Introduction to Electronic Communications Systems
Lecture #1
Significance of Human Communication
Communication is the process of exchanging information. Main barriers are language and distance.
Contemporary society s emphasis is no! the accumulation" pac#aging" and exchange of information.
Methods of communication$
1.%ace to face &.Signals '.(ritten !ord )letters* +.Electrical inno,ations$ -..elegraph /..elephone 0.1adio 2..ele,ision 3.Internet )computer*
Communication Systems
4asic components$
.ransmitter Channel or medium 1ecei,er
Noise degrades or interferes !ith transmitted information.
.ransmitter
.he transmitter is a collection of electronic components
and circuits that con,erts the electrical signal into a signal suitable for transmission o,er a gi,en medium.
.ransmitters are made up of oscillators" amplifiers"
tuned circuits and filters" modulators" fre5uency mixers" fre5uency synthesi6ers" and other circuits.
Communication Channel
.he communication channel is the medium by !hich
the electronic signal is sent from one place to another. .ypes of media include
Electrical conductors 7ptical media %ree space System8specific media )e.g." !ater is the medium for sonar*.
1ecei,ers
9 receiver is a collection of electronic components and
circuits that accepts the transmitted message from the channel and con,erts it bac# into a form understandable by humans. 1ecei,ers contain amplifiers" oscillators" mixers" tuned circuits and filters" and a demodulator or detector that reco,ers the original intelligence signal from the modulated carrier.
.ranscei,ers
9 transceiver is an electronic unit that incorporates
circuits that both send and recei,e signals. Examples are$ .elephones %ax machines Handheld C4 radios Cell phones Computer modems
9ttenuation
Signal attenuation, or degradation" exists in all media
of !ireless transmission. It is proportional to the s5uare of the distance bet!een the transmitter and recei,er.
:oise
Noise is random" undesirable electronic energy that
enters the communication system ,ia the communicating medium and interferes !ith the transmitted message.
.ypes of Electronic Communication
Electronic communications are classified according to !hether they are
1. 7ne8!ay )simplex* or t!o8!ay )full duplex or half
duplex* transmissions &. 9nalog or digital signals.
Simplex
.he simplest method of electronic communication is
referred to as simplex. .his type of communication is one8!ay. Examples are$ 1adio .; broadcasting 4eeper )personal recei,er*
%ull <uplex
Most electronic communication is t!o8!ay and is
referred to as duplex. (hen people can tal# and listen simultaneously" it is called full duplex. .he telephone is an example of this type of communication.
Half <uplex
.he form of t!o8!ay communication in !hich only one
party transmits at a time is #no!n as half duplex. Examples are$ =olice" military" etc. radio transmissions Citi6en band )C4* %amily radio 9mateur radio
9nalog Signals
9n analog signal is a smoothly and continuously
,arying ,oltage or current. Examples are$ Sine !a,e ;oice ;ideo ).;*
<igital Signals
<igital signals change in steps or in discrete
increments. Most digital signals use binary or t!o8state codes. Examples are$ .elegraph )Morse code* Continuous !a,e )C(* code Serial binary code )used in computers*
Many transmissions are of signals that originate in
digital form but must be con,erted to analog form to match the transmission medium. <igital data o,er the telephone net!or#. 9nalog signals.
.hey are first digiti6ed !ith an analog8to8digital )9><*
con,erter. .he data can then be transmitted and processed by computers and other digital circuits.
Modulation and Multiplexing
Modulation and multiplexing are electronic
techni5ues for transmitting information efficiently from one place to another. Modulation ma#es the information signal more compatible !ith the medium. Multiplexing allo!s more than one signal to be transmitted concurrently o,er a single medium.
Modulation at the transmitter.
Multiplexing
Multiplexing is the process of allo!ing t!o or more
signals to share the same medium or channel. .he three basic types of multiplexing are$ %re5uency di,ision .ime di,ision Code di,ision
Multiplexing at the transmitter.
18-$ .he Electromagnetic Spectrum
Figure 1-13: The electromagnetic spectrum.
Fre uenc! and Wavelength: Wavelength
Wavelength &'( ) speed of light * fre uenc! +peed of light ) 3 , 1-. meters/second Therefore: ' ) 3 , 1-. / f Example: What is the wavelength if the fre uenc! is "M#$% ' ) 3 , 1-. / " M#$ ) 01 meters &m(
%re5uency 1anges from '? H6 to '?? @H6
.he electromagnetic spectrum is di,ided into segments$
#igh Fre uencies &#F(
&short waves2 3456 778 9roadcasts2 government and militar! two-wa! communication2 amateur radio6 87.
3:3- M#$
3er! #igh Fre uencies &3#F(
FM radio 9roadcasting &..:1-. M#$(6 television channels ;:13.
3-:3-- M#$
<ltra #igh Fre uencies &<#F(
T3 channels 1":=06 cellular phones6 militar! communication.
