CHAPTER 1CHAPTER 1

Basic Elements in Communication Basic Elements in Communication SystemSystem

Chapter 1 (cont…)Chapter 1 (cont…)

Part 1 Part 1 Introduction to Introduction to Communication Communication SystemSystem

Part 2 Part 2 Noise Noise Part 3 Part 3 Filter Filter

Part 1 Part 1 Introduction Introduction to Communication to Communication

SystemSystem

ObjectivesObjectives To understand the principles of basic To understand the principles of basic

communication systemscommunication systems To define information, message and signalsTo define information, message and signals To differentiate between analog and digital signalsTo differentiate between analog and digital signals To explain the elements of communication systemTo explain the elements of communication system To explain the terms modulation and why they are To explain the terms modulation and why they are

needed in communication systemneeded in communication system To explain the limitations in communication To explain the limitations in communication

systemsystem To define frequency and wavelengthTo define frequency and wavelength To understand the use of decibel (dB) in To understand the use of decibel (dB) in

communications systemcommunications system

Lecture overviewLecture overview Definition of communicationsDefinition of communications Information, message and signalsInformation, message and signals Analog and digital signalsAnalog and digital signals Basic requirements of communication systemBasic requirements of communication system Elements of communication systemElements of communication system ModulationModulation Noise, interference and distortionNoise, interference and distortion Limitations in communication systemLimitations in communication system Frequency and wavelengthFrequency and wavelength dB in communicationsdB in communications

Signals and Systems DefinedSignals and Systems Defined

A A signalsignal is any physical phenomenon which is any physical phenomenon which conveys informationconveys information

SystemsSystems respond to respond to signalssignals and produce new and produce new signalssignals

ExcitationExcitation signalssignals are applied at are applied at systemsystem inputsinputs and and responseresponse signalssignals are produced at are produced at systemsystem outputsoutputs

A Communication System as a A Communication System as a System ExampleSystem Example

A A communication systemcommunication system has an has an information information signalsignal plus plus noise signals noise signals

This is an example of a This is an example of a systemsystem that consists of an that consists of an interconnection of smaller interconnection of smaller systemssystems

Signal TypesSignal Types

Conversions Between Signal Conversions Between Signal TypesTypes

Sampling

Quantizing

Encoding

COMMUNICATION SYSTEM COMMUNICATION SYSTEM DefinitionsDefinitions

Communications:Communications: Transfer of Information from one place to another.Transfer of Information from one place to another. Should be efficient, reliable, and secured.Should be efficient, reliable, and secured.

Communication system:Communication system: components/subsystems act together to accomplish information components/subsystems act together to accomplish information

transfer/exchangetransfer/exchange

Definitions (Cont’d)Definitions (Cont’d) Electronic communication systemElectronic communication system

transmission, reception and processing transmission, reception and processing of information between two or more of information between two or more locations using electronic circuits.locations using electronic circuits.

Information sourceInformation source analog/digital formanalog/digital form

Think!Think!

Have you ever pictured yourself Have you ever pictured yourself living in a world without any living in a world without any communication system?communication system?

Need For CommunicationNeed For Communication

Importance of communication:Importance of communication:

exchange of information between exchange of information between two parties separated in distances in two parties separated in distances in a more faster and reliable way.a more faster and reliable way.

Information, message Information, message and signalsand signals

InformationInformation The commodity produced by the source The commodity produced by the source

for transfer to some user at the for transfer to some user at the destination.destination.

