Search Results for author: Merouane Debbah

Found 64 papers, 4 papers with code

Agent-driven Generative Semantic Communication for Remote Surveillance

no code implementations10 Apr 2024 Wanting Yang, Zehui Xiong, Yanli Yuan, Wenchao Jiang, Tony Q. S. Quek, Merouane Debbah

In the era of 6G, featuring compelling visions of intelligent transportation system, digital twins, remote surveillance is poised to become a ubiquitous practice.

How Bad is Training on Synthetic Data? A Statistical Analysis of Language Model Collapse

no code implementations7 Apr 2024 Mohamed El Amine Seddik, Suei-Wen Chen, Soufiane Hayou, Pierre Youssef, Merouane Debbah

With the aim of rigorously understanding model collapse in language models, we consider in this paper a statistical model that allows us to characterize the impact of various recursive training scenarios.

Language Modelling

GenAINet: Enabling Wireless Collective Intelligence via Knowledge Transfer and Reasoning

no code implementations26 Feb 2024 Hang Zou, Qiyang Zhao, Lina Bariah, Yu Tian, Mehdi Bennis, Samson Lasaulce, Merouane Debbah, Faouzi Bader

Connecting GenAI agents over a wireless network can potentially unleash the power of collective intelligence and pave the way for artificial general intelligence (AGI).

Transfer Learning

CyberMetric: A Benchmark Dataset for Evaluating Large Language Models Knowledge in Cybersecurity

no code implementations12 Feb 2024 Norbert Tihanyi, Mohamed Amine Ferrag, Ridhi Jain, Merouane Debbah

Large Language Models (LLMs) excel across various domains, from computer vision to medical diagnostics.

Internet of Federated Digital Twins (IoFDT): Connecting Twins Beyond Borders for Society 5.0

no code implementations11 Dec 2023 Tao Yu, Zongdian Li, Kei Sakaguchi, Omar Hashash, Walid Saad, Merouane Debbah

In contrast, this paper envisions a novel concept of an Internet of Federated Digital Twins (IoFDT) that holistically integrates heterogeneous and physically separated DTs representing different Society 5. 0 services within a single framework and system.

Do VSR Models Generalize Beyond LRS3?

1 code implementation23 Nov 2023 Yasser Abdelaziz Dahou Djilali, Sanath Narayan, Eustache Le Bihan, Haithem Boussaid, Ebtessam Almazrouei, Merouane Debbah

The Lip Reading Sentences-3 (LRS3) benchmark has primarily been the focus of intense research in visual speech recognition (VSR) during the last few years.

Lip Reading speech-recognition +1

UAV Immersive Video Streaming: A Comprehensive Survey, Benchmarking, and Open Challenges

no code implementations31 Oct 2023 Mohit K. Sharma, Chen-Feng Liu, Ibrahim Farhat, Nassim Sehad, Wassim Hamidouche, Merouane Debbah

However, achieving this immersive experience necessitates encoding omnidirectional videos in high resolution, leading to increased bitrates.

Benchmarking

Causal Reasoning: Charting a Revolutionary Course for Next-Generation AI-Native Wireless Networks

no code implementations23 Sep 2023 Christo Kurisummoottil Thomas, Christina Chaccour, Walid Saad, Merouane Debbah, Choong Seon Hong

We showcase how incorporating causal discovery can assist in achieving dynamic adaptability, resilience, and cognition in addressing these challenges.

Causal Discovery Causal Inference +2

Emergent Communication in Multi-Agent Reinforcement Learning for Future Wireless Networks

no code implementations12 Sep 2023 Marwa Chafii, Salmane Naoumi, REDA ALAMI, Ebtesam Almazrouei, Mehdi Bennis, Merouane Debbah

In different wireless network scenarios, multiple network entities need to cooperate in order to achieve a common task with minimum delay and energy consumption.

Autonomous Driving Continuous Control +4

Joint Semantic-Native Communication and Inference via Minimal Simplicial Structures

no code implementations31 Aug 2023 Qiyang Zhao, Hang Zou, Mehdi Bennis, Merouane Debbah, Ebtesam Almazrouei, Faouzi Bader

Specifically, the teacher first maps its data into a k-order simplicial complex and learns its high-order correlations.

