Spectrum Efficiency Research Articles

Enhanced capsule generative adversarial network for spectrum and energy efficiency of cooperative spectrum prediction framework in cognitive radio network

AbstractCognitive radio network (CRN) is an intellective technology that frequently monitors the unused licensed spectrum in a particular frequency band. When more count of secondary users enters inside the channel may results in collisions. So, the secondary user may not sense the state of inactive and busy state of the primary user resulting reduces the spectrum efficiency (SE) and energy efficiency (EE) of CRN. To overcome these issues, an enhanced capsule generative adversarial network (ECGAN) for spectrum and energy efficiency of cooperative spectrum prediction (CSP) framework in CRN is proposed to improve the channel occupancy. Initially, CRN system is designed to improve the spectrum efficiency and energy efficiency. Then, channel state of primary user is predicted by using the coupled hidden Markov model (CHMM) and ECGAN predictors. Hence, the correlation among the secondary user predict the next channel status, like AND, OR, majority rule fusion methods. The prediction error, spectrum efficiency, energy efficiency based these methods are compared with CHMM and ECGAN predictors as the process of channel occupancy based on. Also, the effect of busy and idle state prediction errors on SE is detected. The proposed method is simulated in MATLAB. Then, the performance of the proposed method shows higher energy efficiency 13.86%, 24.84%, 34.75%, compared with existing methods, such as spectrum and energy efficiency of CSP in CRN (SEE‐CSP‐CRN‐HMM), (SEE‐CSP‐CRN‐MLP), differential evolution based machine learning scheme for secure cooperative spectrum sensing system (SEE‐CSP‐CRN‐EML), cooperative spectrum sensing for primary user detection in CRN utilizing support vector machine (SEE‐CSP‐CRN‐SVM), respectively.

Deep Q-learning multiple networks based dynamic spectrum access with energy harvesting for green cognitive radio network

In cognitive radio (CR), dynamic spectrum access (DSA) can be used for secondary user (SU) to improve its spectrum efficiency under the limited spectrum resources. However, the SU has to consume more energy to sense the state of primary user (PU) before spectrum access. Therefore, high spectrum efficiency and lower energy consumption have become the requirements of CR. In this paper, we propose a sustainable green CR network combining DSA and energy harvesting, which can perform intelligent spectrum sensing, spectrum access and energy harvesting by a reward mechanism of deep Q-learning multiple networks (DQMN). The DQMN model consisting of multiple neural networks is designed to learn multiple learning objectives, including spectrum sensing, channel selection, communication power and access mode in DSA. A sleep mechanism is introduced to optimize the spectrum access mode and further reduce the energy consumption. The simulation results show that the DQMN-based DSA model can autonomously sense the channel state, harvest the energy, and then select the appropriate access strategy. Due to the energy harvesting and sleep mechanism, the proposed system model shows lower energy consumption and higher average effective throughput than the traditional models.

Enhancing NOMA’s Spectrum Efficiency in a 5G Network through Cooperative Spectrum Sharing

Non-orthogonal multiple access (NOMA) is one of the most effective techniques for meeting the spectrum efficiency (SE) requirements of 5G and beyond networks. This paper presents two novel methods for improving the SE of the downlink (DL) NOMA power domain (PD) integrated with a cooperative cognitive radio network (CCRN) in a 5G network using single-input and single-output (SISO), multiple-input and multiple-output (MIMO), and massive MIMO (M-MIMO) in the same network and in a single cell. In the first method, NOMA users compete for free channels in a competing channel (C-CH) on the CCRN. The second method provides NOMA users with a dedicated channel (D-CH) with high priority. The proposed methods are evaluated using the Matlab software program using the three scenarios with different distances, power location coefficients, and transmitting power. Four users are assumed to operate on 80 MHz bandwidths (BWs) and use the quadrature phase shift keying (QPSK) modulation technique in all three scenarios. Successive interference cancellation (SIC) and unstable channel conditions are also considered when evaluating the performance of the proposed system under the assumption of frequency selective Rayleigh fading. The best four-user SE performance obtained by user U4 was 3.9 bps/Hz/cell for SISO DL NOMA, 5.1 bps/Hz/cell for SISO DL NOMA with CCRN with C-CH, and 7.2 bps/Hz/cell for SISO DL NOMA with CCRN with D-CH at 40 dBm transmit power. While 64 × 64 MIMO DL NOMA improved SE performance of the best-use U4 by 51%, 64 × 64 MIMO DL NOMA with C-CH CCRN enhanced SE performance by 64%, and 64 × 64 MIMO DL NOMA with D-CH CCRN boosted performance by 65% SE compared to SISO DL NOMA at 40 dB transmit power. While 128 × 128 M-MIMO DL NOMA improved SE performance for the best U4 user by 79%, 128 × 128 M-MIMO DL NOMA with C-CH CCRN boosted SE performance by 85%, and 128 × 128 M-MIMO DL NOMA with D-CH CCRN enhanced SE performance by 86% when compared to SISO DL NOMA SE performance at 40 dB transmit power. We discovered that the second proposed method, when using D-CH with CCR-NOMA, produced the best SE performance for users. On the other hand, the spectral efficiency is significantly increased when applying MIMO and M-MIMO techniques.