MessageMessage The physical manifestation of information The physical manifestation of information

as produced by the information source.as produced by the information source. SignalsSignals

A physical embodiment of information – A physical embodiment of information – voltage signal or current signalvoltage signal or current signal

Brief History in Brief History in CommunicationCommunication

YearYear EventsEvents1844 1844 TelegraphTelegraph1876 1876 TelephoneTelephone1904 1904 AM Radio AM Radio1923 1923 TelevisionTelevision1936 1936 FM RadioFM Radio19621962 SatelliteSatellite19661966 Optical links using laser Optical links using laser

and and fiber opticsfiber optics1972 Cellular Telephone1972 Cellular Telephone1989 Internet1989 Internet

Development and Development and progressprogress

Communications between human Communications between human beingsbeings Form of hand gestures and facial Form of hand gestures and facial

expressionsexpressions Verbal grunts and groansVerbal grunts and groans

Long distance communicationsLong distance communications Smoke signalsSmoke signals TelegraphTelegraph TelephoneTelephone

Cont’d…Cont’d…

Wireless radio signalsWireless radio signals Triode vacuum tubeTriode vacuum tube Commercial radio broadcastingCommercial radio broadcasting

Analog vs. DigitalAnalog vs. Digital AnalogAnalog

Continuous VariationContinuous Variation Assume the total range of Assume the total range of

frequencies/timefrequencies/time All information is transmittedAll information is transmitted

DigitalDigital Takes samples:Takes samples:

non continuous stream of on/off pulsesnon continuous stream of on/off pulses Translates to 1’s and 0’sTranslates to 1’s and 0’s

Analog vs. DigitalAnalog vs. Digital

Digital CSDigital CSAdvantagesAdvantages::-Inexpensive-Inexpensive-Privacy preserved(data -Privacy preserved(data

encrypted)encrypted)-Can merge different -Can merge different

datadata-error correction-error correction

Disadvantages:Disadvantages:-Larger bandwidth-Larger bandwidth-synchronization problem -synchronization problem

is relatively difficultis relatively difficult

Analog CsAnalog CsDisadvantages:Disadvantages:-expensive-expensive-No privacy preserved-No privacy preserved-Cannot merge different -Cannot merge different

datadata-No error correction -No error correction

capabilitycapability

Advantages:Advantages:-smaller bandwidth-smaller bandwidth-synchronization problem -synchronization problem

is relatively easier.is relatively easier.

Basic Requirements of Basic Requirements of Communication SystemCommunication System

Rate of information transfer:Rate of information transfer: how fast the information can be how fast the information can be

transferredtransferred Purity of signal received:Purity of signal received:

whether the signal received is the same whether the signal received is the same as the signal being transmitas the signal being transmit

Simplicity of the systemSimplicity of the system the simpler the system, the better the simpler the system, the better

ReliabilityReliability

Elements of Elements of Communication Communication

System(CS)System(CS)

Elements of CS(cont’d)Elements of CS(cont’d)

Information Information The communication system exists to The communication system exists to

convey a message.convey a message. Message comes from information Message comes from information

sourcesource Information forms - audio, video, text Information forms - audio, video, text

or dataor data

cont’d…cont’d… Transmitter: Transmitter:

Processes input signal to produce a Processes input signal to produce a transmitted signal that suited the transmitted signal that suited the characteristic of transmission channel. characteristic of transmission channel.

E.g. modulation, coding, mixing, translateE.g. modulation, coding, mixing, translate Other functions performed - Amplification, Other functions performed - Amplification,

filtering, antennafiltering, antenna Message converted to into electrical Message converted to into electrical

signals by transducerssignals by transducers E.g. speech waves are converted to E.g. speech waves are converted to

voltage variation by a microphonevoltage variation by a microphone

Elements of CS(cont’d)Elements of CS(cont’d)

Channel (transmission media):Channel (transmission media): a medium that bridges the distance a medium that bridges the distance

from source to destination. from source to destination. Eg:Atmosphere (free space), coaxial Eg:Atmosphere (free space), coaxial cable, fiber optics, waveguidecable, fiber optics, waveguide

signals undergoes degradation from signals undergoes degradation from noise , interference and distortionnoise , interference and distortion

Elements of CS(cont’d)Elements of CS(cont’d)

Receiver: Receiver: to recover the message signal contained in to recover the message signal contained in

the received signal from the output of the the received signal from the output of the channel, and convert it to a form suitable for channel, and convert it to a form suitable for the output transducer. the output transducer.

