Umts Rf Optimization

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UMTS RF Optimization


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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


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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...................................................................................................................................!$


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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


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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


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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


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>#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


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#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


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>#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


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+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


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>#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


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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


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>#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


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)= 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


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>#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


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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


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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


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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


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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


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>#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


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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


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>#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


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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


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>#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


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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.

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>#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


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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


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>#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


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$ *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


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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


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$.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


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>#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


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loss is also high.

Building transmittance loss

Building transmittance loss means the attenuation o electrical wa"e when passing

through e


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>#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.

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$.& '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


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>#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

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