Carrier Space Research Articles

Progress in optical frequency comb generation techniques towards flexible optical communication network

Abstract A flexible optical communication network is needed to realize a backbone transport network for 6G communication and further higher generation communication technologies. However, the practical implementation of the higher generation network experiences some serious challenges due to the existing multicarrier generation technology i.e. an array of multiple discrete laser sources (less spectrally efficient, complex, bulkier and costlier). Recently, a multicarrier generation technique using the optical frequency comb has been extensively researched. It can reduce the complexity, cost, and size compared to the existing multicarrier generator. Moreover, it increases the utilization of available spectral efficiency due to its capability to tune the operating frequency and carrier spacing. So, considering these advantages, we reviewed the multiple optical frequency comb generation techniques, categorized as mode-locked laser, microresonator and electro-optic modulator based frequency combs. We identify the salient features of different frequency comb generation techniques by keeping the requirements of a flexible optical network in mind. We also reviewed the drawbacks and possible solutions proposed to improve the characteristics of the optical frequency comb. Further, we reviewed the optical frequency comb expansion techniques to broaden the spectrum of the optical frequency comb, which is the requirement in optical frequency comb suitable for communication applications. At last, we summarize the progress in the practical implementation of the optical frequency comb as a multichannel source in a flexible optical network.

A Novel Analysis of the Influence of Zero-Axis Control on Neutral-Point Potential Self-Balancing of Three-Level Converters

The neutral-point potential balance issues in three-level converters have obtained great attention. The popular view thinks that the neutral-point voltage deviation can be suppressed by regulating the injected zero-sequence component, whether via carrier modulation or space vector modulation techniques. However, this paper presents a novel finding: the efficacy of different frame controllers on the self-balancing of neutral-point potential in three-level converters differs when a comprehensive analysis of zero-sequence dynamics, including neutral-point current and PWM modulation, is conducted. That is, the proportional-resonant (PR) controller in the abc frame effectively introduces a zero-axis PR control of the zero-sequence component, which subsequently degrades the stability of neutral-point potential self-balancing. In contrast, the PI control in the dq frame does not incorporate any additional control of the zero-sequence component, thereby enhancing the self-balancing capability of the neutral-point potential. To substantiate this novel finding, a series of simulations and experimental validations were performed.

Cu2WS4 with high-exposure {0 0 1} surfaces promotes efficient charge separation in ZnIn2S4

The spatial segmentation of photogenerated carriers is crucial for achieving efficient photocatalytic H2 production (PHP) rates in photocatalyst. Design studies of crystalline catalyst facets and selective morphology control can facilitate the development of catalysts that expose more advantageous active facets. Herein, Cu2WS4/ZnIn2S4 composites are constructed by growing ZnIn2S4 nanosheets in situ on Cu2WS4 with largely exposed {001} surface. Experiments and density functional theory calculations demonstrate that the electrons of ZnIn2S4 flowed to the {001} surface of Cu2WS4, and the holes vectorially migrated to the {101} surface, during the reaction process, resulting in efficient spatial separation of the photogenerated carriers. The Cu2WS4/ZnIn2S4 achieves a PHP rate of 23.67 mmol g−1 h−1, 13.44-fold increase compared with pure ZnIn2S4. This report combines the advantages of the high-energy activity of the Cu2WS4 {001} surface to morphologically control the ratio of the {001}/{101} surfaces so that ZnIn2S4 can contact a larger area of the {001} surface. Furthermore, under the influence of crystallographic effects on the {001} and {101} surfaces, electrons and holes of ZnIn2S4 are transferred to different crystalline facets, promoting the redox reaction. This paper provides effective ideas for the rational design of photocatalysts with efficient carrier space separation.

