Method and system for navigation employing incremental range difference

• US 4,024,383 A
• Filed: 09/02/1975
• Issued: 05/17/1977
• Est. Priority Date: 09/02/1975
• Status: Expired due to Term

• Current Assignee: Lockheed Aircraft Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Aircraft Corporation (Martin Marietta Corporation)
• Inventors: Beasley, T. James
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Krass, Errol A.
• Application Number:
  US05/609,215
• Time in Patent Office: 623 Days
• Field of Search: 235/150.26, 235/150.27, 235/150.2, 343/10, 343/12 R, 343/15, 343/16 R, 343/112 R, 343/112 C, 343/112 D, 343/112 PT, 343/114, 340/27 NA
• US Class Current: 701/207
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308

Abstract

A navigation method and system suitable for highly accurate all-weather navigation of vehicles such as ships and aircraft. An initial position of the vehicle relative to a plurality of known points each located at predetermined geographic positions is first determined. The distance or range of the initial position from each of the plurality of known points is determined and when the vehicle moves to a second and unknown position, the difference between the propagation time of electromagnetic wave energy transmitted from each of the plurality of known points at the initial and second positions is determined to thereby determine an incremental change in the distance to the second position from each of the plurality of known points. The distance of the initial position and the incremental change in distance from each of the plurality of points are algebraically summed to thereby determine the distance of the second position from each of the plurality of known points, and the second position is determined from the determined distances of the second position from each of the plurality of known points. The invention is compatible with existing navigation systems such as LORAN or other systems which periodically transmit wave energy at regular intervals.

Claims

1. A method of navigation comprising the steps of:

a. determining an initial position relative to a plurality of known points each located at predetermined geographic positions and each having a source of radio frequency electromagnetic wave energy;

b. determining the distance of the initial position from each of the plurality of known points;

c. moving to a second and unknown position;

d. determining the difference between the propagation time of electromagnetic wave energy from each of the plurality of points at the initial and second positions to thereby determine an incremental change in the distance to the second position from each of the plurality of points;

e. algebraically summing the distance of the initial position and the incremental change in distance from each of the plurality of points to thereby determine the distance of the second position from each of the plurality of known points; and

,

f. determining the second position from the determined distances of the second position from each of the plurality of known points.

2. The method of claim 1 wherein the time interval between two initial transmissions of electromagnetic wave energy is known and wherein the difference in propagation time of electromagnetic wave energy from each of the plurality of known points is determined by:

detecting the time of arrival of electromagnetic wave energy from two transmissions subsequent to at least one of the initial transmissions;

determining the elapsed time between the detected times of arrivals of the electromagnetic wave energy;

subtracting the known time interval between initial transmissions of the electromagnetic wave energy from the elapsed time to thereby determine the difference in propagation time of the electromagnetic wave energy without knowing the absolute time of transmission.

3. The method of claim 2 including the steps of:

determining the algebraic sum of the distance of the initial position from each of the plurality of known points, and the distance of the second position from each of the plurality of known points, to obtain a calculated incremental range; and

,

limiting the calculated incremental range to each known position to predetermined maximum values between transmissions.

4. The method of claim 1 including the steps of:

determining the algebraic sum of the distance of the initial position from each of the plurality of known points, and the distance of the second position from each of the plurality of known points, to obtain a calculated incremental range; and

,

limiting the calculated incremental range to each known position to predetermined maximum values between transmissions.

5. A method of vehicle navigation comprising the steps of:

a. determining initial range distances from an initial vehicle position to each of a plurality of known geographic positions spaced from the vehicle;

b. periodically transmitting pulses of wave energy from each of the known geographic positions;

c. receiving the periodically transmitted pulses of wave energy at the vehicle;

d. determining an initial time interval between the receipt of a first transmitted pulse received at an initial known position of the vehicle and a second successive transmitted pulse from each of said known geographic positions the period between said pulses from each of said known geographic positions comprising a respective standard-time-decrement;

e. subtracting the absolute value of said standard-time-decrement from said initial time interval to obtain an adjusted time interval;

f. determining a subsequent time interval between receipt of said second successive transmitted pulse and a third successive transmitted pulse received at a second position of the vehicle, from each of the known positions, said subsequent time interval being adjusted by subtracting the absolute value of said standard-time-decrement from the time between said second successive transmitted pulse and said third successive transmitted pulse, from each of said known geographic positions;

g. calculating an incremental range distance from each of said adjusted time intervals associated with the known positions;

h. algebraically summing the initial range distance to each of the known positions and respective incremental range distances to obtain updated range distances to each of the known positions; and

,

i. computing an updated vehicle position in response to the updated range distances.

6. The method of claim 5 including the steps of:

a. storing the updated initial distance and the determined subsequent time intervals; and

,

b. repeating steps (e) through (i) for each subequently measured time interval.

7. The method of claim 6 including the step of limiting the calculated incremental range distance to each known position to predetermined maximum values related to expected maximum range distance changes between transmissions.

8. The method of claim 5 including the step of limiting the calculated incremental range distance to each known position to predetermined maximum values related to expected maximum range distance changes between transmissions.

9. In a vehicular navigation system including at least two spaced transmitting stations at known geographic positions and each having a means for periodically transmitting pulses of wave energy from each of the known geographic positions, the period between said pulses from each of said known geographic positions comprising a respective standard-time-decrement, the system including a receiver carried by the vehicle for receiving and detecting the periodically transmitted pulses of wave energy at the vehicle, the improvement comprising:

means for storing initial range distances from an initial vehicle position to each of the spaced transmitting stations at the known geographic positions;

means for storing the respective standard-time-decrement associated with the period between pulses from each of said known geographic positions;

means for determining an initial time interval between receipt of first and second successive transmitted pulses received at the initial position of the vehicle from each of the known positions;

means for subtracting the absolute value of said standard-time-decrement from said initial time interval to obtain an adjusted time interval;

means for determining a subsequent time interval between receipt of said second transmitted pulse and a third successive transmitted pulse received at a second position of the vehicle from each of the known positions;

means for subtracting the absolute value of said standard-time-decrement from said subsequent time interval to obtain a second adjusted time interval;

means for calculating an incremental range distance from each of said adjusted time intervals associated with the known positions;

means for algebraically summing the initial range distance to each of the known positions and the respective incremental range to obtain updated initial range distances to each of the known positions; and

,

means for determining an updated vehicle position in response to the updated initial range distances.