Download Poster - Space Weather Services

Development of a Propagation
Prediction Software Tool for
VHF/UHF Terrestrial Wireless
Communications Systems
Phillip Maher
IPS Radio and Space Services, Sydney NSW
[email protected]
Software Aims
• Development of a tool for modeling VHF/UHF radio propagation.
Modeling the physical layer of
– Broadcast communications systems.
– Cellular mobile communications systems.
• Focus on the effect terrain has on signal strength estimates via
– Empirical pathloss models.
– Semi deterministic pathloss models.
• Reliance on Digital Elevation Models that provide topographical and
morphology data input to the propagation models.
Digital Elevation Models and Raster Imagery
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Main input data source being DEM
(Digital Elevation Models) derived
from Satellite and LIDAR sources.
DEM’s measure the highest point
below a nominal observer hovering
the earth (data can include
buildings and trees).
Imported into software in square
tile or irregular format.
Variable resolution from 5m to
1km.
Scaled colour raster image
(bitmap) representation in the GUI.
Project developed in C/C++ within
Borland Builder.
Mapping and Coordinate Systems
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GIS requirements for use on Australian
terrain data.
Incorporating MGA94 (Map Grid of
Australia) and the GDA94 (Geodetic
Datum of Australia) which uses the
Universal Transverse Mercator System
for projections.
Operations to perform conversions
between Grid coordinates
(Eastings/Northings) and Geographical
(Latitude/Longitude) using Redfearn’s
formulae.
Distance and Height Scale factors for
accurate distance calculations on the
ellipsoid.
Bitmap Profiling
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Profiling tool for use on all raster
images.
Profiles created by line intersection
algorithm between pixel values and
simple linear interpolation for
intermediate values.
Height and distance values of
terrain cross section passed
through convex hull algorithm to
produce diffracting radio path.
Profiling performed on terrain for
propagation models Fresnel zone
clearance and LOS obstruction
testing.
Also applied to simulation results
e.g. observing cell boundaries for
cellular systems.
Empirical Propagation Models
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ITU recommended Empirical
Pathloss models such as OkumuraHata and Longely-Rice
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Okumura-Hata model variations for
Large Cities, Medium Cities,
Suburban Area and Open/Rural
Areas. Valid for
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150MHz < f < 1500MHz
 30m < Htx <200m
 1m < Hrx <10m
 1km < d <20km
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COST 231 Hata model
for 1500MHz-2000MHz.
Knife Edge Diffraction
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Semi Deterministic pathloss models
employ knife edge diffraction for
evaluating hilly terrain and finding
losses in shadowed regions.
A terrain cross section profile is
produced between the Tx and Rx
which is then passed through a convex
hull function to find diffracting radio
path.
Decision calculations based on the
knife edge model are performed to
produce the Fresnel-Kirchoff diffraction
parameter ν.
Fresnel-Kirchoff parameter then
substituted into Lee’s approximation of
attenuation over single diffracting edge.
Semi Deterministic Propagation Models
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model differs in its approach
to determining the inputs to the
Fresnel-Kirchoff diffraction
parameter ν equation, and for what
edge contributes most to the loss.
Bullington model takes simplest, least accurate approach
and reduces the profile to a single knife edge
Epstein-Peterson model considers each significant knife edge
individually and sums each loss over the diffracting path
Deygout model identifies a dominant knife edge and
calculates all losses with respect to it.
Giovanelli method identifies a dominant edge and calculates each
loss wrt it, but creates seperate observation planes for each edge.
Vogler model considers each knife edge individually, but
differs with the calculation for each diffraction loss via a
more computation intensive and accurate method.
Antenna modeling
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Vertical and Horizontal gain patterns
loaded in from a manufacturers antenna
data file.
Pattern multiplication performed for a
approximate 3D representation.
Full gain pattern then incorporated into
propagation model via a simple raytrace
function and added to the pathloss
equation.
Mechanical rotation and tilting of the
patterns.
Simulation Results.
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Each simulation is performed over
an area where the transmitter is
located in the middle of variable
sized square region.
Individual transmitters can be
modeled using the variety of
propagation models.
Transmitters operating on similar
frequencies over a network, or
those that may interfere - can be
modeled to produce a “least”
pathloss result.
Full range of attributes such as tx
height, Rx heights, and antenna
frequency/power/bandwidth.
Simulation Types
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Variable colour scale for
results with selectable upper
and lower limits and
quantisation step.
Calculations carried out for
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Pathloss
 Field Strength
 Signal-to-noise ratio (SNR)
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Signal to noise ratio – flat
noise modeling via simple
thermal noise model
for No
Comparisons available with
data sheets from broadcast TV
station field strength estimate.
Future Work
• Network analysis functions for 2G, 3G and future mobile
communication systems and broadcasting systems.
• Smart antenna modeling.
• Incorporating vector data of buildings/structures for small cell
modeling via
– semi deterministic propagation models : Walfish-Ikagami
– deterministic propagation models: Raytracing
• Modeling of mobile transmitter scenarios.
• Calibration mode for feeding in actual field data to fine tune
propagation models.
• Incorporating RadCom database for interference and spectrum
management.