Achieving Precise Real-Time GNSS Positioning with Software-based Receivers

D. Lu, Y. Zhang, S. Lee, C. Chen

Abstract:	The objective of this research is to develop a real-time high precision software GNSS receiver. Two crucial topics have been investigated, precise measurement generation and precise autonomous positioning technologies. Multiple correlators are implemented to improve pseudorange measurement quality. Vector bitwise technique has been developed and compared with vector process technique for tracking process. As to precise positioning technique, the Freedom technology developed at Nexteq Navigation, which optimally applies all possible information from GNSS receiver, is integrated into this software implementation for high positioning accuracy. INTRODUCTION Software GNSS receiver has been receiving increasing attention for its advantages like ease of upgrading to support new techniques and GNSS satellite constellation changes (Akos et al 2001, Ledvina et al 2003, Borre et al 2006). The most critical challenge for real time software receivers, heavy computation burden, has been generally solved by increased computation power and techniques such as SIMD, bit-wise operation (Psiaki 2006, Ledvina et al 2004), pre-stored local code and carrier signals. These techniques unfortunately have a tradeoff in terms of speed and the quality of the code and phase measurements. Due to the increased noise and degraded tracking loop stability, measurements obtained from realtime software receivers cannot match the quality as traditional hardware GNSS receivers, which results in a low positioning accuracy for existing real-time GNSS software implementations, typically at several meters level as the instability of the phase tracking loop generally allows only the nosier CA code pseudorange measurement to be reliably employed for positioning. There are few real-time GNSS software receiver products utilizing both CA code pseudorange and carrier phase measurements. However, as the carrier phase measurement is the key measurement for GNSS precise positioning, techniques for real-time high quality code and phase measurement need to be investigated and developed. The implementation of a real-time 12 channel software GPS receiver prototype is presented. It includes the receiver architecture, re-examination of the real-time tracking process technique, measurement improvement, Nexteq Freedom technology and the testing results.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	281 - 287
Cite this article:	Lu, D., Zhang, Y., Lee, S., Chen, C., "Achieving Precise Real-Time GNSS Positioning with Software-based Receivers," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 281-287.
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