Modernized IRNSS Broadcast Ephemeris Parameters

Abstract

India has successfully stepped into satellite Navigation system with the launch of its first three IRNSS satellites IRNSS 1A, 1B and 1C.  IRNSS provides two types of services, Standard Posting Service (SPS), which is open for civilian use and the Restricted Service (RS), for authorized users.  The system is set to change the facet of navigation, surveying, transportation, precision agriculture, disaster management and telecommunication in India. In any navigation system, broadcast navigation parameters are of paramount importance in arriving user position solution at user receiver end. IRNSS Navigation data is classified as primary and secondary Navigation parameters. Primary navigation data of a satellite principally represents its own orbit and onboard clock offset in the form of quasi-keplerian elements and clock coefficients (Bias, Drift and Drifts rate) respectively. Whereas secondary navigation parameters includes satellite almanac, ionosphere delay correction messages, differential corrections, Earth orientation parameters and  IRNSS Time offset with respect to other GNSS. In existing IRNSS system satellite ephemeris of primary navigation parameters are broadcast in the form of 15 quasi-keplerian elements valid for a period of 2 hours or more. Spacecraft ephemeris which represents orbit in the form of 9 parameters, i.e., position, velocity and acceleration component of spacecraft in Cartesian coordinate system are chosen from Russian Global Navigation satellite system (Glonass) to improve Time to First Fix (TTFF) of IRNSS system with similar existing orbit accuracy. In addition, two models of user receiver orbit propagation algorithms with proposed ephemeris are briefed and their results are compared with standalone Glonass model. Generation of IRNSS ephemeris in Cartesian coordinate system and description of user receiver orbit propagation algorithms using new type of ephemeris to get user position solution is the scope of this paper..

Keywords: IRNSS, TTFF (Time to First Fix), Broadcast ephemeris