Modulation Spaces Research Articles

Autonomous Droid for Terrestrial Research and Intelligence (ATRi)

ATRi (Autonomous droid for Terrestrial Research and Intelligence) is an autonomous and sentient droid designed to assist space crews with various activities and experiments. The artificially intelligent droid autonomously navigates inside crewed space capsules and utilizes voice and visual recognition algorithms to receive commands, record basic readings, and assist the crew in performing various experiments. ATRi's machine learning algorithms can be tailored to the specific astronaut(s) it will accompany in the space capsule. This personalized approach not only assists astronauts but also fosters a sense of companionship. This paper provides details about the physical and algorithmic characteristics of the droid and outlines how it can be trained and deployed in any crewed space capsule. The droid will be powered by a sentient program that incorporates visual recognition (including facial recognition and video recording capabilities), natural language processing, voice recognition, and speech synthesis. Six microphones and two cameras are embedded to capture audio/voice commands and visuals. While the current version of the droid is fixed to the space capsule, future iterations are envisioned to be highly mobile in zero-gravity environments within any crewed space capsule. This mobility is facilitated by a sophisticated motion control system that enables the droid to align in any direction, rotate, and navigate inside the crewed space module. In addition to assisting the crew, ATRi will document all activities inside the capsule through photos and videos. It can process images and videos, automatically categorize them, and periodically communicate the information to ground control.

The nanoscale modulation of interlayer space in two-dimensional nanoclay membranes for osmotic energy conversion

The harvest of osmotic energy based on two-dimensional (2D) nanochannel membranes has been attracting wide attentions for addressing the energy issues. Here, we report the nanoscale modulation of interlayer space in 2D nanochannel membranes based on montmorillonite (MMT) for osmotic energy conversion. Cationic surfactants with different alkyl chain lengths are intercalated between MMT nanosheets to regulate the interlayer spacing of 1.74 and 2.49 nm, thus achieving the modulation of ion flux through the nanoclay membranes. A high power density of ∼4.13 W/m2 can be attained in 300-fold concentration gradient. The mechanism of the influence of nanochannel sizes on osmotic energy conversion performance is investigated by experiments and theoretical simulations. Realizing the nanoscale modulation of interlayer space in 2D nanochannels provides new insights for designing nanofluidic membranes toward clean energy harvesting.

Blind recognition algorithm of modulation mode and space–time block code via convolutional neural network

Blind recognition algorithm of modulation mode and space–time block code via convolutional neural network

Analysis of PAPR reduction of optical-OTFS for 256-QAM using companding and clipping–filtering algorithms

Abstract The article presents an investigation into Peak-to-Average Power Ratio (PAPR) reduction techniques in Optical Orthogonal Time Frequency Space (O-OTFS) modulation. Focusing on clipping and filtering as well as companding methods, the study explores their efficacy in mitigating PAPR challenges inherent in O-OTFS waveforms. The research evaluates the impact of these techniques on signal quality, particularly in the context of a Rician channel. Clipping and filtering (C&F) are examined for their ability to control amplitude peaks, while companding is analyzed for its role in optimizing dynamic range. The study conducts a comprehensive analysis of Bit Error Rate (BER) and power spectrum density (PSD) under varying conditions, shedding light on how these methods influence the reliability and robustness of OTFS communication. The investigation considers the interplay of these PAPR reduction methods with the unique characteristics of the Rician and Rayleigh channel, which includes a dominant line-of-sight component. The findings contribute valuable insights into designing efficient OTFS modulation systems for real-world scenarios. Ultimately, this research aims to provide a deeper understanding of PAPR reduction strategies in OTFS, offering guidance for optimizing signal processing techniques in communication systems where mitigating PAPR is crucial for achieving high performance and reliable data transmission. It is noted that the proposed C&F and companding algorithms outperform the conventional methods and achieved a PAPR gain of 1–3 dB and BER gain of 10.6–2 dB.

Multilinear Fourier integral operators on modulation spaces

Abstract In this article, we study properties of multilinear Fourier integral operators on weighted modulation spaces. In particular, using the theory of Gabor frames, we study boundedness of multilinear Fourier integral operators on products of weighted modulation spaces. Further, we investigate the periodic multilinear Fourier integral operator. Finally, we study continuity of bilinear pseudo-differential operators on modulation spaces for certain symbol classes, namely 𝐒𝐆 {\mathbf{SG}} -class.

