Signal Bandwidth Research Articles

Iterative frequency-domain equalization with multipath interference cancellation for aeronautical telemetry

The increasing transmitted signal bandwidth of aeronautical telemetry systems leads to the channel’s frequency selectivity. Equalization techniques are always adopted to conquer such problems. To optimize the equalization performance, we pursue minimizing the mean square error (MSE) of the equalizers. The solution shows that equalizing the line-of-sight (LOS) signal results in a lower MSE than equalizing the received signal directly. Thus, we proposed an iterative equalization algorithm with multipath interference cancellation (MIC) in this letter. In each iteration, the MIC is used to extract the LOS signal from the received signal. Then, we equalize the LOS signal to reduce the MSE of the equalization. Finally, the symbols are detected from the equalized LOS signal to achieve bit-error-rate (BER) performance improvement. The numerical results demonstrate that the proposed method provides a superior BER performance with lower complexity compared to the state-of-the-art equalizers.

Enhancing transmission reach: performance analysis of WDM RoF PON OFDM system design with varied QAM schemes

Abstract Radio over fiber is upcoming and maturing technology in terms of security, reliability, and coverage for long-distance optical-wireless communication systems. The nonlinear behavior and dispersive nature of optical channels are performance restrictive factors limiting the long reach in such systems. Along with enhancing channel capacity and bandwidth for radio signals over a long distance, the use of OFDM-based such systems can overcome various performance degrading effects like phase modulation, electrical power attenuation, chromatic dispersion, and multipath fading. Here, we propose our design of an 8 channels WDM RoF PON system using the OFDM scheme. Performance analysis is carried out in terms of performance comparison for various modulation schemes like 8, 16, 128, 256, and 512 QAM levels applied on information for long transmission reach of a system up to 500Kms. 8 channels WDM system model is developed to analyze the performance at a higher data rate. System performance is evaluated with Q factor and EVM level parameters of recovered signals at various transmission distances.

MXene-coated quartz tuning fork for sensitive light-induced thermoelastic spectroscopy.

This paper demonstrates a customized quartz tuning fork (QTF) coated with the titanium carbide (Ti3C2Tx) MXene film that can effectively enhance the sensitivity of light-induced thermoelastic spectroscopy (LITES). The MXene film is coated at the root of the customized QTF. The film area is proven to have little impact on resonance frequency, bandwidth, quality factor, and amplitude of the second harmonic signal (2f) based on the fundamental flexural mode. With an optimum film thickness of 1.9 µm, the signal-to-noise ratio (SNR) of the light-induced thermoelastic signal is enhanced up to 8.7 times. A similar enhancement of 2f signals was observed at the overtone frequency. Despite the higher quality factor, the SNR of the 2f signal inspired at the overtone frequency is much lower than that of the 2f signal inspired at the fundamental frequency. Moreover, similar experimental results are observed on the commercial QTF coated with MXene film. The absorption coefficient from 1260 nm to 1680 nm of the MXene film is measured to be larger than 92%. Hence, the MXene film enables a promising application prospect for the LITES system in multiple gas measurements.

Устранение неоднозначности оценок направлений прихода широкополосных сигналов в многосигнальном режиме пеленгования

Direction finding of wideband signals overlapping in the spectral domain by a fixed antenna array requires the correction of steering vector ambiguity and phase differences corresponding to different spectral components. The spectral components of the same signal correspond to unequal values of the distance in wavelengths between the antennas in the array. A method of steering vector ambiguity correction suitable for subspace methods such as MUSIC and ESPRIT is proposed. The ambiguity in the presence of multiple signals is resolved by correcting phase diffe-rences between antennas for each spectral component, with preliminary correlation of the ambiguous steering vector with unambiguous ones obtained for the low-frequency range of the spectrum using maximum correlation. The corrected steering vector for each spectral component is obtained from the adjusted phase differences between the antennas and is used in the direction finding correlation algorithm to obtain unambiguous estimates of the directions of arrival of the wideband signals. Simulation results for direction finding of five sound wideband signals using a square internally filled antenna array consisting of 16 antennas, based on ESPRIT with the proposed method of ambiguity correction, are presented. The proposed method for correcting the steering vector ambiguity caused by different spectral components of wideband signals in the antenna array allows estimation of their directions of arrival, as is done for narrowband radio signals.

