Author: Mischa Dohler
Publisher: John Wiley & Sons
ISBN: 9780470740064
Category : Technology & Engineering
Languages : en
Pages : 464
Book Description
Facilitating Cooperation for Wireless Systems Cooperative Communications: Hardware, Channel & PHY focuses on issues pertaining to the PHY layer of wireless communication networks, offering a rigorous taxonomy of this dispersed field, along with a range of application scenarios for cooperative and distributed schemes, demonstrating how these techniques can be employed. The authors discuss hardware, complexity and power consumption issues, which are vital for understanding what can be realized at the PHY layer, showing how wireless channel models differ from more traditional models, and highlighting the reliance of PHY algorithm performance on the underlying channel models. Numerous transparent and regenerative relaying protocols are described in detail for a variety of transparent and regenerative cooperative schemes. Key Features: Introduces background, concepts, applications, milestones and thorough taxonomy Identifies the potential in this emerging technology applied to e.g. LTE/WiMAX, WSN Discusses latest wireless channel models for transparent and regenerative protocols Addresses the fundamentals as well as latest emerging PHY protocols Introduces transparent distributed STBC, STTC, multiplexing and beamforming protocols Quantifies regenerative distributed space-time, channel and network coding protocols Explores system optimization, such as distributed power allocation and relay selection Introduces and compares analog and digital hardware architectures Quantifies complexity, memory and power consumption of 3G UMTS & 4G LTE/WiMAX relay Highlights future research challenges within the cooperative communications field This book is an invaluable guide for professionals and researchers in communications fields. It will also be of interest to graduates of communications and electronic engineering courses. It forms part of an entire series dedicated to cooperative wireless systems.
Cooperative Communications
Author: Mischa Dohler
Publisher: John Wiley & Sons
ISBN: 9780470740064
Category : Technology & Engineering
Languages : en
Pages : 464
Book Description
Facilitating Cooperation for Wireless Systems Cooperative Communications: Hardware, Channel & PHY focuses on issues pertaining to the PHY layer of wireless communication networks, offering a rigorous taxonomy of this dispersed field, along with a range of application scenarios for cooperative and distributed schemes, demonstrating how these techniques can be employed. The authors discuss hardware, complexity and power consumption issues, which are vital for understanding what can be realized at the PHY layer, showing how wireless channel models differ from more traditional models, and highlighting the reliance of PHY algorithm performance on the underlying channel models. Numerous transparent and regenerative relaying protocols are described in detail for a variety of transparent and regenerative cooperative schemes. Key Features: Introduces background, concepts, applications, milestones and thorough taxonomy Identifies the potential in this emerging technology applied to e.g. LTE/WiMAX, WSN Discusses latest wireless channel models for transparent and regenerative protocols Addresses the fundamentals as well as latest emerging PHY protocols Introduces transparent distributed STBC, STTC, multiplexing and beamforming protocols Quantifies regenerative distributed space-time, channel and network coding protocols Explores system optimization, such as distributed power allocation and relay selection Introduces and compares analog and digital hardware architectures Quantifies complexity, memory and power consumption of 3G UMTS & 4G LTE/WiMAX relay Highlights future research challenges within the cooperative communications field This book is an invaluable guide for professionals and researchers in communications fields. It will also be of interest to graduates of communications and electronic engineering courses. It forms part of an entire series dedicated to cooperative wireless systems.
Publisher: John Wiley & Sons
ISBN: 9780470740064
Category : Technology & Engineering
Languages : en
Pages : 464
Book Description
Facilitating Cooperation for Wireless Systems Cooperative Communications: Hardware, Channel & PHY focuses on issues pertaining to the PHY layer of wireless communication networks, offering a rigorous taxonomy of this dispersed field, along with a range of application scenarios for cooperative and distributed schemes, demonstrating how these techniques can be employed. The authors discuss hardware, complexity and power consumption issues, which are vital for understanding what can be realized at the PHY layer, showing how wireless channel models differ from more traditional models, and highlighting the reliance of PHY algorithm performance on the underlying channel models. Numerous transparent and regenerative relaying protocols are described in detail for a variety of transparent and regenerative cooperative schemes. Key Features: Introduces background, concepts, applications, milestones and thorough taxonomy Identifies the potential in this emerging technology applied to e.g. LTE/WiMAX, WSN Discusses latest wireless channel models for transparent and regenerative protocols Addresses the fundamentals as well as latest emerging PHY protocols Introduces transparent distributed STBC, STTC, multiplexing and beamforming protocols Quantifies regenerative distributed space-time, channel and network coding protocols Explores system optimization, such as distributed power allocation and relay selection Introduces and compares analog and digital hardware architectures Quantifies complexity, memory and power consumption of 3G UMTS & 4G LTE/WiMAX relay Highlights future research challenges within the cooperative communications field This book is an invaluable guide for professionals and researchers in communications fields. It will also be of interest to graduates of communications and electronic engineering courses. It forms part of an entire series dedicated to cooperative wireless systems.
