First Results of a GNSS Signal Generator Using a PC and a Digital-to-Analog Converter

Andrea Pósfay, Thomas Pany and Bernd Eissfeller

Abstract:	Since 2004 at the Institute of Geodesy and Navigation of University FAF Munich a Global Navigation Satellite System (GNSS) signal simulator has been developed. Like in cases of other institutes our motivation was to create a highly flexible, reasonable prized and reliable source of simulated GNSS signals in order to analyze and develop new receiver algorithms and hereby speed up the receiver development for the Global Positioning System (GPS) as well as for the future Galileo system. We present the development of a cost-efficient GNSS signal simulator based on a conventional PC and a commercial digital-to-analogue conversion (DAC) card. The signal simulator is in principle able to simulate arbitrary GNSS signals on arbitrary frequencies. The signals are precomputed for an intermediate frequency (IF) or for baseband on the PC and streamed to the DAC card which converts them to an analogue signal. This signal will be up-converted to RF (e.g. L1 = 1.57542 GHz) in a future project. A GNSS signal simulator is a powerful device, which simulates the received GNSS signal for a given satellite system (e.g. GPS or Galileo) and for a given user antenna trajectory. Satellite system parameters can be changed as well as the signal propagation environment. The benefits of this GNSS IF software signal simulator are demonstrated by two different software simulator applications described in this paper: generation of Galileo signals to make possible interference investigations between GPS and the future Galileo system and of a new BPSK like signal structure (Castle BPSK) to test its properties. In both cases the generated IF signals could be successfully tracked by a software receiver. These experiments show the outstanding benefits of a software based signal simulator: especially its extremely high level of flexibility in contrast to a hardware based signal simulator. To expand the application areas of the software simulator a new chapter of simulation has been started: the conversion of the digital IF samples into an analog signal in order to emit the simulated GNSS signals. The first milestone on this way has been completed. A full-constellation low-bandwidth analogue GPS C/A signal at IF was generated and its properties have been investigated by a spectrum analyzer. The signals could be successfully acquired by feeding it into the analog IF input of the software receiver.
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:	1861 - 1870
Cite this article:	Pósfay, Andrea, Pany, Thomas, Eissfeller, Bernd, "First Results of a GNSS Signal Generator Using a PC and a Digital-to-Analog Converter," 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. 1861-1870.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In