Design of a slotted waveguide antenna to launch lower hybrid fast wave in the KSTAR Tokamak

Lower hybrid fast wave (LHFW) has been proposed for heating and current drive in high density plasmas to overcome the density limit of conventional slow wave current drive (LHCD). The feasibility of the LHFW was tested through coupling experiments in the Versatile Experiment Spherical Torus (VEST) device. We design a 2.45 GHz waveguide antenna for the further investigation of the LHFW in the KSTAR tokamak. RF modelling of a slotted waveguide antenna is conducted in a vacuum and plasma medium using COMSOL in order to launch 2.45 GHz fast waves with n∥0 ∼ 2.87. A slotted waveguide antenna for the LHFW is designed according to simulation results which show field patterns for fast wave polarization, a n∥ spectrum and coupling efficiency between the antenna and plasmas.

HBRO-AlexNet: Honey Badger Remora Optimization Integrated AlexNet for Cooperative Spectrum Sensing in Cognitive Radio Network

Cognitive radio (CR) technology enables a secondary user (SU) to make the most use of the licensed spectrum when the primary user (PU) is inactive, hence increasing spectrum efficiency. SUs are required to complete the spectrum sensing process to identify the spectrum utilization. It is required to effectively detect PU signal to SU for using the idle licensed spectrum bands. Even though various spectrum sensing techniques are designed in CR networks, designing test statistics still results in a complex task. To solve spectrum scarcity issues and to increase spectrum utilization, Honey Badger Remora Optimization-based AlexNet (HBRO-based AlexNet) is developed in this research and the test statistics model is modeled with a deep learning approach with signal parameters, like signal energy, and Eigen statistics. However, SU can use AlexNet to boost the spectrum efficiency of PU's licensed spectrum, which will then permit an increase in the chance of detection in the CR network (CRN). Though considering signal-to-noise ratio (SNR) at 5 dB, the proposed spectrum sensing approach yields the probability of detection and probability of false alarm for the Rician channel as 1 and 0.999, respectively.

Coordinating Multiple Light-Trails in Multicast Elastic Optical Networks With Adaptive Modulation

Optical multicasting has been considered resource efficient for multicast services. Light-tree and light-trail are two technologies that support optical multicasting while the former requires many splitters and thus experiences significant power loss. In this paper, we consider using the light-trail technology for the accommodation of multicast requests in elastic optical networks with adaptive modulation. For better spectrum efficiency, we consider accommodating each multicast by multiple light-trails. We formulate the problem by Mixed Integer Linear Programming (MILP) and propose efficient heuristic algorithms. For the impact of accommodation sequence on the algorithm performance, apart from the traditional sequence among different requests, we consider an additional sequence among the destinations of a multicast. For efficient multicast accommodation, we propose several strategies and compare their performances through a range of cases. To avoid a destination occupying excessive resources in certain cases of joining multiple light-trails, we propose an efficient algorithm to delete some duplicated destinations. Numerical results show that the proposed heuristic algorithms significantly outperform a benchmark algorithm and one performs close to the optimal MILP. Also, the algorithm for deleting certain destination replicas largely reduces the spectrum and transmitter usages, up to 41% and 20% for the cases considered, respectively.

