CN112152724B - Dynamic signal digital demodulation system and method based on beat frequency and software radio - Google Patents
Dynamic signal digital demodulation system and method based on beat frequency and software radio Download PDFInfo
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Abstract
The invention discloses a dynamic signal digital demodulation system and method based on beat frequency and software radio, belonging to the technical field of information transmission. The system comprises a pump laser, a wavelength division multiplexer, an optical fiber laser cavity, a photoelectric detector and a general software radio peripheral; when the dynamic signal is demodulated, the dynamic signal acts on the optical fiber laser cavity to modulate the optical signal therein, the modulated optical signal is reflected to a photoelectric detector through a wavelength division multiplexer, a plurality of beat frequency signals are generated on the photoelectric detector and reach a general software radio peripheral, and frequency conversion, superposition and demodulation are completed on the general software radio peripheral to obtain the demodulated dynamic signal. Since the system performs frequency conversion and superposition on the signals when demodulating the signals, so that the signal-to-noise ratio of the signals is increased along with the increase of the superposition number of the signals, the demodulation can be completed even if the low-frequency dynamic signals are submerged in noise as long as the superposition number is enough.
Description
Technical Field
The invention relates to a dynamic signal digital demodulation system and method based on beat frequency and software radio, belonging to the technical field of information transmission.
Background
The detection of dynamic signals has wide application in the fields of civil engineering, industrial engineering, engineering machinery, aerospace and the like. The method has great significance particularly for the detection of weak low-frequency dynamic signals in important application occasions such as seismic waves, hydrophones and the like. However, due to the harsh environment, the signal is very susceptible to interference, and the detection of weak low-frequency dynamic signals remains an important and challenging subject.
Compared with an electric sensor, the optical fiber vibration sensor has the advantages of reliable work, high precision, high sensitivity, strong anti-interference capability and the like under severe environment, has attracted extensive attention, and is researched by a plurality of people: for example, a method for demodulating dynamic signals by using a fabry-perot interferometer has the advantages of strong anti-interference capability, good stability and the like. However, the fabry-perot sensor has a weak signal, which greatly limits the application of the fabry-perot sensor. For another example, a method for dynamic signal demodulation by using a michelson interferometer has a long sensing arm and high sensitivity. But because the length of the optical fiber used in the sensing arm varies randomly due to temperature fluctuations and other types of environmental disturbances, low frequency random phase shifts in the interferometry signal result. Random phase drift can reduce measurement accuracy and, in the worst case, can even affect the proper operation of the measurement system. There is also a method for dynamic signal demodulation using an interferometer for phase modulation recovery, which effectively reduces external interference by converting a dynamic signal into a phase change. Generally, the above methods are all in improving the sensitivity, signal-to-noise ratio or stability of the sensor. However, these demodulation methods are all used for demodulating through the variation cycle of a certain parameter varying with the vibration frequency in the optical aspect, when the dynamic signal frequency is very low, the variation amplitude of the corresponding parameter is very small, and these demodulation methods are difficult to identify and demodulate, that is, the existing dynamic signal digital demodulation system has certain disadvantages when identifying and demodulating the weak low-frequency dynamic signal.
In recent years, compared with the above-mentioned complicated optical demodulation method, the beat frequency sensing technology has been widely recognized and confirmed due to its advantages of simple structure, convenient construction, low cost, etc. The method only needs one photoelectric detector to convert the optical signal into the electric signal, so that the cost of the detection equipment is greatly reduced, and the beat frequency sensing technology can demodulate a plurality of parameters such as tension, pressure, temperature, vibration and the like. Even large-scale detection can be performed by multiplexing techniques. For example, Gao, l, Liu, s, Yin, z, Zhang, l, Chen, l, & Chen, X (2010), Fiber-optical modulation sensor based on probe frequency and frequency-modulation techniques ieee Photonics Technology Letters,23(1),18-20, discloses a method for demodulating a dynamic signal based on a frequency modulation demodulator, which can directly obtain the frequency of the dynamic signal without conversion of other parameters. However, since the demodulation system is an analog fm demodulation system, the fm demodulation frequency range is limited, and the demodulation system has inherent low-frequency noise, the demodulation system cannot work well in low-frequency demodulation, and meanwhile, for weak low-frequency dynamic signals, the demodulation system cannot perform good demodulation due to the characteristic of low signal-to-noise ratio.
