JPH10164151A - Method, device for fsk demodulation and data receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute demodulation after permitting reception FSK modulation wave to be an excellent state in a state where frequency difference with a reception local signal is cancelled by reducing a hardware amount. SOLUTION: Reception FSK(frequency shift keying) modulation wave is converted into an intermediate frequency, obtained as a voltage corresponding to a data 1 or 0 state by frequency detection by a frequency discriminator 8 after that and, then, data-modulated by judgement in an identifier 11 by a data judging threshold value. In this case, in parallel with that, the shift state of the output of frequency detection is monitored by a demultiplexer 13 and a multiplier 16, etc. When the data judging threshold value is updated and set for the portion of shifting detected by the monitoring, reception FSK modulation wave is in the excellent state so as to be demodulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The signal transmitted as a modulated wave is received on the receiving side,
The present invention relates to an FSK demodulation method when demodulated as data and an apparatus thereof, and further relates to a data reception method when frequency fluctuation between transmission / reception points is large, such as satellite communication and high-speed mobile communication.

[0002]

2. Description of the Related Art FIG. 4 shows a configuration of a demodulating apparatus according to the prior art when an FSK modulated wave is demodulated by frequency detection. In this case, the FSK transmitted from the transmitting side
(Frequency Shift Keying: modulation index is arbitrary) A signal as a modulated wave is received via the antenna 1 on the receiving side. The received signal is then band-limited by a band-pass filter (BPF) 2 and required by a low-noise amplifier (LNA) 3 in a state in which out-of-band noise components have been removed. The signal power is amplified up to the power. After the amplification, the first local signal from the first local signal generator 5 is multiplied by the mixer 4, and as a result of the multiplication, the sum and difference components of the received carrier frequency and the first local frequency are obtained. Of these components, BP
By extracting only the difference component by F6, conversion to an intermediate frequency (IF) is performed.

[0003] The IF signal obtained as described above is then subjected to frequency detection by the frequency discriminator 8 in a state in which the power is amplified and the amplitude is limited by the amplitude limiter 7, so that the received signal is biased (high). , Low), the voltage (including the polarity) of the magnitude corresponding to the degree is obtained. This voltage is then further applied to a low-pass filter (LPF: Low-pass filter).
The high-frequency component is removed by the Pass Filter 9 and the voltage is obtained as a voltage corresponding to the state of the transmission data. This voltage is compared with a reference voltage level (data determination threshold) by the discriminator 11 so that the transmission data is The data is demodulated as data 1 and 0 (for reference, the above configuration and demodulation principle are described in “Digital Communication Technology” (1986)).
Published by Tokai University Press, March 25, pp. 206-21
2))).

FIG. 5 shows the FS in the case where the influence of the Doppler shift cannot be ignored, such as in the case of satellite communication or high-speed mobile communication, that is, when the frequency fluctuation of the transmission / reception point is large.
3 shows a configuration of a K demodulator. As shown, the difference from the one shown in FIG. 4 is that the first local signal (1st local) generator 5
Instead of so-called automatic frequency control (AFC: Auto Fre
quency control) circuit. The IF signal in a state where the power is amplified and the amplitude is limited by the amplitude limiter 7 is input to the frequency discriminator 8 while
The signal is input to a phase difference calculator 20 in the AFC circuit. The phase difference calculator 20 calculates a frequency error with respect to a received local signal, and further passes a voltage controlled oscillator (VCO) through a loop filter 21.
r) 22 is given as a control voltage. By controlling the oscillation frequency of the VCO 22 so as to eliminate the frequency error from the received local signal, a baseband signal having no frequency error is obtained from the frequency discriminator 8.

[0005]

However, in the case of the demodulator shown in FIG. 4, since the data is demodulated by determining whether the output of the frequency discriminator is positive or negative, the frequency error .DELTA.f is modulated. If the degree is negligibly small, the inter-code distances for data "1" and "0" are both equal, as shown in FIG. 6A, and demodulation can be performed efficiently. On the other hand, as the frequency error Δf increases, the output of the frequency discriminator shifts from the reference voltage level (ground level) by an amount corresponding to Δf as shown in FIG. 6B. It is unavoidable that the inter-symbol distance is reduced and the BER (Bit Error Rate) characteristic is degraded.

