Editing Satellite Internet access (section)

==Function==
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[[File:Animated Image of How Satellite Internet Works.gif|thumb|How satellite internet works.]]

Satellite Internet generally relies on three primary components: a satellite{{snd}} historically in [[geostationary orbit]] (or GEO) but now increasingly in [[Low Earth orbit]] (LEO) or [[Medium Earth orbit]] MEO)<ref name="McK"/>{{snd}} a number of ground stations known as gateways that relay Internet data to and from the satellite via radio waves ([[microwave]]), and further ground stations to serve each subscriber, with a small antenna and [[transceiver]]. Other components of a satellite Internet system include a [[modem]] at the user end which links the user's network with the transceiver, and a centralized [[network operations centre]] (NOC) for monitoring the entire system. Working in concert with a broadband gateway, the satellite operates a [[Star network]] topology where all network communication passes through the network's hub processor, which is at the centre of the star. With this configuration, the number of ground stations that can be connected to the hub is virtually limitless.

===Satellite===
Marketed as the centre of the new broadband satellite networks are a new generation of high-powered GEO satellites positioned {{convert|35786|km|mi}} above the equator, operating in K<sub>a</sub>-band (18.3–30&nbsp;GHz) mode.<ref>{{cite web|url=http://www.fcc.gov/encyclopedia/ka-band-permitted-space-station-list |archive-url=https://web.archive.org/web/20120421053243/http://www.fcc.gov/encyclopedia/ka-band-permitted-space-station-list |url-status=dead |archive-date=2012-04-21 |title=Ka-band Permitted Space Station List |publisher=Federal Communications Commission |date=2009-01-25 |access-date=2013-08-29 }}</ref> These new purpose-built satellites are designed and optimized for broadband applications, employing many narrow spot beams,<ref>{{Cite web| title=Satellite technology primer | url=http://www.dbsinstall.com/PDF/WildBlue/Wildblue_Satellite_Basics.pdf | archive-url=https://web.archive.org/web/20100714150832/http://www.dbsinstall.com:80/PDF/WildBlue/Wildblue_Satellite_Basics.pdf | archive-date=2010-07-14}}</ref> which target a much smaller area than the broad beams used by earlier communication satellites. This spot beam technology allows satellites to reuse assigned bandwidth multiple times which can enable them to achieve much higher overall capacity than conventional broad beam satellites. The spot beams can also increase performance and consequential capacity by focusing more power and increased receiver sensitivity into defined concentrated areas. Spot beams are designated as one of two types: subscriber spot beams, which transmit to and from the subscriber-side terminal, and gateway spot beams, which transmit to/from a service provider ground station. Note that moving off the tight footprint of a spotbeam can degrade performance significantly. Also, spotbeams can make the use of other significant new technologies impossible, including 'Carrier in [[Carrier wave|Carrier]]' modulation.

In conjunction with the satellite's spot-beam technology, a [[Transponder (satellite communications)|bent-pipe]] architecture has traditionally been employed in the network in which the satellite functions as a bridge in space, connecting two communication points on the ground. The term "bent-pipe" is used to describe the shape of the data path between sending and receiving antennas, with the satellite positioned at the point of the bend.
Simply put, the satellite's role in this network arrangement is to relay signals from the end user's terminal to the ISP's gateways, and back again without processing the signal at the satellite. The satellite receives, amplifies, and redirects a carrier on a specific radio frequency through a signal path called a transponder.<ref name="howsatcomworks">{{cite web|url=http://www.vsat-systems.com/satellite-internet/how-it-works.html |title=How broadband satellite Internet works |publisher=VSAT Systems |access-date=2013-08-29}}</ref>

Some satellite constellations in LEO such as [[Starlink]] and the proposed [[Telesat]] constellation will employ [[laser communication in space|laser communication]] equipment for high-throughput optical inter-satellite links. The interconnected satellites allow for direct routing of user data from satellite to satellite and effectively create a space-based [[optical mesh network]] that will enable seamless network management and continuity of service.<ref>{{cite web|title=Elon Musk is about to launch the first of 11,925 proposed SpaceX internet satellites — more than all spacecraft that orbit Earth today|url=http://www.businessinsider.com/spacex-starlink-microsat-launch-global-internet-2018-2?r=US&IR=T|website=Business Insider|access-date=15 April 2018}}</ref>

