Advanced Modulation Techniques Research Articles

Frequency-resolved adaptive probabilistic shaping for DMT-modulated IM-DD optical interconnects.

For decades, advanced modulation techniques have been proposed to increase the capacity for intensity-modulation and direct-detection (IM-DD) optical fiber interconnection systems. Typically, the frequency-resolved discrete multi-tone (DMT) modulation was proposed by loading modulations with different bit numbers to fit the channel's frequency response. Capacity can thus be better improved through finer use of the signal-to-noise-ratio (SNR) distribution in the frequency domain. For conventional DMT, the constellations loaded on individual subcarriers are all equip probability distributed. In this work, we propose a probabilistically shaped DMT (PS-DMT) modulation with adaptively loaded entropies referring to channel frequency response for short-reach optical interconnects. Achievable information rate (AIR) improvements of PS-DMT with both Maxwell-Boltzmann and dyadic distribution are investigated based on generalized mutual information (GMI). Moreover, the proposed PS-DMT has been realized experimentally over a multimode optical link using vertical-cavity surface-emitting lasers (VCSELs) with 100-m-long multimode fiber (MMF) transmission. This method can significantly improve the signaling capacity since two significant benefits are simultaneously utilized: 1) the shaping gain of PS at limited SNR condition and 2) the frequency-resolved continuous entropy loading for better fitting to the channel frequency response. Improved capacity, in terms of AIR, can thus be expected for a practical channel when using PS-DMT. This method can potentially be extended to a wide range of application scenarios, including both multimode and single-mode IM-DD fiber-optic communications.

Silica-microsphere-cavity-based microwave photonic notch filter with ultra-narrow bandwidth and high peak rejection.

We propose and experimentally demonstrate a microwave photonic (MWP) notch filter based on a silica microsphere cavity. By using a high-Q-factor (∼1e7) cavity with a diameter of 132um, the filter bandwidth can be easily decreased to 15MHz in terms of simple fabrication and flexible coupling. Then we use the advanced modulation technique based on a dual parallel Mach-Zehnder modulator to further improve peak rejection (PR). The experimental results show that the MWP notch filter with its PR beyond 55dB and frequency tunability range over 8GHz has been achieved in combination with double-sideband modulation. To the best of our knowledge, this is a record for PR and bandwidth considered simultaneously for an MWP filter based on silica microcavities. Thus, the proposed MWP filter will be useful in the fields of microwave photonic signal processing, radar systems, etc.

A Modified Carrier-Based Advanced Modulation Technique for Improved Switching Performance of Magnetic-Linked Medium-Voltage Converters

The high-frequency magnetic link is gaining popularity due to its lightweight, small volume, and inherent voltage balancing capability. Those features can simplify the utilization of a multilevel converter (MLC) for the integration of renewable energy sources to the grid with compact size and exert economic feasibility. The modulation and control of the MLC are crucial issues, especially for grid-connected applications. To support the grid, the converter may need to operate in an overmodulation (OVM) region for short periods depending upon the loading conditions. This OVM operation of the converter causes increased harmonic losses and adverse effects on the overall system efficiency. On top of that, the size and cost of filtering circuitry become critical to eliminate the unwanted harmonics. In this regard, a modified OVM scheme with phase-disposed carriers for a grid-connected high-frequency magnetic-link-based cascaded H-bridge (CHB) MLC is proposed for the suppression of harmonics and the reduction of converter loss. Furthermore, with the proposed OVM technique, the voltage gain with the modulation index can be increased up to the range which is unlikely to be achieved using the classical ones. Extensive simulations are carried out with a 2.24 MVA permanent magnet synchronous generator based wind energy conversion system, which is connected to the 11 kV ac grid through a high-frequency magnetic-link and a five-level CHB MLC. A scaled down laboratory prototype is implemented to validate the performance of the converter.