Superconducting gap modulations: Are they from pair density waves or pair-breaking scattering?

In his seminal work published in <i>Acta Physica Sinica</i> in 1965, Yu Lu pointed out that the superconducting gap exhibits weak modulations near the pair-breaking magnetic impurity in a superconductor. In the past ten year, a series high-resolution scanning tunneling microscopy works reported weak superconducting gap modulations in certain superconductors and explained these phenomena as pair density waves. In line with Yu Lu’s discovery, Lee D H et al. pointed out that in many cases, the interference effect of pair-breaking scattering can also lead to superconducting gap modulations in space. We will discuss the distinction and unification of these two kinds of mechanisms, as well as their relevance to recent experimental observations.

АНАЛИЗ РАДИАЦИОННЫХ НАГРУЗОК В КАЮТЕ МКС ПРИ ИСПОЛЬЗОВАНИИ ЗАЩИТЫ ИЗ КОМПОЗИТНОГО МАТЕРИАЛА

The paper reports the results of calculating doses in the location of a cylindrical container of a protective composite (teflon of 1 cm in thickness and 4.05 g/cm3 density) in the left crew quarter of the ISS Service module (space experiment "Protective composite"). Calculations were compared with the data of passive PILLE-MKS detectors installed inside the container and on the nearby wall. Calculation was performed using ray tracing for the detectors' locations with consideration for the input of galactic cosmic rays and particles in Earth's radiation belts in the conditions modeling the space station compartment. The calculation was made for the ISS orbit in the period between February 21 and September 19, 2022 on the background of increasing solar activity. According to the PILLE-ISS measurements, the protective effect of the composite in terms of absorbed dose made up 1.39 ± 0.03, largely due to a reduced input of Earth's radiation belts which agrees with the calculations.

OTFS Enabled LEO Satellite Communications: A Promising Solution to Severe Doppler Effects

With the advantages of low cost and flexible deployment, low earth orbit satellite (LEO-Sat) communications have received widespread attentions, such as providing global wireless access with enhanced data rates in future 6G networks. However, due to the feature of high-mobility, LEO-Sat communications are facing severe Doppler effects, which heavily degrades the link reliability. The existing approaches for coping with Doppler effects, such as phase locked loop, mainly carry out the prediction and compensation for Doppler frequency shifts, which demands high implementation complexity, as well as accurate channel estimation. Against this background, this article portrays a new paradigm of reliable LEO-Sat communications with the aid of orthogonal time frequency space (OTFS) modulation scheme, which can average out the channel dynamics through modulating information in the delay-Doppler (DD) domain, thereby overcoming severe Doppler effects. In particular, we start with studying the Doppler effect characteristics of LEO-Sat communications, which serves as the motivations of using OTFS. Then, we conceive a case study to show the feasibility of OTFS enabled LEO-Sat communication by evaluating the reliability performance. Finally, we discuss a range of promising research opportunities and potential challenges.

Embedding and Duality of Matrix-weighted Modulation Spaces

Embedding and Duality of Matrix-weighted Modulation Spaces

Fully Generalized Space Modulation Visible Light Communications System Based on Pearson Correlation Coefficient Selection

Fully Generalized Space Modulation Visible Light Communications System Based on Pearson Correlation Coefficient Selection

Symbiotic Radio with Orthogonal Time Frequency Space Modulation over High-Mobility Channels

Symbiotic Radio with Orthogonal Time Frequency Space Modulation over High-Mobility Channels

A Survey on Orthogonal Time Frequency Space Modulation

A Survey on Orthogonal Time Frequency Space Modulation

Excitation generated preferential binding sites for ethane on porous carbon-copper porphyrin sorbents: ethane/ethylene adsorptive separation improved by light.

