CN115996101B - Moon surface multi-scene communication-oriented wireless channel modeling method - Google Patents
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Abstract
The invention discloses a wireless channel modeling method for lunar surface multi-scene communication, which relates to the field of lunar wireless channel modeling, and is characterized in that a ray tracing method is utilized to build different electromagnetic wave ray propagation models for different typical scenes on the lunar surface, and the relation between the depth and width of a merle pit and the number of suggested rays is given when the merle pit is in a scene; meanwhile, respectively establishing propagation loss models in scenes of floating charged particles on the moon-oriented surface; aiming at a scene of floating charged moon dust on a moon surface, a particle scattering absorption model is established, and the relation between an attenuation coefficient and electromagnetic wave frequency, the charged quantity of the moon dust particles and visibility is given; aiming at a scene of lunar floating solar wind charged particles, a channel model is established, and the channel model is divided into a Rayleigh channel model or a Gaussian channel model according to the magnitude of a solar flicker factor; the method for modeling the moon surface wireless channel is quite complete.
Description
Technical Field
The invention relates to the field of lunar wireless channel modeling, in particular to a wireless channel modeling method for lunar surface multi-scene communication.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moon is taken as the largest natural satellite of the earth, and the unique position and resources (such as titanium metal, helium-3 and the like which can be mined) are often taken as the first step of space strategy of each country, so that how to ensure effective communication on the surface of the moon is a vital ring in lunar exploration projects of each country; in recent years, many students have devoted to research on a lunar surface wireless channel modeling method, and there have been many mature research achievements and modeling methods for various typical scenes; however, further research is needed on how to form a wireless channel modeling method of a complete multi-scene facing the lunar surface aiming at a complex electromagnetic wave propagation environment of the lunar surface.
At present, in lunar surface wireless channel modeling, research mainly focuses on the problem of influence of topography on the propagation of electromagnetic waves on the lunar surface, a ground wireless channel modeling method is referred to for one or two typical scenes (an obstacle scene and a diffraction scene) on the lunar surface, and lunar surface typical topography parameters are added to build a lunar surface electromagnetic wave propagation model, but only the influence of topography is considered, the problem of wireless channel modeling in charged particle scenes is not considered, and a wireless channel modeling method which is complete for each typical scene on the lunar surface is lacked.
The research on the scene of the moon dust particles mainly focuses on the influence of flying dust caused by landing of a moon detector and running of a lunar rover on the lunar surface; establishing a moon dust drag model by using Euler-Lagrange methods and the like to obtain the relation between different particle diameters of moon dust particles and flying dust angles and speeds of the moon dust particles, obtaining corrosion characteristics and charging characteristics of the moon dust, and modeling the influence of the corrosion characteristics and the charging characteristics of the moon dust; but only a single scene of a moon dust particle scene is considered, and a wireless channel modeling method which is complete for each typical scene of the moon surface is lacked.
Disclosure of Invention
The invention aims at: aiming at solving the problem that a wireless channel modeling method for each typical scene of a lunar surface is lack and the existing wireless channel modeling method for the lunar surface at present when the lunar surface is communicated, only the influence of topography is considered, and the problem of wireless channel modeling in a charged particle scene is not considered, is provided with the wireless channel modeling method for the multi-scene communication of the lunar surface, on the basis of the original wireless channel modeling of the lunar surface, different typical scenes (a near-lunar free space scene, a lunar sea scene, an obstacle scene and a merle scene) of the lunar surface are oriented by a ray tracing method, different electromagnetic wave ray propagation models are established, and the relation between the depth and the width of the merle and the number of suggested rays is given when the merle scene is formed; meanwhile, respectively establishing propagation loss models in scenes of floating charged particles on the moon-oriented surface; aiming at a scene of floating charged moon dust on a moon surface, a particle scattering absorption model is established, and the relation between an attenuation coefficient and electromagnetic wave frequency, the charged quantity of the moon dust particles and visibility is given; aiming at a scene of solar wind charged particles floating on a lunar surface, establishing a relation between a solar flicker index and a lunar distance and a Rician factor, so as to establish a channel model, and dividing the channel model into a Rayleigh channel model or a Gaussian channel model according to the size of the solar flicker factor; the method for modeling the moon surface wireless channel is more complete, so that the problems are solved.
The technical scheme of the invention is as follows:
a wireless channel modeling method for moon surface multi-scene communication comprises the following steps:
Step S1: dividing a propagation scene of the lunar surface electromagnetic wave into a plurality of typical scenes;
Step S2: respectively establishing electromagnetic wave propagation loss models aiming at different typical scenes of electromagnetic wave propagation on the lunar surface;
Step S3: judging a specific typical scene of the lunar surface where the target is located, and calculating a propagation coefficient according to the corresponding electromagnetic wave propagation loss model.
