CN111580038A - Acoustic underwater beacon signal processing system based on FPGA - Google Patents

Abstract

The utility model provides an acoustics is beacon signal processing system under water based on FPGA, relates to acoustics location and high-speed digital signal processing field, including high-speed AD acquisition module, DDR2 storage module, FPGA module, circuit module on duty, digital pulse signal emission module, TVG control module, SD card storage module and serial ports communication module. The invention has the advantages of better anti-interference capability, lower power consumption and good real-time property.

Description

Acoustic underwater beacon signal processing system based on FPGA

Technical Field

The invention belongs to the field of acoustic positioning and high-speed digital signal processing, and particularly relates to an acoustic underwater beacon signal processing system based on an FPGA (field programmable gate array).

Background

In the exploration and development of ocean resources, the underwater acoustic positioning technology is one of indispensable navigation technologies because of having stable and high-precision positioning capability. The underwater acoustic positioning system can be divided into a long baseline, a short baseline and an ultra-short baseline according to the length of the baseline. The acoustic underwater beacon can be applied to the three underwater sound positioning technologies, the acoustic underwater beacon is installed on a measured carrier, and the distance of a target is determined by transmitting and receiving response signals to measure the time delay difference between an underwater target sound source and each array element, so that the positioning and navigation functions of the underwater target are realized. The function and performance of the underwater beacon signal processor relate to indexes such as positioning accuracy, positioning real-time performance, underwater positioning service time and the like of the whole system, and the underwater beacon signal processor is an important component of an underwater acoustic navigation positioning system.

With the development of embedded microprocessor systems in recent years, the FPGA hardware logic architecture is widely applied to embedded systems due to its characteristics of good parallelism and real-time. The signal processing algorithm of the acoustic underwater beacon system is complex, the algorithm realized by the FPGA has the advantages of high speed and real time, the data processing rate can be improved by several orders of magnitude, and the system is very suitable for the system.

Disclosure of Invention

In order to solve the problems of poor anti-interference capability, high power consumption, poor real-time performance and the like of the conventional acoustic underwater beacon signal processing system, the invention provides the acoustic underwater beacon signal processing system based on the FPGA, which has the advantages of good anti-interference capability, low power consumption and good real-time performance.

The technical scheme adopted for solving the technical problems is as follows:

an acoustics is beacon signal processing system under water based on FPGA, its characterized in that: the system comprises a high-speed AD acquisition module, a DDR2 storage module, an FPGA module, a duty circuit module, a digital pulse signal transmitting module, a TVG control module, an SD card storage module and a serial port communication module. The FPGA module comprises a logic control module, an orthogonal demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module;

the high-speed AD acquisition module is connected with a signal conditioning plate of the underwater beacon responder, and echo signals received by the underwater acoustic transducer enter the high-speed AD acquisition module to be subjected to AD sampling with 80MHz frequency and 16 bits after being conditioned;

the DDR2 storage module comprises an AD original data cache region, a filtering data cache region and a reference signal cache region and is used for storing digital signal data generated by the high-speed AD acquisition module and a calculated intermediate value;

the FPGA module is the core of the signal processing system and comprises a logic control module, an orthogonal demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module, wherein the logic control module is used for controlling the whole signal processing flow and the interaction among the modules; the orthogonal demodulation module is used for moving the received signal frequency spectrum to a baseband signal which can be analyzed to obtain a signal frequency band which needs to be detected; the low-pass filtering module performs low-pass filtering processing on the signal to remove useless high-frequency noise; the down-sampling module performs down-sampling processing on the signal data; the matched filtering module is used for matching the signal with the reference signal;

the atomic clock module is used for accurately timing, and time synchronization of the whole beacon positioning system is guaranteed. The time synchronization of the underwater beacons is the key of the design of the whole navigation positioning system, the clock of each underwater beacon can not only perform laboratory high-precision meter alignment before underwater, but also perform meter alignment in a close distance with an underwater movable carrier in an optical or radio mode and the like, so that the time unification of different underwater beacons is ensured;

