Showing papers in "IEEE\/OSA Journal of Optical Communications and Networking in 2011"

Optical Spatial Modulation

Abstract: In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results demonstrate a close match.

On the Performance of Different OFDM Based Optical Wireless Communication Systems

Abstract: This paper analyzes the performance of indoor orthogonal frequency division multiplexing (OFDM) optical wireless communication systems in the presence of light emitting diode (LED) nonlinear distortions. There are several forms of optical OFDM using intensity modulation [7th Int. Symp. on Communication Systems Networks and Digital Signal Processing (CSNDSP), 2010, pp. 566-570]. In this paper, DC-biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) are considered. ACO-OFDM produces a half-wave symmetry time signal at the output of the OFDM modulator by special assignment of subcarriers, thus allowing signal clipping at the zero level and avoiding the need for DC bias at the expense of data rate reduction. DCO-OFDM assigns data to all possible subcarriers to increase the data rate. However, half-wave symmetry signals cannot be achieved and a high DC bias is needed to convert the bipolar signal to a unipolar signal before modulating the LED intensity. This paper considers a practical LED model and studies the performance of both systems in terms of average electrical OFDM signal power versus bit error ratio in the presence of an additive white Gaussian noise (AWGN) channel. In addition, DC power consumption and the transmitted optical power for the two systems are compared. The analytical results are validated through Monte Carlo simulations and the obtained results demonstrate close match. It is shown that LED clipping has significant impact on the performance of both systems and an optimum system design should take into account the OFDM signal power, DC-bias point, and LED dynamic range.

Design of a Survivable Hybrid Wireless-Optical Broadband-Access Network

Abstract: The hybrid wireless-optical broadband-access network (WOBAN) is a promising architecture for access networks. Although the front-end wireless mesh networks in a WOBAN are self-healing, the back-end passive optical networks do not have survivability due to their tree topology. We propose a cost-effective protection method for WOBAN that deals with network element failures in the optical part of WOBAN. We define the maximum protection with minimum cost (MPMC) problem and show that the problem can be converted to the minimum cost maximum flow (MCMF) problem. We also present an integer linear programming (ILP) model for the MCMF problem. Numerical results are reported for the application of our algorithm to obtain the optimal solutions for different instances of the MPMC problem.

Bandwidth Squeezed Restoration in Spectrum-Sliced Elastic Optical Path Networks (SLICE)

Abstract: With the continuing growth in the amount of backbone traffic, improving the cost-effectiveness and ensuring survivability of the underlying optical networks are very important problems facing network service providers today. In this paper, we propose a bandwidth squeezed restoration (BSR) scheme in our recently proposed spectrum-sliced elastic optical path network (SLICE). The proposed BSR takes advantage of elastic bandwidth variation in the optical paths of SLICE. It enables spectrally efficient and highly survivable network recovery for best-effort traffic as well as bandwidth guaranteed traffic, while satisfying the service level specifications required from the client layer networks. We discuss the necessary interworking architectures between the optical path layer and client layer in the BSR in SLICE. We also present a control framework that achieves flexible bandwidth assignment as well as BSR of optical paths in SLICE. Finally, we describe an implementation example of a control plane using generalized multi-protocol label switching (GMPLS).

Combining Illumination Dimming Based on Pulse-Width Modulation With Visible-Light Communications Based on Discrete Multitone

Abstract: In the field of indoor wireless networks, visible-light communications is garnering increasing attention. One of the type of emitters used in this technology is white light-emitting diodes, which can synergistically provide both illumination and data transmission. Discrete multitone modulation is attractive for visible-light communications. One of the issues to be addressed in these synergetic use cases is how to incorporate light dimming while not corrupting the communication link. In this paper, the performance of a visible-light communication system combining pulse-width modulation for dimming and discrete multitone for data transmission was investigated. Performance indicators were addressed, i.e., the signal-to-interference ratio due to dimming and the achievable bit-error ratio in the absence of additional noise. By aid of simulations it was shown that practical communication is only feasible when the line rate of the dimming modulation is at least twice the frequency assigned to the largest multitone subcarrier frequency. The results demonstrate that under this constraint and when using a suitably modified demodulation scheme, dimming does not influence the data transmission.

