Pseudolites – A Means to Enhance the Applicability of GNSS to Municipal Areas

Christian Altmayer

Abstract:	As GPS was declared operational in 1995 and now extends even into personal navigation, the usage of GNSS in urban environments for navigation with centimeter-accuracy becomes more and more pressing. Unfortunately, urban canyons causing shadowing and multipath represent an adverse environment for GNSS signal reception, thus leading to poor satellite visibility and low positioning accuracy. To overcome poor availability pseudolites can be set up to provide additional ranging signals and aid the carrier phase ambiguity resolution which is crucial for utilizing the full accuracy capability of GNSS. A pseudolite system was developed at the Institute of Flight Guidance and Control consisting of low-cost components such as PC-embedded L1 GPS signal generator cards and low-cost GPS receivers. The pseudolites transmit on L1 and are supplied with an inexpensive free-running clock requiring a compensation scheme which is realized by a monitoring receiver that also acts as a differential station. A typical urban test area was chosen to provide the demanding adverse conditions. Field tests showed that the availability of ranging signals is substantially increased and that the pseudolite range accuracies correspond to the standard DGPS capability of the used low-cost receiver. Antenna diagram shaping was performed to mitigate the near-far problem. The experiments also revealed the necessity to use the carrier phase observable to deal with multipath effects and provide highest accuracy.
Published in:	Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999) June 27 - 30, 1999 Royal Sonesta Hotel Cambridge, MA
Pages:	515 - 524
Cite this article:	Altmayer, Christian, "Pseudolites – A Means to Enhance the Applicability of GNSS to Municipal Areas," Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999), Cambridge, MA, June 1999, pp. 515-524.
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