Communications and Signal Processing Lab (ComSP)

Title	Análisis de prestaciones en canales con desvanecimientos de tipo kappa-mu shadowed
State	Finished
Author	Celia García Corrales
Director/s	José Francisco París Ángel ,  Francisco Javier Cañete Corripio
University	Universidad de Málaga
Center	Escuela Técnica Superior de Ingeniería de Telecomunicación
Department	Ingeniería de Comunicaciones
Reading date	14/07/2021

In recent years, there has been extensive deployment of wireless communications in both land and underwater environments. There is a continuous demand for systems that provide high user mobility and data rates, so the research and characterization of unguided propagation continues to be a topic of great interest. In these scenarios, the channels change frequently and the received signal fluctuates with time and with small displacements, process known as fading. Fading modelling is a key aspect to estimate the performance of a communication system and, due to complexity, a statistical approach is often followed.

This thesis focuses on the study of performance parameters for statistical channel models that characterize fading in SISO wireless communication systems, where narrow-band behaviour can be assumed and the κ-μ shadowed model is the cornerstone of the research work.

For this model, we have found closed analytical expressions for the ergodic Capacity, C, which measures the information rate that can be reliably transmitted through the channel, and for the Amount of Fading, AoF, which quantifies the magnitude of the fading. The ergodic capacity is expressed as a two-variable Meijer-G function that is not implemented in popular mathematical software packages such as Mathematica or Matlab. In order to evaluate C, the function ��1,0 ∶ 2,2 ∶ 1,20,1 ∶ 1,2 ∶ 1,1(·) has been implemented in Mathematica, the tool used for simulations and numerical evaluations in this thesis. The AoF is represented by a simple expression and, due to its inverse relationship with C, it allows to determine in a simple manner the trends of C with the fading parameters of the model.

In order to highlight the flexibility of the κ-μ shadowed model to represent fading in different scenarios and communication systems, it has been applied to an underwater acoustic communications (UAC) environment and to a cellular radio communications scenario.

In the first case, a set of UAC channels of ultrasonic frequencies in shallow waters have been characterized by the κ-μ shadowed and Rice distributions, measured by our Research Group Ingeniería de Comunicaciones and the company Sociedad Anónima de Electrónica Submarina (SAES). The Rice model has been selected as one of the most common in short-range UAC communications. Comparing both approaches, the results show that the fit achieved with the κ-μ shadowed model is better.

In the second case, we have investigated the spatial average of the spectral efficiency in radio cellular networks, ��̅������, with a high density of base stations, and we have found a closed analytical expression under certain approximations. A stochastic geometry has been used to represent large-scale channel phenomena combined with the κ-μ shadowed model for small-scale fading. Due to the fact that, in these scenarios, the links distances are shorter, it is likely that a dominant component exists which has a positive impact on transmission. The increase in ��̅������ by this component have been studied depending on its power and small-scale shadowing. Likewise, the variation of ��̅������ with the fading parameters of the model has been analysed and, also, the possibility of facilitating the knowledge of its trends through the behaviour of the AoF.

Continuing with the research on fading channels, the so-called hyper-Rayleigh (HR) behaviour has been investigated, which is associated with a channel with worse-than Rayleigh fading. A new framework has been proposed to define this characteristic, based on three magnitudes: the amount of fading, the asymptotic outage probability and the asymptotic ergodic capacity, and a metric of three conditions has been established. Depending on the number of conditions that the channel model meets, its HR behaviour is classified on a four-level scale, that corresponds to the greater or lesser suitability of that distribution to scenarios with deep fading. When a model is defined by statistical functions that depend on several parameters, it can present different HR levels according to the value of its parameters. This is related to a greater flexibility of the model to fit to a wide set of scenarios. In such cases, to represent graphically the HR level according to the parameter values, the so-called ‘HR map’ has been proposed.

This classification framework has been applied to the κ-μ shadowed model, which exhibits the four HR levels, highlighting its suitability to very different scenarios. The HR behaviour has also been studied on the distributions derived from it: one-sided Gaussian, Nakagami-m, Hoyt, Rice, Ricean shadowed, κ-μ and η-μ, as well as on the FTR model.