Time and frequency offsets in all optical OFDM systems

Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in optical communication systems to fulfill the emerging demands of 3D multimedia applications, cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier optical communication systems for the data transmission rates 1 Tb/s, we need the high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another way is to group the data carrying subcarriers without a guard bands (tightly spaced) to form a superchannel which gives increase in channel capacity. In a superchannel, the requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are orthogonal and closely packed which gives more suitability to form superchannel. This thesis focuses on the time and frequency offsets in AO-OFDM systems. A theoretical model to investigate the performance of on-off-keying (OOK) modulated AO-OFDM system is developed for analytical simulation. The analytical (statistical) model considers the random characteristics of time and frequency offsets in adjacent subcarriers as well as the common noise sources such as shot and thermal noises to calculate the interference variances for evaluating the BER performance. The effects of time and frequency offsets on the BER performance of AO-OFDM system is evaluated with the number of optical subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP) We further develop an analytical model to evaluate the performance of AO-OFDM system with advanced modulation format (M-QAM) in the presence of time and frequency offsets, and the performance is compared with numerical simulations of other emulation setups (oddand- even subcarriers and decorrelated systems). The performance is investigated with NSC, BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method to reduce the effects of time and frequency offsets is proposed and evaluated. Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is proposed to reduce the interference and the results are compared with existing method using sampling gates. The proposed method using FBG for interference reduction provides a cost-effective design of AO-OFDM system

Orthogonal frequency division multiplexing for next generation optical networks

Next generation optical networks will be required to provide increased data throughput on a greater number of optical channels and will also have to facilitate network flexibility in order to adapt to dynamic traffic patterns. Furthermore, the potentially wide deployment of optical Access and Metropolitan networks in particular require that these challenges are met in a cost effect manner. This thesis examines the use of Orthogonal Frequency Division Multiplexing (OFDM) as a means of helping to meet these requirements for next generation optical systems with a high market volume. OFDM is a multi–carrier modulation technique which exhibits high spectral efficiency and a tolerance to chromatic dispersion making it an excellent candidate for use in next generation optical networks. The work presented in this thesis shows how the use of OFDM in conjunction with novel laser devices and direct detection can be used to construct cost effective, low footprint optical systems. These systems are capable of providing >10Gb/s per optical channel and are suitable for implementation as optical access networks. Furthermore, OFDM is shown to be a realistic candidate for use in an optical switching environment where external modulation is employed and, as such, can be considered for use in next generation metropolitan networks

Design and analysis of adaptively modulated optical orthogonal frequency division multiple access multiband passive optical networks

The aim of this thesis is to explore innovative technical solutions of utilising Optical Orthogonal Frequency Division Multiplexing (OOFDM) in intensity modulation and direct detection (IMDD) based future access networks to provide multi-service capability with a minimum 1 Gb/s per user. This thesis extensively investigates and analyses the feasibility and performance of adaptively modulated optical orthogonal frequency division multiplexing multiple access passive optical networks (AMOOFDMA PONs) upstream transmission systems by numerically simulating AMOOFDMA PONs using experimentally determined parameters. OOFDM transceivers incorporating reflective semiconductor optical amplifiers (RSOAs) and distributed feedback (DFB) lasers are utilised in the transceivers and intensity modulation and direct detection (IMDD) transmission systems are also employed to achieve a low complexity, high speed and large bandwidth PON as a solution for next generation access networks. Numerical simulations has also being undertaken to improve overall AMOOFDMA PON performance and power budget by incorporating optical band-pass filters (OBPFs) at the output of optical network units (ONUs). A major challenge of making PONs spectrally efficient has been addressed in this thesis by investigating the AMOOFDMA PON with ONUs on a single upstream wavelength. The performance of the single upstream wavelength AMOOFDMA PON is compared to the multiple wavelength AMOOFDMA PON. Another major challenge in AMOOFDMA PONs namely improving system capacity has also been addressed by implementing multiband transmission in an AMOOFDMA PON. Results show that for a multiple upstream OOFDMA IMDD PON system over 25 km single mode fibre (SMF) can achieve an aggregated data rate of 11.25 Gb/s and the minimum wavelength spacing between ONUs are independent of the number of ONUs. Results also show that a single upstream wavelength AMOOFDMA IMDD PON with multiband incorporated at the ONUs can achieve a aggregated line rate of 21.25 Gb/s over 25 km SMF

