Transmitting voice and data using electromagnetic waves in open space

Transcription

1 What is Wireless Cmmunicatin? Transmitting vice and data using electrmagnetic waves in pen space Why Wireless? Freedm frm wires N cst f installing the wires, N bunches f wires running arund e.g. Bluetth, Wi-Fi Glbal cverage where wires cmmunicatin is nt feasible r cstly e.g. rural areas, battle field and uter space. Stay Cnnected Flexibility Any where any time Cnnect t multiple devices simultaneusly Wireless Histry Ancient Systems: Smke Signals, Carrier Pigens Using light and flags fr wireless cmmunicatin remained imprtant fr the navy until radi transmissin was intrduced. Even tday a sailr has t knw sme cdes represented by flags if all ther means f wireless cmmunicatin fail. James C Maxwell ( ) laying the theretical fundatin fr EM fields with his famus equatins Heinrich Hertz ( ) was the first t demnstrate the wave character f electrical transmissin thrugh space (1886).(Nte Tday the unit Hz reminds us f this discvery). Radi invented in the 1880s by Marcni The first transatlantic transmissin fllwed in WARC Wrld Administratin Radi Cnference tk place,crdinating wrld wide use f radi frequencies The 1st radi bradcast tk place in 1906 when Reginald A Fessenden transmitted vice and music fr Christmas. The inventin f electrnic vacuum tube in 1906 by Lee De Frest ( ) &Rbert Vn Lieben ( )Helped t reduce the size f sender and receiver. One f the 1st mbile transmitter was n bard at Zeppelin in 1911 In 1915, the first wireless vice transmissin was set up between New Yrk and San Francisc EC2401 Wireless Cmmunicatin Unit 1 Page 1

2 The 1st cmmercial radi statin started in 1920 Nte Sender & Receiver still needed huge antennas High transmissin pwer. In 1926, the first telephne in a train was available n the Berlin Hamburg line 1928 was the year f many field trials fr TV bradcasting. Jhn L Baird ( ) transmitted TV acrss Atlantic and demnstrated clr TV Until 1932, all wireless cmmunicatin used AM which ffered relatively pr quality due t interference. Inventin f FM in 1933 by Edwin H Armstrng [ ]. Bth the mdulatin schemes are still used fr tdays radi bradcasting with FM having much better quality. 1946, Public Mbile in 25 US cities, high pwer transmitter n large twer. Cvers distance f 50 Km. Push t talk, uses 120khz f RF bandwidth.1950 channels dubled and BW 60k, times increase, BW 30khz After 2nd wrld war (in 1958),a netwrk in Germany was build namely the analg A- Netz using a carrier frequency f 160 Mhz. Cnnectin setup was nly pssible frm the mbile statin and n handver was pssible 1982: Grupe Spéciale Mbile was launched t develp standards fr pan-eurpean mbile netwrk GSM nw stands fr Glbal System fr Mbile Cmmunicatins 1992 Official cmmercial launch f GSM in Eurpe 1995 GSM specificatins prted t PCS Wireless LANs Specificatin fr next generatin CDMA starts Qualcmm starts wrk n wideband CDMA spec Bluetth with 1Mbit/s specificatin, single cell Later wrk n 10Mbit/s spec with multi cell capability In 2002 Camera phnes are first intrduced in the U.S. market. In 2005 mbile phne subscribers exceed fixed phne subscriber. itunes Applicatin Stre (July) and Andrid Market (Octber) pen in 2008 In 2010 First 4G handset is intrduced at Internatinal CTIA WIRELESS shw. In 2010 Apple intrduced the ipad, anther revlutin in prtable tablet cmputing. In 2010 FCC prpses Natinal Bradband Plan, recmmending 500MHz f spectrum be allcated fr cmmercial use by In 2012 the number f subscriber reaches 1 millin. EC2401 Wireless Cmmunicatin Unit 1 Page 2

3 Electrmagnetic Spectrum Electrmagnetic waves: Travel at speed f light (c = 3x10 8 m/s and Has a frequency (f) and wavelength (ƛ) c = f x ƛ Higher frequency means higher energy phtns The higher the energy phtn the mre penetrating is the radiatin Wavelength f Sme Technlgies GSM Phnes: frequency ~= 900 Mhz wavelength ~= 33cm PCS Phnes frequency ~= 1.8 Ghz wavelength ~= 17.5 cm Bluetth: frequency ~= 2.4Gz wavelength ~= 12.5cm Federal Cmmunicatins Cmmissin(FCC) PTA EC2401 Wireless Cmmunicatin Unit 1 Page 3

4 Frequency Carries/Channels The infrmatin frm sender t receiver is carrier ver a well defined frequency band. This is called a channel Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate) Different frequency bands (channels) can be used t transmit infrmatin in parallel and independently. Wireless Cmmunicatin System Examples Cellular Telephny Wide Area Wireless Data Systems High Speed Lcal and Persnal Area Netwrks Paging Messaging Systems Satellite Based Mbile System Wireless System Definitins Mbile Switching Center Switching center which crdinates the ruting f calls in a large service area. In a cellular radi system, the MSC cnnectins the cellular base statins and the mbiles t the PSTN (telephne netwrk). It is als called Mbile Telephne Switching Office (MTSO) Subscriber A user wh pays subscriptin charges fr using a mbile cmmunicatin system Transceiver A device capable f simultaneusly transmitting and receiving radi signals Cntrl Channel Radi channel used fr transmissin f call setup, call request, call initiatin and ther beacn and cntrl purpses. Frward Channel Radi channel used fr transmissin f infrmatin frm the base statin t the mbile Reverse Channel Radi channel used fr transmissin f infrmatin frm mbile t base statin Simplex System Cmmunicatin systems which prvide nly ne-way cmmunicatin Examples include Pagers EC2401 Wireless Cmmunicatin Unit 1 Page 4

5 Half Duplex Systems Cmmunicatin Systems which allw tw-way cmmunicatin by using the same radi channel fr bth transmissin and receptin. At any given time, the user can either transmit r receive infrmatin. Push-t-talk and release-t-listen systems Full Duplex Systems Cmmunicatin systems which allw simultaneus tw-way cmmunicatin. Transmissin and receptin is typically n tw different channels (FDD). Handff The prcess f transferring a mbile statin frm ne channel r base statin t an ther. Ramer A mbile statin which perates in a service area (market) ther than that frm which service has been subscribed. Page A brief message which is bradcast ver the entire service area, usually in simulcast fashin by many base statins at the same time. Cellular Telephny It is Characterized by High mbility prvisin Wide-range Tw-way vice cmmunicatin Handff and raming supprt Integrated with sphisticated public switched telephne netwrk (PSTN) When mbile is turned n and nt engaged in a call mnitrs the cntrl channel fr strngest BS. Cellular Telephny Systems Mbile users and handsets Very cmplex circuitry and design Base statins Prvides gateway functinality between wireless and wire line links Mbile switching centers Cnnect cellular system t the terrestrial telephne netwrk EC2401 Wireless Cmmunicatin Unit 1 Page 5

6 Cellular Netwrks First Generatin Analg Systems Analg Mdulatin, mstly FM AMPS Vice Traffic FDMA/FDD multiple access Secnd Generatin (2G) Digital Systems Digital Mdulatin Vice Traffic TDMA/FDD and CDMA/FDD multiple access 2.5G Digital Systems Vice + Lw-datarate Data Third Generatin Digital Vice + Highdatarate DATA Multimedia Transmissin als EC2401 Wireless Cmmunicatin Unit 1 Page 6