Disclosure of Invention
In order to solve the problem that the existing signal demodulation system can not demodulate low-frequency signals, the invention provides a dynamic signal digital demodulation system based on beat frequency and software radio, which comprises: the device comprises a pump laser, a wavelength division multiplexer, an optical fiber laser cavity, a photoelectric detector and a general software radio peripheral;
the pump laser is connected to the optical fiber laser cavity through a wavelength division multiplexer, and meanwhile, the wavelength division multiplexer is sequentially connected with the photoelectric detector and the general software radio peripheral;
when the system demodulates the dynamic signal, the dynamic signal acts on the optical fiber laser cavity to modulate the optical signal therein, the modulated optical signal is reflected to the photoelectric detector through the wavelength division multiplexer, a plurality of beat frequency signals are generated on the photoelectric detector and reach the general software radio peripheral equipment, and the frequency conversion, the superposition and the demodulation are completed on the general software radio peripheral equipment to obtain the demodulated dynamic signal.
Optionally, the general software radio peripheral device includes a radio frequency front end, an analog-to-digital converter, and a multi-channel digital down-conversion system, which are connected in sequence;
the radio frequency front end is used for reducing the beat frequency signal into an analog intermediate frequency signal; the analog-to-digital converter is used for converting the analog intermediate frequency signal into a digital intermediate frequency signal; the multi-channel digital down-conversion system is used for down-converting a digital intermediate frequency signal into a digital baseband signal, extracting, filtering and superposing the digital baseband signal, and then carrying out frequency modulation demodulation to obtain a dynamic signal.
Optionally, the pump laser is configured to provide pump laser light, and the system further includes a computer, where the computer is connected to the general software radio peripheral.
Optionally, the fiber laser cavity adopts a multi-longitudinal mode fiber laser cavity.
Optionally, the fiber laser cavity includes a fiber grating, a section of erbium-doped fiber, and a faraday mirror; the fiber grating and the Faraday reflector are connected through an erbium-doped fiber.
Optionally, the radio frequency front end includes a mixer, a local crystal oscillator, a power amplifier, and a band pass filter.
Optionally, the multichannel digital down-conversion system has multiple channels, each channel includes a pair of mixers, a pair of local oscillators for providing quadrature signals to the mixers, a pair of cascaded integrator comb filters for decimation filtering, a pair of half-band filters, and a pair of FIR filters;
all channels are finally connected to a low-pass filter and a narrow-band frequency modulation system.
The invention also provides a dynamic signal digital demodulation method based on beat frequency and software radio, which adopts the dynamic signal digital demodulation system based on beat frequency and software radio to demodulate, and comprises the following steps:
inputting the optical signal modulated with the dynamic signal into a photoelectric detector to obtain a beat frequency signal;
and inputting the beat frequency signal into a general software radio peripheral to carry out frequency conversion, superposition and demodulation so as to obtain a demodulated dynamic signal.
Optionally, the inputting the beat frequency signal into a general software radio peripheral for frequency conversion, superposition, and demodulation to obtain a demodulated dynamic signal includes:
selecting a beat signal of a desired frequency;
reducing the beat frequency signals of the selected multiple frequencies into analog intermediate frequency signals through a radio frequency front end;
converting the analog intermediate frequency signal into a digital intermediate frequency signal through an analog-to-digital converter;
and performing down-conversion on the digital intermediate frequency signal into a digital baseband signal through a multi-channel digital down-conversion system, extracting, filtering and superposing the digital baseband signal, and performing frequency modulation demodulation to obtain a dynamic signal.
The invention also provides a dynamic signal demodulation terminal, which comprises the dynamic signal digital demodulation system based on the beat frequency and the software radio, and/or adopts the dynamic signal digital demodulation method based on the beat frequency and the software radio to demodulate the dynamic signal.
The invention has the beneficial effects that:
the system comprises a pump laser, a wavelength division multiplexer, a fiber laser cavity, a photoelectric detector and a general software radio peripheral; when the system demodulates the dynamic signal, the dynamic signal acts on the optical fiber laser cavity to modulate the optical signal therein, the modulated optical signal is reflected to the photoelectric detector through the wavelength division multiplexer, a plurality of beat frequency signals are generated on the photoelectric detector and reach the general software radio peripheral equipment, and the frequency conversion, the superposition and the demodulation are completed on the general software radio peripheral equipment to obtain the demodulated dynamic signal. When the system demodulates the signals, the signals are subjected to frequency conversion and superposition in a software radio mode, so that the signal-to-noise ratio of the signals is increased along with the increase of the superposition number of the signals, the demodulation can be finished even if weak low-frequency dynamic signals are submerged in noise as long as the superposition number is enough, and the stability is high.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a dynamic signal demodulation system based on fiber beat frequency provided in an embodiment of the present application.
