There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Encryption of data with high correlation, such as images, is a challenge for block ciphers, since patterns of the original image may remain after encryption. This is due to the deterministic mapping performed by the cipher. To overcome this limitation, a block cipher is used in an adequate mode of operation, such as cipher block chaining, counter mode. It is presented in this work randomized block ciphers inspired by the Rijndael architecture employing chaotic maps as an entropy source. It is shown that the proposal achieves good security and robustness indicators with fewer rounds compared to that obtained with the Rijndael algorithm.

Image encryption using block cipher and chaotic sequences

In recent years, information security is an increasingly vital problem. In this paper, we introduce an audio encryption scheme based on the novel digital programmable multi-scroll chaotic system. The chaotic system is described by three differential equations with piecewise nonlinear functions. More interesting, the number of scrolls of the proposed chaotic system is programmable and can be changed real-time. The system is discretized by Euler method and the digital implementation is provided. Based on this, a chaos-based audio secure communication system is developed by using feedback drive-response synchronization. The number of scrolls changes randomly by extracting control signals from the encrypted data. A series of security analyses are applied, showing good performance of the method. The system is verified through experiment on an Altera Cyclone IV FPGA platform, which effectively confirms the theoretical analysis.

A novel digital programmable multi-scroll chaotic system and its application in FPGA-based audio secure communication

Fifth generation (5G) cellular networks promise to support multi-radio access technologies (multi-RATs) with low and high frequencies aiming at delivering good coverage, several gigabits data rate, and ultra-reliable services. In this context, user-association and resource allocation appear to be a huge challenge due to the variety of specifications and varied propagation environments. In this treatise, the focus is on the technical and administrative difficulties of the adoption of user association (UA) mechanism and spectrum sharing approach (SSA) in millimeter wave (mmWave) systems, for example, the technical design considerations and their underlying options, as well as their impact on users and network performance. In addition, details on the importance of the rules and regulations of SSA are presented. This study also identified a few possible design solutions and potential promising technologies in both UA and SSA. In the context of UA, several mechanisms are identified, such as backhaul-, caching-, and hybrid multi-criteria-aware UA to achieve seamless connectivity and to enhance the network utility. In the context of SSA, this study pinpoints varied subjects that need to be explored, such as joint efficient rules and regulations enactment, assessment of fairness and independence in multi-independent mobile network operators (multi-IMNOs) that support SSA, as well as the implementation of hybrid-SSA via Virtualized Cloud Radio Access Network. Finally, attention is drawn to several key conclusions to enable readers and interested researchers to learn about the most controversial points of mmWave 5G cellular networks.

A survey of mmWave user association mechanisms and spectrum sharing approaches: an overview, open issues and challenges, future research trends

In this article, a high data rate and energy-efficient multiple-input multiple-output transmission scheme is considered by combining two popular and rational modulation techniques: spatial modulation (SM) and code index modulation-spread spectrum (CIM-SS). Since in the considered system, called generalized CIM-SM (GCIM-SM), incoming information bits determine modulated symbols, activated transmit antenna indices as well as their corresponding spreading code indices, data bits are conveyed not only by modulated symbols but also by the indices of the active antenna and spreading codes. Hence, a GCIM-SM scheme accommodates faster data rates while spending less transmission power and possessing better error performance compared to the conventional direct sequence spread spectrum (DS-SS), SM, quadrature SM (QSM), and CIM-SS systems. The mathematical expressions of the GCIM-SM system for bit error rate, throughput, energy efficiency, and the system complexity are derived to analyze the overall system performance. Besides, it has been shown via computer simulations that the GCIM-SM system has lower transmission energy, faster data transmission rate, and better error performance than DS-SS, SM, QSM, and CIM-SS systems. Performance analysis of the considered system was performed on Rayleigh block-fading channels for quadrature amplitude modulation technique.

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Generalized Code Index Modulation and Spatial Modulation for High Rate and Energy-Efficient MIMO Systems on Rayleigh Block-Fading Channel

The rise of the Internet of Things (IoT) presents important challenges for future radio networks. Non-orthogonal multiple access (NOMA), which allows the network to support more than one user per orthogonal resource element, was recently proposed as a promising solution that can ultimately support the daunting requirements of such networks including massive connectivity, high spectral efficiency, and low latency. Nevertheless, numerous ultra-high-reliability applications of IoT present environments that are hampered by impulsive electromagnetic interference, referred to as impulsive noise. Such noise is known to cause degradation to the overall system performance. Moreover, given the non-orthogonal multiplexing in NOMA, such noise is expected to have a relatively more pronounced impact on the system performance. Therefore, this article sheds light on the performance degradation and mitigation of impulsive noise in the context of NOMA-based IoT networks. It proposes a multistage nonlinear processing approach specifically designed for OFDM-based PDM-NOMA systems. To obtain the optimum threshold of the corresponding users, we propose a deep learning approach to estimate the impulsive noise parameters from the received OFDM symbol. This information can consequently be used to evaluate the corresponding optimal threshold using Siegert's ideal observer criterion. Finally, this work sheds light on potential opportunities and challenges that are expected to arise during the implementation of NOMA in impulsive environments.

