10 RF Planning

Introduction to RF Planning

A good plan should address the following Issues :

Provision of required Capacity.Optimum usage of available frequency spectrum.Minimum number of sites.Provision for easy and smooth expansion of the Network in future.Provision of adequate coverage.

Introduction to RF PlanningIn general a planning process starts with the inputs from the customer. The customer inputs include customer requirements, business plans, system characteristics, and any other constraints.

After the planned system is implemented, the assumptions made during the planning process need to be validated and corrected wherever necessary through an optimization process.

We can summarize the whole planning process under the 4 broad headings

Capacity planningCoverage planningParameter planningOptimization

CELLULAR ENGINERING OBJECTIVES

1) To provide adequate coverage

Contiguous coverage of the required areas without appreciable holes

Adequate depth of coverage (i.e. outdoor or indoor , 2 W or 1.2 W mobiles ) to meet the companys marketing plans.

2) To provide adequate network capacity

Accommodating traffic in the busiest hour with only a low probability of blocking (congestion).

3) To accommodate network growth

Extension of coverage in new areas

Expanding the network capacity so that the quality of service is maintained at all times.

4) To achieve a cost effective design

Lowest possible cost over the life of the network while meeting the quality targets.

COST JUSTIFICATION OF CELLULAR RNP

The cellular mobile radio system design can be broken down in the following elements, which have a mutual relationship.

Reuse of frequency channels

Co- channel interference reduction

A desired minimum carrier to interference ratio (C/I)

Handover mechanism

Cell Planning

Historical perspective

Wireless telephony network design is relatively new business with a 10-15 year history

During this period many new tools and techniques have been developed:

More accurate radio coverage prediction

More accurate facility network design

Enhanced field measurement analysis to improve network performance.

New technology applications ( microcells, repeaters, smart antennas systems. )

Better tools and methods to evaluate and predict traffic conditions


The challenge of accurate cellular network planning is still a complex task.

Potential cost of Opportunities Lost Due to Network Planning problems

Lost Subscribers

Lost base subscriber fee revenues

Lost enhanced service fee revenue

Lost airtime revenues (local and long distance)

Damaged reputation will impact competitive strength

Cost Considerations That Include in the Design of a quality network

Design optimal network : extensive modeling and numerous revision of design.

Acquire radio site candidates that meet the design criterion.

Manage delays in permitting / zoning of best candidates

Extensive testing of radio site performance (coverage ) before commissioning.

Integration of field measurements in design.


Design Activity to compensate for Improperly designed or less than than optimal radio site in design.

Modify cell operational parameters (eg. Handover values and location)

Modify output power

Modify equipment (eg. Change antenna )

Move site location

Add new sites (micro or macro cells)


An equation for Costing Comparison of Accurate Network Planning

Option one : Poor design / no redesign

Weak competitive position

Lost disgruntled subscribers

Earn a poor service reputation (Weak attraction for new subscribers ).

Option two : Quality network design

Additional design cost (engineering and equipment ).

Teardown and reinstall cost.

Simple equation for characterizing cost /benefits

Quality network performances = ( Cost of engineering , equipment, installation ) (Lost revenues, cost of engineering, equipment, installation )

The benefits of quality design should farweigh lost revenues particularly in the fact of competition from new wireless companies.

DESIGN CONSTRAINTS

The objective of radio planning is a technical realization of the marketing requirements, taking into account of the following constraints.

Technical requirements from the license conditions.

GSM system specific parameters (e.g. GSM recs 5.05 etc.)

Manufacturer specific features and parameters.

Radio communications principles and fundamentals.

Budgetary factors.

LICENSE CONDITIONS

An example of technical requirements following from a license.

Coverage requirements.

Class 2 or class 4 coverage of 60 % of the population 12 months from commercial launch.

Class 2 or class 4 coverage of 95 % of the population 36 months from the commercial launch.

Quality of coverage

Service to be available in 90 % of the declared area and for 90 % of the time.

Grade of Service

Endeavour to achieve 5 % or better

Frequency Allocation

One of the major limitations in the GSM 900 system is the number of frequencies available to a GSM network operator. There is a relatively small bandwidth available that has to be divided over all the licensed operators. Most network operators are limited to 30-60 frequencies for handeling all traffic.

GSM 1800 offers 75 MHz bandwidth

MANUFACTURER SPECIFIC PARAMETERS

BTS Transmit power

Receiver sensitivity

Combiner performances

Cable loss

Antenna performance

Availability of frequency hopping and power control

Handover algorithm

Capacity number of TRX provided.

RADIO COMMUNICATION FUNDAMENTALS

Propagation loss

Shadowing

Multipath fading

Power link budgets

Interference effects

The (un)predictability of radio wave propagation

QUALITY OF SERVICE SPECIFICATIONS

The service requirement from the marketing should include information on which the technical plan can be based , including :

Coverage Quality : Defined as a part of optimizing the business plan (indoor / outdoor coverae, handheld car, mobile set). Interference should be taken into account for coverage quality including margin of 12 dB) :

Co channel C/I

Adjacent channel C/I

Call completion and Dropped call Rates : Dictated by the lisence conditions and quality of the competing network(includes Blocking rates 2% etc.)

Service availibility

QUALITY OF SERVICE SPECIFICATIONS

Traffic forecast:

Longterm forecast and trends for the network must be developed by the marketing.

Traffic distributions for the existing coverage areas and typical densities may be obtained from the network.

