阅读说明：本技术 一种适用于小型平台的低功耗水下声学目标探测系统 (Low-power-consumption underwater acoustic target detection system suitable for small platform ) 是由 李建龙 蒋丞 颜曦 杨志国 徐文 于 2021-11-15 设计创作，主要内容包括：本发明公开了一种适用于小型平台的低功耗水下声学目标探测系统。本发明适用于小型平台,有着低功耗、小尺寸的特征,可实现长期、大尺度的海洋观测；可为各类水下无人航行器等提供目标信息,为无人潜水器组网协同探测打下基础；同时实现了窄带、宽带声呐的目标探测功能,能在检测目标有无、目标的方位的同时,对目标类型进行识别；能在非平稳时变噪声环境下工作,自适应计算检测门限。本发明硬件采用多芯片封装技术的CPU与FPGA实现；采用的CPU自身集成了大容量存储,降低了电路系统的复杂度,缩小了电子系统的体积；本发明系统整体通过低功耗CPU与FPGA实现,与采用传统DSP芯片实现的检测系统相比,整体功耗大幅下降。(The invention discloses a low-power-consumption underwater acoustic target detection system suitable for a small-sized platform. The invention is suitable for small-sized platforms, has the characteristics of low power consumption and small size, and can realize long-term large-scale marine observation; the target information can be provided for various underwater unmanned aircrafts and the like, and a foundation is laid for networking cooperative detection of the unmanned underwater vehicles; meanwhile, the target detection function of narrow-band and broadband sonar is realized, and the type of the target can be identified while the existence and the direction of the target are detected; the method can work in a non-stationary time-varying noise environment, and the detection threshold is calculated in a self-adaptive mode. The hardware of the invention is realized by adopting a CPU and an FPGA of a multi-chip packaging technology; the adopted CPU integrates large-capacity storage, thereby reducing the complexity of a circuit system and reducing the volume of an electronic system; the system is integrally realized by the low-power-consumption CPU and the FPGA, and compared with a detection system realized by adopting a traditional DSP chip, the overall power consumption is greatly reduced.)

1. A low-power-consumption underwater acoustic target detection system suitable for a small-sized platform is characterized by comprising a preposed conditioning filtering module, an A/D conversion module, a CPU and an FPGA; the CPU comprises a single-channel energy testing module, an FFT module, a threshold detection module and a cluster identification module; the FPGA comprises a beam forming module and a median filtering module;

the preposed conditioning filtering module: filtering low-frequency and high-frequency interference signals in the analog signals of the N channels;

an A/D conversion module: converting the analog signals of the N channels output by the prepositive conditioning and filtering module into digital signals;

single channel energy detection module: the single-channel energy detection module extracts a channel from the digital signal output by the A/D conversion module and detects the energy change of the signal;

an FFT module: when the single-channel energy detection module detects that the signal energy of a certain channel exceeds a threshold value, the FFT module performs Fourier transform on data of all channels and outputs frequency domain data;

a beam forming module: performing frequency domain beam forming on the frequency domain data output by the FFT module to obtain an angle-frequency plane;

a median filtering module: estimating the background noise of the angle-frequency plane output by the beam forming module;

a threshold detection module: calculating a detection threshold plane at the current moment according to the estimated background noise output by the median filtering module, and searching for a suspicious value to obtain a detection result point set;

a clustering identification module: and distinguishing the target and outputting a target identification result comprising the target direction, frequency and target type according to the detection result point set output by the threshold detection module.

2. A low power consumption underwater acoustic target detection system suitable for use with small platforms as claimed in claim 1 wherein the CPU further includes LPDDR2 and a multimedia instruction set; when the FFT module is used for operation, the multimedia instruction set is used for accelerating the FFT operation speed; LPDDR2 provides CPU with memory for calculation; the FPGA also comprises an RAM, and the RAM provides a calculation memory for the FPGA; the A/D conversion module consists of a plurality of low-power-consumption and low-noise A/D chips; the digital signal of N passways that A/D conversion module outputs inserts CPU in the form of the bus.

