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13th Real-Time Linux Workshop from October 20 to 22 at the Faculty of Electrical Engineering, Czech Technical University in Prague

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The Witch Navigator - A Software GNSS Receiver Built on Real-Time Linux

Petr Kacmarik, Czech technical university in Prague, Faculty of electrical engineering, Department of Radio engineering
Pavel Kovar, Czech technical university in Prague, Faculty of electrical engineering, Department of Radio engineering
Ondrej Jakubov, Czech technical university in Prague, Faculty of electrical engineering, Department of Radio engineering
Frantisek Vejrazka, Czech technical university in Prague, Faculty of electrical engineering, Department of Radio engineering

The Witch Navigator (WNav) is an open source project of GNSS (Global Navigation Satellite System) receiver whose hardware is implemented as an ExpressCard hosted in PC with Linux OS.

The employment of PC offers a possibility of an easy implementation of signal processing algorithms since almost no restrictions are introduced by a specific embedded platform (concerning memory requirements or real data type and its arithmetic). As a consequence, the WNav is especially suitable for researchers or students because the signal processing algorithms can there be implemented in a similar manner as in high-level simulations. Furthermore, developers can rely on the wide and well known collection of development tools for Linux on x86 architecture. Unlike similar projects, WNav has capability to achieve performance comparable to professional GNSS receivers.

The WNav receiver is equipped with two front ends which can process any civil GNSS signals on two frequencies simultaneously. The whole receiver task is distributed between the device driver, user space real-time process and other auxiliary processes. The real-time needs are satisfied with RT_PREEMPT kernel patch.

The paper describes the whole conception of WNav with focus on the kernel part (device driver) and the real-time user space process, provides information about the processes synchronization and presents the achieved performance. The first obvious milestone is to develop the fully functional GPS L1 C/A receiver which justifies the selected conception. The achieved results and experience with this legacy signal are presented in the paper, as well.