CDMA 1X BTS LAyout and Site Selection

RG6004 CDMA 1X BTS Layout and Site Selection

RG6004 CDMA 1X BTS Layout and Site Selection

Study ObjectiveStudy Objective

• Learn the contents of BTS survey, work procedures and relevant documentations

After the study of this course, you

should

• Master the conception of site selection, principle of site selection and factors affecting network coverage

•Method of antenna selection

Contents of CourseContents of Course

Chapter 1 Survey

Chapter 2 BTS Layout and Site Selection

Chapter 3 Antenna Selection

Chapter 4 Survey Documentation

Chapter 1 SurveyChapter 1 Survey

Section 1 Brief Introduction to Section 1 Brief Introduction to

ServicesServices

Section 2 Preparations

BTS Survey LocationBTS Survey Location

BTS survey is an important step

in the network planning

•The determination of the preliminary BTS layout is the first job of BTS survey.

The BTS layout includes:

a. Estimate the number of BTSs required according to the capacity

prediction, traffic distribution and coverage requirements

b. Determine the theoretical BTS location

c. Assign values to relevant parameters of BTS (network hierarchy,

transmit power, antenna feeder system, antenna type, antenna

height, antenna angle, antenna downtilt, etc.)

To be vivid, set up a good coverage radio environment

Ideal BTS LayoutIdeal BTS Layout

Site SelectionSite Selection

• Select an ideal site and confirm it.

Once the site is finalized, a detailed BTS survey plan should be prepared.

•The BTS survey is an environmental survey of BTS after

the BTS layout is finalized, including light measurement,

spectrum measurement and site survey.

Sight measurement

Building environment and natural environment around BTS

Spectrum measurement

Electromagnetic background environment

Site survey

Installation condition of antenna and equipment

Power supply and transmission supply

Detailed SurveyDetailed Survey

Chapter 1 SurveyChapter 1 Survey

Section 1 Brief Introduction to Section 1 Brief Introduction to

ServicesServices

Section 2 Preparations

Get familiar with the engineering survey and

collect data related to the project, including Engineering document

Background information

Current network status

Local map

Contracted configuration list

BTS survey table in latest network planning

Project DocumentationProject Documentation

Prepare tools and confirm the tools are workable

before setting about the survey.

Digital camera

GPS satellite receiver

Compass

Tape

Telescope

Portable computer

YBT250

Tool PreparationTool Preparation

Coordination meeting for survey preparation

Before a formal survey, call all relevant personnel together to

hold a coordination meeting for the survey preparations, mainly

including

Electromagnetic background, an electromagnetic

background test if necessary

Finalization of surveyors and cooperators

Vehicle and equipment preparations

Preparation of survey plan and finalization of survey route

Preliminary solution for transmission and power supply

Coordination Meeting for Survey PreparationsCoordination Meeting for Survey Preparations

QuestionQuestion

There are too many sites to be surveyed, so

what preparations can accomplish the survey

with a high quality and a high efficiency?


Chapter 1 Survey




Chapter 2 BTS Layout and Site SelectionChapter 2 BTS Layout and Site Selection

Section 1 Coverage PlanningSection 1 Coverage Planning

Section 2 Cell Layout and Site

Selection

Factors Affecting CoverageFactors Affecting Coverage

Customer requirements

QoS (quality of service) index and coverage area

Equipment

Output power, receiver sensitivity, loss and gain of relevant

parts

Environment

The radio wave will have different propagation characteristics in

different environments

Technical system

Soft handoff gain, system load, diversity receiving

Service

Service type, information rate

Section 1 Coverage PlanningSection 1 Coverage Planning

Section 2 Cell Layout and Site

Selection

Chapter 2 BTS Layout and Site SelectionChapter 2 BTS Layout and Site Selection

Start the site selection after the preparations are all

done and the coverage requirement is obtained.

During the site selection, the following information

should be considered:

Original network status

Population distribution and local customs

City structure and town distribution

Major streets and traffic volume

Natural environment, such as mountain, lake,

river and coastline

Long-term development trend

Conception of Site SelectionConception of Site Selection

Principle of BTS site selection

Population distribution

Traffic distribution

Subscriber tendency

Environment around BTS

Signal propagation quality

Select areas where traffic is high and subscribers are

densely populated

Be careful not to select high mountains, radar, radio station,

forest, or power plant

Conception of Site SelectionConception of Site Selection

Weak Signal Area and Blind Area

The distance between BTSs is too large

The system load is too heavy

Obstructions

Poor indoor coverage

Effects of Unreasonable Cell Layout on Network Performance


Too large overlap coverage area

If there are too many BTSs, the distance between BTSs will be

short and the forward power distribution will be inappropriate.

