RU2834416C1 - Method of locating satellite communication earth station from relayed signal - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to radio engineering, specifically to methods for determining the location (DM) of a radio-frequency source, and can be used for DM of satellite communication earth stations (ES). Additionally, a low-orbit spacecraft (LOS), a control station (CS) of LOS, and the earth station for determining the location (ESDL) is made comprising a two-channel coherent radio receiving device (RRD) with a unit for calculating coordinates and an antenna system of two antennae, one of which automatically tracks the direction to the LOS, and the other is oriented in the direction of the "main" spacecraft (SC), located on the geostationary orbit and providing relay of the ES signals along the main lobe of the beam pattern, on the basis of the descending line of SC signals in the ESDL, the ES signals are detected, demodulated, technical analysis is performed, the central frequency F_i and the spectrum width ΔF_i are determined, based on the frequency plan of the SC, frequency parameters F_Bi and ΔF_Bi of the ES uplink are determined, the obtained values of F_Bi and ΔF_Bi is transmitted to the LOS CS, the functions of which include the prediction of the date and time of the LOS location in the electromagnetic accessibility zone of the ES, the ESDL and the CS, setting the LOS the time for switching on t_on and switching off t_off of the repeater located on its board, parameters of retransmitted signal F_i, ΔF_i and F_bi, ΔF_b£, time of transmitting messages to the CS on the current coordinates of the LOS (x, y, z, t_n), n=1, 2, …, N, N is number of messages during flight over search area, N>3, well-timed orientation of the antenna of the ESDL to the space station is carried out based on the TLE-parameters of its orbit, the current frequency instability of the receiving channels of the RRD in the band ΔF_i at time t_n is eliminated, based on the coordinates of the SC and the LOS and the ES signals relayed by them at fixed time moments t_n, N delays in receiving signals Δτ_1,N are determined and further, using the difference-ranging method, the coordinates of the ES are found.

EFFECT: high accuracy of the DM of the ES signal due to increased spatially independent statistics of estimating signal delays Δτ_1,N, N>3, and maintaining its operability in the absence of two auxiliary spacecraft (SC).

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Description

The method relates to radio engineering, namely to methods for determining the location of radio emission sources, and can be used to determine the location of an earth station (ES) of satellite communications (SC) by receiving and processing their signals retransmitted from spacecraft (SC), i.e. at an earth station for determining the location (ESL).

A method for determining the location of a satellite communication earth station is known (see Russian Patent No. 2653866, IPC G01S 5/06 (2006.01), published on 16.05.2018, Bulletin No. 14). The analogue involves the simultaneous recording of a sequence of readings of the levels of useful signals of the earth station y _s (n) and spurious emissions x(n), received over the observation interval T _н ЗСМО, where n = 1,2,…,N, N is the reading number with a step of Δt, s = 1,2,…, s is the number of the spacecraft with known coordinates. Based on the comparison of y _s (n) and x (n), one-dimensional arrays are formed: A _s with elements A _s (k) - 1, if y _s,k <y _s,k-1 , A _s (k)=1, if y _s,k >y _s,k+1 , A _s (k)=0, if y _s,k =y _s+1 and B with elements B(k)=1, if x _k <x _k+1 , B(k)=-1, if x _k >x _k+1 , B(k)=0, if x _k =x _k+1 , where k=1, 2,…, N-1. For each pair of arrays A _s and B, the obtained feature values are summed up and the number of matches of elements with the same indices W _s is determined. The location of the source of spurious emissions (SSE) is determined by referencing the SS coordinates operating through the spacecraft exposed to the SSE.

The analogue provides for simplified implementation with the elimination of limitations of functionality in areas with a high density of ZS placement when determining the location of the IPI.

The analog method has its own shortcomings that limit its application. The implementation of the analog assumes the availability of information on the exact location of legitimate SS ES operating through one spacecraft. Low measurement efficiency is due to the need to perform Q measurements to obtain one coordinate. The analog has low noise immunity under conditions of interference of various natures.

