A C/A Code GPS-Receiver for Navigation

des Instituts für Geodäsie

Heft 20-1/1985

A C/A Code GPS-Receiver for Navigation

Wolfgang BEIER
Standard Elektrik Lorenz AG, Stuttgart


In: WELSCH, Walter M. / LAPINE, Lewis A. (Hrsg.) [1985]:
International Federation of Surveyors - FIG -
Proceedings Inertial, Doppler and GPS Measurements for National and Engineering Surveys
Joint Meeting of Study Groups 5B and 5C, July 1-3, 1985

Schriftenreihe Universitärer Studiengang Vermessungswesen, Universität der Bundeswehr München, Heft 20-1, Neubiberg, S. 241-255.


A lab model of a 1.5-channel C/A code GPS-receiver was developed in 1983 and 1984. For this receiver analogue correlation and tracking circuitry was used in both channels. The hardware was mainly intended as testbed to enable the accumulation of the GPS software know-how. This includes the processing of the GPS message, the measured data as well as the computations to determine the position and the navigation data for a mobile user. To determine the position four measured pseudoranges (or three pseudoranges for known altitude) are used together with dead reckoning using the velocity as derived from the measured doppler of the satellite signals. The measured accuracy of 40 m (SEP) is as expected for a C/A code receiver.

In a follow on effort the software was extended to determine position updates by means of a Kalman filter using measured pseudoranges to individual satellites. This eliminates the need for simultaneous visibility of 4 (or 3) satellites to enable the determination of a new position and improves the performance of the receiver when the visibility of single satellites is not given from time to time as it may happen due to constructions, trees etc. This improvement was verified by simulations which demonstrated the benefits of the new software for operational receivers.

A condition for the improvement of the hardware towards reduced cost, was the application of a new receiver concept. By means of early digitalisation a maximum of functions could be performed by programmable circuits. This reduced the number of functions needed within the RF part of the receiver, and a simple RF part is the main key for low production costs. The new concept was validated by means of experimental and theoretical investigations. The receiver can be packed into a volume comparable to that of a car radio. Using general terminology the receiver is characterized and decodes the data of four satellites to determine the position and navigation data.

An interesting feature of the receiver is that it reconstructs simultaneously the carrier phases and the pseudoranges of the four satellites.


This work was supported by the Bundesministerium für Forschung und Technologie.

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