PARIS — Satellite fleet operator SES, saying the aeronautical communications market “is one of the biggest opportunities we’ve seen for years in the satellite business,” has concluded that Ku-band is superior to Ka-band for most mobile-broadband applications.
Stepping into a debate being played out as hundreds of commercial aircraft are outfitted with Ku- or Ka-band terminals, Luxembourg-based SES said using the latest frequency-coding techniques, wide Ku-band beams over little-trafficked areas coupled with high-throughput Ku beams for dense routes, offers better value for most customers than a Ka-band network.
Ka-band satellite capacity has been deployed in Europe and North America for consumer broadband, mainly for a stationary customer base, using multiple spot beams that direct concentrated energy over a relatively small area and permit the reuse of the spectrum.
For this kind of application, SES said, Ka-band may well be superior. But for mobile applications, especially over low-density routes, a wide Ku-band beam covering a large swath of territory “can offer very competitive Mbps [megabits per second of throughput], similar to [high-throughput satellites],” said Simon Gatty Saunt, SES’s vice president for Europe, data and mobility.
“Wide beams are well-suited to accommodate traffic growth by gradual capacity increases [and] provide improved economics for low-density and starter routes,” Saunt said in a Nov. 13 SES webcast.
SES is one of many satellite fleet operators looking for pockets of growth as their core television broadcast markets mature. Aeronautical mobility, offering broadband connections to aircraft cockpits, crews and passengers, is viewed as finally beginning its long-promised hockey-stick-shaped growth phase.
There is no clear verdict on which airline business model — free service with the costs embedded in the airline ticket or a pay-per-megabyte or pay-per-flight model — will gain the most traction among airlines.
ViaSat Inc. of Carlsbad, California; Eutelsat of Paris; Intelsat of McLean, Virginia; Telesat of Canada; Thaicom of Thailand; SES; and others are building satellites with mobility beams.
ViaSat and Eutelsat are combining their current and future Ka-band systems to offer what is designed to be a seamless Ka-band access route covering Europe, North America and the North Atlantic air corridor.
Intelsat, Telesat and SES are adopting the frequency-reuse, concentrated-beam architecture of Ka-band systems in Ku-band, taking advantage of Ku-band’s better resistance to precipitation and the fact that they already use Ku-band for direct-to-home television.
Saunt said that some Ka-band high-throughput satellites (HTS) offer compelling per-megabit throughput costs, but that this advantage disappears in the total cost of system ownership. “Ka-band equipment — the antenna and the [solid-state power amplifier] — is much more expensive than Ku,” Saunt said.
ViaSat and other builders of Ka-band systems say that the cost difference in ground gear is disappearing fast as Ka-band systems are deployed and scale economies are generated.
Gez Draycott, SES’s senior manager for satellite engineering, said during the webcast that SES remains “bandwidth agnostic. We use C- and Ku-bands and we are developing Ka-band satellites as well.”
But managing aeronautical customers with a high-throughput satellite with dozens of spot beams requires multiple ground gateways, which add operating costs and complexity to the system, Draycott said. “Capacity reservation on multiple beams is necessary, because not all beams will be hot spots,” he said.
Draycott used the example of a flight from London to Sofia, Bulgaria. To provide full coverage for the flight, a satellite fleet operator with a Ka-band spot-beam satellite likely would need 10 beams for full coverage as the plane moves from gateway to gateway, each with its own IP address.
As a general rule, Draycott said, a Ku-band HTS spot-beam satellite will have beams between 550 and 965 kilometers in diameter, while a similar Ka-band satellite’s beams would be around 480 kilometers in diameter. A wide Ku-band beam covers an entire continent.
SES said a Ku-band HTS system beam typically can offer 200 megabits per second on the forward link and 80 megabits per second on the return path. For Ka-band, the company said, the downlink is 45 megabits per second, with the return link at 4.5 megabits per second.
“A plane traveling at 500 miles per hour [805 kilometers per hour] would be in a given beam only for 45 minutes before it would need to switch,” Draycott said. “This technical complexity adds a lot of extra risk to the service.”
