JPH0242374A - Determination of pseudo range from earth orbit satellite - Google Patents

Abstract

PURPOSE: To determine a pseudo range even without a knowledge about the modulation code sequence being carried on a signal by intercepting the modulated radio frequency signal having a predetermined frequency component transmitted from a satellite at a user station. CONSTITUTION: A user is located at a point 16 on the ground surface. In a global coordinate having an origin at the center 18 of the globe, the user point 16 is represented by → R and the position of a satellite 10 is represented by →ρs. The point 16 exists in an observation horizontal plane 20 intersecting a radial line 22 passing the center 18 perpendicularly. The satellite 10 located oppositely to the globe 12 on the plane 20 at a part of the orbit 14 shown by a solid line can be determined visually by a user at the point 16. User at the point 16 can intercept a radio signal from the satellite so long as the satellite 10 can be seen. Owing to a Doppler frequency shift, frequency fM being measured at the point 16 is maximized when the satellite 10 rises over the plane 20, minimized when goes below the blane 20 and equalized to a receiving frequency fT when the satellite 10 comes to a closest point.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to platform positioning, i.e., a method of tracking and locating points with respect to an earth coordinate system, and more particularly to It concerns the method of finding the range.

BACKGROUND OF THE INVENTION The United States Navy's TRANSIT navigation satellite system consists of a number of satellites in near-Earth polar orbits. The satellite is modulated with satellite position estimator information toward the user station15.
0MHx and 400MH! transmit a carrier wave. The user measures the frequency of the received signal and calculates the range from the transmitting satellite based on the Doppler frequency shift observed by the user and the satellite ephemeris information. in particular,
If the position of the observed satellite and its transmission frequency are known, the Doppler frequency shift of the signal received from the satellite at one point within 15 minutes as the satellite passes over the receiving station is the Allows position determination. T.R.
Details of ANS IT can be found in the H9D Black (H9D) published in the Johns Hopkins APL Technical Digest, Volume 2, No. , B 1ack) in their paper “Satellites for Earth Surveillance and Ocean Navigation.”

The NAVSTAR Global Positioning System, which consists of multiple coded signal transmitting satellites in far-Earth orbit, allows authorized users assigned codes to:
Provides greater accuracy and flexibility than TRANS IT. Currently, there are only six NAVSTARLs in orbit, but plans are to increase the number to 18, with four satellites positioned so that they can be seen from any point on Earth. Each NAVSTAR satellite has a center frequency of approximately 15
The so-called LI band radio signal of 75.42MHI and the center frequency is about 1227.6M H! The L2 band wireless signal is transmitted. The L,band has a suppressed carrier on which a protection information channel, called the P code, and a coarse acquisition channel, called the C/A code, are modulated in the form of double sidebands. The L2 band has a suppressed carrier L2 on which the P code is modulated in a double sideband manner. Both P-code and C/A-code channels are available at a given chip rate, i.e. 10.230MH for P-code! So, C
/A code is 1.0230MH! and carries a binary information signal. The P code sequence is NAVST
Known only to authorized users of the AR system.

Since the P code sequence is known, NAvSTA
Based on the fact that the signal is transmitted at the speed of light, authorized users of can be found. The true range from the satellite to the user is the pseudo range.
It is equal to the difference between the offset of the satellite clock and the user clock with respect to a time reference, such as the Universal Time Aligned Clock. Once the pseudorange has been determined, the user can measure the offset of the user clock and the satellite clock, and can perform a series of tracking and position measurements, called platform positioning, using known techniques.

For those not informed of the P-code sequence, it is impossible to simultaneously utilize the NAVSTAR satellite system to determine highly accurate pseudoranges.

SUMMARY OF THE INVENTION The present invention allows a user to determine a pseudorange from a transmitting satellite without knowing the code sequence of the modulation carried by the signal.

A modulated radio frequency signal transmitted from a satellite and having given frequency components is intercepted at a user station.

