Guide Space/Terrestrial Mobile Networks: Internet Access and QoS Support

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The effects are less pronounced on the lower frequency 'L' and 'C' bands, but can become quite severe on the higher frequency 'Ku' and 'Ka' band. The amount of time during which service is lost can be reduced by increasing the size of the satellite communication dish so as to gather more of the satellite signal on the downlink and also to provide a stronger signal on the uplink. Modern consumer-grade dish antennas tend to be fairly small, which reduces the rain margin or increases the required satellite downlink power and cost.

However, it is often more economical to build a more expensive satellite and smaller, less expensive consumer antennas than to increase the consumer antenna size to reduce the satellite cost. Large commercial dishes of 3. Alternately, larger aperture antennae can require less power from the satellite to achieve acceptable performance. Satellites typically use photovoltaic solar power, so there is no expense for the energy itself, but a more powerful satellite will require larger, more powerful solar panels and electronics, often including a larger transmitting antenna.

The larger satellite components not only increase materials costs but also increase the weight of the satellite, and in general, the cost to launch a satellite into an orbit is directly proportional to its weight. In addition, since satellite launch vehicles [i.

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Modulated carriers can be dynamically altered in response to rain problems or other link impairments using a process called adaptive coding and modulation, or "ACM". ACM allows the bit rates to be increased substantially during normal clear sky conditions, increasing the number of bits per Hz transmitted, and thus reducing overall cost per bit. Adaptive coding requires some sort of a return or feedback channel which can be via any available means, satellite or terrestrial.

An object is in your line of sight if you can draw a straight line between yourself and the object without any interference, such as a mountain or a bend in a road. An object beyond the horizon is below the line of sight and, therefore, can be difficult to communicate with. Typically a completely clear line of sight between the dish and the satellite is required for the system to work optimally.

In addition to the signal being susceptible to absorption and scattering by moisture, the signal is similarly impacted by the presence of trees and other vegetation in the path of the signal. A dish installation in the winter must factor in plant foliage growth that will appear in the spring and summer. Even if there is a direct line of sight between the transmitting and receiving antenna, reflections from objects near the path of the signal can decrease apparent signal power through phase cancellations.


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Whether and how much signal is lost from a reflection is determined by the location of the object in the Fresnel zone of the antennas. Home or consumer grade two-way satellite Internet service involves both sending and receiving data from a remote very-small-aperture terminal VSAT via satellite to a hub telecommunications port teleport , which then relays data via the terrestrial Internet. The satellite dish at each location must be precisely pointed to avoid interference with other satellites. At each VSAT site the uplink frequency, bit rate and power must be accurately set, under control of the service provider hub.

Such systems are frequently marketed as "satellite broadband" and can cost two to three times as much per month as land-based systems such as ADSL.

Space/terrestrial mobile networks : internet access and qos support

The modems required for this service are often proprietary, but some are compatible with several different providers. These types of system are generally unsuitable for use on moving vehicles, although some dishes may be fitted to an automatic pan and tilt mechanism to continuously re-align the dish—but these are more expensive.

Consumer satellite Internet customers range from individual home users with one PC to large remote business sites with several hundred PCs. Home users tend to use shared satellite capacity to reduce the cost, while still allowing high peak bit rates when congestion is absent. There are usually restrictive time-based bandwidth allowances so that each user gets their fair share, according to their payment.

When a user exceeds their allowance, the company may slow down their access, deprioritise their traffic or charge for the excess bandwidth used. The uplink direction for shared user customers is normally time division multiple access TDMA , which involves transmitting occasional short packet bursts in between other users similar to how a cellular phone shares a cell tower. Each remote location may also be equipped with a telephone modem; the connections for this are as with a conventional dial-up ISP.

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Two-way satellite systems may sometimes use the modem channel in both directions for data where latency is more important than bandwidth, reserving the satellite channel for download data where bandwidth is more important than latency, such as for file transfers. In , the European Commission sponsored the UNIC project which aims at developing an end-to-end scientific test bed for the distribution of new broadband interactive TV-centric services delivered over low-cost two-way satellite to actual end-users in the home.

Normal VSAT dishes 1. A voice call is sent by means of packets via the satellite and Internet. Using coding and compression techniques the bit rate needed per call is only These usually come in the shape of a self-contained flat rectangular box that needs to be pointed in the general direction of the satellite—unlike VSAT the alignment need not be very precise and the modems have built in signal strength meters to help the user align the device properly. Some also have an integrated Bluetooth transceiver and double as a satellite phone.

The modems also tend to have their own batteries so they can be connected to a laptop without draining its battery. For many years [ when?

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Due to the low bandwidths involved it is extremely slow to browse the web with such a connection, but useful for sending email, Secure Shell data and using other low-bandwidth protocols. Since satellite phones tend to have omnidirectional antennas no alignment is required as long as there is a line of sight between the phone and the satellite. One-way terrestrial return satellite Internet systems are used with conventional dial-up Internet access , with outbound upstream data traveling through a telephone modem , but downstream data sent via satellite at a higher rate. In the U. GPRS as return improves mobility when the service is provided by a satellite that transmits in the field of kW.

