7617 RF Planning

INTRODUCTION INTRODUCTION TO TO

RF PLANNINGRF PLANNING

• Designing a cellular system - particularly one that incorporates both Macrocellular and Microcellular networks is a delicate balancing exercise.

• The goal is to achieve optimum use of resources and maximum revenue potential whilst maintaining a high level of system quality.

• Full consideration must also be given to cost and spectrum allocation limitations.

• A properly planned system should allow capacity to be added economically when traffic demand increases.

• As every urban environment is different, so is every macrocell and microcell network. Hence informed and accurate planning is essential in order to ensure that the system will provide both the increased capacity and the improvement in network quality where required, especially when deploying Microcellular systems.

INTRODUCTION TO RF INTRODUCTION TO RF PLANNINGPLANNING


• RF planning plays a critical role in the Cellular design process.

• By doing a proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we may encounter in the future and also reduce substantially the cost of optimization.

• On the other hand a poorly planned network not only leads to many Network problems , it also increases the optimization costs and still may not ensure the desired quality.

TOOLS USED FOR RF PLANNINGTOOLS USED FOR RF PLANNING

• Network Planning Tool

• CW Propagation Tool

• Traffic Modeling Tool

• Project Management Tool


Network Planning ToolNetwork Planning Tool

• Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage, doing frequency planning automatically, creating neighbor lists etc.

• With a database that takes into account data such as terrain, clutter, and antenna radiation patterns, as well as an intuitive graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

– Design wireless networks

– Plan network expansions

– Optimize network performance

– Diagnose system problems

• The major tools available in the market are Planet, Pegasos, Cell Cad.

• Also many vendors have developed Planning tools of their own like Netplan by Motorola, TEMS by Ericsson and so on.


Network Planning ToolNetwork Planning Tool (PLANET) (PLANET)


Propagaton Test KitPropagaton Test Kit

• The propagation test kit consists of– Test transmitter.– Antenna ( generally Omni ).– Receiver to scan the RSS (Received signal levels). The receiver

scanning rate should be settable so that it satisfies Lee’s law.– A laptop to collect data.– A GPS to get latitude and longitude.– Cables and accessories.– Wattmeter to check VSWR.

• A single frequency is transmitted a predetermined power level from the canditate site.

• These transmitted power levels are then measured and collected by the Drive test kit. This data is then loaded on the Planning tool and used for tuning models.

• Commonly Graysons or CHASE prop test kits are used.


Propagaton Test KitPropagaton Test Kit


Traffic Modeling ToolTraffic Modeling Tool

• Traffic modelling tool is used by the planning engineer for Network modelling and dimensioning.

• It helps the planning engineer to calculate the number of network elements needed to fulfil coverage, capacity and quality needs.

• Netdim by Nokia is an example of a Traffic modelling tool.


Project Management ToolProject Management Tool

• Though not directly linked to RF Design Planning, it helps in scheduling the RF Design process and also to know the status of the project

• Site database : This includes RF data, site acquisition,power, civil ,etc.

• Inventory Control

• Fault tracking

• Finance Management


RF PLANNINGRF PLANNINGPROCEDURESPROCEDURES

RF PLANNING PROCEDURERF PLANNING PROCEDURE

Propagation tool setupPropagation tool setup

• Set up the planning tool hardware. This includes the server and or clients which may be UNIX based.

• Setup the plotter and printer to be used.

Terrain, Clutter, Vector data acquisition and setupTerrain, Clutter, Vector data acquisition and setup

• Procure the terrain, clutter and vector data in the required resolution.

• Setup these data on the planning tool.

• Test to see if they are displayed properly and printed correctly on the plotter.

PRELIMINARY WORKPRELIMINARY WORK

Setup site tracking databaseSetup site tracking database

• This is done using Project management or site management databases.

• This is the central database which is used by all relevant department, viz. RF, Site acquisition, Power, Civil engineering etc, and avoids data mismatch.

Load master lease site locations in databaseLoad master lease site locations in database

• If predetermined friendly sites that can be used are available, then load this data into the site database.

RF PLANNING PROCEDURERF PLANNING PROCEDUREPRELIMINARY WORKPRELIMINARY WORK

Marketing Analysis and GOS determinationMarketing Analysis and GOS determination

• Marketing analysis is mostly done by the customer.

• Growth plan is provided which lists the projected subscriber growth in phases.

• GOS is determined in agreement with the customer (generally the GOS is taken as 2%)

• Based on the marketing analysis, GOS and number of carriers as inputs, the network design is carried out.

Zoning AnalysisZoning Analysis

• This involves studying the height restrictions for antenna heights in the design area.


Set Initial Link BudgetSet Initial Link Budget

• Link Budget Analysis is the process of analyzing all major gains and losses in the forward and reverse link radio paths.

• Inputs

• Base station & mobile receiver sensitivity parameters

• Antenna gain at the base station & mobile station.

• Hardware losses(Cable, connector, combiners etc).

• Target coverage reliabilty.

• Fade margins.• Output

• Maximum allowable path loss.


Initial cell radius calculationInitial cell radius calculation

• Using link budget calculation, the maximum allowable path loss is calculated.

• Using Okumura hata emprical formula, the initial cell radius can be calculated.

Initial cell count estimatesInitial cell count estimates

• Once the cell radius is known, the area covered by one site can be easily calculated.

• By dividing the total area to be covered by the area of each cell, a initial estimate of the number of cells can be made.


INITIAL SURVEYINITIAL SURVEY

Morphology DefinitionMorphology Definition

• Morphology describes the density and height of man made or natural obstructions.

• Morphology is used to more accurately predict the path loss.

• Some morphology area definitions are Urban, Suburban, rural, open etc.

• Density also applies to morphology definitions like dense urban, light suburban, commercial etc.

• This basically leads to a number of sub-area formation where the link budget will differ and hence the cell radius and cell count will differ.


Morphology Drive TestMorphology Drive Test

• This drive test is done to prepare generic models for network design.

• Drive test is done to characterize the propagation and fading effects.

• The objective is to collect field data to optimize or adjust the prediction model for preliminary simulations.

• A test transmitter and a receiver is used for this purpose.

• The received signals are typically sampled ( around 50 samples in 40λ ).


PROPAGATION MODELPROPAGATION MODEL

Propagation Tool AdjustmentPropagation Tool Adjustment

• The data collected by drive testing is used to prepare generic models.

• For a given network design there may be more than one model like dense-urban, urban, suburban, rural, highway etc.

• The predicted and measured signal strengths are compared and the model adjusted to produce minimum error.

• These models are then used for initial design of the network.

INITIAL DESIGNINITIAL DESIGN

Complete Initial Cell PlacementComplete Initial Cell Placement

• Planning of cell sites sub-area depending on clutter type and traffic required.

Run Propagation AnalysisRun Propagation Analysis

• Using generic models prepared by drive testing & prop test, run predictions for each cell depending on morphology type to predict the coverage in the given sub-areas.

• Planning tool calculates the path loss and received signal strength using Co-ordinates of the site location, Ground elevation above mean sea level, Antenna height above ground, Antenna radiation pattern (vertical & horizontal) & antenna orientation, Power radiated from the antenna.


Reset Cell Placement( Ideal Sites)Reset Cell Placement( Ideal Sites)

• According to the predictions change the cell placements to design the network for contigious coverage and appropriate traffic.

System Coverage MapsSystem Coverage Maps• Prepare presentations as follows

• Background on paper showing area MAP which include highways, main roads etc.

• Phase 1 sites layout on transparency.

• Phase 1 sites composite coverage prediction.

• Phase 2 sites layout transparency.

• Phase 2 composite coverage prediction on transparency.

• If more phases follow the same procedure.



Design Review With The ClientDesign Review With The Client

• Initial design review has to be carried out with the client so that he agrees to the basic design of the network.

• During design review, first put only the background map which is on paper. Then step by step put the site layout and coverage prediction.

• Display may show some coverage holes in phase 1 which should get solved in phase 2 .



Prepare Initial Search RingPrepare Initial Search Ring

• Note the latitude and longitude from planning tool.

• Get the address of the area from mapping software.

• Release the search ring with details like radius of search ring, height of antenna etc.

Release search rings to project management Release search rings to project management

Visit friendly site locationsVisit friendly site locations

• If there are friendly sites available that can be used (infrastructure sharing), then these sites are to be given preference.

• If these sites suite the design requirements, then visit these sites first.

SELECTION OF SITESSELECTION OF SITES


Select Initial Anchor SitesSelect Initial Anchor Sites

• Initial anchor sites are the sites which are very important for the network buildup, Eg - Sites that will also work as a BSC.

Enter Data In Propagation ToolEnter Data In Propagation Tool

• Enter the sites exact location in the planning tool.

Perform Propagation AnalysisPerform Propagation Analysis

• Now since the site has been selected and the lat/lon of the actual site ( which will be different from the designed site) is known, put this site in the planning tool and predict coverage.

• Check to see that the coverage objectives are met as per prediction.



Reset / Review Search RingsReset / Review Search Rings

• If the prediction shows a coverage hole ( as the actual site may be shifted from the designed site), the surrounding search rings can be resetted and reviewed.

Candidate site Visit( Average 3 per ring)Candidate site Visit( Average 3 per ring)

• For each proposed location, surveys should carried out and at least 3 suitable site candidates identified.

• Details of each candidate should be recorded on a copy of the Site Proposal Form for that site. Details must include:

» Site name and option letter Site location (Lat./Long)» Building Height» Site address and contact number

» Height of surrounding clutter

» Details of potential coverage effecting obstructions or other comments(A, B, C,...)



Drive Test And Review Best CandidateDrive Test And Review Best Candidate

• In order to verify that a candidate site, selected based on its predicted coverage area, is actually covering all objective areas, drive test has to be performed.

• Drive test also points to potential interference problems or handover problems for the site.

• The test transmitter has to be placed at the selected location with all parameters that have been determined based on simulations.

• Drive test all major roads and critical areas like convention centers, major business areas, roads etc.

• Take a plot of the data and check for sufficient signal strength, sufficient overlaps and splashes( least inteference to other cells).



Drive Test IntegrationDrive Test Integration

• The data obtained from the drive test has to be loaded on the planning tool and overlapped with the prediction. This gives a idea of how close the prediction and actual drive test data match.

