Doppler collision analysis and mitigation using hybrid approach for NavIC system

Doppler collision has a very important issue in satellite-based navigation systems. Navigation with the Indian Constellation (NavIC) comprises seven operational satellites, among which three are geo-stationary (GEO) satellites, and the rest are geosynchronous satellites. Due to the 'small line of sight velocities' of GEO satellites, estimated ranges suffer from the unique challenge of Doppler collision (DC). In this study, we present an analysis of DC events in both static and dynamic conditions, particularly in aerospace applications. We utilize experimental data acquired from the Indian Regional Navigation Satellite System (IRNSS)-GPS-Satellite Based Augmentation System (SBAS) (IGS) receiver located at a low altitude station to develop algorithms for the prediction, avoidance, and mitigation of DC events. The prediction of DC is based on the moving average method. We have devised an efficient algorithm to avoid the occurrence of DC, considering all possible combinations of IRNSS GEO satellites. Additionally, we perform the mitigation of DC using a proposed hybrid approach that involves both the space segment and user segment. The approach is based on repositioning the IRNSS 1C satellite and varying the loop bandwidth of the Delay Locked Loop (DLL). With the implementation of this proposed hybrid approach, the time duration of DC is reduced by 59.16% in static conditions and 16% in dynamic conditions.