E.g. mixing, demodulation, decodingE.g. mixing, demodulation, decoding Other functions performed: Amplification, Other functions performed: Amplification,

filtering.filtering. Transducer converts the electrical signal at Transducer converts the electrical signal at

its input into a form desired by the system its input into a form desired by the system usedused

ModulationModulation

What is modulation?What is modulation? a process of changing one or more a process of changing one or more

properties of the analog carrier in properties of the analog carrier in proportion to the information signal.proportion to the information signal.

One of the characteristics of the carrier One of the characteristics of the carrier signal is changed according to the signal is changed according to the variations of the modulating signal.variations of the modulating signal. AM – amplitude, AM – amplitude, EE FM – frequency , FM – frequency , ωω PM - phase , PM - phase , θθ

Modulation (cont’d)Modulation (cont’d)

Why modulation is needed?Why modulation is needed? To generate a modulated signal suited To generate a modulated signal suited

and compatible to the characteristics of and compatible to the characteristics of the transmission channel.the transmission channel.

For ease radiation and reduction of For ease radiation and reduction of antenna sizeantenna size

Reduction of noise and interferenceReduction of noise and interference Channel assignmentChannel assignment Increase transmission speedIncrease transmission speed

Noise, interference and Noise, interference and distortiondistortion

NoiseNoise unwanted signals that coincide with the desired unwanted signals that coincide with the desired

signals. signals. Two type of noise:internal and external noise.Two type of noise:internal and external noise.

Internal noiseInternal noise Caused by internal devices/components in the Caused by internal devices/components in the

circuits.circuits. External noiseExternal noise

noise that is generated outside the circuit. noise that is generated outside the circuit. E.g. atmospheric noise,solar noise, cosmic noise, E.g. atmospheric noise,solar noise, cosmic noise,

man made noise.man made noise.

Noise, interference and Noise, interference and distortion (Cont’d)distortion (Cont’d)

InterferenceInterference Contamination by extraneous signals Contamination by extraneous signals

from human sources.from human sources. E.g. from other transmitters, power lines E.g. from other transmitters, power lines

and machineries.and machineries. Occurs most often in radio systems Occurs most often in radio systems

whose receiving antennas usually whose receiving antennas usually intercept several signals at the same intercept several signals at the same timetime

One type of noise.One type of noise.

Noise, interference and Noise, interference and distortion (Cont’d)distortion (Cont’d)

DistortionDistortion Signals or waves perturbation caused Signals or waves perturbation caused

by imperfect response of the system to by imperfect response of the system to the desired signal itself.the desired signal itself.

May be corrected or reduced with the May be corrected or reduced with the help of equalizers.help of equalizers.

Limitations in Limitations in communication systemcommunication system

Technological problemsTechnological problems Includes equipment availability, Includes equipment availability,

economic factors, federal regulations economic factors, federal regulations and interaction with existing systems.and interaction with existing systems.

Problem solved in theory but perfect Problem solved in theory but perfect solutions may not be practical.solutions may not be practical.

Limitations in Limitations in communication system communication system

(cont’d)(cont’d) Physicals limitationsPhysicals limitations

Bandwidth limitationBandwidth limitation Measure of speedMeasure of speed The system ability to follow signal variations The system ability to follow signal variations

depends on the transmission bandwidth.depends on the transmission bandwidth. Available bandwidth determines the Available bandwidth determines the

maximum signal speed.maximum signal speed.

Limitations in Limitations in communication system communication system

(cont’d)(cont’d) Noise limitationNoise limitation

Unavoidable.Unavoidable. The kinetic theory.The kinetic theory. Noise relative to an information signal is Noise relative to an information signal is

measured in terms of signal to noise ratio measured in terms of signal to noise ratio (SNR).(SNR).

