7/23/2019 Umts Rf Optimization
1/36
UMTS RF Optimization
7/23/2019 Umts Rf Optimization
2/36
Contents
1 RF Optimization............................................................................................................................................1
1.1 RF Optimization Flow Chart...............................................................................................................1
1.2 Single Site Spot Check........................................................................................................................1
1.2.1 Checking the Antenna Feeder System......................................................................................2
1.2.2 Checking Foreground and Background Coniguration............................................................2
1.2.! Checking Single Site Functions...............................................................................................!
1.! Co"erage #est.......................................................................................................................................!
1.$ %ata Analysis and #rou&leshooting.....................................................................................................$
1.$.1 Feeder 'ro&lem.........................................................................................................................$
1.$.2 Antenna and (n"ironment 'ro&lems........................................................................................)
1.$.! 'ilot 'ollution 'ro&lem............................................................................................................*
1.$.$ +ando 'ro&lem......................................................................................................................,
1.$.) Other RF 'ro&lems.................................................................................................................1-
1.) aking an Antenna Feeder Ad/ustment Scheme..............................................................................1-
1.).1 RF Optimization ethods......................................................................................................11
1.).2 RF Optimization 0nluence.....................................................................................................11
1.).! 0nluence o RF Optimization on '0....................................................................................12
1.* 0mplementing Antenna Ad/ustment...................................................................................................1!
1. Optimization 3eriication..................................................................................................................1!
2 UMTS Antenna...........................................................................................................................................15
2.1 Basic Antenna nowledge.................................................................................................................1)
2.2 Antenna Classiication and Application............................................................................................14
2.2.1 Omni Antenna.........................................................................................................................14
7/23/2019 Umts Rf Optimization
3/36
2.2.2 %irectional Antenna................................................................................................................14
2.2.! echanical Antenna...............................................................................................................1,
2.2.$ (lectrical Antenna...................................................................................................................1,
2.! Antenna %owntilt Ad/ustment 0nluence...........................................................................................2-
2.!.1 Antenna %owntilt odes........................................................................................................2-
2.!.2 Relationship &etween C%A Antenna %owntilt and Cell Co"erage Radius........................22
2.$ 0ntroduction to Common %irectional Antennas................................................................................2$
2.) Summary............................................................................................................................................2*
3 Electromagnetic Wave Propagation Teor!............................................................................................2"
!.1 (lectromagnetic 5a"e Space 'ropagation odel............................................................................2
!.2 (arth Relection odel.....................................................................................................................2,
!.! (nergy 6oss #hrough edium..........................................................................................................2,
!.!.1 0ntroduction.............................................................................................................................2,
!.!.2 Relection and #ransmittance 6oss........................................................................................!-
!.$ %iraction loss..................................................................................................................................!2
!.$.1 Fresnel 7one and nie8(dge %iraction odel..................................................................!!
!.$.2 ultiple nie8(dge %iraction............................................................................................!$
!.) Scattering 6oss...................................................................................................................................!$
7/23/2019 Umts Rf Optimization
4/36
1 RF Optimization
1.1 RF Optimization Flow Chart
Figure 1 RF optimization low chart
1.2 Single Site Spot Check'urpose9 #o make sure the e:uipment is working normally; so as to pre"ent e:uipment
ailure rom aecting o"erall network perormance.
'erson in charge9 (:uipment engineer
0nput9 Site Commissioning Report
Output9 Single Site Spot Check Report
5ork details9
7/23/2019 Umts Rf Optimization
5/36
Beore network optimization is started; all sites should ha"e &een checked and should
&e assuredly a&le to work normally. 0n an actual pro/ect; howe"er; it is usual that some
&ase stations ail to work normally due to la< or a&sent single site check; aecting
startup o su&se:uent optimization work. #o ensure orderly perormance o network
optimization; spot check is necessary or single sites. Single site spot check needs to
implement the ollowing tasks9
1= Select sites or spot check according to pro/ect size and network situation. >sually
a&out 2-? o the sites should &e included. oreo"er; the selected sites must
in"ol"e all site types; including sites in each area.
2= 'ut orth items that need to &e checked according to the contents indicated in theSite Commissioning Report. ake a spot check plan.
!= Accompany customer ser"ice engineers to check the selected sites as planned; and
put orth inormation that needs correction or any site with pro&lems.
$= 5hen all the selected sites are spot8checked; and o"er 2-? o them are ound with
pro&lems; it is necessary to recheck other sites not in"ol"ed in this spot check. 0
no pro&lem is ound; skip the recheck.
)= Complete a Single Site Spot Check Report&ased on the single site check results
or the purpose o trou&leshooting.
1.2.1 Checking the Antenna Feeder Sstem
1= Ascend the rootop to check the site longitude and latitude; antenna mount height;
antenna downtilt; and directional angle or consistence with the planned "alues.
