Phase Shift Problem Research Articles

Calibration Method of a Wideband AC Resistance Voltage Divider Based on an Equivalent Model.

Aiming at the problem of large measurement error and phase shift in resistance voltage dividers under high-frequency conditions in the field of power measurement, such as power harmonics, an error correction method is proposed for an alternating current (AC) resistance voltage divider based on the equivalence principle. Firstly, the frequency error model of the AC resistance voltage divider precision is established, and the angle difference of the continuous spectrum ratio difference from 50 Hz to 100 kHz is corrected by determining the shielding structure and the resistance parameters and fine-tuning the shielding potential correction method to reduce the capacities error of the AC resistance voltage divider design precision. At the same time, the performance parameters such as the direction and magnitude of the shielding potential compensation capacitive error are investigated. Finally, the precision voltage divider (the maximum voltage applied is 480 V) calibration experiments verify that the important characteristic judgment factor of the voltage divider is independent of the frequency and the equivalent capacitance value, which effectively solves the phase correction problem of harmonic power measurement.

Joint Phase Shift and Beamforming Design in a Multi-User MISO STAR-RIS Assisted Downlink NOMA Network

Simultaneous transmitting and reflecting reconfigurable intelligent surfaces (STAR-RIS) has gradually been considered as a promising technology in the wireless communication networks. Besides, non-orthogonal multiple access (NOMA) is also the key technology in the sixth-generation (6 G) wireless communication system. In this work, we study a multiple input single output (MISO) STAR-RIS assisted NOMA downlink network and investigate the energy efficiency (EE) maximization to achieve the tradeoff between the sum rate and the power consumption. The original formulated problem is non-convex due to the coupled beamforming vectors of the users and phase shifts of the STAR-RIS. To efficiently solve the problem, we split the original non-convex problem into the phase shift and beamforming optimization problems and then solve them alternatively. In the phase shift optimization, fractional programming (FP) is applied to transform the sum rate maximum problem to convex semidefinite relaxation (SDR) one with the rank-one constraint. After this, a novel sequential rank-one constraint relaxation (SROCR) is proposed to convert the rank-one constraint into a convex one, which can effectively overcome the inadequacy of Gaussian randomization, i.e., quality of the solutions and computational complexity. Similarly, FP is applied to solve the beamforming problem by transforming it to SDR problem. It turns out that the optimal solution of the SDR beamforming optimization problem can be guaranteed to be rank-one by the mathematical proof and experiments. The simulation results demonstrate the STAR-RIS NOMA system can achieve the superior performance in EE.

Capacitive Feedbacked Cold-Phase Compensator Analog Pre-Distorter and PAE Enhancer for K-Band CMOS PAs

A K-band two-stage power amplifier (PA) with capacitive-feedbacked cold-phase compensator (cold-PC) linearizer and power-added-efficiency (PAE) enhancer is introduced in 180-nm CMOS technology. This cold-PC consists of two parts. First, a cold-FET analog pre-distorter (APD) with a new capacitive-feedbacked technique is proposed to improve the linear behavior of the PA by enhancing the corresponding APD’s compensation slope. The proposed implementation has a reduced insertion loss and a minimal chip area overhead. Second, a low-pass two-tunable inductive and capacitive PC is proposed to solve the phase shift problem at intermediate nodes that would enhance the PAE of the stacked-transistors configuration. The implemented PA achieves, at 23.5-GHz, a maximum measured PAE of 21.2%, output power at the 1-dB compression point (OP1dB) of 13.4-dBm, and saturated output power of 15-dBm using a total chip area of 0.58 mm2. Employing the proposed cold-PC results in a decrease of the measured error vector magnitude (EVM) of the 400-MHz 5G-NR of 64-QAM modulated signal and an increase of the OP1dB and its PAE by 2.5-dB and 7%, respectively (enhancement by 78% and 72% from the original case, respectively), which, to the best of authors’ knowledge, is the highest reported enhancement of the linearizers of k-band PAs.

