An Analysis of VSWR Error and VSWR Threshold

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An Analysis of VSWR Error and VSWR Threshold Internal Use Only

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TABE O O"TE"TS

# $a%&'ro(nd)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*+ Analysis of VSWR Error)))))))))))))))))))))))))))))))))))))))))),'$) VSWR Error due to Test Instrument$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$C

'$' VSWR Error due to the Base Station$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$9

'$@ VSWR Error due to re0uency onfiguration$$$$$$$$$$$$$$$$$$$$$$$$$D

'$* Summary of VSWR Error$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$)'

- False Minor Alar" d(e !o Lo. VSWR Threshold )))))))))))))))))))))))))))))))))))))))))))))#-

@$)

The Influence from >inor VSWR Threshold upon System$$$$$$$$$$$$$$$$$$$)*

@$' The Influence upon o,erage$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$)6

@$'$) S> D((>7= The Influence upon the o,erage of S> D((>7=

"et#ro.$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$)C

@$'$' S> )9((>7= S> D((>7= The Influence upon the

o,erage of S> )9((>7= "et#ro.$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$)9

@$@ Summary $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$'(

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# $a%&'ro(nd ! " #$ %

&$' ( ( ) " *+ ,-(

./ ,- 0 ,-0 '$( 12*3 4 ,

-0@$(12*%

The VSWR tested #ith Sitemaster is a little different from the VSWR displayed

on O>$

In some pro5ects% the VSWR threshold is too lo#% leading to lots of fault VSWR

alarms$ The industry criteria for setting VSWR threshold are '$( or a-o,e for

minor VSWR alarm and @$( or a-o,e for critical VSWR alarm$

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+ Analysis ofVSWR Error

+)# VSWR Error d(e !o Tes!Ins!r("en!

)$ 5678 $ (9 3

'$ There is slight error in the accuracy of Sitemaster$

@$ 0

*$ VSWR error might occur in the testing process$

: ( ; = ? =

@ AB CD E? F+ G H(F+ G IJK

L$ ( MN($OP;QG($OP;RS%

The VSWR tested #ith Sitemaster is the ,ector superimposition of reflected

,oltages of antenna% feeder% 5umper% testing R ca-le% and adapter at the test

port$ The ,ector superimposition is closely related to the phases of the

instruments mentioned a-o,e% and might -e either ,ector addition or ,ector

reduction$

TU : sitemaster (V WX (; Y ?

Z[(\ ? Z[( 2*%9;]^; ?

Z[(_ ? D\P`@ @ (aWb

" FI" @ ( @ bcd$ )$' (

D (e fgE? 12 KLQGRS( %

Therefore% if Sitemaster is used to test VSWR% R ca-le must -e used during

the cali-ration process$ Other#ise% there #ill -e greater VSWR error in the test$

Test R ca-le must -e connected to the antenna feeder interface of -ase

station ,ia an "8to8FI" adapter% #hich has a )$'/s VSWR$ This VSWR% together

#ith the VSWR of antenna feeder interface% #ill also ma.e the reflection

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coefficient change #ith phase cancellation and addition$ Therefore% e,en if the

Sitemaster is cali-rated #ith R ca-le connected% VSWR error might occur in

the test process$

h D ; )$@1E? ($)@2 (" FI" @

; )$'(V ^ i j*k 0

Suppose the theoretical ,alue of VSWR on the antenna feeder interface is )$@

1the reflection coefficient 3 4 is ($)@2% and the VSWR of "8to8FI" adapter is

)$'% #e can calculate the ma+imum range of VSWR error generated$

E ? 0 The reflection coefficient of antenna feeder is;

13.013.1

13.1

1

1=

+

=

+

=VSWR

VSWR

@ E ? 0 The reflection coefficient of adapter is;

09.012.1

12.1

1

1=

+

=

+

=VSWR

VSWR

e]; E? k j*;0 Therefore% for tests #ith Sitemaster%

the ma+imum reflection coefficient is #ithin the range of 1($)@8($(D28

1($)@G($(D2

E? 0

The relation -et#een VSWR and reflection coefficient is;

+=1

1VSWR

VSWR j*k 0)$(9H)$6:%

Theoretically% the ma+imum ,alue range of VSWR is )$(98)$6:$

; Ck ( k OPl\m Cn (9B )$'H)$* ;op

qpk (e]; bcrs$($) (tH $ ?

