CN103684629B

CN103684629B - A kind of method calculating deep space communication link loss value

Info

Publication number: CN103684629B
Application number: CN201310589891.4A
Authority: CN
Inventors: 周贤伟; 许海涛; 胡显邦; 王洋; 崔凤磊
Original assignee: University of Science and Technology Beijing USTB
Current assignee: Tangshan Jiutian Weixing Aerospace Technology Co ltd
Priority date: 2013-11-20
Filing date: 2013-11-20
Publication date: 2015-08-12
Anticipated expiration: 2033-11-20
Also published as: CN103684629A

Abstract

The invention provides a kind of method calculating deep space communication link loss value, belong to the communications field, first deep space communication Link Fragmentation is near-earth link, deep space repeated link, far link three sections of links by the method; Then the loss value of each section of communication link is calculated respectively; Finally using the loss value sum of each for communication link section as communication link total losses value.The present invention can calculate deep space communication link loss value exactly, provide reference frame, and the present invention having stronger applicable feasibility, can be widely used in various deep space communication system for carrying out loss balancing to signal power in actual deep space communication.

Description

Method for calculating loss value of deep space communication link

Technical Field

The invention relates to the field of deep space communication, in particular to a method for calculating a loss value of a deep space communication link.

Background

At present, deep space exploration mainly refers to exploration of planets and satellites, asteroids, comets and the like of the solar system except the earth, and also includes exploration of the solar system and even the whole universe. The deep space communication technology is an important technical support for deep space detection activities, and has tasks of transmitting instruction information, telemetering remote control information, tracking navigation information, attitude control information, track control information and transmitting data such as scientific data, images, files, sounds and even images, and the success and failure of the deep space detection task are concerned. The quality of deep space communication is not only dependent on the performance of radio system equipment, but also the electromagnetic wave propagation environment is a factor which must be considered to realize high-quality communication, and high-quality electromagnetic wave propagation environment characteristic detection and prediction are therefore particularly important. However, the deep space communication environment is complex and changeable, so that the analysis of various influence factors in the deep space communication environment and the theoretical model are of great significance, wherein the loss analysis can provide a reference basis for loss compensation of signal power in actual deep space communication. However, in the conventional spatial link loss value calculation method, the loss values of the link at different transmission distances are not specifically analyzed and calculated, so that an accurate link loss value cannot be obtained.

Disclosure of Invention

The invention aims to provide a method for calculating a loss value of a deep space communication link, which is used for solving the problem that the loss value of the deep space communication link cannot be accurately calculated by the conventional method for calculating the loss value of the space link. The method for calculating the loss value of the deep space communication link can obtain the accurate total loss value of the deep space communication link, has strong application feasibility, and can be widely applied to a deep space communication system.

The invention provides a method for calculating a loss value of a deep space communication link, which comprises the following steps: a segmented deep space communication link; calculating loss values of all sections of the communication link; and calculating the total loss value of the communication link according to the loss values of all the sections of the communication link.

Preferably, the segmented deep space communication link comprises: segmenting the deep space communication link into a near-earth link, a deep space relay link and a far-earth link; the near-earth link refers to a link between the earth surface and a geostationary satellite; the deep space relay link refers to a communication link from a synchronous satellite to an orbit satellite of other planets; the remote link refers to a link between the orbital satellite of the other planet and the surface detector of the satellite.

Preferably, the calculating the loss value of each segment of the communication link comprises: calculating the near-earth link loss value, calculating the deep space relay link loss value, and calculating the far-earth link loss value.

Preferably, the remote link loss value is a loss value when a currently propagated radio wave propagates in a free space between an orbiting satellite of the other planet and a surface detector thereof.

Preferably, calculating the deep space relay link loss value comprises: and solving the sum of the loss value of the radio wave which is currently transmitted and is transmitted in the free space between the geostationary satellite and the orbit satellite of other planet and the absorption loss value of the radio wave which is currently transmitted and is caused by solar wind.

