Estimation of Total Electron Content using NavIC Signals

Navigation with Indian Constellation (NavIC) formerly known as Indian Regional Navigation Satellite System (IRNSS) provides geo-spatial positioning with regional coverage over Indian landmass extended upto 1500 km. In general, NavIC have three main segments, namely the space segment, the ground segment and the user segment. NavIC satellites broadcast the signals in two different frequencies namely S (2492.045 MHz) and L5 (1575.42 MHz) using which the users can find out its position using an appropriate receiver. The positional accuracy of NavIC user is limited by several sources of errors of which the most predominant error is due to ionosphere which is a function of electron density represented by the total electron content (TEC). In order to get the precise user position, it is necessary to estimate this delay correctly and compensate during position estimation. In this paper, an attempt is made to understand the behaviour of the ionosphere delay using the NavIC signals. Since the ionospheric electron density varies with geographical coordinates and time, the behavior of ionosphere in terms of Total Electron Content is studied using the measurements observed from the NavIC receiver at different laltitude over Indian region. As the NavIC receiver produces two types of measurements, viz. code and carrier phase with the former being an unambiguous measurement but with more measurement noise while the later as ambiguous but precise measurements. A software module has been developed to resolve this ambiguity and compute the TEC. A comparison between the TEC using the code measurements and carrier measurements after integer ambiguity resolution is presented.