eNav: Smartphone-based Energy Efficient Location Sensing for Low-Power Vehicular Navigation

This paper presents eNav, a smartphone-based vehicular GPS navigation system that has an energy-saving location sensing mode capable of drastically reducing navigation energy needs. Traditional navigation systems sample the phone GPS at a fixed rate (usually around 1Hz), regardless of factors such as current vehicle speed and distance from the next navigation waypoint. This practice results in a large energy consumption and unnecessarily reduces the attainable length of a navigation session, if the phone is left unplugged. According to a survey we conducted of 500 drivers, more than 37% said they ran out of battery while using a phone for navigation, and as much as 91% said they would like to have a vehicular navigation application with an energy saving mode. To meet this need, eNav exploits on-board accelerometers for approximate location sensing when the vehicle is sufficiently far from the next navigation waypoint (or is stopped), while using actual GPS sampling only when an accurate estimate is needed. A user test-study of eNav shows that it reduces navigation energy consumption by around 80% without compromising navigation quality and user experience. The paper contributes to low-power location sensing in the context of phone-based vehicular navigation.