Sensing and Sharing Schemes for Spectral Efficiency of Cognitive Radios

Increase in data traffic, number of users and their requirements laid to a necessity of more bandwidth. Cognitive radio is one of the emerging technology which addresses the spectrum scarcity issue. In this work we study the advantage of having collaboration between cognitive enabled small cell network and primary macrocell. Different from the existing works at spectrum sensing stage we are applying enhanced spectrum sensing to avoid probability of false alarms and missed detections which has impact on spectral efficiency. Later power control optimization for secondary users known as Hybrid spectrum sharing is used for further improvement of spectral efficiency. Furthermore, the failed packets of Primary users are taken care by high ranked relays which in turn decreases the average Primary user packet delay by 20% when compared between assisted Secondary user method and non-assisted Secondary user method.

Benefits of improper signaling for underlay cognitive radio

In this letter we study the potential benefits of improper signaling for a secondary user (SU) in underlay cognitive radio networks. We consider a basic yet illustrative scenario in which the primary user (PU) always transmit proper Gaussian signals and has a minimum rate constraint. After parameterizing the SU transmit signal in terms of its power and circularity coefficient (which measures the degree of impropriety), we prove that the SU improves its rate by transmitting improper signals only when the ratio of the squared modulus between the SU-PU interference link and the SU direct link exceeds a given threshold. As a by-product of this analysis, we obtain the optimal circularity coefficient that must be used by the SU depending on its power budget. Some simulation results show that the SU benefits from the transmission of improper signals especially when the PU is not highly loaded.C. Lameiro and I. Santamaría have received funding from the Spanish Government (MICINN) under projects CONSOLIDER-INGENIO 2010 CSD2008-00010 (COMONSENS), TEC2013-47141-C4-3-R (RACHEL) and FPU Grant AP2010-2189; and also from the Deutscher Akademischer Austauschdienst (DAAD) under its programm ”Research grants for doctoral candidates and young academics and scientists”. P. Schreier receives financial support from the Alfried Krupp von Bohlen und Halbach foundation, under its program ”Return of German scientists from abroad”

Interference mitigation under degrees-of-freedom sensing uncertainties in opportunistic transmission

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Inter-system interference may limit the performance of co-existing systems in dense heterogeneous wireless networks. Context-aware waveform design can profitably overcome this limitation. However, the latter substantially depends on degrees-of-freedom (DoF) sensing mechanisms. In this work, we show that total least-squares (TLS)-based waveform design is robust against sensing uncertainties. Given the equivalence of minimum norm and TLS, the latter exhibits the good properties of linear predictors, which are of paramount importance to guarantee minimum inter-system interference and detectability by neighboring nodes. Additionally, since derived solution relies on orthogonal projector onto the so- called noise subspace, we can efficiently and iteratively construct an orthogonal waveform-book enabling the presented transmission scheme in multi-carrier scenarios. Simulation results are presented to support our theoretical contributions, and to highlight any potential advantage of proposed solution in crowded heterogenous wireless networks.This work has been supported by the Spanish Ministry of Science, Innovation and Universities through project WINTER: TEC2016-76409-C2-1-R (AEI/FEDER, UE) and fellowship FPI BES-2017-080071, and by the Catalan Government (AGAUR) under grant 2017 SGR 578.Peer ReviewedPostprint (published version

Physical layer security in cognitive radio networks using improper gaussian signaling

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

Improper Gaussian signaling for multiple-access channels in underlay cognitive radio

