RU2516239C2 - Method of determining maximum usable frequency for ionospheric radio communication - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to ionospheric radio communication and is intended to determine maximum usable frequency. The method involves transmitting radio signals at given frequencies from GPS/GLONASS navigation satellites to the Earth, receiving radio signals transmitted through the "satellite-Earth" distance medium at the receiving side by a single-frequency navigation receiver, standard processing of the received radio signals to determine coordinates of the single-frequency navigation receiver, and displaying calculation results obtained by the single-frequency navigation receiver; coordinates of said navigation receiver are compared with coordinates of the navigation receiver obtained based on a priori geodesic surveying and difference values of coordinates of the navigation receiver are obtained.

EFFECT: providing reliable radio communication at a given time over a long distance.

3 cl, 2 dwg

Description

The invention relates to the field of ionospheric radio communications and is intended to determine the maximum applicable frequency, the knowledge of which is necessary for reliable and reliable radio communications at a given time over long distances. The technical implementation of the invention can be used at transceiver centers, short-wave professional radio stations, for the transmission of digital data and regional and foreign broadcasting programs in the short-wave frequency range, as well as for automatic control of ionospheric radio communication sessions when constructing adaptive radio systems for various purposes, including systems automatic emergency alerts.

The invention is applicable to stationary and mobile short-wave (HF) transmitters, when a periodic change in operating frequencies is required during the day or when the operating time of HF transmitters is a priori unknown, and they can be switched on and off automatically according to a predetermined algorithm at any time of the current day to transmit information.

The operation of the HF radio and radio broadcasting facilities largely depends on the refractive properties of the ionosphere on the propagation path of the radio signal. The state of the ionosphere, as an electrically charged medium, depends on many factors of a natural and anthropogenic nature. The main influence on the state of the ionosphere is made by its electron concentration, which constantly changes depending on time (hour of the day, season, phase of the solar activity cycle), geographical coordinates, altitude, and solar activity. Their daily variations can lead to both a deterioration in the quality of radio communications and broadcasting in the HF band, and its complete disappearance for the constantly selected carrier frequency of the radio transmitter.

The advantage of working in the HF range compared to working at longer wavelengths is that directional antennas can be created in this range. Waves in the HF range propagate over long distances by single or multiple reflection from the ionosphere and the Earth's surface. Therefore, HF communication systems can provide directional information transfer over relatively large distances (units and tens of thousands of kilometers).

The method of propagation of radio waves by reflection from the ionosphere is called hopping and is characterized by the distance of the jump, the number of jumps, the angles of exit and arrival, as well as the maximum applicable frequency (MUF) and the lowest applicable frequency (NFC). MUF is the frequency at which the radio waves sent by the antenna of the radio transmitter are still reflected in the direction to the horizon. At frequencies above the MUF, the layer generally ceases to reflect radio waves sent from the Earth’s surface, and they travel through the ionosphere into space. Radiocommunication in the HF wavelength range plays an important role as a means of internal, zone, mobile and production-dispatch communication of general, departmental and special use and purpose, and is also widely used for professional and amateur radio communications.

Various radio sounding methods and options are known for determining MUFs. Here it is necessary to distinguish vertical, oblique, reciprocal-oblique sounding with various types of signal modulation, which can be narrow-band or wide-band. In recent decades, data on the state and wave processes in the ionosphere have been obtained using a global satellite network such as GPS / GLONASS.

The method of trace (inclined) sounding has high accuracy in the determination of MUFs. The transmitter and receiver of signals are spaced one or more hops apart. At a predetermined time or with a certain period of time, the radio transmitter sequentially broadcasts the radio signal at several frequencies of the HF range. At the receiving end, the audibility and quality of the signals are evaluated and a conclusion is made about suitable frequencies for a given time of day and month. The accumulated statistics are then used to organize radio communications. In this case, the accuracy of determining the MUF will be determined by the step of tuning the emitted frequency by the transmitter. For the purposes of determining the MUF, the use of the HF network of broadcasting stations deserves attention, for each of which its location, frequency of the carrier of the radio transmitter and direction of broadcasting are known.

The essence of the known active methods for determining the MUF is that on the transmitting side, a radio signal is emitted sequentially (parallel) at different frequencies of the HF band, and on the receiving side, this radio signal is received at each frequency, processed and recorded. In this case, either the sounding frequency at which the highest level of the received signal was fixed, or the highest frequency at the nominal value at which the signal was received at the receiving point, is taken as the MUF.

During vertical sounding (VZ), the radio waves of a transmitter located in a specific place are emitted upward and then reflected from the ionosphere. Knowing the speed of their propagation, equal to the speed of light, and the time from the moment of transmission to the moment of reception, you can determine the height of the reflective layer. Vertical ionosondes determine the state of the ionosphere directly above the point of location of the transmitting radio station. Allowing us to obtain the dependence of the distribution of electron concentration on height, they are not very suitable for studying dynamic processes in the ionosphere, and their use is quite expensive because of the need to ensure the operation of radio transmitting and receiving systems. In the case of reciprocating sensing (VNZ), an effect is used that characterizes the reflection of radio waves from the Earth in the opposite direction, the so-called "echo".

In practice, it is often not possible to conduct a sounding procedure before a session for reasons of time pressure or other reasons. In addition, in order to conduct airspace and airborne detection, in addition to a transmitter and a receiving antenna with a given radiation pattern, high accuracy is required in determining the time between the moments of transmission and reception of radio pulses, as well as synchronization of the operation of transmitting and receiving complexes, which is their main drawback.

The principles of remote sensing and monitoring the state of the ionosphere, determining the operating frequencies for the ionospheric radio communication are known [1-4].

