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SCPL: Indoor Device-Free Multi-Subject Counting and Localization Using

Radio Signal Strength

Rutgers University

Chenren Xu

Joint work with Bernhard Firner, Robert S. Moore, Yanyong Zhang

Wade Trappe, Richard Howard, Feixiong Zhang, Ning An

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Device-free Localization

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Device-free Localization

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Why Device-free Localization?

q  Monitor indoor human mobility

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Why Device-free Localization?

q  Monitor indoor human mobility

Elder/health care 5

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Why Device-free Localization?

q  Monitor indoor human mobility

Traffic flow statistics 6

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Why Device-free Localization?

q  Monitor indoor human mobility

Traffic flow statistics 7

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Why Device-free Localization?

q  Monitor indoor human mobility

q Health/elder care, safety

q Detect traffic flow

q  Provides privacy protection

q No identification

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Why Device-free Localization?

q  Monitor indoor human mobility

q Health/elder care, safety

q Detect traffic flow

q  Provides privacy protection

q No identification

q  Use existing wireless infrastructure

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Previous Work

q  Single subject localization

q Fingerprinting-based approach

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Fingerprinting N Subjects

q  Multiple subjects localization

q Needs to take calibration data from N people

for localizing N people

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Fingerprinting N Subjects

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…

9 trials in total for 1 person

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Fingerprinting N Subjects

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…

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Fingerprinting N Subjects

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…

…

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Fingerprinting N Subjects

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…

…

36 trials in total for 2 people!

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Fingerprinting N Subjects

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1 person

9 cells 9

9 × 1 min = 9 min

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Fingerprinting N Subjects

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1 person 2 people

9 cells 9 36

36 cells 36 630

630 × 1 min = 10.5 hr

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Fingerprinting N Subjects

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1 person 2 people 3 people

9 cells 9 36 84

36 cells 36 630 7140

100 cells 100 4950 161700

161700 × 1 min = 112 days The calibration effort is prohibitive !

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SCPL q  Input

q  Collecting calibration data only from 1 subject (D1)

q  Observed RSSI change caused by n subjects

q  Output

q  count and localize N subjects.

q  Main Insight:

q  If the number n is known, localizing n subjects

is strightforward 19

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No Subjects

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One Subject

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Two Subjects

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Measurement

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N = 0 N = 1 N = 2 Link 1 0 4 4 Link 2 0 5 7 Link 3 0 0 5 Total (∆N) 0 9 16

∆N N?

∆N / ∆1 = N?

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Measurement

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Measurement

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Nonlinear problem!

1.6

∆N / ∆1 ≠ N

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Measurement

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4 dB

5 dB

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Measurement

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5 dB

6 dB

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Measurement

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4 dB + 0 dB = 4 dB √ 5 dB + 6 dB = 11 dB ≠ 7 dB X 0 dB + 5 dB = 5 dB √

= + ?

4 dB

5 dB

5 dB

6 dB

5 dB

7 dB

4 dB

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Measurement

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5 dB + 6 dB ≠ 7 dB X

Shared links observe nonlinear fading effect from multiple people

≠ + ! 5 dB 6 dB 7 dB

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SCPL Part I Sequential Counting (SC)

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Counting algorithm

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Phase 1: Detection

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Measurement in 1st round

5 dB

7 dB

4 dB ∆N = 4 + 7 + 5 = 16 dB

∆N > ∆1

Subject Count ++

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Phase 2: Localization

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Measurement in 1st round

5 dB

7 dB

4 dB

Find this guy

PC-DfP:

C. Xu, B. Firner, Y. Zhang, R. Howard, J. Li, and X. Lin. Improving rf-based device-free passive localization in cluttered indoor environments through probabilistic classification methods. In Proceedings of the 11th international conference on Information Processing in Sensor Networks, IPSN ’12

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Phase 3: Subtraction

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Calibration data

5 dB

6 dB

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Phase 3: Subtraction

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Subject count ++ Go to the next iteration…

= -

Measurement in 1st round

Calibration data

Measurement In 2nd round

4 dB

1 dB

5 dB

6 dB

5 dB

7 dB

4 dB

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Phase 3: Subtraction

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Subject count ++ Go to the next iteration…

Hold on …

= -

Calibration data

Measurement in 1st round

Measurement In 2nd round

4 dB

1 dB

5 dB

6 dB

5 dB

7 dB

4 dB

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Phase 3: Subtraction

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Measurement In 2nd round

4 dB

1 dB

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Phase 3: Subtraction

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Measurement In 2nd round

Calibration data

4 dB

1 dB

4 dB

5 dB

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Phase 3: Subtraction

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Measurement In 2nd round

Calibration data

= -

We over-subtracted its impact on shared link!

