Performance Analysis of Non-Ideal MIMO Systems in Fading Channels

En esta tesis se aborda el análisis de prestaciones de sistemas MIMO bajo ciertas condiciones no ideales. Se han considerado limitaciones realistas como son las interferencias co-canal, el canal de retorno con velocidad limitada, y la correlación espacial entre antenas. Bajo estas condiciones, se han analizado las probabilidades de error y de outage para sistemas MIMO que incluyen técnicas de conformación de haz en el transmisor y/o distintas técnicas de diversidad espacial en el receptor. Con el fin de obtener expresiones cerradas y exactas par los indicadores de rendimiento mencionados, se han desarrollo nuevos métodos o herramientas matemáticas que facilitan o, en algunos casos, hacen posible el análisis. En primer lugar, se han obtenido nuevas expresiones cerradas para las integrales del tipo Lipschitz-Hankel y para la distribución de los elementos de la diagonal de matrices Wishart complejas. Posteriormente, estos resultados han sido aplicados al análisis de prestaciones de distintos sistemas MIMO en condiciones no-ideales. Concretamente, se han obtenido nuevas expresiones cerrradas de la probabilidad de outage para: sistemas MRC con interferencia co-canal, sistemas MIMO con correlación espacial entre antenas, y sistemas MIMO MRC con un canal de retorno limitado en velocidad. Además, se han obtenido expresiones cerradas para la probabilidad de error en sistemas de diversidad en recepción que emplean modulaciones no coherentes y no ortogonales

GPU-SUPPORTED SIMULATION FOR ABEP AND QOS ANALYSIS OF A COMBINED MACRO DIVERSITY SYSTEM IN A GAMMA-SHADOWED K-µ FADING CHANNEL

In this paper we have analyzed macro-diversity (MD) system with one macro SC diversity (MD SC) receiver and two micro MRC (mD MRC) receivers over correlated Gamma-shadowed k-µ fading channel. The average bit error probability (ABEP) is calculated using the moment generating function (MGF) approach for BDPSK and BPSK modulations. Graphical representation of the results illustrates the effects of different parameters of the system on its performance as well as the improvements due to the benefits of a combined micro and macro diversity. The obtained analytical expressions are used for the GPU-enabled mobile network modeling, planning and simulation environment to determine the value of Quality of Service (QoS) parameter. Finally, linear optimization is proposed as an approach to improve the QoS parameter of the fading-affected system observed in this paper

Wireless networks physical layer security : modeling and performance characterization

Intrigued by the rapid growth and expand of wireless devices, data security is increasingly playing a significant role in our daily transactions and interactions with different entities. Possible examples, including e-healthcare information and online shopping, are becoming vulnerable due to the intrinsic nature of wireless transmission medium and the widespread open access of wireless links. Traditionally, the communication security is mainly regarded as the tasks at the upper layers of layered protocol stack, security techniques, including personal access control, password protection, and end-to-end encryption, have been widely studied in the open literature. More recently, plenty of research interests have been drawn to the physical layer forms of secrecy. As a new but appealing paradigm at physical layer, physical layer security is based on two pioneering works: (i) Shannon’s information-theoretic formulation and (ii) Wyner’s wiretap formulation. On account of the fundamental of physical layer security and the different nature of various wireless network, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three-fold:(i) exploration of secrecy metrics to more general fading channels; (ii) characterization a new fading channel model and its reliability and security analysis in digital communication systems; and (iii) investigation of physical layer security over the random multiple-input multiple-output (MIMO) α −μ fading channels. Taking into account the classic Alice-Bob-Eve wiretap model, the first contribution can be divided into four aspects: (i) we have investigated the secrecy performance over single-input single-output (SISO) α −μ fading channels. The probability of non-zero (PNZ) secrecy capacity and the lower bound of secrecy outage probability (SOP) are derived for the special case when the main channel and wiretap channel undergo the same non-linearity fading parameter, i.e., α. Later on, for the purpose of filling the gap of lacking closed-form expression of SOP in the open literature and extending the obtained results in chapter 2 to the single-input multiple-output (SIMO) α − μ wiretap fading channels, utilizing the fact that the received signal-tonoise ratios (SNRs) at the legitimate receiver and eavesdropper can be approximated as new α −μ distributed random variables (RVs), the SOP metric is therefore derived, and given in terms of the bivariate Fox’s H-function; (ii) the secrecy performance over the Fisher-Snedecor F wiretap fading channels is initially considered. The SOP, PNZ, and ASC are finalized in terms of Meijer’s G-function; (iii) in order to generalize the obtained results over α −μ and Fisher-Snedecor F wiretap fading channels, a more flexible and general fading channel, i.e., Fox’s H-function fading model, are taken into consideration. Both the exact and asymptotic analysis of SOP, PNZ, and average secrecy capacity (ASC), are developed with closed-form expressions; and (iv) finally, motivated by the fact that the mixture gamma (MG) distribution is an appealing tool, which can be used to model the received instantaneous SNRs over wireless fading channels, the secrecy metrics over wiretap fading channels are derived based on the MG approach. Due to the limited transmission power and communication range, cooperative relays or multi-hop wireless networks are usually regarded as two promising means to address these concerns. Inspired by the obtained results in Chapters 2 and 3, the second main contribution is to propose a novel but simple fading channel model, namely, the cascaded α −μ. This new distribution is advantageous since it encompasses the existing cascaded Rayleigh, cascaded Nakagami-m, and cascaded Weibull with ease. Based on this, both the reliability and secrecy performance of a digital system over cascaded α −μ fading channels are further evaluated. Closed-form expressions of reliability metrics (including amount of fading (AF), outage probability, average channel capacity, and average symbol error probability (ABEP).) and secrecy metrics (including SOP, PNZ, and ASC) are respectively provided. Besides, their asymptotic behaviors are also performed and compared with the exact results. Considering the impacts of users’ densities, spatial distribution, and the path-loss exponent on secrecy issue, the third aspect of this thesis is detailed in Chapter 8 as the secrecy investigation of stochastic MIMO system over α −μ wiretap fading channels. Both the stochastic geometry and conventional space-time transmission (STT) scheme are used in the system configuration. The secrecy issue is mathematically evaluated by three metrics, i.e., connection outage, the probability of non-zero secrecy capacity and the ergodic secrecy capacity. Those three metrics are later on derived regarding two ordering scheme, and further compared with Monte-Carlo simulations

