One of the prerequisites for the development of telecommunication services is the understanding of the propagation of the waves, either acoustic, electromagnetic, radio or light waves, which are used for the transmission of INformation. In this work, we shall limit ourselves to the study of radio waves: this term apply to the electromagnetic waves used in radio communications. Their frequency spectrum is very broad, and is divided into the following frequency bands : ELF waves (f < 3 kHz), VLF (3-30 kHz), LF waves (30-300 kHz), MF waves (300-3000 kHz), HF (3-30 MHz), VHF waves (30-300 MHz), UHF waves (300-3000 MHz), SHF waves (3-30 GHz), EHF waves (30-300 GHz) and sub- EHF waves (300-3000 GHz).
标签： Propagation Radio Wave
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The unguided transmission of INformation using electromagnetic waves at radio frequency (RF) is often referred to as wireless communications, the first demonstration of which took place at the end of the 19th cen- tury and is attributed to Hertz. The technology was, shortly thereafter, commercialised by, amongst others, Marconi in one of the first wire- less communication systems, i.e., wireless telegraphy. In the first half of the 20th century the technology was developed further to enable more than the mere transmission of Morse code. This first resulted in uni- directional radio broadcasting and several years later also in television broadcasting.
标签： Imperfections RF
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The following sections profile many of the vendors in the NFV market. The individual profiles were created through a collaborative effort between SDNCentral’s Research Team and the Vendor’s product experts. SDNCentral worked under the assumption the INformation provided by the vendors was factual, auditing the submissions only to remove unverifiable claims and hyperbole. Extended profiles can be viewed online. While every attempt has been made to validate the capabilities listed in the profiles, SDNCentral advises end users to verify the veracity of each claim for themselves in their actual deployment environments. SDNCentral cannot be held liable for unexpected operations, damages or incorrect operation due to any inaccuracies listed here. SDNCentral welcomes feedback and additional INformation from end users based on their real-world experiences with the products and technologies listed. The SDNCentral research team can be reached at
标签： SDxCentral-Mega-NFV-Report
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This paper presents a Hidden Markov Model (HMM)-based speech enhancement method, aiming at reducing non-stationary noise from speech signals. The system is based on the assumption that the speech and the noise are additive and uncorrelated. Cepstral features are used to extract statistical INformation from both the speech and the noise. A-priori statistical INformation is collected from long training sequences into ergodic hidden Markov models. Given the ergodic models for the speech and the noise, a compensated speech-noise model is created by means of parallel model combination, using a log-normal approximation. During the compensation, the mean of every mixture in the speech and noise model is stored. The stored means are then used in the enhancement process to create the most likely speech and noise power spectral distributions using the forward algorithm combined with mixture probability. The distributions are used to generate a Wiener filter for every observation. The paper includes a performance evaluation of the speech enhancer for stationary as well as non-stationary noise environment.
标签： Telecommunications Processing Signal for
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The idea for this book was born during one of my project-related trips to the beautiful city of Hangzhou in China, where in the role of Chief Architect I had to guide a team of very young, very smart and extremely dedicated software developers and verification engineers. Soon it became clear that as eager as the team was to jump into the coding, it did not have any experience in system architecture and design and if I did not want to spend all my time in constant travel between San Francisco and Hangzhou, the only option was to groom a number of local junior architects. Logically, one of the first questions being asked by these carefully selected future architects was whether I could recommend a book or other learning material that could speed up the learning cycle. I could not. Of course, there were many books on various related topics, but many of them were too old and most of the updated INformation was either somewhere on the Internet dispersed between many sites and online magazines, or buried in my brain along with many years of experience of system architecture.
标签： Telecommunication Gateways System Design for
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Before I can present design concepts or tactical wireless communications and network challenges, I feel the need to mention the challenges of writing for a field where some INformation is not available for public domain and cannot be included in this book’s context. Another challenge is the use of military jargon and the extensive number of abbreviations (and abbreviations of abbreviations!) in the field. Engineering books are naturally dry, and I have attempted to make it light by presenting the concepts in layman’s terms before diving into the technical details. I am structuring this book in such a way as to make it useful for a specialized graduate course in tactical communications and networking, or as a reference book in the field.
标签： Communications Tactical Networks Wireless and
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The use of mobile devices now surpasses that of traditional computers: wireless users will hence soon be demanding the same rich multimedia services on their mobile devices that they have on their desktop personal computers. In addition, new services will be added, especially related with their mobile needs, such as location-based INformation services.
标签： Communications Technology Wireless Trends in
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A mobile ad-hoc network (MANET) is formed by multiple moving nodes equipped with wireless transceivers. The mobile nodes communicate with each other through multi-hop wireless links, where every node can transmit and receive INformation. Mobile ad-hoc networks have become increasingly important in areas where deployment of communications infrastructure is difficult.
标签： Telecommunications Modeling
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Rapid progress in INformation and communications technology (ICT) induces improved and new telecommunications services and contributes greatly to society in general and to vendors and network and service providers. In addition to existing services such as telephony or leased line services, spread of the Internet, the Internet Protocol (IP) phone, and new communications services like IPTV are making great progress with the development of digital subscriber lines (DSL) and high - speed communications technologies like fi ber to the home (FTTH).
标签： Telecommunications Networks
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When 3GPP started standardizing the IMS a few years ago, most analysts expected the number of IMS deploymentsto grow dramatically as soon the initial IMS specifications were ready (3GPP Release 5 was functionallyfrozenin the first half of 2002and completedshortly after that). While those predictions have proven to be too aggressive owing to a number of upheavals hitting the ICT (INformation and Communications Technologies) sector, we are now seeing more and more commercial IMS-based service offerings in the market. At the time of writing (May 2008), there are over 30 commercial IMS networks running live traffic, addingup to over10million IMS users aroundthe world; the IMS is beingdeployedglobally. In addition, there are plenty of ongoing market activities; it is estimated that over 130 IMS contracts have been awarded to all IMS manufacturers. The number of IMS users will grow substantially as these awarded contracts are launched commercially. At the same time, the number of IMS users in presently deployed networks is steadily increasing as new services are introduced and operators running these networks migrate their non-IMS users to their IMS networks.
标签： Multimedia Subsystem The IMS 3G IP
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