Multi Carrier Research Articles

Novel synthesis organic–inorganic heterojunctions of protonated g-C3N4/Fe3O4/AgBr/AgCl/AgI quinary magnetic photocatalyst with enhanced visible-light photocatalytic degradation of methylene blue in water

A novel magnetic quinary nanocomposite, protonated g-C3N4/Fe3O4/AgBr/AgCl/AgI, was synthesized using a wet chemical method. The multi-heterojunction photocatalyst with multi-carrier source and multi-channel carrier transport is constructed to enhance the photocatalytic degradation performance of pure g-C3N4. The design of the quinary nanocomposite is also an effective approach to solve the chemical stability problem of silver halides. The photocatalytic degradation efficiency under visible light irradiation was analyzed for methylene blue (MB) as the target organic pollutant. The quinary nanocomposite with 10 % g-C3N4 displayed high photocatalytic performance, with 83 % of MB degraded under 6 h LED white light irradiation. The effective quinary nanocomposite has good magnetic properties and can be magnetically separated to prevent secondary pollution of the photocatalyst in water. Parameters such as initial concentration of pollutant, initial solution pH, and light source were studied. Zeta potential results showed that the quinary nanocomposite could disperse homogenously to decrease aggregation in the solution. The photocatalytic degradation mechanism was investigated, and the mineralization results were analyzed based on liquid chromatography-mass spectroscopy (LC-MS) and total organic carbon (TOC). It was found that the hydroxyl and superoxide radicals were major reactive species by scavenging experiments. Additionally, protonated g-C3N4/Fe3O4/AgBr/AgCl/AgI nanocomposite showed excellent reusability after magnetic separation and regeneration, thus suggesting it to be a promising photocatalyst for treating wastewater containing organic contaminants.

Retraction Note: A comprehensive survey 5G wireless communication systems: open issues, research challenges, channel estimation, multi carrier modulation and 5G applications

Retraction Note: A comprehensive survey 5G wireless communication systems: open issues, research challenges, channel estimation, multi carrier modulation and 5G applications

Tuning charge density wave of kagome metal ScV6Sn6

Compounds with a kagome lattice exhibit intriguing properties and the charge density wave (CDW) adds an additional layer of interest to research on them. In this study, we investigate the temperature and magnetic field dependent electrical properties under a chemical substitution and hydrostatic pressure of ScV6Sn6, a non-magnetic CDW compound. Substituting 5% Cr at the V site or applying 1.5 GPa of pressure shifts the CDW from 92 K to ∼ 50 K. This shift is attributed to the movement of the imaginary phonon band, as revealed by the phonon dispersion relation. The longitudinal and Hall resistivities respond differently under these stimuli. The magnetoresistance (MR) retains its quasilinear behavior under pressure, but it becomes quadratic after Cr substitution. The anomalous Hall-like behavior of the parent compound persists up to the respective CDW transition under pressure, after which it decreases sharply. In contrast, the longitudinal and Hall resistivities of Cr substituted compounds follow a two-band model and originate from the multi carrier effect. These results clearly highlight the role of phonon contributions in the CDW transition and call for further investigation into the origin of the anomalous Hall-like behavior in the parent compound.

Novel Orthogonal Time Frequency Space Based on Universal Filter Multi Carrier for 6G Wireless Networks

