Terahertz wireless communications are expected to offer the required high capacity and low latency performance necessary for short-range wireless access and control applications. We present an overview of some the activities in this area in the newly started H2020 ITN project CELTA: Convergence of Electronics and Photonics Technologies Enabling Terahertz Applications.
The ROAM (Revolutionizing optical fiber transmission and networking using the Orbital Angular Momentum of light) project investigates the orbital angular momentum (OAM) modes of light for communications and networking applications. OAM modes are exploited as a disruptive means of increasing fibre transmission capacity and as switching resource to improve the switches scalability and power consumption in data-centre scenarios.
The growth of data traffic related to datacenter (DC) interconnection and the expected explosion of services requiring intensive use of telecom networks, such as video and mobile services, are contributing to the increment of the traffic that transport networks need to support. In fact, Cisco has recently forecast that in the next few years IP traffic related to video services will correspond up to the 80% of the total IP traffic and that mobile data traffic will reach about 367 EB per month by 2020. Aiming at reducing Capital Expenditure (CAPEX) and Operational Expenditure (OPEX) required to satisfy demand growth, service providers are exploring new approaches in contrast to traditional ones. From the transport network perspective, aiming at supporting such traffic growth, telecom network operators need to satisfy services requirements without incurring in network performance degradation and in a cost-effective manner. Therefore, cloud-ready transport networks are on the scope of different network providers, including intelligent control architectures and elastic data planes; i.e. based on novel optical technologies. Considering the telecom cloud, where telecom network resources can be offered as a service, in this paper we present three use cases related to DC interconnection, video distribution and 5G networks, and identify their basic connectivity needs from the transport networks according to realistic scenarios.
The paper deals with the problem of resource provisioning in a multilayer network connecting data centers, where a variable number of network nodes is powered by energy produced from renewable resources. We show that an enormous reduction of energy consumed in non-green nodes may be obtained by using the power capping strategy. We consider a rarely investigated set of scenarios covering a wide range of the number of green nodes in the network, starting from the network with one green node up to the case where almost all nodes are powered from renewable energy resources. We show that the effectiveness of the power capping implemented in the network highly depends on the number and location of green nodes as well as on the offered load, and is the greatest in networks with a moderate number of green nodes. Moreover, we show that a small number of nodes powered by renewable energy sources inevitably leads to high blocking probability of those nodes. A possible solution to this problem is also proposed.
Digital signal processing techniques offers many advantages, such as the simplification of the transmission channel, flexibility of transceivers, and efficient compensation of almost any transmission impairment. Digital signal processors have been recently introduced in coherent long-haul optical transmission systems, as well as in non-coherent access networks. In this contribution, we review a number of specific signal processing algorithms that are useful in such systems. We focus on advanced equalizers for linear and nonlinear distortions. We examine the Tomlinson-Harashima precoding approach, as well as advanced flexible non-integer fractionally-spaced equalizers in a butterfly structure. For the compensation of fiber nonlinearities, Volterra based equalization is investigated.
New techniques for defragmenting spectrum on demand without affecting live traffic and not requiring transponder duplication have been recently proposed. However, the efficiency of these techniques is limited by the network state resulting from the planning algorithms used. In this context, we address the comparison between two retuning techniques, push-pull and hop tuning, and their relationship with different planning policies regarding demand ordering and spectrum assignment. The comparison between the push-pull and hop tuning techniques required the development of efficient heuristic algorithms to obtain results quickly over multiple network topologies and initial planning conditions. These algorithms aim to “clean up” the spectral fragments in the network and they can be applied periodically to restore the spectral efficiency of the network. In this paper we present a planning workflow, in order to evaluate the performance of non-disruptive defragmentation techniques for the various network states given by each planning strategy. The results of this analysis highlight the most suitable policy guidelines, suggesting which planning methods are most suitable when non-disruptive defragmentation algorithms are available in the network operation stage.
