JPH09130300A - Multilevel frequency shift keying demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform demodulation at a high speed. SOLUTION: An FFT 10 for inputting modulation signals, performing a fast Fourier transformation processing and detecting plural frequency components included in the modulation signals and a maximum value selector 11 and a decoding circuit 12 for generating code word data signal, based on the plural frequency components detected by the FFT 10 and taking out binary data signal, based on the code word data signals are provided. By the constitution, since an envelope detector is not used and plural band-pass filters are not required, the demodulation is accurately performed at a high speed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to multi-level frequency shift keying (MFSK: Multilevel (or M-ary) Freq).
The present invention relates to a uency shift keying demodulator, and more particularly to a multi-value frequency shift keying demodulator capable of performing high-speed demodulation.

[0002]

2. Description of the Related Art Multivalued frequency shift keying (hereinafter referred to as MFSK) for converting a digital signal into a multifrequency modulated signal.
The modulation method is applied to, for example, a frequency hopping spread spectrum communication system. This communication system switches the transmission frequency of a data signal primary-modulated according to the MFSK system according to a spread code pulse, and spreads (disperses) the transmission frequency in a wide band. Therefore, this communication system is resistant to interference, has signal confidentiality, and enables high-resolution distance measurement, and is therefore widely used mainly in the fields of satellite communication and land communication.

FIG. 6 is a block diagram showing a receiver in a frequency hopping spread spectrum communication system. This receiving device includes an antenna 50, a primary demodulator 51 according to a frequency hopping method, and a 2nd order according to an MFSK method.
A second demodulator (MFSK demodulator) 52 is provided. The primary demodulator 51 includes a mixer 53, a frequency synthesizer 54 and a hopping pattern generator 55. The secondary demodulator 52 includes a plurality (eight in this case) of band pass filters (hereinafter referred to as BPFs) 56, a number of envelope detectors 57, a maximum value selector 58 and a decoding circuit 59 corresponding to each BPF 56. I have it.

The spread spectrum signal received by the antenna 50 is amplified by an amplifier (not shown). The mixer 51 mixes the amplified spread spectrum signal and the hopping local signal from the frequency synthesizer 54 in synchronization with each other, despreads the spread spectrum signal, and generates a primary demodulation signal. That is, the frequency synthesizer 54 switches the local oscillation frequency of the hopping local signal according to the same hopping pattern (despreading code) supplied from the hopping pattern generator 55 on the transmitting side.

Each BPF 56 has a frequency filter that passes different frequency bands, and each BPF 56 separates the primary demodulated signal into eight signals. Each envelope detector 57 performs envelope detection of the signal output from each corresponding BPF 56, and supplies the envelope output signal to the maximum value selector 58. The maximum value selector 58 is
A of the envelope output signal supplied from each envelope detector 57
D (analog-digital) conversion is performed to generate a codeword data signal as a received signal. For example, when the data is encoded on the transmitting side by the arrangement of frequencies appearing in 7 time slots, as shown in FIG.
8 produces a codeword data signal S having 7 codeword chips in a matrix of 8 frequency slots and 7 time slots. Then, the maximum value selector 58 performs maximum likelihood determination between the codeword data signal and a plurality of preset codeword pattern data signals. That is, in this maximum likelihood determination, the codeword pattern data having the highest degree of coincidence with the codeword data is selected as the transmitted codeword data. Thereby, the error of the transmission data is corrected. The decoding circuit 59 decodes the codeword pattern data signal selected by the maximum value selector 58 into a digital signal having a predetermined number of bits, and outputs this digital signal as a secondary demodulation data signal.

[0006]

In the receiver configured as described above, each envelope detector 57 includes a diode and acts as a so-called integrator, so that each detector inputs a signal. There is a problem that it takes time to output the envelope output signal after the start. Therefore, a delay occurs in the supply of the envelope output signal to the maximum value selector 58, and as a result, the maximum value selector 58 can quickly determine the code word data signal corresponding to the envelope output signal. I can't
There is a problem that it takes time to demodulate the secondary demodulated data from the primary demodulated signal.

