Network and Systems Laboratorynslab.ee.ntu.edu.tw

Energy-Accuracy Trade-off for Continuous Mobile Device Location

Kaisen Lin, Aman Kansal, Dimitrios Lymberopoulos, and Feng Zhao

Archiang

Network and Systems Laboratorynslab.ee.ntu.edu.tw

OutlineIntroductionSystem OverviewSystem DesignExperiments and EvaluationConclusions

Network and Systems Laboratorynslab.ee.ntu.edu.tw

IntroductionPopular mobile localization resource

GPS, WiFi, Cell-tower ID, BluetoothContinuous and ubiquitous location access aren’t

available due to energy constraint

Using multiple location sensors simultaneously to make up for this variability in accuracy would further increase energy use.Tradeoff between energy and accuracy

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Goal: a system that automatically manages location sensor availability, accuracy, and energy.GPS, WiFi, Cell-tower ID, BluetoothOpen sky view locations, availability and accuracy.Static and mobile

ExamplePizza stores in PortlandShoppingFinding friends

a - Loc

Network and Systems Laboratorynslab.ee.ntu.edu.tw

System Overview Bayesian estimation

Combine the sensor data and predicted location to provide a ML estimation

Discretization A-Loc uses a 10m step size for space

discretization. A-Loc uses time granularity of 1 minute

Training

Network and Systems Laboratorynslab.ee.ntu.edu.tw

System DesignGPS, WiFi, Bluetooth, and cell-tower

on Android G1 and AT&T Tilt phones

Accuracy Models

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Energy Models

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Selection Algorithm The goal of the selection algorithm

is to determine the most energy efficient sensor to be used, such that the required location accuracy can be achieved.

This algorithm also maintains an estimate of the user’s location that is based on a prediction of user movements.

Use Hidden Markov Model (HMM)

Network and Systems Laboratorynslab.ee.ntu.edu.tw

Experiments and EvaluationPrototype Implementation

Android’s LocationManager API

Application Accuracy Requirement

Network and Systems Laboratorynslab.ee.ntu.edu.tw

System PerformanceAccuracy requirement

A-Loc compares withStatic

Least energy consumptionPeriodicPerfect Models

Best resolution

Network and Systems Laboratorynslab.ee.ntu.edu.tw

In San Diego

Network and Systems Laboratorynslab.ee.ntu.edu.tw

In Portland

Network and Systems Laboratorynslab.ee.ntu.edu.tw

ConclusionsThe authors present a-Loc system that can automatically

tunne the location energy and accuracy trade-off by continually adapting to the dynamic location sensor characteristics and application needs.

A-Loc provides significant energy savings that go beyond existing techniques.