination value.

However, in general, the modulation frequency f does not always coincide with one of the observed frequencies, and as shown in FIG. 7B, k · fstep <f <(k + 1) · fst
It becomes ep. At this time, assuming that the frequency of the spectrum component with the maximum power is the frequency determination value, the frequency determination value is k.
· Fstep or (k + 1) · fstep, which causes an error with respect to the modulation frequency f. If the step size fstep of the observation frequency is sufficiently small, this error will not be a problem. Step size fst
If ep cannot be reduced, the frequency of the received signal may be calculated by interpolation from the power of the spectrum component having the maximum power and the power of the adjacent spectrum component in order to increase the frequency determination accuracy, and may be used as the frequency determination value. That is, the power spectrum component at the observation frequency k · fstep | A (k) |
^2, observation frequency (k + 1) · Power spectral components in fstep | A (k + 1) | 2 with respect, may be obtained frequency determination value fd by the following equation. fd = (k + | A (k + 1) | / (| A (k) | + | A (k + 1) |))
Fstep The frequency judgment value thus obtained is input to the frequency displacement amount judgment circuit 5.

The operations of the frequency displacement amount determination circuit 5 and the data determination circuit 6 are the same as those of FIG.

As in this embodiment, the fast Fourier transform (F
When frequency determination is performed using FT), there is an advantage that the frequency determination accuracy can be made higher than that of the frequency discriminator in a state where the signal-to-noise power ratio (S / N) of the received signal is low.

Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, a direct spreading circuit is added to the modulator in FIG. 3 and a despreading circuit is added to the demodulator to perform spread spectrum.

In the modulator, the operations of the serial-parallel conversion circuit 1, the frequency displacement amount determination circuit 2 and the frequency modulation circuit 3 are the same as those of FIG. Direct diffusion circuit 7
Outputs a signal obtained by multiplying the FSK modulation signal input from the frequency modulation circuit 3 by a signal which repeats a fixed pattern set in advance at a constant cycle. As the fixed pattern, a pattern whose frequency bandwidth is about the same as or wider than the bandwidth of the FSK modulated signal is selected. As a result, the spectrum of the modulated signal is spread, and a plurality of signals have different patterns with low correlation with each other. With the above method, the same band can be shared by a plurality of signals.

In the demodulator, the despreading circuit 8 performs despreading by multiplying the received signal by the fixed pattern used in the direct spreading circuit 7 of the modulator at a constant cycle. At this time, the phase of the fixed pattern to be multiplied is synchronized with the phase of the fixed pattern used for spreading the signal to be demodulated.

For example, as shown in FIG. 6, the frequency spectrum for each symbol of the FSK modulation signal (signal A) output from the frequency modulation circuit 3 is a line spectrum having a component of only the modulation frequency, whereas it is spread. The spectrum of a signal (signal C) spread by multiplying by a spreading code (signal B) having a certain frequency spectrum also becomes a signal having an equivalent spread. In the despreading circuit 8, the signal C
On the other hand, the despread signal (signal E) is obtained by multiplying the despread code (signal D) that is exactly the same as the spreading code (signal B). The signal E obtained in this way becomes equivalent to the signal A, and the frequency spectrum for each symbol also becomes a line spectrum, so that demodulation can be performed by performing frequency determination.

On the other hand, when a signal obtained by spreading an FSK modulated signal (signal A ') different from that in FIG. 6 with a different spreading code (signal B') is despread with the same despreading code (signal D) as in FIG. 6, FIG. As shown in, the despread signal (signal E ')
The frequency spectrum of is not a line spectrum but a broad spectrum. That is, demodulation cannot be performed by despreading with a code different from the spreading code.

When two spread signals C and C'are simultaneously transmitted, the despread code D (= B) corresponding to the spread signal C
When the signal is despread by, the obtained signal (signal E ″) becomes a signal E that interferes with the signal E to be demodulated, as shown in FIG.
It is a composite of ´. Therefore, the frequency spectrum for each symbol is a combination of the line spectrum corresponding to the signal E and the spread spectrum corresponding to the signal E ′, and the line spectrum of the signal E to be demodulated can be easily discriminated. That is, even if there are a plurality of modulated signals that share the same band, it is possible to extract only the signal to be demodulated and demodulate it.

