Conventional Modulation Schemes Research Articles

A Multichannel Phase Tunable Microwave Photonic Mixer With High Conversion Gain and Elimination of Dispersion-Induced Power Fading

A microwave photonic system that can realize frequency up- and down-conversion, multichannel phase shift, high conversion gain, and elimination of dispersion-induced power fading is proposed and experimentally demonstrated. The scheme is based on an integrated dual-polarization quadrature phase shift keying modulator that contains two dual parallel Mach–Zehnder modulators (X-DPMZM and Y-DPMZM). The X-DPMZM implements dual side band carrier suppression (DSB-CS) modulation of radio frequency signal, and the Y-DPMZM implements frequency shift of an optical carrier. They are combined in orthogonal polarizations to implement frequency up- and down-conversion. The polarization multiplexed signal will go through polarization controllers and polarizers to implement multichannel phase shift. In the experiment, the phase shift can be tuned independently over 360° in each channel. By suppressing the optical carrier, the conversion gain and LO isolation are improved by 20.5 dB and 51.26 dB, respectively, compared with conventional dual side band modulation scheme. In addition, the proposed scheme can achieve a spurious-free dynamic range (SFDR) of 103.6 dB·Hz2/3.

An Overview of OFDM-Based Visible Light Communication Systems From the Perspective of Energy Efficiency Versus Spectral Efficiency

In this paper, the energy efficiency and the spectral efficiency for orthogonal frequency division multiplexing (OFDM)-based visible light communication schemes are studied, which is crucial for practical application with limited energy resources. The conventional schemes, including asymmetrically clipped optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multitone, and direct current biased optical OFDM, are compared in terms of energy efficiency and spectral efficiency relationship. The influence of power allocation for asymmetrically clipped dc biased optical OFDM and hybrid ACO-OFDM is also investigated. The energy efficiency and spectral efficiency of layered ACO-OFDM with a variable layer number are calculated and their relationship is also formulated. These conventional and hybrid modulation schemes are analyzed and compared through computer simulations, which should be considered in practice according to the requirements of illumination and transmission.

A Noise-Shaped Randomized Modulation for Switched-Mode DC-DC Converters

We propose a novel low-harmonics low-noise modulation scheme for switched-mode dc–dc converters. The proposed scheme is a hybrid of a randomized modulation scheme, namely, the randomized wrapped-around pulse position modulation scheme (RWAPPM), and a noise-shaper. The RWAPPM mitigates the switching-frequency harmonics in the input current, whereas the noise-shaper mitigates the low-frequency noise therein. We derive an analytical expression for the input current spectrum of the hybrid scheme. We benchmark the hybrid scheme against the conventional pulse width modulation scheme (PWM) and the RWAPPM without the noise-shaper. At 0.5 duty cycle, 3.3-V input voltage, 100-kHz average switching frequency, and with the second-order noise-shaper, the peak spectral power in the input current spectrum of the hybrid scheme is 18.1 dB lower than the PWM. Other randomized and spread-spectrum modulation schemes, in general, have undesirably higher input noise current than that of the PWM. However, the input noise current of the proposed hybrid scheme, obtained at ~73-mA rms (integrated over a 200-kHz bandwidth without an input filter), is comparable with that of the PWM, and is lower by ~16-mA rms compared with that of the RWAPPM without the noise-shaper. We also benchmark the hybrid scheme against other well known randomized and spread-spectrum modulation schemes. We further propose a novel pulse generator structure that embodies the hybrid scheme. We realize a dc–dc converter employing the pulse generator, and measure the converter to verify the derived expression and the characteristics of the hybrid scheme. We also measure the output voltage spectrum, the transient-response, and the operating range of the converter.

