the impacts of antenna azimuth and tilt installation accuracy on

TECHNICAL PAPER

Title: The Impacts of Antenna Azimuth and Tilt Installation Accuracy on

UMTS Network Performance Authors: Esmael Dinan, Ph.D., Aleksey A. Kurochkin—Bechtel Corporation Date: January 2006 Publication/Venue: Bechtel Telecommunications Technical Journal, Vol. 4, No. 1

©2006 Bechtel Corporation. All rights reserved.

© 2006 Bechtel Corporation. All rights reserved. 1

INTRODUCTION

Antenna azimuth and downtilt are twoimportant optimization parameters in

universal mobile telecommunications system(UMTS) networks. Optimization of these twoparameters can significantly improve systemperformance. However, new networks sometimesuse inefficient optimization techniques andimplement default values. Furthermore, incon-sistencies in setting these parameters duringinstallation vary the network coverage andcapacity. This paper presents the results of aquantitative study that investigated the effect ofthese parameters on UMTS network performance.

Many techniques are used to measure antennaazimuth and tilt during installation. The accuracyin setting up the azimuth and tilt depends on the antenna installation processes and humanand instrumentation errors. Inefficient imple-mentation and rigging processes may also causeazimuth or tilt errors. The overall accuracy iswithin ±10 degrees using most traditionaltechniques. Usually, antenna azimuth errors areindependent for antennas belonging to differentsectors. New processes and instruments mayreduce these errors by several degrees, reducerandomness in antenna orientations, and bringerrors consistently within the set tolerance.

This paper investigates the effects of azimuth andtilt inaccuracies on network coverage andperformance and considers the three main UMTSnetwork system quality parameters: service

coverage, the ratio of chip energy to interference(Ec/Io), and soft handoff areas. Two exercises are defined. A variety of errors are introduced for all antennas, and a simulation is performedfor each case. At the end, the results are compared and analyzed. Consistent use of thenew antenna installation processes is promoted tolimit the impact of inconsistencies. Suggestionsare also provided on acceptable installation error limits for use as a baseline to developimplementation processes.

ANTENNA AZIMUTH AND TILT SETTINGS ANDINCONSISTENCIES

Antenna azimuth and tilt errors (Figure 1) arerandomly distributed among the sites and

sectors. For the purpose of this paper, azimutherror is measured as the absolute differencebetween the actual azimuth installed in the fieldand the designed azimuth, as illustrated in Figure 1a. In this definition, all azimuth errors are positive. Tilt errors can be positive ornegative—uptilt errors are considered negative,while downtilt errors are considered positive, asshown in Figure 1b.

An antenna installation technician sets up theazimuth using a compass and alignment tool. Onthe top of the tower, the technician can useseveral mechanisms to install the antenna.However, the technician’s capabilities arerestricted by uncomfortable climbing status,limited time, limited available tools, and

THE IMPACTS OF ANTENNA AZIMUTH AND TILT INSTALLATION ACCURACY ON UMTS NETWORK PERFORMANCE

Abstract—Inconsistencies in setting up antenna azimuth and tilt during installation may reduce overallnetwork performance. However, the degree of quality degradation depends on the amount of the discrepancybetween the designed and installed parameters. The paper investigates the effect of these errors on UMTS RF KPIs, including coverage, signal quality (Ec /Io), and soft-handoff areas. Two examples are studied that include real measurement data. The studies show the effect of azimuth and tilt installation inaccuracies onUMTS network quality.

Issue Date: January 2006

Esmael Dinan, PhD [email protected]

Aleksey A. [email protected]

environmental factors. An example of aninstallation mechanism using landmarks and anoptical alignment tool is shown in Figure 2. Thisfigure shows two pre-specified landmarks for thetechnician to use from the top of the tower. In this example, the respective angles between the antenna aim point and Landmarks A and Bare set to 40 degrees (counterclockwise) and –25 degrees (clockwise) from aim point to target.Once the alignment is set, antenna tilt is adjustedusing a mechanical tilt bracket. Antenna tilt errorsare caused by imperfect vertical adjustment of theantenna support structure.

Bechtel Telecommunications Technical Journal 2

ABBREVIATIONS, ACRONYMS, AND TERMS

Ec/Io ratio of chip energy to interference

GPS global positioning systemKPI key performance indicatorQoS quality of serviceRF radio frequencyRSCP received signal code powerUMTS universal mobile

telecommunications system

Designed Tilt

NegativeErrorPositive

Error

Field Azimuth

Positive Error

Designed Azimuth

Figure 1. Antenna Azimuth and Tilt Errors(a) Azimuth Error; (b) Tilt Error

True North

Optical Alignment Tool

Antenna Support Structure

Target A

Antenna Aim Point

50° Actual Bearing

40° Offset Angle

-25° Offset Angle

90° Specified AntennaAzimuth

115° Actual Bearing

Target B

Figure 2. Example of an Antenna Azimuth Setup and Installation

(a) (b)

The accuracy insetting up the

azimuth and tiltdepends on the antennainstallation

processes andhuman and

instrumentationerrors.

