GPS Receiver With Soft-correlator Approach for Leo-Orbits

G. Vyasaraj, R. Vishwanath, R. Nayak

Abstract:	Autonomous onboard navigation system has become an essential requirement for the Low Earth Orbit satellites with the increase in the constellation density. The system helps in continuously monitoring the satellite navigation without the ground support, reducing the operational cost of the system. Main considerations for the commercial satellites are cost effective, high reliability navigation system with minimal power consumption. This paper presents a novel approach for the onboard navigation system called SOFT-GPS (receiver). This receiver is a C/A code GPS receiver that computes the real time state vectors of the satellite. SOFT-GPS, as the name suggests uses a soft correlator approach for the acquisition, tracking and the data bit demodulation for the GPS signals. The receiver is a standalone system in the sense that it does not depend on any external aid. It is characterized by very short time to first fix in cold start mode. Receiver should accommodate for the high dynamics of the satellite, which demands higher order tracking loops with relatively more bandwidth and large computation power from the processor end. The receiver is equipped with inbuilt fault detection and automatic fault recovery mechanism to take care of the on orbit problems. SOFT-GPS can be used for synchronizing the onboard applications with the precise clock generated and also by another special technique, which reduces the hardware of the onboard computer sub-system. SOFTGPS also has the provision of storing the on-orbit data at a pre-defined rate so that the same can be downloaded when the satellite passes over a ground tracking station. The system also has various interface schemes, compatible with the ground stations. This paper explains in detail the receiver hardware, the techniques used to accomplish the requirements for high signal dynamics and testing philosophy.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	2555 - 2562
Cite this article:	Vyasaraj, G., Vishwanath, R., Nayak, R., "GPS Receiver With Soft-correlator Approach for Leo-Orbits," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 2555-2562.
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