Cellular Telephony

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

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

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

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
  dont have to be constantly on
• More services (SMS)
• Better voice quality usually
• Better authentication to prevent fraud

6
Signal transmission
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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

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

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

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

11
Generations of telephony

• http//www.iec.org/online/tutorials/umts/topic01.h
  tml
• 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
3G

• Various standards worldwide
• W-CDM/UMTS (Europe and Japan)
• Successor to GSM
• CDMA2000 (U.S.)
• Attempt at worldwide standardization
• IMT 2000

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

14
Other packet-switched

• Mobitex
• Originated in Europe
• In U.S. as BellSouth Mobile Data
• 8 Kbps
• What Palm VII use
• ARDIS
• Metricom