New Conception in Modeling the Nonlinearity of the Fading Channel

• Grant number: 24/20097-3
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: March 01, 2025
• End date: February 29, 2028
• Field of knowledge: Engineering - Electrical Engineering - Telecommunications
• Principal Investigator: Michel Daoud Yacoub
• Grantee: Godfred Kumi Tenkorang
• Host Institution: Faculdade de Engenharia Elétrica e de Computação (FEEC). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

The propagation channel in wireless communication systems plays a crucial role in the transmission and reception of signals, which makes its study imperative. A detailed understanding of its behavior is crucial for the development of more efficient and reliable systems, allowing the optimization of technologies and the adequate confrontation of the challenges imposed by the different propagation conditions. Several phenomena can limit signal propagation, often resulting in degradation of the quality of communications. Among these phenomena, large-scale fading and small-scale fading stand out. Large-scale fading, also known as shadowing, occurs when obstacles block the path of radio waves, resulting in a slow fluctuation of the signal. It is widely accepted in the literature that the statistical behavior of this type of fading can be described by the Lognormal distribution. Small-scale fading is caused by multipath, which arises due to phenomena such as diffraction, reflection, and scattering of the signal. The literature is abundant in the description of distributions used to model this type of fading. Among the main ones, the Rayleigh, Rice, Nakagami-m, alpha-mu, kappa-mu, and eta-mu distributions stand out. With the evolution of wireless communication systems to advanced generations (5G, 6G, and beyond), the accommodation of multiple services and varied applications, demanding high transmission rates, requires the use of wider bands, available in higher ranges of the spectrum (gigahertz - GHz - and terahertz - THz). Although the propagation channel is reasonably well characterized in the lower portions of the spectrum, where wireless communication systems normally operate, the use of higher frequencies, such as in the GHz and THz range, can introduce diverse phenomena, which at lower frequencies have little effect on the propagated signal. In these scenarios, classical fading models often prove inadequate to capture the specific characteristics of high-frequency communications, which demands new approaches capable of contemplating the particularities of these emerging environments. One way to satisfy this requirement is to include new parameters that model the various phenomena present in the propagation environment. Among the most comprehensive small-scale complex (phase and quadrature) models of the wireless communications environment, the alpha-eta-kappa-mu model stands out. This model includes various and relevant phenomena, such as the nonlinearity of the environment, power of the scattered waves, power of the dominant components, and multipath clustering, the last three defined for both the in-phase and quadrature components. This granularity provides enormous flexibility to the model, making it suitable for applications in an extended range of the spectrum. However, it is still necessary to develop other approaches that, like the alpha-eta-kappa-mu model, better encompass the relevant fading phenomena. Specifically, models that explore different perspectives for the nonlinearity of the medium are needed, enabling the creation of fading models that, despite having a degree of complexity similar to that of alpha-eta-kappa-mu, and its particular cases, maintain mathematical viability in the first and second-order statistics. Due to the alternative treatment of the nonlinearity of the medium, it is conjectured that, for certain wireless communications applications, these new models may adapt better than those existing in the literature.