CN114070441A - Underwater PCM signal receiving simulation system based on m-sequence coding - Google Patents
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Abstract
The invention relates to an underwater PCM signal receiving simulation system based on m-sequence coding, which comprises a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit and signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends received underwater sound signals to the PCM signal processing unit, the PCM signal processing unit samples, quantizes and encodes the underwater sound signals in sequence and sends the underwater sound signals and the sound field information of the sound field calculation module to the signal simulation, and the signal simulation receives the sound field information and the PCM signals and obtains the underwater information through PCM decoding. The invention combines the sound ray calculation information obtained by the Bellhop calculation model, considers the echo characteristics of multiple bright points and the Doppler frequency shift information at the same time, and increases the authenticity of the received sound signal simulation.
Description
Technical Field
The invention relates to the technical field of underwater signal simulation, in particular to an underwater PCM signal receiving simulation system based on m-sequence coding.
Background
In underwater target detection, the Doppler effect generated by relative movement of a target can directly influence the detection echo waveform and the detection effect thereof, so that a feasible scheme is to use a hyperbolic frequency modulation signal with Doppler invariant characteristic and a single-frequency pulse signal sensitive to Doppler as a combined detection signal, and the multi-parameter combined detection of the azimuth-distance-radial speed of an underwater moving target can be realized by capturing the arrival azimuth and the arrival moment of the hyperbolic frequency modulation echo signal by using a linear receiving array and performing high-precision frequency offset factor estimation on a single-product signal by using a Fourier coefficient interpolation method and a mutual fuzzy function method.
In addition, the chirp signal is also often used as a carrier signal for target detection, because in underwater acoustic channel propagation, the existence of channel multipath effect causes the spreading of signal waveforms transmitted at different times, and the phenomenon of collision easily exists at the receiving end, and the chirp signal has a wider bandwidth compared with a single-frequency carrier signal, can resist frequency selective fading, and has better resistance to doppler shift.
The PCM signal has the characteristics of high fidelity, high decoding speed and the like, but the application in the aspect of underwater target detection is less at present, and related theories, published documents and the like are also mentioned.
Whether hyperbolic frequency modulation signals, single-frequency pulse signals or linear frequency modulation signals exist, part of target information is easily lost when the hyperbolic frequency modulation signals, the single-frequency pulse signals or the linear frequency modulation signals are transmitted in a complex marine environment; the coding of PCM signals is generally carried out by adopting an A-law 13 broken line coding rule, captured signals are easy to decode and decode, and the safety factor is low; the Doppler shift effect is a large factor influencing signal propagation, the influence is more obvious in signal transmission in water, and the influence brought by the Doppler shift effect cannot be considered in conventional PCM signal transmission, so that the simulation of a received sound signal has distortion reality.
Disclosure of Invention
The invention aims to provide an underwater PCM signal receiving simulation system based on m-sequence coding, so as to solve the problems in the prior art.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the underwater PCM signal receiving simulation system based on m-sequence coding comprises a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit and signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends received underwater sound signals to the PCM signal processing unit, the PCM signal processing unit sends the underwater sound signals to the signal simulation together with the sound field information of the sound field calculation module after sampling, quantizing and coding the underwater sound signals in sequence, and the signal simulation receives the sound field information and the PCM signals and obtains the underwater information through PCM decoding.
Compared with the prior art, the invention has the beneficial effects that: based on given environmental parameters and input parameters, a marine physical environment is constructed, and corresponding sound ray information including signal amplitude, time delay, the number of intrinsic sound rays and the like is acquired by combining Bellhop. The coding part in the PCM signal generating process generates corresponding binary digits based on the m sequence, and abandons the original A-law 13 broken line coding rule, for the same signal source, the initial states of the shift registers are different, the coded PCM signals are also different, and on the premise of knowing the initial state of the shift register, the reverse reconstruction of the source signals can be realized.
By combining the acoustic ray calculation information obtained by the Bellhop calculation model, such as time delay, amplitude and the like, the receiving simulation of the PCM signal in a specific marine acoustic environment can be realized, wherein the receiving simulation comprises the influence brought by signal energy loss, multipath propagation effect and the like, and the authenticity of the receiving acoustic signal simulation is increased by considering the echo characteristics of multiple bright spots and Doppler frequency shift information.