Consider individual patents and technical solutions that, in terms of the totality of operations and actions on signals, most fully reflect the essence of the task of determining the MUF for ionospheric radio communications. For sounding the ionosphere, one can use intrinsic radio waves of the HF band frequencies or radio waves with a frequency well above the HF band. Conventionally, the process of sensing the ionosphere can be divided into active and passive methods, from the point of view of the possibility of receiving such radio signals by a typical HF band receiver.

Consider the active methods of sounding the ionosphere. So, for example, the patent of the Russian Federation 94028469 dated 05/20/1996 for a device for determining the maximum applicable frequency for an HF radio link is known [5]. The invention relates to radio communication systems, in particular to systems providing the determination of the frequency range of the passage of radio signals in the HF range, i.e. determining the maximum and lowest applicable frequencies. The essence of sounding is the sequential radiation of the inclined probe signals on the frequency band of the HF range by a radio transmitting device, their reception with subsequent processing and registration. In this case, according to the processing results, either the sensing frequency at which the maximum level of the received signal was fixed, or the highest frequency at which the signal was received at the receiving point, or the frequency at which the signal level is analytically associated with the maximum level received signal. The disadvantage is the loss of significant time for conducting sounding of the ionosphere in the entire frequency range, due to an increase in the number of necessary measurements to achieve a given measurement accuracy.

Known patent of the Russian Federation 2154910 from 08/20/2000 for a system for automatic control of short-wave communication [6]. A system is proposed for automatic control of short-wave communication as a computer-based communications system, autonomous from channel equipment, designed to control short-wave communication. Using only 9 fixed frequencies for testing the HF range, the complex adapts the operation of channel equipment to the daily dynamics of the ionosphere and radio interference. As a result, the equipment always operates at optimal frequencies. Using the property of inertia of the ionosphere, and controlling the dynamics of the correspondent signals at the optimum operating frequency (ORC), the complex predicts the time of occurrence of constant failures and, in advance, even before the occurrence of the failure, reconstructs the communication means of both correspondents to new optimal frequencies. The disadvantage of the system is the need to transmit testing (probing) radio signals emitted at 9 frequencies of the HF range, at short intervals, which constantly creates certain radio interference to other radio stations.

Known patent of the Russian Federation 2307463 from 09/27/2007 on a method for selecting operating frequencies for radio lines of ionospheric waves [7]. Achievable technical result of the invention is the development of a method of selecting operating frequencies for radio lines of ionospheric waves, providing increased reliability of determining the suitability of radio frequencies. The choice of operating frequencies is carried out according to the conditions of suitability of frequencies as a result of reflection from the ionosphere and signal-noise environment.

The disadvantage of this method is to take into account the condition under which the ratio of signal strength and interference is less than the minimum allowable signal-to-noise ratio and also when the current probability of a reception error is less than a predetermined maximum allowable error probability.

Monitoring of the ionosphere using GPS / GLONASS navigation satellites emitting radio waves that pass through the ionosphere provides the ability to determine the spatial distribution of ionosphere parameters. The use of these parameters allows, in principle, the possibility of predicting MUFs in order to effectively plan and conduct HF communication sessions.

In the patent of the Russian Federation 2181490 dated 04/20/2002 for a satellite radiodetermination device and method [8], satellites of the global navigation service are used, for example, GPS system satellites that generate ranging signals, geostationary satellites that relay ranging signals generated in a navigation earth station, containing auxiliary information A, as well as medium-orbit satellites that generate rangefinding signals containing regional auxiliary information RA transmitted from the satellite access node ICAM. The receiver estimates the ionospheric delays for the ranging signals transmitted at the same frequency.

The GPS / GLONASS ground receiver provides signals from several navigation satellites. The constellation of satellites is organized in such a way that at least four satellites are located in the radio visibility zone at almost every point on the Earth’s surface and almost constantly throughout the day. By fixing the differences in the arrival times of signals from different satellites, for which the adopted flight time is used, and taking into account the coordinates of the satellites (transmitted from the board), the receivers of satellite systems calculate the relative ranges to each satellite, and then, based on the obtained four relative ranges, calculates their location in three coordinates and calibrates the local clock. Fluctuations in the delay of signals caused by a change in the state of the ionosphere can reduce the accuracy of radio detection, and, accordingly, to compensate for this undesirable effect, signals are transmitted from each satellite at two frequencies. The main disadvantage of this method is the need for joint use of heterogeneous groups of satellites, including navigation, geostationary and mid-orbit satellites, which leads to a decrease in the reliability of the device.

The patent of the Russian Federation 1840572 dated 08/20/2007 is known for a phase method for measuring the integrated electron concentration in the ionosphere [9]. The invention relates to methods of measurements in radar and can be used to eliminate ionospheric errors in the radar. It carries out the simultaneous measurement of the difference in phase delays of the signals at two frequency pairs having the same spacing. The difference in the obtained phase delay differences determines the integral electron concentration in the ionosphere.

A patent is known for a method for determining the parameters of the ionosphere and a device for its implementation. This is a patent of the Russian Federation 2421753 from 06/20/2011 using signals from navigation satellites [10]. The invention is as follows. First, receive radio signals from navigation satellites at two coherent frequencies F ₁ and F ₂ . Then, the pseudorange D _F1 and D _{F2 are} determined from the received radio signals to the navigation satellite. Using them, the differences of the pseudorange D _{12 are found} . The total electron concentration L _{e is} determined along the satellite – ground point path. It is determined in the field of measuring the altitude profile of the electron concentration of the ionosphere N (z). The phase values F ₁ and F _{2 of the} received radio signals are measured. The pseudorange differences D _{12 are} determined taking into account the phase values F ₁ and F _{2 of the} received radio signals. An iterative procedure is used to solve the inverse problem, based on the use of the conjugate gradient method and a priori information on the background state of the ionosphere to determine N (z) in the measurement domain of the altitude profile of the ionosphere electron concentration.