A method for determining the location of a satellite communication earth station using a retransmitted signal is known (see Russian Patent No. 2663193, IPC H04K 3/00 (2003.01), published on 02.08.2018, Bulletin No. 22). The analogous method uses an earth station for determining location consisting of three antennas Ant. 1, Ant. 2 and Ant. 3, a multi-channel coherent radio receiver (RPU) and a radio transmitter (RTD), with the help of which a test radio signal (TRS) is formed and emitted in the entire operating frequency band of the spacecraft, coherently received over a time interval ΔT using the RPU and its retransmitted copies are stored from at least three spacecraft KA 1, KA 2 and KA 3 with known coordinates located in the electromagnetic availability zone of the ZSMO and ES. The signals from the spacecraft are fed to the corresponding inputs of the multi-channel coherent radio-electronic unit via the corresponding antennas Ant. 1, Ant. 2 and Ant. 3. The frequency instability of each of the coherent channels of the multi-channel radio-electronic unit is compensated for. The slant range from the SSMO to the spacecraft 1, spacecraft 2 and spacecraft 3 is calculated, based on which the coordinates of the spacecraft KA 1, KA 2 and KA 3 are adjusted. Coherent reception of retransmitted copies of signals from a given SS is performed. Delays in reception of SS signals Dt _1,2 and Dt _1,3 are measured using the correlation method from the directions to the spacecraft KA 1, KA 2 and KA 1, KA 3, respectively. The obtained values Δτ _1,2 and Δτ _1,3 are stored. The location of the SS is determined using the difference-range measurement method (DRM).

The analogue ensures a reduction in the measurement error of the coordinates of the ground station by eliminating the procedures for measuring the values of the Doppler shift of the signal frequency and the associated procedures for measuring the angle between the direction-finding bases (DFB) in the selected pairs of DFBs.

However, the prototype has some disadvantages that limit its use. The main one is low noise immunity. There is a situation when the ES signal arrives at the "main" spacecraft along the main lobe of the radiation pattern (RP) under conditions of a low signal-to-noise ratio. One of the reasons may be intentional interference (see Russian Patent No. 2707878, H04K 3/00, G01S 5/00, published on 02.12.2019, Bulletin 34). Another reason is due to the non-optimal placement of the ES relative to the location of the ES for various reasons. In addition, the appearance of a legitimate signal in a given part of the spectrum of a "mirror" spacecraft sharply worsens the signal-to-noise situation. The ES signal arrives at the spacecraft along the side lobe of the radiation pattern (RP) and is significantly inferior in power to the legitimate signal of the spacecraft. Therefore, when they occur, the analogue loses its functionality.

A method for determining the location of a satellite communication earth station using a retransmitted signal is known (see Russian Patent No. 2755058, IPC H04K 3/00 (2008.01), published on September 14, 2021, Bulletin No. 26). In the analog, an earth station for determining location is used, consisting of three antennas Ant.1, Ant.2 and Ant.3, a multi-channel coherent radio receiver and a radio transmitter, a test radio signal is formed and emitted using an RPD in the entire operating frequency band of the spacecraft AF, coherent reception by the RPU is carried out over a time interval ΔT and its retransmitted copies are stored from at least three spacecraft KA 1, KA 2 and KA 3 with known coordinates located in the electromagnetic availability zone of the ZSMO and ES, the spacecraft signals are transmitted through the corresponding antennas Ant. 1, Ant. 2 and Ant. 3 are fed to the corresponding inputs of the multichannel coherent radio receiver and are used to compensate for the frequency instability of each of the coherent channels of the multichannel radio receiver based on the results of receiving the TRS, calculate the slant range from the ES to the spacecraft 1, ES 2 and ES 3, correct the coordinates of the spacecraft ES 1, ES 2 and ES 3 based on them, perform coherent reception of retransmitted copies of signals from a given ES, measure delays in receiving ES signals Δτ _1,2 and Δτ _1,3 using the correlation method from directions to the spacecraft ES 1, ES 2 and ES 1, ES 3, respectively, store the obtained values Δτ _1,2 and Δτ _1,3 , determine the locations of the ES using the difference-range measurement method. Before each measurement of the coordinates of the ZS, the TRS is formed and emitted in a given frequency band ΔF _j . The frequency instability of each of the coherent channels is eliminated. The measured and stored sets of levels are compared signal of the ground station W _j (ΔF _i ) and noise W _jш (ΔF _i ) of each j-th spacecraft, j=2.3, in the frequency band ΔF _i , with a set of levels signal W ₁ (ΔF _i ) and noise W _1ш (ΔF _i ) in the first, main spacecraft. In case of exceeding the threshold level W _min , at least for one j-th spacecraft, the signal ZS S ₁ (ΔF _i ) is selected in the first spacecraft from the set Where S _1ш (ΔF _i ) - the noise signal distributed in ΔF _i and possible concentrated emissions form its copy with an accuracy of up to phase with a high level, and free from noise S _1ш (ΔF _i ), and the measurement of the delay Δτ _1,j is performed by the correlation method using the main spacecraft as a signal

