Presented by: Z.G. Huang May 04, 2011 Did You See Bob? Human Localization using Mobile Phones Romit Roy Choudhury Duke University Durham, NC, USA Ionut ConstandacheXuan BaoMartin Azizyan

Content The issue Current solutions Escort  Main idea of Escort  Challenges  Solutions  Evaluation  Results  Future Work

The issue It can be difficult to find someone in a public place.  Might not know their location  Might be unfamiliar with the area  Maps not always available

Hypothetical Scenario Mobicom – in a big hotel Alice wants to meet her colleague Bob…  Can walk around  Can ask “Did you see Bob?” But these can take a long time and he may be moving  Can call him But he may be in a meeting already Best to have someone escort you… How?

Current Solutions GPS  Drains the battery WiFi/GSM schemes  Not enough accuracy Also, localization services do not provide directions to particular people The authors propose “Escort”: a software which navigates a user to the person she is looking for

Escort Escort does not require:  GPS  signal calibration  maps  floor plans  knowledge of user ’ s absolute location Can be easily implemented

Outline Motivation Recap:  We need efficient and accurate software for people localization: Escort Outline  Main idea of Escort  Challenges  Solutions  Evaluation  Results  Future Work

Main idea Escort consists of two parts:  Navigation Get directions to the person  Visual Identification

Main idea - Navigation Mobile phones capture “movement traces”  A(t), B(t), C(t) Record time-stamp of “encounters”  T_AC, T_BC Reports sent to server  Global view of users’ positions and paths Suppose A wants to find B… A(t) B(t) C(t) T_AC T_BC

Outline Motivation Recap:  We need efficient and accurate software for people localization: Escort Outline  Main idea of Escort  Challenges  Solutions  Evaluation  Results  Future Work

Challenges Accelerometers & Compasses are noisy  Measured path error grows over time No global reference frame  How to correct errors? Even if correct user position, difficult to correct entire trail  Yet is necessary! (routing)

Solutions - 1 Accelerometers & Compasses are noisy  Use: (step size) * (step count) Displacement error using double integration Signature from up and down bounce of human body while walking

Solutions - 1 Accelerometers & Compasses are noisy  Use: (step size) * (step count)  Take into account varying step size (Vary step size with error factor drawn from Gaussian distribution centered on 0 and standard deviation 0.15m) Error with step count method

Challenges Accelerometers & Compasses are noisy  Measured path error grows over time No global reference frame  How to correct errors? Even if correct user position, difficult to correct entire trail  Yet is necessary! (routing)

Solutions - 2 No global reference frame  Use a beacon transmitter! Beacon Transmitter  Location is origin of virtual coordinate system  Uses audio signals to detect encounters  Location diffusion ( single point updates )  Drift cancellation ( path correction )  solutions-3

Challenges Accelerometers & Compasses are noisy  Measured path error grows over time No global reference frame  How to correct errors? Even if correct user position, difficult to correct entire trail  Yet is necessary! (routing)

Solutions - 3 Drift Cancellation User encounters beacon at t_r1, and another beacon or recently updated user at t_r2. Computed-trail Corrected-trail Actual path

Further Solutions Graph computation done by Server  Pruning heuristic necessary Graph – 4 users, 10 minAfter pruningAfter Floyd-Warshall alg

Main idea Escort consists of two parts:  Navigation Get directions to the person  Visual Identification Help you identify the person if she is someone you have not met before (e.g. first-time meeting with a professional colleague at a conference)

Main idea–Visual Identification Perhaps Alice has not met Bob before…  Picture of face not enough In a trusted environment like Mobicom, can  Take many photos of user to generate a “fingerprint”  Broadcast fingerprint to get recognized Totally works in theory!  Currently only implemented offline and requires user input …

Outline Motivation Recap:  We need efficient and accurate software for people localization: Escort Outline  Main idea of Escort  Challenges  Solutions  Evaluation  Results  Future Work

Evaluation Parking Lot Experiment  4 users, 13 min, phones in hand, 40 routing experiments  Use parking spot lines & markers for ground truth Indoor Experiment  2 users, 6 min, 10 routing experiments

Outline Motivation Recap:  We need efficient and accurate software for people localization: Escort Outline  Main idea of Escort  Challenges  Solutions  Evaluation  Results  Future Work

Results – Parking Lot Instantaneous location error over time

Results – Parking Lot Instantaneous location error < 10m:  Inertial ~6% of cases  Beacon & Encounter ~ 68% of cases  Drift Cancellation ~ 84% of cases Final destination distance error 8.2m on average

Results – Indoor Instantaneous location error:  Better overall (due to indoor structure and user guesswork)  Beacon & Encounter ~ 85% of cases  Drift Cancellation ~ 90% of cases Final destination distance error was 7m on average

Results – Visual Identification 80% accurate with 8 people in surroundings

Future Work “Escort is not designed for energy efficiency”  Turn off sensors (except accelerometer) when user not moving  Less audio signaling when many users or beacons nearby  Less frequent uploading of data to server Routing through physical obstacles  People are smart  Visual representation of path may help Long routing paths  Include true-direction arrow to Bob ’ s location

Future Work Routing instructions under low location accuracy  If update too far in past, prompt user to approach beacon  Update path as more info becomes available Phone placement  Need advancement of phone gyroscopes to infer orientation Behavior under heavy user load  Scalability needs to be explored but should improve performance

Thank You Any Questions?