Large Port Count High-Speed Optical Switch Fabric for Use Within Datacenters [Invited]

Abstract: This paper reviews advances in the technology of integrated semiconductor optical amplifier based photonic switch fabrics, with particular emphasis on their suitability for high performance network switches for use within a datacenter. The key requirements for large port count optical switch fabrics are addressed noting the need for switches with substantial port counts. The design options for a 16 × 16 port photonic switch fabric architecture are discussed and the choice of a Clos-tree design is described. The control strategy, based on arbitration and scheduling, for an integrated switch fabric is explained. The detailed design and fabrication of the switch is followed by experimental characterization, showing net optical gain and operation at 10 Gb/s with bit error rates lower than 10-9. Finally improvements to the switch are suggested, which should result in 100 Gb/s per port operation at energy efficiencies of 3 pJ/bit.

Mobile Multigigabit Indoor Optical Wireless Systems Employing Multibeam Power Adaptation and Imaging Diversity Receivers

Abstract: In this paper, we introduce two novel methods (beam power adaptation and diversity imaging) to the design of optical wireless systems to improve link performance. The aim is to reduce the effect of intersymbol interference and to enhance the signal-to-noise ratio (SNR), thus enabling the system to achieve mobility while operating at high bit rates. In good agreement with previous work, the results show that the imaging conventional diffuse system (CDS) with maximum ratio combining (MRC) offers 20 dB better SNR than the nonimaging CDS. The new adaptive line strip multibeam system (ALSMS) with a new imaging diversity receiver provides an SNR improvement of 39 dB over the imaging diversity CDS when both systems employ MRC and operate at 30 Mbits/s. This result illustrates the SNR improvement achieved through the use of our adaptive algorithm coupled with spot diffusing. The lower bit rate (30 Mbits/s) facilitates comparison with previous work. The results also indicate that the combination of transmit power adaptation and spot diffusing coupled with imaging diversity receivers can enable fully mobile 2.5 Gbit/s optical wireless communication. Such a 2.5 Gbit/s system (imaging MRC ALSMS) achieved an SNR improvement of 27 dB over a lower data rate (30 Mbits/s) nonimaging CDS.

Power-Aware Routing and Wavelength Assignment in Multi-Fiber Optical Networks

Abstract: This paper focuses on the energy consumption minimization problem of an optical transport network extending over a very wide area. In particular, the specific problem of power-aware routing and wavelength assignment (PA-RWA) is addressed considering a transparent multi-fiber optical network. An integer linear programming formulation is provided for the static lightpath establishment problem and a few heuristics are proposed to solve the problem in the case of dynamic lightpath establishment. To solve the routing problem we propose a novel algorithm named load based cost; it is based on a cost function that considers the load of each optical fiber to compute link weights. We also propose two new wavelength assignment algorithms: the first one is derived from the first fit heuristic whilst the second one is based on an innovative approach. It works like a least cost routing algorithm assigning a cost to each wavelength for each link in the path and then minimizes the total cost. Our proposal is compared with a number of already known RWA algorithms showing that it is able to reduce the power consumption of the network by about 20-30%, depending on the amount of traffic treated, with respect to state of the art algorithms with a difference of about 10% with respect to the lower bound. In order to provide a complete analysis of the feasibility of the proposed heuristics, the blocking probability is evaluated: the results show that, unlike the other power-aware algorithms here considered, our proposal shows a low impairment with respect to the least congested path-first fit alternative. Another important result regards the better performance of the proposed wavelength assignment algorithm with respect to first fit.

Survivable IP/MPLS-Over-WSON Multilayer Network Optimization

Abstract: Network operators are facing the problem of dimensioning their networks for the expected huge IP traffic volumes while keeping constant or even reducing the connectivity prices. Therefore, new architectural solutions able to cope with the expected traffic increase in a more cost-effective way are needed. In this work, we study the survivable IP/multi-protocol label switching (MPLS) over wavelength switched optical network (WSON) multilayer network problem as a capital expenditure (CAPEX) minimization problem. Two network approaches providing survivability against optical links, IP/MPLS nodes, and opto-electronic port failures are compared: the classical overlay approach where two redundant IP/MPLS networks are deployed, and the new joint multilayer approach which provides the requested survivability through an orchestrated interlayer recovery scheme which minimizes the over-dimensioning of IP/MPLS nodes. Mathematical programming models are developed for both approaches. Solving these models, however, becomes impractical for realistic networks. In view of this, evolutionary heuristics based on the biased random-key genetic algorithm framework are also proposed. Exhaustive experiments on several reference network scenarios illustrate the effectiveness of the proposed approach in minimizing network CAPEX.