Large Language Models for Telecom: Forthcoming Impact on the Industry

no code implementations11 Aug 2023 Ali Maatouk, Nicola Piovesan, Fadhel Ayed, Antonio De Domenico, Merouane Debbah

Large Language Models (LLMs), AI-driven models that can achieve general-purpose language understanding and generation, have emerged as a transformative force, revolutionizing fields well beyond Natural Language Processing (NLP) and garnering unprecedented attention.

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

no code implementations19 Jul 2023 Wei Jiang, Qiuheng Zhou, Jiguang He, Mohammad Asif Habibi, Sergiy Melnyk, Mohammed El Absi, Bin Han, Marco Di Renzo, Hans Dieter Schotten, Fa-Long Luo, Tarek S. El-Bawab, Markku Juntti, Merouane Debbah, Victor C. M. Leung

Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds.

SecureFalcon: The Next Cyber Reasoning System for Cyber Security

no code implementations13 Jul 2023 Mohamed Amine Ferrag, Ammar Battah, Norbert Tihanyi, Merouane Debbah, Thierry Lestable, Lucas C. Cordeiro

Software vulnerabilities leading to various detriments such as crashes, data loss, and security breaches, significantly hinder the quality, affecting the market adoption of software applications and systems.

C++ code Fault localization +1

Revolutionizing Cyber Threat Detection with Large Language Models: A privacy-preserving BERT-based Lightweight Model for IoT/IIoT Devices

no code implementations25 Jun 2023 Mohamed Amine Ferrag, Mthandazo Ndhlovu, Norbert Tihanyi, Lucas C. Cordeiro, Merouane Debbah, Thierry Lestable, Narinderjit Singh Thandi

The field of Natural Language Processing (NLP) is currently undergoing a revolutionary transformation driven by the power of pre-trained Large Language Models (LLMs) based on groundbreaking Transformer architectures.

Language Modelling Privacy Preserving

Reasoning over the Air: A Reasoning-based Implicit Semantic-Aware Communication Framework

1 code implementation20 Jun 2023 Yong Xiao, Yiwei Liao, Yingyu Li, Guangming Shi, H. Vincent Poor, Walid Saad, Merouane Debbah, Mehdi Bennis

Most existing works focus on transmitting and delivering the explicit semantic meaning that can be directly identified from the source signal.

Imitation Learning

Large Generative AI Models for Telecom: The Next Big Thing?

no code implementations17 Jun 2023 Lina Bariah, Qiyang Zhao, Hang Zou, Yu Tian, Faouzi Bader, Merouane Debbah

To be specific, large GenAI models are envisioned to open up a new era of autonomous wireless networks, in which multi-modal GenAI models trained over various Telecom data, can be fine-tuned to perform several downstream tasks, eliminating the need for building and training dedicated AI models for each specific task and paving the way for the realization of artificial general intelligence (AGI)-empowered wireless networks.

Understanding Telecom Language Through Large Language Models

no code implementations9 Jun 2023 Lina Bariah, Hang Zou, Qiyang Zhao, Belkacem Mouhouche, Faouzi Bader, Merouane Debbah

In particular, we fine-tune several LLMs including BERT, distilled BERT, RoBERTa and GPT-2, to the Telecom domain languages, and demonstrate a use case for identifying the 3rd Generation Partnership Project (3GPP) standard working groups.

A Nested Matrix-Tensor Model for Noisy Multi-view Clustering

no code implementations31 May 2023 Mohamed El Amine Seddik, Mastane Achab, Henrique Goulart, Merouane Debbah

In order to study the theoretical performance of this approach, we characterize the behavior of this best rank-one approximation in terms of the alignments of the obtained component vectors with the hidden model parameter vectors, in the large-dimensional regime.

Clustering

Unleashing 3D Connectivity in Beyond 5G Networks with Reconfigurable Intelligent Surfaces

no code implementations8 May 2023 Jiguang He, Aymen Fakhreddine, Arthur S. de Sena, Yu Tian, Merouane Debbah

Reconfigurable intelligent surfaces (RISs) bring various benefits to the current and upcoming wireless networks, including enhanced spectrum and energy efficiency, soft handover, transmission reliability, and even localization accuracy.