A systematic literature mapping on the security of 5G and vertical applications

Background: The deployment of 5G infrastructure is one of the vectors for new application scenarios since it enables enhanced data bandwidth, low latency, and comprehensive signal coverage. This communication system supports various vertical applications such as smart health, smart cities, smart grids, and transportation systems. However, these applications bring new challenges to 5G networks due to specific requirements for such scenarios. Furthermore, as software-based technologies, including network slicing, software-defined networks, network function virtualization, and multi-access edge computing, are a fundamental part of the 5G architecture, the network can expose these applications to new security and privacy concerns. Results: This study summarizes existing literature on 5G vertical applications security. We highlight vulnerabilities, threats, attacks, and solutions for 5G vertical applications. We conducted a systematic literature mapping to discuss security and privacy challenges regarding the 5G vertical applications. We reviewed 389 papers from 2,349 produced by searching with a curated search query and discussed vulnerabilities, threats, attacks, and solutions for 5G vertical applications. Conclusions: Smart cities, Industry 4.0, smart transportation, public services, smart grids, and smart health are vertical applications with relevant security concerns. We observed the need for more research since the 5G and vertical applications continuously evolve.

Present View and Perspectives in the Optimization of Electrical Parameters of Wireless Communication System

Abstract The paper aims to analyze the performance of wireless communication systems by focusing on key electrical parameters such as signal power, bandwidth, signal-to-noise ratio (SNR), attenuation, and modulation techniques. The study utilizes advanced concepts including MIMO (Multiple Input Multiple Output) systems, dynamic power control, and Shannon-Hartley theorem, all analyzed using MATLAB/Octave for simulation and optimization purposes. The investigation is conducted to optimize the efficiency and reliability of wireless networks, ensuring better resource management and improved quality of service (QoS).

An improved digital predistortion scheme for nonlinear transmitters with limited bandwidth

In modern wireless communication systems, wide signal bandwidth is the most straightforward approach to accommodate high data rates. Wide signal bandwidth, on the other hand, introduces severe challenges to the power amplifier (PA) and digital predistortion (DPD) design in both performance and cost. Conventional DPD systems usually ignore the impact of the transmit low-pass filter (Tx LPF) bandwidth and assume the transmit bandwidth is sufficiently large. In wideband signal transmissions, the bandwidth of Tx LPF can become the system bottleneck, limiting DPDs compensation effects. Existing DPD studies mostly investigate the DPD with reduced feedback bandwidth. In this paper, we study the impact of Tx LPF bandwidth on the DPD performance. A full-band error minimization DPD based on direct learning structure is proposed. The DPD coefficients are estimated by minimizing the full-band error between the input signal and PA output signal in the frequency domain. Furthermore, we propose a weighted DPD with improved performance by introducing a weighting diagonal matrix to the error function. Compared to existing solutions, the weighted DPD achieves a good trade-off between the in-band distortion compensation and out-of-band spectral regrowth suppression. Simulations and experiments validate the effectiveness of the proposed DPD schemes.

Cue for rear sound image localization in head-related transfer function below 4 kHz

It is known that notches and peaks at frequencies above 5 kHz in the head-related transfer function (HRTF) act as cues for median plane sound localization. However, it has also been shown that front-back discrimination of the direction of a sound image can be achieved even with only the components below 4 kHz. In the present study, we investigated the cues for rear sound image localization below 4 kHz. First, we analyzed the HRTFs for 118 ears (59 subjects) in the median plane and showed that the sound pressure around 1 kHz in the rear HRTF was larger than that in the front HRTF. This boosted band (hereinafter referred to as P0) coincided with Blauert’s directional band. Next, we proposed a hypothesis that can comprehensively explain the two types of cues that have been proposed in the past: spectral notches and peaks, and directional bands. In order to verify the effects of P0 for rear-direction localization, three preliminary psychoacoustic experiments were conducted. The results showed that eliminating P0 tends to increase localization errors at frequencies below 4 kHz. For wide-band signals, adding P0 to a previous parametric HRTF model (N1N2P1P2) tends to reduce the mean vertical localization error, and made the auditory source width approximately the same as that for the measured HRTF. These preliminary results support our hypothesis and imply that P0 acts as a cue for rear sound image localization.

AI-Driven Electrical Fast Transient Suppression for Enhanced Electromagnetic Interference Immunity in Inductive Smart Proximity Sensors.