For the towers that are not mounta complete the check on the ground.
2= #urn on the power ampliier o one sector; and turn o the others. 0 the power
ampliier gi"es no alarm; measure the pilot signal strength &eneath this sector.#ypically the (c "alue is a&out ))dBm.
!= #his step is perormed simultaneously with Step 2 to check whether the cell
scram&ling code is consistent with the planned "alue.
1.2.2 Checking Foregro!nd and "ackgro!nd Con#ig!ration
1= Check whether the neigh&or list coniguration is consistent with the planned
"alue.
2= 0n the case o idling; the R#5' "alue @namely the uplink RSS0= o each cell on
2
7/23/2019 Umts Rf Optimization
6/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
ode B &ackground should range rom 81- 81-$dBm.
!= Check the "ersion num&er o each type o sotware in use.
$= Set parameters in the search window. #here are settings in &oth 6# and OC8R;
and the setting in 6# is "alid.
1.2.$ Checking Single Site F!nctions
Open all cells; and perorm ser"ice tests or CS and 'S domains respecti"ely. Conduct
soter hando test; and conduct sot hando test again or the areas in"ol"ed in sot
hando.
1.$ Co%erage Test
'urpose9 #o know the co"erage range o each site in the network; and the
corresponding areas that can pro"ide dierent rates o ser"ices
'erson in charge9 #est engineer
0nput9 one
Output9 %ri"e test data
5ork details9
#he RF optimization phase needs no detailed special ser"ice test; and what should &e
done is to ha"e knowledge o the network co"erage &y the ollowing means.
1= Cell cluster co"erage test
2= 5hole network co"erage test
#his co"erage test uses Scanner plus test mo&ile phone to collect data simultaneously.
#he test data collected &y the mo&ile phone is helpul to /udge the uplink co"erage; and
know the change o signal in each section o the road i call hold is perormed
simultaneously.
%ierent rates o ser"ices re:uire dierent signal conditions. #he ta&le &elow lists the
pilot signal strength and :uality reerence "alues o &order co"erage corresponding to
common ser"ices.
#a&le 1 Reerence "alues o &order co"erage corresponding to common ser"ices
Ser"ice Border reerence "alue
3
7/23/2019 Umts Rf Optimization
7/36
>#S RF Optimization
CS12.2 "oice 81-)dBm81!dB
CS*$ "ideo 8,4dBm81-dB
'S*$ 81--dBm811dB
'S124 8,)dBm81-dB
'S!4$ 84)dBm84dB
#he data in this ta&le is pro"ided only or general reerence; and the o&/ect o RF
optimization perormed ater site commissioning is usually an idle network; where the
ser"ice &order will shrink with increasing num&er o users.
1.& 'ata Analsis and Tro!(leshooting
'urpose9 #o analyze the test data to /udge the network co"erage le"el and locate the
areas with pro&lems or trou&leshooting.
'erson in charge9 Optimization engineer
0nput9 %ri"e test data
Output9 're8optimization #est Report
5ork details9
etwork co"erage /udgment9
1= Cell cluster co"erage test. now the distri&ution o each cell in the conte
7/23/2019 Umts Rf Optimization
8/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
#ypically a directional site has three cells; each o which uses two eeders @one or &oth
recei"ing and transmitting and the other or only recei"ing= as its antenna. On the &ase
station side; the eeders are urther connected to O%( B ca&inet through a /umper.
#his series o connections is prone to error during construction o the engineering
team. #he two eeders connected to one antenna are likely to &e connected to any one
or two cells; so the symptom o incorrect eeder connection is that a signal transmitted
&y one antenna o three cells could come rom any one or two o the three cells in this
site.
Anal!%i%&
%uring optimization; it is necessary to check whether each co"erage signal actuallymeasured in an area o each &ase station is consistent with the planned co"erage cell.
ormally; the strongest signal in this direction near each antenna should &e the cell
corresponding to this antenna. 0n the case o occurrence o a strong signal o other
cells; irst check whether there is incorrect eeder connection.
Sol$tion&
0 incorrect eeder connection is ound; contact an e:uipment engineer concerned to
ascend the site to check eeder connection.
1.&.2 Antenna and *n%ironment )ro(lems
According to the result o the whole network co"erage test; check whether the co"erage
signal o each actual test area contains any o"ershooting signal or any signal with
co"erage o&"iously smaller than e
7/23/2019 Umts Rf Optimization
9/36
>#S RF Optimization
direction. Such a result may cause a certain co"erage hole; &ut this pro&lem can &e
impro"ed &y proper ad/ustment o the antenna directional angle. #he actual antenna
downtilt may sometimes de"iate rom the design. #he possi&le cause is that the antenna
pole is not "ertical to the ground or the measurement is not accurate.