Spectral effeciencies : for demonstration within the context of winning maximum points for a mobile license. The spectral efficiency is determined by decisions taken in :

Quality of coverage

Frequency Reuse plan

Use of cell splitting

Design for traffic demend

Feedback into the business plan

Customer support measures

DEFINITION OF COVERAGE QUALITY

Outdoor coverage:

Default definitions of coverage

Refers to 2 Watt class 4 mobiles in the street

Probability of coverage is 95 % averaged across the cell area.

Coverage probability at the edge of cells is less than this value.

In car coverage :

A supplementary level of coverage for highways

Refers to a Class 4 mobile inside car or other vehicles.

Coverage probability is nominally 95% averaged

Coverage is critically dependent on the position of the handheld mobile within the vehicle.

8 Watt Coverage

A Supplementary level of coverage for remote areas.

Refers to class 2 mobile or class 4 with an 8 watt booster and external antenna

DEFINITION OF COVERAGE QUALITY

Indoor coverage

Especially good coverage for city centers and stragetic locations

Refers to a class 2 mobile indoors

Building loss is very variables, so indoor coverages can never be guaranteed

Where indoor coverage is provided , outdoor coverage will be nearly 100 %

BLOCKING RATE ( Grade of Service, GOS )

GOS is defined as the probability that a call will be blocked or delayed due to unavailability of the radio resource. Example for license requirement

5 % Averaged over a defined sub-network (e.g. weighted average by traffic load over the worse 10 cells )

No cell to be worse than 10%

By a particular date , 8 % of the cells permitted to be between 2 % and 10 % GOS.

By a particular date , 5 % of the cells permitted to be between 2 % and 10 % GOS.

Ultimate target is that no cells should be worse than 2 % GOS.

CALL SUCCESS RATE

Call failure may be due to :

Coverage holes

Interference

Congestion

Problem in fixed network

Handover failures

Equipment failures

Call success rate is often expressed as the proportion of calls connected and held for 2 min.

Target is normally 90 % at launch of service

Mature networks achieve in excess of 98 %

Only applies within a declared coverage area.

By a particular date , 95 % of the calls to the network boundary should be set up within four seconds and held for two min.

RADIO PLANNING METHODOLOGY

Overall picture

It is important to create an overall picture of the network before going into the detailed network planning. This is the fact the main objective of this presentation.

Coverage Capacity and Quality

Providing coverage is usually considered as the most important activity of a new cellular operator. For a while , every network is indeed coverage driven. However the coverage is not the only thing. It provides the means of service and should meet certain quality measures.

The starting point is a set of coverage quality requirements.

To guarantee a good quality in both uplink and downlink direction, the power levels of BTS and MS should be balanced at the edge of the cell. Main output results of the power link budget are:

Maximum path loss that can be tolerated between MS and the BTS.

Maximum output power level of the BTS transmitter.

Introduction to RF PlanningA simple Planning Process Description

Business plan.No of Subs.Traffic per Subs.Subs distributionGrade of service.Available spectrum.Frequency Reuse.

Types of coverageRF ParametersField strength studiesAvailable sitesSite surveyCapacityStudiesPlan verificationQuality checkUpdate documentsCoverage&C/I studySearch areasImplementPlanMonitor NetworkOptimizeNetworkCustomerAcquiressitesCapacity StudiesCoverage plan & Interference studiesFrequency plans and interference StudiesAntenna SystemsBSS parameter planningData base & documentation of approved sitesExpansion Plans.

Introduction to RF PlanningData Acquisition

OMC Statistics

A Interface

Drive TestImplemented PlanningDataData EvaluationImplementedRecommendationRecommendations :Change frequency planChange antenna orientation/Down tiltChange BSS ParametersDimension BSS EquipmentAdd new cells for coverageInterference reductionBlocking reductionAugment E1 links from MSC to PSTN

Cell Planning Aspects

At the end of it all, a good cell plan should have the following characteristics :

Coverage as required as predicted.

Co Channel and Adjacent Channel interference levels as predicted.

Minimum antenna adjustments during the optimization process.

Minimum changes to the BSS parameters/database during the optimization phase.

Should be well phased, requiring optimization only for short periods in the initial commissioning phase and during

Facilitate easy expansion of the network with minimal changes in the system.

The Basic Cell Planning Process

The basic approach to cell planning is to provide good coverage and capacity. Initially, both are not known !!

Hence the planning is based on the projections given by the customer. The customer based on market surveys and the company plans, may specify :

Number of sites he want in the city

OR

Number of subscribers expected in a city.

Base on the inputs from the customer, the initial planning process begins. From these we can determine either the capacity that is possible for a given number of sites OR minimum number of sites needed to provide service to a given number of subscribers. The site density required for a specific capacity should also pass the coverage criteria. This aspect will be covered later in the course.


What is the area of coverage needed ?

How many sites are required for this area ? ( cell radius of 1 Km. Means an approximate coverage area of 3 sq. Kms. )

Do we need so many sites ? Can some site be bigger ? Decide number of sites based on capacity and coverage requirements.

Divide city into clutter types such as .

>Urban

>Suburban

>Quasi Open

>Open

>Water.

Identify search areas covering all clutter types.

Customer selects a few sample sites.


Survey sites with reference to :

>Clutter heights

>Vegetation levels.

>Obstructions.

>Sector orientations

>Building strengths and other civil requirements

Prepare Power Budgets.

