Urban Propagation Models
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 sales@remcom.com 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
• 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:
– 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
• 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
• 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
Transmitter
Exact Path Correction
Intersecting
Ray
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
