Transmission impairment of data communication

Transmission impairment of data communication

1. Transmission Impairment
Prepared by
Nusrat Chowdhury
Lecturer, Department of EEE

2. Transmission Impairment
Causes of Transmission Impairment
Attenuation
Distortion
Noise
Lecture Contents

3. TRANSMISSION IMPAIRMENT
Signalstravelthroughtransmissionmedia,which
arenotperfect.
Theimperfectioncausessignalimpairment.This
meansthatthesignalatthebeginningofthe
mediumisnotthesameasthesignalattheendof
themedium.Whatissentisnotwhatisreceived.
Threecausesofimpairmentareattenuation,
distortion,andnoise.

4. Causes of Impairment

5. Attenuation
Means loss of energy -> weaker signal
When a signal travels through a medium it
loses energy overcoming the resistance of
the medium
Amplifiers are used to compensate for this
loss of energy by amplifying the signal.

6. Measurementof Attenuation
To show the loss or gain of energy the unit
“decibel” is used.
dB = 10log
10P
2/P
1
P
1-input signal
P
2-output signal

7. Attenuation

8. Supposeasignaltravelsthroughatransmissionmedium
anditspowerisreducedtoone-half.ThismeansthatP
2
is(1/2)P
1.Inthiscase,theattenuation(lossofpower)
canbecalculatedas
Example3.26
Alossof3dB(–3dB)isequivalenttolosingone-half
thepower.

9. Distortion
Meansthatthesignalchangesitsformorshape
Distortionoccursincompositesignals
Eachfrequencycomponenthasitsown
propagationspeedtravelingthroughamedium.
Thedifferentcomponentsthereforearrivewith
differentdelaysatthereceiver.
Thatmeansthatthesignalshavedifferentphases
atthereceiverthantheydidatthesource.

10. Distortion

11. Noise
There are different types of noise
Thermal-random noise of electrons in the wire
creates an extra signal
Crosstalk-same as above but between two
wires.
Impulse-Spikes that result from power lines,
lightning, etc.

12. Noise

13. Signal to Noise Ratio (SNR)
TomeasurethequalityofasystemtheSNR
isoftenused.Itindicatesthestrengthofthe
signalwithrespecttothenoisepowerinthe
system.
Itistheratiobetweentwopowers.
ItisusuallygivenindBandreferredtoas
SNR
dB.

14. Thepowerofasignalis10mWandthepowerofthe
noiseis1μW;whatarethevaluesofSNRandSNR
dB?
Solution
ThevaluesofSNRandSNR
dBcanbecalculatedas
follows:
Example 3.31

15. ThevaluesofSNRandSNR
dBforanoiselesschannel
are
Example 3.32
Wecanneverachievethisratioinreallife;itisanideal.

16. Two cases of SNR: a high SNR and a low SNR