Document Title:

Guideline For Antenna TiltingRev No:

Revision 2.0Effective Date :

Div. / Dept. Name :

TECHNOLOGY/ RNOPrepared By :

Anita a/p Suroya DemuduApproved By :

Document Title:

Guideline For Antenna TiltingRev No:

Revision 2.0Effective Date :

Div. / Dept. Name :

TECHNOLOGY/ RNOPrepared By :

Anita a/p Suroya DemuduApproved By :

1.1 INDEX:1.Introduction2.Objective of Antenna down Tilt3.Process flow4.Description5.Calculation6. Test Case1.0 INTRODUCTION

Antenna down tilting is the downward tilt of the vertical pattern towards the ground by a fixed angle measured with respect to the horizon. Down tilting of the antenna changes the position of the half-power beam width (HPBW) and the first nulls relative to the horizon. On most antennas the peak of the beam (maximum gain) is at 0 (parallel to the horizon) and never intersects the horizon. A small down tilt places the beam maximum at the cell edge and also brings the first null closer to the site, which may or may not pose a coverage problem.

With appropriate down tilt, the received signal strength within the cell improves due to the placement of the main lobe within the cell radius and falls off in regions approaching the cell boundary and towards the reuse cell.THEORETICAL TILT-EFFECTS

When selecting the optimum tilt angle, the goal is to have as high signal strength as possible in the area where the cell should be serving traffic. Beyond the serving area of the cell, the signal strength should be as low as possible. The basic theory is that down tilting an antenna increases the signal strength in the area close to the site, whereas the signal strength becomes lower at far distances.

The relation between the signal strength and distance from the site depends on:

Down tilt angle

Antenna type Antenna height

Near environment (topography and obstacles)

In an open environment, the effects of antenna down tilting can be fairly accurately estimated by calculating the vertical angle between the antenna and the mobile at various distances from the site.There are two methods of down tilting: mechanical and electrical

Mechanical tilt

When using mechanical tilt, the antenna is mounted with adjustable brackets in a way that the tilt can be adjusted on site.Electrical tilt

Electrical tilt means an in-built tilt that lowers the vertical beam in all horizontal directions. Electrical tilt can be combined with additional mechanical tilt.

Another option is to use Adjustable Electrical Tilt antenna. This antenna type has a variable regulator located behind the antenna. It can be adjusted into different tilt setting by adjusting the regulator.

Electrical Downtilt vs. Mechanical Downtilt

The largest advantage of electrical antenna down tilt is that the horizontal beam width is not affected. With mechanical down tilt, the tilting effect is greater in the 0 direction. At for example +/- 60, the effective tilt angle becomes lower. This effect can be very difficult to predict. With an overall, very high mechanical tilt level in the network, the cells become shorter and wider, more comparable to maybe 90 antennas. The frequency planning becomes more difficult, and the overall interference level in the network becomes higher.

2.0 OBJECTIVEThis document lays out guidelines for down tilting antennas successfully. With this document, tilting tasks can be carried out more efficiently and effectively.

NOTE: OPTION 1 & 2, can be done in any order/ simultaneously4.0 DESCRIPTIONS 4.1DATA COLLECTIONS4.1.1 Statistics

The common counter that shows possibility of overshooting sites is TDISSUL (Dropped connections at low signal strength uplink). Usually drop due to overshooting site occurs since the beginning of the site on air. Thus, the drop cell history might assist to narrow down causes of high TDISSUL.Beside SS issue, quality also might have an impact since potential on cells interfering with other is high after few new sites activated.

Recommendation: to modify the TALIM parameter in order to capture drop due excessive Timing Advance (consider as overshooting) e.g. TALIM = 20.Reason: If there are drops due to TA after we modified the TA value, then this cell can be considered as overshooting. This counter can be as triggering alarm. 4.2PROBLEMS IDENTIFICATIONS & ANALYSIS

4.2.1. Drive test & Site VisitDrive testPurposeWe may encounter cells that are overshooting / interfering with the serving cells. At certain area, we may encounter sites which are serving very far from the targeted area. This may lead to drop (TDISS) due to missing ncell.Expectation/Target To verify if the target areas covered.

To identify new target areas To verify the actual coverage

To provide info on which prediction coverage model is the best reflection the current coverage before running any prediction.

Drive Test procedure recommendations.

In order to verify the coverage, there are several alternatives as follows:

1) Lock to the overshooting cell and drive till the signal ends. Plot with map info format then measure the coverage radius.

Or 2) Normal call setup (either continuous or sequence calls). Plot the common drive test results and select query (find on that particular cell) though MapInfo to study the coverage area.