Performance analysis of energy detector over generalised wireless channels in cognitive radio

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.This thesis extensively analyses the performance of an energy detector which is widely employed to perform spectrum sensing in cognitive radio over different generalised channel models. In this analysis, both the average probability of detection and the average area under the receiver operating characteristic curve (AUC) are derived using the probability density function of the received instantaneous signal to noise ratio (SNR). The performance of energy detector over an ŋ --- µ fading, which is used to model the Non-line-of-sight (NLoS) communication scenarios is provided. Then, the behaviour of the energy detector over к --- µ shadowed fading channel, which is a composite of generalized multipath/shadowing fading channel to model the lineof- sight (LoS) communication medium is investigated. The analysis of the energy detector over both ŋ --- µ and к --- µ shadowed fading channels are then extended to include maximal ratio combining (MRC), square law combining (SLC) and square law selection (SLS) with independent and non-identically (i:n:d) diversity branches. To overcome the problem of mathematical intractability in analysing the energy detector over i:n:d composite fading channels with MRC and selection combining (SC), two different unified statistical properties models for the sum and the maximum of mixture gamma (MG) variates are derived. The first model is limited by the value of the shadowing severity index, which should be an integer number and has been employed to study the performance of energy detector over composite α --- µ /gamma fading channel. This channel is proposed to represent the non-linear prorogation environment. On the other side, the second model is general and has been utilised to analyse the behaviour of energy detector over composite ŋ --- µ /gamma fading channel. Finally, a special filter-bank transform which is called slantlet packet transform (SPT) is developed and used to estimate the uncertain noise power. Moreover, signal denoising based on hybrid slantlet transform (HST) is employed to reduce the noise impact on the performance of energy detector. The combined SPT-HST approach improves the detection capability of energy detector with 97% and reduces the total computational complexity by nearly 19% in comparison with previously implemented work using filter-bank transforms. The aforementioned percentages are measured at specific SNR, number of selected samples and levels of signal decompositionMartyrs Foundatio

On the connection between noncircularly-symmetric and noncentral fading models: univariate and multivariate analysis

This thesis provides new statistical connections between noncircularly-symmetric central and circularly-symmetric noncentral underlying complex Gaussian models. This is particularly interesting since it facilitates the analysis of noncircularly-symmetric models, which are often underused despite their practical interest, since their analysis is more challenging. Although these statistical connections have a wide range of applications in different areas of univariate and multivariate analysis, this thesis is framed in the context of wireless communications, to jointly analyze noncentral and noncircularly-symmetric fading models. We provide an unified framework for the five classical univariate fading models, i.e. the one-sided Gaussian, Rayleigh, Nakagami-m, Nakagami-q and Rician, and their most popular generalizations, i.e the Rician shadowed, η-µ, κ-µ and κ-µ shadowed. Moreover, we present new simple results regarding the ergodic capacity of single-input single-output systems subject to κ-µ shadowed, κ-µ and η-µ fadings. With applications to multiple-input multiple-output communications, we are interested in matrices of the form W=XX^H (or W=X^HX), where X is a complex Gaussian matrix with unequal variance in the real and imaginary parts of its entries, i.e., X belongs to the noncircularly-symmetric Gaussian subclass. By establishing a novel connection with the well-known complex Wishart ensemble, we facilitate the statistical analysis of W and give new insights on the effects of such asymmetric variance profile

