Herecast: An Open Infrastructure for Location-Based Services using - - PowerPoint PPT Presentation

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Herecast: An Open Infrastructure for Location-Based Services using - - PowerPoint PPT Presentation

Feb 03, 2023 267 likes •554 views

Herecast: An Open Infrastructure for Location-Based Services using WiFi Mark Paciga and Hanan Lutfiyya Presented by Emmanuel Agu CS 525M Introduction Users context includes location, time, date, temperature, schedule, etc

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Herecast: An Open Infrastructure for Location-Based Services using WiFi

CS 525M

Mark Paciga and Hanan Lutfiyya Presented by Emmanuel Agu

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Worcester Polytechnic Institute 2

Introduction

  • User’s context includes location, time, date,

temperature, schedule, etc

  • Context-aware Location takes advantage of user

context for computing

  • Location is most widely used piece of context
  • Example location-aware applications:

– Pull up web pages relevant to user location (e.g google search that returns nearest restaurants) – Users publish their presence so friends can find them

  • Also, location-based service:

– E.g find print to closest printer

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Worcester Polytechnic Institute 3

GPS

  • GPS finds location of users worldwide
  • GPS uses satellite constellations
  • Signals cannot penetrate walls
  • Result: GPS works great outdoors, not so well

indoors

  • Even tall buildings cause GPS problems
  • EU planning new GPS standard that can blast

through walls…. Not here now!!!

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Worcester Polytechnic Institute 4

Indoor location sensing

  • Some authors have proposed indoor location sensing
  • Example: Location finger printing method.
  • Used in RADAR (Microsoft), LOCUS (WPI)
  • Location fingerprinting has two stages:

– Calibration (offline) – Look-up (real-time)

  • Calibration:

– Walk around, record signal strength at known location, build database called radio map

  • Look-up:

– As user moves, use current unknown signal strength to infer location (matching)

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Worcester Polytechnic Institute 5

Location Fingerprinting

  • Parameters affecting accuracy/performance

– Number and location of access points – Number of training points – Pattern matching algorithm

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Worcester Polytechnic Institute 6

Obtaining Signal Strength

  • Signal strength varies with

– Location: hence location fingerprinting – Orientation: user direction, antenna omni-directional Vs. directional – Building: construction, walls, attenuation – Time: people moving, doors opening – Sampling: number of SS samples used

  • Important: SS variation due to location >> all other factors

combined

  • SS better measure than SNR
  • Associate SS tuple with location
  • Note: directional antennas improve results
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Worcester Polytechnic Institute 7

Signal Strength Matching

MEASURED TUPLES ::: ::: ::: ::: ::: ::: 44

  • 12

22 145 380 ::: ::: ::: ::: ::: ::: 36 28

  • 16

210 350 ::: ::: ::: ::: ::: ::: 42 39 21 4 355 260 44 36 25

  • 355

220 ::: ::: ::: ::: ::: ::: 6 10 20 36 145 40 8 12 28 32 145 80 ::: ::: ::: ::: ::: ::: AP4 AP3 AP2 AP1 Y X SIGNAL STRENGTH LOCATION 45 36 24

  • AP4

AP3 AP2 AP1 OBSERVED SIGNAL STRENGTH

  • Find closest match in

database

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Worcester Polytechnic Institute 8

Signal Strength Matching

  • Simple: Return closest match
  • Deterministic:

– Smallest Euclidean distance (RADAR, Infocom 2000)

  • sqrt[(ss1’-ss1)2+(ss2’-ss2)2+(ss3’ - ss3)2]

– Elimination via Thresholding

  • Probabilisitic:

– Joint PDF and clustering (Horus, Percom 2003) – Bayesian inference, sensor fusion (LADD, Mobicom 2002) – Markov modeling and Kalman filters (Liu, JSAC 1998)

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Worcester Polytechnic Institute 9

LOCUS MQP

  • Ali Taheri, Arvinder Singh, Best CS MQP WPI
  • Determine physical location of clients on an 802.11b real

wireless network at WPI

  • Software-only, platform independent solution:

– Uses existing access points and wireless cards – Does not use GPS or proprietary tags – Commercial products already from Ekahau, Newbury

  • Performance in WPI Network
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Issues with Location Fingerprinting

  • Location finger printing is very accurate
  • Main issue is that callibration is manual, takes a lot of

time

  • About 12 hours required to callibrate a floor of a

building

  • New directions: community-based systems
  • Main idea: users upload radio map (list of access

points, locations, observed signal strength)