• If they do not match ( say 80 to 90 %) then for that site the model may need tuning.

Visit Site With All Disciplines( SA, Power, Civil etc )Visit Site With All Disciplines( SA, Power, Civil etc )

• A meeting at the selected site takes place in which all concerned departments like RF Engineering, Site acquisition, Power, Civil Engineer, Civil contractor and the site owner is present.

• Any objections are taken care off at this point itself.



PRE-CONSTRUCTION STUDIESPRE-CONSTRUCTION STUDIES

Select Equipment Type For SiteSelect Equipment Type For Site

• Select equipment for the cell depending on channel requirements

• Selection of antenna type and accessories.

Locate Equipment On Site For Construction DrawingLocate Equipment On Site For Construction Drawing

• Plan of the building ( if site located on the building) to be made showing equipment placement, cable runs, battery backup placement and antenna mounting positions.

• Antenna mounting positions to be shown separately and clearly.

• Drawings to be checked and signed by the Planner, site acquisition, power planner and project manager.

PRE-CONSTRUCTION STUDIESPRE-CONSTRUCTION STUDIES

Perform Link Balance CalculationsPerform Link Balance Calculations

• Link balance calculation per cell to be done to balance the uplink and the downlink path.

• Basically link balance calculation is the same as power budget calculation. The only difference is that on a per cell basis the transmit power of the BTS may be increased or decreased depending on the pathloss on uplink and downlink.

EMI StudiesEMI Studies

• Study of RF Radiation exposure to ensure that it is within limits and control of hazardous areas.

• Data sheet to be prepared per cell signed by RF Planner and project manager to be submitted to the appropriate authority.

SYSTEM DESIGNSYSTEM DESIGN

Radio Radio FFrequency requency PPlan/ PN Planlan/ PN Plan

• Frequency planning has to be carried out on the planning tool based on required C/I and C/A and interference probabilities.

System System IInterference nterference PPlotslots

• C/I, C/A, Best server plots etc has to be plotted.

• These plots have to be reviewed with the customer to get the frequency plan passed.

Final Final CCoverage overage PPlotlot

• This presentation should be the same as design review presentation.

• This plot is with exact locations of the site in the network.

SYSTEM DESIGNSYSTEM DESIGN

Identification of coverage holesIdentification of coverage holes

• Coverage holes can be identified from the plots and subsequent action can be taken(like putting a new site) to solve the problem.

RADIO WAVE RADIO WAVE PROPAGATIONPROPAGATION

BASIC DEFINITIONSBASIC DEFINITIONSIsotropic RF SourceIsotropic RF Source

• A point source that radiates RF energy uniformly in all directions (I.e.: in the shape of a sphere)

• Theoretical only: does not physically exist.

• Has a power gain of unity I.e. 0dBi.

Effective Radiated Power (ERP)Effective Radiated Power (ERP)

• Has a power gain of unity i.e. 0dBi

• The radiated power from a half-wave dipole.

• A lossless half-wave dipole antenna has a power gain of 0dBd or 2.15dBi.

Effective Isotropic Radiated Power (EIRP)

• The radiated power from an isotropic source

EIRP = ERP + 2.15 dB

BASIC DEFINITIONSBASIC DEFINITIONS• Radio signals travel through space at the Speed of Light

C = 3 * 108 meters / second• Frequency (F) is the number of waves per second (unit: Hertz)• Wavelength (λ) (length of one wave) = (distance traveled in one second)

(waves in one second)

λ= C / F

If frequency is 900MHZ then

wavelength λ = 3 * 108

900 * 106

= 0.333 meters

BASIC DEFINITIONSBASIC DEFINITIONSdBdB• dB is a a relative unit of measurement used to describe power gain or

loss. • The dB value is calculated by taking the log of the ratio of the measured

or calculated power (P2) with respect to a reference power (P1). This result is then multiplied by 10 to obtain the value in dB.

dB = 10 * log10(P1/P2)

• The powers P1 ad P2 must be in the same units. If the units are not compatible, then they should be transformed.

• Equal power corresponds to 0dB.• A factor of 2 corresponds to 3dB

If P1 = 30W and P2 = 15 W then

10 * log10(P1/P2) = 10 * 10 * log10(30/15)

= 2

BASIC DEFINITIONSBASIC DEFINITIONSdBmdBm• The most common "defined reference" use of the decibel is the dBm, or

decibel relative to one milliwatt.• It is different from the dB because it uses the same specific, measurable

power level as a reference in all cases, whereas the dB is relative to either whatever reference a particular user chooses or to no reference at all.

• A dB has no particular defined reference while a dBm is referenced to a specific quantity: the milliwatt (1/1000 of a watt).

• The IEEE definition of dBm is "a unit for expression of power level in decibels with reference to a power of 1 milliwatt."

• The dBm is merely an expression of power present in a circuit relative to a known fixed amount (i.e., 1 milliwatt) and the circuit impedance is irrelevant.

BASIC DEFINITIONSBASIC DEFINITIONSdBmdBm• dBm = 10 log (P) (1000 mW/watt)

where dBm = Power in dB referenced to 1 milliwatt

P = Power in watts • If power level is 1 milliwatt:

Power(dBm) = 10 log (0.001 watt) (1000 mW/watt)

= 10 log (1)

= 10 (0)

= 0 • Thus a power level of 1 milliwatt is 0 dBm. • If the power level is 1 watt

1 watt Power in dBm = 10 log (1 watt) (1000 mW/watt)

= 10 (3)

= 30

BASIC DEFINITIONSBASIC DEFINITIONSdBmdBm• dBm = 10 log (P) (1000 mW/watt) • The dBm can also be negative value.• If power level is 1 microwatt

Power in dBm = 10 log (1 x 10E-6 watt) (1000 mW/watt)

= -30 dBm

• Since the dBm has a defined reference it can be converted back to watts if desired.

• Since it is in logarithmic form it may also be conveniently combined with other dB terms.

BASIC DEFINITIONSBASIC DEFINITIONSdBdBµµv/mv/m• To convert field strength in dbµv/m to received power in dBm with a

50Ω optimum terminal impedance and effective length of a half wave dipole λ/π

0dBu = 10 log[(10-6)2(1000)(λ/π)2/(4*50)] dBm

At 850MHZ

0dBu = -132 dBm

39dBu = -93 dBm

FREE SPACE PROPAGATIONFREE SPACE PROPAGATION• Friis FormulaFriis Formula

Pr = Pt GtGrλ2

(4πd)2

• Propagation LossPropagation Loss

Lp = 10log [4πd / λ]2

The square term is the propagation exponent. It is greater than 2 when obstructions exist.

• Propagation Loss in dB:Propagation Loss in dB:

L p = 32.44 + 20Log(d) +20Log(f)

f = MHz

d = km

Pt

Gt Gr

PrLp

d

PROPAGATION MECHANISMSPROPAGATION MECHANISMSReflectionReflection• Occurs when a wave impinges upon a smooth surface.• Dimensions of the surface are large relative to λ.• Reflections occur from the surface of the earth and from buildings and

walls.

Diffraction (Shadowing)Diffraction (Shadowing)• Occurs when the path is blocked by an object with large dimensions

relative to λ and sharp irregularities (edges).• Secondary “wavelets” propagate into the shadowed region.• Diffraction gives rise to bending of waves around the obstacle.

ScatteringScattering• Occurs when a wave impinges upon an object with dimensions on the

order of λ or less, causing the reflected energy to spread out or“scatter” in many directions.

• Small objects such as street lights, signs, & leaves cause scattering

MULTIPATHMULTIPATH• Multiple Waves Create “Multipath”• Due to propagation mechanisms, multiple waves arrive at the

receiver• Sometimes this includes a direct Line-of-Sight (LOS) signal

MULTIPATHMULTIPATHMultipath PropagationMultipath Propagation• Multipath propagation causes large and rapid fluctuations in a signal• These fluctuations are not the same as the propagation path loss.

Multipath causes three major thingsMultipath causes three major things• Rapid changes in signal strength over a short distance or time.• Random frequency modulation due to Doppler Shifts on different

multipath signals.• Time dispersion caused by multipath delays• These are called “fading effects• Multipath propagation results in small-scale fading.

WHAT IS FADING ?WHAT IS FADING ?

• The communication between the base station and mobile station in mobile systems is mostly non-LOS.

• The LOS path between the transmitter and the receiver is affected by terrain and obstructed by buildings and other objects.

• The mobile station is also moving in different directions at different speeds.

• The RF signal from the transmitter is scattered by reflection and diffraction and reaches the receiver through many non-LOS paths.

• This non-LOS path causes long-term and short term fluctuations in the form of log-normal fading and rayleigh and rician fading, which degrades the performance of the RF channel.

WHAT IS FADING ?WHAT IS FADING ?

Sig

nal

Po

wer

(d

Bm

)

Large scale fading component

Small scale fadingcomponent

LONG TERM FADINGLONG TERM FADING

• Terrain configuration & man made environment causes long-term fading.

• Due to various shadowing and terrain effects the signal level measured on a circle around base station shows some random fluctuations around the mean value of received signal strength.

• The long-term fades in signal strength, r, caused by the terrain configuration and man made environments form a log-normal distribution, i.e the mean received signal strength, r, varies log-normally in dB if the signal strength is measured over a distance of at least 40λ.

• Experimentally it has been determined that the standard deviation, σ, of the mean received signal strength, r, lies between 8 to 12 dB with the higher σ generally found in large urban areas.

RAYLEIGH FADINGRAYLEIGH FADING• This phenomenon is due to multipath propagation of the signal.

• The Rayleigh fading is applicable to obstructed propagation paths.

• All the signals are NLOS signals and there is no dominant direct path.

• Signals from all paths have comparable signal strengths.

• The instantaneous received power seen by a moving antenna becomes a random variable depending on the location of the antenna.

RICEAN FADINGRICEAN FADING

• This phenomenon is due to multipath propagation of the signal.

• In this case there is a partially scattered field.

• One dominant signal.

• Others are weaker.

• Dopplers shift is the shift in frequency due to the motion of mobile from the actual carrier frequency.

• Consider a mobile moving at a constant velocity v along a path segment having a length d between points X and Y while it receives signal from a remote source S.

