Dual satellite navigation system
First Claim
1. A method for determining the position of an object in a reference coordinate system using a fixed station and a plurality of earth orbit satellites wherein the positions of said fixed station and said satellites are known in said reference coordinate system with respect to a reference point and the distances from said fixed station to said satellites are also known, said method comprising the steps of:
- transmitting from said fixed station a forward periodic signal synchronized to a fixed station transmission clock via first and second satellites to an object whose position is to be determined;
receiving at said object said forward periodic signal;
synchronizing at said object an object clock to said received forward periodic signal transmitted via said first satellite;
measuring at said object a first relative time difference in said forward periodic signal as transmitted via said first and second satellites and received at said object;
transmitting from said object to said fixed station via said first satellite a return signal synchronized with said object clock and modulated with information indicative of said first relative time difference;
receiving at said fixed station said return signal;
synchronizing at said fixed station a fixed station reception clock to said received return signal;
measuring at said fixed station a second relative time difference between said fixed station transmission and reception clocks;
calculating at said fixed station, from said first and second relative time differences, respective distances from said first and second satellites to said object; and
computing the position of said object in said reference coordinate system.
2 Assignments
0 Petitions
Accused Products
Abstract
A method and system for determining the position of an object using a fixed station and a plurality of earth orbit satellites whose positions are known. Separate periodic signals are transmitted from the fixed station via first and second satellites to the object whose postion is to be determined. The phase offset in periodic characteristics of the periodic signals as received from the first and second satellites is measured at the object. The phase offset corresponds to a relative time difference in propagation of the signals traveling two different paths to the object. The object transmits via the first satellite a return signal indicative of the measured relative time difference. This return signal is activated some time in the future according to the object local time, which is slaved to receipt of the periodic signal sent through the first satellite. This future time is the start of the particular time period as decided by the fixed station'"'"'s schedule. At the fixed station, an instantaneous round trip delay, determined by the time offset of the current transmission clock time relative to the receive clock time of reception of the return signal, along with the measured relative time difference sent back on the return signal, is used to calculate the distances between the first and second satellites to the object. From these distances the position of the object is calculated.
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Citations
25 Claims
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1. A method for determining the position of an object in a reference coordinate system using a fixed station and a plurality of earth orbit satellites wherein the positions of said fixed station and said satellites are known in said reference coordinate system with respect to a reference point and the distances from said fixed station to said satellites are also known, said method comprising the steps of:
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transmitting from said fixed station a forward periodic signal synchronized to a fixed station transmission clock via first and second satellites to an object whose position is to be determined; receiving at said object said forward periodic signal; synchronizing at said object an object clock to said received forward periodic signal transmitted via said first satellite; measuring at said object a first relative time difference in said forward periodic signal as transmitted via said first and second satellites and received at said object; transmitting from said object to said fixed station via said first satellite a return signal synchronized with said object clock and modulated with information indicative of said first relative time difference; receiving at said fixed station said return signal; synchronizing at said fixed station a fixed station reception clock to said received return signal; measuring at said fixed station a second relative time difference between said fixed station transmission and reception clocks; calculating at said fixed station, from said first and second relative time differences, respective distances from said first and second satellites to said object; and computing the position of said object in said reference coordinate system. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of object position determination using a plurality of earth orbiting satellites and a fixed station whose positions are known in an Earth-Centered-Earth-Fixed (ECEF) coordinate frame and an earth shape model in which the distance from the center of the earth to any location on the surface of the earth is known within said ECEF coordinate frame, comprising the steps of:
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simultaneously transmitting from a fixed station first and second forward periodic signal, synchronized to a fixed station forward transmission clock, via first and second satellites respectively to an object whose position is to be determined; receiving said first and second forward signals at said object, said first forward signal bearing information indicative of a future time frame which said object will begin transmitting a return signal according to an object clock synchronized to said first forward signal as received at said object; measuring at said object a percent phase offset of a total modulation period between similar portions or received carrier modulation of said first and second forward signals, said percent offset corresponding to a first relative time difference in said first and second forward signals as received at said object; transmitting from said object via said first satellite to said fixed station said return signal encoded with information indicative of said first relative time difference; measuring at said fixed station a round trip delay where said round trip delay is a second relative time difference between said fixed station forward transmission clock and a fixed station return reception clock synchronized with said return signal as received at said fixed station; calculating a first distance from said first satellite to said object according to said round trip delay; calculating a second distance from said second satellite to said object according to said round trip delay and said first relative time difference; and calculating a position of said object within said ECEF coordinate frame according to said first and second distances and said earth shape model. - View Dependent Claims (18, 19, 20, 21)
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22. A system for determining the position of an object in an Earth-Centered-Earth-Fixed reference coordinate system using a fixed station located at a known position and a plurality of earth orbit satellites whose positions are also known along with the distances between the fixed station and the satellites, comprising:
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first communication means located at said fixed station for, generating a periodic signal synchronized to a first communication means transmission clock and transmitting said periodic signal to said object via at least two of said satellites; second communications means located at said object for, receiving said periodic signal, synchronizing a second communications means clock to said received periodic signal transmitted via a first satellite of said at least two of said satellites and received by said second communications means, measuring a first relative time difference between said periodic signal as transmitted via said first satellite and a second satellite of said at least two of said satellites and received by said second communications means, generating a return signal indicative of said first relative time difference, and transmitting said return signal via said first satellite to said first communications means; and wherein said first communication means further is for, receiving said return signal, synchronizing a first communications means reception clock to said received return signal, measuring a second relative time difference between said first communications means transmission and reception clocks, determining from said first and second relative time differences and said known distances between said first and second satellites respective distances between said first and second satellites and said object, and for determining from said known positions of said first and second satellites, said distances between said first and second satellites to said object and a known distance from said object to a reference point within said reference coordinate system, said object position. - View Dependent Claims (23, 24, 25)
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Specification