On the Performance of Terrestrial Free-Space Optical (FSO) Links under the Presence of Generalized Pointing Errors

En ambos grupos se han obtenido expresiones matemáticas en forma cerrada que permiten evaluar la capacidad en todo el rango de valores de SNR (Signal-to-Noise Ratio) en algunos casos y, en otros, solo ha sido posible obtener su comportamiento asintótico debido a la dificultad matemática que presentaba el análisis. A la luz de los resultados obtenidos, podemos concluir que los sistemas MISO FSO son probablemente la solución más interesante en comparación a los sistemas SIMO y MIMO FSO. Al mismo tiempo, los resultados obtenidos en comunicaciones cooperativas permiten concluir que los sistemas cooperativos basados en retransmisión DF son capaces de aumentar la capacidad e incluso mejorar a la capacidad obtenida por un sistema basado en diversidad espacial para determinadas posiciones del nodo retransmisor. En el caso de las contribuciones realizadas en el modelado de errores por desapuntamiento generalizado, los cuales siguen una distribución Beckmann, podemos destacar la aproximación propuesta en esta tesis que nos permite incluir de una forma eficiente y sencilla dichos errores por desapuntamiento al análisis de prestaciones de cualquier sistema de comunicaciones FSO. La herramienta propuesta es válida para analizar cualquier sistema FSO en términos de BER y probabilidad de outage y nos permite detectar qué efecto es dominante, es decir, si la turbulencia atmosférica o los errores por desapuntamiento. El efecto de la correlación también ha sido contemplado, concluyendo que no puede ser ignorado.Los sistemas de comunicaciones ópticas en espacio libre (FSO, Free-Space Optical) para aplicaciones terrestres se presentan en la actualidad como una solución muy interesante para solventar el importante reto provocado por la escasez del espectro RF (Radio-Frequency) disponible. Además, los sistemas FSO se configuran como una seria alternativa frente a otras tecnologías de acceso y transporte como los sistemas de RF debido a las altas tasas de señalización potencialmente muy superiores que se pueden conseguir. Estas ventajas, entre otras, han intensificado la investigación en estos sistemas en las últimas décadas. Por tanto, el análisis de sus prestaciones en términos de probabilidad de error de bit (BER, Bit Error-Rate), probabilidad de outage y capacidad ergódica es de interés relevante, siendo estas altamente afectadas por la turbulencia atmosférica, los errores por desapuntamiento entre transmisor y receptor así como por la niebla densa. En esta tesis, el análisis de las prestaciones de los sistemas FSO ha sido abordado, presentando novedosos resultados para la comunidad científica e investigadora. Dicho análisis de prestaciones se ha dividido en dos grandes áreas de investigación: análisis de la capacidad ergódica, y modelado de errores por desapuntamiento generalizado entre transmisor y receptor. Las contribuciones realizadas dentro del análisis de la capacidad ergódica están divididas en dos grupos: por un lado, el análisis de la capacidad de sistemas FSO avanzados basados en diversidad espacial tales como los sistemas MISO (Multiple-Input/Single-Output), SIMO (Single-Input/Multiple-Output) y MIMO(Multiple-Input/Multiple-Output) FSO; por otro lado, el análisis de la capacidad de sistemas cooperativos basados en retransmisión DF (Detect-and-Forward)

Sobre a capacidade-soma e a probabilidade de bloqueio em canais de múltiplos usuários equipados com múltiplas antenas

