RU2012012C1 - Method for determination of differential corrections - Google Patents

Abstract

FIELD: radio navigation. SUBSTANCE: method involves receiving signals from radio navigation satellites at ground-based correction stations having known coordinates, measuring distances to each satellite, detection of ephemeris information from received signals, calculation of distances according to ephemeris values and coordinates of correction stations, calculation of corrections as average difference between measured and calculated values of distances and speed of change of corrections, transmission of information about corrections and speed of their change to object which seeks its place. Central station process signals with correction data received from peripheral stations to achieve increased zone of operation of navigation system. EFFECT: increased functional capabilities. 6 dwg

Description

 The invention relates to radio navigation and can be used to determine the location of an object with increased accuracy.

 A known method for determining corrections for the propagation of SRNS signals, based on registration at a locating object, for example, in the Navstar system, of ionospheric and tropospheric refraction of radio waves (see V. S. Shebshaevich et al. “On-board satellite navigation devices”, M.: Transport, 1988, pp. 176-181).

 This method includes the following operations.

A pseudo-random sequence of signals is generated on artificial navigation satellites of the Earth (NISH). Form frames containing encoded navigation and service information, and emit modulated signals at two carrier frequencies. The signals from the artificial navigation satellites of the Earth (NIEH) are received at a fixed object, navigation and service information is extracted from the frames, and pseudo-randomness is measured for the time t _o .

 Based on the results of two-frequency measurements of pseudorange, the correction value for the propagation time of the signals of each satellite through the layers of the ionosphere is determined and the ionospheric delays are compensated.

 The correction for the refraction of the NEAH signals in the troposphere is calculated according to the parameters specified for the standard atmosphere and tropospheric delays are compensated.

 The disadvantages of this method include the large residual error of the models of ionospheric and tropospheric corrections, as well as the lack of accounting (inaccuracies) for information on time scales and errors in the calculation of ephemeris at the time of measurement, as a result of which the errors in measuring pseudorange in the two-frequency mode will be limited and will not differ significantly from single-frequency mode.

 A known method for determining corrections for the strongly correlated RNP error in the differential mode of the Navstar system is based on the formation of an integral (general) correction at correction stations (CS) as the difference between the measured pseudorange and the calculated range to each satellite at the time of measurement, transmission of corrections via communication lines to a locating object and entering corrections received at one (selected) station as a result of measurements of pseudorange by consumer equipment (see. Project of final counting by special committee SC N 104. Recommended norms for the differential service "Navstar" of reference RTSМ 9-88 / SC-104-62, 1988). This method is selected as a prototype.

 In the differential mode of operation of the Navstar Navigation and Radar Detector in the correlation zone, the accuracy of determining pseudorange increases compared with the stationary mode.

With the known method, corrective stations are placed at points with known coordinates. In this case, continuous zones of the differential mode are covered (see Fig. 1a); local zones of differential mode (see Fig. 1b). At each ground-based correcting station (CS), they receive the signals of the NHA, measure the pseudorange to all radio-visible NHA (r _{rev. I} ), and isolate the data on the ephemeris of the NHA.

Using the known values of the coordinates of the correction station and the obtained data on the current NESZ ephemeris, the calculated range values (r _{calc. I} ) are found, the integral corrections to the RNP at the time of measurement are determined,
Δr _i (t) = r _{ISM i} (t) - r _{calculation i} (t), (1) where r _ISMi (t) is the measured pseudorange to the i-th NIRS at time t;
r _calculation (t) is the calculated pseudorange for the same conditions.

, (2) где Δ(Δ r_i(t) )- приращение поправок i-го спутника;
Δ t - интервал времени между двумя определенными поправками.The increment of corrections is determined as the difference between the values of corrections in the time interval Δ t and the rate of change of corrections
W _i =

, (2) where Δ (Δ r _i (t)) is the increment of corrections of the ith satellite;
Δ t is the time interval between two defined amendments.

 Corrective information frames are formed containing data on corrections and their rate of change.

 The carrier frequency of the transmitter of the correction station is modulated by the generated frame signals and emit radio signals.