On the Physical Layer Security Performance Over RIS-Aided Dual-Hop RF-UOWC Mixed Network

Since security has been one of the crucial issues for high-yield communications such as 5G and 6G, researchers continuously come up with newer techniques to enhance the security and performance of these progressive wireless communications. Reconfigurable intelligent surface (RIS) is one of those techniques that artificially rearrange and optimize the propagation environment of electromagnetic waves to improve both spectrum and energy efficiency of wireless networks. Besides, in underwater communication, underwater optical wireless communication (UOWC) is a better alternative/replacement for conventional acoustic and radio frequency (RF) technologies. Hence, mixed RIS-aided RF-UOWC can be treated as a promising technology for future wireless networks. This work focuses on the secrecy performance of mixed dual-hop RIS-aided RF-UOWC networks under the intercepting effort of a probable eavesdropper. The RF link operates under generalized Gamma fading distribution; likewise, the UOWC link experiences the mixture exponential generalized Gamma distribution. The secrecy analysis subsumes the derivations of closed-form expressions for average secrecy capacity, exact and lower bound of secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, all in terms of Meijer's <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$G$</tex-math></inline-formula> functions. Capitalizing on these derivations, the effects of heterodyne and intensity modulation/direct detection systems, underwater turbulence resulting from air bubble levels, temperature gradients, and salinity gradients, are measured. Unlike conventional models that merely deal with thermally uniform scenarios, this proposed model is likely to be unique in terms of dealing with secrecy analysis of a temperature gradient RIS-aided RF-UOWC network. Lastly, the derivations are validated via Monte-Carlo simulations.

Experimental investigation on the low-pressure pyrolysis of cyclohexane initiated by 1-nitropropane in a flow tube reactor

An experimental study of 5% 1-nitropropane (1-NP)-initiated cyclohexane pyrolysis was carried out in a flow reactor at 30 Torr (4.0 kPa) over a temperature range of 673–1273 K. The pyrolysis species were detected with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technique. Pyrolysis species from m/z 15–106, including C1-C8 hydrocarbons, CO, NO, NO2, CH2O, CH3OH and C3H5NO, were identified with near-threshold photoionization efficiency (PIE) spectra and quantified at different temperatures. The experimental results indicated that the addition of 1-NP obviously reduced the initial pyrolysis temperature of cyclohexane from 1048 to 1098–723 K, and caused the decreases of the initial formation temperatures for the species from cyclohexane pyrolysis. Almost all the high-temperature pyrolysis species in the mechanisms proposed in the literature were identified in the experiments. Based on the experimental results in this work and rate coefficients proposed in the literature, the primary pyrolysis mechanisms of cyclohexane in the presence of 1-NP were discussed. The 1-NP pyrolysis occurs at a lower temperature than the cyclohexane does, and produces HONO, NO2, C3H7, etc. It was demonstrated that cyclohexane was mainly consumed via the H-atom abstractions by H and OH attacks in this work and the cyclohexyl radical formed via H-atom abstractions mainly isomerized into 1-C6H11-6 radical, which further combines with H to form 1-C6H12.

Multi-Operator Dynamic Spectrum Sharing for Wireless Communications: A Consortium Blockchain Enabled Framework

To enable secure and efficient dynamic spectrum sharing (DSS) with guaranteed revenue and quality of service (QoS) in future wireless communications, we present a consortium blockchain based DSS framework, where the regulators supervise the whole process of DSS, and thus the revenue of each participant can be guaranteed. Each mobile network operator (MNO) on the chain can adaptively act as a spectrum provider or spectrum requestor based on their demand, and the spectrum resource allocation is recorded on the chain with a smart contract. The optimal spectrum pricing and buying strategies are solved based on a multi-leader multi-follower (MLMF) Stackelberg game model, and the equilibrium is solved with the proposed algorithm. We then build a prototype with Hyperledger Fabric consortium blockchain, and the average latency is evaluated. Simulations and prototype evaluations validate the feasibility of blockchain based DSS and show that the average latency increase with the participants, which provides useful insights for real applications.