A improper control of the cell coverage will result in a large overlap

area between BTSs, and eventually

a high soft handoff ratio

pilot pollution

FER increase, or even call drop



Cross-cell Coverage

1. When the BTS is set up on a mountain or extremely high

building in an urban or suburb area, the cross-cell coverage

may occur if it is not well controlled.

2. When the site and the direction of the main beam of the

antenna feeder are finalized, cross-cell coverage may occur

too, if the cell direction is consistent with that of ground

objects (such as street and rivers) that have a waveguide

effect.



The specific principles of site selection are shown

below:

a. The site should be at an ideal location in a regular cell and the

deviation should be less than a fourth of the BTS radius.

b. On condition that the BTS layout is not affected, try to use

existing facilities so as to reduce the construction cost and

construction period.

c. The border of urban area or mountain with a high altitude in suburban (altitude difference between it and the urban area is 100 ~ 300m) is usually not considered, because the avoidance of this site selection, on one hand, helps to control the coverage area, and on the other hand, reduce the engineering construction difficulty and facilitates the maintenance.

Principle of Site SelectionPrinciple of Site Selection

d. The new BTS should be built where the traffic is convenient, mains supply is available,

environment is safe and less fertile land is occupied.

e. Avoid building any BTS near high power radio-transmitting station, radar station or other

interference source.

f. The new BTS should be built far away from forests so as to avoid the rapid fading of

receiving signals.

g. Pay attention to signal reflex and time dispersion in the environment such as mountainous

area, lake with steepy banks/dense lakes , hilly city and high metallic building.

h. For the site selection in urban building clusters, make the best of the heights of buildings

to realize the partition of network hierarchy.

i. The site selection should guarantee a good coverage in the major service areas at the first

stage of network construction when there are fewer BTSs.

j. Prevent the main beam of the antenna from radiating towards streets, rivers and other

ground objects so as to avoid the pilot pollution or isolated island effect resulting from the

waveguide effect.

Principle of Site SelectionPrinciple of Site Selection

QuestionQuestion

How to select a good BTS site and how to lay

out the BTS so as to guarantee the future

network quality?

Chapter 1 Survey





Section 1 Antenna Feeder SystemSection 1 Antenna Feeder System

Section 2 Antenna Feeder Design

Section 3 Antenna Installation

Chapter 3 Antenna SelectionChapter 3 Antenna Selection

Combining and Distribution UnitCombining and Distribution Unit

Introduction to Antenna Feeder System

The antenna feeder system consists of combining &

distribution unit, feeder, tower top amplifier and antenna.

• Combining and distribution unit Functions:

It mainly performs the transmit-receive duplex, combining

and filtering of transmitting signals, filtering of receiving

signals, amplification and division of low noise, provides a

feed circuit for the tower top amplifier, and realizes that

multiple transmitting signals and receiving signals share

one set of antenna.

• Feeder Common feeder types: 1/2“, 7/8” and 5/4”

Principle of feeder selection:

450MHz, usually the 7/8“ feeder, instead of 5/4” is adopted.

800MHz, the 5/4” feeder is adopted if the length is more than 80m.

1900MHz, the 5/4” feeder is adopted if the length is more than 50m. The curvature of feeder should not be too large, and the external

conductor should be well grounded.

Feeder loss:

450M: about 3dB/100m for 7/8” feeder and 2dB/100m for 5/4″feeder.

800M: about 5dB/100m for 7/8” feeder and 3dB/100m for 5/4″feeder.

1900M: about 6dB/100m for 7/8” feeder and 4dB/100m for 5/4” feeder.

FeederFeeder

• Antenna

In the mobile communication system, the directional antenna with

a horizontal beam width of 90º and 65º and the omnidirectional

antenna are generally selected depending on the shape of

service area, service area and the number of channels.

Where the microcell is used for indoors coverage and tunnel

coverage, the spaced antenna and leaky cable can be selected. In the densely-populated area in a city, the 65º antenna is mostly

used to reduce the interference on neighboring cells.