Preferably, calculating the near-earth link loss value comprises: solving the sum of the atmospheric absorption loss value, the rainfall attenuation value, the rain fog attenuation value, the rain cloud attenuation value and the ionosphere attenuation value of the radio wave currently transmitted in the near-earth link; the atmospheric absorption loss value refers to a loss value of radio waves due to an atmospheric absorption effect; the rainfall attenuation value is a loss value of radio waves caused by rainfall; the rain and fog attenuation value is a loss value of radio waves caused by foggy days; the rain cloud attenuation value is a loss value of radio waves caused by rain clouds; the ionospheric attenuation value refers to a loss value of radio waves caused by the ionosphere.

Preferably, the method for calculating the total loss value of the communication link according to the loss values of the sections of the communication link comprises: and taking the sum of the loss values of all the sections of the communication link as the total loss value of the communication link.

The technical scheme of the invention has the following beneficial effects:

according to the method for calculating the loss value of the deep space communication link, the deep space link is segmented according to the characteristics of the deep space communication link, theoretical models of attenuation caused by various factors in each segment are given, each model is calculated and analyzed, and finally the accurate total loss value of the deep space communication link is obtained.

Drawings

FIG. 1 is a schematic flow chart illustrating a method for calculating a loss value of a deep space communication link according to the present invention;

fig. 2 is a schematic diagram of a deep space communication link.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Fig. 1 is a schematic flow chart of a method for calculating a deep space communication link loss value provided by the present invention, including:

s1: a segmented deep space communication link;

s2: calculating loss values of all sections of the communication link;

s3: and calculating the total loss value of the communication link according to the loss values of all the sections of the communication link.

As shown in fig. 2, a schematic diagram of a deep space communication link, where the segmented deep space communication link specifically includes: the deep space communication link is segmented into a near ground link 1, a deep space relay link 2 and a far ground link 3; the near-earth link 1 refers to a link between the earth surface 5 and a geostationary satellite 4, and specifically comprises an earth surface 5 communication link, a link between the geostationary satellite 4 and an earth station 6, and a link between different geostationary satellites 4; the deep space relay link 2 is a communication link between the geostationary satellite 4 which is finally used for transmitting signals to the deep space and the orbit satellite 7 of other planets; the remote link refers to a link between the orbiting satellite 7 of the other planet and the surface detector 8 thereof. For example, when the other planet is mars, the deep space communication link between the earth and the mars is divided into the three parts, wherein the deep space relay link refers to a communication network from a geostationary satellite to a mars orbit satellite of the earth, and a plurality of satellites located at the day-ground and day-fire lagrange points may exist as forwarding nodes in the future.

In S2 of fig. 1, calculating the loss value of each segment of the communication link includes calculating a loss value of the near-earth link 1, calculating a loss value of the deep space relay link 2, and calculating a loss value of the far-earth link 3. A preferred method of calculating the loss value of each link segment will be described in detail below.

1) Method for calculating loss value of remote link

Calculating the far-field link 3 loss value includes calculating a free-space propagation loss value L_fsNamely: the loss values of the currently propagating radio waves as they propagate in the free space between the orbiting satellites 7 of the other planets and their surface detectors 8 are calculated. In the case of mars, because the mars atmosphere is thin and the main component is carbon dioxide, then nitrogen and argon, and a small amount of oxygen and water vapor are also contained, the deep space communication band is usually above the X band even to the extent thatKa band, so the loss caused by Mars atmosphere is very small and can be basically ignored. However, the rarefied Mars atmosphere often has bad weather such as sand storm and the like, and the influence range is wide, if the Mars detector is just in the influence range, the communication with the Mars detector is influenced at the moment, so the loss of the link at the section is mainly free space propagation loss. Free space propagation loss value L_fsThe following formula can be used:

L_fs92.45+20lgd +20lgf (1) in equation (1), d is the distance between the orbiting satellite 7 of the other planet and its surface detector 8, in Km; f denotes the frequency of the radio wave in GHz.

