CN114070441B - 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 a signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends a received underwater sound signal to the PCM signal processing unit, the PCM signal processing unit samples, quantizes and codes the underwater sound signal in sequence and then sends the underwater sound signal to the signal simulation together with sound field information of the sound field calculation module, and the signal simulation receives the sound field information and the PCM signal and obtains the underwater information through PCM decoding. According to the invention, sound ray calculation information obtained by combining Bellhop calculation models is combined, and meanwhile, the multi-bright-point echo characteristics and Doppler frequency shift information are considered, so that the authenticity of the received sound signal simulation is increased.
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 the underwater target detection, the Doppler effect generated by the relative motion of the target can directly influence the detection echo waveform and the detection effect thereof, so that the double-tone frequency signal with the Doppler invariant characteristic and the single-frequency pulse signal sensitive to Doppler are used as a feasible scheme for combined detection signals, and the multi-parameter combined detection of the azimuth-distance-radial speed of the underwater moving target can be realized by capturing the azimuth and the moment of arrival of the double-tone frequency echo signal by adopting a linear receiving array, and carrying out high-precision frequency offset factor estimation on the single-product signal by utilizing a Fourier coefficient interpolation method and a mutual ambiguity function method.
In addition, the linear frequency modulation signal is also often used as a carrier signal for target detection, and is caused by the fact that in the underwater acoustic channel propagation, the wave forms of signals transmitted at different moments are expanded and are easy to collide at a receiving end, and compared with a single-frequency carrier signal, the linear frequency modulation signal has wider bandwidth, can resist frequency selective fading and has better resistance to Doppler frequency shift.
PCM signals have the characteristics of high fidelity, high decoding speed and the like, but the application of the PCM signals in the aspect of underwater target detection is less at present, and related theories, publications and the like are also mentioned.
Whether a hyperbolic frequency modulation signal, a single frequency pulse signal or a linear frequency modulation signal, part of target information is easy to lose when the target information is transmitted in a complex marine environment; the coding of the PCM signal is generally carried out by adopting an A law 13 broken line coding rule, the captured signal is easy to decode and decipher, and the safety coefficient is low; the Doppler shift effect is a large factor affecting signal propagation, and the effect is more obvious in signal transmission in water, whereas the effect caused by the Doppler shift effect cannot be considered in conventional PCM signal transmission, so that simulation of a received sound signal has distortion practicability.
Disclosure of Invention
The invention aims to provide an underwater PCM signal receiving simulation system based on m-sequence coding, which solves the problems in the background technology.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
The underwater PCM signal receiving simulation system based on m-sequence encoding comprises a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit and a signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends a received underwater sound signal to the PCM signal processing unit, the PCM signal processing unit samples, quantizes and encodes the underwater sound signal in sequence and sends 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 signal and obtains the underwater information through PCM decoding.
Compared with the prior art, the invention has the beneficial effects that: based on given environment parameters and input parameters, constructing a marine physical environment, and acquiring corresponding sound ray information including signal amplitude, time delay, intrinsic sound ray number and the like by combining Bellhop. The coding part in the PCM signal generating process generates corresponding binary digits based on m sequences, abandons the original A-law 13-fold line coding rule, and for the same signal source, the initial states of the mobile registers are different, and the coded PCM signals are also different, so that the reverse reconstruction of the source signals can be realized on the premise of knowing the initial states of the mobile registers.
The acoustic line calculation information such as time delay, amplitude and the like obtained by combining Bellhop calculation models can be used for realizing the receiving simulation of the PCM signals in the specific marine acoustic environment, wherein the influence caused by signal energy loss, multi-path propagation effect and the like is contained, and meanwhile, the multi-bright-point echo characteristic and Doppler frequency shift information are considered, so that the authenticity of the receiving acoustic signal simulation is increased.