• The Change in frequency due to dopplers shift is given by

fd = (v/λ) * cos(φ)

• It can be seen from the above equation that if the mobile is moving towards the direction of arrival of wave the dopplers shift is positive I.e. the apparent received frequency is increased. .

X Yd

S

θθ

∆

DOPPLERS SHIFTDOPPLERS SHIFT

LINK BUDGET LINK BUDGET PLANNING PLANNING

AND INITIAL CELL AND INITIAL CELL ESTIMATESESTIMATES

WHY LINK BUDGET ANALYSIS?WHY LINK BUDGET ANALYSIS?

• Link budget analysis provides

– Coverage design thresholds

– EIRP needed to balance the path

– Maximum allowable path loss

• It is important that the uplink and downlink paths be balanced, otherwise not enough signal will survive the transmission process to achieve the required signal to noise ratio(SNR) or the bit-error-rate(BER).

• Path imbalance results from the facts that the gains and losses in the uplink and downlink paths are not the same.

• The calculations have to be done separately on the uplink and the downlink.

THE RF PATHTHE RF PATH

PBS

MSSensitivity

PMS

BSSensitivity

Path LossDownlink

Path LossUplink

• Noise• Fading• Interference

THE RF PATHTHE RF PATHINPUTSINPUTS

• Base station and Mobile receiver Sensitivity Parameters

– Minimum acceptable Signal to Noise ratio

– Environmental / Thermal Noise

– Receiver Noise figure

• Antenna gain at the base station and mobile station.

• Hardware Losses (Cable , Connectors, Combiners, Duplexers etc)

• Target Coverage reliability.• Fade margins.

OUTPUTSOUTPUTS

• Base station ERP

• Maximum allowable path loss

• Cell size estimates

• Cell count estimates

GAINS AND LOSSESGAINS AND LOSSES

GainsGains

• Base station Antenna gain

• Mobile antenna gain

• Diversity gains

LossesLosses

• Hardware losses

– Combiner

– Cables

– Connectors

– Duplexer

• Air Interface

– Fade Margin

– Penetration Losses

• In-car

• In-building

• Body Loss

ANTENNA GAINSANTENNA GAINS

Mobile Station AntennaMobile Station Antenna

• Portable mobile phones antenna have typically gain of 0 to 1 dBd.

• Car mounted antenna has a typical gain of 1 to 3 dBd.

Base Station AntennaBase Station Antenna

• Omni directional antenna typically have a gain of 0-9dBd.

• Directional antenna typically have a gain of 9 to 14 dBd.

DIVERSITY GAINDIVERSITY GAIN

• Diversity is used on the uplink to overcome deep fades due to multipath by combining multiple uncorrelated signals.

• Diversity antenna systems are used mostly at the BTS on the uplink.

• Diversity antenna system can be realised by physically separating two receive antenna in space or by using polarization diversity.

• Diversity gain should be considered in Link Budget Analysis whenever it is used.

• Typically a gain of 3dB is considered whenever diversity is used in the Uplink calculation.

CABLESCABLES

Radio Equipment

Main cable

Jumper cable

• Two types of cables are used, maincable and jumper cable.

• Cable losses are given in per 100feet.

• Jumper cable have more loss than main cable.

• Cable loss is also dependant on frequency

CABLE SIZE RECOMMENDEDTYPE USE 900MHZ 1800MHZ

LDF4-50 1/2 inch Heliax Foam Jumper cable 2.160dBLDF5-50 7/8 inch Heliax Foam Main cable < 55M 1.21dB 1.97dBLDF7-50 1 5/8 inch Heliax Foam Main cable < 90m 0.75dB 1.25dB

LOSS/100 Feet

CABLE LOSSCABLE LOSS

CONNECTOR & COMBINER LOSSCONNECTOR & COMBINER LOSS

Connector LossConnector Loss

• Connectors used to connect RF components have a typical loss of 0.1dB each.

Combiner LossCombiner Loss

• A combiner is a device that enables several transmitters of different frequencies to transmit from the same antenna.

• Two types of combiners are available.

• Hybrid combiners combine two inputs to one output.

• Hybrid combiners have a typical insertion loss of 3dB.

• Cavity combiners combine more input to one output ( typically 5 inputs)

• Cavity combiners have around 3dB loss.

• Cavity combiners cannot be used in cells where synthesizer frequency hopping is used.

DUPLEXERDUPLEXER• A duplexer enables simultaneous transmission and reception of

signals on the same antenna .

• It provides isolation between the transmitted and received signal.

• Duplexers typically have a insertion loss of 0.5 to 1 dB

RadioUnit

Duplexer

Tx/ Rx

Tx Rx

BODY LOSSBODY LOSS• For all receiving environments a loss associated with the effect of

users body on propagation has to be used I.e proximity of the user with the mobile.

• This effect is in the form of few dB loss in both the uplink and downlink directions.

• Body loss is typically taken as 2 dB .

PENETRATION LOSSESPENETRATION LOSSES

• Penetration losses depend on the location of the subscriber with respect to the site.

• Generally 3 types of scenarios are taken into consideration viz. In-building, In-car and on street.

• Body loss is also a type of penetration loss .

Penetration Loss Loss

In-Building Penetration (dB) 15In-car Penetration (dB) 3-10

Body Loss (dB) 2-5

Fade Mar gin Calculat ionFade Mar gin Calculat ionCell Area ProbabilityCell Area Probability• Cell area probability (CAP ) is the percentage of the cell area that

has signal strength greater than the receiver sensitivity.• CAP is dependent on the radio environment, primarily the standard

deviation of the log normal faded signal (σ) and the propagation loss constant (n)

• The CAP is calculated using the following equation

PCA=½ ( 1+ erf (a) + exp ( )(1 - erf( )))

Where:

PCA Cell area probability

a

2ab+1

b 2

ab+1

b

MFADE

σ

Fade Mar gin Calculat ionFade Mar gin Calculat ionCell Area ProbabilityCell Area Probability

B

MFADE Fade margin applied

σ Standard deviation of received signal

n Propagation constant

10nLog10(e)

σ√2

Fade Mar gin Calculat ionFade Mar gin Calculat ionOutdoor Fade MarginOutdoor Fade Margin• The outdoor fade margin depends on the standard deviation of

the lognormal shadowing and the propagation constant• The propagation constant depends on the environment and the

frequency.

• For urban areas propagation constant varies from 2.7 to 5 , with a typical value of 5 for both 850 Mhz and 1900 Mhz.

• Standard deviation also varies on environment and frequency , and may vary slightly with frequency.

• The urban areas have higher standard deviation than rural areas. Typical value ranges from 5-12dB with a typical value of 8dB

• Outdoor fade margin can be calculated using a plot of the CAP equation.

• The next figure shows the CAP plot for a propagation constant of 3.5 and standard deviation of 5, 8 and 12.

• From the figure fade margin to be applied to the Link Budget may be selected depending on the standard of the received signal.

Fade Mar gin Calculat ionFade Mar gin Calculat ionOutdoor Fade MarginOutdoor Fade Margin

RECEIVER SENSITIVITYRECEIVER SENSITIVITY• This figure is provided by the equipment vendor.

• Receiver sensitivity is the ability of the receiver to receive signals in the sense that any signal below the sensitivity is considered as noise and is not usable.

• Receiver sensitivity is given by

S = Antenna Noise(dBm) + Receiver Noise Figure(dB) + C/N(dB)

S = the receivers sensitivity

C/N = Carrier to noise ration required in the presence to achieve a specified BER.

Antenna Noise(dBm) = 10log(kTB)

Where k = Botlzmann constant 1.38 X 10-20 milli Joules / Kelvin

T = Room temperature in degrees kelvin

B = Bandwidth in Hz

UPLINK UPLINK MAXIMUM ALLOWABLE PATH LOSS( MAPL) ON UPLINKMAXIMUM ALLOWABLE PATH LOSS( MAPL) ON UPLINK

MS Antenna gain (Gm )

Body Loss (Lbody )

Gain of receive antenna (GRA )

In-building / Car penetration Loss (LBldg )

Fade Margin (Mfade )

Cable,Connector and

Combiner losses (LCCC )

Diversity gain (GD )

MAPLUP = Pm + Gm - LBody - LBldg - Mfade + GRA + GD - LCCC + RReceiver Sensitivity

IN A NUTSHELL IN A NUTSHELL

• Transmitter power

• Combiner loss

• Cable loss(includes jumper and connector loss)

• Transmit Antenna gain

• Fade margin

• Body loss


• Mobile receiver sensitivity

• Mobile Transmit power


• Body Loss

• Fade Margin

• Receive antenna gain

• Cable loss(includes jumper and connector loss)

• BTS receiver sensitivity

DOWNLINKDOWNLINK UPLINKUPLINK

LINK BUDGET SHEET LINK BUDGET SHEET

Linkbudget For General Purpose

Downlink (BTS to MS) Uplink (MS to BTS)

BTS Tx power 43 dBm MS Tx power 33 dBm

Combining loss 3 dB MS antenna gain 0 dBi

Feeder loss 2 dB Total EIRP 33 dBm

BTS antenna gain 17 dBi

Total EIRP 55 dBm BTS antenna gain 17 dBi

Feeder loss 2 dB

MS Rx Sensitivity -102 dBm Diversity gain 3 dB

MS antenna gain 0 dBi BTS Rx Sensitivity -107.00 dBm

Fading margin 6 dB Fading margin 6 dB

Penetration Loss 0 dB Penetration Loss 0 dB

Antenna/body loss 2 dB Antenna/body loss 2 dB

Max. allowed pathloss 149.00 dB Max. allowed pathloss 150.00 dB

Link balance(downlink - uplink) -1.00 dB

CELL SIZE/COUNT ESTIMATION CELL SIZE/COUNT ESTIMATION

• Once the Maximum allowable pathloss is known, the achievable cell size can be evaluated.

• Cell radius is calculated using MAPL and Hata’s empirical formula.

• Cell radius is the distance from base station where the path loss equals MAPL. Beyond this radius, the signal is too weak to be acceptable.

• Each area has a different correction factor.

• Also the coverage objectives are usually different for Urban, Suburban and Rural areas.