Networking 2006
Author: Fernando Boavida
Publisher: Springer Science & Business Media
ISBN: 3540341927
Category : Computers
Languages : en
Pages : 1301
Book Description
Here are the refereed proceedings of the 5th International IFIP-TC6 Networking Conference, NETWORKING 2006. The 88 revised full papers and 31 poster papers are organized in topical sections on caching and content management, mobile ad-hoc networks, mobility/handoff, monitoring/measurements, multicast, multimedia, optical networks, peer-to-peer, resource management and QoS, routing, topology and location awareness, traffic engineering, transport protocols, wireless networks, and wireless sensor networks.
Publisher: Springer Science & Business Media
ISBN: 3540341927
Category : Computers
Languages : en
Pages : 1301
Book Description
Here are the refereed proceedings of the 5th International IFIP-TC6 Networking Conference, NETWORKING 2006. The 88 revised full papers and 31 poster papers are organized in topical sections on caching and content management, mobile ad-hoc networks, mobility/handoff, monitoring/measurements, multicast, multimedia, optical networks, peer-to-peer, resource management and QoS, routing, topology and location awareness, traffic engineering, transport protocols, wireless networks, and wireless sensor networks.
Handover in DVB-H
Author: Xiaodong Yang
Publisher: Springer Science & Business Media
ISBN: 3540786309
Category : Technology & Engineering
Languages : en
Pages : 177
Book Description
“European industry has already developed successful standards in the past, and I am very con?dent that on the basis of DVB-H, Mobile TV services can developtheeconomiesofscaletheyneedfortake-upacrossEuropeandaround the world,” With these words of EU’s Telecom Commissioner Viviane Reding, DVB-H is destined to be a dominating mobile TV technology in Europe and even in the world. I was ?rst getting in touch with the DVB technology when I was doing my PhD research in Brunel University in UK in 2002. At that time DVB-T was already a mature and widely used digital broadcast technology and anyone could easily buy a DVB-T receiver in the market to try the digital broadcast signals that have been already broadcasted in UK since 1998. Then the DVB technology world changed dramatically. As a more ?exible and robust terr- trial broadcast system targeting handsets, DVB-H was developed based on DVB-T. In 2003 the DVB-H community were continuously working to ?n- ize the standard. Finally in November 2004 DVB-H was adopted as an ETSI standard EN 302 304. I was lucky to see all these changes when I was doing my PhD research in DVB technology. And I was very proud to be involved in the di?erent DVB-H research projects since the beginning of the DVB-H standard development stage. I was also lucky enough that I am one of the ?rst persons who ?nished PhD degree by focusing on DVB-H research.
Publisher: Springer Science & Business Media
ISBN: 3540786309
Category : Technology & Engineering
Languages : en
Pages : 177
Book Description
“European industry has already developed successful standards in the past, and I am very con?dent that on the basis of DVB-H, Mobile TV services can developtheeconomiesofscaletheyneedfortake-upacrossEuropeandaround the world,” With these words of EU’s Telecom Commissioner Viviane Reding, DVB-H is destined to be a dominating mobile TV technology in Europe and even in the world. I was ?rst getting in touch with the DVB technology when I was doing my PhD research in Brunel University in UK in 2002. At that time DVB-T was already a mature and widely used digital broadcast technology and anyone could easily buy a DVB-T receiver in the market to try the digital broadcast signals that have been already broadcasted in UK since 1998. Then the DVB technology world changed dramatically. As a more ?exible and robust terr- trial broadcast system targeting handsets, DVB-H was developed based on DVB-T. In 2003 the DVB-H community were continuously working to ?n- ize the standard. Finally in November 2004 DVB-H was adopted as an ETSI standard EN 302 304. I was lucky to see all these changes when I was doing my PhD research in DVB technology. And I was very proud to be involved in the di?erent DVB-H research projects since the beginning of the DVB-H standard development stage. I was also lucky enough that I am one of the ?rst persons who ?nished PhD degree by focusing on DVB-H research.
