High-quality Transmission Research Articles

Cell-Free Massive MIMO-OFDM for High-Speed Train Communications

Cell-free (CF) massive multiple-input multiple-output (MIMO) systems show great potentials in low-mobility scenarios, due to cell boundary disappearance and strong macro diversity. However, the great Doppler frequency offset (DFO) leads to serious inter-carrier interference in orthogonal frequency division multiplexing (OFDM) technology, which makes it difficult to provide high-quality transmissions for both high-speed train (HST) operation control systems and passengers. In this paper, we focus on the performance of CF massive MIMO-OFDM systems with both fully centralized and local minimum mean square error (MMSE) combining in HST communications. Considering the local maximum ratio (MR) combining, the large-scale fading decoding (LSFD) cooperation and the practical effect of DFO on system performance, exact closed-form expressions for uplink spectral efficiency (SE) expressions are derived. We observe that cooperative MMSE combining achieves better SE performance than uncooperative MR combining. In addition, HST communications with small cell and cellular massive MIMO-OFDM systems are compared in terms of SE. Numerical results reveal that the CF massive MIMO-OFDM system achieves a larger and more uniform SE than the other systems. Finally, the train antenna centric (TA-centric) CF massive MIMO-OFDM system is designed for practical implementation in HST communications, and three power control schemes are adopted to optimize the propagation of TAs for reducing the impact of the DFO.

Time-Synchronized Control of Chaotic Systems in Secure Communication

High-quality data transmission synchronization process is frequently expected in light of secure communication mechanisms (SCMs), especially for space laser communication among the satellite constellation. To improve security and reliability during the data transmission processes prominently, control problems of chaotic synchronization synchronously <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">at the same time</i> are explored. In this paper, several novel error synchronization control protocols are proposed to solve these problems. First, by introducing a norm-normalized sign function (NNSF), unique (fixed-) time-synchronized stability is manifested, such that all non-zero state elements reach the origin synchronously at the same time. And upper bounds of synchronous resident time calculated by offered protocols are irrelevant/relevant to initial states of the error systems. Second, integrated with the (fixed-) time-synchronized stability theories, the (fixed-) time-synchronized sliding mode controllers with special convergent performance are established for two representative types of chaotic systems. Third, the ratio-persistent performance plays a dominating role for simultaneous convergence of the errors. Further, the innovation of the algorithms is reflected in that the decrypted signal is completely consistent with the transmitted message signal within synchronized settling time. Finally, in the simulation, not only theoretical verifications, but also practical verifications of image encryption and decryption processes verify the effectiveness of the SCMs.

Transmit Antenna Selection in NOMA-Based Integrated Satellite-HAP-Terrestrial Networks With Imperfect CSI and SIC

Integrated satellite-high altitude platform-terrestrial networks (IS-HAP-TNs) and non-orthogonal multiple access (NOMA) scheme are considered to be the key components of next generation networks, which can satisfy the demands of high-quality transmission, wide coverage and large-scale connections. In this letter, we analyze the performance of NOMA-based IS-HAP-TNs with transmit antenna selection (TAS) in the presence of imperfect channel state information (CSI) and successive interference cancellation (SIC). Specifically, considering the requirements of different users for spectrum efficiency, two TAS schemes are proposed to balance the system performance and complexity. In addition, the closed-form expressions for the outage probability of the IS-HAP-TNs in the presence of imperfect CSI and SIC are derived to verify the performance of different schemes. Besides, the asymptotic outage behavior and diversity orders at high signal-to-noise ratios are also presented to get further insights. Finally, Monte Carlo simulations manifest the advantages and disadvantages characters of two schemes and reveal the impacts of key parameters on the system performance.

Polarization multiplexed electromagnetically induced transparency metasurface based on VO2 with high-performance sensing application

A vanadium dioxide (VO2) based dielectric metasurface is proposed to realize polarization multiplexed electromagnetically induced transparency (EIT) effect with tunability. In the near-infrared regime, distinct transparency windows with high transmission intensity and quality factor (Q-factor) can be observed under the excitation of two orthogonal polarized lights. By changing the conductivity of VO2, the EIT peak intensity and the group delay of the incident light can be manipulated dynamically. Meanwhile, the narrow transparency window is extremely sensitive to the change of the surrounding refractive index, and the proposed metasurface exhibits high sensitivity and figure of merits in both x- and y-polarization conditions. Therefore, the proposed dielectric metasurface based on VO2 provides a new method for dynamically controlled EIT effects in the near-infrared region and inspires potential applications in optical modulations, tunable slow light devices, and high-performance refractive index sensors, etc.

