The Johns Hopkins University

Mark S Asher

Dennis J Duven

Lloyd A Linstrom

Thomas L Kusterer

William S Devereux

Albert A Chacos

Richard C Morgan

Kim Strohbehn

Stephen J Stafford

Patrick A Stadter

Robert L Henderson

Eric A Olsen

Robert J Heins

Martin G Sommerville

Don M Gruenbacher

Methods and systems to detect navigation signals, including to identify up to multiple range-Doppler hypotheses from each of j range-Doppler correlation grids based on a relatively low first threshold, generate navigation solutions from combinatorial sets of k of the identified hypotheses, evaluate the navigation solutions to identify plausible solutions, iteratively and combinatorially augment the plausible solutions with additional hypotheses from grids that are not represented in the corresponding k-hypotheses based navigation solutions, replace plausible solutions with corresponding augmented plausible solutions when appropriate, and select one of a plurality of plausible solutions as a best plausible solution, j and k being positive integers. Where a grid energy peak exceeds a second threshold, a corresponding hypothesis may be identified as a sole hypothesis for the corresponding navigation signal. The relatively low first threshold permits detection of weaker signals. Subsequent evaluations effectively transform a per-navigation-signal false alarm rate to per-navigation-solution false alarm rate.

Methods and systems to diminish false-alarm rates in multi-hypothesis signal detection through combinatoric navigation

An autonomous navigation system for an orbital platform incorporating a global positioning system based navigation device optimized for low-Earth orbit and medium-Earth orbit applications including a 12 channel, GPS tracking application-specific integrated circuit () operating in concert with a computer system () implementing an extended Kalman filter and orbit propagator which autonomously generates estimates of position, velocity and time to enable planning, prediction and execution of event-based commanding of mission operations.

Extended kalman filter for autonomous satellite navigation system

A method of correcting ionospheric delays induced in received signals by space systems is disclosed. The method takes advantage of received GPS signals and received crosslink signals among spacecraft to estimate the effect of ionospheric delays and correct for such delays in the computation of the range estimation between spacecraft. The method generates and initial estimate of the ionospheric delay by tracking pseudorandom codes on both GPS and crosslink signals at known frequencies to correct an initial relative range vector. Using the corrected range vector generated from the use of code, the method subsequently estimates a more precise correction by considering the carrier phase error as induced by ionospheric delay. This includes estimate the integer ambiguities on both the GPS signals and the crosslink signals iteratively and subsequently estimating a more precise ionospheric delay correction with is applied to the relative position vector using the carrier phase measurements. The method is also applicable to non-navigation applications including measuring dynamic ionospheric structure and variability over a wide range of scale sizes, thereby greatly improving operational models of navigation and communications, and improving interdependent models of atmospheric, ionospheric, magnetospheric, and space weather physics and prediction.

Method for using GPS and crosslink signals to correct ionospheric errors in space navigation solutions

Disclosed is a system and method for increasing the weak signal recovery capability of a Global Positioning System (GPS) receiver correlating each of the plurality of digital signals by multiplying the I and Q phases by the carrier and code, adding a location offset, accumulating the results of the correlation, and latching the results until a predetermined time; coherent combining the accumulated results at the predetermined time; non-coherent combining the coherent combined results for a time period sufficient to raise a correlation peak to a predetermined point above a noise floor to produce a plurality of non-coherent bin observables; determining a maximum value of the plurality of bin observables and comparing the maximum value to predetermined threshold; determining grid locations of bin observables having maximum values greater than the predetermined threshold; determining a bi-quadratic surface using the grid locations; determining an argument maximum of the bi-quadratic surface; estimating epoch pseudorange and Doppler variables based on the argument maximum; estimating errors in at least one of position, velocity, orientation, user clock, frequency, and ionosphere states on the estimated epoch pseudorange and Doppler variables; and determining at least one of position, velocity and orientation by correcting for the estimated errors.

Weak signal and anti-jamming Global Positioning System receiver and method using full correlation grid

An autonomous navigation system for an orbital platform incorporating a global positioning system based navigation device optimized for low-Earth orbit and medium-Earth orbit applications including a 12-channel, GPS tracking application-specific integrated circuit operating in concert with a microprocessor implementing an extended Kalman filter and orbit propagator which autonomously generates estimates of position, velocity, and time to enable planing, prediction and execution of event-based commanding of mission operations.

Autonomous satellite navigation system

Growing community of inventors

Ellicott City, MD, United States of America

Mark S Asher