Orthogonal frequency division multiplexing for optical access networks

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme with numerous advantages that has for years been employed as the leading physical interface in many wired and wireless communication systems. Recently, with advancements made in digital signal processing, there has been a surge of interest in applying OFDM techniques for optical communications. This thesis presents extensive research on optical OFDM and how it is being applied in access networks. With the aid of theoretical analysis, simulations and experiments, it is shown that the system performance of direct-detection optical OFDM (DD-OOFDM) in the presence of MZM non-linear distortion can be improved by proper biasing and selection of appropriate drive to the MZM. Investigations are conducted to illustrate how a variation in the number of subcarriers and the modulation format influences the sensitivity of the DD-OOFDM system to the MZM non-linear distortion. The possibility of improving the spectral efficiency by reduction of the width of the guard band is also investigated. This thesis also looks into the radio-over-fibre (RoF) transmission of Multiband OFDM UWB as a transparent and low-cost solution for distributing multi-Gbit/s data to end-users in FTTH networks. Due to relaxed regulatory requirements and the wide bandwidth available, UWB operation in the 60-GHz band is also considered for this FTTH application scenario. Four techniques for enabling MB-OFDM UWB RoF operation in the 60-GHz band are experimentally demonstrated. The impacts of various parameters on the performance of the techniques as well as the limitations imposed by fibre distribution are illustrated. Finally, a digital pre-distorter is proposed for compensating for the MZM non-linearity. Experimental demonstration of this digital pre-distortion in an UWB over fibre transmission system shows an increased tolerance to the amplitude of the driving OFDM signal as well as an increase in the optimum modulation index of the OFDM signal

Software Defined Applications in Cellular and Optical Networks

abstract: Small wireless cells have the potential to overcome bottlenecks in wireless access through the sharing of spectrum resources. A novel access backhaul network architecture based on a Smart Gateway (Sm-GW) between the small cell base stations, e.g., LTE eNBs, and the conventional backhaul gateways, e.g., LTE Servicing/Packet Gateways (S/P-GWs) has been introduced to address the bottleneck. The Sm-GW flexibly schedules uplink transmissions for the eNBs. Based on software defined networking (SDN) a management mechanism that allows multiple operator to flexibly inter-operate via multiple Sm-GWs with a multitude of small cells has been proposed. This dissertation also comprehensively survey the studies that examine the SDN paradigm in optical networks. Along with the PHY functional split improvements, the performance of Distributed Converged Cable Access Platform (DCCAP) in the cable architectures especially for the Remote-PHY and Remote-MACPHY nodes has been evaluated. In the PHY functional split, in addition to the re-use of infrastructure with a common FFT module for multiple technologies, a novel cross functional split interaction to cache the repetitive QAM symbols across time at the remote node to reduce the transmission rate requirement of the fronthaul link has been proposed.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Transmission of OFDM wired-wireless quintuple-play services along WDM LR-PONs using centralized broadband impairment compensation