On the other hand, in order to avoid such a problem, as shown in FIG. 5 described above, a method of causing a local signal to follow a frequency fluctuation between transmission and reception by an AFC circuit has been generally adopted. In addition to the fact that the frequency pull-in range is limited by the modulation speed, the circuit scale cannot be reduced.

[0007] A first object of the present invention is to demodulate a received FSK modulated wave in a good state without using AFC and in a state where the frequency error with respect to a received local signal has been eliminated by reducing the amount of hardware. An FSK demodulation method and apparatus are provided. A second object of the present invention is to provide, in addition to the first object, an FSK demodulation method capable of demodulating a received FSK modulated wave in a good state and demodulating the received FSK modulated wave in a state where a frequency error with respect to a received local signal has been eliminated from the beginning of reception. To provide the device. A third object of the present invention is to provide an AF control system even when frequency fluctuation between transmission and reception points is large, such as in satellite communication and high-speed mobile communication.
It is an object of the present invention to provide a data receiving method capable of demodulating a received FSK modulated wave in a good state without relying on C and reducing the amount of hardware and eliminating the frequency error from the received local signal. A fourth object of the present invention, in addition to the third object, is to provide a data receiving method capable of demodulating a received FSK modulated wave in a good state in a state where a frequency error with a received local signal has been eliminated from the beginning of reception. To serve.

[0008]

Means for Solving the Problems As various methods for the above purpose, basically, a received signal is converted into an intermediate frequency, and data 1 and 2 are detected by frequency detection by frequency discrimination.
It is obtained as a voltage corresponding to the 0 state, and is determined by the data determination threshold. When demodulation of data 1 and 0 is performed as a determination result, the output of frequency detection is shifted in parallel with the demodulation. This is achieved by monitoring the state, and updating and setting the data determination threshold by the amount of shift detected by this monitoring.
As a component thereof, a voltage corresponding to each of the data 1 state and the data 0 state is separated by using a determination result based on the data determination threshold as a selection signal, and a voltage as a moving average over time is detected, and the data 1 state is handled. Threshold update setting means for continuously updating and setting a data determination threshold by adding and averaging a moving average voltage and a moving average voltage corresponding to a data 0 state, or a determination result by a data determination threshold only during demodulation of a preamble Is used as a selection signal to separate voltages corresponding to the data 1 state and the data 0 state, and detect a voltage as a moving average over time, and obtain a moving average voltage corresponding to the data 1 state and a moving average voltage corresponding to the data 0 state. This is achieved by providing at least threshold update setting means for updating and setting the data determination threshold at regular intervals using the arithmetic mean of .

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention.
3 will be described with reference to FIG. First, before starting the specific description of the present invention, its outline or its theoretical background will be described. As already described with reference to FIG. 6B, if an error Δf occurs in the carrier frequency between transmission and reception, the waveform of the frequency detection output appears as a state shifted by an amount corresponding to Δf. If the comparison is made at the ground level as the threshold value, a problem such as a decrease in inter-symbol distance is caused. In such a case, the data determination threshold value follows the frequency error Δf and is shifted by an amount corresponding to Δf. Thus, the data determination may be performed. For this purpose, the shift state of the frequency detection output corresponding to each of the transmission data 1 and 0 is monitored, and the data determination threshold value may be updated and set by the shift detected by the monitoring. Specifically, transmission data 1,
It is only necessary to update and set the data determination threshold using the average of these moving averages while moving average the frequency detection outputs corresponding to each of the 0s over time.

Now, the present invention will be described in detail with reference to FIG.
1 shows a configuration of an example of the FSK demodulator according to the present invention.
As shown in the drawing, a substantial difference from the one shown in FIG. 4 is that the data determination threshold set for the discriminator 11 is set to be updatable based on the monitoring result for the frequency detection output. Yes, and the rest is the same as that shown in FIG.

