Performance Of Modulation Research Articles

ENHANCING OTFS MODULATION FOR 6G THROUGH HYBRID PAPR REDUCTION TECHNIQUE FOR DIFFERENT SUB-CARRIERS

Peak-to-average power ratio (PAPR) in orthogonal time frequency space (OTFS) is vital for optimizing signal efficiency, minimizing distortion, and enhancing the performance of a beyond fifth-generation (B5G) system. The paper focuses on lowering the PAPR while retaining the bit error rate (BER) and power spectral density (PSD) for 64 and 256 sub-carriers. The PAPR is minimized by using a fractal optimization process known as selective mapping (SLM) and partial transmission sequence (PTS) at the transmitting block of the OTFS framework. The combination of SLM and PTS reduces peak power by selectively modifying the phase of transmitted symbols. SLM generates multiple versions of the signal, while PTS allocates power to these versions optimally, collectively mitigating amplitude peaks and minimizing PAPR. According to the simulation results, the suggested SLM+PTS works better than the traditional SLM and PTS, achieving low spectrum leakage and PAPR improvements of 5.5 dB and 4.9[Formula: see text]dB as well as SNR gains of 2.4[Formula: see text]dB and 2.1[Formula: see text]dB. In the future, SLM+PTS may work on lowering PAPR by making computers faster, researching adaptive algorithms, and combining machine learning methods for real-time optimization in various communication settings. Complex modeling, including fractal-based SLM and PTS approaches, provides a detailed understanding of waveform behavior and interference patterns, enabling more accurate and effective hybrid PAPR reduction techniques. This combination enhances the ability to manage to mitigate non-linear distortion across various sub-carriers, crucial for the performance and efficiency of 6G OTFS modulation.

Quasi-passive modulation for monolithic GaN photoelectronic circuit

Due to the overlap between the electroluminescence spectrum and spectral responsivity curve, gallium nitride (GaN)-based multi-quantum well (MQW) diodes can modulate and detect light emitted by another diode with the same MQW structure. This enables the realization of a monolithic integrated GaN optoelectronic circuit, integrating an MQW-based transmitter, waveguide, modulator, and receiver on a tiny GaN chip. It is well known that the active region of MQW absorbs high-energy photons within the plane, generating electron-hole pairs and forming photogenerated carriers. The change in free carrier concentration causes variations in the refractive index and absorption characteristics of the waveguide, thereby manipulating light propagation within the waveguide. Based on this physical phenomenon, a quasi-passive modulation scheme is proposed for a monolithic GaN photoelectronic circuit. This scheme achieves optical modulation by connecting a variable resistor between the modulator electrodes, avoiding the need for high-precision external electric fields and complex control circuits. The performance of the quasi-passive modulation was tested through on-chip data transmission and real-time audio signal transmission. The results indicate that quasi-passive modulation is highly feasible in optoelectronic systems and shows great promise as a competitive core module for future large-scale photonic integrated circuits.

Enhancing Performance of Continuous-Variable Quantum Key Distribution (CV-QKD) and Gaussian Modulation of Coherent States (GMCS) in Free-Space Channels under Individual Attacks with Phase-Sensitive Amplifier (PSA) and Homodyne Detection (HD).

In recent research, there has been a significant focus on establishing robust quantum cryptography using the continuous-variable quantum key distribution (CV-QKD) protocol based on Gaussian modulation of coherent states (GMCS). Unlike more stable fiber channels, one challenge faced in free-space quantum channels is the complex transmittance characterized by varying atmospheric turbulence. This complexity poses difficulties in achieving high transmission rates and long-distance communication. In this article, we thoroughly evaluate the performance of the CV-QKD/GMCS system under the effect of individual attacks, considering homodyne detection with both direct and reverse reconciliation techniques. To address the issue of limited detector efficiency, we incorporate the phase-sensitive amplifier (PSA) as a compensating measure. The results show that the CV-QKD/GMCS system with PSA achieves a longer secure distance and a higher key rate compared to the system without PSA, considering both direct and reverse reconciliation algorithms. With an amplifier gain of 10, the reverse reconciliation algorithm achieves a secure distance of 5 km with a secret key rate of 10-1 bits/pulse. On the other hand, direct reconciliation reaches a secure distance of 2.82 km.