Drawings
The disclosure of the present invention is described 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 flow chart of the object detection in embodiment 1 of the present invention;
FIG. 2 is a flow chart of the object detection in embodiment 2 of the present invention;
FIG. 3 is a schematic diagram of generating a PCM signal in a PCM signal processing unit according to the present invention;
FIG. 4 is a schematic 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 characteristics, the achievement of the purpose and the effect of the present invention easy to understand, the present invention will now be described in further detail with reference to the accompanying drawings. The drawings are simplified schematic representations which merely illustrate the basic structure of the invention and therefore show only the structures to which the invention pertains.
According to the technical scheme of the invention, a person skilled in the art can propose various alternative structural modes and implementation modes without changing the true spirit of the invention. Accordingly, the following detailed description and drawings are merely illustrative of the invention and are not intended to be exhaustive or to limit the invention to the precise form disclosed.
The technical scheme of the invention is further described in detail below with reference to the accompanying drawings and examples.
Embodiment 1 as shown in fig. 1, an underwater PCM signal reception simulation system based on m-sequence encoding includes a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit, and a signal simulation. The parameter input module comprises an environment parameter, a sonar parameter and a calculation parameter, wherein the environment parameter is used for constructing marine physical environment information, the sonar parameter describes the relevant characteristics of the transmitting array and the receiving array, and the calculation parameter is used for describing a processing method of relevant data in the environment parameter and the sonar parameter.
Specifically, the environmental parameters are used for constructing marine physical environmental information, and mainly include: the type of medium at sea level (vacuum environment, rigid material or acoustic half space); sea surface seabed boundary characteristics for describing the shape of the sea surface seabed; sea water depth, sea water density and acoustic energy attenuation coefficient corresponding to each water layer; a sound propagation horizontal distance for defining a sound ray propagation range; sound velocity profile data for describing the law of underwater sound velocity variation with depth.
The sonar parameter describes the relative characteristics of a transmitting array and a receiving array, and mainly comprises the following steps: transmitting array shape, array element number and array element depth; receiving array shapes, array element numbers and array element depths; a horizontal distance between the transmit array and the receive array; the critical emergent angle of sound ray is used for representing the directivity of the emitted sonar.
The processing method of the relevant data in the calculation parameter description environment parameter and sonar parameter mainly comprises the following steps: interpolation modes (cubic spline interpolation, C-type linear interpolation and N2 linear interpolation) of sound velocity profile data; acoustic energy attenuation coefficient units (dB/m, nepers/m); situation information of the ship and the target and corresponding relative speed.
The parameter input module sends sound field calculation information to a sound field calculation module, and the sound field calculation module is any one of a ray model, a simple wave model, a parabolic equation model, a beam integral model and a marine environment noise field model. Further, 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.
Bellhop the calculation model is mainly based on Gaussian beam tracking theory, is a sound beam tracking model which can be used for predicting the sound pressure field of the ocean environment, can intuitively reflect the propagation track of sound rays in the given ocean environment, and can be downloaded in Matlab version and Python version of the model in the following websites: http:// oalib. Hlsresearch. Com/AcousticsToolbox-
The sound field calculation model can also adopt a plane wave sound field algorithm, so that the calculation step 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 with respect to the construction of the plane wave sound field. Web site: https:// m.doc88.com/p-7953351799462.Html.
As a preferable scheme, the sound field calculation of the sound field calculation module adopts a plane wave sound field calculation method, the generation of input parameters and PCM signals 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 signal to the PCM signal processing unit, the PCM signal processing unit samples, quantizes and encodes the underwater sound signal in sequence and then sends the underwater sound signal to the signal simulation, and the signal simulation receives the sound field information and the PCM signal and obtains the underwater information through PCM decoding.
As a preferred scheme, the signal simulation receives sound field information and PCM signals, decodes the received signals through PCM decoding, and transmits the decoded signals to matched filtering, thereby obtaining underwater information.
The PCM signal is not subjected to any coding and compression processing, and is less susceptible to noise and distortion of the transmission system than the analog signal, and the generation principle thereof 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 change a time-continuous signal into a time-discrete signal, and the analog signal should contain all information in the original signal after sampling, i.e. the original analog signal can be recovered without distortion, so that the sampling rate is greater than twice the signal frequency.
