An Ultra-Sensitive Software GPS Receiver for Timing and Positioning

N. Kishimoto, J. Vavrus, L.R. Weill

Abstract:	This paper describes the latest achievement by Magellan Systems Japan in high-sensitivity GPS technology, an ultrasensitive software assisted GPS (AGPS) receiver for selected timing and positioning applications. A major application area is provision of accurate time for fixed Femtocell and Picocell base stations which are located indoors and typically have very weak GPS signal reception. In these applications the base station is at a fixed location and the receiver undergoes no dynamics. The receiver is designed to provide excellent weak-signal reception at low cost and to be adaptable to many platforms. Since all signal processing is executed in software, all that is needed for full operation is an antenna, conventional RF module with a TCXO, and a host microprocessor in which the software is embedded. Extensive testing of this system with both GPS signal simulators and off-the-air signals has shown that acquisition of ?163 dBm signals (C/N0 = 11 dB-Hz) can occur when assisting with the small time and/or frequency uncertainty characteristic of typical CDMA AGPS systems. On the other hand, reliable acquisition of ?160 dBm signals has been demonstrated with assisting information coming only from the internet and having much larger uncertainties. In both cases signals at ?163 dBm can be tracked. Unlike many high-sensitivity receiver designs, there is no reliance on at least one relatively strong signal to enable acquisition. However, if any strong signals are found, the acquisition search strategy subsequently takes advantage of them to reduce the time to first fix (TTFF). For high acquisition sensitivity, the receiver uses both longterm coherent processing and a final stage of non-coherent processing. The design has features which greatly reduce two well-known difficulties inherent in long-term coherent processing, which are signal-to-noise ratio (SNR) loss due to TCXO phase instability and increased false alarm probability due to a large number of frequency search cells. Additionally, the extreme sensitivity of the system has been enabled by an innovative combination of pseudorange quality algorithms. Sufficient time transfer accuracy for Femtocell and Picocell applications (at the microsecond level) is also achieved. The software is highly optimized to reduce computational demands imposed by the large amount of throughput required for acquisition in applications with larger time and frequency uncertainties in the assisting data.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	448 - 463
Cite this article:	Kishimoto, N., Vavrus, J., Weill, L.R., "An Ultra-Sensitive Software GPS Receiver for Timing and Positioning," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 448-463.
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