Cellular Telephony Mobile and Ubiquitous Computing


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  • The first cellular telephone systems were demonstrated in 1979 by AT&T and Motorola.
    Cellular systems originate in geographically dlimited cells each served by a base station transceiver. The base station hooks the mobile unit to the public phone network and coordinates handing off to other cells as the user moves.
    AMPS stands for Advanced Mobile Phone System.
    Digital cellular technology has recently emerged and offers several advantages. Digitally encoded voice can be sent faster than real speech, so a single frequency channel can share multiple voice channels. Digital cells can be packed more closely, allowing frequency reuse. These factors increase the capacity as much as 12 times over analog.
  • ARDIS stands for Advanced Radio Data Information Service, developed jointly by IBM and Motorola
    Metricom uses a mesh of lamppost mounted radio nodes.
  • Cellular Telephony Mobile and Ubiquitous Computing

    1. 1. Cellular Telephony
    2. 2. Mobile and Ubiquitous 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
    3. 3. Mobile and Ubiquitous 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
    4. 4. Mobile and Ubiquitous 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
    5. 5. Mobile and Ubiquitous 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
    6. 6. Mobile and Ubiquitous Signal transmission
    7. 7. Mobile and Ubiquitous 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
    8. 8. Mobile and Ubiquitous 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
    9. 9. Mobile and Ubiquitous 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
    10. 10. Mobile and Ubiquitous 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
    11. 11. Mobile and Ubiquitous 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
    12. 12. Mobile and Ubiquitous 3G Various standards worldwide W-CDM/UMTS (Europe and Japan) Successor to GSM CDMA2000 (U.S.) Attempt at worldwide standardization IMT 2000
    13. 13. Mobile and Ubiquitous Specialized Mobile Radio initial analog radio dispatch push to talk Motorola made digital added for telephony, paging and packet- switched data Nextel is example
    14. 14. Mobile and Ubiquitous Other packet-switched Mobitex Originated in Europe In U.S. as BellSouth Mobile Data 8 Kbps What Palm VII use ARDIS Metricom