Comparative evaluation of IRNSS performance with special reference to positional accuracy

Abstract

The Indian Regional Navigation Satellite System (IRNSS) is a seven-satellite constellation developed by Indian Space Research Organization (ISRO), India. IRNSS provides two services, with the standard positioning service open for civilian use, and for authorized users (including the military) with an assured absolute positional accuracy. IRNSS is designed to cover all the parts of India and also extending beyond the Indian borders. The coverage area of IRNSS with routes of satellites means and includes area covering entire Pakistan, Afghanistan, most of China and Middle East along with Indian Ocean. IRNSS downlink signals have two bands: S1 band and L5 Band. Presently Indian users are dependent on the civil GPS signals with a positional accuracy of 5 m. IRNSS system is intended to provide an absolute position accuracy of (i) better than 10 m throughout Indian landmass (ii) better than 20 m over the Indian Ocean and (iii) approximately in a region of 1500 km around India. There are 15 ground stations across the country responsible for operating and/or monitoring the IRNSS seven satellite constellation. A comparative analysis of IRNSS and GPS navigational satellites shows that the IRNSS consists of sufficient number of satellites for regional navigation system and it can also exhibit better performance. The main parameters selected for our study are orbital characteristics, position accuracy and positional error including Circular Error Probable (CEP), Altitude variation, Geometric Dilution of Precision (GDOP) with respect to Number of Satellites (NSAT), variations in Carrier to Noise (C/N₀) ratio and scintillation effect of both GPS and IRNSS satellite systems. Our analysis showed that IRNSS systems shall be used as stand-alone systems.