Deep learning based asymmetrical autoencoder for PAPR reduction of CP-OFDM systems

Adoption of Orthogonal Frequency Division Multiplexing (OFDM) in 5th Generation New Radio (5G NR) as a multicarrier modulation technique allows high data rate transmission with lower complexity. However, problem such as peak to average power ratio (PAPR) has decreased the transmitter efficiency. Recently, several attempts have been made to reduce the high PAPR in OFDM utilizing deep learning (DL) based on autoencoder architecture. However, the proposed autoencoder using symmetrical autoencoder (SAE) is followed by high computational complexity at both transmitter and receiver as well as BER performance degradation. Since 5G NR focuses on massive 5G internet of things eco-system, a flexible carrier spacing is used to support diverse spectrum bands which is afterward named as Cyclic Prefix OFDM (CP-OFDM). In this study, we aimed to contribute to this growing area of research by exploring the potential of our proposed asymmetrical autoencoder (AAE) to reduce high PAPR in the CP-OFDM system. Four AAE models have been developed in this study and the performance of the models were evaluated based on comprehensive conditions such as data training at different corruption levels, cyclic prefix length, upsampling factors and loss function levels. The investigation of AAE in 5G CP-OFDM system has shown superior performance using a 5×1 AAE model that can reduce a substantial amount of PAPR, BER degradation and computational complexity compared to conventional SAE. This study lays the groundwork for future research into the asymmetrical approach of autoencoder especially in 5G and beyond networks.

Injection-limited and space-charge-limited conduction in wide bandgap semiconductors with velocity saturation effect

Carrier conduction in wide bandgap semiconductors (WBS) often exhibits velocity saturation at the high-electric field regime. How such effects influence the transition between contact-limited and space-charge-limited current (SCLC) in a two-terminal device remains largely unexplored thus far. Here, we develop a generalized carrier transport model that includes contact-limited field-induced carrier injection, space charge, carrier scattering, and velocity saturation effect. The model reveals various transitional behaviors in the current–voltage characteristics, encompassing Fowler–Nordheim emission, trap-free Mott–Gurney (MG) SCLC, and velocity-saturated SCLC. Using GaN, 6H–SiC and 4H–SiC WBS as examples, we show that the velocity-saturated SCLC completely dominates the high-voltage (102–104 V) transport for typical sub-μm GaN and SiC diodes, thus unraveling velocity-saturated SCLC as a central transport mechanism in WBG electronics.

High-Efficiency GaN-Based Power Amplifiers for Envelope Nonlinearities’ Mitigation in VHF Wideband Polar-Mode Transmitters

Space-based communications at the very high frequency (VHF) band for air traffic management is a new technology application under development that requires energy-efficient architectures to mitigate the power limitations of satellite platforms. The usage of high-efficiency radiofrequency (RF) transmitters can help reduce the power consumption, but nonlinearities concerning the amplified signal in wide fractional bandwidth systems are a problem to solve. This paper proposes a high-efficiency (RF) power amplifier (PA) for satellite communications at the VHF band that aims to reduce the envelope distortion inherent to wide fractional bandwidth multicarrier polar-mode transmitters. Its design is based on a solution called hybrid-coupled switching voltage PA in combination with gallium nitride (GaN) high electron mobility transistor (HEMT) technology. The developed VHF PA prototype delivers up to 95 W from a 28 V power supply, with a drain efficiency about 80% within the 118 MHz to 138 MHz operating band. To test its linearity performance, operating in a polar-mode configuration, a GaN-based wideband envelope amplifier (EA) has been developed to modulate the RF PA supply port. This EA improves its power efficiency by combining it with a slow envelope power supply (SEPS). Some measurements have been taken for a 100 W peak envelope power (PEP) and 10 MHz (maximum carrier spacing) four-tone digitally-modulated test signal, where any distortion product is attenuated 46 dB below the average power of the amplified signal without applying any digital predistortion (DPD) technique.

Improved Digital Predistortion for Concurrent Multiband Transmission Using Frequency Relocation

In concurrent multiband settings with large carrier spacings between bands, digital predistorter (DPD) implementations face the issue of how to linearize a sparse signal spectrum spanned over large bandwidths at low computational complexity. Frequency relocation is one possible approach that involves relocating baseband carriers to have reduced frequency spacing with the help of band-limiting functions, to yield a denser and smaller signal bandwidth for the DPD to linearize. In this letter, frequency relocation for transmitters with frequency-varying gain and phase is explicitly considered. It is shown that band-wise preequalization during frequency relocation can reduce the computational complexity for a certain allowed in-band error.