Obtaining an efficient multicarrier signalling technique is an essential part in signal processing of the (6G) wireless networks. In order to achieve their intended objectives, the 6G mobile networks needs the utilization of a multicarrier scheme that possesses the ability to withstand multipath fading and inter-symbol interference (ISI), as well as exhibit resilience against inter-carrier interference (ICI) and Doppler spread. In recent research, several filter-based methods have been suggested, including Filter Bank Multicarrier (FBMC), as well as various Orthogonal Frequency Division Multiplexing (OFDM) based techniques such as Universal Filtered Multicarrier (UFMC). Orthogonal Time-Frequency Space (OTFS) technique has been identified as a promising candidate waveform for 6G, particularly in high-mobility scenarios, where it has demonstrated superior performance compared to traditional OFDM-based techniques. The OTFS method offers an advantage in that it can be considered the pre-and post-processing stages for techniques based on OFDM. This papaer presents the design (OTFS) using (UFMC) technique. Additionally, a novel structure is proposed for coded/uncoded UFMC-based OTFS technique, which combines the advantages of both strategies while mitigating their limitations. The results of our analysis demonstrate that the UFMC-based OTFS system exhibits superior performance in terms of error probability and time-spectral efficiency compared to the OFDM-based OTFS system.

A novel piecewise nonlinear companding scaling scheme for FBMC PAPR reduction

The performance of offset quadrature amplitude modulation filter bank multi carrier (OQAM-FBMC) has been noticed to be affected by a high peak-to-average power ratio (PAPR). High PAPR causes the transmit power amplifier to become saturated, improving the bit error rate (BER) and causing out of band (OOB) distortions. In this paper, the PAPR of FBMC systems can be reduced by using shifting and scaling the trigonometric companding technique associated with a reduced BER performance and the power spectral density (PSD) with low OOB distortions. The characteristics of low peak signals are not changed by this companding scheme, while the characteristics of high peak signals are transformed into scaling piecewise nonlinear trigonometric functions. By tuning the parameters the suggested technique maintains the average signal power level unchanged. The theoretical analysis of the proposed scheme is also studied and also compared with the simulation results. The performance of the trigonometric companding scheme is also analysed with the μ-law and A-law existing companding methods and the suggested method obtaining 3 dB and 3.2 dB PAPR improvement respectively. The proposed technique determined to be better in terms of BER performance and spectrum efficiency.

Evaluation of FBMC Channel Estimation using multiple Auxiliary symbols for high throughput and low BER 5G and beyond communications

Filter Bank Multi-Carrier (FBMC) modulation has been recognized as a consistent contender and a possible successor for Orthogonal Frequency Division Multiplexing (OFDM) in 5G and beyond because of its outstanding spectral properties. The channel is assessed in FBMC using pilot-symbol aided channel estimation that provides robust estimates even for severe channel conditions. In the present work, neutraliz ing the imaginary interference at the pilot positions is focused while estimating the channel. To neutralize the imaginary in terference, multiple auxiliary symbols have been proposed to enhance the throughput and channel capacity. The Iterative Minimum Mean Squared Error (IMMSE) cancellation scheme has been proposed to reduce the interference at the pilot and data positions. Transmission power, Bit Error Rate (BER) and throughput are computed for Filter Bank Multi Carrier (FBMC), OFDM and proven that better system performance is obtained for FBMC. The performance of channel estimation is evaluated through 5G standards and indicates that the usage of multiple auxiliary symbols per pilot leads to better throughput and low Bit Error Rate at low power transmission.

Towards Flawless Designs: Recent Progresses in Non-Orthogonal Multiple Access Technology

High effectiveness and high reliability are two fundamental concerns in data transmission. Non-orthogonal multiple-access (NOMA) technology presents a promising solution for high-speed data transmission, which has long been pursued by academia and industry. However, there is still a significant road ahead for it to effectively support a wide range of applications. This paper provides a comprehensive study, comparison, and classification of the current advanced NOMA schemes from the perspectives of single-carrier (SC) systems, multicarrier (MC) systems, reconfigurable-intelligent-surface (RIS)-assisted systems, and deep-learning (DL)-assisted systems. Specifically, system implementation issues such as the transition from SC-NOMA to MC-NOMA, the relaxation of distinct channel gains, the consideration of imperfect channel knowledge, and the mitigation of error propagation/intra-group interference are involved. To begin with, we present an overview of the state-of-the-art developments related to the advanced design of SC-NOMA. Subsequently, a generalized MC-NOMA framework that provides the diversity–multiplexing gain by enhancing users’ signal-to-interference-plus-noise ratio (SINR) is proposed for better system performance. Moreover, we delve into discussions on RIS-assisted NOMA systems, where the receiver’s SINR can be enhanced by intelligently reconfiguring the reflected signal propagations. Finally, we analyze designs that combine NOMA/RIS-NOMA with DL to achieve highly efficient data transmission. We also identify key trends and future directions in deep-learning-based NOMA frameworks, providing valuable insights for researchers in this field.

