An Experimental Multi Band Receiver for the German Galileo Test Environment (GATE)

Thorsten Luck, Michael Bodenbach, Jon Winkel and Frank Forster

Abstract:	For the purpose of pre Galileo system verification and testing, the Galileo Test Environment (GATE) is setup in the German Alps to reproduce a realistic test bed for the Galileo satellite navigation system. In fact, a complete miniature navigation system is built up consisting of a control, ground and pseudo-space segment. For system monitoring and testing a receiver is required, which is capable of processing all signals specified in the Galileo system specification. To prove interoperability and for reference purposes the receiver will also process Galileo and GPS signals on L1 in a common processing chain. This paper describes a modular receiver design, developed for the use as a user receiver as well as a system monitor receiver. The receiver is based on a PXI computer framework where the slot zero controller serves as the navigation processor and user interface. Up to three single band receivers with radiofrequency front end and base band processor occupy up to nine slots of the PXI framework to serve any of the Galileo radiofrequency bands E5, E6 and L1. As the base band units are FPGA based, all units are equally designed. To reduce cost the three receiver front-ends have an identical PCB-layout. LO-frequencies and filter characteristics distinguish individual front-end boards. As the whole E5- band including the first side slopes of both E5a and E5b is to be received with one of the three front-ends (AltBOC mode) the requirements on amplitude and group delay flatness in the passband are challenging. The very high bandwidth requires high performance components and a careful design. For the other two bands the bandwidth is more relaxed. All three front-ends have a low-IF architecture with a single analog mixer stage and filter stages that differ for each frequency band in the RF- and IF-domain, respectively. For the subsequent A/D-converter jitter is a major concern. While sampling the clock has to exhibit ultra low jitter in order to prevent degradation of the received signal. The digitized signal is converted to base-band and the sample rate is adapted before delivering to the base-band board. The front-end for each band consists of two PCBboards, which are attached to the baseband board. Together they are placed in the PXI computer framework. Selection of the band to serve is performed by software through programming the appropriate configuration file onto the base-band field programmable gate arrays (FPGA). Two gate arrays of the latest Virtex 4 family are used for the base-band processing. They provide up to thirty channels with up to five correlators each, controlled by embedded microcontrollers (IBM PowerPC). Both gate array and associated microcontroller can be configured independently within the same RF-band allowing to track GPS and Galileo/GATE signals simultaneously on one base-band board. Different tracking methods for BOC, AltBOC signals or combined in phase and quadrature phase signal tracking algorithms are also implemented. All base band boards use the same clock signal provided by a rear PXI backplane mounted oscillator. The oscillator module can be either a rubidium or a temperature compensated crystal oscillator (TCXO) module depending upon the application and requirements. Making use of dedicated clock lines of the PXI backplane, the clock signal is distributed to all receivers providing coherent clocking of all processing modules. To synchronize the local clocks of all receivers, a specialized PXI line is used to distribute a central signal, which triggers the pseudo range measurement on all receiver boards. Using a dedicated eight-bit bus for PXI cross-slot communication, the local clocks of all boards are synchronized to each other. Each receiver board is addressable through the PXI bus. The main controller of each board is embedded in a fourth FPGA, running a Linux operating system. This offers great flexibility and allows addressing and configuring the receiver using standard protocols as TCP/IP or even HTTP and XML.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1896 - 1905
Cite this article:	Luck, Thorsten, Bodenbach, Michael, Winkel, Jon, Forster, Frank, "An Experimental Multi Band Receiver for the German Galileo Test Environment (GATE)," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1896-1905.
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