In FIG. 6, FIG. 7 and FIG. 8, the spread code period is made equal to the symbol period for the sake of convenience.
In implementing the present invention, the period of the spreading code does not necessarily have to be equal to the symbol period.

The signal despread as described above is demodulated by the fast Fourier transform circuit 40, the frequency judging circuit 41, the frequency displacement amount judging circuit 5 and the data judging circuit 6, and these circuits are shown in FIG. Operates in the same manner as those operations.

[0052]

When the modulated signal is subject to frequency deviation and frequency fluctuation due to the influence of Doppler shift or the like on the transmission line, the frequency deviation amount can be regarded as substantially equal between consecutive symbols. At this time, for the assumed maximum frequency shift amount dF, fmin-dF to fma in the demodulation circuit.
When the frequency is determined by observing the band of x + dF, the frequency determination values fd0 and fd are fd0 = f0 + foffset fd = f + foffset for the transmission frequencies f0 and f of two consecutive symbols with the frequency shift amount as foffset. , And equation (10) still holds.

Therefore, according to the present invention, the frequency displacement amount given by the modulator can be correctly determined in the demodulator. That is, no matter how large the frequency deviation / variation occurs in the transmission line,
Data can be correctly demodulated without adding a circuit for tracking fluctuations and without performing initial acquisition of frequency.

Further, in the case of performing spread spectrum, in a plurality of modulators for generating a plurality of modulated signals using the same frequency band, direct spread is performed in advance using fixed patterns having low mutual correlation. . On the other hand, in the demodulator, since despreading is performed by the fixed pattern used for spreading the signal to be demodulated, the signal spread by another pattern does not have a specific frequency component even after despreading, Only the signal to be demodulated will have the modulation frequency component after despreading.

Therefore, according to the present invention, even if there are a plurality of modulated signals sharing the same band, it is possible to extract only the signal to be demodulated and demodulate it. That is, by sharing the frequency band, it is possible to significantly improve the spectrum utilization efficiency as compared with the case where the multilevel FSK signal is used without spectrum spreading.

Further, from the above, the present invention is suitable for a modulation / demodulation method and apparatus in land mobile communication and mobile satellite communication in which a large frequency shift / variation occurs on a transmission line and high spectrum utilization efficiency is desired. , And can contribute to higher quality and higher reliability of those communications.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a digital modulation / demodulation device used in a digital modulation / demodulation method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing correspondence between input data and frequency displacement amount.

FIG. 3 is a block diagram showing a configuration example of a digital modulation / demodulation device used in a digital modulation / demodulation method of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a frequency determination method by FFT.

FIG. 5 is a block diagram showing a configuration example of a digital modulation / demodulation device used in a digital modulation / demodulation method according to a third embodiment of the present invention.

FIG. 6 is a waveform diagram showing the operation of the direct spreading circuit and the despreading circuit of FIG.

FIG. 7 is a waveform diagram showing that demodulation cannot be performed by despreading with a code different from the spreading code.

FIG. 8 is a waveform diagram showing an operation of demodulating one signal from a combined signal of two spread signals.

FIG. 9 is a block diagram showing a configuration example of a conventional digital modulation / demodulation device.

FIG. 10 is an explanatory diagram showing the correspondence between conventional input data and modulation frequencies.

FIG. 11 is a waveform diagram showing an example of FSK modulation.

FIG. 12 is a waveform diagram showing the operation of a conventional frequency discriminator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Serial-parallel converter, 2 ... Frequency displacement amount determination circuit, 3 ... Frequency modulation circuit, 4 ... Frequency discriminator, 5 ... Frequency displacement amount determination circuit, 6 ... Data determination circuit, 7 ... Direct spread circuit, 8 ...
Despreading circuit, 20 ... Frequency determination circuit, 30 ... Frequency modulation circuit, 40 ... Fast Fourier transform circuit, 41 ... Frequency determination circuit.

