Next-generation optical access networks based on Orthogonal Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) is a robust modulation and multiplexing format which is at the base of many present communication standards. The interest of the OFDM application in optical fiber deployments is quite recent. As the next generation of Passive Optical Networks (NG-PONs) is envisioned, targeting greater capacity and user counts, the limitations of TDMA (Time Division Multiplexing Access) approaches to meet the expected increase in requirements becomes evident and therefore new technologies are being explored. Optical OFDMA is an emerging technology which can be a promising candidate. The main goal of this Master Thesis is to study the problem of users multiplexing in access networks, using OFDM as a technology to transmit the user information data. This work has focused in the uplink study of the network, because it is the most challenging part of the network to design. The studies have been conducted both in a theoretical way and also by simulating the targeted environments by means of a fiber optics transmission simulation tool. Virtual Photonics Integrated (VPI) is the software selected for the simulations. This tool is specially designed to simulate optical transmission system environments. The analysis of the Optical Beat Interference, which is a critical impairment in optical carrier multiplexing schemes, is the most important part of the user multiplexing study

Cost-effective optical transmission systems based on orthogonal frequency division multiplexing

Orthogonal frequency division multiplexing (OFDM)is becoming increasingly popular in optical fiber applications because as data rates increase, the computational requirements involved in electronic dispersion compensation for serial modulation formats become impractical. Some investigations explain that OFDM can be used for the electronic compensation of chromatic dispersion and polarization mode dispersion in single-mode optical fiber systems and for mode dispersion in multimode systems. The main goal of this Master thesis is to study on one hand the OFDM systems and on the other, the optical transmission systems and also the combination of the two: optical OFDM systems. A general classification of the present proposals for optical OFDM implementations is presented and two of the identified schemes, those which lead to more cost-effective solutions, have been studied in deeper detail. These are based on conventional Intensity Modulation and Direct Detection (IM/DD) optical transmission systems. The first system relies on a RF up-conversion stage prior to the optical intensity modulation that allows to modulate the real and imaginary parts of the optical OFDM signal into the phase and quadrature components of an RF frequency, while the second involves imposing the Hermitian symmetry among the subcarriers in order to obtain an OFDM signal which is purely real. Starting from a built in demo of the software called Virtual Photonics Inc. (VPI) a practical investigation about OFDM optical systems has been done. This demo is called Long Haul transmission and implements the RF up-conversion optical OFDM scheme. This demo is only an example restricted to a specific scenario and offers little flexibility. That is why a new VPI simulation setup has been created by exploiting the Matlab interface provided by VPI where the OFDM coding and decoding have been developed in Matlab code and can be adjusted and modified to any scenario. Additionally, another VPI simulation setup has been developed which allows to impose the Hermitian symmetry among the subcarriers allowing for the obtention of a purely real OFDM signal to be directly Intensity modulated over an optical carrier. Results and comparisons of the outcome of both, our simulation setups and the VPI demo, are presented showing good agreement. Moreover, our setups have incorporated several improvements based on the investigation of optical OFDM systems carried out. Also, the functionalities of the software have been exploited to come out with user-friendly setups that allow any researcher in the field to carry out advanced simulations with little effort

Digital filter design using root moments for sum-of-all-pass structures from complete and partial specifications

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SPECTRALLY EFFICIENT MULTICARRIER SYSTEMS FOR FIBER-OPTIC TRANSMISSION

The purpose of this research is to provide a comprehensive study of spectrally efficient multicarrier systems for fiber-optic transmission. Multicarrier optical systems partition a high-data rate digital signal in a wavelength channel into multiple subcarriers. The data rate on each subcarrier can be sufficiently low and thus, the tolerance to transmission impairments can be significantly improved. Although different modulation and detection techniques are used, all the multicarrier systems investigated in this dissertation achieve a high spectral efficiency of 1 Baud/s/Hz. Orthogonal frequency-division multiplexing (OFDM) and Nyquist wavelength-division multiplexing (Nyquist-WDM) are the two basic approaches to achieve the 1 Baud/s/Hz spectral efficiency. OFDM allows spectral overlap of adjacent subcarriers and crosstalk elimination by integration at the receiver; Nyquist-WDM limits the spectral spreading of each subcarrier channel to the symbol rate per subcarrier to avoid spectral overlap. In terms of detection method, both direct detection and coherent detection can be applied in multicarrier systems. This dissertation focuses on the use of three high spectral efficiency optical multicarrier systems. In the theoretical and experimental investigation of a 11.1Gb/s FFT-based OFDM system, a simple dual-drive Mach-Zehnder modulator (MZM) was employed in the transmitter and direct detection in the receiver, which provided an OFDM system implementation with reduced complexity. The data was transmitted through 675km uncompensated standard single-mode fiber (SMF). Next, a 22.2Gb/s digital subcarrier multiplexing based (DSCM-based) OFDM system was used in conjunction with 10 subcarrier channels using QPSK modulation. In this system, an IQ modulator was utilized in the transmitter and coherent detection in the receiver. By using coherent detection, the receiver was able to dynamically select the desired subcarrier channels for detection without changing the system configuration. The present research also explored a 22.2Gb/s 10 subcarrier Nyquist-WDM system with coherent detection, compared its system performance with OFDM systems, and subsequently examined the impact of filter roll-off factor. Finally, a systemic comparison of the three proposed multicarrier systems was performed in terms of their transmission performance and system flexibility. The design tradeoffs were analyzed for different applications and summarized principles for the modern multicarrier fiber-optic system design

