Satellite fixed communications service: A forecast of potential domestic demand through the year 2000. Volume 3: Appendices

Voice applications, data applications, video applications, impacted baseline forecasts, market distribution model, net long haul forecasts, trunking earth station definition and costs, trunking space segment cost, trunking entrance/exit links, trunking network costs and crossover distances with terrestrial tariffs, net addressable forecasts, capacity requirements, improving spectrum utilization, satellite system market development, and the 30/20 net accessible market are considered

Performance measurement methodology for integrated services networks

With the emergence of advanced integrated services networks, the need for effective performance analysis techniques has become extremely important. Further advancements in these networks can only be possible if the practical performance issues of the existing networks are clearly understood. This thesis is concerned with the design and development of a measurement system which has been implemented on a large experimental network. The measurement system is based on dedicated traffic generators which have been designed and implemented on the Project Unison network. The Unison project is a multisite networking experiment for conducting research into the interconnection and interworking of local area network based multi-media application systems. The traffic generators were first developed for the Cambridge Ring based Unison network. Once their usefulness and effectiveness was proven, high performance traffic generators using transputer technology were built for the Cambridge Fast Ring based Unison network. The measurement system is capable of measuring the conventional performance parameters such as throughput and packet delay, and is able to characterise the operational performance of network bridging components under various loading conditions. In particular, the measurement system has been used in a 'measure and tune' fashion in order to improve the performance of a complex bridging device. Accurate measurement of packet delay in wide area networks is a recognised problem. The problem is associated with the synchronisation of the clocks between the distant machines. A chronological timestamping technique has been introduced in which the clocks are synchronised using a broadcast synchronisation technique. Rugby time clock receivers have been interfaced to each generator for the purpose of synchronisation. In order to design network applications, an accurate knowledge of the expected network performance under different loading conditions is essential. Using the measurement system, this has been achieved by examining the network characteristics at the network/user interface. Also, the generators are capable of emulating a variety of application traffic which can be injected into the network along with the traffic from real applications, thus enabling user oriented performance parameters to be evaluated in a mixed traffic environment. A number of performance measurement experiments have been conducted using the measurement system. Experimental results obtained from the Unison network serve to emphasise the power and effectiveness of the measurement methodology

Design of event-driven automatic gain control and high-speed data path for multichannel optical receiver arrays