Here, how the data determination threshold value is updated will be described. The frequency detection output from the frequency discriminator 8 from which the high-frequency component has been removed is discriminated by the discriminator 11. While the data is being demodulated by being compared with the data determination threshold at the point in time, in parallel with this data demodulation, the frequency detection output also has its shift state monitored. . That is, in the monitoring method in this example, the demodulated data (determination result) from the discriminator 11 is used as a selection signal, and the frequency detection output from the frequency discriminator 8 is output from the demultiplexer 13 to the data 1
After being separated and sorted according to the state and the data 0 state, the moving average over the time in each of the LPFs 14.1 and 14.2 is obtained with high responsiveness and continuously. Further, these moving averages are added to the adder 1
After addition at 5, the multiplier 16 obtains the average of the addition, and the average is continuously updated and set as the data determination threshold.

The monitoring method will be described in more detail with reference to FIG. 6B. If a frequency error Δf occurs, the frequency detection output shifts from the center level (ground level) by Δf. It has already been described that the waveform appears as the waveform in the state shown in FIG.
By the way, in the demultiplexer 13, the center sample value (indicated by a circle) in one symbol (1 / modulation rate) section is determined by the LPF 14.1, 1 according to the determination result from the discriminator 11.
4.2, the LPFs 14.1 and 14.2 respectively cover a plurality of symbol sections because the sorted ones include noise components and fluctuations due to bit synchronization errors. As a result of the moving averaging, the sorted items can be averaged in a smooth envelope shape.

Here, Δf = 0, C (Carrier) / N (N
oise) = frequency at ∞ detection output of the V _H (data 1 corresponding), V _L (data 0 corresponds), if the output offset by Δf and V _dF, as LPF14.1 output V _H + V _dF, also, LPF 14 .2 outputted from the is determined as V _L + V _dF, after all, as a V _H = -V _L,
The data determination threshold value V _TH is obtained as follows.

[0014]

(Equation 1)

Thus, the frequency error Δ in the initial state
When f is within the data discriminable range, the data judgment threshold value V _TH can follow the frequency error Δf.

However, in this method, since the data distribution by the demultiplexer 13 is performed based on the judgment result from the discriminator 11, if | V _dF |> | V _H |, In the state of | V _L |, the distribution to the LPFs 14.1 and 14.2 is not performed correctly, and the data determination threshold value V _TH cannot follow Δf. To avoid this problem, the transmitting side inserts a preamble whose data pattern is known into the transmission data at regular intervals, while the receiving side inserts the data determination threshold V _TH only when the preamble is received.
Should be updated and set. Of course,
In this method, it is necessary to transmit a preamble as redundant data irrelevant to the transmission data, so that it is unavoidable that the efficiency is reduced in frequency utilization.
In any case, since all corrections for the frequency error Δf can be processed in the baseband band, firmware processing by a DSP or the like becomes possible, and the circuit scale is reduced, and the implementation is simple and easy. It has been accepted.

Finally, the case where frequency detection is performed by digital signal processing will be described. FIG. 2 shows the configuration in that case. As shown, the configuration and operation up to the amplitude limiter 7 are the same as those shown in FIG. Here, the configuration and operation after the amplitude limiter 7 will be described. The output of the amplitude limiter 7 is branched in two directions, and the output of the second local signal generator 18 is π /
2nd local signal with two phases shifted and mixer 17.1, 1
LPF 19.1, 19.2 after multiplication by 7.2
(I: Inphase), quadrature (Q: Quadrature)
And A / D converters 12.1,
The digitally converted state according to 12.2 is digitally processed by the frequency discriminator 8.

In the digital processing, the frequency detection is performed by plotting the I and Q components on the IQ axis and determining the phase change amount Δφ within a minute time interval Δt. It is. FIG. 3 shows how the phase changes on the IQ axis. For example, assuming that the phase changes from a (I1, Q1) to b (I2, Q2) from time t1 to t2, The phase difference Δφ is approximately (I1 ×
Q2−Q1 × I2). Therefore, the frequency component F is obtained as follows, where the modulation index is m.