the on-duty singlechip is used for starting the FPGA regularly to control the power consumption of the system. The underwater beacon system has two states of dormancy and work, the underwater beacon only works on duty by a single chip microcomputer in the dormant state, and other modules are all in a shutdown state;

the digital pulse signal transmitting module is used for outputting coded pulse signals and providing the coded pulse signals to an external transmitting plate to drive the transducer;

the TVG control module is used for outputting a voltage signal for an external receiving conditioning board to use to adjust the gain of an input signal;

the SD card storage module is connected with the logic control module through an SD card controller interface of the FPGA and used for storing parameters, echo data and sensor parameters;

the serial port communication module is used for uploading signal data to an upper computer, and the upper computer can also control parameters of the FPGA module through the serial port communication module.

Further, the acoustic underwater beacon signal processing system mainly receives and identifies two types of signals, one type is a 127-symbol pseudo-random code coded signal for positioning a low-speed underwater moving target, and the other type is a single-frequency pulse signal for positioning a high-speed underwater moving target. There are different processing modes for these two types of signals as follows.

Furthermore, the 127-symbol pseudo-random code coded signal is a sleep signal sent by a mother ship and 3 start signals of different working modes, the pseudo-random coded signal is used for information identification, the signal-to-noise ratio can be effectively improved, the influence of multipath effect and multiple access effect is reduced, because the working range of the system is relatively long, Doppler frequency shift is easy to occur, and errors exist in signals captured by a matched filter, the 4 signals are digitized by adopting matched filtering, the sampling frequency is 80kHz, four signals of Y1(n), Y2(n), Y3(n) and Y4(n) are formed, n is 1, 2, … and 1016, the demodulation frequencies 7450Hz, 7460Hz, 7470Hz, 7480Hz, 7490Hz, 7500Hz, 7510Hz, 7520Hz, 7530Hz, 7540Hz and 7550Hz are respectively used for orthogonal baseband demodulation, and Z1, N2, Z and Z1m (n) are formed by low-pass filtering, down-sampling and conjugation processing, The DDR2 module has four reference signals, namely, forty-four reference signals of Z2m (n2), Z3m (n2) and Z4m (n2), wherein m is 1, 2, … and 11, and n2 is 1, 2, … and 1016, and the reference signals are stored in a buffer area of the DDR2 module.

Further, the received signal is preprocessed, AD sampling is performed on the received signal in whole 10 seconds of an atomic clock, the duration is 10 seconds, the sampling frequency is 80kHz, a sampling sequence signal X (n) is formed, digital quadrature baseband demodulation is performed on the sequence signal X (n), the demodulation frequency is 7.5kHz, X1(n) is formed, low-pass filtering and down-sampling are performed on X1(n), the pass band of the low-pass filtering is 0-5 kHz, the sampling frequency after the down-sampling is 20kHz, and X2(n1) is formed, namely preprocessing is completed.

Further, using Z1m (n2), Z2m (n2), Z3m (n2), and Z4m (n2) as reference signals, the received signal X2(n1) is matched and filtered to obtain matching results P1m (n3), P2m (n3), P3m (n3), and P4m (n3), as follows:

further, energy estimation is performed on the quadrature demodulated received signal X1(n), forming an energy estimation function:

and constructing a detection signal:

Y1m(n3)＝P1m(n3)/X3(n3)

Y2m(n3)＝P2m(n3)/X3(n3)

Y3m(n3)＝P3m(n3)/X3(n3)

Y4m(n3)＝P4m(n3)/X3(n3)

when Y1m (n3), Y2m (n3), Y3m (n3) and Y4m (n3) are larger than the threshold value, namely, the maximum peaks which indicate energy generated when the signals enter the corresponding matched filter are obtained, the content of the received signals is obtained, and the positions of the maximum peaks are the arrival positions of the first code elements of the received starting signals, so that the accurate time delay of the signals is determined.