The internet has become the ubiquitous tool that has transformed the lives of all of us. New broadband applications in the field of entertainment, commerce, industry, healthcare and social interactions demand increasingly higher data rates and quality of the networks and ICT infrastructure. In addition, high definition video streaming and cloud services will continue to push the demand for bandwidth. These applications are reshaping the internet into a content-centric network. The challenge is to transform the telecom optical networks and data centers such that they can be scaled efficiently, at low cost. Furthermore, from both an environmental and economic perspective, this scaling should go hand in hand with reduced power consumption. This stems from the desire to reduce CO2 emission and to reduce network operating costs while offering the same service level as today. In the current architecture of the internet, end-users connect to the public network using the access network of an internet service provider (ISP). Today, this access network either reuses the legacy copper or coaxial network or uses passive optical network (PON) technologies, among which the PON is the most energy efficient and provides the highest data rates. Traffic from the access network is aggregated with Ethernet switches and routed to the core network through the provider edge routers, with broadband network gateways (BNGs) to regulate access and usage. These regional links are collectively called the metro network. Data centers connect to the core network using their own dedicated gateway router. The problem of increasing data rates, while reducing the economic and environmental impact, has attracted considerable attention. The research described in this work has been performed in the context of two projects part of the European Union Seventh Framework Programme (FP7), which both aim for higher data rates and tight integration while keeping power consumption low. Mirage targets data center applications while C3PO focuses on medium-reach networks, such as the metro network. Specifically, this research considers two aspects of the high-speed optical receivers used in the communication networks: increasing dynamic range of a linear receiver for multilevel modulation through automatic gain control (AGC) and integration of multiple channels on a single chip with a small area footprint. The data centers of today are high-density computing facilities that provide storage, processing and software as a service to the end-user. They are comprised of gateway routers, a local area network, servers and storage. All of this is organized in racks. The largest units contain over 100 000 servers. The major challenges regarding data centers are scalability and keeping up with increasing amounts of traffic while reducing power consumption (of the devices as well as the associated cooling) and keeping cost minimal. Presently, racks are primarily interconnected with active optical cables (AOCs) which employ signal rates up to 25 Gb/s per lane with non-return-to-zero (NRZ) modulation. A number of technological developments can be employed in AOCs of the future to provide terabit-capacity optical interconnects over longer distances. One such innovation is the use of multilevel modulation formats, which are more bandwidth-efficient than traditional NRZ modulation. Multilevel modulation requires a linear amplifier as front-end of the optical receiver. The greater part of this dissertation discusses the design and implementation of an AGC system for the data path of a linear transimpedance amplifier (TIA). The metro network is the intermediate regional network between the access and core network of the internet architecture, with link lengths up to 500 km. It is estimated that in the near future metro-traffic will increase massively. This growth is attributed mainly to increasing traffic from content delivery networks (CDNs) and data centers, which bypass the core network and directly connect to the metro network. Internet video growth is the major reason for traffic increase. This evolution demands increasingly higher data rates. Today, dense wavelength division multiplexing (DWDM) is widely recognized as being necessary to provide data capacity scalability for future optical networks, as it allows for much higher combined data rates over a single fiber. At the receiver, each wavelength of the demultiplexed incoming light is coupled to a photo diode in a photo diode array which is connected to a dedicated lane of a multichannel receiver. The high number of channels requires small physical channel spacing and tight integration of the diode array with the receiver. In addition, active cooling should be avoided, such that power consumption per receiver lane must be kept low in order not to exceed thermal operation limits. The second component of this work presents the development of an integrated four-channel receiver, targeting 4 × 25 Gb/s data rate, with low power consumption and small footprint to support tight integration with a p-i-n photo diode array with a 250 μm channel pitch. Chapter 1 discusses the impact of increasing data rates and the desire to reduce power consumption on the design of the optical receiver component, in wide metropolitan area networks as well as in short-reach point-to-point links in data centers. In addition, some aspects of integrated analog circuit design are highlighted: the design flow, transistor hand models, a software design tool. Also, an overview of the process technology is given. Chapter 2 provides essential optical receiver concepts, which are required to understand the remainder of the work. Fundamentals of feedback AGC systems are discussed in the first part of Chapter 3. A basic system model is presented in the continuous-time domain, in which the variable gain amplifier (VGA) constitutes the multistage datapath of a linear optical receiver. To enable reliable reception of multilevel modulation formats, the VGA requires controlled frequency response and in particular limited time-domain overshoot across the gain range. It is argued that this control is hard to achieve with fully analog building blocks. Therefore, an event-driven approach is proposed as an extension of the continuous-time system. Both the structural and behavioral aspects are discussed. The result is a system model of a quantized AGC loop, upon which the system-level design, presented in Chapter 4, is based. In turn, Chapter 5 discusses the detailed implementation of the various building blocks on the circuit level and presents experimental results that confirm the feasibility of the proposed approach. Chapter 6 discusses the design and implementation of a 4 × 25 Gb/s optical receiver array for NRZ modulation with a small area footprint. The focus lies on the input stages and techniques to extend bandwidth and dynamic range are presented. Measurement results for NRZ and optical duobinary (ODB) modulation are presented, as well as the influence of crosstalk on the performance. Finally, Chapter 7 provides an overview of the foremost conclusions of the presented research and includes suggestions for future research. Two appendices are included. Appendix A gives an overview of the general network theorem (GNT), which is used throughout this work and which has been implemented numerically. The results from Appendix B, the analysis of a two-stage opamp compensated with capacitance multipliers, were used to design a building block for the AGC system

Design, Simulation and Validation of Data Offloading Techniques to Support Realistic Vehicle-to-Satellite Communication

openL'obiettivo della tesi è di esaminare l'offloading dei dati dai veicoli ai satelliti, tenendo conto di vari scenari ambientali. Per questo scopo è stato sviluppato un simulatore in grado di valutare i ritardi nella comunicazione in diverse situazioni. L'analisi si basa su un algoritmo che gestisce il processo di simulazione, il quale comprende diversi aspetti, tra cui il posizionamento dei veicoli, la selezione dei satelliti, la modellazione del canale e il calcolo dei ritardi. Tuttavia, è importante sottolineare che l'obiettivo principale non è solo la creazione del simulatore, ma anche l'analisi approfondita del problema di offloading e della comunicazione in generale. Un aspetto notevole di questa ricerca è la sua adattabilità alle condizioni variabili, tra cui la dinamica della mobilità dei veicoli e la disponibilità dei satelliti. Attraverso l'analisi, miriamo a determinare la fattibilità del trasferimento dei dati e identificare scenari ottimali.The thesis aims to investigate data offloading from vehicles to satellites, considering various environmental scenarios. A simulator has therefore been developed to evaluate communication delays in diverse settings. The simulator operates based on an algorithm managing the simulation process, involving components such as vehicle positioning, satellite selection, channel modeling, and delay calculation. A noteworthy aspect of the simulator is its adaptability to changing conditions, including the dynamics of vehicle mobility and satellite availability. This adaptability ensures the practical relevance of simulation results across a wide range of scenarios. Through the analysis, we aim to determine the feasibility of data offloading and identify optimal scenarios

Potential markets for advanced satellite communications

This report identifies trends in the volume and type of traffic offered to the U.S. domestic communications infrastructure and extrapolates these trends through the year 2011. To describe how telecommunications service providers are adapting to the identified trends, this report assesses the status, plans, and capacity of the domestic communications infrastructure. Cable, satellite, and radio components of the infrastructure are examined separately. The report also assesses the following major applications making use of the infrastructure: (1) Broadband services, including Broadband Integrated Services Digital Network (BISDN), Switched Multimegabit Data Service (SMDS), and frame relay; (2) mobile services, including voice, location, and paging; (3) Very Small Aperture Terminals (VSAT), including mesh VSAT; and (4) Direct Broadcast Satellite (DBS) for audio and video. The report associates satellite implementation of specific applications with market segments appropriate to their features and capabilities. The volume and dollar value of these market segments are estimated. For the satellite applications able to address the needs of significant market segments, the report also examines the potential of each satellite-based application to capture business from alternative technologies