Correcting signals of one CS are received at a fixed object within the zone limited by the correlation radius, while the correlation radius is set in advance by calculation or experimentally based on the conditions
σ _dr ≅σ _st.r (3) where σ _d.r - UPC differential mode in the correlation zone;
σ _st.r - UPC standard mode SRNS.

 Receive the signals NISS and measure the pseudorange by one of the known methods (see. Shebshaevich V. S. et al. On-board devices of satellite radio navigation. M.: Transport, 1988, pp. 62-65).

The corrections to pseudo-ranges adopted for determining the coordinates are selected from the total number and the corrections are recalculated at the time of measurement of these pseudo-ranges using the following expression:
Δ Z _i (t _ISM ) = Δ Z _i (t _n ) + W _i (t _ISM - t _n ), where t _ISM is the moment of measuring the pseudorange to the i-th satellite;
t _n is the moment of emission of the correction to the pseudorange to the i-th satellite;
W _i is the rate of change of the i-th correction.

 The disadvantage of this method is the limited area of application of the differential mode, determined by the correlation radius and depending on the level of random noise errors of the measurement of pseudorange, ephemeris-time errors and the aging time of the correction information.

 To expand the zone and ensure differential mode over a significant area in a known manner, it is necessary to install a large number of correction stations at specially calculated points so that neighboring local areas partially overlap. Thus, the task of obtaining a continuous region with a differential regime in a known manner is in some cases impossible at all (for example, in the sea) or is not economically justified.

 The aim of the invention is to expand the coverage of the differential mode (DR) satellite RNS.

 The essence of the invention lies in the fact that at correction stations, each of which is attached to a point with known coordinates, receive signals of radio-visible navigation satellites.

 The pseudorange relative to the satellites whose signals are received at the CS is measured. Information about satellite ephemeris is extracted from the received signals and calculated from the current values of the ephemeris and the coordinates of the pseudorange correction stations.

 Correction signals are generated in the form of averaged differences between the measured and calculated values of the pseudorange and the rate of change of the corrections. Radio signals containing information about corrections and their measurement rates are emitted.

 The signals from the correction station are received at the location object and the obtained information is used in the correlation zone of this correction station.

 New with the proposed method is that from the group of correction stations allocate central and peripheral. The peripheral stations are located uniformly in azimuth around the central one.

 The central station receives signals from peripheral stations with data on corrections and rates of change for all radio-visible satellites. By jointly processing the corrections of the central station and from each peripheral station, their values are brought to the moment of receiving the correction signals from all peripheral stations and to a single base distance of the latter from the central station. Radio signals are emitted that contain information about the basic corrections and rates of change.

 The signals from the peripheral corrections and their rates of change are additionally received from the central station at the locating site. Based on the known coordinates of the central correction station and the current coordinates of the location-determining object, the azimuth of the direction from the central station to the location-determining object is determined.

 By comparing the obtained azimuth value of the direction to the locating object with known azimuths from the central to the peripheral stations, two peripheral stations are allocated, the azimuth to one of which is greater and the azimuth from the central station to the locating object to the other. Based on the values of the peripheral corrections given for the two allocated stations and azimuths from the central station to the allocated peripheral stations and the locating object, intermediate correction signals are generated for the azimuth to the locating object and the base distance.

 From the known coordinates of the locating object and the central station, the distance between the station and the object is determined.

 Taking into account the obtained value of the distance to the locating object, intermediate corrections are converted into local corrections, which are used outside the correlation zone of individual correction stations.

 Thus, by introducing the above operations at the central and peripheral correction stations and the locating object, the correction values are determined for the base distance to the central station and, using the linear correlation of the distance and the linear piecewise correlation, the local corrections are found from the azimuth. By taking into account the laws of amendment changes at a given time, high accuracy is maintained in determining the location of an object in a wider zone with the same number of correction stations.

