Design and Development of Composite Clock-Based Reliable Timing Reference for IRNSS

Abstract

Time plays a crucial role for a navigation system hence IRNSS Network Time (IRNWT), which generate, disseminate, and maintain IRNSS reference time, is a crucial element in the ground segment of Indian Regional Navigation Satellite System (IRNSS). Any anomaly in the timescale will result in a huge error in the range measurements, which causes a hike in the User Range Accuracy (URA). URA is a statistical indicator of the ranging accuracies obtainable with a specific satellite, URA beyond the specified value means the satellite is not usable for user position computation. The hike in the URA values of all satellites results in service outage, which is not acceptable for a reliable satellite system like IRNSS. The present timescale reference architecture for navigation parameter generation of IRNSS is based on master clock concept. This paper demonstrates that composite clock-based algorithm can mitigate master clock limitations and can prevent service outage. A composite clock-based timescale which derives a paper clock named as IRNSS Next-generation Navigation Time (INNT) has been proposed, designed, and developed as a new subsystem. The INNT generation is based on Kalman filter that utilizes measurements of all clocks of IRNSS reference receivers. The paper also presents the detailed design of INNT algorithm including the requirement specification, validation, and its robustness.