Kalman Filter Tracking of Limb Scan Signal using a Bank of Correlators

A combined phase-locked loop/delay-locked loop (PLL/DLL) algorithm is developed for tracking Global Navigation Satellite System (GNSS) carrier phase and code phase using the output from a large number of correlators. This approach has advantages for limb-scanning applications, in which useful meteorological information, available only at the initial rising time of a GPS satellite, is desired. The technique uses a bank of correlators to span wide ranges of uncertainty in code phase and carrier Doppler shift, thereby avoiding the need for a separate acquisition and the associated loss of an initial span of data. A fusion of optimal estimation methods processes the output from these correlators. A batch optimization of a signal model\´s fit at a point in time to many accumulations from the correlator bank provides a Kalman filter with "measurements" of the most likely signal parameters. The Kalman filter utilizes a signal dynamics model to provide estimates that drive the PLL and DLL. The effectiveness of this algorithm is demonstrated by using a truth-model simulation of a limb scan.