Radio Propagation Measurement and Channel Modelling

Chapter 3

Radio Channel Models

Radio channel models for narrowband and wideband transmissions are commonly used to predict coverage of a wireless link and system performance. These are classified as (i) deterministic models, (ii) statistical/empirical models and (iii) semi-deterministic or site specific models. Ray tracing models are deterministic in that the received signal can be computed from knowledge of the geometry of propagation, the electrical properties of the medium of propagation, radar cross section of objects and antenna radiation pattern. A ray tracing algorithm aims to determine all the contributing propagation mechanisms at the receiver location such as free space if a line of sight (LOS) component is present, all the reflected and refracted components, all the diffracted components and all the scattered components. The technique is computationally inefficient for large urban environments and is more suited to small areas such as indoor environments or propagation over small sections of a street. Statistical models are measurement based and thus are dependent on the measurement equipment, the experimental set-up and the environment. Corrections for some of the parameters such as antenna height above ground or frequency are sometimes generated to account for differences between the measured data in the model and the scenario in which the model is to be applied. Such an example is the Okumura model where correction curves have been generated [1]. Semi-deterministic ...