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).
Figure 464: Comparison between P1546 and Hata model.
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.