Communication system Communication system designdesign

Compromise within:Compromise within: Transmission time and powerTransmission time and power SNR performanceSNR performance Cost of equipmentsCost of equipments Channel capacityChannel capacity BandwidthBandwidth

FREQUENCY AND FREQUENCY AND WAVELENGTHWAVELENGTH

CycleCycle - One complete occurrence of - One complete occurrence of a repeating wave (periodic signal) a repeating wave (periodic signal) such as one positive and one such as one positive and one negative alternation of a sine wave.negative alternation of a sine wave.

FrequencyFrequency - the number of cycles of - the number of cycles of a signal that occur in one second.a signal that occur in one second.

PeriodPeriod - the time distance between - the time distance between two similar points on a periodic two similar points on a periodic wave.wave.

WavelengthWavelength - the distance traveled - the distance traveled by an electromagnetic (radio) wave by an electromagnetic (radio) wave during one period.during one period.

One cycle

time

PERIOD AND FREQUENCY COMPARED

Frequency = f = 1/T

T = One period

+

0 time

distance

Frequency and wavelength compared

f = 1/T

T

CALCULATING WAVELENGTHCALCULATING WAVELENGTHAND FREQUENCYAND FREQUENCY

= wavelength in meters

f = frequency in MHz

= 300/f

f = 300/

ELF

103 m

107 m

104 m

105 m

106 m

10 m

1 m

10-1 m

10-2 m

10-3 m

10-4 m

102 m

300

Hz

30 H

z

30 k

Hz

3 k

Hz

300

kH

z

30 M

Hz

3 M

Hz

300

MH

z

3 G

Hz

300

GH

z

30 G

Hz

THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ

UHFVHFHFMFLFVLFVF SHF EHF

Frequency

Wavelength

Mill

imet

erw

aves

( = 300/f)

(f = 300/)

LOW AND MEDIUM LOW AND MEDIUM FREQUENCIESFREQUENCIES

Extremely Low FrequenciesExtremely Low Frequencies - 30 to 300 Hz - 30 to 300 Hz

Voice FrequenciesVoice Frequencies - 300 to 3000 Hz - 300 to 3000 Hz

Very Low FrequenciesVery Low Frequencies - 3 kHz to 30 kHz - 3 kHz to 30 kHz

Low FrequenciesLow Frequencies - 30 kHz to 300 kHz - 30 kHz to 300 kHz

Medium FrequenciesMedium Frequencies - 300 kHz to 3 MHz - 300 kHz to 3 MHz

HIGH FREQUENCIESHIGH FREQUENCIES High FrequenciesHigh Frequencies

- 3 MHz to 30 MHz- 3 MHz to 30 MHz

Very High FrequenciesVery High Frequencies - 30 MHz to 300 MHz- 30 MHz to 300 MHz

Ultra High FrequenciesUltra High Frequencies - 300 MHz to 3 GHz- 300 MHz to 3 GHz (1 GHz and above = (1 GHz and above =

microwaves)microwaves)

Super High FrequenciesSuper High Frequencies - 3 GHz to 30 GHz- 3 GHz to 30 GHz

Extremely High Extremely High FrequenciesFrequencies- 30 GHz to 300 GHz - 30 GHz to 300 GHz

10-3 m

10-4 m

300

GH

zM

illi

met

erw

aves

THE ELECTROMAGNETIC SPECTRUM ABOVE 300 GHZ

Wavelength

0.8

x 10

-6 m

0.4

x 10

-6 m

Infr

ared

Vis

ible

Ult

ravi

olet

X-r

ays

Gam

ma

rays

Cos

mic

ray

s

10-5 m

OPTICAL FREQUENCIESOPTICAL FREQUENCIES

InfraredInfrared - 0.7 to 10 micron - 0.7 to 10 micron

Visible lightVisible light - 0.4 to 0.8 micron - 0.4 to 0.8 micron

UltravioletUltraviolet - Shorter than 0.4 - Shorter than 0.4 micronmicron

Note: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

TYPES OF TYPES OF COMMUNICATIONSCOMMUNICATIONS

TX RX

TX

TX

RX

RX

Simplex:One-way

Duplex:Two-wayHalf duplex:Alternate TX/RXFull duplex:SimultaneousTX/RX

Channel

Channel(s)

