Band of gold

The satellite industry is undecided about which frequency band is best.

The key resource for all communications services, satellites included, is frequency spectrum. In the past four decades, communications satellites have expanded from their early, former haven of C-band to the higher frequency bands, partly as a result of increasing competition from terrestrial users, but also because of the growing need for raw bandwidth.

Today, satellite usage of the spectrum has spread beyond Ku-band, to K- and Ka-band, while developing and retaining important footholds in the lower bands, much of it shared with terrestrial operators. The current technical argument among satellite operators is the degree to which Ka-band should be adopted.

Overview effect

Satellites have built their reputation on what some have called 'the overview effect', an ability to broadcast to continent-sized coverage areas without the need for a terrestrial network. Perhaps less well known is their work in providing cover for fibre networks when cables fail and their unique ability to supply immediate links to disaster zones, and for 'first responders' in general.

Initially, this broad coverage took the form of a single transponder in a single beam, formed by a simple feed-and-dish antenna on the satellite, but this soon developed into multiple feed systems and larger, often steerable dishes. A technical parameter driving this evolution was the increase in frequency, because higher frequencies/ shorter wavelengths allowed - indeed required - smaller onboard hardware, meaning that more of everything could be crammed aboard the mass- and size-limited spacecraft.

The move to Ku-band, pioneered by the European Space Agency in the late 1970s and resulting in the first-generation Eutelsat and Inmarsat satellites, meant that beams could more easily cover regions or countries, as opposed to continents, and that limited frequencies could be 're-used' within the same region without interference. This led ultimately to the development of multiple spot beams for frequency re-use within individual nations, akin to the now-familiar cellphone network pattern.

Way back in the 1980s, it was realised that a natural progression from Ku- to K- and Ka-band (the designations Ku and Ka derive from their positions 'under' and 'above' K-band) would accentuate these technical advantages. But rather than move forward apace, the industry seemed to stall in familiar territory.

Ka or not Ka?

Today, most operators will specify a handful of Ka-band transponders for a new satellite design, largely to service the growing need for broadband applications, but require the majority to operate in Ku-band to serve existing markets. However, changes are afoot.

In January, Eutelsat Communications ordered its first satellite to operate exclusively in Ka-band. Named, somewhat unimaginatively, KA-SAT, it will feature "over 80 spotbeams" and "offer 10-15 times the capacity of a large Ku-band satellite", according to the company. Indeed, in an era of increasing broadband requirements, capacity is a key concern that Ka-band seems well-placed to address: the raw bandwidth of Ka-band (some 13GHz), and the additional 9GHz of K-band typically used for Ka-band satellite downlinks, compares well with the 6GHz of Ku.

Eutelsat's CEO, Guiliano Berretta, extolled the technical virtues of Ka-band at the Satellite 2008 conference in Washington DC in February. "Satellite is the cheapest way to transmit television," he said, quoting a cost of about Є400,000/channel compared with some Є8m/channel for terrestrial systems, but a satellite optimised for TV "wastes power by transmitting to people who are not interested" in a given service. By contrast, he argued: "IPTV [Internet Protocol TV] is about transmitting to a person…and it is impossible to have a cheap solution with current satellites." Hence the move to Ka-band.

Although he admitted there was "nothing magic about Ka-band", Beretta explained that to produce the spot beams required for frequency reuse would require dishes too large to fit comfortably on the satellite. "That's why you go to Ka-band…smaller dishes," he said. As a key part of Eutelsat's 'Hot Bird video neighbourhood' at the 13° E orbital position, KA-SAT is designed to provide broadband communications and 'local' TV channels following its launch in 2010.

However, Eutelsat's chief European competitor, SES Global, remains unconvinced of the merits of a Ka-only satellite. Asked why, the company's president and CEO Romain Bausch appears evasive: "We have hybrid Ku/Ka satellites," he says, but "the service we provide is not [based on] Ka-band".

SES is more interested in pursuing its Astra2Connect high-speed broadband service, which offers download speeds of up to 1024kbps and uploads at 128kbps from "self-installed" terminals priced around Є250-270. "None of us believes we can compete with terrestrial broadband," says Bausch, "but it's a niche market" aimed at the rural communities of Europe.

Returning to the question of Ka-band, Bausch says he expects the broadband service to attract "some 200,000 users over the next five years", adding: "We'll decide later if and when to invest in Ka-band."

Despite this, Telesat's CEO, Dan Goldberg, described 2007 as a "break-out year" for Ka-band satellites, mentioning a number on order or already operated by companies such as HNS, Telesat and WildBlue… and not forgetting the new kid on the block, ViaSat.

Known chiefly as a ground terminal supplier, ViaSat surprised the industry in January by ordering a high capacity satellite of its own, apparently placing it in direct competition with its customers. In fact, with its advertised throughput of 100Gbps, ViaSat-1's capacity exceeds the current combined capacity of all the other two-way C-, Ku- and Ka-band satellites covering North America.

Compete or collaborate?

At one time, satellites were seen as competitors to terrestrial communications suppliers, but today's industry is moving towards a more integrated communications solution. This is particularly noticeable in the mobile satellite industry, which is busy developing its L-band and S-band offerings (from Inmarsat, MSV, Terrestar and ICO Global), while supplementing coverage with ground-based repeaters in a so-called Ancillary Terrestrial Component (ATC).

Nevertheless, satellites will always be cheaper and more spectrum-efficient than terrestrial systems for point-to-multipoint applications, such as broadcast HDTV and GPS-based services. And new satellite payload technology means that smaller beams can target local areas, offering regional TV and radio channels, along with regional advertising, to areas that fibre will never serve.

The potential downside is that 'digital signage' - that all-pervasive favourite of the science-fiction movie - will become "ubiquitous in the next ten years", as Hughes' senior VP Mike Cook predicts. It's already appearing at some filling stations in the US, he notes, with a wry reference to the innovation of 'pump-top TV'.

No wonder there's always a need for more bandwidth! 

Mark Williamson is an independent space technology consultant

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