Joint Code Rate Compatible Design of DP-LDPC Code Pairs for Joint Source Channel Coding Over Implant-to-External Channel

A CM2-S3 transmission link in wireless body area networks (WBAN) is implemented with a joint source channel coding (JSCC) system based on double protograph low-density parity-check (DP-LDPC) code pairs with high reliability and low power consumption. For the practicality and suitability considerations, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -ary differential chaos shift keying scheme is introduced to modulate the CM2-S3 channel with better performance than the standard modulations in WBAN. Due to the non-Gaussian-like distribution of the CM2-S3 channel model, the initial joint protograph extrinsic information transfer (JPEXIT) algorithm does not work as a coding analysis tool. To solve this problem, a numerical Gaussian approximation is employed to modify the iterative mutual information function of the JPEXIT for achieving more precise output. Then, a joint code rate compatible (JCRC) method, designed with compatibility in resisting variable channel variances and adapting different source statistics, is proposed for optimizing the DP-LDPC code pairs. Based on the JCRC method, the code searching algorithm is simplified with lower complexity because of the reduced cycle-index. The simulation results show that optimized code pairs have better bit-error ratio performances compared to existing codes, which provides a strong technical support to promote high-quality data transmission in eHealthcare on the physical layer.

On Atmospheric Retrievals of Exoplanets with Inhomogeneous Terminators

The complexity of atmospheric retrieval models is largely data-driven, and one-dimensional models have generally been considered adequate with current data quality. However, recent studies have suggested that using 1D models in retrievals can result in anomalously cool terminator temperatures and biased abundance estimates even with existing transmission spectra of hot Jupiters. Motivated by these claims and upcoming high-quality transmission spectra, we systematically explore the limitations of 1D models using synthetic and current observations. We use 1D models of varying complexity, both analytic and numerical, to revisit claims of biases when interpreting transmission spectra of hot Jupiters with inhomogeneous terminator compositions. Overall, we find the reported biases to be resulting from specific model assumptions rather than intrinsic limitations of 1D atmospheric models in retrieving current observations of asymmetric terminators. Additionally, we revise atmospheric retrievals of the hot Jupiter WASP-43b (T eq = 1440 K) and the ultra-hot Jupiter WASP-103b (T eq = 2484 K), for which previous studies inferred abnormally cool atmospheric temperatures. We retrieve temperatures consistent with expectations. We note, however, that in the limit of extreme terminator inhomogeneities and high data quality, some atmospheric inferences may conceivably be biased—although to a lesser extent than previously claimed. To address such cases, we implement a 2D retrieval framework for transmission spectra that allows accurate constraints on average atmospheric properties and provides insights into the spectral ranges where the imprints of atmospheric inhomogeneities are strongest. Our study highlights the need for careful considerations of model assumptions and data quality before attributing biases in retrieved estimates to unaccounted atmospheric inhomogeneities.

A comprehensive study on radio over fiber systems: present evaluations and future challenges

Abstract In order to serve the explosive demands of triple play services or multimedia services with high quality of data transmission in Fifth Generation (5G) communication systems which has availability of large spectrum unlike Fourth Generation (4G), low latency, improved transmission, and increased reliability, an access networks with optical fiber distribution network and wireless enabled technology is urgently needed and therefore, a prominent technology known as Radio over Fiber (RoF) is suggested by researcher/Scientists due to a perfect blend of flexible fiber technology and wireless mobility. RoF technology is helping the data transmission systems from last thirty years with great success and has numerous advantages such as scalability, transparency, antenna site complexity reduction, low installation cost, accessibility of radio carrier by diverse antenna sites dynamically. Millimeter waves (Mm waves) integration in 5G wireless RoF systems comes out to be an encouraging candidate to cater the bandwidth hungry current as well as future generation internet application such as high definition TV (HDTV), online games, video conferencing, and voice over IP (VoIP) etc. For the prolonged reach, economical installations, and improved performance, optimal Mm wave generation methods should be incorporated in 5G such as employing multi carrier generation technique (MCG). Deployment of single mode fiber (SMF) in 5G offers high speed, large capacity, improved security, etc., but also has a prominent limitation of nonlinear effects and it is unwanted phenomenon which degrade the system performance by introducing intermodulation distortion, distortion of signal phase, harmonic distortion, and interference in the neighbouring channels. Minimum modifications of architecture and minimum cost should be spent on the compensation of nonlinear effects or Kerr’s effects in RoF systems and recently mode division multiplexing has emerged as an ultimate solution. In this review article, detailed discussion of an evolutionary technology, i.e., RoF is presented with a literature review, present evaluations, and future challenges. Our utmost goal is to enrich the young researchers with precious aspects for RoF technology on single platform and also encourage them to conduct the technology advancement research works in various fields such as nonlinear compensation, Mm wave generation, dispersion compensation, cost reduction, complexity reduction, and security enhancements for 5G RoF systems.