 In FIG. 1 shows the relative position of the correction stations (central and peripheral) and the location of the object (a - extrapolation method, b - interpolation method); in FIG. 2 - graphs of the dependence of the pseudorange correction on azimuth (a) and on distance (b); in FIG. 3 is a structural diagram of a central corrective station; in FIG. 4 is a structural diagram of consumer equipment at a locating facility; in FIG. 5 is a diagram of the algorithm for calculating corrections (a - at the central correction station; b - at the location of the object); in FIG. 6 - calculation of the range of the differential mode in the SRNS.

 In the drawings indicated: 1 - receiving antenna signals NISS; 2 - receiver signals NISS; 3 - pseudorange meter; 4 - block calculation of amendments; 5 - shaper corrective information; 6 - transmitter corrective information; 7 - receiving antenna for communication with peripheral correction stations; 8 - communication receiver; 9 - decoder; 10 - block conversion of peripheral amendments; 11 - receiving antenna of the correction signals; 12 - receiver corrective information; 13 - decoder; 14 - mode switch; 15 - block calculation of the intermediate amendments; 16 is a block for calculating local amendments.

 The method is characterized by a combination of the following operations.

 The central station — the CSC and the group of peripheral stations — the ACL — are selected from the set of corrective stations (see Fig. 1, a, b).

 The peripheral stations are placed uniformly in azimuth around the central station, while the maximum distance from the central station should be limited by the condition of maintaining a linear dependence of the correction value on the distance.

, (4) где R_j - расстояние до j-й периферийной станции;
n - число периферийных станций. За базовое расстояние может быть принята и другая постоянная величина, например 500 км. Все корректирующие станции привязывают к точкам с точно известными координатами, используя, например, государственную геодезическую сеть. На корректирующих станциях с известными координатами принимают сигналы радиовидимых навигационных спутников и измеряют псевдодальности до всех радиовидимых спутников.Calculate a single base distance (R _B ) for all peripheral stations, for example, by the average distance from the central station
R _B =

, (4) where R _j is the distance to the j-th peripheral station;
n is the number of peripheral stations. Another constant value, for example, 500 km, can be taken as the base distance. All correction stations are tied to points with precisely known coordinates, using, for example, the state geodetic network. At correction stations with known coordinates, signals of radio-visible navigation satellites are received and pseudorange to all radio-visible satellites is measured.

 The measurement of pseudorange in a satellite RNS is carried out by known methods (see, for example, V. Shebshaevich S. et al. Network satellite radio navigation systems. M.: Radio and communications, 1982, pp. 87-95).

) и рассчитанной (

) псевдодальностями:
Δr_ij(t)=

(t)-

(t), (5) где i - номер НИСЗ;
j - номер корректирующей станции;
t - момент измерения. Находят скорость изменения поправок
W_ij=

, (6) где Δ t - интервал времени между двумя определениями поправок.From the received navigation signals, data on the ephemeris of the navigation satellites is isolated. According to the received data, current ephemeris information is generated in a known manner (see ibid., Pp. 107-109). Using the known values of the coordinates of the correcting stations and the formed NISS coordinates at the time of measurement, the calculated pseudorange values are found (see ibid., Pp. 136-141). A correction signal is generated for each satellite in the form of an average difference between the measured (

) and calculated (

) pseudorange:
Δr _ij (t) =

(t) -

(t), (5) where i is the number of the NLHA;
j is the number of the correction station;
t is the moment of measurement. Find the rate of change of corrections
W _ij =

, (6) where Δ t is the time interval between two definitions of corrections.

 Corrective information (CI) is transmitted to the locating object and the central corrective station.

 At the central correction station, signals are received from peripheral stations with data on corrections to the RNP and their rate of change for all radio-visible satellites.

Correlation values for pseudo-ranges are given at the time of the end of reception of the correcting information (t _oi ) in accordance with
Δr _ij = Δr _ij (t) + W $\genfrac{}{}{0ex}{}{\text{*}}{\text{i}}$ _j (t _oi -t), (7) where Δ r _ij (t) is the correction for the i-th NISS received at the j-th correction station at time t;
W _ij ^* is the rate of change of the correction for the i-th NISS obtained at the j-th correction station;
t _oi - the moment of the end of taking CI.

