Use of DGPS corrections with low power GPS receivers in a post SA environment

Abstract

With the removal of the dithering effects of Selective Availability (SA), use of Differential GPS (DGPS) corrections can now be applied for extended periods of time allowing enhanced performance for low power configurations of a Si RF based GPS receiver. The software selectable low power settings, implemented by Si RF, employ three states; track, navigate and trickle. During track and trickle states there is no UART communication making reception of DGPS correction unavailable. During the NAV state (when the navigation calculation is performed), corrections may be received. Previously, SA induced error shortened the viable extrapolation time to less than 30 seconds; else significant navigation error would build up between measurements. Additionally, the need to return to a full power state every 30 seconds significantly increased the overall average power dissipation over standard TricklePower/sup TM/ operation. Now that SA (the dominate error source of the DGPS correction) has been removed, the time limit that a DGPS correction can be applied has been extended from 30 seconds to several minutes without significant degradation in navigation performance. This opens up opportunity for low power GPS receiver operation to make use of the DGPS correction to improve navigation without severely impacting the average power requirements. Si RF's implementations of low power operation, leverages off its unique architecture that allows 100 ms signal reacquisition allowing a pseudorange measurement to as little 200 ms. The chipset is then shut down for 800 ms, significantly reducing the power consumption, while still maintaining 1 Hz navigation updates.