Using the Six Sigma process improvementmethodology, Bechtel initiated a task force tomeasure antenna installation accuracies [1]. Theimplementation team analyzed the data relatedto repeatability and reproducibility of differentantenna azimuth adjustment mechanisms. Theresults demonstrated up to 10 degrees of error insimple global positioning system (GPS)-basedadjustment methods. More advanced mecha-nisms can provide accuracies within 5 degreeswith 95 percent probability of confidence.

Figure 3 illustrates another element used in thestudy that is the subject of this paper: thecorrelation of errors between sectors of the samesite. Scenario A illustrates the traditionaltechnique of pointing antennas individually,leading to independent error in each sector. This paper proposes using a technique that offers a consistent error or the same error forantennas belonging to the same site. In thistechnique, shown in Scenario B, the azimuths ofthe second and third antennas are adjustedrelative to the azimuth of the first-installed

antenna. This paper shows that this scenario,offered by recent installation techniques,provides better network performance than thetraditional method.

SIMULATION MODEL AND ASSUMPTIONS

This paper examines two example networkclusters—one with 20 sites and one with

42 sites—that were simulated using planning andoptimization tools. These clusters are shown inFigure 4. The simulation results help to analyzethe effect of azimuth and tilt settings on someaspects of network performance. The followingtasks were included in the study:

• Select cluster areas, antenna types, defaultsite configuration, and system parameters

• Develop simulation scenarios, objectives,and plans

• Develop project setup in the planning andoptimization tools and configure all theparameters

January 2006 • Volume 4, Number 1 3

Error = ∝Error = γ

Error = β

Field Azimuth

Designed Azimuth

Error = ∝Error = ∝

Error = ∝

Field Azimuth

Designed Azimuth

Figure 3. Correlation of Errors Between Sectors of the Same SiteScenario A – Traditional Azimuth Setting; Scenario B – Proposed Azimuth Setting

Figure 4. Cluster Area Elevation Map(a) 20 UMTS Sites – Traffic and Coverage Relevant Area: 17.17 km2

(b) 42 UMTS Sites – Traffic and Coverage Relevant Area: 26.14 km2

Scenario A Scenario B

(a) (b)


• Optimize all antenna azimuths and tilts usingrecursive optimization algorithms (Thisdesign will be considered to be the baselinedesign.)

• Execute the simulation and record thestatistics for the above scenarios and errorparameters

• Analyze the data and compile the finalgraphs

A standard default site configuration wasconsidered. Cell sites included in the test clusterhad the following configuration parameters:

• Antenna radiation center heights in therange of 20 to 25 meters

• Node B transmission power = 20 watts

• Pilot power = 2 watts

• Traffic load = 50 percent, uniform distribution

• Total antenna feeder loss = 3 dB

• Frequency = 2,150 MHz (downlink)

Two example projects were created in theplanning and optimization tools using the aboveconfiguration parameters. Other UMTS systemparameters were set to default values. In thebaseline design, antenna azimuth and tiltconfigurations were optimized for maximumoverall performance of the test cluster. Therefore,changes in these parameters would result inreduced network performance. Antenna azimuthand tilt were optimized using an automatedrecursive optimization tool (Radioplan GmbH’sWireless Network System [WiNeS]). The toolprediction parameters and path loss matrix weretuned using drive test data. For the baselinedesign, a simulation was performed, includingcoverage, interference, and soft handoff analysis.

In the next step, a series of simulations wereperformed to investigate the effect of azimuthand tilt errors on network performance. For bothScenarios A and B, a variety of errors wereintroduced for all the antennas. These errors wererandomly distributed among the cells. For eacherror set, the simulation was executed repeatedlyuntil a steady, consistent result was achieved.Then the performance statistics, includingcoverage, interference, and soft handoff area were calculated and compared. Performancestatistics were recorded and then analyzed toproduce the final graphs.

