Signal Strength Variations and Data Bit Synchronization Issues of High Dynamic NavIC/GPS Receiver During Ascent Phase of a Launch Vehicle Trajectory

One of the most important and challenging part of NavIC/GPS receiver design is the tracking loop realization. NavIC/GPS data bit identification is the terminal phase of tracking loop algorithm. Basic time synchronization between the particular satellite time which is tracked by a channel and receiver local time is achieved using the data bit boundary identification. The probability of inducing error in navigation solution is more if low elevation/low CNDR satellites signal is used for navigation computation. Normally high dynamic GNSS receivers use elevation limit to avoid low elevation satellites, but this may not be always applicable when the receiver is employed in launch vehicles which is having different maneuvers during the trajectory. In such cases when the receiver tracks low elevation satellites, there can be noise induced errors, which lead to misinterpretation of data bits leading to incorrect time synchronization for that particular channel. This leads to error in transmit time computation and further it will affect the position solution as well. The signal strength analysis of a typical NavIC/GPS receiver during the ascent phase of launch vehicle is studied and the possibility of bit synchronization issues during the flight/during ground testing is brought out and mitigation techniques are presented in this paper.