The Model section of the web interface lets you specify which propagation algorithm is used to display your signal coverage when performing a calculation on the map.
You can read more here about selecting the model that is right for your project. That link includes distance/path loss chart visualizations for various frequencies.
The Model panel can be expanded and collapsed by clicking on its title . It will automatically collapse if you open any of the other interface panels. We'll explain each part of the Model panel in this article, including the Propagation model , Environment , Knife-edge diffraction , Random clutter , and Point clutter :
This drop-down selection allows the planning algorithm to be selected. There are different models optimised for different parts of the radio spectrum and geographic scenarios. For example, the free space path loss model is well suited to a SHF point to point microwave link where there are no terrain obstacles, whilst the Hata urban model is specially designed for UHF cellular planning in urban areas where tall buildings are present. Picking the right model will enhance your output accuracy. Picking the wrong one will deliver inaccurate results. If in doubt, choose the ‘Irregular Terrain Model’:
|Model||Frequency Range||Model Description|
|Irregular Terrain model (ITM)||20-20,000MHz||US NTIA general purpose model used by the FCC|
|Line of Sight (LOS)||All||Line of sight model used to determine existence of obstacles.|
|Okumura Hata (Urban)||150-1500MHz||Cellular model optimised for urban areas where transmitter is >30m AGL.|
|ECC33||700-3500MHz||ECC33 model for cellular and microwave communications|
|SUI (WiMax)||1.9-11GHz||Stanford University Interim for WIMAX|
|COST231-Hata (Urban)||1500-2000MHz||European GSM1800 and CDMA2000 cellular model optimised for urban areas where transmitter is >30m AGL.|
Free space path loss
|20-100,000MHz||ITU-R P.525 model which assumes no terrain obstacles exist in the path.|
|Irregular Terrain model with obstructions (ITWOM)||20-20,000MHz||Claims to be an enhancement to the old ITM model with increased diffraction logic but its effectiveness is disputed in academic research.|
|Ericsson 9999||150-1900MHz||Ericsson model for cellular communications up to 1900MHz|
|Egli VHF/UHF||30-1000MHz||General purpose VHF/UHF model. More conservative than FSPL|
The environment selection is only used by variants within the Hata, COST, and SUI models. The choices in the dropdown include Conservative (City), Average, and Optimistic (Unobstructed).
Knife Edge Diffraction
Where a terrain obstacle like a hill is present, diffraction and shadowing will occur on the far side of it. Not all the propagation models factor this in by default so you can manually enable this effect. This option is not necessary for the default Irregular Terrain model, where it is a core feature. The diffraction algorithm used is a custom linear model that uses the obstacle’s height, distance, and angle from the transmitter to determine the resultant diffraction impact.
Wide area obstacles can be rapidly simulated using the slider, up to 9 metres (or feet) high. This will artificially increase the ground height around the site to simulate a layer of buildings above ground level. The width of each clutter item is determined by the output resolution. For the default resolution of 1200 pixels per degree, this is 90m wide.
Much more precise simulations of man-made buildings can be performed by uploading an overlay of points to mark building locations via the database button to the right of the Point clutter On/Off switch. If you choose to have this enabled then your buildings will be factored in to future calculations, otherwise they will be ignored. This overlay should be a KML overlay containing either placemarks, polygon corners, line points with heights in metres defined in the point properties.
A quick way to define a row of wind turbines, for example, is to use Google earth's 'path' feature and click once per turbine then set the path’s altitude to 30 metres in Google earth (Relative to the ground). Save off the path as a .kml file and upload it using the 'Upload a KML' link. A single click will create a 90mx90m wide building. To define a larger building, click each corner or use the polygon feature.
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