Further, the step S1 includes:
According to the difference of the topography of the lunar surface, the propagation scene of the electromagnetic wave on the lunar surface is divided into: a near moon surface free space scene, a moon surface moon sea scene, a moon surface multi-obstacle scene, a moon surface merle scene;
According to the difference of charged particles existing on the moon surface, the propagation scene of the moon surface electromagnetic wave is divided into: a moon surface floating charged moon dust particle scene and a moon surface floating solar wind particle scene.
Further, the step S2 includes:
Establishing an electromagnetic wave propagation loss model facing to a free space scene on the lunar surface;
Establishing an electromagnetic wave propagation loss model facing to a moon surface moon sea scene by using a ray tracing method;
Establishing an electromagnetic wave propagation diffraction loss model facing to a moon surface multi-obstacle scene;
establishing an electromagnetic wave propagation loss model facing to the merle pit scene on the lunar surface by using a ray tracing method;
establishing an electromagnetic wave propagation loss model aiming at a moon surface floating charged moon dust particle scene;
And establishing an electromagnetic wave propagation loss model aiming at a moon surface floating solar wind particle scene.
Further, an electromagnetic wave propagation loss model established for a near-lunar surface free space scene comprises:
Pr＝20lg(d)+20lg(f)+32.44
Wherein:
d is the distance between the receivers and transmitters;
f is the frequency of the electromagnetic wave.
Further, an electromagnetic wave propagation loss model established by using a ray tracing method facing to a lunar sea scene on the lunar surface comprises the following steps:
modeling electromagnetic wave propagation loss by adopting a two-ray model;
The signal received by the receiving antenna can be obtained by superposing direct wave and reflected wave vectors, and the size and the phase of the reflected signal are determined by path length difference and ground reflection coefficient, so that a predicted point field intensity calculation formula and a lunar surface reflection loss calculation formula in the propagation process are obtained:
Wherein:
R 0 is the lunar surface reflection coefficient;
h t is the transmitter height;
h r is the receiver height;
Lambda is the wavelength of the electromagnetic wave.
Further, an electromagnetic wave propagation diffraction loss model established for a moon surface multi-obstacle scene comprises:
estimating the loss by treating the obstacle as a diffraction blade-shaped edge, namely treating the obstacle as a blade-shaped obstacle;
Considering the blade-shaped obstacle as an infinite absorption screen diffraction theory model, theoretically, the diffraction loss of a single blade-shaped obstacle is as follows:
Wherein:
r 0 is the radius of curvature of the arc at the top of the blade-shaped barrier;
d T is the distance from the transmitter tip to the blade-shaped obstacle tip;
d R is the distance from the receiver tip to the blade-shaped obstacle tip;
lambda is the wavelength of electromagnetic waves;
h is the height of the blade-shaped barrier.
Further, an electromagnetic wave propagation loss model established by utilizing a ray tracing method facing to a moon surface merle scene comprises the following steps:
when modeling is performed in a moon surface meteorite pit scene, analyzing field intensity and loss by adopting a ray tracing method, so that the most suitable modeling ray number is selected;
the calculation formula of the reflection loss of the lunar surface in the electromagnetic wave propagation process under the lunar surface meteorite scene is consistent with that under the lunar sea scene;
During simulation, a ray tracing method is used for determining all rays capable of transmitting energy from a transmitting end to a receiving end, and the loss caused by the space and the limited transmission coefficient is calculated, so that the parameters of multipath components are given.
Further, an electromagnetic wave propagation loss model is established for a moon surface floating charged moon dust particle scene, comprising:
The macroscopic influence of charged moon dust particles on electromagnetic wave attenuation is described by utilizing a conventional scattering theory, and the attenuation coefficient is as follows in combination with the actual condition of a moon surface:
Wherein:
a max is the maximum radius of the moon dust particles;
a min is the minimum radius of the moon dust particles;
Q t (a) is the attenuation section of the moon dust particle with the radius of a;
n (a) is the number of moon dust particles between a and a+da per unit volume;
where a 0 is the average radius of the moon dust particles.
