Abstract: A global positioning system (GPS) receiver or navigation apparatus for use on an aircraft is disclosed. The receiver implements improved methods of performing both navigation and fault detection and exclusion (FDE) functions. The GPS receiver includes an antenna adapted to receive GPS satellite signals from each of a multiple GPS satellites. Navigation solution determining circuitry coupled to the antenna receives the GPS satellite signals and performs navigation and FDE functions. The navigation solution determining circuitry is adapted to determine both a horizontal position of a least squares navigation solution for the receiver and a horizontal position of a first navigation solution for the receiver as functions of the received GPS satellite signals. The horizontal position of the first navigation solution for the receiver is offset from the horizontal position of the least squares navigation solution for the receiver.

Abstract: An incremental position encoder makes use of a first and second track of non-identical non-complementary aperiodic patterns to generate a zero mark. A mask with the identical pattern to the first track and a mask with the complementary pattern to the second track correlate with the patterns on the first and second track when the encoder is in zero position. Light transmitted by the masks produce electrical signals that are compared to create the zero mark. An iterative approach improves the discrimination of an initially selected track pattern for its particular application based on developed criteria for good noise immunity and resoltuion. The size of the reference track with respect to the increment track and the placement of each mask on the stator and rotor are optimized. A system for improving noise immunity by biasing the signal from each photodetector is also shown.