An IQ demodulation hardware device applied to a DAS system and its usage method

Abstract

The present invention provides an IQ demodulation hardware device applied to a DAS system and a method for using the same. At present, all DAS systems use high-speed data acquisition cards to recover detection data. The massive data generated by the DAS system places a huge pressure on the processing-end hardware and algorithms. After researchers collect the data, they often use preprocessing methods to reduce the computing cost and then perform signal demodulation. This application proposes a hardware demodulation method, which adopts the IQ demodulation algorithm and designs a hardware module device to synchronously demodulate data at the signal output end of the DAS system. After the signal stream is output from the DAS system, it is directly and real-time demodulated by the IQ hardware demodulation module and synchronously collected by the acquisition card. According to the IQ hardware demodulation method of the DAS system of this application, the structure is simple and effective, the cost is low, it effectively alleviates the processing pressure of the massive data generated by the DAS system, effectively reduces the relevant hardware configuration requirements, improves the signal processing efficiency, and enables the system to have the ability of real-time demodulation.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber communication sensing, and in particular to an IQ demodulation hardware device applied to a DAS system and a using method thereof. Background Art

[0002] The basic principle of the DAS system is to transmit optical pulses into the optical fiber and then receive the Rayleigh scattering signals of the optical pulses along the optical fiber path. External vibrations will cause a series of effects on the optical fiber (such as stretching, twisting, refractive index change, etc.). By detecting the changes in characterization parameters such as the intensity, frequency, phase, and polarization state of the optical signal, the perception of external environmental changes can be realized, the parameter changes along the optical fiber can be measured in real time, with spatial continuity, and the event position can be accurately located.

[0003] According to the above principle, the effects of external vibrations on the optical fiber are complex, and actually correspond to the combined result of multiple effects on the optical signal. Therefore, the optical signal actually cannot truly restore the vibration signal. In addition, in the applications of perimeter security and pipeline security, the optical cable is usually buried underground, and there is also the process of vibration signal propagation between the signal to be detected and the optical cable in the soil. Therefore, the received optical signal and the real signal to be detected are distorted, and the relationship between the two is extremely complex and difficult to model and restore. It is very difficult to directly find the target features from the optical signal.

[0004] In addition, the DAS generates a huge amount of data, about 10 - 100 MB / s (bytes / second). If all data is saved for 1 hour, about 36G - 360GB of data will be generated. Under the existing technical conditions, it is very difficult to store such a large amount of data for a long time. How to save a small amount of key data and make it easy to process, and how to realize real-time data processing to make the system have real-time performance are research problems.

[0005] Assume that the output of the signal conditioning circuit is an intermediate frequency signal with a center frequency f. According to the Nyquist sampling theorem, the sampling rate of the acquisition card should reach at least 2f to ensure perfect reconstruction of the signal; in practical applications, generally, the sampling rate should be 5f to achieve an ideal reconstruction effect, which will result in too high a cost requirement for the data acquisition card and it is difficult to balance the AD quantization bits.

[0006] Currently, traditional DAS systems use high-speed data acquisition cards (DAQ) to recover detection data, asynchronously preprocess the data and then demodulate the signal. Due to the increase in the DAQ sampling rate, the data generated by the DAS system will increase exponentially, putting great pressure on the research of software, hardware and algorithms at the processing end. Therefore, it is necessary to further improve the system performance. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides an IQ demodulation hardware device applied to a DAS system and its usage method, which reduces the signal processing pressure of the DAS system and at the same time enables the system to have real-time demodulation capabilities.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions:

[0009] An IQ demodulation hardware device applied to a DAS system includes a band-pass filter, a power splitter, two radio frequency mixers, two low-pass filters, two voltage-controlled gain amplifiers, a four-channel DDS module, and an FPGA module; wherein, the two radio frequency mixers include radio frequency mixer 1 and radio frequency mixer 2, the two low-pass filters include low-pass filter LPF1 and low-pass filter LPF2, the power splitter is provided with output port 1 and output port 2, and the two voltage-controlled gain amplifiers include voltage-controlled gain amplifier 1 and voltage-controlled gain amplifier 2;