This paper was published in OPTICS EXPRESS and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OE.20.013748 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law[EN] The simultaneous transmission of four orthogonal frequencydivision multiplexing (OFDM)-based signals used to provide quintuple-play services along wavelength division multiplexing (WDM) long-reach passive optical networks (LR-PONs) is demonstrated experimentally. Particularly, the transmission performance of custom signal bearing Gigabit Ethernet data, Worldwide Interoperability for Microwave Access, Long Term Evolution and Ultra Wideband (sub-bands 2 and 3) signals is evaluated for different LR-PONs reaches, considering single-wavelength andWDMtransmission, and using a centralized impairment compensation technique at the central office that is transparent to the services provided. It is shown that error vector magnitude-compliant levels are obtained for all the OFDM-based signals in WDM LR-PONs reaching 100 km and that negligible inter-channel crosstalk is obtained for a channel spacing of 100 GHz regardless the OFDM-based signal considered. The successful multi-format OFDM transmission along the 100 km-long WDM LR-PON is achieved in the absence of optical dispersion compensation or single sideband modulation, and it is enabled by the performance improvement provided by the centralized impairment compensation realized. © 2012 Optical Society of America.M. Morant's work was supported by FPU-MEC grant AP2007-01413. This work was also supported in part by the European FIVER-FP7-ICT-2009-4-249142 project and by Fundacao para a Ciencia e a Tecnologia from Portugal under the TURBO-PTDC/EEA-TEL/104358/2008 project.Alves, T.; Morant Pérez, M.; Cartaxo, A.; Llorente Sáez, R. (2012). Transmission of OFDM wired-wireless quintuple-play services along WDM LR-PONs using centralized broadband impairment compensation. Optics Express. 20(13):13748-13761. https://doi.org/10.1364/OE.20.013748S13748137612013Jia, Z., Yu, J., Ellinas, G., & Chang, G.-K. (2007). Key Enabling Technologies for Optical–Wireless Networks: Optical Millimeter-Wave Generation, Wavelength Reuse, and Architecture. Journal of Lightwave Technology, 25(11), 3452-3471. doi:10.1109/jlt.2007.909201Armstrong, J. (2009). OFDM for Optical Communications. Journal of Lightwave Technology, 27(3), 189-204. doi:10.1109/jlt.2008.2010061Cvijetic, N. (2012). OFDM for Next-Generation Optical Access Networks. Journal of Lightwave Technology, 30(4), 384-398. doi:10.1109/jlt.2011.2166375Shieh, W., & Athaudage, C. (2006). Coherent optical orthogonal frequency division multiplexing. Electronics Letters, 42(10), 587. doi:10.1049/el:20060561Alves, T., Morant, M., Cartaxo, A., & Llorente, R. (2011). Performance Comparison of OFDM-UWB Radio Signals Distribution in Long-Reach PONs Using Mach-Zehnder and Linearized Modulators. IEEE Journal on Selected Areas in Communications, 29(6), 1311-1320. doi:10.1109/jsac.2011.110618Llorente, R., Alves, T., Morant, M., Beltran, M., Perez, J., Cartaxo, A., & Marti, J. (2008). Ultra-Wideband Radio Signals Distribution in FTTH Networks. IEEE Photonics Technology Letters, 20(11), 945-947. doi:10.1109/lpt.2008.922329Alves, T., & Cartaxo, A. (2011). Distribution of Double-Sideband OFDM-UWB Radio Signals in Dispersion Compensated Long-Reach PONs. Journal of Lightwave Technology, 29(16), 2467-2474. doi:10.1109/jlt.2011.2160616Chow, C.-W., Yeh, C.-H., Wang, C.-H., Shih, F.-Y., Pan, C.-L., & Chi, S. (2008). WDM extended reach passive optical networks using OFDM-QAM. Optics Express, 16(16), 12096. doi:10.1364/oe.16.012096Tang, J. M., Lane, P. M., & Shore, K. A. (2006). Transmission performance of adaptively modulated optical OFDM signals in multimode fiber links. IEEE Photonics Technology Letters, 18(1), 205-207. doi:10.1109/lpt.2005.861631Duong, T.-N., Genay, N., Ouzzif, M., Le Masson, J., Charbonnier, B., Chanclou, P., & Simon, J. C. (2009). Adaptive Loading Algorithm Implemented in AMOOFDM for NG-PON System Integrating Cost-Effective and Low-Bandwidth Optical Devices. IEEE Photonics Technology Letters, 21(12), 790-792. doi:10.1109/lpt.2009.2016978Alves, T., & Cartaxo, A. (2009). Performance Degradation Due to OFDM-UWB Radio Signal Transmission Along Dispersive Single-Mode Fiber. IEEE Photonics Technology Letters, 21(3), 158-160. doi:10.1109/lpt.2008.200923