NOMA-Based IoT Networks: Impulsive Noise Effects and Mitigation

In this work, we consider a sparse code multiple access uplink system, where $J$ users simultaneously transmit data over $K$ subcarriers, such that $J > K$ , with a constraint on the power transmitted by each user. To jointly optimize the subcarrier assignment and the transmitted power per subcarrier, two new iterative algorithms are proposed, the first one aims to maximize the sum-rate (Max-SR) of the network, while the second aims to maximize the fairness (Max-Min). In both cases, the optimization problem is of the mixed-integer nonlinear programming (MINLP) type, with non-convex objective functions, which are generally not tractable. We prove that both joint allocation problems are NP-hard. To address these issues, we employ a variant of the block successive upper-bound minimization (BSUM) framework, obtaining polynomial-time approximation algorithms to the original problem. Moreover, we evaluate the algorithms’ robustness against outdated channel state information (CSI), present an analysis of the convergence of the algorithms, and a comparison of the sum-rate and Jain’s fairness index of the novel algorithms with three other algorithms proposed in the literature. The Max-SR algorithm outperforms the others in the sum-rate sense, while the Max-Min outperforms them in the fairness sense.

Fairness and Sum-Rate Maximization via Joint Subcarrier and Power Allocation in Uplink SCMA Transmission

In this work, we consider a sparse code multiple access uplink system, where $J$ users simultaneously transmit data over $K$ subcarriers, such that $J > K$, with a constraint on the power transmitted by each user. To jointly optimize the subcarrier assignment and the transmitted power per subcarrier, two new iterative algorithms are proposed, the first one aims to maximize the sum-rate (Max-SR) of the network, while the second aims to maximize the fairness (Max-Min). In both cases, the optimization problem is of the mixed-integer nonlinear programming (MINLP) type, with non-convex objective functions, which are generally not tractable. We prove that both joint allocation problems are NP-hard. To address these issues, we employ a variant of the block successive upper-bound minimization (BSUM) \cite{razaviyayn.2013} framework, obtaining polynomial-time approximation algorithms to the original problem. Moreover, we evaluate the algorithms' robustness against outdated channel state information (CSI), present an analysis of the convergence of the algorithms, and a comparison of the sum-rate and Jain's fairness index of the novel algorithms with three other algorithms proposed in the literature. The Max-SR algorithm outperforms the others in the sum-rate sense, while the Max-Min outperforms them in the fairness sense.

Fairness and Sum-Rate Maximization via Joint Channel and Power Allocation in Uplink SCMA Networks

An emitter-coupled pair chaotic generator is proposed with a control parameter that can be tuned for distinct chaotic behaviors. The proposed circuit is a compact, high-speed implementation of the chaotic map based on the hyperbolic tangent function. It is demonstrated that the circuit and map parameters are analytically related. As an application, we design a random number generator that passes all NIST statistical tests by applying a post-processing to the balanced bit sequence generated by a quantization of the circuit output.

Emitter-coupled pair chaotic generator circuit

In this paper, we propose an index modulation system suitable for optical communications, based on jointly driving the time and frequency of the signal: an index time-frequency hopping (I-TFH) system. We analyze its performance from the point of view of its efficiency in power and spectrum and its behavior in terms of error probability for the non-turbulent free-space optical channel. We compare I-TFH with already proposed index modulated systems of the same nature, but where the amplitude or the number of transmitters is driven instead of the signal frequency. We derive and compare approximations for the average symbol and bit error probabilities of all these systems. The simulation results show that said approximations are tight enough for a wide range of signal-to-noise ratios and system parameters. Moreover, I-TFH shows to be better performing in bit error rates and/or power efficiency than the comparative alternatives and may offer interesting properties in a variety of contexts.

Joao V. C. Evangelista

Papers

NOMA-Based IoT Networks: Impulsive Noise Effects and Mitigation

Fairness and Sum-Rate Maximization via Joint Subcarrier and Power Allocation in Uplink SCMA Transmission

Fairness and Sum-Rate Maximization via Joint Channel and Power Allocation in Uplink SCMA Networks

Emitter-coupled pair chaotic generator circuit

Design and Performance Analysis of an Index Time-Frequency Modulation Scheme for Optical Communications