Urban Propagation Models
Remcom Inc.
315 S. Allen St., Suite 416  State College, PA 16801  USA
Tel: 1-814-861-1299  Fax: 1-814-861-1308  [email protected]  www.remcom.com
© 2011 Remcom Inc. All rights reserved.
Hybrid SBR/UTD Propagation Model
• Input building and terrain vector data and positions of Tx/Rx
points, and perform pre-processing operations
• Find geometrical ray paths by using a fast and robust ray
tracing procedure based on the Shooting and Bouncing Ray
(SBR) method
• Store geometrical paths obtained from SBR ray-tracing
procedure
• Construct the geometrical optics and the edge-diffracted paths
from the geometrical path database
• Evaluate E-fields using the Uniform Theory of Diffraction (UTD)
and material-dependent-reflection and -transmission
coefficients
• Combine E-fields with antenna patterns to find path loss, delay,
delay spread, angle of arrival, coverage areas, interference, etc.
Application of SBR to Ray Tracing
for GTD Method
• An inherently robust approach applicable to complex
geometries
• Apply ray tracing acceleration techniques to reduce run time
• Shoot and bounce rays from Tx/Rx points and building edges
• Find rays which intersect Tx/Rx collection surfaces
• Sort rays to eliminate duplicate paths
• Construct full or partial paths
– Tx/Rx
– Edge – Rx/Tx
– Edge – Edge
• Save partial paths in RAM and/or
on hard disk for reuse
Line-Of-Sight Rays from Source
Rays Shot From Diffraction Point
Ray Tracing
Locating Diffraction Points
Ray Tracing Acceleration
Reuse Diffracted Paths for Different Tx Sites
Ray Tracing Acceleration
Rx Point Bounding Boxes
• It is usually best to leave collection surface radius and
bounding box parameters to default values. Values can
be reset in the Advanced Receiver Properties window.
Urban Canyon 2D Model
• Fast and robust ray-tracing algorithms for complex urban
environments
• Ray paths stored to allow fast recalculation for different
frequencies, antennas, transmitters, or building wall
types
• Assumes tall buildings and low antenna heights
• Semi-automated building pre-processor has been
developed to reduce unnecessary building complexity
• Assumes a fairly flat ground
• Vertical plane components, including ground effects, are
added analytically
• Reflection and diffraction points must lie on the surface
of the building
Summary of Urban Canyon Model
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Maximum reflections: 30
Maximum transmissions: N/A
Maximum diffractions: 3
Environments: Urban
Terrain: Flat or slightly hilly, maximum of 50 faces
Foliage: Direct rays, no lateral wave
Indoor: N/A
Objects: N/A
Range: Usually < 3 km, but can depend on
application
Summary of Urban Canyon Model (2)
• Antenna heights: Lower than most buildings
• Antenna types: All
• Ray tracing: SBR for horizontal plane, image
method for ground reflection
• Minimum frequency: About 100 MHz
• Maximum frequency: Depends on application
Limitations of the Urban Canyon Model
• Advantage: greatly reduces computation time by executing a 2D
ray trace using only the street level “footprints” of buildings
• Drawbacks:
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Only accurate in a fully high-rise environment with a flat ground
Antennas must be lower than all building roofs
Omits terrain effects
Omits paths over buildings
Full 3D UTD Model
• The most general propagation model
• Primarily intended for urban and indoor
environments
• Can also be applied to propagation over irregular
terrain
• Allows for reflections, transmissions and diffractions
• This model accounts for all polarization changes
due to interactions with the features
• SBR and Eigenray ray-tracing methods
– The Eigenray method is a generalization of the multiple
image method
Summary of Full 3-D Urban Model
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Maximum reflections: 30 (SBR), 3 (Eigenray)
Maximum transmissions: 30 (R + T ≤ 30)
Maximum diffractions: 4 (SBR), 3 (Eigenray)
Environments: Urban, indoor, rural
Terrain: All
Foliage: Attenuation of direct rays, no lateral
wave
• Indoor: All
• Objects: All
• Range: Usually < 10 km, but can depend on
application
Summary of Full 3-D Urban Model (2)
• Antenna heights: All
• Antenna types: All
• Transmitters: Point sources (antennas) and
plane waves (in v2.4)
• Ray tracing: SBR or Eigenray method
• Minimum frequency: Depends on application,
about 100 MHz for urban areas
• Maximum frequency: Depends on application
• API to Full 3-D included
Full 3D Example:
Directional Tx on a Building Rooftop
• Vertically polarized directional
antenna mounted on one of
the taller buildings with a 6°
downtilt, frequency = 1.9 GHz
• Antenna has roughly 45° Hplane and E-plane half-power
beamwidths, 14 dBi maximum
gain
• Calculate received power 2
meters above the ground
• Uses full 3D model with 10
reflections, 2 diffractions, no
transmissions
Full 3D Example:
Directional Tx on a Building Rooftop(2)
• Received Power for 0 dBm transmitted power
Full 3D Example:
Ray Paths to Rx Point in the Main Beam
Receiver
Full 3D Example:
Ray Paths to Rx Point Outside Main Beam
Receiver
Full 3D Example:
Ray Paths to Rx Point Behind Main Beam
Receiver
Vertical Plane (UTD) and MWFDTD
for Over Rooftop Propagation
• The vertical plane UTD
model and the
MWFDTD model are
primarily intended for
predicting propagation
over irregular terrain,
but they can also be
used for propagation
over building rooftops
X3D Ray Model
• The X3D Ray Model is a 3D ray-tracing model with acceleration to
take advantage of multi-core systems and graphics processing units
(GPU).
• Uses Shooting and Bouncing Ray (SBR) technique
• Exact path calculations use image theory to correct paths for
improved accuracy
• Includes absorption losses due to water vapor and oxygen
• Ray paths evaluated with Uniform Theory of Diffraction (UTD)
• GPU ray tracing acceleration provides substantial performance
improvement
– Requires a CUDA-capable GPU
• Multi-threading takes advantage of multi-core CPUs
• X3D places no restriction on object shape, includes transmissions
through surfaces, and supports indoor propagation.
X3D Ray Model
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Ray tracing: SBR, with exact path corrections
Maximum reflections: 30
Maximum transmissions: 8
Maximum diffractions: 3
Environments: all
Foliage: currently no support for foliage
Range: depends on application
Antenna heights: all
Antenna types: all
Minimum frequency: 100 MHz
Maximum frequency: depends on application
Exact Path Correction
Intersecting
Ray
Transmitter
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Ray
misses
Rx
It is unlikely an SBR ray will exactly hit a receiver
To compensate, a collection radius is constructed around the receiver
Rays intersecting the collection radius are considered to reach the receiver
Exact path corrects SBR errors, resulting paths with the accuracy of image method
In the diagram, the intersecting blue ray will be adjusted to the black ray
Method provides more accurate geometric paths, power, time of arrival, phase, etc.
Atmospheric Absorption
• X3D received power & path loss include absorption from oxygen
and water vapor
• Temperature, pressure, & relative humidity are set in the study area
properties window.
X3D Limitations
The following is a list of limitations of the new X3D model.
Upcoming versions of InSite will add these capabilities:
• Requires a GPU
• Ray tracing is not restricted to the study area boundary
• Sinusoid waveforms only
• No foliage modeling
• Outputs
– Animated field output
– Efield vs time, Efield vs frequency, power delay profile
• No output generated for co-located receiver points