Based on the obtained values of the electron concentration of the ionosphere by this method, the MUF value can be further determined. The device is equipped with a processing and display unit, the input of which is connected to the output of the dual-frequency receiver. In this case, the processing and display unit is configured to determine the above parameters.

In this method, as a priori information about the background state of the ionosphere (as a zero approximation of the solution to the problem), a long-term forecast of the ionosphere is used, based on some model of the ionosphere, for example, IRI-2007 (International Reference Ionosphere).

The disadvantage of the considered method is the need to use a priori information about the background state of the ionosphere to determine in the measurement area the altitude profile of the electron concentration of the ionosphere N (z). However, this method has another significant drawback - the measured values of the total electron concentration (total electron content (TEC) are determined accurate to an arbitrary constant, which makes it impossible to unambiguously interpret the measurements. For carrying out two-frequency measurements, a complex calibration procedure of measuring equipment and a stable temperature regime are required, for the calibration coefficients to remain unchanged.

Accurate calculation of calibration coefficients is a time-consuming task, but without using these coefficients, it is impossible to obtain TEC values that have physical meaning (when using incorrect calibration, as a rule, the obtained TEC values are either negative or exceed the physically possible maximum values).

It should be noted that for solving personal navigation problems, GNSS receivers were widely used, making measurements of only pseudorange at a single frequency. The development of an algorithm for processing these measurements will eliminate the need to use expensive accurate dual-frequency GNSS receiving stations and calibrate these stations. Replacing expensive high-precision equipment with “household” devices will open up opportunities for the rapid deployment of a network of measuring navigation receivers.

Single-frequency civilian equipment works only on GPS / GLONASS signals of the L1 subband and there is no possibility of eliminating ionospheric measurement errors using work on two frequencies. Dual-frequency GPS, accessible to civilian consumers, can be disconnected from the second frequency at any time by changing the P-code to the Y-code on the second frequency (Anti-Spoofing mode). Civilian single-frequency GPS / GLONASS is currently the most widely used, compared to dual frequency.

A known patent of the Russian Federation 2208809 from 07.20.2003 on the method of single-frequency determination of the delay of the signals of a navigation satellite system in the ionosphere [11]. The invention relates to the field of satellite navigation and can be used to determine the ionospheric delay propagation of signals from navigation satellites using navigation equipment of consumers of the global navigation satellite system operating on a single frequency. In the proposed method, the determination of the delay of signals in the ionosphere is made by solving a system of equations composed of the differences in the increments of pseudorange, measured by the rangefinder code and the phase of the carrier frequency for each navigation satellite. The disadvantage of this method is that it is necessary to additionally determine the increment of the pseudorange for the time between the current and previous measurements, then to determine the difference in the increment of the pseudorange, which may be insignificant, which leads to a deterioration in the accuracy of the measurements.

When using single-frequency navigation receivers (NP) of the GPS / GLONASS type, the ionospheric delay of radio signals emitted from satellites is the largest source of error in pseudorange measurements and significantly affects the error in determining coordinates and time.

EFFECT: providing, according to the data of single-frequency GPS / GLONASS type NPs, the formation of control signals for finding the values of the maximum applicable ionospheric radio frequency and simplifying the method for determining it.

The technical result is achieved by the fact that, in contrast to the known method of single-frequency determination of the delay of the signals of navigation satellite systems in the ionosphere [11], including the transmission of radio signals at predetermined frequencies from navigation satellites of the GPS / GLONASS type to Earth, the reception of radio signals that have passed the satellite-to-Earth remote environment "on the reception side one-frequency navigation receiver, standard processing of the received signals to determine the position coordinates (x _i, y _i) single-frequency navigation reception ika and mapping calculation results according to the invention obtained by one movement of the navigation receiver coordinates for the location of the navigation receiver (x _i, y _i) is compared with pre-generated based on a priori surveying navigation receiver location coordinates (x _0, y ₀₎ and get the differential values of the coordinates of the navigation receiver Δx _i and Δy _i , then form the normalizing coefficients S ₁ and S ₂ which are equal to the values:

S ₁ = Δx _i / Δx _max and

S ₂ = Δy _i / Δy _max ,

where Δx _i and Δy _i are the current error in determining the coordinates of the navigation receiver, Δx _max and Δy _max are the maximum possible error values when determining the coordinates of the location of the navigation receiver, while the values of the current error are 0≤Δx _i ≤Δx _max and 0≤Δy _i ≤y _max ;

based on the values of the quantities S ₁ and S ₂ form a generalized normalizing coefficient S, the value of which is determined based on the condition:

; $$S=\sqrt{S_{\mathrm{one}}^2+S_2^2}$$

;

then calculate the value of the critical frequency of the HF range f _kp according to the expression:

f _cr = (f _min + S · Δf);

where f _min - the minimum frequency of the HF range,

Δf is the frequency band of the HF range (Δf = f _max -f _min ),

f _max - the maximum frequency of the HF range;

the maximum applicable frequency f _Mpc is determined based on the expression:

f _mpc = f _kp · secφ ₀ = (f _min + S · Δf) secφ ₀ ,

where φ ₀ = π / 2-θ ₀ is the angle of incidence of the radio beam on the ionosphere;

the coefficient, the value of the optimal operating frequency f _{orc of the HF} radio transmitter and receiver is determined from the values of the maximum applicable HF frequency according to the expression:

f _ORC = 0.9 · f _Mpch .