  • Projects: Herecast, PlaceLab (Intel)
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Worcester Polytechnic Institute 11

Herecast Architecture

  • Herecast implemented with examples on Univ. of

Western Ontario campus

  • Wireless access points broadcast MAC address

(unique identifier) that distinguishes it from other Aps

  • Computing device can use it to map location, find

location-based services

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Data modeling and management

  • Location information is associated with AP
  • UML diagram of data model is shown below
  • Example: UWO -> London -> province of Ontario
  • UWO has many buildings (Middlesex, Taylor lib, etc)
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Worcester Polytechnic Institute 13

Access Points

  • Access points constantly being added/deleted
  • Do not want Sys admin to be burdened with city-wide
  • r campus wide database maintenance
  • Solution: community-based AP information

maintenance

  • Users assigned role, some can add new APs found,

delete AP info, etc

  • Users initially assigned few privileges
  • Add more privileges as users observed to give

accurate information

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Worcester Polytechnic Institute 14

Access Point Information

  • Changes stored in change log, can be rolled back
  • Deletions placed in queue to be vetted by high-

ranking user

  • Future: users may vote to accept/reject changes
  • When user finds new AP, fills form to upload info
  • Details filled include city, province, country, area,

street address, floor, etc

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Uploading AP information

  • Entered information is symbolic
  • GPS uses coordinates (longitude, latitude)
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Worcester Polytechnic Institute 16

Symbolic Information

  • Coordinates make it easier to calculate distances
  • Users more comfortable with symbolic representation
  • E.g The name of a building.
  • Client Device software consists of:

– Finding AP Information Component – Maintaining AP Information Component – Communication with server

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Worcester Polytechnic Institute 17

Client Device Software

  • Finding AP Information Component:

– Reads AP MAC address, Signal Strength

  • Maintaining AP Information Component:

– Stores gathered AP info in AccessPoint object – List of AccessPoint objects stored in AccessPointList – Includes method to query highest RSSI – Herecast approach: Location is associated with AP with strongest Signal Strength…. Hmmm!

  • Communication with server

– Information transfer using standard HTTP – HTTP GET to download database info – HTTP POST used by client to upload info to database

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Worcester Polytechnic Institute 18

Client Device Software

  • Data Cache Component:

– Server returns entire AccessPointList to client, not just requested AP info – Thus, the additional information can be cached – Stored using text file to keep it compact for mobile device – On next request, cache is first searched

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Worcester Polytechnic Institute 19

Possible Services

  • Initial screen includes services available at user’s

location

  • Services may

– retrieve location once – Constantly updated

  • Example service:

– Map of UWO, user location

  • Users may subscribe to

services

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Worcester Polytechnic Institute 20

Implementation

  • Written in C++
  • Pocket PC version uses embedded visual C++
  • WiFi Scanner is open source to interface to network

card and discover APs.

  • Can show all available APs at user location
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Worcester Polytechnic Institute 21

Implementation

  • Library code is open-source
  • Consists of WiFi scanner, software to maintain

AccessPointList, software to ask for service subscription

  • Testing work: surveyed approx. 140 APs in 12

buildings at UWO

  • Building with most APs (20) had all APs found in 1 hr
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Applications

  • Area Maps
  • Friend finder

– Automatically publish user locations to his/her friends

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Applications

  • Heresay: location-based message board
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Bandwidth Advisor

  • Users with no connectivity, pull up list of APs in area

and load associated with each AP

  • Device detects congestion, advises user to move to

better location

  • BA also helps balance network
  • User can click
  • n location to

find out load

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Worcester Polytechnic Institute 25

Related work

  • Active badge (infrared)
  • Active bat (radio signals + ultrasound)
  • Cricket, MIT (ultrasound)
  • RADAR, Microsoft (Radio signals)
  • Placelab, Intel (Radio signals, community-based)
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Worcester Polytechnic Institute 26

Discussion

  • Wide-area Vs Local: Herecast can support wide-

area location application

  • Fine Vs Coarse resolution: Herecast is not as fine-

grained as triangulation using multiple access point

  • Privacy: Use opt-in approach
  • Resource consumption: was minimal
  • Ease of development location-aware app: easy…

area map service created in an hour

  • Data management issues: one server okay now,

more needed in future

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Worcester Polytechnic Institute 27

Future Work

  • Future applications
  • GPS integration
  • Warn user when AP signal leakage (signal received

in different building)

  • Autonomous map generation: use symbolic info to

generate map and compare distances