Joint Sensing, Communication, and AI: A Trifecta for Resilient THz User Experiences

no code implementations29 Apr 2023 Christina Chaccour, Walid Saad, Merouane Debbah, H. Vincent Poor

Second, a non-autoregressive multi-resolution generative artificial intelligence (AI) framework integrated with an adversarial transformer is proposed to predict missing and future sensing information.

Tensor Decomposition

The Seven Worlds and Experiences of the Wireless Metaverse: Challenges and Opportunities

no code implementations20 Apr 2023 Omar Hashash, Christina Chaccour, Walid Saad, Tao Yu, Kei Sakaguchi, Merouane Debbah

We then articulate how these experiences bring forth interactions between diverse metaverse constituents, namely, a) humans and avatars and b) connected intelligence systems and their digital twins (DTs).

Low Complexity Optimization for Line-of-Sight RIS-Aided Holographic Communications

no code implementations13 Apr 2023 Juan Carlos Ruiz-Sicilia, Marco Di Renzo, Merouane Debbah, H. Vincent Poor

The synergy of metasurface-based holographic surfaces (HoloS) and reconfigurable intelligent surfaces (RIS) is considered a key aspect for future communication networks.

Regularization of the policy updates for stabilizing Mean Field Games

no code implementations4 Apr 2023 Talal Algumaei, Ruben Solozabal, REDA ALAMI, Hakim Hacid, Merouane Debbah, Martin Takac

This work studies non-cooperative Multi-Agent Reinforcement Learning (MARL) where multiple agents interact in the same environment and whose goal is to maximize the individual returns.

Multi-agent Reinforcement Learning reinforcement-learning

Poisoning Attacks in Federated Edge Learning for Digital Twin 6G-enabled IoTs: An Anticipatory Study

no code implementations21 Mar 2023 Mohamed Amine Ferrag, Burak Kantarci, Lucas C. Cordeiro, Merouane Debbah, Kim-Kwang Raymond Choo

However, we need to also consider the potential of attacks targeting the underlying AI systems (e. g., adversaries seek to corrupt data on the IoT devices during local updates or corrupt the model updates); hence, in this article, we propose an anticipatory study for poisoning attacks in federated edge learning for digital twin 6G-enabled IoT environments.

Federated Learning Privacy Preserving

Robust mmWave Beamforming by Self-Supervised Hybrid Deep Learning

no code implementations9 Mar 2023 Fenghao Zhu, Bohao Wang, Zhaohui Yang, Chongwen Huang, Zhaoyang Zhang, George C. Alexandropoulos, Chau Yuen, Merouane Debbah

Beamforming with large-scale antenna arrays has been widely used in recent years, which is acknowledged as an important part in 5G and incoming 6G.

Harris Hawks Feature Selection in Distributed Machine Learning for Secure IoT Environments

no code implementations20 Feb 2023 Neveen Hijazi, Moayad Aloqaily, Bassem Ouni, Fakhri Karray, Merouane Debbah

Although IoT applications are helpful in smart building applications, they present a real risk as the large number of interconnected devices in those buildings, using heterogeneous networks, increases the number of potential IoT attacks.

feature selection

A Comprehensive Review and a Taxonomy of Edge Machine Learning: Requirements, Paradigms, and Techniques

no code implementations16 Feb 2023 Wenbin Li, Hakim Hacid, Ebtesam Almazrouei, Merouane Debbah

Nevertheless, edge-powered ML solutions are more complex to realize due to the joint constraints from both edge computing and AI domains, and the corresponding solutions are expected to be efficient and adapted in technologies such as data processing, model compression, distributed inference, and advanced learning paradigms for Edge ML requirements.

Edge-computing Model Compression

Optimizing Orthogonalized Tensor Deflation via Random Tensor Theory

no code implementations11 Feb 2023 Mohamed El Amine Seddik, Mohammed Mahfoud, Merouane Debbah

Relying on recently developed random tensor tools, this paper deals precisely with the non-orthogonal case by deriving an asymptotic analysis of a parameterized deflation procedure performed on an order-three and rank-two spiked tensor.

Cooperative Beamforming and RISs Association for Multi-RISs Aided Multi-Users MmWave MIMO Systems through Graph Neural Networks

no code implementations8 Feb 2023 Mengbing Liu, Chongwen Huang, Marco Di Renzo, Merouane Debbah, Chau Yuen

Reconfigurable intelligent surface (RIS) is considered as a promising solution for next-generation wireless communication networks due to a variety of merits, e. g., customizing the communication environment.