The exercises described above were performedmultiple times, each using a different antennatype. The results help provide an understandingof the effect of antenna types on the performancegraphs and conclusions. Overall behavior isconsistent with antennas having the samehorizontal and vertical beamwidth. UMTSnetwork performance sensitivity to azimuth andtilt error increases as beamwidth is reduced. Therelationship between error type and beamwidthis as follows:

• Horizontal beamwidth ↔ Azimuth error

• Vertical beamwidth ↔ Tilt error

Simulation results presented in this paper wereperformed with antennas that have 65-degreehorizontal beamwidth and 7-degree verticalbeamwidth, which is considered to be a typicalantenna type in most UMTS networks.

SIMULATION RESULTS

Simulation results are presented in Figures 5, 6,and 7. Figure 5 considers a simple single site

UMTS networkperformancesensitivity to

azimuth and tilterror increases as beamwidth

is reduced.

0 5 10 15 20 25 3096

96.5

97

97.5

98

98.5

99

99.5

100Single Site Coverage Versus Antenna Azimuth Error

Average Antenna Azimuth Error

Norm

alize

d Co

vera

ge A

rea

RSCP < – 86 dBm

– 3 – 2 – 1 0 1 2 370

75

80

85

90

95

100

105Single Site Coverage Versus Antenna Tilt Error

Average Antenna Tilt Error

Norm

alize

d Co

vera

ge A

rea

RSCP < – 86 dBm

Figure 5. Network Performance Versus Antenna Azimuth and Tilt Installation Error in a Single-Site Configuration(a) Azimuth Error; (b) Tilt Error

(a) (b)


0 5 10 15 20 25 300

1

2

3

4

5

6

7Coverage Gap Versus Antenna Azimuth Error


Incr

ease

in C

over

age G

ap (P

erce

ntag

e)RSCP < –86 dBm, ARSCP < –86 dBm, BRSCP < –92 dBm, ARSCP < –92 dBm, B

–3 –2 –1 0 1 2 3–2

0

2

4

6

8

10

12

14

16Coverage Gap Versus Antenna Tilt Error


Incr

ease

in C

over

age G

ap (P

erce

ntag

e)

RSCP < –86 dBmRSCP < –92 dBm

0 5 10 15 20 25 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5QoS Gap Versus Antenna Azimuth Error


Incr

ease

in S

ervic

e Qua

lity G

ap (P

erce

ntag

e)

Ec/Io < –12 dB, AEc/Io < –12 dB, BEc/Io < –13 dB, AEc/Io < –13 dB, B

–3 –2 –1 0 1 2 3–0.5

0

0.5

1

1.5

2

2.5QoS Gap Versus Antenna Tilt Error


Incr

ease

in S

ervic

e Qua

lity G

ap (P

erce

ntag

e)Ec/Io < –12 dBEc/Io < –13 dB

0 5 10 15 20 25 300

1

2

3

4

5

6

7

8

9

10Soft Handoff Area Versus Antenna Azimuth Error


Incr

ease

in S

oft H

ando

ff Ar

ea (P

erce

ntag

e)

SHO Margin = 5 dB, ASHO Margin = 5 dB, BSHO Margin = 3 dB, ASHO Margin = 3 dB, B

–3 –2 –1 0 1 2 3–6

–5

–4

–3

–2

–1

0

1Soft Handoff Area Versus Antenna Tilt Error


Incr

ease

in S

oft H

ando

ff Ar

ea (P

erce

ntag

e)

SHO Margin = 3 dBSHO Margin = 5 dB

(a) Area with RSCP < –86 dBm = 12.32%, Area with RSCP < –92 dBm = 4.80%

b) Area with Ec /Io < –12 dB = 4.0%, Area with Ec /Io < –13 dB = 1.01%

(c) Soft Handoff Area = 28.05% (Soft Handoff Margin = 5 dB), Soft Handoff Area = 17.58% (Soft Handoff Margin = 3 dB)

Figure 6. Performance Graphs for 42-Site Cluster


(a) Area with RSCP < –86 dBm = 5.76%, Area with RSCP < –92 dBm = 2.0%

(b) Area with Ec /Io < –12 dB = 4.42%, Area with Ec /Io < –13 dB = 0.94%

(c) Soft Handoff Area = 36.34% (Soft Handoff Margin = 5 dB), Soft Handoff Area = 23.0% (Soft Handoff Margin = 3 dB)

SHO Margin = 3 dBSHO Margin = 5 dB

–3 –2 –1 0 1 2 3–6

–5

–4

–3

–2

–1

0

1Soft Handoff Area Versus Antenna Tilt Error


Incr

ease

in S

oft H

ando

ff Ar

ea (P

erce

ntag

e)

0 5 10 15 20 25 300

0.5

1

1.5

2

2.5

3

3.5

4

4.5QoS Gap Versus Antenna Azimuth Error


Incr

ease

in S

ervic

e Qua

lity G

ap (P

erce

ntag

e)

