333 research outputs found

    Spectrum Sharing Opportunities of Full-Duplex Systems using Improper Gaussian Signaling

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    Sharing the licensed spectrum of full-duplex (FD) primary users (PU) brings strict limitations on the underlay cognitive radio operation. Particularly, the self interference may overwhelm the PU receiver and limit the opportunity of secondary users (SU) to access the spectrum. Improper Gaussian signaling (IGS) has demonstrated its superiority in improving the performance of interference channel systems. Throughout this paper, we assume a FD PU pair that uses proper Gaussian signaling (PGS), and a half-duplex SU pair that uses IGS. The objective is to maximize the SU instantaneous achievable rate while meeting the PU quality-of-service. To this end, we propose a simplified algorithm that optimizes the SU signal parameters, i.e, the transmit power and the circularity coefficient, which is a measure of the degree of impropriety of the SU signal, to achieve the design objective. Numerical results show the merits of adopting IGS compared with PGS for the SU especially with the existence of week PU direct channels and/or strong SU interference channels

    Interference Alignment for Cognitive Radio Communications and Networks: A Survey

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    © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Interference alignment (IA) is an innovative wireless transmission strategy that has shown to be a promising technique for achieving optimal capacity scaling of a multiuser interference channel at asymptotically high-signal-to-noise ratio (SNR). Transmitters exploit the availability of multiple signaling dimensions in order to align their mutual interference at the receivers. Most of the research has focused on developing algorithms for determining alignment solutions as well as proving interference alignment’s theoretical ability to achieve the maximum degrees of freedom in a wireless network. Cognitive radio, on the other hand, is a technique used to improve the utilization of the radio spectrum by opportunistically sensing and accessing unused licensed frequency spectrum, without causing harmful interference to the licensed users. With the increased deployment of wireless services, the possibility of detecting unused frequency spectrum becomes diminished. Thus, the concept of introducing interference alignment in cognitive radio has become a very attractive proposition. This paper provides a survey of the implementation of IA in cognitive radio under the main research paradigms, along with a summary and analysis of results under each system model.Peer reviewe

    Physical layer security in cognitive radio networks using improper gaussian signaling

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    Orientador: Prof. Dr. Evelio Martin Garcia FernandezCoorientador: Prof. Dr. Samuel Baraldi MafraTese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa : Curitiba, 25/10/2018Inclui referências: p.55-60Resumo: Em redes de comunicação sem fio que possuem restrições de interferência, a adoção de sinais assimétricos ou impróprios pode atingir taxas de transmissão mais altas do que as obtidas com sinais próprios, devido a maior entropia diferencial destes. Portanto, uma vez que o desempenho de segurança de uma rede está diretamente relacionado a taxa de transmissão de seus usuários, esta tese propõe o emprego de sinais impróprios para melhorar o desempenho do sigilo em redes de Radio Cognitivo. Ate onde sabemos, este e o primeiro trabalho que aborda a Segurança da Camada Física deste tipo de sistema usando sinais assimétricos. Os resultados foram obtidos para dois cenários diferentes em um mesmo modelo de sistema: uma rede cognitiva underlay com uma ligacao direta entre o transmissor secundário e seu receptor, cuja comunicação está sendo espionada. Usuários primários e secundários causam interferência entre si. Em ambos os cenários, apenas a informação estatística do estado do canal foi considerada disponível para os usuários cognitivos. Para o primeiro cenário, em que a localização dos nós do sistema foi definida arbitrariamente, derivamos uma expressao analótica para a Probabilidade de Falha de Sigilo, a principal métrica de desempenho analisada, e foi mostrado que a adoção de sinalização impropria pode ser benéfica tanto para os usuários que causam quanto para os que recebem interferência. Em um segundo cenário, em que a localização dos nos foi distribuída uniformemente sobre uma célula circular, encontramos valores ótimos ou sub-ótimos para a potencia de transmissão e grau de impropriedade dos sinais dos usuários secundários simultaneamente, a fim de otimizar o desempenho de segurança da rede. A otimização foi feita com o auxílio de Algoritmos Genéticos. Em seguida, os benefícios do esquema de transmissão em termos da probabilidade de falha de sigilo e da vazão de dados segura do sistema, bem como o custo de eficiência energética foram avaliados. Os resultados indicam que, para sistemas limitados por interferência, ao buscar por baixas probabilidades de falha de sigilo, e sempre uma estratégia melhor para os usuários secundários adotar algum grau de impropriedade em suas transmissões. Além disso, a adoção de sinais impróprios também pode melhorar as taxas seguras atingíveis no lado dos usuários cognitivos em redes underlay. No entanto, em termos de eficiência energética do sistema, otimizar apenas a potencia de transmissão secundaria e adotar sinais próprios obtém o melhor desempenho. Os resultados apresentados nesta pesquisa são promissores, uma vez que em muitas redes sem fio, inclusive cognitivas, existem restrições de interferência e sinais assimétricos poderiam alcançar um desempenho melhor do que os próprios, o paradigma atual. Palavras-chave: Radio Cognitivo, Segurança na Camada Física, SinaisAbstract: In interference constrained wireless communication networks, adopting asymmetric or improper signals may attain higher transmission rates than those achieved by proper ones, due to the higher differential entropy of the latter. Therefore, since the secrecy performance of a network is directly related to the transmission rate of its users, this thesis proposes employing improper signals in order to enhance the secrecy performance of Cognitive Radio networks. As far as we know, this is the first work that addresses the Physical Layer Security of these type of system by using asymmetric signals. The results were obtained for two different scenarios in the same system model: an underlay cognitive network with a direct link between secondary transmitter and receiver, whose communication is being eavesdropped. Both primary and secondary users cause interference at each other. In both scenarios only Statistical Channel State Information was considered available at the cognitive users. For the first scenario, in which nodes locations were defined arbitrarily, we derived an analytical expression for the Secrecy Outage Probability, the main performance metric analyzed, and it was shown that adopting improper signaling can be beneficial for users either causing or receiving interference. In a second scenario, in which nodes locations were uniformly distributed over a circular cell, we found optimal or suboptimal values of the secondary users transmit power and degree of impropriety, concurrently, in order to optimize the secrecy performance, with the aid of Genetic Algorithms. Then, the benefits of the transmission scheme in terms of the Secrecy Outage Probability and the Secure Throughput of the system, as well as the Secure Energy Efficiency cost were assessed. Results indicate that, for systems with interference constraints, when searching for lower Secrecy Outage Probabilities, it is always a better strategy for the Secondary Users to adopt some degree of impropriety in their transmissions. In addition, adopting improper signals can also improve the achievable secure rates at the cognitive users side in underlay networks. However, in terms of the energy efficiency of the system, optimizing only the secondary transmit power while employing proper signals achieves the best performance. The results presented in this research are promising, since in many wireless channels, including Cognitive Networks, there are interference constraints and asymmetric signals could attain better performance than proper ones, the current paradigm. Keywords: Cognitive Radio Networks, Physical Layer Security, Improper Gaussian Signaling, Secrecy Outage Probability

