Fresh Field Mtc 002 Section 3

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RadioPropagationSection Three

Signal Strength Measurement


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2001 Freshfield Communications Limited.Company Confidential Slide 2

Signal strength measurement and model calibrationSignal strength measurement and model calibration Why undertake signal strength measurement and model

calibration

Advantages of published models

Measurement Systems

System Calibration

Radio Surveys Planning

Site Selection

Route Planning

Measurement Data Post-Processing

Presentation OutlinePresentation Outline


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2001 Freshfield Communications Limited.Company Confidential Slide 3

At the end of this course, attendees will:At the end of this course, attendees will: Have an appreciation of signal strength measurements and

calibration

ObjectivesObjectives


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2001 Freshfield Communications Limited.Company Confidential

Almost all of the published models are restricted mainly toAlmost all of the published models are restricted mainly to

the countries in which they were developed or validatedthe countries in which they were developed or validated

using measurement data applicable mainly to pointusing measurement data applicable mainly to point--toto--

point and broadcast installations.point and broadcast installations.

Models which apply at one frequency are not alwaysModels which apply at one frequency are not always

immediately applicable to other frequencies.immediately applicable to other frequencies.

A more accurate model can be developed for a specificA more accurate model can be developed for a specific

system taking the resolution and accuracy of the terrainsystem taking the resolution and accuracy of the terrainand clutter databases in use into account.and clutter databases in use into account.

The need for CW measurementsThe need for CW measurements


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The use of a calibrated model gives a realistic indication ofThe use of a calibrated model gives a realistic indication of

cell site count, capital outlay and timescales required tocell site count, capital outlay and timescales required to

provide the necessary coverage.provide the necessary coverage.

At various stages in the growth of an operational network,At various stages in the growth of an operational network,there is a need to optimise prediction models to enablethere is a need to optimise prediction models to enable

more accurate estimation of coverage and interferencemore accurate estimation of coverage and interference

and therefore identification of coverage holes and highand therefore identification of coverage holes and high

interference locations.interference locations.



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Nowadays networks may even require different models forNowadays networks may even require different models for

different sectors at a site, particularly if the antennadifferent sectors at a site, particularly if the antenna

heights are significantly different from one sector to theheights are significantly different from one sector to the

other.other.



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Advantages of Published ModelsAdvantages of Published Models

What advantages do published models offer ?What advantages do published models offer ?

Published models highlight specific propagation factors which

should be taken into account when creating a generic model for

a specific system In the absence of measurement data with which to derive a

model, some of the published models can be used for

preliminary coverage area estimation and interference

dimensioning to obtain cell counts


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Measurement SystemsMeasurement Systems

A complete turnkey system required for a measurementA complete turnkey system required for a measurementcampaign will consist of the following components:campaign will consist of the following components:

Portable CW transmitter with associated base station antenna,

feeder cable and power supply

Portable CW receiver with associated mobile antenna, feeder

cable and power supply

Integrated or stand-alone global positioning system

Integrated or stand-alone distance transducer assembly

Personal computer with data logging and post-processing

software


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Measurement Systems (Contd.)Measurement Systems (Contd.)

The characteristics of the system which should be ofThe characteristics of the system which should be ofinterest to the measurement engineer include:interest to the measurement engineer include:

Dynamic Range

The receiver should have a linear dynamic in excess of 70

dB. Noise Floor

The receiver should have a noise floor of between -120

dBm and -130 dBm to enable measurements to be

conducted over long distances up to 8km away from thebase site.


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Measurement Systems (Contd.)Measurement Systems (Contd.)

The characteristics of the system which should be ofThe characteristics of the system which should be ofinterest to the measurement engineer include:interest to the measurement engineer include:

Effective Radiated Power (ERP)

The transmitter and base antenna combination should

provide a high enough ERP which can enable longdistance measurements.

Frequency Stability of Transmitter and Receiver

The transmitter and receiver RFsynthesisercircuitry must

provide a stability of 0.5 - 2 ppm for accuratemeasurements.


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System CalibrationSystem Calibration

A signal level calibration of the CW should be done at leastA signal level calibration of the CW should be done at least

every time a measurement campaign is to be conducted.every time a measurement campaign is to be conducted.


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Site SelectionSite Selection

The selection of sites for measurements is often controlledThe selection of sites for measurements is often controlledby:by:

access to site

availability of electricity for test transmitter

clearance in all directions (360 degrees, for Macrocell) from the

top of the site to provide good launch

The base station antenna must be mounted at least 3The base station antenna must be mounted at least 3--4 m4 m

above the local clutter on top of each selected building.above the local clutter on top of each selected building.


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Route PlanningRoute Planning

The routes for the measurement from a site must be carefullyThe routes for the measurement from a site must be carefullyplanned before the start of the measurement:planned before the start of the measurement:

The measurement routes must be selected to provide a good

combination of wide and narrow streets

Routes with radial, tangential and arbitrary orientation must be

selected

Measurements should be undertaken on all selected routes until

the signal level falls below the noise floor of the measurement

system. Typical coverage will be expected to be between 200 m

and 8 km.


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Route Planning (Contd.)Route Planning (Contd.)

Routes which contain elevated highways, overpasses, tunnelsor underpasses should be clearly identified. Signal levels

recorded in these areas are usually discarded in propagation

model development.

Route planning must take the clutter types into account to

ensure that all clutter types are reasonably represented in

modelling analysis and no bias is introduced.


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Route Planning (Contd.)Route Planning (Contd.)


