|
|
|
|
| There are over 300 communications satellites in the
geostationary orbit, directly above the equator, spaced typically 2 or 3
degrees apart. Because they orbit the earth at the same speed and in the
same direction as the earth rotates they remain fixed in the sky and you can
use a fixed pointing very small aperture terminal (VSAT) to communicate. The
maximum possible coverage area from any one orbit position is approx one
third of the earth, as that is all that is visible from the orbit position
at a height of 35726 km. For example, a
satellite above the equator to south of India can provide coverage which
includes South Africa, Europe to Japan and Australia, as well as India which
is almost directly below it. To help with small dish broadband satellite
operations spot beams are pointed down at particular areas. This web site
shows many such beam coverage areas. In general smaller spot beams permit
smaller earth station dishes. The satellites are owned by large
multinational companies or by specific national companies.
Intelsat, NewSkies and
Eutelsat are examples
of international and regional operators providing broadband internet via
satellite capacity. The capacity for satellite internet is measured in amounts of transponder bandwidth (MHz) and downlink eirp power (dBW) and uplink G/T (dBK) and sensitivity (dBW/^m2) are sold to broadband satellite internet service providers who have teleports with groups of large earth station dishes. The conversion of bandwidth, measured in MHz, to broadband internet bit rate is complex and depends on modulation method (BPSK, QPSK, 8-QAM or 16-QAM) and the forward error correction coding rate (1/2, 3/4 or 7/8) and type for FEC (e.g. Viterbi, Reed Soloman or Turbo code). The size of the dishes used also affects the achieved capacity. Using large dish may markedly reduce costs per Mbit/s. Broadband via satellite internet service providers then sell service to end users by providing them with equipment and with monthly capacity on the satellite. Customer equipment consists of a small dish, from 60cm to 3.7m diameter, at least equipped with a receiver module (LNB definition = Low Noise Block down-converter) and transmit module (BUC definition = Block Up-Converter). The indoor equipment receives the satellite broadband signals and extract data for the customer's PC or local area network. The indoor equipment also prepares data for transmission, typically in very brief TDMA bursts whenever the mouse is clicked to send a request to the internet. Monthly bit rate rental is specified, for example, as 512k down / 64k up shared 20:1 at price $202 per month. This price is per VSAT customer terminal (i.e. $4032 per month in total). Such a service would suit 1 or 2 PCs per site. When you are downloading a file the speed may be up to 512k bit/s. With 50:1 sharing you would find that for much of the time the available bit rate is lower - as other people will be using the capacity at the same time. In shared arrangements there are often monthly download and upload limits (measured in G bytes per month) per customer, so that one user cannot block everyone else. Such "fair-use" policies can be complex and, for example, may allow 40 Mbytes to be downloaded at high speed (say at 355 kbit/s) with such activity then followed by several hours of restricted lower speed 128kbit/s service until the service returns to high speed every 8 hours. Such policies vary greatly from one service provider to another. When calculating the downlink bit rate capacity required, allow at least 10kbit/s per PC, so if you have 100 PCs in your local area network (LAN) you need a 1 Mbit/s dedicated download rate. Uplink bit rates required are about 1/3rd of the downlink rate. If your use is only web browsing then the up/down ratio is about 1/5. If you do lots of VoIP calls then you need equal capacity up and down. Remember you get what you pay for. As a rough estimate, if you see a monthly tariff, divide it by $70 and that will give you the number of PCs that you can connect in your LAN. Don't believe marketing hype about "unlimited" downloads on what are really shared services. If you need dedicated satellite internet capacity, for services like VoIP which require at least 11kbit/s each way all the time the call is in progress then dedicated continuous information rate service (CIR) is appropriate. Dedicated service is many times as expensive than shared service but is suitable for internet cafés, businesses and community ISPs. A VSAT terminal is therefore often shared amongst a community of users to share the cost of the monthly charges. Operation is in frequency bands called C band (4/6GHz) and Ku band (11/14GHz). C band is ideal for heavy rain locations. Ku band is the most popular with dish sizes in the range 60cm - 1.8m diameter. New Ka band satellite broadband services ( Wildblue ) have started in the US and Canada and capacity is rapidly filling up. Hosting: We are on our own SUN NETRA T-1 computer server with Solaris 10. We have several sites sharing with us, to help with the cost of the dedicated computer and internet connection. No more sites are presently being added. But, if you want a very simple web site (like this one) and do not have excessive download requirements (i.e. under 1 - 8 GB per month) and are still interested please click here for more information. I have written a web site for Seaband ( maritime VSAT satellite services ). Emails sent to me asking for space segment leases, asking for VSAT services or equipment or asking for internet services via satellite etc may be forwarded to any possible suppliers unless you specifically request otherwise. This site contains a favourite icon (favicon) Reviews of equipment and services welcome. Please e-mail me Eric Johnston. I am pleased to accept technical reviews and descriptions of alternative technologies and ways of providing services. Please send images also. If you have a web site, please put text links direct to specific pages here, rather than copying pages. Your cooperation would be appreciated, thank you. All content Copyright (c) 1999-2007 Sat. Signals Ltd. All rights reserved. Established web site since 1 Jan 1999. Legal disclaimer, terms of use and conditions and non-privacy statement. This satsig.net web site was successfully transitioned onto our SUN NETRA T-1 server thanks to my son Colin, who is a senior UNIX Systems Administrator and helps me out from time to time with VSAT remotes and VSAT hub network configuration etc. Other links:
France -
Internet par satellite.
Deutschland Highspeed
Satellite Internet uber satellit.
Vipersat VSAT hub.
High resolution
satellite photo images. EU constitution
treaty |
|
Ku band BUC sale. |
If you have a PayPal account you may make a donation to this website |
My recent holidays: |
"Satellite Signals", "SSL",
"SatSig" and "Ivsat" are TradeMarks. Last updated 8 June 2008
Other names used on this page, SUN, Solaris, Wildblue, Intelsat, NewSkies and
Eutelsat are trade names of the respective companies.