Quantification: quantization refers to representing the instantaneous sample value by the nearest level value using a set of specified levels. After sampling and quantizing an analog signal, the obtained pulse amplitude modulation signal is only limited in number.
Encoding: the coding is to express the quantized value by binary digits according to a certain rule, and the quantized value is realized by combining the change of a moving register in an m sequence.
Fig. 4 shows a code sequence generator consisting of n shift registers whose states are dependent on a clocked signal ("0" or "1"), e.g. the state of the i shift register depends on the state of the i-1 shift register after the previous clock pulse.
C 0,C1,...,Cn in fig. 4 is called the feedback coefficient, which represents two possible ways of connecting the feedback lines, C i = 1 represents that the connection is on, and the n-i th stage output is added to the feedback; c i =0 indicates that the line is disconnected, the n-i output does not participate in feedback, and C 0＝Cn =1 is constant, indicating a cyclic sequence. Thus, the general form of the linear feedback logic expression is:
Substituting a n＝C0an on the left side of the equation into the above formula, the arrangement can be obtained:
thus, define
The power of x represents the corresponding position of the element, the above formula is the characteristic polynomial of the linear feedback mobile register, and if F (x) meets the following conditions, F (x) is the primitive polynomial of degree n.
F (x) is irreducible, i.e. the polynomial cannot be subdivided;
F (x) can be divided by x p +1, where p=2 n -1;
f (x) cannot be divided by x q +1, where q < p.
The requirement for generating the m-sequence by the n-level linear feedback shift register is that the characteristic polynomial F (x) of the shift register is a primitive polynomial, so that the generation of the m-sequence is closely related to the solution of the primitive polynomial. The following is a solution method of n-degree primitive polynomials:
factoring x p+1,p＝2n -1 into a simplest mode;
Screening factors greater than or equal to n times in the obtained factor set;
if the resulting factor is not able to divide any x q +1, q < p, then the factor is primitive polynomial and is not unique.
Table 1 lists the octal feedback coefficients for a partial m-sequence. Taking 7-level m-sequence feedback coefficient C i＝(211)8 as an example, the binary expression form of the feedback coefficient C i＝(211)8 is C i＝(010001001)2, so that each level of feedback coefficient is ：C0＝1,C1＝0,C2＝0,C3＝0,C4＝1,C5＝0,C6＝0,C7＝1, respectively, and a corresponding m-sequence generator can be constructed.
The m-sequence construction principle of other stages is the same as the method.
| Series n | Period p | Feedback coefficient C i (octal) |
| 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 for partial m-sequences
The signal simulation receives sound field information and PCM signals and obtains underwater information through PCM decoding, and the receiving signal simulation process is as follows:
The first step: taking a single sonar as a transmitting source as an example, assuming that the quantized original signal is denoted as s quan, the obtained m sequence is s mcode, namely the PCM signal, s PCM＝smcode exists, and the multi-path effect is considered, at this time, the received signal can be expressed as:
wherein A i、τi respectively represents the amplitude and the propagation time of the acoustic signals in different paths, and n propagation paths are taken as a total.
And a second step of: the Doppler shift information is added in view of carrier double-pass propagation, and the received signal can be expressed as:
wherein F c denotes the carrier frequency, Representing the time difference in the acoustic propagation process, embodied as a doppler shift change.
And a third step of: let s=fft (S rece2), considering the multi-shot echo characteristic, the received signal can be expressed as:
where f r denotes the frequency value of the chirp signal, The time delay of the signals reaching the bow and the tail of the ship relative to the signals reaching the ship is shown.
After the simulated received signals are obtained, the reverse recombination of the original signals can be realized based on the generation rule of m sequences, so that the change of the signals is analyzed, and the distance measurement and direction finding of the target are realized by combining the 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 solution, the underwater PCM signal receiving simulation system based on m-sequence encoding further includes a multi-bright-spot echo model, where the multi-bright-spot echo characteristic model is configured to receive the target scale and the sound ray incidence angle parameters of the parameter input module, and send the processed sound field information to the signal simulation, for example, send the target intensity and the 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 represents the bright point echo sequence number, e.g Is the amplitude-frequency response of the mth bright point echo,Representing position information, including incident angle, pitch angle, ω representing the transmitted signal angular frequency; τ m is the time delay, depending on the range of each bright spot relative to the reference bright spot, the phase at which the bright spot echo forms at φ m suddenly changes.
