Give thanks, for once, to the law of unintended consequences. Too often, it seems, the secondary effects of policy decisions turn out to be at least perverse, if not downright detrimental. But in the case of last week’s congressional vote to extend America’s emergency payroll tax-cuts, the knock-on effects look like being doubly beneficial.

That is because half the US$30bn cost of extending the emergency measures will be met by auctioning off a bunch of UHF airwaves that were used by local television stations in America to broadcast on channels below 52. Since the switch to all-digital television in 2009, these airwaves are no longer needed by broadcasters, who are to be bribed to hand them back to the government.

The frequencies in play are a highly coveted swathe below 700MHz — dubbed the “beachfront properties” of spectrum real-estate. What makes them so desirable is their ability to travel for miles, suffer little interference from foliage and the like, and penetrate into all the nooks and crannies within buildings.

The auction for such a huge chunk of spectrum — said to be more than America’s big four wireless carriers currently have between them — should go a long way to overcoming the “spectrum crunch” mobile-phone companies have begun to experience since introducing data-hungry devices like the iPad and other tablet computers.

The auction should offer other benefits as well. Apart from selling off spectrum vacated by broadcasters to mobile carriers, the Federal Communications Commission (FCC) intends to reserve a chunk of television’s old UHF band for unlicensed use by the public. Back in 2008, after years of haggling with the broadcasting industry, the FCC finally voted unanimously to let a new generation of wireless gizmos access the Internet using the gaps (“white space”) between television’s UHF channels.

When UHF television was introduced back in the 1950s, empty guard bands were added between each channel to prevent interference from stations broadcasting on adjacent channels. In some places, these white spaces amounted to as much as three-quarters of the bandwidth available for television broadcasting. Even in the busy Los Angeles television market, a third of the spectrum for analogue broadcasting lay idle.

In making white-space frequencies available for public access to the Internet, the FCC hopes to spawn a wave of wireless innovation similar to the way Wi-Fi shook up the world of short-range data communications a decade ago. Given the longer range and greater penetrating power of television airwaves (that is why they were chosen for television in the first place), the FCC has taken to calling the proposed technology “Super Wi-Fi” (despite protests from the Wi-Fi Alliance, a trade association based in Austin, Texas, which manages Wi-Fi standards and owns the Wi-Fi trademark).

Be that as it may, what made Wi-Fi such a phenomenal success was the way companies with wireless know-how (many of them start-ups) saw an opportunity to exploit the IEEE 802.11 standard for wireless connectivity in mainly the unlicensed 2,4GHz band used by microwave ovens, cordless phones, baby monitors and garage-door openers. Having seen a $50bn Wi-Fi industry spring up from practically nothing, the FCC believes fervently that making unlicensed spectrum publicly available is one of the surest ways of spurring innovation.

That may well be so. But many in the wireless industry have reservations over whether Super Wi-Fi (or IEEE 802.22 as it is known technically) can actually deliver the goods as easily and cheaply as the wonks in Washington seem to imagine. Yes, it would allow broadband to be delivered wirelessly like Wi-Fi, but over much greater distances — in theory, up to 60 miles or so, compared with Wi-Fi’s 400 feet. But that does not mean wireless “hotspots” will suddenly expand from covering a few thousand square feet to sprawling over a few thousand square miles. That is never going to happen.

In crowded urban markets, Super Wi-Fi distributed from a single antenna even just 20 miles away would not be able to supply anywhere near enough data capacity to cope with the demand. With Super Wi-Fi’s broadcasting power limited in urban areas for the foreseeable future to 40 milliwatts, to avoid interfering with local television stations, and the same signal being shared by thousands or even millions of city dwellers, download speeds would be glacially slow. The only way to make Super Wi-Fi work in metro areas would be to install antennas a mile or so apart. Even then, download and upload speeds would be no better than clunky old DSL.

Out in the countryside, things would be a lot different. With homes few and far between, Super Wi-Fi would be a cheaper way of delivering broadband (at, say, 1,5Mbit/s download and 384kbit/s upload) than either cable or DSL.