[0019]

(Equation 2)

By the above calculation, a constant value can be obtained as an output after frequency discrimination regardless of the modulation index m.

[0021]

As described above, according to the first to third aspects, the reception FSK is eliminated without using the AFC, and with the frequency error from the reception local signal eliminated by reducing the amount of hardware. The FSK demodulation method and the FSK demodulation method capable of demodulating a modulated wave in a good state are provided. In the case of the fourth and fifth aspects, the reception FSK modulation is performed in a state where a frequency error with a reception local signal is eliminated from the beginning of reception. An FSK demodulation method and apparatus capable of demodulating a wave in a good state is further provided by the AFC even in the case of claim 6 even when the frequency fluctuation between transmission and reception points is large, such as in satellite communication or high-speed mobile communication. A data reception method capable of demodulating a received FSK modulated wave in a good state without causing a frequency error with respect to a received local signal by reducing the amount of hardware and reducing the amount of hardware. Still further, according to the seventh aspect, a data receiving method capable of demodulating a received FSK modulated wave in a good state and demodulating the received FSK modulated wave in a state in which a frequency error with a received local signal has been eliminated from the beginning of reception can be obtained. ing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of an FSK demodulator according to the present invention;

FIG. 2 is a diagram showing a configuration of an example of an FSK demodulator according to the present invention when frequency detection is performed by digital signal processing;

FIG. 3 is a diagram for explaining a frequency component calculation method in digital frequency detection.

FIG. 4 is a diagram showing a configuration of a demodulation device according to the related art when demodulating an FSK modulated wave by frequency detection.

FIG. 5 is a diagram illustrating a configuration of an FSK demodulator when a frequency variation at a transmission / reception point is large;

FIGS. 6A and 6B are diagrams for explaining the principle of data demodulation by determining whether the output of the frequency discriminator is positive or negative, and a problem in the data demodulation;

[Description of Reference Codes] 1 antenna, 2 band-pass filter, 3 low-noise amplifier, 4, 17.1, 17.2 mixer, 5 first local oscillator, 6 band-pass filter Wave filter, 7 ... Amplitude limiter, 8 ...
Frequency discriminator, 9, 14.1, 14.2, 19.1, 1
9.2: Low-pass filter, 10: Bit synchronization circuit, 11
... Identifier, 12.1, 12.2 A / D converter, 13 ...
Demultiplexer, 15 ... Adder, 16 ... Multiplier, 18
... Second local oscillator

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Soichiro Kotaki 216 Totsukacho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture

Claims (7)

