CN102082618A - Method for analyzing time randomness of receiving-point group paths - Google Patents

Abstract

The invention discloses a method for analyzing the time randomness of receiving-point group paths, which comprises the following seven steps: 1, determining the longitudes and latitudes as well as forecasting time of a launching point and a receiving point so as to construct a dissemination environment; 2, calculating the great circle distance and the value range of a launching elevation angle according to geographic information; 3, solving a ray equation so as to obtain an estimated value of the launching elevation angle; 4, carrying out linear interpolation calculation, and solving an accurate value of the elevation angle; 5, repeating the steps 1 to 4 so as to obtain a value sequence of the group path in different time; 6, processing the sequence of the group path, and calculating a self-correlation coefficient; and 7, obtaining the correlation time of the group path according to the calculation result obtained in the step 6. The method disclosed by the invention has good practical value and a broad application prospect in the technical field of short-wave communication.

Description

A kind of method of analyzing acceptance point group path time randomness

(1) technical field

The present invention relates to a kind of method of analyzing acceptance point group path time randomness, belong to the short wave communication technical field based on ray tracing technique.

(2) background technology

Short wave communication is the main mode of current telecommunication, and its frequency range is 3-30MHz, mainly relies on ionospheric reflection to propagate.In the shortwave propagation process, ionospheric electron concentration is very big to its operating frequency influence, the frequency height of reflection when concentration is high, and the frequency of reflection was low when concentration was low.Because ionospheric height and electron concentration change with the variation of factors such as area, season, time, Sunspot Activities, have certain randomness.Therefore, the electrical wave parameters that receives at acceptance point also can produce corresponding change along with the variation of ionosphere state, as meetings such as group path, time delay, coverages along with the time changes.In order to improve the reliability of short wave communication, the correlation between the electric wave that need receive different time, different location is analyzed and is studied.

The method of current analysis electric wave temporal correlation commonly used mainly is based on experiment test, experiment test need carry out on actual electrical absciss layer link, and natural causes such as ionospheric fundamental characteristics can be in time, season change, need repeatedly to measure just can obtain exact solution, make that the method cost of experiment test is very high, therefore under general condition, select the method for channel simulation usually for use.The channel simulation method is meant by the characteristic of channel is carried out theory analysis, set up channel model, under laboratory environment, carry out similarly simulating with actual channel, it can make various representative channel characteristic environment and electromagnetic environment at an easy rate, the region that can simulate is boundless, is not subjected to the weather condition restriction, can carry out repeatedly repeated experiments at any time, and testing expense is few, can shorten the lead time of communication equipment.In various typical short wave channel models, the gloomy model of water (Watterson model) is owing to the characteristic that in most cases can simulate short wave channel, and complexity is low, and is recommended and be extensive use of by Consultative Committee on International Radio (CCIR) (CCIR).But it is not high that the limitation of this model is precision, needs the user that the ionosphere and the ground magnetic characteristic of specific region are had certain anticipation and understanding, and it is very inconvenient to operate, and only can realize the simulation to typical environment, and universality is not high.

Utilize ray tracing technique to predict short wave communication some characterisitic parameters in using, if the maximum closing to reality of the model that utilizes, just can be identical to a more accurate degree with actual conditions.Ray tracing technique is meant under the situation of high frequency, and electromagnetic wave is approximately ray, according to the environmental condition at ray propagates place, the electromagnetic wave track is calculated.Therefore utilize this technology just can calculate launch point all rays to acceptance point, and, we can calculate all fundamental characteristics (as parameters such as acceptance point field intensity, time delay, group paths) of every ray according to ray tracing, on the basis of emulated data, introduce the time randomness that corresponding algorithm just can obtain group path.What adopt in the application of ray tracing usually mainly is accurate parabolic model, and this model is described below:

The general simple parabolic curve of employing form be similar to electron concentration in this layer with the variation of height layer be referred to as parabolic layer, its mathematic(al) representation is:

$N_e=\left\{\begin{array}{cc}{N}_{\mathrm{em}}[1-{\left(\frac{h-h_m}{Y_m}\right)}^2]& \left(\right|h-h_m|\≤Y_m)\\ 0& \left(\right|h-h_m|\≥Y_m)\end{array}\right.$

N in the formula _EmBe electron concentration maximum, h _mThe height at place when getting maximum for electron concentration, Y _mHalf thickness for parabolic layer.Because this mathematic(al) representation is fairly simple, so often be used.

