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Cellular Telephony Agenda Wireless overview Basics of cellular telephony Paper: context-aware communication Thursday WPAN: Short-range wireless (IR, RF) Next week: Tuesday: WPAN applications Thursday: privacy Wireless Technologies Overview Wireless Wide Area Network (WWAN)

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Presentation Transcript

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Agenda

  • Wireless overview

  • Basics of cellular telephony

  • Paper: context-aware communication

  • Thursday

    • WPAN: Short-range wireless (IR, RF)

  • Next week:

    • Tuesday: WPAN applications

    • Thursday: privacy

Mobile and Ubiquitous Computing


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Wireless Technologies Overview

  • Wireless Wide Area Network (WWAN)

    • Based on cellular telephony

    • GPRS, CDPD, UMTS, CDMA2000

  • Wireless Local Area Network (WLAN)

    • 802.11b (2.4 GHz), 802.11b (5.8 GHz)

  • Wireless Personal Area Network

    • Bluetooth, IrDA, 802.15

Mobile and Ubiquitous Computing


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Cellular telephony

  • Late 1970s - first analog systems

    • First in Scandanavia and Japan

    • Advanced Mobile Phone System (AMPS) is North American standard

  • Base stations, handsets and the handoff

    • Capacity of single cell and system of cells

    • See http://3g.cellular.phonecall.net/secrets.html#htop

    • Operate in 800-900 MHz and 1800-2100 MHz

Mobile and Ubiquitous Computing


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Analog vs. Digital

  • Digital cellular: Voice signal is digitized

    • Compressed voice transmitted faster than real-time, so frequencies can be shared, increasing capacity

    • Smaller handsets (simpler electronics and lower power)

    • Longer battery life because receivers/transmitters don’t have to be constantly on

    • More services (SMS)

    • Better voice quality usually

    • Better authentication to prevent fraud

Mobile and Ubiquitous Computing


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Signal transmission

Mobile and Ubiquitous Computing


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Signal transmission

  • Frequency modulation (FDMA)

    • Analog technique

  • Time Division Multiple Access (TDMA)

    • Each frequency channel divided into time slots

    • Works because digitized voice is compressed

  • Code Division Multiple Access (CDMA)

    • Spread spectrum using pseudo random bit streams to encrypt base station to handset communication

Mobile and Ubiquitous Computing


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GSM

  • Global System for Mobile Communications

  • FDMA & TDMA

  • 124 channels

    • 200kHz frequency bandwidth per channel

    • 8 time slots of 500 milliseconds (7 for voice)

  • European standard GSM-900, GSM-1800

  • N. America GSM-1900

  • incompatible with AMPS

Mobile and Ubiquitous Computing


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Wide Area Data

  • Circuit-switched data

    • analog phone with modem (9.6 - 14.4 Kbps)

    • pay while connected

    • must initiate connection

  • Cellular Digital Packet Data (CDPD)

    • obvious advantages over circuit-switched

    • Initial CDPD offered 19.2 Kbps

Mobile and Ubiquitous Computing


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GSM and Data

  • Regular GSM

    • Circuit-switched

    • One time-slot can carry 9.6 Kbps

  • High Speed Circuit Switched Data (HSCSD)

    • Uses up to 4 time slots to obtain 38.4 Kbps

  • General Packet Radio Service (GPRS)

    • Packet-switched

    • Uses up to 8 time slots to get over 100 Kbps

Mobile and Ubiquitous Computing


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Generations of telephony

  • http://www.iec.org/online/tutorials/umts/topic01.html

  • 1G - Analog

  • 2G - Digital

    • e.g., GSM

  • 2.5G – Digital with packet-switched data

    • e.g., GPRS

  • 3G – CDMA-based

    • up to 2 Mbps

    • e.g., W-CDMA and CDMA2000

Mobile and Ubiquitous Computing


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3G

  • Various standards worldwide

    • W-CDM/UMTS (Europe and Japan)

      • Successor to GSM

    • CDMA2000 (U.S.)

  • Attempt at worldwide standardization

    • IMT 2000

Mobile and Ubiquitous Computing


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Specialized Mobile Radio

  • initial analog radio dispatch

    • push to talk

  • Motorola made digital

    • added for telephony, paging and packet-switched data

  • Nextel is example

Mobile and Ubiquitous Computing


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Other packet-switched

  • Mobitex

    • Originated in Europe

    • In U.S. as BellSouth Mobile Data

    • 8 Kbps

    • What Palm VII use

  • ARDIS

  • Metricom

Mobile and Ubiquitous Computing


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