[0010] The input end of the band-pass filter is connected to the input signal returned by the DAS system and the band-pass filter filters the signal. The input end of the power splitter is connected to the output end of the band-pass filter and the power splitter divides the signal into two. The radio frequency input end of radio frequency mixer 1 is connected to output port 1 of the power splitter. The radio frequency input end of radio frequency mixer 2 is connected to output port 2 of the power splitter. The output port 1 of the four-channel DDS module is connected to the input end of voltage-controlled gain amplifier 1 and the four-channel DDS module generates a sine signal for voltage-controlled gain amplifier 1. The output port 2 of the four-channel DDS module is connected to the local oscillator signal input end of voltage-controlled gain amplifier 2 and the four-channel DDS module generates a cosine signal for voltage-controlled gain amplifier 2. The local oscillator input end of radio frequency mixer 1 is connected to the output end of voltage-controlled gain amplifier 1 and voltage-controlled gain amplifier 1 amplifies the sine signal and outputs it to radio frequency mixer 1. The input end of low-pass filter LPF1 is connected to the output end of radio frequency mixer 1 and radio frequency mixer 1 generates an intermediate frequency signal. The local oscillator input end of radio frequency mixer 2 is connected to the output end of voltage-controlled gain amplifier 2 and voltage-controlled gain amplifier 2 amplifies the cosine signal and outputs it to radio frequency mixer 2. The input end of low-pass filter LPF2 is connected to the output end of radio frequency mixer 2 and radio frequency mixer 2 generates an intermediate frequency signal. The two output ends of the FPGA module are respectively connected to low-pass filter LPF1 and low-pass filter LPF2 and low-pass filter LPF1 and low-pass filter LPF2 respectively filter the signal. The output end of the FPGA module is connected to the host computer and the FPGA module converts the analog signal into a digital signal and outputs it to the host computer.

[0011] The present invention also provides a method of using an IQ demodulation hardware device applied to a DAS system. The DAS sensing system converts the scattered light signal carrying vibration information into an analog electrical signal, which is received by the IQ demodulation hardware device applied to the DAS system and filtered and denoised by a band-pass filter. Based on the IQ demodulation principle, the denoised signal is equally divided into two signals by a power divider. The radio frequency signal source generator generates a sine signal and a cosine signal with the same frequency as the signal to be demodulated, which are amplified by voltage-controlled gain amplifiers respectively, and then enter the radio frequency mixer to mix with the signals at its local oscillator input terminal, and generate intermediate frequency signals that enter the low-pass filter LPF1 and the low-pass filter LPF2. Finally, the filtered signal is input into the FPGA module, converted into a digital signal and output to the host computer signal processing system for subsequent relevant signal processing.

[0012] The present invention is further configured as: the DAS system detects a signal input to obtain the phase change information caused by an external acoustic wave signal, including: inputting a coherent optical pulse into the optical fiber to obtain the phase change, and performing optoelectronic conversion on the phase-changed optical signal to obtain the phase change signal.

[0013] The present invention is further configured as: the center frequency of the band-pass filter is 80 MHz and the bandwidth is 10 M.

[0014] The present invention is further configured as: the frequency range of the power divider is 10 - 200 MHz.

[0015] The present invention is further configured as: the bandwidth of the radio frequency mixer is 0.5 - 500 MHz.

[0016] The present invention is further configured as: the cut-off frequencies of the low-pass filter 1 and the low-pass filter 2 are both 5 M.

[0017] The present invention is further configured as: the four-channel DDS module can generate a sine signal and a cosine signal with a frequency of 80 MHz.

[0018] The present invention is further configured as: the gain adjustment range of the voltage-controlled gain amplifier is -2.5 dB to +42.5 dB.

[0019] The present invention is further configured as: the host computer for receiving demodulation information, characterized in that it has at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set are loaded and executed by a processor to implement.

[0020] The present invention has the following advantages: The signal returned by the DAS system is directly demodulated by the hardware module IQ and then output to the host computer through the synchronous analog-to-digital conversion of the FPGA module, which reduces the operation cost, improves the calculation efficiency of the DAS system, and realizes the real-time demodulation function, providing the real-time detection and analysis ability of the DAS system. Description of the Drawings

[0021] Figure 1 It is the structural schematic diagram of the demodulation hardware device in the embodiment of the present invention. Detailed Embodiments

[0022] The technical solutions in the present invention will be further described below in conjunction with the drawings and embodiments.

