Satellite communication systems paper presentation

Publicado em Agosto 2017

This type of an orbit reduces transmission times as compared to GEO. The primary advantage of distributed computing is that each node can be purchased as commodity hardware, which when combined can produce similar computing resources to a multiprocessor supercomputer, but at lower cost. Grid computing is emerging as a new environment for solving difficult problems. The infrastructure and programming considerations needed to do this on each type of platform are different, however. The difficulties inherent in this are obvious. The primary performance disadvantage is that the various processors and local storage areas do not have high-speed connections. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. Submarine cables have been used most frequently. One problem that these satellites have is that since the are not geostationary (they are contsantly orbiting around the earth) they cannot talk continuously to that same ground station. Within each cell’s time slot, the full frequency allocation is available to support communication channels. On the uplink, each active terminal is assigned one or more frequency slots for the call’s duration and can send one packet per slot each scan period (23. The researcher said dissertation cover page latex he discovered the vulnerabilities by "reverse engineering" - or decoding - highly specialized software known as firmware, used to operate communications equipment made by Cobham Plc, Harris Corp, EchoStar Corp's Hughes Network Systems, Iridium Communications Inc and Japan Radio Co Ltd. satellite communication systems paper presentation The first is the improvement of performance and the reduction of costs due to the combining of resources. 4-19. Guard time intervals eliminate overlap between signals received from time-consecutive cells. In the case of a telecom satellite, the primary task is to receive signals from a ground station and send them down to another ground station located a considerable distance away from the first. This ARR protocol is an improvement over GBN in that it allows the receiver to request a retransmit of only that packet that it needs, instead of that packet and all that follows it. The Teledesic Network uses a combination of multiple access methods to ensure efficient use of the spectrum. It is, slowly but surely, changing the face of computing in our industry. Scientists, who use applications that require enormous resources in terms of computing or data processing, are large consumers of computational grids. For instance, Cobham, whose Aviation 700 aircraft satellite communications equipment was the focus of Santamarta's research, said it is not possible for hackers to use WiFi signals to interfere with critical systems that rely on satellite communications for navigation and safety. Grid computing can be thought of as distributed and large-scale cluster computing and as a form of network-distributed parallel processing. 048 Mbps ("E1"), and for special applications up to 1. The direct-to-home industry has gathered even greater momentum since the introduction of digital direct broadcast service. Groups like the international satellite consortium Intelsat have fulfilled much of the world's need for this type of service. The receiver, after receiving a bad packet and requesting a satellite communication systems paper presentation retransmit, can continue to accept any good packets that write an essay on love are coming. GEO's high points are that it's satellites are geostationary, which means that the difficulties of intersatellite communications are avoided. 3 GHz for uplinks) links the satellite and the gateways and earth terminals. Conventional supercomputers also create physical challenges in supplying sufficient electricity and cooling capacity in a single location. The Grid is not only a low level infrastructure for supporting computation, but can also facilitate and enable information and knowledge sharing at the higher semantic levels, to support knowledge integration and dissemination. The cells are scanned in a regular cycle by the satellite’s transmit and receive beams, resulting in time division multiple access (TDMA) among the cells in a supercell. The resource access and management is one of the most important key factors for grid computing. A major player in this are is Teledesic. The three primary types of grids are summarized below. The possibility of creating virtual organizations to establish collaboration between teams with scarce and costly data and resources is another. Grid computing requires the use of software that can divide and farm out pieces of a program to as many as several thousand computers. Two qualitites of Asynchronous Transfer Mode (ATM) made it highly desirable for the implementation of satellite links within hybrid networks. 38 GHz. The first is the ATM's asynchrony and the second is its ability to use variable transfer rates. In some cases, an entire series of programming is transmitted at once and recorded at the affiliate, with each segment then being broadcast at appropriate times to the local viewing populace. Santamarta, a consultant with cyber security firm IOActive, is scheduled to lay out the technical details of his research at this week's Black Hat hacking conference in Las Vegas, an annual convention where thousands of hackers and security experts meet to discuss emerging cyber threats and improve security measures. However their high altitude causes a long delay, so two way communications, which would need to be uploaded and then downloaded over a distance of 72,000 km, are not often used with this type of orbit. Although this acronym has been used amongst telecom groups for some time now to describe small earth stations, the concepts of VSAT are being applied to modern hand held satellite communications units, such as GPS (Global Positioning System), portable Inmarsat phones and other types of portable satellite communication devices. However, as you consider developing applications that may