The components are recovered from the intercepted signals. Also, the phase and frequency of the components are measured. From these measurements and similar measurements from other satellites, the pseudorange of the satellite can be determined. Specifically, the fractional phase is determined from the measured phase and frequency of the intercepted signal. The Doppler range value is also determined from the satellite's measured frequency. Dotsupura・
Divide the range value by the wavelength of the given frequency and calculate the integer and remainder. Add an integer to the fractional phase to obtain a value proportional to the pseudorange.

From the pseudorange, various platform positionings can be performed using known techniques, such as positioning of the user point in the earth coordinate system, differential positioning of the user relative to a fixed point, satellite positioning, and ionosphere calibration.

DETAILED DESCRIPTION OF THE EMBODIMENTS Although the present invention is applicable to other types of earth-orbiting transmitting satellite systems, we will focus on the NAVSTAR Global Positioning System, which provides signals extremely useful for pseudoranging measurements in accordance with the present invention. This will be explained below in relation to the system.

FIG. 1 shows a transmission N orbiting the earth 12 along an orbit 14.
AVSTAR satellite 10 is shown. The user on the ground is at point 1
Located at 6. In a coordinate system based on the earth with the origin at the center 18 of the earth, from a part of the user point 16 to the satellite 1
The distance to 0 is ρ. Point 16 is point 16 and center 1
8 is located in the observation horizontal plane 20 orthogonal to a radial line 22 passing through 8. As shown by the solid line portion of the trajectory 14, the plane 2
0, the portion of orbit 14 located opposite Earth 12, satellite 10 is visible to the user at point 16.

While satellite 10 is visible, a user at point 16 is listening to radio signals from the satellite. The distance 1ρ1 from the satellite IO to the user ranges from a maximum value when the satellite is above the plane 20 to a minimum value at the time when it crosses the radial line 22, i.e. at the time of closest approach (TCA), and further as (R changes to another maximum value when the Kali satellite, which is not necessarily located within the satellite orbit plane, sinks below plane 20. This relationship is shown by curve 24. For NAVSTAR, this range is , from about 20.000.000m to 25
．． 000.000m. Due to the Doppler frequency shift, the frequency intercepted at point 16 is different from the frequency transmitted from satellite IO, and the measured frequency f at point 16 when satellite 1G rises above plane 20. becomes the maximum, becomes the minimum when the satellite IO sinks below the plane 20, and becomes the same as the transmission frequency (T) when the satellite 10 approaches the closest point. This relationship and the range of the Doppler frequency are shown by the curve z6. .

Figure 2 shows how the satellite position affects the frequency shift of the signal intercepted by the user at point 16.
Let the angle between the imaginary line passing through 6 be a, and it is proportional to cot a. That is, the first satellite, which has just risen above the observation horizontal plane, is at an angle al, that is, approximately 77°,
Its Doppler frequency shift will be maximum. The second satellite at the moment of closest approach has an angle a2 of 900 and a Doppler frequency shift of 0. The angle a3 of the third satellite located between the point of closest approach and the observation horizontal plane is approximately 1t13
°, and the Doppler frequency shift is negative. In general, point 16 must be located on an imaginary conical surface whose apex is at the satellite position and whose apex angle is half a.

In the two-dimensional case, only two satellites are sufficient to determine the position of point 16 by a Doppler frequency shift measurement at point 16, since the cone of the two satellites determines the position of point IIl. In the case of 3D, the frequency standard on the receiving side is NA
If the frequency standard on the VSTAR satellite side is exactly the same, three satellites are required.

In implementing the present invention, any frequency component of a signal transmitted from a satellite is regenerated. To understand how the present invention determines the pseudorange from the user to the satellite, consider that the distance between the two consists of an integer number N of wavelengths of the selected frequency component and a fractional number N. Bye. The portion of the wavelength, hereinafter referred to as the fractional phase and designated φ, is determined by measuring the frequency IM and the time T between a given point of the selected component and the reference signal.

