A word about off-axis power density…

The other day I wrote a blog about Qest’s new Ku-band antenna system, the KuStream 1000, which is being developed in tandem with Tecom (BTW, the pairing’s new web site is now live).

In that blog, I said ViaSat – which has expressed concerns about Row 44′s antenna-pointing accuracy – will need to show the FCC that it can meet its own expectations, “which are high, very high”.

A competitor to Row 44 in that it plans to offer Ku-band-based connectivity to airlines, ViaSat responded to me directly, saying it would like to point out that its expectations “are only that system operators meet applicable domestic and international radio regulations”.

The company says that it is not asking the FCC to impose higher standards on Row 44 “than those required by their existing rules, nor do we ask the Commission to impose standards on Row 44 or others that ViaSat itself is not prepared to meet”.

Furthermore, it says: “The FCC and ITU regulations were put in place not at ViaSat’s request, but rather as a result of years of policy discussions by the regulatory administrations around the world, who in turn take inputs from local industry.”

Has ViaSat taken umbrage with my posting? “We don’t take umbrage at all. I just want to make it clear that these aren’t our requirements, they are those of the regulatory world and they’ve been put in to place after a lot of input from industry around the world.”

Bugger, and here I thought I had something controversial to report.

But what’s this about off-axis power density, RWG? Are you taking your meds today?

With respect to Row 44, the issue, to ViaSat, is not simply a particular antenna performance specification like antenna pointing error. Indeed, it says it has been an advocate of relaxing antenna pointing error requirements where conditions permit.

“The issue is off-axis power density. The higher the off-axis power density, the better the antenna pointing must be in order to protect the adjacent satellite systems,” says the firm.

“An antenna is only part of the off-axis power density problem, the modulation used in conjunction with the antenna is another part of the story, as is the performance of the satellite being used – it’s a systems problem.

“If the off-axis power density gets too high and is right at the regulatory limits, then the pointing accuracy needs to be near perfect, but if it is very low – as in the case of the Qualcomm OmniTracs system, pointing error can be quite large – even though their antenna beamwidth is very wide and their pointing performance is poor.

“The OmniTracs system in fact does not even do any pointing at all in the elevation direction and relies on the wide beamwidth of the antenna. But due to their low power density, the OmniTracs system has been operating for over 20 years without causing any grief to adjacent satellite operators.”

Good gracious, who needs more coffee? I make note of ViaSat’s comments for one reason. It is now exceedingly clear that despite the launch of Row 44 trials on Southwest Airlines and Alaska Airlines – about which we celebrated here and at the tail end of here, respectively - ViaSat has no intention of backing down in its objections to the California-based firm’s application to the FCC. What will it mean for Row 44 or the likes of these Wi-Fi happy Alaska Airlines passengers? 

Good question!

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