Z[ ( F+ G ? %

This is an ultimate ,alue range% and VSWR seldom reaches these t#o ,alues in

actual application$ But )$'8)$* is a normal ,alue range% this means% there #ill -e

a VSWR error of ($) at least$ An e+tra VSWR error #ill -e superimposed% if

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Sitemaster is cali-rated #ithout connecting R ca-le$

+)+ VSWR Error d(e !o !he$ase S!a!ion

u b (RRU H(; =RRU

D@ l CDAB CD E? F+ G H(F+

G IJKL$ ( MN($OP;QG($OP;RS3

D@ v8bce; )$'( D@ KL :ubwx(KOPy(

\uwxOP K*y%

The same as Sitemaster% the VSWR of the -ase station #ith RRU is the ,ector

superimposition of reflected ,oltages of antenna% feeder% 5umper% and antenna

connector at the test port$ The ,ector superimposition is closely related to the

phases of the instruments mentioned a-o,e% and might -e either ,ector

addition or ,ector reduction$ Usually% the amplitude of the antenna connector

VSWR is )$'% and the phase difference is smaller in the same -atch of antenna

connector and is greater for different -atches of antenna connector$

& 78 78#zby(_ b!bcd;{ |1

2z( }~el\m ( bx d Z[(P?

KLA 19\P @ 2(9V bx

\OPdZ[bx(TU e *by(rse $

($) UM %

Besides% limited -y the cost 1a test instrument is much more e+pensi,e than the

#hole -ase station2% the test -y -ase station is less accurate than the test #ith

instrument$ Test instruments #ill -e cali-rated in each test% and the phase

offset due to R ca-le can -e eliminated 1-ut the error of adapter cannot2$ But

this is impossi-le for -ase station% thus% the VSWR error of -ase station is

greater than that of e0uipment% at least ($)$

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+)- VSWR Error d(e !oFre/(en%y Confi'(ra!ion

; ( H; H(9

RRU H(; ( > (\u

%

The VSWR of antenna changes #ith fre0uency$ The Sitemaster tests the #hole

#or.ing fre0uency -and% -ut the test result of RRU is the mean VSWR ,alue of

the fre0uency used in the -ase station% if fre0uency8hopping is adopted% the

VSWR of different fre0uency com-ination #ill change #ith the fre0uency of

antenna$

)$ B ( JAT7REI"A( W

X; )$63

According to the standards of famous antenna manufactures% such as

Jatherin% the SWR should -e )$6$

'$ V *+ H(ub *(

r k 0)$(H)$6 % O v (

< O0 K ( 8*(OP

*( \b % e];B pp"

\u \u_3

We ha,e made a lot of antenna tests% #hich sho# that the VSWR of the

same antenna changes greatly #ith fre0uency% and the ,ariation range

may e,en reach )$(8)$6$ In the follo#ing figures% the cur,es sho# that

antenna VSWR is closely related #ith fre0uency% and that the #ider the

fre0uency -and% the greater the fluctuation$ The fluctuation of e,eryantenna is different$ This is #hy% in actual application% antenna VSWR

,aries in the -ase stations configured #ith different fre0uency$

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+)0 S(""ary of VSWRError


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- False Minor Alar" d(e !o Lo.

VSWR Threshold

)$ uMT( ; 3

Antenna VSWR changes #ith fre0uency$

'$ bc WXd;)$*H)$63

Usually% the acceptance standard of SWR is )$*8)$6$

@$ S ,-( d ,- $b

k %t ,- 0 '$@( 4 ,-

;0@$)( ./ ,- 0 ,-0 '$(

12*3 4 ,-0@$(12*%

To eliminate false alarms caused -y VSWR error% e,ery -ase station

e0uipment manufacturer has an alarm threshold tolerance% for e+ample

one of our competitors sets the threshold for minor VSWR alarm as '$@

and the threshold for critical VSWR alarm as @$)$ According to industry

criteria% the threshold is '$( or a-o,e for minor VSWR alarm and @$( or

a-o,e for critical VSWR alarm$

*$


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recommended ,alue is '$(% thus% if there are missed alarms #hen VSWR

gets #orse% system performance #ill not -e affected% and there #on/t -e

lots of false VSWR alarms$

-)# The Infl(en%e fro" Minor VSWR Threshold

(1on Sys!e"

2 ,- (\ fg ( :qp\B

% s .( 78$ i ,-(h


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Suppose po#er reflection is on the output port of -ase station% and the output

po#er is !;

VSWR

Re!(rn

Loss

E?Refle%!ion

Po.er

?T2

Po.er

?

T2 Po.er

Chan'e

3Co"1are

d .i!h

VSWR #)*4

_i Inser!ion

Loss

d(e !o

S!andin'

Wa5e

#)*

Inser!ion

Loss

3Co"1ared

.i!h VSWR

#)*4

)$6 )*$(dB ($(*! ($DC! KK ($)::dB KK

)$: ))$:dB ($(C:! ($D@@! 8($(':! ($@(' ($)'6

)$9 )($99 ($(9'! ($D)9! 8($(*'! ($@: ($)D@

'$( D$6dB ($)))! ($9D! 8($(:! ($6))dB ($@@*

)$6 l)$:1 )$91 '$( i 0

The follo#ing sections focus on the influence upon co,erage #hen VSWR

changes from )$6 to )$:% )$9 and '$( respecti,ely$

-)+ The Infl(en%e (1on Co5era'eU ( ? *:$9dBmC(#(h Q

)6dBi( *dB($ ? 0EIR!L*:$9G)68*L69$9dBm(

If single carrier is adopted% the T+ po#er of the -ase station is *:$9dBm 1C(#2$

Suppose the antenna gain is )6dBi and the feeder loss is *dB% the effecti,e

reflection po#er is EIR!L*:$9G)68*L69$9dBm$

&j ;89(dBm(R+e, L EIR!8!ath oss (TU ?