The method can be implemented in such a way that, based on the optimal operating frequency f _orc , a digital control signal is generated, presented in a sequential binary code, the bit depth of which is determined by the maximum possible number of frequency channels organized n for ionospheric radio communication of the HF range from the expression:

n = (f _Mpc -f _npc ) / Δf ₀ , where f _npc is the lowest applicable frequency,

Δf ₀ - frequency band, which is one channel of radio transmission,

n≤2 ^m , m is the number of bits of the digital control signal,

m = 1,2,3, ..., Z.

The method can be implemented so that if there is a change in the maximum applicable frequency f _Mpc at certain time intervals Δt _i , due to its increase or decrease, relative to its initial value at time t ₁ , t ₂ , ... t _n , which characterize the beginning conducting radio communication sessions at new optimal operating frequencies in the HF range for the automatic switching of the carrier frequency of the radio transmitter and receiver, the digital control signal is generated to another new optimal hydrochloric operating frequency.

The use of existing single-frequency GPS / GLONASS type NPs and the signals generated by them makes it possible to quickly, relatively simply and without high costs, along with performing the task of determining the coordinates of the location of the object (receiver), determine the value of the maximum applicable frequency, and continuously, since the group of navigation spacecraft will have sufficient time be in the field of view of the NP. Due to the low cost of single-frequency GPS / GLONASS-type NPs, it is possible to organize a large number of reception centers (which is important for the extended territory of the Russian Federation) that simultaneously operate in several directions (radio paths) instead of one, as when using equipment of vertical, inclined, reciprocal-inclined or transionospheric sounding .

The technical result is achieved due to the exclusion in the known methods of operations, including the indirect determination of the electron density or delay of the radio signals in the ionosphere for their subsequent use to find the MUF. In this method, a new specific operation is introduced, which includes determining the discrepancy in the measurement of the parameters of the current coordinates by single-frequency GPS / GLONASS type NPs in comparison with previously known a priori data on the coordinates of the location of the NPs, the values of which serve as the initial standard for conducting a comparative assessment of the measurement data.

This approach leads to the provision of the necessary calibration for reading signals and linking the measurement results, which is explicitly absent in the known methods, further provides a simplification of the method for estimating the MUF, allows to achieve the necessary accuracy with high speed data measurement. In this case, objective accounting of the daily and seasonal variations in the state of the ionosphere, which are manifested in the real change in the delay of the radio signals of navigation satellites, is achieved.

The proposed method for determining MUF is based on the following provisions. From the theory of propagation of radio waves, it is known that ionized layers are completely characterized by the height of the maximum electron concentration h and the critical frequency f _kp - the maximum frequency of the reflected wave during vertical sounding. The critical frequency depends only on the electron concentration in the ionospheric layer and is determined as:

$$f^2{}_{\mathrm{to}R}=80.8\cdot N_e,(\mathrm{one})$$

where N _e is the number of electrons in 1 m ³ (f _cr determined in Hz) or if the number of electrons in 1 cm ³ (f _cr determined in kHz). So, for example, if at summer noon the electron concentration in layer E reached 10 ¹² electrons / m ³ , then f _kp ≈ 9 · 10 ⁶ Hz or 9 MHz.

With increasing signal frequency, vertically incident waves cease to be reflected, but hollow incident waves are still reflected. At the same time, a “dead zone" is formed around the radio transmitter, in which the signal is not heard. At large distances, the signal can be quite strong.

Since the refractive index of the ionosphere depends on the frequency, the frequency of the radio waves f _Mpc , experiencing total internal reflection at a height h at a value of the elevation angle θ ₀ can be determined from the expression

$$f_{MPH}=\frac{\sqrt{80.8N_{\mathrm{<figure-callout\; id="0"\; label="e\; sin\; \theta "\; filenames="00000020.png"\; state="\{\{state\}\}">e\; </figure-callout>}}}}{\sin {\theta }_{}}=f_{\mathrm{TO}R}\cdot \sec {\varphi }_0(2)$$

where N _e is the electron concentration at the turning point, f _cr is the critical (intrinsic) frequency of the ionosphere, φ ₀ = π / 2-θ ₀ is the angle of incidence of the radio beam on the ionosphere.

MUF is the frequency at which the waves sent by the antenna of the radio transmitter in the direction to the horizon are still reflected. At frequencies above the MUF, the layer generally ceases to reflect waves sent from the Earth’s surface, and they go through the ionosphere into space.

Typically, on ionospheric radio links, communication is possible at operating frequencies from NFC to MUF. At the operating frequency, a radio signal is generated with a frequency band equal to Δf ₀ . Thus, on the radio link, it is possible to organize several radio channels, the number of which

$$n=(f_{mPh}-f_{nPh})/\Delta f_0(3)$$

Each channel is characterized by an operating frequency, for which the average frequency from the band Δf _{0 is} taken. Due to the variability of the ionosphere - the reflection medium of the radio signal and the multipath nature of its reception, the reliability of HF radio communications at individual operating frequencies may not be high enough. The solution to the problem of ensuring the established requirements for the reliability and noise immunity of radio communications is associated with the adaptation of the HF communication system to the changing frequency of propagation of radio waves in terms of operating frequency.

Navigation equipment of consumers (NAP) or navigation receivers (NP) of global navigation satellite systems (GNSS) is used to create modern navigation and orientation systems. This is due, first of all, to their characteristic, such as the ability to determine with high accuracy the coordinates, speed and orientation of an object located anywhere in the world.

One of the main problems when using GNSS NPs is the susceptibility of GNSS navigation satellite signals to the environment and interference. Significant influence on the accuracy of navigation determinations by the signals of the GLONASS / GPS systems is exerted by the conditions of the passage of the signal "top-down". Studies show that the ionosphere has the greatest influence on the measurement error of GLONASS / GPS systems.