The attenuation section can be divided into a scattering section and an absorption section, and the differential scattering section expression of the moon dust particles is as follows:
Wherein:
k is the beam of electromagnetic waves;
Epsilon 0 is the vacuum dielectric constant;
epsilon s is the dielectric constant of the moon dust particles;
Sigma is the charge quantity of the moon dust particles in unit area;
e 0 is the electric field generated by the electrification of the moon dust particles;
θ 0 is the charge distribution angle;
an included angle between an electric field introduced under the spherical coordinates and an x axis;
the scattering cross section is a cross section in which total scattering energy is generated in all directions around the moon dust particles, and the moon dust particles are approximated by Rayleigh, which can be expressed as:
After Rayleigh approximation of the moon particles, the square of the internal electric field modulus of the moon particles can be written as:
Wherein:
Using integral expressions Solving for δ 2 yields the final expression:
As with the moon dust particle expression without charge, meaning that the charge has no effect on the absorption cross section, the total attenuation portion can be added by the scattering portion and the receiving portion:
when the moon dust particles are considered to have the same radius a, the attenuation coefficient is:
Wherein:
V is the volume of the spherical particles, and is represented by optical visibility V b because it is difficult to measure;
Finally, the relation between the attenuation coefficient and the optical visibility V b is obtained:
Further, an electromagnetic wave propagation loss model is established for a moon surface floating solar wind particle scene, comprising:
during the period of solar wind activity or solar corona activity, the sun can externally throw out a large amount of irregular charged particles;
the flicker index m is defined as the comparison of the root mean square value and the average amplitude value of the fluctuation amplitude of the signal, and m has a certain relation with SEP.
In general, SEP is inversely proportional to m, and the calculation formula of the flicker index m is as follows:
Wherein:
α1＝0.85；
r min is the shortest distance from the receiver to the transmitter to the solar link;
c no is a coefficient corresponding to the variation of the signal fluctuation amplitude, and the relationship with the charged particle density σ nε is as follows:
Wherein:
l 0 is the turbulent outer dimension;
weak flicker and strong solar flicker can be distinguished according to the flicker index; it is generally believed that the scintillation index m <1 pertains to weak solar scintillation; wherein m from 0.3 is excessive before saturation; the flicker index m is 1, namely the strong flicker is generated after saturation is reached;
the envelope of the flicker coefficient, i.e. the intensity flicker, has Rician statistics with a probability density function of:
Wherein:
K＝Ks Is the Rician factor, which is the power ratio of the specularly reflected and scattered signals of the received signal;
i 0 (·) is the Bessel function of the zero-order first-class modification;
K s is proportional to the video range received signal power;
n sc (t) is a complex gaussian random signal of non-line-of-sight transmission scattered by charged particles;
the solar flicker index m decreases with increasing signal frequency and decreases with increasing solar to lunar distance;
The electromagnetic wave can generate multipath effect when passing through the charged particles, the envelope distribution of the multipath signal follows the Rician distribution, and the Rician factor K has the following relation with the solar flicker index m:
m approaches 0, K approaches ≡; when m=1, k=0;
Rician distribution is reduced to:
At this time, the channel becomes a Rayleigh channel;
when K is larger, i.e. n sc Smaller, the complex gaussian random process with non-zero mean |α sc (t) | is developed:
Wherein:
phi is the random phase shift uniformly distributed on [ -pi, pi ];
re { e -jφnsc } is zero mean, variance is The gaussian process, such that p sc (r) can be approximated as:
at this time, p sc (r) may be approximately gaussian.
Compared with the prior art, the invention has the beneficial effects that:
1. The wireless channel modeling method for the lunar surface multi-scene communication is characterized in that on the basis of original lunar surface wireless channel modeling, different typical scenes of the lunar surface are built by using a ray tracing method, different electromagnetic wave ray propagation models are built, and when the meteorite is in a meteorite scene, the relation between the depth and the width of the meteorite pit and the number of suggested rays is given, and the more complete lunar surface wireless channel modeling method is given.
2. A wireless channel modeling method for moon surface multi-scene communication is used for respectively establishing propagation loss models for scenes of floating charged particles on the moon surface. Aiming at a scene of floating charged moon dust on a moon surface, a particle scattering absorption model is established, and the relation between an attenuation coefficient and electromagnetic wave frequency, the charged quantity of the moon dust particles and visibility is given; aiming at a scene of solar wind charged particles floating on the lunar surface, a relation between a solar flicker index and a lunar distance and a Rician factor is established, so that a channel model is established, and the channel model is divided into a Rayleigh channel model or a Gaussian channel model according to the size of the solar flicker factor.
Drawings
FIG. 1 is a flow chart of a wireless channel modeling method for lunar surface-oriented multi-scenario communication;
FIG. 2 is a schematic diagram of a lunar surface reflection dual path model;
FIG. 3 is a schematic view of a knife-edge shaped obstruction;
FIG. 4 is a schematic view of the merle scene;
FIG. 5 is the transmission loss of electromagnetic waves in a near-lunar free space scenario;
FIG. 6 is a lunar sea level scene electromagnetic wave propagation loss;
FIG. 7 is an obstacle scene electromagnetic wave propagation loss;
FIG. 8 is a schematic diagram of field strength predictions for a four-ray model and a free space model;
FIG. 9 is a schematic diagram of field strength predictions for a six-ray model and a free space model;
fig. 10 is a plot of ground sand particles and moon particles versus signal attenuation.
