On the Filter Narrowing Issues in Elastic Optical Networks

This paper describes the problematic filter narrowing effect in the context of next-generation elastic optical networks. First, three possible scenarios are introduced: the transition from an actual fixed-grid to a flexigrid network, the generic full flexi-grid network, and a proposal for a filterless optical network. Next, we investigate different transmission techniques and evaluate the penalty introduced by the filtering effect when considering Nyquist wavelength division multiplexing, single side-band direct-detection orthogonal frequency division multiplexing, and symbol-rate variable dual polarization quadrature amplitude modulation. Also, different approaches to compensate for the filter narrowing effect are discussed. Results show that the specific needs per each scenario can be fulfilled by the aforementioned technologies and techniques or a combination of them, when balancing performance, network reach, and cost

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

Digital Phase Noise Compensation for DSCM-Based Superchannel Transmission System With Quantum Dot Passive Mode-Locked Laser

We propose a simplified digital phase noise compensation technique for a Nyquist pulse-shaped digital subcarrier multiplexed (DSCM) coherent optical transmission system, employing an optical frequency comb based on Quantum dot passive mode-locked laser (QD-PMLL). Our results show that the impact of dominant common mode phase noise can be efficiently compensated at the receiver by digitally mixing the data sideband with the complex conjugate of the residual carrier component. This digital mixing technique resulted in better bit error rate performance compared to the conventional mth power Viterbi-Viterbi algorithm for QPSK and blind phase noise compensation for 16-quadratic-amplitude modulation formats, especially in the presence of large phase noise. To this end, exploiting the mutual coherence between the mode-locked comb lines of QD-PMLL, we numerically demonstrate its potential applicability as a transmission source for coherent optical superchannel transmission

Sparse orthogonal circulant transform multiplexing for coherent optical fiber communication

This paper introduces a new multicarrier system, named sparse orthogonal circulant transform multiplexing (S-OCTM), for optical fiber communication. This technique uses an inverse sparse orthogonal circulant transform (S-OCT) matrix, which is simple and contains only two nonzero elements in each column, to multiplex information of different subcarriers. We compared the proposed scheme with conventional orthogonal frequency division multiplexing (OFDM), orthogonal chirp division multiplexing (OCDM), and discrete-Fourier-transform spreading OFDM (DFT-S-OFDM) in a coherent optical communication system. It is shown that S-OCTM, while exhibiting the complexity among the least, avoids the performance disadvantages of all investigated conventional schemes. It is theoretically proved that the S-OCT matrix equalizes the bandwidth limitation effect that degrades the performance of conventional OFDM. It also shows a greatly reduced peak-to-average power ratio and higher tolerance to fiber nonlinearity than OFDM and OCDM. On the other hand, compared to DFT-S-OFDM, S-OCTM shows a better dispersion tolerance under insufficient length of cyclic prefix and is more tolerable to strong optical filtering. The performance advantages and low complexity enable the proposed scheme to be a promising multicarrier solution for optical communications

Interference analysis and power allocation in the presence of mixed numerologies

The flexibility in supporting heterogeneous services with vastly different technical requirements is one of the distinguishing characteristics of the fifth generation (5G) communication systems and beyond. One viable solution is to divide the system bandwidth into several bandwidth parts (BWPs), each having a distinct numerology optimized for a particular service. However, multiplexing of mixed numerologies over a unified physical infrastructure comes at the cost of induced interference. In this paper, we develop an analytical system model for inter-numerology interference (InterNI) analysis in orthogonal frequency-division multiplexing (OFDM) systems with and without filter processing in the presence of mixed numerologies. With the analytical model, the level of InterNI is quantified by the developed analytical metric, which is expressed as a function of several system parameters. This leads to an analysis and evaluation of these parameters for meeting a given distortion target. Moreover, a case study on power allocation utilizing the derived analysis is presented, where an optimization problem of maximizing the sum rate is formulated, and a solution is also provided. It is also demonstrated that a filtered-OFDM system better accommodates the coexistence of mixed numerologies. The proposed model provides an accurate analytical guidance for the multi-service design in 5G and beyond systems

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