run in a grid environment, remember that the type of grid environment that you will be using will affect many of your decisions. If a problem can be adequately parallelized, a "thin" layer of "grid" infrastructure can allow conventional, standalone programs to run on multiple machines (but each given a different part of the same problem). Just as the internet provided an means for explosive growth in information sharing, grid computing provides an infrastructure leading to explosive growth in the sharing of computational resources. It is being used more and more systematically, and for many reasons. All the available resources (work stations, servers, software, storage, etc. A data grid would allow them to share their data, manage essays about cars new technologies the data, satellite communication systems paper presentation and manage security issues such as who has access to what data. The system is planned to provide "on-demand" channel rates from 16 Kbps up to 2. This method is the most efficient method for satellite transmissions of the three ARR methods discussed. Discrepancies would identify malfunctioning and malicious nodes. One slot corresponds to a standard terminal’s 16 Kbps basic channel with its associated 2 Kbps signaling and control channel. In addition, ATM fits well into existing networks satellite communication systems paper presentation with its wide range of upper-layer services and its ability to operate in a wide range of environments. Hence, such applications should be one of the main driving forces behind the development of Grid computing. Linear and nonlinear optimization problems can be computationally expensive. Systems such as the Digital Broadcast Satellites used for television signal distribution would become inordinately expensive if they had to make use of ARR, since the home based receiver would now need to be a transmitter, and the 18 inch dish would be inadequate for the requirements of transmitting back to a satellite. LEO networks use low orbits, which allows for much less latency that do GEO based networks. The designers of the system must thus introduce measures to prevent malfunctions or malicious participants from producing false, misleading, or erroneous results, and from using the system as an attack vector. Aggregate power of computing resources connected by networks—of the Grid— exceeds that of any single supercomputer by many orders of magnitude. A total of 1800 slots per cell scan interval are available for standard terminals. It can be costly and difficult to write programs so that they can be run in the environment of a supercomputer, which may have a custom operating system, or require the program to address concurrency issues. Grid computing provides a framework and deployment platform that enables resource do my essay for me sharing, accessing, aggregation, and management in a distributed computing environment based on system performance, users' quality of services, as well as emerging open standards, such as Web services. Grid computing is an active research area which promises to provide a flexible infrastructure for complex, dynamic and distributed resource sharing and sophisticated problem solving environments. This free viewing of corporate content by individuals led to scrambling and subsequent resale of the descrambling codes to individual customers, which started the direct-to-home industry. This often involves assigning work randomly to different nodes (presumably with different owners) and checking that at least two different nodes report the same answer for a given work unit. Grid Computing has many application fields. It requires a mechanism with automatically making decisions ability to support computing tasks collaborating and scheduling. In the 1970's, it became possible for private individuals to download the same signal that the networks and cable companies were transmitting, using c-band reception dishes. This is the era of Service Computing. Each cell within a supercell is assigned to one of nine equal time slots. Due to the lack of central control over the hardware, there is no way to guarantee that nodes will not drop out of the network at random times. satellite communication systems paper presentation Still another use for satellites is observation, wherein the satellite is equipped with cameras or various sensors, and it merely downlinks any information it picks up from its vantagepoint. The ground station's job is two-fold. The network uses fast packet switching technology based on the Asynchronous Transfer Mode (ATM) using fixed-length (512) bit packets.. Nor are leading industries staying behind: grids are massively present in the automobile and aeronautical business, where digital simulation plays an important part. The aim is to combine material resources for several services by reallocating them in a dynamic way depending on performance peaks. ARR is not very good in a channel with high noise, since many retransmissions will be required, and the noise levels that corrupted the initial packet will be likely to cause corruption in subsequent packets. Since propagation delay varies with path length, satellite transmissions are timed to ensure that cell N (N=1, 2, 3,... At the core of the system is an element called a resource broker, which handles resource supply and demand according to technical and economic criteria. Santamarta published a 25-page research report in April that detailed what he said were multiple bugs in firmware used in satellite communications equipment made by Cobham, Harris, Hughes, Iridium and Japan Radio Co for a wide variety of industries, including aerospace, military, maritime transportation, energy and communications. The system will use intersatellite crosslink transmissions that will take place in the Ka frequency band between 23. More recently, grids have emerged in other areas with the purpose of optimising company business. This allows for them to provide constant coverage of the area and eliminate blackout periods of ordinary orbiting satellites, which is good for