This paper investigates a movable-antenna-assisted dual-hop space-air-ground non-terrestrial network (NTN) operating under an underlay spectrum sharing paradigm. A satellite communicates with multiple unmanned aerial vehicles (UAVs) over free-space optical (FSO) links, while each UAV simultaneously serves a cluster of ground users over radio-frequency (RF) channels subject to interference constraints imposed by a primary receiver. To efficiently exploit the complementary advantages of FSO and RF transmission and the additional spatial degrees of freedom offered by movable antennas, a joint optimization framework is developed to maximize the system sum rate. The proposed framework jointly optimizes satellite and UAV power allocation, multi-antenna precoding at the UAVs, and the positions of multiple movable antennas mounted on each UAV. An alternating-optimization algorithm is employed, where minimum mean square error (MMSE) based precoding accounts for both communication and interference channels, power allocation is convexified using auxiliary rate variables and successive convex approximation, and antenna locations are optimized via Taylor-based convex surrogates. Simulation results demonstrate that the proposed approach significantly outperforms benchmark schemes with fixed antenna locations, heuristic optimization and reinforcement learning methods, while providing robust performance across different system parameters.

Message authentication using tag embedding has been widely adopted for Internet of Things (IoT) networks due to its efficient performance and lower resource consumption compared to other tag appending approaches. Specifically, in tag embedding, the authentication tag and the message are superimposed in one signal to save time, energy, and spectral resources, making it an ideal alternative for networks with limited resources, such as IoT networks. However, due to the lower power allocated to the tag symbols (compared to the message symbols) in the conventional scheme, the received tag experiences higher transmission errors, increasing the authentication failure rate (AFR). Moreover, an Eve might be able to capture either the message, the tag or both as they are transmitted unprotected in the conventional scheme. In this work, a novel message authentication scheme is proposed to enhance the performance of the tag embedding scheme. Specifically, the proposed scheme involves precoding the tag signal prior to being superimposed with the message signal and emitted over the channel. The conducted analysis and evaluation reveal that the proposed scheme can significantly reduce both the tag error rate (TER) and the message error rate (MER), which should be directly reflected in improving the AFR. In addition, the performance at the eavesdropper is shown to be degraded due to the precoding of the tag signal induced in the proposed scheme. The included analysis and explored results investigate the impact of power allocation at the transmitter between the tag and message signals to minimize MER, TER or AFR.

The growing demand for spectrum resources necessitates the urgent need for innovative physical-layer solutions that maximize spectral efficiency. Over the past decades, multiple access (MA) schemes have been extensively developed to improve spectral utilization and support more users. However, existing standards are based solely on orthogonal multiple access (OMA) schemes, which restrict multiple users from sharing the same channel, inherently limiting overall spectral efficiency. Although recent research has proposed various non-orthogonal multiple access (NOMA) alternatives, these approaches face significant practical challenges, including receiver complexity, fairness issues, and scalability concerns, which cast doubt on their short-term feasibility. To address these limitations, a new uplink MA framework, termed cooperative modulation (CoM), is introduced. The scheme enables simultaneous multiuser transmission over a single channel through user-side channel pre-equalization combined with a deterministic phase-rotation design. In CoM, users transmit precoded modulated symbols that cooperatively form a structured composite constellation at the receiver. This precoding requires no information exchange among users; each user independently applies channel pre-equalization and a fixed phase shift prior to transmission. Unlike existing rotation-based or NOMA schemes, the phase-rotation optimization in CoM is rendered channel-independent due to pre-equalization, allowing the design to scale to arbitrary numbers of users and modulation orders through offline lookup tables. It is also noted that practical limits on the number of users arise from computational complexity and the minimum Euclidean distance of the composite constellation rather than from theoretical constraints. Unlike conventional NOMA, CoM avoids iterative decoding and successive interference cancellation, making it more suitable for practical large-scale deployments. The phase-shift design is identified as a critical performance factor and is examined in detail. Through theoretical analysis and extensive simulations, including the impact of imperfect CSI across a wide range of SNR values and user densities, substantial gains in error performance, spectral efficiency, and computational complexity are demonstrated relative to OMA, NOMA, and recent index-modulated MA schemes. These results position CoM as a promising approach for future spectrally efficient uplink communication systems.

This article proposes a two-fold triple system (TFTS)-based obfuscation scheme as a structured physical-layer transmission technique for multiple-input multiple-output (MIMO) systems. TFTS is a class of combinatorial block designs that enables index-based spatial signaling without cryptographic keys or additional computational overhead. The proposed scheme constructs a space-modulation matrix derived from a TFTS of orderv, where each row corresponds to a unique antenna activation pattern transmitting unmodulated carriers. The TFTS combinatorial space is generated by merging two non-isomorphic Steiner triple systems, yielding a mapping space that grows super-exponentially withv. This growth becomes extreme even for moderate dimensions; for example, atv= 40, the number of valid TFTS realizations exceeds 1010258, rendering exhaustive reconstruction computationally infeasible. The TFTS constellation matrix is assumed to be pre-shared and securely stored at the legitimate transceivers, while an eavesdropper is modeled as a fully informed and computationally unbounded adversary that lacks the correct TFTS mapping and therefore operates under mismatched decoding. Under this adversary model, Eve’s demodulation decisions degrade to random guesses, resulting in an average bit error rate (ABER) approaching 0.5 and negligible exploitable information. Accordingly, the proposed framework is explicitly positioned as a physical-layer obfuscation mechanism rather than a secrecy-capacity or cryptographic security scheme. The obfuscation strength of the system is evaluated through information-leakage analysis, quantifying the mutual information between transmitted indices and Eve’s observations, as well as detectability analysis based on hypothesis testing. Simulation results demonstrate that the proposed TFTS-obfuscation scheme preserves strong performance for the intended receiver in terms of ABER, mutual information, and achievable rate, while maintaining minimal information leakage and low detectability at the eavesdropper.

Non-terrestrial networks (NTNs) using unmanned aerial vehicles (UAVs) as temporary base stations enable flexible coverage in disaster-stricken areas and congested regions. This paper presents a beamforming design for rate splitting multiple access (RSMA) enabled UAV underlay networks that addresses untrusted users (potential eavesdroppers), enforces max–min fairness in achievable user rates, accommodates imperfect CSI, and limits interference to a licensed primary receiver. We transform the non-convex optimization problem via auxiliary-variable-based reformulation and successive convex approximation (SCA), obtaining a tractable convex semi-definite program (SDP). Simulations demonstrate that the proposed framework achieves perfect rate fairness (Jain’s fairness index = 1.0) across all users while delivering robust sum-rate performance under varying numbers of users, UAV transmit antennas, and secrecy requirements.

