Short range optical data links are experiencing bandwidth limitations making it very challenging to cope with the growing data transmission capacity demands. Parallel optics appears as a valid ...short-term solution. It is, however, not a viable solution in the long-term because of its complex optical packaging. Therefore, increasing effort is now put into the possibility of exploiting higher order modulation formats with increased spectral efficiency and reduced optical transceiver complexity. As these type of links are based on intensity modulation and direct detection, modulation formats relying on optical coherent detection can not be straight forwardly employed. As an alternative and more viable solution, this paper proposes the use of carrierless amplitude phase (CAP) in a novel multiband approach (MultiCAP) that achieves record spectral efficiency, increases tolerance towards dispersion and bandwidth limitations, and reduces the complexity of the transceiver. We report on numerical simulations and experimental demonstrations with capacity beyond 100 Gb/s transmission using a single externally modulated laser. In addition, an extensive comparison with conventional CAP is also provided. The reported experiment uses MultiCAP to achieve 102.4 Gb/s transmission, corresponding to a data payload of 95.2 Gb/s error free transmission by using a 7% forward error correction code. The signal is successfully recovered after 15 km of standard single mode fiber in a system limited by a 3 dB bandwidth of 14 GHz.
The first edition Surveyors advising in respect of the Electronic Communications Code guidance note highlights the main factors that could influence surveyors' roles in the telecommunications sector. ...While not providing exhaustive guidance, it will help identify the main issues and inform advice given to clients.
This paper investigates a natural generalization of the κ - μ fading channel in which the line-of-sight (LOS) component is subject to shadowing. This fading distribution has a clear physical ...interpretation and good analytical properties and unifies the one-side Gaussian, Rayleigh, Nakagami- m, Rician, κ - μ, and Rician shadow fading distributions. The three basic statistical characterizations, i.e., probability density function (pdf), cumulative distribution function (cdf), and moment-generating function (mgf), of the κ - μ shadowed distribution are obtained in closed form. Then, it is also shown that the sum and maximum distributions of independent but arbitrarily distributed κ - μ shadowed variates can be expressed in closed form. This set of new statistical results is finally applied to modeling and analysis of several wireless communication systems, e.g., the proposed distribution has applications to land mobile satellite (LMS) communications and underwater acoustic communications (UAC).
We present TLR, a traffic-light-based intelligent routing strategy for NGEO satellite IP networks. In TLR, a set of traffic lights are used to indicate the congestion status at both the current node ...and the next node. When a packet travels along a pre-calculated route to the destination, it may adjust the route dynamically, according to the real-time color of traffic lights at each intermediate node. Through the combination of preliminary planning and real-time adjustment, each packet can eventually get an approximately optimal transmission path. The multi-path routing mechanism in TLR can help achieve a good distribution of traffics when the network traffic increases. The Public Waiting Queue scheme in TLR can fully utilize free spaces of the buffer queues and lower the packet drop rate. While the concept of TLR has many advantages, it may result in endless-loop of routing. To eliminate this phenomenon, a defense scheme is incorporated in the design of TLR. A set of simulations are conducted using the Network Simulator (version 2) to verify the good performance of TLR, in terms of lower packet drop rate, better distribution of traffics and higher throughput, over the entire satellite constellation.