Ec/Io < –12 dB, AEc/Io < –12 dB, BEc/Io < –13 dB, AEc/Io < –13 dB, B

–3 –2 –1 0 1 2 30

0.5

1

1.5

2

2.5

3

3.5

4QoS Gap Versus Antenna Tilt Error


Incr

ease

in S

ervic

e Qua

lity G

ap (P

erce

ntag

e) Ec/Io < –12 dBEc/Io < –13 dB

0 5 10 15 20 25 30

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2Coverage Gap Versus Antenna Azimuth Error


Incr

ease

in C

over

age G

ap (P

erce

ntag

e)

RSCP < –86 dBm, ARSCP < –86 dBm, BRSCP < –92 dBm, ARSCP < –92 dBm, B

–3 –2 –1 0 1 2 3–1

0

1

2

3

4

5

6

7Coverage Gap Versus Antenna Tilt Error


Incr

ease

in C

over

age G

ap (P

erce

ntag

e)

RSCP < –86 dBmRSCP < –92 dBm

–

0 5 10 15 20 25 300

1

2

3

4

5

6

7

8Soft Handoff Area Versus Antenna Azimuth Error


Incr

ease

in S

oft H

ando

ff Ar

ea (P

erce

ntag

e)

SHO Margin = 5 dB, ASHO Margin = 5 dB, BSHO Margin = 3 dB, ASHO Margin = 3 dB, B

Figure 7. Performance Graphs for 20-Site Cluster


Azimuth error in the range of 6 to 8 degrees

is tolerable,depending on

the installationscenario and initial

coverage area.

configuration to provide an initial reference resultfor comparison purposes. In this example nointerference or inter-cell soft handoff areas exist;only coverage plots are shown. Only Scenario Awas considered because in Scenario B all the site’santennas were rotated with the same azimutherror; therefore, overall coverage performancedid not change.

As illustrated in Figure 5a, coverage shrinkswhen azimuth error increases. Coverage isreduced by 4 percent when there is a 30-degreeerror in azimuth setting. The coverage area has analmost inverse linear relationship with azimutherror. Figure 5b shows that coverage is also verysensitive to downtilt errors. Coverage changes upto 29 percent when downtilt error varies in therange of –3 to +3 degrees. This example shows asystem with no interference and inter-cell softhandoff coverage. To study and capture realnetwork performance behavior, multiple sites are needed.

Figure 6 shows the results for a 20-site cluster,and Figure 7 shows the results for a 42-sitecluster. These provide realistic examples inperformance graphs.

Azimuth errors in the range of 0 to 30 degreeswere considered for both Scenarios A and B. Tilterrors varied between –3 and +3 degrees. Theareas are represented as the percentage of thecluster area. The performance graphs arecategorized by coverage area, coverage quality,and soft handoff area.

Coverage AreaCoverage area is measured in reference toreceived signal code power (RSCP). Twodefinitions were considered for coverage gap: thearea with less than –86 dBm RSCP and the areawith less than –92 dBm RSCP. Figures 6a and 7ashow the variations in coverage gaps when thereare inconsistencies in antenna azimuth and tiltsettings. A higher coverage percentage and fewer coverage gaps is desirable whenimplementing a UMTS network.

Coverage QualityQuality of service (QoS) or coverage quality ismeasured by Ec/Io. Two definitions wereconsidered for QoS gap: the area with Ec/Io lessthan –12 dB and the area with Ec/Io less than –13 dB. Figures 6b and 7b show the variations inareas with QoS gaps when there are incon-sistencies in antenna azimuth and tilt settings. Ahigher QoS and fewer QoS gaps is desirable whenimplementing a UMTS network.

Soft Handoff AreaSoft handoff area is defined as the area coveredby more than one sector belonging to differentNode Bs. Two different settings were consideredfor soft handoff threshold. Performance graphsare shown for soft handoff areas when the softhandoff margin is 3 dB and 5 dB. Figures 6c and7c show the variations in soft handoff areas whenthere are inconsistencies in antenna azimuth andtilt settings. It is desirable to achieve the targetsoft handoff area recommended by the serviceoperator when implementing a UMTS network.A smaller soft handoff area results in increasedcall drop rate, and a higher soft handoff arearesults in inefficient use of radio resources andexcessive interference.

