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Fading Mitigation Techniques

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Fading Mitigation Techniques

Three techniques commonly use to

combat the effect of fading without

increasing TX Power and BW: diersity!

channel encoding! and equali"ation#

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$

FMT: %iersity

%iersity e&'loits the random nature of radio

'ro'agation by finding the inde'endent signal

'aths# (f one 'ath undergo a dee' fade! another

'ath may hae a strong signal#

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Mobile)omm*ystem+M,(+-$ .

*'atial %iersity

/se two or more receiing antenna

While one antenna sees a null signal! the

others may receie a 'ea0 signals# )an be im'lemented in both B* and M*

receier

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Mobile)omm*ystem+M,(+-$ 1

*electie )ombiner

3

2

m

*witching

4ogic

or

%emodulator

out'ut

5ariable gain

6nt# 3

6nt# 2

6nt# m

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Mobile)omm*ystem+M,(+-$ 7

*electie )ombining

8eceier only select one strongest signal to detect#

(f aerage *98 of receied signal in a branch , and

threshold *98 ! then 'robability that Mbranches of

antenna receie signals with *98 below the threshold is:

P;i < = PM;)= (3 > e> / )

(n other word! 'robability that receied signal *98 aboe

the threshold is :

P;i ? = 3 >PM;)= 1 (3 > e> / )

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@

*electie )ombining

A&am'le: . antenna diersity is used# (f aerage *98 is 2- dB!determine the 'robability that *98 will dro' below 3- dB ;badrece'tion=! and also that good rece'tion ;*98 aboe 3- dB= willmostly ta0e 'lace# )om'are with single antenna receier

6nswer:

Threshold *98 3- dB! 2- dB! / -#3

P.;i-#3=. -#----D2! and

P.;i?3- dB= 3> ;3 C e>-#3=. -#EEEE3D or EE#EE3D

With single antenna:

P;i-#3= -#-E1! and

P;i?3- dB= 3> ;3 C e>-#3= -#E-1 or E-#1

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Mobile)omm*ystem+M,(+-$ D

)hannel Aquali"er

)hannel equali"er is em'loyed to com'ensate (*(# *ince multi'ath fading channel is dynamic! equali"er must

be ada'tie

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Mobile)omm*ystem+M,(+-$ E

)hannel Ancoding

)hannel encoding is done by encode the data into as'ecial form! and introduce redundancies in thetransmitted data#

(t 'rotects data+information from error and distortion

introduced by the channel# 8edundant bits increase data rate hence the bandwidth!

but im'roe BA8 'erformance es'ecially in fadingchannel#

8educe BW efficiency of the lin0 in high *98 condition!but 'roide e&cellent 'erformance in low *98 condition

Two ty'es mostly used: Bloc0 )ode and )onolutionalcode