1. Cellular Telephony

2. 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

3. 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

4. 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

5. 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

6. Signal transmission Mobile and Ubiquitous Computing

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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