The range ρ (t) in radio engineering measurements is characterized by the propagation time of the signal from the satellite to the NP. In the case when this time is precisely known (with the exception of the delay of the radio signal by the ionosphere), the true range will be

$${\rho }_{\mathrm{and}}(t)=c\cdot \Delta t,(\mathrm{four})$$

where c is the speed of propagation of radio waves in space vacuum; Δt is the interval between the moment of emission of the spacecraft signal and the moment of its reception PI. Due to the delay of the radio signal by the ionosphere, a pseudorange ρ _p (t) appears, which differs from the true

$${\rho }_P(t)=c\cdot (\text{Δt}+\Delta t_s),(5)$$

where Δt _s is the delay of the radio signal by the ionosphere. Wherein

$$\Delta {\rho }_s(t)=c\cdot \Delta t_s(6)$$

Given expression (5), we can write that

$${\rho }_P(t)={\rho }_{\mathrm{and}}(t)+\Delta {\rho }_s(t)(7)$$

The magnitude of the signal delay in the ionosphere depends on the period of the 11-year cycle of solar activity, seasonal and daily variations in the electron concentration in the ionosphere, elevation and azimuth of the satellite, as well as on the latitude and longitude of the location of the NP.

The ionospheric refraction of the satellite radio signal, caused by differences in the dielectric constant of layers located at different heights, as well as local inhomogeneities, varies over a wide range. Depending on the region of the Earth where the NP is located, time of day, year, solar and geomagnetic activity, etc., the delay of the satellite radio signal in the ionosphere can be 5 ... 500 ns, which is equivalent to a range measurement error of 1.5 ... 150 m .

The average value of this error for elevation angles close to 90 ° is 5 ... 10 ns at night and 30 ... 50 ns at daytime. At elevation angles of the order of 15 °, these values increase by 2 ... 3 times. It should be noted that a radio signal delay of 1.0 ns introduces an error in the measurement of the true range by 1.5 meters.

It should be noted that the higher the concentration of electrons in the ionosphere, the greater the delay of the radio signals when they are received and, accordingly, the error in measuring the range will increase. This feature can be used to determine f _MPH .

The proposed method for determining the MUF for ionospheric radio communications is based on the following provisions.

First, it is a priori known that the HF range is frequencies from f _min = 3 MHz (100 m) to f _max = 30 MHz (10 m). It is also known that radio waves with an operating frequency f _slave > f _{max are} not reflected from the ionosphere, but pass through the ionosphere into outer space, and vice versa frequencies for which f _slave <f _max are reflected from the ionosphere, as from a mirror surface.

The proposed method for determining the maximum applicable frequency takes into account these objective features. The critical frequency is represented by an expression that contains information about its fixed part and its changing component in the form

$$f_{\mathrm{to}R}=(f_{\min }+\Delta f_i),(8)$$

the maximum value of Δf _{i is} known and equal to Δf _max = (f _max -f _min ). The value of Δf _i primarily depends on the parameters of the ionosphere, which can be determined through its electron density, the value of the signal delay, etc.

We represent the value Δf _i in the form Δf _i = S · Δf _max , where the value S is the input normalizing coefficient. The value of S is determined based on the delay value of the radio signal in the ionosphere (which in turn depends on its electron density) and is expressed in this method through the error in determining the coordinates Δx _i , Δy _{i by the} navigation receiver, the true position of which on the ground is known a priori.

Consider how the quantities Δx _i and Δy _i are determined. Let the radio signal NP be located at point A with coordinates (x, y) determining the a priori known latitude and longitude of its location. Due to the error in measuring the true ranges (due to the delay of the signal in the ionosphere), there will be an error in the exact determination of the coordinates of the NP by Δx _i and Δy _i (Fig. 1).

At the same time, it can be written that if there is an error in measuring the coordinates of point A (location of the NP) from the true one it will shift by

$$A(x_0\pm \Delta x_i,{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="00000020.png"\; state="\{\{state\}\}">y</figure-callout>}}_0\pm \Delta y_j),(9)$$

where Δx _i and Δy _i is the error in determining the true coordinates of objects, expressed in meters.

Then, knowing a priori the true location of the NP (its coordinates), and their possible displacement due to range measurement errors (delay of the radio signal due to the ionosphere), we can determine the quantities Δx _i and Δy _j characterizing the error in measuring the coordinates of point A (x ₀ , y ₀ )

$$A(x_0\pm \Delta x_i,{\mathrm{<figure-callout\; id="0"\; label="y"\; filenames="00000020.png"\; state="\{\{state\}\}">y</figure-callout>}}_0\pm \Delta y_i)-A({\mathrm{<figure-callout\; id="0"\; label="x"\; filenames="00000020.png"\; state="\{\{state\}\}">x</figure-callout>}}_0,y_0)=A(\pm \Delta x_i,\pm \Delta y_i)(10)$$

Let us represent, according to expression (9), the position of the NP in the Cartesian coordinate system. In this case, we conditionally fix the true position of the NP at point A, assuming that the quantities Δx ₀ = 0 and Δy ₀ = 0 (Fig. 1).

Then, knowing the true value of the coordinates, it is possible to determine the values Δx _i , Δy _j , which will characterize the deviation of the coordinates from the true value according to the measurement results using GPS / GLONASS NP.

