rf planning criteria

7/28/2019 RF Planning Criteria

1/57

RF Engineering

Continuing Education & Training

RF Planning CriteriaFor Wireless System Designs

Prepared by:

SAFCO Technologies, Inc.

600 Atlantis Rd.Melbourne, FL 32904 USA

Phone: (407) 952-8300Fax: (407) 725-5062

www.safco.com

Copyright 1997 by SAFCO Technologies, Inc.

All rights reserved. No part of this book shall bereproduced, stored in a retrieval system or transmitted

by any means, electronic, mechanical, photocopying,

recording, or otherwise, without written permissionfrom SAFCO Technologies, Inc.


2/57

RF Engineering Continuing Education & Training

RF Planning Criteria for Wireless System Designs

Copyright 1997 by SAFCO Technologies, Inc. Revision Ai

Approximate Unit Length: 8.0 hours

This unit provides an overview of RF engineering procedures used to design and build-out aradio network. The emphasis is placed on the engineering procedure. By focusing on the

engineering procedure, the material is applicable to a multitude of RF network design work:

existing cellular networks, new PCS systems, Wireless Local Loop design, etc. At thecompletion of the unit, the student should understand the following concepts:

1. The three stages of network design2. The way a link budget, and its assumptions, can affect the design.

3. The technical information needed from the service provider and equipmentvendor for a RF design.

4. The reasons and objectives of the market analysis.

5. The preliminary design is an iterative process allowing the engineer to makechanges to the design, check these changes, and maintain the build-out

schedule.

6. A coverage plot using coverage bands developed from the link budget.7. A Final Design is a continuation of the design process and is never reallyfinished.

8. How to generate and interpret interference plots within the propagation model.9. The deliverables required at the completion of the Nominal Design,

Preliminary Design, and Final Design Stages.


3/57



Copyright 1997 by SAFCO Technologies, Inc. Revision Aii

Table of Contents

1 INTRODUCTION..............................................................................................................................................1

1.1 WHY HAVE AN RF DESIGN PROCESS? .............................................................................................................11.2 ORGANIZING THE DESIGN PROCESS .................................................................................................................2

1.3 THE NOMINAL DESIGN STAGE .........................................................................................................................3

1.4 THE PRELIMINARY DESIGN STAGE...................................................................................................................3

1.5 THE FINAL DESIGN AND SYSTEM OPTIMIZATION STAGE .................................................................................4

2 THE NOMINAL DESIGN STAGE..................................................................................................................5

2.1 CLASSIFYING MARKETING AND DESIGN OBJECTIVES ......................................................................................5

2.1.1 Defining Market Boundaries..................................................................................................................5

2.1.2 Defining Coverage Objectives ...............................................................................................................6

2.1.3 Determining Traffic Requirements ........................................................................................................8

2.2 DECIDING ON A TECHNOLOGY AND SELECTING A VENDOR ...........................................................................10

2.2.1 General Technology Types ..................................................................................................................11

2.2.2 Vendor Selection..................................................................................................................................12

2.3 DETERMINING THE TECHNICAL PARAMETERS FOR THE LINK BUDGET...........................................................132.3.1 Technical Parameters Related to the Equipment.................................................................................13

2.3.2 Technical Parameters Related to RF Environmental Factors.............................................................15

2.3.3 Reliability Margin Calculation............................................................................................................16

2.3.4 Other Technical Parameters................................................................................................................16

2.4 EVALUATING THE LINK BUDGET....................................................................................................................16

Base Station Equipment ........... ............ ......... ............ ............ ........ ........... ............ ......... ............ ............ ........ .....18

Mobile Equipment ............ ........... ......... ........... ........... .......... ........... ............ ......... .......... ............ .......... ........... ...18

Environmental Losses ........... ........... .......... ............ ........... ......... .......... ............ .......... ........... ............ ......... ........18

2.5 CALCULATING THE CELL RADIUS AND DETERMINING CELL PLACEMENT......................................................18

2.5.1 Cell Layout Strategies..........................................................................................................................19

2.6 CREATING THE PROJECT IN A PROPAGATION MODEL .....................................................................................23

2.6.1 Data Required for Coverage Predictions ............................................................................................23

2.6.2 Data Suggested for the Project ............................................................................................................232.7 ANALYZING NOMINAL CELL COVERAGE .......................................................................................................25

2.8 DETERMINING THE DESIGN CAPACITY...........................................................................................................26

2.9 DETERMINING NOMINAL SITE COUNT AND BUDGET......................................................................................27

3 THE PRELIMINARY DESIGN STAGE.......................................................................................................29

3.1 THE MARKET ANALYSIS ................................................................................................................................29

3.1.1 Preparing for the Market Visit.............................................................................................................29

3.1.2 The Market Visit ..................................................................................................................................31

3.2 PROPAGATION MODEL VALIDATION..............................................................................................................32

3.2.1 Collecting Drive Test Data for the Propagation Study........................................................................323.2.1.1 Data Post Processing....................................................................................................................................... 33

3.2.2 Performing Data Analysis to Obtain Optimized Slope and Intercept ..................................................34

3.3 DEVELOP THE PRELIMINARY DESIGN.............................................................................................................36

3.4 SITE ACQUISITION..........................................................................................................................................37

3.4.1 Issuing Search Area Maps (SAMs) ......................................................................................................37

3.4.2 Candidate Site Evaluation ...................................................................................................................38

3.4.3 Obtaining Property or Site Lease ........................................................................................................40

3.5 FINAL CONSIDERATIONS PRIOR TO BUILD-OUT .............................................................................................403.5.1.1 Interference Analysis....................................................................................................................................... 41

4 THE FINAL DESIGN STAGE .......................................................................................................................43

4.1 INITIAL SITE INTEGRATION (SITE COMMISSIONING) ......................................................................................43


4/57



Copyright 1997 by SAFCO Technologies, Inc. Revision Aiii

4.1.1 Site Functionality Testing ....................................................................................................................43

4.1.2 Initial Site Optimization.......................................................................................................................44

4.2 OPTIMIZING SYSTEM PERFORMANCE .............................................................................................................46

4.2.1 Switch Data..........................................................................................................................................46

4.2.2 Periodic Drive Tests ............................................................................................................................47

4.2.3 Customer Complaints ..........................................................................................................................47

4.3 CONTINUED

PROPAGATION

MODEL

OPTIMIZATION

.......................................................................................484.4 UPDATING FREQUENCY PLAN ........................................................................................................................48

4.5 PLANNING FOR FUTURE GROWTH ..................................................................................................................48

5 CONCLUSION.................................................................................................................................................52

List of Figures

FIGURE 1: ONE EXAMPLE OF A NOMINAL DESIGN FLOW CHART ...................................................................................3

FIGURE 2: ONE EXAMPLE OF A PRELIMINARY DESIGN FLOW CHART.............................................................................4

FIGURE 3: ONE EXAMPLE OF A FINAL DESIGN FLOW CHART ........................................................................................4

FIGURE 4: POPULATION DENSITY FOR A TEST MARKET (CLOSE-UP OF THE MAJOR POPULATION CENTER IN THE INSET) 7FIGURE 5: AVERAGE FAMILY INCOME DISTRIBUTION FOR A TEST MARKET ..................................................................9

FIGURE 6 : AN EXAMPLE OF A CORNER SPLIT (A) AND A SIDE SPLIT (B) ......................................................................21

FIGURE 7: THREE DIFFERENT RE-USE PATTERNS, N = 7 (A), N = 4 (B), N = 3 (C) ........................................................22

FIGURE 8: AN EXAMPLE OF THE FREQUENCY PLANNING PROBLEMS ASSOCIATED WITH N = 4 SIDE SPLIT..................22

FIGURE 9: AN EXAMPLE OFWIZARD

OVERLAYS DISPLAYING WATER, ROADS, CITIES, MARKET BOUNDARIES, AND

INITIAL SITE PLACEMENTS...................................................................................................................................25

