Design and Development of a Precise Time Scale System for NavIC

摘要

Navigation with Indian Constellation (NavIC) or Indian Regional Navigation Satellite System (IRNSS) is a constellation of seven GSO satellites along with the associated ground segment, realised by Indian Space Research Organization (ISRO) for providing independent position, navigation and timing (PNT) services over the Indian region and the surrounding area extending up to 1500 km beyond its geographical boundary. The major element of ground segment of NavICis the navigation center which is linked with a number of one-way and two-way ranging stations and a precise timing facility called the IRNSS Network Timing facility (IRNWT). This paper presents the design and development of an indigenous time scale for NavIC, which has been established and is currently operational at ISRO Navigation Centre (INC-2) at Lucknow. The system engineering aspects including the requirements specification, design, realisation and validation of the In-house Time Scale system (I-TS) is brought out in this paper.I-TS is configured with one Active Hydrogen Maser (AHM) and two standard performance Cesium Clocks and the output is generated through an ensemble of these participating clocks. The hardware and software design aspects of the precise time scale are elaborated. The ensemble and steering algorithms are discussed in depth. The traceability of I-TS time to UTC is discussed. The performance of I-TS is compared with IRNWT-1 and an improvement of 1.5 m in user position was obtained. This improvement is attributed to the new generation maser with better stability characteristics as well as the better performance of the in-house developed steering algorithm by suitable filtering of noisy measurements.