GPS Capability in Power Sensitive ITS Applications 1999-01-2954
As the Intelligent Transportation Systems (ITS) industry grows in both commercial and industrial applications, so does the need for power efficient components used in providing position and timing information. The Global Positioning System (GPS) is fast becoming the technology of choice as significant performance improvements have been demonstrated in recent years (1. Turetzky et al, 1997, 3. Gehue et al. 1998). GPS related ITS applications can perform adequately in even the toughest of conditions such as dense foliage and urban canyons.
The next identified hurdle in many ITS systems is a higher level of integration and power efficient operation. A low power version of the SiRFstarI (SiRFstarI/LX) chipset has been developed by SiRF Technology Inc. of Santa Clara, California to address the expectations of future ITS integrated systems. This innovated architecture provided an initial decrease in operational power by moving from a 0.5 micron to 0.35 micron process (4.Gehue et al, 1998) with no degradation in performance.
Current receiver designs draw approximately 150 ma (nominal), but in power saving modes this can be reduced significantly (< 25 ma) for intermittent updates allowing ultra low power (Trickle Power™) applications. This is possible by exploiting the 100 ms signal re-acquisition capability unique to the SiRFstarI/LX chipset allowing the GPS receiver to turn off key components once they have completed their task (2.Turetzky et al, 1997). This ultra low power operation ushers in new opportunities for applications such as asset tracking and fleet management as well as the possibility of long term battery powered applications such as containers, trailers, road side traffic monitoring systems etc. where periodic position information is required.
There is now a decision requirement of performance versus power consumption that is very much application dependent. Performance evaluation of the SiRFstarI/LX chip set under urban canyon, dense foliage and open sky environments is being investigated so that optimal selection for the application can be identified. The accuracy and integrity of navigation data as a function of low power settings and data rates will set a baseline for many ITSapplications. Smart software also allows the changing of low power modes to address changing conditions or dynamics of the application.
