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Diversity Techniques

Diversity Techniques

Abstract

This is a technical document detailing on Diversity Techniques used in MobileCommunication.

Version 0.1 NDC Confidential R and !ireless "lanning #rou$ "age 1 of 3 Oct. 2000

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Diversity Techniques

C%NT&NT'

Frequency Planning

(1.0) Introuction Page 3

(2.0) !"ace Diversity Page 3

(3.0) Polarisation Diversity Page 3

(#.0) Frequency Diversity Page 3

Diversity Techniques

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Diversity Techniques

(1.0) Introuction$

'everal reflected radio (aves arriving at the receiver from various directions (ith different

am$litude and $hase) cause $ea*s and di$s in the received signal level) (hich is commonly*no(n as fading. Diversity system) a combining and+or com$aring technique of the signalsreceived from t(o different $aths) is used in ,T' to reduce the effect of fading. Theim$rovements de$end on the correlation coefficient bet(een the signals received at thediversity antenna and increases) as the correlation coefficient becomes smaller.

-n systems using s$ace or $olarisation diversity) the value of the correlation coefficientde$ends on the characteristics of the $ro$agation $ath and the $hysical configuration of thediversity antenna. '$ace and "olarisation diversity along (ith frequency diversity arediscussed belo(

(2.0) !"ace Diversity$

-n s$ace diversity t(o different receiving antenna are used. /oriontally se$arated antennaare recommended for mobile system (ith s$ace diversity) as it gives lo(er correlation thanone (ould have obtained (ith vertically se$arated antennas. This in turn is because mostreflections for mobile system come from vertical surface (alls2 and not from horiontal

surface ground2. Ty$ically horiontal se$aration is about 10

. 'e$aration bet(een t(o

receiving antennas also de$ends on the antenna height.

/oriontal se$aration bet(een t(o R3 antennas can be roughly calculated as4

h%10

!here is the se$aration distance and his the height of the antenna above ground level.

!hen t(o R3 antennas are horiontally se$arated by fe( (avelengths) received signal bythese antennas (ill have different fading correlation in a multi$ath environment and therefore(ill differ in $hase and in am$litude. Combining the signals from both the antennas (ill resultin a better gain. /o(ever) the gain) (hich can be achieved by antenna diversity stronglyde$ends on the $ro$agation environment and velocity of the mobile. Ty$ically a gain u$ to5d, is achieved by using s$ace diversity in urban environment.

(3.0) Polarisation Diversity$

"olarisation is the direction of electrical f ield radiated from the antenna. -n $olarisationdiversity) only one receiving antenna is used (ith t(o different elements using $olarisation of

56(ith res$ect to horiontal $lane. -n an urban mobile environment) the reflected radio

signal undergoes a random and frequent change in $olarisation. Thus the signal arriving froma mobile in a multi$ath environment (ill e3hibit a random change in $olarisation to bereceived by t(o elements se$arately. The gain achieved in $olarisation diversity is normallysame as in s$ace diversity (hen used in a dense urban environment.

(#.0) Frequency Diversity4

-n frequency diversity) different frequencies are used simultaneously. -n #'M) frequencyho$$ing is used to im$rove C+-) thereby minimising the effect of interference. Minimising theeffect of interference (ill im$rove the overall gain. -n frequency ho$$ing) the radiotransmitters use a number of frequencies on random basis or in a $re7defined ho$$ingsequence. The frequency ho$$ing in #'M is analogous to frequency diversity.

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