FIGURE 10: THE NOMINAL DESIGN COVERAGE FOR A TEST MARKET (NOTE THE POOR COVERAGE IN THE SOUTHERN

PART OF THE MARKET DUE TO TERRAIN) .............................................................................................................26

FIGURE 11:ACOMPARISON OF DESIGN CAPACITY AND PROJECTED ERLANG DEMAND (YEARS 16)........................27

FIGURE 12:ATOPOGRAPHIC MAP OF A SAMPLE MARKET (NOTE THE TERRAIN IN THE SOUTH) ..................................30

FIGURE 13: AN EXAMPLE OF HOWWIZARDAVERAGES DRIVE TEST DATA WITHIN A BIN........................................34

FIGURE 14: PLOT OF THE MEASURED DATA, PREDICTED RSL, AND THE DELTAS FOR AN UN-OPTIMIZED MODEL ......35

FIGURE 15: PLOT OF THE MEASURED DATA, PREDICTED RSL, AND THE DELTAS FOR AN OPTIMIZED MODEL ............35FIGURE 16:ACOMPARISON BETWEEN OPTIMIZED AND UN-OPTIMIZED COVERAGE PREDICTIONS .............................36

FIGURE 17:ASAMPLE SEARCH AREA MAP..................................................................................................................39

FIGURE 18: AN EXAMPLE OF AN INITIAL FREQUENCY PLAN USING THE HEXAGONAL GRID LAYOUT TO ASSIGN AMPS

FREQUENCY GROUPS ..........................................................................................................................................42

FIGURE 19: TYPICAL DAILY TRAFFIC IN A WIRELESS NETWORK (NOTE THE BUSY HOUR) ...........................................49

FIGURE 20: AN EXAMPLE OF HISTORICAL TRAFFIC DATA USED TO PROJECT DEMAND...............................................50

List of Tables

TABLE 1 : DESCRIPTION OF MORPHOLOGICAL AREA TYPES...........................................................................................7

TABLE 2: AN EXAMPLE OF STANDARD PROPAGATION PARAMETERS VALUES PER MORPHOLOGY ERROR! BOOKMARKNOT DEFINED.

TABLE 3: TYPICAL RANGES FOR BUILDING AND VEHICLE ATTENUATION .............ERROR! BOOKMARK NOT DEFINED.

TABLE 4: ENVIRONMENTAL FACTORS THAT ATTENUATE RF SIGNALS ........................................................................15

TABLE 5: TYPICAL SLOPE AND INTERCEPT VALUES PER MORPHOLOGY.......................................................................16

TABLE 6: SAMPLE AMPS LINK BUDGET FOR SUBURBAN IN-BUILDING COVERAGE ....................................................18

TABLE 7: NOMINAL CELL RADIUS CALCULATIONS......................................................................................................19

TABLE 8: INTERFERENCE THRESHOLDS FOR VARIOUS TECHNOLOGIES ........................................................................20

TABLE 9: THEORETICAL C/I RATIO FOR VARIOUS RE-USE SCHEMES...........................................................................21

TABLE 10: MODIFICATIONS TO THE NOMINAL CELL RADIUS DUE TO CELL SPLITTING..................................................21


5/57



Copyright 1997 by SAFCO Technologies, Inc. Revision Aiv

List of Equations

EQUATION 1: AVERAGE BUSY HOUR TRAFFIC PER SUBSCRIBER ...................................................................................8

EQUATION 2: THE REQUIRED OFFERED LOAD (ROL)....................................................................................................8

EQUATION 3: EQUATION FOR CALCULATING RECEIVER SENSITIVITY ..........................................................................14

EQUATION 4: W.C.Y. LEE MODEL ..............................................................................................................................19EQUATION 5: THEORETICAL INTERFERENCE RATIO .....................................................................................................20

EQUATION 6: FREE SPACE LOSS EQUATION .................................................................................................................33

EQUATION 7: EQUATION FOR THE NOISE FLOOR OF A RECEIVER .................................................................................34


6/57


7/57



Copyright 1997 by SAFCO Technologies, Inc. Revision A2

1.2 Organizing the Design Process

The design process is composed several tasks. The material presented in this class introducesone method of organizing the tasks. Circumstances and personal preferences will change the

order in which these steps are followed. All the items identified are important to the design

process and should be included, regardless of the order.

The engineering procedure may be broken down into three design phases: the Nominal Design,Preliminary Design and Final Design Stages. Each design phase represents a group of related

tasks. The end of each design phase can be used as a stopping point where assumptions arechecked and design parameters are reviewed before proceeding to the next design phase.

The Nominal Design Stage

Classify marketing and design objectives Decide on a technology and select a vendor Determine nominal technical parameters for defining the equipment specifications

and RF propagation environment Evaluate the link budget(s) Calculate nominal cell radii and determine cell layout Determine system capacity using Erlang calculations Analyze the nominal cell coverage using a propagation model Determine nominal cell and radio count for budgetary purposes

The Preliminary Design Stage

Verify market environmental parameters through market analysis Validate the propagation model through RF testing Develop a preliminary design and issue search area maps

Analyze candidate cell sites and acquire site leases Determine final cell and radio count for system deployment

The Final Design Stage

Develop site configuration including frequency plan, neighbor lists, default handoffcontrol settings, and power budget

Perform interference analysis using the propagation model and interpret the analysisresults

Optimize cell site parameters after initial turn on Optimize coverage based on drive testing and consumer feed back Update the frequency plan Plan for future growth.

This list includes all the jobs that an RF engineer must perform during each stage of the design.The details of each phase are given in Chapter 2. A general definition is given below.


8/57




1.3 The Nominal Design Stage

The Nominal Design is the application of a business plan to a theoretical RF design. The goal isto arrive at a project budget based on technical and marketing assumptions, coverage

requirements, and nominal cell site counts. Since the design is largely theoretical, some

estimates must be made. A majority of the technical work is performed during this stage to

ensure that these estimates are as accurate as possible. It is important that the engineering designteam, the system operator, and the equipment vendor be in agreement with the technicalspecifications before the nominal design begins. Figure 1 gives one method of organizing the

steps involved in this stage of development.

Technology Decision &

Vendor Selection

Grids / Cell

Splits

Nominal

Cell Radius

Link

Budget

Technical

Parameters

Marketing

Objectives

Coverage

Prediction

Develop Project in

Propagation Model

Erlang

Calculation

Figure 1: One Example of a Nominal Design Flow Chart

1.4 The Preliminary Design Stage

The Preliminary Design is the application of market specific parameters and conditions to the

Nominal Design. The goal is to refine the Nominal Design using market and technology specific

parameters prior to deploying the network. The Preliminary design involves verifyingmorphologies, collecting data for propagation model validation, investigating zoning issues, andsite acquisition. Most of these tasks require the engineer to be present in the market. The

process must be flexible, allowing many tasks to proceed in parallel. Typically, an iterativeprocess is employed to allow flexibility.

The flow chart below (Figure 2) is an attempt to organize a set of processes that occurconcurrently. Initially, the engineer needs to proceed with propagation model validation and the

market visit before issuing search area maps. Time constraints often prevent the engineer fromfollowing the exact order of events illustrated. Further, the processes are performed in a

repeating sequence. As site acquisition returns with candidate site locations, the RF engineer

needs to evaluate and accepted or rejected the proposed site location.