[Claims] An FSK demodulation method in which a signal transmitted as an FSK modulated wave from a transmitting side is received by a receiving side and then demodulated as data, wherein the received signal is converted to an intermediate frequency. After that, after being obtained as a voltage corresponding to the data 1, 0 state by frequency detection by frequency discrimination, by being determined by the data determination threshold,
When demodulation of data 1 and 0 is performed as a determination result,
An FSK demodulation method in which the shift state of the output of the frequency detection is monitored in parallel with the demodulation, and the data determination threshold value is updated and set by the shift detected by the monitoring. 2. An FSK demodulation method in which a signal transmitted as an FSK modulated wave from a transmitting side is received by a receiving side and then demodulated as data, wherein the received signal is converted to an intermediate frequency. After that, after being obtained as a voltage corresponding to the data 1, 0 state by frequency detection by frequency discrimination, by being determined by the data determination threshold,
When the data 1 and 0 are demodulated as the determination result, the determination result based on the data determination threshold is used as the selection signal and the data 1 and 0 are demodulated.
A voltage corresponding to each of the state and the data 0 state is separated, a voltage as a moving average over time is detected, and data determination is performed based on an addition average of the moving average voltage corresponding to the data 1 state and the moving average voltage corresponding to the data 0 state. FSK demodulation method in which the threshold for use is continuously updated and set. 3. An FSK demodulator for receiving a signal transmitted as an FSK modulated wave from a transmitting side on a receiving side and demodulating the data as data, comprising: frequency conversion means for converting the received signal to an intermediate frequency; Frequency detecting means for detecting the intermediate frequency from the frequency converting means by frequency discrimination and outputting a voltage corresponding to the data 1,0 state; and detecting the data 1,0 state from the frequency detecting means. A data determination unit that demodulates data 1 and 0 as a determination result by determining the voltage using the data determination threshold;
Using the determination result based on the data determination threshold as a selection signal, a voltage corresponding to each of the data 1 state and the data 0 state is separated, and a voltage as a moving average over time is detected. FSK including at least threshold update setting means for continuously setting and updating a data determination threshold using an addition average with a 0-state-corresponding moving average voltage.
Demodulator. 4. An FSK demodulation method in which a signal transmitted as a FSK modulated wave from a transmitting side and having a preamble inserted at regular intervals is received by a receiving side and demodulated as data. Then, after the received signal is converted to the intermediate frequency, it is obtained as a voltage corresponding to the data 1 and 0 states by frequency detection by frequency discrimination, and is determined by the data determination threshold, thereby obtaining a determination result. When the data 1 and 0 are demodulated, only during the demodulation of the preamble is performed, the determination result based on the data determination threshold is used as a selection signal to separate the voltages corresponding to the data 1 state and the data 0 state, respectively, and to be separated in time. Of the data 1 state and the moving average voltage corresponding to the data 0 state, and a data determination threshold value. FSK demodulation method in which is updated and set at regular intervals. 5. An FSK for receiving a signal with a preamble inserted at regular intervals, which is transmitted from a transmitting side as an FSK modulated wave, at a receiving side and demodulating the signal as data.
An SK demodulation device, comprising: frequency conversion means for converting a received signal to an intermediate frequency; and frequency detection of the intermediate frequency from the frequency conversion means by frequency discrimination, and then outputting a voltage corresponding to the data 1, 0 state. Frequency detection means,
A data judging means for demodulating data 1 and 0 as a judgment result by judging a voltage corresponding to a data 1 and 0 state from the frequency detecting means by a data judging threshold, and only while demodulating a preamble is performed. By using the determination result based on the data determination threshold as a selection signal, voltages corresponding to the data 1 state and the data 0 state are separated, and a voltage as a moving average over time is detected. An FSK demodulator comprising: at least threshold update setting means for updating and setting a data determination threshold at regular intervals using an addition average with a data 0 state-corresponding moving average voltage. 6. A data receiving method in a case where frequency fluctuation between transmission and reception points is large, such as in satellite communication and high-speed mobile communication, wherein a signal transmitted as an FSK modulated wave from a transmission point is received at a reception point. After being converted to the intermediate frequency, the data is obtained as a voltage corresponding to the state of the data 1 and 0 by frequency detection by frequency discrimination, and is determined by the data determination threshold. At the time of demodulation, the determination result based on the data determination threshold is used as a selection signal to separate voltages corresponding to the data 1 state and the data 0 state, and a voltage as a moving average over time is detected to handle the data 1 state. Moving average voltage and data 0
A data receiving method in which a threshold value for data determination is continuously updated and set based on an addition average with a moving average voltage corresponding to a state. 7. A data receiving method in a case where frequency fluctuation between transmission / reception points is large, such as in satellite communication or high-speed mobile communication, wherein a preamble is transmitted as a FSK modulated wave from a transmission point and inserted at regular intervals. The received signal is received at the receiving point and is converted to an intermediate frequency. After that, the signal is obtained as a voltage corresponding to the data 1 and 0 states by frequency detection by frequency discrimination, and is determined by the data determination threshold. Thus, when data 1 and 0 are demodulated as the determination result, only during the demodulation of the preamble, a voltage corresponding to each of the data 1 state and the data 0 state is used as a selection signal using the determination result based on the data determination threshold as a selection signal. After separating, detecting the voltage as a moving average over time,
A data receiving method in which a data determination threshold is updated and set at regular intervals by adding and averaging a moving average voltage corresponding to a data 1 state and a moving average voltage corresponding to a data 0 state.