• Therefore MAPL has to be calculated for each area and then cell size determined separately.

• Once the cell radius is calculated, cell count estimates can be made.

HATA´S EMPIRICAL FORMULA HATA´S EMPIRICAL FORMULA

• PL = 69.55 +26.6log10fc - 13.82log10hb + (44.9 - 6.55log10hb) log10R -

a(hm) -CF

where fc - Frequency in MHZ

hb - Transmitter antenna height

hm - Receiver antenna height

R - Radius in Km

a(hm) is the correction factor for effective mobile antenna height

• Solving backwards the cell radius is given by

log10R = MAPL +CF - 69.55 +26.6log10fc + 13.82log10hb + a(hm)

(44.9 - 6.55log10hb)

•

INITIAL CELL COUNT INITIAL CELL COUNT

• Once the cell radius for each area is calculated, then the minimum number of cells required to provide coverage can be determined.

• For each area

A = 2.6R2

Where R - radius of cell

A - Area of the corresponding hexagon.

• Cell count = Urban Area(Km2) + Suburban area(Km2) + Rural Area(Km2)

Aurban(Km2) Asuburban(Km2) Arural(Km2)

DRIVE TEST FOR DRIVE TEST FOR MODEL TUNINGMODEL TUNING

• Predesign drive test for measurement integration

• This is at beginning of design when no site has been built or even selected. All test sites are temporary.

• Drive test is performed mostly for characterization of propagation and fading effects in the channel. The object is to collect field data to optimize and adjust the prediction model for preliminary simulations.

• Post design drive test for site verification / optimization

• Drive test is performed to verify if they meet the coverage objectives.

• Overlaps are checked for hand-offs.

Predesign drive test Postdesign drive test

Drive test types

INTRODUCTION INTRODUCTION

INTRODUCTION INTRODUCTION

• In field measurement we have to collect variations due to propagation and slow fading.

• The received signals are typically sampled and averaged over spatial windows called bins.

• There are several sampling issues to be considered like

Sampling rate

Averaging window

Number of bins to be measured

SAMPLING CRITEREA SAMPLING CRITEREA

• When measuring the RF signal strength certain sampling criterea must be met to eliminate the short-term fading components from the long-term component ( I.e. log normal fading )

• The RF signal strength measurements must be taken over a radio path or mobile path distance interval of 40λ, where λ is the wavelength of the RF signal.

• If the distance interval is too short, the short term variation cannot be smoothed out and will affect the local mean.

• If the distance interval is too long, the averaged output cannot represent the local mean since it washes out the detailed signal changes due to the terrain variations.

• The number of RF measurements taken within the 40λ distance should be greater than 50.

• Depending on the speed of the vehicle during the drive test, the sampling interval in time is selected.

• Measurements have to be stopped whenever the vehicle is not moving.

SAMPLING CRITEREA SAMPLING CRITEREA • If f = 1900MHZ, then

λ = 3 * 108 / 1900 * 106

= 0.158 m

∴ 40 λ = 40 * 0.158

= 6.32 m• 50 measurements must be recorded every 6.32m or 1 measurement

every 0.1264m• The conversion from sampling distance to mobile velocity can be done

as follows

minimum sampling rate ( per second ) = v / (0.1264 m/sample)• If velocity of vehicle is 50 kph then

Sampling rate( per second ) = (50000/ 3600) / 0.1264

= 110 samples / sec• TEMS kit cannot be used for this purpose as it can report RF signal

strength measurements at a maximum rate of 1 sample per second

WINDOW SIZE WINDOW SIZE

• In field measurements the interest is on local averages of received signals.

• The size of averaging window have to be small enough to capture slow variations due to shadowing and large enough to average out the fast variations due to multipath.

• A typical range is 20 to 1500 m.

• The bin size is typically selected in 40λ to 1500m, i.e. all measurements in this size square are averaged to one value.

• Normally the post processing tool takes care of averaging the collected data over different bins.

NUMBER OF BINS NUMBER OF BINS

• The predicted and measured signal strengths for all bins within the drive route is compared and the best set of correction factors to minimize the prediction errors is determined.

• All the bins within the coverage area cannot be drive tested. So a large enough sample set should be considered.

• The more the number of bins, the larger the confidence level of results.• Generally for acceptable confidence at least 300 to 400 bins have to

be considered.

Bin

PROPAGATION KIT PROPAGATION KIT

• The propagation test kit consists of– Test transmitter.– Antenna ( generally Omni ).– Receiver to scan the RSS (Received signal levels). The receiver

scanning rate should be settable so that it satisfies Lee’s law.– A laptop to collect data.– A GPS to get latitude and longitude.– Cables and accessories.– Wattmeter to check VSWR.

TransmitterRECEIVER LAPTOP

GPS Antenna

Receiver AntennaTransmit Antenna

CABLE INTEGRITY TEST CABLE INTEGRITY TEST

TESTTRANSMITTER

WATTMETER 50 Ohms termination

• Cable integrity is checked by measuring VSWR.• A good known cable is connected from the test transmitter to the

wattmeter.• The cable under test is placed between the wattmeter & 50 Ohms load.• Forward and reverse power levels are measured and VSWR can be

calculated as VSWR = ( 1 + √PR/PF)/(1 - √ PR/PF).

• Each cable should be checked and any that exhibit greater than 1.2 : 1 VSWR must be replaced.

• Cable integrity check must be performed on all jumpers and antenna feedlines.

CABLE LOSS CABLE LOSS

• All cables used for testing must be measured and clearly labelled with insertion loss before they are used.

• These are normal wear items and so it is important to replace any cables that become kinked or frayed or that are worn or damaged connectors.

• Step 1

• Connected a cable ‘A’ directly to the wattmeter.

• Terminate the other end of the wattmeter with a 50 ohms resistance.

• Insert 1 Watt element in forward position. • Adjust to full deflection . • Record reading ‘A’

TESTTRANSMITTER

WATTMETER

50 Ohms termination

Cable A

CABLE LOSS CABLE LOSS

• Step 2• Connect cable ‘B’ as shown. • Turn transmitter on. • Record reading ‘B’.

• Cable Loss for cable B in dB = 10 log10(B/A)

TESTTRANSMITTER

WATTMETER

50 Ohms termination

Cable A Cable Bto be tested

TRANSMITTER SETUP TRANSMITTER SETUP

• If the propagation test is being done for model tuning to produce a generic model for macro cells, then a high point in the particular area has to be selected.

• The transmitter and the transmit antenna will be placed at this point (say the roof of the building ).

• The transmit antenna is connected to the transmitter via a RF cable.

• Check to see that the cable is connected properly and tight.

• Loosely connected or faulty cable can increase the VSWR.

• A test frequency has to selected from the frequency band allocated to the operator. Set the transmitter to this test frequency.

TESTTRANSMITTER

TEST SITE SELECTIONTEST SITE SELECTION• Site selection is based on a number of criteria. It may not be possible

to satisfy all these criteria at the same time, but it is important to select the best sites available.

• Drive test sites should be selected to give a good representative sample of the system coverage area. The exact number of sites required will depend on the size of the system coverage area and the variability of the characteristics of the coverage area.

• All terrain and clutter types in the area should be represented in the drive test data for proper prediction tuning.– Typical terrain types are: Flat, Rolling Hills, Large Hills, Mountains– Typical clutter types are: Water, Open Land, Forest, Commercial /

Industrial, Low Density Urban, Medium Density Urban, High Density Urban, City Center, Airport.

• City maps, topographical maps and aerial photographs can be useful in determining the terrain and clutter types for an area. It may also be necessary to drive the area and observe building types and density.

TEST SITE SELECTIONTEST SITE SELECTIONSite AvailabilitySite Availability• Test sites must be available for use during the drive test.• The site owner/supervisor should approve access to the site for as

long as needed to complete the testing. This may involve multiple visits to the site, possibly on short notice.

• Test sites must also be physically accessible to allow setup of the transmitter equipment and mounting of the antenna. For this reason building top sites are preferred to tower sites.

Site VisitSite Visit• Each site selected should be visited before testing to verify that is

suitable for use. • The inspection should be done by the same people who will be doing

the site setup for the actual drive test. Familiarity with the site should speed up the site setup during the drive test.

BUILDING SITE SELECTIONBUILDING SITE SELECTION

• When inspecting a building site the rooftop should be checked for any obstructions that would interfere with signal propagation. This could include objects on the rooftop itself or other nearby buildings or structures.

• The antenna location should be selected and a sketch of the rooftop made to identify this location relative to other objects nearby.

• Photographs should be taken of the location where the antenna will be mounted and in all directions looking away from the site.

BUILDING SITE SELECTIONBUILDING SITE SELECTION

TOWER SITE SELECTIONTOWER SITE SELECTION

• When inspecting a tower site the best location to mount the antenna to the tower must be deter-mined.

• This should be selected such that the tower doesn’t interfere with the propagation pattern of the transmit antenna. This will usually require that the antenna be above the tower or on an arm extending from the side of the tower.

• The area around the tower should be checked for any obstructions that would interfere with signal propagation.

TEMPORARY STRUCTURETEMPORARY STRUCTURE

• Generally cranes are used for temporary structure.• When cranes are used power generators have to be arranged in

advance.• The location should be selected such that the antenna will be above

any nearby obstacles.

TEMPORARY STRUCTURETEMPORARY STRUCTURE

DRIVE TEST PLANDRIVE TEST PLAN

verification to check that the positioning information in the drive test file is correct.

• A separate map should be prepared for each route.• Both line of site (LOS) and non-LOS points have to be included in the

drive test.• The data collected should represent typical coverage scenarios.• In urban area the effect of street orientations have to be considered.• The selection of drive test route should be based on the terrain

variations, Major highways and throughfares, potential shadowing areas and handoff region.

• Each drive route should be marked on a detailed road map showing the exact route to be driven.

• These maps should be used during the actual drive for navigation of the test vehicle.

• They can also be used during the drive test

DRIVE TEST PROCEDUREDRIVE TEST PROCEDURE

• The actual dive test must be performed carefully to insure that the data collected is accurate.

• It is important that all equipment used be tested and all setup information be recorded.

• If any of the procedures are not followed or any of the data is not properly recorded then the drive test data will not be usable and the drive will have to be repeated.

