The broadband market came down to Earth last year. Cable, wireless, and DSL once promised to provide high data rates at low cost, but all three have suffered major setbacks. With fiber far from most areas, it seems we're stuck with either high-priced T1 or slow dial up.
Cable targets the residential market. Incumbent carriers that would rather pay fines than allow competitors to challenge their monopoly have driven DSL providers out of business. AT&T and Sprint are both winding down their fixed-wireless divisions, citing lack of demand and technical issues.
But one type of broadband is still flying high. Satellite networks are finding a new way to compete in the local loop, providing high speeds and global coverage. These networks are about to get faster and cheaper, thanks to a new generation of satellites launching this year. In this article you'll learn about broadband satellite services, how they work, and what to expect from these services in the future.
Three companies plan to build and operate these new broadband networks: Spaceway (www.spaceway.com), developed by General Motors' spin-off Hughes; Astrolink (www.astrolink.com), from aerospace giant Lockheed Martin; and Euro Skyway (www.euroskyway.it), from Italian company Alenia Spazio.
These networks use satellites containing their own switches, along with highly focused antennas that target particular neighborhoods or individual customers. The companies say these networks will enable them to serve anyone, from an individual consumer to the largest enterprise. Only Spaceway and Hughes promise global service; Alenia Spazio will only cover Europe and Asia. (See table).
RING TOPOLOGY
Don't confuse these new networks with the ill-fated Low Earth Orbit (LEO) constellations such as Iridium (www.iridium.com) and Globalstar (www.globalstar.com), which need dozens of satellites and are aimed at mobile telephony. Though some companies have broadband LEOs on the drawing board, they won't launch until some financial and technical problems are resolved. LEOs have been four years away for most of the last decade.
The services rolling out in 2002 and 2003 are based on a variant of tried-and-tested fixed satellite technology, used by thousands of businesses and millions of TV viewers worldwide. The satellites fly in a Geostationary Earth Orbit (GEO), which is tied to the earth's rotation, so the satellites seem to hang in a fixed position in the sky. Customers access them through a Very Small Aperture Terminal (VSAT), not necessarily dish-shaped anymore. And some VSATs don't have to be pointed at the satellite, though all require a direct line of sight.
The next generation of fixed satellite technology will add new technology to overcome two of the GEO's longstanding problems: It's a long way from Earth-22,300 miles-and the orbit forces satellites over the equator. The great distance means that, even at the speed of light, radio waves take a noticeable time to travel to the satellites and back. This distance caused the time delay that once plagued international phone calls, but this delay has now all but disappeared because the signals are routed over fiber instead.
The delay is exacerbated by the "bent pipe" architecture of existing networks. The satellite amplifies a signal and sends it back to a switch on the ground for processing (see Figure 1). If both ends of a communications link rely on this satellite, the data has to make two roundtrips into space, pushing latency to more than half a second.
Engineers can't change the speed of light, but they can reduce the distance signals have to travel. Spaceway, Astrolink, and Euro Skyway will all put switching intelligence onboard the satellite, so two users can communicate directly. Spaceway also has Intersatellite Links (ISL), which can bypass the Earth even when different satellites serve the two users. When the network becomes truly global in 2004, data might travel through several satellites going from one side of the Earth to the other.
Equatorial orbits make satellites difficult for people to use at latitudes in the far north or south for two reasons. First, radio waves have to pass through a large cross section of the atmosphere to reach high latitudes, reducing signal strength and requiring users to have a larger dish (see Figure 2). Second, if the satellite lies low on the horizon, buildings or trees can block the line of sight.
GEO satellites can't surmount this blocking barrier, which led the LEO constellations to tout the benefits of satellites scattered all over the sky. (If you're outside, you can almost always reach an Iridium or Globalstar LEO satellite.) However, the blocking problem actually affects few users. High buildings tend to be in major business districts, where fiber is a better alternative to satellite. It's true that low-lying snowdrifts can block the field of view in the polar regions, but most people who pass through the Arctic aren't on the ground, they're in planes, where a line of sight is guaranteed.
The new fixed satellite technologies overcome atmospheric fading by increasing signal strength. They use targeted beams, which point a transmission directly to whoever needs it. This approach also gives the networks increased capacity by reusing the same spectrum in different areas, meaning users don't need to filter out data intended for others. Existing satellites are inherently point-to-multipoint, broadcasting data throughout their coverage area, so it's wasteful to use them for point-to-point applications, such as corporate network access and interactive Web surfing.
"Satellite capacity is still very expensive, and its big advantage is that you can broadcast it to a lot of users at once," says Jonathan Barter, data broadcast manager at Kingston Consulting (www.kingstonconsulting.com), a system integrator specializing in satellites. Without localized beams, that advantage is lost.
BLOATED WINDOWS
Spaceway is set to launch in 2002, but will initially serve only the continental United States ("Conus," in satellite parlance.) Global coverage, and the Spaceway network's competitors, won't arrive until 2003 or 2004. If you can't wait, you can still find some innovative new services that use existing satellites. These services employ new technology in the ground segment, including the user's VSAT, the service provider's switch, or both.
The point-to-multipoint bias of most satellites is usually a problem, but there are two ways that it can be turned into an advantage. The most obvious is to connect an entire network to the satellite, treating it rather like a large Ethernet hub. Whenever a user sends data to the satellite, it gets automatically rebroadcasted to everyone. Again, as in Ethernet, the transmissions are not coordinated, so collisions occur if the network becomes overloaded. Whenever this occurs, the data is simply re-sent.
