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TECHNICAL PAPER

Title: The Impacts of Antenna Azimuth and Tilt Installation Accuracy onUMTS 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 two

important optimization parameters in

universal mobile telecommunications system

(UMTS) networks. Optimization of these two

parameters can significantly improve system

performance. However, new networks sometimes

use inefficient optimization techniques and

implement default values. Furthermore, incon-

sistencies in setting these parameters during

installation vary the network coverage and

capacity. This paper presents the results of a

quantitative study that investigated the effect of

these parameters on UMTS network performance.

Many techniques are used to measure antenna

azimuth and tilt during installation. The accuracy

in setting up the azimuth and tilt depends on

the antenna installation processes and human

and instrumentation errors. Inefficient imple-

mentation and rigging processes may also cause

azimuth or tilt errors. The overall accuracy is

within ±10 degrees using most traditional

techniques. Usually, antenna azimuth errors are

independent for antennas belonging to differentsectors. New processes and instruments may

reduce these errors by several degrees, reduce

randomness in antenna orientations, and bring

errors consistently within the set tolerance.

This paper investigates the effects of azimuth and

tilt inaccuracies on network coverage and

performance and considers the three main UMTS

network 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 performed

for each case. At the end, the results are

compared and analyzed. Consistent use of the

new antenna installation processes is promoted to

limit the impact of inconsistencies. Suggestions

are also provided on acceptable installation

error limits for use as a baseline to develop

implementation processes.

ANTENNA AZIMUTH AND TILT SETTINGS AND

INCONSISTENCIES

Antenna azimuth and tilt errors (Figure 1) are

randomly distributed among the sites and

sectors. For the purpose of this paper, azimuth

error is measured as the absolute difference

between the actual azimuth installed in the field

and the designed azimuth, as illustrated in

Figure 1a. In this definition, all azimuth errors

are positive. Tilt errors can be positive or

negative—uptilt errors are considered negative,while downtilt errors are considered positive, as

shown in Figure 1b.

An antenna installation technician sets up the

azimuth using a compass and alignment tool. On

the top of the tower, the technician can use

several mechanisms to install the antenna

However, the technician’s capabilities are

restricted 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 UMTSRF KPIs, including coverage, signal quality (Ec / I o ), and soft-handoff areas. Two examples are studied thatinclude 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. Kurochkin

[email protected]



environmental factors. An example of an

installation mechanism using landmarks and an

optical alignment tool is shown in Figure 2. This

figure shows two pre-specified landmarks for the

technician to use from the top of the tower. In

this example, the respective angles between

the antenna aim point and Landmarks A and B

are 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 errors

are caused by imperfect vertical adjustment of the

antenna support structure.

Bechtel Telecommunications Technical Journal2

ABBREVIATIONS, ACRONYMS, AND TERMS

Ec/Io ratio of chip energy tointerference

GPS global positioning system

KPI key performance indicator

QoS quality of service

RF radio frequency

RSCP received signal code power

UMTS universal mobiletelecommunications system

Designed Tilt

Negative

ErrorPositive

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

4 0 ° O

f f s e t

A n g l e

- 2 5 ° O f f s e t A n g l e

90° Specified Antenna Azimuth

115° Actual Bearing

Target B

Figure 2. Example of an Antenna Azimuth Setup and Installation

(a) (b)

The accuracy in

setting up the

azimuth and tilt

depends on

the antenna

installation

processes and

human and

instrumentation

errors.



Using the Six Sigma process improvement

methodology, Bechtel initiated a task force to

measure antenna installation accuracies [1]. The

implementation team analyzed the data related

to repeatability and reproducibility of different

antenna azimuth adjustment mechanisms. The

results demonstrated up to 10 degrees of error in

simple global positioning system (GPS)-based

adjustment methods. More advanced mecha-

nisms can provide accuracies within 5 degreeswith 95 percent probability of confidence.

Figure 3 illustrates another element used in the

study that is the subject of this paper: the

correlation of errors between sectors of the same

site. Scenario A illustrates the traditional

technique 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 for

antennas belonging to the same site. In this

technique, shown in Scenario B, the azimuths of

the second and third antennas are adjusted

relative to the azimuth of the first-installed

antenna. This paper shows that this scenario,

offered by recent installation techniques,

provides better network performance than the

traditional method.

