Research Highlights

Work Package 1, Aston University, UK

MAIN ACHIEVEMENTS (ESR1):

  1. Developed Multi-Task Learning Algorithms Used in Neural Network-Based Equalizers: enhanced the generalizability and performance of neural network-based equalizers for coherent optical systems, resulting in a paper at The European Conference on Optical Communication 2023.
  2. Pioneered Parallelization Techniques: improved the efficiency of recurrent neural network-based equalizers through knowledge distillation, enabling parallelizable processing, resulting in a publication in the Journal of Lightwave Technology in 2024.
  3. Optimized Hardware Implementation: Reduced computational complexity and resource usage in FPGA platforms for neural network-based optical channel equalizers, resulting in a publication in the Journal of Lightwave Technology in 2024.

ESR1 Sasipim Srivallapanondh studied crucial advancements in reducing the computational complexity of NN-based equalizers, ensuring they are both effective and practical for real-world applications. Several complexity reduction methods aimed at optimizing these systems—knowledge distillation, weight clustering, and multi-task learning—were explored in the main body of work. Each technique was designed to simplify the operation of neural networks, reducing their complexity and the resources required for operation. In addition, the work was evaluated using the complexity metrics for the training and inference phases of the NN, to highlight different aspects of complexity considerations. Lastly, the practical application of these methods showed them to be highly effective.

 

Significant progress was made in neural network-based equalization for coherent optical communication systems. ESR1 worked on leveraging multi-task learning (MTL) to enhance the generalizability of neural network equalizers, enabling a single model to adapt to varying transmission conditions without the need for re-training. Q-factor improved by up to 4 dB compared to conventional digital signal processing techniques. Also developed was the parallelization of recurrent neural network equalizers via knowledge distillation for faster and more efficient data processing, useful for technologies such as 6G. Enhanced connectivity and good data transmission is crucial for efficient digital infrastructure and the proliferation of data-intensive applications.

 

The key results are as follows:

  1. Sasipim Srivallapandondh, Pedro Freire, Guiseppe Parisi, Mariano Devigili, Nelson Costa, Bernhard Spinnler, Antonio Napoli, Jaroslaw E Prilepsky, Sergei Turitsyn. “Low complexity neural network equalizer for nonlinear mitigation in digital subcarrier multiplexing systems,” Optics Express, 17 January 2025, Vol 33, Issue 2. Open Access link here.
  2. Sasipim Srivallapanondh, Pedro Freire, Bernhard Spinnler, Nelson Costa, Wolfgang Schairer, Antonio Napoli, Sergei Turitsyn, Jaroslaw E Prilepsky. “Experimental Validation of XPM mitigation using a generalizable multi-task learning neural network,” Optics Letters, 2 December 2024, Vol 49, Issue 24. Open Access link here.
  3. Sasipim Srivallapanondh, Pedro J. Freire, Bernhard Spinnler, Nelson Costa, Antonio Napoli, Sergei K. Turitsyn, and Jaroslaw E. Prilepsky. “Parallelization of recurrent neural network-based equalizer for coherent optical systems via knowledge distillation.” Journal of Lightwave Technology, Vol 42, no. 7 (2024): 2275-2284. Open Access link here.

Work Package 2, DTU, Denmark

MAIN ACHIEVEMENTS (ESR2):

  • Satellite-to-ground optical links bit error rate (BER) performance analysis over gamma-gamma distributed atmospheric time-variant weak-to-strong-turbulence channels.
  • Optical turbulent time-variant channels performance monitoring using a simplified predictor based on Gaussian Process Regression (GPR) to better capture the dynamics and fine details of the time-variant turbulent channels compared to stacked-layers neural networks.
  • Backward-pumped and bidirectional-pumped Raman amplifiers numerical modeling in the C-band for practical Raman amplifiers performance evaluation, resulting in a poster at the European Conference on Optical Communication in Frankfurt.2024.
  • A physics-informed neural networks-based solver of Raman coupled differential equations was proposed to facilitate the design of Raman optical amplifiers.
  • Using the MoleNetwork tool to generate backbone, metro core and metro core aggregation network topologies which satisfy the network settings and statistics provided by Telecom Italia Mobile.