Specifically, by multiplying the measurement frequency IM by the time T, an accurate fractional phase φ can be obtained. Accuracy depends on the wavelength of the selected component. The total number of wavelengths is determined by measuring the Doppler frequency shift of selected components from separate satellites and based on this, the Doppler range ρ is determined below. The total Doppler range value, called , is determined by measuring the total Doppler range value by known Doppler ranging techniques. The pseudorange is the sum of the number of wavelengths expressed as an integer and a fraction of wavelengths between the satellite and the user. Therefore, the pseudorange can be expressed by the following formula.

ρ' = (C/ IT) [IM - T + N] where,
ρ' is the pseudorange, C is the speed of light, fT is the true frequency of the selected component transmitted by the satellite, IM is the measured frequency of the selected component intercepted by the user, reflecting the Doppler frequency shift, T is time, and N is the It is the number of total wavelengths.

Total Doppler range value ρ. By dividing N by the wavelength λ of the selected component, the number N of wavelengths and the remainder are obtained. If the measurements to obtain the Doppler range ρ are made to provide an accuracy higher than 1/2 wavelength, then the total number of wavelengths N is accurate, but the remainder is inaccurate, i.e. Contains errors.

In principle, by truncating this remainder and instead adding the extremely accurate fractional phase φ to the total number N of wavelengths, we obtain an accurate pseudorange ρ′, but the accuracy depends on the wavelength λ of the selected component. Dependent. (In addition, to obtain the total number of wavelengths,
Some measurements must be discarded or the quotient must be rounded up to the next total number, as described below in connection with FIG. ) FIG. 3 shows a receiving device for regenerating selected components of signals transmitted from NAVSTAR satellites.

For convenience, the selected frequency components of the signals transmitted from the NAVSTAR satellites and their characteristics are shown in the following table.

Selected component Frequency Effective reproduction Doppler (MH
Wavelength (III) Spread 1575.42.
095 ±8.3kH! 1227.6. 12
2 ±6.5kHz L1 carrier L2 carrier P code chip rate 1G, 230 29.3 ±27H1C/
A code chip rate 1.0230 293 ±2.7H
! Signals transmitted from the NAVSTAR satellites are intercepted by antenna 30. As previously mentioned, this signal is connected to the L1 band of the suppressed carrier, on which the P code channel and the C/A code channel are modulated in double sideband form, and the L1 band on which the P code channel is modulated in double sideband form. and the L2 band of the suppressed carrier wave L2. The underlined numbers in FIG. 3 are frequencies at specified locations in MHs units unless otherwise specified. The numbers in parentheses represent the passband of the filter and the time delay of the associated delay circuit. The antenna 30 is connected via a bandpass filter 32 and an amplifier 34 to a power divider 36 that separates the L band and the L2 band.
Connect to the input of The frequency reference 38 consists of a stable atomic clock, such as the Hewlett-Paracard HP 5065A, synchronized to the satellite's frequency reference, although a relatively simple crystal oscillator such as the Hewlett-Paracard HP 105 would suffice, for example. The frequency reference 38 includes a frequency synthesizer 40 that uses frequency multipliers and dividers to form eight different frequencies for use in the receiver.
Connect to. Therefore, the eight frequencies produced by synthesizer 40 as shown are precisely synchronized to frequency reference 38. Frequency reference 38 also supports universal time alignment (
output that provides clock time (UTC) and 1 per second
Clock 4 with an output that generates pulses (IPPS)
It is also connected to 1.

From the output of one of the power dividers 36, the L, bands are fed through a filter 42 to a mixer 44 where they are downconverted by one of the signals from the synthesizer 40. The output of mixer 44 is connected via amplifier 46 to power divider 48 .

The L, carrier component is regenerated by connecting two of the outputs of power divider 48 to mixer 50.

The output of mixer 50 is fed through filter 52 to mixer 54 where it is downconverted by the signal from synthesizer 40 . Filter 52
The output of is set at its center at 70.84MHI and L
It has a range twice the Doppler frequency spread appearing in the I carrier wave, and therefore the effective reproduction wavelength is 0.095 m.

L, a low frequency narrowband sinusoidal signal exhibiting a Doppler frequency shift and fractional phase of the carrier is output from mixer 54 to L.
1 carrier signal processor 56 . The condition with zero Doppler frequency shift is shown in the form of a 1 OkHr sine wave.