Common-mode voltage reduction for space vector modulated three- to five-phase indirect matrix converter

All available Pulse Width Modulation (PWM) techniques employed to different Matrix Converter (MC) topologies generally generate switching Common-Mode Voltage (CMV), which introduces numerous operational concerns in electric drives. Although a body of research for the three-phase case has been undertaken to either reduce or eliminate CMV, corresponding discussions for multiphase MC remain scarce. Interestingly enough, the three- to five-phase (3×5) Indirect MC (IMC) is a potential converter topology for five-phase based high power motor drives. In this paper, the different available switching states of a 3×5 IMC are classified based on their corresponding CMV levels. Accordingly, two different Space Vector Modulation (SVM) techniques are proposed, which can successfully reduce the peak CMV by 28% and 48%, respectively, when compared with the conventional modulation strategy, while the same maximum Voltage Transfer Ratio (VTR) is preserved. Although the 28% reduction has been alternatively achieved in literature based on carrier-based PWM, the 48% reduction attained in this study represents the maximum achievable reduction for this MC topology. The main concept is firstly introduced; then, both simulations and experiments are used to validate the proposed schemes.

Time-frequency bandwidth product estimation of Sinusoidal Non-linear Chirp Keying scheme

Sine Non-linear Chirp Keying (SNCK) is a kind of high-efficient modulation scheme, which provides a potential new beamforming method in communication and radar systems. It has been proved to have advantages in some parameter estimation issues over conventional modulation schemes. In this paper, a novel transform termed as Discrete Sinusoidal Frequency Modulation transform (DSFMT) is proposed. Then, the DSFMT of SNCK signal is deduced and classified into three types, based on which, the time-bandwidth product is estimated by the proposed algorithm. Simulation results show that the noise has a significant impact on the localization of the peak value and the time-bandwidth product can be estimated by using local ratio values when 5 NR > 5dB.

Enhanced subcarrier-index modulation-based asymmetrically clipped optical OFDM using even subcarriers

In this paper, we propose a subcarrier-index modulation-based asymmetrically clipped optical orthogonal frequency division multiplexing (SACO-OFDM) scheme for optical wireless communication (OWC) systems, which benefits from the subcarrier-index modulation (SIM) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) techniques. SACO-OFDM conveys additional information via the subcarrier indexing, and the error rate of the bit transmitted by the subcarrier indexing is much lower than that of the conventional M-ary modulation scheme. On the other hand, as the signal constellation in M-ary modulation is relieved, SACO-OFDM has simple transceiver structure and low detection complexity. Moreover, considering the spectral, an enhanced SACO-OFDM (ESACO-OFDM) using even subcarriers is proposed. In this technique, the odd subcarriers are activated for SACO-OFDM, and the imaginary part of even subcarriers are activated for pulse-amplitude-modulated discrete multitone (PAM-DMT). Clearly, ESACO-OFDM achieves better spectral efficiency than the conventional optical OFDM, since all subcarriers are used for data transmission. Simulation results verify the significant bit error rate (BER) and peak-to-average power ratio (PAPR) improvement by the proposed ESACO-OFDM, especially for the medium-to-high signal-to-noise ratio (SNR) regime.

Space-Vector-Based Generalized Discontinuous Pulsewidth Modulation for Three-Level Inverters Operating at Lower Modulation Indices

Conventional three-level discontinuous pulsewidth modulation (DPWM) templates typically provide maximum switching loss reduction capability for load power factor angles in the range from 30° lagging to 30° leading. This paper proposes three space-vector-based DPWM templates for lower power factors and a generalized DPWM strategy for three-level inverters operating with modulation indices lower than 0.5. For different power factors, the proposed strategy adapts the inverter pulse sequence by combining different portions of the proposed and conventional DPWM templates within one operating fundamental cycle and ensures minimum switching instances when changing templates. Consequently, the strategy aligns the PWM clamping intervals with the respective load-current peaks, achieving around 50% switching loss reduction capability extended to all operating power factor angles (90° lagging to 90° leading). The simulation and experimental results demonstrate the effectiveness of the proposed three-level generalized DPWM strategy over the conventional three-level modulation strategies.

Zero reduction codes for efficient transmission and enhanced brightness in visible light communication

In this study, the authors propose novel zero reduction codes to simultaneously provide effective illumination and communication services in visible light communications (VLC). In general, the brightness of light-emitting diode illuminations can be enhanced by increasing the duty cycle ratio (DCR) but in such cases, the bit error rate (BER) performance is significantly degraded in the VLC systems. This is because the decision interference of received 0 and 1 bits is increased owing to the decision boundary overlapped. The proposed coding scheme can improve the brightness without increasing DCR and also achieve the enhanced BER performance compared to the conventional modulation schemes such as variable pulse-position modulation or variable on–off keying. The simulations results demonstrate that the proposed coding scheme provides the superior brightness and BER performances.