providing television broadcasting. The primary role of a satellite is to reflect electronic signals. In this method, data is broken into packets. The L-Band (1616-1626. Within each cell’s time slot, terminals use Frequency Division Multiple Access (FDMA) on the uplink and Asynchronous Time Division Multiple Access (ATDMA) on the downlink. This is the earth segment. The Teledesic Network uses a constellation of 840 operational interlinked low-Earth orbit satellites. One way to get around the need in ARR for the receiver to have to request retransmit via an expensive and slow satellite link is to use a saket saurabh phd thesis form of hybrid network. This strategy offers considerable cost cutting thanks to better management of resources, administrative tasks and maintenance. If the error code reflects a loss of integrity in a packet, the receiver can request the sender to resend that packet. VSAT stands for Very Small Aperture Terminal. The high-end scalability of geographically dispersed grids is generally favorable, due to the low need for connectivity between nodes relative to the capacity of the public satellite communication systems paper presentation Internet. ) as well as a set of tools that could be compared to an operating system, make up the computing grid. In the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to base band signal. Another use of the satellite is when, as is the case with television broadcasts, the ground station's uplink is then downlinked over a wide region, so that it may be received by many different customers possessing compatible equipment. Satellites have been used for since the 1960's to transmit broadcast television signals between the network hubs of television companies and their network affiliates. A LEO orbit can also be used to cover a polar region, which the GEO cannot accomplish. Grid computing can be used in a variety of ways to address various kinds of application requirements. Applications which rely on steady bandwidth, like multimedia, will definately be affected. Because the economies of scale of producing commodity hardware, compared to the lower efficiency of designing and constructing a small number of custom supercomputers. The Grid has the potential to fundamentally change the way science and engineering are done. This refers to satellites that are placed in orbit such that they remain stationary relative to a fixed spot on earth. ARR is more suitable to relatively noise free channels. ARR methods can be demonstrated to provide a usable error correction scheme, but it is also the most expensive, in terms of hardware. There are currently several consortiums that are working on global voice via satellite. These variations can be accommodated by assigning large work units (thus reducing the need for continuous network connectivity) and reassigning work units when a given node fails to report its results as expected. Physical separation (space division multiple access (SDMA) and a checkerboard pattern of left and right circular polarization eliminate interference between cells scanned at the same time in adjacent supercells. LEO stands for Low Earth Orbit, and it refers to satellites in orbit at less that 22300 miles above the earth. The IRIDIUM system will use a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA) signal multiplexing to make the most efficient. This relay action can be two-way, as in the case of a long distance phone call. Security and access are in turn managed by the Grid Security Infrastructure, which handles the identification of each resource solicitor as well as access authorization up to a certain level to guarantee confidentiality. Both supercomputers and grids can be used to run multiple parallel computations at the same time, which might be different simulations for the same project, or computations for completely different applications. Users are not concerned with where this data is located as long as they have access to the data. The satellites will use dissertation conte philosophique argumentation a LEO orbit so that very small handheld terminals can be used by ground-based cutomers. This makes it possible to write and debug programs on a single conventional machine, and eliminates complications due to multiple instances of the same program running in the same shared memory and storage space at the same time One feature of distributed grids is that they can be formed from computing resources belonging to multiple individuals or organizations (known as multiple administrative domains). Grid computing technologies are entering the mainstream of computing in the financial services industry. This arrangement is thus well-suited to applications in which multiple parallel computations can take place independently, without the need to communicate intermediate results between processors. Grid computing is a special type of parallel computing which relies on complete computers (with onboard CPU, storage, power supply, network interface, etc. In one form of hybrid network, the reciever transmits its requests back to the sender via a terrestrial link. Each satellite in the constellation is a node in the fast packet switch network, and has intersatellite communication links with eight adjacent satellites. Next comes a scheduler which is responsible for distributing resources to the various machines. Some nodes (like laptops or dialup Internet customers) may also be available for computation but not network communications for unpredictable periods. One finds for instance many grids in particle-physics experiments. This is making possible functionality that was previously unimaginable -- near real time portfolio rebalancing scenario analysis; risk analysis models with seemingly limitless complexity; and content distribution with speed and efficiency hereunto unparalleled. This key is often of the cyclic redundancy check (CRC) sort. This has been accomplished in several ways. The ideas of the grid (including those from distributed computing, object oriented programming, cluster computing, web services and others) were