The satellite has its own set of antennas to receive communication signals from Earth and to transmit signals to their target location. These antennas and transponders are part of the satellite's "payload", which is designed to receive and transmit signals to and from various places on Earth. What enables this transmission and reception in the payload transponders is a repeater subsystem (RF (radio frequency) equipment) used to change frequencies, filter, separate, amplify and group signals before routing them to their destination address on Earth. The satellite's high-gain receiving antenna passes the transmitted data to the transponder which filters, translates and amplifies them, then redirects them to the transmitting antenna on board. The signal is then routed to a specific ground location through a channel known as a carrier. Beside the payload, the other main component of a communications satellite is called the bus, which comprises all equipment required to move the satellite into position, supply power, regulate equipment temperatures, provide health and tracking information, and perform numerous other operational tasks.<ref name="howsatcomworks" />

===Gateways===
Along with dramatic advances in satellite technology over the past decade, ground equipment has similarly evolved, benefiting from higher levels of integration and increasing processing power, expanding both capacity and performance boundaries.
The [[Gateway (telecommunications)|gateway]]—or gateway Earth station—is also referred to as a ground station, teleport or hub. The term is sometimes used to describe just the antenna dish portion, or it can refer to the complete system with all associated components.
In short, the gateway receives radio wave signals from the satellite on the last leg of the return or upstream payload, carrying the request originating from the end-user's site. The satellite modem at the gateway location demodulates the incoming signal from the outdoor antenna into IP packets and sends the packets to the local network. Access server/gateways manage traffic transported to/from the Internet. Once the initial request has been processed by the gateway's servers, sent to and returned from the Internet, the requested information is sent back as a forward or downstream payload to the end-user via the satellite, which directs the signal to the subscriber terminal. Each Gateway provides the connection to the Internet backbone for the gateway beam(s) it serves.

The system of gateways comprising the satellite ground system provides all network services for satellite and corresponding terrestrial connectivity. Each gateway provides a multiservice access network for subscriber terminal connections to the Internet.

As the continental United States is north of the equator, all gateway and subscriber dish antenna must have an unobstructed view of the southern sky. Because of the satellite's geostationary orbit, the gateway antenna can stay pointed at a fixed position.

===Antenna dish and modem===
For the customer-provided equipment (i.e. PC and router) to access the broadband satellite network, the customer must have additional physical components installed:

====Outdoor unit (ODU)====
At the far end of the outdoor unit is typically a small (2–3-foot, 60 to 90&nbsp;cm diameter), reflective dish-type radio antenna. The VSAT antenna must also have an unobstructed view of the sky to allow for proper [[Sightline|line-of-sight]] (L-O-S) to the satellite. 
There are four physical characteristic settings used to ensure that the antenna is configured correctly at the satellite, which are: [[azimuth]], elevation, [[Antenna (radio)|polarization]], and [[Skew (antenna)|skew]]. The combination of these settings gives the outdoor unit a L-O-S to the chosen satellite and makes data transmission possible. These parameters are generally set at the time the equipment is installed, along with a beam assignment (K<sub>a</sub>-band only); these steps must all be taken prior to the actual activation of service.
Transmit and receive components are typically mounted at the focal point of the antenna which receives/sends data from/to the satellite. The main parts are:
* Feed – This assembly is part of the VSAT receive and transmit chain, which consists of several components with different functions, including the feed horn at the front of the unit, which resembles a funnel and has the task of focusing the satellite microwave signals across the surface of the dish reflector. The feed horn both receives signals reflected off the dish's surface and transmits outbound signals back to the satellite.
* [[Block upconverter]] (BUC) – This unit sits behind the feed horn and may be part of the same unit, but a larger (higher wattage) BUC could be a separate piece attached to the base of the antenna. Its job is to convert the signal from the modem to a higher frequency and amplify it before it is reflected off the dish and towards the satellite.
* [[Low-noise block downconverter]] (LNB) – This is the receiving element of the terminal. The LNB's job is to amplify the received satellite radio signal bouncing off the dish and filter out the noise, which is any signal not carrying valid information. The LNB passes the amplified, filtered signal to the satellite modem at the user's location.

====Indoor unit (IDU)====
The satellite [[modem]] serves as an interface between the outdoor unit and customer-provided equipment (i.e. PC, router) and controls satellite transmission and reception. From the sending device (computer, router, etc.) it receives an input [[bitstream]] and converts or modulates it into radio waves, reversing that order for incoming transmissions, which is called [[demodulation]]. It provides two types of connectivity:
* Coaxial cable (COAX) connectivity to the satellite antenna. The cable carrying electromagnetic satellite signals between the modem and the antenna generally is limited to be no more than 150 feet in length.
* [[Ethernet]] connectivity to the computer, carrying the customer's data packets to and from the Internet content servers.
Consumer grade satellite modems typically employ either the [[DOCSIS]] or [[WiMAX]] telecommunication standard to communicate with the assigned gateway.