3. A low power consumption underwater acoustic target detection system suitable for small platforms as in claim 1 wherein in the single channel energy detection module, the extracted channel passes through a band pass filter bank before energy detection.

4. A low power consumption underwater acoustic target detection system suitable for small platforms as claimed in claim 1 wherein the FFT module, threshold detection module, cluster identification module, beam forming module and median filtering module are turned off when no target is detected by the single channel energy detection module.

5. A low power consumption underwater acoustic target detection system adapted for use with a compact platform as claimed in claim 1 wherein in the FFT module, inkThe first of time of day receptionnSignals of the channels _n,k (t) The vector signal after Fourier transform isG _n,k (f) The following formula:

wherein the content of the first and second substances,n=1~N，findicating the scanning frequency.

6. The system of claim 5, wherein the beamforming module is configured to perform beamforming on the N channels of frequency domain signalsG _n,k (f) Performing azimuth beam scanning to obtain an angle-frequency planeB _k (θ,f) At the same time willB _k (θ,f) Store in buffer queue(ii) a The formula is as follows:

B _k (θ,f)=w(θ,f)^H·G _k (f)

wherein the content of the first and second substances,θwhich represents the angle of the scan, is,w(θ,f) Is the scan vector, and the superscript H denotes the conjugate transpose.

7. A low power consumption underwater acoustic target detection system for small platforms as in claim 6 wherein the median filtering module estimates by vector signal processingkThe background noise of the angle-frequency plane at the moment is calculated by the following steps:

wherein the content of the first and second substances,for the estimated background noise level, mid represents median filtering,as the queue length, | ·| non-conducting phosphor₂Representing a 2-norm.

8. A low power consumption underwater acoustic target detection system suitable for use with small platforms as recited in claim 7 in which the threshold detection module comprises:

(1) based on estimated background noiseComputingkTime of day detection threshold planeT _k (θ,f)：

Wherein the content of the first and second substances,χ ²the distribution of the Chinese character 'chi' square is,P _fa is the expected false alarm probability;

(2) traverse angle-frequency planeB _k (θ,f) Find out to satisfyB _k (θ,f)>T _k (θ,f) And forming a set;Ia set of detection result points consisting of peak points as，i=1,…,IWhereinAndrespectively representiAzimuth and frequency for each peak.

9. A low power consumption underwater acoustic target detection system suitable for small platforms as in claim 8 wherein the threshold detection module calculates in the traversal angle-frequency planeT _k (θ,f) While simultaneously comparingB _k (θ,f)>T _k (θ,f) And the detection result can be obtained only by traversing once.

10. The system of claim 8, wherein the cluster identification module comprises:

(a) for the detection result point setCarrying out mean shift clustering on the internal signals according to angles to obtainLClusters, each cluster representing one target, each cluster f _l Consisting of close angles and corresponding frequencies,l=1~L；

(b) each cluster r _l The frequency of the cluster is matched and identified with the features in the target feature library Ψ to obtain the target type represented by each cluster, and the specific identification method is as follows:

wherein the content of the first and second substances,for saving the firstlThe target type of the cluster to be identified finally;for the number of frequencies in each cluster,is as followslIn a clusterpThe frequency of each of the plurality of frequencies,αto scale factor, Ψ _m,j Is the first in ΨmThe second of the candidate object typejA characteristic frequency.

Technical Field

The invention belongs to the field of underwater target detection, and particularly relates to a low-power-consumption underwater acoustic target detection system suitable for a small-sized platform.

