Going the Long Way Round
Connexion makes use of geostationary Ku-band satellites that can relay data from ground stations to fixed and moving receivers across geographic areas of a few hundred square miles. Satellites contain multiple transponder pairs - separated by receive and transmit - which cover a given region. The Ku-band is 10.7 to 12.75 gigahertz (GHz) which allows for an extremely high data broadcast rate.
There are several dozen Ku-band satellites operated by a number of different companies over the U.S. and around the world. Boeing has contracts with different satellite operators and the option to purchase more service as necessary.
"The solution was to use a frequency of satellites that had enough throughput to give people in aircraft an experience similar to that on ground," said Stan Deal, Vice President, Commercial Aviation Business for Connexion by Boeing. Rather than invent new technology, Deal said, Connexion decided to put together a "business case around a set of existing technology to bring this into the market efficiently."
The engineering challenge was to build a system that could handle airplanes traveling at 600 miles per hour at various latitudes and elevations that would allow the simultaneous broadband use by dozens of passengers.
Figure 2: How Connexion Works
(image courtesy of Boeing)
(click image to enlarge)
The technical and financial key to making Connexion work is the antenna used for satellite communications. "The antenna on the airplane is really the conduit inside and outside the airplane to the satellite," said Deal. "It's designed to be as efficient as possible in transacting signal to and from the satellite."
The more efficient it is, the less cost to Boeing, and the more capacity that's available. Deal noted that the best antenna would be the largest one, but "it's gotta fly." And the same antenna design had to work on planes that scale from a Boeing 737 up to an Airbus A380. (In fact, most of the early Connexion deployments have been on Airbus planes.)
The solution was to design an antenna that can track satellite positions, which allows Connexion to use the smallest possible footprint. On-board avionics already in use for flight information track a plane's absolute global position, which is then handed off to the Connexion system to correlate against a table of known geostationary satellites. The antenna is constantly tracked against the optimum satellite, with changeover automatically handled by the on-board system.
"That allows us to essentially have aircraft equipped to look at these satellites that are parked above the equator at 23,000 miles above the earth and have coverage up to 75 degrees" north and south latitude, Deal said, which he estimates is about 99.2 percent of all air traffic. "There are a few aircraft - and there are coming more over time - that are starting to fly over the poles," he noted, which would not be able to offer the service.
Access is supposed to be available throughout a flight. But reports from passengers indicate that while it's generally reliable, there can be moments of disruption. However, those moments don't last long if they occur at all.
Deal wouldn't comment on reports last year that retrofitting a plane for Connexion could take as long as 20 days. However, in a publicity flight over Washington State in November 2004, Deal said that Connexion had recently reduced installation time from 10 days to under seven days. Seven days is a typical window for routine major maintenance intervals on commercial aircraft.
The planes use their swiveling antennas to talk to the satellite which in turn maintain fixed communications with ground stations. Boeing currently has stations in Littleton, Colorado; Japan; Lake Switzerland; and Moscow. A fifth hasn't been announced, but will be up and running in April.
The raw speed delivered to the planes through this arrangement is rated at 5 megabits per second (Mbps) downstream (ground-to-satellite-to-plane) and 1 Mbps upstream (plane-to-satellite-to-ground). Deal said that the service can deliver up to 20 Mbps to a single plane, but no airline had yet requested more than 5 Mbps.
Connexion's partner airlines have mostly chosen to use only Wi-Fi to distribute access throughout a plane. A few planes may be equipped with Ethernet jacks, such as certain Lufthansa models, but only in business and first class. (That's where power jacks are located, too, on planes that have them.)
As we'll see from real-world experiences, however, these theoretical maximums govern a plane's overall bandwidth, and not what each user will see.