[0023] An IQ demodulation hardware device applied to a DAS system includes a band-pass filter, a power splitter, two radio frequency mixers, two low-pass filters, two voltage-controlled gain amplifiers, a four-channel DDS module and an FPGA module; wherein, the two radio frequency mixers include radio frequency mixer 1 and radio frequency mixer 2, the two low-pass filters include low-pass filter LPF1 and low-pass filter LPF2, the power splitter is provided with output port 1 and output port 2, and the two voltage-controlled gain amplifiers include voltage-controlled gain amplifier 1 and voltage-controlled gain amplifier 2;

[0024] It should be noted that the DAS system, namely the distributed fiber optic acoustic sensing system, can detect signals such as sound or vibration within a range by using the phase rather than the intensity of the coherent Rayleigh backscattered light. The DAS system has the functions of emitting coherent light pulses and processing signals to obtain the position information of the target.

[0025] In this embodiment, the DAS system inputs narrow linewidth coherent laser pulses into the sensing fiber and obtains the optical signal S(n) after the phase change of Rayleigh scattering affected by external vibrations. The optical signal is subjected to optoelectronic conversion to obtain a phase change signal, that is, an electrical signal including phase change information, which is input into a band-pass filter with a center frequency of 80M. After filtering out some noise signals, the obtained signal is equally divided by the power splitter. One path of the signal is multiplied by a sine signal of 80MHz or 81MHz generated by the radio frequency signal source generator to generate a low-frequency component, and the obtained is the Q-channel signal. Similarly, the other path of the signal is multiplied by a cosine signal of 80M or 81M generated by the radio frequency signal generator and amplified by the voltage-controlled gain amplifier to generate a low-frequency component, and the obtained is the I-channel signal. This is the mixing part of the algorithm.

[0026] The two mixed signals generated after multiplication can be expressed as:

[0027]

[0028]

[0029] wherein, sin(Δw n n) and cos(Δw n n) respectively represent the sine and cosine signals of the same frequency generated by a computer.

[0030] Δw n = 2πΔf / f s is the digital angular frequency corresponding to Δw n , and the phase is the initial phase of the local optical signal in the DAS system, and n is the sampling point number.

[0031] It can be seen from the above formula that multiplying S(n) by the quadrature signal generates the sum-frequency component and the difference-frequency component respectively. In I' and Q', cos(2Δw n n + φ S (n)) and sin(2Δw n n + φ S (n)) are the sum-frequency signals among them, and their frequency is twice the AOM modulation frequency. While cosφ s (n) and sinφ s (n) are the difference-frequency components, and their high-frequency terms have been canceled, only the phase components exist. To demodulate and obtain the phase φ s (n) in the demodulator, the sum-frequency signal needs to be filtered out, that is, a low-pass filter (Low-pass Filter, LPF) is used for low-pass filtering to obtain the I and Q signals. In addition to the filtering function, the LPF also has the function of denoising S(n) to obtain better signal quality.

[0032] In this embodiment, the I-channel signal and the Q-channel signal are respectively low-pass filtered by low-pass filters LPF1 and LPF2 with a cut-off frequency of 5M. After obtaining the I and Q signals, the amplitude and phase of the S(n) signal can be obtained respectively through the following formula:

[0033]

[0034]

