Satellite InternetSuch 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. Special IP stacks and proxies can also reduce latency through lessening the number of roundtrips, or simplifying and reducing the length of protocol headers.
The modems themselves are also expensive, usually costing between $1000 and $4000. For many years now satellite phones have been able to connect to the internet. Even if all other signalling delays could be eliminated it still takes electromagnetic radio waves about 250 milliseconds, or one quarter of a second, to travel from ground level to the satellite and back to the ground, a total of over 71,400 km (44,366 mi) to travel from the source to the destination, and over 143,000 km (88,856 mi) for a round trip (user to ISP, and then back to user—with zero network delays).
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 2006 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. 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.
Factoring in other normal delays from network sources gives a typical one-way connection latency of 500–700 ms from the user to the ISP, or about 1,000–1,400 milliseconds latency for the total Round Trip Time (RTT) back to the user. In the U.S., an FCC license is required for the uplink station only; no license is required for the users. Another type of 1-way satellite internet system involves the use of General Packet Radio Service (GPRS) for the back-channel.
Filtering is usually provided by the DVB card driver. Often, non-standard IP stacks are used to address the latency and asymmetry problems of the satellite connection. The UNIC architecture employs DVB-S2 standard for downlink and DVB-RCS standard for uplink. Normal VSAT dishes (1.2 - 2.4m dia) are widely used for VoIP phone services.
The current LEO constellations of Globalstar and Iridium satellites have delays of less than 40 ms round trip, but their throughput is less than broadband at 64 kbps per channel. At each VSAT site the uplink frequency, bit rate and power must be accurately set, under control of the service provider hub. There are several types of two way satellite Internet services, including time division multiple access (TDMA) and single channel per carrier (SCPC).
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. Onboard batteries would be charged during daylight hours by solar panels covering the wings, and would provide power to the plane during night.
Compared to ground-based communication, all geostationary satellite communications experience high latency due to the signal having to travel to an altitude of 35,786 km (22,236 mi) above sea level (from the equator) out into space to a satellite in geostationary orbit and back to Earth again. Instead as the signal propagates away from the transmitting dish, it widens towards the centerpoint between the two dishes and then narrows again as it approaches the receiving dish.
They are also expensive, costing in the range of US$600 to $2000. The two-way iLNB used on the ASTRA2Connect terminal dish has a 500 mW transmitter and single-polarity receive LNB, both operating in the Ku band. The software at the remote site must filter, store, present a selection interface to and display the data.
The modems required for this service are often proprietary, but some are compatible with several different providers. These types of technologies are generally referred to as TCP acceleration, HTTP pre-fetching and DNS caching. While also effective for terrestrial communications, the use of ad-blocking software such as Adblock for Firefox is exceptionally beneficial for satellite Internet, as most Internet advertising websites use cache busting in order to render the browser and ISP s cache useless, by displaying advertisements (for the purpose of maximizing the number of ad views seen by the affiliate marketing company s server). Advanced Wireless Services · Amateur television · Analog television · Digital radio · Digital television · Digital television in Europe · Digital terrestrial television (DTT or DTTV) · Digital Video Broadcasting: ( Terrestrial - Satellite - Handheld ) · DVB-MS · Ku band · Local Multipoint Distribution Service (LMDS) · Microwave · Mobile TV · Multichannel Multipoint Distribution Service (MMDS) now known as Business Radio Service (BRS) · Instructional Television Fixed Service (ITFS) now known as Educational Broadband Service (EBS) · MVDS · MVDDS · Satellite Internet access · Satellite radio · Satellite television · Wi-Fi · WiMAX · Wireless local loop .
As the radio frequency decreases, to below 900 MHz, penetration through vegetation increases, but most satellite communications operate above 2 GHz making them sensitive to even minor obstructions such as tree foliage. Pricing for Astra2Connect modems range from 299 to 350€.
The technology for ASTRA2Connect was delivered by a Belgian company called Newtec. The satellite Internet service by Tooway is currently operating in both Ku and Ka-band. Satellite internet customers range from individual home users with one PC to large remote business sites with several hundred PCs. Home users tend to make use of shared satellite capacity, to reduce the cost, while still allowing high peak bit rates when congestion is absent. For satellite Internet services in tropical areas with heavy rain, use of the C band (4/6 GHz) with a circular polarisation satellite is popular.