Further, since each BPF 56 is an analog circuit, there are variations in the characteristics indicating the respective performances. Therefore, the maximum value selector 58 may not be able to accurately obtain the received signal via the envelope detector 57. Further, in order to separate the primary demodulated signal supplied from the mixer 53, eight BPFs 56 having different frequency bandwidths are required, which causes a problem that the circuit area increases.

The present invention has been made to solve the above problems, and an object thereof is to provide a multilevel frequency shift keying demodulator capable of performing demodulation at high speed and accurately.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 is a demodulator for extracting a data signal from a modulated signal in a communication system using a multi-value frequency shift keying system. Therefore, the gist of the present invention is to include arithmetic means for inputting the modulated signal and performing a fast Fourier transform, and extracting the data signal based on the arithmetic result of the arithmetic means.

According to a second aspect of the present invention, there is provided a demodulator for extracting a data signal from a modulated signal in a communication system using a multivalued frequency shift keying method, wherein the modulated signal is input to the fast Fourier transform. A detection means for performing a process to detect a plurality of frequency components included in the modulated signal; and a demodulation means for extracting the data signal based on the plurality of frequency components detected by the detection means. Use as a summary.

According to a third aspect of the present invention, in the demodulator according to the second aspect, the detecting means synchronizes a time window with a time slot assigned when the modulated signal is generated, and performs a fast Fourier transform process. The point is to do. According to a fourth aspect of the present invention, in the demodulator according to the third aspect, the demodulating means has a plurality of frequency components detected by the detecting means in a plurality of time windows synchronized with a predetermined number of the time slots. Codeword data generating means for generating a codeword data signal, an error correcting means for correcting an error of the codeword data signal generated by the codeword data generating means, and an error correcting means for correcting the error. The gist of the present invention is to include a conversion means for converting a code word data signal into the data signal.

According to a fifth aspect of the present invention, there is provided a demodulator for extracting a data signal from a modulated signal in a communication system using a multivalued frequency shift keying method, wherein the modulated signal is input to the fast Fourier transform. Processing means for detecting a plurality of frequency components and a plurality of phase components included in the modulated signal, and the data signal based on the plurality of frequency components and a plurality of phase components detected by the detecting means. The gist is to have a demodulation means for taking out.

According to a sixth aspect of the present invention, the demodulator according to any one of the second to fifth aspects allows the demodulator to pass a frequency band corresponding to a plurality of frequency components included in the modulated signal. And an AD converter for converting the modulated signal supplied from the band-pass filter into a digital signal and supplying the digital signal to the detecting means.

According to the first aspect of the invention, the fast Fourier transform of the modulated signal is performed by the computing means, and the data signal is extracted based on the result of the computation, so that the demodulation can be performed at high speed. Becomes Further, unlike the conventional configuration using a plurality of band pass filters, there is no variation in characteristics, so that demodulation can be performed accurately. According to the second aspect of the present invention, the fast Fourier transform processing is performed by the detection means to detect a plurality of frequency components included in the modulated signal, and the demodulation means is based on the detected plurality of frequency components. Then, the data signal is taken out. Therefore, without using an envelope detector as in the past,
Moreover, since there is no variation in characteristics, demodulation can be performed quickly and accurately.

According to the third aspect of the present invention, the fast Fourier transform process is performed by synchronizing the time window with the time slot assigned when the modulating signal is generated by the detecting means. Therefore, since a plurality of frequency components of the modulated signal are detected in synchronization with the time slot, demodulation can be performed reliably. According to the invention described in claim 4, the codeword data generating unit generates the codeword data signal based on the plurality of frequency components detected in the plurality of time windows synchronized with the predetermined number of time slots. The error of the code word data signal is corrected by the error correcting means, and the code word data signal is converted into the data signal by the converting means. Therefore, since a plurality of frequency components of the modulated signal are detected for each predetermined number of time slots, the demodulation can be reliably performed.

According to the fifth aspect of the invention, the fast Fourier transform processing is performed by the detecting means to detect a plurality of frequency components and a plurality of phase components contained in the modulated signal, and the demodulating means detects the detected frequency component and phase components. A data signal is extracted based on the plurality of frequency components and the plurality of phase components thus obtained. Therefore, demodulation can be performed at high speed and accurately.