Fuzzy hyperspheres via confining potentials and energy cutoffs

We simplify and complete the construction of fully O(D)-equivariant fuzzy spheres , for all dimensions , initiated in Fiore and Pisacane (2018 J. Geom. Phys. 132 423–51). This is based on imposing a suitable energy cutoff on a quantum particle in subject to a confining potential well V(r) with a very sharp minimum on the sphere of radius r = 1; the cutoff and the depth of the well diverge with . As a result, the noncommutative Cartesian coordinates generate the whole algebra of observables on the Hilbert space ; applying polynomials in the to any we recover the whole . The commutators of the are proportional to the angular momentum components, as in Snyder noncommutative spaces. , as carrier space of a reducible representation of O(D), is isomorphic to the space of harmonic homogeneous polynomials of degree Λ in the Cartesian coordinates of (commutative) , which carries an irreducible representation of . Moreover, is isomorphic to . We resp. interpret , as fuzzy deformations of the space of (square integrable) functions on S d and of the associated algebra of observables, because they resp. go to as Λ diverges (with fixed). With suitable , in the same limit goes to the (algebra of functions on the) Poisson manifold ; more formally, yields a fuzzy quantization of a coadjoint orbit of that goes to the classical phase space .

Separable Convolution Network With Dual-Stream Pyramid Enhanced Strategy for Speech Steganalysis

Steganography based on fixed codebook has become one of the most important branches of speech steganography due to its high imperceptibility and having the largest available carrier space. As its countermeasure technique, this paper presents a novel steganalysis method based on separable convolution network (SepSteNet) with dual-stream pyramid enhanced strategy (DPES). Specifically, to better acquire discriminative representations, we design the pulse-aware separable block to capture the pulse correspondence along independent levels of pulse positions, where the pulse-aware excitation module is plugged to avoid noisy clue accumulation by adaptively emphasizing the salient part. Moreover, the global attending block is introduced to enhance correspondence features through calculating global responses at distinct subframes. In addition, to eliminate the negative impact of sample content, DPES is leveraged to incorporate cross-domain coherence features by the inverted connected dual-stream branches. With the original and calibration speech samples, two branches enable the correspondence of two detection feature domains to interact with each other to generate coherence features independent of sample content, thereby improving the detection performance. The performance of the presented method is comprehensively evaluated and compared with the state of the arts. The experimental results demonstrate that the presented method significantly outperforms the existing ones. Furthermore, DPES is shown to be a general enhancement strategy that can effectively improve the performance of the existing deep neural network for speech steganalysis. The source code for this work will be publicly available on GitHub.

Hilbert Space Structure of the Low Energy Sector of U(N) Quantum Hall Ferromagnets and Their Classical Limit

Using the Lieb–Mattis ordering theorem of electronic energy levels, we identify the Hilbert space of the low energy sector of U(N) quantum Hall/Heisenberg ferromagnets at filling factor M for L Landau/lattice sites with the carrier space of irreducible representations of U(N) described by rectangular Young tableaux of M rows and L columns, and associated with Grassmannian phase spaces U(N)/U(M)×U(N−M). We embed this N-component fermion mixture in Fock space through a Schwinger–Jordan (boson and fermion) representation of U(N)-spin operators. We provide different realizations of basis vectors using Young diagrams, Gelfand–Tsetlin patterns and Fock states (for an electron/flux occupation number in the fermionic/bosonic representation). U(N)-spin operator matrix elements in the Gelfand–Tsetlin basis are explicitly given. Coherent state excitations above the ground state are computed and labeled by complex (N−M)×M matrix points Z on the Grassmannian phase space. They adopt the form of a U(N) displaced/rotated highest-weight vector, or a multinomial Bose–Einstein condensate in the flux occupation number representation. Replacing U(N)-spin operators by their expectation values in a Grassmannian coherent state allows for a semi-classical treatment of the low energy (long wavelength) U(N)-spin-wave coherent excitations (skyrmions) of U(N) quantum Hall ferromagnets in terms of Grasmannian nonlinear sigma models.

