Evaluation of L2C Observations and Limitations

O. al-Fanek, S. Skone, G. Lachapelle and P. Fenton

Abstract:	With the recent launch of Block IIR-M satellites and modernization of the GPS, a new L2C signal has been introduced for civilian applications. It is anticipated that ranging measurements on L2C will offer improved observation quality and independent tracking performance, as compared with L2 semicodeless observations. PRN 17 with L2C capabilities was launched in late 2005, with PRN 31 and PRN 12 following in late 2006. In order to make use of new L2C observations in conjunction with legacy L2 P(Y) a number of issues must be resolved. Due to differences in code modulation offsets (L2C versus L2 P(Y)) a satellite- and receiver-dependent differential code C2-P2 bias arises that must be quantified and accounted for. Additionally, the tracking noise and multipath characteristics of L2C observations are expected to be similar to those for the C/A code. An investigation of L2C observation quality and robustness is necessary to assess potential capabilities of exploiting these new measurements. NovAtel OEMV3 receivers with L2C tracking capabilities, and equipped with specialized firmware that allows acquisition of both L2C and L2 semicodeless observations for a given satellite using a single receiver, are used. At present observations from as many as three Block IIR-M satellites are available simultaneously in Calgary, allowing inter-satellite comparisons. Zerobaseline tests and inter-receiver comparisons are conducted using live data for the Block IIR-M satellites currently available, in order to assess the quality of L2C versus L1C/A and L2 semicodeless observations. In this paper, investigations of phase and code observation quality for the L2C signals are presented. Zero-baseline tests are conducted with multiple receivers to assess measurement noise, and linear code-phase combinations are used to compute multipath statistics. Tracking performance is assessed for degraded signal strengths – to determine performance under challenging scenarios such as weak signal environments. Differential code biases (C2-P2) are determined, and the limitations in combining new L2C observations with legacy L2 P(Y) are assessed for practical implementations.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2510 - 2518
Cite this article:	al-Fanek, O., Skone, S., Lachapelle, G., Fenton, P., "Evaluation of L2C Observations and Limitations," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2510-2518.
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