an analysis of vswr error and vswr threshold
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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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