Inductive proximity sensors are relevant in position-sensing applications in many industries but, in order to be used in harsh industrial environments, they need to be immune to electromagnetic interference (EMI). The use of conventional filters to mitigate these perturbations often compromises signal bandwidth, ranging from 100 Hz to 1.6 kHz. We have exploited recent advances in the field of artificial intelligence (AI) to study the ability of neural networks (NNs) to automatically filter out EMI features. This study offers an analysis and comparison of possible NN models (a 1D convolutional NN, a recurrent NN, and a hybrid convolutional and recurrent approach) for denoising EMI-perturbed signals and proposes a final model, which is based on gated recurrent unit (GRU) layers. This network is compressed and optimised to meet memory requirements, so that in future developments it could be implemented in application-specific integrated circuits (ASICs) for inductive sensors. The final RNN manages to reduce noise by 70% (MSEred) while occupying 2 KB of memory.

Joint DOA and distance estimation via spatial diversity wideband signal synthesis calibrated by distance parameter

Wideband signal synthesis is a technique designed to achieve large bandwidth detection capabilities by utilizing multiple relatively narrow bandwidth signals. Traditional single-antenna, time-diversity wideband synthesis method is inefficient, which has led to using Multiple-Input Multiple-Output (MIMO) architectures to introduce spatial diversity. However, this method introduces challenges such as frequency-phase inconsistencies in the self-mixing signals from different array elements due to differences in wave travel distances. In previous research, we studied the calibration of frequency and phase for synthesized sub-signals using DOA parameters, which required additional high-precision direction of arrival (DOA) estimation algorithms. In contrast, this paper proposes a novel spatial-diversity wideband synthesis method that utilizes distance parameter calibration for joint DOA and distance estimation (JDDE). A key advantage of this method is the relative simplicity of obtaining distance parameters. To address the issue where the accuracy of distance parameters does not meet the requirements for synthesis, we proposed a grid search synthesis method in this paper. Furthermore, we introduced a search synthesis based on optimization algorithms to reduce computational load and enhance the synthesis performance. Theoretical analysis and simulations confirm the high accuracy of our JDDE method. Under conditions of high signal-to-noise ratios, our method significantly reduces the DOA's root mean square error—approximately halving it compared to the multiple signal classification algorithm within the same wideband self-mixing framework. Additionally, both distance resolution and range accuracy exceed those achieved with pre-synthesis methods.

Design of a calibratable optical antenna system based on ring array light source

Abstract This study presents a multi-wavelength, multi-channel, and high-capacity optical antenna system. This approach is intended to allow parallel transmission with many channels and wavelengths by employing a ring array of vertical-cavity surface-emitting lasers, with reception accomplished via a ring detector array. The system employs spatially multiplexed techniques to send the target with numerous independent signals at the same time, effectively increasing bandwidth and reducing signal interference. The method used in this design provides benefits such as effective decreasing losses caused by blocking and removing aberrations. To overcome the spatial alignment difficulty caused by the array light source’s tiny beam size during long-distance transmission, this study introduces a high-precision acquisition, pointing, and tracking system as a reverse communication channel. The system’s wide beam can be used to align the installation of optical antenna equipment and facilitate information transmission.

Telemedicine technologies in combat settings: efficiency and prospects (literature review)

Relevance. Large-scale military conflicts involving a technically well-equipped peer enemy are associated with a higher risk of delayed evacuation of the wounded which therefore requires extended medical care at advanced medical evacuation stages, especially amid absence or shortage of skillful medical professionals. Telehealth can offer solutions to overcome the difficulties in medical care provision amid combat settings. The objective is to study the prospects and efficiency of telemedicine technologies in enhancing availability of medical care during modern military operations.Methods. The PubMed database and the Scientific Electronic Library (eLIBRARY.ru) were used to collect research papers published from 2014 to 2024 studying the development and implementation of telemedicine technologies to backup combat operations.Results and discussion. Consultations by phone together with transfer of photos and text messaging remain the most common technology to provide telehealth assistance in combat settings. Teleconference connection allowing for two-way audio and video communication involving real-time data transfer is a most promising telecommunication format. Telehealth capacities can be expanded by augmented and mixed reality technologies, AI, drones, or robotic surgery. In combat environments, however, using telemedicine is limited by cybersecurity concerns and the signal bandwidth of modern communications systems. An efficient military telemedicine requires an integral centralized system involving multidisciplinary teams of experienced medical consultants providing round-the-clock emergency and routine telemedicine care to military units, including those engaged in combat operations.Conclusion. In combat settings telemedicine technologies have great untapped potential and can contribute largely in terms of evidence-based decision-making in process of medical triage and evacuation, thus optimizing the distribution of medical capacities and resources and improving the results of injury treatment. Although unfit to replace advanced combat medicine training, telemedicine can reinforce existing capacities by providing specialized medical advice to combat medics.