Improved pulse‐width modulation scheme for T‐type multilevel inverter

In recent times, reduced switch count multilevel inverter (RSC-MLI) has become an emerging area of research in power electronic converters. To control these RSC-MLI topologies, various novel modulation schemes are reported. Multi-reference is one of such modulation scheme reported for various RSC topologies, such as T-type. However, the performance of this conventional scheme results in high total harmonic distortion (THD) in line voltages, when compared with the conventional level shifted pulse-width modulation scheme. This observation is clearly presented in this study and the reason for its degraded THD performance has been deeply discussed. To alleviate this problem, a modified multi-reference dual-carrier modulation technique with multiple references and two carriers is proposed. To implement this proposed modulation technique, an alternate carrier and modulation signals arrangement with multiple carriers and single reference is also presented. Finally, a comparative THD performance of the proposed and conventional modulation schemes is carried out on a five-level T-type MLI and obtained simulation results are validated experimentally.

A Random Forest Regression Based Space Vector PWM Inverter Controller for the Induction Motor Drive

This paper presents a random forest (RF) regression based implementation of space vector pulse width modulation (SVPWM) for a two-level inverter to improve the performance of the three-phase induction motor (TIM) drive. The RF scheme offers the advantage of rapid implementation and improved prediction for the SVPWM algorithm to improve the performance of a conventional space vector modulation scheme. In order to show the superiority of the proposed RF technique to other techniques, an adaptive neuro fuzzy inference system (ANFIS) and artificial neural network (ANN) based SVPWM schemes are also used and compared. The proposed speed controller uses a backtracking search algorithm to search for the best values for the proportional-integral controller parameters. The robustness of the RF-based SVPWM is found superior to the ANFIS and ANN controllers in all tested cases in terms of damping capability, settling time, steady-state error, and transient response under different operating conditions. The prototype of the optimal RF-based SVPWM inverter controller of induction motor drive is fabricated and tested. Several experimental results show that there is a good agreement of the speed response and stator current with the simulation results which are verified and validated the performance of the proposed RF-based SVPWM inverter controller.

Ultra-high capacity WDM-SDM optical access network with self-homodyne detection downstream and 32QAM-FBMC upstream.

Towards 100G beyond large-capacity optical access networks, wavelength division multiplexing (WDM) techniques incorporating with space division multiplexing (SDM) and affordable spectrally efficient advanced modulation formats are indispensable. In this paper, we proposed and experimentally demonstrated a cost-efficient multicore fiber (MCF) based hybrid WDM-SDM optical access network with self-homodyne coherent detection (SHCD) based downstream (DS) and direct detection optical filter bank multi carrier (DDO-FBMC) based upstream (US). In the DS experiments, the inner core of the 7-core fiber is used as a dedicated channel to deliver the local oscillator (LO) lights while the other 6 outer cores are used to transmit 4 channels of wavelength multiplexed 200-Gb/s PDM-16QAM-OFDM signals. For US transmission, 4 wavelengths with channel spacing of 100 GHz are intensity modulated with 30 Gb/s 32-QAM-FBMC and directly detected by a ~7 GHz bandwidth receiver after transmission along one of the outer core. The results show that a 4 × 6 × 200-Gb/s DS transmission can be realized over 37 km 7-core fiber without carrier frequency offset (CFO) and phase noise (PN) compensation even using 10 MHz linewidth DFB lasers. The SHCD based on MCF provides a compromise and cost efficient scheme between conventional intradyne coherent detection and intensity modulation and direct detection (IM/DD) schemes. Both US and DS have acceptable BER performance and high spectral efficiency.