COMMUNICATIONS COMMUNICATIONS SIGNAL VARIATIONSSIGNAL VARIATIONS

BasebandBaseband - The original - The original information signal such as audio, information signal such as audio, video, or computer data. Can be video, or computer data. Can be analog or digital.analog or digital.

BroadbandBroadband - The baseband signal - The baseband signal modulates or modifies a carrier modulates or modifies a carrier signal, which is usually a sine signal, which is usually a sine wave at a frequency much higher wave at a frequency much higher than the baseband signal.than the baseband signal.

Various forms of Various forms of communication systemcommunication system

Broadcast: radio and televisionBroadcast: radio and television Mobile communicationsMobile communications Fixed communication system- land Fixed communication system- land

lineline Data communication-internetData communication-internet

Frequency Spectrum Frequency Spectrum &Bandwidth&Bandwidth

The frequency spectrum of a waveform The frequency spectrum of a waveform consists of all frequencies contained in consists of all frequencies contained in the waveform and their amplitudes the waveform and their amplitudes plotted in the frequency domain.plotted in the frequency domain.

The bandwidth of a frequency The bandwidth of a frequency spectrum is the range of of frequencies spectrum is the range of of frequencies contained in the spectrum.It is contained in the spectrum.It is calculated by subtracting the lowest calculated by subtracting the lowest frequency from the highest. frequency from the highest.

Frequency Spectrum Frequency Spectrum &Bandwidth&Bandwidth

(cont’d)(cont’d) Bandwidth of the information signal Bandwidth of the information signal

equals to the difference between the equals to the difference between the highest and lowest frequency highest and lowest frequency contained in the signal.contained in the signal.

Similarly, bandwidth of Similarly, bandwidth of communication channel is the communication channel is the difference between the highest and difference between the highest and lowest frequency that the channel lowest frequency that the channel allow to pass through itallow to pass through it

Power gainPower gain

Power gainPower gain It is the ratio of output power, PIt is the ratio of output power, Poutout over over

input power, Pinput power, Pinin. . Absolute power gain (unitless),Absolute power gain (unitless),

Power gain, APower gain, App = P = Poutout/P/Pinin

Absolute power gain can be converted to a Absolute power gain can be converted to a dB value,dB value,

Power gain (dB), APower gain (dB), Ap(dB) p(dB) = 10 log (A= 10 log (App))

A positive (+) dB value indicates a power A positive (+) dB value indicates a power gain or amplification.gain or amplification.

A negative (-) dB value indicates a power A negative (-) dB value indicates a power loss or attenuation.loss or attenuation.

Voltage Gain in Voltage Gain in CommunicationCommunication

In communication, due to known In communication, due to known characteristic impedance of the characteristic impedance of the channel, the power and voltage channel, the power and voltage gains become explicit.gains become explicit.

Voltage gain in dB = 20 log (VVoltage gain in dB = 20 log (Voutout/V/Vinin) ) dB.dB.

Alternatively:Alternatively:

Power gain Power gain = 10= 10 (gain in dB/10)(gain in dB/10)

Voltage gain Voltage gain = 10 = 10 (gain in dB/20)(gain in dB/20)

Example:Example:

A 64 dB gain means 10A 64 dB gain means 1066..44 = 2.5212x10 = 2.5212x1066 watts.watts.