According to the sixth aspect of the present invention, the band pass filter allows the frequency band corresponding to the plurality of frequency components included in the modulation signal to pass therethrough, removes unnecessary signals, and the AD converter converts the modulation signal. Are converted into digital signals. Then, this digital signal is supplied to the detecting means, and the fast Fourier transform is performed. Therefore, it is not necessary to use a plurality of band pass filters having different frequency bandwidths as in the conventional case, the characteristics can be eliminated and demodulation can be accurately performed, and the circuit area can be simplified. .

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is embodied in a receiver in frequency hopping spread spectrum communication will be described below with reference to the drawings. This receiving device includes an antenna 1, a primary demodulator 2 according to a frequency hopping system, and a secondary demodulator (MFSK demodulator) according to an MFSK system.
3 is provided. The primary demodulator 2 includes a mixer 5, a frequency synthesizer 6 and a hopping pattern generator 7. The secondary demodulator 3 includes a band pass filter (hereinafter, BP
F) 8), AD (analog-digital) converter 9, fast Fourier transformer (hereinafter referred to as FFT) 10,
A maximum value selector 11 and a decoding circuit 12 are provided.

The mixer 5 is received by the antenna 1,
Further, the spread spectrum signal amplified by the amplifier (not shown) and the hopping local signal from the frequency synthesizer 6 are mixed in synchronization with each other to despread the spread spectrum signal and generate a primary demodulation signal. This one
The next demodulation signal is a signal modulated by the MFSK modulation method. That is, the frequency synthesizer 6 switches the local oscillation frequency of the hopping local signal according to the same hopping pattern (despreading code) supplied from the hopping pattern generator 7 on the transmitting side. In this embodiment, since the primary modulation scheme is a receiver in a frequency hopping spread spectrum communication system of MFSK modulation scheme of 8 frequencies, the frequency bandwidth of the primary demodulated signal after despreading is 8 frequencies. It is an area including.

The BPF 8 has a frequency filter, passes the band of 8 frequencies from the primary demodulated signal to remove unnecessary signals, and supplies it to the AD converter 9 as a baseband signal. The AD converter 9 has a BPF as shown in FIG.
The baseband signal from 8 is converted into a digital signal DS as shown in FIG.
Supply to T10.

The FFT 10 cuts out the digital signal from the AD converter 9 for each preset time window to perform fast Fourier transform, and simultaneously detects (extracts) a plurality of frequency components of the digital signal. Then, as shown in FIG. 2C, the FFT 10 supplies a plurality of frequency components in the digital signal to the maximum value selector 11. In addition,
In FIG. 2C, f indicates the sampling frequency of the AD converter 9. At this time, the time window when the FFT 10 cuts out the digital signal is MF on the transmitter side.
It is set to be synchronized with the time slot of SK modulation. The reason for this is that MFSK demodulation on the receiving device side is matched with MFSK modulation for converting the transmission data signal into a signal that forms a matrix of 8 frequency slots and 7 time slots on the transmitting device side. Therefore, by setting the time window in this way, the FFT 10 on the receiving device side can detect a plurality of frequency components of the digitized baseband signal in synchronization with the time slot. Then, the plurality of frequency components detected in this way are transmitted to the MFS on the transmitter side.
It corresponds to eight frequency slots assigned in K modulation. In this embodiment, 6-bit data is converted into 8 bits.
An example of encoding (M-ary FSK) by a sequence of seven frequencies selected so as not to overlap from each other will be described.

The maximum value selector 11 outputs the F from the FFT 10.
The FT output signal is monitored every predetermined number (7 in this case) of time slots, and as shown in FIG. 3, changes in frequency components showing a plurality of maximum amplitude values during 7 time slots (3 in FIG. 3). Only changes in frequency components are detected). Then, as shown in FIG. 4, the maximum value selector 11
In accordance with the change in the detected frequency component, a code word data signal S1 having a plurality of (7 in this case) code word chips is generated as a received signal in a matrix of 8 frequency slots and 7 time slots.

