  Integrated GPS receivers have become a basic module in today's mobile
devices. While serving as the cornerstone for location based services, GPS
modules have a serious battery drain problem due to high computation load. This
paper aims to reveal the impact of key software parameters on hardware energy
consumption, by establishing an energy model for a standard GPS receiver
architecture as found in both academic and industrial designs. In particular,
our measurements show that the receiver's energy consumption is in large part
linear with the number of tracked satellites. This leads to a design of
selective tracking algorithm that provides similar positioning accuracy (around
12m) with a subset of selected satellites, which translates to an energy saving
of 20.9-23.1\% on the Namuru board.