IRS Empowered Robust Secure Transmission for Integrated Satellite-Terrestrial Networks

In this letter, we investigate an intelligent reflecting surface (IRS) empowered robust secure transmission approach for an integrated satellite and terrestrial network (ISTN) with multiple eavesdroppers. The satellite transmits multicast signals to earth stations (ESs) within its coverage, while the base station (BS) serves many terrestrial users (TUs) with the aid of IRS. To improve the security of the satellite system, by assuming that only imperfect channel state information is available, we formulate a weighted sum rate maximization problem subject to the intercept probability constraints, the quality-of-service requirement of each ES and TU, and the transmit power budget of the satellite platform and BS. To tackle this non-convex problem, we jointly employ the Charnes-Cooper approach, the second order Taylor expansion and Bernstein-type inequality, and propose a successive convex approximation based algorithm to obtain the satellite beamforming weight vector, the BS power allocation and the IRS phase shifts. Finally, simulation results demonstrate that our proposed scheme can improve the spectrum efficiency and secrecy performance of ISTNs compared to the benchmarks.

Geometrically-Shaped Multi-Dimensional Modulation Formats in Coherent Optical Transmission Systems

Shaping modulation formats in multi-dimensional (MD) space is an effective approach to harvest spectral efficiency gains in both the additive white Gaussian noise (AWGN) channel and the optical fiber channel. In the first part of this paper, existing MD geometrically-shaped modulations for fiber optical communications are reviewed. It is shown that large gains can be obtained by exploiting correlation in the dimensions or/and by increasing the cardinality of the modulation format. Practical limitations and challenges are also discussed together with efficient solutions. In the second part, we extend the recently proposed four-dimensional (4D) modulation format family based on the constraint of orthant-symmetry to high spectrum efficiencies up to 10 b/4D-sym by maximizing generalized mutual information for AWGN channel. Reach increases of up to 25% for a multi-span optical fiber transmission system are reported. Lastly, with the help of a recently introduced nonlinear interference (NLI) model, an optimization for designing nonlinear-tolerant 4D modulation formats is introduced for a single-span optical fiber system. Simulation results show that the proposed NLI model-based 4D modulation format could increase the effective SNRs by 0.25 dB with respect to the AWGN channel-optimal 4D modulation format.

Outage Analysis of Rate Splitting Networks With an Untrusted User

Rate splitting (RS) can significantly improve the spectrum efficiency and degrees of freedom of multi-access transmissions. However, due to the characteristics of RS decoding, the secure transmission remains a challenge especially when there is an untrusted near user. Thus, two RS schemes are proposed with different successive interference cancellation (SIC) layers. For both schemes, the users first decode the common stream. In the one-layer-SIC scheme, the users then decode their own private streams without interference via zero-forcing. For the two-layer-SIC scheme, maximum ratio transmission is adopted for the trusted far user. The users decode the private stream of the untrusted user and then decode the other. Outage probability and secrecy outage probability are analyzed based on the channel statistics and the achievable rate. Simulation results verify the theoretical results and demonstrate the advantages of two schemes in terms of the common stream transmission and the security of far user.

Secure Beamforming for IRS-Enhanced NOMA Networks

Owing to the increasing demand of higher spectrum efficiency and large-scale connectivity, non-orthogonal multiple access (NOMA) has become a highly competitive candidate for the upcoming sixth-generation (6G) systems. Nevertheless, the instable wireless propagation environment and potential wireless security risk become bottlenecks in applications of NOMA. Fortunately, intelligent reflecting surface (IRS) that can construct the three-dimensional beamforming and reconfigure the channels emerges as a highly efficient technology to break through the limitations of NOMA. Thus, in this article, we first present an overview of NOMA, and particularly illustrate its main shortcomings and security risks. Then, we introduce the IRS technology and provide further enhancement by applying IRS to NOMA networks. In addition, typical security threats in IRSNOMA networks are shown, followed by two countermeasures based on the joint transmit beamforming and IRS reflecting beamforming towards external and internal eavesdropping, respectively. Simulation results are carried out to demonstrate the feasibility and effectiveness of these two schemes. Several challenges and future directions are also discussed.