Performance Evaluation of Fractal Wavelet Packet Transform on Wireless Communication Systems

The performance of the phase shift keying (PSK) modulation technique over additive white Gaussian noise (AWGN) and multipath propagation channels generally becomes worse for higher-order modes. Therefore, a new modulation technique should be provided in order to have a system that is capable of transmitting data with higher efficiency while maintaining better performance at the same time. This paper presents the development of a fractal wavelet packet transform incorporated within the M-ary PSK system, namely M-ary PSK orthogonal wavelet division multiplexing (OWDM), which is proposed to obtain high performance of modulation in terms of spectrum efficiency and bandwidth resources intended for wireless communication systems. To demonstrate performance improvement over a Rayleigh frequency selective fading channel and in the presence of AWGN noise, the proposed system was evaluated and compared to the basic modulation system and M-ary PSK employing orthogonal frequency division multiplexing (OFDM). The performance results show that M-ary PSK OWDM had better performance in comparison with M-ary PSK OFDM and the conventional system. By utilizing 16 subcarriers, QPSK OWDM achieved bit error rate performance improvement from 1.5 × 10-3 to 1 × 10-4 for Eb/N0 of 20 dB with efficient bandwidth.

Performance of adaptive M-PAM modulation for FSO systems based on end-to-end learning

Performance of adaptive M-PAM modulation for FSO systems based on end-to-end learning

The primary frequency modulation control strategy based on fuzzy active disturbance rejection control for gas turbines

Gas turbines play a core role in clean energy supply and construction of comprehensive energy system, and the control performance of primary frequency modulation (PFM) of gas turbine has a great impact on the frequency control of the power grid. However, there are some control difficulties in the PFM control of gas turbines, such as the coupling effect of fuel control loop and speed control loop, slow tracking speed and large variation of operating conditions. To relieve the above difficulties, a control strategy based on the fuzzy-modified active disturbance rejection control (F-MADRC) proposed in this paper. Based on the analyses of the parameter stability region for active disturbance rejection control (ADRC), fuzzy tuning rules of parameters for F-MADRC are designed. Finally, the proposed F-MADRC is applied to the PFM system of MS6001B heavy-duty gas turbine. The simulation results show that the gas turbine unit with the proposed method can obtain the best control performance of the PFM with strong ability to deal with system uncertainties. The proposed method shows good engineering application potential.

Dual-mode luminescence light intensity modulation characteristics and optical radiation dependence of stannate photochromic ceramics

Alkaline earth stannate is characterized by good physicochemical stability. It has been applied in the field of optical information storage by coupling photoluminescence intensity modulation and photochromic performance, which has attracted the attention of researchers. The development of alkaline earth stannate ceramics with high light intensity modulation properties and non-destructive reading of optical information is of great research value. In this study, Er3+-doped Ca2SnO4 photochromic ceramics were prepared by high-temperature solid-phase reaction method. Alternating UV light irradiation and thermal stimulation, the ceramics achieve a reversible transition between light and dark gray. Er3+ doping gives the ceramics dual-mode luminescence light intensity modulation performance. When the doping amount of Er3+ is 0.01 mol, there is a maximum down-conversion luminous intensity modulation ratio of 93%, which is higher than most of the same type of photochromic materials. The photochromic behavior is explained using the capture-release model of traps for carriers, and the dual-mode luminescence light-intensity modulation behavior is analyzed through the energy transfer mechanism. The optical radiation response properties were investigated and the optimum light response wavelength is found to be 290 nm, which is related to the optical band gap Eg. And the selection of the optimal light response wavelength can effectively improve the performance of photochromic and light intensity modulation. This study provides a promising strategy for performance enhancement of photochromic materials.