9/57




Frequency

Plan

Evaluate

Candidates

Adjust Site

Locations

Coverage &

Interference

Cell & Radio

Count

Site

Acquisition

Search

Area Maps

Prop Model

Validation

Re-EvaluateDesign

Coverage

Market

Analysis

Figure 2: One Example of a Preliminary Design Flow Chart

1.5 The Final Design and System Optimization Stage

The Final Design involves both the deployment of new sites (whether growth sites in an existingsystem or sites for a new network) and the maintenance of a commercially operating RF

network. The goal is to achieve a given level of network performance. Deploying new sites

requires the engineer to establish a default site configuration, commission the site, and integrateit into the existing system. System maintenance involves optimizing coverage, frequency

planning, and projecting future growth. Figure 3 illustrates one method of organizing thesesteps.

Plan Future

Growth

Optimize

System

Update

Freq. Plan

Commission &

Integrate New Sites

Figure 3: One Example of a Final Design Flow Chart


10/57




2 The Nominal Design Stage

The Nominal Design Stage is performed so that marketing assumptions, coverage objectives, and

technical parameters can be established and translated into a site count. The site count is used toarrive at a nominal project budget. The assumptions also serve as engineering guidelines for the

network design. The list of design considerations was presented in Chapter 1 and is repeatedbelow in detail.

Classify marketing and design objectives Decide on a technology and select a vendor Determine nominal technical parameters for defining the equipment specifications

and RF propagation environment

Evaluate the link budget(s) Calculate nominal cell radii and determine cell layout Determine system capacity using Erlang calculations Analyze the nominal cell coverage using a propagation model Determine nominal cell and radio count for budgetary purposes

Existing systems will periodically re-visit tasks that are associated with the nominal design stage.

When Erlang demand exceeds the network capacity, the engineer must design new sites toincrease the capacity. The engineer will use the design process to document technical

assumptions. This documentation also provides a means of tracking the progress of project (just

in case the boss asks how it is going).

The Nominal Design considerations listed above are important to designing new sites, regardlessof whether the operator has an existing system or not. For a new network design, the items listed

must be carefully defined and agreed to by all parties involved in the process (the design team,service provider, and equipment vendor). Certain assumptions will have to be made regarding

the RF environment, subscriber demand, and site configuration.

2.1 Classifying Marketing and Design Objectives

The first task during the Nominal Design Stage is to translate the marketing objective into sound

engineering guidelines. This includes defining the market boundaries, clearly stating coverage

objectives, and estimating the required Erlang capacity per coverage area.

2.1.1 Defining Market Boundaries

The FCC license requirements and market borders can have a dramatic affect on the designobjectives. The FCC license granted to each provider defines the market borders using

geographic boundaries developed by the Rand-McNally Corporation. Rand-McNally has dividedthe country, based on geography and economic statistics, into service areas and trading areas.

These geographic borders help the engineer define the cities and major highways that need to becovered. The FCC licensing requirements also set standards for market coverage.


11/57




The FCC licenses in the 850 MHz band are divided into Metropolitan Statistical Areas (MSAs)

and Rural Service Areas (RSAs). These areas are comprised of one or more counties. Counties

with major cities, like Chicago or Pittsburgh, are designated as MSAs. RSAs are comprised ofadjacent rural counties with few major cities within the market borders. Capacity issues will

drive the design for an MSA network. An RSA network design, however, will require taller sites

with large coverage areas. RSAs may include a few sites to cover suburban areas, howevercoverage, not capacity, is the primary focus in these designs.

The FCC license requirements for cellular operator (850 MHz) states that the network mustprovide the licensed territory with RF coverage out to the 32 dBu contour (defined by the FCC).

This means that the design team has to protect the geographic area with RF coverage, regardlessof population. This legal requirement results in a design that includes tall sites transmitting over

large areas near the less inhabited market borders. These border sites do not necessarily enhance

the network performance or capacity.

The FCC licenses in the 1900 MHz PCS bands are divided into Major Trading Areas (MTAs)

and Basic Trading Areas (BTAs). MTAs are larger than BTAs, with four to ten BTAs makingup a single MTA. These areas stretch across state lines so the engineer must look up the marketborders to determine the highways and cities that would be considered major coverage

objectives.

The FCC rules governing the PCS market coverage are based on population. The PCS service

provider is required to offer coverage to 90% of the population in the market within 5 or 10 years(depending on the PCS frequency block). The design, therefore, concentrates coverage around

the major population centers and connecting highways. The PCS networks do not need toprovide RF coverage to remote areas of the market, therefore the design will not include

boomer sites as seen in Cellular.

2.1.2 Defining Coverage Objectives

The design team needs to arrive at some clear coverage objectives including identifying themajor cities and highways and quality of coverage. For example, a coverage objective may

require 90% area reliability for in-building suburban coverage.

The first step in defining coverage objectives is to define the morphology within the targeted

cities. Morphology is a term used to characterize the RF environment of a region. For example,the city of Philadelphia is not homogeneous. The downtown will contain different types of

buildings than the suburbs. As such, the radio environment for each will be different.

One efficient way of defining morphology in the initial stages of the design is to rely onpopulation statistics from census data. Programs such as MapInfo are used to geographically

represent the population statistics. The statistics are then divided into population density bands,with each band defining a morphology. An example of one set of land classification parameters

is provided in Table 1.


12/57




Table 1 : Description of Morphological Area Types

Morphological

Type Area Description

Population

Density Ranges

Dense Urban

The central business district consisting of many very closely groupedconcrete, glass, and steel reinforced high rise buildings. The buildings

typically exceed 12 stories.

20,000+(persons/sq. mile)

Urban

A business and residential district consisting of many closely grouped

concrete and reinforced steel buildings. Buildings in the area range

from 4 to 12 stories.

9,000 - 20,000

(persons/sq. mile)

Suburban

A decentralized business district mixed with residential housing.

Buildings are closely spaced 2 to 5 stories made of wood, concrete

block, or brick.

500-9,000

(persons/sq. mile)

Rural

A small residential and business population amongst open terrain,

heavy foliage and small man-made structures.

0 - 500

(persons/sq. mile)

Pop. DensityPopulation per Square Mile

0 - 500

500 - 9,000

20,000 +

9,000 - 20,000

Suburban

Dense Urban

Urban

Rural

0 2

Miles

4

Figure 4: Population Density for a Test Market

There is one limitation to using population statistics. Areas, such as city parks and centralbusiness districts, will appear as having a low population density (i.e. rural propagation

characteristics). The engineer will need to interpret the results from the population densitystatistics.

The targeted coverage areas have now been defined to proceed with the design. The quality of

the coverage now needs to be defined. Area reliability is used to assign a quality metric to thecoverage predictions. An accepted industry standard for Cellular / PCS is 90% area reliability.

The exact procedure for calculating the reliability is beyond the scope of this class.


13/57




2.1.3 Determining Traffic Requirements

The coverage objectives and traffic requirements are interrelated. The capacity objectives shape

the design by requiring more sites in high traffic areas. The required capacity for the design mustbe calculated to properly evaluate the nominal design.

For a new market, the required capacity for the design is typically calculated using projectedsubscriber rates. This information can be obtained from the business plan. The operatorsbusiness plan for the market will have stated objectives for market penetration. The engineer has

to translate these numbers into an Erlang demand.

Average Busy Hour Traffic per Subscriber (Tsub)

The average busy hour traffic per subscriber (Tsub) is defined as the average call holding timeduring the busy hour divided by one hour, times the average busy hour call attempts per

subscriber. Equation 1 gives the formal definition of the concept.

TH

OneHour Asub sub (in Erlangs per subscriber)

Equation 1: Average Busy Hour Traffic per Subscriber

The average call holding time, H, could be estimated or assigned as a distribution (either a

Poisson or Gaussian distribution). The average call attempts per subscriber, Asub, is derived fromstatistics (i.e. average call attempt are given as a percentage of active users). Note that the

answer to Equation 1 is given in Erlangs per subscriber. This figure will have to be converted toand Erlang demand.

