CS805y Reading Course

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CS805y Reading Course Indoor Location
Systems Nathan Lemieux
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Introduction

• What is location?
• A space or area in which an object may be found
• It is an important context that changes whenever
  the object moves
• What is a context?
• describes the state of the environment where the
  application is used
• e.g. computing, user, physical, time

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Introduction

• An application is context-aware if it has the
  ability to adapt its behaviour from information
  extracted and interpreted in the environment in
  which they are used
• Some contexts are easily determined while others
  are easier said than done
• Location is one such context that seems easy, but
  has provided many challenges.

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Location-Aware Applications

• Tracking and monitoring of assets
• Navigation and guide systems
• Games
• Emergency services
• Shopping assistance
• Follow-me services

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Motivation

• GPS has been providing outdoor location
  estimations for many years (15 m)
• However GPS has proven to be unreliable in highly
  populated urban areas and indoor environments
• Line of sight requirements
• Location accuracy

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Presentation Overview

• Techniques
• Signals, Sensors, Scene Analysis
• Technologies
• Signals, Sensors, Scene Analysis
• Developed Systems
• Current Research
• Conclusions
• Questions

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Techniques - Signals

• Multilateration
• Location of two or more reference points is known
  
• Measure the distance between the user and each
  reference point
• TOF, Signal level measurements, TDOA
• Convergence point is location of user
• Triangulation
• Angle measurements and at least one known
  distance

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Techniques - Signals

• Proximity or Cell of Origin (CoO)
• Location is described in a cell around the
  transmitter
• More accurate with dense deployment of
  transmitters
• Fingerprinting
• Compare received signal strength measurements to
  previous recorded values at known locations

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Techniques - Signals

• Shortfalls
• Multi-path propagation
• Signals reaching antenna by two or more paths
• Reflection
• Signals bouncing off objects before reaching
  antenna
• Shadow fading
• Variation in signals due motion of the receiving
  antenna
• Moving/changing reference points
• Solution
• Combine signaling techniques
• Obtain more information from other technologies

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Techniques - Sensors

• Inertia Navigation Systems / Dead-Reckoning
• Position is calculated by collecting and
  analyzing data from sensors, such as speed, time,
  altitude and direction from a known starting
  position
• Distance traveled is determined by two steps
• Step detection
• Measuring/detecting vertical acceleration
• Estimation of step length
• Fixed or variable length

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Techniques - Sensors

• Shortfalls
• Suffers from constant growing positioning error
  known as drift
• Drift-error occurs due to slight errors
  introduced in the manufacturing process of
  sensors
• The error is small but the error is accumulative
• Solution
• Provide INS periodically with accurate position
  updates

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Techniques Scene Analysis

• Direct Image Comparison
• Compare images to set of already gathered images
  with location information. Look for similar
  images
• Feature Extraction
• Operation of uncovering various image features
  for identifying or interpreting meaningful
  objects from images
• E.g. colour, tone, edges, patterns, optical flow
  and objects/shapes

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Techniques Scene Analysis

• Shortfalls
• ability to distinguish usable and unusable
  features in a reasonable amount of time
• Images are taken at different times of the day,
  different lighting conditions, taken at different
  angles and images may have obstructions that
  distort the image

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Technologies - Signals

• Wi-Fi
• Signal range of 50-100 meters
• Many existing networks / access points already
  available
• Requires knowledge of AP location
• Can apply many signaling techniques
• Radio Frequency IDentification (RFID)
• No line-of-sight requirements
• Passive Vs. Active tags (read range / cost /
  lifetime)
• Good accuracy requires dense deployment of RFID
  readers
• Only CoO, no information about signal strength

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Technologies - Signals

• Bluetooth
• Cheap devices with limited bandwidth
• Variable read ranges (1/10/50 meters)
• Frequency channel hopping for communication can
  have large delays (2-10 seconds)
• CoO technique or Trilateration depending on mode
  used
• GPS
• Currently used for outdoor navigation
• Line-of-sight requirements
• Uses Trilateration with location accuracy lt15
  meters in ideal conditions

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Technologies - Signals

• Infrared
• Inexpensive devices, low power
• Sensitive to sunlight, line-of-sight requirement
• CoO technique, 5-10 meters
• Ultrasound
• Inexpensive with precise measurements possible,
  within a few cm with dense deployment
• Line-of-sight requirement
• Time Of Flight Trilateration

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Technologies - Sensors

• Accelerometers
• Measure acceleration forces, e.g. Wii Remote
• Can been used to determine activities such as
  walking, running, standing still
• Must distinguish between static and dynamic
  forces
• Digital Compasses
• Provide the direction (or heading) of the user
• Determines Earths magnetic north
• Sensitive to magnetic disturbances
• Gyroscopes
• Measures or maintains orientation (pitch, yaw,
  roll)
• Replacement for digital compasses

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Technologies - Sensors

• Altimeter
• Determine altitude of the user based on changes
  in air pressure
• Sensitive to air currents and changes in weather
• Pressure
• Senses that physical contact has occurred
• Light
• Measures the amount of light it detects or
  frequency of fluorescent light flicker

