lect22 - 1.264 Lecture 22 Telecom: wireless technology Long...

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1.264 Lecture 22 Telecom: wireless technology Long range: satellite Metro range: cellular telephony Short range: wireless LANs
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Long-range wireless: satellite communications Figure by MIT OCW.
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Satellite applications Not competition for mobile telephony Iridium, Teldesic not successful: too expensive Global positioning system (GPS) Communications with ships at sea Morse service ended last year for commercial vessels Trucking and rail information systems Direct broadcast TV Video programming (TV stations, CATV distribution)
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Satellite links Figure by MIT OCW.
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Satellite data Delay: 250 milliseconds (1/4 second) delay between two Earth stations communicating via GEO satellite Noticeable for voice communications Requires special treatment of data TCP/IP will assume network congestion or dropped packets with these delays; must use special parameters or equipment to spoof acknowledgements Rain absorption Sun transit outage at equinoxes Power is limited on satellite Limited signal to noise ratio, limits bandwidth DBS satellites are overpowered to allow small consumer antennas; overall system costs are high
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Satellite services Voice, fax paging (Iridium) still available 10 kbps Internet access data rate Inmarsat for marine applications 300,000 ships, vehicles, aircraft 432 kbps Internet access data rate Very small aperture terminal (VSAT) Used for point of sales terminals in remote or rural areas 9.6 kbps to 64 kbps typically
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Metro-range wireless services Mobile telephony is dominant; alternatives are: Specialized mobile radio (SMR), used primarily for local dispatch About 3,000 licensed SMR providers in US (taxi, trucking. .) Nextel
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lect22 - 1.264 Lecture 22 Telecom: wireless technology Long...

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