With that said, expression (8), which determines the critical frequency, can be represented as

$$f_{\mathrm{to}R}=(f_{\min }+S\cdot \Delta f_{\max }),(\mathrm{eleven})$$

where S is the normalizing coefficient characterizing the delay of the radio signal, depending on the electron density of the ionosphere. It is assumed that

$$S=\sqrt{S_{\mathrm{one}}^2+S_2^2},gde{S}_{\mathrm{one}}=\Delta x_i/\Delta x_{\max }\mathrm{and}{S}_2=\Delta y_i/\Delta y_{\max },(12)$$

where Δx _i and Δy _i - the current error in determining the coordinates of the object, Δx _max and Δy _max - the maximum possible error when determining the coordinates of the location of the navigation receiver, which is set a priori. It is observed that 0≤Δx _i ≤Δx _max and 0≤Δy _i ≤y _max , and the value of the normalizing coefficient can take values in the range 0≤S≤1 depending on the state of the ionosphere.

Expression (11) can be rewritten as

$$f_{\mathrm{to}R}=(f_{\min }+S\cdot \Delta f_{\max })=(3.0+S\cdot 27.0)(MGc)(13)$$

When S = 1, f _cr = f _{cr (max)} = 30.0 MHz and when S = 0, f _cr = f _{cr (min)} = 3.0 MHz.

The maximum applicable frequency of the ionospheric radio communication is determined according to the expression

$$f_{mPh}=f_{\mathrm{to}R}\cdot \mathrm{<figure-callout\; id="0"\; label="sec\; \phi "\; filenames="00000020.png"\; state="\{\{state\}\}">sec\; </figure-callout>}{\varphi }_{}{}_0=(f_{\min }+s\cdot \Delta f_{\max })\cdot \mathrm{<figure-callout\; id="0"\; label="sec\; \phi "\; filenames="00000020.png"\; state="\{\{state\}\}">sec\; </figure-callout>}{\varphi }_{}{}_0,(\mathrm{fourteen})$$

and the value of the optimal operating frequency is determined according to the expression

$$f_{\mathrm{about}Rh}=0.9\cdot f_{mPh}(\mathrm{fifteen})$$

The optimal operating frequency (ORC) is understood to mean such a frequency that ensures the maximum duration of the HF transmitter without tuning to other frequencies.

In accordance with (14), the MUF obliquely incident on the ionosphere will be secφ ₀ times higher than the critical frequency. Given the sphericity of the Earth and the ionosphere, which limits the angle of incidence of the wave on the ionosphere, the maximum value of secφ ₀ ≈ 4.1, that is, the ratio M = f _mpc / f _kp <4.1.

The system for determining the maximum applicable frequency for ionospheric communication that implements the proposed method (Fig. 2) comprises a remote receiving satellite antenna 1, a single-frequency navigation receiver 2, a differential signal shaper 3, a source of true coordinates for longitude and latitude 4, a signal shaper of a normalizing coefficient 5 , a source of signals of the maximum error in determining coordinates 6, a calculator of critical frequency values 7, a calculator of values of the maximum applicable frequency and optimal operating frequencies s 8, a calculator of the parameters of the radio signal 9, a signal generator of graphic and tabular data 10. a display device for the visual perception of information 11. a remote control for input of a priori data and control 12, a data input, storage and retrieval unit 13, an analyzer and driver of control signals for automatic control the operation of the radio transmitter and the radio 14, the communication channel 15 and 18, the radio transmitter 16 transmitting the HF antenna 17, the radio 19, the receiving HF antenna 20.

The system operates as follows. The radio signal from the output of the receiving antenna 1 is fed to the input of the receiver 2. From the output of the receiver 2, signals characterizing the measured coordinates (in longitude and latitude) are fed to the first and second inputs of the differential signal generator 3, the third and fourth inputs of which receive true coordinate signals from signal source 4. The difference signal is determined according to expression (10). Comparing the known coordinates in a shaper 3 a priori as a result of a precision geodetic survey with the measured coordinates, differential signals (x and y) are received at the output of the shaper 3, which are fed to the first and second inputs of the shaper 5. The third and fourth inputs of the shaper 5 signals are supplied from source 6 that characterize the maximum possible error value Δx _max and Δy _max when determining the coordinates of the location of the navigation receiver. The shaper operation algorithm is reduced to finding the normalizing coefficient S in accordance with expression (12), which, depending on the error in determining the coordinates (a greater or lesser degree of delay of the radio signal), will change its values in the interval 0≤S≤1. This will lead to the fact that the critical frequency values will vary in the frequency range from f _min to f _max .

From the output of the shaper 5, the signal is fed to the input of the calculator of critical frequency values 7, which implements the operations, according to expression (13). From the output of the calculator 7, the signal determining the value of the critical frequency f _cr is fed to the input of the calculator 8, in which the value of the maximum applicable frequency f _{Mpc is determined} according to expression (14) and the optimal operating frequency f _orc , according to expression (15).

The signal from the first output of the calculator 8 enters the first input of the calculator of the parameters of the radio signal 9, from the second and third outputs of the calculator 8 to the first and second inputs of the shaper of graphic and tabular data 10. The calculation of the parameters of the signals in the calculator 9 is necessary to assess the noise immunity of the signal (at known power transmitter and radio sensitivity, antenna gain, etc.). Based on the data of calculators 8 and 9, the shaper 10 generates tabular data signals, constructs graphs showing the dependence of f _MPH on the current time and other dependencies.

From the fourth output of the calculator 8, the signal is fed to the third input of the input, storage and data retrieval unit 13, the first input of which receives the signal from the output of the calculator 7, the second input is the signal from the fourth output of the a priori data input and control panel 12, and the fourth input of the unit 13 the signal from the first output of the shaper 10. The signals from the first, second, third and fifth outputs of the console 12 are received respectively at the inputs of the signal source 4, the signal source 6, the second input of the calculator 9 and the second input of the analyzer and shaper 14. Using From the input of a priori data through source 6, the value of the coefficient S in the shaper 5 can be adjusted for subsequent calculation of the critical frequency value in the calculator 7. The input of a priori data from the remote control 12 is also necessary for setting the algorithm and automatic operation of the analyzer and the shaper 14.