2) Method for calculating loss value of deep space relay link

The method for calculating the loss value of the deep space relay link 2 comprises the following steps: and solving the sum of the free space propagation loss value of the radio wave currently propagating in the range of the deep space relay link 2 and the absorption loss value caused by solar wind. The free space propagation loss value refers to a propagation loss value of radio waves in a free space between a geostationary satellite and an orbital satellite of other planet; the absorption loss value caused by solar wind refers to the value of radio wave loss caused by the influence of solar flicker, wherein the solar flicker refers to the rapid change of solar wind power parameters, so that the absorption intensity of the solar wind power parameters on radio waves fluctuates to cause the rapid change of signal levels.

Wherein the free space propagation loss value L of the radio wave currently propagating in the range of the deep space relay link 2_mfsThe same applies to equation (1). Still take the communication link between the earth and the mars as an example: the free space propagation loss between the earth and the mars changes constantly along with the orbital motion of the earth and the mars, but the loss change caused by the orbital motion of the star is not obvious in a short time because the distance between the earth and the mars is too far. At the upper time, the distance between the Mars and the earth is farthest, which is about 2.6826225(AU), and the radio wave at the time is transmitted from the Mars to the ground and has the largest free space propagation loss, and the Ka wave band is 32GHzThe loss of the uplink is about 294.58 dB; during the convergence period, the distance between the Mars and the earth is closest to the earth and is about 0.3979728(AU), the radio waves at the moment are transmitted from the Mars to the ground with the minimum free space propagation loss, and the loss of a Ka-band 32GHz downlink is about 277.9985 dB.

Since the higher the communication frequency is, the less the communication frequency is affected by the sun's glint, when the communication link is about 4 times the sun's radius from the sun's center, the signal-to-noise ratio of the X-band signal has a fading of 8.2dB compared to the channel without glint, while the Ka-band signal has a fading of only about 0.4 dB. This shows that, in order to compensate the influence of the sun flash on the radio signal, when the communication link is designed, 8.2dB and 0.4dB link margins need to be reserved for the X-band and the Ka-band, respectively, to normally complete the communication. Absorption loss value L caused by solar wind_sunThe following equation can be used to solve:

<math> <mrow> <msub> <mi>L</mi> <mi>sun</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mn>1.15</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>21</mn> </mrow> </msup> <mo>×</mo> <msub> <mo>&Integral;</mo> <mrow> <msub> <mi>L</mi> <mi>S</mi> </msub> <mo>/</mo> <mi>c</mi> </mrow> </msub> <msub> <mi>N</mi> <mi>e</mi> </msub> <mo>×</mo> <mi>v</mi> <mo>×</mo> <mi>dl</mi> </mrow> <msup> <mi>f</mi> <mn>2</mn> </msup> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

in the formula (2), the first and second groups,is the inclination (inclined path length L) along the entire transmission path (L) between the earth station and the detector_S) Full electron content STEC, N_eIs the solar wind electron density (unit m)^-3) Which is a function of the radial distance. v is the plasma collision frequency (Hz, a function of temperature) and f is the signal frequency (in GHz). According to the formula (2), for a 2.3GHz radio signal, the total absorption of the radio signal is only 0.01dB when the transmission path length is 3X 108km, which can be ignored.

Therefore, the loss value L of the deep space relay link_mComprises the following steps:

L_m=L_mfs+L_sun (3)

3) method for calculating loss value of near-earth link

The method for calculating the loss value of the near-earth link 1 comprises the following steps: and solving the sum of the atmospheric absorption loss value, the rainfall attenuation value, the rain fog attenuation value, the rain cloud attenuation value and the ionosphere attenuation value.

