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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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Cellular Telephony


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agenda
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

wireless technologies overview
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

cellular telephony4
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

analog vs digital
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

signal transmission
Signal transmission

Mobile and Ubiquitous Computing

signal transmission7
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

slide8
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

wide area data
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

gsm and data
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

generations of telephony
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

slide12
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

specialized mobile radio
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

other packet switched
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