Detailed Description
It is noted that relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The features and capabilities of the present invention are described in further detail below in connection with examples.
Example 1
Referring to fig. 1, a wireless channel modeling method for lunar surface multi-scene communication includes:
Step S1: dividing a propagation scene of the lunar surface electromagnetic wave into a plurality of typical scenes;
Step S2: respectively establishing electromagnetic wave propagation loss models aiming at different typical scenes of electromagnetic wave propagation on the lunar surface; preferably, the loss is modeled in two parts, attenuation due to the topography of the lunar surface and attenuation due to charged particles present on the lunar surface;
step S3: judging a specific typical scene of the lunar surface where the target is located, and calculating a propagation coefficient according to a corresponding electromagnetic wave propagation loss model; such as moon surface reflection coefficient, etc.;
The amplitude and phase of the moon surface reflected wave depend on the reflection coefficient at the reflection point, and the reflection coefficients are different in different polarization modes (horizontal polarization or vertical polarization);
The reflection coefficient of which depends on some relevant parameters, mainly the conductivity sigma and the dielectric constant epsilon.
For horizontally polarized electromagnetic waves, the reflection coefficient is given by:
For vertically polarized electromagnetic waves, the corresponding reflection coefficients are:
Where ε' =ε/ε 0-jσ/(wε0), θ is the angle of incidence.
In this embodiment, specifically, the step S1 includes:
According to the difference of the topography of the lunar surface, the propagation scene of the electromagnetic wave on the lunar surface is divided into: a near moon surface free space scene, a moon surface moon sea scene, a moon surface multi-obstacle scene, a moon surface merle scene;
According to the difference of charged particles existing on the moon surface, the propagation scene of the moon surface electromagnetic wave is divided into: a moon surface floating charged moon dust particle scene and a moon surface floating solar wind particle scene.
In this embodiment, specifically, the step S2 includes:
Establishing an electromagnetic wave propagation loss model facing to a free space scene on the lunar surface;
Establishing an electromagnetic wave propagation loss model facing to a moon surface moon sea scene by using a ray tracing method;
Establishing an electromagnetic wave propagation diffraction loss model facing to a moon surface multi-obstacle scene;
establishing an electromagnetic wave propagation loss model facing to the merle pit scene on the lunar surface by using a ray tracing method;
establishing an electromagnetic wave propagation loss model aiming at a moon surface floating charged moon dust particle scene;
And establishing an electromagnetic wave propagation loss model aiming at a moon surface floating solar wind particle scene.
In this embodiment, specifically, both the lunar surface and the outer space are vacuum environments, which can be considered as ideal propagation environments, so the electromagnetic wave propagation loss model established for the free space scene of the lunar surface comprises:
Pr＝20lg(d)+20lg(f)+32.44
Wherein:
d is the distance between the receivers and transmitters;
f is the electromagnetic frequency used to calculate the maximum range for air-to-air communication.
In this embodiment, referring specifically to fig. 2, an electromagnetic wave propagation loss model established by using a ray tracing method facing a lunar sea scene on a lunar surface includes:
the moon sea is a relatively low-lying plain, when communication is carried out in a moon sea area, the condition of single-path propagation is rarely caused, and the phenomenon of two-path propagation generally occurs, so that the electromagnetic wave propagation loss is modeled by adopting a two-ray model;
The signal received by the receiving antenna can be obtained by superposing direct wave and reflected wave vectors, and the size and the phase of the reflected signal are determined by path length difference and ground reflection coefficient, so that a predicted point field intensity calculation formula and a lunar surface reflection loss calculation formula in the propagation process are obtained:
Wherein:
R 0 is the lunar surface reflection coefficient;
h t is the transmitter height;
h r is the receiver height;
lambda is the wavelength of electromagnetic waves;
And/> Losses respectively caused by the electromagnetic wave and the angle between the transmitter and the receiver.
In lunar sea modeling, when the distance between the transmitter and the receiver is large enough, the angle change is small and can be ignored. Therefore, it is simplified as:
in this embodiment, referring specifically to fig. 3, an electromagnetic wave propagation diffraction loss model established for a moon surface multi-obstacle scene includes:
Estimating the loss by treating the obstacle as a diffraction blade-shaped edge when the occlusion is caused by a single object or a mountain, namely treating the obstacle as a blade-shaped obstacle;
Considering the blade-shaped obstacle as an infinite absorption screen diffraction theory model, theoretically, the diffraction loss of a single blade-shaped obstacle is as follows:
Wherein:
r 0 is the radius of curvature of the arc at the top of the blade-shaped barrier;
d T is the distance from the transmitter tip to the blade-shaped obstacle tip;
d R is the distance from the receiver tip to the blade-shaped obstacle tip;
lambda is the wavelength of electromagnetic waves;
h is the height of the blade-shaped barrier.