Rectangular Differential Spatial Modulation for Open-Loop Noncoherent Massive-MIMO Downlink

In this paper, a novel differential space-time coding scheme is conceived for open-loop noncoherent multiple-input multiple-output (MIMO) downlink scenarios, where the transmission rate increases logarithmically in a scalable manner upon increasing the number of transmit antennas. More specifically, the proposed scheme relies on the projection of a differentially encoded square matrix to its rectangular counterpart and so is capable of reducing the number of symbol intervals needed for block transmission. This is especially beneficial for massive MIMO scenarios, in which the number of transmit antennas is very high. Another advantage exclusive to the presented scheme is that no channel state information (CSI) is required at either the transmitter or the receiver, which eliminates pilot overhead, CSI estimation, CSI feedback, and time-division duplex reciprocity. Furthermore, the rectangular transmission matrix of the proposed scheme contains only a single non-zero element per column, and hence, the transmitter may rely on only a single RF chain, similar to the conventional coherent spatial modulation scheme.

Modified hybrid modulation scheme with even switch thermal distribution for H‐bridge hybrid cascaded inverters

Hybrid cascaded multilevel inverters have been recognised as an important alternative in the medium-voltage inverter market due to their high-quality output and outstanding availability. To optimise the performance of voltage-source converters, modulation technologies have attracted more and more attention. With conventional modulation technologies, the switches within a cell are not utilised at a uniform switching frequency, which is not benefit for reliability and modularity. To solve this problem, a modified hybrid modulation strategy based on unipolar frequency doubling is proposed for H-bridge hybrid cascaded inverters. The equivalence of different multilevel carrier-based modulation strategies is revealed and corresponding implement methods are provided. Based on the equivalent hybrid modulation strategy, a modified hybrid modulation strategy is presented by using unipolar frequency doubling. Compared with the conventional modulation strategies, the proposed strategy makes a more uniform use of the switches within a cell. The proposed strategy keeps the output quality and efficiency while the maximum switching frequency is decreased by half. The strategy has been successfully substantiated by the simulation and experimental results of a seven-level hybrid cascaded inverter.

Photonic crystal nanocavity assisted rejection ratio tunable notch microwave photonic filter

Driven by the increasing demand on handing microwave signals with compact device, low power consumption, high efficiency and high reliability, it is highly desired to generate, distribute, and process microwave signals using photonic integrated circuits. Silicon photonics offers a promising platform facilitating ultracompact microwave photonic signal processing assisted by silicon nanophotonic devices. In this paper, we propose, theoretically analyze and experimentally demonstrate a simple scheme to realize ultracompact rejection ratio tunable notch microwave photonic filter (MPF) based on a silicon photonic crystal (PhC) nanocavity with fixed extinction ratio. Using a conventional modulation scheme with only a single phase modulator (PM), the rejection ratio of the presented MPF can be tuned from about 10 dB to beyond 60 dB. Moreover, the central frequency tunable operation in the high rejection ratio region is also demonstrated in the experiment.

Comparative study of conventional modulation schemes in terms of conducted and radiated EMI generated by three-phase inverters

In this paper, a comparative study is carried out between the carrier (SPWM), third harmonic injection (THIPWM), and space vector (SVPWM) modulation schemes in terms of conducted (common and differential modes) and radiated electromagnetic interference (EMI) generated by three-phase two-level voltage source inverters. For this purpose, an experimental setup of the converter feeding an induction machine is developed with the aim to measure the conducted emission propagated back into the dc source and the radiated field in the vicinity of the power conversion device. Experimental results are given and analyzed in time and frequency domains. The comparative study between the three modulation methods carried out in the frequency domain shows that the SVPWM method has better EMI performance. Moreover, a high frequency model of the converter feeding the induction machine is simulated using SPICE-based simulation software. Good agreement is found between the experimental and simulation results in terms of conducted interferences.

A Study on Effective Dimming Control Scheme Using Optical Spreading Codes in Visible Light Communication

In this paper, we proposed a new dimming control scheme by using direct sequence spreading coding (DSSC) scheme in visible light communication (VLC). VLC systems using LED lighting can provide illumination functions and communication services at the same time. In order to provide simultaneous illumination and communication services, dimming control should be considered. Dimming control means that LED lighting should maintain a constant brightness in accordance with user requirements while communication services are offered. In IEEE 802.15.7 VLC standard, on-off keying (OOK) and variable pulse position modulation (VPPM) are defined as pulse modulation schemes for dimming control. In particular, 4B/6B, 8B/10B block coding and Manchester coding schemes have been proposed for stable dimming control in OOK. However, in such a case, stable dimming control is possible although the communication performance is degraded. In order to solve those problems, we propose a VLC system based on OOK modulation with DSSC. The proposed system can simultaneously stabilize dimming control and improve communication performance by obtaining spread diversity gain. The simulation results show that the proposed system provides superior dimming and BER performances compared to conventional dimming modulation schemes.