Multiobjective Genetic Algorithms for Solving the Impairment-Aware Routing and Wavelength Assignment Problem

Abstract: In future transparent (all-optical) WDM networks, the signal quality of transmission (QoT) will degrade due to physical layer impairments. In this paper, we propose two genetic algorithms for solving the static impairment-aware RWA (IA-RWA) problem by accounting for the impact of physical impairments in the optimization process when searching for the optimum routing path and wavelength channel. The first algorithm indirectly considers the physical impairments through the insertion of the path length and the number of common hops in the search process, using classical multiobjective optimization (MOO) strategies. The second algorithm is a single-objective genetic algorithm (GA) that uses the Q factor for the evaluation of the feasibility of the selected RWA solution. The Q factor is used in each iteration of the algorithm in a self-learning mode in order to evaluate the fitness of each solution to the RWA problem and trigger the evolution of the population. Performance results have shown that considering path length and number of common hops for indirectly handling impairments provide an efficient solution to the IA-RWA problem.

Genetic Algorithm for the Topological Design of Survivable Optical Transport Networks

Abstract: We develop a genetic algorithm for the topological design of survivable optical transport networks with minimum capital expenditure. Using the developed genetic algorithm we can obtain near-optimal topologies in a short time. The quality of the obtained solutions is assessed using an integer linear programming model. Two initial population generators, two selection methods, two crossover operators, and two population sizes are analyzed. Computational results obtained using real telecommunications networks show that by using an initial population that resembles real optical transport networks a good convergence is achieved.

Double-Laser Differential Signaling for Reducing the Effect of Background Radiation in Free-Space Optical Systems

Abstract: In order to reduce the impact of background radiation on the performance of terrestrial free-space optical systems, we propose to use two laser wavelengths and to perform the data detection at the receiver in a differential mode. We consider first the case of simple on-off keying modulation and show the performance improvement by using the proposed technique when the background noise dominates. We also extend our study to the case of pulse position modulation while proposing special signaling schemes that allow an increase in the data transmission rate at the same time as reducing the background noise effect.

An Analytical Approach for Dynamic Wavelength Allocation in WDM–TDMA PONs Servicing ON–OFF Traffic

Abstract: Optical access systems are now considered a feasible alternative to the predominant broadband access technologies, while, at the same time, passive optical networks (PONs) are viewed as an attractive and promising type of fiber access system. In this paper we present and analyze three basic dynamic wavelength allocation scenarios for a hybrid wavelength division multiplexing-time division multiple access (WDM-TDMA) PON. We propose new teletraffic loss models for calculating call-level performance measures, like connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength). The PON accommodates bursty service-classes of ON-OFF traffic. The proposed models are extracted from one-dimensional Markov chains, which describe the wavelength occupancy in the PON, and two-dimensional Markov chains, which describe the bandwidth occupancy inside a wavelength. The accuracy of the proposed models is validated through simulation and is found to be quite satisfactory. Moreover, these models are computationally efficient because they are based on recursive formulas.

Anycast Routing for Survivable Optical Grids: Scalable Solution Methods and the Impact of Relocation

Abstract: In this paper, we address the issue of resiliency against single link network failures in optical grids and show how the anycast routing principle, which is typical of grids, can be exploited in providing efficient shared path protection. We investigate two different integer linear program models for the full anycast routing problem, deciding on the primary and backup server locations as well as on the lightpaths toward them. The first model is a classical integer linear programming (ILP) model, which lacks scalability. The second model is a large-scale optimization model which can be efficiently solved using column generation techniques. We also design two new heuristics: the first one is an improvement of a previously proposed one which, although providing near optimal solutions, lacks scalability, while the second one is highly scalable, at the expense of reduced accuracy. Numerical results are presented for three mesh networks with varying node degrees. They allow an illustration of the scalability of the newly proposed approaches. Apart from highlighting the difference in performance (i.e., scalability and optimality) among the algorithms, our case studies demonstrate the bandwidth savings that can be achieved by exploiting relocation rather than using a backup path to the original (failure-free) destination site. Numerical results for varying network topologies, as well as different numbers of server sites show that relocation allows bandwidth savings in the range of 7-21%.