In this case, the selection of the ES signal in the first spacecraft S ₁ (ΔF _i ) is carried out using adaptive filtering and subsequent evaluation of its main characteristics at the first stage: the operating frequency band, the value of the carrier frequency, the type of modulation and manipulation, the speed of manipulation, and, on their basis, demodulation of the signal, with subsequent restoration of the ES signal at the second stage with an accuracy of up to the phase and its amplification to a value that ensures the determination of the coordinates of the ground station.

The analogue provides increased noise immunity of the measurement of the coordinates of the ground station by isolating the ground station signal from the noise, mainly the spacecraft, analyzing it, forming a copy of it with an accuracy of up to the phase with a high level and free from noise and interference, with its subsequent use in the RDS.

However, the analogue has a drawback that limits its application. In practice, situations are not uncommon when auxiliary satellites may be absent, or there is no more than one. As a result, the analogue loses its functionality. In addition, the technical complexity is the restoration of the ES signal S ₁ (ΔF _i ) with an accuracy of phase.

The closest in its technical essence to the claimed method is a method for determining the coordinates of a satellite communication earth station using a retransmitted signal (see Russian Patent No. 2749456, IPC H04K 3/00 (2006.01), published on 11.06.2021, Bulletin No. 17), which consists of using an earth station for determining location consisting of three antennas Ant. 1, Ant. 2 and Ant. 3, a multi-channel coherent radio receiver and radio transmitter (RRT), the formation and emission by the RRT of a test radio signal in the entire operating frequency band of the spacecraft ΔF and the coherent reception by the RPU on the interval ΔT and the storing of its retransmitted copies from at least three spacecraft KA 1, KA 2 and KA 3 with known coordinates located in the electromagnetic accessibility zone of the ZSOM and ES, the signals of which through the corresponding antennas Ant. 1, Ant. 2 and Ant. 3 are fed to the corresponding inputs of the multi-channel coherent radio receiver, compensation for the frequency instability of each of the coherent channels of the multi-channel radio receiver based on the results of receiving the TRS, calculating the slant range from the ZCOM to the spacecraft 1, spacecraft 2 and spacecraft 3 with subsequent correlation on their basis of the coordinates of spacecraft 1, spacecraft 2 and spacecraft 3, before each subsequent measurement of the coordinates of the ZS, the TRS is formed and emitted in a given frequency band ΔF _i , the current frequency instability of each of the coherent receiving channels is eliminated, the previously measured and stored noise levels P _j (ΔF _i ), j = 2,3, of the selected j-th spacecraft in the frequency band ΔF _i are compared with their current level in case of exceeding the noise level increment in the j-th spacecraft P _j (ΔF _i ) threshold level Δd, ΔP _j >Δd, make a decision on the appearance in the frequency band ΔF _i of signals of the l-th ES, retransmitted by the j-th spacecraft, select the detected signals of the l-th ES S ₁ (ΔF _i ) of the j-th spacecraft by subtracting from the set signals of the j-th spacecraft: Where - a set of signals from the l-th earth station, the coordinates of which are to be determined, and noise, measure the delays in receiving the ES signals Δτ _1,2 and Δτ _1,3 using the correlation method from the directions of KS 1, KS 2 and KS 1, KS 3, respectively, store the obtained values Δτ _1,2 and Δτ _1,3 , and determine the location of the ES using the difference-range measurement method.

The prototype method ensures increased noise immunity of the measurement of the coordinates of the ground station by using the procedure of isolating the noise signal and subtracting it from the group signal.

However, the prototype has a drawback that limits its application. In many practical situations, auxiliary spacecraft suitable for measurements may be absent, or their number does not exceed one. As a result, the prototype loses its functionality.

The purpose of the claimed technical solution is to develop a method for determining the location of a satellite communication earth station based on a retransmitted signal using a radar, which ensures an increase in the accuracy of the OM ES by increasing the spatially independent statistics of signal delay estimation Δτ _1,N , N>3, and maintaining its operability in the absence of two auxiliary spacecraft.

