CN102082618B - 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 based on ray tracing technique, belong to New Technology Of Shortwave Communication field.

(2) background technology

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

The method of current conventional analysis electric wave temporal correlation is mainly based on experiment test, experiment test need to carry out on actual electrical absciss layer link, and the natural causes such as ionospheric fundamental characteristics can be in time, season change, need to repeatedly measure just and can obtain exact solution, make the method cost of experiment test very high, therefore under general condition, conventionally select the method for channel simulation.Channel simulation method refers to by the characteristic of channel is carried out to theory analysis, set up channel model, under laboratory environment, carry out similarly simulating with actual channel, it can manufacture various representative channel characteristic environments and electromagnetic environment at an easy rate, the region that can simulate is boundless, and climate condition restriction, can repeatedly not repeat experiment 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 in most cases can simulating the characteristic of short wave channel, and complexity Di，Er Bei Consultative Committee on International Radio (CCIR) (CCIR) recommends and is widely used.But it is not high that the limitation of this model is precision, need user to have certain anticipation and understanding to the ionosphere of specific region and ground magnetic characteristic, operate very inconvenient, and only can realize the simulation to typical environment, universality is not high.

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

The general simple parabolic curve of different forms 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 formula _emfor electron concentration maximum, h _mthe height at place while getting maximum for electron concentration, Y _mhalf thickness for parabolic layer.Because this mathematic(al) representation is fairly simple, therefore be often used.

For ray tracing technique, generally all adopt two-dimentional form of calculation, situation about showing generally only has the great-circle distance of communication two places, therefore, in the introducing of ionospheric model and the introducing great majority in earth magnetic field, it is simple approximate model, in the use of model, can only be to adopt average form in addition, can not adopt reconstruct environmental model step by step, the error existing in the precision of using be like this larger.The model in earth magnetic field generally can not introduced.But under actual conditions, earth magnetic field is larger on the impact of ray.Adopt accurate parabolic ionospheric model extensively not approved as the basis of ray tracing technique, in addition, in model use procedure, the formal parameter of model obtains existing problems, and ionosphere constantly changes according to time place, and the situation that there will be layering 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 Geomagnetic Field Model, and the introducing of Geomagnetic Field Model is seldom explained.In addition, adopt two-dimentional demonstration and account form, to the utilizability of the parameter calculating not high (as angle of arrival of ray etc.).So existing technology, to calculate accuracy and realistic situation not high, is also difficult to accomplish to the further application of parameter of calculating.

(3) summary of the invention

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

(2) technical scheme:

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

Step 1: determine geographical latitude and longitude coordinates and the predicted time of launch point and acceptance point, build accordingly ionospheric electron density distribution and earth magnetic field and distribute, and according to magneto-ionic theory, further determine the spatial distribution of refractive index.

Step 2: according to the geographical location information of launch point and acceptance point, can obtain between launch point and acceptance point the 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 having built, solve spherical coordinate system (r, θ,

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

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

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

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

wherein, real part is got in Re representative; W is angular frequency.

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

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 different predicted times, these values form a discrete-time series.

Step 6: group path sequence is processed, 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 Calculation of correlation factor 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,

for the mean value of x (n), N refers to the length of x (n).Utilize above-mentioned formula, in Calling MATLAB instrument, XCORR function calculates coefficient correlation.

Step 7: in order to further illustrate 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 time, think uncorrelated.According to result of calculation, when coefficient correlation is 0.05, corresponding time value is the correlation time of group path.

(3) advantage and effect:

The present invention take international ionosphere with reference to IRI as Foundation ray propagates environment, in accuracy and confidence level, be all greatly improved.Analysis to acceptance point group path time randomness has made up current deficiency, can instruct the application of short wave communication.

In the use, the parameters such as the time in the time of only need to using the corresponding geographical position of transmitting, acceptance point, prediction for user, antenna directivity just can and predict near group path time randomness acceptance point in practicality, have larger breakthrough correlation time.As three-dimensional ray tracing technique, aspect visual, there is larger advantage in addition, use more intuitively the method.

