Lockheed Martin Corporation

Other

Lockhead Martin Corp.

Henry Michaels Beisner

Jack George Rudd

Robert H Benner

Timothy C Parker

Arthur G Gower

Arthur J Dorsey

The direct path of a radio signal from the transmitter to the receiver is frequently interfered with by reflections of the transmitted signal from stationary and moving objects. These reflections are known as multipath noise. The multipath canceler of this invention takes as input the direct path signal plus multipath noise. The canceler, after canceling the multipath noise, outputs a purified version of the direct path signal nearly devoid of multipath noise. The output of the canceler is fed back to a bank of delayers and frequency shifters. The outputs of this bank of delayers and frequency shifters are multiplied by a set of adjustable coefficients. These coefficients are adjusted to form very accurate replicas of the multipath reflections caused by each reflector. Which replicas are subtracted from the input which is the original direct path signal plus the multipath noise. The result of this subtraction is called the residual and is a purified version of the direct path signal nearly devoid of multipath noise. The coefficients are determined by nonlinear least squares which finds that set of coefficients which minimize the mean square of the residual. Each coefficient is associated with a delay and a frequency shift. The amplitude of a coefficient is a measure of the magnitude of a reflector and the differential delay and frequency shift caused by said reflector. If an object is a target, its differential range, range rate and magnitude is got from the measured differential delay, frequency shift and amplitude of the coefficient. Position and velocity of the target can be obtained by geometric triangulation with multiple transmitters. Target angle can be measured from the relative phase angles of the corresponding filter coefficients, if complex, across multiple antennas receiving the same signal from the same transmitter. The system, comprising the antennas, receivers, signal processor, multipath cancelers and target estimators, can be used on a surveillance aircraft to cancel ground reflections and track targets.

Adaptive filter to reduce multipath

A method for measuring the effectiveness of a wide-area differential global positioning system by projecting the least-squares error covariance of the space vehicles and ground reference stations through the central control station. Through generation of the differential corrections at the central control station, the space vehicle-ground reference station error covariance is then projected onto the wide-area differential global positioning system user locations. A covariance analysis approach is then used to capture the dependencies of the space vehicle and observability of the space vehicle by the ground reference stations and to the user locations within the wide-area differential global positioning system coverage area.

Method for establishing coverage area and accuracy of a wide-area differential global positioning system

In a global positioning system, satellites transmit navigation signals to users which determine their position from the received navigation signals. A wide area differential correction system employs receiving stations in fixed positions on the ground and compares ranges between the receiving stations and the satellites measured from the navigation signals with the actual ranges between the satellites and the receiving stations to determine correction information including corrections in the satellite clock times and the satellite positions to be transmitted to the users and from which the users can more accurately determine their positions. The site locations of the receiving stations to be used in the wide area differential correction system are determined by first determining an initial estimate of the site locations by means of a global positioning system and storing these initial estimates in a data base and then removing each receiving station from the wide area differential correction system in turn and calculating the wide area differential corrections without use of the site location of the removed receiving station. The site location of the removed station is then determined using the global positioning system and the wide area differential calculations and the site location of the removed station is updated in the data base with the site location thus determined. This process is repeated for each receiving station in turn three times to determine an accurate updated data base of site locations for the receiving stations to be used in the wide area differential correction system.

Monitoring station location determination for a satellite navigation

In a global monitoring system having four or more satellites which transmit messages to user stations by which the user stations can determine the user position, the satellite messages include the time of transmission of the messages as indicated by satellite clocks and includes a correction message. The correction message consists of time correction values for the satellite clocks. The satellite time correction values are determined from a clocks only model wherein three or more monitoring stations having known positions on the ground receive the satellite messages and determine pseudoranges between the satellites and the monitoring stations. The satellite time correction values are determined statistically by nonlinear least squares from a clocks only model relating the ranges between the satellites and the monitoring stations to the measured pseudoranges, the satellite time correction values and monitoring stations time correction values.

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Rockville, MD, United States of America

Henry Michaels Beisner