Conduct propagation tests

Calculate Coverage probabilities based on the drive test results.

Verify Power budget sensitivityagainst drive test result , modify planning tools parameters.

Prepare final coverage maps.

.

A typical Power Budget

RF Link BudgetULDLTransmitting EndMSBTS

Tx Rf power output33 dBm43 dBmBody Loss-3 dB0 dBCombiner Loss0 dB0 DbFeeder Loss(@2 Db/100 M)0 dB- 1.5 dBConnector loss0 dB- 2 DbTx antenna gain0 dB17.5 dBEIRP30 dBm 57 dBm

A typical Power Budget

RF Link BudgetULDLReceiving EndMSBTSRx sensitivity-107 dBm -102 dBmRx antenna gain17.5 dBm 0 dBDiversity gain3 Db0 dBConnector Loss- 2 dB0 dBFeeder loss- 1.5 dB0 dBInterference degradation margin3 dB3 DbBody loss0 dB-3 dBDuplexer loss0 dB 0 dBRx Power-121 dBm-96 dBmFade margin4 dB4 dBReqd Isotropic Rx. Power-117 dBm-92 dBmMaximum Permis. Path los147 Db149 dB

Summary

A good RF Planning ensures that the mobiles receive certain minimum signal strength for specified percentage of time over a specified area of coverage.

The MS receive signal strength depends on the path loss depends on the path loss between the MS and the BTS.

The path loss in a mobile environment includes :

> Free space path loss

>Additional Loss due to Topography of the site ( clutter Factor )

>Confidence level required. (Probability of area coverage )

In general RF Planning means the understanding of :

> Propagation Models

> Coverage aspects

> Link Budgets ( Power Budgets)

> Antenna considerations

> Frequency planning and reuse aspects.

Urban Propagation Environment

This is the most common and yet unpredictable propagation environment for a mobile system.

Building Penetration:

Building are responsible for the reflection and shadowing of signals. Trees and foliages also contribute to shadowing as well as scattering of radio signals.

Attenuation of signals by building is measured by taking the difference between the median signal level in front of the building and inside the bu9ilding. Obviously, the building attenuation depends on the type of construction and the material used as well as how big or small it is.

Typically the attenuation values may cause the signal levels to vary by 40 to +80 Db The negative value implies that the signal is attenuated and the positive values implies that the increase in the signal level.

Windows and Doors in general give a good penetration of RF signals. Another important factor is the angle of arrival of RF signals in to the building. Generally, a building facing the BTS site has better penetration than the one that is side facing and without windows.

The furniture used in the building also contributes to attenuation. Typically a furnished building gives a loss of 2-3 dB more than an empty one.

Propagation EnvironmentSome Typical values for Building Attenuation

Type of buildingAttenuation in dBsFarms, Wooden houses, Sport halls0-3Small offices,Parking lots,Independent houses,Small apartment blocks4-7Row Houses, offices in containers, Offices, Apartment blocks8-11Offices with large areas12-15Medium factories, workshops without roof tops windows16-19Halls of metal, without windows20-23Shopping malls, ware houses, buildings with metals/glass24-27

Propagation ModelsClassical Propagation models :-

Log Distance propagation modelLongley Rice Model (Irregular terrain model )OkumaraHataCost 231 Hata (Similar to Hata, for 1500-2000 MHz bandWalfisch Ikegami Cost 231Walfisch-Xia JTCXLOS (Motorola proprietary Model )BullingtonDu path Loss ModelDiffracting screens model

Propagation ModelsImportant Propagation models :-

Okumara Hata model (urban / suburban areas )( GSM 900 band )Cost 231 Hata model (GSM 1800 band )Walfisch Ikegami Model (Dense Urban / Microcell areas )XLOS (Motorola proprietary Model )

Okumara Hata ModelsIn the early 1960 , a Japanese scientist by name Okumara conducted extensive propagation tests for mobile systems at different frequencies. The test were conducted at 200, 453, 922, 1310, 1430 and 1920 Mhz.The test were also conducted for different BTS and mobile antenna heights, at each frequency, over varying distances between the BTS and the mobile.The Okumara tests were valid for :

150-2000 Mhz.1-100 Kms.BTS heights of 30-200 m.MS antenna height, typically 1.5 m. (1-10 m.)The results of Okumara tests were graphically represented and were not easy for computer based analysis.Hata took Okumaras data and derived a set of empirical equations to calculate the path loss in various environments. He also suggested correction factors to be used in Quasi open and suburban areas.

Hata Urban Propagation ModelThe general path loss equation is given as :-Lp = Q1+Q2Log(f) 13.82 Log(Hbts) - a(Hm)+{44.9-6.55 Log(Hbts)}Log(d)+Q0Lp = L0 +10r Log (d) path loss in dBF = frequency in Mhz.D = distance between BTS and the mobile (1-20 Kms.)Hbts = Base station height in metres ( 30 to 100 m )A(hm)={ 1.1log(f) - 0.7 } hm - {1.56log(f) - 0.8} for Urban areas and = 3.2{log(11.75 hm)2 - 4.97 for dense urban areas.Hm= mobile antenna height (1-10 m)Q1 = 69.55 for frequencies from 150 to 1000 MHz. = 46.3 for frequencies from 1500 to 2000 MHz.

Q2 = 26.16 for frequencies from 150 to 1000 MHz. = 33.9 for frequencies from 1500 to 2000 MHz.