Space charge formation in the high purity semi-insulating bulk 4H–silicon carbide

We investigated the carrier transport and space charge formation in the high purity semi-insulating 4H-SiC bulk single crystal. Using the Laser–induced Transient Current Technique we observed anomalous short current waveform oscillations that are caused by very short carrier lifetime ≤ 1 ns. We conclude from a detailed inspection of current waveform shape completed by the analysis of collected charge that the electron mobility decreases in an increasing electric field. The saturation value of electron drift velocity 8.7 × 106 cm2s-1 was evaluated. The Hall effect measurement revealed the n-type electrical conductivity and dominant donor energy of ED = 0.85 eV. We also observed the blocking character of prepared Au contacts, which induce the electron depletion and positive space charge formation in biased sample. The continuous increase of the space charge in a wide time interval of 10-1 s – 104 s, attested to testified on a presence of a dispersed impurity band localized below the Fermi energy. Based on these findings, we proposed a theoretical model describing the observed phenomena very well.

Comparative Analysis of Torque Ripple for Direct Torque Control based Induction Motor Drive with different strategies

ABSTRACT Direct Torque Control (DTC) method is one of the most outstanding and proficient control techniques of the induction motor. The foremost drawback of DTC induction motor drive is high torque pulsation, variable frequency of inverter switching. The main reason of torque pulsation is torque and flux hysteresis band utilised in DTC. DTC method is utilising hysteresis comparators which produce high torque pulsation and unpredictable switching frequency. In this paper, torque ripple analysis of fuzzy logic controller (FLC) based Direct Torque Control (DTC) of three-phase induction motor drive has been discussed. The space vector pulse width modulation (SVPWM) based DTC technique, which operates with the regular switching frequency, helps to solve the fundamental issues of torque pulsation. In addition to this, literature proposes different solutions like a prediction scheme, fuzzy logic controller technique, global minimum torque ripple strategy, constant frequency torque controller (CFTC) Technique, optimal switching instant scheme, duty cycle control scheme, SVPWM DTC for torque ripple reduction. The fuzzy logic controller capabilities for DTC technique are applied with the induction motor (IM) drive for high-performance applications. The simulation results of Conventional DTC, SVPWM DTC, Carrier SVPWM DTC and FLC-DTC method for the induction motor are illustrated. Fuzzy-based DTC technique compared with CSVPWM DTC method and conventional DTC method are presented. The torque ripple of 7.4% for 5 HP induction motor is achieved by FLC-based DTC method. Hardware results for DTC induction motor drive are also demonstrated and discussed. This paper presents improvement in torque ripple reduction with the help of carrier space vector pulse width modulation (CSVPWM) and FLC-based DTC.

Quadrature Acoustic Frequency Combs Multiplexing for Massive Parallel Underwater Acoustic Communications

AbstractUnderwater acoustic (UWA) communication has been developing rapidly over the past decades for its crucial position in resource exploration, environmental monitoring, and scientific research. However, the transmission data rate of UWA communication is limited by the narrow bandwidth of the underwater acoustic channel. Here, the generation of quadrature acoustic frequency combs (AFCs) is first reported. Massive parallel channels achieved with multiplexing of AFCs for UWA communication are demonstrated. The generated AFCs have unique characteristics which have a stable and precise division in frequency and time domain simultaneously with carrier spacing of 1 Hz with the stability of 10−8. The different frequency spacing in combs leads to different teeth spacings in time, which is orthogonal and separable in the time domain. The orthogonality among AFCs provides a new dimension for multiplexing and can drastically increase channel efficiency. The underwater acoustic communication experiments demonstrate that it is drastically increasing the transmission rate to 45.33 kb s−1 and high spectral efficiency of 1.51 (channel s−1) Hz−1 without utilizing other modulation techniques by a single transducer. Since AFCs multiplexing is a completely independent degree of freedom that can be readily integrated with other high order modulation techniques, such as quadrature amplitude modulation and phase‐shift keying, in a single channel, AFCs multiplexing opens a new dimension for acoustic communication.

