## 7 5G Radio Propagation Mechanisms
### General 5G Models  
As illustrated and explained below, there are up to nine general 5G models that have been created over time for various frequency bands. * COST 2100 Channel Model: The COST 2100 channel model, which focuses on frequencies less than 6 GHz band, was derived from the COST 259 channel model and the COST 273 channel models [27]. It categorizes clusters into three types, namely single-bounced clusters, local clusters, and twin clusters. The local clusters are close to the BS or MS, the single-bounced and twin clusters are far from the BS and MS, and the single clusters can be located using the delays and angular parameters. However, both sides must describe the twin clusters' locations. * QuaDRiGa: The QUAsi-Deterministic Radlo channel GenerAtor (QuaDRiGa) is a GBSM that evolved from the WINNER+ channel model and added many other enhancements. The most recent form of QuaDRiGa can be used for frequencies ranging from 0.45 to 100 GHz. One major improvement in the QuaDRiGa is its ability to generate correlated large-scale parameters (LSPs). The correlated maps in QuaDRiGa were created using a 2D map covering all receiver locations. * mmMAGIC Channel Model: The mmWave-based Mobile Radio Access network channel model for fifth Generation Integrated Communications (mmMAGIC) was developed using the 3 GPP channel modeling approach and the QuaDRiGa as a foundation. In the mmMAGIC, the measurement data for modeling in frequency bands ranging from 6 GHz to 100 GHz can be obtained through measurement campaigns in environments such as airports, indoor offices, outdoor-to-indoor, UMi open square, and indoor offices. * METIS Channel Model: Mobile and wireless communications Enablers for the Twenty-twenty Information Society (METIS) uses a map-based model, a stochastic model, and their combination, that is, a hybrid model, to achieve flexible and scalable channel modeling. The stochastic model and the map-based approach support frequency ranges of up to 100 GHz and 70 GHz, respectively. The map-based model was created using an RT methodology, a simplified 3D geometric description of a propagation environment, and additional random shadowing objects. Specular reflection, diffraction, diffuse scattering, and blocking were all considered propagation mechanisms. Specular and diffuse components can be enabled or disabled to improve accuracy or reduce complexity. * The 5 GCMSIG: The special interest group (SIG), which is made up of several academic and industrial institutes, proposed the 5G Channel Model Special Interest Group (5 GCMSIG) channel model. It has a large bandwidth and a wide frequency range (0.5-100 GHz) (100 MHz for below 6 GHz and 2 GHz for above 6 GHz). The 5 GCMSIG extended the 3 GPP 3D model to support higher frequency bands on the basis of extensive measurements and ray tracing simulations. This channel model consists of known models, such as shadowing, path loss, LOS probability, preliminary fast fading, and blockage models. * The 3 GPP Channel Model: The most recent 3 GPP channel model (3 GPP TR38.901) is an expansion of the 3 GPP 3D channel model and incorporates a number of additional modeling components. It has a large bandwidth and a wide frequency range (0.5-100 GHz), providing up to 10 percent of the carrier frequency. The 3 GPP channel model was used to model the oxygen absorption at 53-67 GHz as a function of center frequency, delay, and 3D separation between the transmitter and the receiver. * IMT-2020 Channel Model: In order to add many new features, such as support for a broad frequency range up to 100 GHz, large bandwidth, 3D propagation modeling, spatial consistency, large antenna array, blockage modeling, and other emerging features, the IMT-2020 channel model was developed. It is a GBSM that builds on the IMT-Advanced channel model and the 3 GPP TR36.873 channel model.