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Technologies Scene Analysis

• Image Capturing Devices
• Camera Phone
• Mobile, compact and inexpensive
• Low resolution images, relies on cellular
  hardware for communication
• Webcam
• Can be mobile, takes both video/pictures and
  inexpensive
• Closed-Circuit Television (CCTV)
• Installed at known locations, optical tracking is
  possible
• Expensive to deploy
• Stereo Camera
• Generates 3D images, thus able to estimate 3D
  coordinates and distance
• Expensive

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Developed Systems

• Wi-Fi Systems
• RADAR
• Uses signal strength as a indicator of distance
  by applying signal propagation model. Queries
  central DB for location of Access Points (APs)
• Location within 5-10 meters
• Ekahau
• Relies on the fingerprint technique to obtain
  signal strength measurements of APs at known
  locations
• Relies on a central DB, proprietary
  software/protocol for communication
• Location within 5 meters
• Herecast
• Based on CoO technique. Each AP is associated
  with a zone
• User groups update/create zone and post location
  specific info
• Location within 25-35 meters

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Developed Systems

• Radio Frequency IDentification (RFID)
• BlueBot
• Used to track moving assets with passive RFID
  tags
• However location is determined by Wi-Fi
• Robot moves throughout environment and updates
  RFID tag locations when they are encountered
• LANDMARC
• Investigated different RFID setups
• Placed multiple RFID readers in a room creating
  regions, in each region had active RFID reference
  tags (landmarks). Mobile tags when detected are
  placed at the closest reference tag
• Assisted Indoor Location for First Responders
• Examines the possibility of creating a location
  system with both INS and RFID technology
• Passive tags installed would update INS locations
  reducing drift-error

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Developed Systems

• Bluetooth
• Privacy Conscious Bluetooth
• Place USB Bluetooth location beacons on existing
  computers at known locations
• User has a lookup table, a mapping between
  Bluetooth device addresses to locations
• BIPS
• Centralized positioning server maintains
  locations of users
• Workstations with Bluetooth interfaces scan for
  users. When detected, devices create connection
  with user to retrieve device information and then
  update positioning server
• Infrared
• Active Badge
• Users wear IR badge that emits unique IR signal
  periodically
• Sensors installed at known locations detect the
  unique signal and update centralized DB with
  location information.

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Developed Systems

• Ultrasound
• Cricket
• Device listens for two signals (RF, Ultrasound)
  that simultaneously originate from a base
  station.
• Base stations are installed at known locations in
  the ceiling.
• Using the time interval between the arrival of
  the two signals of the users device, distance to
  the base station can be calculated
• Active Bat
• Ceiling embedded with ultrasonic receivers.
• Mobile transmitter (or bat) emits ultrasonic
  pulses
• Central controller coordinates transmitters and
  receivers allowing you to locate a particular bat

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Developed Systems

• Sensors Based
• LuxTrace
• Investigated the use of solar cells to collect
  energy and light levels
• Uses the fingerprint technique of radiant energy
  from indoor illumination to derive location
  estimations
• Changing light bulbs requires re-calibration
• Smart Floor
• Used pressure sensors embedded in the floor to
  detect footsteps
• Hard to determine user based footsteps alone

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Developed Systems

• Vision Based
• Indoor localization using camera phones
• Demonstrated the feasibility of determining a
  users location based on images captured by a
  smart phone
• Utilized off-the-shelf image algorithms for
  direct image comparison to determine similarities
  in images stored in a DB.
• Slow upload times (few seconds) over cellular
  network
• Room level accuracy 80 of the time
• Easy Living
• Used three high performance stereo cameras to
  capture 3D images in a room
• Applied optical tracking algorithms to obtain
  good positioning estimation
• Required significant amount of processing power
  and time
• Proposed using different technologies to give
  location estimations at different levels
  (building, room, corner of a room)

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Developed Systems

• Problems/Shortfalls
• Installation of specialized hardware
• Time consuming calibration or recalibration
• Placement and maintenance of tags
• Privacy concerns using centralized positioning
  server
• Power consumption
• Cost and scalability

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Current Research - Hybrid

• Why Hybrid?
• Combine complementary technologies such that
  advantages of one technology or technique
  compensates for drawbacks of another
• Quality of Service
• Different levels of location accuracy
• Reduced Security and Privacy concerns
• Apply one centralized / one localized location
  estimation technology
• Reliability
• More information/data to infer location or other
  contexts

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Current Research

• Additional Hybrid Systems
• Place Lab
• Community based positioning system that combines
  Wi-Fi, Bluetooth and Cellular signaling
  technologies to derive location using stored
  fingerprints
• Dead-Reckoning Supports Vision Tracking
• Combination of Stereo Vision object tracking and
  inertia navigation systems
• INS component is used when there are no cameras
  tracking the user
• GETA Sandals
• Combination of sensors and RFID. Sandals
  embedded with sensors are used to provide step
  detection and step length estimations for INS.
  RFID tags scattered in the environment are used
  to calibrate dead-reckoning drift-error

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Conclusions

• There are many location systems, everyone with
  their own benefits and drawbacks
• Every location system requires either
  installation, calibration or specialized
  hardware, idea is to reduce this as much as
  possible
• Further investigation of hybrid location systems
  combing different techniques and technologies
  needs to be conducted
• Location-based services are becoming a reality as
  mobile computing continues to grow in popularity.
  However, we need finer granularity in terms of
  location accuracy in indoor environments as users
  have a higher degree of freedom in their possible
  location

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Questions ?