Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to intersymbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a tutorial overview of OFDM highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by single mode optical fiber, multimode optical fiber and optical wireless are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.

OFDM for Optical Communications

The space division multiplexing elastic optical networks (SDM-EONs) based on multi-core fiber (MCF) are an effective solution to improve transmission capacity. In SDM-EONs, spectrum resources take on three-dimensional (3D) properties (i.e., frequency, time, and space), which brings new spatial constraints to network resource allocation. Meanwhile, the spectrum fragmentation in the network also presents same characteristics with the setup and release of dynamic lightpath. To improve the success rate of transmission and the utilization of network resources, it is necessary to evaluate network fragmentation effectively from the three dimension. Therefore, this paper focuses on a new fragmentation measurement for SDM-EONs. Firstly, the 3D fragmentation metric is carried out considering the frequency-time-space domain. Then, routing, core, and spectrum allocation (RCSA) scheme is proposed to allocate the spectrum resource with minimal future fragmentation and core resource with maximal free resource reservation. Simulation results show the proposed scheme better in blocking probability, spectrum utilization, and fragmentation rate.

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3D Fragmentation Metric and RCSA Scheme for Space Division Multiplexing Elastic Optical Networks

Quality of transmission-aware control plane performance analysis for elastic optical networks

In this paper, we explore the problem of routing, modulation and spectrum assignment (RMSA) for advance reservation (AR) requests in elastic optical networks (EONs), with the objective to further reduce the blocking probability and improve the spectrum utilization. On the one hand, we propose a minimum resource consumption routing policy (MRC) for leaving more free resources for future requests. On the other hand, we introduce a two-dimensional (2D) path resource model, in which each AR request can be transformed into a rectangle block whose length and width are related to request bandwidth and request duration respectively. Therefore, the spectrum assignment problem of AR requests is simplified to the two-dimensional rectangle packing problem. Furthermore, we design several factors to evaluate the two-dimensional fragmentation caused by a rectangle packing operation, where we consider the fragmentation situation in the rectangle block neighborhood for the first time. Based on these factors, we propose a two-dimensional fragmentation-aware spectrum assignment strategy (2D-FA). Through the combination of MRC and 2D-FA, we propose a novel RMSA algorithm named MRC-2D-FA for dynamically provisioning AR requests in EONs. Simulation results show that MRC-2D-FA can achieve lower bandwidth blocking probability and higher spectrum utilization compared with several well-performed benchmark algorithms.

/pdf/temporal-and-spectral-2d-fragmentation-aware-rmsa-algorithm-32w7w2wfly.pdf

Temporal and Spectral 2D Fragmentation-Aware RMSA Algorithm for Advance Reservation Requests in EONs

Elastic Optical Networks (EONs) are a promising optical technology to deal with the ever-increasing traffic and the vast number of connected devices of the next generation of the Internet, associated to paradigms like the Internet of Things (IoT), the Tactile Internet or the Industry 4.0, to name just a few. In this kind of optical network, each optical circuit or lightpath is provisioned by means of superchannels of variable bandwidth. In this manner, only the necessary bandwidth to accommodate the demand is allocated, improving the spectrum usage. When establishing a connection, the EON control layer determines the modulation format to be used and allocates a portion of the spectrum in a sequence of fibers from the source to the destination node providing the user-demanded bandwidth. This is known as the routing, modulation level and spectrum assignment (RMSA) problem. In this work, we firstly review the most important contributions in that area, and then, we propose a novel RMSA algorithm, multi-path best-fit (MP-BF), which uses a split spectrum multi-path strategy together with a spectrum assignment technique (best-fit), and which jointly exploit the flexibility of EONs. A simulation study has been conducted comparing the performance of EONs when using MP-BF with other proposals from the literature. The results of this study show that, by using MP-BF, the network can increase its performance in terms of lightpath request blocking ratio and supported traffic load, without affecting the energy per bit or the computation time required to find a solution.

