Receiver Clock Estimation for RTK-Grade Multi-GNSS Multi-Frequency Synthetic Aperture Processing

There are several techniques that deal with multipath mitigation either on the observation level, i.e. satellite pseudorange and carrier-phase, or directly during the tracking process of the signals within a Global Navigation Satellite System (GNSS) receiver. One of these techniques is Synthetic Aperture Processing (SAP) [1] or “Supercorrelation” [2] which takes the advantage from using a longer coherent integration time, up to couple of seconds, or equivalently very low Phase Locked Loop (PLL) bandwidths. This effectively realizes a Synthetic Antenna Aperture (SAA) being proportional to the inverse of the PLL bandwidth multiplied by the velocity of the antenna. Large SAAs mitigate multipath well and thus the bandwidth of carrier-phase tracking loops should be decreased, e.g. down to 0.1 Hz or lower. This requires removal of Line of Sight (LOS) dynamics from the PLL via inertial aiding and additionally, proper tracking of the oscillator jitter by all tracking channels, so-called Cooperative Tracking Loops (Co-Op). Within an innovative research oriented MATLAB based GPS/Galileo L1/E1/L5/E5a receiver, this will be demonstrated in this paper with real satellite signals. Real Time Kinematics (RTK) processing of the produced GNSS observations demonstrates the high accuracy of this signal processing method.