ESR2 Li Zhang’s work at DTU mainly focused on the atmospheric turbulence time-variant channels modelling and prediction. At Orange Labs in Lannion, the topic was fiber Raman amplifiers modelling. Orange Labs provided a standard numerical model for Raman amplifiers modelling and performance evaluation and this model served as a benchmark for ESR2’s work. ESR2’s work proposed an accurate and efficient neural networks-based tool to model and learn the complex physical effects inside the fiber.

 

ESR2 also worked on network topology and this continued at Telecom Italia Mobile. Telecom Italia developed an open-source tool (MoleNetwork) to generate backbone and metrocore and metrocore aggregation topologies. Based on this MoleNetwork tool ESR2’s work aimed to improve the generation of metrocore aggregation topologies from the point of view of practical applications and more efficient generation.

 

Of note is the new neural networks-based solver in the C-band with backward-pumped and bidirectional-pumped schemes. The outlook for the next generation of fiber-optic communication systems operating over ultra-wide band, Raman amplifiers are attractive solutions due to their broad bandwidth, and the ability to provide arbitrary gain profiles in a controlled way. Crucial to optimizing Raman amplifiers over large bandwidths is the proper allocation of pump powers and wavelengths. The new neural networks-based solver could be used to foresee the impact of Stimulated Raman Scattering on the fiber span of a C+L or S+C+L-band system and to design the distributed Raman amplifiers to compensate for this effect. Also, this new neural networks-based solver could be used to optimize wide-bandwidth (C+L- or S+C+L-band) Raman amplifiers to properly select multiple pump wavelengths and powers for desired gain profiles. It is an effective way for Raman amplifier modelling and performance evaluation before the real fiber Raman amplifiers are fabricated.

 

Key results are published here:

  • The European Conference on Optical Communication (ECOC), Frankfurt, Germany, 25 September 2024. Open Access link here.

Work Package 3, Sant’Anna, Italy

ESR3 Lareb Zar Khan and ESR4 Abdennour Ben Terki at SSSA worked on Work Package 3.

 

MAIN ACHIEVEMENTS (ESR3):

  • Data augmentation technique was proposed to address data scarcity for training ML models for failure management in optical networks, and findings were shared with the research community through publications in top-tier conferences and a journal.
  • Model-centric and data-centric approaches were investigated experimentally to overcome the issue of limited availability of failure data for training ML models, and consequently optimizing the failure recovery process in optical networks. The results were published in a top-tier journal.
  • A novel approach was proposed to significantly reduce the computational complexity of neural networks, which in turn reduces the energy consumption and cost of running ML models. The results were presented at the Optical Network Design and Modeling (ONDM) conference in 2024.
  • A sophisticated data pre-processing approach was proposed that converts raw alarms data from commercial network management systems to a ML-friendly form. The effectiveness of the proposed approach was presented at the Optical Network Design and Modeling (ONDM) conference in 2023.
  • Unsupervised ML technique was investigated to address the issue of unavailability of labelled failure data for distinguishing relevant failure alarms from false alarms. Findings were presented at PSC conference in Japan.

Computational complexity reduction of ML models will impact not just optical networks but the world of AI. AI/ML-based data centres consume one order of magnitude more power than traditional data centres which means that larger ML models consume high power. Our work on computational complexity reduction of ML models can be used to minimize the carbon footprint, analysing and predicting equipment failures, vendor-agnostic solutions for alarm management, and developing ML-based algorithms for failure prediction; there are contributors in maintaining a stable network operation, minimizing downtime. The potential here is to revolutionize optical network management, reducing operational costs and enhancing service provisioning. This contributes to advancing automation and optimization technologies.