Q0 = 0 dB for Urban = 3 dB for Dense Urban

Path Loss & Attenuation SlopeThe path loss equation can be rewritten as :Lp = L0 + { 44.9 6.55 + 26.16 log (f) 13.83 log (hBTS)-a(Hm)Where L0 is = [69.55 + 26.16 log (f) 13.82 log ( HBTS ) A (Hm)Or more convenientlyLp = L0 + 10 log(d)

is the SLOPE and is = {44.9 6.55 log(hBTS)}/10Variation of base station height can be plotted as shown in the diagram.We can say that Lp 10 log(d) typically varies from 3.5 to 4 for urban environment.When the environment is different, then we have to choose models fitting the environment and calculate the path loss slope. This will be discussed subsequently.

Non line of Sight PropagationHere we assume that the BTS antenna is above roof level for any building within the cell and that there is no line of sight between the BTS and the mobileWe define the following parameters with reference to the diagram shown in the next slide:W the distance between street mobile and buildingHm mobile antenna heighthB BTS antenna heightHr height of roof hB difference between BTS height and roof top. Hm difference between mobile height and the roof top.

Non line of Sight PropagationThe total path loss is given by:Lp = LFS+LRFT+LMDBLFS= Free space loss = 32.44+20 log(f) + 20 log(d)Where,LFS = Free space loss.LRFT = Rooptop diffraction loss.LMDB = Multiple diffraction due to surrounding buildings.LRFT = -16.9 10 log(w) +10log(f) +20log(^Hm)+L(0)Where hm=hr-hmL( ) = Losses due to elevation angle.L( ) = -10 + 0.357 ( -00) for 0<

Non line of Sight PropagationThe losses due to multiple diffraction and scattering components due to building are given by :

LMBD = k0 + ka +kd.log(d) +kf.log(f) 9.log(w)WhereK0 = - 18 log (1+ hB)Ka = 54 0.8 ( hB)Kd = 18 15 ( hB/hr)Kf = - 4 +0.7 {f/925) 1 } for suburban areasKf = - 4 +1.5 {f/925) 1 } for urban areasW= street width hB= hB hrFor simplified calculation we can assume ka = 54 and kd = 18

Choice of Propagation Model

Environment Type ModelDense UrbanStreet Canyon propagationWalfish Ikegami,LOSNon LOS Conditions, Micro cellsCOST231Macro cells,antenna above rooftop Okumara-HataUrbanUrban AreasWalch-ikegamiMix of Buildings of varying heights, vegetation, and open areas.Okumara-HataSub urbanBusiness and residential,open areas.Okumara HataRuralLarge open areas,fields,difficult terrain with obstacles.Okumara-Hata

Calculation of Mobile Sensitivity.The Noise level at the Receiver side as follows:

NR= KTBWhere,K is the Boltzmanns constant = 1.38x10-20 (mW/Hz/0Kelvin)T is the receiver noise temperature in 0KelvinB is the receiver bandwidth in Hz.

Signal VariationsFade margin becomes necessary to account for the unpredictable changes in RF signal levels at the receiver. The mobile receive signal contains 2 components :A fast fading signal (short term fading )A slow fading signal (long term fading )

Probability Density FunctionThe study of radio signals involve actual measurement of signal levels at various points and applying statistical methods to the available data.A typical multipath signal is obtained by plotting the RSS for a number of samples.We divide the vertical scale in to 1 dB bin and count number of samples is plotted against RF level . This is how the probability density function for the receive signal is obtained.However, instead of such elaborate plotting we can use a statistical expression for the PDF of the RF signal given by :P(y) = [1/2 ] e [ - ( - y m )2 / 2 ( )2

Where y is the random variable (the measured RSS in this case ), m is the mean value of the samples considered and y is the STANDARD DEVIATION of the measured signal with reference to the mean .The PDF obtained from the above is called a NORMAL curve or a Gaussian Distribution. It is always symmetrical with reference to the mean level.

Probability Density FunctionPlotting the PDF :

A PLOT OF RSS FOR A NUMBER OF SAMPLES

Probability Density FunctionPlotting the PDF :

NORMAL DISTRIBUTIONP(x) = ni/NNi = number of RSS within 1 dB bin for a given level.

Probability Density FunctionA PDF of random variable is given by :P(y) = [ ] e [ - (y-m)2 / 2( )2 ]Where, y is the variable, m is the mean value and is the Standard Deviation of the variable with reference to its mean value.The normal distribution (also called the Gaussian Distribution ) is symmetrical about the mean value. A typical Gaussian PDF :

Probability Density FunctionThe normal Distribution depends on the value of Standard DeviationWe get a different curve for each value of The total area under the curve is UNITY

Calculation of Standard DeviationIf the mean of n samples is m, then the standard deviation is given by:

= Square root of [{(x1-m)2 + ..+( xn-m)2 }/(n-1)]

Where n is the number of samples and m is the mean.For our application we can re write the above equation as :

= Square root of [{RSS1-RSSMEAN)2+..+(RSSN-RSSMEAN)2/(N-1)}]

Confidence IntervalsThe normal of the Gaussian distribution helps us to estimate the accuracy with which we can say that a measured value of the random variable would be within certain specified limits.The total area under the Normal curve is treated as unity. Then for any value of the measured value of the variable, its probability can be expressed as a percentage.In general, if m is mean value of the random variable within normal distribution and is the Standard Deviation, then,The probability of occurrence of the sample within m and any value of x of the variable is given by :P=

By setting (x-m)/ = z, we get,

P=

Confidence IntervalsThe value of P is known as the Probability integral or the ERROR FUNCTIONThe limits (m n )are called the confidence intervals.From the formula given above, the probability

P[(m- ) < z < (m+ )] = 68.26 % ; this means we are 68.34 % confident.P[(m- ) < z < (m+ )] = 95.44 % ; this means we are 95.44 % confidentP[(m- ) < z < (m+ )] = 99.72 % ; this means we are 99.72 % confident.

