Ultra-stable Oscillators: Limits of GNSS Coherent Integration

Pascal O. Gaggero, Daniele Borio

Abstract:	Oscillators are indispensable hardware components of many RF circuits and wireless systems whose precision has continuously increased in the last few decades. The development of such ultra-stable oscillators has motivated the design of reliable techniques for assessing their performance. Global Navigation Satellite Systems (GNSSs) provide an extremely accurate frequency reference, indispensable for precise positioning. This reference is freely available to the user and therefore can be used for assessing the oscillator performance. In this work a wide set of high quality oscillators, manufactured by the Swiss companies Oscilloquartz, Fordahl and Micro Crystal, has been analyzed by using the GPS signal as frequency reference. GPS L1 samples have been collected using a front-end driven by the oscillator under test, post-processed and analyzed by custom developed software. Several frequency errors, such as Doppler frequency and bit transitions have been removed possibly leaving only the errors induced by the local and satellite’s oscillators. Perfect frequency sources would have led to an accumulated power linearly growing with the integration time. The appearance of artifacts and the saturation of the accumulated power reveal the limits of the considered oscillators. If the local oscillator is ultra-precise, extremely long coherent integrations are possible allowing indoor positioning. More specifically coherent integrations longer than one minute have been obtained and used for indoor location in the context of Assisted GPS under attenuated signal conditions of up to 45 dB.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	565 - 575
Cite this article:	Gaggero, Pascal O., Borio, Daniele, "Ultra-stable Oscillators: Limits of GNSS Coherent Integration," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 565-575.
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