Comparison of assisted GPS and high sensitivity GPS under weak signal conditions.

摘要

The Federal Communications Commission (FCC) E-911 mandate, Location-Based Services, as well as personal and vehicular navigation applications are among the main forces driving the need for a navigation capability in degraded signal environments such as in urban areas and indoors. Since the positioning accuracy produced by GPS methods is superior to that of other positioning technologies, most wireless carriers are exploring Assisted GPS (AGPS) as a potential strategy for meeting the FCC criteria. In this thesis the performance of AGPS was investigated under various field test conditions as measured through a range of acquisition and tracking tests. Tests were performed in several settings, including: a suburban environment, residential garage, speed-skating track and a steel-reinforced concrete basement. Distinct aiding scenarios were explored to investigate the effects of aiding data on AGPS signal acquisition. Limited simulation tests were also carried out to determine acquisition sensitivity and the effects of different aiding data on AGPS. Simulation tests showed that AGPS had higher sensitivity as compared to high sensitivity GPS (HSGPS) and a standard receiver; it also demonstrated the importance of satellite ephemeris data in terms of factors such as higher sensitivity (11 dB) and lower Time-To-First-Fix (TTFF). The field tests illustrated the limitations of HSGPS; its inability to acquire in weak signal conditions and longer TTFFs in comparison to AGPS. Acquisition tests using AGPS demonstrated the importance of accurate time and position assistance in obtaining a shorter TTFF under weak signal conditions which refer to test sites such as the speed-skating track and the concrete basement. Tracking tests showed similar results for AGPS and HSGPS receivers in terms of factors such as positioning accuracy and solution availability.