!athoss a:;EIR!8R+e,L69$98189(2L)@9$9dB%

If the minimum outdoor R+ le,el in ur-an area is 89(dBm% R+e, L EIR!8!ath

oss% the T+ !ath loss should -e less than;EIR!8R+e,L69$98189(2L)@9$9dB

)$6 )$:(


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increase% thus% the T+ po#er #ill -e reduced$ It could -e learnt from the a-o,e

ta-le that the increase of VSWR from )$6dBm to )$: e0uals ($)'6dB/s increase

of insertion loss in T+ path$

7=

h); -ase station antenna height% m

h';>S antenna height% m

d; the distance from >S to -ase station% .m

a1h'2; the gain factor of >S antenna height% dB

a1h'2L1)$)lgf8($:2h'8)$6ClgfG($9 1middle8si=ed city% small city2

L@$'Mlg1))$:6h'2N'8*$D: 1>etropolis2

terrain; terrain L 6dB for dense ur-an

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h ? ;fLD*6>7=( z8 0h)L@(m( ! z80

h'L)$6m%

Suppose f 1the T+ fre0uency of the -ase station2 LD*6>7=% h) 1-ase station

antenna height2 L @(m% h' 1>S antenna height2 L)$6m$

)$6=)$:=)$9='$(B S>D((> ( H 0

The ta-le -elo# sho#s the co,erage of S>D((> net#or. for VSWR )$6% )$:%

)$9% and '$( respecti,ely$

VSWR

K #)*? QG3d$4

Inser!ion Loss

In%rease 3d$4

3%o"1ared

.i!h VSWR

#)*4

&j:

;7d$"3d$4

Pass Loss

3d$4

3"ini"("

o(!door

R2Le5

;7d$"4

3


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@

MOUNl( S>D((> ,- )$62 )$:1 '$((

P A i (5OU#%

It could -e learnt from a-o,e that the e0uipment performance and net#or.

co,erage are -arely affected #hen the VSWR alarm threshold of S>D((>

changes from )$6 to )$: or '$($

-)+)+ GSM #;77M89 GSM 677M89 The Infl(en%e (1on !heCo5era'e of GSM #;77M89 Ne!.ro&

OST'@) 7ata ; EURO8OST gOST 7ata

5( B ) 6((>7= l ' (((>7= %

OST'@) 7ata model is the e+tended ,ersion of the 7ata model de,eloped -y

OST committee% and applies to fre0uency range ) 6((>7=8' (((>7=$

OST'@) 7ata ^ 0

The empirical formula of OST'@) 7ata model for calculating path loss is;

!athoss 1ur-an2 L

*C$@G@@$Dlgf8)@$9'lgh)G1**$D8C$66lgh)2lgd8a1h'2G >

(C>0*Zq_3

C>; correction factor for metropolis

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u!" O.umura

Other parameters are defined the same as O.umura model

h ? ;fL)9@6>7=( z8 0h)L@(m( ! z

80h'L)$6m%

Suppose f 1the T+ fre0uency of the -ase station2 L )9@6>7=% h) 1-ase station

antenna height2 L @(m% h' 1>S antenna height2 L)$6m

)$6=)$:=)$9='$(B S>)9((> ( H 0

The ta-le -elo# sho#s the co,erage of S>)9((> net#or. for VSWR )$6%

)$:% )$9% and '$( respecti,ely$

K #)*? QG3d$4

&j:

;7d$"3d$4

3


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-)- S(""aryMOUNl( S>)9((> ,- )$62 )$:1 )$91

'$(( P A i (;4 #$ %

5OU#%

It could -e learnt from a-o,e that the e0uipment performance and net#or.

co,erage are -arely affected #hen the VSWR alarm threshold of S>)9((>

changes from )$6 to )$:% )$9 or '$($ Only the o,erlapped areas change a little%

#hich could -e neglected$

V*+ *+ ^ j

)$:12*by ( '$(( \ _

4 ,- P (O*+ ,-%

Based on our field #or. e+perience and theoretical calculation% it is -etter to set

the threshold for minor VSWR alarm as )$: or higher$ And the recommended

,alue is '$(% thus% if there are missed alarms #hen VSWR gets #orse% system

performance #ill not -e affected% and there #on/t -e lots of false VSWR alarms$

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An Analysis of VSWR Error and VSWR Threshold

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