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Could rain put a damper on Global Xpress?

Could rain put a damper on Global  Xpress?
Inmarsat is promoting its Global Xpress (GX) service as the next big thing in satcoms that will see satellite communications in shipping are about to take off in a big way.

GX promises to make bandwidth considerations no worrying than on land-based broadband connections, with information transfer so voluminous (provided you can pay) that your seafarers will not be able to use up the data as quickly as you can provide it for them. At the “consistent high-performance download speeds of up to 50Mbps” promised on Inmarsat’s website, crew could download every episode of Game of Thrones in just over four hours. Not bad.

But will this work in practice? When Inmarsat is able to launch its $1.6bn trio of Global Xpress satellites into geostationary orbit, which is likely to be delayed until late 2015 after a Proton-M launch failure earlier this year, we will find out; in the meantime, however, many are concerned about the problem of rain fade.

Occurring in precipitous environments such as rain, snow, fog, and ice – which, it is alleged, vessels are wont to encounter now and then - rain fade causes short-wavelength satcoms connections to fail, and vessels will have to switch to lesser-but-stable frequencies like L- (1-2GHz) and C-Band (4-8GHz) in order to maintain a connection.

Rain fade normally affects frequencies over 11GHz, and will now and then cause issues on the Ku-Band frequency – between 12 and 18GHz – which is the existing high-throughput frequency broadly used by shipping today. However, Ka-Band, which Inmarsat’s GX service will be using, has a much shorter wavelength, and is much more vulnerable to the phenomenon.

This is something that Intelsat’s maritime product manager Danielle Edwards has been calling attention to of late. “According to a recent white paper by Harris CapRock,” Edwards told Seatrade, “in downlink, rain dissipates 3 to 10 times more energy at Ka-band than at Ku-band (11 GHz vs. 20 GHz). In uplink, it dissipates 63 to 400 times more energy at Ka-band than at Ku-band (14 GHz vs. 30 GHz).

“Given that it rains as much as 100 days per year in the tropics, with typically 100 inches per year—but as much as 400 inches—the likelihood of losing link due to rain is not insignificant.”

Edwards’ own company is launching a different high-volume data service, EpicNG (“Next Generation”,) which combines the type of wide-beam Inmarsat’s service will use with “spot beams” which provide more concentrated data volumes over a smaller area. “When all factors are equal, the Ku-band signal will provide more throughput,” says Edwards. “Talking specifically to current programmes and keeping dish size constant at 45 centimeters, Epic delivers as much as 20 times per terminal as compared to certain Ka-band systems that are marketing to the mobility world.”

Inmarsat’s first satellite, F1, is currently in orbit and will be entering service soon, says Inmarsat: “…the start of commercial GX services on a regional basis using F1… will not be impacted by any delay in global service availability.”

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