Required Offered Load (ROL)

The required offered load (ROL) is defined as the average busy hour traffic that a particular cell,or cells, must carry. The ROL is computed by multiplying the number of subscribers (#subs) by

the percent of subscribers that are active during the busy hour, times the average busy hour

traffic per subscriber (Tsub). The answer is expressed in Erlangs.

ROL subs ActiveDuringBusyHour Tsub # % (in Erlangs)

Equation 2: The Required Offered Load (ROL)

The number of subscribers can be derived from actual subscriber rates. The percentage ofsubscribers active at the busy hour is estimated or derived from the switch data. Note that the

results of Equation 2 can be stated as the Erlang requirement on a site-by-site basis or calculatedfor a group of sites in a region.

The engineer converts the market penetration figures into an Erlang requirement in the followingmanner. The engineer starts by assuming a value for traffic demand per subscriber, Tsub, based

on experience or standard engineering practice (generally ranges from 15 to 35 mErl / sub). Thetotal population for a targeted area is then multiplied by the subscriber penetration rate, obtained

from the business plan. This will provide the engineer with an estimate of the number of


14/57




subscribers to be expected in a given region. The Erlangs per subscriber, Tsub, multiplied by the

number of subcribers will result in an estimate of the Erlang requirement for the area. An

example is provided below to illustrate this process.

Example: The business plan for a new market estimates that the provider will have a 5% market

penetration by the fifth year of operation. If there are 100,000 people in the market, what is theestimated capacity objective for the nominal design?

Estimate the Erlang demand per subscriber:15 mErl / sub (typical for an area where service is not used often)

Estimate the projected number of subscribers in year five:

100,000 (total population) x 5% (projected market penetration)

= 5,000 subscribers in year five

Estimate the total Erlang demand on the system:

5,000 (subscribers) x 0.015 Erl / sub = 75 Erlangs

The Nominal Design, therefore, should provide at least 75 Erlangs total with all

sites.

There are several techniques to help the engineer refine these estimates. Each technique attempts

to distribute the Erlang demand more realistically across the market. Automobile trafficstatistics, obtained from the State Department of Transportation, can be used to model busy

thoroughfares. Average family income statistics, derived from census data, allows the engineerto focus capacity in high income neighborhoods (see Figure 5). These areas of high income may

be assigned a higher Erlang per sub since a higher percentage of people in the area will likely

subscribe to the network services. The traffic distribution can also be modeled by assigningdifferent Erlang per subscriber values to different morphologies. In this manner, a higher trafficdemand can be assigned to urban areas, and a lower traffic demand assigned the rural areas.

Average Family

Income

$20,000 - $40,000

$0 - $20,000

$60,000 - $80,000

$40,000 - $60,000

$100,000 +

$80,000 - $100,000

0 2

Miles

4

Figure 5: Average Family Income Distribution for a Test Market


15/57




Calculating the capacity required for new sites in an existing network require fewer assumptions.

Data downloaded from the switch can be analyzed to arrive at a variety of traffic variables.

These variables can be evaluated for the system as a whole, a small area of the network, or on asector by sector basis. By compiling traffic data in this way, the engineer can project future

demand and determine the capacity that will have to be offloaded to the new site(s). The designengineer should use the switch data whenever it is available.

Finally, the Erlang requirement can be converted into the number of traffic channels per sector

using the Erlang tables.

2.2 Deciding on a Technology and Selecting a Vendor

Deciding on a technology and selecting a vendor is one of the most important steps in the

nominal design process. The technology used will establish basic technical parameters that willbe included in the link budget. Without these parameters, it is impossible to arrive at an accurate

link budget.

An existing network has an established vendor and technology. Therefore, technical parameters

for the base station and mobiles are already available. However, existing AMPS markets areswitching to newer digital technologies.

The process of choosing a technology can include a Request For Information (RFI). This RFI is

a document sent to various equipment vendors requesting information on their radio systems.The responses gathered from the RFI are then reviewed to determine which vendor can provide

the best equipment to meet the business objectives. There will always be a compromise between

the cost of the equipment, speed of implementation, and the quality of the work. The decisionconcerning which technology to use is shaped by a number of factors such as:

The purpose of the design: Is the design to fill-in coverage holes in an existing market oris it a brand new market design?

The frequency block being used: Can the user roam in neighboring markets? The amount of traffic expected: Is the technology to support a large number of

subscribers with a minimum amount of sites (i.e. channel re-use)?

The current network hierarchy: Will the technology support operations from the presentswitch or is a separate switch required?

The subscriber options desired in the market: Can the costs of paging, voice mail, anddata transfer options on the equipment be justified by a higher market share?

This is not an exhaustive list of factors shaping the technology decision. This list is provided tohelp the engineer understand some of the concerns that need to be addressed when choosing the

technology.


16/57




2.2.1 General Technology Types

Wireless hardware/software exists to support a variety of air interfaces. Analog technology,

commonly referred to as AMPS, relies on a Frequency Division Multiple Access (FDMA) airinterface. Digital technologies digitally encode the voice or data before transmission. Digital

systems use either a Time Division Multiple Access (TDMA) or Code Division Multiple Access

(CDMA) air interface. The details of each technology are beyond the scope of this class. Thematerial below simply gives a general overview of the technologies that are commonly in usetoday.

AMPS Technology (Analog, Interim Standard 553)Advanced Mobile Phone System (AMPS) is the most common system in the United States and

uses FDMA technology. AMPS uses analog signals produced by standard FM modulation of thevoice or data information onto the carrier frequency. The allocated RF spectrum is divided into

30 kHz blocks. Each 30 kHz block supports control channel overhead and one subscriber withquality service. The systems operate effectively if the carrier-to-interference (C/I) ratio is kept

above 17 dB.

This technology is gradually being phased out for a few reasons. The primary reason is thatAMPS systems are reaching the limits of their design capacity. There are also problems with

security. The new digital technologies offer more user features that can only be accomplished in

AMPS with expensive add-on hardware.

NAMPS Technology (Analog, Interim Standard 88, 89, and 90)Narrowband Advanced Mobile Phone System (NAMPS) is a Motorola product, which reduced

the RF spectrum requirements to support a subscriber. Using an FDMA air interface, thetechnology integrates well with AMPS. Through hardware and software implementations,

NAMPS can support a subscriber in one 10 kHz band. In other words, the network provider can

triple the capacity of a single AMPS channel. The system does require a higher C/I ratio,typically 19 to 21 dB.

NAMPS technology is especially useful where the network design calls for a phased build out

due to increased traffic requirements. Existing sites can be configured with this technology totriple the capacity, thus eliminating the need for new towers and site leasing. Mobile units were

phased in which can complete a link on both NAMPS and AMPS technology. When planningfor this integrated AMPS/NAMPS network, some adjustments have to be made to the frequency

plan.

DAMPS Technology (Digital, Interim Standard 54C)

Digital Advanced Mobile Phone System (DAMPS) uses AMPS air interfacing for the set-upchannel. However, DAMPS digitally encodes the voice and uses a TDMA air interface for the

voice channels. This digital data is more secure than the FDMA systems, offering some degreeof user privacy.

Each of the 30 kHz channels are split into three time slots (users). When upgrading an AMPS

system with DAMPS capability, the frequency plan needs to be adjusted to handle the newtechnology. Digital processing gains allow the technology to operate effectively with a C/I ratio


17/57




between 17 dB and 20 dB. The provider would also be required to phase-in new mobile units

that are compatible with both DAMPS and AMPS.

GSM Technology (Digital, PCS 1900 & European Standard)

Global System for Mobile Communications (GSM) was developed in Europe for the 900 MHz

band and has been translated in the United States to GSM PCS 1900 (1900 MHz band). Theallocated RF spectrum is broken into 200 kHz blocks. Each of the blocks are divided into 8 timeslots (a TDMA scheme) allowing for one control channel and seven voice channels. This

technology is more efficient than regular AMPS because of the tighter frequency reuse. Thetechnology can operate effectively with a C/I ratio of 12 to 15 dB.