Trajectory Optimization and Phase-Shift Design in IRS-Assisted UAV Network for Smart Railway

The recent trend towards the smart transportation system has spurred the development of the smart railway. However, enabling trains with seamless wireless connectivity using the roadside units (RSUs) is extremely challenging, mostly due to the lack of line of sight link. To address this issue, we propose a novel framework that uses intelligent reflecting surfaces (IRS)-enabled unmanned aerial vehicle (UAV) to provide line of sight communication to the smart railway system. First, we formulate the optimization problem where the objective is to maximize the minimum achievable rate of trains by jointly optimizing the trajectory of UAV and the phase-shift of IRS. Due to the non-convex nature of the formulated problem, it is decomposed into two subproblems: IRS phase-shift problem and UAV trajectory optimization problem. Next, a Binary Integer Linear Programming (BILP) and a Soft Actor-Critic (SAC) are constructed in order to solve our decomposed problems. Finally, comprehensive numerical results are provided in order to show the effectiveness of our proposed framework.

The fundamental phase shift compensation scheme in a digital-controlled VIENNA rectifier with variable carrier-fundamental frequency ratio under unbalanced grid conditions

In the DC power distribution systems, One-cycle control (OCC) based three-phase VIENNA rectifiers achieves high power factor (PF) easily. However, under unbalanced grid conditions, the fundamental phase shift between the input current and corresponding phase voltage obviously deteriorates PF, especially when carrier-fundamental frequency ratio varies. In this paper, based on the mathematical model of the rectifier with OCC control under unbalanced grid conditions, the fundamental phase shift problem is analyzed in detail, including variable carrier-fundamental frequency ratio. Moreover, aiming at solving this problem, a fundamental phase shift compensation scheme is proposed. By introducing a second order generalized integrator (SOGI) to generate the complex vector grid currents feedback, which combines with unbalanced grid voltages, three-phase modulation signals are dynamically modified to eliminate the fundamental phase shift. To facilitate the digital control for the rectifier, the digital implementation of the proposed compensation scheme is described in this paper. At last, a digital-controlled VIENNA rectifier experimental test bench is built, and the effectiveness of the proposed scheme is verified by experimental results.

Celestial Spectrum Velocimetry With Non-Linear Fourier Phase Shift and Its CRLB

To solve the problem of the non-linear Fourier phase shift caused by the wavelength shift in the celestial spectrum velocimetry, a celestial spectrum velocimetry method based on non-uniform discrete Fourier transform and compressed sensing is proposed. First, according to the properties of the non-uniform discrete Fourier transform with non-periodic celestial spectra, the non-linear relationship between the spectral wavelength shift and the Fourier phase shift is deduced theoretically. And then, the discrete cosine transform is used to decompose and reconstruct the spectrum to construct the phase dictionary of the non-periodic spectrum. In this dictionary, the spectral wavelength shift has a non-linear relationship with the Fourier phase shift. Finally, the non-uniform Fourier transform matrix is used as the measurement matrix. And the Doppler wavelength shift is estimated by using a non-linear and super-resolution matching algorithm to estimate the velocimetry. Experimental results show that when the spacecraft’s velocity is high, the celestial spectrum velocimetry method with non-linear Fourier phase shift (CSV-NFPS) can effectively measure the velocity from the spectrum, and its accuracy approaches the theoretical Cramer-Rao lower bounds (CRLB). Compared with the traditional Taylor method, the CSV-NFPS has an average accuracy improvement of 16.18% and a computational complexity reduction of 25.07%. In short, our method eliminate the non-linear bias in the celestial spectrum velocimetry and reduce a certain computational complexity.