Reconfigurable high-Q terahertz filtering of VO2-based metamaterials using optical tunneling

Up to date, reconfigurable terahertz (THz) band-pass filters based on the design of metamaterials with vanadium dioxide (VO2) have been investigated extensively. However, VO2-based THz metamaterials with high-quality tunable narrowband transmission and good stop-band rejection have yet to be reported, which are essential for THz wave filtering components or systems. Here, we propose a reconfigurable filter in combination with a dielectric metastructure and a VO2 thin film. Utilizing the optical tunneling effects of a cavity layer, the filter has a high band-pass transmission up to 98% at 0.246 THz with a narrow bandwidth of 0.0009 THz, an ultra-high Q-factor of 273, and two broad nearly-suppressed sidebands. The transmission intensity can be modulated by the phase transition of VO2, and the modulation depth is as high as 96.4%. By efficiently tuning the cavity layer thickness, the filter can be designed for a series of transmission wavelengths and further accomplish the switch between the narrow band-pass filtering and wideband reflection. Moreover, the manipulation of the incident angle and polarization can be adopted as an additional degree to achieve a similar switching function. Our study implies a potential for developing various THz applications, where reconfigurable high-Q THz filtering is required.

Leveraging Machine Learning for Millimeter Wave Beamforming in Beyond 5G Networks

Millimeter wave (mmWave) communication has attracted considerable attention as a key technology for the next-generation wireless communications thanks to its exceptional advantages. MmWave leads the way to achieve a high transmission quality with directed narrow beams from source to multiple destinations by adopting different antenna beamforming (BF) techniques, which have a pivotal role in establishing and maintaining robust links. However, realizing such BF gains in practice requires overcoming several challenges, such as severe signal deterioration, hardware constraints, and design complexity. The elevated complexity of configuring mmWave BF vectors encourages researchers to leverage relevant machine learning (ML) techniques for better BF configurations deployment in 5G and beyond. In this article, we summarize mmWave BF strategies employed for future wireless networks. Then, we provide a comprehensive overview of ML techniques plus its applications and promising contributions toward efficient mmWave BF deployment. Furthermore, we discuss mmWave BF’s future research directions and challenges. Finally, we discuss a single and concurrent mmWave BF case study by applying multiarmed bandit to confirm the superiority of ML-based methods over conventional ones.

High-throughput finite-element design of dielectric composites for high-frequency copper clad laminates

Dielectric substrates with low dielectric constant and good thermal stability are highly desired for high-frequency and high-speed signal transmission. It is however challenging to rationally design the demand-satisfied polymer-based composites due to the inadequate understanding of the contradictory effect of inorganic fillers on modulating dielectric-thermal-mechanical properties. In this work, taking Polytetrafluoroethylene (PTFE)-SiO2 composite as the example, we perform high-throughput finite-element calculations to systematically study the filler effects on the dielectric constant of composites εrcomposite and the coefficient of thermal expansion of composites (CTE-c). A series of influencing factors including intrinsic property, volume fraction, shape, distribution, and orientation of fillers have been considered in our models to establish the structure-property mapping of dielectric composites. It is found that CTE-c is more sensitive to the filler structure of PTFE-SiO2 composites than εrcomposite. Finally, guided by the calculation results, a skeleton structure is proposed to realize the performance targets of εrcomposite< 2.3 and CTE-c < 60 ppm/K with lower SiO2 filler content. This work provides a universal data-driven strategy for the rational design of dielectric composites with multi-objective requirements, and it is expected to spark more experimental efforts to design novel dielectric composites for high-quality signal transmission.

Bound states in the continuum in all-van der Waals photonic crystals: a route enabling electromagnetically induced transparency.

Recent studies have demonstrated that multilayer transition metal dichalcogenides can serve as promising building blocks for creating new kinds of resonant optical nanostructures due to their very high refractive indices. However, most of such studies have focused on excitonic regimes of light-material interaction, while there are few on the low-loss region below the bandgap. Here, we conceptually propose all-van der Waals photonic crystals made of electronically bulk MoS2 and h-BN, designed to operate in the telecom wavelengths. And we demonstrate that, due to extremely low absorption loss and destructive interaction between symmetry-protected and resonance-trapped bound states in the continuum, high-quality factor transmission peaks associated with electromagnetically induced transparency (EIT) are observed, thus rendering our proposed structures highly useful for applications like slow light and optical sensing. Furthermore, EIT-like effects are demonstrated in well-engineered MoS2 nanostructures with broken symmetry. We argue that this work is not only of significance for light harvesting in nanostructured van der Waals materials, but provides also a simple path of constructing classical analogues of EIT using dielectric photonic crystals.