Further, the maximum value selector 11 has a plurality of types of codeword patterns preset according to the codeword data signal S1 and the type of bit pattern of the secondary demodulation data (64 types in this case). Maximum likelihood determination is performed with the data signal S2 to correct an error in transmission data. That is, the maximum value selector 11 selects the codeword pattern data having the maximum degree of coincidence with the codeword data as the transmitted codeword data in the maximum likelihood determination, and selects the selected codeword pattern data signal. S2 is supplied to the decoding circuit 12. The decoding circuit 12 decodes the codeword pattern data signal selected by the maximum value selector 58 into a digital signal having a predetermined number of bits (in this case, 6 bits) using a conversion table (not shown), and this digital signal 2
Output as the next demodulation data signal.

Next, the operation of the receiver configured as described above will be described. Received via antenna 1 and
The spread spectrum signal amplified by the amplifier (not shown) is mixed by the mixer 5 in synchronization with the hopping local signal from the frequency synthesizer 6. As a result, the spread spectrum signal is despread and a primary demodulation signal is generated. As shown in FIG. 2A, the primary demodulated signal passes through the band of 8 frequencies through the BPF 8 and is supplied to the AD converter 9 as a baseband signal. Next, as shown in FIG. 2B, the baseband signal is converted into a digital signal by the AD converter 9.

The digital signal is cut out by the FFT 10 for each preset time window, fast Fourier transform is performed, and a plurality of frequency components of the digital signal are simultaneously detected. At this time, the time window is set so as to be synchronized with the time slot for MFSK modulation on the transmitting device side. Then, as shown in FIG. 2C, a plurality of frequency components in the digital signal are supplied to the maximum value selector 11 as FFT output signals.

The FFT output signal supplied from the FFT 10 is monitored by the maximum value selector 11 for every 7 time slots, and as shown in FIG. (FIG. 3 shows only the changes of three frequency components) are detected. Then, as shown in FIG. 4, the maximum value selector 11 selects 8 frequency slots and 7 frequency slots according to the change in the detected frequency component.
In a matrix with time slots, a codeword data signal S1 having 7 codeword chips is generated. In this case, the generated code word data signal S1 is set to "2-5-0-4
―6―7-1 」. The code word data signal S1 is processed by the maximum likelihood determination using the 64 types of code word pattern data signals S2 preset by the maximum value selector 11. In this maximum likelihood determination, the codeword pattern data having the highest degree of coincidence with the codeword data is selected as the transmitted codeword data. In this case, the code word data signal S1
"2-5-0-4-6-7-1-1" and one of 64 types of codeword pattern data signal S2 "3-5-0-4-6-6-7-1"
Since the number of coincidences of codeword chips between and is "6", the codeword pattern data is selected. Then, the selected code word pattern data signal S2 "3-5
"0-4-6-6-1""is decoded by the decoding circuit 12 into a digital signal DS" 110100 "of 6 bits by using a conversion table (not shown).
Is output as a secondary demodulated data signal.

As described in detail above, the present invention can obtain the following effects. In the present invention, a BPF 8 that passes a band for 8 frequencies corresponding to the MFSK modulation of the primary demodulation signal, and an AD
The FFT 10 for cutting out the digital signal from the converter 9 for each preset time window and performing the fast Fourier transform to simultaneously detect a plurality of frequency components of the digital signal.
And provided. With this configuration, unlike the prior art, eight frequency band BPFs for separating the primary demodulated signal are provided.
Also, it is not necessary to provide an envelope detector, the characteristic variation is eliminated, demodulation can be accurately performed, and the circuit configuration can be simplified. Furthermore, FFT
10 is faster than when a conventionally provided envelope detector supplies an envelope output signal, and F includes a plurality of frequency components.
The FT output signal is supplied to the maximum value selector 11. As a result, the maximum value selector 11 can determine the codeword data signal at high speed according to the FFT output signal, and can perform demodulation at high speed.

The time window when the FFT 10 cuts out a digital signal is set so as to be synchronized with the time slot of MFSK modulation on the transmitter side. Therefore, FF
T10 can detect a plurality of frequency components of the digitized baseband signal in synchronization with the time slot, and as a result, reliable demodulation can be performed.

The present invention is not limited to the above embodiment, but may be carried out as follows. (1) Since the FFT 10 can detect phase components in addition to frequency components, not only the frequency components shown in FIG. 5C but also the phase components corresponding to the frequency components shown in FIG. 5D are detected. You may do it. The frequency component and the phase component thus obtained are effective in demodulating a data signal that is modulated by a hybrid modulation method that is a combination of an MFSK modulation method and a PSK (Phase Shift Keying) modulation method, for example. Can be used for.

