Radio wave propagation can be categorized as LOS (line of sight) and non-LOS modes. LOS is direct point-to-point propagation with no obstructions in between. Non-LOS is indirect propagation in the absence of a LOS path consisting of diffraction, reflection, and scattering. In the HF band (3 – 30 MHz), propagation uses mainly sky waves for long distance communications. VHF and UHF waves (30 MHz – 3 GHz) travel by LOS and ground bounce propagation. The SHF wave (3 to 30 GHz) strictly uses LOS propagation.

The goal of propagation modeling is to determine the probability of satisfactory performance of a wireless system that depends on the propagation of radio waves. For RF system planning, propagation modeling is intended for RF coverage analysis. This analysis uses the propagation model and terrain data to predict the RF coverage area of ​​a transmitter, the received signal strength at the end of a wireless link, the path loss from the transmitter to a remote receiver, the transmitter antenna tilt angle, the minimum antenna height to establish the line-of-sight communication path, and channel degradation such as propagation delay due to multipath fading.

The US government, private organizations, and standards bodies such as the International Telecommunications Union (ITU) have developed propagation models for different applications, environments, and terrain. These models are based on a large amount of empirical data collected in order to characterize the propagation for that application. Since propagation models are created using statistical methods, no single model will exactly fit a particular application. It is a good idea to employ two or more independent models and use the results as bounds on expected performance. The following is a list of the most widely used near-Earth propagation models.

longley rice
The Longley-Rice model predicts the long-term median transmission loss over rough terrain. It is designed for a frequency of 20 MHz to 20 GHz and a path length of 1 to 2000 km. The model takes into account terrain, climate, subsurface conditions and ground curvature. The Longley-Rice model has two modes, point-to-point and area. Point-to-point mode uses detailed terrain features and data to predict path loss, while area mode uses general information about terrain features to predict path loss.

okoumura
Okumura’s model is based on measurements made in Tokyo in 1960, between 200 and 1920 MHz. The measured values ​​are used to determine the median field strength and numerous correction factors. Correction factors include adjustment for degree of urbanization, terrain roughness, base station antenna height, mobile antenna height, and localized obstruction. Okumura’s model is especially applicable in urban areas for general coverage calculation where there are numerous obstructions and buildings.

Cost 231
The Cost 231 model, also called the PCS extension of the Hata model, is used in most commercial mobile RF planning tools. The Cost 231 model coverage is frequency between 1500 to 2000 MHz, transmitting antenna effective height between 30 to 200 m, receiving antenna effective height between 1 to 10 m and link distance from 1 to 20 km. The Cost 231 model is restricted to applications where the base station antenna is above adjacent roofs.

Church
The Egli model is a simplified model based on the empirical matching of the measured data with the mathematical formula. Its ease of implementation makes it a popular choice to use for first analysis. Assumes a gently rolling hill height of approximately 50 feet and no terrain elevation data between the transmitter and receiver is needed for the model. The median path loss is adjusted for the height of the transmitting and receiving antenna above the ground. The model consists of a single equation for the path loss.

ITU
The ITU terrain model is based on diffraction theory which provides a method for predicting mean path loss. The model predicts path loss based on the height of the path block and the first Fresnel zone for the transmission link. The model is ideal for modeling line-of-sight links on any terrain and is good for any frequency and path length. The model takes into account obstructions in the middle of the communication link, making it suitable for use both within cities and in open fields. The model is considered valid for losses greater than 15 dB.