Further, when the acoustic underwater beacon works in a high-speed positioning mode, the underwater mobile station needs to be quickly positioned, and can actively send a frequency conversion signal to the beacon, specifically, a fixed frequency signal is sent every second from the whole 10 seconds. The signal processing system performs AD sampling on a received signal, the frequency of the received signal is 80kHz, a sampling sequence signal X (n) is formed, data with the length of 150ms is sequentially taken from the sequence signal X (n) to the sequence signal X (n) from n to 1, short-time fast Fourier transform analysis is performed, spectrum analysis data Y (n) FFT (X (n)) is formed, n is 1, 2, … and 12000, and the intensity of frequency components of the corresponding signals is extracted.

Furthermore, inverse fast fourier transform is performed on 10 sets of short-time fourier transform spectral lines of different frequencies to form 10 filtered subband time domain signals xm (n) (IFFT (ym (n)) (m) (1, 2, …, 10).

Further, Xm (n) is subjected to sliding energy integration for 50ms to form 10 energy integration sequences

Comparing the maximum value of XXm (n) with the detection threshold value, the received signal is the transmitting frequency corresponding to m, and estimating the arrival time of the incoming wave by combining the point and the sampling frequency, and judging the initial arrival position of the signal.

The invention has the beneficial effects that: the invention can acquire and process sonar signals in real time, quickly and accurately identify signal contents to realize corresponding working modes, can emit coded digital pulse signals and dynamically adjust input signal gain, can store result data and parameters in an SD card, and can upload the data to an upper computer through a serial port for display, thereby meeting the requirements of real-time performance and accuracy of acoustic underwater beacon calculation.

Drawings

Fig. 1 is a block diagram showing the overall structure of the system.

Fig. 2 is a schematic block diagram of the signal processing flow of the system, wherein (a) the received signal is a positioning service mode pseudo-random code signal, and (b) the received signal is a high-speed positioning mode mono-frequency pulse signal.

Detailed Description

In order to make the technical implementation of the present invention more clear, the present invention is further explained below with reference to specific schematic diagrams.

Referring to fig. 1 and 2, an acoustic underwater beacon signal processing system based on an FPGA includes a high-speed AD acquisition module, a DDR2 storage module, an FPGA module, a duty circuit module, a digital pulse signal transmitting module, a TVG control module, an SD card storage module, and a serial communication module. The FPGA module comprises a logic control module, an orthogonal demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module;

the high-speed AD acquisition module is connected with a signal conditioning plate of the underwater beacon responder, and echo signals received by the underwater acoustic transducer enter the high-speed AD acquisition module to be subjected to AD sampling with 80MHz frequency and 16 bits after being conditioned;

the DDR2 storage module comprises an AD original data cache region, a filtering data cache region and a reference signal cache region and is used for storing digital signal data generated by the high-speed AD acquisition module and a calculated intermediate value;

the FPGA module is the core of the signal processing system and comprises a logic control module, an orthogonal demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module, wherein the logic control module is used for controlling the whole signal processing flow and the interaction among the modules; the orthogonal demodulation module is used for moving the received signal frequency spectrum to a baseband signal which can be analyzed to obtain a signal frequency band which needs to be detected; the low-pass filtering module performs low-pass filtering processing on the signal to remove useless high-frequency noise; the down-sampling module performs down-sampling processing on the signal data; the matched filtering module is used for matching the signal with the reference signal;

the atomic clock module is used for accurately timing, and time synchronization of the whole beacon positioning system is guaranteed. The time synchronization of the underwater beacons is the key of the design of the whole navigation positioning system, the clock of each underwater beacon can not only perform laboratory high-precision meter alignment before underwater, but also perform meter alignment in a close distance with an underwater movable carrier in an optical or radio mode and the like, so that the time unification of different underwater beacons is ensured;

the on-duty singlechip is used for starting the FPGA regularly to control the power consumption of the system. The underwater beacon system has two states of dormancy and work, the underwater beacon only works on duty by a single chip microcomputer in the dormant state, and other modules are all in a shutdown state;

the digital pulse signal transmitting module is used for outputting coded pulse signals and providing the coded pulse signals to an external transmitting plate to drive the transducer;

the TVG control module is used for outputting a voltage signal for an external receiving conditioning board to use to adjust the gain of an input signal;

the SD card storage module is connected with the logic control module through an SD card controller interface of the FPGA and is used for storing result data such as parameters, echo data, sensor parameters and the like;

the serial port communication module is used for uploading signal data to an upper computer, and the upper computer can also control parameters of the FPGA module through the serial port communication module.