The P code chip rate component is one of the power dividers 48.
One output is connected directly to mixer 58 and another output of power divider 48 is connected to a
It is reproduced by connecting to the mixer 58 via a delay circuit 60 which introduces a time delay corresponding to two periods.

The output of mixer 58 is fed via filter 62 to mixer 64 where it is downconverted by the signal from synthesizer 4G. Filter 62
The output of is a sine wave at the P code chip rate.

A low frequency narrowband sinusoidal signal exhibiting a Doppler frequency shift and fractional phase of the P-code chip rate component is:
From mixer 64 a P code chip rate signal processor 66 is provided.

The C/A code chip rate component is passed through power divider 48.
one output of the power divider 48 is connected directly to the mixer 68 and a further output of the power divider 48 is connected through a delay circuit 70 that introduces a delay corresponding to one-half period of the C/A code chip rate. It is played by connecting to mixer 68. The output of mixer 68 is fed through filter 72 to mixer 74 where it is downconverted by the signal from synthesizer 40. The output of filter 72 is a sine wave at the C/A code chip rate. A low frequency narrowband sinusoidal signal exhibiting a Doppler frequency shift and fractional phase of the C/A code chip rate component is output from mixer 74 to the C/A code chip rate component.
A chip rate signal is provided to processor 76.

The other output of power divider 36 supplies the L2 band through filter 78 to mixer 80 .
is downconverted by one of the signals from synthesizer 40 at . The output of mixer 80 is connected via amplifier 82 to the input of power divider 84 .

The L2 carrier component is regenerated by connecting two of the outputs of power divider 84 to mixer 86 .

The output of mixer 86 is passed through filter 88 to mixer 9.
0, and in the mixer 90 the synthesizer 4
It is down-converted by the signal from 0. The output of the filter 88 has its center set at 7G, 84 MHI, and L
It has a range twice that of the Doppler frequency wave appearing in two carrier waves, so the effective reproduction wavelength is 0, I22m.

A low frequency narrowband sinusoidal signal exhibiting a Doppler frequency shift and fractional phase of the L2 carrier is transmitted from the mixer 9θ to the L2 carrier.
A two-carrier signal processor 92 is provided. The state of zero Doppler frequency is indicated by the lOkHw sine wave.

The P-code chip rate component of the L2 channel connects one output of power divider 84 directly to mixer 94 and connects another output of power divider 84 to 1/2 period of the P-code chip rate. is reproduced by connecting to mixer 94 through a delay circuit 96 that introduces a time delay corresponding to . The output of the mixer 94 is sent to the filter 9
8 to the mixer 10G, and the mixer 10
0 by the signal from synthesizer 40. The output of the filter 98 is the P code chip.
It is a sine wave of rate. A low frequency narrowband sinusoidal signal exhibiting a Doppler frequency shift and fractional phase of the P-code chip rate component is output from mixer 100 to the P-code chip rate component.
A chip rate signal is provided to processor 102.

Figure 4 shows the C/A code chip rate component,
The distance, or range, between satellite 104 and user 106 is shown. The full wavelength λC/A and fractional phase φC/A of the majority (NC/A) of C/A code components extend between satellite 104 and user I[16. The fractional phase φC/A is measured,
The number of wavelengths N e/A is the total Doppler range value ρ. It is determined by asking for .

