One of the more interesting potential side effects of the digital dividend (i.e. converting analog terrestrial TV signals to digital, thus freeing up spectrum for wireless broadband services) is the creation of "white space" spectrum. In essence, whatever slivers of spectrum in the VHF/UHF frequency bands that aren't being used by DTT, LTE or Wimax could be used it to develop new kinds of wireless broadband services.
Companies like Google, Microsoft and Yahoo have been championing white-space as a ticket to providing wireless broadband to underserved areas in the US, where the FCC approved the use of "white spaces" in September last year. The UK's Ofcom is also interested in white-space spectrum to the point where it's even looking at the possibilities of white-space frequencies in the FM radio bands (87 to 108 MHz) as analog radio stations migrate to Digital Audio Broadcasting (DAB). Meanwhile, the ITU is also looking at the aspects of white-space spectrum as part of its overall work on the digital dividend.
There's even an official standard for it now from the IEEE: 802.22, which uses white-space spectrum to create Wireless Regional Area Networks (WRANs) delivering data downlink speeds up to 22 Mbps at ranges of up to 100 km.
The 802.22 standard isn't the only technology being proposed to exploit white-space frequencies. In February, the Wireless Innovation Forum (formerly known as the SDR Forum) created a new task group that will address application scenarios using TD-LTE in white-space bands. There are also proprietary technologies targeting white-space - UK-based Neul, for example, recently announced a white-space radio solution called "Weightless" aimed at M2M apps.
Part of the attraction of white-space is that, like the ISM bands used by Wi-Fi and Bluetooth, it's unlicensed, open spectrum. The question is whether it will - or should - stay that way.
In the US Republican party lawmakers have proposed a new bill governing how the FCC reallocates digital dividend spectrum that includes a controversial provision requiring the FCC to put unlicensed white-space spectrum up for auction. Companies that want it to stay unlicensed and open would have to collectively outbid any company willing to buy it for themselves.
The debate raises some serious but important issues over the role of open spectrum as both a driver of innovation and a competitive force. Proponents of open spectrum argue that the true value of open unlicensed spectrum is the inherent innovation opportunities that we've already seen with technologies like Wi-Fi.
The interference issue
Conversely, the main argument for licensing white-space spectrum has centered primarily around interference concerns from both the mobile and the broadcasting sectors. However, the FCC approved white-space spectrum in part because open-spectrum proponents demonstrated that white-space devices could operate without cutting into existing signals. In fact, last month, the FCC appointed Microsoft to administrate a white-spaces database that devices can ping to ensure that a frequency isn't occupied by a licensed user.
Apart from that, the case for licensing white-space spectrum seems slim, at least in the US. Different markets have different spectrum availability issues and regulatory requirements that might prevent an open-spectrum approach. On the other hand, I'm not aware of any market that can say that opening the 2.4-GHz band has been a complete disaster with no benefits whatsoever. Surely the operators deploying Wi-Fi access points to offload their mobile broadband traffic are glad they didn't have to spend billions to secure the spectrum for it, or that they don't have to fork out access fees to the operator that won the auction.
I realize, of course, that governmental comms departments and ministries tend to see any new spectrum as something else they can sell to the highest bidder. But given that many of those same ministries claim to see broadband as an economic growth driver that benefits all, surely there's an argument to be made that underserved communities benefit from innovative technologies that don't require them to spend millions on spectrum.