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227 lines
11 KiB
Markdown
227 lines
11 KiB
Markdown
---
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title: "08-proximity sensors"
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tags:
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- lecture
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- info305
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---
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Lecture 8: Location Sensors 2 Tobias Langlotz INFO 305: Advanced Human-Computer Interaction and Interactive Systems 2
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Proximity Sensors & Near Field Communication
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- Different technologies for sensing proximity or exchanging data (often dual purpose)
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- Stand-alone infrastructure approaches
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- Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
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- Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa 3
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Proximity Sensors & Near Field Communication
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- Different protocols on top of Bluetooth LE
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- iBeacon (Apple)
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- Broadcasts a UUID
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- ID is used with database integrated in the app
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- Further information on request (e.g. range information) Different iBeacon capable beacons Range Information from iBeacons 4
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Proximity Sensors & Near Field Communication
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- Different protocols on top of Bluetooth LE
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- iBeacon (Apple)
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- Broadcasts a UUID
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- ID is used with database integrated in the app
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- Further information on request (e.g. range information) Different iBeacon capable beacons
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- Eddystone (Google)
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- Beacons broacasts information about the beacon (telemetry frame e.g. battery or sensor information)
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- Beacons broadcasts and redirects to an URL (physical web) Eddystone lighthouse, role model for Eddystone functionality 5
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Proximity Sensors & Near Field Communication
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- Different technologies for sensing proximity or exchanging data (often dual purpose)
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- Stand-alone infrastructure approaches
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- Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
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- Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa 6
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Proximity Sensors & Near Field Communication
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- RFID: Radio-frequency identification
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- Uses radio-frequency waves to transfer data between a reader and a movable item
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- Identify,
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- Categorize,
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- Track,
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- Tag objects of interests
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- No physical sight or contact needed RFID Tag
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Proximity Sensors & Near Field Communication 7
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- RFID: Radio-frequency identification
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- Basic Types:
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- Active
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- Tag transmits radio signal
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- Battery powered memory, radio & circuitry
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- High Read Range (300 feet)
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- Passive
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- Tag reflects radio signal from reader
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- Reader powered
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- Shorter Read Range (4 inches - 15 feet)
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- Tags can be read-only or read-write RFID Tag Active RFID Tags
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Proximity Sensors & Near Field Communication 8 RFID Tag
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- Host Manages Reader(s) and Issues Commands
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- Reader and tag communicate via RF signal
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- Carrier signal generated by the reader
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- Carrier signal sent out through the antennas
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- Carrier signal hits tag(s)
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- Tag receives and modifies carrier signal
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- Antennas receive the modulated signal and send signal to the Reader
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- Reader decodes the data Different RFID Tags Hitachi "powder" type RFID chip measuring 0.05 x 0.05 mm
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> [!INFO] can get implants of RFID
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> usually connected to a database which identifies stuff. e.g., this tag is this cow
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> small rfids you need to be very close as the signal is not very strong
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Proximity Sensors & Near Field Communication 9 Hitachi "powder" type RFID chip measuring 0.05 x 0.05 mm Other RFID form factors
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Proximity Sensors & Near Field Communication 10
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- Different substandards (frequencies) RFID Tag
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Proximity Sensors & Near Field Communication 11
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- Near Field Communication (NFC)
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- Subgroup of RFID techniques (13.56 MHz)
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- Operating distance typical up to 10 cm (but up to 1m)
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- Data exchange rate today up to 424 kilobits/s
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- Usually used for Smartcards, digital payment, or device to device communication/ authentification NFC smartcards
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> [!INFO] small transmitters can be read with a large reader
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> nfc is one specific spectrum of rfid
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> [!INFO] phones are a reader. but they can also emulate a tag
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Proximity Sensors & Near Field Communication 13
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- Each full NFC device can work in three modes:
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- NFC card emulation
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- NFC-enabled devices act like smart cards, allowing users to perform transactions such as payment or ticketing.
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- NFC reader/writer
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- NFC-enabled devices to read information stored on inexpensive NFC tags embedded in labels or smart posters.
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- NFC peer-to-peer
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- Enables two NFC-enabled devices to communicate with each other to exchange information in an adhoc fashion. 14
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> [!INFO] Three modes. emulation, writer, p2p.