Satellite communications on the Ka band (19/29 GHz) can use special techniques such as large rain margins, adaptive uplink power control and reduced bit rates during precipitation. Rain margins are the extra communication link requirements needed to account for signal degradations due to moisture and precipitation, and are of acute importance on all systems operating at frequencies over 10 GHz. 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 produce a more intense transmission 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. Large commercial dishes of 3.7m to 13m diameter are used to achieve large rain margins and also to reduce the cost per bit by requiring far less power from the satellite. Modern download DVB-S2 carriers, with RCS feedback, are intended to allow the modulation method to be dynamically altered, in response to rain problems at a receive site. Note that most Internet protocols will not work correctly over one-way access, since they require a return channel.
A voice call is sent by means of packets via the satellite and internet. .
Globalstar also provides internet access at 9600 bit/s—like Iridium and ACeS a dial-up connection is required and is billed per minute, however both Globalstar and Iridium are planning to launch new satellites offering always-on data services at higher speeds. This is much like TV or radio content which offers little user interface. Similar to one-way terrestrial return, satellite Internet access may include interfaces to the public switched telephone network for squawk box applications.
Bandwidth varies from about 2400 bit/s for Iridium network satellites and ACeS based phones to 15 kbit/s upstream and 60 kbit/s downstream for Thuraya handsets. A dish installation in the winter must factor in plant foliage growth that will appear in the spring and summer. The radio signal width between two ground satellite dish receivers is not perfectly straight and uniform, as if it were a beam of light.
Many customers in the Middle East and Africa are also encouraged to do self installs. The modems have commonly used connectors such as Ethernet or Universal serial bus.
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 cumbersome and very expensive. When a user exceeds their Mbytes allowances, the company may slow down their access, deprioritise their traffic or charge for the excess bandwidth used.
The delay is primarily due to the great distances travelled which, even at the speed of light (about 300,000 km/second or 186,000 miles per second), can be significant. An Internet connection is not required, but many applications include a File Transfer Protocol (FTP) server to queue data for broadcast. Most one-way multicast applications require custom programming at the remote sites.
This is far worse than most dial-up modem users experience, at typically only 150–200 ms total latency. However, Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) satellites do not have such great delays. Download speeds can be very fast compared to dial-up. Remote sites use the proxy server at the earth station (teleport), which is configured to route all outbound traffic to the QoS server, which makes sure no user exceeds their allotted bandwidth or monthly traffic limits.
Satellite Internet services are used in locations where terrestrial Internet access is not available and also for users who move frequently. Broadband Internet access via geostationary satellite is available almost worldwide, including vessels at sea and mobile land vehicles. However these problems are more than tolerable for basic email access and web browsing, and in most cases are barely noticeable. For geostationary satellites there is no way to eliminate this problem.
The software at the transmitting station must provide access control, priority queuing, sending, and encapsulating of the data. 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. Such acceleration features are present in recent technology developments embedded in new satellite Internet services like Tooway. The signal delay can be as much as 250 milliseconds to 900 milliseconds (one way), which makes this service unusable for applications requiring real-time user input, such as online games or remote surgery.
The phones can be connected to a laptop or other computer using a USB or RS-232 interface. With Thuraya phones the 9600 bit/s dial-up connection is also possible, the 60 kbit/s service is always-on and the user is billed for data transferred (about $5 per megabyte).
The most common such system is INMARSAT s BGAN—these terminals are about the size of a briefcase and have near-symmetric connection speeds of around 350–500 kbit/s. The DVB packets are then sent to the DVB modem and then to the transmitter (BUC). One-way multicast satellite Internet systems are used for Internet Protocol (IP) multicast-based data, audio and video distribution.
The proposed O3b Networks MEO constellation scheduled for deployment in 2010 would orbit at 8,062 km, with RTT latency of approximately 125 ms. The Globalstar constellation orbits 1,420 km above the earth and Iridium orbits at 670 km altitude.
Ground-based satellite dishes would relay signals to and from the aircraft, resulting in a greatly reduced round-trip signal latency of only 0.12 milliseconds. This delay can be irritating with interactive applications, such as VoIP, videoconferencing, or other person to person communication.