Analysis and design of a sustainable microgrid primarily powered by renewable energy sources with dynamic performance improvement

Sustainable microgrid primarily powered by renewable energy sources is a recent concept to fulfill the pledge of delivering reliable power supply for upcoming power systems. This study presents a microgrid system primarily powered by wind and solar energy sources and identifies the issues related to the design, operation, and control of the system. The system is designed and simulated to detect the practical issues involved in the control and operation of the sustainable microgrid system based on wind and solar sources. The technical challenges and a brief plan of conceptual methods to detect some of the technical issues are presented for further analysis. To achieve power quality improvement, effective control architecture is described here. Furthermore, an advanced random pulse position modulation technique for the voltage source inverter is proposed to influence the DC-link inductor which further reduces the harmonic distortion. A current injected control loop (CICL) is also proposed to improve the dynamic behavior of microgrid, due to change in solar radiation and wind speed, which causes DC bus voltage oscillation and, hence, affects in proper system operation. The simulation results report that the microgrid system powered by renewable energy sources have a good performance.

Comparative analysis of capacity oriented Integrated AMI modulation technique for the deployment of radio over fiber system

To improve the spectral efficiency and to reduce non-linear distortion in the optical system, various advanced modulation techniques have been investigated for radio over fiber (RoF) system. The investigation indicates the high data rate distortion less transmission for long-haul RoF system still further investigation is required to improve spectral efficiency and to get the reduction in signal degradation. In this paper, an advanced modulation technique referred as integrated alternate mark inversion modulation technique based upon external modulation (electro-absorption modulator) has been designed and simulated. The results show better performance in terms of performance metrics i.e. Q-factor (25.15) and BER (4e−140) and also enhance the data transmission capabilities up to 100 Gbps covering the long distance of 250 km resulting a reasonable reduction in signal degradation particularly chromatic dispersion effects for long-haul transmissions.

Design and Hardware Implementation Considerations of Modified Multilevel Cascaded H-Bridge Inverter for Photovoltaic System

Inverters are an essential part in many applications including photovoltaic generation. With the increasing penetration of renewable energy sources, the drive for efficient inverters is gaining more and more momentum. In this paper, output power quality, power loss, implementation complexity, cost, and relative advantages of the popular cascaded multilevel H-bridge inverter and a modified version of it are explored. An optimal number of levels and the optimal switching frequency for such inverters are investigated, and a five-level architecture is chosen considering the trade-offs. This inverter is driven by level shifted in-phase disposition pulse width modulation technique to reduce harmonics, which is chosen through deliberate testing of other advanced disposition pulse width modulation techniques. To reduce the harmonics further, the application of filters is investigated, and an LC filter is applied which provided appreciable results. This system is tested in MATLAB/Simulink and then implemented in hardware after design and testing in Proteus ISIS. The general cascaded multilevel H-bridge inverter design is also implemented in hardware to demonstrate a novel low-cost MOSFET driver build for this study. The hardware setups use MOSFETs as switching devices and low-cost ATmega microcontrollers for generating the switching pulses via level shifted in-phase disposition pulse width modulation. This implementation substantiated the effectiveness of the proposed design.

Advanced Modulation Techniques for Flexible Optical Transceivers: The Rate/Reach Tradeoff

This tutorial paper reviews advanced modulation techniques that have been proposed in the literature for the implementation of flexible (or reconfigurable) transceivers, which are fundamental building blocks of next-generation software-defined optical networks. Using a common reference multi-span propagation system scenario, the performance of transceivers employing standard quadrature amplitude modulation with variable-rate forward error correction, probabilistic constellation-shaping, and time-domain hybrid formats is assessed, highlighting the achievable flexibility in terms of continuous tradeoff between transmission rate and distance. The combination of these techniques with sub-carrier multiplexing, which enables an increase of the fiber nonlinearity tolerance thanks to the optimization of the symbol rate per sub-carrier, is also discussed.

Performance of Hybrid OCDMA/WDM Scheme Under DPSK and QPSK Modulation Using Spectral Direct Detection Technique for Optical Communication Networks

Abstract The hybrid optical code-division multiple-access over wavelength-division multiplexing (OCDMA/WDM) scheme has attractive features of supporting system reach, multi Gbps data rates, security, and robustness for optical communication networks. This paper presents the performance of such scheme under DPSK and QPSK modulation formats using spectral direct detection technique. The modified double weight (MDW) code is used as spectral amplitude coding which also acts as a signature address code for the OCDMA system. The MDW code has the advantage of reducing the multiple access interference (MAI) and enhancing the security of the proposed hybrid system. The study focuses on the comparison between the two advanced modulation techniques (DPSK, QPSK) using spectral direct detection. Simulation results show bit-error-rate (BER) ≤10–09 for up to 25 km distance at the bit rate of 1 Gbps for optical communication networks.

