System using leo satellites for centimeter-level navigation

• US 6,373,432 B1
• Filed: 07/25/2000
• Issued: 04/16/2002
• Est. Priority Date: 03/21/1997
• Status: Expired due to Term

• Current Assignee: Integrinautics Corporation (Kubota Corporation)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Cohen, Clark E., Lawrence, David G., Rabinowitz, Matthew, Parkinson, Bradford W.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/625,419
• Time in Patent Office: 630 Days
• Field of Search: 342/357.01, 342/357.04, 342/357.06, 342/357.02, 342/357.16, 701/213, 455/12.1
• US Class Current: 342/357.29
• CPC Class Codes: G01S 19/04 providing carrier phase data
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/20 Integrity monitoring, fault detection or fault isolation of space segment
• CPC Class Codes: G01S 19/44 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method
• CPC Class Codes: G01S 19/46 the supplementary measurement being of a radio-wave signal type
• CPC Class Codes: H04B 7/18552 using a telephonic control signal and a second ranging satellite determining absolute distances from a plurality of spaced points of known location G01S5/14

Abstract

Disclosed herein is a system for rapidly resolving position with centimeter-level accuracy for a mobile or stationary receiver [4]. This is achieved by estimating a set of parameters that are related to the integer cycle ambiguities which arise in tracking the carrier phase of satellite downlinks [5,6]. In the preferred embodiment, the technique involves a navigation receiver [4] simultaneously tracking transmissions [6] from Low Earth Orbit Satellites (LEOS) [2] together with transmissions [5] from GPS navigation satellites [1]. The rapid change in the line-of-sight vectors from the receiver [4] to the LEO signal sources [2], due to the orbital motion of the LEOS, enables the resolution with integrity of the integer cycle ambiguities of the GPS signals [5] as well as parameters related to the integer cycle ambiguity on the LEOS signals [6]. These parameters, once identified, enable real-time centimeter-level positioning of the receiver [4]. In order to achieve high-precision position estimates without the use of specialized electronics such as atomic clocks, the technique accounts for instabilities in the crystal oscillators driving the satellite transmitters, as well as those in the reference [3] and user [4] receivers. In addition, the algorithm accommodates as well as to LEOS that receive signals from ground-based transmitters, then re-transmit frequency-converted signals to the ground.

Claims

1. A method for estimating a position of a user device in a satellite-based navigation system, the method comprising:

transmitting carrier signals from a set of satellites, wherein the set of satellites includes a set of LEO satellites;

accumulating and sampling at a reference station the carrier signals to obtain reference carrier phase information comprising geometrically diverse reference carrier phase information from the set of LEO satellites;

accumulating and sampling at the user device the carrier signals to obtain user carrier phase information comprising geometrically diverse user carrier phase information from the set of LEO satellites; and

calculating the precise position of the user device based on the reference carrier phase information and the user carrier phase information, wherein the geometrically diverse reference carrier phase information and geometrically diverse user carrier phase information from the set of LEO satellites are used to resolve parameters related to integer cycle ambiguities in the reference carrier phase information and the user carrier phase information.

2. The method of claim 1 further comprising:

receiving code signals from a set of navigation satellites;

measuring at the reference station the code signals to obtain reference code phase information;

measuring at the user device the code signals to obtain user code phase information;

estimating user and reference clock biases from the user and reference code phase information; and

correcting for clock offsets using the estimated user and reference clock biases.

3. The method of claim 1 further comprising initializing a device navigation algorithm by estimating an approximate user position using code phase signals received from a set of navigational satellites.

4. The method of claim 1 further comprising communicating differential code phase correction data and the reference carrier phase information from the reference station to the user device.

5. The method of claim 1 further comprising communicating LEO satellite ephemeris data to the user device directly from the reference station, or using a satellite data link.

6. The method of claim 1 wherein the step of calculating the precise position of the user device comprises predicting present reference carrier phase information based on past reference carrier phase information.

