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Network Design

Network configuration

Cell coverageComparison of half power beam widths

Vertical downtiltMechanical downtiltElectrical downtilt

Adjustable electrical downtilt

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DownlinkConnection

UplinkConnection

Base Station

Mobile Station Base StationEquipment

RadioLink

Antenna System

Network Design / Base station

Downlink frequencies :

GSM 900 : 935 - 960 MHz

GSM 1800 : 1805 - 1880 MHz

Uplink frequencies :

GSM 900 : 890 - 915 MHz

GSM 1800 : 1710 - 1785 MHz

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Network Design / Configuration

honeycomb structure

omni base stations using omni-directional antennas for low trafficcellssector sites with 3 cells (directionalantennas) of different frequenciesfor a higher amount of subscribers

smaller cells (micro cells, pico cells)in high traffic areas (cities, citycenters)the topography, the repeatability ofthe frequencies and the real basestation locations influence the

network planning

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Cell coverage

To avoid interferences to adjacent cells the target is to provide coverage justfor the concerning sector but not beyond the sector border

tools for cell matchinghalf power beam widthtilt of the vertical pattern

Network Design / Cell Coverage

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Network Design / Half Power Beam Width

Which half power beam width isneeded to cover a 120 sector ?

standard comparison indicatessignificant differences at the sectorborders

6590105120

mistake : gain variation is notconsidered

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Network Design / Half Power Beam Width

antennas with the same verticallength but different horizontal halfpower beam width differ in the overallgain value

example : 900 MHz / 1.3m length

65 15.5 dBi90 14.0 dBi105 13.5 dBi120 13.0 dBi

result : no significant differencebetween 90, 105 and 120 regardinghalf power beam width andoverlapping area to the adjacent cell

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Conclusion :

the range of half power beam widths can be limited to 65 and 90

field of application :

urban areas : 65Theoretically the overlapping area between the cells is too small. But due toreflections from the surrounding the half power beam width is increased.

rural areas : 90 (65)Reflection intensity is much lower. Therefore many network planners prefer 90to provide sufficient overlapping. But also 65 is used

Network Design / Half Power Beam Width

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as a standard the vertical beam is pointing to the horizon

downtilting of the pattern provides the following benefits :- the majority of the radiated power is concentrated within the sector- the reduction of the power towards the horizon avoids interference problems

with the next sector

good results when fieldstrength in the horizon is reduced by about 6 dB

Network Design / Vertical Downtilt

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Network Design / Mechanical Downtilt

a mechanical downtilt kit increases theupper distance to the mast and makesthe antenna pointing downthe requested downtilt angle isachieved only in main directionat +/- 90 from the main direction thedowntilt angle is always zero (rotationaxis)effective downtilt varies across theazimuth

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Network Design / Mechanical Downtilt

Horizontal pattern 105 / mechanical DT

Mechanical Downtilt

0 68 10effect on the horizontal pattern atthe horizon :

reduction of the fieldstrength inmain direction without any change+/- 90 to it results in deformationof the horizontal patternthis effect of changing half powerbeam width can hardly beconsidered in the network planningand reduces the predictionaccuracy

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Network Design / Electrical Downtilt

Electrical Downtilt :0 68 10the fixed phase distribution appliesto all azimuth directions

electrical downtilt angle isconstantthe shape of the horizontal patternremains constantaccurate network planning isassured

Horizontal pattern 105 / electrical DT

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maximum flexibility is achieved with adjustable electrical downtilt by combiningthe adjustability of the mechanical DT and the technical advantage of the

electrical DT

Adjustable Electrical DT

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Adjustable Electrical DT

phase shifters at each dipole provide variable phase distributions

for sidelobe control the dipoles are fed with different powermax. electrical DT angle approx. 14 due to growing upper sidelobes

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= 0

= 0

= 0

= 0

= 0

connector

dipoles

Adjustable Electrical DT

identicalphases

Double phase shifter

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= + 140

= + 70

= 0

= - 70

= -140

connector

dipoles

Adjustable Electrical DT

differentphases

Longer path

shorter path

Double phase shifter

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Antenna Type 741 988Xpol F-Panel 1710-2170 88 14dB i 0-10T

Vertical pattern example at 9 T(polar-logarithmic scale)

Vertical pattern example at 3T(polar-logarithmic scale)

Downtilt Angle versus Vertical Half Power Beam Width

A greater vertical half power beam width means a higher downtilt angle in order toreceive similar results.

Antenna Type 741 990Xpol F-Panel 1710-2170 88 18dBi 0-6T

9 3

The selected downtilt angle is linked to the respective vertical half power beam width.

6dBpoint

6dBpoint

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Antenna Type 742 212 / Xpol F-Panel 1710-2170 65 18dBi 0-8T

Vertical pattern example at 0T(polar-logarithmic scale)

Vertical pattern example at 8T(polar-logarithmic scale)

Max. power reduction towards the horizon is achieved with the first null.

A higher downtilt angle increases the power again due to the first upper sidelobe.

Maximum Electrical Downtilt Angle

Max. DT angle is determined by the angle between the mainlobe and the first sidelobe .

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Special Cases

In special cases,

i.e. antenna mounting on high rise buildings or in special test scenarios,

a higher downtilt angle could be stipulated.

In general: Adjustable electrical downtilt is normally used for coverage fine tuning.

In this cases,an acceptable compromise is to combine electrical and mechanical DT

mechanical downtilt kit : primary downtilting

adjustable electrical downtilt : fine tuning