Due to the expected exploitation of high frequency bands to meet increasing demands on high data rates, multi-hop links are being under investigation as a solution for limited transmission distances over these bands. As such, many of recent transmission schemes are analyzed over multi-hop scenarios. To this end, in this paper, we design a dual-hop system of Index Modulation based Orthogonal Frequency Division Multiple Access (IM-OFDMA) with the help of decode-and-forward relays. Two different scenarios are considered, with single and multiple DF relays. Moreover, the average error rate is analyzed for the proposed system considering the two different scenarios. Our results indicate that the overall performance in the case of a single DF relay is governed by the performance of the second hop. Also, results reveal that a significant gain can be attained if a single relay is assigned to each user rather than one relay for all users.

This paper investigates the performance of satellite-based quantum key distribution (QKD) under realistic channel conditions, emphasizing the adverse effects of photon loss introduced by pointing errors and the presence of background photons. By leveraging a stochastic framework, we model the probability distribution of the number of photons detected at the receiver, considering Gaussian beam propagation, finite receiver aperture, and Poisson-distributed background noise. We then evaluate essential QKD performance metrics—such as the quantum key rate, quantum bit error rate (QBER), and outage probability—across a wide range of beam waist sizes and tracking accuracies. Numerical simulations demonstrate how subtle increases in the pointing error variance can drastically reduce the secure key generation rate, particularly for tightly focused beams. These findings highlight the importance of precise pointing systems and careful selection of optical parameters to ensure an acceptable QBER and a sufficiently high secret key rate in inter-satellite QKD links.

High peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals presents a persistent challenge in satellite communications (SatCom), impacting signal quality and causing adjacent channel interference. This paper introduces a novel framework that combines the elastic net-based machine learning (ML) model with the partial transmit sequence (PTS) technique to effectively reduce PAPR. Additionally, the potential of artificial intelligence (AI) approaches are investigated, specifically swarm intelligence and ML methods, for high-performance, low-complexity solutions. In this regard, ML models are applied to mitigate PAPR in SatCom networks under the presence of a traveling wave tube amplifier (TWTA) model and a land mobile satellite (LMS) channel, employing 16-quadrature amplitude modulation (16-QAM). Compared with the baseline schemes, simulation results demonstrate that the proposed ML framework, integrating principal component analysis (PCA) with the elastic net learning model, achieves comparable PAPR performance and minimal computational complexity.

In this paper, a robust enhanced Sybil attack detection scheme is proposed using both the Doppler shift and received signal strength (RSS) as physical layer parameters to identify Sybil nodes in a mobile network. The proposed scheme employs the absolute value of the difference between Doppler shift and RSS values for all pairs of nodes as test statistics, where threshold-based statistical hypothesis testing is performed to detect Sybil nodes. A performance evaluation of the scheme is provided in terms of its true positive rate (TPR) and false positive rate (FPR), and where an approximate expression for both metrics is provided for the particular two-user case. The proposed scheme yields a significant security enhancement compared to its single-attribute Doppler shift- and RSS-based schemes, where the proposed scheme's TPR manifests an increase surpassing 32% and 255%, with respect to the two aforementioned schemes, respectively. The performance evaluation shows the potential of incorporating multiple channel-based features for a robust Sybil attack detection scheme in mobile networks.

The next generation of wireless communication networks must offer robust connectivity to serve users in remote or disaster-stricken regions where terrestrial infrastructure is unavailable or compromised. High-altitude platforms (HAPs), functioning as non-terrestrial network (NTN) nodes, can rapidly restore coverage and extend service reach by transmitting directly to ground users. To further enhance communication performance, simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) can be deployed alongside HAPs, intelligently shaping the wireless channel to improve channel reliability. In this work, we investigate a HAP-assisted NTN in which a STAR-RIS aids downlink transmission to multiple ground users under a rate-splitting multiple access (RSMA) protocol with imperfect successive interference cancellation (SIC). The joint design of power allocation at the HAP and STAR-RIS beamforming presents a challenging non-convex problem because of the coupled rate expressions and rank-one constraints on the STAR-RIS matrices. To address this, we introduce auxiliary variables and apply successive convex approximation (SCA) to convexify rate functions, while employing a difference-of-convex (DC) programming approach to handle the rank-one requirement. An alternating optimization framework is then developed to iteratively solve a convex power allocation subproblem and a penalized semi-definite program for STAR-RIS beamforming. Simulation results show the efficacy of the proposed framework, showing excellent performance even under imperfect SIC and with discretized phase shifts at the STAR-RIS.

In this paper, a robust machine learning (ML)-based scheme for Sybil attack detection in mobile networks is proposed. The proposed scheme exploits three physical-layer features, namely the Doppler shift, received signal strength (RSS), and channel state information (CSI) for identifying Sybil nodes. By employing a Bayesian optimization method, an optimized Random Forest ML classifier is utilized for the classification phase by exploiting the estimated and processed physical-layer attributes, yielding an efficient node classification and Sybil attack detection in a mobile network. A thorough performance evaluation of the proposed scheme is performed in terms of its receiver operating characteristic (ROC) curve, demonstrating higher node classification accuracy gains. Furthermore, the proposed scheme outperforms its benchmark schemes, namely the single- and dual-attribute schemes and the three-features hypothesis-based one. Specifically, the proposed scheme improves the true positive rate (TPR) by 12.5% compared to its dual-feature RSS-Doppler shift-based counterpart, and enhances the Doppler shift-, RSS-, and CSI-based single-attribute ones by 216%, 137%, and 36%, respectively, in terms of the TPR.

This paper addresses the challenge of optimizing user grouping in Index Modulation-based Orthogonal Frequency-Division Multiple Access (IM-OFDMA) systems within dynamic and stochastic noise environments. Utilizing the eXtreme Gradient Boosting (XGBoost) machine learning algorithm, we devised a framework capable of accurately predicting the optimality of user groupings across varying Signal-to-Noise Ratio (SNR) levels. Six models corresponding to different noise conditions were created, showcasing adaptability to adjacent noise levels via distribution shift handling, thereby ensuring robust performance across a wide noise spectrum. To accurately identify the most appropriate optimality prediction model for dynamic environments, we introduced a specialized model for precisely estimating the system’s internal noise power. The accuracy of this model is crucial for the selection process and was significantly enhanced by implementing sequential Bayesian updating, facilitating a more precise estimation of internal noise power. Following this, we introduced a provisional optimization algorithm designed to refine user groupings within dynamic IM-OFDMA systems. Simulation results highlight the algorithm’s effectiveness in markedly improving system performance, evidenced by a significant decrease in bitrate errors. These findings illuminate the significant potential of applying machine learning strategies to wireless communication systems, providing insightful contributions to the enhancement of IM-OFDMA systems in practical settings.