The stated objective is achieved by using an earth station for determining the location as part of an antenna system, a multi-channel coherent radio receiver with a coordinate calculation unit and a radio transmitter; generating and emitting a test radio signal by the RPD in the spacecraft operating frequency band ΔF and coherently receiving the RPU over a time interval ΔT, storing copies of the signal retransmitted from the spacecraft located in the electromagnetic availability zone of the ZSOM, which are fed through the corresponding antennas of the antenna system to the corresponding inputs of the multi-channel coherent RPU; compensating for the frequency instability of each of the coherent channels of the multi-channel RPU based on the results of receiving the TRS; calculate the slant range from the ES to the spacecraft with subsequent correction of the spacecraft coordinates based on them, generate TRS emissions in a given frequency band ΔF _i before each subsequent determination of the ES coordinates, eliminate the current frequency instability of each of the coherent receiving channels, compare the previously measured and stored noise levels P _j (ΔF _i ), where j is the spacecraft number, in the i-th frequency band ΔF _i , ΔF _i ∈ ΔF, with their current level in case of exceeding the noise level increment in the j-th spacecraft ΔP _j (ΔF _i ) threshold level Δd _j , ΔP _j (ΔF _i )>Δd _j , make a decision on the appearance in the frequency band ΔF _i of signals of the l-th ES, retransmitted by the j-th spacecraft, and the selection of the detected signals of the l-th ES S _l (ΔF _i ) of the j-th spacecraft by subtracting from the set signals of the j-th spacecraft: Where - a set of signals from the l-th earth station, the coordinates of which are to be determined, and noise, measuring the delay in receiving signals Δτ _1,j using the correlation method, storing the obtained values Δτ _1,j and determining the location of the l-th ES using the difference-ranging method, additionally using a low-orbit spacecraft (LOS), a control point (CP) of the LOS, and the LSOM contains a two-channel coherent RPU with a coordinate calculation unit and an antenna system of two antennas, one of which Ant. 2 automatically tracks the direction to the LOS, and the other Ant. 1 is oriented in the direction of the "main" SC 1, located in geostationary orbit and providing retransmission of signals of the l-th ES along the main lobe of the radiation pattern, based on the downlink of signals of SC 1 in the coordinate calculation unit of the RPU ZSOM, detection of signals of the l-th ES, demodulation, technical analysis, determination of the central frequency F _i and the spectrum width ΔF _i are carried out, based on the frequency plan of SC 1, frequency parameters F _вi and ΔF вi _of the uplink of the l-th ES are determined, the values of F _вi and ΔF _вi obtained in the ZSOM are transmitted to the NCSC control unit, the functions of which include forecasting the date and time of the NCSC's location in the electromagnetic availability zone (EMA) of the l-th ES, the ZSOM and the control unit, assignment of the NCSC via a low-speed communication channel of the time of switching on t _on and switching off t _{off of} the repeater located on board it, parameters of the retransmitted signal F _i , ΔF _i and F _вi , ΔF _вi , time of transmission of messages to the PU about the current coordinates of the NSC (x, y, z, t _n ), n = 1, 2, ..., N, N is the number of messages during the flight over the search area, N> 3, t _n is the time of measurement of the coordinates of the NSC at the n-th point, the NSC sequentially transmits coordinate-time data to the PU and then to the ESOM, timely orientation of Ant. 2 on the NSC is carried out according to the TLE parameters of its orbit, current frequency instability of the receiving channels of the RPU in the frequency band ΔF _i at times t _n is eliminated, when determining the coordinates of the l-th ES, the NSC receives signals of the 1st ES in the frequency band ΔF _вi and retransmits them to the ESOM in the band ΔF _i , which through Ant. 2 arrive at the second input of the RPU, simultaneously the signals of the 1st ES, retransmitted by the spacecraft 1, arrive at the first input of the RPU through Ant. 1, and based on the coordinates of the spacecraft 1 and the NSA and the signals of the 1st ES retransmitted by them at fixed moments of time t _{n ,} the correlation method is used to determine N delays in the reception of signals Δτ _1,N .

