Abstract: A vector extended range correlation (ERC) apparatus and method tracks signals transmitted from satellites in a GPS network in extremely low signal to interference plus noise ratio (SINR) environments. A GPS receiver antenna receives the signals transmitted from the satellite, and the signals are converted into digital input signals for each satellite on individual channels. A pseudorange error measurement is generated for each individual channel, and the pseudorange error measurements for all of the individual channels are operated on to generate line-of-sight (LOS) signal tracking commands for each individual channel that are based on the pseudorange error measurements for all of the individual channels. Timing and frequency states for each individual channel are updated based on the LOS signal tracking commands for the respective individual channel.

Abstract: A method of estimating the carrier phase difference between two antennas under low signal conditions (typically called state 3) of a global positioning system (GPS) carrier signal transmitted from one of a constellation of satellites in the GPS for use in attitude determination systems is proposed. The method involves the use of multiple antennas tracking the same satellite signal and utilizing a code tracking loop filter to aid in maintaining track of the GPS waveform when the effects of doppler (i.e., the distance from a GPS satellite to the antenna is changing with time) are present.