Fig. 2 is a flow chart of a dynamic signal demodulation system based on fiber beat frequency provided in an embodiment of the present application.
Fig. 3 is a schematic diagram of a fiber laser cavity principle.
Fig. 4 is a schematic structural diagram of an rf front end provided in an embodiment of the present application.
Fig. 5 is a schematic diagram of a structure of a multi-channel digital down-conversion device provided in an embodiment of the present application.
Fig. 6 is a simulation graph of snr gain of demodulation of superimposed signals according to an embodiment of the present application.
Fig. 7 is a simulation diagram of demodulation stability of a superimposed signal according to an embodiment of the present application.
FIG. 8 is a simulation of the demodulation results for a 1Hz to 500Hz dynamic signal in one embodiment of the present application.
FIG. 9 is a simulation of the demodulation results for a 1600Hz to 5000Hz dynamic signal in one embodiment of the present application.
FIG. 10 is a simulation of the accuracy results for a 1Hz to 5000Hz dynamic signal demodulation in one embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The first embodiment is as follows:
the embodiment provides a dynamic signal digital demodulation system based on beat frequency and software radio, comprising: pump source (Laser), Wavelength Division Multiplexer (WDM), fiber Laser Cavity (Laser Cavity), Photodetector (PD), and Universal Software Radio Peripheral (USRP).
The pumping source is connected to the optical fiber laser cavity through a wavelength division multiplexer, and meanwhile, the wavelength division multiplexer is sequentially connected with the photoelectric detector and the general software radio peripheral.
When the system demodulates the dynamic signal, the pumping source generates laser, the laser reaches the optical fiber laser cavity through the wavelength division multiplexer, and resonance is generated in the optical fiber laser cavity; the dynamic signal acts on the optical fiber laser cavity to modulate the optical signal therein to obtain a modulated optical signal, namely a modulated signal, the modulated optical signal is reflected to a photoelectric detector through a wavelength division multiplexer, a plurality of beat frequency signals are generated on the photoelectric detector and reach a general software radio peripheral, and frequency conversion, superposition and demodulation are completed on the general software radio peripheral to obtain a stable dynamic signal with high signal-to-noise ratio.
Example two:
the present embodiment provides a dynamic signal digital demodulation system based on beat frequency and software radio, as shown in fig. 1, the system includes: a pump source (Laser)1, a Wavelength Division Multiplexer (WDM)2, a fiber Laser Cavity (Laser Cavity)3, a Photodetector (PD)4, a Universal Software Radio Peripheral (USRP)5 and a computer (PC) 6.
When the system demodulates the dynamic signal, the pumping source 1 generates laser, the laser reaches the optical fiber laser cavity 3 through the wavelength division multiplexer 2, and resonance is generated in the optical fiber laser cavity 3; meanwhile, a vibration exciter generates a dynamic signal, the dynamic signal acts on the optical fiber laser cavity 3 to modulate an optical signal therein to obtain a modulated optical signal, namely a modulated signal, the modulated optical signal is reflected to reach the photoelectric detector 4 through the wavelength division multiplexer 2, a plurality of beat signals are generated on the photoelectric detector 4 and reach the general software radio peripheral 5, frequency conversion, superposition and frequency demodulation are completed on the general software radio peripheral 5 to obtain a stable dynamic signal with a high signal-to-noise ratio, and finally the demodulated dynamic signal is displayed on the computer 6.
In the system, a pump source 1 is used for outputting laser, in this embodiment, laser with a wavelength of 980nm output by the pump source 1 is taken as an example for description, the laser enters an optical fiber laser cavity 3 through a wavelength division multiplexer 2 with a wavelength of 980nm &1550nm, multi-longitudinal-mode laser is generated through the optical fiber laser cavity 3, meanwhile, the optical fiber laser cavity 3 receives a dynamic signal, and the dynamic signal acts on the optical fiber laser cavity 3, so that an optical signal therein is modulated, and a modulated optical signal, i.e., a modulated signal, is obtained.