The acoustic underwater beacon signal processing system disclosed by the invention is the core of an underwater beacon navigation positioning system, and the underwater beacon navigation positioning system mainly has two working modes: a location service mode and a high speed location mode. As shown in fig. 2, the underwater beacon signal processing system of the present invention has different signal processing flows for two different operation modes.

In the positioning service mode, the mother ship obtains the position of the underwater vehicle by inquiring the underwater beacon, and the time of 3 positioning units of the system is strictly synchronized by an atomic clock. In the process, the signal received and identified by the acoustic underwater beacon signal processing system is a 127-symbol pseudo-random code coded signal, and the method mainly comprises the following steps as shown in fig. 2:

firstly, a sleep signal and 3 kinds of start signals are digitized, a sampling frequency is 80kHz, four kinds of signals of Y1(n), Y2(n), Y3(n) and Y4(n) are formed, n is 1, 2, … and 1016, orthogonal baseband demodulation is carried out by using demodulation frequencies of 7450Hz, 7460Hz, 7470Hz, 7480Hz, 7490Hz, 7500Hz, 7510Hz, 7520Hz, 7530Hz, 7540Hz and 7550Hz respectively, and forty-four reference signals of Z1m (n2), Z2m (n2), Z3m (n2) and Z4m (n2) are formed through low-pass filtering, down-sampling and conjugation, m is 1, 2, …, 11, n2 is 1, 2, … and 1016, and the reference signals are all stored in a buffer area of a DDR2 module.

Further, preprocessing the received signal, performing AD sampling on the received signal within 10 seconds of an atomic clock, wherein the duration is 10 seconds, the sampling frequency is 80kHz, forming a sampling sequence signal X (n), performing digital quadrature baseband demodulation on the sequence signal X (n), the demodulation frequency is 7.5kHz, forming X1(n), performing low-pass filtering and down-sampling on X1(n), the passband of the low-pass filtering is 0-5 kHz, the sampling frequency after the down-sampling is 20kHz, and forming X2(n1), namely completing the preprocessing.

Still further, using Z1m (n2), Z2m (n2), Z3m (n2), and Z4m (n2) as reference signals, the received signal X2(n1) is subjected to matched filtering processing to obtain matching results P1m (n3), P2m (n3), P3m (n3), and P4m (n3), which are respectively as follows:

further, energy estimation is performed on the quadrature-demodulated received signal X1(n), forming an energy estimation function:

and constructing a detection signal:

Y1m(n3)＝P1m(n3)/X3(n3)

Y2m(n3)＝P2m(n3)/X3(n3)

Y3m(n3)＝P3m(n3)/X3(n3)

Y4m(n3)＝P4m(n3)/X3(n3)

when Y1m (n3), Y2m (n3), Y3m (n3) and Y4m (n3) are larger than the threshold value, namely, the maximum peaks which indicate energy generated when the signals enter the corresponding matched filter are obtained, the content of the received signals is obtained, and the positions of the maximum peaks are the arrival positions of the first code elements of the received starting signals, so that the accurate time delay of the signals is determined.

In the high-speed positioning mode, the underwater mobile station sends an acoustic positioning signal to the surrounding underwater beacon once every 10 seconds, the signal is sent according to a frequency every second, coding is not needed, and the time of a mother ship, the underwater mobile station and the underwater beacon in the system is strictly synchronous. In the process, the signal received and identified by the acoustic underwater beacon signal processing system is a single-frequency pulse signal, and the main steps are as follows as shown in fig. 2:

first, the signal processing system AD samples a received signal at a frequency of 80kHz to form a sample sequence signal x (n), and performs short-time fast fourier transform analysis on data of 150ms in sequence starting from n (1) for the sequence signal x (n), thereby forming spectral analysis data y (n) (FFT (x (n)) and n (1), 2, …, and 12000, and extracting the intensities of frequency components of the respective corresponding signals.

