Lecture Notes on Transmission Fundamentals

8/16/2019 Lecture Notes on Transmission Fundamentals

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Wireless Technology

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In This Lecture

Signals for Conveying Information

Analog and Digital Data Transmission

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ElectromagneticSignals

Electromagnetic signals used as a means to transmit

information.

An electromagnetic signal is a function of time, but it can

also be expressed as a function of frequency t!at is, t!e

signal consists of components of different frequencies.

So, t!ere is t"o important vie" of a signal.

Time vie", #requency vie"



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Time and FrequencyViews

$#D% signal in time and frequency domain.



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Time Domain Concepts

In time domain t!e signal is vie"ed as a function of time.

T!e domain is time.



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Time Domain Concepts

&ie"ed as a function of time, an electromagnetic signal

can be eit!er analog or digital.

Analog signal:

An analog signal is one in "!ic! t!e signal intensity varies

in a smoot! fas!ion over time.

In ot!er "ords, t!ere are no brea's or discontinuities in

t!e signal.



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Analog Signal

Analog Signal : a good example is ecg signal recorded

by analog EC( device.

Time DomainConcepts

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Digital Signal

Digital Signal:

A digital signal is one in "!ic! t!e signal intensity

maintains a constant level for some period of time and

t!en c!anges to anot!er constant level.

Time DomainConcepts



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Periodic and Aperiodic

SignalPeriodic and aperiodic Signal in mathematic view:

%at!ematical s)t* is periodic if

"!ere t!e constant T is t!e period of t!e signal )T is

smallest value t!at satisfies t!e equation*.

Time DomainConcepts



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Sine a!e

T!e sine "ave is t!e fundamental analog signal. A general

sine "ave can be represented by t!ree parameters+ peak

amplitude, frequency, and phase.

T!e peak amplitude is t!e maximum value or strengt! of

t!e signal over time.

T!e frequency is t!e rate at "!ic! t!e signal repeats.

Phase is a measure of t!e relative position in time "it!in a

single period of a signal, as illustrated later.

Time DomainConcepts



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Sine a!e

Consider t!is original Sine -ave. See t!e effect of c!angingeac! of parameters.

$riginal

ea'amplitude

#requency

!ase

Time DomainConcepts



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Sine a!e

Wave length and velocity:

T!e "avelengt! of a signal is t!e distance occupied by a

single cycle, or, t!e distance bet"een t"o points of

corresponding p!ase of t"o consecutive cycles.

Assume t!at t!e signal is traveling "it! a velocity v. T!en

t!e "avelengt! is related to t!e period as follo"s+ / vT.

Equivalently, f / v.

Time DomainConcepts



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Frequency DomainConcepts

An electromagnetic signal "ill be made up of many frequencies.

#or example

T!e components of t!is signal are 0ust sine "aves of frequencies f and

1f. T!e second frequency is an integer multiple of t!e first frequency.



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"undamental "requency

-!en all of t!e frequency components of a signal are

integer multiples of one frequency, t!e latter frequency is

referred to as t!e fundamental frequency.

T!e period of t!e total

signal is equal to t!e

period of t!e fundamental

frequency.

Frequency Domain



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Frequency Components

2sing a discipline 'no"n as Fourier analysis, t!at any

signal is made up of sinusoid components at various

frequencies, amplitudes and p!ases.

3y adding toget!er enoug! sinusoidal signals, eac! "it!

t!e appropriate amplitude, frequency, and p!ase, any

electromagnetic signal can be constructed4

T!e sub0ect of #ourier analysis is introduced in Appendix

3 of t!e main text boo'.

Frequency Domain



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Frequency Components

Frequency Domain



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Spectrum

T!e spectrum of a signal is t!e range of frequencies t!at

it contains.

#or t!e previous slide, t!e spectrum extends from f to 1f.

Example+ Typical energy spectrum of a "ideband speec!

signal.

Frequency Domain



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#andidth

The asolute andwidth of a signal is the width of the

spectrum!

"an we ideally limit a signal to a certain and offrequencies#

%ost of signals !ave an infinite andwidth, but "it! most

of t!e energy contained in a relatively narro" band offrequencies. T!is band is referred to as t!e

effective band"idt!, or 0ust band"idt!.