This is basically the area under the Normal Curve.

The Concept of Normalized Standard DeviationThe probability that a particular sample lies within specified limits is given by the equation :

P=

We define z = (x-m)/ as the Normalized Standard Deviation.

The probability P could be obtained from Standard Tables (available in standard books on statistics ).

A sample portion of the statistical table is presented in the next slide..

Calculation of Fade MarginTo calculate the fade margin we need to know :

Propagation constant() >From formulae for the Model chosen>Or from the drive test plotsArea probability : >A design objective usually 90 %Standard Deviation() >Calculated from the drive test results using statistical formulae or>Assumed for different environments.To use Jakes curves and tables.

Calculation of Edge Probability and Fade MarginFrom the values of and we calculate := /

Find edge probability from Jakes curves for a desired coverage probability, against the value of on the x axis.

Use Jakes table to find out the correlation factor required Look for the column that has value closest to the edge probability and read the correlation factor across the corresponding row.

Multiply by the correction factor to get the Fade Margin.

Add Fade Margin to the RSS calculated from the power budget

Significance Of Area and Edge Probabilities

Required RSS is 85 dBm.

Suppose the desired coverage probability is 90 % and the edge probability from the Jakes curves is 0,75

This means that the mobile would receive a signal that is better than 85 dBm in 90 % of the area of the cell

At the edges of the cell, 75 % of the calls made would have this minimum signal strength (RSS).

In Building CoverageRecalculate Fade Margin.>Involves separate propagation tests in buildings.>Calculate and for the desired coverage ( say 75 % or 50% )>Use Jakes Curves and tables to calculate Fade Margin.>Often adequate data is not available for calculating the fade margin accurately.>Instead use typical values.Typical values for building penetration loss :

Area75 % coverage50 % coverageCentral business area< 20 dB< 15 dBResidential area< 15 dB< 12 dBIndustrial area< 12 dB< 10 dBIn Car6 to 8 dB

Fuzzy Maths and Fuzzy LogicThe models that we studied so far are purely empirical.The formulas we used do not all take care of all the possible environments.Fuzzy logic could be useful for experienced planners in making right guesses.We divide the environment into 5 categories viz., Free space, Rural, Suburban, urban, and dense urban.We divide assign specific attenuation constant values to each categories , say Fuzzy logic helps us to guess the right value for , the attenuation constant for an environment which is neither rural nor suburban nor urban but a mixture, with a strong resemblance to one of the major categories.The following simple rules can be used :Mixture of Free space and Rural :Mixture of Rural and Suburban :Mixture of Suburban and Urban :Mixture of Urban and Dense urban :

Cell Planning and C/I IssuesThe 2 major sources of interference are:Co Channel Interference.Adjacent Channel Interference.The levels of these Interference are dependent on The cell radius The distance cells (D)The minimum reuse distance (D) is given by : D = ( 3N ) RWhere N= Reuse pattern = i2 + i j + j2 Where I & j are integers.

Cell Planning and C/I IssuesRD

Cell Planning and C/I Issues

Assuming the cells are of the same size .

All cells reansmit the same power.

The path loss is not free space and is governed by the attenuation constant .

By geometry, for every cell there are 6 interfering cells in the first layer.

The reuse distance Dand cell radius R are related to the c/I as given below

(D/R) = 6 (C/I)

The C/I is in absolute value.


Co Channel Interference C/I for Omni Cells

D/R = 3N

C/I = 10 Log [ 1/m (D/R ) ], where m is the number of interferers.

M= 1 to 6 for the first layer of interfering cells.

Assuming = 3.5, m = 6 (worst case ), we calculate the theoretical C/I available for various reuse plans as shown below :

N

D/R = 3N

C/I = 10 Log [ 1/6 (D/R) ]

3

3

8.917 dB

4

3.46

13.29 dB

7

4.58

21.80 dB

9

5.19

25.62 dB

12

6

29.99 dB


Adjacent Channel Interference :

Adjacent Chl Interference = - 10 Log [1/m (D/R) ]+

Where is the isolation offered by post modulation filters

Minimum value of is 26 dB , as per EIA standards.

If ( C/I ) for co channel interference is 10 dB, then for adjacent channel interference it is 36 dB.

Frequency Planning Aspects

The primary objective of frequency planning is to ensure that, given the limited RF spectrum, we achieve the required capacity (traffic channels), keeping the interference within specified limits.

There are two types of frequency planning :

>Frequency planning based on Reuse patterns (manual)

>Frequency planning based on heuristic algorithm (automatic)

Manual planning is done by dividing the available frequencies in to a number of frequency groups (as per a selected reuse pattern ) and assigning frequencies to various sectors / cells.

Suppose we have n frequencies . For a 3 cell repeat pattern with 3 sectors, we have 9 frequency groups, each group having n/9 frequencies.

The sectors are labeled A1,A2,A3,B1,B2,B3 and so on..