R_Б, (8) где Δ r_ij(R_Бj) - значение поправки в точке с координатами R_Б, α_j - относительно центральной станции;
Δ r_iц - значение поправки на центральной станции для i-го спутника;
Δ r_ij(R_j α_j) - значения поправки на периферийной станции для i-го спутника;
R_j - расстояние до j-й периферийной станции;
α_j - азимут на j-ю периферийную станцию;
R_Б - базовое расстояние.Allocate corrections signals of the central station and each peripheral station for joint processing. Using together the corrections of two stations (central and peripheral) and the adopted single base distance R _B , the peripheral corrections for each station are recalculated to the base distance for time t _{о о} according to the following formula:
Δr _ij (R _Б , α _j ) = Δr _iц +

R _B , (8) where Δ r _ij (R _Bj ) is the correction value at the point with coordinates R _B , α _j is relative to the central station;
Δ r _iс is the correction value at the central station for the i-th satellite;
Δ r _ij (R _j α _j ) is the correction value at the peripheral station for the i-th satellite;
R _j is the distance to the j-th peripheral station;
α _j - azimuth to the j-th peripheral station;
R _B - the base distance.

 Signals containing corrective information are emitted to a locating object. At a fixed object in the correlation zone of one correction station, the signals of this station are received and used to correct the results of the measurement of pseudorange.

Outside the correlation zone of an individual station at a location, the signals of reduced peripheral corrections and their rate of change are additionally received from the central station. The azimuth of the direction from the central station to the locating object (α _m ) is determined by the known coordinates of the central correction station and the weaving coordinates of the locating object.

Using the known azimuths of directions from the central station to the peripheral correction stations (α _j ) for comparison with the azimuth to the location object. Two correction stations for which the conditions are satisfied are distinguished by comparing the obtained azimuth value to a location object with azimuths to peripheral stations
α _j <α _m ≅ α _{j + 1} , (9) where α _j , α _{j + 1} are the azimuths to two neighboring peripheral stations;
α _m is the azimuth to the locating object.

(α_j+1-α_м), (10) где Δ r_iм(R_Б , α_м) - промежуточная поправка для i-го НИСЗ в точке с координатами R_Б и α_м относительно центральной станции;
Δ r_ij, R_Б, α_j - то же, в точке с координатами R_Б и α_j (первая ПКС);
Δ r_i,j+1(R_Б, α_j+1) - то же, в точке с координатами R_Б и α_j+1(вторая ПКС);
α_м, α_j, α_j+1 - азимуты с центральной станции соответственно на местоопределяющийся объект, на пару выделенных ПКС.Using the basic corrections for the selected peripheral stations, known azimuths from the central to the peripheral stations and the locating object, intermediate correction signals are generated in accordance with the expression
Δr _{i, m} (R _B , α _m ) = Δr _ij (R _B , α _j ) +

(α _{j + 1} -α _m ), (10) where Δ r _im (R _B , α _m ) is the intermediate correction for the i-th NESA at the point with coordinates R _B and α _m relative to the central station;
Δ r _ij , R _B , α _j - the same, at a point with coordinates R _B and α _j (first PCS);
Δ r _{i, j + 1} (R _B , α _{j + 1} ) - the same, at a point with coordinates R _B and α _{j + 1} (second PCS);
α _m , α _j , α _{j + 1} - azimuths from the central station, respectively, to the location of the object, to a pair of allocated PKS.

 From the known coordinates of the locating object and the central station, the distance between the station and the object is determined.

R_м, (11) где Δr_iм - значение местной поправки для i-го НИСЗ в точке нахождения местоопределяющегося объекта.Convert the intermediate correction signals to local amendments in accordance with the expression:
Δr _{i, m} (R _m , α _m ) = Δr _iс +

R _m , (11) where Δr _im is the value of the local correction for the i-th NESA at the location of the location of the object.

 Use the local corrections obtained at the time the measurements were taken to correct the pseudorange.

Graphs explaining the method for determining local corrections at a location object are shown in FIG. 2 a, b, where Δ r _i (α) and Δr _i (R) are the values of the corrections of the i-th NISS depending on the azimuth from the central correction station α and the distance R,
· C is the correction value at the central station;
about - the values of the corrections received at the peripheral stations and reduced to the base distance R _B ;
⊙в - value of the intermediate correction for the base distance;
· M - local amendment.