Thermally Deposited Pt/InSe/Nb2O5/Ag Stacked Layers Designed as Negative Capacitance Sources and Antennas for 5 G/6 G Networks

Herein, Pt/InSe/Nb2O5/Ag (ISNO) stacked layers are designed as multichannel 5 G/6 G network antennas and negative capacitance (NC) sources. The devices are fabricated using thermal deposition technique to coat Pt/InSe thin films with transparent Nb2O5 dielectric windows. While Pt thin films induce the crystallinity of InSe, the Nb2O5 layer remains amorphous. The impedance spectroscopy studies show that the Pt/InSe/Ag (IS) and (ISNO) antenna channels exhibit resonance–antiresonance peaks at driving frequencies of ≈0.4 and ≈1.1 GHz, respectively. Both the IS and ISNO antenna channels exhibit the NC effect in a wide range of frequency domain. In addition, ISNO antennas show signal transmission above 1.70 GHz with a return loss value of 28 dB and voltage standing wave ratios of 1.20. The range of frequencies over which the antenna performs well (bandwidth) extends from 1.54 to 1.80 GHz. Practical tests of one‐port and two‐port reflection/transmission using a network analyzer operative in the frequency domain of 0.01–6.0 GHz highlight the system's differing isolation and coupling characteristics at 2.43 and 6.0 GHz, respectively. The high levels of isolation at 6.0 GHz assure the suitability of the system for applications requiring minimal reverse transmission and high signal integrity. The NC effect, wide bandwidth, and high signal isolation characteristics are preferable in electronics and 5 G/6 G networks.

Efficient gridless wideband sparse array synthesis with tapped delay-lines

In this paper, we propose a new wideband sparse array synthesis method based on gridless compressed sensing to solve the basis mismatch problem for discrete grids. Considering the tapped delay-lines (TDL) structure for space-time domain processing, and using successive frequency-varying atoms for sparse representation of wideband signals, an arbitrary sampling-atomic norm minimization is introduced to model the group sparsity-constrained wideband arrays in which the positions and the excitation values of array element are obtained with a high freedom. The above nonconvex problem is then transformed into a convex relaxation, which is solved using the Prolate Spheroidal Wave Functions (PSWFs). The experimental results show that the proposed sparse array design has higher matching accuracy and sparsity, compared with the discretized wideband sparse array design, which verifies the effectiveness and efficiency of this method.

Флуктуации корреляционных характеристик в шумовой системе радиосвязи

Ultra-wideband noise communication system using the transmitted reference technique with the time diversity is proposed for a covert data transmission through additive white Gaussian noise channel. Spectrum modulation of transmitted signals is performed as a result from linear superposition between the noise references and informative noise carriers delayed at the time diversity significantly exceeding the coherent time. The delayed noise carriers are multiplied by antipodal symbols at the same rate of binary data stream. Spectral power density of result noise signals is modulated by antipodal harmonic functions with the period in inverse proportion to diversity time delay. The time delay in the correlation receiver corresponds to the diversity time delay of informative noise signals. The correlation estimation problem appears in the case of data transmitting on the base of continuous noise carriers. Fluctuation analysis of correlation estimations with nonstationary trend at the data rate is performed. The intersystem jamming occurring in digital noise communications increase the correlation fluctuations at the receiver output and initiate asymptotic limitation of correlation performances without thermal noise in a wireless channel. Nonstationary trends of output correlation estimations become little if the informative time delay significantly exceeds the coherent times as noise carriers as additive white Gaussian noise. The forming of digital noise carriers is produced by the time window method. Simulation of noise communications shows that utilizing continuously noise carriers with time windows permits to decrease randomly fluctuations of correlation performances in the case when the product of noise signal bandwidth by bit duration exceeds one hundred units.

Generation of Wideband Signals Based on Continuous-Time Photonic Compression

A detailed study on continuous-time photonic compression (CTPC) for generating wideband signals is presented in this paper. CTPC enables the conversion of parallel analog waveforms from multiple channels into a time-compressed continuous-time waveform with increased bandwidth. We demonstrate a CTPC system with a compression factor of two in a proof-of-concept experiment. Subsequently, the origin of the distortion in the generated signals is investigated, and we proposed a method based on bandpass filtering to remove the periodic dips observed in the generated waveforms. In addition, a predistortion method is proposed to eliminate the distortion caused by the non-ideal spectral property of the multichannel system. Further simulation results are presented to show the potential of the proposed approach.