Anal!%i%&
An easy way to measure the downtilt is using the antenna8attached scale la&el pro"ided
&y the antenna manuacturer. #his method needs irst to paste a correct scale la&el to
the antenna and then make ine ad/ustment against the scale. A more accurate method
to measure the downtilt is to use a gradienter directly. #he prere:uisite o these two
methods is that the antenna pole or support is installed "ertical to the ground; ensuringthat the measured antenna downtilt is actually its downtilt relati"e to the ground.
#hereore; or those antennas that are mounted on a tower or whose poles are mounted
on walls; it is a must to measure whether their poles are "ertical to the ground.
Sol$tion&
#he pro&lems a&o"e can &e ound &y measurement with special tools. >pon inding
such a pro&lem; notiy the engineering team to correct it. 0 there is an o&struction or a
pole cannot &e "ertical to the ground; impro"ement is possi&le &y ad/usting the
directional angle and downtilt. %ecrease o downtilt is lia&le to cause o"ershooting and
increase intererence; while increase o downtilt tends to cause a co"erage hole.
oreo"er; e
7/23/2019 Umts Rf Optimization
10/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
+igh site o"ershooting. 0 the space link loss caused when an antenna pilot signal rom
a remote high site reaches a test point is the same as the link loss caused when a pilot
signal rom a near low site reaches the same test point; it is pro&a&le that se"eral pilot
pollution areas with close (c0o "alues are caused at this test point. Furthermore;
presence o a high site may usually cause a large antenna downtilt; resulting in antenna
&eam distortion. And the co"erage wa"eorm may s:ueeze against the side lo&e;
resulting in pilot pollution in the side lo&e co"erage area.
Figure 2 Schematic diagram o pilot pollution due to high site o"ershooting
Ring layout o &ase stations. As the &ase stations are arranged into a ring; the ring
center can recei"e a ew pilot signals rom around; and the pilot (c0o "alues are close.
Figure ! Schematic diagram o pilot pollution due to ring layout o &ase stations
Signal distortion caused &y street eect and strong relectors. %ue to the propagation
characteristics near the >#S downlink 2--- re:uency; the downlink signal has
7
Base station
Base station co"erage area
eigh&or &ase station
R1
R2
7/23/2019 Umts Rf Optimization
11/36
>#S RF Optimization
strong relection; and propagation o remote pilot signal along tu&ular streets is likely
to cause intererence to co"erage areas o other cells. oreo"er; strong relection o
signal &y some &uildings and walls may also cause pollution to near&y pilot co"erage.
(n'l$ence o' pilot poll$tion& 'ilot pollution has a negati"e eect on network
perormance. #he symptom and analysis are detailed as ollows9
1= Access is diicult; and call ailure pro&a&ility is increased9 Beore >( originates a
call; it has &een perorming cell reselection. %ue to e( irst initiates random uplinkaccess; and meanwhile waits or an AC message. 0 successul; >( will initiate
RRC signaling e#RA. 0n this process; >( will not perorm
hando as there is no interaction o measurement control or measurement report.
RRC interaction must &e completed &eore RC can deli"er a measurement
control message and wait or a measurement report su&mitted rom >(. #hat is to
say; during the a&o"e8descri&ed process until >( su&mits a measurement report;
>( perorms operations with >#RA within the cell where the call is originated.
Once >( starts mo"ing; the signal o this cell may go &ad; and it is possi&le to
pre"ent recei"ing and transmitting o su&se:uent signaling and result in call
ailure.
2= #he call ailure pro&a&ility o high8speed data ser"ice is increased o&"iously.
Denerally speaking; high8speed data ser"ices need higher pilot (c0o and more
sta&le radio en"ironment; &ut in the case o pilot pollution; it is hard to ind a pilot
signal in the steadily strongest position; and this is e( communicates with multiple cells;
8
7/23/2019 Umts Rf Optimization
12/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
increasing downlink load on the &ase station; &ut decreasing system capacity.
Sol$tion& #he key o pilot pollution optimization is to orm a main pilot. 0n the RFoptimization phase; the ad/ustment means a"aila&le include9
1= First consider ad/ustment o the antenna directional angle and downtilt.
2= Ad/ust pilot signal power o some cells.
!= Ad/ust antenna mount height
$= Ad/ust antenna position
)= >se electronic ad/usta&le antennas
*= Add sources
1.&.& +ando## )ro(lem
Cause9
+ando pro&lems generally lie in length o the hando area and strength change o
each signal in the hando area. 0 the hando area is too small; there may &e no
suicient time or completing hando process in the case o dri"ing too ast; and
hando may ail as a result. A too large hando area is likely to occupy e
7/23/2019 Umts Rf Optimization
13/36
>#S RF Optimization
For the relationship &etween antenna downtilt and co"erage distance; please reer to
section 2.!.