1) The Myth: Sixty years of research following Shannon's pioneering paper has led to telecommunications solutions operating arbitrarily close to the channel capacity-"flawless telepresence" with zero ...error is available to anyone, anywhere, anytime across the globe. 2)The Reality: Once we leave home or the office, even top of the range iPhones and tablet computers fail to maintain "flawless telepresence" quality. They also fail to approach the theoretical performance predictions. The 1000-fold throughput increase of the best third- generation (3G) phones over second-generation (2G) GSM phones and the 1000-fold increased teletraffic predictions of the next decade require substantial further bandwidth expansion toward ever increasing carrier frequencies, expanding beyond the radiofrequency (RF) band to optical frequencies, where substantial bandwidths are available. 3) The Future: However, optical and quantum-domain wireless communications is less developed than RF wireless. It is also widely recognized that the pathloss of RF wireless systems monotonically increases with the carrier frequency and this additional challenge has to be tackled by appropriate countermeasures in future research. Hence, we set out to seek promising techniques of tackling the aforementioned challenges and for resolving the conflicting design constraints imposed on the flawless telepresence systems of the future. To disspell the myth, we evaluate both the operational 3G as well as the emerging fourth-generation (4G) wireless systems and demonstrate that there is a substantial difference between their theoretical and their practically attainable performance. The reality is that the teletraffic predictions indicate further thirst for bandwidth, which cannot be readily satisfied within the most popular 1-2-GHz carrier-frequency range, where the best propagation conditions prevail. We briefly consider the 10-300-GHz unlicensed band as a potential source of further spectrum, followed by a review of advances way beyond the upper edge of the RF range at 300 GHz, namely to the realms of optical wireless (OW) communications. As the carrier frequency is increased, the pathloss is also increased, which results in ever smaller cells. Furthermore, the high-frequency RF waves predominantly obey line-of-sight (LOS) propagation-like visible light. The future requires advances in both infrared and visible-light communications for circumventing the LOS nature of light. We hypothesize that light-emitting diode (LED) arrays acting as "massive" multiple-input-multiple-output (MIMO) components as well as transmitter/receiver cooperation might be conceived. The heterogeneous networks of the near future will rely on seamless, near-instantaneous handovers among OW hotspots, RF hotspots, and oversailing larger cells. These "massive" MIMOs might impose a high complexity, hence their reduced-complexity noncoherently detected counterparts might be favored. Finally, we conclude by touching upon the promising research area of quantum-domain communications, which might be expected to circumvent the aforementioned complexity problem of massive MIMOs with the aid of efficient quantum-domain search techniques-a truly exciting research era
We address perturbative models for the impact of nonlinear propagation in uncompensated links. We concentrate on a recently-proposed model which splits up the signal into spectral components and then ...resorts to a four-wave-mixing-like approach to assess the generation of nonlinear interference due to the beating of the signal spectral components. We put its founding assumptions on firmer ground and we provide a detailed derivation for its main analytical results. We then carry out an extensive simulative validation by addressing an ample and significant set of formats encompassing PM-BPSK, PM-QPSK, PM-8QAM, and PM-16QAM, all operating at 32 GBaud. We compare the model prediction of maximum system reach and optimum launch power versus simulation results, for all four formats, three different kinds of fibers (PSCF, SMF, and NZDSF) and for several values of WDM channel spacing, ranging from 50 GHz down to the symbol-rate. We found that, throughout all tests, the model delivers accurate predictions, potentially making it an effective general-purpose system design tool for coherent uncompensated transmission systems.
Augmentative and Alternative Communication: Models and Applications, Second Edition describes augmentative and alternative communication (AAC) comprehensively and offers a framework for understanding ...how AAC intervention can be used in the process of communication. This textbook is intended to serve as the primary text for graduate-level courses in augmentative and alternative communication in speech-language pathology programs. It also serves as an essential resource for practicing clinicians.
Video relay service (VRS) is a federally funded service that
provides telecommunications access for deaf people. It is also a
for-profit industry with guidelines that may limit the autonomy of
the ...sign language interpreters who work in VRS settings. In this
volume, Erica Alley examines how VRS interpreters, or
"Communication Assistants," exercise professional autonomy despite
the constraints that arise from rules and regulations established
by federal agencies and corporate entities. Through interviews with
VRS interpreters, Alley reveals the balance they must achieve in
providing effective customer service while meeting the quantitative
measures of success imposed by their employer in a highly
structured call center environment. Alley considers the question of
how VRS fits into the professional field of interpreting, and
discovers that-regardless of the profit-focused mentality of VRS
providers-interpreters make decisions with the goal of creating
quality customer service experiences for deaf consumers, even if it
means "breaking the rules." Her findings shed light on the
decision-making process of interpreters and how their actions are
governed by principles of self-care, care for colleagues, and
concern for the quality of services provided. Professional
Autonomy in Video Relay Service Interpreting is essential
reading in interpreter education courses and interpreter training
programs.
We propose a new scheme for increasing the throughput of video files in cellular communications systems. This scheme exploits (1) the redundancy of user requests as well as (2) the considerable ...storage capacity of smartphones and tablets. Users cache popular video files and-after receiving requests from other users-serve these requests via device-to-device localized transmissions. The file placement is optimal when a central control knows a priori the locations of wireless devices when file requests occur. However, even a purely random caching scheme shows only a minor performance loss compared to such a "genie-aided" scheme. We then analyze the optimal collaboration distance, trading off frequency reuse with the probability of finding a requested file within the collaboration distance. We show that an improvement of spectral efficiency of one to two orders of magnitude is possible, even if there is not very high redundancy in video requests.
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