Urban Ray Optical Propagation Models

Highly accurate Ray Optical Prediction Models

Introduction


The wave propagation in urban areas is characterized by multi-path propagation. Empirical models like the COST 231 Walfisch-Ikegami Model do not consider propagation phenomena like multiple reflections, wave guiding effects in streets and diffractions at vertical wedges of buildings. Ray optical models consider these effects.

Ray Optical Propagation Models

There are two ray optical approaches: Ray Launching and Ray Tracing.

Ray Tracing
Ray Launching

 

 
With classical ray tracing, the received power at each receiver pixel R is computed independently of all other receiver pixels.
For the determination of reflected and diffracted rays, images of the transmitter are computed, i.e. the image of the transmitter (T) relative to the the reflecting plane (T' or T'').
This leads to a very high accuracy - because all relevant objects (also all diffraction wedges) are always considered for the selection of interactions.

But the computation time is extremely high - because for each receiver pixel the computation must start again and loop all walls and wedges...

Because of this disadvantage, a classical ray tracing is not integrated into WinProp.
With ray launching the rays are launched from the transmitter with a discrete angle increment. Each ray is computed individually.
After an intersection with a reflecting wall, the reflected ray will be computed and traced further.
After an intersection with a wedge, the rays of the diffraction cone will be computed with a given angle increment.
Each time a ray intersects the prediction plane, the field strength values are accumulated at this pixel.

The disadvantages are the constant angle increment between two adjacent rays (so that it is not always sure that the wedges are hit by rays) and the huge number of new rays after each diffraction (most of them not relevant for the receiver pixels).

Because of this disadvantage, a ray launching is not integrated into WinProp.

IRT - Intelligent Ray Tracing


As listed above, ray tracing and ray launching have their advantages. But also their disadvantages.
So the combination of the advantages (and elimination of the disadvantages) would be the perfect solution.
WinProp offers this combination: The unique 3D Intelligent Ray Tracing (IRT).



Prediction with 3D IRT in an urban scenario


In a preprocessing step the database is prepared for the prediction. This includes all advantages of the ray tracing approach: Each diffraction wedge is considered exactly, each possible reflection at each wall in the building database is analyzed, etc. Transmitters are not considered during the preprocessing - so the result of the preprocessing can be used for all transmitters located in the scenario (city).
The result of the preprocessing is saved in a file.


Based on the preprocessed data file, the prediction for a transmitter is computed with an approach similar to the ray launching. This approach is extremely fast (only a few seconds for the prediction of a cell) - but due to the preprocessing it is also very accurate. All diffraction wedges are considered correctly. All reflections are determined without any problems. And only the relevant wedges and walls are considered (which saves a lot of computation time).


The IRT combines the accuracy and quality of a ray tracing with the speed of a ray launching and is therefore the perfect solution for the ray-optical propagation modeling in urban scenarios.

 

Brochure with urban propagation models

See a comparison between different urban prediction models.

Read more about the 3DUrban Intelligent Ray Tracing (IRT)

 

 

 


Some propagation paths in
an urban scenario.