4 dB

1 dB

4 dB

5 dB -4 dB

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Measurement

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Measurement

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1st round

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Measurement

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1st round

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Measurement

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1st round

2st round

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Phase 3: Subtraction

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We need to multiply a coefficient β ϵ [0, 1] when subtracting each link

= -

Calibration data

Measurement in 1st round

Measurement In 2nd round

4 dB

1 dB

5 dB

6 dB

5 dB

7 dB

4 dB

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Location-Link Correlation

q  To mitigate the error caused by this over-

subtraction problem, we propose to

multiply a location-link correlation

coefficient before successive subtracting:

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Phase 3: Subtraction

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Subject count ++ Go to the next iteration…

= - 4.6 dB 6 × 0.4 dB

Measurement in 1st round

Calibration Data

Measurement in 2nd round

5 × 0.8 dB

4 dB

5 dB

7 dB

4 dB

1 dB

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Phase 3: Subtraction

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Measurement in 2nd round

Calibration data

= -

Measurement in 3rd round

We are done !

4.6 dB

4 dB

1 dB

6 × 0.6 dB

4 × 0.8 dB 1 dB

1 dB

1 dB

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SCPL Part II Parallel Localization (PL)

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Localization

q  Cell-based localization

q Allows use of context information

q Reduce calibration overhead

q Classification problem formulation

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C. Xu, B. Firner, Y. Zhang, R. Howard, J. Li, and X. Lin. Improving rf-based device-free passive localization in cluttered indoor environments through probabilistic classification methods. In Proceedings of the 11th international conference on Information Processing in Sensor Networks, IPSN ’12

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Linear Discriminant Analysis q  RSS measurements with person’s presence in each

cell is treated as a class/state k

q  Each class k is Multivariate Gaussian with common

covariance

q  Linear discriminant function:

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Link 1 RSS (dBm) L

ink

2 R

SS (d

Bm

) k = 1 k = 2

k = 3

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Localization

q  Cell-based localization

q  Trajectory-assisted localization

q  Improve accuracy by using human mobility

constraints

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Human Mobility Constraints

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You are free to go anywhere with limited step size inside a ring in free space

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Human Mobility Constraints

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In a building, your next step is constrained by cubicles, walls, etc.

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Phase 1: Data Likelihood Map

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Impossible movements

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Impossible movements

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Phase 2: Trajectory Ring Filter

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Phase 3: Refinement

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Here you are!

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Viterbi optimal trajectory

q  Single subject localization

q  Multiple subjects localization

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ViterbiScore =

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System Description

q  Hardware: PIP tag

q Microprocessor: C8051F321

q Radio chip: CC1100

q Power: Lithium coin cell battery

q  Protocol: Unidirectional heartbeat (Uni-HB)

q Packet size: 10 bytes

q Beacon interval: 100 msec 61

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Office deployment

62 Total Size: 10 × 15 m

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Office deployment

63 37 cells of cubicles, aisle segments

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Office deployment

64 13 transmitters and 9 receivers

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Office deployment

65 Four subjects’ testing paths

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Counting results

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Counting results

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Localization results

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Open floor deployment

69 Total Size: 20 × 20 m

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Open floor deployment

70 56 cells, 12 transmitters and 8 receivers

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Open floor deployment

71 Four subjects’ testing paths

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Counting results

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Localization results

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Conclusion and Future Work q  Conclusion

q  Calibration data collected from one subject can be used to

count and localize multiple subjects.

q  Though indoor spaces have complex radio propagation

characteristics, the increased mobility constraints can be

leveraged to improve accuracy.

q  Future work

q  Count and localize more than 4 subjects 74

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Q & A

Thank you

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