The atmospheric absorption loss value refers to a loss value of radio waves due to an atmospheric absorption effect; the rainfall attenuation value is a loss value of radio waves caused by rainfall; the rain and fog attenuation value is a loss value of radio waves caused by foggy days; the rain cloud attenuation value is a loss value of radio waves caused by rain clouds; the ionospheric attenuation value refers to a loss value of radio waves caused by the ionosphere. The calculation method of each value is as follows:

A. atmospheric absorption loss value L_atmCalculation method

For high-frequency electromagnetic waves, the absorption effect of the atmosphere is obvious and is an important loss factor. The atmospheric absorption effect is mainly caused by the absorption of water vapor and oxygen molecules to electromagnetic waves, and when the frequency is below 15GHz and between 35GHz and 80GHz, the absorption of the oxygen molecules to the electromagnetic waves is dominant, and resonance absorption occurs near 60GHz and 118.74GHz, so that a large loss peak appears. The attenuation peaks of water molecules appear at 22.3GHz,183.3GHz and 323.8 GHz. The factors influencing the composition and structure of the atmosphere include 3 factors, namely temperature, pressure and water vapor density. Therefore, the signal attenuation is not only frequency dependent, but also these 3 factors.

When the working frequency is lower than 350GHz (except 57-63 GHz) and the electric wave passes through the atmosphere in an inclined path, the median gas absorption attenuation L when the density of the water vapor of the dry air and the atmosphere is rho_atm(in dB) can be solved using the following equation:

in formula (4), El is the earth station elevation angle; h is₀The equivalent height of oxygen is generally 6 Km; h is_sIs the average altitude in Km of the terminal position of the earth station; h is_wIs the equivalent height of water vapor, unit Km; theta is the elevation angle of the communication link and the unit degree; g (h)₀) Is a characteristic loss of oxygen; g (h)_w) Characteristic losses for water vapor; wherein h is₀、h_w、γ₀、γ_wCalculated by the following equations, respectively:

the characteristic loss g (h) can be calculated by the following formula:

in the formulae (5) to (8), f is the frequency of radio waves in GHz; rho is the water vapor density in g/m³The value is calculated according to the following formula:

in the formula (10), H is relative humidity; t is the absolute temperature.

B. Rainfall attenuation value L_rainCalculation method

The signal fading caused by rainfall is the most serious propagation loss experienced by Ka-band satellite communication, and when the signal frequency is less than 1GHz, the rainfall attenuation is negligible, and the rainfall attenuation increases with the increase of the frequency of radio waves. Rainfall attenuation is related to rainfall and effective distance passing through a rain area, the greater the rainfall and the effective distance, the greater the attenuation, hail, ice crystals and snow have lower water content, and the attenuation influence is smaller.

The specific calculation steps of rainfall for the signal attenuation in the near-earth link are as follows, Step1-Step 5:

step 1: calculating the local actual rainfall height h_R(unit Km):

whereinThe latitude of the location of the earth station.

Step 2: calculating the inclined path length L_s:

Wherein θ is the elevation angle of the communication link; h is_RIs the local actual rainfall height calculated in S1; h is_sIn the same formula (4), the average altitude (km) of the earth station terminal position is expressed; r_eThe effective radius of the earth (in km).

Step 3: calculating a reduction factor:

when the intensity of rainfall R_0.01<At 100mm/h, the reduction factor is:

wherein when R is_0.01>At 100mm/h, taking R_0.01Calculation is carried out with a value of =100 mm/h.

