Lighting a Fire Under Satellite Broadband
The root of satellite speed is processing power on the ground
17 February 2012—ViaSat is hoping to leave the rest of the satellite broadband universe in the dust. On 10 January, it launched Exede, a new satellite broadband service that the Carlsbad, Calif., satellite communications company claims will be as good as or better than the average optical fiber connection on the ground. ViaSat plans to offer the service to about a million subscribers across the United States and Canada.
Subscribers will be able to download at speeds of 12 megabits per second and upload at 3 Mb/s. With obvious pride, Erwin Hudson, chief technology officer of ViaSat communications, calls the US $49-per-month service “screamingly fast.”
Speed is good news for rural residents who depend on satellite broadband. ViaSat’s existing satellite broadband service, WildBlue, suffers from an ailment ubiquitous in the industry: slowness. It’s slow enough to make an agonizing ordeal out of loading graphics- and video-heavy pages like those at CNN.com or ESPN.com. Part of the reason is the limited bandwidth of first-generation satellites, the best of which have a mere tenth of the 140-gigabit-per-second capacity of ViaSat-1, the new satellite at the center of the Exede service. But the other, more challenging problem is the half-second lag time between a satellite broadband subscriber’s computer and the Internet.
Delay is intrinsic to satellite communications. The signal sent from the subscriber’s antenna on Earth takes an eighth of a second to reach the satellite 35 786 kilometers up in geostationary orbit, and another eighth of a second to make the return trip to the Earth-based server connected to the Internet. The server’s response takes another two-eighths of a second to relay back.
ViaSat’s solution to the space-based delay was to invest in a fast, efficient ground network system. On a typical network, when a computer requests a website, it gets an inventory of Web-based objects to call up and assemble. If the computer is wired to the Web, that assembly happens so quickly that the user doesn’t notice. But if the computer is linked to the Web via satellite broadband, every object request has to go through the half-second call-and-response routine. A page like CNN.com can have hundreds of objects, and the computer has to call each one individually.
ViaSat, however, does most of the back-and-forth work for the subscriber’s computer in advance. When an Exede subscriber accesses a website, ViaSat’s ground network preassembles it and beams it up in a tight package, reducing lag time to the half-second minimum. The company calls this system AcceleNet. Not only does it speed a subscriber’s Web experience, it conserves bandwidth on the satellite by sending the Web page in a single shot.
AcceleNet is powered by five large data-processing centers located in Dallas, Denver, Fort Worth, Salt Lake City, and Seattle; each has 100 to 200 blade servers. The data centers handle security and other traditional Internet service provider tasks, but much of their processing power is devoted to AcceleNet.
It’s no coincidence that the data-processing centers and the 20 Earth-based transmitters that connect them to the satellite are all in the western half of the United States, which has a drier climate. Previous satellite broadband services tended to lose their signal in wet weather (a phenomenon known as rain fade), and the problem was most pronounced for satellites using the highest frequencies. ViaSat-1 transmits on the relatively high-frequency Ka-band—uplinking at 28.1 to 30 gigahertz and downlinking at 18.3 to 20.2 GHz—parts of the spectrum that are susceptible to rain fade.
But subscribers aren’t limited to the American West. To overcome wet weather, ViaSat has equipped every subscriber’s modem with an adaptive transmitter that optimizes its signal in real time. The transmitter constantly measures signal quality and reengineers the waveform it transmits. ViaSat’s earth-based transmitter modems use the same process.
“ViaSat is good at [adaptive modems],” says Keith Barker, president and chief executive officer of the Questiny Group, an engineering consultancy specializing in wireless communications technology. “Bringing this technology to the Ka-band satellite market will be a competitive advantage, but likely not a sustainable one,” he says. That may be bad news for ViaSat but good news for satellite broadband users who want more bandwidth and competition in the market.
Of course, ViaSat isn’t waiting for competitors to catch up. It has plans for a new satellite with more than double the bandwidth—300 to 500 Gb/s—and this is just the beginning, the company says.
“Our view is that we are just scratching the surface,” Hudson says.
About the Author
Kim Krieger is a freelance science writer in Norwalk, Conn.