Energy-efficient separation of C2H6/C2H4 is a great challenge, for which adsorptive separation is very promising. C2H6-selective adsorption has big implications, while the design of C2H6-sorbents with ideal adsorption capability, particularly with the C2H6/C2H4-selectivity exceeded 2.0, is still challenging. Instead of the current strategies such as chemical modification or pore space modulation, we propose a new methodology for the design of C2H6-sorbents. With a Cu-TCPP [TCPP = 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin] framework dispersed onto a microporous carbon and a hierarchical-pore carbon, two composite sorbents are fabricated. The composite sorbents exhibit enhanced C2H6-selective adsorption capabilities with visible light, particularly the composite sorbent based on the hierarchical-pore carbon, whose C2H6 and C2H4 adsorption capacities (0 °C, 1 bar) are targetedly increased by 27% and only 1.8% with visible light, and therefore, an C2H6-selectivity (C2H6/C2H4 = 10/90, v/v) of 4.8 can be realized. With visible light, the adsorption force of the C2H6 molecule can be asymmetrically enhanced by the excitation enriched electron density over the adsorption sites formed via the close interaction between the Cu-TCPP and the carbon layer, whereas that of the C2H4 molecule is symmetrically altered and the forces cancelled each other out. This strategy may open up a new route for energy-efficient adsorptive separation of C2H6/C2H4 with light.

Development of a Hybrid Learning Virtual Space Module Based on Local Saluan Language Wisdom in Science Education for Elementary School Students

This research aims to develop a hybrid learning virtual space design based on local Saluan language wisdom in science subjects for fifth grade students at SDN 3 Luwuk. The research method used is development research using the Borg and Gall model. Development steps include requirements analysis, design, development, implementation, and evaluation. The hybrid learning virtual space design developed contains science learning materials with content related to the local wisdom of the Saluan ethnic language. Learning material is presented in interactive multimedia form and equipped with various activities that can increase student participation in the learning process. Evaluation is carried out by measuring the quality of the hybrid learning virtual space in terms of effectiveness, efficiency and student satisfaction. It is hoped that this research can provide interesting learning alternatives and can increase the interest and learning outcomes of fifth grade students at SDN 3 Luwuk in science subjects by utilizing the local wisdom of the Saluan ethnic language. The targeted outcomes of this research are (1) design of a hybrid learning virtual space based on local wisdom of the Saluan language in science subjects for fifth grade students at SDN 3 Luwuk; (2) teaching materials and learning media that can improve student learning outcomes, interest and motivation; (3) alternative science learning media with hybrid learning virtual space; (4) increasing local wisdom in learning

Optimizing the annual energy yield of a residential bifacial photovoltaic system using response surface methodology

This study investigates the impact of ground albedo, module spacing, height, and tilt angle on the annual energy output of a small-scale residential photovoltaic (PV) system. The study used response surface methodology (RSM) integrated with PVsyst simulation tool for the analysis. The results obtained from PVsyst are verified by comparing them with data from existing literature. Two significant contributions were demonstrated in this study: a parametric analysis that evaluates the influence of several parameters on the annual energy output, and a detailed statistical analysis that utilizes RSM with optimization. The central composite design with 30 runs was used for the experimental design. Within the tested ranges, the findings indicate that ground albedo, module spacing, and module tilt angle significantly affect annual energy generation. The RSM generated a statistical model that predicts the system's annual energy generation, with a determination coefficient (R2) of 0.99. Moreover, the RSM can identify the optimal values of the studied controllable parameters, which can lead to improved system performance and increased energy output. The optimization analysis reveals that the system's highest annual energy output is attained when the ground albedo is set at 0.82, the module spacing is 8.95 m, the module height is 1.35 m, and the module tilt angle is 35.7°. These parameters were determined based on the weather conditions in Sharjah, UAE. The findings reveal that the annual energy production of the tilted bifacial PV (T-BiPV's) improves by 12.4 %, when ground albedo is increased from 0.2 to 0.8. Also, the output increases by 69.47 % when spacing is increased from 2 m to 8 m. Additionally, increasing the height of the T-BiPV modules from 0.5 m to 2 m results in an increase in energy output by 5.63 %. This study can serve as a basis for further investigations into optimizing bifacial PV systems using RSM, particularly under restricted module spacing or when taking land cost into account in the optimization.

Time-frequency analysis and coorbit spaces of operators

To analyse the time-frequency content of an ordered data set, it is desirable to consider cross-correlation of time-frequency contents of data points, while maintaining the order of such correlations. To this end, we introduce an operator-valued short-time Fourier transform for certain classes of operators with operator windows, and show that the transform acts in a way analogous to the way the short-time Fourier transform for functions acts, in particular giving rise to a family of vector-valued reproducing kernel Banach spaces, the so-called coorbit spaces, as spaces of operators. As a result of this structure, the operators generating equivalent norms on the function modulation spaces are fully classified. We show that these classes of operators have the same atomic decomposition properties as the function spaces, and use this to give a characterisation of the spaces using localisation operators.

