Spot Fi Decimeter Level Localization using Wi Fi

Spot. Fi: Decimeter Level Localization using Wi. Fi Proposed by - Manikanta Kotaru, Kiran Joshi, Dinesh Bharadia, Sachin Katti Stanford University Presented by – Mohammad Nasim Imtiaz Khan and Abdullah Ash Saki

Applications of Indoor Localization Targeted Location Real Life Analytics Indoor Navigation Based Advertising (e. g. Airport Terminals) (Gym, Office, etc. . ) Indoor localization platform providing decimeter-level accuracy could enable a host of applications 2

Requirement for Ideal Localization System

1. Easily Deployable • Commercial Wi. Fi chips 3

1. Easily Deployable • Commercial Wi. Fi chips • No hardware or firmware change 4

1. Easily Deployable • Commercial Wi. Fi chips • No hardware or firmware change • No User Intervention 5

2. Universal • Localize any Wi. Fi device • No specialized sensors 6

3. Accurate • Error of few tens of centimeters 1 m 7

State-of-the-art System Deployable Universal Accurate RADAR, Bahl et al, ’ 00 HORUS, Youssef et al, ’ 05 Array. Track, Xiong et al, ’ 13 Pin. Point, Joshi et al, ’ 13 CUPID, Sen et al, ’ 13 LTEye, Kumar et al, ’ 14 Phaser, Gjengset et al, ’ 14 Ubicarse, Kumar et al, ’ 14 9

State-of-the-art System Deployable Universal Accurate RADAR, Bahl et al, ’ 00 HORUS, Youssef et al, ’ 05 Array. Track, Xiong et al, ’ 13 Pin. Point, Joshi et al, ’ 13 CUPID, Sen et al, ’ 13 LTEye, Kumar et al, ’ 14 Phaser, Gjengset et al, ’ 14 Ubicarse, Kumar et al, ’ 14 Spot. Fi, Kotaru et al, ’ 15 10

System Overview 11

Localization - Overview 12

Localization - Overview 13

Challenge - Multipath 14

Solving The Multipath Problem State-of-the-art Subcarriers Model signal on antennas alone Spot. Fi Model signal on both antennas and subcarriers Antennas 15

Step 1: Resolve Multipath 16

Signal Modeling Equal Distance Line 17

Phase 1 / frequency 0 Distance travelled by the Wi. Fi signal 18

Signal Modeling – Ao. A (Angle of Arrival) Equal Phase Line 19

Signal Modeling - Ao. A 3 2 1 20

Say There Are Two Paths… 21

Say There Are Two Paths… 22

Say There Are Two Paths… 23

Problem Statement CSI - Known 24

Problem Statement Parameters - Unknown 25

Problem Statement 26 Number of paths (or Ao. As) < Number of antennas (or equations)

Typical Indoor Multipath 27

That’s A Problem State-of-the-art Commodity Wi. Fi chips Number of antennas/equations should be at least 5 28

How To Obtain More Equations? Subcarriers Model signal on both antennas and subcarriers Antennas 29

Each Subcarrier Gives New Equations 30

Signal Modeling – To. F (Time of Flight) 31

Estimate both Ao. A and To. F More number of equations in terms of parameter of our interest 32

Say There Are Two Paths… 33

Say There Are Two Paths… 34

Problem Statement 35 Subcarrier 2 Subcarrier 1 CSI - Known

Problem Statement 36 Subcarrier 2 Subcarrier 1 Parameters - Unknown

37 Subcarrier 2 Number of equations = Number of Subcarriers x Number of Antennas Subcarrier 1 Problem Statement

Ao. A, To. F Estimates 38

Step 2: Identify Direct Path 39

Ao. A, To. F Estimates 40

Use Multiple Packets 41

Use Multiple Packets 42

Use Multiple Packets 43

Use Multiple Packets 44

Direct Path Likelihood • Smaller To. F Higher weight Lower weight Higher weight 45

Direct Path Likelihood • Smaller To. F Lower weight • Tighter Cluster Higher weight Lower weight 46

Direct Path Likelihood • Smaller To. F Lower weight • Tighter Cluster Higher weight • More Packets Higher weight Lower weight 47

Highest Direct Path Likelihood 48

Step 3: Localize The Target 49

Use Multiple APs Direct Path Ao. A = 45 degrees Signal Strength = 10 d. B Direct Path Ao. A = 10 degrees Signal Strength = 30 d. B 50 Direct Path Ao. A = -45 degrees Signal Strength = 20 d. B Find location that best explains the Ao. A and Signal Strength at all the APs

Use Different Weights Direct Path Ao. A = 45 degrees Signal Strength = 10 d. B Direct Path Likelihood Direct Path Ao. A = 10 degrees Signal Strength = 30 d. B Direct Path Likelihood 51 Direct Path Ao. A = -45 degrees Signal Strength = 20 d. B Direct Path Likelihood Use different weights for different APs

Evaluation 52

Testbed 40 m Target Access point 53 52 m AP Locations Target Locations

Indoor Office Deployment 10 m 40 m Ubicarse Spot. Fi 0. 3 m 0. 4 m Empirical CDF 16 m Array. Track 1 0, 8 0, 6 0. 4 m 0, 4 0, 2 0 0, 05 0, 5 5 Localization Error (m) 52 m Target Locations 54 AP Locations

Stress Test – Obstacles Blocking The Direct Path 40 m 52 m Target Locations 55 AP Locations

Stress Test – Obstacles Blocking The Direct Path 40 m Empirical CDF 1 0, 8 0, 6 1. 3 m 0, 4 0, 2 0 0, 049999958532 Localization Error (m) 52 m Target Locations 56 AP Locations

Effect of Wi. Fi AP Deployment Density Empirical CDF 1 0, 8 0, 6 3 APs 4 APs 5 APs 0, 4 0. 8 m 0, 2 0 0, 05 0, 5 5 Localization Error (m) 57

Conclusion • Deployable: Indoor Localization with commercial Wi. Fi chips • Accurate: Accuracy comparable to state-of-the-art localization systems which are not suitable for wide deployments • Universal: Simple localization targets with only a Wi. Fi chip 58

References • J. Xiong and K. Jamieson, “Arraytrack: A fine-grained indoor location system, ” NSDI ’ 13. • S. Kumar, S. Gil, D. Katabi, and D. Rus, “Accurate indoor localization with zero start-up cost, ” Mobi. Com ’ 14. • P. Bahl and V. N. Padmanabhan, “Radar: An in-building rf-based user location and tracking system, ” INFOCOM 2000. • S. Kumar, E. Hamed, D. Katabi, and L. Erran Li, “Lte radio analytics made easy and accessible, ” SIGCOMM ’ 14. • J. Gjengset, J. Xiong, G. Mc. Phillips, and K. Jamieson, “Phaser: Enabling phased array signal processing on commodity wifi access points, ” Mobi. Com ’ 14. • M. Youssef and A. Agrawala, “The horus wlan location determination system, ” Mobi. Sys ’ 05. • S. Sen, J. Lee, K. -H. Kim, and P. Congdon, “Avoiding multipath to revive inbuilding wifi localization, ” Mobi. Sys ’ 13. • K. Joshi, S. Hong, and S. Katti, “Pinpoint: localizing interfering radios, ” NSDI ’ 13. • M. Kotaru, K. Joshi, D. Bharadia, S. Katti, "Spot. Fi: Decimeter Level Localization Using Wi. Fi, " ACM SIGCOMM 2015. • All the icons are from the Noun Project https: //thenounproject. com/