Furthermore, inverse fast fourier transform is performed on 10 sets of short-time fourier transform spectral lines with different frequencies to form 10 filtered subband time domain signals xm (n) ═ IFFT (ym (n)), where m is 1, 2, …, and 10.

Still further, sliding energy integration of 50ms is performed on Xm (n), forming 10 energy integration sequences

Comparing the maximum value of XXm (n) with the detection threshold value, the received signal is the transmitting frequency corresponding to m, and estimating the arrival time of the incoming wave by combining the point and the sampling frequency, and judging the initial arrival position of the signal.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other modifications, substitutions, combinations, and alterations without departing from the spirit and principle of the present invention should be considered as equivalent substitutions within the scope of the present invention.

Claims (10)

1. An acoustics is beacon signal processing system under water based on FPGA, its characterized in that: the system comprises a high-speed AD acquisition module, a DDR2 storage module, an FPGA module, a duty circuit module, a digital pulse signal transmitting module, a TVG control module, an SD card storage module and a serial port communication module;

the high-speed AD acquisition module is connected with a signal conditioning plate of the underwater beacon responder, and echo signals received by the underwater acoustic transducer enter the high-speed AD acquisition module to be subjected to AD sampling with 80MHz frequency and 16 bits after being conditioned;

the DDR2 storage module comprises an AD original data cache region, a filtering data cache region and a reference signal cache region and is used for storing digital signal data generated by the high-speed AD acquisition module and a calculated intermediate value;

the FPGA module is the core of the signal processing system and comprises a logic control module, an orthogonal demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module;

the atomic clock module is used for accurately timing, and ensuring the time synchronization of the whole beacon positioning system;

the on-duty single chip microcomputer is used for starting the FPGA regularly to control the power consumption of the system, the underwater beacon system has two states of dormancy and work, the underwater beacon only works on the on-duty single chip microcomputer in the dormant state, and other modules are in the shutdown state;

the digital pulse signal transmitting module is used for outputting coded pulse signals and providing the coded pulse signals to an external transmitting plate to drive the transducer;

the TVG control module is used for outputting a voltage signal for an external receiving conditioning board to use to adjust the gain of an input signal;

the SD card storage module is connected with the logic control module through an SD card controller interface of the FPGA and used for storing parameters, echo data and sensor parameters;

the serial port communication module is used for uploading signal data to an upper computer, and the upper computer controls parameters of the FPGA module through the serial port communication module.

2. The system for processing the acoustic underwater beacon signal based on the FPGA of claim 1, wherein the FPGA module comprises a logic control module, a quadrature demodulation module, a low-pass filtering module, a down-sampling module and a matched filtering module, and the logic control module is used for controlling the whole signal processing flow and the interaction among the modules; the orthogonal demodulation module is used for moving the received signal frequency spectrum to a baseband signal which can be analyzed to obtain a signal frequency band which needs to be detected; the low-pass filtering module performs low-pass filtering processing on the signal to remove useless high-frequency noise; the down-sampling module performs down-sampling processing on the signal data; and the matched filtering module is used for matching the signal with the reference signal.

3. The system of claim 1 or 2, wherein the system receives and identifies two types of signals, one type is a 127-symbol pseudo-random code coded signal for positioning a low-speed underwater moving target, and the other type is a single-frequency pulse signal for positioning a high-speed underwater moving target.