 

The potentials of machine learning (ML) have been investigated to enhance control and management functionalities for optical networks, even assuming multi-band optical networks. Such functionalities span from resource allocation strategies accounting for transmission performance to (soft-)failure management. Several ML models have been proposed, demonstrated, and tested even experimentally. First, reinforcement learning and deep reinforcement learning techniques have been proposed to optimize routing and spectrum assignment in multi-band optical networks, while accounting for transmission performance in wide-band transmission systems in the presence of Stimulated Raman Scattering (SRS). Then, failure management (e.g., failure identification) assisted by neural networks (NNs) has been studied facing with issues coming from live networks (e.g., data scarcity associated to specific failures). ML models have been proposed, also relying on generative AI techniques such as data augmentation. A specific attention has been also given to the NN-complexity reduction to create sustainable networks even in terms of power consumption. Overall, activities in WP3 demonstrated that ML can actually empower control and management functionalities revolutionizing optical networks control and operation.

 

Key results have been published in:

  • L. Z. Khan, J. Pedro, N. Costa, A. Sgambelluri, A. Napoli and N. Sambo, “Model and data-centric machine learning algorithms to address data scarcity for failure identification,” in Journal of Optical Communications and Networking, vol. 16, no. 3, pp. 369-381, March 2024. Open Access link here.
  • L. Z. Khan, J. Pedro, N. Costa, L. De Marinis, A. Napoli and N. Sambo, “Data augmentation to improve performance of neural networks for failure management in optical networks,” in Journal of Optical Communications and Networking, vol. 15, no. 1, pp. 57-67, January 2023. Open Access link here.

MAIN ACHIEVEMENTS (ESR4):

  • Conducted a comprehensive literature review on routing and spectrum assignment (RSA) in multi-band optical networks using Machine Learning techniques, resulting in a paper at Photonics in Switching and Computing (PSC) Italy, in 2023.
  • Proposed novel RSA techniques based on Reinforcement Learning and Deep Reinforcement Learning.
  • Simulated and validated the proposed techniques, comparing them against heuristic methods.
  • ML model to identify the type, severity, and localization of failures.

ESR4’s work focused on applying Reinforcement Learning (RL) and Deep Reinforcement Learning (DRL) to enhance RSA in multi-band optical networks. This research leveraged the Generalized Gaussian Noise (GGN) model to simulate physical layer impairments accurately, crucial for assessing Quality of Transmission (QoT) and optimizing network performance. Results showed that RL and DRL strategies adapt dynamically to network conditions, effectively minimizing blocking probability and improving throughput across various network topologies compared to k-Shortest Path and First-Fit (k-SP FF) strategy. Then, a multi-stage ML technique has been proposed and demonstrated to infer with high accuracy the type, severity, and localization of failures in an experimental testbed based on commercial equipment.

 

Key results have been published in:

  • A. B. Terki, J. Pedro, A. Eira, A. Napoli and N. Sambo, “Deep Reinforcement Learning for Resource Allocation in Multi-Band Optical Networks,” 2024 International Conference on Optical Network Design and Modelling (ONDM 2024), Madrid, Spain, 2024. Open Access link here.
  • A. B. Terki, J. Pedro, A. Eira, A. Napoli and N. Sambo, “Routing and spectrum assignment based on reinforcement learning in multiband optical networks,” Photonics in Switching and Computing (PSC), (Mantova, Italy, 26-29th September 2023. Open Access link here.

Work Package 4, UPC, Spain

ESR5 Mariano Devigili and ESR6 Prasunika Khare at UPC worked on Work Package 4.

 

MAIN ACHIEVEMENTS (ESR5):

  • Development of algorithms based on the analysis on of the optical constellations for failure detection, identification and severity estimation which were evaluated based on data obtained through simulations. Presented at one of the most important conferences in the field of optical communications, OFC 2024 in San Diego.
  • Development of QoT estimation models based on the analysis of optical constellations and assessment based on simulation and experimental data.
  • Implementation of a MATLAB-based similar for digital subcarrier multiplexed coherent optical systems and generation of data sets made available in open data repositories. Presented at ECOC 2022 in Basel.
  • Development of models and algorithms for lightpath provisioning. The models were evaluated both with synthetic and experimental data sets.
    Implementation of software to monitor and control QSFP28 form factor optical amplifiers. Collection of experimental data to characterize and modelling the amplifiers.