Advance Technology in Application of Four Leg Inverters to UPQC

This article presents a novel application of four leg inverter with conventional Sinusoidal Pulse Width Modulation (SPWM) Scheme to Unified Power Quality Conditioner (UPQC). The Power Quality problem became burning issues since the starting of high voltage AC transmission system. Hence, in this article it has been discussed to mitigate the PQ issues in high voltage AC systems through a three phase Unified Power Quality Conditioner (UPQC) under various conditions, such as harmonic mitigation scheme, non linear loads, sag and swell conditions as well. Also, it proposes to control harmoincs with various artificial intelligent techniques. Thus application of these control technique such as Artifical Neural Networks, Fuzzy Logic makes the system performance in par with the standards and also compared with existing system. The simulation results based on MATLAB/SIMULINK<sup>TM </sup>are discussed in detail to support the concept developed in the paper.

Colorless beat interference cancellation receiver for the orthogonally polarized SSB-OOFDM signal with reduced guard band.

In the paper, we have proposed a novel optical orthogonal frequency division multiplexing (OOFDM) link scheme with the colorless beat interference cancellation receiver (BICR) structure for the single-sideband OOFDM (SSB-OOFDM) signal with an orthogonally polarized optical carrier and sideband, which is generated by using a polarization modulator and an optical band-pass filter. The BICR, employing only a polarization beam splitter and a balanced photodiode pair, can colorlessly mitigate the signal-signal beat interference (SSBI) induced by the square-law detection in a photodiode and thus the spectral efficiency (SE) is improved by reducing the guard band (GB) between the optical carrier and OOFDM signal. A simulation link for the 40 Gbit/s 16-QAM SSB-OOFDM signal with a reduced GB is built to demonstrate the feasibility of our proposed scheme. The simulation results indicate that the link has a higher SE compared to the conventional intensity modulation and direction detection scheme and the BICR exhibits a better performance in suppressing SSBI according to the error vector magnitude and the constellation diagrams.

40 Gb/s NRZ-DQPSK data wavelength conversion with amplitude regeneration using four-wave mixing in a quantum dash semiconductor optical amplifier

Differential quadrature phase shift keying (DQPSK) modulation is attractive in high-speed optical communications because of its resistance to fiber nonlinearities and more efficient use of fiber bandwidth compared to conventional intensity modulation schemes. Because of its wavelength conversion ability and phase preservation, semiconductor optical amplifier (SOA) fourwave mixing (FWM) has attracted much attention. We experimentally study wavelength conversion of 40 Gbit/s (20 Gbaud) non-return-to-zero (NRZ)-DQPSK data using FWM in a quantum dash SOA with 20 dB gain and 5 dBm output saturation power. Q factor improvement and eye diagram reshaping is shown for up to 3 nm pump-probe detuning and is superior to that reported for a higher gain bulk SOA.

Open-Switch Fault Diagnosis and Fault Tolerant for Matrix Converter With Finite Control Set-Model Predictive Control

To improve the reliability of the matrix converter (MC), a fault diagnosis method to identify a single open-switch fault is proposed in this paper. The introduced fault diagnosis method is based on finite control set-model predictive control (FCS-MPC), which employs a time-discrete model of the MC topology and a cost function to select the best switching state for the next sampling period. The proposed fault diagnosis method is realized by monitoring the load currents and judging the switching state to locate the faulty switch. Compared to the conventional modulation strategies such as carrier-based modulation method, indirect space vector modulation, and optimum Alesina–Venturini, the FCS-MPC has known and unchanged switching state in a sampling period. It is simpler to diagnose the exact location of the open switch in MC with FCS-MPC. To achieve better quality of the output current under single open-switch fault conditions without any redundant hardware, a fault tolerant strategy based on predictive control is also studied. The fault tolerant strategy is to select the most appropriate switching state associated with the remaining normal switches of the MC. Experiment results are presented to show the feasibility and effectiveness of the proposed fault diagnosis method and fault tolerant strategy.