• Engineer should study the drive test plan ahead of time and highlight the intended drive test routes.

• For each drive test a team of two people should get involved.• The measurement process should be stopped the car stops ( eg near

traffic lights) or whenever the sampling and measurements look suspect.

DRIVE TEST OUTPUTDRIVE TEST OUTPUT

• The result of drive test is a collection of data files which has lat, long, Received Signal Strength Indicator(RSSI) at that point and the frequency.

• The location information ( lat, long ) is used by the post processing tools as a reference of correlation between the measured vs. predicted signal levels for measurement integration.

• This file has to be transferred onto the planning tool either by a floppy or by data transfer using LAN.

Lat Long RSSI Freq

X1 Y1 M1 F

X2 Y2 M2 F

X3 Y3 M3 F

DRIVE TEST OUTPUTDRIVE TEST OUTPUT

COMPUTER COMPUTER MODELINGMODELING

• Models are used to predict path loss.• Different models are used for different purpose. Eg:- Rural Macro-cell

-Okumura hata model, Microcells - Ray tracing• Models have to be tuned using data collected by drive testing.• Good propagation tool + Sound engineering ingenuity = Sound RF

design.

• Some of the popular prediction models are Okumura hata, Walfisch Ikegemi, COST231, Ray tracing etc.

INTRODUCTIONINTRODUCTION

COMPUTER MODELLINGCOMPUTER MODELLINGOkumura Hata ModelOkumura Hata Model• This is used for Macro cell modeling.• It has become the most popular propagation model for mobile

environments.• It is best applicable for cell ranges of 5 to 20 kms.• Below a range of 1 km it becomes very unreliable since obstacles in the

close vicinity of receiver and transmitter become the dominant scattering influences which are not taken into account in the formula.

• Path loss = K1 + K2log(d) + K3log(Heff) + K4 * Diff + K5log(Heff)log(d) + K6log(Hmeff) +K7log(f) + Kmorphology

K1 - 1Km intercept value. Upto this point model assumes free space loss

K2 - Slope value

K3 - Effective height coefficient

K4 - Coefficient for diffraction calculation

K5 - Hata model multiplier

K6 - Multiplier for mobile height

K7 - factor for frequency

COMPUTER MODELCOMPUTER MODELLINGLINGWalfish-Ikegami ModelWalfish-Ikegami Model• Walfish and Ikegami is a propagation model used in urban

environment. It takes into account near-by building structures. It assumes a regular grid pattern throughout the city.

• The model has four main parameters:

– Building separation (in meters)(b) : It is the distance between the centre of two buildings.

– Average building height (h) : This is the average height of all buildings in the cell’s coverage area.

– Road width (w)

– Road orientation angle (Φ )

• The model has separate equations for LOS and NLOS conditions. In NLOS roof-top-to-street diffraction and scatter loss and multi-screen diffraction loss for the immediate surroundings at mobile’s location are taken into account.

COMPUTER MODELCOMPUTER MODELLINGLING

h

w

b

d

Walfish Ikegami Model

COMPUTER MODELCOMPUTER MODELLINGLINGRay Tracing • In microcellular environments cells are generally location below rooftops

and average cell coverage area is around 1 Km or less. This makes it difficult to do coverage predictions.

• Most of the popular models like Okumara Hata model have been found to be unreliable in such conditions. In any statistical analysis a large sample is required inorder to get reliable results.

• In microcellular environment situations change rapidly in the small coverage area making it difficult to provide reliable results using any statistical models.

• Deterministic models have been created inorder to overcome this problem.

COMPUTER MODELCOMPUTER MODELLINGLINGRay TracingRay Tracing • Ray tracing is one such method and is used commonly in microcellular

environments. • Ray tracing follows a certain number of rays from the point of

transmission to the point under calculation.There are different threshold for the number of rays to be taken in consideration as the ray becomes negligible after it has experienced a certain number of reflections.

• There are primarily two methods for ray tracing : Ray launching and mirror image methods.For the method of ray launching a receiving circle is defined . The rays that cross this circle are taken into account when evaluating field strength level at the centre of the circle.

• The limitations of this method are that the map has to be precise, the buildings have to be modelled reliably and the computational load might turn out to be enormous. This is especially the case when a large number of reflections have to be taken into account.

COMPUTER MODELCOMPUTER MODELLINGLING

Ray Launching MethodRay Launching Method

ReceivingCircle

single pointsignal source

COMPUTER MODELCOMPUTER MODELLINGLINGMODEL TUNING• Propagation models use clutter and terrain data to predict cell

coverage at a site. However usually the terrain and clutter data available from the maps are not perfect.

• This means that the actual cell coverage could be different from the predicted cell coverage. This could in turn result in wrong cell designing.

• To avoid this model tuning is done.

• In model tuning data collected from the propagation test is loaded on the planning tool.

• This data represents the real life condition cell coverage.

• The prediction for that cell is then done using the same conditions as were for the propagation tests (i.e. using the same antenna type, same height of the antenna at the site, same downtilts, same transmit power etc. ).

COMPUTER MODELCOMPUTER MODELLINGLINGMODEL TUNINGMODEL TUNING• Ideally both the propagation test cell coverage and the predicted cell

coverage should match.

• If they match then the model does not require to be tuned.

• If the models do not match then the certain parameters in the propagation model equation are altered so that they both match.

• Once both the cell coverage match the model is then said to be tuned.

• Now the actual antenna type, height of antenna, transmit power are used and prediction done.

• This prediction can then be assumed to be correct.

• Cell designing is then done using this prediction.

COMPUTER MODELCOMPUTER MODELLINGLINGMODEL TUNINGMODEL TUNING• Ideally model tuning needs to be done for all the sites.

• However in many cases , the Network is divided into different clutter types (around 7 to 8) (e.g. urban,dense urban, semi urban, rural etc.) and models are tuned for each clutter types.

• The sites are then categorized in these clutter types and then fitted in the model tuned for that clutter type.

• This method though not perfect is widely accepted and saves lot of time and money for the operator.

COMP UTER M ODE LINGCOMP UTER M ODE LINGTuning Of Model In PlaNET• We will have a look at a general process of model tuning in PLANET

using Okumura Hata Model.• Load the Prop Test Survey data on PLANET• Do a prediction using same antenna type, height, transmit power, etc.

as used during survey.• Check if surveyed data matches that of prediction, if yes model tuning

not required, if not we proceed with model tuning.

• Planet has analysis capability with which it can compare predicted and surveyed data to give RMS and mean error for the predicted with respect to the surveyed data.

• It displays it with a Log d versus slope graph.• To tune the model we should try to bring mean error to zero and the

slope to zero. • We do this by varying the values of K1 and K2

COMP UTER M ODE LINGCOMP UTER M ODE LINGTuning Of Model In PlaNET

Steps In Tuning• Set Okumura Hata constants to initial values• K1 = -20 K2 = -44.9 K3 = -5.83• K4 = 0.5 K5 = 6.55 K6 = 0• Set all clutter values to zero• Analyse model with surveyed data, PLANET will give you new

suggested values for K1 and K2 and RMS and mean errors.• This is also displayed on Log(d) versus error graph. Our objective is to

get a line with no slope and centred on zero.• Use suggested values for K1 and K2 and analyse again.• Repeat this procedure till we get mean error to be zero.• After getting mean error to be zero our next aim is to obtain the line on

the graph with no slope. This is done by varying the value of K2 positively or negatively depending on the graph.

• Once we get the line with no slope, note the suggested value of K1 for that K2.

COMP UTER M ODE LINGCOMP UTER M ODE LINGTuning Of Model In PlaNET

Steps In Tuning• Analyse again with these values for K1 and K2. This should centre the

line and will have no slope.• Now add clutter factors and analyse again.• If the line remains centred on zero and has no slope ,the model is

tuned.• If not we need to repeat the process of varying the values of K1 and K2

till we get the line centred on zero and with no slope to tune the model.

ANTENNASANTENNAS

ANTENNASANTENNAS• Antennas form a essential part of any radio communication system.

• Antenna is that part of a transmitting or receiving system which is designed to radiate or to receive electromagnetic waves.

• An antenna can also be viewed as a transitional structure between free-space and a transmission line (such as a coaxial line).

• An important property of an antenna is the ability to focus and shape the radiated power in space e.g.: it enhances the power in some wanted directions and suppresses the power in other directions.

• Many different types and mechanical forms of antennas exist.

• Each type is specifically designed for special purposes.

ANTENNAS TYPESANTENNAS TYPES• In mobile communications two main categories of antennas used are

– Omni directional antennaOmni directional antenna

• These antennas are mostly used in rural areas.

• In all horizontal direction these antennas radiate with equal power.

• In the vertical plane these antennas radiate uniformly across all azimuth angles and have a main beam with upper and lower side lobes.

ANTENNAS TYPESANTENNAS TYPES– Directional antennaDirectional antenna

• These antennas are mostly used in mobile cellular systems to get higher gain compared to omnidirectional antenna and to minimise interference effects in the network.

• In the vertical plane these antennas radiate uniformly across all azimuth angles and have a main beam with upper and lower side lobes.

• In these type of antennas, the radiation is directed at a specific angle instead of uniformly across all azimuth angles in case of omni antennas.

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSRadiation PatternRadiation Pattern

• The main characteristics of antenna is the radiation pattern.

• The antenna pattern is a graphical representation in three dimensions of the radiation of the antenna as a function of angular direction.

• Antenna radiation performance is usually measured and recorded in two orthogonal principal planes (E-Plane and H-plane or vertical and horizontal planes).

• The pattern of most base station antennas contains a main lobe and several minor lobes, termed side lobes.

• A side lobe occurring in space in the direction opposite to the main lobe is called back lobe.

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSRadiation PatternRadiation Pattern

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSAntenna GainAntenna Gain

• Antenna gain is a measure for antennas efficiency.

• Gain is the ratio of the maximum radiation in a given direction to that of a reference antenna for equal input power.

• Generally the reference antenna is a isotropic antenna.

• Gain is measured generally in “decibels above isotropic(dBi)” or “decibels above a dipole(dBd).

• An isotropic radiator is an ideal antenna which radiates power with unit gain uniformly in all directions. dBi = dBd + 2.15

• Antenna gain depends on the mechanical size, the effective aperature area, the frequency band and the antenna configuration.