Outage Capacity for MISO Intensity-Modulated Free-Space Optical Links With Misalignment

Abstract: The outage capacity of slow-fading free-space optical channels is analyzed for a multiple-input/single-output configuration in the presence of atmospheric and misalignment fading. A spatial repetition code is considered at the transmitter and a closed-form expression for the outage capacity is developed. In addition, a simple asymptotic closed-form expression is derived at high signal-to-noise ratio. Two methods are considered for system design using the derived outage capacity results with different beam configurations. The outage capacity is optimized over a predetermined set using numerical techniques. Using the asymptotic form of the outage capacity, however, a closed form for the optimum beamwidth is derived. A comparison of simulation results in both cases gives very similar performance indicating the effectiveness of the asymptotic form to provide a near-optimum expression for the beamwidth.

Connectivity Issues for Ultraviolet UV-C Networks

Abstract: This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with on-off keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e., transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice.

A Scalable Space–Time Multi-plane Optical Interconnection Network Using Energy-Efficient Enabling Technologies [Invited]

Abstract: This paper presents an energy-efficient multi-plane optical interconnection network to interconnect servers in a data center. The novel architecture uses the time domain to individually address each port within a card and the space domain to address each card. Optical enabling technologies passively time-compress serial packets by exploiting the wavelength domain and perform a broadcast-and-select to a destination card with minimum power dissipation. Scalability of both the physical layer and the overall power dissipation of the architecture is shown to be enhanced with respect to the existing interconnection network architectures based on space and wavelength domains. The space-time network architecture is scalable up to 216 ports with space-switches exhibiting energy efficiency of the order of picojoules per bit, thanks to the self-enabled semiconductor-optical-amplifier-based space-switches.

Performance and Power Consumption Analysis of a Hybrid Optical Core Node

Abstract: Hybrid optical switching (HOS) is a switching paradigm that aims to combine optical circuit switching, optical burst switching, and optical packet switching on the same network. This paper proposes a novel integrated control plane for an HOS core node. The control plane makes use of a unified control packet able to carry the control information for all the different data formats and employs an appropriate scheduling algorithm for each incoming data type. Three possible node architectures are presented and an analytical model is introduced to analyze their power consumption. Also, the concept of increase in power efficiency is introduced to compare the considered architectures. The performance and power consumption analysis of the node have been carried out through the use of a simulation model developed specifically for the scope. The obtained results show the effectiveness of HOS networks.

New Strategies for Connection Protection in Mixed-Line-Rate Optical WDM Networks

Abstract: Today's optical wavelength division multiplexing backbone networks need to support traffic demands with very diverse capacity requirements. Recent studies have shown how to design an optical transport network that supports mixed line rates (MLR), where the wavelength channels of the optical paths (i.e., lightpaths) can have a variety of capacities (10/40/100 Gbps). Some preliminary work on the design of MLR optical networks has already appeared, but survivability, which is a key concern in optical network design, is a nascent topic in MLR networks. This study investigates the problem of protection in MLR optical networks: in particular, we study how to design a cost-effective transparent MLR network that provides dedicated protection at the lightpath level. We propose three mechanisms: MLR-at-p-lightpath protection (MLR-p), MLR-at-lightpath protection (MLR-l), and MLR-with-backup-flow-grooming protection (MLR-g). The design problem is solved by two different approaches: (1) a two-step approach that formulates part of the problem as an integer linear program and (2) a heuristic approach. Our results show that, by appropriate assignment of rates to lightpaths, MLR networks can provide protection for diverse traffic demands with much lower transponder cost compared to single-line-rate networks.

Evaluation of Optical Wireless Technologies in Home Networking: An Analytical Hierarchy Process Approach

Abstract: Home networks (HNs) will play a crucial role in achieving broadband service delivery and enabling the future Internet. Optical wireless (OW) is a promising technology for realizing this vision. This paper presents the main results of a roadmapping effort undertaken within the project ICT-OMEGA concerning the potential of OW HNs. Using the framework of the analytic hierarchy process, five different optical home networking scenarios are identified and ranked. Within this framework, the importance of several economic, social and performance criteria is also evaluated. The obtained results are justified taking into account the technical particularities of each architecture. A sensitivity analysis is also performed to further elaborate on the results.