In this case, the total Doppler range value ρ. is the P code.
It is obtained from the Doppler frequency shift of the chip rate component. Because if the amplitude S/N ratio is lO:1, then 50 m
or less precision, i.e. about 1/6 of the wavelength λC/A
This is because it can be determined with an accuracy of Total Doppler range value ρ. The uncertainty, or possible error, of the total Doppler range value ρ is indicated by bracket 107. means that it comes somewhere within the parentheses. Total Doppler range value ρ. By dividing λC/A by the wavelength λC/A of the C/A code chip rate component, a quotient consisting of an integer and a remainder is obtained. In principle, the remainder is rounded down and the integer as the number of complete wavelengths NC/A is calculated as the fractional phase φC/A
The accurate pseudorange value ρ C/A is obtained by adding to ρ C/A. If the remainder is thicker than a given value that depends on the signal-to-noise ratio, e.g., for an amplitude signal-to-noise ratio of 10:1 than 5/6 of the wavelength λC/A, the fractional phase φC/A is For example, for an amplitude S/N ratio lO:1, the wavelength λC/A
1. /6, ignore this particular measurement of the total Doppler range value or calculate the number of total wavelengths NC7A to be added to the fractional phase φC/A by adding 1 to the quotient; Accurate pseudorange value ρ C/^
get. If the amplitude S/N ratio is IO:1, the pseudorange value ρ
C/A can be determined with an accuracy of 5 m or better.

FIG. 5 shows a signal processor 76 that performs the operations described in connection with FIG. The output of mixer 74 (FIG. 3) is provided to phase detector 108 and frequency counter 110. C/A code chip for the pulse that appears at the timing of 1 pulse per second generated from the clock 41
The phase of the rate component is detected by a phase detector 10g. The frequency of this component is set to 1 under the control of clock 41.
It is counted by frequency counter 110 in pps intervals. Phase detector 108 and frequency counter 1
10 is connected to a multiplier +12, which forms the fractional phase φC/A at its output. The output of mixer 64 (FIG. 3) is connected to frequency counter 114.

The output of the frequency counter 114 is connected to a Doppler position finder 116 which receives the U from the clock 41.
TC clock time is also provided. position finder 116
Magnavox Document MX-TM-3346-81, No. 10058, published in February 19112.
G, Jie, Hoa (G.

Based on the principles described in "Satellite Surveying" by J. Hoar), 10.
Magnavox 150 performs data processing at 23MHI
A commercially available device such as Type 2 can be employed. The position finder 116 determines the total Doppler range value ρ. Determine. The output of the position finder 11G is connected to an integer generator 118, which forms a value for the total number of wavelengths λC/A. The output of the multiplier 112 and the output of the integer generator are supplied to an adder circuit 120, and the output of the adder circuit 120 is sent to a multiplier +22. In this multiplier 122, the fractional phase φC/A and the total number of wavelengths N C/ The sum of A is multiplied by the speed of light C divided by the C/A code chip rate component frequency IC/^ without Doppler shift.

FIG. 6 shows the distance, or range, between satellite 104 and user 106 for the P code chip rate component. A large number of P-code chip rate components (N
p) full wavelength λ, and fractional phase φ, extend between satellite 104 and user 106. The fractional phase φ2 is measured and the number of wavelengths Np is determined by using the already obtained pseudorange value ρ C/^ with an accuracy of less than 1/6 of the P code chip rate component wavelength λ. The uncertainty, or possible error, of the pseudorange value ρ C/A is shown in parentheses 109, meaning that it falls somewhere within the parentheses. By dividing the pseudorange value ρ C/A by the P code chip rate component wavelength, a quotient consisting of the total number of wavelengths, N, and the remainder is obtained. In principle, this surplus is rounded down,
By adding an integer representing the total number of wavelengths Np to the fractional phase φ, an accurate pseudorange value ρ' is obtained. If the remainder is less than a given value depending on the S/N ratio, e.g. the amplitude S/
If the N ratio lO:1 is greater than 5/6 of the wavelength λ, and the fractional phase φ, is less than a given value, for example, the amplitude S/N ratio 10
:1, if it is smaller than 1/6 of the wavelength λ1, ignore the total Doppler range value or add 1 to the integer of the quotient to obtain the total number of wavelengths Np to be added to the fractional phase φ, , the exact pseudorange value ρ′.

must be obtained. If the amplitude S/N ratio is lO:1,
Pseudorange value ρ with an accuracy of 30 cm or higher
′, can be found.

