Rapid satellite signal acquisition in a satellite positioning system

• US 5,418,538 A
• Filed: 05/21/1993
• Issued: 05/23/1995
• Est. Priority Date: 05/21/1993
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Lau, Chung
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/065,839
• Time in Patent Office: 732 Days
• Field of Search: 342/357, 342/358, 375/1
• US Class Current: 342/357.75
• CPC Class Codes: G01S 19/072 Ionosphere corrections
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

A method for fast acquisition of Satellite Positioning System (SATPS) signals from a satellite-based positioning system, such as GPS or GLONASS, that does not require permanent storage of satellite almanac 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 reacquired. A nearby reference SATPS station, whose location coordinates are known with high accuracy, provides the new SATPS station with differential positioning SATPS information, and, optionally, with SATPS satellite ephemeride information on each SATPS satellite visible from the reference station. The new station then uses this differential SATPS information to establish channels to search for (only) the SATPS satellites that are visible from the reference station. By limiting the search to the frequency range and code-phase attributes, such as the distinctive pseudo-random noise code used by each SATPS satellite, corresponding to these visible SATPS satellites, the ranges to be searched are decreased. When a first SATPS satellite signal is acquired and locked onto by the new station, the frequency range for searching is narrowed to a range corresponding to the Doppler shift frequency range for the visible satellites, and acquisition of additional SATPS satellite signals proceeds quickly. This system also allows the use of less accurate timing sources for the new stations. A new station need not store the ephemeride information for the SATPS satellites but may call upon and use the ephemeride information stored at the reference station.

Claims

1. A method for rapid acquisition of one or more Satellite Positioning System (SATPS) satellite signals by an SATPS station, referred to as a new SATPS station, that seeks to acquire or to reacquire such SATPS signals, the method comprising the steps of:

(1) providing a reference SATPS station, whose location coordinates are known with high accuracy, with a transmitter to broadcast differential SATPS information to other nearby SATPS stations, including the new SATPS station;

(2) providing differential SATPS information from the reference station to the new station, including satellite number or equivalent satellite indicia, for each SATPS satellite that is visible from the reference station, referred to as an SATPS reference/visible satellite;

(3) establishing a selected number of channels to acquire SATPS signals from each of the SATPS reference/visible satellites;

(4) stepping through the frequency range and code-phase attributes for each of the SATPS reference/visible satellites to acquire and lock onto the SATPS signals;

(5) after a first SATPS satellite signal is acquired, reducing the frequency tuning range to a smaller frequency range, based upon that satellite'"'"'s expected Doppler shift frequency range; and

(6) using this smaller frequency range to search for and acquire an SATPS signal from at least one additional SATPS satellite.

2. 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.

3. A method for acquisition of one or more SATPS satellite signals by an SATPS station, referred to as a new SATPS station, that seeks to acquire or to reacquire such SATPS signals, without requiring storage of SATPS satellite ephemeride information at the new station, the method comprising the steps of:

(1) providing a reference SATPS station, whose location coordinates are known with high accuracy, with a transmitter to broadcast differential SATPS information to other nearby SATPS stations, including the new SATPS station;

(2) providing differential SATPS information from the reference station to the new station, including satellite number or equivalent satellite indicia, for each SATPS satellite that is visible from the reference station, referred to as an SATPS reference/visible satellite, and information on the ephemeride for each SATPS reference/visible satellite;

(3) establishing a selected number of channels to acquire SATPS signals from each of the SATPS reference/visible satellites;

(4) stepping through the frequency range and code-phase attributes for each of the SATPS reference/visible satellites to acquire and lock onto the SATPS signals;

(5) after a first SATPS satellite signal is acquired, reducing the frequency tuning range to a smaller frequency range, based upon that satellite'"'"'s expected Doppler shift frequency range; and

(6) using this smaller frequency range to search for and acquire an SATPS signal from at least one additional SATPS satellite.

4. The method of claim 3, further comprising the step of choosing said Satellite Positioning System to be a Global Positioning System or a Global Orbiting Navigation Satellite System.

5. A method for rapid acquisition of one or more SATPS satellite signals by an SATPS station referred to as a new SATPS station, that seeks to acquire or to reacquire such SATPS signals, the method comprising the steps of:

(1) providing a reference SATPS station, whose location coordinates are known with high accuracy, with a transmitter to broadcast differential SATPS information to other nearby SATPS stations, including the new SATPS station;

(2) providing differential SATPS information from the reference station to the new station, including satellite identifying number or equivalent indicia, for each SATPS satellite that is visible from the reference station, referred to as an SATPS reference/visible satellite, where the reference station and the new station each have a timing source and the new station timing source has an associated inaccuracy of as high as 20 parts per million;

(3) establishing a selected number of channels to acquire SATPS signals from each of the SATPS reference/visible satellites;

(4) stepping through the frequency range and code-phase attributes for each of the SATPS reference/visible satellites to acquire and lock onto the SATPS signals;

(5) after a first SATPS satellite signal is acquired, reducing the frequency tuning range to a smaller frequency range, based upon that satellite'"'"'s expected Doppler shift frequency range; and

(6) using this smaller frequency range to search for and acquire an SATPS signal from at least one additional SATPS satellite.

6. The method of claim 5, further comprising the step of choosing said Satellite Positioning System to be a Global Positioning System or a Global Orbiting Navigation Satellite System.