Assuming that an operator has 32 frequencies, say, from ARFCN 63 to 94, the frequencies could be grouped as shown in the table opposite.


Say, for 32 frequencies (ARFCN 63 94 ), for a 3*3 reuse pattern, the frequencies are grouped as shown below

A1

A2

A3

B1

B2

B3

C1

C2

C3

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

OR

A1

B1

C1

A2

B2

C2

A3

B3

C3

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94


The Frequency reuse could be done in either of 2 ways mentioned in the tables in the previous slide :


Directional reuse :

In a sectorised site, a group of channels (ARFCN) is transmitted in the direction of antenna orientation , This is based on tri cellular platform consisting of 3 identical cells as shown in the diagram in the last slide.

Every cell is considered as an omni logically. The cells are excited from the corners, separated by 1200

The axes of the diagram represent the 3 directions of reuse. These are designated as { f(00)}, {f(1200)} and {f(2400)}

Because we use directional antennas, the worst co channel interference will be from only one interfering station in the same direction


We form a generic combination of the tricell pattern using 7 such pattern, as shown in fig. Down. From this we can see that each of three axes has three parallel layers.

This result in a total of six or multiples of six frequency GROUPS.

While assigning frequencies to individual calls we have to take the directions of reuse into account.

Antenna Considerations

Uniform coverage in all cells

Alignment with hexagonal pattern

Space availability

Connectivity to BSC/MSC

Urban areas may have the following conditions :

Several sites may be needed.

Frequency reuse is unavoidable

In building penetration is must

Building act as RF shield and contain coverage.

Buildings reflect signals and provide coverage to areas where LOS would have failed.

Such additional paths improve in building penetration.

Antenna at a very high point may not meet in building coverage requirements

Tackling Multipath Fading

In general we have the following methods to combat Multipath fading:

In time domain

Interleaving and coding

In Freq. Domain

Frequency hopping

In spatial domain

Space diversity

In the polarization domain Polarization diversity

The last two are related to Antenna Systems.

Diversity Antenna Systems

A diversity antenna System essentially has :

Two or more antenna

A combiner circuitry.

Signals A and B should have minimum correlation between them typically the correlation coefficient


Antenna Spacings :

Separation

D/

900 Mhz

1800Mhz

Horizontal

10

3.3 m

1.7 m

Vertical

17

5.7 m

2.8 m

>Figures in the table are of minimum required separation

>If space is not a constraint, larger separation is always recommended.

>Horizontal separation is preferred because it provides low correlation values.

>However, horizontal separation suffers from angular dependence (demonstrated in the diagram, next page ).

>Vertical separation does not suffer much from the angular dependence.

>It also requires minimum supporting fixtures and does not occupy a lot of space.

>But as the distance increases the correlation between the RF signal at the antenna points increases rapidly, thereby negating the very advantage of space diversity.


Space diversity can be achieved using:

3 antenna system

2 antenna system

The 3 antenna system provides very good spatial separation between the two receive antenna and avoids the use of duplexers. This reduces the risk of generating intermodulation products.

The 2 antenna system is preferred where the space for the antenna structure is limited or where the operators want to use less number o antenna.


Advantages of dual polarization :

Reduced support structure for the antenna

Reduced weight

Slim towers and hence quicker construction and low cost.

Cost of one dual polarized antenna is generally lower than the cost of two space diversity antenna.

Choice of Dual Polarized type

H/V type :

As most mobile are held at an angle 450, H/V is more likely to cause balanced signals at the two branches.

The diversity performance is less dependent on the mobile location

Slant type

Correlation between the two elements is angular dependent.

Unbalanced signals at the two arms of the receive antenna, since one of the signal could be at the same angle as the mobile

General Antenna Specifications

Typical parameters of importance :

Polarization

Linear polarization :Evector contained in one plain

Horizontal polarization :H Vector parallel to the horizontal plane

Vertical Polarization : E Vector parallel to the vertical plane

Circular / Elleptical Polarization

The extremity of the E or H field describes a circle or an ellipse in the direction of propagation

Radiation pattern

This is a plot of electric field intensity as a function of direction from the antenna, measured at the fixed distance.

General Antenna Specifications

When the main radiation lobe of the antenna is intentionally adjusted above or below its plane of propagation, the result is known as a beam tilt. When tilted downward, we get the Downtilt.

Down tilt can be done in two ways :

Electrical down tilt

Mechanical down tilt


Overall picture

It is important to create an overall picture of the network before going into the detailed network planning. This is the fact the main objective of this presentation.

Coverage Capacity and Quality

Providing coverage is usually considered as the most important activity of a new cellular operator. For a while , every network is indeed coverage driven. However the coverage is not the only thing. It provides the means of service and should meet certain quality measures.

The starting point is a set of coverage quality requirements.

To guarantee a good quality in both uplink and downlink direction, the power levels of BTS and MS should be balanced at the edge of the cell. Main output results of the power link budget are:

Maximum path loss that can be tolerated between MS and the BTS.

Maximum output power level of the BTS transmitter.


These values are calculated as a result of design constraints.

BTS and MS receiver sensitivity.

MS output power level

Antenna Gain

Diversity reception

Losses in combiners, cables etc.

The cell ranges are derived with propagation loss formulas such as Okumara Hata or Walfisch Ikegami, which are simply to use . Given a maximum path loss, differences in the operating environment and the quality targets will result in different cell ranges.

The traffic capacity requirement have to be combined with the coverage requirements, by allocating frequencies. This also may have impact on the cell range.