Solution9
Change the hando area position and signal distri&ution &y ad/usting the antenna
directional angle and downtilt. 0 the hando area is too small; reduce the downtilt or
ad/ust the antenna direction properly. 0 the signals in the hando area change too
re:uently; consider ad/usting the downtilt and directional angle to ensure signal
strength in indi"idual cells changes smoothly.
1.&., Other RF )ro(lems
%uring RF optimization; it also should &e noted to make sure the &ase station
transmitting power works normally rom the &ase station RF end to the antenna side.
Standing wa"e ratio is an important inde
7/23/2019 Umts Rf Optimization
14/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
)= Re"iew the ad/ustment scheme
1.,.1 RF Optimization Methods
Ad/ust the antenna directional angle
Ad/ust the antenna downtilt
Ad/ust antenna mount height
Ad/ust antenna position
Ad/ust antenna eeder connection
>se characteristic antenna
Ad/ust accessories; such as a tower ampliier
1.,.2 RF Optimization n#l!ence
RF optimization means to change the co"erage distri&ution o downlink >#S signal
&y ad/usting each engineering parameter o antenna; and there&y change the
distri&ution o eecti"e co"erage areas; network hando areas; and pilot pollution
areas. Another purpose is to increase the co"erage distance; and reduce the intererence
&etween users. Adding tower ampliiers is another important approach to RF
optimization.
0mpro"e downlink co"erage :uality
Change hando areas
Change pilot pollution areas
0mpro"e &ase station work perormance
Change uplink co"erage areas
Currently; the antenna model used most in each network is an Andrew directional
antenna Andrew umwdG-*)1*G2d.
Antenna parameter characteristics determine the act that the ma
7/23/2019 Umts Rf Optimization
15/36
>#S RF Optimization
5hen the downlink co"erage :uality o some sites changes; the (c0o o corresponding
recei"ed signals will change as well. As network hando is /udged according to the
size o (c0o o recei"ed signals; the network hando area will also change e"en i the
hando algorithm is not changed practically.
'ilot pollution typically means there are many signals with close (c0o "alues or there
are strong signals alien to the planning design; so changing downlink co"erage :uality
&y ad/usting engineering parameters o antenna can also eliminate some pilot pollution
areas.
Feeder connection ad/ustment can sol"e the pro&lem o a&normal recei"ing and
transmitting o &ase station signals resulting rom in"erse eeder connection; andnormal standing wa"e ratio is another prere:uisite or a &ase station to work normally.
Adding power ampliiers can increase eecti"e co"erage distance o a &ase station.
Denerally; the reason or &ase station uplink co"erage limitation is that the uplink
transmitting power o a >#S mo&ile phone is only 21dBm. A tower ampliier can
oset the loss o uplink signals along the eeder.
1.,.$ n#l!ence o# RF Optimization on /)
RF optimization has an o&"ious eect on the ollowing '0s. As each cell has dierent
engineering parameters and en"ironments; their signal co"erage states are also
dierent. #hereore; the strongest cells and hando areas in dierent places o a
network ha"e dierent signal co"erage :uality; so RF optimization inluences not only
co"erage; &ut also se"eral inde
7/23/2019 Umts Rf Optimization
16/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
0nput9 Antenna Ad/ustment Scheme
Output9 Antenna Ad/ustment Record
5ork details9
1= Contact the engineering team to determine the num&er o antennas that need
ad/ustment and the operation date
2= Contact the operatorEs person in charge to conirm necessary procedures and
ac:uire an e:uipment room key
!= onitor and "eriy ad/usted parameters and engineering :uality
$= ecessary au
7/23/2019 Umts Rf Optimization
17/36
2 UMTS Antenna
2.1 "asic Antenna /nowledge
#he main parameters o antenna perormance include pattern; gain; input impedance;
standing wa"e ratio; polarization; lo&e width; and ront8to8&ack ratio.
1. Antenna inp$t impe)ance
Antenna input impedance is the ratio o input "oltage to input current at theantenna eeding end. #he optimal result o antenna8eeder connection is that the
antenna input impedance is pure resistance and e:ual to characteristic impedance
o the eeder. 0n this case; there is neither power relection on the eeder terminal
nor standing wa"e on the eeder; and the antenna input impedance changes mildly
with re:uency. Antenna matching is to eliminate the reacti"e component rom the
antenna input impedance; making the reacti"e component as close to the
characteristics impedance o the eeder as possi&le. atching :uality is usually
measured with our parameters9 relection coeicient; tra"eling wa"e coeicient;
standing wa"e ratio; and echo loss. Between these our parameters there are i
7/23/2019 Umts Rf Optimization
18/36
match. - means total relection; while ininity means perect match. 0n a mo&ile
communications system; echo loss is usually re:uired to &e larger than 1$dB.