Roadmapping ICT: An Absolute Energy Efficiency Metric

Abstract: We describe an absolute energy efficiency metric (measured in dBe) that can be universally applied to any ICT system, subsystem and component. It shows what energy efficiency improvements are possible for any data processing/transmission/storage system. The metric's versatility is also displayed by applying it to biologically based and quantum-level information systems. As an exemplar, we identify ten different and independent approaches, each of which on its own could achieve at least a 50% energy efficiency saving, so as to enable a thousand-fold (i.e., 30 dB) improvement in overall energy efficiency in photonic telecommunications networking.

Numerical Evaluation of PPM for Deep-Space Links

Abstract: We numerically evaluate the deep-space communication performance in a broadband lossy channel of coherent pulse position modulation (PPM) with an on/off receiver, single-symbol square root detection, and Holevo information. We also consider quadrature amplitude modulation (QAM) signals and phase-shift keying signals with dyne-type detections. We show the quantitative gap between these detection strategies in terms of the capacity, particularly in the quantum-limited region where the quantum noise seriously limits the transmission rate. In particular, we find that for an extremely weak signal input power, use of a multilevel PPM system is a good strategy, whereas for an extremely strong signal, use of a multilevel QAM system is recommended.

Dimensioning the Future Pan-European Optical Network With Energy Efficiency Considerations

Abstract: This paper studies the overall energy consumption of a pan-European optical transport network for three different time periods: today and in five and ten years from now. In each time period the pan-European network was dimensioned using traffic predictions based on realistic data generated by the optical networking roadmap developed in the framework of the European project Building the Future Optical Network in Europe-BONE. A wavelength routed wavelength division multiplexed optical network based on either transparent or opaque node architectures was examined considering exclusively either 10 Gbit/s or 40 Gbit/s per channel data rates. The results manifest that transparent optical networking technologies are expected to provide significant energy savings of the order of 35% to 55%. It was also shown that the migration towards higher data rates, i.e., from 10 Gbit/s to 40 Gbit/s, is assisting in improving the overall energy efficiency of the network.

Convergence Comparison of the CMA and ICA for Blind Polarization Demultiplexing

Abstract: An algorithm based on independent component analysis for blind polarization demultiplexing in a coherent transmission system is presented. A comparison with the constant modulus algorithm in terms of the convergence properties is performed, and it is found that the suggested algorithm has a significantly faster convergence rate and does not have any singularity problems. We also demonstrate that the algorithm convergence is strongly dependent on the choice of starting condition and show how this can be exploited to increase the convergence rate.

Adaptive Optimization of a Free Space Laser Communication System Under Dynamic Link Attenuation

Abstract: Free space laser communication is a potentially attractive technology that can offer intrinsically high data rates and resistance to jamming, and facilitates low probability of interception and low probability of detection (LPI/LPD). However, practical links established in the atmosphere are adversely affected by signal attenuation and dynamic turbulence, which can create spatial and temporal variations in the refractive index. The resulting distortions lead to reduced signal power and increased bit error rate (BER), even over short ranges. To overcome possible signal degradation under adverse conditions, laser communication systems must increase power and reduce the communication bit rate. Under dynamic link attenuation both of these parameters can be tuned to optimize performance. In this paper, we present and compare three methods for optimizing optical link efficiency. The work is based on experiments conducted with a commercially available system, and its scaled-down laboratory prototype. The proposed methods demonstrate different degrees of optimization capabilities under practical operating conditions, but, in general, they maintain the highest possible bit rate at the minimum power consumption, while obtaining an acceptable BER.

Scalable Passive Optical Network Architecture for Reliable Service Delivery

Abstract: A scalable and reliable architecture for both a wavelength division multiplexing passive optical network and a hybrid wavelength and time division multiplexing passive optical network with self-healing capability is presented and evaluated. Our protection scheme is compatible with a cascaded arrayed waveguide grating that can accommodate an ultra-large number of end users. A simple interconnection pattern between two adjacent optical network units (ONUs) is applied in order to provide protection for distributed fibers between a remote node and the ONUs. Therefore, the investment cost on a per-user basis can be significantly reduced. Meanwhile, the performance evaluation shows that our approach can achieve high connection availability while maintaining the support of long reach and high splitting ratio.