Blocking

RSMA for Dual-Polarized Massive MIMO Networks: A SIC-Free Approach

no code implementations9 Dec 2022 Arthur S. de Sena, Pedro H. J. Nardelli, Daniel B. da Costa, Petar Popovski, Constantinos B. Papadias, Merouane Debbah

Aiming at overcoming practical issues of successive interference cancellation (SIC), this paper proposes a dual-polarized rate-splitting multiple access (RSMA) technique for a downlink massive multiple-input multiple-output (MIMO) network.

Less Data, More Knowledge: Building Next Generation Semantic Communication Networks

no code implementations25 Nov 2022 Christina Chaccour, Walid Saad, Merouane Debbah, Zhu Han, H. Vincent Poor

In this tutorial, we present the first rigorous vision of a scalable end-to-end semantic communication network that is founded on novel concepts from artificial intelligence (AI), causal reasoning, and communication theory.

Novel Concepts Representation Learning

Dual-Polarized Massive MIMO-RSMA Networks: Tackling Imperfect SIC

no code implementations2 Nov 2022 Arthur Sousa de Sena, Pedro H. J. Nardelli, Daniel Benevides da Costa, Petar Popovski, Constantinos B. Papadias, Merouane Debbah

This paper takes advantage of this additional DoF to alleviate practical issues of successive interference cancellation (SIC) in rate-splitting multiple access (RSMA) schemes.

Semantic-Native Communication: A Simplicial Complex Perspective

no code implementations30 Oct 2022 Qiyang Zhao, Mehdi Bennis, Merouane Debbah, Daniel Benevides da Costa

In this paper, we study semantic communication from a topological space perspective, in which higher-order data semantics live in a simplicial complex.

The Interplay of AI and Digital Twin: Bridging the Gap between Data-Driven and Model-Driven Approaches

no code implementations26 Sep 2022 Lina Bariah, Merouane Debbah

The evolution of network virtualization and native artificial intelligence (AI) paradigms have conceptualized the vision of future wireless networks as a comprehensive entity operating in whole over a digital platform, with smart interaction with the physical domain, paving the way for the blooming of the Digital Twin (DT) concept.

Mixed Reality

Machine Learning and Analytical Power Consumption Models for 5G Base Stations

no code implementations23 Sep 2022 Nicola Piovesan, David Lopez-Perez, Antonio De Domenico, Xinli Geng, Harvey Bao, Merouane Debbah

The energy consumption of the fifth generation(5G) of mobile networks is one of the major concerns of the telecom industry.

Green, Quantized Federated Learning over Wireless Networks: An Energy-Efficient Design

no code implementations19 Jul 2022 Minsu Kim, Walid Saad, Mohammad Mozaffari, Merouane Debbah

In this paper, a green-quantized FL framework, which represents data with a finite precision level in both local training and uplink transmission, is proposed.

Federated Learning Quantization

Environment Sensing Considering the Occlusion Effect: A Multi-View Approach

no code implementations2 Jul 2022 Xin Tong, Zhaoyang Zhang, Yihan Zhang, Zhaohui Yang, Chongwen Huang, Kai-Kit Wong, Merouane Debbah

In this paper, we consider the problem of sensing the environment within a wireless cellular framework.

Curriculum Learning for Goal-Oriented Semantic Communications with a Common Language

no code implementations21 Apr 2022 Mohammad Karimzadeh Farshbafan, Walid Saad, Merouane Debbah

In contrast, in this paper, a holistic goal-oriented semantic communication framework is proposed to enable a speaker and a listener to cooperatively execute a set of sequential tasks in a dynamic environment.

Variational Autoencoders for Reliability Optimization in Multi-Access Edge Computing Networks

no code implementations25 Jan 2022 Arian Ahmadi, Omid Semiari, Mehdi Bennis, Merouane Debbah

In this paper, a novel framework is proposed to optimize the reliability of MEC networks by considering the distribution of E2E service delay, encompassing over-the-air transmission and edge computing latency.