This paper focuses on the optimal design of a modulated retroreflector (MRR) laser link to establish a high-speed downlink for cube satellites (CubeSats), taking into account the weight and power limitations commonly encountered by these tiny satellites. To this end, first, a comprehensive channel modeling is conducted considering key real channel parameters including mechanical gimbal error, fast steering mirror angle error, laser beamwidth, MRR area, atmospheric turbulence, and channel coherence time. Accordingly, a closed-form expression for the distribution of the received signal is derived and utilized to propose a maximum likelihood based method to sense and estimate the initial position of the satellite. Subsequently, the distribution of the distance estimation error during the sensing phase is formulated as a function of the laser beamwidth and the gimbal error, which enables us to fine-tune the optimal laser beamwidth to minimize sensing time. Moreover, using the sensing and initial satellite distance estimation, two positioning algorithms are proposed. To compare the performance of the proposed positioning method, we obtain the lower bound of the positioning error as a benchmark. Finally, by providing comprehensive simulations, we evaluate the effect of different parameters on the performance of the considered MRR-based system in both the sensing and positioning phases.

Given the growing significance of CubeSats for real-time Earth monitoring and space networking, there is an increasing demand for high-speed links for CubeSats facing constraints related to the weight, dimensions, and power consumption of telecommunication equipment. This article addresses such a need by designing a modulating retroreflector (MRR)-based optical downlink system tailored for fast-moving CubeSats, highlighting joint tracking and communication operations using a single transmitter for high data rates. Key contributions encompass precise system characterization, the design of a dual-transmitter system to maximize channel capacity, derivation of channel capacity as a function of 2M + 4 random variables, and the development of an MRR-based CubeSat downlink system. Subsequently, leveraging the obtained analysis and results, we design a system with a single transmitter, enabling simultaneous tracking and communication operations through optimal adjustments of beam timing and placement in the satellite’s vicinity. Pertinent analyses demonstrate optimal laser beam adjustments to achieve maximum capacity while maintaining tracking accuracy. Monte Carlo simulations are used to validate a closed-form expression for efficient optimization of system parameters. Comprehensive simulations assess the effect of different parameters, offering crucial insights for optimal system design.

Low Earth orbit (LEO) satellite constellations are emerging as a key enabler of next-generation communications, offering global coverage and significantly lower latency compared to traditional terrestrial networks and geostationary satellites. However, further latency reduction is essential for time-critical applications such as real-time sensing, autonomous systems, and interactive services. One critical bottleneck is the optical-to-electrical (O/E) and electrical-to-optical (E/O) conversions at intermediate nodes in multi-hop links, which introduce unwanted processing delays. To address this, we investigate an all-optical relay system based on Optical Hard Limiters (OHL), which operate purely in the optical domain to suppress noise and restore signal quality without requiring O/E conversions. First, we present a rigorous analysis of inter-satellite multi-relay communication under the OHL relaying architecture, comparing it against conventional Amplify-and-Forward (AF) and Decode-and-Forward (DF) schemes. Through this comparison, we highlight both the advantages and limitations of OHL relays, including their particular sensitivity to parameter choices such as the threshold setting and divergence angle at the transmitter. Recognizing that a LEO constellation is inherently time-varying—satellites move relative to one another, causing continuous changes in link distances and tracking errors—we propose a joint optimization strategy. This scheme adaptively tunes the OHL decision threshold and beam divergence in real time to maintain optimal performance, ultimately lowering error rates and latency. Extensive simulations in a large-scale LEO network demonstrate the viability of our method and offer insights into practical implementation for next-generation inter-satellite communication systems.

Terahertz (THz) band is widely nominated to be exploited in next wireless networks to meet the high demand on data rates. However, unlike lower frequency bands, several challenges come up while designing a transmission system over the THz band. Among these challenges is the hardware impairments at the transmitter front-end. It is well known that hardware impairments limit the error performance of any transmission system, where a lower bound on the error rate is usually noticed. Such an impact becomes more severe as the operating frequency increases, which significantly degrades the transmission over THz band. To this end, this paper proposes an adaptive modulation scheme that is able to overcome this problem. Moreover, the optimal detector for the proposed adaptive modulation scheme is presented. Mathematical modeling and analysis of the performance of the conventional QAM and the proposed modulation scheme are included along with simulation results that verify the analytical findings. Results indicate that the error performance of the proposed scheme is much better than conventional QAM where no error floor is noticed.

The Internet of Things (IoT) is a popular technology that refers to a network of internet-connected physical devices that interact to perform tasks with minimal human intervention. However, as these networks expand, ensuring their security becomes challenging due to the communication broadcasting nature and extensive data exchanges. Traditional cryptographic security methods may not be optimal due to the constrained resources of loT devices. In this study, we propose a novel secure key distribution scheme from a physical layer perspective suitable for an loT environment. The proposed scheme takes advantage of the availability of Channel State Information (CSI) at both ends of the communication to enhance security. Specifically, CSI is utilized to precode the key symbols during the key distribution process. Additionally, the scheme employs the xor operation to add an extra layer of difficulty for potential eavesdroppers that attempt to retrieve the transmitted key symbols. The performance of the proposed scheme is evaluated in terms of Key Error Rate (KER) at legitimate nodes and eavesdroppers by using Monte Carlo simulations.

Involving Unmanned Aerial Vehicles (UAVs) in wire-less networks has been widely investigated in the literature considering different scenarios such as emergency scenarios in which UAV(s) can play a significant role by compensating the damaged/lost network's components. For example, Sensor Networks (SNs) in emergency scenarios may lose some sensor nodes or the Central Entity (CE) itself, which requires fast, prompt and efficient alternative to replace them. Therefore, UAVs are widely nominated to such a role due to their flexibility and maneuverability. However, compared to ground-based entities, UAVs suffer from the continuous position fluctuations, which directly affects the antenna's orientation. Such an effect becomes a serious challenge in high frequency links such as millimeter wave (mmWave) links which are very sensitive to antennas misalignment. In this paper, the performance of UAV-based SNs is addressed by analyzing the impact of UAV's vibration on the performance metrics including detection and false-alarm probabilities. To this end, two network models are adopted, namely, Ground-based Hybrid SN (G-HSN) and Aerial-based Hybrid SN (A-HSN), depending on whether the CE is ground or aerial node. A mathematical framework is followed to express performance metrics in closed form expressions considering practical conditions including channel fading, orientation fluctuations of directional mmWave antennas and path loss. Simulation results validate the accuracy of the derived mathematical expressions and depict the impact of different operational parameters.