Enhanced Metaheuristic Methods for Selective Harmonic Elimination Technique

Metaheuristic techniques have shown remarkable performance in a vast variety of engineering problems. Accurate solving of nonlinear equation set in selective harmonic elimination (SHE) has been one of the widely discussed numerical problems in power electronics. Current study aims at conducting an inclusive comparison of prominent stochastic methods adopted for SHE and modified SHE (MSHE) pulse width modulation techniques. The problem is defined as finding local optima of cascaded H-bride converter operation parameters. The survey investigates key indices of low-order harmonic components and weighted total harmonic distortion. Floating fundamental component is introduced for SHE and MSHE to achieve higher rate of flexibility for optimization techniques. Finally, an advanced modulation technique is proposed to address the dc-link voltage ripples. Simulation and experimental results are presented as a proof of concept.

Development of a ROF-based System Using DQPSK through IsOWC Channel for Long Haul Data Rate Applications

Abstract In order to achieve large capacity inter-satellite communication, optical wireless communication (OWC) is emerging as a promising area of research amongst the academic and research groups. While radio over fiber (ROF) and advanced modulation technique is considered to be a key enabling technology in the development of OWC based access networks for high-speed data transmission. This paper has proposed a novel ROF based system model using OWC for long haul high data rate applications. This system is designed using differential quadrature phase shift keying (DQPSK) through inter-satellite optical wireless communication (IsOWC) channel. The verification of the performance is performed at bit rates of 100 and 200 Gbps over a space distance range up to 1000 to 50000 km under different transmitted power. The simulative investigation has been carried out in terms of important parameters like BER, Q-factor and eye diagrams.

Design of Multichannel Optical OFDM System Using Advanced Modulation Techniques

Abstract Existing single-channel orthogonal frequency division multiplexing (OFDM) system can transmit data from single source to single destination occupying the entire link but bit error rate (BER) provided by these systems is quite high. The multichannel system gives the liberty to route the traffic through the different channels depending upon the availability. So there is a need to design a multichannel system which can transmit the data at higher rate by transmitting multiple symbols simultaneously with improved BER. So, in this research work, we propose a multichannel OFDM system by using an advanced modulation technique, i. e. quadrature amplitude modulation which not only improves the capacity but also makes the system power efficient. In order to demonstrate that our proposed system is power efficient, a set of simulations have been performed. Results show that BER (as a function of power) obtained for the proposed system is low in comparison to the already existed phase shifting keying- and differential phase shift keying-based system.

Design of Cyclic Prefix Characteristic-Based OFDM System for WiMAX Technology

Worldwide interoperability for microwave access (WiMAX) offers the wireless connectivity using orthogonal frequency division multiplexing (OFDM) modulation is a proficient wireless technology that capacities high-speed data transmission facilities. The existing WiMAX techniques have the problem of increase in inter-symbol interference (ISI) and bit error rate (BER) at reduced power spectrum that degrades the performance of WiMAX system due to high data rate transmission. The utilization of different adaptive modulation techniques seen as a potential solution to reduce the ISI and BER for high data rate transmission. In this paper, OFDM is adapted using advanced modulation technique for WiMAX system. The technique proposes the cyclic prefix (CP) is utilized that include supplementary bits at the stage of the transmitter. The proposed technique offers minimization of ISI and improvement in BER. It is defined that performance of the existing CP system is equated with the designed single cyclic prefix (SCP) and double cyclic prefix (DCP) and non-cyclic prefix (NCP). BER, probability of error, and power spectral density are utilized to analyse the performance of the designed system. The OFDM based SCP and DCP and NCP for WiMAX are demonstrated for modulation techniques such as; QPSK, BPSK, and QAM. It is determined that BPSK has the smallest BER when compared to QPSK, 16-QAM, and 64-QAM modulations. It is also demonstrated that QPSK is also very competent, however, it has a higher BER as compared to BPSK modulation. It is also observed that 16-QAM and 64-QAM are less efficient in terms of BER compared to QPSK and BPKS modulations. 64-QAM offers the high data rates, and due to high SNR ratio. The designed system is tested for under AWGN and Rayleigh fading channel, and effect power spectral density of signal to noise ratio on OFDM for rayleigh fading channel are demonstrated for SCP and DCP and NCP. It is determined that the OFDM transmitter with proposed DCP for random signals is efficiently reducing the BER and ISI for WiMAX system.