In this embodiment, referring specifically to fig. 4, an electromagnetic wave propagation loss model established by using a ray tracing method for a moon surface merle scene includes:
when modeling is performed in a moon surface meteorite pit scene, analyzing field intensity and loss by adopting a ray tracing method, so that the most suitable modeling ray number is selected;
When electromagnetic waves strike the plane of the medium, reflection and refraction phenomena occur. When the moon surface uses UHF wave band communication, most of electromagnetic waves incident to the moon surface are reflected, and the small part is refracted; the calculation formula of the reflection loss of the lunar surface in the electromagnetic wave propagation process under the lunar surface meteorite scene is consistent with that under the lunar sea scene;
During simulation, a ray tracing method is used for determining all rays capable of transmitting energy from a transmitting end to a receiving end, and loss caused by space and limited transmission coefficients is calculated, so that parameters (loss and field intensity) of multipath components are given;
assuming that the number of rays selected in the ray tracing method is n (n is more than or equal to 2 and less than or equal to 6), the T-R distance is less than When, i.e. the diameter (D) and depth (H) of the merle are satisfied/>In this case, the number of rays in the ray tracing method may be set to n.
In this embodiment, specifically, an electromagnetic wave propagation loss model is built for a scene of floating charged moon dust particles on the lunar surface, including:
The macroscopic influence of charged moon dust particles on electromagnetic wave attenuation is described by utilizing a conventional scattering theory, and the attenuation coefficient is as follows in combination with the actual condition of a moon surface:
Wherein:
a max is the maximum radius of the moon dust particles;
a min is the minimum radius of the moon dust particles;
Q t (a) is the attenuation section of the moon dust particle with the radius of a;
n (a) is the number of moon dust particles between a and a+da per unit volume;
where a 0 is the average radius of the moon dust particles.
The attenuation section can be divided into a scattering section and an absorption section, and the differential scattering section expression of the moon dust particles is as follows:
/>
Wherein:
k is the beam of electromagnetic waves;
Epsilon 0 is the vacuum dielectric constant;
epsilon s is the dielectric constant of the moon dust particles;
Sigma is the charge quantity of the moon dust particles in unit area;
e 0 is the electric field generated by the electrification of the moon dust particles;
θ 0 is the charge distribution angle;
an included angle between an electric field introduced under the spherical coordinates and an x axis;
the scattering cross section is a cross section in which total scattering energy is generated in all directions around the moon dust particles, and the moon dust particles are approximated by Rayleigh, which can be expressed as:
After Rayleigh approximation of the moon particles, the square of the internal electric field modulus of the moon particles can be written as:
Wherein:
Using integral expressions Solving for δ 2 yields the final expression:
As with the moon dust particle expression without charge, meaning that the charge has no effect on the absorption cross section, the total attenuation portion can be added by the scattering portion and the receiving portion:
/>
when the moon dust particles are considered to have the same radius a, the attenuation coefficient is:
Wherein:
V is the volume of the spherical particles, and is represented by optical visibility V b because it is difficult to measure; the optical visibility V b refers to the maximum horizontal distance that a normal person can see and recognize the outline of a target object (black, moderate in size) from the sky background under the current weather conditions; the night is the maximum horizontal distance of the luminous point of the lamplight with certain intensity, which is expressed in kilometers and is related to the experience relationship;
Finally, the relation between the attenuation coefficient and the optical visibility V b is obtained:
In this embodiment, specifically, an electromagnetic wave propagation loss model is built for a scene of floating solar wind particles on the lunar surface, including:
during the period of solar wind activity or solar corona activity, the sun can externally throw out a large amount of irregular charged particles; this effect can cause signal flicker or interruption, and has a great influence on communication quality and efficiency;
the flicker index m is defined as the comparison of the root mean square value and the average amplitude value of the fluctuation amplitude of the signal, and m has a certain relation with SEP.