Reconfigurable Intelligent Surfaces (RISs) have shown great prospects in securing mmWave communication from potential eavesdropping by configuring reflecting elements to strengthen the signal strength at the desired location and creating nulls at potential eavesdropping locations. Acquiring perfect channel information is crucial for optimizing RIS configuration; however, obtaining such information is costly and, as a result, should be performed sparingly. This work studies the impact of the age of channel information on the secrecy performance of a RIS-assisted mmWave network. In particular, we investigate how outdated channel information affects the joint optimization of transmit beamforming and RIS configuration. In our Monte-Carlo simulations, we first identify the factors influencing the aging process of a RIS-assisted mmWave channel in both the near and far fields of the RIS. Subsequently, we examine the impact of channel aging on secrecy capacity and demonstrate that adequate secrecy capacity can still be achieved even when channel information is slightly outdated, thus reducing the need for frequent RIS configuration.

Index Modulation Orthogonal Frequency Division Multiple Access (IM-OFDMA) is a spectral-efficient uplink multiple access scheme that has been recently proposed. IM-OFDMA relies on the index modulation concept and allows for multiple users to simultaneously share the same spectrum resources. It has been demonstrated that IM-OFDMA outperforms its conventional and recent counterparts in terms of the error performance and the number of served users. However, as IM-OFDMA employs a joint maximum likelihood detection to decode the received signals, it suffers from the computational complexity required at the receiver. The computational complexity becomes serious challenge especially at a large number of users, a large number of frequency subcarriers or a high modulation order. Therefore, this paper aims to reduce the computational complexity of the detection process in IM-OFDMA systems by employing the Successive Interference Cancellation (SIC) detection method. Specifically, the implementation of SIC in IM-OFDMA is in detail described, followed by the analysis of the error performance and the reduction of the computational complexity. Our results reveal that the SIC detector can reduce the computational complexity with a significant percentage as compared to the maximum likelihood detection. Also, the results show that the impact on the error performance is minimal if the served users in each frequency chunk are carefully selected.

Exploiting the high-frequency bands, such as millimeter wave band (mmWave), has become a pressing need due to the increasing demand on the high data rates. However, two main challenges are still hindering the usage of mmWave band, which are represented by the short transmission distance and strict Line-of-Sight (LoS) requirements. To this end, relaying schemes have been widely nominated to address these two challenges, where the transmission distance can be extended and the LoS can be attained by the aid of a well-positioned relay. One of the promising spectral-efficient relaying schemes is the well known Two-Way Relaying (TWR). In this paper, the performance of the TWR scheme is investigated for aerial links operating over the mmWave band. Specifically, the bit error rate (BER) is analyzed for a dual-hop system in which source, relay and destination are represented by hovering unmanned aerial vehicles. A closed form expression of the average BER is derived considering the impact of the antennas' fluctuations, modulation order, transmission distance, beamwidth, path loss and channel fading. Simulation results are explored to investigate the impact of all operational parameters.

The pervasiveness of the Internet of Things (IoT) in our daily lives has been remarkably increasing over the past years. Due to their massive connectivity and limited resources, ensuring decent security levels for these networks has been challenging. In this article, a novel and efficient physical layer key exchange scheme for IoT devices is proposed. The proposed scheme leverages on the well-known index modulation (IM) technique for the key exchange process by exploiting IM-based selected carrier frequency indices at the legitimate transceiver pairs (i.e., Alice and Bob) to exchange key symbols. Additionally, a random power level selection along with channel precoding is performed for each symbol transmission to enhance the secrecy level against potential eavesdroppers. The performance of the proposed scheme is analyzed based on the upper-bound expression for the key error probability (KEP) metric. As compared to the benchmark scheme, results reveal a promising performance in the KEP, where a minimum of 10 dBW can be gained at the legitimate node, while the KEP at the eavesdropper is kept close to one regardless of its channel conditions. Moreover, extensive numerical results corroborate the accuracy of the derived mathematical framework and endorse the proposed scheme’s robustness under the existence of a smart and powerful adversarial node.

The rapid growth of Internet of Things (IoT) networks brings new security challenges for service providers. Due to the resource constrained nature of IoT networks, conventional security methods are not always suitable. Therefore, physical layer security (PLS) has come to the forefront, providing a high level of security while respecting the limited resources of IoTs. A Sybil attack is an insider attack in which a malicious node illegitimately fakes multiple identities, to impersonate legitimate nodes in the IoT network. This study introduces a novel Sybil attack detection scheme for mobile IoT networks that corresponds to time-varying channel. doppler-shift caused by mobile IoT nodes is considered as a novel detection metric to identify available Sybil attacks. The proposed scheme is analyzed by both the true positive rate and the false positive rate, which are mathematically formulated to verify the simulation results. Results demonstrate that as the randomness in the mobility pattern of IoT nodes increases, the proposed detection mechanism based on doppler-shift offers improved identification of the Sybil nodes. Moreover, this work provides receiver operating characteristics (RoCs) for mobile IoT networks to evaluate the effect of different system parameters, including carrier frequency, velocity, subcarrier spacing (SCS), and the size of cyclic prefix (CP). The performance of the proposed scheme improves with an increase in both the carrier frequency and velocity, as the doppler-shift becomes more pronounced.

IoT (Internet of Things) networks are becoming an integral part of everyday life. The exponential growth in these networks poses various privacy and security threats for the users and the vendors. Among these threats are Sybil attacks, which occurs due to poor authentication capabilities and thus a malicious node gets access to any information on the host. The malicious node uses its' fake identities to impersonate legitimate nodes and transmit misleading data to the central entity. However, conventional cryptographical approaches are not always suitable for IoT nodes due to the their limited resources. Therefore, physical layer security (PLS) solutions become more and more important for IoT networks. In this regard, this study introduces a novel technique for detecting Sybil attacks in mobile networks, which stands in contrast to the current methods developed for stationary environment, i.e., time-invariant channel. Specifically, this work exploits the Doppler shift caused by the mobility in the environment to identify Sybil nodes in the network. If the nodes belong to the same terminal, they experience the same amount of Doppler shift. The detection performance of the proposed scheme has been evaluated under different system configurations. The obtained results show that the performance of the proposed scheme improves as the amount of Doppler shift increases.

