Reduction of time to first fix in an SATPS receiver
First Claim
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1. A method for rapid acquisition of one or more Satellite Positioning System (SATPS) satellite signals at an SATPS station that seeks to acquire or to reacquire one or more SATPS signals, the method comprising the steps of:
- (1) receiving and analyzing SATPS signals from one or more SATPS signal-transmitting satellites at an SATPS reference station and transmitting estimated reference station location and satellite ephemeris information for at least one SATPS satellite that is visible from the reference station, referred to as a “
reference/visible satellite”
, whose SATPS signal is received at the reference station with an associated carrier signal frequency;
(2) receiving at least one SATPS signal from at least one reference/visible satellite at a second SATPS station, which seeks to acquire or reacquire and to lock onto an SATPS signal from one or more reference/visible satellites, the second station having Doppler shift means for searching an incoming SATPS signal over a selected range of Doppler shifted carrier frequencies;
(3) receiving the estimated reference station location and the satellite ephemeris information at the second station, and estimating a Doppler shifted carrier frequency range for the at least one SATPS signal, using the received satellite ephemeris information, by;
(3a) estimating a location vector rm and a velocity vector vm for the second station at the time the second station receives the SATPS signals; and
(3b) estimating a frequency f=fs+Δ
f in the Doppler frequency shift range for the at least one SATPS signal received, where fs is a known carrier frequency with which the SATPS signals are transmitted, by estimating the frequency shift using the relationwhere c′
is a representative velocity of propagation of electromagnetic signals in the ambient medium through which the SATPS signals propagate, rm(t) and vm(t) are estimated location and velocity vectors for the second station at a selected time t, and rs(t′
) and vs(t′
) are estimated location and velocity vectors for the selected reference/visible satellite at a selected time t′
; and
(4) scanning the estimated Doppler shifted carrier frequency range to acquire and to lock onto an SATPS signal from the at least one reference/visible satellite, whereby a time interval required to acquire and lock onto the at least one reference/visible satellite does not exceed about 39 seconds.
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Abstract
A method for fast acquisition, in as little as 6-15 seconds, of signals from a satellite in a Satellite Positioning System (SATPS), such as GPS or GLONASS, that does not require permanent storage of satellite ephemeris information at an SATPS ground station. This SATPS signal acquisition method can be used whenever the “new” station initially powers up or has lost lock on one or more SATPS signals that must be (re)acquired. A reference SATPS station provides the new SATPS station with an estimated reference station location and ephemeris information for one or more identified SATPS satellites visible from the reference station. The new station receives and uses this information to establish carrier frequency ranges to search for the identified SATPS satellite, by limiting the search to a reduced frequency range based upon estimated Doppler shift of SATPS signals received from this satellite. The actual frequency shift may differ from the estimated Doppler shift, due in part to errors in a frequency source used by the new station. When a first SATPS satellite signal is acquired and locked onto by the new station, the error in the new station frequency source is estimated, and the frequency range for searching for an SATPS signal from another satellite is reduced. Acquisition of additional SATPS satellite signals occurs more quickly. This system also allows the use of less accurate timing sources for the new stations. A new station need not store ephemeris information for the SATPS satellites but may call upon and use the ephemeris information available at the reference station.
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Citations
12 Claims
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1. A method for rapid acquisition of one or more Satellite Positioning System (SATPS) satellite signals at an SATPS station that seeks to acquire or to reacquire one or more SATPS signals, the method comprising the steps of:
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(1) receiving and analyzing SATPS signals from one or more SATPS signal-transmitting satellites at an SATPS reference station and transmitting estimated reference station location and satellite ephemeris information for at least one SATPS satellite that is visible from the reference station, referred to as a “
reference/visible satellite”
, whose SATPS signal is received at the reference station with an associated carrier signal frequency;
(2) receiving at least one SATPS signal from at least one reference/visible satellite at a second SATPS station, which seeks to acquire or reacquire and to lock onto an SATPS signal from one or more reference/visible satellites, the second station having Doppler shift means for searching an incoming SATPS signal over a selected range of Doppler shifted carrier frequencies;
(3) receiving the estimated reference station location and the satellite ephemeris information at the second station, and estimating a Doppler shifted carrier frequency range for the at least one SATPS signal, using the received satellite ephemeris information, by;
(3a) estimating a location vector rm and a velocity vector vm for the second station at the time the second station receives the SATPS signals; and
(3b) estimating a frequency f=fs+Δ
f in the Doppler frequency shift range for the at least one SATPS signal received, where fs is a known carrier frequency with which the SATPS signals are transmitted, by estimating the frequency shift using the relationwhere c′
is a representative velocity of propagation of electromagnetic signals in the ambient medium through which the SATPS signals propagate, rm(t) and vm(t) are estimated location and velocity vectors for the second station at a selected time t, and rs(t′
) and vs(t′
) are estimated location and velocity vectors for the selected reference/visible satellite at a selected time t′
; and(4) scanning the estimated Doppler shifted carrier frequency range to acquire and to lock onto an SATPS signal from the at least one reference/visible satellite, whereby a time interval required to acquire and lock onto the at least one reference/visible satellite does not exceed about 39 seconds. - View Dependent Claims (2, 3, 4, 5, 6, 8)
(5) after said SATPS signal from said at least one reference/visible satellite is acquired and locked onto by said second station, estimating a frequency error associated with a second station signal analyzer and determining a second reduced frequency range within which an additional SATPS signal is received by said second station from an additional reference/visible satellite, based upon the frequency error estimated by the signal analyzer;
(6) estimating a Doppler frequency shift for the additional SATPS signal received by said second station; and
(7) using the second reduced frequency range to search for, identify, acquire and lock onto the additional SATPS signal at said second station.