Step 4: using correlation coefficients k, alpha and R_0.01Calculating the characteristic attenuation g_R(unit dB/km):

r_R＝k(R_0.01)^α (14)

wherein,

α＝[K_Hα_H+K_Vα_V+(K_Hα_H-K_Vα_V)×cos²(El)cos2τ]/2k (16)

wherein: k_H、K_VAnd alpha_H、α_VThe values of k and a for linear polarization (subscript H for horizontal polarization and subscript V for vertical polarization) and horizontal path, respectively, are shown. Specific values can be obtained by the following table:

TABLE 1 frequency-dependent coefficient K_H、K_VAnd alpha_H、α_VValue of (A)

If the frequency correlation value cannot be directly found in table 1, the following principle can be used: k_H、K_VValues, which may be logarithmic in frequency, K_H、K_VThe value is also a logarithmic scale and is obtained by an interpolation method; alpha is alpha_H、α_VThe value, which may be logarithmic in frequency, alpha_H、α_VThe values are linear scales and are obtained by the interpolation method.

El in equations (13) to (15) is the elevation angle of the earth station, and τ is the polarization tilt angle between the linearly polarized electric field vector and the horizontal direction. The calculation of the value of τ is described in ITU-R recommendation 791, appendix 1. Generally, when circular polarization is used for downstream transmission, τ =45 °.

Step 5: rainfall decay L that exceeds 0.01% of the average year_rainNamely L_0.01Most typically, the calculation method is as follows:

L_0.01＝γ_R×L_s×r_0.01 (17)

if the length of the rain zone through which the communication link passes is about 40km, and the attenuation caused by Ku and Ka bands is about 45dB and 272dB, as calculated by the lowest elevation angle, such large loss directly causes the link to be broken, so that the communication link is no longer practical. High-frequency rain attenuation can be avoided by multi-station reception at different sites. At present, the height of a rain area for calculating rainfall attenuation is about 4-6 kilometers, and when the height of the rain area is 6km, the rainfall loss of a deep space communication Ka frequency band 32GHz radio wave is about 38.55 dB.

C. Rain fog attenuation value calculation method

Rain fog attenuation value L caused by foggy weather_fogIt can be calculated from the following empirical formula:

wherein: f is the frequency of the radio wave signal in GHz; upsilon is_mIs the visibility, in m.

D. Cloud attenuation value L_cloudThe calculation method comprises the following steps:

the loss of radio waves by rain clouds is comparable to the attenuation caused by very intense rainfall, but when the intensity of the rainfall exceeds 50mm/h, the rainfall attenuation becomes the main source of attenuation in the atmosphere.

Cloud attenuation value L_cloudIt can be calculated by the following formula:

<math> <mrow> <msub> <mi>L</mi> <mi>cloud</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mi>Δh</mi> <mo>·</mo> <msub> <mi>γ</mi> <mi>c</mi> </msub> </mrow> <mrow> <mi>sin</mi> <mi>θ</mi> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>19</mn> <mo>)</mo> </mrow> </mrow> </math>

delta h is the effective thickness of the cloud layer, statistical data of the cloud layer thickness does not exist in China at present, and international universal average thickness is adopted, namely delta h is 1 km; gamma ray_cCalculating the characteristic loss value of the cloud layer by adopting the following formula:

γ_c＝K_L×M （20）

in the formula (20), M is the water vapor density (unit g/M) of the cloud layer³）；K_LFor a specific attenuation coefficient (unit dB/(km. g. m)³) The value can be obtained by the following equation:

in equation (21):

wherein:₁＝5.48，₂＝3.51，

in the above formula, T is absolute temperature in Kelvin; f. of_p、f_sGHz is taken as a unit for primary and secondary relaxation frequencies; f is the frequency of the radio wave signal in GHz.

From the above cloud attenuation model, we can find that the loss of the cloud to the radio wave is related to the frequency of the radio wave, the elevation angle of the communication link, and the water vapor density of the cloud. The elevation angle is limited to 5 degrees, and the water vapor density is 0.5g/m³The attenuation of Ka-band 32GHz radio waves due to the influence of cloud layers is about 3.41 dB.

