Considerations for Calibration of Frequency Dependent Delays

Andrew Cartmell

Abstract:	Frequency dependent delays are a problem long associ- ated with measurements from the Global Orbiting Navigation Satellite System (GLONASS). The delays occur within the analogue components of a Global Navigation Satellite System (GNSS) receiver. GLONASS satellites transmit at different frequency channels and signals from each satellite will experience a different delay, resulting in errors between range measurements. Global Positioning System (GPS) satellites all transmit at the same frequency, each satellite signal will therefore experience the same delay. This paper identifies the individual delays that are present on GNSS measurements due to the analogue components in the receive chain and investigates the characteristics of each with respect to signal frequency. It is described how the delays experienced by a GNSS signal are dependent on the signal frequency and bandwidth. The impact of the delays on GNSS applications is addressed using exam- ples. Current techniques to reduce the delays are detailed and are described to be limited by the unknown stability of the delays. A novel extension to the calibration signal tech- nique, to continually measure the delays without interrupting tracking of the GNSS signals, is highlighted as a potential solution to this problem. Important considerations when designing such a calibra- tion system are addressed, with the most important being the accurate duplication of the GNSS signals. This paper also details the calibration code selection and generation, analogue and digital modulation schemes, attenuation levels, and combining of the calibration and GNSS sig- nals. The calibration signal described is shown to require only minimal modifications to the receiver design. Initial calibration results obtained using this signal are provided. These include an assessment of the duplicate GNSS signal and show that the calibrated double differ- ence biases are typically less than a nanosecond.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	799 - 809
Cite this article:	Cartmell, Andrew, "Considerations for Calibration of Frequency Dependent Delays," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 799-809.
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