Advances in Computing and Communications, Part I
Author: Ajith Abraham
Publisher: Springer Science & Business Media
ISBN: 3642227082
Category : Computers
Languages : en
Pages : 771
Book Description
This volume is the first part of a four-volume set (CCIS 190, CCIS 191, CCIS 192, CCIS 193), which constitutes the refereed proceedings of the First International Conference on Computing and Communications, ACC 2011, held in Kochi, India, in July 2011. The 68 revised full papers presented in this volume were carefully reviewed and selected from a large number of submissions. The papers are organized in topical sections on ad hoc networks; advanced micro architecture techniques; autonomic and context-aware computing; bioinformatics and bio-computing; cloud, cluster, grid and P2P computing; cognitive radio and cognitive networks; cyber forensics; database and information systems.
Publisher: Springer Science & Business Media
ISBN: 3642227082
Category : Computers
Languages : en
Pages : 771
Book Description
This volume is the first part of a four-volume set (CCIS 190, CCIS 191, CCIS 192, CCIS 193), which constitutes the refereed proceedings of the First International Conference on Computing and Communications, ACC 2011, held in Kochi, India, in July 2011. The 68 revised full papers presented in this volume were carefully reviewed and selected from a large number of submissions. The papers are organized in topical sections on ad hoc networks; advanced micro architecture techniques; autonomic and context-aware computing; bioinformatics and bio-computing; cloud, cluster, grid and P2P computing; cognitive radio and cognitive networks; cyber forensics; database and information systems.
Ultra-Wideband and 60 GHz Communications for Biomedical Applications
Author: Mehmet R. Yuce
Publisher: Springer Science & Business Media
ISBN: 1461488966
Category : Medical
Languages : en
Pages : 265
Book Description
This book investigates the design of devices, systems, and circuits for medical applications using the two recently established frequency bands: ultra-wideband (3.1-10.6 GHz) and 60 GHz ISM band. These two bands provide the largest bandwidths available for communication technologies and present many attractive opportunities for medical applications. The applications of these bands in healthcare are wireless body area network (WBAN), medical imaging, biomedical sensing, wearable and implantable devices, fast medical device connectivity, video data transmission, and vital signs monitoring. The recent technological advances and developments proposed or used in medicine based on these two bands are covered. The book introduces possible solutions and design techniques to efficiently implement these systems in medical environment. All individual chapters are written by leading experts in their fields. Contributions by authors are on various applications of ultra-wideband and the 60 GHz ISM band including circuit implementation, UWB and 60 GHz signal transmission around and in-body, antenna design solution, hardware implementation of body sensors, UWB transceiver design, 60 GHz transceiver design, UWB radar for contactless respiratory monitoring, and ultra-wideband based medical Imaging. The book will be a key resource for medical professionals, bio-medical engineers, and graduate and senior undergraduate students in computer, electrical, electronic and biomedical engineering disciplines.
Publisher: Springer Science & Business Media
ISBN: 1461488966
Category : Medical
Languages : en
Pages : 265
Book Description
This book investigates the design of devices, systems, and circuits for medical applications using the two recently established frequency bands: ultra-wideband (3.1-10.6 GHz) and 60 GHz ISM band. These two bands provide the largest bandwidths available for communication technologies and present many attractive opportunities for medical applications. The applications of these bands in healthcare are wireless body area network (WBAN), medical imaging, biomedical sensing, wearable and implantable devices, fast medical device connectivity, video data transmission, and vital signs monitoring. The recent technological advances and developments proposed or used in medicine based on these two bands are covered. The book introduces possible solutions and design techniques to efficiently implement these systems in medical environment. All individual chapters are written by leading experts in their fields. Contributions by authors are on various applications of ultra-wideband and the 60 GHz ISM band including circuit implementation, UWB and 60 GHz signal transmission around and in-body, antenna design solution, hardware implementation of body sensors, UWB transceiver design, 60 GHz transceiver design, UWB radar for contactless respiratory monitoring, and ultra-wideband based medical Imaging. The book will be a key resource for medical professionals, bio-medical engineers, and graduate and senior undergraduate students in computer, electrical, electronic and biomedical engineering disciplines.
