Convergence between the two largest networks (Telecom and IP) is taking place very rapidly and at diff erent levels: (1) network level: unifi cation of IP networks with traditional Telecom networks through evolving standards (Session Initiation Protocol (SIP), Realtime Transfer Protocol (RTP), SS7, 3G) to support interopera- bility; (2) service level: traditional Telecom services like voice calls are being provi- sioned on the IP backbone (VoIP), while traditional IP services (most data-driven services such as multimedia, browsing, chatting, gaming, etc.) are accessible over the Telecom network.
标签： Platforms Delivery Service
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Short-range communications is one of the most relevant as well as diversified fields of en- deavour in wireless communications. As such, it has been a subject of intense research and development worldwide, particularly in the last decade. There is no reason to believe that this trend will decline. On the contrary, the rapidly crystallizing vision of a hyper-connected world will certainly strengthen the role of short-range communications in the future. Concepts such as wireless social networks, Internet of things, car communications, home and office network- ing, wireless grids and personal communications heavily rely on short-range communications technology.
标签： Communications Short-Range Wireless
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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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Software Radio (SR) is one of the most important emerging technologies for the future of wireless communication services. By moving radio functionality into software, it promises to give flexible radio systems that are multi-service, multi- standard, multi-band, reconfigurable and reprogrammable by software. Today’s radios are matched to a particular class of signals that are well defined bytheircarrierfrequencies,modulationformatsandbandwidths.Aradiotransmitter today can only up convert signals with well-defined bandwidths over defined center frequencies, while, on the other side of the communication chain, a radio receiver can only down convert well-defined signal bandwidths, transmitted over specified carrier frequencies.
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Radio frequency spectrum is a scarce and critical natural resource that is utilized for many services including surveillance, navigation, communication, and broadcast- ing. Recent years have seen tremendous growth in the use of spectrum especially by commercial cellular operators. Ubiquitous use of smartphones and tablets is one of the reasons behind an all-time high utilization of spectrum. As a result, cellular operators are experiencing a shortage of radio spectrum to meet bandwidth demands of users. On the other hand, spectrum measurements have shown that much spectrum not held by cellular operators is underutilized even in dense urban areas. This has motivated shared access to spectrum by secondary systems with no or minimal impact on incumbent systems. Spectrum sharing is a promising approach to solve the problem of spectrum congestion as it allows cellular operators access to more spectrum in order to satisfy the ever-growing bandwidth demands of commercial users.
标签： Spectrum Sharing Between Radars
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A wireless communication network can be viewed as a collection of nodes, located in some domain, which can in turn be transmitters or receivers (depending on the network considered, nodes may be mobile users, base stations in a cellular network, access points of a WiFi mesh etc.). At a given time, several nodes transmit simultaneously, each toward its own receiver. Each transmitter–receiver pair requires its own wireless link. The signal received from the link transmitter may be jammed by the signals received from the other transmitters. Even in the simplest model where the signal power radiated from a point decays in an isotropic way with Euclidean distance, the geometry of the locations of the nodes plays a key role since it determines the signal to interference and noise ratio (SINR) at each receiver and hence the possibility of establishing simultaneously this collection of links at a given bit rate. The interference seen by a receiver is the sum of the signal powers received from all transmitters, except its own transmitter.
标签： Stochastic Geometry Networks Wireless Volume and II
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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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The ability to analyze system or circuit behavior is one of the key requirements for successful design. To put an idea to work, a designer needs both the knowledge and tools for analyzing the behavior of that new system architecture or that experi- mental circuit topology. Design decisions are grounded on the results obtained from analysis.
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Wireless communications has become a field of enormous scientific and economic interest. Recent success stories include 2G and 3G cellular voice and data services (e.g., GSM and UMTS), wireless local area networks (WiFi/IEEE 802.11x), wireless broadband access (WiMAX/IEEE 802.16x), and digital broadcast systems (DVB, DAB, DRM). On the physical layer side, traditional designs typically assume that the radio channel remains constant for the duration of a data block. However, researchers and system designers are increasingly shifting their attention to channels that may vary within a block. In addition to time dispersion caused by multipath propagation, these rapidly time-varying channels feature frequency dispersion resulting from the Doppler effect. They are, thus, often referred to as being “doubly dispersive.”
标签： Time-Varying Channels
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In this book we focus on the basic signal processing that underlies current and future ultra wideband systems. By looking at signal processing in this way we hope this text will be useful even as UWB applications mature and change or regulations regarding ultra wideband systems are modified. The current UWB field is extremely dynamic, with new techniques and ideas being presented at every communications and signal-processing conference. The basic signal-processing techniques presented in this text though will not change for some time to come. Thus, we have taken a somewhat theoretical approach, which we believe is longer lasting and more useful to the reader in the long term than an up-to-the-minute summary that is out of date as soon as it is published.
标签： Wideband Signals Systems Ultra 1st
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