In practical applications, the pump source 1 and the wavelength division multiplexer 2 may use other parameters, such as a pump source with a wavelength of 1480nm, a wavelength division multiplexer with a wavelength of 1480nm &1550nm, and the like. Fig. 3 shows a structure of a fiber laser cavity 3 comprising a fiber grating (FBG), a length of Erbium Doped Fiber (EDF) and a faraday mirror (FRM) connected by a length of erbium doped fiber.
In the embodiment, the 3-dB bandwidth of the fiber grating is 240pm, the wavelength is 1550.4nm, and the reflectivity is 90%; the wavelength of the Faraday reflector is 1550 nm; the absorption coefficient of the erbium-doped fiber at 1532nm is 8 dB/m.
It should be noted that, in practical applications, the fiber laser cavity 3 may use devices with other parameters, for example, another fiber grating may be used instead of the faraday mirror, a ring cavity structure may also be used, or other structures capable of generating multi-longitudinal mode laser may also be used, and the present application is not limited thereto.
The modulated signal is reflected by the wavelength division multiplexer 2 and enters the photodetector 4, and the photodetector 4 generates a plurality of beat signals, i.e. the signal output by the photodetector 4 is a beat signal which modulates the dynamic signal, i.e. the modulated signal.
The photodetector 4 inputs the modulated signal into a general software radio peripheral 5 for processing and then displays the processed signal in a computer 6.
The universal software radio peripheral 5 comprises a radio frequency front end, an analog-to-digital converter and a multi-channel digital down-conversion system, wherein the radio frequency front end, the analog-to-digital converter and the multi-channel digital down-conversion system are sequentially connected, and specifically:
referring to fig. 4, fig. 4 illustrates an architecture of the rf front-end in the general software radio peripheral 5, which is used to down-convert the beat signal modulated by the dynamic signal to an analog if signal. In this embodiment, the rf front-end comprises a Mixer (Mixer), a Local Oscillator (LO) for providing a driving signal to the Mixer, a Power Amplifier (PA) and a band-pass filter (BPF). In practical applications, other structures capable of reducing the frequency of the signal to the analog intermediate frequency signal can be used to replace the structure, for example, other FPGA development boards having a function of reducing the beat frequency signal modulated by the dynamic signal to the analog intermediate frequency signal.
Referring to fig. 5, in fig. 5, the ADC is an analog-to-digital converter, the CIC is a cascade integrator comb filter, the HBF is a half-band filter, the FIR is a filter, the LPF is a low-pass filter, and the NBFM is a narrow-band fm system. Fig. 5 shows a structure of an analog-to-digital converter ADC and a multi-channel digital down-conversion system, which is configured to down-convert a plurality of channels of digital intermediate frequency signals output by the analog-to-digital converter into digital baseband signals, decimate and filter the plurality of channels of digital baseband signals, and perform fm demodulation after superposition.
Specifically, as shown in fig. 5, the digital down-conversion system has multiple paths, each path including a pair of mixers (mixers), a pair of Local Oscillators (LOs) for providing quadrature signals to the mixers, a pair of cascaded integrator comb filters (CIC) for decimation filtering, a pair of half-band filters (HBF), and a pair of FIR filters. All channels are finally connected to a Low Pass Filter (LPF) and a narrowband frequency modulation system (NFBM). In practical applications, other structures capable of performing digital down-conversion on the digital intermediate frequency signal into a digital baseband signal can be used as a channel in a multi-channel digital down-conversion system, for example, other FPGA development boards have functions of performing down-conversion on the digital intermediate frequency signal to obtain a digital baseband signal, performing decimation filtering, and performing superposition.
Similarly, a narrowband fm system is only one type of demodulation scheme used in this example, and other demodulation schemes such as wideband fm or other fm schemes may be used.
The processing process of superposing and demodulating a plurality of beat signals is as follows:
any two different longitudinal modes produce a number of beat signals on the photodetector, the frequency of the first beat signal can be expressed as:
where c is the speed of light, neffIs the effective index of the fiber and L is the length of the laser cavity.
The beat signals are equally spaced in frequency, so that the second beat signal is twice as frequent as the first beat signal, and the frequency of the pth beat signal can be expressed as:
when a dynamic signal is applied, the dynamic microstrain induced by the dynamic signal can be expressed as:
ε＝Amcos(2πfmt)
wherein A ismAmplitude of dynamic microstrain, fmIs the frequency of the dynamic signal.
The change in the beat frequency signal frequency caused by the dynamic signal is:
wherein p iseT represents time as the effective elasto-optic coefficient of the fiber.
