WiMAX and TV White Space Spectrum - A Short Tutorial

Will WiMAX make a big impact in the new unlicensed spectrum TV White Space? We look at the basics of what you need to know.

With the FCC ruling in the last week that it would allow unlicensed use of TV "White Space" spectrum for the US many camps are all aflutter about the potential for this technology to be a big front for WiMAX growth. 

So will it? Well, I guess that depends on your point of view.  My short answer is I don't think anytime soon.  But it maybe could.  So why and what is it about this spectrum that has so many so excited?

The FCC has been testing devices and taking comments from many interested parties, both pro and con.  Testing actually took two phases and the first phase of tests did not go so swimmingly.  There were problems.  And actually in my opinion the second phase of testing was not without some hiccups.  There were some problems.  I think that the testing did not have enough field trials to really be definitive.  Radios did not sense active signal in all cases, but I think those are mostly solvable issues. 

In any event finally the FCC has ruled.  The basics are this: Devices can be used for both fixed and portable use (an important element) but they must also possess a geolocate feature, be able to sense active licensed spectrum channels and, at least initially, they must be able to download a database of spectrum in use for a given area.  They also must be able to sense wireless microphones which are allowed via Part 74 of FCC rules.  Sound complicated? Well, a bit maybe, but I don't see any of this as a big hurdle for device manufacturers.  We will have devices relatively quickly I think, possibly in the next 12 months even. 

The FCC will require testing for all devices of course, which will take some time.  So where is this "White Space?" Basically devices will operate in UHF channels 21-51.  And most of the devices tested out to sensitivities below -110 dBm and some quite a bit better. 

Okay so we have covered the basics of the ruling and devices (the very basics), now why is everyone so excited about this spectrum.  Well, being unlicensed it would free up vendors and users to define creative and valuable ways to use the spectrum.  And it could be especially useful in rural areas.  The why of that, is that the physics of spectrum dictate that the lower the frequency the better signal propagates over distance and the easier it is for it to penetrate solid objects.  So a carrier would need fewer base stations and mobile devices could receive signal indoors more easily.  So what is the catch---I mean it sounds perfect right? The catch is bandwidth.  And notwithstanding the fact that the nation's carriers spent unprecedented money to acquire 700 MHz spectrum this past year, bandwidth is the big bugaboo.  The lower the frequency the lower the theoretical limits of bandwidth and information that can be transmitted. 

The reason carriers loved this spectrum in licensed bands is they could cover wide swaths of area for much less base station cost.  I think this spectrum will be a nice addition to the panoply of unlicensed frequencies, especially when taken in concert.  But I will blog more on the creative use of multiple spectrum in future posts.  The key here is that I think hardware is slowly moving to real cognitive capability where radios can work in multiple spectrum ranges and sense what is available.  Now why will WiMAX be a while getting involved? I think WiMAX vendors will focus on radios for carriers with licensed spectrum because that will initially be where the money is.  To date the WiMAX Forum has set just one product profile for unlicensed spectrum and I think they won't jump on this quickly---just my opinion of course.  What do you think?

Tim Sanders
www.TheFinalMile.net
 
 

Monday, November 10, 2008 in Applications  | Permalink |  Comments (1)