A High Performance GPS Solution for Mobile Use

Katsuyuki Tanaka, Takayasu Muto, Katsuya Hori, Mikio Wakamori, Koichiro Teranishi, Hideki Takahashi, Masayuki Sawada and Matt Ronning

Abstract:	Modern mobile GPS receivers must realize small size, low power, low cost, rapid positioning, and high sensitivity. To meet these requirements, a GPS receiver prototype System on Chip (SoC) has been developed and is described in this paper. Unlike conventional GPS receivers, our new baseband block has distinct acquisition and tracking units which process the digitized IF signal separately. The acquisition unit correlates, in coarse resolution, the IF signal and a replica of the C/A code. Then, from the correlation results, the tracking unit tracks the C/A code and the carrier, and calculates, in fine resolution, the pseudorange and Doppler shift frequency. To hasten the acquisition process, the acquisition unit applies the digital matched filter technique. Acquisition sensitivity can be improved greatly with continuous correlation in real-time. The results of the acquisition unit - the satellite number, phase of their C/A code, IF carrier frequency, and signal strength - are transferred to the tracking unit by the CPU. The tracking unit contains 12 tracking loops, each comprised of a delay lock loop (DLL) and a Costas Loop, as in a conventional GPS receiver. The tracking unit differs from convention in that its initial state is obtained from the acquisition unit, which is reasonably accurate. Due to this initialization, a narrower despread signal low pass filter (LPF) bandwidth and a longer correlation integration time is available on startup. This endows the GPS receiver with high sensitivity. The tracking unit is also capable of dynamically adjusting the LPF’s despread signal bandwidth and the DLL and Costas loop’s loop bandwidth according to signal strength. Thus, the tracking loop can respond to high acceleration. The frequency of the TCXO that drives the prototype SoC is customizable. This feature is realized by a flexible implementation of the baseband block. Test results indicate significant improvement in automobile and indoor positioning availability.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1648 - 1655
Cite this article:	Tanaka, Katsuyuki, Muto, Takayasu, Hori, Katsuya, Wakamori, Mikio, Teranishi, Koichiro, Takahashi, Hideki, Sawada, Masayuki, Ronning, Matt, "A High Performance GPS Solution for Mobile Use," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1648-1655.
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