Modified DDFTN Algorithm for Band-Limited Short-Reach Optical Interconnects

Inter symbol interference (ISI) degrades the performance of intensity modulation and direct detection (IM/DD) transmission systems due to various transceiver and channel impairments. To overcome the ISI of IM/DD transmission systems, the direct detection faster than Nyquist (DDFTN) algorithm has been widely used. However, when a system is subjected to severe ISI, the performance of the conventional DDFTN algorithm is suboptimal. To further improve the performance of IM/DD transmission systems, a modified DDFTN algorithm is proposed. We add least squares (LS) channel estimation after the postfilter. The coefficients of maximum likelihood sequence estimation (MLSE) are close to the initial channel response with LS channel estimation. The performance of the conventional and modified DDFTN algorithms is compared for 112, 140, and 160 Gbit/s PAM4 signals over 2 km, 1 km, and 500 m standard single-mode fibers (SSMFs) in a 3 dB bandwidth, 19 GHz IM/DD system in the C band. For 140 Gbit/s signal transmission over 1 km, the modified DDFTN algorithm achieves the optimal receiver sensitivity of -1.5 dBm at a 7% forward error correction (FEC) threshold of 3.8E-3, which is better than the receiver sensitivity of -0.5 dBm achieved with the conventional DDFTN algorithm. Furthermore, for 160 Gbit/s signal transmission over 500 m, the modified DDFTN algorithm achieves the optimal receiver sensitivity of 1 dBm at 3.8E-3, which is also a superior result compared to the conventional DDFTN algorithm.

Enhancing the power amplifier performance of an optical-OTFS modulation for optical communication system

Abstract Future wireless networks extensively employ the two-dimensional Optical-Orthogonal Time Frequency Space (O-OTFS) modulation system due to its increased dependability, flexibility, and data throughput. When there is a lot of movement, OTFS offers improved connectivity performance. While OFDM functions in the time-frequency domain, O-OTFS modulation acts in the delay-Doppler domain. This study provides an overview of how OTFS functions in the delay-Doppler domain, as well as its benefits and drawbacks. Next-generation networks utilize this modulation method in various applications, such as vehicle-to-vehicle communication, communication in mountainous areas, high-speed mobility, and train communication. This paper provides an easy-to-understand overview of the PAPR algorithms and its reduction in O-OTFS modulation.

Enhanced Performance of Intensity Modulation with Direct Detection Using Golay Encoded Nyquist Pulses and Electronic Dispersion Compensation

Enhanced Performance of Intensity Modulation with Direct Detection Using Golay Encoded Nyquist Pulses and Electronic Dispersion Compensation

Long-range underwater wireless optical communication system based on 490 nm vertical-external-cavity surface-emitting laser