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 main curvature radius of the scatterer, and R is the distance between the sound source and the scattering point; θ is the angle between the direction of the incident wave and the axis of the cylinder, β=klsin θ, λ is the wavelength of the incident wave, and L is the cylinder length. Therefore, the amplitude-frequency response can be obtained from the target intensities of different shapes.
Under normal conditions, the target is equivalent to a three-bright-spot model, and the positions of bright spots are respectively the bow, the middle and the tail of the ship. The target echo signal is represented by a signal S 0 (t), the fourier transform result is S (f), and the received signal can be represented by:
where f r denotes the frequency value of the chirp signal, The time delay of the signals reaching the bow and the tail of the ship relative to the signals reaching the ship is shown.
In addition, the underwater PCM signal receiving simulation system based on m-sequence coding also comprises Doppler frequency shift information, wherein the Doppler frequency shift information is used for receiving signal frequency shift and relative speed parameters of the parameter input module, and transmitting processed sound field information to signal simulation, such as frequency shift information to signal simulation.
The doppler shift can be expressed as:
let the relative movement speed of the target be v (θ), which is a quantity having a direction. The transmitted signal is s (T), and the pulse width is T. If at time t, the distance between the target and the sonar is L, the back round trip time of the pulse front through the target is t 1, and when the back round trip time of the pulse back through the target is t 2. The received signal pulse width becomes:
Therefore, due to the relative motion between the sonar and the target, the signal with the pulse width T becomes a signal with the pulse width alpha T at the receiving point after the signal with the pulse width T is reflected by the target.
When there is a propagation delay τ, the received signal may be expressed as:
wherein δ=2v (θ)/c; representing the complex envelope of the signal.
Example 3, unlike examples 1 and 2, is: after processing the underwater acoustic signal, the PCM signal processing unit sends the coded signal to a carrier wave, and the PCM signal is sent to the signal simulation after the carrier wave processing.
Under the influence of factors such as multi-path effect, the underwater acoustic signal is easy to generate signal collision access phenomenon at the user terminal, thereby causing signal loss or access blockage. In consideration of performance performances in the aspects of collision resistance, collision resistance and the like, the linear frequency modulation signal is used as a carrier signal to carry out simulation test so as to overcome the technical problem. The mathematical expression of the chirp signal is:
Where T is a time variable, T is a pulse duration, k=b/T is a rate of change of signal frequency, or called a chirp rate, in Hz/s, representing the ratio between signal chirp width B and signal duration T.
In embodiment 4, referring to fig. 5, the parameter input module further includes signal parameters on the basis of embodiments 1 to 3, and the parameter input module including the signal parameters can be used as a signal input module to send the original signal to the PCM signal processing unit. The signal parameters are mainly the information of center frequency, bandwidth, signal time length and the like.
The invention constructs the ocean physical environment based on given environment parameters and input parameters, and obtains corresponding sound ray information including signal amplitude, time delay, intrinsic sound ray number and the like by combining Bellhop. The coding part in the PCM signal generating process generates corresponding binary digits based on m sequences, abandons the original A-law 13-fold line coding rule, and for the same signal source, the initial states of the mobile registers are different, and the coded PCM signals are also different, so that the reverse reconstruction of the source signals can be realized on the premise of knowing the initial states of the mobile registers.
