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?