COVERAGE PLANNING STRATEGIES

The selection of site configurations, antenna and cables in the core of the coverage planning strategy. The right choice will provide cost saving and guarantees smooth network evolution.

Some typical configurations are :

3 sector site for (sub)urban areas

2 sector site for road coverage.

Omni site for rural areas.

These are not the ultimate solutions, decisions should be based on careful analysis.

Cell Range and Coverage Area :

For any site configurations, the cell ranges can be determined given the equipment losses and gains. The site coverage areas can be calculated then and these will lead to required number of sites for a given coverage region. This makes it possible to estimate the cost, eg. Per km2, to be used for strategic decisions

After getting the overall picture, the actual detailed radio network planning is done with a RNP tool.


Marketing specifications

Define design rules and parameters.

Set performance targets.

Design nominal cell plan.

Implement cell plan.

Produce frequency plan.

Optimize network.

Monitor performances.

METHODOLOGY EXPLAINED

Define design rules and parameters

Identify design rules to meet coverage and capacity targets efficiently

Acquire software tools and databases

Calibrate propagation models from measurements.

Set performance targets

Clear statement of coverage requirements (rollout and quality)

Forecast traffic demand and distribution.

Test business plan for different roll out scenarios and quality levels.

Design nominal cell plan.

Use computer tool to place sites to meet coverage an d capacity targets.

Verify feasibility of meeting service requirements

Ensure a frequency plan can be made for the design.

Estimate equipment requirement and cost.

Develop implementation and resource plans (including personal requirements)

Radio plan will provide input to fixed network planning.


Implement Cell plan

Identify physical site locations near to nominal or theoretical locations, using search areas.

Modify nominal design as theoretical sites are replaced with physical sites

Modify search areas in accordance with envolving network.

Produce Frequency Plan

Fixed Cluster configration, can be done manually.

Flexible, based on interference matrix using an automatic tool.


Optimize the network

Campaign of measurements

Analyze results

Adjust network parameters such as : antenna directions, handover parameters, and frequencies.

Expand the network

In accordance with rollout requirements

In accordance with forecast traffic levels

To improve coverage quality.

To maintain blocking performances.

RF Planning Process

1 Understand the Customers requirements

Coverage requirements

In building coverage experiments

Initial Roll out plans

Pre determined number of sites ?

2 Survey

Traffic Distribution and Pattern

Growth areas

High density business/ residential areas

Propagation tests for in building coverage estimates and model calibrations

3. Prepare Planning Tool

Get Digitized maps

Load maps in the planning tool.

Use survey data and run the programme.

RF Planning Process

4. Draft Plan

Divide the city into number of regions-

Busy business areas

Areas that need excellent inbuilding coverage areas

Use appropriate model and link budgets to calculate the number of sites required per region.

5. Fine Tune plan.

Perform more with drive test, confirm plan predictions.

Review plan with customer and fine tune the plan.

RF Planning Process

Understanding Customer Requirements :

What are the boundaries for the network ?

Are there any special pockets to be covered due to Govt. requirements ?

What are the areas in which medium to average in building coverage is acceptable ?

What are the areas where excellent in building coverage is needed ?

Areas with high growth potential

Need colonies under development

High revenue areas

Shopping malls , offices complex, industrial estates etc.

RF Planning Process

Initial Implementation Strategy :

High usage, high revenue users first ?

High end residential and business areas ?

Street coverage first ?

Special areas like 5 star hotel, commercial building with fine in building coverage ?

High way coverage critical ?

Total coverage on day one ?

Number of sites more than the competition ?

Any Budget Limitations ?

Give an ideal plan to start with.

Let the customer cut corners.

Not an easy job !!

RF Planning Process

City Surveys :

Basically a scouting exercise

Looking for :-

Major traffic routes

Markets

Business Centres

Shopping malls

General customer behaviors

Telephone density

Congested areas with narrow lanes

Narrow water canals/lakes/ponds

General city layout

Prestigious residential areas.

VIP areas

Parks/ playground/open areas.

General Building types.. Multistoried, Row houses, apartments, colonies etc.

Airport coverage

RF Planning Surveys

In building Coverage Surveys :

Classify Buildings-

Hotel/restaurants

Commercial

Industrial

Residential

Shopping malls/markets

Propagation tests in a number of buildings in each variety.

Rf signal on road Vs. inside building gives building penetration loss.

Repeat tests in as many buildings as possible to get an estimate of building loss for the area.

In building coverage affected mostly in ground floor/basement

Typical values (examples only) :

> Hotel restaurants 15 dB

> Commercial buildings 20 dB

> Shopping malls

15 dB

> Industrial Estates 12-15 dB

> Residential buildings 15-20 dB

> Old/Historical buildings 25-30 dB

RF Propagation Test Kits

Battery powered Transmitter.

10 or 20 Watts output : frequency in GSM 900/1800 Mhz.

Portable mast

Adjustable upto 5 m. With 1 m antenna on top, effective height above ground is 6 m.

Transmit antenna

High gain omni or directional antenna as required

Receiver TEMS mobile

Hand held mobile phone with RS232 connection to a laptop. Or an accurate portable RF sensitivity meter / CW receiver if model calibration is required.

Positioning system

GPS system, with PCMCIA card

Computer

Laptop PC with TEMS software and GPS software

Cables accessories

Calibrated cable lengths (10 m) of low loss feeder with known attenuation values; 12 Volts battery with appropriate cable to connect to transmitter.