Conservative but Stable: A SARSA-Based Algorithm for Random Pulse Jamming in the Time Domain

As a dynamic jamming pattern, random pulse jamming is stochastic, sudden, and not easily perceived or addressed. Random pulse jamming can exert a negative influence on the quality of wireless communication. This paper models an anti-jamming communication under random pulse jamming as a Markov Decision Process and proposes a SARSA-based Time-domain Anti-jamming Algorithm (STAA). Differently from previous research, this study attempts to use the SARSA algorithm to counter random pulse jamming in the time domain. The proposed STAA can achieve high-quality transmission while maintaining small fluctuations in transmission performance when the risk of external interference is high.

Security enhanced optimal trajectory selection for mobile sink using reinforcement learning

Wireless visual sensor networks (WVSNs) have emerged as a strategic inter disciplinary category of WSN with its visual sensor based intelligence that has garnered considerable attention. The growing demand for energy efficient and maximized life time networks in highly critical applications like surveillance, military and medicine has opened up more prospects as well as challenges in the deployment of WVSNs. Multi-hop communication in WVSN results in overloading of intermediate sensor nodes due to its dual function in the network which results in hotspot effect. This can be mitigated with the help of mobile sinks and rendezvous points based route design. But mobile sinks has to visit every cluster head to gather data which results in longer traversal path and higher latency and power consumption related issues if not addressed properly will impact the performance of the network. Our objective is to analyze and determine the optimal trajectory for mobile sink node traversal with the help of a high quality transmission architecture integrated with reinforcement learning and isolation forest based anomaly detection to propose an energy efficient meta-heuristic approach to enhance the performance of network by reducing the latency and securing the network against possible attacks.

Lamellae preparation for atomic-resolution STEM imaging from ion-beam-sensitive topological insulator crystals

Good specimen quality is a key factor in achieving successful scanning transmission electron microscope analysis. Thin and damage-free specimens are prerequisites for obtaining atomic-resolution imaging. Topological insulator single crystals and thin films in the chalcogenide family such as Sb2Te3 are sensitive to electron and ion beams. It is, therefore, challenging to prepare a lamella suitable for high-resolution imaging from these topological insulator materials using standard focused ion-beam instruments. We have developed a modified method to fabricate thin focused ion-beam (FIB) lamellae with minimal ion-beam damage and artifacts. The technique described in the current study enables the reliable preparation of high-quality transmission electron microscope (TEM) specimens necessary for studying ultra-thin surface regions. We have successfully demonstrated that the careful selection of FIB milling parameters at each stage minimizes the damage layer without the need for post-treatment.

Management of Telecommunication Operator Services in Serbia – Case Study Eastern Serbia

The development of telecommunication technology in the last three or more decades has created the conditions for high quality and high speed data transmission between physically separated devices (central computers, terminals, mobile devices). Telecommunication can be defined as the electronic connection of physically (geographically) remote computers, and the telecommunication system as a component of compatible telecommunication devices connecting physically separated devices that can transmit text, image, audio and video information. The paper focuses on the choice of telecommunication providers in Serbia. It examines the attitudes of service users and what influences their choice of a particular mobile network. Consumer attitudes can influence the improvement of service management of mobile operators in Serbia. The paper represents a modest contribution to the use of telecommunication technologies to improve the existing offer on the market of mobile operators in Serbia and especially in the eastern region of the country. The city of Zajecar, the largest city in the eastern region of Serbia, is included in the study as a representative example.

TSN-Based Backbone Network of Train Control Management System

Time-sensitive network (TSN), as one of the latest real-time Ethernet techniques, has achieved great success in several scenarios that require strict communication latency and packet loss. This paper reviews the state-of-the-art in time-sensitive networks and investigates the drawbacks of current vehicle networks. By introducing TSN into the TCMS backbone network, next-generation smart vehicles can achieve high-quality data transmissions. This paper also analyzes the priority of the vehicle data and calculates the time-aware shaper slot to ensure that the control data is not affected by the multimedia data. Using the proposed structure, experimental results suggest that the network efficiency can be improved in the rail transit systems.