AFC-CE Hybrid Precoding for Energy-Efficient mmWave MIMO Systems

In this letter, an energy-efficient hybrid precoding method based on cross-entropy (CE) is proposed for the adaptive fully-connected (AFC) structure in millimeter wave massive multiple-input multiple-output systems, named the AFC-CE algorithm. By the nonlinear Tomlinson-Harashima precoding method, the non-convex spectrum efficiency maximization problem is transformed into a matrix residual minimization problem between the hybrid precoding matrix and the optimal precoding matrix. Then, using CE theory, the matrix residuals minimization problem is transformed into a probability distribution optimization problem of switching precoding matrix elements. Finally, the probability distribution parameters are updated adaptively by minimizing the CE between the estimated value and the expected value, until the residual converges and the switching precoding matrix is obtained. On this basis, the generalized power method and the least square method are used to give the phase shifts precoding matrix and the digital precoding matrix, respectively. Theoretical analysis and simulation results verify that the proposed method not only has lower computational complexity but also can provide better spectral efficiency and energy efficiency.

Over-the-Air Integrated Sensing, Communication, and Computation in IoT Networks

To facilitate the development of Internet of Things (IoT) services, tremendous IoT devices are deployed in the wireless network to collect and pass data to the server for further processing. Aiming at improving the data sensing and delivering efficiency, the integrated sensing and communication (ISAC) technique has been proposed to design dual-functional signals for both radar sensing and data communication. To accelerate the data processing, the function computation via signal transmission is enabled by over-the-air computation (AirComp), which is based on the analog-wave addition property in a multi-access channel. As a natural combination, the emerging technology namely over-the-air integrated sensing, communication, and computation (Air-ISCC) adopts both the promising performances of ISAC and AirComp to improve the spectrum efficiency and reduce latency by enabling simultaneous sensing, communication, and computation. In this article, we provide a promptly overview of Air-ISCC by introducing the fundamentals, discussing the advanced techniques, and identifying the applications.

Blockchain-enhanced cross-ISP spectrum assignment framework in SDONs: SpectrumChain

Huge potentials of optical networks provide an excellent choice in meeting the exponential growth in bandwidth demand. In particular, Elastic Optical Networks (EONs), with its promising potentials in increased availability, failure resilience, load-balancing, and efficient resource allocations, are good candidates for the future high-speed networks. When EONs are augmented with the emerging Software Defined Networking (SDN) architecture, which decouples the data and control planes, an agile and synergistic combination emerges under a general term of Software Defined Optical Networking (SDON), albeit with operational challenges such optimal and efficient spectrum assignments. In this paper, we present a blockchain-enhanced QoS-concentrated cross-Internet Service Provider (ISP) spectrum assignment framework for SDONs, SpectrumChain (SC), to eliminate centralized mediators while coordinating QoS-based inter-ISP traffic. This study introduces a new blockchain use-case with reduced QoS signaling overhead while performing inter-ISP routing in SDONs. We also experience the proposed framework under Hop-by-Hop Wavelength Switching (HWS), Border-Node-Only Wavelength Switching (BWS), and No Wavelength Switching (NWS) scenarios to analyze its performance. Our extensive simulation results show that the SC framework can effectively handle the QoS-enabled inter-ISP routing in SDON architecture in terms of Flow Setup Time (FST), Messages Processed (MEP), Requests Serviced (RS), and Acceptance Ratio (AR) metrics under HWS, BWS, and NWS scenarios.

SWIPT-Based Cooperative NOMA for Two-Way Relay Communications: PSR versus TSR

Spectrum and energy efficiency with simultaneous wireless information and power transfer (SWIPT) to prolong the lifetime of power-constrained wireless devices in cooperative relaying nonorthogonal multiple access (CR-NOMA) has received great attention in the last decade. This paper investigates a two-way relay channel in a CR-NOMA system where two users exchange data with the assistance of a relay. Power-splitting relaying (PSR) and time-switching relaying (TSR) protocols are employed at the relay to harvest RF energy and process information from two users. We firstly derive the exact expressions of outage probability (OP) and system throughput (ST). The impacts of signal quality, energy coefficients, the distance of the nodes, and the data rate of two users on these performance metrics are then evaluated through several system settings to reflect practical network scenarios. It is shown that the OP and ST of the TSR are superior to that of the PSR protocol. Specifically, numerical results indicate that a higher throughput of up to 8% can be achieved with the TSR when compared to the PSR. It is further revealed that the OP and ST of the PSR are strongly affected by energy harvesting (EH) coefficients, while the performance obtained with the TSR is nearly independent of the EH capability at the relay.

