Communication Technology

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Communication Technology

• Soochow University Library
• Chen Jiacui

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Outline

• Mobile Communication
• Satellite Communications
• Optical Fiber Communication
• Wireless Communication

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wireless LAN
cordlessphones
cellular phones
satellites
1980CT0
1981 NMT 450
1982 Inmarsat-A
1984CT1
1983 AMPS
1986 NMT 900
1987CT1
1988 Inmarsat-C
1991 D-AMPS
1991 CDMA
1989 CT 2
199x proprietary
1991 DECT
1992 GSM
1992 Inmarsat-B Inmarsat-M
1995/96/97 IEEE 802.11, HIPERLAN
1993 PDC
1994DCS 1800
1998 Iridium
2005? MBS, WATM
analog
2005? UMTS/IMT-2000
digital
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Mobile Networks

• Problems
• Mobility increase fading and bit error rate
• Lower throughput and higher delay
• Awareness of mobile computing environment
• Location of mobile unit
• (e.g. route information services, local yellow
  pages)
• Tariff switch to different interface for
  various functions
• (e.g. email, ftp)
• Variable bandwidth and device/interface
• Disconnected operations

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Technical Issues in Mobile Networks(1)

• Mobility network layer must
• Know where a user is
• Problem host IP name is bound to its network
  address and we can determine the network address
  but not the physical location
• When a host moves, techniques to determine its
  recent address are
• Broadcast
• Central Services(GSM Global System for Mobile
  Communications)
• Home base(Mobile IP)
• Route message to mobile users
• Store info about current location of users
• Mobile IP solution
• Cellular phone network solution

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Technical Issues in Mobile Networks(2)

• Ad-hoc networking
• Mobile hosts form networks without fixed
  infrastructure
• Dynamic topology structure
• Dynamic source routing use cached info and
  route discovery protocol

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Technical Issues in Mobile Networks(3)

• Portability
• Low power
• Power saving methods
• Risk of data loss
• Replicate to more secure site
• Small user interface
• Handwriting recognition
• Speech recognition
• Pen-point devices
• Small storage capacity
• No disk use ROM
• Script language reduces program size

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Wireless Communications

• Wireless Networks
• Involves wireless communication media not
  necessarily mobile Aloha network
• Problems
• Shared media
• Increased bit error rate(BER)
• Lower radio transmission power

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Problems cont

• Shared media
• Low bandwidth
• Technique for increasing bandwidth
• Divide into cells(sub-networks) overlap cells
  on different wavelength (scarce spectrum) and
  reuse channels from cell to cell
• Reduce range to increase number of cells ( fewer
  objects per cell)
• Compression and logging(combine short messages
  into long ones)

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Problems cont

• Increased bit error rate(BER) due to
• Fading multipath and long-term fading
• Noise quality of transmission media
• Interference concurrent usage of communication
  media
• Frequent disconnection

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Problems cont

• Lower radio transmission power
• Scarce energy resource in mobile units
• Limits transmission power to avoid interference
• Signal strength decrease with inverse square of
  distance
• Higher frequency(3-5 GHz) increase attenuation
  and decrease range