Real-Time Simulation of Power System Electromagnetic Transients on FPGA Using Adaptive Mixed-Precision Calculations

The massive integration of renewable energy sources and power electronics into the power grid leads to the strong need of real-time Electromagnetic Transients (EMT) simulation of power system using field-programmable gate array (FPGA) platform due to its high efficiency and superior performance. FPGA based EMT simulations – A key for Digital Twin were mainly based on Single-Precision calculations, but ignored potential accumulation displacement. To address this problem, this paper proposes full Double-Precision and Mixed-Precision Floating-Point schemes to achieve optimal balance between numerical accuracy and computational resource cost in FPGA-based EMT simulation even for long duration simulations. Furthermore, adjustable pipeline, address dynamic access and sequence controller techniques for solving high fanout and long datapath hardware implementation are developed to optimize resource usage and timing constraints for all schemes. For non-rotating components, full Double-Precision and full Single-Precision both shows excellent convergence. For rotating components, extra Single-Precision iteration method and Mixed-Precision calculations are compared for Synchronous Machines (SG) with strong nonlinearity, and it is found that only full Double-Precision could avoid phase shift problem. Based on component-level sensitivity analysis, proposed system-level Mixed-Precision scheme is able to achieve close accuracy to that of full Double-Precision scheme and additional average 20% resource reduction for Kundur's system.

A phase‐shift‐free synchronous reference frame filter‐based position sensorless control method for open‐winding permanent magnet generator system

An open-winding permanent magnet generator (OWPMG) system that offers features like fewer switching devices and high integration can be used in multi-input generator systems. To achieve high-accuracy position sensorless operation for the OWPMG system, this study investigates a phase-shift-free synchronous reference frame filter (SRFF-PSF) for use in the sliding mode observer (SMO) position sensorless algorithm. The proposed SRFF-PSF can completely restore the fundamental component of back-electromotive force (EMF) without phase shift and filter out the high-order harmonics owing to the following two improvements. First, the fundamental phase lag is eliminated by removing the low-pass filter between the back-EMF and the SRFF. Second, the error iteration of the output position angle is avoided by using the synchronous angle information from an additional phase locked loop module for the coordinate transformation of the SRFF. Based on the aforementioned improvements, the proposed method can effectively solve the phase shift problem in position estimation. The correctness and effectiveness of the method are verified by the experimental results.

Power Minimization for Two-Cell IRS-Aided NOMA Systems With Joint Detection

Intelligent reflecting surface (IRS) is a revolutionizing technology to boost the energy and spectrum efficiency by reconfiguring wireless propagation environment. In this letter, IRS is leveraged to improve the performance of the cell-edge user as well as the coordinated multi-point transmission (CoMP). Particularly, an uplink power minimization problem is formulated to jointly optimize the power allocation and the phase shifts in a two-cell IRS-aided non-orthogonal multiple access (NOMA) system with joint detection. To render the original problem tractable, the joint optimization problem of power allocation and phase shift is converted into a pure phase shift determination problem. Furthermore, a low-complexity method with closed-form solution is developed to address the transformed problem. It is shown by simulation that the power consumption of the proposed scheme is quite close to the lower bound and is less than those of various benchmarking schemes.

Bidirectional coherent optical communication system combining unidirectional optical signal amplification

A new type of bidirectional coherent optical communication system is proposed combining unidirectional optical signal amplification. We analyze the application of discrete Raman amplifier (DRA) on the basis of dispersion compensating fiber in this system, and optimize the amplifier configuration considering the influence factors such as Rayleigh backscattering noise and amplified spontaneous emission noise. In addition, the gain and pump efficiency improvement in a novel design of double-pass DRA. The feasibility of the single-fiber bidirectional coherent optical communication system is ensured by the theoretical analyses and MATLAB coding. The system greatly decreases the phase shift problem caused by the frequency offset between the transmitter and local oscillator as well as the laser linewidth. It has practical value for secure communication systems.