7. The method of claim 1 wherein the step of calculating the precise position of the user device comprises compensating for frequency dependent phase delay differences between navigation carrier signals and LEO carrier signals in user and reference receiver circuits.

8. The method of claim 1 wherein the step of accumulating and sampling the carrier signals at the user device comprises reading navigation carrier information and LEO carrier information within a predetermined time interval selected in dependence upon an expected motion of the user device and the motion of the set of LEO satellites.

9. The method of claim 1 wherein the calculating step comprises accounting for a carrier phase offset between two LEO beams from a single LEO satellite.

10. The method of claim 1 wherein the calculating step comprises calibrating LEO oscillator instabilities using navigation satellite information.

11. The method of claim 1 wherein the calculating step comprises compensating for phase disturbances resulting from a bent pipe LEO communication architecture.

12. The method of claim 1 further comprising the step of monitoring the integrity of the calculating step.

13. A satellite-based navigation system comprising:

a set of satellites to transmit carrier signals, wherein the set of satellites includes a set of LEO satellites;

a reference station to track the carrier signals to obtain reference carrier phase information comprising geometrically diverse reference carrier phase information from the set of LEO satellites;

a user device including a receiver to track the carrier signals to obtain user carrier phase information comprising geometrically diverse user carrier phase information from the set of LEO satellites and a microprocessor to calculate a precise position of the user device based on the reference carrier phase information and the user carrier phase information, wherein the microprocessor uses the geometrically diverse reference carrier phase information and geometrically diverse user carrier phase information from the set of LEO satellites to resolve parameters related to integer cycle ambiguities in the reference carrier phase information and user carrier phase information; and

a communications link between the reference station and the user device.

14. The system of claim 13 wherein the set of satellites further comprises a set of navigational satellites and wherein the communications link conveys differential code phase correction data and the reference carrier phase information from the reference station to the user device.

15. The system of claim 13 wherein the communications link conveys LEO satellite ephemeris data to the user device from the reference station.

16. A user device for providing satellite-based navigation, the device comprising:

at least one antenna to couple to carrier signals transmitted from a set of satellites wherein the set of satellites includes a set of LEO satellites;

a first receiver for to track the carrier signals to accumulate and sample carrier phase information comprising geometrically diverse user carrier phase information from the LEO satellites;

a second receiver, not necessarily distinct from the first receiver, to obtain reference carrier phase information transmitted from a reference station, wherein the reference carrier phase information comprises geometrically diverse reference carrier phase information from the set of LEO satellites; and

a microprocessor to calculate a position of the user device based on the reference carrier phase information and the user carrier phase information, wherein the microprocessor uses the geometrically diverse reference carrier phase information and geometrically diverse user carrier phase information from the set of LEO satellites to resolve parameters related to integer cycle ambiguities in the reference carrier phase information and user carrier phase information.

17. The device of claim 16 wherein:

the set of satellites further comprises navigation satellites;

the first receiver measures navigation code signals to obtain user code phase information;

the second receiver receives reference code phase information transmitted from the reference station; and

the microprocessor estimates user and reference clock biases from the user code phase information and reference code phase information, and uses the estimated clock biases to correct for clock offset errors.

18. The device of claim 16 wherein the first receiver reads navigation carrier phase information and LEO carrier phase information at times separated by no more than a predetermined time interval which is dependent upon expected movement of the device and the movement of the LEO satellites.

19. A user device for providing satellite-based navigation, the device comprising:

at least one antenna to couple to signals transmitted from a set of satellites, wherein the set of satellites includes a set of navigation satellites and a set of LEO satellites;

a receiver to track the signals to obtain code phase information and carrier phase information comprising geometrically diverse carrier phase information from the set of LEO satellites; and

a microprocessor to calculate a position of the user device based on the code phase information and the carrier phase information, wherein the microprocessor uses the geometrically diverse carrier phase information from the set of LEO satellites to resolve parameters related to integer cycle ambiguities in the carrier phase information from the set of navigation satellites.