The signal from the first output of block 13 is fed to the second input of the calculator 7, and also from the second output to the second input of the calculator 8. If necessary, signals from external sources of information (other GPS receivers, etc.) can be received in the input, storage and retrieval unit 13. .) through the fifth entrance (a). In block 13, data is entered, stored, stored and sampled as necessary with the possibility of long-term data storage (day, night, summer, winter, etc.).

The signal from the output of the calculator 9 goes to the third input of the shaper 10, from the second output of which the signal goes to the input of the display device for the visual perception of information 11.

The operator of this system, on the basis of the analysis of the received information about the MFR and ORCH, takes, for example, the necessary organizational and technical measures for setting the optimal operating frequency in the radio transmitter, and brings this information in known ways to set the same frequency on the receiving side.

Along with the purpose of the system for operating in the on-line mode, automation of the processes of establishing radio communication sessions is relevant and necessary for continuous operation of stationary and mobile HF transmitters, when a periodic change of operating frequencies is required during the day or when the operating time of HF transmitters is a priori unknown, and they can turn on and turn off automatically according to the specified algorithm at any time of the current day to transmit information.

To automatically control the operating mode of the exciter of the HF transmitter and tune the radio receiver to the optimal operating frequency in the system (Fig. 2), an analyzer and a driver of control signals 14 are additionally introduced for the automatic control mode of the operation of the radio transmitter and radio receiver. With its help, a digital control signal is generated in a serial binary code, the bit depth of which is determined by the maximum possible number of organized frequency channels for ionospheric radio communication

$$n=(f_{mPh}-f_{nPh})/\mathrm{<figure-callout\; id="0"\; label="\Delta \; f"\; filenames="00000020.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}{f}_{}{}_0,gden\le 2^m,(16)$$

where m is the number of bits of the digital control signal m = 1,2,3,4, ... Z.

For these purposes, the signal from the fifth output of the calculator 8, reflecting the optimal operating frequency f _{ч r, is} fed to the input of the shaper 14, from the first output of which the signal enters the communication channel 15, and from the second output the signal enters the input of the communication channel 18. Communication channels 15, 18 contain the necessary transmitting and receiving channel-forming equipment.

From the output of the communication channel 15, the control signal is fed to the input of the radio transmitter 16 (to the frequency synthesizer unit), the output of which the radio signal is fed to the input of the transmitting HF antenna 17 and is broadcast. From the output of the communication channel 18, the control signal is supplied to the second input of the radio 19. By this control signal, the radio is tuned to receive the optimal operating frequency of the HF transmitter. The radio signal emitted by the transmitter, through the antenna 17 reaches the ionosphere, and, reflected from it, is fed to the input of the receiving antenna 20, from the output of which is fed to the first input of the radio 19.

Automatic switching of the carrier frequency of the radio transmitter to another new optimal operating frequency, when conducting radio communication sessions, can be carried out according to various accepted algorithms for analyzing their progress during the day. This can be done, for example, by generating a digital control signal for automatically switching the carrier frequency of the radio transmitter and receiver, if there is a change in the maximum applicable frequency at certain time intervals Δt _i , due to its increase or decrease, relative to its initial value at time t ₁ , t ₂ , ... t _n , which characterize the beginning of a radiocommunication session at the new optimal operating frequencies in the HF range during the day.

The necessary algorithms and operating modes for changing the optimal operating frequency are set using block 12. A digital signal of a certain code sequence that carries information about the optimal operating frequency at the current time is transmitted to the radio transmitter and receiver via standard communication channels or the Internet.

Figure 2 shows that the MFC determination system, including the main units 1-14, has its location at point A (x, y). The radio transmitter (blocks 16-17) and the radio receiver (blocks 19-20) have their location at points B (x, y) and C (x, y). Let us single out the following situations of radiation of radio waves in the direction of the receiver (correspondent):

- the transmitting antenna of the transmitter emits vertically directed to the ionosphere of the radio wave;

- the transmitting antenna of the transmitter radiates obliquely to the ionosphere of the radio wave. Reception of reflected radio waves is carried out at a distance of one jump.

For the first case, radio waves are emitted upward. Then they are reflected back from the ionosphere. In this case, the state of the ionosphere and, accordingly, MUF is determined directly above the point of location of the transmitting radio station. Receiving radio signals for this case is possible at distances of up to several hundred kilometers in any direction from the radio transmitter (with a radius of about 500 km). According to the accepted notation in figure 2, the location of the system A (x, y) and the radio transmitter B (x, y) is almost the same. The location of the radio at point C (x, y) can be up to 500 km from the radio transmitter.

For the second case, the radio waves are emitted obliquely (for example, with an emission angle of 80 ° ... 20 °) in a given direction. With a single-hop reflection of the radio wave from the ionosphere, they will be reflected from the ionosphere at approximately distances from 1000 to 2000 km from the radio transmitter. Reception of radio signals for this case is possible approximately at distances from 2000 to 4000 km from the radio transmitter. The MUF detection system should be located at location B (x, y), where direct reflection of the radio wave from the ionosphere occurs at the top (this location depends on the angle of radiation of the radio waves into the ionosphere by the transmitter from point A (x, y)). In this case, the navigation receiver and the MUF detection system are located approximately in the middle of the radio path between the radio transmitter and the radio receiver, that is, between points A (x, y) and C (x.y). Table 1 shows the locations of the interacting components in two variants of the direction of the radio beam to the ionosphere.