• Antennas for GSM1800 can achieve some 5 to 6 dB more gain than antennas for GSM900 while maintaining the same mechanical size.

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSMain Lobe Axis

½ Power Beamwidth

Side Lobe

Back Lobe

First Null

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSFront-to-back ratioFront-to-back ratio

• It is the ratio of the maximum directivity of an antenna to its directivity in a specified rearward direction.

• Generally antenna with a high front-to-back ratio should be used.

First Null BeamwidthFirst Null Beamwidth

• The first null beamwidth (FNBW) is the angular span between the first pattern nulls adjacent to the main lobe.

• This term describes the angular coverage of the downtilted cells.

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSAntenna LobesAntenna Lobes

• Main lobe is the radiation lobe containing the direction of maximum radiation.

• Side lobes

Half-power beamwidthHalf-power beamwidth

• The half power beamwidth (HPBW) is the angle between the points on the main lobe that are 3dB lower in gain compared to the maximum.

• Narrow angles mean good focusing of radiated power.

PolarisationPolarisation

• Polarisation is the propagation of the electric field vector .

• Antennas used in cellular communications are usually vertically polarised or cross polarised.

ANTENNA CHARACTERISTICSANTENNA CHARACTERISTICSFrequency bandwidthFrequency bandwidth

• It is the range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard.

• VSWR of an antenna is the main bandwidth limiting factor.

Antenna impedanceAntenna impedance

• Maximum power coupling into the antennas can be achieved when the antenna impedance matches the cables impedance.

• Typical value is 50 ohms.

Mechanical sizeMechanical size

• Mechanical size is related to achievable antenna gain.

• Large antennas provide higher gains but also need care in deployment and apply high torque to the antenna mast.

COUPLING BETWEEN COUPLING BETWEEN ANTENNASANTENNAS

• Antenna radiation pattern will become superimposed when the distance between the antennas becomes too small.

• This means the other antenna will mutually influence the individual antenna patterns.

• Generally 5 to 10λ horizontal separation provides sufficient decoupling of antenna patterns.

• The vertical distance needed for decoupling is usually much smaller as the vertical beamwidth is generally less.

• A 1λ separation in the vertical direction is sufficient in most cases.

ANTENNA INSTALLATIONANTENNA INSTALLATION

• Antenna installation configurations depend on the operators preferences.

• It is important to keep sufficient decoupling distances between antennas.

• If TX and RX direction use separated antennas, it is advisable to keep a horizontal separation between the antennas in order to reduce the TX signal power at the RX input stages.

ANTENNA DOWNTILTINGANTENNA DOWNTILTING

• Network planners often have the problem that the base station antenna provides an overcoverage.

• If the overlapping area between two cells is too large, increased switching between the base station (handover) occurs.

• There may even be interference of a neighbouring cell with the same frequency.

• If hopping is used in the network, then limiting the overlap is required to reduce the overall hit rate.

• In general, the vertical pattern of an antenna radiates the main energy towards the horizon.

• Only that part of the energy which is radiated below the horizon can be used for the coverage of the sector.

• Downtilting the antenna limits the range by reducing the field strength in the horizon.

ANTENNA DOWNTILTINGANTENNA DOWNTILTING

• Antenna downtilting is the downward tilt of the vertical pattern towards the ground by a fixed angle measured w.r.t the horizon.

• Downtilting of the antenna changes the position of the half-power beamwidth and the first null relative to the horizon.

• Normally the maximum gain is at 0• (parallel to the horizon) and never intersects the horizon.

• A small downtilt places the beams maximum at the cell edge

• With appropriate downtilt, 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.

• There are two methods of downtilting

– Mechanical downtilting

– Electrical downtilting.

MECHANICAL DOWNTILTINGMECHANICAL DOWNTILTING

• Mechanical downtilting consists of physically rotating an antenna downward about an axis from its vertical position.

• In a mechanical downtilt as the front lobe moves downward the back lobe moves upwards.

• This is one of the potential drawback as compared to the electrical downtilt because coverage behind the antenna can be negatively affected as the back lobe rises above the horizon.

• Additionally , mechanical downtilt does not change the gain of the antenna at +/- 90deg from antenna horizon.

• As the antenna is given downtilt, the footprint starts changing with a notch being formed in the fron’t while it spreads on the sides.

• After 10 degrees downtilt the notch effect is quiet visible and the spread on the sides are high. This may lead to inteference on the sides.



MECHANICAL DOWNTILTINGMECHANICAL DOWNTILTINGVertical antenna pattern at 0°

Vertical antenna pattern at 15° downtilt

Backlobe shoots over the horizon

ELECTRICAL DOWNTILTELECTRICAL DOWNTILT• Electrical downtilt uses a phase taper in the antenna array to angle the

pattern downwards.

• This allows the the antenna to be mounted vertically.

• Electrical downtilt is the only practical way to achieve pattern downtilting with omnidirectional antennas.

• Electrical downtilt affects both front and back lobes.

• If the front lobe is downtilted the back lobe is also downtilted by equal amount.

• Electrical downtilting also reduces the gain equally at all angles on the horizon. The that adjusted downtilt angle is constant over the whole azimuth range.

• Variable electrical downtilt antennas are very costly.

ELECTRICAL DOWNTILTELECTRICAL DOWNTILT

ELECTRICAL DOWNTILTELECTRICAL DOWNTILTHorizontal and vertical pattern for allgon 7144 antenna

Horizontal Beamwidth = 90° Vertical Beamwidth = 16° Electrical Downtilt = 16°

OBSTACLE REQUIREMENTOBSTACLE REQUIREMENT

• Nearby obstacles are those reflecting or shadowing materials that can obstruct the radio beam both in horizontal and vertical planes.

• When mounting the antenna on a roof top, the dominating obstacle in the vertical plane is the roof edge itself and in the horizontal plane, obstacles further away like surrounding buildings, can act as reflecting or shadowing material.

• The antenna beam will be distorted if the antenna is too close to the roof. Hence the antenna must be mounted at a minimum height above the rooftop or other obstacles.

• If antennas are wall mounted, a safety margin of 15 degrees between the reflecting surface and the 3-dB lobe should be kept.

OBSTACLE REQUIREMENTOBSTACLE REQUIREMENT

Main RadiationDirection

Half Power Beamwidth

Safety Margin15 Degrees

Building

OPTIMAL DOWNTILTOPTIMAL DOWNTILT• Although the use of downtilt can be a effective tool for controlling

interference, there is a optimum amount by which the antenna can be downtilted whereby both the coverage losses and the interference at the reuse cell can be kept at a minimum.

downtilt angle (D)

3 dB Beamwidth

Main lobe

Height (H)

Cellmax

Φ

Φ

OPTIMAL DOWNTILTOPTIMAL DOWNTILT

• The figure shows a cells coverage area. • The primary illumination area is the area on the ground that receives the

signal contained within the 3dB vertical beamwidth of the antenna.• The distance from the base station to the outer limit of the illumination

area is denoted by Cellmax. • It should be noted that the cellmax can be different from the cell

boundary area which is customer defined.

• Ideally in a well planned network Cellmax should always be less than the co-channel reuse distance to minimise interference.

• We now derive the relation between height (H), downtilt angle (D), 3dB vertical beamwidth and Cellmax.

• As shown in the schematic φ is the angle between the upper limit of the 3dB beamwidth and the horizon.

OPTIMAL DOWNTILTOPTIMAL DOWNTILT

• tan (Φ ) = Cellmax / H

Φ = D - 0.5 * 3dB vertical beamwidth

Cellmax = H * tan (D - 0.5 * 3dB vertical beamwidth)• For the Cellmax to be a positive quantity , downtilt angle must be more

than half of the 3dB vertical beamwidth.• When the downtilt angle is less than half of the 3dB beamwidth, part of

the signal from the main beam shoots over the horizon .• The signal directed towards or above the horizon can potentially cause

interference at the reuse sites.

DIVERSITY ANTENNA DIVERSITY ANTENNA SYSTEMSSYSTEMS

Divers ity Antenna Di vers ity Antenna Syst emsSyst ems

NEED OF DIVERSITY

Building

Building

Building

Divers ity Antenna Divers ity Antenna Syst emsSyst ems

NEED OF DIVERSITY• In a typical cellular radio environment, the communication between the

cell site and mobile is not by a direct radio path but via many paths.• The direct path between the transmitter and the receiver is obstructed

by buildings and other objects. • Hence the signal that arrives at the receiver is either by reflection from

the flat sides of buildings or by diffraction around man made or natural obstructions.

• When various incoming radiowaves arrive at the receiver antenna, they combine constructively or destructively, which leads to a rapid variation in signal strength.

• The signal fluctuations are known as ‘multipath fading’.


Multipath PropagationMultipath Propagation• Multipath propagation causes large and rapid fluctuations in a signal• These fluctuations are not the same as the propagation path loss.

Multipath causes three major thingsMultipath causes three major things• Rapid changes in signal strength over a short distance or time.• Random frequency modulation due to Doppler Shifts on different

multipath signals.• Time dispersion caused by multipath delays• These are called “fading effects• Multipath propagation results in small-scale fading.


DIVERSITY TECHNIQUE• Diversity techniques have been recognised as an effective means

which enhances the immunity of the communication system to the multipath fading. GSM therefore extensively adopts diversity techniques that include

Diversity techniquesInterleaving

In time domain

Frequency HoppingIn Frequency domain

Spatial diversityIn spatial domain

Polarisation diversityIn polarisation domain


CONCEPT OF DIVERSITY ANTENNA SYSTEMS• Spatial and polarisation diversity techniques are realised through

antenna systems.• A diversity antenna system provides a number of receiving branches

or ports from which the diversified signals are derived and fed to a receiver. The receiver then combines the incoming signals from the branches to produce a combined signal with improved quality in terms of signal strength or signal-to-noise ratio (S/N).

• The performance of a diversity antenna system primarily relies on the branch correlation and signal level difference between branches.