+. Antenna polarization
Antenna polarization reers to the electric intensity direction resulting rom
antenna radiation. 5hen the electric intensity direction is "ertical to the ground;
this electric wa"e is called "ertically polarized wa"e when the electric intensity
direction is parallel to the ground; this electric wa"e is called horizontally
polarized wa"e. %ue to electric wa"e characteristics; the signal propagated in the
horizontal polarization mode may produce polarized current on the earth surace
when it tra"els close to the ground. #his polarized current is aected &y earthimpedance to generate thermal energy; resulting in :uick attenuation o electric
signal. By contrast; the "ertical polarization mode rarely produces polarized
current; thus a"oiding immense attenuation o energy and ensuring eecti"e
propagation o signals.
#hereore; in a mo&ile communications system; propagation is usually
implemented in the "ertical polarization mode. 0n addition; a kind o dual8
polarized antenna is introduced recently with de"elopment o new technologies. 0n
terms o design conception; it is classiied into two modes9 "ertical J horizontal
polarization and K$)L polarization. #he latter is generally superior to the ormer in
perormance; so it is adopted currently in most cases.A dual8polarized antenna
com&ines two antennas that are in cross8polar directions o M$)L and 8$)L and
work simultaneously in the recei"ing and transmitting duple< mode; which can
reduce the num&er o antennas needed in each cell. oreo"er; cross polarization
in K$)L directions can eecti"ely ensure good di"ersity reception.@0ts polarized
di"ersity gain is a&out )dB; which is 2dB higher than a single8polarized antenna.=
5. Antenna gain
Antenna gain is used to measure a&ility o an antenna to recei"e and transmit
signals in a speciic direction. 0t is one o the most important parameters or
selecting a &ase station antenna.
Denerally speaking; gain is impro"ed mainly &y reducing the lo&e width o
radiation on the "ertical plane; &ut maintaining omni radiation on the horizontal
plane. Antenna gain is e
7/23/2019 Umts Rf Optimization
19/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
0ncreasing gain can enlarge the co"erage range o a network in a speciic
direction; or increase gain margin in a speciic range. Any cellular system is a
two8way process; and increasing antenna gain can decrease the gain &udget
margin o a two8way system. 0n addition; the parameters that represent antenna
gain are dBd and dBi. dBi means the gain relati"e to an isotropic antenna; with
uniorm radiation in all directions dBd means the gain relati"e to a symmetric
array antenna. #he relationship &etween these two parameters is9 dBi N dBd M
2.1). >nder the same condition; the higher the gain; the urther the electric wa"e
can tra"el. #ypically; the antenna gain or a DS directional &ase station is 14dBi;
and 11dBi or an omni &ase station.
,. Antenna lo-e *i)t
6o&e width is another important parameter common to a directional antenna. 0t
reers to the width o an enclosed angle ormed &y the locations !dB lower than
the peak in the antenna pattern @antenna pattern is an inde< or measuring a&ility
o an antenna to recei"ing and transmitting signals in each direction; and typically
represents the relationship &etween power strength and enclosed angle in a
graphic way.=
3ertical lo&e width o an antenna is usually related to the co"erage radius in the
direction corresponding to this antenna. #hereore; cell co"erage :uality can &e
impro"ed &y ad/usting the antenna "erticality @pitch angle= within a certain range.
#his is also a method re:uently used in network optimization. #his method
in"ol"es two aspects9 horizontal lo&e width and "ertical lo&e width. #he hal8
power angle on the horizontal plane @+8'lane +al 'ower &eamwidth=9 @$)L; *)L;
,-L; etc.= deines the &eamwidth o the horizontal plane o an antenna. #he larger
the angle; the &etter the co"erage at the sector edge. +owe"er; increasing antenna
downtilt is more likely to cause &eam distortion and o"ershooting. #he smaller the
angle; the worse the co"erage at the sector edge. 0ncreasing antenna tilt can
impro"e co"erage at the sector edge in terms o mo&ility; and relati"ely; is less
likely to cause o"ershooting across other cells.0n an ur&an center; a &ase station
should adopt an antenna with a small +8'lane +al 'ower &eamwidth as the site
spacing is small and the antenna tilt is large. For a su&ur&; an antenna with a large
+8'lane +al 'ower &eamwidth should &e adopted. #he hal8power angle on the
"ertical plane @38'lane +al 'ower &eamwidth=9 @$4L; !!L; 1)L; and 4L= deines
the &eamwidth o the "ertical plane o an antenna. #he smaller the hal8power
7
7/23/2019 Umts Rf Optimization
20/36
>#S RF Optimization
angle on the "ertical plane; the :uicker the signals attenuate when de"iated rom
the main &ean direction; the easier to control the co"erage range precisely &y
ad/usting antenna tilt.