GSM is being be implemented in the design of new markets. The technology is not compatible

with AMPS or any of its derivatives, so it is unlikely that an operator with an existing AMPS

system would choose GSM. GSM is a digital technology that provides good voice quality andoffers subscriber options like text messaging, paging, call waiting, and FAX/data transmission.

Subscriber information is contained on integrated circuits printed on "SIM cards/chips"

(Subscriber Identity Module). This card allows the subscriber to travel into other GSM marketscarrying their billing information on the encoded chip. The digital encoding employed in

transmissions also serves to secure the system against cloning.

CDMA Technology (Digital, Interim Standard 95 & 95A)CDMA uses a digital spread spectrum transmission scheme, utilizing a very large RF spectrum

block of 1.25 MHz. Instead of sub-dividing this block or allocating specific time slots, CDMAcan use this one frequency block for a multitude of users by assigning a unique code to each

user. In this way, many calls are handled on the same carrier wave. Knowledge of the codeallows the mobile to pick out and decode its intended transmission. Since every user is on the

same frequency, there is a maximum number of users that can access a cell because of

interference issues.

CDMA technology can be employed in the design of a new market (generally in the PCS band)

or as an overlay to an existing AMPS system (hand-offs from CDMA to AMPS can beimplemented). A system designed with CDMA technology will have good digital voice quality

and will be secure against cloning.

2.2.2 Vendor Selection

Once a technology has been chosen for the project, it is necessary to decide on the equipmentvendor(s). The technical specifications should meet the design requirements and should be

incorporated into the link budget. The engineer should review the vendor specifications paying

special attention to the technical specifications.

The Interim Standards are a minimum standard for defining the air interface and hardware

required for each technology. As a result, there are differences between manufacturers withinthe same technology. Some vendors offer add-on features that will enable the network to

provide more services to the subscriber.


18/57




Service and reputation may determine which vendor receives the contract. The design engineer

will look for a good warranty on the equipment. There may be a service contract that will

obligate the manufacturer to fix equipment malfunctions once they are installed. Vendors ofteninclude engineering services along with the contract for their equipment.

Site co-location is becoming a necessity in the design process. The engineer can limit theproblems associated with co-location by carefully selecting a vendor whose equipment meets theneeds. Base station equipment that is self-contained and has a small profile is desirable. This

limits the need to share space in a shelter. Antennas with low wind loading also help. Towersare rated for a maximum wind loading and by choosing smaller antennas, the design can be

deployed on existing towers without exceeding the towers maximum loading.

A general contractor can coordinate the system build-out and coordinate hardware purchases at

this stage of the design process. Some equipment vendors will include installation contracts withthe purchase of the equipment. This is appealing since their personnel are intimately familiar

with the equipment being installed. Often, they can help at this stage by suggesting compatible

hardware.

An advisory group of design engineers is also suggested during the vendor selection, serving as

an impartial third party. The advisory group generally acts as a review board. They can reviewthe Request For Proposals (RFPs) for technical issues. The group can review the nominal design

and ensure the link budget and equipment specifications are adequate.

2.3 Determining the Technical Parameters for the Link Budget

The link budget is the most important aspect of the Nominal Design. The technical parametersthat are entered into the link budget must be researched thoroughly. The engineer must arrive at

link budget values for the equipment, environmental factors, and calculate a reliability margin.

The design team, service provider, and equipment vendor should agree to these values. Most ofthe nominal design review will be spent evaluating the validity of the technical parameters in thelink budget, so it is important to carefully define these values at this stage of development.

2.3.1 Technical Parameters Related to the Equipment

Technical parameters relating to the equipment is a broad category that includes technicalspecifications for:

The base station (BS) and mobile maximum transmit power BS and mobile receiver sensitivity BS and mobile antenna gain

Cable and connectors losses Other equipment specifications

Transmit filter Amplifier Duplexer Combiner


19/57


20/57




The base station equipment vendor often employs a tower mounted amplifier (TMA). The

engineer must identify the technical specifications and typical configuration for the TMA.

Typically, a TMA is used on the reverse link to overcome cable losses.

Cable losses include the loss associated with small diameter jumpers at the top and bottom of the

tower, the larger diameter coaxial cable, and the connectors used to put the cable systemtogether. The engineer can use vendor catalogs to collect information regarding cable losses.

These losses are given in dB of loss per 100 of cable. The value for dB/100 is dependent onthe diameter of the cable and the transmit frequency. The engineer must account for this whendetermining the cable losses.

The specifications for the mobile unit are determined in the same manner as that used to specify

the base station equipment. A receiver sensitivity is calculated using Equation 3 and the

maximum transmit power must be obtained from the vendor. The antenna gain should bespecified by the vendor as well.

The engineer must make sure that the antenna gain specified for the mobile is consistent with theother items in the link budget. An antenna gain specified in dBi requires the transmit power forthe mobile and base stations to be entered as EiRP. If antenna gains are given in dBd, the

transmit powers are entered as ERP values. The engineer also must account for the differentmobile classification (maximum transmit power rating) to be used in the market.

2.3.2 Technical Parameters Related to RF Environmental Factors

The link budget includes items that affect the balanced path, but are not part of the equipment

specification. These additional factors relate to the RF path between the base station antenna andmobile antenna. The most common factors included in the link budget are list in Table 2 along

with some typical values assigned to the parameter.

Table 2: Environmental Factors that Attenuate RF Signals

Environmental

FactorTypical Attenuation (dB)

Building Penetration 2015 dB (urban environment)

1510 dB (suburban environment)

Vehicle Penetration 410 dB (all environments)

Foliage Penetration 36 dB (rural environments)

Head Loss 0.52 dB (all environments)

Dividing the market into morphologies for the purpose of classifying the RF environmentbecomes important for assigning nominal propagation characteristics in the propagation model.Typical values for the slope and intercept in each morphology are given in Table 3 below to

refresh the students memory. The student should understand that the values of slope andintercept are dependent on the actual environment and the frequency range being transmitted.


21/57




Table 3: Typical Slope and Intercept Values per Morphology

Morphology Slope Intercept

Urban -45 dB / decade -79 dBm

Suburban -38 dB / decade -69 dBm

Rural -40 dB / decade -64 dBm

2.3.3 Reliability Margin Calculation

The reliability margin is a statistically derived loss factor that essentially provides a margin oferror in the link budget calculations. Since reliability margin is statistically derived, it provides

the engineer with a quantitative method of determining the confidence of coverage predictions.

The higher the target reliability, the larger the margin of error. For example, a design that hastargeted 90% area coverage reliability will have a smaller margin than a design targeting 95%

area coverage.

2.3.4 Other Technical Parameters

The diversity gain is a gain entered into the reverse link budget to account for two receiveantennas. It is well documented that two receive antennas placed a set distance apart will result

in an overall gain. The actual gain at any point in time will vary, but the average affect can beincorporated into the link budget (typically 2 to 4 dB). This gain can apply to any technology

that employs diversity receive antennas at the base station.

GSM has a feature called frequency hopping, which reduces the required C/I from 12dB to 9dB.The technique allows a single call to hop between frequencies on a sector, thus limiting the

chance that the call will experience co-channel interference.

CDMA handsets have the ability to process up to three signals from three different base stations.

By combining signals in this way, the link budget can include a gain, called a soft handoff gain(typically 2 to 4 dB).

2.4 Evaluating the Link Budget

The goal of evaluating the link budget is to arrive at a balanced path for each of the differentbase station configurations and environmental conditions. The balanced path determines the

maximal sustainable path loss for a given configuration. The value calculated is used todetermine the nominal cell radius and calculate coverage bands used to interpret the coverage

predictions. The student can begin to understand why it is important to thoroughly define the

technical parameters before reaching this phase.