Coherent Wireless Optical Communications With Predetection and Postdetection EGC Over Gamma–Gamma Atmospheric Turbulence Channels

Abstract: Wireless optical communication systems with coherent detection are analyzed for Gamma-Gamma distributed turbulence channels. In addition to the shot noise, we consider the impacts of both turbulence amplitude fluctuations and phase fluctuations on the error performance. Error rate analyses of predetection and postdetection equal gain combining (EGC) are carried out. We derive the exact error rate expressions for predetection and postdetection EGC using a characteristic function method. In the case of predetection EGC, we also study the impact of phase noise compensation error on the error rate performance. It is shown that the error rate performance of predetection EGC is sensitive to phase noise compensation errors for both weak and strong turbulence conditions. In order to alleviate the impact of phase noise, postdetection EGC with differential phase-shift keying is introduced and analyzed. In addition, postdetection EGC is compared with predetection EGC in the presence of phase noise compensation errors, and it is found to be an effective alternative to predetection EGC with low complexity implementation.

5 Gbit/s Full-Duplex Radio-Over-Fiber Link With Optical Millimeter-Wave Generation by Quadrupling the Frequency of the Electrical RF Carrier

Abstract: A scheme to implement the full-duplex radio-over-fiber (RoF) link by quadrupling the frequency of the electrical RF carrier without a lightwave source at the remote base station (RBS) is proposed. Not only does the scheme reduce the complexity of the RBS and its frequency requirement for the devices, but the generated optical millimeter-wave (mm-wave) signal also has good transmission performance because both the fading effect and the bit walk-off effect caused by fiber dispersion are avoided. A 5 Gbit/s full duplex RoF simulation link with a 40 GHz optical mm-wave signal is built. It shows that the eye diagrams of both the uplink and downlink signals remain open and clear even after the signals are transmitted over 60 km standard single-mode fibers. The simulation results agree well with our theoretical prediction.

Wavelength Assignment for Physical-Layer-Impaired Optical Networks Using Evolutionary Computation

Abstract: This paper presents a wavelength assignment algorithm suitable for optical networks mainly impaired by physical layer effects, named the Intelligent Wavelength Assignment algorithm (iWA). The main idea is to determine the wavelength activation order for a first-fit algorithm that balances the impact of the physical layer effects by using a training algorithm inspired by evolutionary concepts. The iWA presents some recently proposed concepts in intelligent optimization algorithms, such as an external archive to store the best solutions. Some different physical layer effects, such as four-wave mixing and residual dispersion, were considered in the tests of our proposal. We tested our proposal for transparent optical networks. However, we believe iWA can be used in other types of network, such as opaque networks and translucent networks. The proposed wavelength assignment algorithm was compared with five other wavelength assignment algorithms for two network topologies in three different scenarios. The iWA algorithm outperformed the other WA algorithms in most cases. The robustness of our proposed algorithm to the load distribution changes was also analyzed.

Experimental Demonstration of Impairment-Aware PCE for Multi-Bit-Rate WSONs

Abstract: In emerging multi-bit-rate wavelength switched optical networks (WSONs), the coexistence of lightpaths operating at different bit-rates and modulation formats (e.g., based on amplitude and phase modulation) induces relevant traffic dependent detrimental effects that need to be considered during impairment-aware routing and wavelength assignment (IA-RWA). The considerable complexity of IA-RWA computation has driven the Internet Engineering Task Force (IETF) to propose specific path computation element (PCE) architectures in support of IA-RWA for WSONs. In this paper, following the IETF indications, we expand two PCE architectures and experimentally evaluate five different PCE architectural solutions, performing either combined or separated impairment estimation and RWA, with on-line and off-line computation of impairment validated paths, and with the possible utilization of a novel PCE Protocol (PCEP) extension. Results in terms of traffic engineering performance, path computation delivery time and amount of exchanged PCEP messages are reported and discussed to highlight the benefits and application scenarios of the considered PCE architectures.