From the values of Δr _i (α _j ) and Δ r _i (α _{j + 1} ) (see points A and B in Fig. 2, a), find point B corresponding to the basic intermediate correction for azimuth α _m .

Then transfer point B to the graph Δr _i = f (e) (see Fig. 2, b), draw a line between points c and c, determine the local correction for the range R _m (point M).

 At the correcting central station (Fig. 3), operating according to the proposed method, a radio receiver 2, a pseudorange meter 3, a correction calculation unit 4, a correction information generator 5, a transmitter with an antenna 6 are connected to the output of the satellite antenna 1 receiving signal, and to the output of the receiving the antenna signals of the peripheral stations 7 are connected in series to a communication receiver with peripheral stations 8, a decoder 9 and a peripheral corrections conversion unit 10, the output of which is connected to the second input of the driver 5.

 At corrective peripheral stations, an example of the arrangement of which is shown in FIG. 1, a receiving antenna of satellite signals 1, a radio receiver 2, a pseudorange meter 3, a correction calculation unit 4, a correction information generator 5, a transmitter with a transmitting antenna 6 are connected in series.

 At a locationable object (see FIG. 4), a receiver 12, a decoder 13, a switch 14, an intermediate calculation unit 15 and local corrections 16 are connected to the output of the receiving antenna 11, while the second input of the switch is connected to the output of the local correction calculation unit.

 Most of the blocks of the correction station and equipment of the fixed object are known and used in radio systems. Additional blocks at the central correction station and at the location of the object can be built on the basis of computer technology and using the proposed algorithms.

The algorithm for recalculating peripheral corrections begins with recording the number of correction stations (n), the number of received satellites (K), and the distances to correction peripheral stations (R _j ).

In addition, the correction time for the i-th satellite at the j-th station (t _ij ) and the end time of the measurements (t _ok ), as well as the corrections for all satellites for all peripheral stations Δ r _ij and corrections received at the central stations (Δ r _ij ).

Consistently by arithmetic operations find the basic distance R _B , the difference (t _ok - t _ij ), the rate of change of the amendment, the increment of the amendment over time t _ij ^o , the value of the correction at time t _approx . In block 10, the ratio of the base distance R _B to the distance to the j-th station (R _j ) is determined, the difference between the errors obtained at the peripheral and central stations, the product of two obtained values and the values of the basic corrections at time t _approx .

 Similarly, local errors are calculated in two steps.

 The positive effect in the implementation of the proposed method compared with the prototype was considered taking into account the following: the determining errors in satellite RNS are systematic errors; systematic errors equal to the sum of the errors of the ephemeris and the departure of the time scale, errors due to ionospheric and tropospheric refraction of radio waves, are highly correlated in terms of the distance between points on the Earth's surface; within the range of 1000-1500 km, the values of frequency errors, and, consequently, of the total error, linearly change with distance from the central station; the law of variation of errors from the angle is more complex, but with high accuracy can be represented by a piecewise linear function. The positive effect, expressed in increasing the coverage of the differential mode while maintaining the accuracy of the system and the same number of correction stations, can be estimated as follows.

 Find the distance bounding the differential mode zone.

In this extended zone, the errors of the proposed method should not exceed the errors of the known method at the border of the correlation zone (R _o ). The error at the boundary of the correlation zone for one station consists of two components and is equal to
σ _gr = R _o tgβ ± l, where β is the angle of inclination of the function Δ r _i = f (R);
l is the noise error;
Ro is the correlation radius.

 Consider the graph shown in FIG. 6.

Points A and B correspond to the true values of the corrections for the CCS and PKS. The line drawn through these points expresses the function Δ r _i = f (R). Due to noise errors, corrections to the CS are determined with an error of ± l.