Evaluation of 5G techniques affecting the deployment of smart hospital infrastructure: Understanding 5G, AI and IoT role in smart hospital

Smart Hospital will play a key role in improving the quality of services (QoS) related to the health sector. In the present scenario, it is impossible to accommodate an ageing population with the current infrastructure and facilities provided by conventional hospitals. However, the integration of technologies with the conventional hospital is enhancing the medical services and also making it easier for the public, who can save time and money by getting all the necessary medical facilities while sitting at home. The deployment of the fifth generation (5G) is taking place all over the world. The 5G network offers a better service that can be used in hospitals to make it a smart health service provider with online facilities such as video monitoring, suggesting a proper medical prescription based on medical data, remote surgery, and so on. High bandwidth, a fast data rate, low latency, and a low peak-to-average power ratio (PAPR) are some requirements that need to be fulfilled by the 5G radio. In this work, we focus on improving the power savings, spectral access, latency, and Bit error rate (BER) of the advanced 5G waveforms such as non-orthogonal multiple access (NOMA), filter bank multi carrier (FBMC), and orthogonal frequency division multiplexing (OFDM). In the first part of the article, we proposed a PAPR reduction algorithm to improve the power efficiency of the power amplifier (PA) for 5G waveforms. Several algorithms are applied to the 5G waveforms, and their performances are estimated in terms of PAPR curves. In the second part, we have utilised advanced detection algorithms to improve the signal detection of the 5G waveforms. The simulation results reveal that the proposed algorithms efficiently enhance the throughput of the framework. In the third part, we improve the spectral efficiency of the 5G waveforms by applying spectrum sensing (SS) algorithms. It is seen that the SS methods efficiently reduce the spectrum leakage of the multi-carrier waveforms (MCW). Finally, we examined the role and challenges of the Internet of Things (IoT) and artificial intelligence (AI) in smart hospitals. Overall, it is concluded that hospitals can become more effective, cut expenses, and provide better patient care with the aid of AI and IoT. Hospitals can improve patient outcomes and the state of the healthcare system as a whole by utilising these technologies.

A Constellation Diagram Learning-Based Adaptive Sparse Nonorthogonal Wavelet Division Multiplexing for Sonar Image Underwater Acoustic Transmission

In underwater Internet of Things (IoT) applications, efficient and reliable transmission is demanding. Recently, the non-orthogonal multicarrier (MC) modulation is utilized as a promising spectrum-efficient solution in the UWA channel, where generally, the constellation mapping (CM) methods (such as 8-PSK and 16-QAM) are utilized to further increase the transmission rate. In this paper, we focus on the transmission of sonar images among IoT nodes and a constellation diagram learning-based adaptive sparse non-orthogonal wavelet division multiplexing (CDLA-SNOWDM) system is proposed to combat complex channel states between IoT nodes. We found that different CM methods contribute to unique time-frequency characteristics in constellation diagrams. We first utilize the time-frequency characteristics in designing the non-orthogonal subcarriers. The complex-valued CM signals are regarded as a new type of image. We introduce dictionary learning (DL) to non-orthogonal subcarrier designing, with the idea that designing CM signal adaptive non-orthogonal subcarriers can be regarded as designing an adaptive subcarrier dictionary. The CDLA-SNOWDM modulation is performed as a projection of the CM image to the subcarriers with an adaptive dictionary. The learned adaptive subcarriers can represent constellation diagrams more efficiently and improve transmission reliability. Both simulations and experiments show that the proposed scheme improved the reliability in transmitting sonar images over other orthogonal and non-orthogonal modulation schemes in UWA scenarios.

