Method and apparatus for detecting cycle slips in navigation signals received at a receiver from a satellite-based navigation system

• US 6,175,806 B1
• Filed: 07/16/1993
• Issued: 01/16/2001
• Est. Priority Date: 07/16/1993
• Status: Expired due to Term

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Thuente, Perry John
• Primary Examiner(s): NGUYEN, TAN QUANG
• Application Number:
  US08/092,684
• Time in Patent Office: 2,741 Days
• Field of Search: 364/449, 364/444, 364/453, 364/457, 342/355-359, 342/451, 342/461, 340/988, 340/993, 370/75, 701/213, 701/214, 701/216, 701/220
• US Class Current: 701/213
• CPC Class Codes: G01S 19/43 using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled

Abstract

Carrier signal cycle slip errors occurring at a receiver in a satellite-based navigation system, such as NAVSTAR GPS, are detected. A continuous navigation signal is received from a satellite. Cycles of the carrier wave of the navigation signal are counted over a time Δt. The cycle count and the time Δt are used to compute a first velocity of the receiver along a vector between the receiver and the satellite. A second velocity of the receiver is received from an inertial reference unit associated with the receiver. A component of the second velocity along the vector to the satellite is computed. A difference between the first and second velocities is then computed and compared to predetermined value. If the difference exceeds the predetermined value, then a cycle slip error is indicated.

Claims

1. A method for detecting carrier signal cycle slip errors in a position determining system which receives navigation signals at a receiver from a plurality of satellites, the method comprising the steps of:

(a) receiving, at the receiver, a navigational signal from a satellite, said navigation signal including a continuous carrier wave;

(b) counting cycles of said carrier wave over a time Δ

t;

(c) computing, from said time Δ

t and said cycle count, a first velocity of the receiver along a vector between the receiver and said satellite;

(d) receiving a second velocity of the receiver from an inertial reference unit;

(e) computing a component of said second velocity along said vector;

(f) computing a difference between said first velocity and said component of said second velocity;

(g) comparing said difference to a predetermined value; and

(h) indicating a cycle slip error if said difference exceeds said predetermined value.

2. A method for computing the position of a receiver at or near the surface of the Earth using a satellite-based navigation system having a plurality of satellites, the method comprising the steps of:

(a) receiving, at the vehicle, a continuous navigation signal from each of the plurality of satellites over a time period Δ

t between time t₁ and time t₂, each said continuous navigation signal having a continuous carrier wave;

(b) counting cycles of each said continuous carrier wave over said time Δ

t for each said continuous navigation signal;

(c) monitoring each cycle count for a cycle slip error, wherein step (c) comprises, for each satellite, the steps of,

(1) computing, from said time Δ

t to said cycle count, a first velocity of the receiver along a vector between the receiver and said satellite,

(2) computing a second velocity of the receiver along said vector based on data from an inertial reference unit associated with the receiver,

(3) computing a difference between said first and second velocities, and

(4) determining whether said difference exceeds a predetermined value, and if so, indicating that a cycle slip has occurred for said satellite;

(d) computing a satellite position for each of the plurality of satellites at time t₂ based upon ephemeris data provided by each said continuous navigation signal;

(e) computing a code pseudorange for each of the plurality of satellites at time t₂ based on each of said continuous navigation signals;

(f) for each satellite for which a cycle slip was not detected at step (c), computing a refined pseudorange from said code psuedorange and said cycle count;

(g) for each satellite for which a cycle slip was detected at step (c), computing a refined pseudorange from said code pseudorange; and

(h) computing the position of the receiver from said satellite positions and said refined pseudoranges.

3. An apparatus for detecting carrier wave cycle slip errors in a position determining system which receives navigation signals at a receiver from a plurality of navigation satellites and which counts cycles of the carrier wave for each navigation signal, the apparatus comprising:

carrier means for computing a first velocity of the receiver along a vector between the receiver and the satellite for each satellite based on cycle count data;

inertial means for measuring a second velocity of the receiver based on movement of the receiver;

comparison means for comparing said first velocity with a component of said second velocity along said vector; and

means for indicating a cycle slip error when a difference between said first velocity and said component of said second velocity along said vector exceeds a predetermined value.

4. An apparatus for computing an estimated position relative to the surface of the Earth based on navigation signals received from a satellite-based navigation system, the apparatus comprising:

a receiver configured to receive a navigation signal from a each of a plurality of satellites, to compute a code pseudorange for each satellite, to compute a position for each satellite, and to count cycles of a carrier wave of each navigation signal;

carrier means for receiving said cycles of said carrier wave from said receiver and for computing, for each satellite, a first velocity of the receiver along a vector between the receiver and each satellite;

inertial means for measuring a second velocity of the receiver based on movement of the receiver;

means for comparing said first velocity with a component of said second velocity along said vector and for indicating a cycle slip error when a difference between said first velocity and said component of said second velocity along said vector exceeds a predetermined value;

pseudorange filter means for receiving said code pseudoranges, said cycle counts and said indication of a cycle slip error and for computing a refined pseudorange for each satellite; and

filter means for receiving said satellite positions and said refined pseudoranges and for computing a position of said receiver therefrom.