Propagation Environment Models

Built-in signal propagation models can be used to simulate multipath propagation in rural, sub-urban and urban areas. Used propagation models are specified in ITU-R Recommendation M.1225, “Guidelines for evaluation of radio transmission technologies for IMT-2000” (see Section 2.1.4 Parameters of the wideband models). The document is available on the ITU website (http://www.itu.int/rec/R-REC-M.1225/en).

The ITU model corresponds to a tapped-delay line structure with a fixed number of taps: 3 taps in rural and sub-urban environments and 5 taps in an urban environment.

The first tap (i.e. the direct path) may be either Rice or Rayleigh fading, corresponding to LOS and NLOS situations, respectively. The other taps are always Rayleigh fading.

The ITU model describes multipath propagation for a single satellite either in a LOS or NLOS situation. Propagation environment model generates multipath taps for the entire satellite constellation. Based on the satellite elevation angle, the satellites are divided into three zones, as illustrated below:

• Open Sky, Multipath Zone, Obstruction Zone

ITU multipath propagation model

Satellites above the Open Sky limit are not affected by multipath propagation.

Satellites in the Multipath Zone (elevation angle between Obstruction Limit and Open Sky Limit) are considered LOS signals, but affected by multipath propagation. The ITU model for LOS situation is used for these satellites.

For satellites in the Obstruction Zone (elevation angle below Obstruction Limit), the direct signal path may be obstructed, e.g., by a building. This is modelled by giving a probability for an NLOS situation. With the given probability, the simulator classifies satellites as NLOS and takes the ITU model for the NLOS situation into use. The NLOS situation changes only when a satellite leaves the Obstruction Zone.

Note that, in addition to the two elevation limits mentioned above, the Elevation mask setting applies to the simulation as normally.

The Propagation environment is defined by the environment type (open/rural/sub-urban/ urban) and three parameters:

• Open sky limit, Obstruction limit and NLOS probability.

Default values for the parameters in each environment type are given in the table below. The Open environment type is the default, meaning that all satellites assume free-space propagation.

Propagation environment type parameters

Environment	Open sky limit	Obstruction limit	NLOS probability
Rural	20°	15°	0.1
Suburban	40°	30°	0.2
Urban	60°	40°	0.3

The Propagation environment model is taken into use by setting an event scenario propenv. If stated without parameters, the default parameter values given above will be used. In this case the format of the even line is:

TIME scenario propenv {open|rural|suburban|urban}

Note: For more information on Event simulation, see Event Data.

Alternatively, parameter values can be provided in the format:

TIME scenario propenv {rural|suburban|urban} OPENSKYLIMIT OBSTRUCTIONLIMIT NLOSPROBABILITY

Example

0.0 scenario propenv suburban

300.0 scenario propenv urban

600.0 scenario propenv urban 90.0 60.0 0.75

The example event file above will create a simulation starting from sub-urban environment (default parameters). After five minutes the simulation changes to an urban environment (default parameters) and after ten minutes to a highly obstructed urban environment where open sky satellites do not exist (open sky limit at 90 degrees), and satellites below 60 degrees elevation are likely to be NLOS (NLOS probability 0.75).

The Propagation environment model can be defined in the scenario configuration by using the Scenario editor in StudioView.

The Propagation environment model can also be set by using the corresponding SCPI commands (see SOURce:SCENario:PROPenv).