Edge-computing

On the Tradeoff between Energy, Precision, and Accuracy in Federated Quantized Neural Networks

no code implementations15 Nov 2021 Minsu Kim, Walid Saad, Mohammad Mozaffari, Merouane Debbah

In this paper, a quantized FL framework, that represents data with a finite level of precision in both local training and uplink transmission, is proposed.

Federated Learning Quantization

Common Language for Goal-Oriented Semantic Communications: A Curriculum Learning Framework

no code implementations15 Nov 2021 Mohammad Karimzadeh Farshbafan, Walid Saad, Merouane Debbah

In this paper, a comprehensive semantic communications framework is proposed for enabling goal-oriented task execution.

Reinforcement Learning (RL)

Towards Federated Learning-Enabled Visible Light Communication in 6G Systems

no code implementations7 Oct 2021 Shimaa Naser, Lina Bariah, Sami Muhaidat, Mahmoud Al-Qutayri, Ernesto Damiani, Merouane Debbah, Paschalis C. Sofotasios

Nevertheless, concerns pertaining to privacy and communication overhead when sharing raw data of the involved clients with a server constitute major bottlenecks in the implementation of centralized ML techniques.

Federated Learning

Joint Multi-User Communication and Sensing Exploiting Both Signal and Environment Sparsity

no code implementations6 Sep 2021 Xin Tong, Zhaoyang Zhang, Jue Wang, Chongwen Huang, Merouane Debbah

As a potential technology feature for 6G wireless networks, the idea of sensing-communication integration requires the system not only to complete reliable multi-user communication but also to achieve accurate environment sensing.

object-detection Object Detection

Spectrum Learning-Aided Reconfigurable Intelligent Surfaces for 'Green' 6G Networks

no code implementations3 Sep 2021 Bo Yang, Xuelin Cao, Chongwen Huang, Yong Liang Guan, Chau Yuen, Marco Di Renzo, Dusit Niyato, Merouane Debbah, Lajos Hanzo

In the sixth-generation (6G) era, emerging large-scale computing based applications (for example processing enormous amounts of images in real-time in autonomous driving) tend to lead to excessive energy consumption for the end users, whose devices are usually energy-constrained.

Autonomous Driving

Wavenumber-Division Multiplexing in Line-of-Sight Holographic MIMO Communications

no code implementations23 Jun 2021 Luca Sanguinetti, Antonio A. D'Amico, Merouane Debbah

The simplest implementation provides the same spectral efficiency of a singular-value decomposition architecture with water-filling when the receiver size is comparable to the transmission range.

Seven Defining Features of Terahertz (THz) Wireless Systems: A Fellowship of Communication and Sensing

no code implementations15 Feb 2021 Christina Chaccour, Mehdi Naderi Soorki, Walid Saad, Mehdi Bennis, Petar Popovski, Merouane Debbah

Based on these fundamentals, we characterize seven unique defining features of THz wireless systems: 1) Quasi-opticality of the band, 2) THz-tailored wireless architectures, 3) Synergy with lower frequency bands, 4) Joint sensing and communication systems, 5) PHY-layer procedures, 6) Spectrum access techniques, and 7) Real-time network optimization.

Information Theory Information Theory

Multi-hop RIS-Empowered Terahertz Communications: A DRL-based Hybrid Beamforming Design

no code implementations22 Jan 2021 Chongwen Huang, Zhaohui Yang, George C. Alexandropoulos, Kai Xiong, Li Wei, Chau Yuen, Zhaoyang Zhang, Merouane Debbah

We investigate the joint design of digital beamforming matrix at the BS and analog beamforming matrices at the RISs, by leveraging the recent advances in deep reinforcement learning (DRL) to combat the propagation loss.

Predictive Ultra-Reliable Communication: A Survival Analysis Perspective

no code implementations22 Dec 2020 Sumudu Samarakoon, Mehdi Bennis, Walid Saad, Merouane Debbah

Results show that the accuracy of detecting channel blocking events is higher using the model-based method for low to moderate reliability targets requiring low sample complexity.

Survival Analysis Networking and Internet Architecture

Phase Configuration Learning in Wireless Networks with Multiple Reconfigurable Intelligent Surfaces

no code implementations9 Oct 2020 George C. Alexandropoulos, Sumudu Samarakoon, Mehdi Bennis, Merouane Debbah

Reconfigurable Intelligent Surfaces (RISs) are recently gaining remarkable attention as a low-cost, hardware-efficient, and highly scalable technology capable of offering dynamic control of electro-magnetic wave propagation.