An Optimized Hybrid SVPWM Strategy Based on Multiple Division of Active Vector Time (MDAVT)

This paper presents a new advanced bus-clamped space vector pulsewidth modulation (SVPWM) technique to reduce line current harmonic distortion as well as switching loss. The proposed sequence introduces multiple division of active vector time (MDAVT) in a subcycle. An analysis of optimal subdivision of active vector dwell time is presented. Existing bus-clamping pulsewidth modulation techniques use double-switching clamping sequences, which use only one zero state and apply an active vector twice in a subcycle. The proposed MDAVT-based SVPWM technique presents a hybrid SVPWM technique. The additional switching is added when the fundamental voltage crosses zero. The switching patterns for the other two phases are not changed. The harmonic performance and switching loss characteristics of the proposed hybrid SVPWM techniques over the existing SVPWM is verified with experimental results on a 415-V, 2.2-kW induction motor drive.

Performance Analysis of Inter-Satellite Optical Wireless Communication

The evolution of optical communications systems from long fibers to robust wireless system has led to the idea of connecting two satellites using an optical wireless link. The rapid developments in satellite communication point to the possibilities of satellite networks as a method for them to communicate with each other. The optical wireless communication (OWC) enables the information exchange between satellites at higher speed and also satellites can act as a relay between two satellites or between a satellite and ground station. Light signal of high frequency is used as a carrier for the optical link between satellites and lasers are commonly used as a source of light. One of the primary reason for preferring OWC over RF link is high data rate with acceptable bit error rate (BER). The communication between two lower earth orbit (LEO) satellites is studied under this project. The quality factor (Q-factor) or BER is used as a metric to analyze the performance of the inter-satellite link (ISL). This work presents the performance enhancement of the system by using multiple antennas and advanced modulation technique.

Investigation of dynamic routing and spectrum allocation methods in elastic optical networks

Abstract The introduction of flexible frequency grids and advanced modulation techniques to optical transmission, namely an elastic optical network, requires new routing and spectrum allocation techniques. In this paper, we investigate dynamic two-step routing and spectrum allocation (RSA) methods for elastic optical networks. K-shortest path-based methods as well as spectrum allocation methods are analysed and discussed. Experimental verification of the investigated techniques is provided using simulation software. Simulation results present effectiveness of routing and spectrum allocation methods for analyzed networks using requested bandwidth of connections. Moreover, performance of shortest path first methods improves considerably when a number of candidate paths increases in the UBN24 topology.

Combined Hybrid DFE and CCK Remodulator for Medium-Range Single-Carrier Underwater Acoustic Communications

Advanced modulation and channel equalization techniques are essential for improving the performance of medium-range single-carrier underwater acoustic communications. In this paper, an enhanced detection scheme, hybrid time-frequency domain decision feedback equalizer (DFE) combined with complementary code keying (CCK) remodulator, is presented. CCK modulation technique provides strong tolerance to intersymbol interference caused by multipath propagation in underwater acoustic channels. The conventional hybrid DFE, using a frequency domain feedforward filter and a time domain feedback filter, provides good performance along with low computational complexity. The error propagation in the feedback filter, caused by feedbacking wrong decisions prior to CCK demodulation, may lead to great performance degradation. In our proposed scheme, with the help of CCK coding gain, more accurate remodulated CCK chips can be used as feedback. The proposed detection scheme is tested by the practical ocean experiments. The experimental results show that the proposed detection scheme ensures robust communications over 10-kilometre underwater acoustic channels with the data rate at 5 Kbits/s in 3 kHz of channel bandwidth.