The exploration and utilization of marine resources has promoted the rapid development of marine science and technology, and has put forward higher requirements for underwater communication technology. Long distance underwater wireless optical communication (UWOC) requires the selection of light source on the transmitter side. Laser diodes (LDs) have excellent portability and maneuverability, and have been widely used in the UWOC systems. However, their beam quality is not so good and it is difficult to modulate under high power. In recent years, vertical-external-cavity surface-emitting laser (VECSEL) has received much attention due to its high output power and good beam quality. This work is to explore the advantages of using a 490-nm blue VECSEL as a light source in UWOC, and to improve the performance of the UWOC system by the soft-decision pulse-position modulation (PPM). First, the optical power attenuation coefficient of the channel is obtained, and the measured <i>c</i> is about 0.0591 m<sup>–1</sup> in a 96-m-long tap channel. Subsequently, soft-decision and hard-decision are simulated and experimentally verified. Both simulations and measurements show that the bit error rate (BER) can be significantly reduced with soft-decision. Afterwards, we improve the system by using the soft-decision algorithm and investigate the communication performance of 64 PPMs at different bandwidths by adjusting the PPM signal rate. Finally, 50 MHz is chosen as a signal rate in the experiment. Then a UWOC system is demonstrated in this work. The transmitter side consists of a 490-nm VECSEL light source with an acousto-optic modulator (AOM). The pseudo-random binary sequence (PRBS) is loaded into the arbitrary waveform generator (AWG) for digital-to-analog conversion after PPM modulation, and the analog signal is sent to the driver of the AOM for acousto-optic modulation of the incident beam. The laser is focused before entering the AOM and then collimated after having exited to reduce its divergence. The modulated laser beam passes through a distance of 96 m in the tank by using multiple mirrors on both sides of the tank. Then, the beam is focused by a lens to the avalanche photodiode (APD) for photoelectric conversion in the end, and the signal is processed by a mixed signal oscilloscope (MSO) after data acquisition. A soft-decision algorithm is introduced to further optimize the performance of the PPM modulation. When the optical signal passes through a relatively long distance of 96 m, the measured BER is as low as 1.9 × 10<sup>–5</sup>. This indicates that the soft-decision PPM-based 490 nm blue VECSEL UWOC system performs very well.

On the Performance of RIS-Aided Spatial Modulation for Downlink Transmission

On the Performance of RIS-Aided Spatial Modulation for Downlink Transmission

Ratio Shift Keying Modulation for Time-Varying Molecular Communication Channels.

Molecular Communications (MC) is a bio-inspired communication technique that uses molecules to encode and transfer information. Many efforts have been devoted to developing novel modulation techniques for MC based on various distinguishable characteristics of molecules, such as their concentrations or types. In this paper, we investigate a particular modulation scheme called Ratio Shift Keying (RSK), where the information is encoded in the concentration ratio of two different types of molecules. RSK modulation is hypothesized to enable accurate information transfer in dynamic MC scenarios where the time-varying channel characteristics affect both types of molecules equally. To validate this hypothesis, we first conduct an information-theoretical analysis of RSK modulation and derive the capacity of the end-to-end MC channel where the receiver estimates concentration ratio based on ligand-receptor binding statistics in an optimal or suboptimal manner. We then analyze the error performance of RSK modulation in a practical time-varying MC scenario, that is mobile MC, in which both the transmitter and the receiver undergo diffusion-based propagation. Our numerical and analytical results, obtained for varying levels of similarity between the ligand types used for ratio-encoding, and varying number of receptors, show that RSK can significantly outperform the most commonly considered MC modulation technique, concentration shift keying (CSK), in dynamic MC scenarios.

A Survey on Spatial Modulation OFDM: Optimal Detection and Performance Analysis

Spatial modulation is a novel modulation scheme that aims to acquire a trade-off between the two adverse purposes in wireless communications, namely the improvements of data rate and data reliability, by adjusting the operational transmit antenna index in the emitted bits. To fight against inter-symbol interference (ISI) present in frequency selective channels, orthogonal frequency division multiplexing (OFDM) as become a extensively accepted and used mechanism. We investigate in this work the performance of SM-OFDM modulation over frequency selective MIMO channel using quadrature amplitude modulation (QAM) scheme. At the receiver side, a group of detectors is proposed to recover the active transmit antenna index (Tx-antenna) and the emitted data sequence. In this paper, a new SM-OFDM-based scheme is proposed, which adds another element of information in the transmitted SM-data block consisting of a chosen constellation among the available rotated set. To attain this, an additional index is used to select the specific constellation. At the receiver, a set of detectors is proposed to jointly estimate the transmitted symbol, as well as the used constellation and the active transmit antenna indices. The comparison of the performance of this new scheme against the conventional SM-OFDM shows an increased spectral efficiency at the price of a slight degradation in bit error rate. The proposed scheme permits a trade-off between the quality of the communication and the achieved spectral efficiency. Some concluding remarks are drawn over simulation results.