In general, SEP is inversely proportional to m, and the calculation formula of the flicker index m is as follows:
Wherein:
α1＝0.85；
r min is the shortest distance from the receiver to the transmitter to the solar link;
c no is a coefficient corresponding to the variation of the signal fluctuation amplitude, and the relationship with the charged particle density σ nε is as follows:
Wherein:
L 0 is the turbulent outer dimension; the coefficient c no corresponding to the amplitude variation is proportional to lambda 2;
weak flicker and strong solar flicker can be distinguished according to the flicker index; it is generally believed that the scintillation index m <1 pertains to weak solar scintillation; wherein m from 0.3 is excessive before saturation; the flicker index m is 1, namely the strong flicker is generated after saturation is reached;
the envelope of the flicker coefficient, i.e. the intensity flicker, has Rician statistics with a probability density function of:
Wherein:
Is the Rician factor, which is the power ratio of the specularly reflected and scattered signals of the received signal;
i 0 (·) is the Bessel function of the zero-order first-class modification;
K s is proportional to the video range received signal power;
n sc (t) is a complex gaussian random signal of non-line-of-sight transmission scattered by charged particles;
the solar flicker index m decreases with increasing signal frequency and decreases with increasing solar to lunar distance;
The electromagnetic wave can generate multipath effect when passing through the charged particles, the envelope distribution of the multipath signal follows the Rician distribution, and the Rician factor K has the following relation with the solar flicker index m:
m approaches 0, K approaches ≡; when m=1, k=0;
Rician distribution is reduced to:
At this time, the channel becomes a Rayleigh channel;
when K is larger, i.e Smaller, the complex gaussian random process with non-zero mean |α sc (t) | is developed:
Wherein:
phi is the random phase shift uniformly distributed on [ -pi, pi ];
re { e -jφnsc } is zero mean, variance is The gaussian process, such that p sc (r) can be approximated as:
at this time, p sc (r) may be approximately gaussian.
Example two
The second embodiment shows the accuracy of the modeling method for describing the electromagnetic wave propagation characteristics under the multi-scene moon surface.
The simulation scene is set as a moon surface typical scene (a near-lunar free space scene, a lunar sea level, and a merle pit scene), a ray tracing model is established, the suggested ray number is given, and then the loss modeling of electromagnetic wave propagation caused by charged particles (lunar dust particles) floating on the moon surface is performed.
As can be taken from fig. 5, the propagation loss of an electromagnetic wave in a near-lunar free space scene is related to the propagation distance and the frequency of the electromagnetic wave, and is related to the frequency and the propagation distance of the electromagnetic wave in pairs; the moon surface has no atmosphere, and basically belongs to a vacuum state, so that the modeling propagation loss on the moon surface is the same as that in the vacuum, and the attenuation law of path loss index n=2 is obeyed; the transmission loss of the electromagnetic wave with 259.7MHz frequency is 22dB at 3.8 feet (one wavelength), which is consistent with that in an Apollo lunar report, and is used for calculating the maximum range of ground-to-air communication, so that the accuracy of a modeling method in a near-lunar free space scene is verified.
Fig. 6 is a graph of modeling electromagnetic wave propagation loss when facing a lunar sea scene, using a ray two-path model and a theoretical model in an Apollo early lunar installation report in the present invention, and experimental results show that: when the receiving transceiver distance is within 10 feet, the two models model the electromagnetic wave propagation loss to be basically consistent; when the distance between the receiver and the transmitter is more than 10 feet, the loss of the two-path model is 2-3dB greater than that of the Apollo early theoretical model, and the two-path model is verified in the subsequent lunar exploration engineering because the lunar surface reflection coefficient is corrected and the lunar surface is detected to be not a smooth plane.
FIG. 7 is a graph showing the modeling of electromagnetic wave propagation loss using the diffraction loss model of the present invention and the theoretical model in the Apollo early-stage lunar-climbing report, respectively, when the obstacle is present, the diffraction loss model is 2-3dB larger than the Apollo model, because the standard edge diffraction equation used in the Apollo early-stage lunar-climbing report is not applicable when the rough edge, and the loss larger than the smooth surface is generated, which is not considered in the Apollo early-stage lunar-climbing report, and the loss of the part is modeled by adding the ground reflection coefficient in the model of the present invention.
FIGS. 8 and 9 are, respectively, the free space model and the ray tracing model in the Apollo early lunar logging report modeling the propagation of electromagnetic waves in the merle pit, and the free space model does not take into account the reflection of electromagnetic waves in the merle pit and the pit bottom when modeling the propagation of electromagnetic waves in the merle pit, so that the ray tracing method is more accurate and is also verified in the subsequent lunar exploration engineering. According to the theory prediction result of propagation loss and field intensity, the method can give out the reference of ray data to merle pits with different sizes for the lunar merle scene, and the number of rays selected in the ray tracing method is n (n is more than or equal to 2 and less than or equal to 6), and the T-R distance is less thanWhen, i.e. the diameter (D) and depth (H) of the merle are satisfied/>In this case, the number of rays in the ray tracing method may be set to n.