For ray tracing technique, the general form of calculation that all adopts two dimension, situation about showing generally has only the great-circle distance of communication two places, therefore, in the introducing of ionospheric model and the introducing great majority in earth magnetic field is simple approximate model, can only be to adopt average form in addition in the use of model, can not adopt reconstruct environmental model step by step, the error that exists on the precision of using be bigger like this.The model in earth magnetic field generally can not introduced.But the earth magnetic field is bigger to the influence of ray under the actual conditions.Adopt accurate parabolic ionospheric model extensively not approved as the basis of ray tracing technique, in addition, in the model use, the formal parameter of model obtains existing problems, and ionosphere constantly changes according to the time place, and the situation of layering can occur according to local local time, this situation is difficult to embody when utilizing accurate parabolic model, and the situation credible and that gear to actual circumstances of model reduces greatly.In general application, seldom introduce the earth magnetic field model, and the introducing of magnetic field model is explained seldom over the ground.In addition, adopt the demonstration and the account form of two dimension, to the utilizability of the parameter that calculates not high (as the angle of arrival of ray etc.).So existing technology is not in that to calculate accuracy and realistic situation high, further application also is difficult to accomplish to parameters calculated.

(3) summary of the invention

(1) goal of the invention: the purpose of this invention is to provide a kind of method of analyzing acceptance point group path time randomness, this method has overcome the deficiencies in the prior art, it adopts international reference ionosphere (IRI) and international earth magnetic field to make up communication environments with reference to (IGRF), utilize the three-dimensional ray tracing technology that radio wave propagation is carried out emulation, the data that tallied with the actual situation more.On the basis of emulated data, utilize the sequence time relevance algorithms to analyze the time randomness of group path and calculated correlation time.Therefore, analyze acceptance point ensemble path time correlation in the short wave communication, can instruct the application of short wave communication based on this ray tracing technique.

(2) technical scheme:

As shown in Figure 1, a kind of method of analyzing acceptance point group path time randomness of the present invention, these method concrete steps are as follows:

Step 1: determine the geographical latitude and longitude coordinates and the predicted time of launch point and acceptance point, make up ionosphere electron concentration distribution and earth magnetic field in view of the above and distribute, and, further determine the spatial distribution of refractive index according to magneto-ionic theory.

Step 2: according to the geographical location information of launch point and acceptance point, can obtain between launch point and acceptance point great-circle distance along earth surface, and the possible span of rough estimate launching elevation.

Step 3: for a certain tranmitting frequency, under the ray propagates space environment that has built, find the solution spherical coordinate system (r, θ,

) under ray equation, and launching elevation is carried out linear interpolation calculates, that is: in possible the span at the elevation angle, elevation value is from a certain initial value, calculates double counting after 1 ° of the back increase at every turn, until reaching stop value;

In spherical coordinate system, ray equation can be write as the form of component:

Wherein, P ' is a group path, k _r, k _θ,

Be three components of wave vector in spherical coordinate system, c is the light velocity, and H is a Hamiltonian.The pass of H and wave vector k, phase refractive index n is:

Wherein, real part is got in the Re representative; W is an angular frequency.

Step 4:, can obtain ray and can just get at the approximate elevation value that reaches the acceptance point place by the rapid calculating of previous step; Under normal conditions, this value is unique, but when the ionosphere distribution is inhomogeneous relatively, may obtain a plurality of elevation value, also is so-called angle of elevation ripple and low angle ripple; The elevation value that obtains is further carried out interpolation calculation, obtain accurate relatively elevation value, make the ray of launching at this elevation angle just in time arrive acceptance point and also store the group path value that obtains.

Step 5: repeat above-mentioned steps one to step 4, predicted time is set to different time, and other condition is constant, can obtain the group path value under the different predicted times, and these values constitute a discrete-time series.

Step 6: the group path sequence is handled, and calculated auto-correlation coefficient

For stationary random process, auto-correlation coefficient

Wherein, R (τ) is the auto-correlation function of x (t), and m is the time average of x (t).

For discrete-time series, utilize the coefficient correlation computing formula to obtain:

$\mathrm{\ρ}\left(m\right)=\frac{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}(x_{n+m}-\stackrel{\‾}{x})(x_n-\stackrel{\‾}{x})}{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}{(x_n-\stackrel{\‾}{x})}^2}$

Here, Be the mean value of x (n), N refers to the length of x (n).Utilize above-mentioned formula, call XCORR function calculation coefficient correlation in the MATLAB instrument.

Step 7: in order to further specify the significance of group path time randomness, further calculate group path correlation time according to the result of calculation of step 7.In engineering, when coefficient correlation is lower than 0.05, then think uncorrelated.According to result of calculation, pairing time value is the correlation time of group path when coefficient correlation is 0.05.