The beat frequency signal on the photoelectric detector is modulated by the dynamic signal, and the output modulated signal SPD(t) is:
wherein, apAmplitude of signal, k, output for photodetectorpFor intermediate variables, the expression is:
the beat frequency sensing system generates a plurality of beat frequency signals on the photoelectric detector, and the dynamic signals modulate the beat frequency signals to generate a plurality of modulated signals. The modulated signal is transmitted to a general software radio peripheral for demodulation.
First, the modulated signal output on the photodetector is input to the analog portion of the general software radio peripheral. The signal is down-converted by a mixer to obtain an analog intermediate frequency signal SMIX(t)：
After the power amplifier amplifies its power and is smoothed by a band pass filter. Converting the modulated signals of different frequencies into a digital signal S by an analog-to-digital converterADC(nT)。
Where m (nT) is the sampling point.
The plurality of digital modulated signals output by the analog-to-digital converter are input into different channels of a digital down-conversion device of a digital part of a general software radio peripheral.
Frequency conversion of the modulated signal by a digital mixer:
after the FIR filter extracts and filters through cascading an integrator comb filter and a half-band filter, a baseband signal output from the digital down-conversion equipment can be simplified as follows:
for applied dynamic signals, especially dynamic signals with relatively low frequency and low energy
Satisfy the requirement of
The signal output by the digital down-conversion device can therefore be reduced to:
via narrow band frequency modulation system (NBFM):
the superposition output of each path of signals is as follows:
according to the processing process, the multichannel signal superposition in the dynamic signal digital demodulation system based on the optical fiber beat frequency and the software radio improves the amplitude of the demodulated dynamic signal output by the narrow-band frequency modulation system and improves the signal-to-noise ratio of the signal. Even for dynamic signals with extremely low energy, the method can realize the detection of weak dynamic signals only by increasing the number of superposed channels to improve the energy and the signal-to-noise ratio of output signals.
In order to verify the demodulation result of the dynamic signal demodulation system based on the optical fiber beat frequency, the simulation experiment is specially carried out:
first, a comparative experiment was performed on the method of demodulating the present application by superimposing a plurality of beat signals:
in the experiment, five channels were used in the digital down-conversion system, each having a beat frequency of 1556.94MHz, 1567.16MHz, 1577.29MHz, 1588.28MHz, and 1598.74MHz, respectively, as a carrier. Fig. 6 is a simulation diagram of the corresponding demodulation results, in which the dotted line represents the individual demodulation results of the beat signals of the above five frequencies, and the solid line represents the demodulation results of the signals obtained by superimposing these five signals.
As can be seen from fig. 6, the signal demodulation signal-to-noise ratio after the superposition is much larger than that of the single signal demodulation. Therefore, the method for demodulating the superposed beat frequency signals can improve the signal-to-noise ratio of the superposed signals.
In practical application, the number of the digital down-conversion channels can be changed according to practical application, and the beat frequency signal frequencies of different carriers can also be selected. As the number of digital down-conversion channels increases, the signal-to-noise ratio of the demodulated signal will also increase, so that even if the low frequency dynamic signal is buried in noise, the demodulation can still be accomplished as long as the number of superpositions is sufficient.
Next, the present application performed experiments on the demodulation stability of dynamic signals with a vibration frequency of 1000Hz, in which the results were tested every 15 minutes for 300 minutes, as shown in fig. 7, the highest offset was only 0.67 Hz. The dynamic signal demodulation system based on the fiber beat frequency provided by the application is proved to have high stability and be capable of demodulating stable dynamic signals.
Finally, the application performs demodulation experiments on dynamic signals with frequencies ranging from 1Hz to 5000Hz, and particularly for dynamic signals with frequencies lower than 500 Hz:
the demodulation results of the dynamic signals from 1Hz to 500Hz are shown in fig. 8, and it can be seen from fig. 8 that the signal-to-noise ratios obtained by superimposing the dynamic signals from 1Hz, 200Hz and 500Hz in the dynamic signal demodulation system based on the fiber beat frequency provided by the present application are 15dB, 18dB and 24dB, respectively.
The demodulation results of the 1600Hz to 5000Hz dynamic signals are shown in fig. 9, and it can be seen from fig. 9 that the signal-to-noise ratios obtained by superimposing the 1600Hz, 3000Hz and 5000Hz dynamic signals in the dynamic signal demodulation system based on the fiber beat frequency provided by the present application are 30dB, 34dB and 40dB, respectively.