An Ultrawide Bandwidth Digital Backend System Based on PFB Algorithm for QTT

For the planning of the QiTai radio Telescope ultrawide bandwidth low-frequency pulsar receiving system, we designed and implemented a Field-Programmable Gate Array (FPGA)+CPU/GPU hybrid architecture digital backend system based on the Polyphase FilterBank (PFB) channeling algorithm. We used the FPGA signal acquisition and processing platform to implement ultrawide bandwidth signal sampling and designed the PFB algorithm to realize the digital channelization of multiple analog bandwidth signals. We also developed data encapsulation and multichannel parallel distribution firmware algorithms and realized the real-time parallel transmission of high-speed astronomical data streams based on the VLBI Data Interchange Format. We developed the Ultra Wide bandwidth Low-frequency pulsar data process PIPEline, which realized the real-time processing and data packaging of massive pulsar signals. Using the L-band (964–1732 MHz bandwidth) receiving system of the Nanshan 26 m radio telescope, we conducted a systematic test on the designed digital backend system and obtained high-quality observation data. By using the professional pulsar data processing software DSPSR to process the observation data, we obtained high signal-to-noise ratio pulse profiles.

A novel artificial intelligence‐based antenna designing model for optimizing 5G mobile communication

AbstractAntenna designing involves the creation of devices to transmit or receive electromagnetic signals for various applications. It encompasses optimizing parameters such as size, shape, and frequency response to achieve desired performance characteristics, including signal strength, bandwidth, and efficiency, across diverse communication systems and frequencies. In this research, we intend to establish a novel artificial intelligence (AI)‐based antenna designing model for optimizing 5th generation (5G) mobile communication. We proposed Multi‐Objective Zebra Optimization (MOZO) to enhance 5G antenna design, aiming to minimize return loss () and maximize gain (G) concurrently. MOZO efficiently explores design space, offering Pareto‐optimal solutions that balance objectives. This approach ensures optimal antenna performance across the desired frequency range, advancing 5G communication efficiency. Our model enhances the functionality of a small, rectangular patch antenna designed for the 5G band, specifically operating at 30 GHz. Additionally, we conducted a comparative analysis between the performance of our optimized rectangular 5G antenna and several recently employed 5G‐millimeter wave (mmWave) antennas. This comparison sheds light on the efficacy and competitiveness of our optimized design within the 5G‐mmWave antenna landscape.

Generation of frequency-shift keying (FSK) and amplitude-shift keying (ASK) RF signals by diode-tuned Fourier domain mode-locked opto-electronic oscillator.

An approach to the generation of frequency-shift keying (FSK) and amplitude-shift keying (ASK) RF signals with a diode-tuned Fourier domain mode-locked opto-electronic oscillator (FDML OEO) is proposed and demonstrated. We use a low-cost varactor diode tuned phase shifter to form a high speed tunable bandpass filter (TBF) to implement the FDML-OEO. When a square wave modulation signal is used to drive the TBF, FSK RF signals are generated, with the flexibility to easily change the center frequency and tuning bandwidth of the FSK signals. For the ASK RF signal generation, a band-pass filter (BPF) with a bandwidth less than the TBF tuning range is added to the FDML OEO RF feedback loop. When the TBF center frequency hops in and out of the BPF bandwidth within a mode locking period, the FDML OEO generates ASK RF signals. The phase noises of the FSK and ASK RF signals generated by our FDML-OEO are both measured to be -123dBc/Hz at 10 kHz offset frequency. The key significance of this approach is that no microwave source is required to generate the ASK signal and reconfigurable FSK and signals, which may find wide applications in future radar and communications systems.

ADAPTIVE COMPLEX FILTERS BASED TRANSMITTER IQ IMBALANCE REJECTION

This paper presents an efficient method for compensation of frequency-dependent (FD) transmitter In-phase Quadrature (IQ) imbalance. Proposed method compensates imbalance by exploiting indirect learning architecture (ILA) and complex filters whose coefficients are determined in an iterative process. Compensation performance is assessed after the method has been implemented in a Software Defined Radio (SDR) platform, capable of transmitting modulations at different central frequencies. Measured results demonstrate that the imbalance related images are reduced down to the noise floor. After applying the proposed IQ imbalance correction method, the transmitter image rejection ratio (IRR) is increased by 15dB in the case of an SDR transmitter operating at central frequency of 1.7 GHz. The ADC/DAC sampling rate is 61.44MS/s, while the signal bandwidth, for which the compensation is performed, is 30.72MHz. The advantage of the proposed method is low complexity in terms of a reduced number of coefficients. The method is generic and can be utilized for IQ imbalance compensation when wideband signals are transmitted.