At present, no simulation and measurement work is performed on the influence of the moon dust particles, so that the influence of the moon dust particles on the electromagnetic wave propagation with the same frequency is compared by utilizing the sand dust particles similar to the moon dust particles in the invention. Fig. 10 compares attenuation effects caused by charged sand particles and moon dust particles in the earth desert environment when the simulation operating frequency is 415MHz (the communication frequency of the third flying in the air), and the main factors causing the difference are the difference of the particle radius and complex dielectric constants of the sand and the moon dust. It can be found that the attenuation effect of the lunar surface environment is significantly lower than that of the desert environment of the earth under the same visibility, and the obtained simulation result corresponds to the actual lunar surface plan.
The above examples merely illustrate specific embodiments of the application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that it is possible for a person skilled in the art to make several variants and modifications without departing from the technical idea of the application, which fall within the scope of protection of the application.
This background section is provided to generally present the context of the present invention and the work of the presently named inventors, to the extent it is described in this background section, as well as the description of the present section as not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Claims (7)
1. The wireless channel modeling method for moon surface multi-scene communication is characterized by comprising the following steps of:
Step S1: dividing a propagation scene of the lunar surface electromagnetic wave into a plurality of typical scenes;
Step S2: respectively establishing electromagnetic wave propagation loss models aiming at different typical scenes of electromagnetic wave propagation on the lunar surface;
step S3: judging a specific typical scene of the lunar surface where the target is located, and calculating a propagation coefficient according to a corresponding electromagnetic wave propagation loss model;
The step S1 includes:
According to the difference of the topography of the lunar surface, the propagation scene of the electromagnetic wave on the lunar surface is divided into: a near moon surface free space scene, a moon surface moon sea scene, a moon surface multi-obstacle scene, a moon surface merle scene;
according to the difference of charged particles existing on the moon surface, the propagation scene of the moon surface electromagnetic wave is divided into: a moon surface floating charged moon dust particle scene and a moon surface floating solar wind particle scene;
the step S2 includes:
Establishing an electromagnetic wave propagation loss model facing to a free space scene on the lunar surface;
Establishing an electromagnetic wave propagation loss model facing to a moon surface moon sea scene by using a ray tracing method;
Establishing an electromagnetic wave propagation diffraction loss model facing to a moon surface multi-obstacle scene;
establishing an electromagnetic wave propagation loss model facing to the merle pit scene on the lunar surface by using a ray tracing method;
establishing an electromagnetic wave propagation loss model aiming at a moon surface floating charged moon dust particle scene;
And establishing an electromagnetic wave propagation loss model aiming at a moon surface floating solar wind particle scene.
2. The method for modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 1, wherein the electromagnetic wave propagation loss model established for the free space scene of the lunar surface comprises:
Pr＝20lg(d)+20lg(f)+32.44
Wherein:
d is the distance between the receivers and transmitters;
f is the frequency of the electromagnetic wave.
3. The method for modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 2, wherein the electromagnetic wave propagation loss model established for lunar surface-oriented lunar sea scene by using a ray tracing method comprises:
modeling electromagnetic wave propagation loss by adopting a two-ray model;
The signal received by the receiving antenna can be obtained by superposing direct wave and reflected wave vectors, and the size and the phase of the reflected signal are determined by path length difference and ground reflection coefficient, so that a predicted point field intensity calculation formula and a lunar surface reflection loss calculation formula in the propagation process are obtained:
Wherein:
R 0 is the lunar surface reflection coefficient;
h t is the transmitter height;
h r is the receiver height;
lambda is the wavelength of electromagnetic waves;
d s represents the direct path distance from the transmitting end to the receiving end, and s 1+s2 represents the reflected path distance from the transmitting end to the receiving end through the lunar surface.
4. The method for modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 3, wherein the model for propagation diffraction loss of electromagnetic waves established for lunar surface-oriented multi-obstacle scene comprises:
estimating the loss by treating the obstacle as a diffraction blade-shaped edge, namely treating the obstacle as a blade-shaped obstacle;
Considering the blade-shaped obstacle as an infinite absorption screen diffraction theory model, theoretically, the diffraction loss of a single blade-shaped obstacle is as follows:
Wherein:
r 0 is the radius of curvature of the arc at the top of the blade-shaped barrier;
d T is the distance from the transmitter tip to the blade-shaped obstacle tip;
d R is the distance from the receiver tip to the blade-shaped obstacle tip;
lambda is the wavelength of electromagnetic waves;
h is the height of the blade-shaped barrier.
