Development of Differential NavIC Algorithms for Precise Positioning

Abstract

India has developed its own satellite based navigation system \NavIC". It is a constellation of GEO and GSO satellites. Satellites transmit signals at L5 band (1176.45 MHz) and S band(2492.028 MHz).NavIC receiver receive this signal and generate carrier phase and code phase measurements. Relative NavIC positioning system is used to cancel common errors such as satellite/receiver clock biases and atmospheric effects. The common approach is to use differential NavIC carrier phase measurements to provide centimeter level accuracy. Differential NavIC uses single difference and double difference techniques in order to cancel out common errors. However, carrier phase based differential NavIC positioning requires resolution of Integer Ambiguity (IA) and is sensitive to cycle slip. In order to resolve integer ambiguity many algorithms have been developed. In order to resolve integer ambiguity and achieving centimeter level accuracy I will going to developed an algorithm that can be used for post processing as well as real time mode. Post processing algorithms may find application in areas such as survey and land records. Whereas real time algorithms can be used to develop Real-Time-Kinematic (RTK) receivers. In this report, data was collected by Accord receivers for 24-hours at SAC, Ahmedabad, India. Double-differenced pseudorange carrier-phase measurements of base rover receivers were used for study. A smoothing filter (Hatch Filter) was developed and implemented in C on double differenced data. Achieved RMS-3D position error for NavIC with 7 satellites of without smoothing is 2.18 m and 2.35 m and of with smoothing is 1.06 m and 1.08 m respectively for two datasets.Achieved standard deviation for NavIC with 7 satellites of without and 1.12 m and 1.13 m and with moothing is 0.47 m and 0.48 m respectively for two datasets. An Extended Kalman Filter (EKF) was implemented in C language. Analysis was done on 24-hour data of 25 Aug 2018 collected at SAC, Ahmedabad. RMS-3D error of 15cm and standard deviation of 8 cm is achieved.