Divers ity Antenna Di vers ity Antenna Syst emsSyst ems

Transmission media 1

Transmission Tmedia 2

Peak

Fade

ReceiverInformation

CONCEPT OF DIVERSITY ANTENNA SYSTEMS


CORRELATION BETWEEN BRANCHES• The branch correlation coefficient (r) represents the degree of

similarity between the signals from two different receiving branches. • The correlation coefficient ranges from 0 to 1. • r=1 means the signals from two different branches behave exactly

the same. In this case, the signals are coherent.• r=0 means the signals from two different branches behave

completely different. In this case, the signals are uncorrelated.

• To achieve the best performance, a diversity antenna system is required to provide uncorrelated signals.

• For r=1, the diversity antenna becomes ineffective in combating the multipath fading.

• In reality, however, it is not always practical to have a diversity antenna system which guarantees r=0. Extensive research in this field has revealed that a diversity antenna system can perform satisfactorily provided that r £0.7.


Time

Sig

nal

Str

ength

Combined signalSignal 1Signal 2

Combining

Combined signalfed to receiver Signal 2

Signal 1


SIGNAL LEVEL DIFFERENCE• The second key parameter for a good diversity antenna system is

the mean signal level difference. • The difference is a statistical parameter which indicates the balance

of the signal strengths from the two receiving branches.• In a real system, the statistical balance can be verified by comparing

the mean values of the two signals measured over a lengthy period.

• If the ratio betn the median values is 0dB, the two receiving branches are statistically balanced.

• The performance of the diversity system will deteriorate while the ratio increases or decreases from 0dB.


Signal level difference

Sig

nal s

tren

gth

Time

SIGNAL LEVEL DIFFERENCE


SPATIAL DIVERSITY ANTENNA SYSTEMS• The spatial diversity antenna system is constructed by physically

separating two receiving base station antennas.• Once they are separated far enough, both antennas receive

independent fading signals. As a result, the signals captured by the antennas are most likely uncorrelated.

• The further apart are the antennas, the more likely that the signals are uncorrelated.

• The types of the configuration used in GSM networks are:

• horizontal separation

• vertical separation• composite separation.


TYPICAL SPATIAL ANTENNA DIVERSITY CONFIGURATIONS

Horizontal Separation Vertical Separation


Branch correlation• The physical limitation of the supporting structure should also be

considered while selecting the spatial diversity antenna configuration. For example, if a wide framework is not permitted on top of a mounting tower, vertical separation is a alternative to be considered.

• To achieve the required correlation coefficient (r £0.7) different configurations require different separations.

• The separation indicated in Table below shows that low values of correlation are more easily obtained with horizontal rather than vertical separation.

• That is why most of the diversity antenna systems in GSM networks use horizontal separation.

CRITERIA FOR SELECTING TYPE OF SPATIAL SEPARATION

d/ 900MHZ 1800MHZ d/ 900MHZ 1800MHZSeparation 10 3.3m 1.7m 17 5.7m 2.8m

Horizontal Separation Vertical Separation

λ λ


CRITERIA FOR SELECTION OF SPATIAL SEPARATION

Signal level difference• A system using horizontally separated diversity antennas has a

symmetrical configuration and is therefore able to provide balanced signal strengths.

• A system using vertically separated antennas needs large separation to meet the required correlation.

• The consequence is that the two antennas have different antenna height gains, which may result in imbalance between the two signal strengths.


CRITERIA FOR SELECTION OF SPATIAL SEPARATION

Angular dependence

• Angular dependence reflects the dependence of the performance of a diversity antenna system on the angular position of a mobile relative to the boresight of the antenna.

• Horizontally separated antenna system has high dependence on the mobile’s angular position.

• The effective separation reduces as the mobile moves away from the antenna boresight.

• As the mobile is 90° off the antenna boresight, the effective separation becomes zero.

• In such a case, the signals from two antennas are very likely coherent which will then lead to a deterioration of the diversity performance.


ANGULAR DEPENDANCE

•Most of the GSM cell sites are 3 sectored cell sites.

•The maximum angular offset is therefore approximately 60°.

•Simulation shows that the performance of a horizontally separated antenna system experiences noticeable deterioration only when the angular offset exceeds 70° .

SeparationReduced

SeparationZero

Separation

View from boresight View from 45 deg off boresight View from 90 deg off boresight


PROS AND CONS OF HORIZONTAL CONFIGURATION

Advantages

• Easier to achieve low values of correlation and balance between the signals. Hence widely used.

Disadvantages

• High angular dependence. The impact is however marginal for sectorised applications.

• Require sizeable headframe on the supporting structure.


PROS AND CONS OF VERTICAL CONFIGURATION

Advantages

• Slim supporting structure.

• Angular independence

Disadvantages

• Require large separation for low values of correlation.

• May cause imbalance between the two diversity branches.

• Generally not used.


THREE ANTENNA SPATIAL CONFIGURATION

10λ Separation

Receive 1 Transmit Receive 2


TWO ANTENNA SPATIAL CONFIGURATION

10λ Separation

Receive 2Tx Rx

Transmit Receive 1

Duplexer


POLARISATION DIVERSITY ANTENNA SYSTEMS• A single (say vertical) polarised electromagnetic wave is converted

to a wave with two orthogonal polarised fields while it is propagating through scattering environment.

• It has also been found that the two fields exhibit some extent of decorrelation.


DUAL POLARISED ANTENNAS• A dual-polarisation antenna consists of two sets of radiating

elements which radiate or, in reciprocal, receive two orthogonal polarised fields.

• The antenna has two input connectors which separately connects to each set of the elements.

• The antenna has therefore the ability to simultaneously transmit and receive two orthogonally polarised fields.

H / V Slant 45°


ADVANTAGES OF DUAL POLARISED ANTENNAS• The best advantage of using the dual polarisation antenna is the

reduction in the number of antennas per sector.• Reduced size of the headframe of the supporting structure• Reduced windload and weight.• Reduced difficulty in site acquisition and installation.• Cost saving

– Requiring slim tower– Requiring less installation time.– Cost of one dual polarisation antenna is generally lower than that

of two – Single polarised antennas


DUAL POLARISED ANTENNA CONFIGURATIONSD

UA

L P

OL

E A

NT

EN

NA

T R

TX RX RX

DU

AL

PO

LE

AN

TE

NN

AS

ING

LE

PO

LE

AN

TE

NN

A

RX RX

TX

DU

AL

PO

LE

AN

TE

NN

A

T TR R

TX RX TX RX

INTERFERENCEINTERFERENCE

WHAT IS INTERFERNCE ?WHAT IS INTERFERNCE ?

• Interference is the sum of all signal contributions that are neither noise not the wanted signal.

EFFECTS OF INTERFERNCE EFFECTS OF INTERFERNCE

• Interference is a major limiting factor in the performance of cellular systems.

• It causes degradation of signal quality.

• It introduces bit errors in the received signal.

• Bit errors are partly recoverable by means of channel coding and error correction mechanisms.

• The interference situation is not reciprocal in the uplink and downlink direction.

• Mobile stations and base stations are exposed to different interference situation.

SOURCES OF INTERFERNCE SOURCES OF INTERFERNCE

• Another mobile in the same cell.

• A call in progress in the neighboring cell.

• Other base stations operating on the same frequency.

• Any non-cellular system which leaks energy into the cellular frequency band.

TYPES OF INTERFERNCE TYPES OF INTERFERNCE

• There are two types of system generated interference

– Co-channel interference

– Adjacent channel interference

Co-Channel InterferenceCo-Channel Interference

• This type of interference is the due to frequency reuse , i.e. several cells use the same set of frequency.

• These cells are called co-channel cells.

• Co-channel interference cannot be combated by increasing the power of the transmitter. This is because an increase in carrier transmit power increases the interference to neighboring co-channel cells.

• To reduce co-channel interference, co-channel cells must be physically separated by a minimum distance to provide sufficient isolation due to propagation or reduce the footprint of the cell.



• Some factors other then reuse distance that influence co-channel interference are antenna type, directionality, height, site position etc,

• GSM specifies C/I > 9dB.

Carrier f1 Interferer f1

dB

Distance

C

I

TYPES OF INTERFERNCE TYPES OF INTERFERNCE Co-Channel InterferenceCo-Channel Interference

• In a cellular system, when the size of each cell is approximately the same, co-channel interference is independent of the transmitted power and becomes a function of cell radius(R) and the distance to the centre of the nearest co-channel cell (D).

C1

C2C3

C1

C2C3

D



• Q = D / R = √3N

• By increasing the ratio of D/R, the spatial seperation between the co-channel cells relative to the coverage distance of a cell is increased. In this way interference is reduced from improved isolation of RF energy from the co-channel cell.

• The parameter Q , called the co-channel reuse ratio, is related to the cluster size.

• A small value of Q provides larger capacity since the cluster size N is small whereas a large value of Q improves the transmission quality.


Adjacent-Channel InterferenceAdjacent-Channel Interference

• Interference resulting from signals which are adjacent in frequency to the desired signal is called adjacent channel interference.

• Adjacent channel interference results from imperfect receiver filters which allow nearby frequencies to leak into the passband.

• Adjacent channel interference can be minimized through careful filtering and channel assignments.

• By keeping the frequency separation between each channel in a given cell as large as possible , the adjacent interference may be reduced considerably.


Adjacent-Channel InterferenceAdjacent-Channel Interference

Carrier f1 Interferer f2dB

A

C

Distance

COUNTERING INTERFERENCE COUNTERING INTERFERENCE

POWER CONTROLPOWER CONTROL• RF power control is employed to minimise the transmit power required

by MS or BS while maintaining the quality of the radio links.• By minimising the transmit power levels, interference to co-channel

users is reduced.• Power control is implemented in the MS as well as the BSS.• Power control on the Uplink also helps to increase the battery life.• Power received by the MS is continously sent in the measurement

report.• Similarly uplink power received from the MS by the BTS is measured

by the BTS.• Complex algorithm evaluate this measurements and take a decision

subsequently reducing or increasing the power in the Uplink or the downlink.

COUNTERING INTERFERENCE COUNTERING INTERFERENCE

SECTORIZATIONSECTORIZATION

• For 120 degrees sectored site as compared to an omni site almost 1/3rd interference is received in the uplink.

• The more selective and directional is the antenna, the smaller is the interference.

• Reduction in interference results in higher capacity in both links.