The claimed method is illustrated by drawings:

Fig. 1 shows the conditions when two spacecraft, KA 1 in geostationary orbit and KA 2 in low-orbit orbit, are located in the zone of electromagnetic availability of the ZS and ZSOM;

Fig. 2 shows a generalized algorithm for determining the location of a satellite station earth station using a retransmitted signal;

Fig. 3 shows the external appearance of the CubeSat-based NSC;

Fig. 4 shows a generalized structural diagram of the NCA;

Fig. 5 shows a generalized algorithm for the operation of the NCA;

Fig. 6 shows the results of modeling the proposed method:

a) dependence of the standard deviation (SD) of the error in determining the location of a radio emission source (RES) on the number of measurements N;

b) dependence of the standard deviation of the positioning error of the ground station on the signal-to-noise ratio in the navigation spacecraft;

c) dependence of the standard deviation of the error in delay measurement on the signal-to-noise ratio in the NCA.

The essence of the proposed method is as follows. Geolocation systems using three or more spacecraft to determine the location of the earth station are currently widely used. For their operation, a number of requirements must be met. The latter include: the presence of at least two additional repeater satellites ("mirror" spacecraft) that have the same frequencies of uplinks, polarization of the antenna system, and coverage area. In addition, knowledge of the exact location of the spacecraft involved in the measurements is required.

The multimedia architecture for determining the location of the ground station involves the use of differential-range, differential-Doppler methods or their combinations (see Char M. Application of a dual satellite geolocation system on locating sweeping interference//World Academy of Science, Engineering Technology. -2012. V. 6, #9, p. 1029-1034).

The repeater satellite KA 1 is the "main" one, since it ensures the retransmission of the signal of the l-th ES along the main lobe of the RP. In the analogs and the prototype, the second and third KA are adjacent, are located at some distance from KA 1 and are capable of transmitting the same radiation received along the side lobes of the ES RP, but with greater attenuation. If the ES is located in the EMD zone formed by the antenna systems of the named KA, then its multi-channel RPU will be able to receive signals from these KA, their further processing and determination of the ES coordinates. At the same time, situations are not uncommon when the auxiliary spacecraft KA 2 and KA 3 may be absent, or there is no more than one of them. It is proposed to solve this problem using a low-orbit spacecraft with a signal repeater placed on board. Fig. 1 shows a variant of such a solution, when the source signals are retransmitted by a pair: KA 1 in geostationary orbit and the NS. The movement of the NSC allows for sequential measurements of Δτ _1,n , n=1,2,…,N in time, obtaining not only the position lines, but also the coordinates of the ES. It is advisable to use CubeSat (English CubeSat ← cube + satellite) as the NSC - a format of small (ultra-small) artificial Earth satellites with dimensions of 10×10×10 cm and a mass of no more than 1.33 kg (see the electronic resource https://www.webcitation.org/6ABSpR8qR?url=http://www.cubesat.org/images/developers/cds_rev12.pdf. Rev. 6.05.2024).

At the preparatory stage (see Fig. 1, 2) a noise-like test radio signal is emitted in the operating frequency band of the satellite AF using the RPD and received by the first channel of the RPU during the time interval ΔT, the frequency instability of the first channel of the RPU is compensated for based on the results of receiving the TRS. The low power of the TRS used in this case does not have a destructive effect on the operation of the satellite communication system. Using this reference signal, the frequency plan of the satellite is determined or refined (uplink channel frequencies based on the observed downlink channel frequencies). The implementation of these procedures is known (see Patent RF No. 2172495, IPC G01S 5/00 (2000.01), G01S 5/06 (2000.01), published 20.08.2001, Bulletin No. 23; Volkov R.V. et al. Fundamentals of the construction and operation of difference-range systems for coordinate measurement of radio emission sources. - St. Petersburg: VAS, 2003. - 116 p.). In turn, the definition of EMD zones formed by the antenna systems of the spacecraft is known (see Chelyshev V.D., Yakimovets V.V. Radio-electronic systems of administrative and military control. Part one. Radio interfaces of mobile radio service systems: Textbook. - St. Petersburg: VAS, 2006. - 576 p.). The slant range D ₁ = с⋅Δτ ₁ /2 from the ES to the SC 1 located in the geostationary orbit is calculated with subsequent correction of the SC 1 coordinates based on it. Here Δτ ₁ is the measured value of the delay received after retransmission of the TRS through the CS 1, c is the speed of light. Then, the signals of the 1st ES are detected by comparing the previously measured and stored noise levels P1(ΔF _i ) in the frequency band ΔF _i , ΔF _i ∈ ΔF, with their current level P _1,current (ΔF _i ). If the noise level in spacecraft 1 ΔP ₁ (ΔF _i ) exceeds the threshold level Δd ₁ , ΔP ₁ (ΔF _i )>Δd ₁ , ΔР ₁ (ΔF _i )=P _1,тех (ΔF _i )-P ₁ (ΔF _i ), a decision is made about the appearance in the frequency band ΔF _i of signals of the l-th ES, retransmitted by spacecraft 1.