/pdf/routing-modulation-and-spectrum-assignment-algorithm-using-2hyya8adev.pdf

Routing, Modulation and Spectrum Assignment Algorithm Using Multi-Path Routing and Best-Fit

Impact of BER in fragmentation-aware routing and spectrum assignment in elastic optical networks

The paper presents design methodologies for elastic optical networks (EONs) with due considerations to the survivability against link failures and guardband-constrained spectral allocations, using ILP and heuristic algorithms. The obtained results show that, there should be a tradeoff between the number of guardband slots and the spectrum utilization in EONs. Further, a comparative study has been carried out for blocking probabilities of general (unprotected) and survivable EONs with two different protection mechanisms, with due consideration to guardband slots.

Design methodologies for survivable elastic optical networks with guardband-constrained spectral allocation

The continuous increase of data traffic for present-day applications necessitates the development of Elastic Optical Networks (EONs). Significant advancements in efficient Routing and Spectrum Assignment (RSA) algorithms for EONs have been noticed in the recent past. These existing algorithms did not mention constraints on the number of transceivers per node in a network. However, for the planning of a realistic network, it is necessary to estimate the number of transceivers required at each node for the efficient operation of a network. Therefore, transceiver constraints should be taken into account while designing the RSA algorithms. In this paper, we present the impact of putting a limit to the number of transmitters and receivers available at each node of an EON. Moreover, the cost of a network heavily depends on the number of transceivers that each node in the network may offer. Hence, estimating the required number of transceivers per node in a network is vital to approximate the design cost of a network. Here, we present an Integer Linear Programming (ILP) formulation that includes the transceiver constraints and also develop a transceiver-aware heuristic algorithm for routing and spectrum assignment in EONs. Simulation results help us provide a proper design tool to estimate the number of transceivers per node in elastic optical networks.

Design considerations for transceiver-limited elastic optical networks

The current research focuses on examining the negative impacts of blue light on human eyes. With the increasing usage of digital devices such as laptops, smartphones, and televisions, individuals are spending most of their time in front of screens. This prolonged screen time puts immense strain on the eyes, and blue light with wavelengths between 415 nm and 455 nm is a significant contributor to eye strain and damage. To understand the extent of damage, we considered various parameters such as the size of the screen, light intensity, and luminous intensity. We used a TCS34725 RGB sensor to measure the blue light emissions reaching the human eye and established a relationship between sensor outputs and light intensity. To classify the data, we utilized both KNN and Naïve Bayes algorithms for efficient analysis and quicker results.

Eye Health Monitoring System

Nonlinear impairments especially Four-Wave Mixing (FWM) affect the overall optical signal-to-noise ratio (OSNR) by introducing additional crosstalks into the system. FWM is a fiber nonlinearity, in which the interaction of three frequencies generates a fourth frequency known as the FWM component that produces crosstalk with the channel frequencies having the same frequencies as the generated ones. The impact of FWM crosstalk is severe in the case of Elastic Optical Networks (EONs) because a considerable amount of FWM crosstalk is created by inter and intra-channel interferences due to the small channel spacings. Therefore, it is necessary to reduce the FWM crosstalk effect in EONs to improve the OSNR for the established optical connections. The relevant research works on this field take into account the overall nonlinear effect on EONs; however, depreciation of FWM components in EONs is not considered explicitly. Therefore, in this paper, we propose a unique approach to suppress the FWM crosstalk, which we understand, has not been considered for EONs till now. The simulation results show that the number of FWM components has been reduced significantly using the proposed approach.

Devlina Adhikari

Papers

Impact of BER in fragmentation-aware routing and spectrum assignment in elastic optical networks

Design methodologies for survivable elastic optical networks with guardband-constrained spectral allocation

Design considerations for transceiver-limited elastic optical networks

Eye Health Monitoring System

A Dynamic Spectrum Allocation Scheme to limit the FWM Effects in Elastic Optical Networks