Reconfigurable Intelligent Surfaces and Metamaterials: The Potential of Wave Propagation Control for 6G Wireless Communications

no code implementations19 Jun 2020 George C. Alexandropoulos, Geoffroy Lerosey, Merouane Debbah, Mathias Fink

Motivated by the late research excitement on the RIS potential for intelligent EM wave propagation modulation, we describe the status on RIS hardware architectures and present key open challenges and future research directions for RIS design and RIS-empowered 6G wireless communications.

On the Optimality of Reconfigurable Intelligent Surfaces (RISs): Passive Beamforming, Modulation, and Resource Allocation

no code implementations2 Oct 2019 Minchae Jung, Walid Saad, Merouane Debbah, Choong Seon Hong

In this paper, the asymptotic optimality of achievable rate in a downlink RIS system is analyzed under a practical RIS environment with its associated limitations.

Information Theory Signal Processing Information Theory

Distributed Power Control for Large Energy Harvesting Networks: A Multi-Agent Deep Reinforcement Learning Approach

no code implementations1 Apr 2019 Mohit K. Sharma, Alessio Zappone, Mohamad Assaad, Merouane Debbah, Spyridon Vassilaras

In the proposed framework, we model the online power control problem as a discrete-time mean-field game (MFG), and analytically show that the MFG has a unique stationary solution.

Multi-agent Reinforcement Learning reinforcement-learning +1

Deep Learning Based Online Power Control for Large Energy Harvesting Networks

no code implementations8 Mar 2019 Mohit K. Sharma, Alessio Zappone, Merouane Debbah, Mohamad Assaad

In this paper, we propose a deep learning based approach to design online power control policies for large EH networks, which are often intractable stochastic control problems.

A Globally Optimal Energy-Efficient Power Control Framework and its Efficient Implementation in Wireless Interference Networks

1 code implementation17 Dec 2018 Bho Matthiesen, Alessio Zappone, Karl-L. Besser, Eduard A. Jorswieck, Merouane Debbah

Specifically, thanks to its reduced complexity, the proposed method can be used to train an artificial neural network to predict the optimal resource allocation.

User Association and Load Balancing for Massive MIMO through Deep Learning

no code implementations17 Dec 2018 Alessio Zappone, Luca Sanguinetti, Merouane Debbah

This work investigates the use of deep learning to perform user cell association for sum-rate maximization in Massive MIMO networks.

Deep Learning Power Allocation in Massive MIMO

no code implementations10 Dec 2018 Luca Sanguinetti, Alessio Zappone, Merouane Debbah

The use of deep learning significantly improves the complexity-performance trade-off of power allocation, compared to traditional optimization-oriented methods.

Distributed Federated Learning for Ultra-Reliable Low-Latency Vehicular Communications

no code implementations21 Jul 2018 Sumudu Samarakoon, Mehdi Bennis, Walid Saad, Merouane Debbah

In this paper, the problem of joint power and resource allocation (JPRA) for ultra-reliable low-latency communication (URLLC) in vehicular networks is studied.

Information Theory Information Theory

Problem-Adapted Artificial Intelligence for Online Network Optimization

no code implementations30 May 2018 Spyridon Vassilaras, Luigi Vigneri, Nikolaos Liakopoulos, Georgios S. Paschos, Apostolos Destounis, Thrasyvoulos Spyropoulos, Merouane Debbah

To this end, we propose the framework of Online Network Optimization (ONO), which seeks to maintain both agile and efficient control over time, using an arsenal of data-driven, online learning, and AI-based techniques.

Management

Federated Learning for Ultra-Reliable Low-Latency V2V Communications

no code implementations11 May 2018 Sumudu Samarakoon, Mehdi Bennis, Walid Saad, Merouane Debbah

It is shown that FL enables the proposed distributed method to estimate the tail distribution of queues with an accuracy that is very close to a centralized solution with up to 79\% reductions in the amount of data that need to be exchanged.

Federated Learning

Cannot find the paper you are looking for? You can Submit a new open access paper.