". Frontto-ac/ ratio
#his parameter indicates how well the antenna can suppress the &ack lo&e. 0 an
antenna with a low ront8to8&ack ratio is selected; its &ack lo&e is likely to cause
o"ershooting; resulting in disorderly hando relationships and call drop. #his ratio
usually ranges rom 2)dB to !-dB. An antenna with a ront8to8&ack ratio o !-dB
should &e preerred.
2.2 Antenna Classi#ication and Application
According to its directi"ity; a mo&ile communication antenna can &e classiied into two
types9 directional mo&ile antenna and omni mo&ile antenna. For a >#S system; an
antenna can &e su&categorized into mechanical antenna and electric antenna. #he
ollowing will analyze and compare these types o antennas in terms o inluence o
change o mo&ile antenna downtilt on antenna pattern and radio networks.
2.2.1 Omni Antenna
An omni antenna can produce uniorm radiation around !*- degrees in the horizontal
pattern; namely what is reerred to as non8directi"ity; and also can produce a &eam with
a certain width in the "ertical pattern. Denerally; the smaller the lo&e width; the larger
the gain. 0n a mo&ile communications system; an omni antenna is typically applied to a
large8area site in a su&ur&an county; or its co"erage range is large.
2.2.2 'irectional Antenna
A directional antenna can produce radiation within a certain angle in the horizontal
pattern; namely what is reerred to as directi"ity; and also can produce a &eam with a
certain width in the "ertical pattern. 6ike an omni antenna; the smaller the lo&e width;
the larger the gain. 0n a mo&ile communications system; a directional antenna is
typically applied to a small8area site in an ur&an; or its co"erage range is small; &ut
with high user density.
According to networking re:uirement; &uild dierent types o &ase stations; or which
dierent types o antennas can &e selected as needed. #he &asis o selection is the
technical parameters descri&ed a&o"e. For e
7/23/2019 Umts Rf Optimization
21/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
antenna with practically the same gain in all horizontal directions; while a directional
station uses a directional antenna whose horizontal gain changes o&"iously. #ypically;
an antenna with horizontal &eamwidth @B= o *)L is selected in an ur&an; while an
antenna with horizontal &eamwidth @B= o *)L; ,-L or 12-L can &e selected in a su&ur&
@depending on site type coniguration and local geographic en"ironment=. 0n a rural; it
is the most economic to select an omni antenna that can pro"ide large8scale co"erage.
2.2.$ Mechanical Antenna
A mechanical antenna reers to a mo&ile antenna whose downtilt is ad/usted
mechanically.
5hen a mechanical antenna is mounted "ertical to the ground; it is necessary to change
the antenna tilt &y ad/usting the position o the rear support i network optimization is
re:uired. %uring the ad/ustment; the co"erage distance o its main lo&e direction is
changed o&"iously; &ut the ma
7/23/2019 Umts Rf Optimization
22/36
>#S RF Optimization
2.2.& *lectrical Antenna
An electrical antenna reers to a mo&ile antenna whose downtilt is ad/usted electrically.
#he electrical downtilt principle is to tilt "ertical antenna pattern &y changing the phase
o antenna elements in the same array; changing the ma
7/23/2019 Umts Rf Optimization
23/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
oten applied when a downtilt angle is less than 1-L. 5hen the antenna downtilt angle
is increased urther; dents appear in the ront o co"erage; and &oth sides are pressed
lat. #hat is; the antenna pattern is distorted; resulting in insuicient co"erage in the
ront o this antenna and aggra"ated intererence to &ase stations on &oth sides.
Another deect o mechanical downtilt is warping o the rear lo&e; which may cause
intererence to ad/acent sectors; resulting in call drop o high8le"el users in near&y
areas.
Ao downtilt (lectrical downtilt .echanical downtilt
Figure $ Comparison &etween &ase station antenna downtilt modes
#he electrical downtilt principle is to tilt "ertical antenna pattern &y changing the phase
o antenna elements in the same array; changing the ma
7/23/2019 Umts Rf Optimization
24/36
>#S RF Optimization
site are ad"antageous in perormance and cost; while a remote8controlled electrical
downtilt antenna is eecti"e to sol"e the co"erage and intererence pro&lems in a dense
ur&an.
2.$.2 Relationship (etween C'MA Antenna 'owntilt and Cell Co%erage Radi!s
Antenna downtilt9 when an antenna is mounted "ertically; its transmitting direction is
horizontal. 0n "iew o co8channel intererence and time dispersion; an antenna o a
small8area cellular network usually has a downtilt angle. Antenna downtilt modes
include mechanical downtilt and electrical downtilt.
