Self-Calibrating Receivers for Precision Phase Observations

S. Ganguly, N. Bhatia, A. Jovancevic, A. Brown, M. Kirchner, D. Saxena, J. Noronha, S. Zigic

Abstract:	With the improvements in digital electronics, the uncertainties or errors in modern navigational receivers are mostly shifted towards the analog sections, i.e. the portion before the digitalization. Current trends are bringing the digitalization closer to the antennas. Nevertheless, significant errors are caused by analog filters, downconverters, and even cables before the digitizers. The phase center displacements in the antennas also contribute in these errors. The amount of these errors is generally small and neglected in most of the receivers. For specialized receivers, such as those involved with phase relationships between multiple antennas (such as those employing CRPA, attitude determination, etc.) or those involving phase relationships between different frequency bands (such as ionospheric measurements, time measurements, etc.), these unknown phase relationships create considerable difficulties. These phase errors also vary with temperature, aging, etc. and a simple factory calibration is not adequate. This is reflected in the uncertainties in ionospheric Total Electron Content (TEC), reported by numerous receivers. The reported TEC values appear to have significant biases, over and above what are assumed for receiver biases. This limits the utility of using TEC values for precise estimation of ionospheric parameters such as those used in tomographic reconstruction. A rather straightforward solution is provided to calibrate the receivers. The software-based receiver developed by CRS performs most of the processing using various digital processors (FPGA, DSPs, and GPPs). These processors are also used for generating an exact replica of satellite signals with known (or without) ionospheric contribution. These built-in simulated signals are used to calibrate the receivers, whenever necessary. We have developed such receivers and present some results describing their performances. Use of these receivers in ionospheric research has demonstrated that TEC accuracies can be obtained with better than 0.1 TECU on a regular basis.
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:	2788 - 2797
Cite this article:	Ganguly, S., Bhatia, N., Jovancevic, A., Brown, A., Kirchner, M., Saxena, D., Noronha, J., Zigic, S., "Self-Calibrating Receivers for Precision Phase Observations," 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. 2788-2797.
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