Titolo della tesi: THz band communications: next frontier for impulse radio Ultra Wide Band
In recent years the demand for high data rate transmission is growing for indoor wireless communication systems. One of the most promising candidates that can fulfill the necessity for higher data rates in wireless communications is the TeraHertz (THz) band (0.1-10 THz). However, THz frequencies have peculiar propagation characteristics such as high free space loss, high molecular absorption, and high diffuse scattering attenuation. Therefore, it is necessary to consider all possible sources of attenuation and distortion in order to propose a propagation model for the THz range of frequencies.
Presently, there exist numerous statistically based channel models, which are generally considered adequate for outdoor environment planning. For indoor wireless services, though, these statistically based models do not provide suffi- cient information because of the complexities and variations of the propagation environments, which are usually rich in reflections and scattering.
A feasible propagation model, based on geometrical ray tracing, can be used to predict details about an indoor environment with known parameters such as geometry and building materials. A suitable model for almost any indoor situ- ation can be generated by adjusting these specific parameters. Moreover, the model needs to be sufficiently general to accommodate signal properties such as polarization and channel parameters such as geometry, dielectric constants of the surfaces, and the like. This research proposes a multipath channel model to predict the propagation of wireless signals in indoor environments more accurately. Although a plethora of works has been done on different aspects of THz channel modeling, a detailed tutorial from the physical nature to the implementation of THz channel modeling has been missed so far to the best of the author’s knowledge. The aim of this work is to give a well description of different type of attenuation at THz frequencies and explore the fundamental concepts behind developing a unified channel model which accurately charac- terizes the Terahertz spectrum peculiarities. Besides, a self-implemented ray tracer is also proposed to analyze the THz range channel model, taking into account the impact of most characterizing factors, including free-space path loss, molecular absorption, and scattering. Numerical results will be verified along with the theory and measurements.
In this thesis, an introduction to THz characteristics such as free space atten- uation, molecular attenuation, and diffuse scattering is given in Chapter 2, along with a complete picture of diffuse scattering and Kirchhoff theory, which will be covered later in the study.
Chapter 3 presents the statistical description of the most commonly used sur- faces in indoor environments. Also, we discuss different methods for generating randomly rough surfaces often used in indoor environments. Then a multi ray propagation model is proposed, which includes THz band characteristics.
In chapter 4, a homemade ray-tracing simulator is proposed. This chapter covers a description of the image-based ray tracing method besides a full description of the indoor environment, including obstacles. Moreover, the way of applying the Kirchhoff theory in the ray-tracing simulator is introduced. To model the THz channel model, the surface profile, which is generally unknown, is required first. Thus the generation of a random surface model followed by a description of computing scattered power from the generated random rough surface is presented.
In chapter 5, the results obtained by using the proposed ray-tracing tool are presented. The results focus on comparing the measured reflection coefficient in the specular direction and the theory, showing the impact of specific parameters affecting the received power, and discussing the power delay profile and the frequency-dependent channel impulse response (CIR) at each center frequency. Finally, in chapter 6, we provide a summary of the research and some con- clusions. We also provide possible directions for future work in this research area.