5G Physical Layer
Author: Ali Zaidi
Publisher: Academic Press
ISBN: 012814579X
Category : Computers
Languages : en
Pages : 324
Book Description
5G Physical Layer: Principles, Models and Technology Components explains fundamental physical layer design principles, models and components for the 5G new radio access technology – 5G New Radio (NR). The physical layer models include radio wave propagation and hardware impairments for the full range of frequencies considered for the 5G NR (up to 100 GHz). The physical layer technologies include flexible multi-carrier waveforms, advanced multi-antenna solutions, and channel coding schemes for a wide range of services, deployments, and frequencies envisioned for 5G and beyond. A MATLAB-based link level simulator is included to explore various design options. 5G Physical Layer is very suitable for wireless system designers and researchers: basic understanding of communication theory and signal processing is assumed, but familiarity with 4G and 5G standards is not required. With this book the reader will learn: - The fundamentals of the 5G NR physical layer (waveform, modulation, numerology, channel codes, and multi-antenna schemes). - Why certain PHY technologies have been adopted for the 5G NR. - The fundamental physical limitations imposed by radio wave propagation and hardware impairments. - How the fundamental 5G NR physical layer functionalities (e.g., parameters/methods/schemes) should be realized. The content includes: - A global view of 5G development – concept, standardization, spectrum allocation, use cases and requirements, trials, and future commercial deployments. - The fundamentals behind the 5G NR physical layer specification in 3GPP. - Radio wave propagation and channel modeling for 5G and beyond. - Modeling of hardware impairments for future base stations and devices. - Flexible multi-carrier waveforms, multi-antenna solutions, and channel coding schemes for 5G and beyond. - A simulator including hardware impairments, radio propagation, and various waveforms. Ali Zaidi is a strategic product manager at Ericsson, Sweden. Fredrik Athley is a senior researcher at Ericsson, Sweden. Jonas Medbo and Ulf Gustavsson are senior specialists at Ericsson, Sweden. Xiaoming Chen is a professor at Xi'an Jiaotong University, China. Giuseppe Durisi is a professor at Chalmers University of Technology, Sweden, and a guest researcher at Ericsson, Sweden.
Publisher: Academic Press
ISBN: 012814579X
Category : Computers
Languages : en
Pages : 324
Book Description
5G Physical Layer: Principles, Models and Technology Components explains fundamental physical layer design principles, models and components for the 5G new radio access technology – 5G New Radio (NR). The physical layer models include radio wave propagation and hardware impairments for the full range of frequencies considered for the 5G NR (up to 100 GHz). The physical layer technologies include flexible multi-carrier waveforms, advanced multi-antenna solutions, and channel coding schemes for a wide range of services, deployments, and frequencies envisioned for 5G and beyond. A MATLAB-based link level simulator is included to explore various design options. 5G Physical Layer is very suitable for wireless system designers and researchers: basic understanding of communication theory and signal processing is assumed, but familiarity with 4G and 5G standards is not required. With this book the reader will learn: - The fundamentals of the 5G NR physical layer (waveform, modulation, numerology, channel codes, and multi-antenna schemes). - Why certain PHY technologies have been adopted for the 5G NR. - The fundamental physical limitations imposed by radio wave propagation and hardware impairments. - How the fundamental 5G NR physical layer functionalities (e.g., parameters/methods/schemes) should be realized. The content includes: - A global view of 5G development – concept, standardization, spectrum allocation, use cases and requirements, trials, and future commercial deployments. - The fundamentals behind the 5G NR physical layer specification in 3GPP. - Radio wave propagation and channel modeling for 5G and beyond. - Modeling of hardware impairments for future base stations and devices. - Flexible multi-carrier waveforms, multi-antenna solutions, and channel coding schemes for 5G and beyond. - A simulator including hardware impairments, radio propagation, and various waveforms. Ali Zaidi is a strategic product manager at Ericsson, Sweden. Fredrik Athley is a senior researcher at Ericsson, Sweden. Jonas Medbo and Ulf Gustavsson are senior specialists at Ericsson, Sweden. Xiaoming Chen is a professor at Xi'an Jiaotong University, China. Giuseppe Durisi is a professor at Chalmers University of Technology, Sweden, and a guest researcher at Ericsson, Sweden.
