Design and Testing of an Advanced Eurofix Demodulator

Design and Testing of an Advanced Eurofix Demodulator

Helwig, A.W.S.

Van Willigen, D. (mentor)
Offermans, G.W.A. (mentor)

Electrical Engineering, Mathematics and Computer Science

Telecommunicatie- en Verkeersbegeleidingssystemen

1995-11

In the Eurofix system, DGPS corrections are transmitted using an already existing infrastructure: the Loran-C system. Primarily, this provides a cost-effective way to supply coverage for DGPS-corrections over a large area. Secondly, the use of the Loran-C navigation system in combination with normal GPS will yield a combined system with improved integrity and availability. In this report, the capabilities of the Eurofix datalink are investigated. The goal is to optimize the datalink for speed and error-rate. Both 2-level and 3-level Eurofix coding are investigated. The Eurofix datalink is a difficult one: there is a number of factors limiting the performance. The largest reduction in performance is caused by a phenomenon that is inherent to the way that Loran-C operates: Cross-rate. Secondly, atmospheric effects can overpower the normal Loran-C signal. A method is devised to detect whether individual Loran-C pulses are distorted by Cross-rate or severe atmospheric conditions. Then, a demodulation scheme is presented that is capable of demodulating both 2- and 3-level Eurofix modulation. A new method of testing is developed that allows normal (unmodulated) Loran-C signals to appear to the demodulator under test as if they were modulated. This method is very realistic. The 2-level coding scheme gives a lower pulse error rate than the 3-level coding scheme. On the other hand, the transmitted Loran-C signals can be more balanced with 3-level than with 2-level modulation. Distortion detecting certainly prevents the demodulator from making incorrect decisions. Since it is easier for an error-correcting code to deal with erasures than with errors, distortion detection will improve the performance of the Eurofix datalink. The proposed demodulator works as expected. It is difficult, however, to develop a theoretical model that accounts for all effects to which the Eurofix datalink is subjected.

Eurofix
Loran-C
Linear cross-correlation demodulation
Distortion detection

http://resolver.tudelft.nl/uuid:e05f8946-8cb8-45b9-be4e-10997393c703

Student theses

master thesis

(c) 1995 A.W.S. Helwig