Optimized MIMO Based Enhanced OFDM for Multi Carrier System with 5G Waveforms

Optimized MIMO Based Enhanced OFDM for Multi Carrier System with 5G Waveforms

Design of Multi-Layer Protocol Architecture using Hybrid Optimal Link State Routing (HOLSR) Protocol for CR Networks

There is a lack of spectrum due to the rising demand for sensing device communication and the inefficient use of the existing available spectrum. Through opportunistic access to licenced bands, which does not obstruct the primary sensory users (PU), it is feasible to enhance the inefficient use of the current sensor device frequency spectrum. Cognitive settings are a demanding environment in which to carry out tasks like sensor network routing and spectrum access since it is difficult to access channels due to the presence of PUs. The basic goal of the routing problem in sensor networks is to establish and maintain wireless sensor multihop paths between cognitive sensor nodes. The frequency to be used as well as the number of hops at each sensor node along the path must be determined for this assignment. In order to improve performance while using less energy, scientists suggested a unique adaptive cross-layer optimisation subcarrier distribution technique with the HOLSR protocol for wireless sensor nodes. Throughput and energy consumption parameters are used to analyse the sensor network architecture protocol that has been developed. The energy usage of the sensor nodes in the network has increased by 50%. The performance of the proposed HOLSR algorithm is assessed using the simulation results, and the results are contrasted with those of a conventional multicarrier (MC) system in terms of bit error rate and throughput.

Spectrum-efficient mode selection and fair resource allocation for D2D-enabled uplink/downlink MC-NOMA networks

The application of device-to-device (D2D) communication and multi-carrier (MC) non-orthogonal multiple access (NOMA) have been considered as promising technologies to enhance energy efficiency, network connectivity, and spectrum efficiency in the next generation of communication systems. This paper investigates a joint optimization problem of spectrum-efficient mode selection, fair sub-channel (SC) allocation, and power allocation of user pairs for a D2D-enabled MC-NOMA network. In the proposed network, user pairs are enabled to transmit and receive data in either underlaid D2D mode or cellular mode, and the NOMA technique is adopted in both downlink and uplink transmission. To maximize the throughput of the system and to manage the co-channel interference, the joint optimization problem is formulated under the constraint of guaranteeing all users with a certain amount of resources while satisfying the minimum signal-to-interference-plus-noise ratio (SINR) requirements of users. As an NP-hard problem, the optimization problem is first transformed into two sub-problems namely 1- the joint SC allocation and mode selection and 2- the power allocation. Then, to jointly solve the SC allocation and mode selection sub-problem, an enhanced three-side many-to-one matching algorithm is proposed and to obtain the solution to the power allocation problem, the known sequential convex programming method is used. Moreover, an iterative algorithm is used to enhance the performance of the system in terms of sum-rate. Finally, a mathematical expression is introduced to check the quality of service (QoS) of the proposed fair resource allocation algorithm and the results of the simulation are stated to indicate improved system performance.

Trapezoidal reference-based single carrier pulse width modulation method for multilevel converters with novel FPGA implementation

Recent attention has focused on trapezoidal reference-based pulse width modulation (PWM) schemes in multilevel converters (MLCs) with easier implementation and better harmonic performance. Nevertheless, these studies utilize trapezoidal reference only for multi carrier PWM methods and details of FPGA implementation are not provided. This paper proposes a trapezoidal reference-based single carrier PWM (TSC-PWM) with its novel FPGA implementation. Design parameters of TSC-PWM is determined such that harmonic performance is maximized and architectural details of FPGA implementation of TSC-PWM are provided. Results reveal that TSC-PWM significantly reduces the resource utilization compared to other methods. Single-phase three-module cascaded H-bridge MLC (CHB-MLC) is established in both simulation and experimental platforms. Results indicate that the TSC-PWM provides better harmonic performance along with higher DC utilization ratio compared to other methods. Moreover, both half-wave and quarter-wave symmetries are ensured with TSC-PWM.

