Thoughts on white space spectrum

One of the panels I moderated yesterday at the Open Mobile Summit was focused on US regulatory trends around open access, focusing on this year's 700MHz auctions, and also recent moves to free up spare spectrum in what are known as "white spaces". One of the speakers was from the FCC, so I got a pretty definitive view on what's going on and why.


For those people not familiar with the US White Space phenomenon, I thought I'd give a quick round-up of what it's all about:


- In the US, there are many areas that have spare (unused) channels among the TV broadcast spectrum. Because of the regional nature of the US TV industry, there's a geographic patchwork of "white space" frequencies that could be used .
- Some of these channels are already used by wireless microphones, eg at conferences or sporting events
- There is a strong push by some organisations to exploit the spare spectrum, especially by Internet players like Google and Microsoft, for purposes like mobile broadband, or perhaps a wide-area equivalent to unlicenced WiFi
- There has been push-back against the concept by incumbent network operators (particularly those like T-Mobile that worry about interference), and special interest groups like microphone users (a constituency notably championed by Dolly Parton!)
- The FCC has been broadly supportive of the concept, on the basis that "wasted" spectrum is undesirable, although so is interference. It has tested a variety of prototype devices from assorted manufacturers, which have demonstrated that avoidance of conflict with other users of those bands is possible, albeit with mixed initial results
- After lots of testing and lobbying, the FCC has essentially now given a green light to the general principle of white space utilisation, with a lot of caveats about using a combination of geolocation and databases of used channels, plus device-based monitoring, to avoid interference with TV broadcasts or wireless microphones
- there are various proposed rules that will limit how (eg fixed vs mobile, different power levels) and where (eg not around microphone-laden sports venues or theatre districts like Broadway), the spectrum might be used.

Various companies have already professed huge enthusiasm for the move, hailing it as a new era in WiFi-type business models.

My take?

Well, yes, sort of. At the risk of sounding like a broken record, my initial opinion is that utilising white spaces in a meaningful way is "a great idea in principle, but not as easy as it looks in practice".

There is clearly going to be a lot of necessary work first - not the least of which is going from several proprietary radio types to something which is at least roughly standardised. In particular, the location look-up / sensing approach will need a lot of work, especially for fully-mobile devices. (It should be easier for fixed devices which can be registered / activated centrally). The location accuracy won't need to be as good as GPS for emergency E-911, though.

At the moment, it's not even clear what the radio candidates are, of who is promoting them. It would be incredibly unusual to see just a single united approach, so we'll probably be in something of a battle to get to market. It will presumably also be necessary to ensure that white space devices don't interfere with each other, as well as with TV and microphone signals - which could be a challenge if there are two or more radio technologies involved.

I'd expect the main initial beneficiaries of white space to be people living in rural parts of the US - there are large areas without 3G or WiMAX coverage, or decent fixed broadband. Next may be inclusion of white space capability in large devices like laptops (Dell has already made positive noises). But given all the variables involved, I wouldn't expect to see massmarket urban users touting white-space handsets any time soon.

On a side note, I reckon this trend towards sharing little-used spectrum will become increasingly important on a more general basis in the next few years. It sort of fits with the moves by Ofcom in the UK to get access to swathes of frequencies used by the Ministry of Defence, Civil Aviation Authority and the like. To use a specific example - some bands are mostly used for maritime radar, such as the coastguards, pointing out to sea. In theory, that spectrum should be re-usable for commercial broadband for users who are inland.

A lot of this also fits in with general moves towards software-defined or "agile" radio technology, which is still at very early stages of maturity. But given the likely congestion of established mobile bands in coming years, it's good to see moves like White Spaces as smart ways to squeeze more from a limited resource.