[0035] Where k is an integer. The value range of the arctangent function arctan is (-π / 2, π / 2). In this embodiment, the obtained filtered signal is subjected to analog-to-digital conversion through the FPGA module, and the data is transmitted to the upper computer. The ratio of the I and Q signals is arctangent, and the arctangent result is extended to the range of (-π, π) according to the quadrant where the values of I and Q are located. Then, through phase unwrapping processing, the phase result of the actual backward Rayleigh scattering optical signal is finally obtained. The center frequency of the band-pass filter therein is 80 MHz, and the bandwidth is 10 M. The frequency range of the power splitter is 10 - 200 MHz, the bandwidth of the radio frequency mixer is 0.5 - 500 MHz, the cut-off frequencies of both low-pass filter 1 and low-pass filter 2 are 5 M, the four-channel DDS module can generate sine and cosine signals with a frequency of 80 MHz, and the gain adjustment range of the voltage-controlled gain amplifier is -2.5 dB to +42.5 dB. Moreover, this application also sets a DC linear voltage stabilizing power supply module with an output voltage of 5V, and the DC linear voltage stabilizing power supply module is used for the voltage-controlled gain amplifier.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An IQ demodulation hardware device applied to a DAS system, characterized in that: It includes a band-pass filter, a power splitter, two RF mixers, two low-pass filters, two voltage-controlled gain amplifiers, a four-channel DDS module and an FPGA module; among them, the two RF mixers include RF mixer 1 and RF mixer 2, the two low-pass filters include low-pass filter LPF1 and low-pass filter LPF2, the power splitter is provided with output port 1 and output port 2, and the two voltage-controlled gain amplifiers include voltage-controlled gain amplifier 1 and voltage-controlled gain amplifier 2; The input end of the band-pass filter is connected to the input signal returned by the DAS system and the band-pass filter filters the signal. The input end of the power splitter is connected to the output end of the band-pass filter and the power splitter divides the signal into two. The RF input end of the RF mixer 1 is connected to output port 1 of the power splitter. The RF input end of the RF mixer 2 is connected to output port 2 of the power splitter. The output port 1 of the four-channel DDS module is connected to the input end of the voltage-controlled gain amplifier 1 and the four-channel DDS module generates a sine signal and supplies it to the voltage-controlled gain amplifier 1. The output port 2 of the four-channel DDS module is connected to the local oscillator signal input end of the voltage-controlled gain amplifier 2 and the four-channel DDS module generates a cosine signal and supplies it to the voltage-controlled gain amplifier 2. The local oscillator input end of the RF mixer 1 is connected to the output end of the voltage-controlled gain amplifier 1 and the voltage-controlled gain amplifier 1 amplifies the sine signal and outputs it to the RF mixer 1. The input end of the low-pass filter LPF1 is connected to the output end of the RF mixer 1 and the RF mixer 1 generates an intermediate-frequency signal. The local oscillator input end of the RF mixer 2 is connected to the output end of the voltage-controlled gain amplifier 2 and the voltage-controlled gain amplifier 2 amplifies the cosine signal and outputs it to the RF mixer 2. The input end of the low-pass filter LPF2 is connected to the output end of the RF mixer 2 and the RF mixer 2 generates an intermediate-frequency signal. The two output ends of the FPGA module are respectively connected to the low-pass filter LPF1 and the low-pass filter LPF2 and the low-pass filter LPF1 and the low-pass filter LPF2 respectively filter the signal. The output end of the FPGA module is connected to the upper computer and the FPGA module converts the analog signal into a digital signal and outputs it to the upper computer.

2. A method of using the IQ demodulation hardware device applied to the DAS system as described in claim 1, characterized in that: The DAS system converts the scattered light signal carrying vibration information into an analog electrical signal, which is received by the IQ demodulation hardware device applied to the DAS system, and is filtered and denoised by the band-pass filter. Based on the IQ demodulation principle, the denoised signal is equally divided into two signals by the power splitter. The RF signal source generator generates a sine signal and a cosine signal with the same frequency as the signal to be demodulated, amplifies the signals through the voltage-controlled gain amplifiers respectively, and then enters the RF mixers respectively to mix with the signals at their local oscillator input ends, and generates intermediate-frequency signals and enters the low-pass filter LPF1 and the low-pass filter LPF2. Finally, the filtered signals are input into the FPGA module, which is converted into digital signals and output to the upper computer signal processing system for subsequent relevant signal processing.

3. The usage method of an IQ demodulation hardware device applied to a DAS system as described in claim 2, characterized in that: The DAS system detects the input of a signal to obtain the phase change information caused by an external acoustic wave signal, including: inputting a coherent optical pulse into an optical fiber to obtain the phase change, and performing optoelectronic conversion on the optical signal after the phase change to obtain the phase change information.

4. The usage method of an IQ demodulation hardware device applied to a DAS system as described in claim 2, characterized in that: The center frequency of the band-pass filter is 80 MHz, and the bandwidth is 10 M.

5. The usage method of an IQ demodulation hardware device applied to a DAS system according to claim 2, wherein: The frequency range of the power splitter is 10 - 200 MHz.

6. The usage method of an IQ demodulation hardware device applied to a DAS system according to claim 2, characterized in that: The bandwidth of the radio frequency mixer is 0.5 - 500 MHz.

7. The usage method of an IQ demodulation hardware device applied to a DAS system according to claim 2, characterized in that: The cut-off frequencies of the low-pass filter LPF1 and the low-pass filter LPF2 are both 5 M.

8. The usage method of an IQ demodulation hardware device applied to a DAS system according to claim 2, characterized in that: The four-channel DDS module can generate sine and cosine signals with a frequency of 80 MHz.

9. The usage method of an IQ demodulation hardware device applied to a DAS system as described in claim 2, characterized in that: The gain adjustment range of the voltage-controlled gain amplifier is -2.5 dB to +42.5 dB.

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