An o"erlarge mechanical downtilt angle may result in se"ere distortion o the antenna
pattern; thus &ringing a&out many uncertain actors to network co"erage and
intererence; so antenna downtilt angle is recommended not larger than 2) degrees; and
mechanical downtilt angle should not e
7/23/2019 Umts Rf Optimization
25/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
2.$.2.1 Relationship (etween Antenna 'owntilt and Cell Co%erage Radi!s in a +igh Tra##icArea
Figure ) Schematic diagram o antenna downtilt in a dense ur&an and ur&an
A high traic area here reers to an ur&an; especially a dense ur&an; where &ase stations
are dense and likely to interere with each other. #o ena&le most energy to radiate
within the co"erage area and reduce intererence to neigh&or cells; it is necessary to
align the hal power points on the main lo&e with the co"erage area edge when setting
an initial downtilt angle; as shown in Figure ). #he calculation ormula o a downtilt
angle is as ollows9
Ge2
=6
+@arctg += @1=
0n this ormula;
is an initial mechanical downtilt angle
+ is eecti"e height o this site; namely the dierence &etween antenna mount
height and a"erage height o am&ient co"erage areas
6 is the distance rom the antenna o this site to the edge that needs to &e co"ered in
this sector
is "ertical lo&e width
Geis an electrical downtilt angle.
23
7/23/2019 Umts Rf Optimization
26/36
>#S RF Optimization
2.$.2.2 Relationship (etween Antenna 'owntilt and Cell Co%erage Radi!s in a 3ow Tra##icArea
Figure * Schematic diagram o antenna downtilt in a su&ur& and rural
For a low traic area; like a su&ur&; rural; road; and sea; to e
7/23/2019 Umts Rf Optimization
27/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
deine the horizontal and "ertical angles that are !dB weaker than the main lo&e.
At present; 7#( mainly uses a directional antenna Andrew umwdG-*)1*G2d in >#Snetworks throughout China.
#a&le 2 Andrew umwdG-*)1*G2d antenna perormance parameters
ame 3alue
Central re:uency 211-.- +7
Antenna gain 1.-dBi
(lectrical downtilt 2 degrees
Front8to8&ack ratio !-dB
+orizontal !dB width *1.) degrees
3ertical !dB width * degrees
'olarization 3ertical polarization
Figure +orizontal antenna pattern
Figure 4 3ertical antenna pattern
#he gain in the main lo&e direction is 1dBi; and rom these two antenna patterns we
25
7/23/2019 Umts Rf Optimization
28/36
>#S RF Optimization
can ind out the dierence &etween antenna transmitting gain in each horizontal and
"ertical direction and the main lo&e direction. For e
7/23/2019 Umts Rf Optimization
29/36
$ *lectromagnetic 4a%e )ropagation Theor
5hen electromagnetic wa"e is tra"eling in space; the occurring power loss is mainly
the path loss resulting rom space spread o electromagnetic wa"e; and the relection
@transmittance=; diraction; scattering losses resulting rom o&struction on the
transmission route. #he actors that may inluence these losses include distance
&etween a transmitter and a recei"er; height o these two de"ices; material; height and
relati"e positions o o&structions; and electromagnetic wa"e re:uency. #hese actors
descri&e ield strength change in a long distance &etween a transmitter and a recei"er;
which is also called a large8sized propagation model. On the other hand; the
propagation model that descri&es :uick luctuation o reception ield strength in a short
distance or short time is called a small8sized attenuation model. ultipath transmission
is a ma/or actor that may inluence a small8sized attenuation model. As this chapter
descri&es only space transmission characteristics; and will not consider multipath
transmission. #he ollowing will pro"ide a detailed analysis o "arious losses o a
large8sized propagation model under dierent conditions.
$.1 *lectromagnetic 4a%e Space )ropagation Model
Regarding electromagnetic wa"e space transmission; the simplest case is ree space
propagation. #he ree space propagation model is used to predict the reception signal
ield strength when a line o sight path without any o&struction e
7/23/2019 Umts Rf Optimization
30/36
distance and re:uency. +owe"er; this ree space model has a small eecti"e range.
5hen line o sight electromagnetic wa"e e( and O%( B. 6ine o sight propagation is su&/ect to o&struction &y
"arious &uildings; trees; hills; and "ehicles. #hen a lot o non8line8o8sight
electromagnetic wa"es are generated rom relection; reraction; and diraction &y
these o&structions. #his is how well8known multipath transmission comes.
Relection
%iraction
#ransmittance
%uring multipath transmission; reception power attenuation is much aster than that
during ree space propagation with increase o the distance &etween a transmitter and a
recei"er. Denerally speaking; in a dense ur&an or a room; reception power is in in"erse
proportion no longer to s:uare o the distance; &ut appro
7/23/2019 Umts Rf Optimization
31/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
$.2 *arth Re#lection Model
Among mo&ile radio channels; a single line o sight path &etween a &ase station and a
mo&ile station is rarely a uni:ue route or propagation. #hereore; only a ree space
model cannot relect accurately the actual situation. #hen a dual8line earth relection
model &ased on geometric optics can &e applied in more cases. An earth relection
model takes into consideration the earth relection path &etween a transmitter and a
recei"er; so it can &e used accurately within a range o se"eral kilometers. #his model
supposes that; during electromagnetic wa"e transmission; apart rom a line o sight
path; there is only one earth relection path.