Claims (8)

[Claims] 1. A transmission side divides input data into blocks by dividing each of a fixed number of bits, and makes a frequency displacement amount correspond one-to-one to a combination of bits in each block. Multi-valued frequency shift keying (FSK) modulation is performed by displacing the frequency of the modulated signal for each symbol according to the amount, and the frequency of the received signal is obtained for each symbol by the frequency discriminator on the receiving side. A displacement amount from the frequency obtained for the symbol before the symbol is calculated, a block consisting of a combination of a fixed number of bits is uniquely associated with the frequency displacement amount, and the bits in the block are output as demodulation data. The digital modulation / demodulation method is characterized in that the received signal is demodulated by. 2. On the transmitting side, input data is divided into blocks each having a fixed number of bits, and each block is associated with a frequency displacement amount in a one-to-one correspondence with a combination of bits in the block. Multivalued frequency shift keying (FSK) modulation is performed by displacing the frequency of the modulated signal for each symbol according to the amount, and the received signal is converted into a frequency spectrum by the fast Fourier transform for each symbol at the receiving side, The frequency of the component having the maximum power in the spectrum is obtained, the displacement amount from the frequency obtained for the symbol one symbol before is calculated for the frequency, and the displacement amount for the frequency is calculated as
A digital modulation / demodulation method characterized in that a block made up of a fixed number of bits is uniquely associated with each other, and the bits in the block are output as demodulation data to demodulate a received signal. 3. On the transmitting side, input data is divided into blocks each having a fixed number of bits, and each block is associated with a one-to-one frequency displacement amount with respect to a combination of bits in the block. Multivalued frequency shift keying (FSK) modulation is performed by displacing the frequency of the modulated signal for each symbol according to the amount, and the received signal is converted into a frequency spectrum by the fast Fourier transform for each symbol at the receiving side, The frequency of the received signal is determined by interpolating the observed frequency by the fast Fourier transform based on the component having the maximum power and the adjacent component in the spectrum, and the displacement from the frequency obtained for the symbol one symbol before Calculate the amount and uniquely identify a block consisting of a certain number of bit combinations for the frequency displacement amount. Is response, the digital modulation and demodulation method is characterized in that so as to demodulate the received signal by outputting the bits in the block as demodulated data. 4. A signal on the transmitting side that performs spread spectrum modulation by multiplying an FSK modulated signal by a code signal that periodically repeats a fixed pattern, and a signal on the receiving side that periodically repeats the same fixed pattern as on the transmitting side. 4. The despreading of the received signal is performed by multiplying the received signal by.
A digital modulation / demodulation method according to any one of 1. 5. A means for discriminating the frequency of a received signal for each symbol, a means for calculating a displacement amount from the frequency obtained for a symbol one symbol before the frequency, and a constant number for the frequency displacement amount. A digital demodulation device comprising means for uniquely associating a block composed of a combination of bits and means for outputting the bits in the block as demodulated data. 6. A means for converting a received signal into a frequency spectrum by a fast Fourier transform for each symbol, a means for obtaining a frequency of a component of the frequency spectrum having the maximum power, and the received signal obtained by the means. For each symbol, a means for calculating a displacement amount from the frequency obtained for the symbol one symbol before the frequency, and a block composed of a combination of a fixed number of bits for the frequency displacement amount. A digital demodulating device comprising means for uniquely associating and means for outputting bits in the block as demodulated data. 7. A means for converting a received signal into a frequency spectrum by fast Fourier transform for each symbol, and interpolating an observed frequency by the fast Fourier transform based on a component having the maximum power and an adjacent component in the frequency spectrum. And a means for determining the frequency of the received signal, a means for determining the frequency of the received signal obtained by the means for each symbol, and a displacement amount from the frequency obtained for the symbol one symbol before the frequency. And a means for uniquely associating a block composed of a combination of a fixed number of bits with the frequency displacement amount, and a means for outputting the bits in the block as demodulated data. Demodulator. 8. A means for despreading the received signal by multiplying the received signal by a signal that periodically repeats a fixed pattern, before the means for determining the frequency of the received signal for each symbol. The digital demodulator according to any one of claims 5 to 7.