Some providers oblige the customer to pay for a member of the provider s staff to install the system and correctly align the dish — although the European ASTRA2Connect system encourages user-installation and provides detailed instructions for this. The modems also tend to have their own batteries so they can be connected to a laptop without draining its battery.
This allows the bit rates to be increased substantially during normal clear sky conditions, thus reducing overall costs per bit. Typically a completely clear line of sight between the dish and the satellite is required for the system to work. This latency problem with satellite communications can be mitigated with TCP acceleration features that shorten the round trip time (RTT) per packet by splitting the feedback loop between the sender and the receiver.
Similar, but slower Internet service is also available through Low Earth Orbit (LEO) satellites, however their coverage areas also include the polar regions at extreme latitudes, making them truly global. End users must be aware of the different types of satellite communication systems and the technical issues involving each, such as latency and signal loss due to precipitation, in order to make informed decisions on which system would serve them best. Latency is the delay between requesting data and the receipt of a response, or in the case of one-way communication, between the actual moment of a signal s broadcast and the time received at its destination. Smaller modems exist like those offered by Thuraya but only connect at 144 kbit/s in a limited coverage area. Using such a modem is extremely expensive—bandwidth costs between $5 and $7 per megabyte.
In the U.S., a Federal Communications Commission (FCC) license is required only for the uplink station and no license is required for users. Traffic is then sent to the encapsulator, which puts the IP packets inside of DVB packets.
The proposed new network is also designed for much higher throughput with links well in excess of 1 Gbps (Gigabits per second). A proposed alternative to geostationary 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 20,000 meters. The signal path through space must be clear not only for direct line of sight, but must also be clear for the expanding fresnel zone, which may be several meters larger in diameter than the ground-based satellite dish. Two-way satellite Internet service involves both sending and receiving data from the remote VSAT site via satellite to a hub teleport, which then sends relays data via the terrestrial Internet.
Some also have an integrated Bluetooth transceiver and double as a satellite phone. Using a 33 cm wide satellite dish, a notebook and a normal GPRS equipped GSM phone, users can get mobile satellite broadband. The transmitting station (also called teleport , head end , uplink facility , or hub ) has two components: At the remote location (Earth station) the setup consists of: Remote sites require a minimum of programming to provide authentication and set proxy server settings.
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 do not need to accept the latency inherent in a satellite connection. 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.
The satellite dish at each location must be precisely pointed to avoid interference with other satellites. Two-way systems can be simple VSAT terminals with a 60–100 cm dish and output power of only a few watts intended for consumers and small business or larger systems which provide more bandwidth.
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. 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.
The functionality of live interactive access to a distant computer can also be subject to the problems caused by high latency. Instead, voice calls on Tooway are transported over a dedicated line with proper quality (20Kbps on each link). The uplink direction for shared user customers is normally TDMA, which involves transmitting occasional short packet bursts in between other users (similar to how a cellphone shares a cell tower) Business users tend to opt for dedicated bandwidth services where any congestion is under their local control. Each remote location may also be equipped with a telephone modem; the connections for this are as with a conventional dial-up ISP.
By utilizing a connection that is offered in standard GPRS or EDGE, the upload volume is very low and since this service is not per-time charged, but charged by volume uploaded, users are able to surf and download in broadband speeds. Another view of using GPRS as return would be the mobility when the service is provided by a satellite that transmits in the field of 50 to 53 dBW.
Using coding and compression techniques the bit rate needed per call is only 10.8 kbit/s each way. 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. This is known as the fresnel zone, and limits the usefulness of satellite dishes in locations where there is extremely limited open sky for signal reception.
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, and latency is high, as it is for any satellite based Internet (minimum of 240 ms one-way, resulting in a minimum round-trip time of almost 500ms). There are usually restrictive time based bandwidth allowances so that each user gets their fair share, according to their payment.
For consumer satellite internet, the allowance can range from 200MB to 17GB per month. Since satellite phones tend to have omnidrectional 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 traditional dial-up access to the Internet, with outbound data traveling through a telephone modem, but downloads sent via satellite at a speed near that of broadband Internet access.