Conditional intensity: A powerful tool for modelling and analysing point process data

SummaryThe conditional intensity function of a spatial point process describes how the probability that a point of the process occurs ‘at’ a particular point in its carrier space depends on the realisation of the process in the remainder of the carrier space. Provided that the point process is simple, the conditional intensity determines all of the properties of the process, in particular its likelihood function. In this paper, we review the use of the conditional intensity function in the formulation of point process models and in making inferences from point process data, giving separate consideration to temporal, spatial and spatiotemporal settings. We argue that the conditional intensity function should take centre‐stage in spatiotemporal point process modelling and analysis.

Bifunctional Regenerated Cellulose/Polyaniline/Nanosilver Fibers as a Catalyst/Bactericide for Water Decontamination.

For antagonizing urgent water pollution and increasing environmental consciousness, the integration of renewable resources and nanotechnologies has become a trend to improve water quality in the ecosystem. Here, we designed a green route to fabricate regenerated cellulose fibers (CFs) with 3D micro- and nanoporous structures in NaOH/urea aqueous solvent systems via a scalable wet-spinning procedure as support materials for nanoparticles (NPs). Modification of CFs with polyaniline@Ag nanocomposites through in situ reduction of the silver ion with aqueous aniline led to enhanced pollutant removal efficiency of functional cellulose-based fibers (FCFs), demonstrating both rapid hydrogenation catalytic performance for the reduction of p-nitrophenol and high antibacterial properties for in-flow water purification. Most importantly, the hierarchically porous structures of FCFs not only provided carrier space but also formed a limiting domain guaranteeing the homogeneity of FCFs even with a Ag NP content as high as 36.47 wt %. The prepared functional fibers show good behavior in in-flow water purification, representing significant advancement in the use of biomass fibers for catalytic and bactericidal applications in liquid media.

Performance Analysis of 3GPP NB-IoT Downlink System towards 5G Machine Type Communication (5G-MTC)

5G Technology is the most recent scientific development in wireless communication and it is evolving day by day to meet the demand of near future. As per 3GPP, NB-IoT is chosen as a most promising technology that has been specified for 5G machine type communication (5G-MTC). Since 5G relies on low power wide area networks (LPWAN) and NB-IoT is suitable low power technology in deploying MTC in 5G networks. NB-IoT operates in a licensed spectrum bands and has the potential to guarantee quality of service (QoS). NB-IoT is a specified LPWAN that is based upon system bandwidth of 180 kHz and sub carrier spacing can be considered as 3.75 kHz and 15 kHz as per 3GPP, NB-IoT in downlink system only supports 15 kHz sub carrier spacing. NB-IoT is a top competitor for other low power networks that operates in both licensed and unlicensed spectrum ad 3GPP has specialized NB-IoT as a top priority in 5G networks to support massive machine type communication. In this article, we have studied the technologies for NB-IoT and its implementation in 5G MTC. We also designed a NB-IoT downlink system based on 3GPP guidelines considering sub carrier spacing as 15 kHz and its performance analysis is carried out for MTC scenario. The analysis is performed with two different antenna configurations and compared its performance analysis in terms of BER, FER and QPSK constellation of NPDCCH and NPDSCH after channel estimation. The BER and FER of both NPDCCH and NPDSCH decrease with SNR, resulting the better performance towards machine type communications in 5G.

Matrix elements of unitary group generators in many-fermion correlation problem. II. Graphical methods of spin algebras

This second instalment continues our survey inter-relating various approaches to the evaluation of matrix elements (MEs) of the unitary group generators, their products, and spin-orbital U(2n) generators, in the basis of the electronic Gel’fand–Tsetlin (G–T) [or Gel’fand–Paldus (G–P) or P-] states spanning the carrier spaces of the two-column irreducible representations (irreps) of the unitary group approach (UGA) to the many-electron correlation problem. Exploiting an intimate relationship between the U(n), $${\mathcal {S}}_N$$ , and SU(2) groups we rely here on the SU(2) formalism within the confines of UGA rather than on an earlier approach relying on the permutation group $${\mathcal {S}}_N$$ . The key is a close relationship between the P-states of UGA and the Yamanouchi–Kotani (Y–K) states of SU(2) that differ only in a phase. This enables one to exploit the powerful graphical techniques of spin (or angular momentum) algebras as first developed by Jucys. We show the usefulness and power of these techniques in the problem of UGA ME evaluation which, moreover, leads automatically to their segmentation, first derived for single generators by Shavitt and for generator products by Boyle and Paldus. We also show how the same technique can be successfully employed for MEs of spin-dependent U(2n) generators in the UGA P-basis.