Drawings
The disclosure of the present invention is illustrated with reference to the accompanying drawings. It is to be understood that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention. In the drawings, like reference numerals are used to refer to like parts. Wherein:
FIG. 1 is a flowchart of object detection in example 1 of the present invention;
FIG. 2 is a flowchart of the object detection in embodiment 2 of the present invention;
FIG. 3 is a schematic diagram illustrating the generation of a PCM signal in the PCM signal processing unit according to the present invention;
FIG. 4 is a diagram of an n-stage linear shift register according to the present invention;
fig. 5 is a flowchart of the object detection in embodiment 4 of the present invention.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the effects of the invention easy to understand, the invention is further described in detail with reference to the attached drawings. These drawings are simplified schematic views illustrating only the basic structure of the present invention in a schematic manner, and thus show only the constitution to which the present invention relates.
According to the technical scheme of the invention, a plurality of alternative structural modes and implementation modes can be provided by a person with ordinary skill in the art without changing the essential spirit of the invention. Therefore, the following detailed description and the accompanying drawings are merely illustrative of the technical aspects of the present invention, and should not be construed as all of the present invention or as limitations or limitations on the technical aspects of the present invention.
The technical solution of the present invention is further described in detail with reference to the accompanying drawings and examples.
Specifically, the environmental parameters are used for constructing marine physical environment information, and mainly include: the type of medium at sea surface (vacuum environment, rigid matter or acoustic half-space); the sea surface seabed boundary characteristic is used for describing the shape of the sea surface seabed; the seawater depth, and the seawater density and the acoustic energy attenuation coefficient corresponding to each water layer; the sound propagation horizontal distance is used for defining a sound ray propagation range; and sound velocity profile data is used for describing the rule that the underwater sound velocity changes along with the depth.
The sonar parameters describe the relevant characteristics of the transmitting array and the receiving array, and mainly comprise: transmitting array shapes, the number of array elements and the depth of the array elements; receiving array forms, the number of array elements and the depth of the array elements; a horizontal distance between the transmit array and the receive array; and the sound ray critical emergent angle is used for expressing the directivity of the transmitted sonar.
The processing method for calculating the relevant data in the parameter description environment parameters and the sonar parameters mainly comprises the following steps: interpolation modes of sound velocity profile data (cubic spline interpolation, C-type linear interpolation, N2 linear interpolation); acoustic energy attenuation coefficient units (dB/m, Nepers/m); the situation information of the ship and the target and the corresponding relative speed.
The parameter input module sends the sound field calculation information to the sound field calculation module, and the sound field calculation module is any one of a ray model, a normal wave model, a parabolic equation model, a beam integral model and an ocean environment noise field model. Furthermore, the sound field calculation module is a Bellhop calculation model in the ray model, and sound ray calculation information is output to the signal simulation through the Bellhop calculation model.
The Bellhop calculation model is mainly based on a Gaussian beam tracking theory, is a sound beam tracking model which can be used for predicting a sound pressure field of a marine environment, can intuitively reflect the propagation track of sound rays in the given marine environment, and can download the Matlab version and the Python version of the model from the following websites: http:// oallib.hlsresearch.com/acoustics toolbox
The sound field calculation model can also adopt a plane wave sound field algorithm, so that the calculation steps can be simplified, the sound pressure change rule of any point in the sound field can be obtained, and the simulation generation of the sound field of the point sound source in the website link can be referred to for the structure of the plane wave sound field. Website address: https:// m.doc88.com/p-7953351799462. html.
Preferably, the sound field calculation of the sound field calculation module adopts a plane wave sound field calculation method, the generation of the input parameters and the PCM signal is consistent with the original scheme, and the calculation parameters do not contain situation information of the ship and the target.
The signal input module sends the received underwater sound signals to the PCM signal processing unit, the PCM signal processing unit sends the underwater sound signals and sound field information of the sound field calculation module to signal simulation after sampling, quantizing and encoding, and the signal simulation receives the sound field information and the PCM signals and obtains the underwater information through PCM decoding.
As a preferable scheme, the signal simulation receives sound field information and PCM signal and decodes the received signal through PCM decoding, and the decoded signal is sent to matched filtering, thereby obtaining underwater information.