Next-generation optical access networks based on Orthogonal Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) is a robust modulation and multiplexing format which is at the base of many present communication standards. The interest of the OFDM application in optical fiber deployments is quite recent. As the next generation of Passive Optical Networks (NG-PONs) is envisioned, targeting greater capacity and user counts, the limitations of TDMA (Time Division Multiplexing Access) approaches to meet the expected increase in requirements becomes evident and therefore new technologies are being explored. Optical OFDMA is an emerging technology which can be a promising candidate. The main goal of this Master Thesis is to study the problem of users multiplexing in access networks, using OFDM as a technology to transmit the user information data. This work has focused in the uplink study of the network, because it is the most challenging part of the network to design. The studies have been conducted both in a theoretical way and also by simulating the targeted environments by means of a fiber optics transmission simulation tool. Virtual Photonics Integrated (VPI) is the software selected for the simulations. This tool is specially designed to simulate optical transmission system environments. The analysis of the Optical Beat Interference, which is a critical impairment in optical carrier multiplexing schemes, is the most important part of the user multiplexing study

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

High Data Rate Coherent Optical OFDM System for Long-Haul Transmission

The growth in internet traffic has driven the increase in demand for bandwidth and high data rates. Optical Orthogonal Frequency Division Multiplexing is considered as a promising technology to satisfy the increased demand for bandwidth in broadband services. Optical OFDM received a great attention after proposing it as a modulation technique for the long-haul transmission in both direct and coherent detection. However, Coherent Optical OFDM (CO-OFDM) is the next generation technology for the optical communications, since it integrates the advantages of both coherent systems and OFDM systems. It has the ability to overcome many optical fiber restrictions such as chromatic dispersion (CD) and polarization mode dispersion (PMD). Moreover, Integrating the Coherent Optical OFDM with Wavelength Division Multiplexing (WDM) systems will provide the transmission system with a high bandwidth, a significant data rates, and a high spectral efficiency without increasing the cost or the complexity of the system. WDM systems help to enhance the capacity and the data rate of the system by sending multiple wavelengths over a single fiber. This research focuses on the implementation and performance analysis of high data rate coherent optical OFDM for long-haul transmission. The study starts with a single user and extends to the implanting of the WDM system. OptiSystem-12 simulation tool is fully used to design and implement the system. The system utilizes to carry range of data rates start from 10 Gbps to 1 Tbps, 4-QAM (2 bits-per-symbol) is used a modulation type for the OFDM signal, Optical I/Q modulation is employed at the transmitter and coherent detection is employed at the receiver. The performance of the system is studied and analyzed system in terms of Bit-Error-Rate (BER), the effect of the transmission distance on the Optical-Signal-to-Noise-Ratio (OSNR), and the relation of BER and OSNR with regard to the transmission distance

Comprehensive investigation of coherent optical OFDM-RoF employing 16QAM external modulation for long-haul optical communication system

Given the growing need for long haul transmission that requires a high rate of data, the orthogonal frequency division multiplexing scheme (OFDM), is regarded as a technique with high potentials for high-capacity optical networks. OFDM transmits over both optical and wireless channels, with the data distributed over a huge amount of the subcarrier, and the data is distributed over a huge number of subcarriers. OFDM achieves RF signal for a long-haul transmitting by utilizing Radio over Fiber (RoF) system, which is known to produce higher orthogonality of the OFDM modulated signal designed for the wireless network. RoF systems comprise of heterogeneous networks designed through the use of wireless and optical links. The aim of this paper is to carry out an investigation of the performance of the external modulation in RoF links, while analyzing the shortcomings caused by the various elements of the optical system. The Mach–Zehnder modulator (MZM) can be applied in external modulation, and exhibits a more robust performance when implemented with the OFDM modulation technique