The signal traveling from the base station (BS) to the mobile station (MS) is termed the downlink(DL) or the forward link (FL). The signal traveling in the reverse direction (the MS to BS) is

termed the uplink (UL) or the reverse link (RL). Typically, the link budget will show that thereverse link is the limiting factor. The BS transmit power then need to be decreased by an

amount sufficient to balance the path to ensure the same quality on both links.


22/57




The link budget is an RF accounting ledger. The base station configuration is considered first

on the forward link. Commonly, this will include the antenna gain, base station transmit power,

equipment losses, reliability margin, and any environmental factors chosen by the design team.The gains are added to the total while the losses are subtracted. The resulting value is a measure

of the maximal sustainable path loss in the forward link. The reverse link path loss is evaluated

in the same manner. The reverse link path loss is compared to the forward link path loss andadjustments are made to balance the path.

An example of a link budget for a AMPS system is provided in Table 4. Analyzing the entries,the student can determine the nominal configuration.

The base station in this link budget is 150 feet tall suggesting that the link budget is calculated

for a suburban site. The vendor employs a low noise amplifier in the reverse link that

compensates for the cable and equipment loss. A duplexer, combiner, and transmit filter areused at the base station. The base station has two receive antennas providing a diversity gain.

The market is using Class 3 type mobiles based on the mobile transmit power. The goal of thedesign is 90% area reliability for in-building suburban coverage based on the reliability marginand building attenuation. It should also be noted that the path is balanced in the forward and

reverse links.


23/57




Table 4: Sample AMPS Link Budget for Suburban In-Building Coverage

Link Budget Parameters Down Link Up Link

Base Station Equipment

Antenna Gain (in dBd) 14.00 14.00Receiver Sensitivity (in dBm) -100.00

Low Noise Amplifier Gain (in dB) 3.78

Maximum Transmit Power (in dBm) 42.00

Main Feeder Loss (150 ft. with 1.45 dB of loss per 100) -2.18 -2.18

Jumper Loss (33 ft. with 3.00 dB of loss per 100) -1.00 -1.00

Duplexer Loss -0.60 -0.60

Transmit filter Loss (in dB) -2.00

Diversity Gain (in dB) 3.00

Combiner Insertion Loss (in dB) -3.50

Nominal ERP (dBm) 46.72

Mobile Equipment

Antenna Gain (in dBd) 0.00 0.00

Receiver Sensitivity (in dBm) -95.00

Transmit Power (in dBm) 23.0

Feeder Loss (in dB) -0.50 -0.50

Environmental Losses

In-Vehicle Penetration (in dB) 0.00 0.00

In-Building Penetration (in dB) -8.00 -8.00

Human Loss (in dB) 0.00 0.00

Reliability Margin based on 90% area reliability (in dB) -8.40 -8.40

Maximum Allowable Path Loss (in dB) 124.82 124.10

2.5 Calculating the Cell Radius and Determining Cell Placement

The link budget results in a maximal allowable path loss for the link. This information is used to

calculate the nominal cell radius. The nominal cell radius defines the region of coverage for

individual sites in the design. As such, the calculation of the nominal radius determines howmany sites are needed to meet the coverage objectives.

The calculation is based on the propagation model used for the design. The most common

models use the W.C.Y. Lee, the Hata-Okamura or COST-231 equations. The process ofcalculating the nominal cell radius, outlined below, is identical, regardless of which model is

used. Recall that this effort is made only to arrive at a nominal cell count, which should bewithin 10% of the final cell count. The example below used the Lee equation.


24/57




10log*10

150log*15loglog101

mb

ref

tmile

hhRm

P

PPRSL

Equation 4: W.C.Y. Lee Model

Where,RSL = The median signal level, in dBm. In this case, it represents the received signal

at the edge of the cell

P1mile = The 1-Mile Intercept used in the propagation model (in dBm)Pt = The output power at the antenna, calculated by the link budget to provide a

balanced path (ERP in watts)Pref = The reference transmit ERP (in Watts)

m = The slope, the rate of decay in signal strength (in dB per decade)R = The distance to a particular point. In this case, it represents the edge of the cell

hb = The actual height of the base station antenna in feet

hm

= The actual height of the mobile antenna in feet

This equation is manipulated to solve for the distance from the site, R. By subtracting themaximal path loss from the total base station ERP (transmit power less equipment and cable

losses plus the antenna gain), the engineer can estimate the received signal level at the cell edge.This value is used in the equation for radius to determine the nominal cell radius.

Table 5: Nominal Cell Radius Calculations

Variable Variable Urban Suburban Rural /

Highway

hb BS Antenna Height (ft.) 120' 150' 240'

Pt BS Transmit Power to EnsureBalanced Path (watts) 35(3.2W) 35(3.2W) 35(3.2W)

RSL Calculated Balanced RSL (dBm)

(Pt - max. allowable path loss)

-87.4 -93.1 -96.8

ht Mobile Antenna Height (ft.) 10' 10' 10'

n Slope (dB/decade) 40 38 35

P1-mile 1-Mile Intercept RSL (dBm) -68 -59 -57

R Nominal Cell Radius (mi.) 1.19 3.2 6.29

The task is now to match the nominal cell radii from this calculation with a cell splitting scheme.The engineer must first determine the C/I requirements for the design technology. The C/I

requirement will dictate the frequency re-use scheme and suggest a cell splitting strategy.

2.5.1 Cell Layout Strategies

Each technology has a specified C/I requirement to maintain adequate good call quality. Table 6gives typical values for the various technologies.


25/57




Table 6: Interference Thresholds for Various Technologies

Technology C/I Requirement

AMPS 17 dB

NAMPS 22 dB

TDMA / DAMPS 17 to 20 dB

GSM 9 to 12 dB

CDMA -15 dB

The engineer must select a frequency re-use scheme that, theoretically, will provide the required

dB separation between co-channel sites. The engineer has several re-use plans to choose, eachdesignated by a re-use number, N. A frequency re-use of 1, 3, 4, 7, and 12 are all used by

service providers. The most common re-use schemes are N = 7 or N = 12. The engineer cancalculate the interference separation provided by each using Equation 5. Note that the cell

radius, R, and distance to the first tier re-user, D, change depending on the re-use scheme.Further, when solving for the C/I, it is convenient to define the distance, D, in terms of the cell

radius, R. This equation is valid if it is assumed that all base stations are transmitting at equal

power and their radiation centerlines are the same.

C

I

R

D

n

i

n

i

io

1

Equation 5: Theoretical Interference Ratio

Where,

C/I = The carrier to interference ratio seen at the mobile (in dB)

R = The affective coverage radius of the cell (in miles)n = The path loss exponent (in dB / decade)io = The number of co-channel interfering cells

D = The distance of the ith

interfering cell (in miles)

Table 7 gives the results of solving the equation above for the various re-use schemes. From thistable, it should be apparent that certain re-use schemes offer logical grid layouts for the design of

each technology. For example, AMPS networks require a C/I ratio of 17 dB which suggests a re-use of N = 7, while N = 4 provides enough separation for GSM.


26/57




Table 7: Theoretical C/I Ratio for Various Re-Use Schemes

Re-use Scheme, N Theoretical C/I Ratio

1 -3.41 dB

3 8.48 dB4 11.43 dB

7 17.50 dB

12 21.35 dB

The engineer now has a method of placing sites in an ordered fashion. Unfortunately, the designrequires cells of different sizes; one radius for urban, another for suburban, etc. There is a

method for merging different sized grids, called cell splitting.

Cell splitting provides a mathematical transition from one morphological region to another.