FIG. 7 shows a signal processor 66 or signal processor 1G2 that performs the operations described in connection with FIG. The output of mixer 64 or mixer 100 (FIG. 3) is provided to phase detector 124 and frequency counter 114 (FIG. 5). The phase of the P code-chip rate component relative to the pulses generated one pulse per second from clock 41 is detected by phase detector 124 . The frequency of this component is counted by a frequency counter 114 at lPP5 intervals under the control of a clock 41. The phase detector 124 and the frequency counter 114 are connected to a multiplier 126 which presents the fractional phase φ, at its output. The output of multiplier 122 (FIG. 5) is connected to an integer generator 128 which forms a value representing the number of wavelengths λ. Multiplier 1
26 and the output of the integer generator 128 are added to the adder circuit 13.
0, and the output of the adder circuit 130 is supplied to a multiplier 132, where the sum of the fractional phase φ and the number of wavelengths N is added to the P code φ chip number which is not accompanied by the Doppler shift. is multiplied by the value obtained by dividing the speed of light C by the frequency fp of the component.

FIG. 8 shows the distance, or range, between satellite 104 and user 106 for the L carrier component. satellite 10
4 and user 1[16 are a large number of L carrier components (r'
rt) complete wavelength λ1 and fractional phase φ.

But a satellite! 04 and user IQ6. The fractional phase φ, is measured, and the number of wavelengths Nt, is determined using the previously determined pseudorange value ρ′, which has an accuracy of less than 1/6 of the L carrier component wavelength λ,. The uncertainty in the pseudorange ρ', ie, the possible error, is shown in parentheses to mean that it will fall somewhere within the parentheses. However, 23
A relatively high S/N ratio of G+1 is required. By dividing the pseudorange value ρ' by the L carrier component wavelength λ, a quotient consisting of the total number of wavelengths N and the remainder is obtained. In principle, an accurate pseudorange value ρ can be obtained by cutting off the remainder and adding the total number of wavelengths NL to the fractional phase φ.
'1 is obtained. If the remainder is less than a given value depending on the S/N ratio, for example, if the amplitude S/N ratio is 10:1, then 5 of the wavelength λL
/6 and the fractional phase φ, is smaller than a given value, e.g. less than l/6 of the wavelength λ, with an amplitude S/N ratio of 10:1, then ignore the total Doppler range value or , 1 is added to the integer part of the quotient to obtain the total number of wavelengths NL to be added to the fractional phase φ1, and an accurate pseudorange value ρ5 must be obtained. If the amplitude S/N ratio is lQ:1, then 2
The pseudorange value ρ' can be determined with an accuracy of mm or better.

FIG. 9 shows a signal processor 56 or 92 that performs the operations described in connection with FIG. The output of mixer 54 or mixer 90 (FIG. 3) is provided to phase detector 134 and frequency counter 136. The phase of the carrier wave relative to the pulses generated one pulse per second from the clock 41 is detected by the phase detector 134. The frequency of this component is counted by a frequency counter H6 at lPP5 intervals under the control of a clock 41. The phase detector 134 and the frequency counter 136 are connected to a multiplier 13g which forms a fractional phase φ, at its output. The output of multiplier 132 (FIG. 7) is connected to an integer generator 140 which forms a value representing the total number of wavelengths λ. Multiplier 1
38 and the output of the integer generator 140 are added to the adder circuit 14.
2, and the output of the adder circuit 142 is supplied to a multiplier 144, where the sum of the fractional phase φ and the total number of wavelengths NL is converted to the speed of light C without Doppler shift or at the carrier component frequency IL. is multiplied by the divided value.

The explanation will be given again with reference to FIGS. 4, 6, and 8. Although the fractional phase φ is measured accurately in all cases, there is an ambiguity. That is, in addition to the fractional phase φ, the total path length connecting the satellite 104 and the user 106, that is, the pseudorange ρ
There is a total number N of cycles constituting '. For any selected component, fractional phase measurements are not very accurate, but measurements made with an accuracy within about 1/6 of the selected component wavelength can resolve the ambiguity and accurately determine the number of wavelengths N. . That is, in the above example, the ambiguity in the C/A chip rate code component is resolved by Doppler position measurements, and the ambiguity in the P code chip rate component is resolved by measurements associated with the C/A chip rate component. The ambiguity in the L carrier component is resolved by utilizing the pseudorange obtained from measurements associated with the P-code chip rate component.