S-, C- and L-band transmission over a 157 nm bandwidth using doped fiber and distributed Raman amplification

We investigate optical transmission of an ultra-wideband signal in a standard single mode fiber. Using a near continuous optical bandwidth exceeding 157 nm across the S-, C- and L-bands, we combine doped-fiber amplifiers covering S, C and L-bands with distributed Raman amplification to enable high-quality transmission of polarization division multiplexed (PDM)-256-quadrature-amplitude modulation (QAM) signals over a 54 km standard single-mode fiber. We receive 793 × 24.5 GBd signals from 1466.34 nm to 1623.57 nm and measure a data rate estimated from the generalized mutual information (GMI) of 256.4 Tb/s and an LDPC decoded throughput of 244.3 Tb/s. The measured data rates exceed the highest previously measured in a single mode fiber, showing the potential for S-band transmission to enhance achievable data rates in optical fibers.

An enhanced algorithm for improving real-time video transmission for tele-training education.

Tele-training in surgical education has not been effectively implemented. There is a stringent need for a high transmission rate, reliability, throughput, and reduced distortion for high-quality video transmission in the real-time network. This work aims to propose a system that improves video quality during real-time surgical tele-training. The proposed approach aims to minimise the video frame’s total distortion, ensuring better flow rate allocation and enhancing the video frames’ reliability. The proposed system consists of a proposed algorithm for Enhancing Video Quality, Distorting Minimization, Bandwidth efficiency, and Reliability Maximization called (EVQDMBRM) algorithm. The proposed algorithm reduces the video frame’s total distortion. In addition, it enhances the video quality in a real-time network by dynamically allocating the flow rate at the video source and maximizing the transmission reliability of the video frames. The result shows that the proposed EVQDMBRM algorithm improves the video quality with the minimized total distortion. Therefore, it improves the Peak Signal to Noise Ratio (PSNR) average by 51.13 dB against 47.28 dB in the existing systems. Furthermore, it reduces the video frames processing time average by 58.2 milliseconds (ms) against 76.1, and the end-to-end delay average by 114.57 ms against 133.58 ms comparing to the traditional methods. The proposed system concentrates on minimizing video distortion and improving the surgical video transmission quality by using an EVQDMBRM algorithm. It provides the mechanism to allocate the video rate at the source dynamically. Besides that, it minimizes the packet loss ratio and probing status, which estimates the available bandwidth.

An Adaptive CMT-SCTP Scheme: A Reinforcement Learning Approach

With the continuous increase of end users and types of services, the scale of the network has shown explosive growth, which has brought tremendous pressure and challenges to network data transmission. How to achieve high-quality data transmission has become a core issue. Single-path transmission has been difficult to meet the above requirements. The concurrent multipath transfer extension for stream control transmission protocol (CMT-SCTP), which supports multipath and independent data streams, can solve this problem. However, the current transmission path assessment scheme has too large granularity to make full use of the resources of the transition zone. Most studies ignore the different requirements of different services, a single transmission strategy, and the lack of an intelligent dynamic adjustment mechanism. Therefore, we designed a QCMT(Q-learning based CMT-SCTP) scheduling method. This method considers the multi-dimensional characteristics of the path and the characteristic preferences of different services, periodically evaluates and trains the reinforcement learning model for service adaptation, and makes scheduling decisions dynamically. Experimental results show that dynamic scheduling based on path parameters and service preferences can reduce message delay and improve network throughput.

An Efficient HAPS Cross-Layer Design to Mitigate COVID-19 Consequences

This paper proposes a new cross-layer communication system for the provision of Internet services and applications to mitigate the negative impacts of COVID-19, due to which the massive online demands are affecting the current communication systems’ infrastructures and capabilities. The system requirements and model are investigated where it utilizes high-altitude platform (HAP) for fast and efficient connectivity provision to bridge the communication infrastructure gap in the current pandemic. The HAP is linked to the main server or gateway station located on ground and can provide communication narrow beams towards isolated areas which suffer from poor terrestrial radio coverage or lack of communication infrastructure. The vital e-learning applications using Internet services provision from the proposed HAP system are described and modelled including system adaptation parameters such as the application and physical layers to control the data rates of different e-learning applications and the overall cell data rate. On the other hand, the provision of high-speed Internet services from the proposed system is supported by using adaptive antenna arrays onboard HAP which provides high-gain beams to achieve the required high-quality transmission data rates at the student premises and provides the capability of coverage cell area adaptation for load balancing. The concentric circular antenna arrays with tapered feeding are proposed in this adaptive antenna system to control the cell mainlobe gain and reduce the out-of-coverage radiation as well. In addition, the system feasibility has been proved in two coverage scenarios including single-beam and multibeam HAP communications.