Background

Underwater target detection has wide application in the fields of civil use, national defense safety and the like. Because electromagnetic waves are greatly attenuated in water, underwater targets are generally detected by using an acoustic means. The traditional acoustic target detection equipment is large in size, high in energy consumption and low in intelligent degree. Generally, a conventional target detection system is mounted on a large-scale platform such as a ship or a warship, and first, acoustic signals are collected through a large-aperture array, and then, monitoring and identification are manually performed through an operator. An operator firstly judges whether a target appears according to the received signal, then determines the azimuth angle of the target, and finally identifies the target according to the signal characteristics.

With the development trend of miniaturization, intellectualization and networking of unmanned platforms, the application of target detection in various small-sized underwater/water surface unmanned platforms draws more and more attention. The small platform can be observed in the ocean for a long time because the small platform does not need to be operated by personnel.

The traditional detection system is directly applied to a small platform, and the defects of low autonomy, high energy consumption and the like of the detection method exist. The low autonomy reduces the detection and target parameter estimation performance of the small platform, and the long-term endurance of the small platform is reduced due to the excessive energy consumption. Therefore, an underwater acoustic array target detection system which is low in power consumption, high in autonomy and suitable for a small platform is extremely necessary.

Disclosure of Invention

The invention aims to provide a low-power-consumption underwater acoustic target detection system suitable for a small-sized platform aiming at the defects of the prior art. The invention realizes the detection, orientation and identification of the target on the target detection algorithm; the embedded real-time processing and low-power consumption long-term watching miniaturization and low-power consumption hardware circuit is realized on hardware.

The purpose of the invention is realized by the following technical scheme: a low-power-consumption underwater acoustic target detection system suitable for a small-sized platform comprises a preposed conditioning filtering module, an A/D conversion module, a CPU and an FPGA; the CPU comprises a single-channel energy testing module, an FFT module, a threshold detection module and a cluster identification module; the FPGA comprises a beam forming module and a median filtering module;

the preposed conditioning filtering module: filtering low-frequency and high-frequency interference signals in the analog signals of the N channels;

an A/D conversion module: converting the analog signals of the N channels output by the prepositive conditioning and filtering module into digital signals;

single channel energy detection module: the single-channel energy detection module extracts a channel from the digital signal output by the A/D conversion module and detects the energy change of the signal;

an FFT module: when the single-channel energy detection module detects that the signal energy of a certain channel exceeds a threshold value, the FFT module performs Fourier transform on data of all channels and outputs frequency domain data;

a beam forming module: performing frequency domain beam forming on the frequency domain data output by the FFT module to obtain an angle-frequency plane;

a median filtering module: estimating the background noise of the angle-frequency plane output by the beam forming module;

a threshold detection module: calculating a detection threshold plane at the current moment according to the estimated background noise output by the median filtering module, and searching for a suspicious value to obtain a detection result point set;

a clustering identification module: and distinguishing the target and outputting a target identification result comprising the target direction, frequency and target type according to the detection result point set output by the threshold detection module.

Further, the CPU also includes LPDDR2 and a multimedia instruction set; when the FFT module is used for operation, the multimedia instruction set is used for accelerating the FFT operation speed; LPDDR2 provides CPU with memory for calculation; the FPGA also comprises an RAM, and the RAM provides a calculation memory for the FPGA; the A/D conversion module consists of a plurality of low-power-consumption and low-noise A/D chips; the digital signal of N passways that A/D conversion module outputs inserts CPU in the form of the bus.

Furthermore, in the single-channel energy detection module, the extracted channel firstly passes through a band-pass filter bank and then carries out energy detection.

Further, when the single-channel energy detection module does not detect the target, the FFT module, the threshold detection module, the cluster identification module, the beam forming module and the median filtering module are closed.

Further, in the FFT module, inkThe first of time of day receptionnSignals of the channels _n,k (t) The vector signal after Fourier transform isG _n,k (f) The following formula:

wherein the content of the first and second substances,n=1~N，findicating the scanning frequency.