The phase detector is, for example, a so-called time interval counter that includes a clock pulse source (eg at a frequency of 5 MHI) supplying pulses to the counter.

This counter starts counting clock pulses when supplied with the lPP5 pulse from clock 41 and stops counting clock pulses at positive zero crossings of the component whose phase is being sensed. Similarly, the frequency counter consists of a counter that counts the number of cycles of the selected component occurring in a given time, for example one second determined by the clock 41.

FIG. 10 shows integer generator 11g in more detail.

(The integer generators 128 and 140 are exactly the same.

) Doppler position finder 116 (multiplier 1 in FIG.
A divider 170 to which the output of the multiplier 132 (multiplier 132 in FIG. 9) is connected divides the input value by the wavelength value λC/A (λ2 in FIG. 7, λ in FIG. 9).

The output of divider 170 is connected to adder circuit 120 (+30° in FIG. 7 and 142 in FIG. 9) via transmission gate 172 and isolation gate 174. The output of divider 170 is also connected to adder circuit 120 (130 in FIG. 7,
142) in FIG. The same signal provided to divider 170 is also provided to threshold detector 1110. Multiplier 112 (+26 in FIG. 7, 138 in FIG. 9)
) is provided to a threshold detector 182. The outputs of threshold detectors 180 and 182 are provided to the inputs of AND gate 184. The output of AND gate 184 is directly connected to the control terminal of transmission gate 178 and connected to inverter 18
6 to the control terminal of the transmission gate 172.

Threshold detectors 180 and 182, AND gate 184, and inverter 186 are digital control circuits, whereas divider 17G, +1 circuit 176, and transmission gate 17
2 and 178, and isolation gate 174 are analog or digital signal transmission circuits. Threshold detector 1
80, the signal fed to its input is of wavelength λC/A.
Outputs a high binary value if it is greater than a threshold representing a quotient with a remainder greater than /6. Threshold detector 182 outputs a high binary value when the signal applied to it exhibits a fractional phase less than or equal to 1/6 of the wavelength λC/A.

When these two conditions are met, AND gate 184 outputs a high binary value causing transmission gate 178 to open and transmit a value representing the integer quotient from divider 170 plus one. Otherwise, the transmission gate 172
Provides a value representing the integer quotient from divider 170.

The signals and components shown in FIGS. 5, 7, and 9 may be analog or digital. In the case of digital, although not shown, a sequential timing circuit is provided. These operations are
It can also be done with a programmed digital computer.

For the selected component of the L2 band without an e/A code channel, the wavelength λ, as explained in connection with FIGS. 4 and 5. The Doppler range is determined based on the Doppler frequency shift of the P code component with sufficient accuracy to allow the derivation of the total number of wavelengths λA, N, rather than 7A. This total number of wavelengths Np is added to the fractional phase φ of the P code chip rate component instead of the C/A code chip number rate component. In this case, a higher signal-to-noise ratio is required to resolve the phase ambiguity of the C/A code, which is not the condition required for positioning with 50 m accuracy, but to resolve the wavelength λ, l/6 (5 m). .

When processing signals from multiple satellites with a directional antenna, a set of processors 56.66, 76, 92 and 102 is required, since only signals from one satellite are received at a time. It is only necessary to provide a signal processor. When an omnidirectional antenna is used, a separate set of signal processors must be installed for each of the satellites to be observed at a given time, for example, four satellites. Signals received from different satellites can be distinguished by frequency differences due to Doppler frequency shifts. For example, they can be separated from each other by a <C-shaped filter.

