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Institute of Information & Communication Technologies (I 2CT)Mehran University of Engineering & Technology, Jamshoro, Pa istan

ADVANCED SIMULATION TOOLS

!a" # $% oll 'um"er

Rayleigh Fading ChannelSimulations5.1 Performance Objectives

After this lab, you should be able to: To understand the basics of Multipath FadingGet the basic idea of Channel modeling in MATLABAcquire basic understanding of ayleigh FadingBe able to generate noise signal !ith ayleigh e"ect#Be able to analy$e the e"ect of ayleigh Fading in %imulin&

5.2 !ui"ment Re!uired

'C !ith (indo!sMATLAB )#* or latest !ith %ignal 'rocessing and Communication Toolbo+

5.# $ntroduction to %ulti"ath Channel nvironment

5.#.1 %ulti"ath

For establishing !irelesscommunication, it is preferred thatantennas are to be located atplaces !here there is a direct lineof sight L-%. path from transmitterto the recei/er# This is generally thecase for many satellite facilitiesand for point0to0point micro!a/elin&s# 1o!e/er, the direct L-% pathis not a/ailable e#g#, in cellularcommunication !here there areobstacles in abundance# Because of these obstacles !hen the radio!a/e propagates from the basestation to the mobile station, thesignal can be re2ected of suchobstacles so that multiple copies of the signal !ith /arying amplitudesand delays are recei/ed as sho!n

in Figure *#3# 4n some cases, theremay be no direct signal# 5ependingon the di"erences in the pathlengths of the direct and re2ected!a/es, the composite signal can beeither larger or smaller than thedirect signal#For mobile telephony andcommunication to antennas thatare not !ell sited, multipathconsiderations can be paramount#

Institute of information & Communication Technology (IICT), MUET 1

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Figure *#3: 5epiction of Multipathinterference

5.#.2 %ulti"ath Fading

The term fading refers to the time/ariation of recei/ed signal po!ercaused by changes in thetransmission medium or path s.# 4na 6+ed en/ironment, fading isa"ected by changes in atmosphericconditions, such as rainfall# But inthe mobile en/ironment, !here oneof the t!o antennas is mo/ingrelati/e to the other, the relati/elocation of /arious obstacleschanges o/er time, creatingcomple+ transmission e"ects#

The generic name of a radio !a/ein !hich the time of arri/al isretarded in comparison !ith thedirect !a/e is called a delayed!a/e# Then, the reception

en/ironment characteri$ed by asuperposition of delayed !a/es iscalled a multipath propagationen/ironment# 4n a multipathpropagation en/ironment, therecei/ed signal is sometimesintensi6ed or !ea&ened# This

phenomenon is called multipathfading and the signal le/el of therecei/ed !a/e changes frommoment to moment# Multipathfading raises the error rate of therecei/ed data, !hen a digital radio

signal is transmitted in the mobilecommunication en/ironment#

Figure *#7 depicts direct and ma8orre2ected paths bet!een astationary radio transmitter and amo/ing recei/er# The shadedshapes represent re2ectors such asbuildings#

Figure *#7: Multipath fadingen/ironment

ayleigh Fading: ayleigh fadingoccurs !hen there are multipleindirect paths bet!een transmitterand recei/er and no distinctdominant path, such as an L-%

path# This represents a !orst0casescenario#

ician Fading: ician fadingcharacteri$es a situation !herethere is a direct L-% path inaddition to a number of indirectmultipath signals# The ician model


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is more applicable in smaller cellsor in more open outdooren/ironments#

5oppler shift: The relati/e motionbet!een the transmitter andrecei/er causes 5oppler shifts#

Local scattering typically comesfrom many angles around the

mobile# This scenario causes arange of 5oppler shifts, &no!n asthe 5oppler spectrum# Thema+imum 5oppler shiftcorresponds to the local scatteringcomponents !hose directione+actly opposes the mobile9s

tra8ectory#

5.& Rayleigh Fading Channel Simulations

5.&.1 %odel for FadingChannels

Considering the channel to benarro! band, that is, the fading is2at across the channel band!idth!ith no frequency selecti/e fading#(e can model 2at fading channelas belo!:

Figure # : Model for Flat FadingChannel

5.&.2 Po'er of a Faded Signal

The code belo! plots a fadedsignal9s po!er /ersus samplenumber.# The code also illustratesthe synta+ of the 6lter andrayleighchan functions and thestate retention of the channelob8ect# ;otice from the output that

;um%amples'rocessed equals thenumber of elements in the signal#

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0 200 400 600 800 1000 1200 1400 1600 1800 2000-35

-30

-25

-20

-15

-10

-5

0

5

10

Figure # : Model for Flat FadingChannel

5.&.2 Com"aring m"irical 'ith(heoretical Results

The code belo! creates afrequency02at ayleigh fadingchannel ob8ect and uses it toprocess a 5B'% signal consistingof a single /ector# The e+amplecontinues by computing the biterror rate of the system fordi"erent /alues of the signal0to0noise ratio# ;otice that thee+ample uses 6lter before a!gn@this is the recommended sequence

to use !hen you combine fading!ith A(G;#

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5.&.# Simulin) %odel

A !ireless system is supposed to transmit data using B'% modulation# Testthe system for B performance and scatter plots under A(G; and ayleighfading en/ironment#

Figure *#): %imulin& Model for B'% o/er A(G; and ayleigh channel

5.5 Revie' *uestions

3# 5e6ne the term fadingJ

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7# (hat is the 5i"erence bet!een ician and ayleigh FadingJ KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK



# +plain the 5oppler %hiftJ KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK



# 4n rban n/ironment !hich model you !ill prefer ;ame Most%uitable.J


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*# A demonstration for this e+periment !as gi/en in %imulin&en/ironment, !ith B'% under ayleigh and A(G; en/ironment# Buildanother %imulin& model !ith di"erential 50 '% and discuss thedi"erence in results based on some plots#


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