Furthermore, in the beam forming module, the frequency domain signals of N channels are processedG _n,k (f) Performing azimuth beam scanning to obtain an angle-frequency planeB _k (θ,f) At the same time willB _k (θ,f) Store in buffer queue(ii) a The formula is as follows:

B _k (θ,f)=w(θ,f)^H·G _k (f)

wherein the content of the first and second substances,θwhich represents the angle of the scan, is,w(θ,f) Is the scan vector, and the superscript H denotes the conjugate transpose.

Further, in the median filtering module, estimation is carried out through vector signal processingkBackground of angular-frequency planes of time of dayThe noise is calculated by the following method:

wherein the content of the first and second substances,for the estimated background noise level, mid represents median filtering,as the queue length, | ·| non-conducting phosphor₂Representing a 2-norm.

Further, the threshold detection module comprises:

(1) based on estimated background noiseComputingkTime of day detection threshold planeT _k (θ,f)：

Wherein the content of the first and second substances,χ ²the distribution of the Chinese character 'chi' square is,P _fa is the expected false alarm probability;

(2) traverse angle-frequency planeB _k (θ,f) Find out to satisfyB _k (θ,f)>T _k (θ,f) And forming a set;Ia set of detection result points consisting of peak points as，i=1,…,IWhereinAndare respectively provided withIs shown asiAzimuth and frequency for each peak.

Further, the threshold detection module calculates in the traversal angle-frequency planeT _k (θ,f) While simultaneously comparingB _k (θ,f)>T _k (θ,f) And the detection result can be obtained only by traversing once.

Further, the cluster identification module comprises:

(a) for the detection result point setCarrying out mean shift clustering on the internal signals according to angles to obtainLClusters, each cluster representing one target, each cluster f _l Consisting of close angles and corresponding frequencies,l=1~L；

(b) each cluster r _l The frequency of the cluster is matched and identified with the features in the target feature library Ψ to obtain the target type represented by each cluster, and the specific identification method is as follows:

wherein the content of the first and second substances,for saving the firstlThe target type of the cluster to be identified finally;for the number of frequencies in each cluster,is as followslIn a clusterpThe frequency of each of the plurality of frequencies,αto scale factor, Ψ _m,j Is the first in ΨmThe second of the candidate object typejA characteristic frequency.

The invention has the beneficial effects that:

(1) the invention is suitable for small-sized platforms, has the characteristics of low power consumption and small size, and can realize long-term large-scale marine observation;

(2) the invention can provide target information for various underwater unmanned aircrafts and the like, and lays a foundation for networking cooperative detection of unmanned underwater vehicles;

(3) the invention simultaneously realizes the target detection function of narrow-band and broadband sonar, and can identify the type of the target while detecting the existence and the direction of the target;

(4) the invention can work in the non-stationary time-varying noise environment and adaptively calculate the detection threshold;

(5) the hardware of the invention is realized by adopting a CPU and an FPGA of a multi-chip packaging technology, the CPU realizes FFT acceleration by using a self-contained multimedia instruction set in the operation process, and data buffering is realized by the LPDDR2 integrated with the CPU in the operation process, thereby improving the calculation efficiency;

(6) the CPU adopted by the invention integrates large-capacity storage, thereby reducing the complexity of a circuit system and reducing the volume of an electronic system;

(7) the data buffering in the beam forming and median filtering processes is realized by an RAM inside an FPGA, the whole system is realized by a low-power-consumption CPU and the FPGA, and compared with a detection system realized by adopting a traditional DSP chip, the whole power consumption is greatly reduced.

Drawings

One or more embodiments are illustrated by way of example in the accompanying drawings, which correspond to the figures in which like reference numerals refer to similar elements and which are not to scale unless otherwise specified.

FIG. 1 is a block diagram of a low power consumption underwater acoustic target detection system of the present invention;

FIG. 2 is a diagram illustrating a signal detection result at a certain time according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a target recognition result according to an embodiment of the present invention.