The PCM signal is not subjected to any encoding and compression processing, and is less susceptible to noise and distortion in the transmission system than the analog signal, and the principle of generation is shown in fig. 3.
The specific processing flow of the PCM signal processing unit is as follows:
sampling: sampling refers to periodically scanning an analog signal to convert a continuous signal into a discrete signal, and the sampled analog signal should contain all the information in the original signal, i.e., the original analog signal can be recovered without distortion, so that the sampling rate should be greater than twice the signal frequency.
And (3) quantification: quantization refers to representing the instantaneous sample value by the closest level value using a set of specified levels. After sampling and quantizing an analog signal, the obtained pulse amplitude modulation signal is only a limited number of values.
And (3) encoding: the coding is realized by combining the change of a shift register in an m sequence according to a certain rule and expressing a quantized value by using binary digits, and compared with the original A-law 13-broken line coding rule, the coding and decoding rate of the signal is improved, and meanwhile, the signal safety is improved to a certain extent.
Fig. 4 shows a code sequence generator comprising n shift registers whose states are determined by a clock-controlled input signal ("0" or "1"), e.g. the i-th shift register state is determined by the state of the i-1 th shift register after the previous clock pulse.
C in FIG. 40,C1,...,CnCalled feedback coefficient, which represents two possible ways of connecting the feedback line, C i1 represents that the connection is connected, and the output of the nth-i stage is added into feedback; ci0 means that the connection is broken, the output of the n-i stage does not participate in feedback, and there is C0＝CnA cyclic sequence is always true for 1. Thus, a general form of linear feedback logic expression is:
a to the left of equationn＝C0anSubstituting the formula into the formula to obtain:
thus, define
Wherein the power of x represents the corresponding position of the element, the above formula is the characteristic polynomial of the linear feedback shift register, if F (x) satisfies the following condition, F (x) is the original polynomial of degree n.
F (x) irreducible, i.e., no longer resolvable polynomial;
f (x) can divide x completelyp+1, where p ═ 2n-1；
F (x) is not capable of dividing xq+1, wherein q < p.
The essential condition for generating the m-sequence by the n-stage linear feedback shift register is that the characteristic polynomial F (x) of the shift register is a primitive polynomial, and therefore, the generation of the m-sequence is closely related to the solution of the primitive polynomial. The following is a solving method of the primitive polynomial of degree n:
x is to bep+1,p＝2n-1 factorization to simplest mode;
screening the factors which are more than or equal to n times in the obtained factor set;
if the resulting factor is unable to divide any x exactlyq+1, q < p, the factor is a primitive polynomial and is not unique.
Table 1 lists the octal feedback coefficients for a partial m-sequence. Feedback coefficient C with 7-level m-sequencei＝(211)8For example, the binary expression is Ci＝(010001001)2Thus, the feedback coefficients of each stage are respectively: c0＝1，C1＝0，C2＝0，C3＝0，C4＝1，C5＝0，C6＝0，C7This results in the construction of a corresponding m-sequence generator, which is equal to 1.
The m-sequence construction principle of other series is the same as the method.
| Number of stages n | Period p | Feedback coefficient Ci(eight system) |
| 3 | 7 | 13 |
| 4 | 15 | 23 |
| 5 | 31 | 45，67，75 |
| 6 | 63 | 103，147，155 |
| 7 | 127 | 203，211，217，235，277，313，325，345，367 |
| 8 | 255 | 435，453，537，543，545，551，703，747 |
| 9 | 511 | 1021，1055，1131，1157，1167，1175 |
| 10 | 1023 | 2011，2033，2157，2443，2745，3471 |
| 11 | 2047 | 4005，4445，5023，5263，6211，7363 |
| 12 | 4095 | 10123，11417，12515，13505，14127，15053 |
| 13 | 8191 | 20033，23261，24633，30741，32535，37505 |
| 14 | 16383 | 42103，51761，55753，60153，71147，67401 |
| 15 | 32765 | 100003，110013，120265，133663，142305 |
Table 1 feedback coefficient table of partial m-sequence
The method comprises the following steps of receiving sound field information and PCM signals through signal simulation, and obtaining underwater information through PCM decoding, wherein the received signal simulation process comprises the following steps:
the first step is as follows: taking a single sonar as an emitting source as an example, assuming that the quantized original signal is represented as squanThe resulting m sequence is smcodeI.e. PCM signal, having sPCM＝smcodeConsidering the multipath effect, the received signal can be expressed as:
wherein A isi、τiRespectively representing the amplitude and the propagation time of the acoustic signal in different paths, and the total number of the n propagation paths is n.
