US 6,243,648 B1 · Fast acquisition position reporting system

Abstract

A geographic tracking system with minimal power and size required at the mobile terminal collects observation data at the mobile terminal, forwards the data to a processor, which calculates the position. The mobile terminal needs only to gather a few milliseconds of observation data, and to relay this observation data to the processor. The range from the satellite (or other airborne transponder) to the terminal is determined using the known positions of an interrogating transmitter and a satellite, and a known terminal delay between the received signal and the transmission of the return signal, and the round trip time. An arc of locations is determined by computing an intersection of a sphere centered at the satellite having a radius given by the calculated range with a model of the Earth's surface. Only that portion of the arc within the region bounded by the satellite beam pattern is retained. Next, the time when the mobile terminal collected the GPS signal is determined. A satellite orbit model estimates the positions of the GPS satellites at their time of transmission. Using discrete points on the arc as an initial guess, an iterative least squares technique fits the observation data to the predicted data and minimizes residual error. After convergence, this estimated position solution is then screened against the known satellite range, satellite beam boundaries, an acceptable altitude range, and a maximum residual threshold. Those position estimates not meeting these criteria are discarded. The remaining points are then subjected to a final improved position estimate and residual calculation and the best point is selected.

Claims35

Dependent claims

A system for determining a location of a remote terminal located on or near the surface of the Earth by communicating with an orbiting communications satellite, said system comprising:

a) a satellite gateway broadcasting an interrogation signal to the remote terminal via the communications satellite;
b) said remote terminal including:
(i) a receiver receiving the interrogation signal from the communications satellite, said receiver receiving a plurality of signals being broadcast from a plurality of GPS satellites;
(ii) a processor measuring at least one characteristic in each of the plurality of signals being broadcast from the plurality of GPS satellites at a first predetermined time relative to receipt of the interrogation signal from the communications satellite;
and
(iii) a transmitter transmitting a reply signal at a second predetermined time relative to receipt of the interrogation signal to the communications satellite, wherein said reply signal includes the measured characteristic in each of the plurality of signals being broadcast from the plurality of GPS satellites;
c) an earth station receiving the reply signal from the communications satellite, and measuring time of arrival information;
and
d) an operations center calculating a position of the remote terminal using time of arrival information and the measured characteristics returned by the remote terminal.

6 more elements

A method for determining a position of a remote terminal on or near the surface of the Earth comprising the steps of:

a) broadcasting an interrogation signal to a remote terminal unit;
b) receiving the interrogation signal at the remote terminal unit;
c) receiving a plurality of signals being broadcast from a plurality of GPS satellites at the remote terminal unit;
d) measuring at least one characteristic in each of the plurality of signals being broadcast from the plurality of GPS satellites upon receipt of the interrogation signal from a communications satellite;
e) transmitting a reply signal at a predetermined time relative to receipt of the interrogation signal, wherein said reply signal includes the at least one measured characteristics in each of the plurality of signals being broadcast from the plurality of GPS satellites;
f) receiving the reply signal at a satellite gateway;
g) measuring time of arrival information in the satellite gateway;
and
h) calculating a position of the remote terminal unit using the time of arrival information and the at least one measured characteristics returned by the remote terminal unit.

6 more elements

Dependencies are inferred from the claim text.

Fast acquisition position reporting system

Life of this patent

Fast acquisition position reporting system

Life of this patent

Abstract

Claims35