Figure 10 shows the accuracy results of demodulating 1Hz to 5000Hz dynamic signals using the system of the present invention. It can be seen that the lowest resolution of the system in the invention to the frequency can reach 1Hz, that is, the lowest signal frequency capable of being demodulated is 1Hz, and the system has high accuracy.
The present example only provides frequencies up to 5000Hz due to experimental equipment limitations. In various embodiments, the system of the present invention still provides demodulation capability for higher frequency dynamic signals.
Some steps in the embodiments of the present invention may be implemented by software, and the corresponding software program may be stored in a readable storage medium, such as an optical disc or a hard disk.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A system for digital demodulation of dynamic signals based on beat frequency and software radio, the system comprising: the device comprises a pump laser, a wavelength division multiplexer, an optical fiber laser cavity, a photoelectric detector and a general software radio peripheral;
the pump laser is connected to the optical fiber laser cavity through a wavelength division multiplexer, and meanwhile, the wavelength division multiplexer is sequentially connected with the photoelectric detector and the general software radio peripheral;
when the system demodulates the dynamic signal, the dynamic signal acts on the optical fiber laser cavity to modulate the optical signal therein, the modulated optical signal is reflected to a photoelectric detector through a wavelength division multiplexer, a plurality of beat frequency signals are generated on the photoelectric detector and reach a general software radio peripheral device, frequency conversion, superposition and demodulation are completed on the general software radio peripheral device, and the demodulated dynamic signal is obtained;
the universal software radio peripheral comprises a radio frequency front end, an analog-to-digital converter and a multi-channel digital down-conversion system which are sequentially connected;
the radio frequency front end is used for reducing the beat frequency signal into an analog intermediate frequency signal; the analog-to-digital converter is used for converting the analog intermediate frequency signal into a digital intermediate frequency signal; the multi-channel digital down-conversion system is used for down-converting a digital intermediate frequency signal into a digital baseband signal, extracting, filtering and superposing the digital baseband signal, and then carrying out frequency modulation demodulation to obtain a dynamic signal.
2. The system of claim 1, wherein the pump laser is configured to provide pump laser light, the system further comprising a computer, the computer being coupled to the general purpose software radio peripheral.
3. The system of claim 2, wherein the fiber laser cavity employs a multi-longitudinal mode fiber laser cavity.
4. The system of claim 3, wherein said fiber laser cavity comprises a fiber grating, a length of erbium doped fiber, and a faraday mirror; the fiber grating and the Faraday reflector are connected through an erbium-doped fiber.
5. The system of claim 1, wherein the radio frequency front end comprises a mixer, a local crystal, a power amplifier, and a band pass filter.
6. The system of claim 1, wherein the multi-channel digital down-conversion system has multiple channels, each channel comprising a pair of mixers, a pair of local oscillators for providing quadrature signals to the mixers, a pair of cascaded integrator comb filters and a pair of half-band filters for decimation filtering, and a pair of FIR filters;
all channels are finally connected to a low-pass filter and a narrow-band frequency modulation system.
7. A digital demodulation method for dynamic signals based on beat frequency and software radio, which is characterized in that the method adopts the digital demodulation system for dynamic signals based on beat frequency and software radio of any one of claims 1-6 to demodulate, and the method comprises:
inputting the optical signal modulated with the dynamic signal into a photoelectric detector to obtain a beat frequency signal;
and inputting the beat frequency signal into a general software radio peripheral to carry out frequency conversion, superposition and demodulation so as to obtain a demodulated dynamic signal.
8. The method of claim 7, wherein inputting the beat signal into a general software radio peripheral for frequency conversion, superposition, and demodulation to obtain a demodulated dynamic signal comprises:
selecting a beat signal of a desired frequency;
reducing the beat frequency signals of the selected multiple frequencies into analog intermediate frequency signals through a radio frequency front end;
converting the analog intermediate frequency signal into a digital intermediate frequency signal through an analog-to-digital converter;
and performing down-conversion on the digital intermediate frequency signal into a digital baseband signal through a multi-channel digital down-conversion system, extracting, filtering and superposing the digital baseband signal, and performing frequency modulation demodulation to obtain a dynamic signal.
9. A dynamic signal demodulation terminal, characterized in that the terminal comprises a digital demodulation system for dynamic signals based on beat frequency and software radio according to any one of claims 1 to 6, and/or adopts the method of claim 7 or 8 to perform demodulation processing for dynamic signals.
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