Power meter, VSWR meter.

RF Planning Tool

Planning Tool preparation and Model Calibration :

There are many planning tool available toaday :

PLANET (MSI)

Cell Cad (LCC)

Odessy (Aethos)

Asset (Aircom)

NetPlan (Motorola)

A planning tool Should be :

Easy to use

Compatible with tools like TEMS

Minimum hardware requirements.

Economical.

Maps collected from authorized sources.

1:50000 or 1:25000 scale

50 m resolution for macro

Less than 30 m resolution for Micro cell planning using Ray tracing Tool

Maps are digitized under 3 categories :

LandUse

Digital Terrain Map

Vectors (Roads, Railways, etc.)

RF Planning Tool


Most Planning tools use corrections for the land use or clutter.

Propagation Model tuned by assigning the values to

Clutter factor (Gain or Loss due to clutter )

Clutter Heights (for diffraction modeling)

Different types of clutter are defined in these models/ tools

1. Dense Urban

2. Urban

3. Suburban

4. Suburban with Dense Vegetation

5. Rural

6. Industrial area

7. Utilities (marshalling yards, docks, container depots etc. )

8. Open area

9. Quasi Open Area

10. Forest

11. Water

Too many clutter type definitation complicate planning process 10 to 15 is typical.

RF Planning Tool


DTM

Provided by the map vendor

Provides contour information as a digital map.

Vectors

Highways

Main Roads

Railways

Canals / water ways.

Coast line

Rivers.

Each categories is digitized as different layer

Displayed separately if required

Map information is set up in the planning tool.

Model calibration carried out.

Model Calibration

All tools have provision for manipulating clutter values.

Different tools have different directory structures and means of handling geographical data.

The procedure mainly talks about ensuring correct data header files to include.

BTS location

EIRP of BTS

Antenna Type

BTS antenna height

Description of surrounding area.

Procedure uses a general core model equation :

The equation has constant k1 to k6 and a constant of clutter, kclutter

Initial values for the constants are set as per the model chosen (say Okumara Hata )

PLANET programme is run repeatedly to make RMS error values for all data files ZERO or a minimum.

For each run of the programme, the values of k1 to k6 are manipulated.

This completes model calibration.

Link Budget and other Steps

Key Points To be Considered :

Coverage Probability

Expected inbuilding coverage

Edge probability

Fade margin required

Maximum permissible path loss ( from the link Budget )

What is the radius of the cell ?

Number of sites required (from coverage point of view )

Is the number of sites calculated as above adequate for capacity ?

Decide on more sites for capacity.

Capacity Calculations

Capacity calculations :

Check if number of sites is enough to give capacity.

Depends on

Spectrum available

This decides the site configuration.

Availability of features like frequency hopping etc.

If Capacity is not met, add more sites.

If number of site is not OK with the customer, then :-

Recalculate site density, for 50 % in building coverage in place of 75 %

Fine Tune The Plan

Use Planning tool to return Coverage predictions

Iterate the process in consultation with the customer.

Finalize Plan and document it.

Search Areas

Planner issues search areas for each site location with information on :

Location

Lat/Long

Antenna heights

Specific target areas if any

Size of search areas

Size acquisition team scouts for buildings.

3-5 alternatives preferred.

Site Selection

Central Business area

Small Search areas (100 m)

Avoid near field obstruction.

Antenna at or slightly above the average clutter height.

Orientation is critical.

Try solid structure (lift room ) for antenna mounting.

This helps reduce backlobe radiation problems

Avoid towers on building tops. This reduces interference to neighbouring cells.

Residential suburban areas :

Larger search areas (200 m)

Location not very critical.

Antenna 3-5 metres above average clutter height.

Antenna orientation less critical.

Site Selection

Industrial area :

A suitable central location.

Avoid proximity to electrical installations like towers, transformers etc.

Towers are common

Quasi / open Highways

Larger search areas (500 m)

Limited by terrain and not the clutter. Hilly areas need care.

Highways need closer search areas along road.

Tall sites give better coverage.

Extending Cell Range

Extended cell range reduces number of sites.

Cell range improvement achieved through :

BTS transmit power enhancement

BTS sensitivity enhancement

Combination of both


Increasing BTS transmit EIRP:

To maximize BTS O/P power, single carrier cells can be used.

This will avoid the combination losses of multiple carrier cells.

The output power at the top of the cabinet could be set to 40 Watt, giving an increase in signal strength of 3 Db.

For cells with more than aone carrier, air combination can be implemented so that the combination loss is minimized.

Another way to maximize Tx and Rx signals is to implement lowloss feeder cable.

A typical 7/8 Andrewscoaxial cable has an attenuation of 3.92 dB/100 m. If a 5/8 Andrews cable with an attenuation of 2.16 dB/100 m is used, then an increase of 1.6 dB can be obtained per 100m.


Improving BTS receiver sensitivity :

Better devices in the BTS receiver.

Using Mast Head amplifiers with very low noise figures.

Better RF cables.


Improvement in the transmit side gives 2 dB advantage.

MHAs extend the BTS receiver sensitivity to 110 dBm instead of the usual 107 dBm.

Overall improvements result in 4-5 dB advantage in path loss, leading to extended coverage.

This improves quality of coverage.

Experiments with MHAs have shown improvements

In areas with 50 % probability to approximately 70 % probability.




Documents

10 RF Planning