An attenuation by 0.01= 10 log(0.01)An attenuation by 0.01= 10 log(0.01)= -20 dB= -20 dB

Example:Example: Let there be two amplifiers in cascade. Let there be two amplifiers in cascade.

Their gains are 13 dB and 10 dB Their gains are 13 dB and 10 dB respectively. respectively.

The overall gain is 13+10 = 23 dB.The overall gain is 13+10 = 23 dB. In terms of ratio:In terms of ratio: 23 dB = 1023 dB = 10(23/10)(23/10)= 200= 200

OROR 13 dB = 1013 dB = 10(13/10)(13/10)= 20= 20 10 dB = 1010 dB = 10(10/10)(10/10)= 10= 10 Overall gain in terms of ratio Overall gain in terms of ratio 20 x 10 20 x 10

= 200.= 200.

same

Sum

Relative dBRelative dB

It is convenient to express signals with It is convenient to express signals with some some referencereference such as such as

1mW power or, 1mW power or,

1 1 V voltage level. V voltage level. This permits input- and output- signals to This permits input- and output- signals to

be expressed in terms of relative dB.be expressed in terms of relative dB. When referenced to 1mW, it is written dBWhen referenced to 1mW, it is written dBmm

When referenced to 1 When referenced to 1 V, it is written as V, it is written as dBdBVV

The dBm unit is expressed The dBm unit is expressed mathematically as:mathematically as:

Where P is any power in watts and Where P is any power in watts and 1mW is the reference power1mW is the reference power

Relative dB is not a gain but is termed Relative dB is not a gain but is termed as gain with respect to a referenceas gain with respect to a reference

ExampleExample

Convert a power level of 5 watts signal to Convert a power level of 5 watts signal to dBm, dBm,

In relative dB; dBm = 10 log(5W/1mW) In relative dB; dBm = 10 log(5W/1mW)

= 36.99 dB= 36.99 dBmm

Convert a voltage level of 500 Convert a voltage level of 500 V signal to V signal to dBdBV V ::

In relative dB; dBIn relative dB; dBV V = 20 log(500 = 20 log(500 V /1 V /1 V ) V )

= 53.98 dB= 53.98 dBV V

ExampleExample

Convert 10dBm to wattsConvert 10dBm to watts Solution:Solution:

10dBm = 10 log (P10dBm = 10 log (P2 2 / 1mW)/ 1mW)

antilog (1) = Pantilog (1) = P22 / 1mW / 1mW

PP22 = 0.01W = 0.01W

Power levels, gains and Power levels, gains and losseslosses

When power levels are given in When power levels are given in watts and power gains are given in watts and power gains are given in absolute values, the output power is absolute values, the output power is determined by multiplying the input determined by multiplying the input power times the power gains.power times the power gains.

ExampleExample

Given: A three-stage system comprised Given: A three-stage system comprised of two amplifiers and one filter. The of two amplifiers and one filter. The input power Pinput power Pinin = 0.1 mW. The absolute = 0.1 mW. The absolute power gains are Apower gains are Ap1p1 = 100, A = 100, Ap2 p2 = 40 and = 40 and AAp3p3 = 0.25. Determine: = 0.25. Determine:

(a)(a)The input power in dBm.The input power in dBm.

(b)(b)Output power (POutput power (Poutout) in watss and dBm) in watss and dBm

(c)(c)The dB gain of each of the thress stagesThe dB gain of each of the thress stages

(d)(d)The overall gain in dBThe overall gain in dB

ExampleExample

For a three-stage system with an For a three-stage system with an input power Pinput power Pinin= -20 dBm and power = -20 dBm and power gains of the three stages as Agains of the three stages as Ap1p1 = 13 = 13 dB, AdB, Ap2p2 = 16 dB and A = 16 dB and Ap3p3 = -6 dB, = -6 dB, determine the output power (Pdetermine the output power (Poutout) in ) in dBm and watts. dBm and watts.

End of Chapter 1 End of Chapter 1 Part 1Part 1