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4. The method of claim 3, further comprising the step of acquiring and locking onto said SATPS signal from said additional reference/visible satellite in a time interval that does not exceed about 13 seconds.
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5. The method of claim 1, further comprising the step of choosing said Satellite Positioning System to be a Global Positioning System or a Global Orbiting Navigation Satellite System.
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6. The method of claim 1, further comprising the steps of:
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(5) after said SATPS signal from said at least one reference/visible satellite is acquired and locked onto by said second station, estimating a frequency error associated with said at least one reference/visible satellite carrier frequency and determining a second Doppler shifted carrier frequency range within which an additional SATPS signal is received by said second station from an additional reference/visible satellite, based upon the estimated frequency error;
(6) estimating a second Doppler shifted carrier frequency for the additional SATPS signal received by said second station; and
(7) using the estimated second Doppler shifted carrier frequency to acquire and lock onto the additional SATPS signal at said second station.
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8. The method of claim 1, further comprising the step of acquiring and locking onto said SATPS signal from said at least one reference/visible satellite in a time interval that does not exceed about 20 seconds.
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7. A method for rapid acquisition of one or more Satellite Positioning System (SATPS) satellite signals at an SATPS station that seeks to acquire or to reacquire one or more SATPS signals, the method comprising the steps of:
-
(1) receiving and analyzing SATPS signals from one or more SATPS signal-transmitting satellites at an SATPS reference station and transmitting an estimated reference station location vector and information on location vector rs and velocity vector vs for at least one SATPS satellite that is visible from the reference station, referred to as a “
reference/visible satellite”
, whose SATPS signal is received at the reference station with an associated carrier signal frequency;
(2) receiving at least one SATPS signal from at least one reference/visible satellite at a second SATPS station, which seeks to acquire or reacquire and to lock onto an SATPS signal from one or more reference/visible satellites, the second station having Doppler shift means for searching an incoming SATPS signal over a selected range of Doppler shifted carrier frequencies;
(3) receiving the location vector and velocity vector information for the at least one reference/visible satellite at the second station, and estimating a Doppler shifted carrier frequency range for the at least one SATPS signal, using the received satellite location vector and velocity vector information, by;
(3a) estimating a location vector rm and a velocity vector vm for the second station at the time the second station receives the SATPS signals; and
(3b) estimating a frequency f=fs+Δ
f in the Doppler frequency shift range for the at least one SATPS signal received, where fs is a known carrier frequency with which the SATPS signals are transmitted, by estimating the frequency shift using the relationwhere c′
is a representative velocity of propagation of electromagnetic signals in the ambient medium through which the SATPS signals propagate, rm(t) and vm(t) are estimated location and velocity vectors for the second station at a selected time t, and rs(t′
) and vs(t′
) are the location and velocity vectors for the at least one reference/visible satellite at a selected time t′
; and(4) scanning the estimated Doppler shifted carrier frequency range to acquire and to lock onto an SATPS signal from the at least one reference/visible satellite, whereby a time interval required to acquire and lock onto the at least one reference/visible satellite does not exceed about 39 seconds. - View Dependent Claims (9, 10, 11, 12)
(5) after said SATPS signal from said at least one reference/visible satellite is acquired and locked onto by said second station, estimating a frequency error associated with a second station signal analyzer and determining a second reduced frequency range within which an additional SATPS signal is received by said second station from an additional reference/visible satellite, based upon the frequency error estimated by the signal analyzer;
(6) estimating a Doppler frequency shift for the additional SATPS signal received by said second station; and
(7) using the second reduced frequency range to search for, identify, acquire and lock onto the additional SATPS signal at said second station.
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10. The method of claim 9, further comprising the step of acquiring and locking onto said SATPS signal from said additional second station/visible satellite in a time interval that does not exceed about 13 seconds.
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11. The method of claim 7, further comprising the step of choosing said Satellite Positioning System to be a Global Positioning System or a Global Orbiting Navigation Satellite System.
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12. The method of claim 7, further comprising the steps of:
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(5) after said SATPS signal from said at least one reference/visible satellite is acquired and locked onto by said second station, estimating a frequency error associated with said at least one reference/visible satellite carrier frequency and determining a second Doppler shifted carrier frequency range within which an additional SATPS signal is received by said second station from an additional reference/visible satellite, based upon the estimated frequency error;
(6) estimating a second Doppler shifted carrier frequency for the additional SATPS signal received by said second station; and
(7) using the estimated second Doppler shifted carrier frequency to acquire and lock onto the additional SATPS signal at said second station.
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Specification
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Current AssigneeTrimble Navigation Limited (Trimble Inc.)
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Original AssigneeTrimble Navigation Limited (Trimble Inc.)
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InventorsLau, Chung, Loomis, Peter V. W., Eschenbach, Ralph, Braisted, Paul
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Primary Examiner(s)Issing, Gregory C.
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Application NumberUS09/663,669Time in Patent Office396 DaysField of Search342/357.15, 342/357.12, 342/352, 342/418US Class Current342/357.75CPC Class CodesG01S 19/06 employing an initial estima...G01S 19/07 providing data for correcti...G01S 19/254 relating to Doppler shift o...G01S 19/258 relating to the satellite c...