brought together by Ian Foster, Carl Kesselman and Steve Tuecke, widely regarded as the "fathers of the grid". Terrestrial link allows for quicker, more economical and less error prone transmission from the reciever, and the costs associated with the receivers hardware are greatly reduced when compared to the costs involved if it had to transmit back over the satellite link. Of course, there are no hard boundaries between these grid types and often grids may be a combination of two or more of these. Other systems employ measures to reduce the amount of trust "client" nodes must place in the central system such as placing applications in virtual machines. The number of slots assigned to a terminal determines its maximum available transmission rate. There are products on the market today that allow a home user to get intenet access at around 400MB via digital satellite, while its retransmit signals are sent via an inexpensive modem or ISDN line. In many cases, the participating nodes must trust the central system not to abuse the access that is being granted, by interfering with the operation of other programs, mangling stored information, transmitting private data, or creating new security holes. 1-29. This is in contrast to the traditional notion of a supercomputer, which has many processors connected by a local high-speed computer bus. The Ka-Band (19. ) connected to a network by a conventional network interface, such as Ethernet. This can facilitate commercial transactions, as in utility computing, or make it easier to assemble volunteer computing networks. In practice, grids are very useful in crash simulations, as well as for computer-aided design. 18 and 23. The satellite itself is also known as the space segment, and is composed of three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder.  Data grid: A data grid is responsible for housing and providing access to data across multiple organizations. The terminal downlink uses the packet’s header rather than a fixed assignment of time slots to address terminals. Each satellite is normally linked with four satellites within the same plane (two in front and two behind) and with one in each of the two adjacent planes on both sides. Grid computing is applying the resources of many computers in a network to a single problem at the same time - usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data. Often, grids are categorized by the type of solutions that they best address. Within each packet is included an error checking key. Since it does not appear stationary to earth stations, however, earth stations need an antenna assembly that will track the motion of the satellite. The goal of SATIN is to create a fully integrated hybrid network in which the method of communication, which can incorporate networks of local, metropolitan and wide area scope, Broadband ISDN, Integrated Network Management, AIN (Advanced Intelligent Networks) and PCS (Personal Communications Services), in addition to ATM (Asynchronous Transfer Mode) over satellite, is totally transparent to the user. In the case of an uplink, or transmitting station, terrestrial data in the form of baseband signals, is passed through a baseband processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. 5 MHz), is used to link the satellite and IRIDIUM the subscribers equipment. One of the most prominant is the IRIDIUM constellation, which will consist of 66 interconnected satellites orbiting 420 nautical miles above the earth. All communication takes place between the satellite and the terminals in that cell during its assigned time slot . GEO stands for Geostationary Earth Orbit. The hackers must have physical access to Cobham's equipment, according to Cobham spokesman Greg Caires. The way this is overcome is by using intesatellite communications, so that the sattellites function together as a blanket of coverage. Since the beginnings of the long distance telephone network, there has been a need to connect the telecommunications networks of one country to another. Terminal transmissions to a satellite are also timed to ensure that transmissions from the same numbered cell in all supercells in its coverage area reach that satellite at the same time. However, there are many occasions where a large long distance carrier will choose to establish a satellite based link to connect to transoceanic points, geographically remote areas or poor countries that have little communications infrastructure. To optimize its functioning, the resources must be defined beforehand and as precisely as possible. At the same time, our ability to carry out computations of the scale and level of detail required, for example, to study the Universe, or simulate a rocket engine, are severely constrained by available computing power. Differences in latency, noise, bandwidth and reliability must be equalized in all the media that will encompass the network. This is in part due to the buffering memory that is required, but more importantly to the cost of the receiver, which needs to be able to transmit re-requests. The problem arises due to the latency delays caused by the high orbit. This last application field is of particular interest to France Telecom, as we shall see. Each satellite keeps the same position relative to other satellites in its orbital plane. 6 GHz for downlinks and 29. One disadvantage of this feature is that the computers which are actually performing the calculations might not be entirely trustworthy. If a satellite is placed at 35,900 km above the earth, its angular velocity is equal to that of the earth, thereby causing it to appear to be over the same point on earth. They may be geographically remote and work according to different rules. 111 msec). 9) of all supercells receive transmissions at the same time. The term Grid computing originated in the early 1990 as a metaphor for making computer power as easy to access as an electric power grid in Ian Foster and Carl Kesselmans seminal work, "The Grid: Blueprint for a new computing infrastructure". 24416 Gbps ("OC-24").