Splitting is accomplished by centering the next smaller grid on the corner or the side of the next

larger hexagon. Figure 6 demonstrates how the side-split and corner-split are accomplished.The cell splits also help the engineer maintain the C/I ratio required by different technologies.

(A) ( B )

Figure 6 : An Example of a Corner Split (A) and a Side Split (B)

The splits also provide a mathematical scale between the larger and smaller grid sizes. A side-split will generate a hex that is one half the size of the original while a corner-split will result in a

hex that has a radius 1 3/ smaller than the original. This mathematical relationship allowsthe engineer to modify the original nominal cell radii so that there is a smooth transition between

areas (see Table 8).

Table 8: Modifications to the nominal cell radius due to cell splitting

Grid

Type

Calculated

Nominal Radius

Corner-Split

(Rurb * 3 )

Side-Split

(Rurb * 2)

Rural 6.29 3.57 4.76

Suburban 3.20 2.06 2.38

Urban 1.19 1.19 1.19


27/57




Cell splitting and hex grids anticipate the need to re-use frequencies and plan their distribution

throughout the network. The nominal design does not require a frequency plan. It is important,

though, to design the network so that spacing between the sites allows for easy frequency re-use(see Figure 7).

1

2

7

4

6

3

5

1

7

4

6

5

1

2

4

6

3

5

1

2

7

4

6

3

5

2

7

4

6

3

5

1

2

7

4

6

3

5

1

7

4

6

3

5

(A)

43

12

43

12

43

12

41

43

24

31

43

2

(B)

3

1

2

3

1

2

1

2

3

1

2

3

1

2

3

1

2

3

1

2

(C)

Figure 7: Three different re-use patterns, N = 7 (A), N = 4 (B), N = 3 (C)

Some caution must be practiced when choosing a re-use scheme and cell splitting technique. For

example, limits do exist regarding the cell splits allowed by each N-factor re-use pattern. The N= 7 pattern allows both side-splitting and corner-splitting. However, the engineer can only use

corner-splits when using an N = 4 (note the problem with frequency planning presented in Figure

8). The N = 3 re-use pattern does not allow for any further splitting, so it should be reserved forspecial circumstances.

1

2

3

4

Figure 8: An Example of the Frequency Planning Problems Associated with N = 4 Side Split


28/57




2.6 Creating the Project in a Propagation Prediction Tool

The propagation model used for coverage predictions is more than an RF tool. The model allowsthe engineer to develop sophisticated graphical displays that aid in the placement of sites and aid

in evaluating the design coverage. It is important that the project have the necessary data and

parameters setup to accurately run predictions. It is equally important the project includes

geographic and data base references to aid in the placement of sites.

2.6.1 Data Required for Coverage Predictions

The propagation prediction tools are terrain-based models. The model requires a database ofterrain elevations for the market. These databases can be obtained from the United States

Geological Service (USGS).

RF energy can be diffracted by obstructions that lie between the mobile and base station.

Different tools model this situation in various ways. WIZARD models the terrain obstructions

affect by implementing Knife Edge Diffraction (KED).

Clutter data can be used to model boundaries between different propagation environments. For

example, a clutter file may be created to define different attenuations for urban, suburban, andrural morphologies. As more information is gathered about the market, sophisticated clutter files

can further divide the market into regions of heavy foliage and open fields.

Urban areas often present problems when attempting to run accurate coverage predictions. Thisis due to the surrounding buildings that can reflect, refract, and guide the RF energy in a

multitude of ways. It is helpful to incorporate a building database in these areas.

2.6.2 Data Suggested for the Project

Some items are not important to the operation and predictive capability of the model. However,some pictures and graphic overlays brought into the model help the engineer by offering a frame

of reference.

Overlays within the propagation model are more than cosmetic; they offer a reference to theengineer. Nominal cell sites need to be placed in the market at specific geographic locations

referenced to the coverage objectives (city boundaries or highways). Several general overlaysshould be included in every project to provide a visual reference. These overlays provide

boundaries for the project and information on subscriber locations. The most valuable overlaysto include when deciding where to place sites are:

Market boundaries City boundaries Interstates and US highways Population density or some other subscriber-oriented map Hexagonal grids for site placement (one grid for each area type)


29/57




This list of overlays aid in cell site place in many ways. The market boundaries, city boundaries

and highway maps are helpful references in identifying targeted cities and highways. The

population density overlay, developed while defining the coverage objectives, provides a moredetailed reference of where subscribers are located in the market. Finally, the hexagonal grid

gives the engineer a reference to the theoretical distance that should be maintained between sites.

Developing one for each morphological region allows the engineer to clearly see where the cellsplits need to occur.

The next set of overlays serve as important references in determining where sites should not beplaced. These overlays include:

Bodies of water Microwave path database (especially for PCS bands) Airports database

Without the water overlay, it is difficult to determine if the cell site is being placed on a river or

small lake. The PCS bands use spectrum currently occupied by incumbent microwave users.These microwave links must be re-located to the 6 GHz band before a market is built-out. An

overlay of licensed microwave users can aid in finding and clearing the spectrum. Finally, FAArules limit the height of towers near airports. The engineer should include a database of major

and minor airports located within the market to avoid problems with tower location.

Many markets are being designed using a large percentage of existing towers. Indeed, some PCS

providers set a goal that 40% to 70% of the design sites be co-located with existing structures.The following data bases can aid the engineer in meeting these objectives.

Building database FAA / FCC Tower database

Most of this information can be purchased commercially or created by the design team. SAFCO

Technologies, Inc.s WIZARD propagation tool supports a database of FAA and FCC towers.

WIZARD

also allows the engineer to import .MIF files generated in MapInfo. There are

literally dozens of databases formatted for display in MapInfo which allows the engineer to

generate any type of overlay needed for the project. If a database is not available, digitized maps

generated with a CalComp digitizing board can be used. This provides the engineer even moreflexibility in building relevant databases.


30/57




Figure 9: An example of geographic overlays

2.7 Analyzing Nominal Cell Coverage

The goal of the nominal design is to arrive at a nominal site count. The number of sites requiredto meet the design objectives is determined by evaluating the theoretical coverage. The engineer

needs to confirm that the marketing objectives earlier defined are being met. These included:

Targeted cities and highways Defined morphological regions within the targeted areas In-building, in-vehicle, or outdoor coverage per region Area coverage reliability

Typically, the coverage prediction is based on a strongest server type analysis. The strongest

server analysis does not require a frequency plan; it is simply an evaluation of the RF signalstrength. The engineer uses this prediction to determine if any coverage holes exist within the

targeted regions. Coverage holes will occur at different RSL values for each of the coverageconditions. The path loss and transmit powers for the urban, suburban, and rural will result in

different RSLs at the cell edge.

If holes are identified, the engineer may have to move or add more sites to the design. The holes

may be the result of hilly terrain. The coverage should be kept within the market region, as well.The whole process of adjusting site locations, adding sites, and evaluating coverage will undergo

several iterations until the design meets the coverage objectives.

The design team must be allowed some latitude to make these adjustments. The service providershould be prepared to set some priorities for the coverage objectives. This may be a set of high


31/57




priority targeted cities and interstates. Coverage objectives excluded from the priority list need

to be covered, however the criteria may be relaxed. The provider will typically make allowances

of this sort by designating some areas as requiring contiguous coverage and other low priorityareas as non-contiguous coverage. Another method that can be used is to adjust the attenuation

requirements for various environments. For example, the design may only have to provide in-

vehicle coverage for suburban areas outside major metropolitan areas instead of the typical in-building coverage.

The nominal design is generated to arrive at a budgetary estimate for the project. It does notresult in a perfect design, ready for commercial deployment. The link budget was evaluated

using certain assumptions. The propagation model used to predict the coverage is un-optimized.There are uncertainties associated with the design. By carefully establishing the link budget

parameters, though, the engineer should be able to arrive at a nominal site count that will be

within 10% of the final design count. An example of one such nominal design is given in Figure10.

