Fix-tracking system

• US 5,191,342 A
• Filed: 08/06/1981
• Issued: 03/02/1993
• Est. Priority Date: 08/06/1981
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Jelks, Edward C., Alsup, James M.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/292,767
• Time in Patent Office: 4,226 Days
• Field of Search: 343/453, 343/465, 343/387, 343/389, 343/451, 343/444, 364/452
• US Class Current: 342/465
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

An apparatus determines the location of a signal source having coordinatesx,y). The source may be located as far away as two thousand km and does not require knowledge of ionospheric height or layer structure. The apparatus comprises at least three receivers adapted to receive the signals from the signal source. The coordinates, (x₁,y₁), (x₂,y₂) and (x₃,y₃), of each of the receivers are very precisely known. One receiver is capable of receiving signals from the other two receivers through different means (e.g. a wide-band telephone link). A plurality of at least three timers, one connected to each receiver, measures precisely the time difference of arrival (TDOA) of the signals from the signal source. A plurality of at least three means, connected one to each of the receiving means, determine the vertical angles φ at which the signal from the signal source is received by each of the receivers. More precisely, each receiver is in reality a phased array of individual antenna elements whose joint output can be used to measure both vertical angle and azimuth. Means are provided for calculating the coordinates (x,y) of the signal source from the measured vertical angles and the time differences of arrival.

Claims

1. System for determining the location of a signal source having coordinates (x,y), which are to be determined, and which may be located as far away as 2000 km, the system not requiring knowledge of ionospheric height or layer structure, comprising:

a plurality of at least three signal receiving means, adapted to receive the signals from the signal source, the receiving means being located in a non-colinear relationship with respect to each other, however, the coordinates (x₁,y₁), (x₂,y₂) and (x₃,y₃) of each of the receivers being very precisely known, each means for receiving being capable of receiving signals from the other two receivers;

a plurality of at least three measuring means, one connected to each receiving means, for measuring precisely the time difference of arrival (TDOA) of the signals from the signal source;

a plurality of at least two means, connected to at least two of the receiving means, for determining the vertical angle θ

_i, i=1, 2 or 3, at which the signal from the signal source is received by the receivers; and

means for calculating the coordinates (x,y) of the signal source from the measured vertical angles and the time delays of arrival.

2. A method for determining the location of a distant signal source having coordinates (x,y), which are to be determined, the method not requiring knowledge of ionospheric height or layer structure, the method comprising the steps of:

placing three signal-receiving means in a non-colinear relationship with each other and at distances apart from each other which are of the same order of magnitude as the assumed distance from the signal source to any of the receiving means, the earth coordinates, latitude and longitude, of the three receiving means being known, each receiving means being capable of receiving signals from the other two receivers;

determining the values of R, the earth'"'"'s radius at the center of the receivers;

measuring θ

_i, i=two of the values 1, 2 or 3, the vertical angle at each means for receiving;

estimating m_i, i=1, 2 and 3, the number of hops at the site of each receiving means;

measuring the time delays of arrival, Δ

t₂₁ and Δ

t₂₃ between pairs of the receiving means;

making an initial assumption for the earth coordinates, α

₀,β

₀, of the signal source;

solving the equation

space="preserve" listing-type="equation">J(α

.sub.n+1,β

.sub.n+1)=J(α

.sub.n,β

.sub.n)-J.sup.-1 (α

.sub.n,β

.sub.n)·

Z(α

.sub.n,β

.sub.n)

where Z=(z₁,z₂) is a vector pair comprised of the functions

space="preserve" listing-type="equation">z.sub.1 =w.sub.2 -w.sub.1 -(cΔ

t.sub.21 /2·

R) and

space="preserve" listing-type="equation">z.sub.2 =w.sub.2 -w.sub.3 -(cΔ

t.sub.23 /2·

R), and

J(α

,β

) is a 2-by-2 matrix of derivatives;

##EQU7## and iterating the above mentioned equation until the solution converges to the earth coordinates of the source, (α

,β

).