In Elastic Optical Networks (EONs), two communications requests sharing common fiber links have to be separated in the spectrum domain by a guard band to prevent the interference or satisfy the security requirement, since there are types of physical impairments or attacks in the optical layer. For different interference or security levels, the size of guard band should be adapted, while it is supposed to be identical in most of the literature. To be more agile and realistic, we rise a new spectrum assignment model called Distance Spectrum Assignment (DSA): the size of guard band between two communications sharing a common fiber link varies according to the specific circumstance, and the goal is to minimize the maximum index of frequency slots assigned to satisfy all the guard band constraints. Since DSA is a strongly NP-hard problem, we propose an Integer Linear Program (ILP) model for computing the optimal solution. For solving the DSA problem in large-scale EONs, we develop a heuristic algorithm with time complexity O(n3Δ), where n is the number of requests and Δ is the maximum degree of the conflict graph. We prove that the proposed algorithm achieves an approximate ratio of O(log(n)) in complete conflict graphs. Numerical results demonstrate the proposed heuristic algorithm can find near-optimal spectrum assignments for solving the DSA problem in general topologies.
A detailed investigation of multigigabit wavelength reuse DWDM system tolerance to bidirectional crosstalk, conditioned by the maximum seed power budget and channel spacing, was preformed. Maximum tolerated seed powers were measured for DSF and SMF, for 10 Gb/s NRZ US signal. We demonstrated that high power regime reveals that the most dominant nonlinear impairment arises for the seed frequency shift coinciding with the SBS anti-Stokes. We assess the optimal seed frequency shift range, allowing a successful trade-off between the seed power budget and enabled spectral efficiency.
In this work, the tolerance to in-band crosstalk of virtual carrier (VC)-assisted direct detection (DD) multi-band orthogonal frequency division multiplexing (MB-OFDM) metro networks, with and without signal-to-signal beat interference (SSBI) mitigation, is compared numerically for 4-ary, 16-ary and 64-ary quadrature amplitude modulation (QAM) formats in the OFDM subcarriers. Our results show that the tolerance to in-band crosstalk is improved for lower modulation format orders. The tolerance to in-band crosstalk of DD OFDM receivers considering 4-QAM modulation format at the DD OFDM subcarriers is above 14 dB higher than the one obtained for the 64-QAM modulation format, regardless the receiver configuration. We have also shown that, the tolerance to in-band crosstalk for a given modulation format order depends on the difference between the virtual carrier-to-band power ratio (VBPR) of the selected and interfering signals, as interferers with same VBPR as the selected signal leads to equal tolerance to in-band crosstalk, independently from the DD OFDM receiver configuration and the subcarrier modulation format order considered.
Fibre-optic communication systems, especially when operating in the nonlinear regime, generally do not perform exactly as theory would predict. A number of methods for data-based evaluation of nonlinear fibre-optic link parameters, both for accurate performance emulation and optimization, are reviewed. In particular, single-step nonlinear impairment based on the Gaussian mixture model, adaptive digital backpropagation, and extension to higher-dimensional spaces using Monte Carlo Markov chains are discussed.
In this paper, we provide a comprehensive view of the most advanced techniques and solutions we contributed to design and validate for adaptation operations in Elastic Optical Networks (EONs). Data, control and monitoring aspects are discussed, identifying potentials and open issues, also in the context of challenging multi-vendor/domain scenarios as the case of elastic alien wavelength.
An analytical tool based on the moment generating function of the receiver decision variable that can evaluate the impact of multiple in-band crosstalk signals in DP-QPSK (Dual-Polarization Quadrature Phase-Shift Keying) signals is presented. It is shown that when the number of interferers increases from 1 to 64 the crosstalk level, that assure a 2dB power penalty, becomes more stringent, -12 dB for the single interferer scenario and -15 dB for 64 interferers. The Gaussian approximation is also used for comparison purposes.
In this work, we experimentally implement an adaptive polarization demultiplexing (PolDemux) technique based on the representation of the state of polarization (SOP) of the signal in the Stokes space in bidirectional ultra-dense wavelength-division-multiplexed (U-DWDM) optical metro networks. BER measurement is used to assess the quality of DP-QPSK and DP-16QAM signals in back-to-back and after 80 km of standard single-mode fibre. In addition, the resiliency of the optical metro network based on Stokes PolDemux technique is evaluated over hybrid optical fibre and free space optics (FSO). Results show that the adaptive Stokes algorithm is transparent to both modulation formats, thus being an attractive digital PolDemux solution for flexible optical metro networks.