A Novel Low Complexity Two-Stage Tone Reservation Scheme for PAPR Reduction in OFDM Systems.

Orthogonal frequency division multiplexing (OFDM) has the characteristics of high spectrum efficiency and excellent anti-multipath interference ability. It is the most popular and mature technology currently in wireless communication. However, OFDM is a multi-carrier system, which inevitably has the problem of a high peak-to-average power ratio (PAPR), and s signal with too high PAPR is prone to distortion when passing through an amplifier due to nonlinearity. To address the troubles caused by high PAPR, we proposed an improved tone reservation (I-TR) algorithm to alleviate the above native phenomenon, which will pay some modest pre-calculations to estimate the rough proportion of peak reduction tone (PRT) to determine the appropriate output power allocation threshold then utilize a few iterations to converge to the near-optimal PAPR. Furthermore, our proposed scheme significantly outperforms previous works in terms of PAPR performance and computational complexity, such as selective mapping (SLM), partial transmission sequence (PTS), TR, tone injection (TI), etc. The simulation results show that in our proposed scheme, the PAPR is appreciably reduced by about 6.44 dB compared with the original OFDM technique at complementary cumulative distribution function (CCDF) equal to 10-3, and the complexity of I-TR has reduced by approximately 96% compared to TR. Besides, as for bit error rate (BER), our proposed method always outperforms the original OFDM without any sacrifice.

An Artificial Intelligence-Assisted Expectation Propagation Detection for MIMO Systems

Multiple-input multiple-output (MIMO) technology is one of the key technical approaches to improve the spectrum efficiency of wireless communication. Modern communication systems employ MIMO and high-order quadrature amplitude modulation (QAM) to maximize spectral efficiency. However, with the increase in the number of antennas and modulation orders, it is very challenging to design a low-complexity and high-efficiency MIMO receiver. In recent years, with the rapid development of new technologies such as artificial intelligence, more and more researchers have tried to apply machine learning techniques in the field of communication to break through the performance of traditional communication algorithms. In this paper, we propose a new low-complexity MIMO detection algorithm: an artificial intelligence-assisted expectation propagation (EP) detection algorithm. Neural network models are used to learn and map some of the time-consuming steps in the EP detection algorithm, converting the complex operation process into a few matrix multiplication operations in order to reduce the complexity of the detection algorithm. It is verified that the method proposed in this paper can approximate the performance of the original EP detection algorithm with reduced complexity and is applicable in different scenarios.

Deep Non-Orthogonal Multiple Access Network Assisted by Intelligent Reflecting Surface

The intelligent reflecting surface (IRS) assisted non-orthogonal multiple access (NOMA) symbiotic communication technology is expected to enhance the access performance, energy efficiency and spectrum efficiency of the communication network, and is regarded as an important candidate technology to support the evolution of the sixth-generation (6G) towards large-scale, high-capacity and sustainable development. However, the relevant research of this technology is still at the initial stage, and many key challenges have not been fully studied. Therefore, it is urgent to open up relevant research ideas and methods to promote its development and early implementation, so as to make it an effective 6G technology. In view of this, this paper intends to carry out the research on the theory and method of IRS assisted NOMA symbiotic transmission, starting from the analysis of the active and passive symbiotic mechanism of NOMA transmission protocol. Based on this, we further study the efficient symbiotic modulation transmission technology and multi-dimensional resource optimization allocation method. The research content of this paper is to explore the transmission theory and technology of high energy efficiency and high frequency spectrum efficiency for 6G, and break through the bottleneck problem of spectrum and energy consumption encountered by wireless communication, which has important practical significance for the wireless communication.