Orientadores: Gustavo Fraidenraich, Behnaam AazhangTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O uso de múltiplas antenas em comunicações sem fio permitiu, inicialmente, garantir que um sinal transmitido fosse recebido com maior energia, o que diretamente aumenta a probabilidade de sucesso na recuperação dos dados transmitidos. Posteriormente, foi possível aumentar a capacidade de uma comunicação sem fio utilizando múltiplas antenas transmitindo e recebendo ao mesmo tempo. Atualmente, os dispositivos móveis como telefones celulares e computadores pessoais já são equipados com múltiplas antenas garantindo uma flexibilidade entre taxas maiores, quando as condições são favoráveis, ou aumento da confiabilidade de recepção, em condições menos favoráveis. Além dos graus de liberdade trazidos com a utilização de múltiplas antenas para uma comunicação ponto-a-ponto, os benefícios para uma rede onde um ou mais elementos façam uso destas é notável. Neste trabalho, apresentamos um estudo sobre o impacto do uso de múltiplas antenas em diversos tipos de redes compostas por múltiplos usuários fazendo uso do canal sem fio ao mesmo tempo. Como será visto, em algumas situações o objetivo será reduzir a probabilidade de que ocorra uma falha na comunicação, havendo ou não interferência. Em outras situações, faremos um estudo da capacidade soma de vários usuários ao transmitirem ao mesmo tempo. Em todos os casos, o conhecimento ou não do canal no transmissor é fator determinante para decidir como os sinais serão distribuídos nas múltiplas antenas do transmissor e se estes estarão sujeitos a uma probabilidade de bloqueio ou uma determinada capacidade. Em todos os casos, para uma dada configuração da rede (número de transmissores, receptores), iremos obter a métrica adequada em função da relação sinal ruído e apresentaremos uma modelagem teórica do problema comparando os resultados propostos com simulações de forma a validar estes resultadosAbstract: The first use of multiple antennas in wireless communications aimed to the improvement of the reliability of a transmission by improving the signal to noise ratio at receiver. More energy of the desired signal means that the receiver has higher probability to correctly decode the transmitted signal. Later, it was possible to increase the capacity of a wireless communication by the use of multiple antennas to transmit and receive at the same time. Nowadays, even the inexpensive mobile devices such as smartphones and personal computers are equipped with multiple antennas that provide flexibility between more data rate in favourable channel situations and more reliability in poor channel conditions. Besides the degrees of freedom that multiple antennas provide in single user communication, it dramatically increases the network data rate. In this work, we study the impact of multiple antennas in several multi-user scenarios with concurrent transmission. Whenever is possible, we provide closed-form expressions or approximations for outage probability or sum capacity depending on the type of network. The derived expressions allow us to quantify the impact of the number of users and number of antennas in the performance of the network. We quantify either outage or sum capacity in terms of signal-to-noise ratio for channels under fading conditionsDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia Elétrica10714/14-6CAPESBE

Uticaj nesavršene ekstrakcije referentnog nosioca na performanse diverziti prijemnika digitalno fazno modulisanih signala u kanalu sa fedingom

The results of the research, presented in this dissertation, refer to the analysis of imperfect reference signal recovery influence on performance of digital systems with BPSK and QPSK modulation and diversity at the reception applied. In order to make the content easy for understanding, the theoretical basics, necessary for calculations performed in the following chapters, has been presented at the beginning. In the analysis of the imperfect reference signalrecovery influence on the performance of single channel systems for BPSK and QPSK signal detection two cases have been considered. The analysis has been performed for Hoyt and composite Kg fading channel. ..

Ratio of Products of Mixture Gamma Variates with Applications to Wireless Communications Systems

The fading scenario of many realistic wireless communication transmission systems, such as, multi-hop communications and spectrum sharing in cognitive radio networks (CRNs), can be modelled by the product and the ratio of the product of the random variables (RVs) of the channel distribution. However, there is no work has been investigated in the literature to provide unified statistics of the product and the ratio of the products that can be used for a wide range of non-composite and composite fading conditions. Accordingly, in this paper, the statistical properties, namely, probability density function (PDF), cumulative distribution function (CDF), and moment generating function (MGF) of the product and the ratio of the product of independent and non-identically distributed (i.n.d.) mixture Gamma (MG) RVs are derived. A MG distribution has been widely employed to approximate with high accuracy most of the conventional fading models, for example, Rayleigh, Nakagami-m, Nakagami-q (Hoyt), and Nakagami-n (Rician) as well as the generalised composite fading channels, such as, generalised- (),− /gamma, − /gamma, and − /gamma. Hence, the derived PDF, CDF, and MGF are utilized for the Beaulieu–Xie and −−− shadowed fading channels that have not been yet presented by the previous works due to mathematical intractability of their statistics. Thus, the equivalent parameters of a MG distribution for these channels are given. To this end, simple closed-form mathematically tractable expressions of the performance metrics are obtained. The derived statistics are applied to analyse the outage probability (OP), the average error probability for different modulation schemes, the effective rate (ER) of wireless communication systems and the average area under the receiver operating characteristics (AUC) curve of energy detection over cascaded fading channels. Moreover, the OP of the multi-hop communications systems with co-channel interference (CCI), both the lower bound of secure OP (SOPL) and probability of non-zero secrecy capacity (PNSC) of the physical layer security (PLS), and the outage and delay-limited capacities of CRNs are studied via using the statistics of the ratio of the product of MG variates. A comparison between the numerical results and the Monte Carlo simulations is presented to verify the validation of our analysis