Postacademic Interuniversity Course in Information Technology – Module C1p1 Contents Communications Theory –Parallel vs. serial transmission –Transmission Capacity (Shannon) –Error detection and correction Communications Media –Optical fibers –Coaxial cables –Twisted pairs –Wireless

Postacademic Interuniversity Course in Information Technology – Module C1p2 Wireless Communications Mobile terminals Cost of wiring Why Not ? Lower data rates Lower reliability Potential Lack of Security Why ?

Postacademic Interuniversity Course in Information Technology – Module C1p3 Wireless Communications Main restriction: Limited availability of bandwidth in the electromagnetic spectrum Some solutions: Displace some heavy users Reuse of frequencies at different locations (cellular radio, infrared LAN’s) Sharing of a set of frequencies (spread spectrum radio)

Postacademic Interuniversity Course in Information Technology – Module C1p4 Reuse of Frequencies P(r) = P t /r 2 r transmitter r max = PtPt P min 

Postacademic Interuniversity Course in Information Technology – Module C1p5 Cellular Radio Automatic handover allows continuous operation of mobiles

Postacademic Interuniversity Course in Information Technology – Module C1p6 Cellular Radio k = number available frequencies per cell S = Area of a cell n = Number of simultaneous calls per km 2 p t = Power of transmitter p m = Minimal power at receiver input n = k / S p t = p m * S With smaller cells, - more antenna sites are needed... - more simultaneous calls are possible - transmitted power can be reduced

Postacademic Interuniversity Course in Information Technology – Module C1p7 Cellular Radio in practice FlandersArdennes

Postacademic Interuniversity Course in Information Technology – Module C1p8 Digital Cellular Telephony Name Freq.(MHz) # rad.ch. P.max.(W) r.max.(Km) Voicerate (Kb/s) Capacity (E/Km 2 ) DECT GSM DCS

Postacademic Interuniversity Course in Information Technology – Module C1p9 Infrared LAN’s Limited to line of sight, within a few meters. IR technology also widely used for data transfers between laptops, PDA’s and mobile phones.

Postacademic Interuniversity Course in Information Technology – Module C1p10 Bluetooth Micro-lan’s designed to eliminate desktop wires and connectors on hand-held devices Frequency : 2.4 GHz unlicensed general purpose band Power : Class 3 = 1 mW (Cl. 2 = 10 mW, Cl.1 = 100 mW) Distances : Class 3 = 5m, up to 100m with class1.

Postacademic Interuniversity Course in Information Technology – Module C1p11 Wireless Local Loop Radio is sometimes cheaper than digging the streets !

Postacademic Interuniversity Course in Information Technology – Module C1p12 Wireless Local Loop Using planes or balloons could be simpler than getting building permits for antennas !!!

Postacademic Interuniversity Course in Information Technology – Module C1p13 Microwave Links Cost effective for line of sight communications (30 Km) High transmission capacity (several Mb/s) transmission impaired by heavy rain

Postacademic Interuniversity Course in Information Technology – Module C1p14 Satellite Communications Km Geostationary Round trip Delay = 240 ms High power ground stations Used for TV and paging broadcasting and for point to point links where terrestrial lines would be unpractical or too expensive

Postacademic Interuniversity Course in Information Technology – Module C1p15 Satellite Communications Low Orbit Short round trip delays Low power ground stations Upcoming applications: Narrowband mobile communications (TFTS airline phones, IRIDIUM mobile phones, INMARSAT communications,...)

Postacademic Interuniversity Course in Information Technology – Module C1p16 Introduced concepts Serial transmission Baud rate vs. throughput An upper limit for transmission capacity Error detection and correction Optical transmission and switching Coaxial cables and Twisted pairs Cellular radio and handover Point to point radio Geostationary and low orbit satellites