quartz/content/notes/08-proximity sensors.md

title	tags
08-proximity sensors	lecture info305

Lecture 8: Location Sensors 2 Tobias Langlotz INFO 305: Advanced Human-Computer Interaction and Interactive Systems 2

Proximity Sensors & Near Field Communication

• Different technologies for sensing proximity or exchanging data (often dual purpose)
• Stand-alone infrastructure approaches
• Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
• Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa 3

Proximity Sensors & Near Field Communication

• Different protocols on top of Bluetooth LE
• iBeacon (Apple)
• Broadcasts a UUID
• ID is used with database integrated in the app
• Further information on request (e.g. range information) Different iBeacon capable beacons Range Information from iBeacons 4

Proximity Sensors & Near Field Communication

• Different protocols on top of Bluetooth LE
• iBeacon (Apple)
• Broadcasts a UUID
• ID is used with database integrated in the app
• Further information on request (e.g. range information) Different iBeacon capable beacons
• Eddystone (Google)
• Beacons broacasts information about the beacon (telemetry frame e.g. battery or sensor information)
• Beacons broadcasts and redirects to an URL (physical web) Eddystone lighthouse, role model for Eddystone functionality 5

Proximity Sensors & Near Field Communication

• Different technologies for sensing proximity or exchanging data (often dual purpose)
• Stand-alone infrastructure approaches
• Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
• Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa 6

Proximity Sensors & Near Field Communication

• RFID: Radio-frequency identification
• Uses radio-frequency waves to transfer data between a reader and a movable item
• Identify,
• Categorize,
• Track,
• Tag objects of interests
• No physical sight or contact needed RFID Tag

Proximity Sensors & Near Field Communication 7

• RFID: Radio-frequency identification
• Basic Types:
• Active
• Tag transmits radio signal
• Battery powered memory, radio & circuitry
• High Read Range (300 feet)
• Passive
• Tag reflects radio signal from reader
• Reader powered
• Shorter Read Range (4 inches - 15 feet)
• Tags can be read-only or read-write RFID Tag Active RFID Tags

Proximity Sensors & Near Field Communication 8 RFID Tag

• Host Manages Reader(s) and Issues Commands
• Reader and tag communicate via RF signal
  • Carrier signal generated by the reader
  • Carrier signal sent out through the antennas
  • Carrier signal hits tag(s)
  • Tag receives and modifies carrier signal
  • Antennas receive the modulated signal and send signal to the Reader
  • Reader decodes the data Different RFID Tags Hitachi "powder" type RFID chip measuring 0.05 x 0.05 mm

[!INFO] can get implants of RFID usually connected to a database which identifies stuff. e.g., this tag is this cow small rfids you need to be very close as the signal is not very strong

Proximity Sensors & Near Field Communication 9 Hitachi "powder" type RFID chip measuring 0.05 x 0.05 mm Other RFID form factors

Proximity Sensors & Near Field Communication 10

• Different substandards (frequencies) RFID Tag

Proximity Sensors & Near Field Communication 11

• Near Field Communication (NFC)
  • Subgroup of RFID techniques (13.56 MHz)
  • Operating distance typical up to 10 cm (but up to 1m)
  • Data exchange rate today up to 424 kilobits/s
  • Usually used for Smartcards, digital payment, or device to device communication/ authentification NFC smartcards

[!INFO] small transmitters can be read with a large reader nfc is one specific spectrum of rfid

[!INFO] phones are a reader. but they can also emulate a tag

Proximity Sensors & Near Field Communication 13

• Each full NFC device can work in three modes:
• NFC card emulation
  • NFC-enabled devices act like smart cards, allowing users to perform transactions such as payment or ticketing.
• NFC reader/writer
  • NFC-enabled devices to read information stored on inexpensive NFC tags embedded in labels or smart posters.
• NFC peer-to-peer
  • Enables two NFC-enabled devices to communicate with each other to exchange information in an adhoc fashion. 14

[!INFO] Three modes. emulation, writer, p2p.