Performance of Adaptive Bit-Interleaved Polar Coded Modulation in FSOC System

This paper proposes an adaptive bit-interleaved polar coded modulation (A-BIPCM) method based on minimum logarithmic upper bound weight (MLUW). It is designed to reduce the fading effects and long string of bit error interference caused by atmospheric turbulence in free-space optical communications (FSOC). To assess the effectiveness of this method across turbulent channels of varying intensities, we conducted an evaluation of the bit error rate (BER) performance of polar codes in turbulent channels. The results demonstrate significant performance improvements provided by the A-BIPCM method compared to conventional polar code encoding and decoding. Specifically, under weak, moderate, and strong turbulence conditions, the A-BIPCM method achieves performance gains of 0.96 dB, 1.66 dB, and 1.35 dB, respectively. Additionally, an experimental verification platform for FSOC employing intensity modulation direct detection (IM/DD) with an atmospheric turbulence simulation channel, is established in this work. When the optical power of the detector is −16 dBm, the traditional polar code encoding and decoding performance at BER = 2.36 × 10−5, whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 2.11 × 10−6. The BER has been improved by representing an order of magnitude.

BEP evaluation of 5G LDPC codes in a pre-amplified optical PPM receiver

We present results for the performance of a pre-amplified optical pulse-position modulation (PPM) receiver that utilizes the low-density parity-check (LDPC) correction codes of the 5G standard. The code construction is suitable for correcting burst errors that are introduced by PPM. Simulation results show that the LDPC codes can provide a very significant real gain, provided that the code rate is chosen appropriately. We find that the code rates that minimize the bit-error-probabilities (BEPs) of the system range between 2/3 and 22/26, with higher code rates being required in receivers that operate under increased optical noise. It is also shown that a comparable real gain is obtained for both the sum–product and min-sum decoders, while the power penalty of the latter one is only limited to 0.2 dB, when the aforementioned code rates are utilized.

Combined intra symbol frequency domain averaging channel estimation for polarization division multiplexed coherent optical OFDM/OQAM systems

Intrinsic imaginary interference (IMI) induced by chromatic dispersion (CD) and polarization mode dispersion (PMD) seriously degrades the performance of optical orthogonal frequency division multiplexing offset-quadrature amplitude modulation (O-OFDM/OQAM) systems. Therefore, effective channel estimations are required for such systems to maintain good transmission performance. In the previous publications, both the full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods for polarization-division-multiplexed (PDM) coherent optical OFDM/OQAM (CO-OFDM/OQAM) systems have been proposed. However, for these frequency-domain methods, the channel frequency-domain responses caused by the correlation of the amplified spontaneous emission (ASE) noise are not considered. In this paper, we systematically discuss the frequency-domain channel transmission model for PDM CO-OFDM/OQAM systems. With the analysis of the correlation of the ASE noise, we propose a combined intra symbol frequency-domain averaging (CISFDA) channel estimation method for PDM OFDM/OQAM systems. Compared with the full-loaded frequency-domain channel estimation (FL-FD) method, the CISFDA method promotes the system robustness against the ASE noise and fiber nonlinear effect significantly. The proposed method is validated by numerical Monte Carlo simulations of the PDM CO-OFDM/OQAM system. Our new algorithm outperforms the FL-FD method in the 36 Gb/s PDM OFDM CO-OFDM/OQAM system, and the transmission distance is improved by 500 km with the bit-error-rate (BER) target at 3.8×10-3.