An abstract approach to Marcinkiewicz-Zygmund inequalities for approximation and quadrature in modulation spaces

We study the approximation and quadrature error of points that satisfy Marcinkiewicz-Zygmund inequalities. First, we investigate the use of Marcinkiewicz-Zygmund inequalities in an abstract Hilbert space for an abstract approximation and quadrature rule. The setting is then specified to Sobolev spaces induced by Freud weights e − 2 σ | x | α e^{-2\sigma |x|^\alpha } with α > 1 \alpha >1 and σ > 0 \sigma >0 , and we derive specific bounds for the approximation and quadrature error. For the Gaussian weight e − 2 π x 2 e^{-2\pi x^2} , we verify that the Sobolev spaces essentially coincide with a specific class of modulation spaces that are well known in (time-frequency) analysis.

Integrated Sensing and Communication via Orthogonal Time Frequency Space Signaling with Hybrid Message Passing Detection and Fractional Parameter Estimation.

For the orthogonal time frequency space (OTFS) modulation, we generally multiplex symbols on a new type of carrier waveform in the delay-Doppler (DD) domain. These two parameters can be used to infer the range (R) and velocity (V) of the communication user and sensing target; thus, it is natural for the OTFS to be implemented in integrated sensing and communication (ISAC). A framework for ISAC based on OTFS modulation is proposed in this paper, in which the matched filter scheme with fractional parameter estimation is implemented for radar sensing. In addition, the hybrid message passing (MP) detection algorithm is developed for OTFS symbol demodulation. According to the simulation results, fractional DD shifts associated with multiple targets can be accurately obtained through the proposed framework. Meanwhile, the bit error rate under the proposed detector is less than 10-4 when the signal-to-noise ratio is high enough.

On the Doppler Squint Effect in OTFS Systems Over Doubly-Dispersive Channels: Modeling and Evaluation

Extensive work has demonstrated the excellent performance of orthogonal time frequency space (OTFS) modulation in high-mobility scenarios. Time-variant wideband channel estimation serves as one of the key compositions of OTFS receivers since the data detection requires accurate channel state information (CSI). In practical wideband OTFS systems, the Doppler shift brought by the high mobility is frequency-dependent, which is referred to as the Doppler Squint Effect (DSE). Unfortunately, DSE was ignored in overall prior estimation schemes employed in OTFS systems, which leads to severe performance loss in channel estimation and the consequent data detection. In this paper, we investigate DSE of wideband time-variant channel in delay-Doppler domain and concentrate on the characterization of OTFS channel coefficients considering DSE. The formulation and evaluation of OTFS input-output relationship are provided for both ideal and rectangular waveforms considering DSE. The channel estimation is therefore formulated as a sparse signal recovery problem and an orthogonal matching pursuit (OMP)-based scheme is adopted to solve it. Simulation results confirm the significance of DSE and the performance superiority compared with traditional channel estimation approaches ignoring DSE.

GAMP-Based Low-Complexity Sparse Bayesian Learning Channel Estimation for OTFS Systems in V2X Scenarios

Vehicle to everything (V2X) is widely regarded as a critical application for future wireless communication networks. In V2X, large relative speeds between vehicles may severely deteriorate the performance of communication between vehicles. Orthogonal time frequency space (OTFS) modulation, which converts time- and frequency-selective channels into non-selective channels in the delay-Doppler (DD) domain, provides a solution for establishing reliable wireless communications in V2X scenarios. However, in the complex multi-scattering scenarios, the channel also suffers from a serious inter-Doppler interference (IDI) problem, which poses a great challenge to the accurate demodulation of OTFS receiver signals. To address the above problems, this paper considers the variation of Doppler sampling points within one symbol when deriving the channel model, which effectively overcomes the IDI problem, and employs a basis expansion model (BEM) to convert the channel estimation into a sparse recovery problem for the basis coefficients. In addition, to better utilize the sparse nature of the OTFS channel, a generalized approximate message passing-sparse Bayesian learning (GAMP-SBL)-based algorithm is employed to estimate the basis coefficients of the channel. The complexity of this algorithm is greatly reduced compared to the conventional SBL algorithm. Finally, system simulation results are reported to verify the superiority of the proposed scheme.