Proximity Sensors & Near Field Communication

• Different technologies for sensing proximity or exchanging data (often dual purpose)
• Stand-alone infrastructure approaches
• Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
• Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa Location Sensors - GPS

GPS - Overview

• (Navstar-) GPS is a satellite-based navigation system that provides users with Positioning (and Timing services
  • Provides information anywhere on Earth with unobstructed Line Of Sight
  • Operates in any weather conditions (but with accuracy constraints)
  • Available to military, commercial and civil users
• Similar systems:
  • Glonass (Russia, Operational)
  • Beidou/Compass/Beidu 2 (China, operational since 2020)
  • Galileo (Europe, expected operational since 2020)
  • Local coverage (DORIS, IRNSS, ..)

[!INFO] initally only for millitary. now open to anyone but need under open sky

GPS - Applications

• Numerous GPS applications & GPS Receivers:
  • Military
    • initally for remote guided bombs
  • Car navigation
  • Marine
  • Flight control
  • Agriculture
  • Recreation
• For mobile devices
  • Car an personal navigation
  • Location-based services
  • Augmented Reality

GPS - History

• GPS project was developed in 1973 by U.S. Department of Defence (successor of Transit/NAVSAT
• Originally comprised of 24 satellites, now 30 (including redundant satellites), 65 launched
• Originally intended for military applications
• U.S government to open GPS to civilian use in 1983 (after a Soviet jet accidentally shot a civil Korean airplane, due to navigation errors)
• Civil based GPS was limited through Selective Availability (SA)
• Accuracy errors of 100m
• SA was removed for civilian users in 2003.
• GPS achieved initial operational capability (24 Satellites) in 1993 GPS – Satellites

GPS – Satellites

• Constellation of 24 + X satellites transmitting radio signals to users
• Altitude of 20,000km (approx.)
• Each satellite orbits Earth twice/day
• Arranged in 6 orbital planes
• Each plane has four slots
• At least four satellites from virtually anywhere on earth (we come back to this..)
• Satellites use high precision atomic clock

[!INFO] constantly transmitting signal. they send the route they are flying, and where the other satelittes are flying

GPS - Signal

• GPS satellite constantly transmits radio signals (L1 signal for privat, L2 military
• The navigation message is made up of three major components:
  • GPS date and time, plus the satellite's status and an indication of its health
  • Orbital information called ephemeris data and allows the receiver to calculate the position of the satellite (valid ~4h)
  • Almanac, contains information and status concerning all the satellites; their locations and PRN numbers needed to find satellites (valid ~180days)
• Each satellite has a unique ID called “Gold codes” or PRNs (pseudo-random noise sequences) to differentiate each satellite

[!INFO] get data from four satellites, (position, time, etc).

GPS - Receiver

• Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location

GPS - Receiver

• Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location Triangulation = working with angles Trilateration = working with distances

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 2D (3 Circles) Dunedin

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 2D (3 Circles) Dunedin

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 2D (3 Circles) Dunedin

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 3D (4 Spheres) Dunedin

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 3D (4 Spheres) Dunedin

GPS - Receiver

• Uses messages received from satellites (n"4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location In 3D (4 Spheres) Dunedin But our receiver does not have an atomic clock!!

GPS - Receiver

• Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
• Gives roughly distance to satellite
• Applies Trilateration for computing location
• The receiver has four unknowns, the three components of GPS receiver position and the clock bias [x, y, z, b]
• Using four (or more) satellites, we can set up 4 linear equations to solve for x, y, z, b
• In some cases we know z or b we need less satellites! Urban Canyon
• Urban environment similar to a natural canyon
• Can impact radio reception of GPS receivers
• Buildings reflect and occlude satellite signals
• Reducing precision of positioning in urban environments
• Makes positioning impossible Urban Canyon
• Urban environment similar to a natural canyon
• Can impact radio reception of GPS receivers
• Buildings reflect and occlude satellite signals
• Reducing precision of positioning in urban environments
• Makes positioning impossible www.hci.otago.ac.nz The end!