Indoor Ray Optical Propagation Models

Highly accurate ray optical prediction models

Introduction


The wave propagation inside buildings is characterized by multi-path propagation. Empirical models like the Multi Wall Model do not consider propagation phenomena like reflection, wave guiding effects in corridors and diffractions at vertical or horizontal wedges. 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 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.

WinProp offers two different Ray Tracing Models:
  • 3D Standard Ray Tracing (SRT)
    • very accurate
    • phase of rays can be considered
    • output of transmission matrix for each ray
    • output of complex field strength vector for each ray
    • recommended for highly accurate analysis of single points
  • 3D Intelligent Ray Tracing (IRT)
    • very fast
    • single preprocessing of building data is required
    • limited resolution due to preprocessing
    • recommended for radio network planning
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 and the penetrated 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 is 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.

Because of this disadvantages, a Ray Launching is not integrated into WinProp.

Predicted Results


Ray optical models can predict not only the signal level. Due to the consideration of multiple propaghation paths, they can also be used to predict

  • delay spread
  • angular spread (at BS or at MS location)
  • power delay profile (channel impulse response)
  • angular profile
Spatial Channel Impulse Response



Part of a prediciton with multiple
propagation paths to one pixel.

Consideration of Propagation Phenomena


The loss due to reflections and diffractions must be computed in a ray-optical propagation model. WinProp offers two different models to compute the loss due to interactions with walls:.

 

Empirical Interaction Model (EI)
Deterministic Interaction Model (DI)
The empirical interaction model EI uses simple equations to model the penetration, reflection, and diffraction loss of rays due to interactions with objects (walls). For penetration and reflection the user can optionally enable the angle dependency.
For the EI model the user has to define five material parameters
  • reflection loss (in dB) 
  • penetration loss (in dB)   
  • min. diffraction loss (in dB)
  • max. diffraction loss (in dB)
  • diffraction loss of diffracted ray (in dB)
The actual loss used in the prediction is based on these parameters and on the angle of incidence.

The EI has the following advantages:
  • required material properties are easier to obtain with measurements than the physical parameters required for the DI.
  • parameters can more easily be calibrated with measurements (auto-calibration).
In case of many measurements available, the EI is recommended.
The deterministic interaction model DI uses
  • Fresnel Equations for the determination of the reflection and transmission loss
  • GTD/UTD for the determination of the diffraction loss.
For the DI model the user has to define three physical material parameters
  • (relative) permittivity
  • (relative) permeability
  • conductivity
for all walls and objetcs in the database.

Additionally the thickness of the wall is used for the computation of the penetration loss of walls.

The DI has the following advantages:
  • required material properties can be found in literature.
If no or only a few measurements are available, the DI is recommended.

Computation of the direct ray

 

Ray optical propagation models consider a maximum number of reflections and diffractions. Due to that limited number, not all prediction points might be reached with the classical ray optical algorithms (especially far away from the transmitter).

 

WinProp offers the option to compute additionally the direct ray with an unlimited number of penetrations to obtain a prediction for each pixel in the prediction area.


Without direct ray
With direct ray




 

Download a brochure with all indoor prediction models.

See a comparison between different indoor prediction models.

Read more about the  Indoor 3D Standard Ray Tracing (SRT).

Read more about the Indoor 3D Intelligent Ray Tracing (IRT).

Read more about  indoor propagation models.

 

 

 

 

 
Computation of propagation paths from tower to airplane.

 

 



Some propagation paths
in an indoor scenario.




Example prediction
in an indoor scenario.

 

3D Standard Ray Tracing

 

3D SRT

 

The Standard Ray Tracing (SRT) works in full 3D mode.
No proprocessing of the database is required.

3D Intelligent Ray Tracing

 

3D IRT

 

The Intelligent Ray Tracing (IRT) is a rigorous 3D model.
A preprocessing of the database guarantees very short prediction times.