Cognitive radios (CRs) have been proposed as a promising solution for improving spectrum utilization via opportunistic spectrum sharing. In a CR network environment, primary (licensed) users have priority over secondary (unlicensed) users when accessing the wireless channel. Thus, if a malicious secondary user exploits this spectrum access etiquette by mimicking the spectral characteristics of a primary user, it can gain priority access to a wireless channel over other secondary users. This scenario is referred to in the literature as primary user emulation (PUE). This dissertation first covers three approaches for detecting primary user emulation attacks in cognitive radio networks, which can be classified in two categories. The first category is based on cyclostationary features, which employs a cyclostationary calculation to represent the modulation features of the user signals. The calculation results are then fed into an artificial neural network for classification. The second category is based on video processing method of action recognition in frequency domain, which includes two approaches. Both of them analyze the FFT sequences of wireless transmissions operating across a cognitive radio network environment, as well as classify their actions in the frequency domain. The first approach employs a covariance descriptor of motion-related features in the frequency domain, which is then fed into an artificial neural network for classification. The second approach is built upon the first approach, but employs a relational database system to record the motion-related feature vectors of primary users on this frequency band. When a certain transmission does not have a match record in the database, a covariance descriptor will be calculated and fed into an artificial neural network for classification. This dissertation is completed by a novel PUE detection approach which employs a distributed sensor network, where each sensor node works as an independent PUE detector. The emphasis of this work is how these nodes collaborate to obtain the final detection results for the whole network. All these proposed approaches have been validated via computer simulations as well as by experimental hardware implementations using the Universal Software Radio Peripheral (USRP) software-defined radio (SDR) platform.

With a growing demand for spectrum availability, spectrum sharing has become a high-profile solution to overcrowding. In order to enable spectrum sharing between incumbent/primary and secondary users, incumbents must have spectrum protection and privacy from malicious new entrants. In this Spectrum Access System (SAS) advancement, Primary Users (PUs) are obfuscated with the efforts of the SAS and the cooperation of obedient new entrants. Further, the necessary changes to the SAS to support this privacy scheme are exposed to suggest improvements in PU privacy, Citizens Broadband Radio Service Device (CBSD)-SAS relations, and punishment for unauthorized transmission. Results show the feasibility for PU obfuscation with respect to malicious spectrum sensing users. Simulation results indicate that the obfuscation scheme can deliver location and frequency occupation privacy with 75% and 66% effectiveness respectively in a 100% efficient spectrum utilization oriented obfuscation scheme. A scheme without spectrum utilization constraint shows up to 91% location privacy effectiveness. Experiment trials indicate that the privacy tactic can be implemented on an open-source SAS, however environmental factors may degrade the tactic's performance. / Master of Science / With a growing demand for spectrum availability, wireless spectrum sharing has become a high-profile solution to spectrum overcrowding. In order to enable spectrum sharing between incumbent/primary (e.g.,federal communications, naval radar, users already grandfathered into the band) and secondary users (e.g., commercial communications companies), incumbents must have spectrum protection and privacy from malicious new entrants. In this Spectrum Access System (SAS) advancement, Primary Users (PUs) are obfuscated with the efforts of the incumbent informed SAS and the cooperation of obedient new entrants. Further, the necessary changes to the SAS to support this privacy scheme are exposed to suggest improvements in PU privacy, Citizens Broadband Radio Service Device (CBSD)-SAS relations, and punishment for unauthorized transmission. Results show the feasibility of PU obfuscation with respect to malicious spectrum sensing users. Simulation results indicate that the obfuscation tactic can deliver location and frequency occupation privacy with 75% and 66% effectiveness respectively in a 100% efficient spectrum utilization oriented obfuscation scheme. A scheme without spectrum utilization constraint shows up to 91% location privacy effectiveness. Experiment trials indicate that the privacy tactic can be implemented on an open-source SAS, however environmental factors may degrade the tactic's performance.

