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Instructions for completing the RF Engineering sections of the KGT SiteQualification Report

RF

Radio

Bl

Ac Unacc

The engineer should examine the buildings surrounding the site and make an assessment of theirlikelihood of blocking the signal sufficiently to cause holes in the proposed service area. The assessmentshould be summarised as acceptable if the blocking wont restrict the performance of the site andunacceptable if it will. If the blocking is at the edge of the site then it is acceptable. The approximate siteradius for urban sites will be about 600 metres ; suburban sites will be 1 km; and rural sites will be as

large as possible without causing interference.

Pr

Ac Unacc

The site should be close to the coverage area. Unacceptable should be selected even if a site will providecoverage although it is not close to the coverage area because poor service control will be experienced.

Is

S Insuffi

Other RF sources are defined as existing RF services located on the same roof as the proposed DCS1800site that could cause interference with the DCS1800 receiver. The isolation required at the DCS1800receiver depends on the transmitted power, frequency and modulation of the interfering signal. As a roughrule for DCS1800 services in Taiwan if the isolation between the potential interfering antenna and theDCS1800 receiver is less than 50 dB then there may be interference and additional studies will need to be

performed if the site is acceptable in other aspects and there are no alternative sites.

The RF Engineer should calculate the isolation between the potential interferer and the DCS1800receiver taking into account free space propagation losses between the two antennas and the directivity ofthe two antennas.

In the example below the following calculation leads to an isolation of 62 dB which is acceptable.

Assume that the existing omni antenna has gain of 6dBi.


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Omni gain: +6Free space loss (at 1.8 GHz)

(38 + 20 log R) (R in m) -64Gain of sectorised antenna

at 80 -1 (17 gain at 0 minus 18 loss at 80)

Feeder losses -3Isolation -62 dB

P

Y No

Delay spread is caused when there is a weak direct signal (typically delivered by diffraction) and a verystrongly reflected signal that arrives at the GSM1800 Mobile delayed with respect to the direct signal. The

path of the reflected signal would typically be over water or flat land with no obstructions . If the two

signals arrive at the MS separated by more than 15 s (or 4.5 km) then there is potential for delay spread.

The diagram below illustrates how to assess the potential for delay spread. If the difference between thedirect (diffracted) path and the reflected (line-of-sight) path is greater than 4.5 km then there is a potentialfor delay dispersion.

Cellular

20 m

80

Existing omniantenna

Closest proposedGSM sectorisedantenna

Proposed antenna orientation

Edge of roof

Area of weak coverageprovided by direct pathvia diffraction

DCS 1800site

Low loss line-of-sight reflected path overwater or flat land (>4.5 km differencewith direct path may cause delaydispersion)

Reflecting structure


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Subsc

Goo

Fair

Bad

The RF Engineer should assess the need for the base station in this area based on the expected cellularservice demand. They should consider:

Large office blocks and businesses

Roads and freeways

Sports stadiums

Convention Centers

Tr

Y No

If there are any areas within the service area within which there is likely to be concentrated traffic (hotspots) they should be well served by the site. This means they should be within line-of-sight of theantennas.

Network

H

S Unsuit

The coverage from the site should overlap satisfactorily with adjacent sites but not extend into thecoverage areas of the next adjacent sites.

Int

Hi Low

The coverage of the site should not extend beyond the site service area into areas where it is likely therewill be frequency re-use. This interference potential will be high if the site is particularly high and close toother sites.

Antennas:

Cl

S Insuffi

There must be a place on the site to mount all antennas so that they are clear of obstructions in thehorizontal plane. In addition this location must be suited from a coverage viewpoint.

Omni antennas must be clear of all surrounding obstructions in the service direction. Sectorised antennas

must have 10 more clearance than the horizontal beamwidth of the antenna. So for a 65 antenna there

must be 42 clearance around the antenna direction.


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Cl

S Insuffi

To allow for changes to the horizontal orientation of the antenna during optimisation there must beadditional clearance around the antenna. Allow an additional 5 thereby increasing the horizontal

clearance angle to 47

Cl

S Insuffi

During optimisation the antenna may be mechanically downtilted. Allow up to 3 for this in the vertical

plane in addition to the amount required for roof edge clearance in the Roof edge clearance anglecriterion below.

Ac

S Unsuit

During installation and optimisation RF Technicians will need to access the antenna. Therefore allowsufficient room around the antenna to allow them access.

S

S Insuffi

There must be sufficient room to allow for 3 metres of horizontal separation between the antennas. Foromni antennas this separation will be perpendicular to the direction of most important coverage as shown

below.

R

S Insuffi

3 metres

Diversity direction anddirection to mostimportant coverage areaOmni antenna


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The antennas must be mounted close enough to the edge of the building so that the angle between the

lower edge of the antenna and the edge of the roof or parapet wall is greater than 24 . This does not allow

for elevation changes as addressed by the Clearance from structure for elevation changes criterionabove.

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