SIMULATION MODEL AND ASSUMPTIONS

This paper examines two example network

clusters—one with 20 sites and one with

42 sites—that were simulated using planning andoptimization tools. These clusters are shown in

Figure 4. The simulation results help to analyze

the effect of azimuth and tilt settings on some

aspects of network performance. The following

tasks were included in the study:

• Select cluster areas, antenna types, default

site configuration, and system parameters

• Develop simulation scenarios, objectives,

and plans

• Develop project setup in the planning and

optimization tools and configure all the

parameters

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 Site

Scenario 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 using

recursive optimization algorithms (This

design will be considered to be the baseline

design.)

• Execute the simulation and record the

statistics for the above scenarios and error

parameters

• Analyze the data and compile the final

graphs

A standard default site configuration was

considered. Cell sites included in the test cluster

had the following configuration parameters:

• Antenna radiation center heights in the

range 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 the

planning and optimization tools using the above

configuration parameters. Other UMTS system

parameters were set to default values. In the

baseline design, antenna azimuth and tilt

configurations were optimized for maximum

overall performance of the test cluster. Therefore,

changes in these parameters would result in

reduced network performance. Antenna azimuth

and tilt were optimized using an automated

recursive optimization tool (Radioplan GmbH’s

Wireless Network System [WiNeS]). The tool

prediction parameters and path loss matrix weretuned using drive test data. For the baseline

design, a simulation was performed, including

coverage, interference, and soft handoff analysis.

In the next step, a series of simulations were

performed to investigate the effect of azimuth

and tilt errors on network performance. For both

Scenarios A and B, a variety of errors were

introduced for all the antennas. These errors were

randomly distributed among the cells. For each

error set, the simulation was executed repeatedly

until a steady, consistent result was achieved.

Then the performance statistics, including

coverage, interference, and soft handoff areawere calculated and compared. Performance

statistics were recorded and then analyzed to

produce the final graphs.

The exercises described above were performed

multiple times, each using a different antenna

type. The results help provide an understanding

of the effect of antenna types on the performance

graphs and conclusions. Overall behavior is

consistent with antennas having the same

horizontal and vertical beamwidth. UMTS

network performance sensitivity to azimuth and

tilt error increases as beamwidth is reduced. The

relationship between error type and beamwidth

is as follows:

• Horizontal beamwidth↔ Azimuth error

• Vertical beamwidth↔ Tilt error

Simulation results presented in this paper were

performed with antennas that have 65-degree

horizontal beamwidth and 7-degree vertical

beamwidth, which is considered to be a typical

antenna 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 network

performance

sensitivity to

azimuth and tilt

error 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

N o r m a

l i z e

d C o v e r a

g e

A r e a

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

N o r m a

l i z e

d C o v e r a

g e

A r e a

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


I n c r e a s e i

n C o v e r a

g e

G a p

( P e r c e n

t a g e

)

RSCP < –86 dBm, A

RSCP < –86 dBm, B

RSCP < –92 dBm, A

RSCP < –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


I n c r e a s e i

n C o v e r a

g e

G a p

( P e r c e n

t a g e

)

RSCP < –86 dBm

RSCP < –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

Average Antenna Azimuth E rror

I n c r e a s e

i n S e r v

i c e

Q u a

l i t y G a p

( P e r c e n

t a g e

)Ec /Io < –12 dB, A

Ec /Io < –12 dB, B

Ec /Io < –13 dB, A

Ec

/Io

< –13 dB, B

–3 –2 –1 0 1 2 3–0.5

0

0.5

1

1.5

2

2.5

QoS Gap Versus Ant enna Tilt E rror


I n c r e a s e

i n S e r v

i c e

Q u a

l i t y G a p

( P e r c e n

t a g e

)Ec /Io < –12 dB

Ec /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


I n c r e a s e

i n S o

f t H a n

d o

f f A r e a

( P e r c e n

t a g e

)SHO Margin = 5 dB, A

SHO Margin = 5 dB, B

SHO Margin = 3 dB, A


–3 –2 –1 0 1 2 3–6

–5

–4

–3

–2

–1

0

1Soft Handoff Area Versus Antenna Tilt Error


I n c r e a s e

i n S o

f t H a n

d o

f f A r e a

( P e r c e n

t a g e

)