Next, the detected signal of the 1st ZS KA 1 is selected:

Where - a set of signals of the l-th ES, the coordinates of which are to be determined, and noise. On its basis, an assessment of the characteristics S _l (ΔF _i ) is performed: the operating frequency band ΔF _i , the value of the carrier frequency F _i , the type of modulation and manipulation, the speed of manipulation.

Based on the obtained values of ΔF _i and F _{i ,} the characteristics of the signals of the l-th ES uplink F _вi and ΔF _вi are determined according to the frequency plan, which is necessary for setting the task of geolocation of the NSC.

Planning of the geolocation session includes the following. Based on the TLE parameters (see Appendix) of the SV orbit, the date and time of its location in the EMD zone of the 1st ES, the time of switching on t _on and switching off t _{off of} the SV repeater, the parameters of the relayed signals F _i , ΔF _i and F _вi , ΔF _вi , the time of transmitting messages to the PU about the current coordinates of the SV (x, y, z, t _n ), n = 1, 2, ..., N, N is the number of messages during the flight over the search area, t _n is the time of measuring the coordinates of the SV at the n-th point are determined. The above values are sent from the ES to the PU and then via a low-speed communication channel to the SV. The SV parameters (x, y, z, t _n ) are also used for timely orientation of the Ant. 2.

In the interests of increasing the accuracy of measuring the coordinates of the ES, by analogy with the prototype, at moments of time t _{n ,} the values of the slant range from the ESOM to SC 1 and the NSC are corrected, and the frequency instabilities of the coherent channels of the two-channel RPU are compensated. For this purpose, a noise-like TRS with known parameters is formed and emitted via the RPD. In this case, the power of the TRS P _TRS is less than P ₁ (ΔF _i ) and P _NSC (ΔF _i ). After its retransmission from SC 1 and the NSC via Ant. 1 and Ant. 2, it is received by the coherent RPU and, using correlation procedures (of the emitted TRS with its received retransmitted copies), the values of delays characterizing the slant range from the ESOM to the corresponding SC 1 and the NSC are calculated.

The slant range D between the ZSOM and the spacecraft is calculated using the formula

where Δτ is the calculated value of the delay of the received TRS after retransmission through the corresponding spacecraft, c is the speed of light. In addition, based on the results of distortions of the received versions of the retransmitted TRS, obtained as a result of passing through the corresponding receiving paths of the radio receiver, the amplitude-frequency characteristics of each of the receiving channels in the frequency band ΔF _i are corrected. The implementation of these procedures is known (see Russian Federation Patent No. 2172495, IPC G01S 5/00 (2000.01), G01S 5/06 (2000.01) published on 20.08.2001, Bulletin No. 23).

During the time interval ΔT, signals of the 1st ES retransmitted from the spacecraft 1 and the navigation spacecraft are received and the signal delay Δτ _1,n is determined at the time t _n using the correlation method. To find the latter, the refined coordinates of the spacecraft 1 and the navigation spacecraft are used.

At the next t _n+1 moment in time, the procedures for testing the receiving paths, refining the coordinates of SC 1 and the NSC, and measuring the delays Δτ _1,n+1 are repeated. As a result of the NSC flying over the search area, N values of the signal delays Δτ _1,N are obtained, N>3, which allows increasing the accuracy of determining the coordinates of the l-th ES. Determining the location of the RDS ES is performed similarly to the prototype method. For this, the well-known method of coordinatometry is used (see Dvornikov S.V., Sayapin V.N., Simonov A.N. Theoretical Foundations of Coordinatometry of Radio Emission Sources. - SPb: VAS, 2007). The latter includes the following stages:

measurement of one of the coordinate-information parameters (CIP) of radio signals of the earth station, retransmitted by the spacecraft;

determination of the position parameters corresponding to each instrumentation control point;

construction of lines (surfaces) of position based on its parameters;

determination of the location of the ground control system on the surface of the position lines (surfaces).

The physical coordinates of the ES are found from the system of equations given in Patent. RF No. 2663193, p. 6, the solution to which is known (see Sevidov V.V. Implementation options for the difference-range method for determining the coordinates of earth stations using signals from repeater satellites // Radio engineering, electronics and communications (RE i S - 2015). International scientific and technical conference. - St. Petersburg: VAS, 2015. pp. 303-308).