The acoustic line calculation information such as time delay, amplitude and the like obtained by combining Bellhop calculation models can be used for realizing the receiving simulation of the PCM signals in the specific marine acoustic environment, wherein the influence caused by signal energy loss, multi-path propagation effect and the like is contained, and meanwhile, the multi-bright-point echo characteristic and Doppler frequency shift information are considered, so that the authenticity of the receiving acoustic signal simulation is increased.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the scope of the invention, but to limit the invention to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (7)
1. An underwater PCM signal receiving simulation system based on m-sequence coding is characterized in that: the system comprises a parameter input module, a sound field calculation module, a signal input module, a PCM signal processing unit and a signal simulation, wherein the parameter input module sends sound field calculation information to the sound field calculation module, the signal input module sends a received underwater sound signal to the PCM signal processing unit, the PCM signal processing unit samples, quantizes and encodes the underwater sound signal in sequence and then sends the underwater sound signal to the signal simulation together with sound field information of the sound field calculation module, and the signal simulation receives the sound field information and the PCM signal and obtains the underwater information through PCM decoding; when the PCM signal processing unit is used for encoding, the quantized value is represented by binary digits by combining the change of a moving register in the m sequence;
The PCM signal processing unit processes the underwater acoustic signal, then sends the coded signal to a carrier wave, and sends the PCM signal to the signal simulation after the carrier wave processing; the signal simulation receives sound field information and a PCM signal, decodes the received signal through PCM decoding, and sends the decoded signal to matched filtering so as to obtain underwater information;
the signal simulation receives sound field information and a PCM signal and obtains underwater information through PCM decoding, and the receiving signal simulation process is as follows:
The first step: taking a single sonar as a transmitting source as an example, assuming that the quantized original signal is denoted as s quan, the obtained m sequence is s mcode, namely the PCM signal, s PCM＝smcode exists, and the multi-path effect is considered, at this time, the received signal can be expressed as:
wherein A i、τi respectively represents the amplitude and the propagation time of acoustic signals in different paths, and n propagation paths are totally adopted;
and a second step of: the Doppler shift information is added in view of carrier double-pass propagation, and the received signal can be expressed as:
wherein F c denotes the carrier frequency, Representing the time difference in the acoustic propagation process, and particularly representing Doppler frequency shift change;
And a third step of: let s=fft (S rece2), considering the multi-shot echo characteristic, the received signal can be expressed as:
where f r denotes the frequency value of the chirp signal, Representing the time delay of signals reaching the bow and the tail of the ship relative to signals reaching the ship;
After the simulated received signals are obtained, the reverse recombination of the original signals can be realized based on the generation rule of m sequences, so that the change of the signals is analyzed, and the distance measurement and direction finding of the target are realized by combining matched filtering treatment; 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.
2. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 1, wherein: the parameter input module comprises an environment parameter, a sonar parameter and a calculation parameter, wherein the environment parameter is used for constructing marine physical environment information, the sonar parameter describes the relevant characteristics of a transmitting array and a receiving array, and the calculation parameter is used for describing a processing method of relevant data in the environment parameter and the sonar parameter;
The sound field calculation module is any one of a ray model, a simple wave model, a parabolic equation model, a wave beam integral model and an ocean environment noise field model.
3. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 2, wherein: the parameter input module further comprises signal parameters, and the parameter input module containing the signal parameters can be used as a signal input module for sending the original signals to the PCM signal processing unit.
4. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 2, wherein: the sound field calculation module is Bellhop calculation models in the ray models.
5. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 1, 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 the signal simulation.
6. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 1, wherein: the Doppler frequency shift information is used for receiving parameters of the parameter input module and transmitting the processed sound field information to the signal simulation.
7. An m-sequence encoding based underwater PCM signal reception simulation system according to claim 1, wherein: the moving register adopts a linear feedback moving register, and the charging condition of the n-level linear feedback moving register for generating m-sequence is that the characteristic polynomial F (x) of the moving register is the primitive polynomial.
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| CN104734795B (en) * | 2015-02-11 | 2017-03-01 | 哈尔滨工业大学深圳研究生院 | A kind of time- variant channel Capacity Simulation model |
| CN105262609A (en) * | 2015-09-02 | 2016-01-20 | 南京奇幻通信科技有限公司 | MATLAB (Matrix Laboratory)-based PCM (Pulse Code Modulation) communication system simulation method and system |
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