Trajectory-based services require continuous user location
sensing. GPS is the most common outdoor location sensor
on mobile devices. However, the high energy consumption
of GPS sensing prohibits it to be used continuously in many
applications. In this paper, we propose a Low Energy Assisted
Positioning (LEAP) solution that carefully partitions
the GPS signal processing pipeline and shifts delay tolerant
position calculations to the cloud. The GPS receiver only
needs to be on for less than a second to collect the submillisecond
level propagation delay for each satellites signal.
With a reference to a nearby object, such as a cell tower, the
LEAP server can infer the rest of the information necessary
to perform GPS position calculation. We analyze the accuracy
and energy benefit of LEAP and use real user traces to
show that LEAP can save up to 80% GPS energy consumption
in typical trajectory-based service scenarios.