Investigation and validation of PV fed reduced switch asymmetric multilevel inverter using optimization based selective harmonic elimination technique

Pulse width modulation for Selective Harmonics Elimination (SHE) is mostly employed in the reduction of lower order harmonics. The PV system in this research provides input voltage to the reduced switch 31-level inverter, which is based on the Artificial Bee Colony algorithm. With a high gain DC-DC single-ended primary-inductor converter (SEPIC), the PV panel output voltage is kept constant. The Grey wolf optimization algorithm (GWO) approach is used to get the most power out PV scheme. Multi Carrier modulation, a high-frequency modulation technology, is also used in this novel design of the inverter to reduce upper order harmonics. The suggested Artificial Bee Colony (ABC) algorithm, harmonics is compared to a SHE technique based on a genetic algorithm. The hardware findings were confirmed using DSPIC30F2010 controller simulation, and the recommended system was validated using Matlab simulation.

PERFORMANCE OF MU-MC-DS-CDMA SYSTEM IN RAYLEIGH FADING CHANNEL

The Multi user Multi Carrier Direct sequencing Code Division Multiple Access (MU-MC-DS-CDMA) strategy was developed in response to rising demand for system capacity, higher data rates, and multimedia services. It's essentially a combination of CDMA and OFDM schemes. As a result, MC-CDMA takes the advantages of both CDMA and OFDM technologies. CDMA improves bandwidth consumption performance, whereas OFDM helps to minimize Inter Symbol Interference (ISI) and multipath fading. This dissertation suggests a method for evaluating the performance of multi user MC-DS-CDMA system. BER and PAPR are used to evaluate the results. The Bit Error Rate (BER) output of the proposed method is then examined using MATLAB for various modulation techniques. By using Walsh-Hadamard (W-H) code is used because it eliminates Multiple Access Interference (MAI). In terms of BER, it can be shown that BPSK performs better than QPSK. Key Words: AWGN, BER, ISI, MC-CDMA, Rayleigh Fading Channel, SNR, QPSK, MAI

Range-angle-dependent beamforming for FDA radar with Hamming interelement spacing and sinusoidal multicarrier approach

By employing a tiny frequency offset across the array elements, a frequency diverse array (FDA) produces a beampattern with the property of being range-angle-dependent. However, the beampattern of a traditional FDA has many maxima at undesired range-angle couples, which is unfavorable for target localization and jamming suppression. In this paper, a novel FDA scheme with Hamming interelement spacing, namely, the HIS-FDA, is proposed. By adopting Hamming window weighted interelement spacing and frequency offsets optimized by the genetic algorithm, the HIS-FDA produces a dot-shaped well-performed beampattern, which has superior performance over the existing FDA systems, especially in the angle dimension. The multiple input multiple output technique and multiple matched filters are employed at the receiver to solve the time-varying problem. A new multicarrier (MC) technique termed the sinusoidal MC approach is also presented to improve the beampattern performance, especially in the range dimension. Our proposed scheme outperforms the existing FDA systems in terms of the mainlobe width in the range and angle profiles, the sidelobe level, and the range-angle spatial region of the mainlobe. Comparison results are provided to validate the superiority of the proposed scheme.

Quasi-Optimization of Resource Allocation and Positioning for Solar-Powered UAVs

Unmanned Aerial Vehicles (UAVs) will be an integral part of future smart cities to provide applications such as traffic management, environment monitoring and data collection. UAVs offer flexible deployment, dynamic mobility, and Ultra-Reliable and Low Latency Communications (URLLC). However, UAVs are power-hungry devices, and their limited battery capacity cannot support their flight and communication operations for a long period. Additionally, multi-carrier (MC) techniques will be vital for supporting futuristic multi-user communication systems. To overcome these issues, we propose a solar-powered UAV MC system to support URLLC services for multi-users. In this regard, we aim to maximize the system sum throughput and we jointly optimize UAV positioning and sub-carrier allocation. To solve the optimization problem, we propose the low-complexity coordinate descent approximation algorithm (CDAA). Lastly, we show the proposed algorithm converges quickly and simultaneously yields superior performance than fixed benchmark schemes for two simulated environments.