E. Ionospheric attenuation value L_ionCalculation method

The absorption characteristic of the ionosphere for radio waves has a relationship with the electron concentration, and the greater the electron concentration, the stronger the absorption characteristic. The absorption characteristics of the ionosphere for radio waves also have a relationship with the frequency of the radio waves, the higher the frequency of the radio waves, the weaker the absorption characteristics. When the frequency of radio wave is more than 300MHz, the absorption characteristic of ionosphere to radio wave is not obvious, and the frequency band used for deep space communication is generally S, C, X or even higher, so we reasonably believe that the loss of ionosphere to deep space communication is negligible.

To sum up, A-E, the near-earth link loss value L_nThe values of (A) are:

L_n＝L_atm+L_fog+L_rain+L_ion+L_cloud (28)

total loss value L of communication link_sumThe sum of loss values of all communication links is:

L_sum＝L_fs+L_m+L_n+L_else (29)

wherein: l is_fs、L_m、L_nRespectively adopting formulas (1), (3) and (28) to calculate; l is_elseRepresents the sum of other subtle losses not mentioned above, and is usually negligible. According to the formula analysis, the link loss between the fixed earth station and the deep space probe needs to be calculated, firstly, the communication frequency band and frequency, the earth station position (latitude and altitude) and the communication elevation angle need to be determined, parameters such as the air temperature, the atmospheric relative humidity, the visibility, the cloud layer water vapor density and the rainfall intensity near the earth station are obtained according to the weather conditions, and finally, the link loss between the fixed earth station and the deep space probe, which is more accurate, can be determined by combining the link distance determined by the real-time deep space probe orbit parameters and substituting the link distance into the formula (28).

In summary, the method for calculating the loss value of the deep space communication link provided by the invention is used for segmenting the deep space link according to the characteristics of the deep space communication link, providing the theoretical model of attenuation caused by various factors in each segment, analyzing and calculating each model, and finally obtaining the accurate total loss value of the deep space communication link.

The foregoing is a preferred embodiment of the present invention, and it should be noted that it is obvious to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements should be construed as the protection scope of the present invention.

Claims

1. A method for calculating a loss value of a deep space communication link is characterized by comprising the following steps:

a segmented deep space communication link;

calculating loss values of all sections of the communication link;

calculating the total loss value of the communication link according to the loss values of all the sections of the communication link;

wherein the segmented deep space communication link comprises: segmenting the deep space communication link into a near-earth link, a deep space relay link and a far-earth link;

the near-earth link refers to a link between the earth surface and a geostationary satellite;

the deep space relay link refers to a communication link from a synchronous satellite to an orbit satellite of other planets;

the remote link refers to a link between the orbital satellite of other planet and the surface detector thereof;

wherein the calculating the loss value of each section of the communication link comprises: calculating the near-earth link loss value, calculating the deep space relay link loss value and calculating the far-earth link loss value;

wherein the remote link loss value is a loss value when the radio wave currently propagating propagates in a free space between the orbiting satellite of the other planet and the surface detector thereof;

wherein calculating the deep space relay link loss value comprises: solving the sum of the loss value of the radio wave transmitted currently in the free space between the geostationary satellite and the orbit satellite of other planet and the absorption loss value of the radio wave transmitted currently by the solar wind;

wherein calculating the near-earth link loss value comprises: solving the sum of the atmospheric absorption loss value, the rainfall attenuation value, the rain fog attenuation value, the rain cloud attenuation value and the ionosphere attenuation value of the radio wave currently transmitted in the near-earth link;

the atmospheric absorption loss value refers to a loss value of radio waves due to an atmospheric absorption effect;

the rainfall attenuation value is a loss value of radio waves caused by rainfall;

the rain and fog attenuation value is a loss value of radio waves caused by foggy days;

the rain cloud attenuation value is a loss value of radio waves caused by rain clouds;

the ionosphere attenuation value is a loss value of the ionosphere to radio waves;

the method for calculating the total loss value of the communication link according to the loss values of all the sections of the communication link comprises the following steps: and taking the sum of the loss values of all the sections of the communication link as the total loss value of the communication link.