GPS receiver using coarse orbital parameters for achieving a fast time to first fix

摘要

A GPS receiver having a fast time to first fix by comparing measured range rates for GPS satellites to GPS satellite velocities that are calculated from coarse GPS satellite orbital parameters. The coarse GPS satellite parameters are GPS almanac parameters or GPS ephemeris parameters that are older than the GPS-specified curve fit interval. The GPS receiver includes a satellite velocity calculator and a satellite line-of-sight calculator using the coarse GPS satellite orbital parameters previously stored in memory for calculating GPS satellite velocities and unit vectors to GPS satellites, respectively; a range rate measurer using GPS signal carrier measurements for determining range rates to GPS satellites; a user velocity calculator using the satellite velocities, unit vectors, and range rates for calculating a user velocity; and a user location integrator for integrating the user velocity from the last user location for a first location fix. Optionally, the user velocity calculator provides user direction information that can be used for initializing an inertial navigation device.