Figure 10: The nominal design coverage

2.8 Determining the Design Capacity

The design has reached a stage where the nominal sites are placed and the coverage is deemed to

meet the design objectives. The design team must now determine if the design has the capacityto meet the projected subscriber demand.

One of the first steps taken in the nominal design was to translate the subscriber rates into anErlang demand. To evaluate the Erlang capacity, the engineer starts with the number of sites

(sectors) used to provide coverage of the market. From the cell site count, the number of traffic

channels available for each sector can be determined. The technology used in the design is also a


32/57




factor in determining the traffic channels per sector. However, a capacity comparison between

the different technologies is beyond the scope of this class.

Once the traffic channels per sector has been determined, the engineer uses one of the Erlang

tables (Erlang B, Erlang C, or Poisson) to convert the number of channels into an offered load

for each sectors. Multiplying the offered load by the number of sectors in the system results inthe system Erlang capacity. The designs capacity is compared to the marketing projections todetermine if the design meets the capacity requirements of the design.

561

729

Ma rket 1

Ma rket 2

1s t Yr Erlang Proj. 2nd Yr Erlang Proj. 3rd Yr Erlang Proj.

4th Yr Erlang Proj. 5th Yr Erlang Proj. 6th Yr Erlang Proj.

Design Capacity (Erlang)

Figure 11: A Comparison of Design Capacity and Projected Erlang Demand (Years 1 6)

It is clear that both Market 1 and Market 2 meet the capacity objectives out to the sixth year.This capacity is provided using cells designed to meet the coverage objectives. Had the

projected demand exceeded the design capacity, the engineer would be forced to add additional

sites to the coverage design to meet the demand.

2.9 Determining Nominal Site Count and Budget

It is important for the design team to generate a report outlining the results of the nominal design.The report will include all the information necessary to assess the design. This informationshould clearly state the assumptions that were included in the design. These assumptions are

typically summarized in the nominal link budget. The report will include plots and tables thatsummarize the coverage objectives used to guide the design efforts. Plots indicating the nominal

coverage, generated by the propagation model, will also be included. These plots should indicatethe RSL for each coverage band. The slope and intercept values used for each environment are

also necessary to interpret the coverage predictions.

This stage of the design is a good point for a design review. The design assumptions and resultsare the critical issues that must be discussed in the review. Very often, the link budget is themain topic since it summarizes all the design assumptions. If agreement can be reached on the

link budget, the design is generally accepted as valid. The coverage is discussed to ensure thatthe coverage is adequate (i.e. the targeted cities and highways are covered and coverage holes, if

any, are explained).


33/57




All the participants involved in the system build out need to be present at this review meeting.

The design team explains the design and answer questions about the methodology. The service

provider (or boss) will also be present during the review to ensure that all the coverage andmarketing objectives are met. It is strongly suggested that the meeting include the equipment

vendor and any contractors (site acquisition, site construction, etc.). Personnel from these

organizations can provide valuable input. They can point out issues involved in the constructionand build out that have not been addressed yet.

The nominal design report will also aid in developing a budget for the rest of the project. Thedesign team developed the network based on marketing and engineering guidelines. Project cost

was a secondary concern. The service provider will most certainly view the budget as a primaryconcern and often request changes to the site count in an attempt to contain costs. The goal of

the design engineer is to clearly explain the tradeoffs involved in reducing the site count.

Coverage may be sacrificed to keep the cost in line with the customers demand. The engineercan help by suggesting changes to the design that will have a low impact on the overall market

coverage. Limiting highway coverage is one suggestion. Relaxing coverage requirements inoutlying areas to providing in-vehicle coverage, instead of in-building coverage, will also helpreduce site count.


34/57




3 The Preliminary Design Stage

The Preliminary Design is the application of market specific parameters and conditions to the

Nominal Design. The goal is to refine the Nominal Design using market and technology specificparameters prior to deploying the network. This stage of development involves a lot of

fieldwork to address issues such as verifying morphologies, collecting data for propagationmodel validation, investigating zoning issues, and site acquisition.

The preliminary design requires coordination and good communication between several parties.The project will involve the design team, the service provider, a site acquisition team, and the

equipment vendor. The design will change as zoning and site acquisition force site locations tobe adjusted. Time lines will be moved as equipment and backhaul delay installation. In the end,

a good preliminary design will have contingency plans that allow work to continue despite thesedelays. A list of considerations, presented in Chapter 1, is given below to review the steps taken

during the Preliminary Design Stage.

Verify market environmental parameters through market analysis Validate the propagation model through RF testing Develop a preliminary design and issue search area maps Analyze candidate cell sites and acquire site leases Determine final cell and radio count for system deployment

3.1 The Market Analysis

The market analysis serves as a bridge between the nominal design and the preliminary design.

During the market analysis the engineer will validate the morphology of each targeted area andnote man-made structures or terrain features that will present problems. The engineer can

provide valuable information on market specific coverage objectives not accounted for in the

nominal design (ball parks, major airports, convention centers, etc.).

The only way to verify all these assumptions is for the engineer to visit the market. The market

analysis will assist in the next step (PMV) by acquiring test sites.

3.1.1 Preparing for the Market Visit

Markets generally cover large geographic areas. It would be impossible to investigate the entireregion in detail. Therefore, it is wise to narrow the scope of the trip before ever leaving the

office. The trip should concentrate on areas where the subscribers are located and theidentification of problem areas.

The population density maps, developed during the nominal design, provide material for

focusing on particular regions. The population density splits the targeted cities into four general

morphological types: dense urban, urban, suburban, and rural. By dividing the market in thismanner, the engineer has an idea of which cities are a priority for the market visit. The engineer

can further refine the scope of the visit by looking at the average family income for givenregions. Concentrations of high population and high income will be investigated first.


35/57




Several other sources of information exist to aid in planning the market visit. Major

thoroughfares into the targeted cities can be identified using road maps. Coverage for

commuters along these roads will be a priority. The State DOT will often have statistics onvehicular traffic to help identify key roads. The Chamber of Commerce can help identify

congested roads and the approximate times of rush hour, as well.

The local Chamber of Commerce can also assist in planning the visit by providing informationabout local events and facilities. The Chamber often has brochures and information packages

that identify area airports, convention centers, and stadiums.

Identifying areas of rough terrain can also be used to focus the market visit on important issuesapplicable to the design. The coverage predictions developed during the nominal design will

typically direct the engineers attention to problem areas. Topographic maps can be used to

identify areas where dramatic elevation changes or rolling hills will affect the RF propagation.The topographic map in Figure 12, for example, indicates a region of interest that should be

targeted during the visit. Notice that the terrain appears most rugged in the southern part of the

market. Coverage areas in this region should be a priority of the visit.

Figure 12: A Topographic Map of a Sample Market (note the terrain in the south)

Specific equipment should be packed for the market visit. A hand-held GPS unit is useful for

pinpointing the coordinates of sites identified in the market. These sites can be added to a towerdatabase as a co-location candidate. The sites can also be used as test sites for the propagation

model validation. It is important to document the market using an audio tape recorder, a camera

with plenty of film, and a laptop. A cellular phone can be used as a simple measurement device.The engineer can do crude measurements of the competitor's coverage, noting where cover is


36/57




poor. At times, it is useful to have a compass and binoculars. This list of equipment will allow

the engineer to fully document the market for future reference back at the office.

Finally, the engineer will want to draw on the information gathered during the nominal design

stage. It is useful to pack maps and plots generated by the design team. These items serve as a

reference when trying to identify coverage problems seen in the nominal design or determinewhere different morphologies lie. A list of common references from the nominal design is listedbelow.

A plot of the Nominal Design coverage predictions A plot of th

rf planning criteria

Documents