Fig. 3 shows the external appearance of the NSC. The latter contains an antenna system consisting of: UHF antenna 1, global navigation satellite system antenna 2, 6-18 GHz range antenna 3, 0.8-6 GHz range antenna 4, X-band antenna 5, solar panel 6, spatial orientation sensor unit 7, repeater module 8, NSC control unit (on-board computer) 9, radio modem 10, power supply 11, storage batteries 12, flywheel and magnetic coil control unit 13, flywheel unit 14, magnetic coil unit 15 and magnetometer 16. A generalized structural diagram of the NSC is shown in Fig. 4, and a generalized algorithm of its operation is shown in Fig. 5.

The low-orbit spacecraft operates as follows. The geolocation plan developed on the LOCOM is sent to the control unit and then via a low-speed communication channel to the NSC. The latter contains the following data: the time of switching on t _on and switching off the repeater 8, the operating frequencies of the repeater 8 along the uplink F _вi , ΔF _вi and downlink F _i , ΔF _i , fixed moments of time t _n for determining the NSC's own coordinates and their number N. The geolocation data are received by the antenna 1 and the radio modem 10 and are sent to the input of the NSC control unit 9. Unit 9 generates a control command for the repeater 8. As a result, unit 8 tunes the receiving path to the frequency band ΔF _вi with the central frequency F _вi , and the transmitting path to the frequencies ΔF _i , F _i . Upon reaching the time t _{on ,} the repeater 8 is switched on and retransmits the signals of the l-th ES. Upon reaching the next fixed time moment t _n , n ∈ N, the coordinates of the spacecraft (x, y, z, t _n ) are determined using GNSS signals. These data can be immediately (sequentially) transmitted via a low-speed communication channel through blocks 10, 1 of the spacecraft, PU to the ZSOM or accumulated on board the spacecraft. In the latter case, they arrive at the ZSOM after the spacecraft has flown over the controlled area. During the time between t _on and t _off, N operations are performed to determine the coordinates of the spacecraft. Upon reaching time t _off, the repeater 10 is switched off.

During the flight of the NSC, the operability of all support subsystems is monitored, the results of which are periodically communicated to the ZCOM via a low-speed communication channel. The CP of the SC acts as a repeater of signals from the ZCOM and the NSC.

The efficiency of the proposed method is assessed based on modeling in the Matlab environment (see Fig. 6a, b, c). The UHF range (225-400 MHz) was used in the modeling. The signal frequency is F _i = 263.625 MHz, ΔF _i = 30 kHz, continuous carrier. The Intelsat 22 (NORAD 38098) satellite was selected as the main one (SC 1), and the CubeSat (NORAD 57202) was used as the NSC. The signal source is the ES with coordinates [60,30,0], St. Petersburg. The geolocation duration is 5 min, the time is 05/23/2024 19:20:00-19:25:00 (UTC +3). The number of measurements is N = 30 (at a time interval of 10 s), the analysis interval is 1 s. The signal-to-noise ratio in the main receiving channel was 10 dB, in the NCA receiving channel 7 dB.

Fig. 6a shows the dependence of the standard deviation of the error in determining the position of the ground station on the number of measurements N. The latter indicates that for N>20, the error in determining the coordinates estimated by the standard deviation is hundreds of meters. A positive result in the proposed method is achieved by forming N ellipses passing through a point with the sought coordinates of the ground station at different angles, some of which are the most informative (close to the mutual angle of 90°). In the prototype method, two ellipses are formed intersecting at an angle far from 90°. It is generally not possible to select other spacecraft to improve the geometry of the calculations.

Fig. 6b shows the dependence of the standard deviation of the ES positioning error on the SNR in the NSC. The latter indicates a significant dependence of the standard deviation on the SNR. Due to the fact that the NSC provides a better SNR compared to this indicator on the auxiliary satellites KA 2 and KA 3 of the prototype method, a positive effect on the accuracy of determining the coordinates of the ES is achieved in the proposed method. The reason is the different communication distance for the NSC and the SC in geostationary orbit.

Fig. 6c shows the dependence of the standard deviation of the error in measuring the signal delay on the SNR on the NSC. A decrease in the SNR entails significant errors in measuring the signal delay, and as a consequence, errors in determining the location of the ES.