Detailed Description

In order to meet the requirement of low power consumption, the hardware part of the invention is realized by adopting a low-power consumption Central Processing Unit (CPU) based on a multi-chip packaging technology and a low-power consumption Field Programmable Gate Array (FPGA) based on a flash architecture; the CPU and the FPGA are connected by adopting a parallel bus.

As shown in FIG. 1, the invention relates to a low-power-consumption underwater acoustic target detection system suitable for a small platform, which comprises a preposed conditioning filtering module, an A/D conversion module, a CPU and an FPGA. The CPU comprises a single-channel energy testing module, an FFT module, a multimedia instruction set, a threshold detection module, a cluster identification module and a low voltage memory rate 2 (LPDDR 2) memory; the FPGA includes a beamforming module and a median filtering module and Random Access Memory (RAM). LPDDR2 provides the CPU with computational memory and RAM provides the FPGA with computational memory.

(1) Assuming that the acoustic array carried on the small platform has N channels, firstly, acoustic analog signals of the N channels of the array pass through a preposed conditioning filtering module to filter low-frequency and high-frequency interference signals.

(2) And converting the analog signals of the N channels output by the preposed conditioning filtering module into digital signals through an A/D conversion module. The A/D conversion module is composed of a plurality of low-power-consumption and low-noise A/D chips.

(3) The digital signal of N passways that A/D conversion module outputs inserts CPU in the form of the bus. In order to reduce the calculation power consumption, when a target is not detected, a signal of one channel is extracted by a CPU through a single-channel energy detection module to carry out real-time detection, and the energy change of the signal is detected by adopting a conventional energy detection method. The extracted channel firstly passes through a band-pass filter bank and then single-channel energy detection is carried out. The filter bank can improve the detection performance of weak signals.

When the single-channel energy detection module detects that the signal energy of a certain channel exceeds a threshold value, the FFT module performs Fourier transform (FFT) on data of all channels, otherwise all subsequent detection algorithm modules are closed, wherein the subsequent detection algorithm modules comprise an FFT module, a threshold detection module, a cluster identification module, a beam forming module and a median filtering module, the single-channel energy detection module is only used for guarding, and the power consumption of the system is reduced.

When FFT operation is carried out, the multimedia instruction set of the selected CPU is utilized to accelerate the FFT operation speed. Under some special application scenes (such as high-risk target searching, platform energy abundance and the like), all subsequent detection algorithm modules can be continuously started, and the overall target detection and identification efficiency of the system is improved under the condition of sacrificing energy consumption.

In thatkThe first of time of day receptionnSignals of the channels _n,k (t) The vector signal after time-frequency conversion isG _n,k (f) The following formula:

wherein the content of the first and second substances,n=1~N，findicating the scanning frequency.

(4) And the FFT module outputs frequency domain data to a beam forming module of the FPGA to complete frequency domain beam forming.

For frequency domain signals of N channelsG _n,k (f) Performing azimuth beam scanning to obtain an angle-frequency planeB _k (θ,f) At the same time willB _k (θ,f) Store in buffer queue(ii) a The concrete formula is as follows:

B _k (θ,f)=w(θ,f)^H·G _k (f)

wherein the content of the first and second substances,θwhich represents the angle of the scan, is,w(θ,f) Is the scan vector, and the superscript H denotes the conjugate transpose. The signal receiving signal-to-noise ratio can be improved by the beam forming, and the performance gain of subsequent detection and identification is improved.

(5) And estimating the background noise of the angle-frequency plane output by the beam forming module by using a median filtering module, and outputting the result to the CPU.

Estimation by vector signal processingkThe background noise of the angle-frequency plane at the moment is calculated by the following steps:

wherein the content of the first and second substances,for the estimated background noise level, mid represents median filtering,as the queue length, | ·| non-conducting phosphor₂Representing a 2-norm.

(6) The CPU threshold detection module calculates the current detection threshold plane according to the estimated background noise output by the median filtering module in one traversalT _k (θ,f) And suspicious values are searched, so that the calculation amount and the memory consumption are saved.

