Energy saving techniques for GPS based tracking applications

Several GPS based positioning and tracking applications need to be very conservative in terms of energy consumption. Some of these applications can even compromise on real time performance and accuracy to lower energy consumption. In the process of acquiring a GPS location fix, the GPS ephemeris download takes a long time, especially in poor GPS signal conditions, hence forming a significant component of the energy consumption of GPS receiver systems. This is one of the major reasons for the GPS receivers to perform poorly under thick coverage like foliage and concrete. The ephemeris acquisition problems were prominently observed during the development of a low power elephant tracking collar using GPS and GSM. Currently, assisted GPS or AGPS is used to solve this problem where GSM connectivity is available. Here, ephemeris is fed via the GSM network. But existing AGPS systems do not work in remote areas where mobile networks do not provide coverage. Other augmentation systems like Wide Area Augmentation System (WAAS) focus primarily on improving the accuracy and reliability of the GPS fix but do not help in getting a faster GPS fix. In this paper various methods to reduce the Time-To-First-Fix (TTFF) by avoiding ephemeris download are proposed, thus reducing energy consumption.