Frequency Domain



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Data $ate and#andwidth

-!at is data rate5

Simply, information6carrying capacity.

-!at is t!e relation bet"een data rate and band"idt! of a

signal5

T!ere is a direct relations!ip bet"een t!e information6

carrying capacity of a signal and its band"idt!.

T!e greater t!e band"idt!, t!e !ig!er t!e information6

carrying capacity.

#andwidth



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#or a better intuition, consider t!e square "ave. "e let a

positive pulse represent binary 7 and a negative pulse

represent binary 8. T!en t!e "aveform represents t!e

binary stream 78787. ...

Duration of eac! pulse / 89:f

Data rate / :f bps

It can be seen, If "e increase t!e frequency, data rate "ill

be increased too.



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Another task : Now, suppose that we are using a digitaltransmission system that is capable of transmitting signalswith a bandwidth of 4 MHz.

et us attempt to transmit a se!uence of alternating "s and#s as the s!uare wa$e.

%efore doing this task, lets see fre!uency components ofs!uare wa$e.



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Anot!er tas'+

;oo' t!e follo"ing s!ape



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ase *:

ets appro'imate the s!uare wa$e with -ust fre!uency components f, f, /f.

(he signal bandwidth 0 /f 1 f 0 4f

#f f 0 * MHz then %20 4MHz 3$ery pulse as one bit occurs e$ery ./ micro sec.

5o, data rate is 6Mbps.

(herefore, %204MHz data rate 0 6Mbps



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ase *:

#f f 0 * MHz then %20 4MHz data rate 0 6Mbps



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ase 6:

ets appro'imate the s!uare wa$e with -ust fre!uency components f, f, /f in the same way but

with higher f06MHz.

(he signal bandwidth 0 /f 1 f 0 4f

#f f 0 6 MHz then %20 7MHz 3$ery pulse as one bit occurs e$ery .6/ micro sec.

5o, data rate is 4Mbps.

(herefore, %207MHz data rate 0 4Mbps



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ase 6:

#f f 0 6 MHz then %20 7MHz data rate 0 4Mbps



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ase :

#f f 0 6 MHz then %20 4MHz data rate 0 4Mbps



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(o summarize,

8 ase #: %andwidth 0 4 MHz9 data rate 0 6Mbps

8 ase ##: %andwidth 0 7 MHz9 data rate 0 4Mbps

8 ase ###: %andwidth 0 4 MHz9 data rate 0 4Mbps

2hich one is better

#andwidth



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Data Transmission


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Analog and Digital Data

T!e same as signals, data also "e !ave analog and digital

data.

Analog DATA : Analog data ta'e on continuous values in someinterval.

For e$ample% voice and video are continuously varying

patterns of intensity. Also %ost data collected by sensors, suc!

as temperature and pressure.

Digital DATA : Digital data ta'e on discrete values examples

are text and integers.

Data Transmission



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i i



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Speech and %usicSpectrum

T!e most familiar example of analog data is audio, "!ic!, in t!e form of

acoustic sound "aves, can be perceived directly by !uman beings.

#requency components of typical speech may be found bet"een approximately )** '(

and & k'(!

Alt!oug! muc! of t!e energy in speec! is concentrated at t!e lo"er frequencies, tests

!ave

s!o"n t!at frequencies belo" =77 or >77 ?@ add very little to t!e intelligibility of

speec! to t!e !uman ear.

Typical speec! !as a dynamic range of about : d3

t!at is, t!e po"er produced by t!e loudest s!out may be as muc! as 177 times greater t!an t!at of t!e least "!isper.

Data Transmission

i i



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Analog and DigitalSignaling

Signaling: data propagation from one point to anot!er by

means of electromagnetic signals.

Analog Signaling: ropagation of a continuously varying

electromagnetic "ave t!at may be propagated over avariety of media.

%edia depending on frequency examples are copper

wire media, fier optic cale and atmosphere or space

propagation )"ireless*.Digital Signaling: ropagation of a sequence of voltage

pulses.