This paper considers an unlicensed multiple-access channel (MAC) that coexists with a licensed point-to-point user, following the underlay cognitive radio paradigm. We assume that every transceiver except the secondary base station has one antenna and that the primary user (PU) is protected by a minimum rate constraint. In contrast to the conventional assumption of proper Gaussian signaling, we allow the secondary users to transmit improper Gaussian signals, which are correlated with their complex conjugate. When the secondary base station performs zero-forcing, we show that improper signaling is optimal if the sum of the interference channel gains (in an equivalent canonical model) is above a certain threshold. Additionally, we derive an efficient algorithm to compute the transmission parameters that attain the rate region boundary for this scenario. The proposed algorithm exploits a single-user representation of the secondary MAC along with new results on the optimality of improper signaling in the single-user case when the PU is corrupted by an improper noise.The work of C. Lameiro and P. J. Schreier was supported by the German Research Foundation (DFG) under grants SCHR 1384/6-1 and LA 4107/1-1. The work of I. Santamaría was supported by the Ministerio de Economía y Competitividad (MINECO) and AEI/FEDER funds of the UE, Spain, under projects RACHEL (TEC2013-47141-C4-3-R) and CARMEN (TEC2016-75067-C4-4-R)

Contributions to Resource Allocation in Cognitive Radio Networks

The continuous increase in the number of wireless devices and the huge demand for higher data rates have promoted the development of new wireless communications technologies with improved spectrum sharing features. Recently, the concept of cognitive radio (CR) has gained increased popularity for the efficient utilization of radio frequency (RF) spectrum. A CR is characterized as a communication system which is capable to learn the spectrum environment through sensing, and to adapt its signaling schemes for a better utilization of the radio frequency resources. Resource allocation, which involves scheduling of spectrum and power resources, represents a crucial problem for the performance of CR networks in terms of system throughput and bandwidth utilization. In this dissertation, we investigate resource allocation problems in a CR network by exploring a variety of optimization techniques. Specifically, in the first part of the dissertation, our goal is to maximize the total throughput of secondary users (SUs) in an orthogonal frequency division multiple access (OFDMA) CR network. In addition, the power of SUs is controlled to keep the interference introduced to primary users (PUs) under certain limits, which gives rise to a non-convex mixed integer non-linear programming (MINLP) optimization problem. It is illustrated that the original non-convex MINLP formulation admits a special structure and the optimal solution can be achieved efficiently using any standard convex optimization method under a general and practical assumption. In the second part of the dissertation, considering the imperfect sensing information, we study the joint spectrum sensing and resource allocation problem in a multi-channel-multi-user CR network. The average total throughput of SUs is maximized by jointly optimizing the sensing threshold and power allocation strategies. The problem is also formulated as a non-convex MINLP problem. By utilizing the continuous relaxation and convex optimization tools, the dimension of the non-convex MINLP problem is significantly reduced, which helps to reformulate the optimization problem without resorting to integer variables. A newly-developed optimization technique, referred to as the monotonic optimization, is then employed to obtain an optimal solution. Furthermore, a practical low-complexity spectrum sensing and resource allocation algorithm is proposed to reduce the computational cost

Maximally improper signaling in underlay MIMO cognitive radio networks

Improper Gaussian signaling is a well-known technique that has been shown to improve performance in different multi-user scenarios. In this paper, we analyze the benefit of improper signaling in underlay cognitive radio when users are equipped with multiple antennas. Specifically, we assume that the primary user is protected by the so-called interference temperature constraint, which guarantees a prescribed rate requirement. In this setting, we study how the maximum tolerable interference power changes when the interference is additionally constrained to be maximally improper (strictly noncircular, or rectilinear). We observe that the correlation structure of a maximally improper interference is an additional degree of freedom that can be exploited to improve the SU performance. Because of that, we propose two different protection strategies for the PU where this structure is either constrained or unconstrained, and derive the interference temperature threshold for both cases. We then focus on the secondary user and provide designs of the transmission parameters under the proposed protection strategies.The work of C. Lameiro and P. J. Schreier was supported by the German Research Foundation (DFG) under Grants SCHR 1384/6-1 and LA 4107/1-1. The work of I. Santamaría was supported by the Ministerio de Economía y Competitividad and AEI/FEDER funds of the UE, Spain, under Project CARMEN (TEC2016-75067-C4-4-R)