Branch-cut phase unwrapping method based on deep learning

ObjectiveAs a typical representative of the phase unwrapping algorithm, the branch-cut method has good anti-noise performance in the phase unwrapping process. However, the branch-cut generated by the traditional branch-cut method cannot accurately block error propagation. MethodThis study proposes a branch-cut phase unwrapping method based on deep learning, which transforms the traditional problem of connecting residual points into a semantic segmentation learning problem, to improve the blocking effect of the branch-cut to the error. The article analyzes the performance of modulation and residue maps in representing phase errors and finds that residue maps have a poor perception of error information in shadow areas in the wrapped phase map. Therefore, a new branch-cut connection criterion is proposed that combines modulation maps and sets the bound of shadow and non-shadow areas as part of branch-cut. Positive and negative residual points are connected by curves along the path of poor modulation, and their polarities are accumulated to maintain branch-cut balance. By using the new branch-cut connection criterion to provide learning samples and using the U-Net++ network structure as the deployment network of branch-cut, the network generates a branch-cut for phase unwrapping, which phase unwrapping path bypasses the branch-cut. ResultsThe experimental results show that the deployment of branch-cut using the U-Net++ network structure can achieve the expected training effect, and the branch-cut generated based on the new connection principle can more effectively block the propagation of errors during phase unwrapping.

Dirac semimetal-assisted near-field radiative thermal rectifier and thermostat based on phase transition of vanadium dioxide.

The near-field thermal radiation has broad application prospects in micro-nano-scale thermal management technology. In this paper, we report the Dirac semimetal-assisted (AlCuFe quasicrystal) near-field radiative thermal rectifier (DSTR) and thermostat (DST), respectively. The DSTR is made of a Dirac semimetal-covered vanadium dioxide (VO2) plate and silicon dioxide (SiO2) plate separated by a vacuum gap. The left and right sides of DST are consisted of the SiO2 covered with Dirac semimetal, and the intermediate plate is the VO2. The strong coupling of the surface electromagnetic modes between the Dirac semimetal, SiO2, and insulating VO2 leads to enhance near-field radiative transfer. In the DSTR, the net radiative heat flux of VO2 in the insulating state is much larger than that in metallic state. When the vacuum gap distance d=100 nm, Fermi level EF=0.20 eV, and film thickness t=12 nm, the global rectification factor of DSTR is 3.5, which is 50% higher than that of structure without Dirac semimetal. In the DST, the equilibrium temperature of the VO2 can be controlled accurately to achieve the switching between the metallic and insulating state of VO2. When the vacuum gap distance d=60 nm, intermediate plate thickness δ=30 nm, and film thickness t=2 nm, with the modulation of Fermi level between 0.05-0.15 eV, the equilibrium temperature of VO2 can be controlled between 325-371 K. In brief, when the crystalline state of VO2 changes between the insulating and metallic state with temperature, the active regulation of near-field thermal radiation can be realized in both two-body and three-body parallel plate structure. This work will pave a way to further improve performance of near-field radiative thermal management and modulation.

Two Low-Complexity Efficient Beamformers for an IRS- and UAV-Aided Directional Modulation Network

As excellent tools for aiding communication, an intelligent reflecting surface (IRS) and an unmanned aerial vehicle (UAV) can extend the coverage area, remove the blind area, and achieve a dramatic rate improvement. In this paper, we improve the secrecy rate (SR) performance of directional modulation (DM) networks using an IRS and UAV in combination. To fully explore the benefits of the IRS and UAV, two efficient methods are proposed to enhance the SR performance. The first approach computes the confidential message (CM) beamforming vector by maximizing the SR, and the signal-to-leakage-noise ratio (SLNR) method is used to optimize the IRS phase shift matrix (PSM), which is called Max-SR-SLNR. To reduce the computational complexity, the CM, artificial noise (AN) beamforming, and IRS phase shift design are independently designed in the following method. The CM beamforming vector is constructed based on the maximum ratio transmission (MRT) criteria along the channel from Alice-to-IRS, the AN beamforming vector is designed by null-space projection (NSP) on the remaining two channels, and the PSM of the IRS is directly given by the phase alignment (PA) method. This method is called the MRT-NSP-PA. The simulation results show that the SR performance of the Max-SR-SLNR method outperforms the MRT-NSP-PA method in the cases of small-scale and medium-scale IRSs, and the latter approaches the former in performance as the IRS tends to a larger scale.