That said, unlicensed white space is just too valuable a public resource not to be fully exploited. Indeed, the mobile-phone companies, far from seeing Super Wi-Fi operating in white space as a threat to their proprietary networks, have big plans for offloading much of their data traffic onto these public airwaves. According to comScore, a market research company headquartered in Reston, Virginia, more than 37% of mobile-phone traffic, and over 90% of tablet traffic, already goes by Wi-Fi rather than the carriers’ own cellular networks.

With spectrum scarce, the mobile-phone companies have been building regular Wi-Fi hotspots as fast as they can — so they can offload data from their congested private networks to Wi-Fi’s unlicensed public bands. Doing so, helps them maintain the quality of service for other customers texting or trying to make phone calls.

So far, AT&T has built some 30 000 hotspots to help cope with the tripling in data traffic it has experienced over the past year, with a further tripling expected in the year ahead as the iPad 3 hits the market along with dozens of slicker Android tablets. Altogether, there are now 1,3m hotspots across America, a figure that is expected to grow to 5m by 2015, reckons Informa Telecoms and Media, a market research firm based in the UK. Like other mobile carriers, AT&T considers unlicensed white space as an ideal way for hauling data back from the hotspots it has built in neighborhoods to its cellular network, without having to use its own precious spectrum.

Indeed, backhaul looks like being the biggest single application for white space. At Rice University in Houston, Texas, home to the first residential Super Wi-Fi network, white-space is used to carry data back from a series of conventional Wi-Fi routers scattered around the campus. In the future, white space will have other, more prosaic applications — such as linking machines autonomously to other machines in a so-called “Internet of things”.

Before then, “real” Super Wi-Fi will have arrived. “Gigabit Wi-Fi” (known technically as IEEE 802.11ac) will be at least three times faster than existing Wi-Fi (IEEE 802.11n) — thanks to having up to four times the frequency bandwidth available to it, and up to twice as many antennas as the best of today’s wireless routers. But operating exclusively in the 5GHz band, it will have a somewhat shorter range than regular Wi-Fi (which functions mostly in the congested, but slightly longer range, 2,4GHz band, as well as 5GHz these days). Even so, Gigabit Wi-Fi’s raw speed will come in handy for moving data-intensive files like high-definition video around the place. Rumour has it that the iPad 3 will ship with a gigabit Wi-Fi chip inside it.

Meanwhile, one final piece of the evolving Wi-Fi puzzle is dropping into place. This is a way of letting people with smartphones, tablets or laptops roam from one Wi-Fi hotspot to another, without having to log on repeatedly and authenticate themselves. For lots of users, the fiddle of having to enter credentials, encryption keys and other details is enough to prevent them wandering around.

So, if wireless carriers are to charge subscribers for using their Wi-Fi services (and they will, because someone has to pay for all the maintenance and backhaul), then users have the right to demand that moving from one hotspot to another becomes as seamless as roaming on a proprietary cellular network.

To the rescue, the Wi-Fi Alliance has developed something called Passpoint, which implements an emerging IEEE protocol (known as 802.11u) to automate the whole cumbersome process of network discovery, registration and access that users have to do manually today. In the process, Passpoint ensures that all certified Wi-Fi networks operate seamlessly and securely with one another — to provide a ubiquitous, hassle-free service.

Put Passpoint together with white space or even gigabit Wi-Fi, and the 802.11 scene begins to look remarkably like the cellular one. Coexisting side by side, they would appear to be a pair of parallel wireless universes — one closed and proprietary, the other open and as freely available as Wi-Fi is today.

Unfortunately, that is not how it is likely to play out. Users are going to find choosing one mode of access over the other not that easy to do. Indeed, most will not even know they have a choice. A few knowledgeable folk might opt to use third-party services like Boingo to remain online while moving from airport terminal to hotel lobby. But when the carriers integrate Wi-Fi fully into their mobile services, subscribers are unlikely to know whether they are using a cellular network or a Wi-Fi one.

Thanks, though, to the unintended consequences of last week’s congressional decision to extend the payroll tax-cuts, mobile subscribers should at least suffer fewer dropped calls, have less of a hassle staying online while roaming around, and be able to download movies in a trice without so much as a hiccup. That sounds not too bad a deal. — (c) 2012 The Economist