    Rate splitting in MIMO RIS-assisted systems with hardware impairments and improper signaling

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    In this paper, we propose an optimization framework for rate splitting (RS) techniques in multiple-input multiple-output (MIMO) reconfigurable intelligent surface (RIS)-assisted systems, possibly with I/Q imbalance (IQI). This framework can be applied to any optimization problem in which the objective and/or constraints are linear functions of the rates and/or transmit covariance matrices. Such problems include minimum-weighted and weighted-sum rate maximization, total power minimization for a target rate, minimum-weighted energy efficiency (EE) and global EE maximization. The framework may be applied to any interference-limited system with hardware impairments. For the sake of illustration, we consider a multicell MIMO RIS-assisted broadcast channel (BC) in which the base stations (BSs) and/or the users may suffer from IQI. Since IQI generates improper noise, we consider improper Gaussian signaling (IGS) as an interference-management technique that can additionally compensate for IQI. We show that RS when combined with IGS can substantially improve the spectral and energy efficiency of overloaded networks (i.e., when the number of users per cell is larger than the number of transmit/receive antennas).The work of Ignacio Santamaria has been partly supported by the project ADELE PID2019-104958RB-C43, funded by MCIN/AEI/10.13039/501100011033. The work of Eduard Jorswieck was supported in part by the Federal Ministry of Education and Research (BMBF, Germany) in the program of “Souver¨an. Digital. Vernetzt.” joint project 6G-RIC, project identification number: 16KISK020K and 16KISK031

    NOMA-based improper signaling for multicell MISO RIS-assisted broadcast channels

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    In this paper, we study the performance of reconfigurable intelligent surfaces (RISs) in a multicell broadcast channel (BC) that employs improper Gaussian signaling (IGS) jointly with non-orthogonal multiple access (NOMA) to optimize either the minimum-weighted rate or the energy efficiency (EE) of the network. We show that although the RIS can significantly improve the system performance, it cannot mitigate interference completely, so we have to employ other interference-management techniques to further improve performance. We show that the proposed NOMA-based IGS scheme can substantially outperform proper Gaussian signaling (PGS) and IGS schemes that treat interference as noise (TIN) in particular when the number of users per cell is larger than the number of base station (BS) antennas (referred to as overloaded networks). In other words, IGS and NOMA complement to each other as interference management techniques in multicell RIS-assisted BCs. Furthermore, we consider three different feasibility sets for the RIS components showing that even a RIS with a small number of elements provides considerable gains for all the feasibility sets.The associate editor coordinating the review of this manuscript and approving it for publication was Prof. Sangarapillai Lambotharan. The work of Ignacio Santamaria was supported by the Project ADELE funded by MCIN/ AEI /10.13039/501100011033, under Grant PID2019-104958RB-C43. The work of Eduard Jorswieck was supported by the Federal Ministry of Education and Research (BMBF, Germany) through the Program of Souverän. Digital. Vernetzt.” joint Project 6G-RIC, under Grants 16KISK020K and 16KISK031
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