ESR5 Mariano Devigili‘s work focused mainly on the applications of OCATA: an optical layer digital twin. In particular, the applications investigated were failure management (i.e. failure detection, identification and severity estimation), quality of transmission estimation for lightpath provisioning (e.g., design of models and algorithms supporting the establishment of optical connections) and finally optical amplifier control (e.g., algorithms for the control and the optimization of optical amplifiers). Regarding the investigation on failure management, a journal paper titled, “Applications of the OCATA time domain digital twin: from QoT estimation to failure management” was published in the Journal of Optical Communications and Networking (JOCN), Open Access here. Elsewhere, part of the work done on QoT estimation for lightpath provisioning was presented orally at the Optical Fiber Communication Conference (OFC) 2024.

 

Key results have been published in:

  • Mariano Devigili; Marc Ruiz; Nelson Costa; Carlos Castro; Antonio Napoli; Joao Pedro; Luis Velasco. “Applications of the OCATA time domain digital twin: from QoT estimation to failure management.”  Journal of Optical Communications and Networking, Optica Publishing Group, Vol 16, Issue 2, pp 221-232, 1st February 2024, open access link here.
  • Devigili, D. Sequeira, P. Torres-Ferrera, S. Srivallapanondh, N. Costa, M. Ruiz, C. Castro, A. Napoli, J. Pedro, and L. Velasco. “Twining Digital Subcarrier Multiplexed Optical Signals with OCATA for Lightpath Provisioning,” IEEE/OPTICA Journal of Lightwave Technology, 14 November 2024. Open Access link here.

MAIN ACHIEVEMENTS (ESR6):

  • Developing MultiBand simulator, leading to an invited presentation at The International Conference on Transparent Optical Networks (ICTON), Romania, 2023.
  • Proposing Digital Twin for MultiBand optical network.
  • Machine Leaning based model for real time optical network system.
  • Method for quality of transmission (QoT) estimation of MultiBand system, presenting at the International Conference on Transparent Optical Networks (ICTON), Italy, July 2024.
  • Industrial collaboration to produce scientific papers.

ESR6 Prasunika Khare developed software for multiband optical networks. ESR6 simulated the optical light path propagation using 4th order Runge-Kutta method and then generated the symbols/constellation to study the linear and non-linear effects in C+L+S optical system. ESR6 introduced SSMS, a multiband optical fiber simulator entirely developed in MATLAB. SSMS solves the generalized nonlinear Schrödinger equation relying on the 4th order Runge-Kutta method in Interaction Picture (RK4IP) with adaptive step size approach and compare it with the widely used split-step Fourier method (SSFM). Then, ESR6 proposed digital twin models based on deep neural networks that propagate optical constellation features, related to RO1 and putting in to practice TO1. Remarkable accuracy is shown for optical C+L+S bands.

 

Alongside failure management, WP4 worked on the OCATA optical layer digital twin and investigated its applications e.g. light path provisioning and optical amplifier control. These applications if verified will enable effective network optimization, accurate failure management, thereby reducing the network margins and loads. The societal implications would consist in a more efficient and sustainable infrastructure supporting Internet. WP4 has also worked on Adaptive Neural Network-based models for C+L+S band scenario. The proposed adaptive neural network-based model is able to provide a more efficient and accurate way to handle highly non-linear optical network transmission. MB optical transmission is considered the next technological evolution in optical WDM transport capable of dealing with 5G and beyond in a cost-effective manner. Hence, a revolution to optical network management.

 

Key results have been published in:

  • Ghasrizadeh, P. Khare, N. Costa, M. Ruiz, A. Napoli, J. Pedro, L. Velasco, “Digital Twin-Assisted Lightpath Provisioning and Nonlinear Mitigation in C+L+S Multiband Optical Networks,” Sensors, MDPI, Switzerland, 17 December 2024. Open access link here.

MENTOR pioneered the development of high-capacity optical networks

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