Antennas and Propagation for Body-Centric Wireless Communications, Second Edition
Author: Peter S. Hall
Publisher: Artech House
ISBN: 1608073769
Category : Technology & Engineering
Languages : en
Pages : 404
Book Description
Now in a newly updated and revised edition, this timely resource provides you with complete and current details on the theory, design, and applications of wireless antennas for on-body electronic systems. The Second Edition offers readers brand new material on advances in physical phantom design and production, recent developments in simulation methods and numerical phantoms, descriptions of methods for simulation of moving bodies, and the use of the body as a transmission channel. You also find a completely revised chapter on channel characterization and antenna design at microwave frequencies. This cutting-edge volume brings you the state-of-the-art in existing applications like Bluetooth headsets together with detailed treatment of techniques, tools, and challenges in developing on-body antennas for an array of medical, emergency response, law enforcement, personal entertainment, and military applications on the horizon. The book briefs you on energy propagation around and into the body and how to estimate performance of on-body wireless links, and then dives into the nuts-and-bolts of designing antenna systems that deliver the goods. It covers on-body communication channels at microwave frequency bands and at low frequency bands, as well as ultra wideband systems for WPANs and WBANs. You get details on body-centric UWB antennas and channels, as well as advances in wearable mobile, EBG, and smart fabricù antennas for cellular and WLAN communications. Chapters on telemedicine applications, such as remote diagnoses, and implantable medical devices cover crucial propagation issues and other obstacles that need to be addressed. Rounding out the coverage is a section on antenna design for body-sensor networks and their emerging military and space applications. Packed with hands-on guidance from noted experts, this volume will be indispensable for your efforts in designing and improving body-centric communication systems.
Publisher: Artech House
ISBN: 1608073769
Category : Technology & Engineering
Languages : en
Pages : 404
Book Description
Now in a newly updated and revised edition, this timely resource provides you with complete and current details on the theory, design, and applications of wireless antennas for on-body electronic systems. The Second Edition offers readers brand new material on advances in physical phantom design and production, recent developments in simulation methods and numerical phantoms, descriptions of methods for simulation of moving bodies, and the use of the body as a transmission channel. You also find a completely revised chapter on channel characterization and antenna design at microwave frequencies. This cutting-edge volume brings you the state-of-the-art in existing applications like Bluetooth headsets together with detailed treatment of techniques, tools, and challenges in developing on-body antennas for an array of medical, emergency response, law enforcement, personal entertainment, and military applications on the horizon. The book briefs you on energy propagation around and into the body and how to estimate performance of on-body wireless links, and then dives into the nuts-and-bolts of designing antenna systems that deliver the goods. It covers on-body communication channels at microwave frequency bands and at low frequency bands, as well as ultra wideband systems for WPANs and WBANs. You get details on body-centric UWB antennas and channels, as well as advances in wearable mobile, EBG, and smart fabricù antennas for cellular and WLAN communications. Chapters on telemedicine applications, such as remote diagnoses, and implantable medical devices cover crucial propagation issues and other obstacles that need to be addressed. Rounding out the coverage is a section on antenna design for body-sensor networks and their emerging military and space applications. Packed with hands-on guidance from noted experts, this volume will be indispensable for your efforts in designing and improving body-centric communication systems.
Advanced Computing in Industrial Mathematics
Author: Krassimir Georgiev
Publisher: Springer
ISBN: 3319972774
Category : Technology & Engineering
Languages : en
Pages : 440
Book Description
This book gathers the peer-reviewed proceedings of the 12th Annual Meeting of the Bulgarian Section of the Society for Industrial and Applied Mathematics, BGSIAM’17, held in Sofia, Bulgaria, in December 2017. The general theme of BGSIAM’17 was industrial and applied mathematics, with a particular focus on: high-performance computing, numerical methods and algorithms, analysis of partial differential equations and their applications, mathematical biology, control and uncertain systems, stochastic models, molecular dynamics, neural networks, genetic algorithms, metaheuristics for optimization problems, generalized nets, and Big Data.