(2) In addition to the secondary demodulation in the frequency hopping spread spectrum communication system, the present invention may be applied to a receiving device corresponding to a transmitting device according to the MFSK system. (3) In the present embodiment, the positive frequency is used as the FFT output, but when complex data is used as the input data to the FFT 10, a negative frequency is also output as the FFT output. The same processing as in the above embodiment can be performed by using.

[0031]

As described above in detail, according to the present invention, the fast Fourier transform of the modulated signal is performed, and the data signal is extracted based on the calculation result, so that the demodulation can be performed at high speed and accurately. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a receiving device according to an embodiment.

FIG. 2 shows processing of a received signal, (a) is a waveform diagram showing a baseband signal, (b) is a waveform diagram showing an AD-converted baseband signal, and (c) is detected by FFT processing. The graph which shows a frequency component.

FIG. 3 is a graph showing changes in detected frequency components.

FIG. 4 is a diagram for explaining error correction processing of codeword data.

FIG. 5 shows the processing of the received signal in another embodiment,
(A) is a waveform diagram showing a baseband signal, (b) is AD
A waveform diagram showing the converted baseband signal, (c) is
A graph showing frequency components detected by the FFT processing,
(D) is a graph showing the phase components detected by the FFT processing.

FIG. 6 is a block diagram showing a conventional receiving device.

FIG. 7 is a diagram for explaining codeword data.

[Explanation of symbols]

8 ... Band-pass filter 9 ... AD converter 10 ... FFT as calculation means and detection means 11 ... Maximum value selector as codeword data generation means and error correction means 12 ... Decoding circuit (11, 12 as conversion means) Configure the demodulation circuit.)

Claims (6)

[Claims] 1. A demodulator for extracting a data signal from a modulated signal in a communication system using a multi-valued frequency shift keying method, the calculating means (10) performing a fast Fourier transform by inputting the modulated signal. And a multi-value frequency shift keying demodulator, wherein the multi-valued frequency shift keying demodulator is provided based on a calculation result of the calculation means (10). 2. A demodulator for extracting a data signal from a modulated signal in a communication system using a multivalued frequency shift keying method, wherein the modulated signal is input to perform a fast Fourier transform process.
A detection means (10) for detecting a plurality of frequency components included in the modulated signal, and a demodulation means (1) for extracting the data signal based on the plurality of frequency components detected by the detection means (10).
1, 12) and a multivalued frequency shift keying demodulator. 3. The multi-valued frequency shift keying demodulator according to claim 2, wherein the detecting means (10) synchronizes a time window with a time slot allocated when the modulated signal is generated, and performs a fast Fourier transform. A multi-valued frequency shift keying demodulator characterized by performing processing. 4. The multivalued frequency shift keying demodulator according to claim 3, wherein the demodulation means (11, 12).
Is a codeword data generation means (11) for generating a codeword data signal based on a plurality of frequency components detected by the detection means (10) in a plurality of time windows synchronized with a predetermined number of the time slots. And an error correction means (11) for correcting an error of the codeword data signal generated by the codeword data generation means (11).
And a conversion means (12) for converting the codeword data signal corrected by the error correction means (11) into the data signal, the multi-value frequency shift keying demodulator. 5. A demodulator for extracting a data signal from a modulated signal in a communication system using a multivalued frequency shift keying method, wherein the modulated signal is input to perform a fast Fourier transform process.
Detecting means (10) for detecting a plurality of frequency components and a plurality of phase components contained in the modulated signal; and the data based on the plurality of frequency components and a plurality of phase components detected by the detecting means (10). A multi-valued frequency shift keying demodulator comprising demodulation means (11, 12) for extracting a signal. 6. The multivalued frequency shift keying demodulator according to claim 2, wherein the bandpass filter (8) passes a frequency band corresponding to a plurality of frequency components included in the modulated signal. ) And an AD converter (9) for converting the modulated signal supplied from the band pass filter (8) into a digital signal and supplying the digital signal to the detection means (10). Multi-valued frequency shift keying demodulator.