FIG. 11 illustrates the application of the invention to differential positioning, ie, positioning a user relative to a fixed point in the earth coordinate system. NAVSTAR satellite! 50 transmits to first and second fixed ground stations. Let the distance from the satellite 150 to the first station be 9 times, and the distance to the second station be ρ2. Let S be the unit distance from the first station to the satellite. The baseline vector from the first station to the second station is the amount B to be sought. At the first fixed station, the satellite signal is
It is intercepted by an antenna 152 that connects to a receiver and signal processor 154. A receiver and signal processor 154 extracts frequency and time interval values for selected components of the intercepted signal and transmits this information to a transmission line 158.
to remote computer +56. However, time-tagging these values may cause some delay in the information during transmission. Similarly, at the second user station, satellite signals are intercepted by an antenna 160 that connects to a receiving device and signal processor 162. A receiver and signal processor 162 extracts frequency and time interval values for selected components of the intercepted signal and transmits this information to the computer 1 via a transmission line 164.
Send to 56. The known quantities S 11+R and ρ,1 are also supplied to the computer 156 , which
has attached the list as Appendix A.
A baseline vector B is formed by a program. For each of the four satellites observed simultaneously, the computer +56 solves the following equation.

+CT = C/I (12T2 - f+ T
t ) + C/f (N2 - N+) However, ΔTul is the clock offset at the first station, ΔTU2 is the clock offset at the second station, T
TM is an air transmission medium error that differs for each signal entering each station.
II is the measurement frequency of the selected component at the first station, T is the measurement time interval of the selected component at the first station, 1
2 is the measurement frequency of the selected component at the second station, T2 is the second
The measurement time interval of the selected component at the station, and δ=Δρ−B2/2ρX. The receiver and signal processor 154, 162 is configured in the manner described in connection with FIG. 3, with frequency counters and phase detectors as described in connection with FIGS. 5, 7 and 9. Ru.

The embodiments of the present invention described above are merely presented as preferred embodiments and for the purpose of detailed explanation of the present invention, and the scope of the present invention is not limited to these embodiments. Those skilled in the art will be able to devise various modifications without departing from the spirit and scope of the invention. One feature of the present invention is that pseudoranging is achieved by Doppler positioning, which utilizes only the simultaneous reception of modulated radio signals from multiple satellites and the recovery of components from said signals for comparison with the frequencies of the transmitted components. It lies in seeking. Through said comparison, the user position can be determined as described above. The description of the present invention is attached as Appendix B, the disclosure of which is incorporated into the present specification as appropriate.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a single satellite in Earth orbit for the purpose of clarifying the relationships and terminology used in the description of the present invention; FIG. FIG. 3 is an explanatory diagram showing three artificial satellites orbiting the earth; FIG. 3 is a schematic block diagram of a receiving device incorporating the principles of the present invention; FIGS. 4, 6, and 8; FIG. is a sketch for explaining the present invention; FIGS. 5, 7, and 9 are schematic block diagrams of the signal processor of FIG. 3; and FIG. Schematic block diagram of the integer generator in Figures 7 and 9.
FIG. 11 is a schematic diagram of a differential positioning system incorporating the principles of the present invention. 10... Transmitting NAVSTAR satellite 12... Earth
14...Orbit 16...User's point 1B...Center of the earth 2o...Observation horizontal plane ρ...Distance from Marsa to the satellite ρ,...Distance from the observation horizontal plane to the satellite R...・Earth's radius 24...Range curve 26
... Curve showing the Doppler frequency range 30 ... Antenna 104 ... Satellite position 106 ... User position 112.122.126. N2. +38144・
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Claims (2)

[Claims] (1) A method for determining a pseudorange from a user to a transmitting satellite in one earth orbit transmitting radio frequency information carrying a signal with a suppressed carrier of a given frequency, the method comprising intercepting the signal at the user's location. a method comprising the steps of: recovering a suppressed carrier from an intercepted signal; determining a phase of the suppressed carrier; and determining a frequency shift of the suppressed carrier for a given frequency. (2) A method of determining the pseudorange from the user to one transmitting satellite that transmits a radio frequency signal having a given frequency component, in which the signal is intercepted from each satellite at the user's position, and the pseudorange is calculated from the intercepted signal. A method comprising the steps of: regenerating the component; measuring the phase of the component; and measuring the frequency of the component.