Utilizing the terahertz (THz) band in wireless communication systems has been usually motivated by the unlimited data rates afforded. However, the small coverage area is a main limitation of adopting THz band in several applications and scenarios. Relaying concept has been widely brought up in the literature to extend the coverage area of different wireless systems. It implies placing a relay (or multiple relays) at the cell edge, which will act as an intermediate point to assist in delivering data to/from the central base station. In this paper, the relaying in THz-based transmission system is considered. Specifically, the outage probability is analyzed at a set of mobile users being served by a central base station (BS) and by the aid of distributed relays. The impact of all the involved system parameters, including the users’ mobility range, the outage threshold, the number of relays and the relay-BS distance, are thoroughly analyzed and discussed. Derived mathematical formulas of the outage probability are presented.

Non-Orthogonal Multiple Access (NOMA) has been widely considered as an efficient multiple access scheme for future wireless networks. This is due to the promising performance of NOMA in terms of the larger number of served users and better error performance as compared to traditional multiple access schemes. Therefore, NOMA has received significant research efforts in analyzing its performance under different scenarios and assumptions. In this paper, we analyze the performance of a downlink NOMA scheme considering mobile users, in order to characterize the impact of mobility on the system performance. Specifically, the average bit error rate at mobile users is derived in a closed form expression. The users’ mobility is considered to follow the well-known random waypoint mobility model. Mathematical formulas have been verified using Monte Carlo simulations and compared to different scenarios.

Design of simple transceiver architectures is inevitable in order to provide low computational complexity, low power consumption and affordable cost in beyond 5G (B5G) wireless systems, but it results in hardware impairments that significantly degrade the performance reliability of transmission. In this paper, among these hardware impairments, we discuss in-phase and quadrature (IQ) imbalance in orthogonal time frequency space (OTFS), which is a recent waveform considered as a potential candidate for B5G systems to relax the vulnerability against time-variant wireless channels. To mitigate the effect of IQ imbalance for OTFS, we propose an energy and spectral efficient IQ imbalance compensation scheme with the aid of index modulation (IM), which provides an attractive flexibility in the system design. In contrast to conventional solutions used in classical wireless technologies, such as iterative and pilot-based techniques, the proposed scheme avoids additional energy consumption and significant spectral efficient loss during the estimation and compensation of the IQ imbalance effect. The obtained bit error rate (BER) results validate the accuracy of the proposed compensator for different OTFS system configurations considering perfect/imperfect channel state information in practical scenarios.

Security is a critical issue in Internet of Things (IoT) networks and it has been under investigation by researchers worldwide. Different from other wireless networks, IoT networks suffer from conventional security mechanisms due to complexity and resource consumption which cannot be tolerated in IoT networks. Among the recently proposed security schemes for IoT networks is the tag-embedding message authentication scheme in which a tag is embedded to the modulated message and concurrently sent over the same channel. Although it has avoided significant resource expenditure, its performance still requires improvement especially in terms of immunity against nearby eavesdroppers. In this article, a novel scheme is proposed that is able to enhance the authentication rate and the tag confidentiality without inducing any extra requirements. The proposed scheme implies performing tag puncturing at the transmitter side where only a part of the tag is embedded to the message based on the instantaneous channel phase. The performance of the proposed scheme is mathematically analyzed where the authentication failure probability is derived in closed-form expression, and compared to the conventional tag-embedding scheme.

The recently proposed index modulation-based up-link orthogonal frequency division multiple access (IM-OFDMA) scheme has outperformed the conventional schemes in terms of spectral efficiency and error performance. However, the induced computational complexity at the receiver forms a bottleneck in real-time implementation due to the joint detection of all users. In this paper, based on deep learning principles, a convolutional neural network (CNN)-based signal detector is proposed for data detection in IM-OFDMA systems instead of the optimum Maximum Likelihood (ML) detector. A CNN-based detector is constructed with the created dataset of the IM-OFDMA transmission by offline training. Then, the convolutional neural network (CNN)-based detector is directly applied to the IM-OFMDA communication scheme to detect the transmitted signal by treating the received signal and channel state information (CSI) as inputs. The proposed CNN-based detector is able to reduce the order of the computational complexity from O(n2n) to O(n2) as compared to the ML detector with a slight impact on the error performance.

Subcarrier Index Modulation (SIM) has recently received a significant research efforts analyzing its different performance aspects. In this paper, performance analysis of SIM over TeraHertz (THz) frequency band is conducted considering mobile users. The mobility model adopted is Random WayPoint (RWP) model with different numbers of mobility dimensions. Moreover, different resource allocation schemes are considered, including fixed, random and distance-aware resource allocation schemes. Closed form expression for the average bit error rate are derived for THz-based SIM considering mobile users and all considered resource allocation schemes. Simulation results with the molecular absorption effect on THz-based system validate the accuracy of the derived mathematical formulas.

Tag-embedded has been proposed in the literature as an efficient message authentication scheme due to low spectrum, power and time resources required as compared to the conventional tag-appending schemes. This work addresses the mathematical analysis of the performance of the tag-embedded message authentication scheme, which has never been presented in the literature. The authentication fail probability, as a performance evaluation metric, has been derived in closed form expressions based on two different detection methods, namely, joint detection and successive detection. The derived formulas are validated through simulation results where exact matching is noted.

Hybrid Free-Space Optical (FSO) and millimeter Wave (mmWave) systems have emerged as a promising candidate for high data rate wireless transmissions due to the unique complementary properties against the different channel and environment conditions. Consequently, in this study, we investigate the hybrid FSO-mmWave systems from a physical-layer security point of view in the presence of a hybrid type eavesdropper, where the communication between two legitimate peers takes place over both FSO and RF links simultaneously. We examine practical scenarios to eavesdrop the legitimate communication and discuss the effects of random radio power of mmWave link and optical irradiance of FSO link on the probability of achieving a secure transmission. The impact of the fundamental physical layer parameters on the secrecy performance of the hybrid system is analyzed by obtaining closed-form derivations of the probability of strictly positive secrecy capacity (SPSC) for correlated wiretap channels.