The second step is that: doppler shift information is added to allow for carrier two-way propagation, where the received signal can be represented as:
wherein, FcWhich is indicative of the carrier frequency,
representing the time difference in the course of the acoustic propagation, as reflected in the doppler shift variation.
The third step: let S be fft (S)rece2) Considering the multi-spot echo characteristics, the received signal can be expressed as:
wherein f isrWhich represents the frequency value of the chirp signal,
and the time delay of the signals arriving at the bow and the stern relative to the signals arriving in the ship is shown.
After the simulated received signal is obtained, reverse recombination of the original signal can be realized based on the generation rule of the m sequence, the change of the signal is further analyzed, and the distance measurement and direction finding of the target are realized by combining matched filtering processing. The carrier signal is restored through matching processing, the PCM signal is extracted from the carrier signal, and the reverse recombination of the PCM signal can be realized by combining the generation rule of the m sequence, so that the target underwater information is obtained.
In embodiment 2, in the foregoing scheme, the underwater PCM signal receiving simulation system based on m-sequence coding further includes a multi-bright-spot echo characteristic model, where the multi-bright-spot echo characteristic model is used to receive a target scale and a sound ray incident angle parameter of the parameter input module, and send processed sound field information to signal simulation, for example, send target intensity and relative delay to the signal simulation.
In the multi-bright-spot echo model, the target echo is formed by overlapping a plurality of bright-spot echoes, and the total transfer function is as follows:
wherein m denotes the number of the echoes of the bright spot, e.g.
The amplitude-frequency response of the echo of the mth bright spot,
representing position information including an incidence angle and a pitch angle, wherein omega represents angular frequency of a transmitting signal; tau ismFor time delay, depends on the acoustic path of each spot relative to the reference spot, phimThe phase of the bright spot echo is suddenly changed.
When the geometric object is a sphere, the target intensity is:
TS＝10logR2/4(1+R/r)2
when the geometric object is a cylinder, the target strength is:
TS＝10log[(RL2/2λ(1+R/r))(sinβ/β)2cos2θ]
wherein R is the principal curvature radius of the scatterer, and R is the distance between a sound source and a scattering point; theta is an included angle between the incident wave direction and the axis of the cylinder, beta is kL sin theta, lambda is the incident wave wavelength, and L is the length of the cylinder. Therefore, the amplitude-frequency response can be obtained according to the target intensities of different shapes.
Under the normal condition, the target is equivalent to a three-bright-spot model, and the positions of the bright spots are respectively a ship bow, a ship middle and a ship tail. By a signal s0(t) represents a target echo signal, the fourier transform result is s (f), and the received signal can be represented by taking into account the multi-bright-spot echo characteristics:
wherein f isrWhich represents the frequency value of the chirp signal,
and the time delay of the signals arriving at the bow and the stern relative to the signals arriving in the ship is shown.
In addition, the underwater PCM signal receiving simulation system based on the m-sequence coding further comprises Doppler frequency shift information, wherein the Doppler frequency shift information is used for receiving the signal frequency shift and the relative speed parameter of the parameter input module and sending processed sound field information to the signal simulation, for example, sending the frequency shift information to the signal simulation.
The doppler shift can be expressed as:
the target relative movement velocity is assumed to be v (θ), which is a quantity having a direction. The emission signal is s (T), and the pulse width is T. If the distance between the target and the sonar is L at the time t, the back round trip time of the front edge of the pulse passing through the target is t1When the back edge of the pulse is reflected by the target, the round-trip time is t2. The received signal pulse width becomes:
therefore, due to the relative motion between the sonar and the target, the transmitted signal with the pulse width T becomes a signal with the pulse width α T at the receiving point after being reflected by the target.
When there is a propagation delay τ, the received signal can be expressed as:
wherein δ is 2v (θ)/c;
representing the complex envelope of the signal.