(3) advantage and effect:

The present invention is that the ray propagates environment is set up on the basis with international ionosphere with reference to IRI, all is greatly improved on accuracy and confidence level.Analysis to acceptance point group path time randomness has remedied current deficiency, can instruct the application of short wave communication.

In the use, only need just can and predict that bigger breakthrough is arranged near the group path time randomness acceptance point correlation time on practicality for the user to the corresponding geographical position of emission, acceptance point, parameters such as time, antenna directivity when prediction is used.As three-dimensional ray tracing technique, aspect visual, bigger advantage is arranged in addition, use this method more intuitively.

(4) description of drawings

A kind of method flow block diagram of analyzing acceptance point group path time randomness of Fig. 1 the present invention

Ionospheric electron density distribution schematic diagram under Fig. 2 certain condition

Near group path auto-correlation coefficient distribution schematic diagram Fig. 3 acceptance point

Near group path schematic diagram correlation time Fig. 4 acceptance point

(5) embodiment

See Fig. 1, a kind of method of analyzing acceptance point group path time randomness of the present invention, these method concrete steps are as follows:

Step 1: determine launch point and acceptance point geographical coordinate and predicted time section, make up the spatial distribution of refractive index.

Launch point coordinate setting is in Zhengzhou, and its coordinate is (E113.63 a °, N34.80 °), and acceptance point coordinate setting is in Qingdao, and its coordinate is (E120.30 a °, N36.10 °), and selecting predicted time is the 20:00 on October 1st, 2009.Utilize international reference ionosphere IRI and international earth magnetic field to obtain ray propagates environmental condition under the precondition with reference to the IGRF prediction and calculation.The ionosphere electron concentration distribution situation of center, two places when 20:00, as shown in Figure 2.

Step 2: according to the geographical location information of launch point and acceptance point, can obtain between launch point and acceptance point great-circle distance along earth surface, and the possible span of rough estimate launching elevation.

The great-circle distance computing formula is: D=R * φ wherein: D is a great-circle distance, and R is an earth radius, is taken as 6370km, and φ is the corresponding radian of being determined by longitude and latitude, can calculate D=620.992km.Rough estimate, the elevation angle between 5 ° to 45 °, with this as the launching elevation scope.

Step 3: it is 8MHz that tranmitting frequency is set, and under the ray propagates space environment that has built, finds the solution spherical coordinate system (r, θ ) under ray equation, and launching elevation is carried out linear interpolation calculates.In spherical coordinate system, ray equation can be write as the form of component:

Wherein P ' is a group path, ordinary circumstance, and r is an earth radius, θ is the pi/2-geographic latitude,

Be geographic logitude (0-360) $k_r=\frac{\mathrm{\ω}}{c}\cos \mathrm{\β}$ $k_{\mathrm{\θ}}=-\frac{\mathrm{\ω}}{c}\cos \mathrm{\β}\cos \mathrm{\α},$

β is the emission inclination angle in the formula, and α is the emission drift angle, is specifically calculated by the longitude and latitude of launch point and acceptance point two places and obtains.k _r, k _θ, Be three components of wave vector in spherical coordinate system, c is the light velocity, and H is a Hamiltonian.The pass of H and wave vector k, phase refractive index n is:

Wherein, real part is got in the Re representative; W is an angular frequency.

Initial value is set is:

R is 6370, and θ is pi/2-36.1*pi/180, Be 120.3*pi/180,

$k_r=\frac{\mathrm{\ω}}{c}\cos \mathrm{\β}$ $k_{\mathrm{\θ}}=-\frac{\mathrm{\ω}}{c}\cos \mathrm{\β}\cos \mathrm{\α},$

Be made as under 5 ° in the fixed elevation value, the initial value substitution equation right-hand member with variable obtains new variate-value, brings the equation right-hand member once more into, so circulation, final ray tracing when being 5 ° at the elevation angle.Then, elevation value is increased by 1 °, recomputate ray tracing, so circulation is gone down, up to 45 ° of the maximums that arrives elevation coverage.The ray tracing data that obtain are handled, and according to great-circle distance that obtains and actual great-circle distance contrast, can judgement arrive acceptance point, and preserve data.It is as follows to obtain part result of calculation:

Sequence number	Tranmitting frequency (MHz)	Launching elevation (degree)	Spherical distance (kilometer)
				1	8	43.00	683.26
2	8	44.00	663.90
				3	8	45.00	642.49
4	8	46.00	621.46
				5	8	47.00	601.26
6	8	48.00	582.15
				7	8	49.00	567.57

By contrasting with actual great-circle distance, we can see, can arrive acceptance point when at the elevation angle being 46 ° of left and right sides.