'r N 'tDtDrht
2
hr
2
d
$
#his model pro"ides a simple indication that space path loss is in in"erse proportion to
the ourth power o this path in a city; and when the distance is large9
d Q 2- hthrP; and reception power is irrele"ant with re:uency. 0t is noteworthy that in
a >#S system; wa"elength is a&out 1)cm; co"erage distance does not e
7/23/2019 Umts Rf Optimization
32/36
>#S RF Optimization
$.$.2 Re#lection and Transmittance 3oss
5hen electromagnetic wa"e passes &y a medium; some part is relected. According to
the energy con"ersation law; the sum o the energy o relected wa"e and transmittance
wa"e should &e e:ual to the energy o incident wa"e. oreo"er; when electromagnetic
wa"e passes through a medium; energy loss occurs due to dissipation resulting rom
polarization.
#o calculate relected and transmitted energy; it is necessary to calculate relection and
transmittance coeicient o ield strength or power. #his coeicient depends on
medium characteristics; and is deined as electric permitti"ity r. >sually the insulation
constant o an ideal dielectric @without loss= should &e N -r.0 energy loss occurs
during transmittance; the insulation constant takes the orm o a comple
7/23/2019 Umts Rf Optimization
33/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
loss is also high.
Building transmittance loss
Building transmittance loss means the attenuation o electrical wa"e when passing
through e
7/23/2019 Umts Rf Optimization
34/36
>#S RF Optimization
#his diagram shows the loss characteristics in the case that &oth transmitter and
recei"er are located indoors. #he loss ranges rom )-dB to 4-dB when the spacing
is 1-.
For 2.$D+z; path loss @in dB= N $- M !) T6OD @% in meters=U
#hat is; the indoors transmission loss is a&out !)dB1- multiples o thread.
Body loss
For a handset; the recei"ed signal ield strength will &e $8dB or 182dB lower
when it is attached to the waist or shoulder o a user than when the antenna is a
ew wa"elengths away rom the &ody.
Denerally &ody loss is set to !dB.
0n8"ehicle loss
#he in8"ehicle loss caused &y a metal8structured "ehicle cannot &e ignored.
(specially in an economically de"eloped city; people spend part o their time in a
"ehicle.
#ypically in8"ehicle loss ranges rom 4dB to 1-dB.
For a >#S system; where the operating re:uency is close to 14--+z and
wa"elength diers little; transmittance loss is also close.For those modern
&uildings with large glass windows; transmittance loss typically ranges rom dB
to 1-dB.
32
7/23/2019 Umts Rf Optimization
35/36
Chapter ! (lectromagnetic 5a"e 'ropagation #heory
$.& 'i##raction loss
0n a radio communications system; signals may ha"e additional loss when encountering
o&structions during radio propagation. #his loss is diraction loss.
$.&.1 Fresnel 5one and /ni#e6*dge 'i##raction Model
0iraction loss can &e e
7/23/2019 Umts Rf Optimization
36/36
>#S RF Optimization
#he num&er o Fresnel zones &eing o&structed @n= can &e o&tained rom this ormula9 n
N "22.
#he Fresnel diraction parameter is in direct proportion to 12 power o re:uency.
#his means diraction loss increases with re:uency.
#hen it is known that diraction loss depends mainly on o&struction height and
position relati"e to a transmitter and a recei"er when electromagnetic wa"e is
o&structed on the propagation route during space propagation. 0 the relati"e height @h=
is smaller than or e:ual to zero; it means the loss is "ery small; and it is allowed to
neglect o&struction position @hN-; lossN*dB=.On the contrary; the urther an o&struction
is away rom the center o line o sight path; the smaller the Fresnel zone; namely thelarger the inluence on radio links &y the o&struction. 0n this case; it is necessary to
consider the inluence o the o&struction position. As a transmitter is normally much
higher than a recei"er @outdoors=; the diraction loss o high &uildings near a recei"er
on the transmission route is larger than that o e:ually high &uildings near a transmitter.
$.&.2 M!ltiple /ni#e6*dge 'i##raction
0 there are multiple o&structions on the propagation path; diraction loss needs
recalculation. 0 there are only two o&structions; they can &e made e:ui"alent to a new
o&struction delineated rom the incidence route o the irst o&struction and the
diraction route o the second o&struction. 0 there are more o&structions; it is a more
comple< case; which is not handled here.
$., Scattering 3oss
Scattering occurs when the wa"e transmission media contain o&/ects that are smaller
than the wa"elength and there are a great num&er o o&structions in a unit "olume. #he
main eect o scattering is to transmit and propagate electromagnetic wa"e in all
directions; thus pro"iding e