Orthogonal time frequency space (OTFS) technique is a recent two-dimensional (2-D) modulation aiming to exploit both time and frequency selectivity of doubly dispersive wireless channel, which significantly affects the reliability of conventional wireless communication systems. In OTFS transmission, delay-Doppler domain is utilized for conveying the data symbols. Besides channel characteristics, the performance of wireless communications systems is severely limited due to the impairments at the RF front-end. One of these impairments is the in-phase and quadrature (IQ) imbalance that occurs due to inevitable imperfections existing between in-phase and quadrature branches at either transmitter (Tx) or receiver (Rx) architecture. The aim of this paper is to reveal and investigate the physical effect of IQ impairment in delay-Doppler domain, which is unknown in the literature. Hence, we provide theoretical models to explicitly understand the impact of IQ imbalance at different stages of OTFS-based communication systems including Tx, Rx, and jointly Tx-Rx. Importantly, we show that although the performance of OTFS transmission depends on both delay and Doppler axes, IQ imbalance leads to an interference originating only from the mirror Doppler axes, which we name mirror Doppler interference (MDI), along with power degradation. Moreover, we assess the performance of IQ imbalanced OTFS under various communication scenarios considering ideal and practical pulse shapes with maximum likelihood (ML) and minimum mean square error (MMSE) detectors, respectively.

Abstract In 5G and beyond communication systems, distinct numerologies can coexist to serve diverse requirements for users and applications. However, the inter‐numerology interference (INI) is a main challenge that significantly impacts the system performance. Therefore, the performance under INI has become an essential evaluation metric for the suitability of the different transmission schemes in the future communication systems. This paper analyzes the impact of INI on the performance of orthogonal frequency division multiplexing with index modulation (OFDM‐IM) systems. Specifically, an analytical expression of the INI level in OFDM‐IM systems is presented as a function of the subcarrier activation ratio (SAR) and subcarrier activation probability (SAP). Furthermore, aiming at reducing the INI level, an adaptive subcarrier mapping scheme (SMS) is proposed based on the conventional combinatorial mapping scheme. Moreover, analysis and evaluation of SAR and SAP are performed regarding the requirements of 5G and beyond services. It is proved that the INI level in OFDM‐IM systems is highly dependent not only on the number of active subcarriers but also on their position in an OFDM block.

It is vital and challenging to devise new efficient transmission techniques for next generation wireless networks that support internet of things (IoT) systems. Long range (LoRa) wireless networks are based on the deployment of connected devices with limited energy and where end-devices need higher data rates. This system is a key technology that enables smart city applications. The chirp spread spectrum is used as the modulation technique for LoRa networks which consists of assigning various orthogonal spreading factors (SF) among the connected devices in the network. In particular, each device uses a fixed SF for data transmission, which is assigned based on its distance from the gateway. This paper proposes a new SF assignment scheme aiming at enhancing the overall performance. In particular, the proposed scheme no longer assigns SFs based on the distance; but instead, it assigns them depending on the instantaneous channel realizations. Such a dynamic assignment of the SFs among LoRa users significantly enhances the overall performance compared to conventional SF assignment schemes. The proposed system is evaluated in terms of symbol error rate (SER) via numerical simulations.

Hybrid Free-Space Optical (FSO) and millimeter Wave (mmWave) systems have emerged as a promising candidate for high data rate wireless transmissions due to the unique complementary properties against the different channel and environment conditions. A main issue in hybrid FSO-mmWave systems is the mechanism followed to activate one of the links. Most of the proposed selection mechanisms suffer from the high overhead and the required information at the transmitter. In this study, a novel selection mechanism is proposed for hybrid FSO-mmWave systems without a need for any feedback or channel state information at the transmitter side. The activation of each link, either FSO or mmWave, is determined by the use of Index Modulation (IM) concept. The proposed link selection mechanism, called IM-based mechanism, is compared to the conventional switching mechanisms under various scenarios including different modulation orders, link distances, and weather conditions. In the light of the numerical and simulation results, it is shown that the proposed system significantly improves the overall system performance in terms of the spectral efficiency and the bit-error-rate (BER).

Massive connectivity and spectral efficiency are among the main defining terms of the future communications era. Therefore, revolutionary technologies are required to keep up with the connectivity and spectrum demands. Non-orthogonal multiple access (NOMA) and Index modulation (IM) techniques have emerged as promising candidates to satisfy the spectral efficiency and capacity demands. In this paper, a novel downlink multiple access scheme, called IM-NOMA, is proposed reaping the advantages of both NOMA and IM. In IM-NOMA, the bit block to be sent to each user is divided into two sub-blocks. While the first sub-block is modulated, the second sub-block determines a subset from the available set of channels to carry the modulated symbol. As in power-domain NOMA, the base station (BS) superimposes the modulated symbols carried by the same frequency carrier after a proper power allocation. In such, spectral efficiency is boosted by the extra bits carried by the indexes of the used carriers and the error performance is improved by spreading the users' signals in power domain as well as diversifying the symbols of each user over multiple channels. An upper bound on the average BER is derived in a closed form expression under maximum likelihood (ML) detection method and Rayleigh fading channel. Simulation results show a significant improvement in the BER of the proposed IM-NOMA as compared to the conventional NOMA scheme.

With the expected explosive growth in the user density in wireless networks, recent works have investigated the integration of index modulation (IM) with multiple access schemes, namely the non-orthogonal multiple access (NOMA) scheme. IM-based NOMA schemes have shown appealing advantages in terms of error performance and power efficiency. However, the advantages come with higher detection complexity as an inherited disadvantage of applying IM. In this paper, we propose a constellation rotation-based approach to reduce the detection complexity of the successive interference cancellation (SIC) algorithm. Specifically, we assume two orthogonal constellations to be utilized for transmission. Hence, the introduced rotated-constellations result in orthogonality in the users' signals space which reduces the inter-user interference domains. Therefore the SIC detection complexity is reduced as well. The proposed approach is shown to have a 50% average reduced complexity as compared to classical SIC. Numerical simulations show a significant improvement in terms of error performance as compared to IM-NOMA scheme.

Most of the energy consumed in target‐detection wireless sensor networks (WSNs) is due to the decision gathering process. As such, several energy‐efficient decision gathering schemes have been proposed to improve energy efficiency. In this study, a new multi‐hop decision gathering scheme for target‐detection WSNs is presented. The proposed scheme creates paths to gather the nodes' decisions, where each path includes a set of nodes. Nodes in the same path cooperate to deliver their decisions by using multi‐hop transmissions. At each hop, the relay node combines the received decisions with its own decision and uses a higher modulation order to forward them to the next node in the path. Two different setup scenarios are considered to evaluate the proposed scheme, namely, fixed transmit power scenario and fixed bit error rate scenario. In the former scenario, results demonstrate that the proposed scheme achieves better error rate at short hop distances when compared to the conventional single hop scheme. On the other hand, results of the fixed bit error rate scenario show that a significant amount of the saved power can be attained by the proposed scheme with a slight loss in the decision error rate.