FREQUENCY FREQUENCY PLANNINGPLANNING

INTRODUCTIONINTRODUCTION• The objective of a cellular system is to provide quality communication

to the maximum number of users in a defined area.

• The number of users supported by the system can be increased by using more frequencies.

• Frequency resources are however always limited.

• Hence RF Planning engineers are required to maximise spectrum efficiency.

• In order to accommodate a maximum number of subscribers per network, the available frequencies need to be reused as often as possible.

• This creates interference towards other cells, which have detrimental impact to the link quality.

• Finding the optimum compromise between dense re-use and least interference is the objective of frequency planning.

INTRODUCTIONINTRODUCTION• The system design and planning of the system has to be done so as

to reuse the frequencies as often as possible while keeping the co-channel and adjacent channel interference within acceptable limits.

• Also a minimum received signal level has to be provided throughout the coverage area of the network.

• Frequency planning can be done

• Manually by skilled expert RF Engineers.

• With powerful planning tool having the option of automated frequency planning.

FREQUENCY PLANNING STEPSFREQUENCY PLANNING STEPS• The steps to be followed in manual frequency planning are

– Calculating the frequency reuse distance theoratically.

– Determining the cell repeat pattern

– Planning the frequency groups.

– Inputting the planned frequency into the planning tool.

– Generating the C/I and C/A plots and checking out the results.

– Rectifying the fault areas.

FREQUENCY PLANNING STEPSFREQUENCY PLANNING STEPSDetermining the cell repeat patternDetermining the cell repeat pattern

• Frequencies have to be reused at different cells throughout the network to maximise capacity.

• The distance cells using the same set of frequencies is called the frequency reuse distance.

• This reuse distance depends on the number of frequency reuse groups N.

• Once N has been determined every Nth cell will be assigned the same frequencies.

• Also a minimum received signal level has to be provided throughout the coverage area of the network.

• The cell repeat pattern is dependent on the frequency spectrum available, the traffic required and most important on the way the network is planned.

• Generally 7/21 or 7 site repeat pattern and 4 site repeat patterns are used.

FREQUENCY PLANNING STEPSFREQUENCY PLANNING STEPSCell reuse patternCell reuse pattern

• The distribution of the C/I ratio desired in a system determines the number of frequency groups, F, which may be used.

• If we have N carrier frequencies then

No of carriers / group = N/F

• Since the number of frequency groups are fixed, a smaller number of frequency groups(F) results in more carriers per set and per cell.

• Hence a reduction in the number of frequency groups would allow each site to carry more traffic.

• However decreasing the number of frequency groups and reducing the frequency reuse distance results in lower average C/I distribution in the system.

• Generally 7/21 and 4/12 reuse patterns are used.

FREQUENCY PLANNING STEPSFREQUENCY PLANNING STEPS7/21 Cell reuse pattern7/21 Cell reuse pattern

• Say we have 42 frequencies and we require 2 carriers per site then we can use 7 site repeat pattern.

• Hence a cluster will be formed of 7 sites.

• The frequencies for manual frequency planning for a cluster size of 7 are arranged a s shown below

A1 B1 C1 D1 E1 F1 G1 A2 B2 C2 D2 E2 F2 G2 A3 B3 C3 D3 E3 F3 G3Carrier1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21Carrier2 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


B1

B2B3

C1

C2C3

A1

A2A3

G3 G2

G1

F1

F2F3

D3 D2

D1

E1

E2E3

B1

B2B3

C1

C2C3

A1

A2A3

G3 G2

G1

F1

F2F3

D3 D2

D1

E1

E2E3


• Say we have 48 frequencies and we require 4 carriers per site then we can use 4 site repeat pattern.

• Hence a cluster will be formed of 4 sites.

• The frequencies for manual frequency planning for a cluster size of 4 are arranged a s shown below

A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3Carrier1 1 2 3 4 5 6 7 8 9 10 11 12Carrier2 13 14 15 16 17 18 19 20 21 22 23 24Carrier3 25 26 27 28 29 30 31 32 33 34 35 36Carrier4 37 38 39 40 41 42 43 44 45 46 47 48


D1 D2

D3

B1

B2B3

C1

C2C3

A1

A2A3

D1 D2

D3

B1

B2B3

C1

C2C3

B1

B2B3

D1 D2

D3

B1

B2B3

C1

C2C3

A1

A2A3

A1

A2A3

B1

B2B3

C1

C2C3

INTERFERENCE PREDICTIONINTERFERENCE PREDICTION

• Once the repeat pattern is determined the frequencies should be entered in the planning tool.

• Enter the C/I threshold and C/A threshold. For GSM put 12dB(GSM specifies > 9dB) as C/I and 0dB( GSM specifies C/A > -9dB) as C/A.

• Generate a C/I and C/A plot.

• Analyse the plot and check for problems.

• Debug and solve the interference problems.

• Note that to get a correct C/I and C/A plot, all the sites prediction on the tool should be completed.

• Morever the models should be correctly tuned and the coverage predicted by the propagation model should match the coverage on the field.

AUTOMATIC FREQUENCY PLANAUTOMATIC FREQUENCY PLAN

• Planning tools nowadays have automatic frequency planning options.

• This tool uses predictions. Hence the models have to be accurately tuned.

• Morever Co-cell and co-site separations, allowed frequency bands, target levels for allowed co-channel and adjacent channel interference need to be defined.

FREQUENCY CO-ORDINATIONFREQUENCY CO-ORDINATION

• On international borders frequencies are commonly co-ordinated with neighboring countries to avoid mutual interference.

• Generally sets of reserved or preferential frequencies are negotiated between the national authorities of the respective countries.

SITE SELECTIONSITE SELECTION

INTRODUCTIONINTRODUCTION

Site LocationSite Location

• Proper site location determines usefulness of its cells.

• Site are expensive and have to be chosen carefully.

• The planner needs to visit each and every site.

Good Site SelectionGood Site Selection• We need to understand various factors we must take into account to

ensure that the selected site is good. • Simple way is to ask yourself three questions

1) Why am I putting this site ?2) Will this selected site serve that purpose ?3) Are there any possible problems that might arise if i select this site. If yes can I solve or avoid those problems ?

BAD SITE SELECTIONBAD SITE SELECTION

Desired cell boundary

Uncontrolled interference

Interleaved coverage areaweak own signal, strong foreign signal

• Hilltop locations for a BTS site should be avoided as they cause

• Uncontrolled interference

• Interleaved coverage

• Awkward HO behaviours

• But are good for microwave links

GOOD SITE SELECTIONGOOD SITE SELECTION

• Sites off hilltop locations are preferable for a BTS site as

– hills can be used to separate cells

– interference can be easily controlled

– minimum overlapping will result

– can face problems for microwave linksDesired cell boundary

SITE SELECTION CRITERIASITE SELECTION CRITERIARadio criteria for site selectionRadio criteria for site selection

• Good view in the main beam direction

• No surrounding nearby high obstacle

• Good visibilty of terrain

• Room for antenna mounting

• LOS to the two microwave site and if possible to the BSC

• Short cabling distance

Non-radio criteriaNon-radio criteria

• Space for equipment

• Availaibilty of lease lines or microwave links

• Power supply

• Access restrictions

• Rental costs

• Ease of acquisition

REPEATERSREPEATERS

REPEATERSREPEATERS

• Repeater units are designed to receive signals from a donor site, amplify and rebroadcast the donor sites signals into poor coverage areas or to extend the coverage range of the donor site.

• These repeater are bi-directional and do not translate frequency and subsequently are limited in output power and gain.

• Repeaters provide between 50 to 80 dB of gain.

Donor Cell

INTRODUCTION Donor side antenna Mobile side antenna

Poor Coverage area

Repeater receives Donor signal at

~ -90dBm

Repeater amplifiesthe signal and

rebroadcasts thesignal

REPEATERSREPEATERSINTRODUCTION

• There are two types of repeater band selective and channel selective.

• Band selective repeater amplifies a band of frequency. Hence it amplifies any frequency that falls within its band.

• Channel selective repeater allows selection of a number of individual channels to amplify and rebroadcast.

• Typically a channel selective repeater allows selection of 2 to 4 channels.

• If the GSM900 or DCS1800 network incorporates frequency hopping, then only band selective repeaters should be used.

REPEATERSREPEATERSANTENNA ISOLATION

• Since repeaters are non-frequency translating, the isolation between the donor-side and mobile-side antenna needs to be much greater than the gain of the repeater.

• If antenna isolation is less than or equal to the repeater gain, the repeater will begin to amplify its own feedback and oscillate.This condition must be avoided.

• The isolation between the antenna needs to be at least 10 dB greater than the gain of the repeater.

– Iso = Grep + 10dB

• Following equation can be used to calculate antenna isolation

– Vertical separation Iso = 28 + 40log( d / λ )

– Horizontal separation Iso = 22 + 20log( d / λ ) - (GA + GB)

– where d = Separation distance(feet)

λ = Wavelength

– GA = Gain of donor-side antenna in direction of Mobile side antenna.

– GB = Gain of mobile-side antenna in direction of donor- side antenna.


• Separation type is based on site type. If the site is a roof, then horizontal separation should be used while if the site is on a tower vertical separation should be used.

• If directional antennas are used then the required horizontal spacing is given by

– Iso = 22 + 20log( d / λ ) - (Gamax - Gaback) - (Gbmax - Gbback )

– and


– If gain of the directional antenna is 17dBi and front-to-back >25dB and the repeater( gain of 80dB) is used on GSM900 then

– 80 + 10 = 22 + 20log(d/1) - (17-25) - (17-25)– 90 = 22 +20log(d) + 8 + 8– 22+20log(d) = 74– 20log(d) = 52– log(d) = 2.6– d = 398 feet


• Hence a horizontal separation of 398 feet is required to provide a isolation of 90dB between the donor-side and the mobile-side antenna which is quite unreasonable.

• Large antenna separation produce large cable losses and reduce repeater output power.

• Some obstruction should be in between both the antennas to reduce this separation.

• If vertical spacing is given by

– Iso = 28 + 40log( d / λ )

– and


– if the repeater is used on GSM900 then– 80 + 10 = 28 + 40log(d/1)– 90 = 28 + 40log(d)– 40log(d) = 62– d = 35.48 feet

ENDEND

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7617 RF Planning