A Sensor-less Surface Mounted PMSM for Electronic Speed Control in Multilevel Inverter

Recent advancements in power electronics technology evolves inverter fed electric motors. Speed signals and rotor position are essential for controlling an electric motor accurately. In this paper, the sensorless speed control of surface-mounted permanent magnet synchronous motor (SPMSM) has been attempted. SPMSM wants a digital inverter for its precise working. Hence, this study incorporates fifteen level inverter to the SPMSM. A sliding mode observer (SMO) based sensorless speed control scheme is projected to determine rotor spot and speed of the multilevel inverter (MLI) fed SPMSM. MLI has been operated using a multi carrier pulse width modulation (MCPWM) strategy for generation of fifteen level voltages. The simulation works are executed with MATLAB/SIMULINK software. The steadiness and the heftiness of the projected model have been investigated under no loaded and loaded situations of SPMSM. Furthermore, the projected method can be adapted for electric vehicles.

Design and Implementation of Adaptive Universal Filtered Multi Carrier for 5G and Beyond

The current generation (5G) mobile communication system promises to accommodate a wide range of new applications and use scenarios, resulting in more flexible and unified connection. To satisfy the required criteria, the current waveform was replaced with new UF-OFDM, which combines the advantages of OFDM with enhanced spectral characteristics and greater resilience against time-frequency misalignments. However, its biggest disadvantage is the transmitter's computational complexity, which may be up to two hundred times that of OFDM if there is no reduction in complexity. The majority of current research on unique waveforms has focused on filter modification or performance enhancement strategies. UFMC with the use of adaptive filter (UFMC -FSK) is offered as a revolutionary technique in this study. The filter designed and used to transport information through the index modulation technique. As a result, each UF-OFDM sub band's used filter is chosen, so the data rate is enhanced according to a filter configured depending on original input data bits. The combined Maximum-likelihood (ML) decision metric for each sub band that is calculated at the receiver. Each sub band has a filter as well as data symbols that provide the minimal metric for making decisions are discovered. Furthermore, the bit error rate and power spectrum density are enhanced over the UF-OFDM technique, however there is some trade-off. Overall, the proposed system outperform typical UF-OFDM. Matlab simulations are used to assess the performance of the Adaptive UFMC system.

Orthogonal Delay-Doppler Division Multiplexing Modulation

Inspired by the orthogonal time frequency space (OTFS) modulation, in this paper, we consider designing a multicarrier (MC) modulation on delay-Doppler (DD) plane, to couple the modulated signal with a doubly-selective channel having DD resolutions. A key challenge for the design of DD plane MC modulation is to investigate whether a realizable pulse orthogonal with respect to the DD plane’s fine resolutions exists or not. To this end, we first indicate that a feasible DD plane MC modulation is essentially a type of staggered multitone modulation. Then, analogous to orthogonal frequency division multiplexing, we propose an orthogonal delay-Doppler division multiplexing (ODDM) modulation, and design the corresponding transmit pulse. Furthermore, we prove that the proposed transmit pulse is orthogonal with respect to the DD plane’s resolutions and therefore a realizable DD plane orthogonal pulse does exist. The orthogonality of this particular pulse significantly eases the derivation of the ODDM’s DD domain channel input-output relation, and yields a channel matrix with an elegant block-circulant-like structure. We demonstrate that the ODDM outperforms the OTFS in terms of out-of-band emission and bit error rate, by achieving perfect coupling between the modulated signal and the DD channel.