Index Modulation (IM) concept is exploited to propose a novel uplink multiple access technique called, IM-multiple access (IMMA). In IMMA, part of the transmitted block for each user is used to modulate a complex symbol that is transmitted on a specific time slot determined by the remaining bits in that block. Concurrent transmissions from different users are probable in IMMA since the operating time slot for each user is individually selected and the scheme can be considered as a non-orthogonal multiple access (NOMA) technique. Yet, it is revealed that the error rate at the centralized receiver is better than other orthogonal multiple access schemes. Adopting a maximum likelihood detector to jointly decode all the transmitted blocks from various users is shown to be computationally complex. Hence, a reduced-complexity detection scheme is proposed where a substantial reduction in computational complexity of more than 50% is attained with a marginal performance penalty. Besides, an analytical upper bound of the average bit error rate (BER) and the probability of collision are derived in a closed form expression. It is also disclosed through simulation results that a significant enhancement in the BER is achieved for the proposed IMMA scheme as compared with the conventional TDMA system and to sparse code multiple access NOMA scheme.

In this paper, three non-coherent index modulation (IM) schemes are proposed and analyzed. All schemes are based on subcarrier index modulation (SIM) in which an OFDM symbol is divided to groups of subcarriers and part of the subcarriers within each group are only active. The first scheme is called differential subcarrier index shift keying (DSISK). In DSISK, the index of the active subcarrier within a group is the only source of information and no modulated data symbol is transmitted. The second scheme is named differential subcarrier index modulation (DSIM), which transmits a modulated symbols on the active subcarriers and data bits are conveyed in both the index of the active subcarriers and the transmitted data symbols. The last scheme named as differential subcarrier index quadrature modulation (DSIQM) enhances the data rate of DSIM by activating two subcarrier indexes. One subcarrier will transmit the real part of the modulated symbol, whereas the second active subcarrier modulates the quadrature component of the active subcarrier. A unified upper bound formula for computing the average bit error probability is derived for all presented schemes. Analytical results are corroborated through Monte Carlo simulation results, where a close match is reported at pragmatic signal-to noise ratio (SNR) values.

In the forthcoming Smart City scenario, Service Providers will require users to authenticate themselves and authorize their mobile applications to access their remote accounts. In this scenario, OAuth 2.0 has been widely adopted as a de facto authentication and authorization protocol. However, the current OAuth 2.0 protocol specification does not consider the user privacy issue and presents several vulnerabilities that can jeopardize users’ privacy rights. Therefore, in this paper we propose an OAuth 2.0 based protocol for Smart City mobile applications that addresses the user privacy issue by integrating a pseudonym-based signature scheme and a signature delegation scheme into the OAuth 2.0 protocol flow. The proposed solution allows users to self-generate user-specific and app-specific pseudonyms on-demand and ensure privacy-enhanced user authentication at the Service Provider side. The proposed protocol has been validated with Proverif and its performance has been evaluated in terms of time and space complexity. Results show that the proposed protocol can provide users with efficient and effective means to authenticate towards service providers while preventing user tracking and impersonation from malicious entities located in the network side or in the users’ mobile device.

The recently proposed quadrature spatial modulation (QSM) has drawn an increasing attention due to its high spectral efficiency compared with the previous space modulation schemes. In this study, the performance of QSM in two‐way decode‐and‐forward relaying cooperative networks is investigated. In two‐way relaying cooperative networks, two source nodes are allowed to simultaneously transmit data on the same time slot to a relay node. The relay node decodes the transmitted data from both transmitting nodes and retransmits them in the next time slot. Using network coding techniques, each node is able to decode the data of the other node upon accomplishing the second time slot. Considering QSM as the adopted modulation at all nodes, the average bit error rates at the source nodes and the relay are formulated in a closed form expression. Obtained results reveal that QSM‐based two‐way relaying can achieve better error performance than other related scenarios.

Exploiting physical layer in achieving different security aspects in wireless communications has been widely encouraged. In this work, the authors propose an entity authentication scheme for mobile devices with multiple antennas, which is purely based on physical layer parameters. According to the proposed scheme, in order to authenticate a device, a number of predefined authentication signals should be detected at the receive antennas on the authenticator side. The transmitted signals are designed based on the instantaneous channel responses in order to deliver the authentication signals to the receiver. The proposed scheme works efficiently even for mobile users, which is considered a significant improvement over previous related works. Mathematical analysis of the different involved factors along with sufficient simulations show the high performance of the proposed authentication scheme.

Quadrature spatial modulation (QSM) is a recent multiple input multiple output transmission scheme that attracted significant research interest. QSM expands the spatial constellation diagram of spatial modulation (SM) to enhance the overall spectral efficiency while retaining all SM inherent advantages. In this paper, differential QSM (DQSM) is proposed to alleviate the requirement of channel knowledge at the receiver side. Receiver channel knowledge is crucial in QSM as part of the data are encoded in the Euclidean difference among different channel paths. Time dimension and orthogonal in-phase and quadrature spatial dimensions of QSM are exploited to facilitate differential modulation and demodulation while maintaining single RF-chain transmitters. In addition, a systematic design of the transmission blocks is provided for arbitrary number of transmit and receive antennas. Besides, a novel analytical framework for analyzing the performance of DQSM is derived and shown to predict accurate performance for differential SM and differential space shift keying systems as well. Analytical and simulation results are shown to match closely over a wide range of signal to noise ratios and for different system parameters.

Spectrum sensing in cognitive radio technology consumes a significant amount of time and energy resources. Thus, it has a direct effect on the achievable throughput and consumed energy. In case of multi-channel systems, the problem becomes more effective since both the resources expenditure and the performance influence of spectrum sensing increase. Considering energy detection as the spectrum sensing method, a number of energy samples should be collected from each channel. Unlike the conventional scheme, the number of samples collected from each channel should be different due to the variant channel conditions. In this paper, the number of samples collected from each channel is optimized based on different setups, namely, throughput maximization setup, interference minimization setup, and sensing energy minimization setup.