Transmission of a broadband FSK signal from a dynamically tuned narrowband antenna

A frequency reconfigurable patch antenna is dynamically tuned to transmit frequency-shift keying (FSK) signals over a range of frequencies much broader than the static impedance bandwidth of the antenna. Experiments are conducted for two binary FSK schemes having different carrier spacing. In both cases, dynamic tuning of the antenna is shown to increase the amplitude of the radiated signal by providing a better match than the static antenna. However, the average energy of the radiated bit at each carrier frequency decreases as the symbol rate increases beyond the 3 dB bandwidth of the antenna. Therefore, the bandwidth of the antenna is found to be a limiting factor for the maximum achievable data rate in this scheme. As an alternative to shorter bit durations, the authors show that a higher level FSK scheme using dynamic tuning is able to increase throughput beyond what is possible with a static antenna.

Carrier Design and Motion Control of Marine Underwater Robot

Wang, K.; Wang, M.-Y., and Zhao, Y.-F., 2020. Carrier design and motion control of marine underwater robot. In: Qiu, Y.; Zhu, H., and Fang, X. (eds.), Current Advancements in Marine and Coastal Research for Technological and Sociological Applications. Journal of Coastal Research, Special Issue No. 107, pp. 181-184. Coconut Creek (Florida), ISSN 0749-0208.The underwater robot is a complex intelligent system, which can replace human beings to carry out underwater work in complex and hard environment. Underwater robot is a complex system integrating many disciplines, including mechanical, electronic, computer, fluid, structure, material and other disciplines, which has become the main tool in underwater observation, underwater archaeology, underwater search and rescue, aquaculture and other aspects. Through the underwater robot, we can use it in many ways, such as marine environment monitoring, seabed resource exploration, military application, etc., which can replace human beings to complete observation, camera, information collection and other work in the deep water environment. The underwater robot must face the complex marine environment, which requires its carrier to have a variety of high requirements, such as pressure resistance, water tightness and carrying capacity. Through high-quality carrier design, we can better improve the carrier's promotion efficiency and space operation ability. By establishing a perfect integrated motion control system, the underwater robot can realize behavior reflection and information control, which will improve the robot's motion control technology. First, this paper classifies the underwater vehicles. Then, the basic principle of the underwater vehicle is analyzed. Then, this paper designs the underwater vehicle. Finally, this paper analyzes the motion control structure.

Reconfigurable Digital Delta-Sigma Modulation Transmitter Architecture for Concurrent Multi-Band Transmission

This paper presents a reconfigurable delta-sigma modulation (DSM) architecture for concurrent multi-band transmission. The reconfigurability in terms of carrier spacing and the number of simultaneous carrier transmission is useful for applications such as carrier aggregation in 5G. This paper uses $4^{th}$ order reconfigurable multi-band DSM (RMB-DSM) such that the zeros of the noise transfer function can be reconfigured to fall at multiple frequencies, where the carriers are being aggregated. The quantization noise between the transmission bands is a critical issue in the case of multi-band transmission. Therefore, a multi-band additional noise shaping (ANS) function is also introduced, which generates notches around each carrier and reduces the noise level between the multiple pass-bands. The proposed scheme has been validated in simulation, as well as in experiment for aggregating up to four 15 MHz long term evolution (LTE) signals with an overall aggregated bandwidth of 60 MHz. Measurement results show a 10-25% improvement in coding efficiency and 15-35 dB improvement in noise level near the operating frequency band using the proposed multi-band augmented noise shaping technique, as compared to the standard DSM. The corresponding improvement of 8% in the overall efficiency is observed by using the proposed multi-band augmented noise shaping technique.