The transmitting station has two components, consisting of a high speed Internet connection to serve many customers at once, and the satellite uplink to broadcast requested data to the customers. The ISP's routers connect to proxy servers which can enforce quality of service QoS bandwidth limits and guarantees for each customer's traffic. Often, nonstandard IP stacks are used to address the latency and asymmetry problems of the satellite connection. As with one-way receive systems, data sent over the satellite link is generally also encrypted, as otherwise it would be accessible to anyone with a satellite receiver.

Many IP-over-satellite implementations use paired proxy servers at both endpoints so that certain communications between clients and servers [33] need not to accept the latency inherent in a satellite connection. For similar reasons, there exist special Virtual private network VPN implementations designed for use over satellite links because standard VPN software cannot handle the long packet travel times.

Upload speeds are limited by the user's dial-up modem, while download speeds can be very fast compared to dial-up, using the modem only as the control channel for packet acknowledgement. Latency is still high, although lower than full two-way geostationary satellite Internet, since only half of the data path is via satellite, the other half being via the terrestrial channel. One-way broadcast satellite Internet systems are used for Internet Protocol IP broadcast -based data, audio and video distribution. Note that most Internet protocols will not work correctly over one-way access, since they require a return channel.

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However, Internet content such as web pages can still be distributed over a one-way system by "pushing" them out to local storage at end user sites, though full interactivity is not possible. This is much like TV or radio content which offers little user interface.


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  • The broadcast mechanism may include compression and error correction to help ensure the one-way broadcast is properly received. The data may also be rebroadcast periodically, so that receivers that did not previously succeed will have additional chances to try downloading again. The data may also be encrypted, so that while anyone can receive the data, only certain destinations are able to actually decode and use the broadcast data.

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    Authorized users only need to have possession of either a short decryption key or an automatic rolling code device that uses its own highly accurate independent timing mechanism to decrypt the data. Similar to one-way terrestrial return, satellite Internet access may include interfaces to the public switched telephone network for squawk box applications. Most one-way broadcast applications require custom programming at the remote sites. The software at the remote site must filter, store, present a selection interface to and display the data. The software at the transmitting station must provide access control, priority queuing, sending, and encapsulating of the data.

    In its report released in February, , the Federal Communications Commission noted significant advances in satellite Internet performance. Much of the slowdown associated with satellite Internet is that for each request, many roundtrips must be completed before any useful data can be received by the requester.

    It covers the European continent with 80 spot beams—focused signals that cover an area a few hundred kilometers across Europe and the Mediterranean. Spot beams allow for frequencies to be effectively reused in multiple regions without interference.

    sirftrepadter.tk The result is increased capacity. ViaSat-1 , the highest capacity communications satellite in the world, [38] was launched Oct. Passengers aboard JetBlue Airways can use this service since Since , the O3b satellite constellation claims an end-to-end round-trip latency of ms for data services. In and , the Australian Government launched two satellites to provide internet to regional Australians and residents of External Territories, such as Norfolk Island and Christmas Island.

    From Wikipedia, the free encyclopedia. Latency also impacts the initiation of secure Internet connections such as SSL which require the exchange of numerous pieces of data between web server and web client. Although these pieces of data are small, the multiple round-trips involved in the handshake produce long delays compared to other forms of Internet connectivity, as documented by Stephen T. Cobb in a report published by the Rural Mobile and Broadband Alliance.

    One should thoroughly test the functionality of live interactive access to a distant computer—such as virtual private networks. Many TCP protocols were not designed to work in high-latency environments. For example:. Unlike geostationary satellites, low- and medium-Earth orbit satellites do not stay in a fixed position in the sky. Consequently, ground-based antennas cannot easily lock into communication with any one specific satellite. As with GPS , for a receiver the satellites are only visible for a part of their orbit, therefore multiple satellites are necessary to establish a permanent internet connection, with low-Earth orbits needing more satellites than medium-Earth orbits.

    The network has to switch data transfer between satellites to keep a connection to a customer. A proposed alternative to relay satellites is a special-purpose solar-powered ultralight aircraft, which would fly along a circular path above a fixed ground location, operating under autonomous computer control at a height of approximately 20, meters.

    For example, the United States Defense Advanced Research Projects Agency Vulture project envisaged an ultralight aircraft capable of station-keeping over a fixed area for a period of up to five years, and able to provide both continuous surveillance to ground assets as well as to service extremely low-latency communications networks. Onboard batteries would charge during daylight hours through solar panels covering the wings, and would provide power to the plane during night.

    Ground-based satellite internet dishes would relay signals to and from the aircraft, resulting in a greatly reduced round-trip signal latency of only 0.

    The planes could potentially run for long periods without refueling. Several such schemes involving various types of aircraft have been proposed in the past. Satellite communications are affected by moisture and various forms of precipitation such as rain or snow in the signal path between end users or ground stations and the satellite being utilized. This interference with the signal is known as rain fade. The effects are less pronounced on the lower frequency 'L' and 'C' bands, but can become quite severe on the higher frequency 'Ku' and 'Ka' band.