Publisher: Springer
ISBN: 3319972774
Category : Technology & Engineering
Languages : en
Pages : 440
Book Description
This book gathers the peer-reviewed proceedings of the 12th Annual Meeting of the Bulgarian Section of the Society for Industrial and Applied Mathematics, BGSIAM’17, held in Sofia, Bulgaria, in December 2017. The general theme of BGSIAM’17 was industrial and applied mathematics, with a particular focus on: high-performance computing, numerical methods and algorithms, analysis of partial differential equations and their applications, mathematical biology, control and uncertain systems, stochastic models, molecular dynamics, neural networks, genetic algorithms, metaheuristics for optimization problems, generalized nets, and Big Data.
A Study of Black Hole Attack Solutions
Author: Iraj Sadegh Amiri
Publisher: Syngress
ISBN: 0128053798
Category : Computers
Languages : en
Pages : 124
Book Description
Mobile Ad Hoc Networks (MANETs) are a popular form of network for data transfer due to the fact that they are dynamic, require no fixed infrastructure, and are scalable. However, MANETs are particularly susceptible to several different types of widely perpetrated cyberattack. One of the most common hacks aimed at MANETs is the Black Hole attack, in which a particular node within the network displays itself as having the shortest path for the node whose packets it wants to intercept. Once the packets are drawn to the Black Hole, they are then dropped instead of relayed, and the communication of the MANET is thereby disrupted, without knowledge of the other nodes in the network. Due to the sophistication of the Black Hole attack, there has been a lot of research conducted on how to detect it and prevent it. The authors of this short format title provide their research results on providing an effective solution to Black Hole attacks, including introduction of new MANET routing protocols that can be implemented in order to improve detection accuracy and network parameters such as total dropped packets, end-to-end delay, packet delivery ratio, and routing request overhead. - Elaborates on the basics of wireless networks, MANETs - Explains the significance behind the need of wireless networks and MANET security - Understand MANET routing protocols, namely the ADOV method
Publisher: Syngress
ISBN: 0128053798
Category : Computers
Languages : en
Pages : 124
Book Description
Mobile Ad Hoc Networks (MANETs) are a popular form of network for data transfer due to the fact that they are dynamic, require no fixed infrastructure, and are scalable. However, MANETs are particularly susceptible to several different types of widely perpetrated cyberattack. One of the most common hacks aimed at MANETs is the Black Hole attack, in which a particular node within the network displays itself as having the shortest path for the node whose packets it wants to intercept. Once the packets are drawn to the Black Hole, they are then dropped instead of relayed, and the communication of the MANET is thereby disrupted, without knowledge of the other nodes in the network. Due to the sophistication of the Black Hole attack, there has been a lot of research conducted on how to detect it and prevent it. The authors of this short format title provide their research results on providing an effective solution to Black Hole attacks, including introduction of new MANET routing protocols that can be implemented in order to improve detection accuracy and network parameters such as total dropped packets, end-to-end delay, packet delivery ratio, and routing request overhead. - Elaborates on the basics of wireless networks, MANETs - Explains the significance behind the need of wireless networks and MANET security - Understand MANET routing protocols, namely the ADOV method
Multidisciplinary Perspectives in Cryptology and Information Security
Author: Sadkhan Al Maliky, Sattar B.
Publisher: IGI Global
ISBN: 1466658096
Category : Computers
Languages : en
Pages : 463
Book Description
With the prevalence of digital information, IT professionals have encountered new challenges regarding data security. In an effort to address these challenges and offer solutions for securing digital information, new research on cryptology methods is essential. Multidisciplinary Perspectives in Cryptology and Information Security considers an array of multidisciplinary applications and research developments in the field of cryptology and communication security. This publication offers a comprehensive, in-depth analysis of encryption solutions and will be of particular interest to IT professionals, cryptologists, and researchers in the field.
Publisher: IGI Global
ISBN: 1466658096
Category : Computers
Languages : en
Pages : 463
Book Description
With the prevalence of digital information, IT professionals have encountered new challenges regarding data security. In an effort to address these challenges and offer solutions for securing digital information, new research on cryptology methods is essential. Multidisciplinary Perspectives in Cryptology and Information Security considers an array of multidisciplinary applications and research developments in the field of cryptology and communication security. This publication offers a comprehensive, in-depth analysis of encryption solutions and will be of particular interest to IT professionals, cryptologists, and researchers in the field.