Cognitive radio (CR) is one of the most prominent technique to deal with the radio spectrum scarcity problem. CR systems can improve radio spectrum utilization by opportunistically accessing the underutilized spectrum resource of the licensed users. In interweave implementation, the secondary user (SU) has to wait and locate spectrum holes before its transmission. Therefore, the extended delivery time (EDT) for the secondary user consist of both wait slots and transmission slots. We study the EDT analysis of fixed size secondary packet transmission over multiple primary channel. In particular, we introduce a birth-death based approach to model the cognitive transmission of the secondary user over multiple primary channels. We use this approach to derive the exact probability density function and probability mass function of EDT of the secondary transmission for both continuous and periodic sensing cases. We also present selected numerical and simulation results to verify our analytical approach and to illustrate the mathematical formulation. / Graduate

Wireless communication is facing an increasingly severe spectrum scarcity problem. Hybrid free space optical (FSO)/ millimetre wavelength (MMW) radio frequency (RF) systems and cognitive radios are two candidate solutions. Hybrid FSO/RF can achieve high data rate transmission for wireless back haul. Cognitive radio transceivers can opportunistically access the underutilized spectrum resource of existing systems for new wireless services. In this work we carry out accurate performance analysis on these two transmission techniques. In particular, we present and analyze a switching based transmission scheme for a hybrid FSO/RF system. Specifically, either the FSO or RF link will be active at a certain time instance, with the FSO link enjoying a higher priority. We consider both a single threshold case and a dual threshold case for FSO link operation. Analytical expressions are obtained for the outage probability, average bit error rate and ergodic capacity for the resulting system. We also investigate the delay performance of secondary cognitive transmission with interweave implementation. We first derive the exact statistics of the extended delivery time, that includes both transmission time and waiting time, for a fixed-size secondary packet. Both work-preserving strategy (i.e. interrupted packets will resume transmission from where interrupted) and non-work-preserving strategy (i.e. interrupted packets will be retransmitted) are considered with various sensing schemes. Finally, we consider a M/G/1 queue set-up at the secondary user and derive the closed-form expressions for the expected delay with Poisson traffic. The analytical results will greatly facilitate the design of the secondary system for particular target application. / Graduate

Made available in DSpace on 2014-12-17T15:43:55Z (GMT). No. of bitstreams: 1 MarciaCSP_DISSERT.pdf: 958298 bytes, checksum: 682327afdd332f7ff86be1e18e700c66 (MD5) Previous issue date: 2013-12-19 / O presente estudo tem por objetivo avaliar a satisfa??o dos usu?rios em rela??o ? qualidade da Aten??o Prim?ria ? Sa?de no Rio Grande do Norte. Trata-se de Pesquisa Avaliativa observacional transversal, com abordagem quantitativa, a qual faz parte da Avalia??o Externa do Programa de Melhoria do Acesso e da Qualidade da Aten??o B?sica (PMAQ), da Universidade Federal do Rio Grande do Norte. Foram utilizados dados secund?rios de todas as entrevistas com usu?rios das equipes que participaram da Avalia??o Externa do PMAQ no Estado do RN. A pesquisa foi realizada em 167 munic?pios do Estado do Rio Grande do Norte, na qual a popula??o foi composta por 1.650 usu?rios. A amostra se deu por conveni?ncia a partir dos seguintes crit?rios: usu?rios que estavam presentes na Unidade B?sica de Sa?de (UBS) para realizar qualquer tipo de procedimento e que consentisse em participar da avalia??o. Foram exclu?dos os que tinham ido pela primeira vez na unidade e aqueles que n?o frequentaram h? mais de 12 meses. A coleta dos dados foi realizada no per?odo de setembro a novembro de 2013. Para tanto, foi elaborado um protocolo de pesquisa contendo as seguintes dimens?es: organizacional, interpessoal e estrutural. Em rela??o ? dimens?o organizacional os resultados mostram que a marca??o de consultas tem se configurado em empecilho ao acesso do usu?rio ao servi?o de sa?de, uma vez que se faz necess?rio para o atendimento, enfrentar filas, antes da abertura da unidade para pegar fichas. No tocante ao funcionamento da unidade, se destaca o fato dos usu?rios referirem que o hor?rio de funcionamento da unidade atende ? suas necessidades, apesar de funcionar 5 (cinco) dias por semana, a maioria das unidades permanece fechada no hor?rio de almo?o. Outro dado importante refere-se ? coordena??o do cuidado, cujos resultados apresentam diferen?as maiores entre os usu?rios da regi?o metropolitana e do interior do Estado em rela??o ? Capital. Essa diferen?a se expressa principalmente em rela??o de marca??o de consulta com outros profissionais especialistas. A dimens?o interpessoal, no que diz respeito ? categorias intera??o usu?rio-servi?o-equipe e v?nculo, demonstraram alguns avan?os, contudo os melhores resultados foram observados em rela??o a satisfa??o com o cuidado, onde mais de 50% dos usu?rios se mostraram satisfeitos com o cuidado recebido nas unidades. Em contrapartida, o estudo mostrou que, na opini?o de 56% dos usu?rios da capital, a falta de materiais e equipamentos influencia negativamente no cuidado. Por fim, o estudo contribuiu para refor?ar a ideia de que a avalia??o da satisfa??o dos usu?rios dos servi?os de sa?de pode ser uma ferramenta importante para subsidiar o processo de decis?o compartilhada, de forma a se repensar as pr?ticas profissionais, reorganizar o processo de trabalho desenvolvido, realocar recursos, readequar a??es e redefinir objetivos que estejam coerentes com o projeto de sa?de estabelecido