In the suburb area where subscribers are less dense, generally,

the 90º directional antenna or the omnidirectional antenna is

selected. The brands of antenna available now include Kathrein, Allgon,

Xi’an Haitian, Andrew etc.

AntennaAntenna

Performance Index of Antenna

The performance indices of antenna diversify, but the most important

indices in the network planning mainly include the following:

Frequency Range

Gain

Polarization

Horizontal/Vertical half-power beam width)

Downtilt

Performance Index of AntennaPerformance Index of Antenna

Spaced Antenna System

As the mobile communication network develops, subscribers

are putting forward higher and higher demand on the mobile

communication network. To realize the high quality coverage

in special areas such as large building indoor,

highway/railway tunnel, and subway brings the demand on

spaced antenna system.

The spaced antenna system includes leaky cable, coaxial

feeder spaced antenna and optical fiber feeder spaced

antenna.

Spaced AntennaSpaced Antenna





Antenna Selection

The antenna is a very important part that determines the

network quality.

According to the coverage, service quality, traffic distribution

and terrain features in the BTS service area, select the antenna

in consideration of the coverage and interference of the entire

network.

The application environment of antenna can be classified into

the following types according to the terrain features or traffic

distribution:

Urban area, suburb area, rural area, highway,

mountainous area, offing, tunnel and indoor.

Antenna SelectionAntenna Selection

BTS antenna in urban area

a. Usually a horizontal half-power angle of 60 ~ 65º.

b. Usually a moderate gain of 15dBi or so.

c. A downtilt of 3 ~ 6º.

d. Dual polarization

BTS antenna in Sub-urban area

a. A horizontal half-power angle of 65º or 90º depending on the

practical situation.

b. A moderate and high gain of 15 ~ 18dBi.

c. A preset downtilt if necessary

d. Dual polarization or vertical polarization


BTS antenna in rural area

a. A 90˚ or 120˚ directional antenna or omnidirectional antenna can be selected depending on the practical situation and requirements.

b. The gain of the directional antenna is usually high (16 ~ 18dBi).

c. Usually the antenna with a preset downtilt is not selected, and the zero-filled antenna is preferred for a high BTS.

d. Vertical polarization is recommended. BTS antenna near highway

a. Usually a directional antenna with a narrow beam and a high gain is selected, or an 8-shaped antenna, omnidirectional or anamorphic omnidirectional antenna can be selected depending on the practical situation.

b. The coverage distance of highway BTS is required to be long, so the antenna with a preset downtilt is usually not selected.

c. Vertical polarization antenna is recommended.

d. The front-to-rear ratio should not be too large.


Design Principle of Antenna Height The height of antennas may differ in different cells in the same BTS,

depending on the installation space in a direction or the cell planning

requirements.

The effective antenna height is usually 25m or so in a flat urban

area.

The antenna height can be properly lengthened for a BTS in a

suburb county, usually 40m or so.

Too high an antenna will reduce the coverage level near the antenna

(“blind area under tower”), and this phenomenon is especially

obvious for an omnidirectional antenna.

Too high an antenna will cause the serious cross-cell coverage,

which affects the network quality.

Antenna HeightAntenna Height

•Design Principle of Antenna Angle

The antenna angle should be designed in consideration of the entire network. On condition that the coverage requirement is met, the azimuth angle of three sectors of each BTS in the urban area should be consistent and only need partial trimming. The azimuth angle of antenna can be adjusted according to the major coverage objects at the junction of urban and suburb, along the arterial traffic and in suburb isolated island.

The main beam of antenna should point to the dense traffic area, which can intensify the signal strength in this area and improve the call quality.

The deviation of the main beam of antenna from the co-frequency cell can effectively control interference.

The cross coverage depth of antennas between sectors in the urban area should not exceed 10%.

The cross coverage depth between neighbor cells in suburb area and towns should not be too high. The included angle between the antennas in neighbor sectors in the same BTS should be greater than 90º.

To avoid cross-cell coverage, the main beam of antenna should not direct to straight streets in a densely-populated urban area.

Antenna AngleAntenna Angle

•Design Principle of Antenna Downtilt

The beam tilt of antenna is the basic technology of improving the

frequency reuse capability.

The antenna downtilt technology can effectively control coverage

area and reduce the system interference.