Careful investigation of the results of the graphsin Figures 6 and 7 leads to the followingconclusions:

• Antenna Azimuth: Network performancevariations depend on antenna azimuth errorvariations and the installation process.Overall degradation in Scenario B is 40 to 60percent less than in Scenario A. Therefore,the same error in all sectors is preferable.Azimuth error in the range of 6 to 8 degreesis tolerable, depending on the installationscenario and initial coverage area.Performance degrades noticeably if the erroris greater than 10 degrees. Soft handoff areas are the least sensitive to azimuth error. The coverage gap is 30 percent greater with 30 degrees of error in antennaazimuth. A comparison of the coveragegraphs in Figures 6 and 7 shows that when the coverage/quality gap is smaller, itssensitivity to error is higher.

• Antenna Tilt: Both coverage and qualityperformances are very sensitive to antennatilt variations. There is up to a 100 percentincrease in coverage and quality gaps with ±3 degrees of tilt error. Soft handoff areas arethe least sensitive to tilt error. The graphs inFigures 6c and 7c show less than a 10 percentvariation in soft handoff area with ±3 degreesof tilt error.

SUMMARY AND CONCLUSIONS

Both the 20- and 42-site examples produceconsistent network performance behavior

and lead to the same conclusions. If equal errorsare introduced to cell site sectors, there is lessnetwork performance degradation (Scenario A),compared with random errors (Scenario B). For


practical purposes, azimuth error in the range of 6 to 8 degrees is tolerable for networkperformance. Performance degradation isnoticeable if the azimuth error is greater than 10 degrees. Network performance is almost tentimes more sensitive to antenna tilt variations,compared with azimuth variations. Bothcoverage and quality gaps increase by up to 100 percent with ±3 degrees of tilt error.

If possible, only one antenna should be orientedand the other antenna azimuths set in reference to that one (Scenario B). However, rooftop sizeand configuration may interfere with thisrecommendation. If Scenario B installationtechniques can be applied to the site, simplermethods (instead of the more expensive methods)have the same effect on network performance.

Considering these conclusions, the followingUMTS network implementation standard can bepractically recommended for antenna azimuthand tilt tolerances:

1. For the Scenario A technique: Azimuthsetting tolerance of ±6 degrees

2. For the Scenario B technique: Azimuthsetting tolerance of ±8 degrees

3. For both scenarios: Tilt setting tolerance of±0.5 degrees

The cluster with more sites experiences lessnetwork quality degradation due to azimuth andtilt errors. However, this could be a subject forfurther studies. �

ACKNOWLEDGMENTS

The authors would like to thank Lacy Kiserfrom the Bechtel Six Sigma Team and Jeff

Bryson from the Bechtel Construction Team forthe valuable data and information they provided.Special thanks go to Radioplan GmbH forproviding WiNeS software for this study.

REFERENCES

[1] Six Sigma PIP TI-81, Report and Data Analysis,Bechtel Telecommunications, 2005.

[2] E. Dinan, “UMTS RF Network OptimizationProcess,” Document Number 3DP-T04G-50009,Bechtel Telecommunications Network PlanningDepartment, 2005.

BIOGRAPHIES

Esmael Dinan, a senior RF technologist with BechtelTelecommunications, hasbeen instrumental in manyaspects of the business unit’sresearch activities and the Cingular RF engineeringproject. He has designedand engineered an RF

engineering data management system, developedCingular project RF engineering processes andprocedures, designed UMTS networks, andverified and tested Dupont cryogenic TMAperformance.

Before joining Bechtel in 2002, Dr. Dinan was product manager for the GMPLS controlplane of the RAYStar DWDM optical switch at Movaz Networks, and lead network architect at MCI. He has conducted research and development on access methods andperformance modeling of 3G wireless commu-nications and high-speed optical networks.

Dr. Dinan received his PhD in ElectricalEngineering from George Mason University,Fairfax, Virginia, and is a registered ProfessionalEngineer in Maryland. He has authored morethan 25 conference papers and journal articlesand has filed a patent on a novel signalingmechanism developed for 3G cellular networks.He is a member of the Institute of Electrical andElectronics Engineers.

Aleksey Kurochkin iscurrently senior director,Site Development andEngineering, in the BechtelT e l e c o m m u n i c a t i o n sTechnology group, a groupthat he originated. He isexperienced in internationalt e l e c o m m u n i c a t i o n s

business management and network imple-mentation. Before joining Bechtel, he worked at Hughes Network Systems, where he built an efficient multi-product team focused on RF planning and system engineering. Hisengineering and marketing background hasgiven him both theoretical and hands-onknowledge of most wireless technologies.

Aleksey has an MSEE/CS degree in AutomaticTelecommunications from Moscow TechnicalUniversity of Communications and Informatics,Russia.

Both coverage and quality gaps

increase by up to 100 percent

with ±3 degrees of tilt error. Tilt setting

tolerance of ±0.5 degrees

is recommended.

the impacts of antenna azimuth and tilt installation accuracy on

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