ch. 3 data transmission part 1

8/7/2019 Ch. 3 Data Transmission Part 1

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Data and Computer

Communications

Ninth Edition

by William Stallings

Chapter 3 Data Transmission

Data and Computer Communications, Ninth

Edition by William Stallings, (c) PearsonEducation - Prentice Hall, 2011

Data Transmission

The successfultransmission of

data depends on

two factors:

quality of the signal

being transmitted

characteristics of the

transmission medium


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Transmission Terminology

Data transmission occurs between transmitterand receiver over some transmission medium.

Communicationis in the form ofelectromagnetic

waves.

Guidedmedia

twisted pair,coaxial cable,optical fiber

Unguidedmedia

(wireless)

air, vacuum,seawater

TransmissionTerminology


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TransmissionTerminology

Simplex

signals transmitted in one direction eg. Television

Half duplex

both stations transmit, but only one at a time eg. police radio

Full duplex

simultaneous transmissions eg. telephone

Frequency, Spectrum andBandwidth

analog signal

signal intensity varies smoothly with no breaks

digital signal

signal intensity maintains a constant level andthen abruptly changes to another level

periodic signal

signal pattern repeats over time

aperiodic signal

pattern not repeated over time

Time Domain Concep s


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Analog and Digital Signals

Periodic

Signals


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Sine Wave

peak amplitude (A) maximum strength of signal

typically measured in volts

frequency (f) rate at which the signal repeats

Hertz (Hz) or cycles per second

period (T) is the amount of time for one repetition

T = 1/f

phase (J)

relative position in time within a single period of signal

(periodic continuous signal)

Varying Sine Wavess(t) = A sin(2Tft +*)


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Wavelength (P)

the wavelength ofa signal is the

distance occupiedby a single cycle

can also be stated as thedistance between two

points of correspondingphase of two consecutive

cycles

assuming signalvelocity v, then the

wavelength is relatedto the period as P = vT

or

equivalentlyPf = v

especially when v=c

c = 3*108 ms-1(speed of light infree space)

Frequency Domain Concepts

signals are made up of many frequencies

components are sine waves

Fourier analysis can show that any signal

is made up of components at various

frequencies, in which each component is a

sinusoid can plot frequency domain functions


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Frequency

Domain

Representations

frequency domain

function of Fig 3.4c

frequency domain

function of single

square pulse

Spectrum & Bandwidth


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Signal with dc Component

Data Rate and Bandwidthany t ansmission

system has alimited band o

equencies

this limits the dataate that can beca ied on the

t ansmission medium

squa e waveshave in inite

components and

hence an in initebandwidth

most ene gy ini st ew

components

limitingbandwidth

c eates

disto tions

The e is a di ect elationship between

data ate and bandwidth.

ch. 3 data transmission part 1

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