Table 1 The direction of the radio beam to the ionosphere HF transmitter location at Location of the MUF detection system HF receiver location at Vertical A (x, y) Near A (x, y) C (x, y) Inclined A (x, y) B (x, y) C (x, y)

The proposed method affects the reception of radio signals not only from satellite systems such as GPS / GLONASS. The proposed technical solutions can be extended to other space systems, for example, to the European global navigation satellite system GALILEO.

The principle of operation and a description of the operation of the system under consideration, including ways to find MUFs, signal processing, and other issues can be found in the following publications [1-4, 12]:

 Information sources

1. Rhodes L.Ya. Electrodynamics and radio wave propagation: a training manual / L.Ya. Rhodes. - San.-Pb.: Because of NWTU, 2007, - 90 p.

2. Soloviev Yu.A. Satellite navigation systems. M .: Eco-Trends, 2000 .-- 268 p.

3. Kazantsev M.Yu., Fateev Yu.L. Determination of the ionospheric error of measuring pseudorange in single-frequency equipment of GLONASS and GPS systems // Journal of Radio Electronics No. 12, 2002

4. Pat. 6163295 USA, MKI7 H04B 7/185. Ionospheric correction for single frequency GPS receivers using two satellites / V. Nagasamy, M. Usman, J. Sun (USA); VSIS, Inc. (USA). Claim 04/09/99; Publ. 12/19/2000, etc.).

5. RF patent 94028469 dated 05/20/1996 for a device for determining the maximum applicable frequency for an HF radio link.

6. RF patent 2154910 dated 08/20/2000 for an automatic short-wave communication control system.

7. RF patent 2307463 from 09/27/2007 on a method for selecting operating frequencies for radio lines of ionospheric waves.

8. RF patent 2181490 dated 04/20/2002 for a device and method for satellite radiodetermination.

9. RF patent 1840572 dated 08/20/2007 for a phase method for measuring the integrated electron concentration in the ionosphere.

10. RF patent 2421753 from 06/20/2011 on a method for determining the parameters of the ionosphere and a device for its implementation.

11. RF patent 2208809 of July 20, 2003 for a method for single-frequency determination of the delay of signals of a navigation satellite system in the ionosphere.

12. Grudinskaya G.P. Propagation of radio waves. Textbook allowance for radio tech. specialist. universities. M., Higher School, 1975.260 p.

Claims (3)

1. A method for determining the maximum applicable frequency for ionospheric radio communications of the KB range, including transmitting radio signals at predetermined frequencies from GPS / GLONASS navigation satellites to Earth, receiving radio signals that have passed the satellite-to-Earth remote environment on the receiving side by a single-frequency navigation receiver, standard processing received signals to determine position coordinates (x _i, y _i) single-frequency navigation receiver, and displaying the results of computation, characterized in that the obtained s via one movement navigation receiver coordinates for the location of the navigation receiver (x _i, y _i) is compared with pre-generated based on a priori surveying navigation receiver location coordinates (x _0, y ₀₎ to obtain difference values navigation receiver coordinates Δx _i and Δy _i, then form normalizing coefficients S ₁ and S ₂ , which are equal to the values:
S ₁ = Δx _i / Δx _max and
S ₂ = Δy _i / Δy _max ,
where Δx _i and Δy _i are the current error in determining the coordinates of the navigation receiver, Δx _max and Δy _max are the maximum possible error values when determining the coordinates of the location of the navigation receiver, while the values of the current error are 0≤Δx _i ≤Δx _max and 0≤Δy _i ≤Δy _max ;
based on the values of the values of S _i and S ₂ form a generalized normalizing coefficient S, the value of which is determined based on the condition:
$$S=\sqrt{S_{\mathrm{one}}^2+S_2^2}$$

;
then carry out the calculation of the critical frequency values KB range f _cr according to the expression:
f _cr = (f _min + S · Δf);
where f _min is the minimum frequency of the KB range,
Δf is the frequency band of the KB range (Δf = f _max -f _min ),
f _max - the maximum frequency of the KB range;
the maximum applicable frequency f _Mpc is determined based on the expression:
f _mpc = f _cr · secφ ₀ = (f _min + S · Δf) secφ ₀ ,
where φ ₀ = π / 2-θ ₀ is the angle of incidence of the radio beam on the ionosphere;
the coefficient, the value of the optimal operating frequency f _{orch of the} radio receiver and radio transmitter of the KB range is determined from the values of the maximum applicable frequency of the KB range according to the expression:
f _ORC = 0.9 · f _Mpch . 2. The method for determining the maximum applicable frequency for ionospheric radio communication of the KB range according to claim 1, characterized in that on the basis of the optimal operating frequency f _orc , a digital control signal is generated, presented in a serial binary code, the bit depth of which is determined by the maximum possible number of organized frequency channels n for ionospheric radio communication KB range from the expression:
n = (f _mph · f _npc ) / Δf ₀ ,
where f _NPC is the lowest applicable frequency,
Δf ₀ is the frequency band occupied by one radio transmission channel, n≤2 ^m , m is the number of bits of the digital control signal, m = 1,2,3, ..., Z. 3. The method of determining the maximum applicable frequency for ionospheric radio communication of the KB range according to claim 2, characterized in that if there is a change in the maximum applicable frequency f _Mpc at certain time intervals Δt _i , due to its increase or decrease, relative to its initial value, at times time t _1, t _2, ... t _n, which characterize the beginning of the communication sessions to the new optimum operating range of frequencies in the KB, for automatically switching the carrier frequency transmitter and a radio receiver suschestvlyayut formation digital control signal to another new optimum operating frequency.

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