The antenna downtilt must be determined in such a way according

to the specific situation that it can not only reduce the interference

between co-frequency cells, but also meet the coverage

requirement.

The antenna downtilt should be designed in consideration of

factors, such as BTS transmit power, antenna height, cell coverage

area and radio propagation environment.

DowntiltDowntilt

The beam tilt of antenna can be obtained electrically or mechanically.

The beam tilt in the electrical way is related to the selected antenna, and

usually is fixed. The beam tilt in the mechanical way is adjustable, but is

subject to installation accessories and propagation characteristics of

radio signals, and usually does not exceed 15º.

The beam tilt in the electrical and mechanical ways will generate different

surface radiations. The difference is little when the beam tilt is not large,

but it will become significant as the beam tilt increases:

Beam TiltBeam Tilt





Pay attention to the following during installation:

a. Installation environment The installation environment includes environment around

the antenna and that around BTS. For the environment

around antenna, the isolation between antennas and the

effects of tower and building on the antenna should be

considered. For the environment around BTS, the effects of

high buildings within the distance of 500m on the radio signal

propagation should be mainly considered.

Installation EnvironmentInstallation Environment

During the installation of BTS antenna, please see whether a

large shaded area will form in the coverage. Obstructions

should be avoided. For example, the barrier of the building

top to the radio signals should be avoided and the antenna

should be installed as near the edge of building top as

possible when the antenna is installed.

Installation EnvironmentInstallation Environment

b. Antenna isolation The receiver and transmitter of the BTS should be isolated to

some extent.

The isolation between antennas is the signal attenuation from

one antenna port to another antenna port in the practical

installation.

CDMA system: The isolation between two transmitter

antennas, and between the receiver antenna and transmitter

antenna should be 30dB at least.

Vertical layout of antenna: Lv=28+40log(k/λ)(dB)

Horizontal layout of antenna: Lv=22+20log(d/λ)-(G1+G2)-

(S1+S2)(dB)

Antenna IsolationAntenna Isolation

c. Meet the requirement of space diversity gain distance:

In the case of space diversity, the distance between two receiver antennas

should be 12 ~18λ.

The higher the antenna is installed, the longer the horizontal distance

between diversity antennas is. Generally, the horizontal distance between

diversity antennas is 0.11 times as long as the effective antenna height.

To achieve the same diversity effect, the vertical diversity distance must be 5

~ 6 times as long as that in the case of the horizontal diversity antenna.

To reduce the mutual influence of two antennas, the distance between

horizontal diversity antennas should be greater than 3m in the case of any

effective antenna height.

Space Diversity DistanceSpace Diversity Distance

•CDMA and GSM share BTS

•Save construction cost

•Shorten construction period

•Isolation between systems in the case of

construction of shared BTS

•Spurious interference requirement

Isolation for Shared BTSIsolation for Shared BTS

UP LINK

825 835 870 880MHZ

CDMA--GSMinterference

Frequency bands available to CDMA 1X system

= 》 Isolation between two antennas: 57dB

DOWN LINK

UP LINK DOWN LINK

UP LINK DOWN LINK

Frequency bands available to China Mobile GSM

891.4

909

936.4

954

909MHZ 954MHZ

915MHZ 960MHZ

Frequency bands available to China Unicom GSM

Spurious interference index stipulated in the protocol: -

13dbm/100khz

Attenuation at 890MHZ: 56dB

Attenuation at 909MHZ: 80dB

Isolation RequirementIsolation Requirement

D=5.3m

•Distance between CDMA-GSM horizontal antennas


•Distance between CDMA-GSM vertical antennas


D=

0.3m

Chapter 1 Survey





BTS Survey Report

The precise and standard documentation serves the

subsequent network planning and optimization. It is not only a

strong guarantee of engineering quality, but also the basis for

the future capacity expansion planning.

The BTS survey report includes two parts: BTS survey table

and memorandum.

One BTS survey table is configured for each BTS, which

mainly records latitude and longitude of BTS, antenna design

and surrounding environment.

The survey report should be consistent from front to back,

and also comply with the contract. What is inconsistent

should be specified in the memorandum.

Survey DocumentationSurvey Documentation

BTS Distribution Map in a Urban Area (Example)

BTS Distribution Map in a Urban Area (Example)

Date post:	26-Jan-2016
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CDMA 1X BTS LAyout and Site Selection

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