Postglacial sea-level change: novel insights from physical and statistical modelling

Developing accurate projections of future sea-level change is a key challenge for the entire science community under the current warming climate. Due to the fact that modern instrumental sea-level observations are only available since the 19-20th century, sea-level projections based on them can only capture short-term effects, leaving physical processes that dominate over longer timescales underestimated. Therefore, an essential step towards accurate and robust long-term sea-level projections is to investigate the physical processes that impact the spatio-temporal evolution of sea-level change over centennial to millennial timescales. Due to sometimes scarce and often noisy palaeo sea-level observations, mechanisms of sea-level change over geological timescales are still not well-understood, with many outstanding questions to be resolved. This thesis develops novel physical and statistical models to better understand the mechanisms behind postglacial sea-level change. Specifically, this thesis focuses on three outstanding problems that are not only important in postglacial sea-level change but also in understanding past ice sheet dynamics and palaeoclimate change. Firstly, a statistical framework is developed to invert the sources of meltwater pulse 1A, the largest and most rapid global sea-level rise event of the last deglaciation, with sophisticated treatment of uncertainties associated with sea-level reconstructions and geophysical modelling. The results suggest there were contributions from North America, 12.0 m (5.6-15.4 m; 95% probability), Scandinavia, 4.6 m (3.2-6.4 m), and Antarctica, 1.3 m (0-5.9 m), giving a total global mean sea-level rise of 17.9 m (15.7-20.2 m) in 500 years. Secondly, the missing ice problem (distinctive imbalance between observed global mean sea-level rise and the reconstructed amount of ice-sheet melt) is revisited by including an extra physical process (sediment isostatic adjustment, SIA) which has not been considered in this problem before. In particular, this thesis investigates the impact of SIA on local RSL variation across the Great Barrier Reef (GBR), the world's largest mixed carbonate-siliciclastic sediment system. Based on a Bayesian calibration method, SIA can contribute up to 1.1 m relative sea-level rise in the outer shelf of the southern central GBR from 28 ka to present. Because the SIA-induced RSL rise is unrelated to ice mass loss, failing to correct for this signal will lead to systematic overestimation of grounded ice volume. Therefore, incorporating the SIA process will reduce the global grounded ice volume estimate for the Last Glacial Maximum (LGM), which can help to mitigate the missing ice problem. Lastly, robust global barystatic sea-level maps with minimum dependency on the detailed geometry of past ice sheet change are reconstructed. Estimating such maps requires physical simulation of relative sea-level corresponding to thousands of different ice histories, which is computationally prohibitive. To improve this situation, this thesis develops a statistical emulator which can mimic the behaviour of a physics-based model and is computationally much cheaper to evaluate. The results highlight the Seychelles as an exceptionally good place to map barystatic sea level throughout the last deglaciation because RSL at this location only slightly departs from global barystatic sea level, with minor dependency on the assumed ice history. Together, these physical and statistical models present powerful tools to yield novel insights into postglacial sea-level change mechanisms and hence they have the potential to yield more robust, accurate and trust-worthy sea-level change projections

Analog methods for power system analysis and load modeling

This dissertation explores how and why analog computation may be utilized to study several aspects of power system load behavior. An analog computer is one which utilizes continuous electrical signals instead of discrete bits, 0’s and 1’s, to represent numerical values. Generally, it is utilized to solve a set of complex nonlinear differential equations: a process referred to as analog emulation. In the first chapters, this work examines how load may be represented in a modern analog computer designed to emulate the behavior of a multi-bus power system and perform fast power-flow analysis. Focus is placed on the design, testing, and fabrication of a printer circuit (PC) board for this purpose. In later chapters, it examines the effect of system size and model complexity on analog and hybrid (combination of analog and digital hardware) computation times. Focus is placed on static security analysis (SSA) as well as a method to minimize these computation times through reduced actuation and data acquisition. In the final chapters, this work examines how analog hardware may be utilized to perform measurement-based composite load modeling. Focus is placed on the theory, design, and testing of an analog circuit to estimate the parameters of an assumed load model from network observation. The accuracy of a power-flow analysis is only as accurate as the models and parameters that it utilizes. For this reason, the utilization of analog hardware to both represent load in power-flow analysis (state determination) and model load behavior (parameter estimation) are addressed in this dissertation.Ph.D., Electrical Engineering -- Drexel University, 200

Satellite provided customer premise services: A forecast of potential domestic demand through the year 2000. Volume 3: Appendices

Voice applications, data applications, video applications, impacted baseline forecasts, market distribution, potential CPS (customers premises services) user classes, net long haul forecasts, CPS cost analysis, overall satellite forecast, CPS satellite market, Ka-band CPS satellite forecast, nationwide traffic distribution model, and intra-urban topology are discussed