Introduction
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Special requirements in time variant scenarios forced the development
of a new ray tracing model. The new approach is able to consider time
variant effects (doppler shift, slow fading) and is able to handle very
large scenarios due to an improved modelling of complex objects (e.g. vehicles).
Besides this new model, all propagation models available for indoor scenarios can also be used
for the time-variant scenarios.
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Scenario
with several vehicles.
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3D
Ray Tracing
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With the 3D ray tracing
model the received power at each receiver location is computed. For the
determination of
reflected and diffracted rays, images of the transmitter are computed,
i.e. the image of the transmitter relative to the the reflecting plane.
This leads to a very high accuracy - because all relevant objects (also
all diffraction wedges) are always considered for the selection of
interactions.
This
approach is described in detail in the 3D Indoor SRT section.
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Computed
propagation paths inside a building.
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Scattering
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Scattering on rough surfaces, such as building walls or road surfaces
is a very important topic, especially in vehicluar ad-hoc networks.
Because of that an approach for the consideraction of scattering is
available in the propagation model. E.g. measured data of road surfaces
can be used in the algorithm to obtain accurate prediction results.
The
scattering approach is described in detail in the publication:
Prediction
of Spatial Channel Impulse Responses for Time Variant Wireless Ad-hoc
Networks Using a 3D Ray Tracing Model with Radar Cross Sections
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Measured
scattering behavior of a road surface.
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Doppler
Shift
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The consideration of the doppler shift is possible with the new
approach. Each time an interaction (reflection, diffraction,
scattering) on a moving obstacle occurs, the doppler shift according to
the following equation is determined:
After
prediction all computed propagation paths with additional information
about interactions and doppler shift are available in an easy-to-use
ASCII file. These files can be easily postprocessed with other analysis
tools, such as Matlab.
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Computed
Doppler shift.
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Radar
Cross Sections
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The usage of polygonal car models is possible with the new ray tracing
algorithm. However one problem is the complexity of the models: To
obtain a realistic image of the reality very complex car models have
to be used. This leads to much computation effort and extrem long
prediction times. The other way is to use simplified models with only
some polygons. But these models do not represent the reality, because
only few reflections and diffractions occur on such models. WinProp
offers a new approach to avoid all these problems: The usage of radar
cross sections (RCS) is supported. Complex polygonal models can be
substituted by several bistatic RCS, which can be measured or computed.
The image on the right shows a polygonal model which was substituted by
20 RCS. The follwing equation is used to determine the scattered field:
The scattering matrix depends on the incident and
scattered angles of the ray path on the scattering center.
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Substitution
of polygonal model with radar cross sections.
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API
available
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There is an application programming interface (API) available for the
complete channel simulator. This allows customers to integrate the
simulator in their own simulation chain in a very simple way.
The
popular file format WaveFront OBJ is supported for the definition of
objects in scenarios. E.g. vehicles defined by OBJ files can directly
be loaded by the API and used to generate time variant environments.
Buildings, road courses, road signs and other elements can be added to
the environment.
The
channel simulator is already used by several car manufactor suppliers
to develop and improve their products.
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Prediction
Results
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The following images show some computation results of WinProp. Please
click on the images to enlarge them:
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Spatial
channel impulse response (CIR)
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Doppler
shift for several snapshots
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Some
computed propagation paths in a suburban Car-2-Car scenario
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Adaptive
Cruise Control (ACC):
Some
computed propagation paths.
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Wave
propagation phenomena and propagation paths
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