Thus, the proposed method maintains its operability in the absence of two auxiliary spacecraft and ensures an increase in the accuracy of determining the location of the ES by increasing the spatially uncorrelated statistics of measuring the signal delay Δτ _1,N , N >> 2.

Claims (1)

A method for determining the location of an earth station (ES) for satellite communications (SC) based on a retransmitted signal from spacecraft (SC), which consists of using an earth station for determining location (ES) as part of an antenna system, a multi-channel coherent radio receiver (RRU) with a coordinate calculation unit, and a radio transmitter (RT); forming and emitting a test radio signal (TRS) by the RRU in the SC operating frequency band ΔF and coherently receiving it by the RRU over a time interval ΔT, storing copies of the signal retransmitted from the SC located in the electromagnetic availability zone of the ES, which are fed through the corresponding antennas of the antenna system to the corresponding inputs of the multi-channel coherent RRU; compensating for the frequency instability of each of the coherent channels of the multi-channel RRU based on the results of TRS reception; calculation of the slant range from the ES to the spacecraft with subsequent correction of the spacecraft coordinates based on them, formation of TRS emissions in a given frequency band ΔF _i before each subsequent determination of the ES coordinates, elimination of the current frequency instability of each of the coherent receiving channels, comparison of previously measured and stored noise levels P _j (ΔF _i ), where j is the spacecraft number in the i-th frequency band ΔF _i , ΔF _i ∈ ΔF, with their current level in case of exceeding the threshold level of the noise level in the j-th spacecraft ΔP _j (ΔF _i ) making a decision on the appearance in the frequency band ΔF _i of signals of the l-th ES, retransmitted by the j-th spacecraft, identifying the detected signals of the l-th ES S _l (ΔF _i ) of the j-th spacecraft by subtracting from the set signals of the j-th spacecraft: Where - a set of signals from the l-th earth station, the coordinates of which are to be determined, and noise, measuring the delay in receiving signals Δτ _1,j by the correlation method, storing the obtained values Δτ _1,j and determining the location of the l-th ES by the difference-ranging method, characterized in that a low-orbit spacecraft (LOS), a control post (CP) of the LOS are additionally used, and the LSOM contains a two-channel coherent RPU with a coordinate calculation unit and an antenna system of two antennas, one of which Ant. 2 automatically tracks the direction to the LOS, and the other Ant. 1 is oriented in the direction of the "main" SC 1, located in geostationary orbit and providing retransmission of signals of the l-th ES along the main lobe of the radiation pattern, based on the downlink of signals of SC 1 in the coordinate calculation unit of the RPU ZSOM, detection of signals of the 1st ES, demodulation, technical analysis, determination of the central frequency F _t and the spectrum width ΔF _i are carried out, based on the frequency plan of SC 1, frequency parameters F _вi and ΔF вi _of the uplink of the 1st ES are determined, the values of F _вi and ΔF _вi obtained in the ZSOM are transmitted to the NCSC PU, the functions of which include forecasting the date and time of the NCSC location in the electromagnetic availability zone (EMA) of the l-th ES, the ZSOM and the PU, assignment of the NCSC via a low-speed communication channel of the time of switching on t _on and switching off t _вык of the repeater located on its board, parameters of the retransmitted signal F _i , ΔF _i and F _вi , ΔF _вi , the time of transmission of messages to the PU about the current coordinates of the NSC (x, y, z, t _n ), n = 1, 2, …, N, N is the number of messages during the flight over the search area, N> 3, t _n is the time of measuring the coordinates of the NSC at the n-th point, the NSC sequentially transmits coordinate-time data to the PU and then to the ESOM, the timely orientation of Ant. 2 on the NSC is carried out according to the TLE parameters of its orbit, the current frequency instability of the receiving channels of the RPU in the frequency band ΔF _i at times t _n is eliminated, when determining the coordinates of the l-th ES, the NSC receives signals from the 1st ES in the frequency band ΔF _вi and retransmits them to the ESOM in the band ΔF _i , which through Ant. 2 arrive at the second input of the RPU, simultaneously the signals of the 1st ES, retransmitted by the spacecraft 1, arrive at the first input of the RPU through Ant. 1, and based on the coordinates of the spacecraft 1 and the NSA and the signals of the 1st ES retransmitted by them at fixed moments of time t _{n ,} the correlation method is used to determine N delays in the reception of signals Δτ _1,N .

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