Analysis, Modelling and Mitigation of Cross-Rate Interference in eLoran

J. Safar, P. Williams, A. Grant, F. Vejrazka

Peer Reviewed

Abstract: The General Lighthouse Authorities of the UK and Ireland (GLA) have selected eLoran as the most cost-effective way of complementing GNSS to provide resilient Positioning, Navigation and Timing (PNT) within their waters. The GLA has established eLoran Initial Operational Capability (IOC) in the seven busiest UK ports and port approaches along the east coast. It is anticipated that the GLA eLoran service will expand to cover all of the waters around the United Kingdom and Ireland, including the English Channel as part of the system’s Final Operational Capability (FOC). This will require a number of new transmitting stations to be installed, which must work with those already in situ. Recent developments in new technology transmitters have created the potential for cost-effective eLoran signal provision. However, due to the nature of eLoran transmissions new stations can contribute as sources of interference which is often referred to as Cross-Rate Interference (CRI), and, if left uncompensated, is one of the major sources of measurement error. This paper reports on some of the findings of a PhD study which investigated the impact of CRI on the positioning accuracy of eLoran and explored ways of mitigating this impact through modern receiver signal processing and the judicious choice of the signal Group Repetition Intervals (GRI). The paper starts with a review of the eLoran signal specification and a discussion of the key characteristics of the eLoran radio channel. A received signal model is formulated and an optimal receiver structure is proposed based on the principles of Maximum Likelihood estimation. Special attention is paid to modern receiver CRI mitigation algorithms – CRI blanking and CRI cancelling. Based on the proposed signal and receiver models, a set of analytical models are derived describing the pseudorange and positioning error under a variety of noise and interference conditions and different receiver modes. The analytical approach yields closed-form results and provides a valuable insight into the nature of CRI in eLoran systems. The analytical models are verified by computer simulations performed in the Simulink® and MATLAB® environment. The models are further validated against the results of receiver test bench and field experiments involving commercially available eLoran equipment. The paper also details the design and development of an eLoran signal simulator used as part of this study in order to enable the receiver testing under controlled radio conditions. Finally, the paper illustrates the application of the developed approach to improve eLoran coverage and performance prediction and optimal GRI selection for new transmitting stations.
Published in: Proceedings of the 2015 International Technical Meeting of The Institute of Navigation
January 26 - 28, 2015
Laguna Cliffs Marriott
Dana Point, California
Pages: 1 - 26
Cite this article: Safar, J., Williams, P., Grant, A., Vejrazka, F., "Analysis, Modelling and Mitigation of Cross-Rate Interference in eLoran," Proceedings of the 2015 International Technical Meeting of The Institute of Navigation, Dana Point, California, January 2015, pp. 1-26.
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