SHO Margin = 3 dB

SHO 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 dB

SHO Margin = 5 dB

–3 –2 –1 0 1 2 3–6

–5

–4

–3

–2

–1

0

1Soft Handoff Area Versus Antenna Tilt Error


I n

c r e a s e

i n S o

f t H a n

d o

f f A r e a

( P e r c e n

t a g 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


I n c r e a s e

i n S e r v

i c e

Q u a

l i t y G a p

( P e r c e n

t a g e

)Ec /Io < –12 dB, A

Ec /Io < –12 dB, B

Ec /Io < –13 dB, A

Ec /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 E rror


I n c r e a s e

i n S e r v

i c e

Q u a

l i t y G a p

( P e r c e

n t a g e

) Ec /Io < –12 dB

Ec /Io < –13 dB

0 5 10 15 20 25 300

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2Coverage Gap Versus Antenna Azimuth Error


I n c r e a s e i n

C o v e r a

g e

G a p

( P e r c e n

t a g e

)

RSCP < –86 dBm, A

RSCP < –86 dBm, B

RSCP < –92 dBm, A

RSCP < –92 dBm, B

–3 –2 –1 0 1 2 3–1

0

1

2

3

4

5

6

7Coverage Gap Versus Antenna Tilt Error


I n c r e a s e i n

C o v e r a

g e

G a p

( P e r c e n

t a g e

)

RSCP < –86 dBm

RSCP < –92 dBm

–

0 5 10 15 20 25 300

1

2

3

4

5

6

7

8Soft Handoff Area Versus Antenna Azimuth Error


I n c r e a s e

i n S o

f t H a n

d o

f f A r e a

( P e r c e n

t a g e

)





Figure 7. Performance Graphs for 20-Site Cluster




Azimuth error

in the range of

6 to 8 degrees

is tolerable,

depending on

the installation

scenario and initial

coverage area.

configuration to provide an initial reference result

for comparison purposes. In this example no

interference or inter-cell soft handoff areas exist;

only coverage plots are shown. Only Scenario A

was considered because in Scenario B all the site’s

antennas were rotated with the same azimuth

error; therefore, overall coverage performance

did not change.

As illustrated in Figure 5a, coverage shrinks

when azimuth error increases. Coverage isreduced by 4 percent when there is a 30-degree

error in azimuth setting. The coverage area has an

almost inverse linear relationship with azimuth

error. Figure 5b shows that coverage is also very

sensitive to downtilt errors. Coverage changes up

to 29 percent when downtilt error varies in the

range of –3 to +3 degrees. This example shows a

system with no interference and inter-cell soft

handoff coverage. To study and capture real

network 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-site

cluster. These provide realistic examples in

performance graphs.

Azimuth errors in the range of 0 to 30 degrees

were considered for both Scenarios A and B. Tilt

errors varied between –3 and +3 degrees. The

areas are represented as the percentage of the

cluster area. The performance graphs are

categorized by coverage area, coverage quality,

and soft handoff area.

Coverage AreaCoverage area is measured in reference to

received signal code power (RSCP). Two

definitions were considered for coverage gap: the

area with less than –86 dBm RSCP and the area

with less than –92 dBm RSCP. Figures 6a and 7a

show the variations in coverage gaps when there

are inconsistencies in antenna azimuth and tilt

settings. A higher coverage percentage and

fewer coverage gaps is desirable when

implementing a UMTS network.

Coverage QualityQuality of service (QoS) or coverage quality is

measured by Ec/Io. Two definitions were

considered for QoS gap: the area with Ec/Io less

than –12 dB and the area with Ec/Io less than

–13 dB. Figures 6b and 7b show the variations in

areas with QoS gaps when there are incon-

sistencies in antenna azimuth and tilt settings. A

higher QoS and fewer QoS gaps is desirable when

implementing a UMTS network.

Soft Handoff Area

Soft handoff area is defined as the area covered

by more than one sector belonging to different

Node Bs. Two different settings were considered

for soft handoff threshold. Performance graphs

are shown for soft handoff areas when the soft

handoff margin is 3 dB and 5 dB. Figures 6c and

7c show the variations in soft handoff areas when

there are inconsistencies in antenna azimuth and

tilt settings. It is desirable to achieve the targetsoft handoff area recommended by the service

operator when implementing a UMTS network.

