Post on 29-May-2018
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RadioPropagationSection Three
Signal Strength Measurement
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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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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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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.
The need for CW measurementsThe need for CW measurements
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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.
The need for CW measurementsThe need for CW measurements
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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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Model Calibration (Contd.)Model Calibration (Contd.)
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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Model Calibration (Contd.)Model Calibration (Contd.)
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Model Calibration (Contd.)Model Calibration (Contd.)
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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Model Calibration (Contd.)Model Calibration (Contd.)
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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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