For the most unfavorable case, when the errors at the stations have a different sign, the line Δ r _i (R) will pass through points A ₁ and B ₂ . Due to a change in the slope Δ r _i (R), the local correction will be determined with an error, which is expressed on the graph by the segment CC ₁ .

tgβ -

R, (12) где R_j - удаление до периферийной станции.The analytically estimated dependence of the change in the correction taking into account the measurement is expressed by the following formula
Δr _i (R) = Δr _iс + l +

tgβ -

R, (12) where R _j is the removal to the peripheral station.

·R_п (14) Для существующих приемоиндикаторов инструментальная погрешность измерения не превышает 3-5 м. С учетом условий распространения радиоволн изменение поправки на границе зоны корреляции достигает 15-20 м. Тогда получим
R_гр = (4,0 - 7,1) ˙ R_п Если R_п = 500 км, то Rгр = 2000-3500 км. Оценим увеличение площади зоны N_S при использовании предлагаемого способа
N_S=

=

, (15) где К_с - число корректирующих станций. Можно ограничиться К_с= 7. Принято, что R_o = 300 км. Тогда N_S = 7-26, т. е. площадь зоны дифференциального режима увеличивается в среднем на порядок (при сохранении числа корректирующих станций).We draw a line parallel to the speaker and removed at σ _gr . This straight line expresses dependence
Δr $\genfrac{}{}{0ex}{}{\text{o}}{\text{i}}$ (R) = Δr _ic -δ _gr + Rtgβ (13)
Solving formulas (12) and (13) together, we obtain the intersection point C ₁ , which determines the boundary radius (R _gr ) of the differential mode zone
R _gr =

· R _p (14) For existing pick-up indicators, the instrumental measurement error does not exceed 3-5 m. Taking into account the propagation conditions of the radio waves, the correction at the boundary of the correlation zone reaches 15-20 m. Then we obtain
R _gr = (4.0 - 7.1) ˙ R _p If R _p = 500 km, then R gr = 2000-3500 km. Estimate the increase in the area of the zone N _S using the proposed method
N _S =

=

, (15) where К _с is the number of correction stations. You can limit yourself to K _c = 7. It is accepted that R _o = 300 km. Then N _S = 7-26, i.e., the area of the differential mode zone increases on average by an order of magnitude (while maintaining the number of correction stations).

Claims (1)

 METHOD FOR DETERMINING DIFFERENTIAL AMENDMENTS to the radio navigation parameter in a satellite radio navigation system, based on the fact that on the ground correction stations, each of which is tied to a point with known coordinates, the signals of radio navigation satellites are received, relative to each of which all-range measurements are measured, information about received signals satellite ephemeris, calculated from the current values of the ephemeris and the coordinates of the correction stations of the pseudorange, form signals An avoc in the form of averaged differences between the measured and calculated values of the pseudorange and the rate of change of the correction signals, emit radio signals containing information about the corrections and rates of change, receive signals from the correction station at the location object and use the information received in the correlation zone for this correction station, characterized in that, in order to expand the coverage area of the differential mode of the satellite radio navigation system, from the group of correction stations select central and peripheral, and the peripheral stations are located uniformly in azimuth around the central, the central station receives signals from the peripheral stations with data on corrections and rates of change for all radio-visible satellites, by jointly processing the corrections of the central station from each peripheral, bring their values to the moment the end of receiving corrective signals from all peripheral stations and to a single base distance of the latter from the central station, emit radio signals containing information on the given corrections and rates of their change, the signals of reduced peripheral corrections and the rates of their changes are additionally received from the central station from the central station, the azimuth of the direction from the central station to the location of the object is determined by the known coordinates of the central correction station and the current coordinates of the fixed object, by comparing the received azimuth values for a locating object with known azimuths from central to peripheral stations Antennas distinguish two peripheral stations, the azimuth to one of which is greater and the other is less than or equal to the azimuth from the central station to the location object, and from the values of the reduced peripheral corrections of the two selected stations and the azimuth from the central station to the selected peripheral stations and the location object, they form intermediate corrections for the azimuth of the positioning object and the base distance, the distance between the st ntsiey and the object, taking into account the obtained distance value is converted into local intermediate corrections that use correlation zone is separate correction stations.

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