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Microsoft strolls into white space

Ten days until we can join them

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It's ten days until the FCC will tell us the hows and whos of white space spectrum, but Microsoft has already switched on its campus-wide white-space network and is expecting great things.

The Microsoft network was demonstrated a month ago, as part of the company's propaganda war to convince the FCC to allocate the white spaces the way Redmond wants, and is now providing connectivity to shuttle busses and buildings across the 200-hectare campus from only two hot-spots - Wi-Fi on steroids indeed.

Microsoft, along with Google, wants white space radios ("white fi" as Redmond terms it) to be unrestricted. Ideally such devices would use detect-and-avoid technology to establish which TV-broadcast frequencies aren't being used locally, and then make use of them.

Unfortunately such detect-and-avoid technology dosen't actually work, for both technical and architectural reasons. Even if it did not everyone wants the free-for-all that Microsoft is proposing, and with the FCC set to announce its decision in ten days (23 September) the submissions to the regulator are increasing in both frequency and acrimony, with companies desperate to ensure that their opinions are heard.

The FCC has already said that white spaces - TV channels that aren't being used locally - will be made available for other purposes, but there are lots of details still to be decided.

Given the failure of detect-and-avoid the FCC decided to back up detect-and-avoid with a national database: devices will be required to report their location to the database, which allocates a frequency to that device for a set time period after which it is required to check back again.

How often devices check with the database has proved a contentious question, and it seems there will be two kinds of device. Mode 1 devices are stationary and might only have to check in daily, while Mode 2 (portable) devices will have to check in every few minutes but only have to contact the nearest Mode 1 device to do that. Those numbers are hotly debated, particularly as it looks as though the FCC is going to drop the detect-and-avoid requirement to keep the kit cheap.

Not that anything is decided yet - one consortium, led by FiberTower, has been lobbying hard to have some channels reserved for point-to-point backhaul. In its filings FiberTower argues that a 75-mile link could be established for as little as $200,000, as compared to over $2m to achieve the same thing at microwave frequencies.

Such connections would, of course, require protection as they would be carrying commercial backhaul. Other lobbyists, such as those representing the Wireless Internet Service Providers, argue that FiberTower's proposals would hand white spaces to the cellular operators (the biggest users of backhaul), which was hardly the idea.

Other arguments surround the minimum and maximum antenna heights - currently the minimum is 10 metres, taller than most domestic homes, while the maximum is 30 metres, to keep the range low, but both are still being debated along with the reservation of a couple of channels for the licenced wireless microphones that have been lurking in white space for the last few decades.

Deployments like Microsoft's, and those put up by Spectrum Bridge, show what white space can do, but things will change once everyone is trying to do the same thing in the same spectrum. The FCC is treading carefully, but come 23 September at least half and probably more of those involved will be claiming the end of the world as we know it, and not in a good way. ®

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