(6.1) estimating the background noiseComputing kTime of day detection threshold planeT _k (θ,f)：

Wherein the content of the first and second substances,χ ²the distribution of the Chinese character 'chi' square is,P _fa is the expected false alarm probability.

(6.2) traversing the angle-frequency planeB _k (θ,f) Find out to satisfyB _k (θ,f)>T _k (θ,f) And form a set. Assume consensus IA peak value of IA set of detection result points consisting of peak points as，i=1,…,IWhereinAndrespectively representiAzimuth and frequency for each peak. Due to the influence of environmental noise and mechanical noise of the underwater platform, the set may contain detection results caused by random interference.

In practical implementation, the CPU calculates in traversing angle-frequency planeT _k (θ,f) At the same time compareB _k (θ,f)>T _k (θ,f) The detection result can be obtained only by traversing once without traversing calculation in advance and storingT _k (θ,f) Meanwhile, the calculation amount of the algorithm and the memory consumption are saved.

(7) And the cluster identification module of the CPU distinguishes the target and outputs a target identification result according to the detection result point set output by the threshold detection module.

(7.1) set of detection result pointsThe mean shift clustering is carried out on the signals in the space according to the angles, and the signals can be obtained after the clustering is setLClusters, each cluster representing one target, each cluster f _l Consisting of close angles and corresponding frequencies,l=1~L。

(7.2) dividing each cluster r _l The frequency of the cluster is matched and identified with the features in the target feature library Ψ to obtain the target type represented by each cluster, and the specific identification method is as follows:

wherein the content of the first and second substances,for saving the firstlThe target type that is ultimately identified for each cluster.For the number of frequencies in each cluster,is as followslIn a clusterpThe frequency of each of the plurality of frequencies,αto scale factor, Ψ _m,j Is the first in ΨmThe second of the candidate object typejA characteristic frequency;is associated with the target type, provided by the target feature library Ψ.

(7.3) outputting detection and identification results including the target azimuthFrequency ofAnd type of object。

Taking the system of the present invention mounted on an AUV as an example, the AUV performs a target search task in a certain water area. There are three targets in the water domain, 2 targets of type a and 1 target of type B. Different types of targets have a range of different line spectral features.

At some point, the actual azimuth angles for type A targets are about-60 and-23, and type B targets are located about 29.

At this time, the signals collected by the system pass through an angle-frequency plane obtained in the FPGAB _k (θ,f) As shown in fig. 2, where the x-axis is the scan angle and the y-axis is the frequency.

After the CPU runs the detection algorithm, the system detects the signal point setMarked with an "x" in figure 2. Can be seen at-60 degrees, -23 degreesAnd a series of signals with certain regular frequency are detected near 29 degrees, and three randomly distributed noise interferences exist.

The detection result is compared with the target feature library Ψ by a cluster identification module in the CPU, and the obtained target number and identification result are shown in fig. 3. For convenience of illustration, fig. 3 shows different target types with different marks, and the recognition results are also marked near the respective detection points. The system identifies 3 targets in total, 2 targets of type a and 1 target of type B, and other random interferences are also marked separately. It can be seen that the results of the target type, the target orientation, etc. are all consistent with the actual situation.

In the embodiment, because the low-power-consumption central processing unit and the FPGA which adopt the multi-chip packaging technology are adopted, the detection system is small in size and can be directly carried on various types of small Autonomous Underwater Vehicles (AUV), underwater gliders and the like, such as a portable small AUV of 50 kg grade and a swallow underwater glider of 70 kg grade.

In the aspect of using power consumption, the self endurance time of a certain domestic 50 kg-level AUV is about 5 hours, and the endurance time of a system carrying the system is about 5 hours. The swallow glider continues the voyage for about 90 days, and the subsequent voyage time of carrying the invention is about 90 days, so that the system has extremely low power consumption and almost no influence.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.