International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 01 | Jan 2019 www.irjet.net p-ISSN: 2395-0072 © 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 1020 REVIEW ON DIFFERENT CLOCK ERROR ESTIMATION METHODS FOR IRNSS RECEIVER Megha V Goudar 1 , Dr K L Sudha 2 1 M.Tech Student, ECE, DSCE, Bengaluru 2 PG Coordinator, ECE, DSCE, Bengaluru ----------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - The review on Indian Regional Navigation Satellite System (IRNSS), also known as NAVIC (Navigation with Indian Constellation) provides real time positioning and timing services. IRNSS-GPS-SBAS (IGS) receiver designed and developed by ISRO is used to receive signals from both L5 and S band for IRNSS. Every receiver has a crystal oscillator which provides time that should be synchronized with the onboard satellite precise and stable atomic clocks. Clock is an important parameter in providing position accuracy. In this paper, the satellite and receiver clock error is observed and clock error estimation methods for IRNSS satellites are discussed. Key Words: IRNSS, IGS receiver, Clock error estimation I. INTRODUCTION The Indian Regional Navigation Satellite System (IRNSS) with an operational name NAVIC is an autonomous regional satellite navigation system that is being set up by India that will be used to provide accurate real-time positioning and timing services over India and the region extending to 1,500 kilometres (930 mi) around India. The present constellation of NAVIC comprises of seven satellites, 3 GEO (Geostationary Earth orbit) satellites and 4 GSO (Geosynchronous orbit) satellites are shown in fig1. IRNSS will provide two types of services, namely, Standard Positioning Service (SPS) which is provided to all the users and Restricted Service (RS), which is an encrypted service provided only to the authorized users. The IRNSS satellite signals are in L band and S band. Fig 1: IRNSS constellation NAVIC will provide two levels of service, the standard positioning service will be open for civilian use, and a restricted service (an encrypted one) for authorized users (including the military). Navigation signals transmitted on each carrier frequency are imperfectly synchronized due to different hardware paths corresponding to each signal. Each satellite’s navigation message contains parameters describing the timing bias. A user receiver uses these parameters to compute the clock correction for each observation. IMPORTANCE OF CLOCK ESTIMATION ISRO have included atomic clock, which are used in navigation satellites to measure precise position. Clock is the important parameter in finding an accurate position of any object or position. The receiver's built-in clock is not as accurate as the atomic clocks on-board the satellites, and it is not exactly synchronized with satellite onboard clock, hence a variable clock offset is observed between receiver and satellite clocks. The correction parameters bias, drift and drift rate are available in navigation data. Which are estimated by ISRO and sending it for increasing receiver accuracy which in turn increases position accuracy. The clock estimation is necessary to reduce the clock errors. II. RELATED WORK Estimation is a process of finding an approximation, which is a value that is usable for some purpose even if input data may be incomplete, uncertain or unstable. Estimation involves using the value derived from a sample to estimate the value of corresponding parameter. The clock estimation for the satellite is an important parameter for precise position. ISRO has included atomic clocks which are installed in navigation satellites to measure precise location data. The receiver clock is not exactly synchronized with satellite onboard clock, hence a variable clock offset is observed between receiver and satellite clocks. So the clock error estimation of the satellite is necessary to reduce the clock errors [1]. In GNSS (Global navigation satellite system) several methods are used to determine precise position, orbit determination and clock estimation for GPS satellite. Nonlinear Least Squares (LS) method is used for position computation from pseudo ranges, Linearization is done to convert non linear into linear system. The accuracy of the positioning results is compared for various numbers of required iterations using real GPS data so as to increase the accuracy in reference [2].