Emerging Optical Access Network Technologies for 5G Wireless

With the advancement of radio access networks, more and more mobile data content needs to be transported by optical networks. Mobile fronthaul is an important network segment that connects centralized baseband units (BBUs) with remote radio units in cloud radio access networks (C-RANs). It enables advanced wireless technologies such as coordinated multipoint and massive multiple-input multiple-output. Mobile backhaul, on the other hand, connects BBUs with core networks to transport the baseband data streams to their respective destinations. Optical access networks are well positioned to meet the first optical communication demands of C-RANs. To better address the stringent requirements of future generations of wireless networks, such as the fifth-generation (5G) wireless, optical access networks need to be improved and enhanced. In this paper, we review emerging optical access network technologies that aim to support 5G wireless with high capacity, low latency, and low cost and power per bit. Advances in high-capacity passive optical networks (PONs), such as 100  Gbit/s PON, will be reviewed. Among the topics discussed are advanced modulation and detection techniques, digital signal processing tailored for optical access networks, and efficient mobile fronthaul techniques. We also discuss the need for coordination between RAN and PON to simplify the overall network, reduce the network latency, and improve the network cost efficiency and power efficiency.

Design and development of high performance solar photovoltaic inverter with advanced modulation techniques to improve power quality

ABSTRACTIn addition to the focus towards growing demand on electrical energy due to the increase in population, industries, consumer loads, etc., the need for improving the quality of electrical power also needs to be considered. The design and development of solar photovoltaic (PV) inverter with reduced harmonic distortions is proposed. Unlike the conventional solar PV inverters, the proposed inverter provides the advantages of reduced harmonic distortions thereby intend towards the improvement in power quality. This inverter comprises of multiple stages which provides the required 230VRMS, 50 Hz in spite of variations in solar PV due to temperature and irradiance. The reduction of harmonics is governed by applying proper switching sequences required for the inverter switches. The detailed analysis is carried out by employing different switching techniques and observing its performance. With a separate mathematical model for a solar PV, simulations are performed in MATLAB software. To show the advantage of the system proposed, a 3 kWp photovoltaic plant coupled with multilevel inverter is demonstrated in hardware. The novelty resides in the design of a single chip controller which can provide the switching sequence based on the requirement and application. As per the results obtained, the solar-fed multistage inverter improves the quality of power which makes this inverter suitable for both stand-alone and grid-connected systems.

GA Based Selective Harmonic Elimination for Five-Level Inverter Using Cascaded H-bridge Modules

Multilevel inverters (MLI) have been commonly used in industry especially to get quality output voltage in terms of total harmonic distortion (THD). In addition, development in semiconductor technology and advanced modulation techniques make MLI implementation more attractive. Selective Harmonic Elimination (SHE) that can be applied MLI at desired switching frequency offers elimination of harmonics in the output voltage. Also, by using SHE technique with cascaded multilevel inverters, the necessity of using filter in the output can be minimized. In this paper, SHE equations have been solved by using of Genetic Algorithm (GA) Toobox&Matlab and it has been aimed to eliminate desired harmonic orders at fundamental output voltage. Simulation results have clearly demonstrated that GA based SHE techniques can eliminate the demanded harmonic orders.

Experimental Demonstration of a 33.5-Gb/s OFDM-Based PON With Subcarrier Pre-Emphasis

Spectral efficiency is one of the critical issues in passive optical networks (PONs). Thus, next generation PON systems must employ advanced modulation techniques and channel compensation to improve the network performance and provide more bandwidth for end users. In this letter, we have experimentally demonstrated a spectral efficiency improvement in PONs based on the bandwidth scalable orthogonal frequency division multiplexing (BSOFDM-PON), considerably reducing the recommended optical guard band of such direct detection systems. The experimental results show that this efficiency can be achieved in a 33.5-Gb/s BSOFDM-PON on one wavelength channel when subcarrier pre-emphasis is used.