A Very Low Complexity Successive Symbol-by-Symbol Sequence Estimator for Faster-Than-Nyquist Signaling

In this paper, we investigate the sequence estimation problem of binary and quadrature phase shift keying faster-than-Nyquist (FTN) signaling and propose two novel low-complexity sequence estimation techniques based on concepts of successive interference cancellation. To the best of our knowledge, this is the first approach in the literature to detect FTN signaling on a symbol-by-symbol basis. In particular, based on the structure of the self-interference inherited in FTN signaling, we first find the operating region boundary defined by the root-raised cosine pulse shape, its roll-off factor, and the time acceleration parameter of the FTN signaling where perfect estimation of the transmit data symbols on a symbol-by-symbol basis is guaranteed, assuming noise-free transmission. For noisy transmission, we then propose a novel low-complexity technique that works within the operating region and is capable of estimating the transmit data symbols on a symbol-by-symbol basis. To reduce the error propagation of the proposed successive symbol-by-symbol sequence estimator (SSSSE), we propose a successive symbol-by-symbol with go-back- $K$ sequence estimator (SSSgb $K$ SE) that goes back to re-estimate up to $K$ symbols, and subsequently improves the estimation accuracy of the current data symbol. Simulation results show that the proposed sequence estimation techniques perform well for low intersymbol interference scenarios and can significantly increase the data rate and spectral efficiency. Additionally, results reveal that choosing the value of $K$ as low as 2 or 3 data symbols is sufficient to significantly improve the bit-error-rate performance. Results also show that the performance of the proposed SSSgb $K$ SE, with $K = 1$ or 2, surpasses the performance of the lowest complexity equalizers reported in the literature, with reduced computational complexity.

A new embedded 5(3) pair of modified Runge–Kutta–Nyström methods for the numerical solution of the Schrödinger equation

A new embedded 5(3) pair of modified Runge–Kutta–Nystrom methods for the numerical solution of the Schrodinger equation is developed in this paper. The asymptotic expressions of the principal local truncation errors for large energies are obtained. We apply the new fifth-order method to the resonance problem, and apply the new embedded 5(3) pair to elastic scattering phase-shift problem. The numerical results show good numerical performance of the new embedded pair and the fifth-order method.

Study on discrete acceleration feedback control with time delay

This paper addresses the design problem of a discrete controller with time delay and acceleration feedback. The delta operator is firstly used to describe the discrete acceleration signal and convert the delayed continuous-time state equation into the delayed discrete-time system. Then the delayed discrete-time system is transformed into the delay-free one by applying a discrete reduction method. Based on the delay-free discrete-time system, the optimal output delta state feedback controller is designed by minimizing a discrete non-standard quadratic performance index and the feedback gain of the controller is obtained by a convergent algorithm. On the basis of the optimal output delta state feedback controller, the discrete time-delayed acceleration feedback controller is achieved by using the inverse reduction method, and the corresponding recursive control algorithm is developed. The controller saves the process of performing numerical integration and eliminating direct current and trend term in designing the displacement or velocity feedback control, so as to make the closed-loop system become simpler. Moreover, it can solve the problem of phase shift of the measured signal caused by time delay. The proposed controller with a low order model-based control algorithm is implemented on a smart cantilever beam with an accelerometer and piezoelectric actuator for different controller gain-delay combinations, and the control performance is evaluated. Simulation and experimental results demonstrate that the controller can effectively reduce the free vibration response of the smart cantilever beam.

A new modified embedded 5(4) pair of explicit Runge–Kutta methods for the numerical solution of the Schrödinger equation

In this work a new modified embedded 5(4) pair of explicit Runge–Kutta methods is developed for the numerical solution of the Schrodinger equation. We investigate the error of the new pair, based on the error analysis we apply the higher order method to the resonance problem, also we apply the new embedded pair to elastic scattering phase-shift problem. The applications show the efficiency of our new developed embedded pair and the higher order method.

Design and Realization of the Dynamic Magnetic Measurement System for Soft Magnetic Material

A dynamic magnetic measurement system for soft magnetic material based on virtual instrument technology is presented. High frequency AC excitation power supply is adopted to drive soft magnetic material. High speed data transport system composed by FPGA chip ALTERA EP1C12Q240C8N and USB microcontroller Cypress CY7C68013A. The problem of phase-shift of hardware integrator which is difficult to control is solved by digital integration. LabVIEW with powerful data processing capabilities is used to simplifies the hardware structure and improve the testing accuracy and automation level of measurement. The paper also points out problems of digital integration and gives a solution.