Thesis( M. A. (Computer Science)) -- University of Limpopo , 2021 / In Software Defined Cognitive Radio Network (SDCRN), network security is a significant issue. This issue arises when Software Defined Network (SDN) architecture integrates with the Cognitive Radio Network (CRN) technology. SDN is designed to improve network resource management, while CRN technology is meant at improving spectrum management. These technologies are vulnerable to several malicious attacks. These attacks include Distributed Denial of Service (DDoS) and Primary User Emulation (PUE). Both the DDoS and PUE can be disrupt services in the SDCRN. To curb these attacks, schemes which hardens the security of SDCRN need to be designed. Thus, in this study we propose a security mechanism called Extreme_Controller_Mechanism (XCM) that reduce the effects of DDoS and PUE. The proposed XCM scheme was designed and evaluated in three simulation environment, the OMNeT++, Octave, and MATLAB simulators. The SDCRN data set was generated using the Neural Network back propagation algorithms. The data set was then used in Matlab to evaluate the effectiveness of the prosed XCM scheme. XCM proved to be effective and efficient at detection and prevention of DDoS and PUE attacks in SDCRN. In terms of memory and processor utilisation, XCM proved to the best when compared to other schemes such as the Advanced Support Vector Machine (ASVM) and deep learning convolution network (CDLN). But in terms of detection time, the ASVM was found to be the best performing scheme. Regarding our test for detection rate, false positive and false negative, the XCM, ASVM and CDLM performed the same. The results of the XCM were therefore the best and superior to the ASVM and CDLM. This can be attributed to the fact that the XCM scheme is optimised for DDoS and PUE attacks. We can therefore conclude that our XCM scheme is the best performing scheme compared to the ASVM and CDLN schemes.

The tremendous success of various wireless applications operating in unlicensed bands has resulted in the overcrowding of those bands. Cognitive radio (CR) is a new technology that enables an unlicensed user to coexist with incumbent users in licensed spectrum bands without inducing interference to incumbent communications. This technology can significantly alleviate the spectrum shortage problem and improve the efficiency of spectrum utilization. Networks consisting of CR nodes (i.e., CR networks)---often called dynamic spectrum access networks or NeXt Generation (XG) communication networks---are envisioned to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. In recent years, the operational aspects of CR networks have attracted great research interest. However, research on the security aspects of CR networks has been very limited. In this thesis, we discuss security issues that pose a serious threat to CR networks. Specifically, we focus on three potential attacks that can be launched at the physical or MAC layer of a CR network: primary user emulation (PUE) attack, spectrum sensing data falsification (SSDF) attack, and control channel jamming (CCJ) attack. These attacks can wreak havoc to the normal operation of CR networks. After identifying and analyzing the attacks, we discuss countermeasures. For PUE attacks, we propose a transmitter verification scheme for attack detection. The scheme utilizes the location information of transmitters together with their signal characteristics to verify licensed users and detect PUE attackers. For both SSDF attacks and CCJ attacks, we seek countermeasures for attack mitigation. In particular, we propose Weighted Sequential Probability Ratio Test (WSPRT) as a data fusion technique that is robust against SSDF attacks, and introduce a multiple-rendezvous cognitive MAC (MRCMAC) protocol that is robust against CCJ attacks. Using security analysis and extensive numerical results, we show that the proposed schemes can effectively counter the aforementioned attacks in CR networks. / Ph. D.