Example 3, in contrast to examples 1 and 2: after the PCM signal processing unit processes the underwater sound signal, the coded signal is sent to a carrier wave, and the PCM signal is sent to signal simulation after the carrier wave processing.
Due to the influence of factors such as multipath effect, underwater acoustic signals are prone to generate signal collision access phenomena at a user terminal, and therefore signal loss or access blockage is caused. In consideration of performance performances in the aspects of collision resistance, collision resistance and the like, the technical problem is solved by taking the linear frequency modulation signal as a carrier signal to carry out simulation test. The mathematical expression for the chirp signal is:
where T is a time variable, T is a pulse duration, and K ═ B/T is a signal frequency change rate, or called chirp rate, in Hz/s, which represents a ratio between a signal chirp width B and a signal duration T.
The method is based on given environmental parameters and input parameters, a marine physical environment is constructed, and corresponding sound ray information including signal amplitude, time delay, the number of intrinsic sound rays and the like is acquired by combining Bellhop. The coding part in the PCM signal generating process generates corresponding binary digits based on the m sequence, and abandons the original A-law 13 broken line coding rule, for the same signal source, the initial states of the shift registers are different, the coded PCM signals are also different, and on the premise of knowing the initial state of the shift register, the reverse reconstruction of the source signals can be realized.
By combining the acoustic ray calculation information obtained by the Bellhop calculation model, such as time delay, amplitude and the like, the receiving simulation of the PCM signal in a specific marine acoustic environment can be realized, wherein the receiving simulation comprises the influence brought by signal energy loss, multipath propagation effect and the like, and the authenticity of the receiving acoustic signal simulation is increased by considering the echo characteristics of multiple bright spots and Doppler frequency shift information.
The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An underwater PCM signal receiving simulation system based on m-sequence coding is characterized in that: the underwater sound simulation system comprises a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit and signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends received underwater sound signals to the PCM signal processing unit, the PCM signal processing unit sends the underwater sound signals to the signal simulation together with the sound field information of the sound field calculation module after sampling, quantizing and encoding, and the signal simulation receives the sound field information and the PCM signals and obtains the underwater information through PCM decoding.
2. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: the parameter input module comprises environmental parameters, sonar parameters and calculation parameters, wherein the environmental parameters are used for constructing marine physical environment information, the sonar parameters are used for describing relevant characteristics of a transmitting array and a receiving array, and the calculation parameters are used for describing a processing method of relevant data in the environmental parameters and the sonar parameters;
the sound field calculation module is any one of a ray model, a normal wave model, a parabolic equation model, a beam integral model and an ocean environment noise field model.
3. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 2, wherein: the parameter input module also comprises signal parameters, and the parameter input module containing the signal parameters can be used as a signal input module to send the original signal to the PCM signal processing unit.
4. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 2, wherein: the sound field calculation module is a Bellhop calculation model in a ray model.
5. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: the system further comprises a multi-bright-spot echo characteristic model, wherein the multi-bright-spot echo characteristic model is used for receiving parameters of the parameter input module and sending processed sound field information to signal simulation.
6. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: the Doppler frequency shift information is used for receiving the parameters of the parameter input module and sending the processed sound field information to the signal simulation.
7. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: and when the PCM signal processing unit codes, according to a certain rule and the change of a shift register in the m sequence, the quantized value is represented by binary digits.
8. The underwater PCM signal reception simulation system based on m-sequence coding of claim 7, wherein: the shift register adopts a linear feedback shift register, and the essential condition for generating the m sequence by the n-stage linear feedback shift register is that a characteristic polynomial F (x) of the shift register is a primitive polynomial.
9. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: and the PCM signal processing unit is used for processing the underwater acoustic signal, sending the coded signal to a carrier, and sending the PCM signal to signal simulation after carrier processing.
10. The underwater PCM signal receiving simulation system based on m-sequence coding as claimed in claim 1, wherein: the signal simulation receives sound field information and PCM signals, decodes the received signals through PCM decoding, and sends the decoded signals to matched filtering, so that underwater information is obtained.
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| CN109192216A (en) * | 2018-08-08 | 2019-01-11 | 联智科技（天津）有限责任公司 | A kind of Application on Voiceprint Recognition training dataset emulation acquisition methods and its acquisition device |
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