GAGAN is an Indian implementation of Satellite Based Augmentation System (SBAS), developed jointly by Airports Authority of India (AAI) and Indian Space Research Organisation (ISRO). It is in final operational phase with all the required ground and space segments ready. With the availability of GAGAN signal-in-space (SIS), the improvement in position solution is investigated using the two collocated dual frequency GPS receivers. One of the receivers was configured as SBAS receiver and the other was kept as GPS stand-alone receiver. It is found that accuracy in position improved significantly in SBAS receiver due to GAGAN correction. The impact of scintillation on GNSS was also investigated in terms of position degradation and loss of lock of the satellite signals. The manyfold effects of scintillation on GPS and SBAS are discussed in detail. The results indicate ~15% reduction in number of measurements due to loss of lock during severe scintillation.