Step 4: the elevation value that obtains is further carried out interpolation calculation, as step-length, repeat the rapid computational process of previous step, obtain accurate relatively elevation value, make the ray of launching at this elevation angle just in time arrive acceptance point with 0.01 degree.Part result of calculation is as follows:

Sequence number	Launching elevation (degree)	Group path (kilometer)	Spherical distance (kilometer)	Sequence number	Launching elevation (degree)	Group path (kilometer)	Spherical distance (kilometer)
								1	45.39	931.02	621.88	6	45.44	930.12	620.69
2	45.40	930.42	621.36	7	45.45	927.22	618.60
								3	45.41	930.42	621.25	8	45.46	929.92	620.33
4	45.42	930.42	621.13	9	45.47	929.92	620.22
								5	45.43	930.22	620.98	10	45.48	929.82	620.04

We can obtain arriving acceptance point just when the elevation angle is 45.43 ° through calculating, and this moment, corresponding group path was 930.22km, with this group path records of values and preservation.

Step 5: repeat above-mentioned steps one to step 4, predicted time is set to 20:00 to 20:30, calculates the primary group path every 15 seconds, amounts to 121 times, and other condition is constant.Can obtain the group path value under the different predicted times, these values constitute a discrete-time series.

Step 6: the group path sequence is handled, and calculated auto-correlation coefficient.

Data in the step 5 are brought in the coefficient correlation computing formula, as follows:

$\mathrm{\ρ}\left(m\right)=\frac{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}(x_{n+m}-\stackrel{\‾}{x})(x_n-\stackrel{\‾}{x})}{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}{(x_n-\stackrel{\‾}{x})}^2}$

Can obtain group path auto-correlation coefficient ρ (m), as shown in Figure 3.

Step 7: obtain group path correlation time according to the result of calculation of step 7.

In engineering, when coefficient correlation is lower than 0.05, then think uncorrelated.According to result of calculation, pairing time value is about 10 minutes when coefficient correlation is 0.05, and promptly group path is about 10 minutes correlation time, as shown in Figure 4.

Claims (1)

1. method of analyzing acceptance point group path time randomness, it is characterized in that: these method concrete steps are as follows:

Step 1: determine the geographical latitude and longitude coordinates and the predicted time of launch point and acceptance point, make up ionosphere electron concentration distribution and earth magnetic field in view of the above and distribute, and, further determine the spatial distribution of refractive index according to magneto-ionic theory;

Step 2: according to the geographical location information of launch point and acceptance point, obtain between launch point and acceptance point great-circle distance, and estimate the possible span of launching elevation along earth surface;

Step 3: for a certain tranmitting frequency, under the ray propagates space environment that has built, find the solution spherical coordinate system (r, θ,

) under ray equation, and launching elevation is carried out linear interpolation calculates; That is: in the possible span at the elevation angle, elevation value is from a certain initial value, and double counting after each calculating back increases by 1 ° is until reaching stop value;

In spherical coordinate system, ray equation can be write as the form of component:

Wherein, P ' is a group path, k _r, k _θ,

Be three components of wave vector in spherical coordinate system, c is the light velocity, and H is a Hamiltonian, and the pass of H and wave vector k, phase refractive index n is:

Wherein, real part is got in the Re representative; W is an angular frequency;

Step 4:, obtain ray and can just get at the approximate elevation value that reaches the acceptance point place by the rapid calculating of previous step; Under normal conditions, this value is unique, but when the ionosphere distribution is inhomogeneous relatively; The elevation value that obtains is further carried out interpolation calculation, obtain accurate relatively elevation value, make the ray of launching at this elevation angle just in time arrive acceptance point;

Step 5: repeat above-mentioned steps one to step 4, predicted time is set to different time, and other condition is constant, obtains the group path value under the different predicted times, and these values constitute a discrete-time series;

Step 6: the group path sequence is handled, and calculated auto-correlation coefficient;

For stationary random process, auto-correlation coefficient

Wherein, R (τ) is the auto-correlation function of x (t), and m is the time average of x (t);

For discrete-time series, utilize the coefficient correlation computing formula to obtain:

$\mathrm{\ρ}\left(m\right)=\frac{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}(x_{n+m}-\stackrel{\‾}{x})(x_n-\stackrel{\‾}{x})}{\underset{n=0}{\overset{N}{\mathrm{\Σ}}}{(x_n-\stackrel{\‾}{x})}^2}$

Utilize above-mentioned formula, call XCORR function calculation coefficient correlation in the MATLAB instrument;

Step 7: obtain group path correlation time according to the result of calculation of step 7; In engineering, when coefficient correlation is lower than 0.05, then think uncorrelated; According to result of calculation, pairing time value is the correlation time of group path when coefficient correlation is 0.05.

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