wiki:Manual/PropagationModels/Introduction

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Propagation loss on the path between transmitter and receiver

Path loss along a given transmitter-receiver path is calculated as a function of:

  • frequency;
  • height of receiver antenna;
  • height of transmitter antenna;
  • distance between transmitter and receiver antennas (in horizontal plane);
  • environment factor (if relevant for the model).

This function is evaluated by calling a particular propagation model selected for the concerned path (VLT-VLR, ILT-ILR, ILT-VLR and ILT-VLT) in the scenario. The in-built SEAMCAT models do not take into account any path-specific topographic considerations (i.e. no terrain).

Guidance on selecting the propagation model

You can select any propagation model(s) depending on the scenario and purposes of your simulation, e.g. type of radio systems and environment considered in the scenario.

To aid in the selection process, the following table provides an indication of the application ranges and typical areas of suitability of the in-built propagation models in SEAMCAT:

Model Frequency Range Distance Range Typical Application Area
ITU-R P.1546 model (ITU-R Rec.P.1546-1 and ITU-R Rec.P.1546-4 available in SEAMCAT)30 MHz - 3 GHz1-1000 kmBroadcasting and other terrestrial services, typically considered in cases with high mounted transmitter anttena (e.g. above 50-60 m). Note that ITU-R Rec.P.1546-4 proposes a solution where values of distances less than 1 km may occur and where short-range propagation model is not practicable and a simple means is required to converge towards free-space field strengths for arbitrarily short distances (see section 14 of ITU-R Rec.P.1546-4).
Extended Hata model30 MHz - 3 GHzUp to 40 kmMobile services and other services working in non-LOS/cluttered environment . Note that in theory, the model can go up to 100 km since the curvature of the earth is included, but in practice it is recommended to use it up to 40 km.
Extended Hata-SRD model30 MHz - 3 GHzUp to 300 mShort range links under direct-LOS assumption, important: antenna heights up to 3 m
Spherical diffraction (ITU-R P.452) modelAbove 3 GHzUp to and beyond radio horizonInterference on terrestrial paths in predominantly open (e.g. rural) areas
Free space loss modelAbove 30 MHzLOS-limitedFixed links and other systems/paths were direct-LOS could be assumed
ITU-R P.452-14 modelabout 0.7 GHz to 50 GHzup to a distance limit of 10 000 kmPrediction method for the evaluation of interference between stations on the surface of the Earth at frequencies above about 0.1 GHz, accounting for both clear-air and hydrometeor scattering interference mechanisms.
User-defined model (Propagation plug-in)model specific model specific model specific

Testing the propagation model

YOu can test the the selected propagation model separately, i.e. without setting complete scenario and running full EGE simulations. You can use the Test Propagation Models function. It is available using menu option Tools then Test Propagation Models or directly with CTRL+SHIfT+M.

Note: It is highly recommended that user tests the newly selected propagation model before proceeding to simulations, and in particular any user-developed propagation model plugin should be tested before employing it''

Additional notes on using the Extended Hata vs. P.1546 models

The most usually used SEAMCAT in-built propagation models in typical SEAMCAT scenarios are the Extended Hata model and the ITU-R Rec. P.1546 model. Therefore, when choosing between those two models, you should be aware of their similarities and differences:

  • The Hata model (also referred to as Okumura-Hata) was originally developed for non-Line-Of-Sight (Non-LOS) paths in urban environments typical of mobile services - that is with low-height mobile terminals moving in cluttered environment.
  • The P.1546 model was originally developed for broadcasting environment (at that time being the ITU-R Rec. P.370), however later, it was modified into a universal terrestrial propagation model, by approximating between the original P.370 curves and curves of other models, incl. those of Okumura-Hata model.

Therefore the P.1546 and Hata models may yield comparable results at distances of some 10-40 km (the typical range of Hata model) in certain range of conditions and for certain combinations of transmitter and antenna heights.

Regarding the antenna heights it is important to keep in mind that the Hata and P.1546 models use different definitions of antenna heights.

  • The Hata model assumes simply the height of transmitting antenna above ground.
  • The P.1546 model assumes that the height of transmitting antenna (h1, ht) is the effective height above the average height of terrain over the propagation path (taken between 3-15 km). In that regard it should be noted that SEAMCAT by itself does not have any knowledge about the actual terrain, therefore user should carefully consider the appropriate value of transmitting antenna height, following guidance in P.1546-1.

On the other hand, it should be noted that the P.1546 model does not have a distinction between urban and rural propagation conditions except when calculating correction for receiving antenna height. Thus, the setting of URBAN, SUBURBAN or RURAL environment when selecting P.1546 model simply leads to an assumption of certain height of local clutter, surrounding the receiver antenna. This is then compared with the height of receiver antenna and depending on their relationship, the appropriate correction will be made. For example, if the receiver antenna height is less than the assumed height of local clutter, then the propagation loss will increase.

By default SEAMCAT assumes the height of local clutter to be 10 m for both RURAL and SUBURBAN environment and 20 m for URBAN environment. In SEAMCAT, you are given the option to define its own local clutter height, which may be then different from the above default values. Therefore, when using P.1546 model, it is very important to consider the height of receiver antenna with regards to the assumed height of local clutter.

The figure below shows an example of how the median propagation loss calculated with P.1546 model would change depending on the height of receive antenna (h2), and how it compares with the corresponding Hata model results (the curves are for 600 MHz, 50% time, 50% locations, default local clutter setting in P.1546).

When the height of receiver antenna h2 in P.1546 is set to 1.5 m, which is much below the assumed height of local clutter (the default value of 10 dB was used in these simulations), then the propagation loss is much higher (by almost 20 dB) than the one generated with P.1546 for h2=10 m (i.e. when receiver antenna was set equal to the height of local clutter). In the latter case, the P.1546 losses are quite close to the results produced with Hata model, especially for shorter distances.

The latest available version P.1546-1 (2003) had been implemented, which in particular contains revised definition of transmitter antenna height and some additional corrections, such as the correction for short urban/suburban paths.

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