--- title: "08-proximity sensors" tags: - 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 ![table of freqs](https://i.imgur.com/IuJ0mnq.png) 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 ![Proximity Sensors & Near Field Communication 12 NFC-based communication / authentification ](https://i.imgur.com/WwidfDA.png) > [!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 ![original gps diagram](https://i.imgur.com/PJYIoMo.png) 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!