3--:3--- M#$
Microwaves and +uper #igh Fre uencies &+#F(
+atellite communication6 radar6 wireless >5?s6 microwave ovens
1:3- @#$
Extremel! #igh Fre uencies &E#F(
+atellite communication6 computer data6 radar
3-:3-- @#$
7ptical Spectrum
.he optical spectrum exists directly abo,e the
millimeter !a,e region. .hree types of light !a,es are$ Infrared ;isible spectrum Altra,iolet
.ransmitting B 1ecei,ing Systems
.elegraph
.he first electronic communication system %. 4. Morse built a telegraph line in 12+' .he first telegraph cable !as laid across 9tlantic 7cean in 12-2 .elegraph system C Dey" =o!er source" Sounder and (ires 888 Morse Code
.elephone
@raham 4ell !as a teacher of the deaf 9 telephone mouthpiece contains tiny carbon grains Louder speech 888 grains are tightly pac#ed Soft speech 888 grains are loosely pac#ed .he amount of the current flo! changes as !e change the !ay !e spea# 9 thin piece of metal ,ibrates in the earpiece on the recei,er 9mplifiers" repeaters are needed for the long distance transmission to increase the electric current Connection b>! t!o telephone 888 .elephone S!itching 888 <igital to 9nalog con,ersion
.elephone
%iber optic 888 1?"??? con,ersations" Micro!a,e 888 1??? con,ersations <igital technology 888 for!arding" !aiting" ,oice synthesi6er Cordless phone 888 transmission to a nearby telephone Cellular phone 888 radio !a,e 888 particular area 9utomatic telephone s!itching 888 Stro!ger s!itches
1adio
Max!ell 888 signals can be sent through air Marconi heard the three shorts of the Morse Code for the letter S" sent across the 9tlantic 1egular radio broadcasts began in the 13&?s 888 antennas 1adio lets us listen to music" ne!s and sporting e,ents and also pro,ides us a mode of t!o !ay communication 9lternating ,oltage is sent to an antenna 888 an electromagnetic !a,e is launched into the air Lo! fre5uency 888 high !a,elength and ,ice ,ersa (a,e length C speed of the !a,e > fre5uency of the !a,e
1adio
High fre5uency )H%* radio !a,es bounce off the atmosphere s upper layer" the ionosphere 888 for t!o points on the earth Super high fre5uency )SH%* radio !a,es are used for satellite communication .he channel is the part of the electromagnetic spectrum used for the signal 7ne transmitter" many recei,ers 888 broadcasting" e.g. %M B 9M 7ne transmitter" one recei,er 888 point to point
.ele,ision
Much li#e the radio except that the transmission can be seen also ;ideo camera is needed at the transmitting station and a monitor at the recei,ing station ;ideo signals may be stored 888 ;C1 Color signals brea# do!n light into red" green and blue Cable .;" =ay per ,ie!
Micro!a,e Communication
Micro!a,es are radio signals that use higher fre5uencies than %M radio signals or .; broadcasts Ased for telephone and .; signal transmission %re5uency distribution for different uses on page 100
Satellite Communication
.hey are radio relay stations called repeaters .hey ha,e to be geosynchronous Aplin# and do!nlin#
Historical re,ie!
Early history of communication
1033 9lessandro ;olta in,ented electric battery" 12'0 Samuel Morse demonstrated telegraph and 12++ first telegraph line )(ashington84altimore* became operational
Early history of !ireless communication
12'1 %araday demonstrates electromagnetic induction E. Max!ell )12'1803*$ theory of electromagnetic %ields" !a,e e5uations )12/+* H. Hert6 )12-083+*$ demonstrates !ith an experiment the !a,e character of electrical transmission through space)1222" in Darlsruhe" @ermany" at the location of today s Ani,ersity of Darlsruhe*
Historical re,ie!
Early history of !ireless communication I
123
@uglielmo Marconi
first demonstration of !ireless telegraphy )digitalF* long !a,e transmission" high transmission po!er necessary )G &??#!*
13?0
Commercial transatlantic connections (ireless ,oice transmission :e! Hor# 8 San %rancisco <isco,ery of short !a,es by Marconi
huge base stations )'? 1??m high antennas*
13113&?
reflection at the ionosphere smaller sender and recei,er" possible due to the in,ention of the ,acuum tube )13?/" Lee <e%orest and 1obert ,on Lieben*
13&/
.rain8phone on the line Hamburg 8 4erlin
!ires parallel to the railroad trac#
Elements
of a communication system )information inputs*
4asic concepts
,oice )audio*" text" image>,ideo and data
Sources Signals
9nalogue signals" <igital signals
:oises
.hermal noise" man8made noise" atmospheric noise" etc
Sin#s )information output de,ices*
Computer screens" spea#ers" .; screens" etc
Signal Processing
m( t )
Carrier Circuits
Transmission Medium
Carrier Circuits
Signal Processing
(t ) m
s(t)
TRANSMITTER
CHANNEL
r(t)
RECEIVER
%re5uencies for communication
coax ca9le optical transmission
twisted pair 1 Mm 3-- #$ 1- Am 3- A#$
1-- m 3 M#$
1m 3-- M#$
1- mm 3- @#$
1-- m 3 T#$
1 m 3-- T#$
3>F
>F
MF
#F
3#F
<#F
+#F
E#F
infrared
visi9le light <3
3>F ) 3er! >ow Fre uenc! >F ) >ow Fre uenc! MF ) Medium Fre uenc! #F ) #igh Fre uenc! 3#F ) 3er! #igh Fre uenc!
<#F ) <ltra #igh Fre uenc! +#F ) +uper #igh Fre uenc! E#F ) Extra #igh Fre uenc! <3 ) <ltraviolet >ight
Fre uenc! and wave length: ) c/f wave length 6 speed of light c 3x1-.m/s6 fre uenc! f 1. "-
