presented by: z.g. huang may 04, 2011 did you see bob? human localization using mobile phones romit...
TRANSCRIPT
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 Constandache Xuan Bao Martin 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 personVisual 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 min After pruning After 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 implementedoffline 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 movingLess audio signaling when many users or beacons nearbyLess frequent uploading of data to server
Routing through physical obstaclesPeople are smartVisual representation of path may help
Long routing pathsInclude 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 beaconUpdate path as more info becomes available
Phone placementNeed advancement of phone gyroscopes to infer orientation
Behavior under heavy user loadScalability needs to be explored but should improve performance
Thank You
Any Questions?