Or 3) Scanning Mode. (two options)a. Change the current BCCH to a clean test frequency. Perform scanning (without decode BSIC more real time scanning) and study the result.

b. Scan the existing BCCH but decode the BSIC. But with this will slower down the scanning speed. Study the result. Site visitPurposeThis will provide us info on the visual input. Any blockage (building or tree) which is not provided in the prediction tools may affected our judgments. Hardware capabilities such as availability of tilt bracket of space will strengthen the WO issued.

Expectations/Target Additional input (visual) on the blockage or potential roof reflection (if rooftop site)

To verify the compatibility such as if the tilt bracket available or not.

4.2.2 PMR/MRR Recording

Purpose

In areas where cells cover larger areas, these tools can be used to identify the problem. By using the Timing Advance information, we can see the mobiles served by the cell and the distance between the mobiles and the BTS.Expectation/Target [From PMR] Cells with;TA > 10 km needs to be analyzedPath Balance > 10 (positive value) is above 30%

Note: take into consideration the terrain and serving area (might be due to indoor coverage-multipath fading 4.2.3 COVERAGE PREDICTIONSCoverage prediction module provided in planning tools is a good way to overview the coverage populations. Clutters (prediction model) in ASSET play an important role in producing a good prediction result. Identify the most suitable model is essential (e.g. rural flat, rural hilly etc).We could compare the current setting predictions with the drive test result we have. With this we could identify the most suitable clutter for our recommendation setting. Recommendation:

It is advisable to generate prediction on cell basis and whole area.5.0 BASIC CALCULATION

In an open environment, the effects of antenna down tilting can be fairly accurately estimated by calculating the vertical angle between the antenna and the mobile at various distances from the site.

Formula:

The distance from the base station to the outer limit of this illumination area is denoted by Cellmax.

Formula derivation:

Tan =Height/Cellmax =Tilt angle- [1/2(3db vertical beam width)}

E.g. of calculation

Height of base station= 50 m

Cellmax = 4000 m

Antenna used: Katherine Directional Dual band Antenna- HPBW (half power beam width): 8

Tilt angle=

Tan =50/4000

0.7= -{1/2 (8)}

=4+0.7

=4.7RECOMMENDED TILT-VALUES

Areas with large cells (approximately 800 meter site-site distance or more):

Around 3.5for an 18 dBi antenna, and 7 for 15 dBi antenna could be used as default tilting values. Compared to having no tilt at all, this may give a possible minor positive impact on the C/I levels, without any significant loss of coverage. The effect of such small tilt is however minimal.

Areas with small cells (approximately 700 meter site-site distance or less): Recommended default-values is a tilt that corresponds to around 5 dB loss at the horizon. This means around 4for an 18 dBi antenna, and 8for a 15 dBi antenna.With very small cells, with a range of 300 meter or less, the antennas should definitely be downtilted, or the first null in the antenna diagram might create poor coverage at the cell border. This may lead to interference problems in the cell, and the quality will definitely benefit from antenna down tilt.Overall

There is no point in tilting an antenna less than the angle which gives a 3 dB loss at the horizon. A smaller tilt gives a limited impact and is hardly worth the effort. Tilt calculators are also available and can be used to get a suitable tilt degree.6.0 TEST CASERegion:

Southern

BSC:

BJB2

Site Id:

6955A

Site Name:

Putri Wangsa 2

Identified Problems:

Site overshooting and the coverage distribution is not optimized.

6.1 Statistical Analysis

6.2 Drive Test Result (Pre)

6.3 PMR/MRR Recording

6.4 Coverage Prediction

Example of ASSET prediction pattern as below. 6.4.1 Current Setting

6.4.2 Recommended Setting

CONCLUSIONAntenna down tilt can be a good tool in order to keep interference levels under control in a network. Antenna down tilt does have most effect with high gain, narrow vertical beam-width antennas. Best result is achieved in areas with small cells, and/or high antenna positions. With large cells, antenna down tilt can still be useful in order to solve local interference problems, or to reduce the cell-size. This is however at the cost of reduced coverage. The result of an antenna down tilt, if not very minor, should always be verified. It is especially important to verify the effect that the down tilt has on the coverage and quality in the area close to the down tilted cell itself.

YES

YES

NO

END

IDENTIFY PREDICTION MODEL

IDENTIFY NEW TARGET AREAS

NO

B

3

2

ANALYSIS

IS THERE A BACKUP COVERAGE?

COVERAGE PREDICTION

D/TEST & SITE VISIT

TIMING ADVANCE

PATH BALANCE

RUN PREDICTION

TA> 10 KM

% DL>UL greater than 30 %

Analysis

OTHER OPTI OPTIONS

Data collections

B

PMR/MRR RECORDING

SUSPECTED OVERSHOOTING CELLS

DRIVE TEST

STATISTIC

1

START

IMPLEMENTATION

& VERIFICATION

YES

YES

IS TARGET AREAS COVERED?

YES

Problems Identification

NO

NO