4. The system of claim 3, wherein the 127-symbol pseudo-random code coded signals are a sleep signal and 3 start signals of different operation modes transmitted by the mother ship, the pseudo-random coded signals are used for information identification, the sleep signal and the 3 start signals are processed by matched filtering, the 4 signals are digitized, the sampling frequency is 80kHz, four signals of Y1(n), Y2(n), Y3(n) and Y4(n) are formed, n is 1, 2, … and 1016, orthogonal baseband demodulation frequencies are 7450Hz, 7460Hz, 7470Hz, 7480Hz, 7490Hz, 7500Hz, 7510Hz, 7520Hz, 7530Hz, 7540Hz and 7550Hz respectively, four reference signals of Z1m (n2), Z2m (n2), Z3m (n) and Z4 (n m) are formed by low pass filtering, down-sampling and conjugation, m is 1, 2, … and 11, n2 is 1, 2, … and 1016, and the reference signals are all stored in a buffer area of the DDR2 module.

5. The FPGA-based acoustic underwater beacon signal processing system of claim 4, wherein the received signal is pre-processed, AD sampling is performed on the received signal for 10 seconds of atomic clock, the duration is 10 seconds, the sampling frequency is 80kHz, a sampling sequence signal X (n) is formed, digital quadrature baseband demodulation is performed on the sequence signal X (n), the demodulation frequency is 7.5kHz, X1(n) is formed, low-pass filtering and down-sampling are performed on X1(n), the pass band of the low-pass filtering is 0-5 kHz, the sampling frequency after the down-sampling is 20kHz, and X2(n1) is formed, namely the pre-processing is completed.

6. An acoustic underwater beacon signal processing system based on FPGA according to claim 4, characterized in that, with Z1m (n2), Z2m (n2), Z3m (n2) and Z4m (n2) as reference signals, the received signal X2(n1) is matched and filtered to obtain matching results P1m (n3), P2m (n3), P3m (n3) and P4m (n3), which are respectively as follows:

7. the FPGA-based acoustic underwater beacon signal processing system of claim 4, wherein the energy estimation is performed on the quadrature demodulated received signal X1(n) to form an energy estimation function:

and constructing a detection signal:

Y1m(n3)＝P1m(n3)/X3(n3)

Y2m(n3)＝P2m(n3)/X3(n3)

Y3m(n3)＝P3m(n3)/X3(n3)

Y4m(n3)＝P4m(n3)/X3(n3)

when Y1m (n3), Y2m (n3), Y3m (n3) and Y4m (n3) are greater than the threshold value, the maximum peak value of energy generated when the signal enters the corresponding matched filter is represented, and the content of the received signal is obtained; and the position of the maximum peak is the arrival position of the first code element of the received starting signal, so as to determine the accurate time delay of the received starting signal.

8. The system for processing the acoustic underwater beacon signal based on the FPGA according to claim 4, wherein when the acoustic underwater beacon operates in a high-speed positioning mode, an underwater mobile station needs to be quickly positioned and actively transmits a variable frequency signal to the beacon, specifically, a fixed frequency signal is transmitted once per second from the time of the whole 10 seconds; the signal processing system performs AD sampling on a received signal, the frequency of the received signal is 80kHz, a sampling sequence signal X (n) is formed, data with the length of 150ms is sequentially taken from the sequence signal X (n) to the sequence signal X (n) from n to 1, short-time fast Fourier transform analysis is performed, spectrum analysis data Y (n) FFT (X (n)) is formed, n is 1, 2, … and 12000, and the intensity of frequency components of the corresponding signals is extracted.

9. An FPGA-based acoustic underwater beacon signal processing system according to claim 4, wherein 10 sets of short-time Fourier transform lines of different frequencies are inverse fast Fourier transformed to form 10 filtered subband time domain signals Xm (n) IFFT (ym (n)) (m 1, 2, …, 10).

10. The FPGA-based acoustic underwater beacon signal processing system of claim 4, wherein Xm (n) is subjected to sliding energy integration for 50ms to form 10 energy integration sequences

Comparing the maximum value of XXm (n) with the detection threshold value, the received signal is the transmitting frequency corresponding to m, and estimating the arrival time of the incoming wave by combining the point and the sampling frequency, and judging the initial arrival position of the signal.

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