Intelligent Transportation Systems (ITS) require reliable location information with emphasis being put on sensor level integration and low power consumption. The Global Positioning System (GPS) has been proposed as a potential technology to provide this information but has been hampered by poor performance (in urban environments) and power hungry board level solutions. Increased pressure on in-vehicle sensor power consumption has driven SiRF Technology Inc. to develop the SiRFstar1/LX GPS chip set (GSP1LX and GRF1LX). This improved chip set architecture enables lower power consumption without sacrificing tracking or navigation performance specifically in difficult urban canyons.
Most GPS systems have been designed as stand-alone board level solutions that can be used in high-level system integration. Recent advances in silicon, GPS chipset architecture and software technology have enabled new methods to increase the signal availability (through rapid signal acquisition), accuracy and use of GPS solutions in difficult satellite tracking environments (using 1or 2 satellites for updates). Taking advantage of already on board memory and processors, chip level integration of navigation technology can be achieved.
The improvements to the GSP1 (175 ma @ 5 v) digital chip to the low power version, GPS1LX (50 ma @ 3.3 V) created an decrease in required power by 71 %. The GRF1LX chip (55 Ma @ 3.3 V) enjoys a decrease in power consumption by over 15 % compared to its predecessor the GRF1 (65 ma @ 5V) for a combined overall decrease of 71 % for the SiRFstarI/LX while maintaining continuous 1Hz measurements and all enhanced features of the receiver.
To ensure that the previously achieved benchmarks for tracking and performance set by the SiRFstarI (GSP1, GRF1) were not degraded due to lower power versions SiRFstarI/LX, a test vehicle was used to collect GPS position data under normal traffic conditions in downtown San Francisco (a difficult urban area for signal reception). To ensure fairness of performance, several platforms well as competitive GPS receivers were operated under the same navigation environment. The data was then analyzed under varying scenarios to investigate the ability of this Low power generation GPS technology to provide similar performance to the SiRFstarI and superior performance to the competition.
Multiple test data will show that the navigation solution availability with the SiRFstarI and the SiRFstarI/LX GPS receiver maintain the near 100 percent contiguous coverage. Other GPS receivers tested showed lesser navigation availability under the same conditions.
These results were obtained in a GPS only environment with further improvements expected through data sharing via vehicle motion sensors and spatial map information. The results and architecture used for these tests demonstrate the feasibility of the SiRFstarI/LX GPS receiver as a low power, reliable navigation component for vehicle location information as part of an ITS system.