1. The NearMe Wireless Proximity Server John Krumm and Ken Hinckley Microsoft Research Redmond, WA, USA

2. What is NearMe A server, algorithms, APIs Requirement: –Clients equipped with 802.11 Functionality: –Discover what is already nearby E.g. people, places –Estimate how far away they are

3. The basic idea 802.11 Wi-Fi access point NearMe Proximity Server

4. Client: Wi- Fi Signature NearMe Proximity Server Client functions: 1.GUID  register(); 2. Report Wi-Fi signature {GUID, (m1, s1), (m2, s2)} 3. Query for nearby people and place.

5. Server: Access Point Layout A B C E D - AP topology in server DB - Recomputed every hour CEBA D

6. Two types of proximity Short Range Proximity Long Range Proximity

7. Distance function for Short Range Proximity Distance features: –n ∩ : number of access points in common –ρs : Spearman rank coefficient of access points in common –ssd ∩ = sum of squared differences of rssi in common –n u = number of access points not in common 4 features + polynomials to 3rd degree = 45 different test functions –d (n ∩,ρ s ) = -2.53∙n ∩ – 2.90∙ρ s - 22.31 Heuristic sort function on server: D = n ∩ + ρ s

8. Hops, Travel time for Long Range Proximity Hops = Distance Estimate Travel time –Compute from the timestamp on the Wi-Fi signature every hour. –Minimum observed client travel time between access points

9. Applications Send email to people nearby Stitching Look up URLs of nearby people

10. Summary Works on existing Wi-Fi devices Minimal setup –No calibration –Capability grows with use Short range proximity –Accounts for different Wi-Fi hardware –Sorted by distance Long range proximity –Hop distances via adjacency analysis –Travel times via timestamp analysis

11. The End Reference: http://research.microsoft.com/~jckrumm/NearMe.htm