Data Transmission

D T i i



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Advantage of Digital Signaling:

Digital signaling is generally cheaper t!an analog

signaling and is less susceptible to noise interference.

Disadvantage is t!at digital signals suffer more fromattenuation. 3ecause of t!e attenuation% or reduction of

signal strength at higher frequencies, t!e pulses

become rounded and smaller . loss of t!e information

Can you explain t!e role of frequency in attenuation5

Data Transmission

D t T i i



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3ot! analog and digital data can be represented, and

!ence propagated, by eit!er analog or digital signals.

Data Transmission

D t T i i



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Analog Data y Analog Signal

Analog data are a function of time and occupy a limited

frequency spectrum.

An +nteresting ,esult for Speech Transmission

-Telephone.: As sound waves !ave frequency range of /* '( to /* k'(.

%ost of t!e speech energy is in range of bet"een )** '( and & k'(.

T!e standard spectrum of voice signals is 0** to 01** '(, and t!is

is quite adequate to propagate speec! clearly.

In telep!one for all sound input in t!e range of 177 to 1B77 ?@, an

electromagnetic signal "it! t!e same frequency6amplitude pattern is

produced. T!e process is performed in reverse to convert t!e

electromagnetic energy bac' into sound.

Data Transmission

D t T i i



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Digital Data y Analog Signal :

Digital data can be represented by analog signals by use of a modem

)modulator6demodulator*.

T!e modem converts a series of binary voltage pulses into an analog

signal by modulating a carrier frequency.

T!e most common modems represent digital data in t!e voice

spectrum and !ence allo" t!ose data to be propagated over

telep!one lines.

At t!e ot!er end of t!e line, a modem demodulates t!e signal torecover t!e original data.

Data Transmission

D t T i i


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Analog Data y Digital Signal :

Analog data can be represented by digital signals.

T!e device t!at performs t!is function for voice

data is a codec)coder6decoder*.

Codec ta'es an analog signal of voice data and approximates t!at

signal by a bit stream.

At t!e ot!er end, a codec uses t!e bit stream to reconstruct t!eanalog data.

Data Transmission

D t T i i


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Digital Data y Digital Signal :

To improve propagation c!aracteristics, t!e binary data

are often encoded into a more complex form of digital

signal.

Data Transmission

l d i i lD t T i i


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'ow to make Analog or Digital signaling for Analog or

Digital Signals -Summary.

Data Transmission


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A l d Di i lData Transmission


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,easons for the choice of Analog or Digital signaling

for Analog or Digital Signals:

Analog data% analog signal: Analog data are easily converted to ananalog signal.

Analog data% digital signal: Conversion of analog data to digital form

permits t!e use of modern digital transmission and s"itc!ing

equipment for analog data.

Data Transmission

A l d Di it lData Transmission


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Analog and DigitalTransmission

Analog Transmission:

Transmission of data )digital or analog* in form of analog

signals "it!out regard to t!eir content.

Disadvantage: T!e analog signal "ill suffer attenuation t!at limits t!e length of the transmission lin'.

Solution: To ac!ieve longer distances, t!e analog

transmission system includes amplifiers t!at boost t!e

energy in t!e signal.Prolem+ T!e amplifier also boosts t!e noise

components.

T!e more distances, t!e more amplifiers, t!e more

distortion, and for digital data, also the more error 4

Data Transmission



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Digital Transmission:

is concerned "it! t!e content of t!e signal.

Disadvantage: Digital signal suffers attenuation more

t!at limits t!e length of the transmission lin'.Solution: To ac!ieve longer distances, repeaters are

used.

,epeater + A repeater receives t!e digital signal, recovers

t!e pattern of ones and @eros, and retransmits a ne"signal.

Data Transmission



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Digital Transmission:

is concerned "it! t!e content of t!e signal.

In t!e case of using analog signal for digital transmission

instead of repeaters, retransmission is used.

T!e retransmission device recovers t!e digital data from

t!e analog signal and generates a ne", clean analog

signal, and transmit it again4

Data Transmission


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To #e Continued &

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Lecture Notes on Transmission Fundamentals