On Differential Demodulation in GNSS Receivers

S. Rao

Abstract:	All GNSS satellites transmit navigation information. For a receiver to be able to operate autonomously, it is critical that the receiver be able to demodulate and decode this information under a wide range of channel conditions. Demodulation at the receiver can either be (a) coherent or (b) differential. Differential demodulation eases the carrier synchronization requirements at the receiver and thus allows for more choices in the cost performance trade off. Also as explained in this paper, differential demodulation can allow GNSS receivers to operate at Signal to Noise ratios that are below the operating range of the receivers synchronization mechanisms. Consequently, differential demodulation is an important tool in the design of the physical layer of the GNSS receiver. Differential demodulation architectures are currently commonly employed in GPS receivers. However, as explained in this paper, these techniques cannot be used to demodulate and decode signals from other GNSS satellites such as Galileo, WAAS where the navigation data is channel coded. The paper explains this problem, and introduces a novel frame work to solve the problem. The solution in the case of Galileo and WAAS signals is presented. More generally, the framework introduced in this paper will aid in the analysis and development of channel coding schemes for GNSS systems that are ‘friendly’ to both coherent and differential demodulators.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2867 - 2874
Cite this article:	Rao, S., "On Differential Demodulation in GNSS Receivers," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2867-2874.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In