(4) accompanying drawing explanation

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, the method concrete steps are as follows:

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

Launch point coordinate setting is in Zhengzhou, and its coordinate is (E113.63 °, N34.80 °), and acceptance point coordinate setting is in Qingdao, and its coordinate is (E120.30 °, 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 the ray propagates environmental condition under precondition with reference to IGRF prediction and calculation.The ionospheric electron density 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 the great-circle distance along earth surface, and the possible span of rough estimate launching elevation.

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

Step 3: it is 8MHz that tranmitting frequency is set, under the ray propagates space environment having built, solves spherical coordinate system (r, θ

) under ray equation, and launching elevation is carried out to linear interpolation calculating.In spherical coordinate system, ray equation can be write as the form of component:

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

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

in formula, β is transmitting inclination angle, and α, for transmitting drift angle, is specifically calculated and obtained by the longitude and latitude of launch point and acceptance point two places.K _r, k _θ,

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

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

Initial value is set is:

R is that 6370, θ is pi/2-36.1*pi/180, for 120.3*pi/180,

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

In fixed elevation value, be made as under 5 °, the initial value substitution equation right-hand member by variable, obtains new variate-value, again brings equation right-hand member into, so circulation, final ray tracing when being 5 ° at the elevation angle.Then, elevation value is increased to 1 °, recalculate ray tracing, so circulation is gone down, until arrive 45 ° of the maximums of elevation coverage.The ray tracing data that obtain are processed, and according to the great-circle distance obtaining and the contrast of actual great-circle distance, can judgement arrive acceptance point, and save data.Can obtain some numerical results as follows:

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, while being 46 ° of left and right at the elevation angle, can arrive acceptance point.

Step 4: the elevation value obtaining is further carried out to interpolation calculation, using 0.01 degree as step-length, repeat the computational process of previous step, obtain relatively accurate elevation value, make the ray of launching at this elevation angle just in time arrive acceptance point.Some numerical results 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

Through calculating us, can obtain when the elevation angle is 45.43 °, just arriving acceptance point, now corresponding group path is 930.22km, and this group path records of values is also preserved.

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

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

Data in step 5 are brought in Calculation of correlation factor 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 time, think uncorrelated.According to result of calculation, when coefficient correlation is 0.05, corresponding time value is about 10 minutes, and group path is about 10 minutes correlation time, as shown in Figure 4.

Claims (1)

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

Step 1: determine geographical latitude and longitude coordinates and the predicted time of launch point and acceptance point, build accordingly ionospheric electron density distribution and earth magnetic field and distribute, and according to magneto-ionic theory, further determine the spatial distribution of refractive index;

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

Step 3: for a certain tranmitting frequency, under the ray propagates space environment having built, solve spherical coordinate system (r, θ,

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

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

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

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

wherein, real part is got in Re representative; W is angular frequency;

Step 4: by the calculating of step 3, obtain ray and can just get at the approximate elevation value that reaches acceptance point place; Under normal conditions, this value is unique, but when ionosphere distribution is relatively inhomogeneous; The elevation value obtaining is further carried out to interpolation calculation, obtain relatively accurate 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 different predicted times, these values form a discrete-time series;

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

For stationary random process x (t), auto-correlation coefficient $\mathrm{\ρ}\left(\mathrm{\τ}\right)=\frac{R\left(\mathrm{\τ}\right)}{R\left(0\right)}=\frac{E\left\{\right[x(t+\mathrm{\τ})-m\left]\right[x\left(t\right)-m\left]\right\}}{E\left({[x\left(t\right)-m]}^2\right)}$

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 Calculation of correlation factor 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, in Calling MATLAB instrument, XCORR function calculates coefficient correlation;

Step 7: obtain group path correlation time according to the result of calculation of step 6; In engineering, when coefficient correlation is lower than 0.05 time, think uncorrelated; According to result of calculation, when coefficient correlation is 0.05, corresponding time value is the correlation time of group path.

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