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Measurement CampaignMeasurement Campaign

Whilst conducting the measurement campaign the followingWhilst conducting the measurement campaign the followingmust be carried out:must be carried out:

Photographs depicting views from the base site and views along

typical routes should be taken

Routes which have special characteristics should be noted

Clutter classifications provided in the modelling tool should be

checked against observations in the field


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Measurement Campaign (Contd.)Measurement Campaign (Contd.)


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Measurement Data PostMeasurement Data Post--ProcessingProcessing

Upon completion of the measurement campaign, theUpon completion of the measurement campaign, themeasurement data must be premeasurement data must be pre--processed before modelling:processed before modelling:

Data preparation (all data files should contain accurate

information such as EiRP, site location, antenna type)

Filtering on the basis of signal level e.g. -40dBm to -115dBm

Filtering on the basis of distance e.g. 200 m up to the

maximum distance recorded

Filtering for specific conditions e.g. removal of measurementsconducted on bridges or in tunnels


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Measurement Data PostMeasurement Data Post--ProcessingProcessing


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Model CalibrationModel Calibration

Accurate and meaningful model calibration requires aAccurate and meaningful model calibration requires aprocedure which is not only mathematically and statisticallyprocedure which is not only mathematically and statistically

acceptable yielding a low RMS error but which also explainsacceptable yielding a low RMS error but which also explains

the physical propagation mechanisms at work.the physical propagation mechanisms at work.

The first step involved in the calibration process is to adopt aThe first step involved in the calibration process is to adopt a

suitable model structure:suitable model structure:

P P C C d C d h C h C K

C K C K G G

RX TX CT d d h b h b DIFF KN DIFF KN

DIFF RD DIFF RD CLUTTER CLUTTER T R

!

log log log log

( , ) ( , )

, , ,

, , U J U J


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Model Calibration (Contd.)Model Calibration (Contd.)

PPRXRX is the received signal strength (dBm)is the received signal strength (dBm)

PPTXTX is the transmitter power (dBm)is the transmitter power (dBm)

CCCTCT is a fixed correction term accounting for the effect of frequency and other unknownsis a fixed correction term accounting for the effect of frequency and other unknowns

CCdd is the multiplying coefficient describing distance dependenceis the multiplying coefficient describing distance dependence

dd is the distance in metresis the distance in metres

CCd,hd,h is the multiplying coefficient for log d log hbis the multiplying coefficient for log d log hb

hhbb is the base station effective antenna height (metres)is the base station effective antenna height (metres)

CChh is the multiplying coefficient for the height gain functionis the multiplying coefficient for the height gain function

CCDIFF,KNDIFF,KN

is the multiplying coefficient for knifeis the multiplying coefficient for knife--edge diffraction lossedge diffraction loss

KKDIFF,KNDIFF,KN is the knifeis the knife--edge diffraction loss (Bullington, Deygout,...)edge diffraction loss (Bullington, Deygout,...)

CCDIFF,RDDIFF,RD is the multiplying coefficient for the rounded hill diffraction lossis the multiplying coefficient for the rounded hill diffraction loss


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KKDIFF,RDDIFF,RD is the Rounded hill diffraction loss (Hacking, Causebrook)is the Rounded hill diffraction loss (Hacking, Causebrook)CCCLUTTERCLUTTER is the multiplying coefficient for the statistical clutter effectis the multiplying coefficient for the statistical clutter effect

KKCLUTTERCLUTTER is the clutter factoris the clutter factor

GGTT(0,0)(0,0) is the transmitter antenna gain in the elevation or vertical (0)is the transmitter antenna gain in the elevation or vertical (0)

and azimuthal or horizontal (0) directionsand azimuthal or horizontal (0) directions

GGRR(0,0)(0,0) is the receiver antenna gain in the elevation or vertical (0)is the receiver antenna gain in the elevation or vertical (0)

and azimuthal or horizontal (0) directionsand azimuthal or horizontal (0) directions


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The next step is to use the facilities provided by theThe next step is to use the facilities provided by themodelling tool in use to obtain coefficients which will yield:modelling tool in use to obtain coefficients which will yield:

zero mean error

RMS error e.g. 6-9 dB

and high correlation e.g. 0.6-1.0


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Selecting Initial GuestimatesHatas coefficients, although only applicable for quasiHatas coefficients, although only applicable for quasi--

smooth areas have been found to be good initial guestimatessmooth areas have been found to be good initial guestimates

for the coefficients of an empirical model.for the coefficients of an empirical model.

Parameter Initial Value

CCT Arbitrary

Cd -44.9

Cd,h 6.55

Ch -5.83

CDIFF,KN -0.5CDIFF,RD -0.5

CCLUTTER 1.0


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2001 Freshfield Communications Limited.

Company Confidential

Model TestingModel Testing

Before accepting a model, the following should beBefore accepting a model, the following should beconsidered:considered:

The model should be fully tested for different locations. The

performance of the model should be assessed on:

on a data file-by-data file basis on a per clutter basis

for line-of-sight, partial-line-of-sight and non-line-of-sight

regions

It worthwhile displaying the residual error contour to determinelocations where the model is failing.


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Model TestingModel Testing

Before accepting a model, the following should beBefore accepting a model, the following should beconsidered:considered:

The model should be capable of predicting signals at short,

medium and long distance from the base station.

The model should be generic i.e. applicable for the wholecountry.

The resulting RMS should be low.


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Residual ErrorsResidual Errors


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Possible Sources Of ErrorsPossible Sources Of Errors

Possible sources of error which may result in thePossible sources of error which may result in thedevelopment of an undevelopment of an un--acceptable model include:acceptable model include:

Errors in the navigation system

Clutter misclassification (more noticeable at boundaries)

Errors in the measurement system employed for the

measurement campaign

Fresh Field Mtc 002 Section 3

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