A smaller soft handoff area results in increased

call drop rate, and a higher soft handoff area

results in inefficient use of radio resources and

excessive interference.

Careful investigation of the results of the graphs

in Figures 6 and 7 leads to the following

conclusions:

• Antenna Azimuth: Network performance

variations depend on antenna azimuth error

variations and the installation process.Overall degradation in Scenario B is 40 to 60

percent less than in Scenario A. Therefore,

the same error in all sectors is preferable.

Azimuth error in the range of 6 to 8 degrees

is tolerable, depending on the installation

scenario and initial coverage area.

Performance degrades noticeably if the error

is 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 antenna

azimuth. A comparison of the coverage

graphs in Figures 6 and 7 shows that whenthe coverage/quality gap is smaller, its

sensitivity to error is higher.

• Antenna Tilt: Both coverage and quality

performances are very sensitive to antenna

tilt variations. There is up to a 100 percent

increase in coverage and quality gaps with

±3 degrees of tilt error. Soft handoff areas are

the least sensitive to tilt error. The graphs in

Figures 6c and 7c show less than a 10 percent

variation in soft handoff area with ±3 degrees

of tilt error.

SUMMARY AND CONCLUSIONS

Both the 20- and 42-site examples produce

consistent network performance behavior

and lead to the same conclusions. If equal errors

are introduced to cell site sectors, there is less

network 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 network

performance. Performance degradation is

noticeable if the azimuth error is greater than

10 degrees. Network performance is almost ten

times more sensitive to antenna tilt variations,

compared with azimuth variations. Both

coverage and quality gaps increase by up to

100 percent with ±3 degrees of tilt error.

If possible, only one antenna should be oriented

and the other antenna azimuths set in reference

to that one (Scenario B). However, rooftop size

and configuration may interfere with this

recommendation. If Scenario B installation

techniques can be applied to the site, simpler

methods (instead of the more expensive methods)

have the same effect on network performance.

Considering these conclusions, the following

UMTS network implementation standard can be

practically recommended for antenna azimuth

and tilt tolerances:

1. For the Scenario A technique: Azimuth

setting tolerance of ±6 degrees

2. For the Scenario B technique: Azimuth

setting tolerance of ±8 degrees

3. For both scenarios: Tilt setting tolerance of

±0.5 degrees

The cluster with more sites experiences less

network quality degradation due to azimuth and

tilt errors. However, this could be a subject for

further studies.

ACKNOWLEDGMENTS

The authors would like to thank Lacy Kiser

from the Bechtel Six Sigma Team and Jeff

Bryson from the Bechtel Construction Team for

the valuable data and information they provided.

Special thanks go to Radioplan GmbH for

providing 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 Optimization

Process,” Document Number 3DP-T04G-50009,Bechtel Telecommunications Network PlanningDepartment, 2005.

BIOGRAPHIES

Esmael Dinan, a senior

RF technologist with Bechtel

Telecommunications, has

been instrumental in many

aspects of the business unit’s

research activities and

the Cingular RF engineering

project. He has designed

and engineered an RFengineering data management system, developed

Cingular project RF engineering processes and

procedures, designed UMTS networks, and

verified and tested Dupont cryogenic TMA

performance.

Before joining Bechtel in 2002, Dr. Dinan

was product manager for the GMPLS control

plane of the RAYStar DWDM optical switch

at Movaz Networks, and lead network

architect at MCI. He has conducted research

and development on access methods and

performance modeling of 3G wireless commu-nications and high-speed optical networks.

Dr. Dinan received his PhD in Electrical

Engineering from George Mason University,

Fairfax, Virginia, and is a registered Professional

Engineer in Maryland. He has authored more

than 25 conference papers and journal articles

and has filed a patent on a novel signaling

mechanism developed for 3G cellular networks.

He is a member of the Institute of Electrical and

Electronics Engineers.

Aleksey Kurochkin is

currently senior director,Site Development and

Engineering, in the Bechtel

T e l e c o m m u n i c a t i o n s

Technology group, a group

that he originated. He is

experienced in international

t 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. His

engineering and marketing background has

given him both theoretical and hands-on

knowledge of most wireless technologies.

Aleksey has an MSEE/CS degree in Automatic

Telecommunications from Moscow Technical

University 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 degreesis recommended.

impact of antenna accuracy for 3g

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