Network operators have worked in interoperable scenarios for transport network from several years. The main motivation is to have a rich ecosystem, which encourages the competition to have more efficient network solutions. The bandwidth increment in the transport network puts a lot of pressure to have revenues on an environment where the end-user is willing to pay less and less for the service. Software Define Networks presents a new hope to achieve such desire multi-vendor interoperability. The aim of this paper is to present some architecture to enable interoperability in transport networks. Some of these architectures are market ready and they have been tried in the field, while there are some approaches which are under standardization.
Secure communications at the physical layer will become a requirement by end users soon. Current security enabling techniques involve cryptography and other higher layer methods to secure the transmitted data. This does not resolve in full the psychological need for trust, especially in access scenarios where the user may be located in public spaces. We propose to use Ultra-Wideband communications, which can be seamlessly transported over fiber or wireless, and show different transmission experiments ranging from 2 Gbit/s to 35 Gbit/s. To achieve these record bit rates, the multi-band approach of Carrierless Amplitude Phase modulation scheme is employed.
Advancement of communication technologies and business patterns has contributed to the increase of consumer demand and machine-to-machine network traffic. Following this, a steep downward trend in revenue per bit and a slower decay in cost per bit transported is being observed. This poses serious challenge for network operators to correctly choose the technologies and architecture for transporting both packet and legacy TDM traffic. Thus, future expansion of the network should exploit the architecture that results in the most cost-effective transport of both packet and TDM traffic, aiming to keep TCO at its lowest while ensuring traffic meets its designated SLAs. In this paper we address metro, regional and long haul networks with varying traffic patterns (both packet and TDM) looking at the fundamental problems in network scalability and point to some solutions to ensure that cost-effective network traffic scaling can continue to enable future communications services.
Terahertz wireless communications are expected to offer the required high capacity and low latency performance necessary for short-range wireless access and control applications. We present an overview of some the activities in this area in the newly started H2020 ITN project CELTA: Convergence of Electronics and Photonics Technologies Enabling Terahertz Applications.
We compare the cost efficiency of optical networks based on elastic transponders when accounting for link margins due to network ageing and on fixed 100 Gb/s PDM-QPSK interfaces technologies. Germany50 and Italian photonic backbone networks are used for providing results during a 10-year period given different throughputs, traffic growth rates and the cost erosions of elastic optical transponders. We also investigate the distribution of the ageing margins and modulation schemes that might be changed during the life of the network, before its end-of-life (EoL).
We review progress on high-capacity multi-core fiber systems based on homogeneous, single mode MCF and focus on the limits of high capacity transmission. We discuss issues of inter-core crosstalk, dynamic inter-core skew and their impact on multi-core fiber systems such as pilot-tone transmission and high-dimensional modulation formats. We summarize existing work and include some new results about a high capacity, homogeneous, single-mode, 22-core fiber system.
New technologies are emerging to make optical transport networks increasingly flexible and cost-effective. Transponder modules capable of rate adaptation and sliceability promise a scalable way to support the upcoming traffic growth. The deployment of these flexible modules on the line-side can be enhanced with a pay-as-you-grow approach also on the client-side, where capacity is provisioned on demand for maximum cost-efficiency. Bridging these two elements together with flexible client-to-line interconnection switch fabrics ties together the concept of a fully-flexible next-generation optical transport network. Such a high degree of configurability greatly expands the ability to automatically reuse equipment modules in multiple situations over the course of the network lifecycle. On the other hand, manual re-provisioning of available equipment is an alternative to improve resource reuse in otherwise rigid network designs based on fixed transponders and client-to-line interconnections. The policy each operator chooses regarding the level of manual reconfigurations it allows in its network to reuse idle hardware can have a lasting impact on the overall cost of deploying a transport infrastructure. This paper addresses, through a multi-period planning simulation, the effect of idle part handling on network deployment cost and resource efficiency. The analysis is conducted for multiple transport architectures, ranging from traditional transponders and muxponders to more flexible designs on both the client- and line-sides.
