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Communication Technology. Soochow University Library Chen Jiacui. Outline. Mobile Communication Satellite Communications Optical Fiber Communication Wireless Communication. cordless phones. wireless LAN. cellular phones. satellites. 1980: CT0. 1981: NMT 450. 1982: Inmarsat-A.
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Communication Technology Soochow University Library Chen Jiacui Jane Chen - SUL
Outline • Mobile Communication • Satellite Communications • Optical Fiber Communication • Wireless Communication Jane Chen-SUL
cordlessphones wireless LAN cellular phones satellites 1980:CT0 1981: NMT 450 1982: Inmarsat-A 1984:CT1 1983: AMPS 1986: NMT 900 1987:CT1+ 1988: Inmarsat-C 1991: CDMA 1991: D-AMPS 1989: CT 2 199x: proprietary 1991: DECT 1992: GSM 1992: Inmarsat-B Inmarsat-M 1995/96/97: IEEE 802.11, HIPERLAN 1993: PDC 1994:DCS 1800 1998: Iridium analog 2005?: MBS, WATM 2005?: UMTS/IMT-2000 digital Jane Chen-SUL
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 Jane Chen-SUL
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 Jane Chen-SUL
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 Jane Chen-SUL
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 Jane Chen-SUL
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 Jane Chen-SUL
Problems – con’t • 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) Jane Chen-SUL
Problems –con’t • 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 Jane Chen-SUL
Problems –con’t • 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 Jane Chen-SUL