Validation of comprehensive dynamics analysis predictions for a rotor in descending flight

PurposeThe purpose of this paper is to evaluate the prediction capability of comprehensive structural dynamics (CSD) analysis codes for the higher harmonic control aeroacoustic rotor test (HART) II data.Design/methodology/approachA nonlinear flexible multibody dynamics analysis code DYMORE, as well as the comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD) II, are used to perform the task. The predicted results on rotating free vibration analysis, airloads, blade elastic motions, and structural moments are correlated with the measured data for the baseline, minimum noise, and minimum vibration cases.FindingsThe DYMORE analysis results with a free wake model show a good performance in capturing blade vortex interaction peaks in the prediction of section normal forces but apparently with a phase shift problem. The high‐frequency behavior in the airloads signal does not affect much on the aeroelastic response and structural moments of the rotor.Originality/valueThe present approach uses two separate CSD codes to systematically validate the HART II data. The accuracy of each code on structural dynamic aspects of HART II rotor is assessed using a consistent set of inputs. The effects of blade tip deflections on the interaction of blades and their trailed vortices leading to a reduced noise emission are also investigated.

Algebraic dynamics algorithm: Numerical comparison with Runge-Kutta algorithm and symplectic geometric algorithm

Based on the exact analytical solution of ordinary differential equations, a truncation of the Taylor series of the exact solution to the Nth order leads to the Nth order algebraic dynamics algorithm. A detailed numerical comparison is presented with Runge-Kutta algorithm and symplectic geometric algorithm for 12 test models. The results show that the algebraic dynamics algorithm can better preserve both geometrical and dynamical fidelity of a dynamical system at a controllable precision, and it can solve the problem of algorithm-induced dissipation for the Runge-Kutta algorithm and the problem of algorithm-induced phase shift for the symplectic geometric algorithm.

Robust Delay Control for Audio Streaming over Wireless Link

The audio delay is becoming an important factor in audio streaming over short-range wireless network. In this study, we propose an efficient two-level delay control method, called frame sequence adaptation and audio sampling frequency compensation, for achieving stable audio delay with a small variation. To prove the effectiveness of our scheme, we implemented and evaluated the scheme on a Bluetooth network. Experimental results show that our scheme can control audio delay robustly and remove phase shift problem in multi-channel stereophonic audio broadcasting as well.

Modified back-propagation algorithm applied to decision-feedback equalisation

This study presents a modified back-propagation (BP) algorithm for a multilayer perceptron (MLP) to perfect its ability to cope with the problem of binary phase shift keying channel equalisation. For a typical BP algorithm, the error signal is obtained from the comparison between the target and estimated signal. The error signal is propagated layer by layer from the output layer to the input layer to adaptively adjust all weights in the MLP. Therefore all parameters of the MLP are obtained by a single BP algorithm. However, the structure of the MLP with a hidden layer provides the feasibility to modify the BP algorithm to improve its performance. The MLP can be divided from the hidden layer into two sub-MLPs, and each sub-MLP is optimised by its own BP algorithm. Accordingly, the whole MLP is adjusted by two BP algorithms independently. In this study, the modified BP algorithm is utilised to cope with the problem of channel equalisation. The simulation results show that the modified BP algorithm indeed improves the typical BP algorithm especially for an environment with nonlinear distortion, frequency offset, and phase and timing errors. Moreover, the computation complexity of the proposed algorithm almost equals that of the conventional BP algorithm.

AN EMBEDDED 5(4) PAIR OF MODIFIED EXPLICIT RUNGE–KUTTA METHODS FOR THE NUMERICAL SOLUTION OF THE SCHRÖDINGER EQUATION

A new way for constructing efficient embedded modified Runge–Kutta methods for the numerical solution of the Schrödinger equation is presented in this paper. The methods of the embedded scheme have algebraic orders five and four. Applications of the new pair to the elastic scattering phase-shift problem and coupled differential equations of Schrödinger type indicate that the new pair is much more efficient than other well known comparable embedded Runge–Kutta pairs.