The heart of every RF simulation tool is the prediction model. There are many models that predict RF propagation, but the most known is the 'Hata-Okumura' model. This model is 'the mother of all models'.

Over the years, new models have been developed where the growth of commercial cellular networks like GSM, UMTS, and now Wimax are the main drive. These networks operate in the UHF and SHF bands (450 to 2400 MHZ). Other frequencies are used for the broadcast of Radio and TV (VHF and UHF, 50-800 MHz) and a small portion for PAMR and PMR networks. Their focus is in the VHF and low UHF frequencies (50-500 MHz).

The prediction models used for these networks are divided by coverage distance. For GSM, DCS and UMTS (900-2400 MHz), these models are limited to predictions over a short range. Due to the nature of broadcast, the distance over which predictions are made is significantly bigger than for cellular networks.

The difference in range for the model is divided into two main categories:

This choice is strongly influenced by the end-user terminal. If an uplink is required, a handheld terminal will limit the coverage because these devices have limited transmit power and poor antenna performance. In the case of broadcast, A Radio receiver does not need to talk back to the broadcaster, so bigger powers do no harm to the link budget.

When predictions over small distances are required to be accurate, it is important that the influence of local buildings (clutter) is taken into account. When predictions are performed over bigger distances, the dominance of clutter decreases and eventually can be left out of the calculations. This simplifies the formula for calculating RF propagation.

Accurate RF predictions require detailed clutter and height data, but this data is generally expensive and only affordable when the income from the exploitation of a radio network is high. For amateur radio, emergency services, and students, for example, it is not realistic to have this accurate data available. Therefore, low-budget and easily accessible data must be accessed. Radio Mobile uses geodata that is available on the internet for free.

Based on the Hata model, many other models have been derived. Also, models have been improved for their specific purpose. But some general models have been almost the same and available for free. One very well-known model is the Longley-Rice model. This model is accurate over a wide range of frequencies and various distances. Based on this model, the US Institute for Telecommunications Science (ITS) created a propagation prediction model known as the Irregular Terrain Model or ITM.

Radio Mobile uses the ITM model.

To understand the operation and limitations of the model, I have collected information about the Longly-Rise and ITM models on this website.

The chapters cover general and background information about the propagation model in Radio Mobile. Also, specific implementations in Radio Mobile are described.