Abstract Cognitive radio is envisaged as a promising solution to cope with the problem of spectrum scarcity. In cognitive radio networks, users can sense the medium and opportunistically use available frequency bands. Users can cooperate in order to increase the reliability of the sensing process, which is called cooperative spectrum sensing (CSS). However, cooperative paradigms are threatened by the behavior of malicious users. Two types of attacks represent the main threats for CSS network operation, namely, spectrum sensing data falsification (SSDF) and incumbent emulation (IE). These two types of attacks have received a considerable amount of attention in the literature, but they have always been studied separately. In this paper, we propose a novel mechanism based on lightweight cryptography that considers both SSDF and IE attacks combined in a CSS network for the first time. Lightweight cryptography, in contrast to previous techniques used (such as intrusion detection or reputation systems), provides higher resilience to such attacks when a high number of mobile malicious users exist, providing better energy efficiency. Analytical and simulation results show the outperformance of the proposed algorithm compared with previous mechanisms, in terms of lower false alarm probability (i.e., higher chance of using the free frequency bands) and hence better energy ratings. Copyright © 2015 John Wiley & Sons, Ltd.

Cooperative Spectrum Sensing (CSS) was envisioned to improve the reliability of spectrum sensing process in cognitive radio networks. However, CSS is prone to security threats that degrade the overall performance. A popular attack in CSS is called spectrum sensing data falsification (SSDF) attack. In SSDF attack, a malicious user sends false spectrum sensing results to the fusion center, which significantly degrades detection accuracy and energy efficiency. In this paper, an attacker-punishment policy is proposed. The proposed policy is based on relating the scheduling probability for each user to its sensing performance, representing a punishment for attackers and a reward for honest users. The proposed policy includes identifying attackers, ignoring their reported results, and assigning a proper scheduling probability to each user. Two different approaches are presented to accomplish the proposed policy, namely, Majority-based Assessment and Delivery-based Assessment. Simulation results show that the proposed policy improves the individual energy efficiency of the honest CUs, and degrades the energy efficiency of the attackers.

Cooperative spectrum sensing (CSS) represents a key factor in the success of cognitive radio networks. CSS implies that users report their local sensing results to a fusion center in order to process them. The two popular reporting schemes are soft and hard schemes. In hard scheme, local sensing result is conveyed by a single bit, whereas the sensing result is reported as it is in the soft scheme. The more detection accuracy attained by soft scheme is confronted by more resource efficiency in hard scheme. This paper provides analytic comparison between both schemes in terms of throughput, energy consumption and energy efficiency. Our work includes deriving the sufficient conditions on the frame length by which the hard scheme outperforms soft scheme for each comparison aspect. Our results show that hard scheme always achieves higher throughput, while, at short frames and large number of users, it consumes less energy and attains higher energy efficiency.

One of the main challenges in cooperative spectrum sensing (CSS) for cognitive radio networks (CRN) is spectrum sensing falsification (SSDF) attack. A SSDF attack consists in a cognitive user providing false data about the spectrum status. SSDF attack can hugely degrade the achievable detection accuracy and energy efficiency of CRNs. In this paper, a robust CSS algorithm against SSDF attack is proposed. The proposed algorithm assigns a specific weight to each user, which is able to (i) completely eliminate the resulting effects on CSS caused by many types of SSDF attacks, (ii) convert some types of SSDF attacks to be honest users, and (iii) alleviate the influence of other honest users that suffer from poor sensing performance or/and very noisy reporting channels. Simulation results show that, compared to many previous works, a significant improvement in detection accuracy and energy efficiency can be attained by the proposed algorithm.

Although employing cooperation in spectrum sensing for cognitive radio (CR) systems improves the detection accuracy by mitigating the shadowing and multi-path fading faced by cognitive users, it increases the energy consumption especially because spectrum sensing is a periodic process. Therefore, for battery-powered terminals, energy efficiency represents a favorable metric in system design. One of the ways to improve the energy efficiency in CR is to optimize the fusion rule (FR) by which the individual results are processed. In this paper, we optimize the well known FR K-out-of-N for maximizing energy efficiency and detection accuracy. Mathematical expressions for the optimal N and K for both objectives are obtained. Simulation and analytical results show that significant improvement in energy efficiency can be achieved through FR optimization while satisfying a predefined threshold on the missed detection probability.

Energy efficiency during spectrum sensing in cognitive radio has received a lot of attention during recent years. Such issue becomes challenging, especially with battery-powered terminals, because of its direct influence on achievable performance represented by detection accuracy. In this paper, we present a novel reporting scheme for spectrum sensing results, which significantly reduces the energy consumption without any effect on the detection accuracy. The proposed scheme is based on the observation that sensing results are consecutively reported to a Fusion Center (FC), which allows the FC to terminate the process whenever the received results are enough to make a decision according to the employed Fusion Rule (FR). Hence, the energy consumed in results' reporting is reduced as the number of reporting users is lower. Mathematical expressions for the average number of reporting users for several FRs are obtained. Simulation and analytical results show a significant reduction of the energy consumption.

Energy efficiency in cooperative spectrum sensing in cognitive radio is investigated in this paper, where a novel approach is proposed for reducing the energy consumed in spectrum sensing and improving the resultant energy efficiency of the cognitive transmission. The proposed approach is based on limiting the number of users that participate in the spectrum sensing task. The participation decision of each user is taken individually by the user itself, where each user estimates the expected amount of consumed energy based on its distance from the base station, and compares it to a predefined threshold. The user will participate only if the estimated energy is less than the threshold. Besides reducing energy consumption, our proposal increases the amount of successfully transmitted data as well. Moreover, an optimization of the threshold is carried out through simulation in order to optimize the energy efficiency. Our results show a considerable amount of reduction in energy consumption (up to 80%) compared to the conventional approach.

Cognitive Radio provides a promising solution for the spectrum scarcity in wireless systems. The main stage of a successful cognitive transmission is the spectrum sensing stage, where the spectrum is sensed to detect and avoid interfering with licensed users. Unfortunately, regardless of the type of the spectrum sensing technique employed, the probability of missed detection can still be relevant. This paper investigates the effects of missed detection probability on the energy resources of the cognitive system, and provides a new algorithm for power allocation in OFDM systems, which reduces the loss in energy resources, and guarantees the target Quality-of-Service (QoS) of the served users. Unlike the current algorithms, the proposed algorithm is based on the Sensing Side Information (SSI) and the Channel State Information (CSI) as well. Simulation results underline a relevant reduction in terms of power loss (with gains up to 50%) and a consequent improvement in QoS satisfaction.

One of the main challenges in Cognitive Radio Networks (CRN) is the high energy consumption during the spectrum sensing stage, especially employing a cooperative approach. The algorithm proposed in this paper aims to reduce the energy consumption while maintaining the probability of detection and false alarm probability to the desired thresholds. The algorithm is based on decreasing the number of sensing users using a simple and practical approach. The performance of our approach is then compared in terms of energy efficiency with the different data fusion rules available in the literature. As a result, more than 95% energy saving can be achieved, as shown through mathematical equations and confirmed by simulation results.