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Proximity Sensors & Near Field Communication
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- Different technologies for sensing proximity or exchanging data (often dual purpose)
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- Stand-alone infrastructure approaches
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- Not widely accepted due to special hardware requirements infrastructure costs (for tracking)
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- Conceptually often similar to cell-based approaches but require extra infrastructure NFC (Example: PayWave) Bluetooth RFID IrDa Location Sensors - GPS
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GPS - Overview
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- (Navstar-) GPS is a satellite-based navigation system that provides users with Positioning (and Timing services
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- Provides information anywhere on Earth with unobstructed Line Of Sight
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- Operates in any weather conditions (but with accuracy constraints)
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- Available to military, commercial and civil users
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- Similar systems:
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- Glonass (Russia, Operational)
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- Beidou/Compass/Beidu 2 (China, operational since 2020)
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- Galileo (Europe, expected operational since 2020)
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- Local coverage (DORIS, IRNSS, ..)
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> [!INFO] initally only for millitary. now open to anyone but need under open sky
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GPS - Applications
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- Numerous GPS applications & GPS Receivers:
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- Military
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- initally for remote guided bombs
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- Car navigation
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- Marine
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- Flight control
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- Agriculture
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- Recreation
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- For mobile devices
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- Car an personal navigation
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- Location-based services
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- Augmented Reality
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GPS - History
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- GPS project was developed in 1973 by U.S. Department of Defence (successor of Transit/NAVSAT
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- Originally comprised of 24 satellites, now 30 (including redundant satellites), 65 launched
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- Originally intended for military applications
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- 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)
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- Civil based GPS was limited through Selective Availability (SA)
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- Accuracy errors of 100m
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- SA was removed for civilian users in 2003.
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- GPS achieved initial operational capability (24 Satellites) in 1993 GPS – Satellites
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GPS – Satellites
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- Constellation of 24 + X satellites transmitting radio signals to users
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- Altitude of 20,000km (approx.)
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- Each satellite orbits Earth twice/day
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- Arranged in 6 orbital planes
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- Each plane has four slots
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- At least four satellites from virtually anywhere on earth (we come back to this..)
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- Satellites use high precision atomic clock
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> [!INFO] constantly transmitting signal. they send the route they are flying, and where the other satelittes are flying
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GPS - Signal
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- GPS satellite constantly transmits radio signals (L1 signal for privat, L2 military
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- The navigation message is made up of three major components:
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- GPS date and time, plus the satellite's status and an indication of its health
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- Orbital information called ephemeris data and allows the receiver to calculate the position of the satellite (valid ~4h)
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- Almanac, contains information and status concerning all the satellites; their locations and PRN numbers needed to find satellites (valid ~180days)
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- Each satellite has a unique ID called “Gold codes” or PRNs (pseudo-random noise sequences) to differentiate each satellite
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> [!INFO] get data from four satellites, (position, time, etc).
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GPS - Receiver
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- Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location
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GPS - Receiver
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- Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location Triangulation = working with angles Trilateration = working with distances
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 2D (3 Circles) Dunedin
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 2D (3 Circles) Dunedin
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 2D (3 Circles) Dunedin
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 3D (4 Spheres) Dunedin
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 3D (4 Spheres) Dunedin
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GPS - Receiver
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- Uses messages received from satellites (n"4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location In 3D (4 Spheres) Dunedin But our receiver does not have an atomic clock!!
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GPS - Receiver
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- Uses messages received from satellites (n≥4) to determine the satellite positions and time sent
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- Gives roughly distance to satellite
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- Applies Trilateration for computing location
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- The receiver has four unknowns, the three components of GPS receiver position and the clock bias [x, y, z, b]
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- Using four (or more) satellites, we can set up 4 linear equations to solve for x, y, z, b
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- In some cases we know z or b we need less satellites! Urban Canyon
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- Urban environment similar to a natural canyon
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- Can impact radio reception of GPS receivers
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- Buildings reflect and occlude satellite signals
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- Reducing precision of positioning in urban environments
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- Makes positioning impossible Urban Canyon
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- Urban environment similar to a natural canyon
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- Can impact radio reception of GPS receivers
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- Buildings reflect and occlude satellite signals
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- Reducing precision of positioning in urban environments
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- Makes positioning impossible www.hci.otago.ac.nz The end! |