5. The method for modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 1, wherein the electromagnetic wave propagation loss model established by using a ray tracing method for the lunar surface meteorite pit scene comprises:
when modeling is performed in a moon surface meteorite pit scene, analyzing field intensity and loss by adopting a ray tracing method, so that the most suitable modeling ray number is selected;
the calculation formula of the reflection loss of the lunar surface in the electromagnetic wave propagation process under the lunar surface meteorite scene is consistent with that under the lunar sea scene;
During simulation, a ray tracing method is used for determining all rays capable of transmitting energy from a transmitting end to a receiving end, and the loss caused by the space and the limited transmission coefficient is calculated, so that the parameters of multipath components are given.
6. The method of modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 5, wherein the step of modeling propagation loss of electromagnetic waves for a lunar surface floating charged lunar dust particle scene comprises:
The macroscopic influence of charged moon dust particles on electromagnetic wave attenuation is described by utilizing a conventional scattering theory, and the attenuation coefficient is as follows in combination with the actual condition of a moon surface:
Wherein:
a max is the maximum radius of the moon dust particles;
a min is the minimum radius of the moon dust particles;
Q t (a) is the attenuation section of the moon dust particle with the radius of a;
n (a) is the number of moon dust particles between a and a+da per unit volume;
wherein a 0 is the average radius of the moon dust particles;
The attenuation section can be divided into a scattering section and an absorption section, and the differential scattering section expression of the moon dust particles is as follows:
Wherein:
k is the beam of electromagnetic waves;
Epsilon 0 is the vacuum dielectric constant;
epsilon s is the dielectric constant of the moon dust particles;
Sigma is the charge quantity of the moon dust particles in unit area;
e 0 is the electric field generated by the electrification of the moon dust particles;
θ 0 is the charge distribution angle;
an included angle between an electric field introduced under the spherical coordinates and an x axis;
the scattering cross section is a cross section in which total scattering energy is generated in all directions around the moon dust particles, and the moon dust particles are approximated by Rayleigh, which can be expressed as:
After Rayleigh approximation of the moon particles, the square of the internal electric field modulus of the moon particles can be written as:
Wherein:
Using integral expressions Solving for δ 2 yields the final expression:
As with the moon dust particle expression without charge, meaning that the charge has no effect on the absorption cross section, the total attenuation portion can be added by the scattering portion and the receiving portion:
when the moon dust particles are considered to have the same radius a, the attenuation coefficient is:
Wherein:
V is the volume of the spherical particles, and is represented by optical visibility V b because it is difficult to measure;
Finally, the relation between the attenuation coefficient and the optical visibility V b is obtained:
7. The method of modeling a wireless channel for lunar surface-oriented multi-scene communication according to claim 6, wherein the modeling of propagation loss of electromagnetic waves for a lunar surface floating solar wind particle scene comprises:
during the period of solar wind activity or solar corona activity, the sun can externally throw out a large amount of irregular charged particles;
Defining a flicker index m as the comparison between the root mean square value and the amplitude mean value of the signal fluctuation amplitude, wherein m has a certain relation with SEP;
In general, SEP is inversely proportional to m, and the calculation formula of the flicker index m is as follows:
Wherein:
α1＝0.85；
r min is the shortest distance from the receiver to the transmitter to the solar link;
c no is a coefficient corresponding to the variation of the signal fluctuation amplitude, and the relationship with the charged particle density σ nε is as follows:
Wherein:
l 0 is the turbulent outer dimension;
weak flicker and strong solar flicker can be distinguished according to the flicker index; it is generally believed that the scintillation index m <1 pertains to weak solar scintillation; wherein m from 0.3 is excessive before saturation; the flicker index m is 1, namely the strong flicker is generated after saturation is reached;
the envelope of the flicker coefficient, i.e. the intensity flicker, has Rician statistics with a probability density function of:
Wherein:
Is the Rician factor, which is the power ratio of the specularly reflected and scattered signals of the received signal;
i 0 (·) is the Bessel function of the zero-order first-class modification;
K s is proportional to the video range received signal power;
n sc (t) is a complex gaussian random signal of non-line-of-sight transmission scattered by charged particles;
the solar flicker index m decreases with increasing signal frequency and decreases with increasing solar to lunar distance;
The electromagnetic wave can generate multipath effect when passing through the charged particles, the envelope distribution of the multipath signal follows the Rician distribution, and the Rician factor K has the following relation with the solar flicker index m:
m approaches 0, K approaches ≡; when m=1, k=0;
Rician distribution is reduced to:
At this time, the channel becomes a Rayleigh channel;
when K is larger, i.e Smaller, the complex gaussian random process with non-zero mean |α sc (t) | is developed:
Wherein:
phi is the random phase shift uniformly distributed on [ -pi, pi ];
zero mean, variance/> The gaussian process, such that p sc (r) can be approximated as:
at this time, p sc (r) may be approximately gaussian.
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