Di frequenza (scarsa) in frequenza

Come il petrolio, anche le radiofrequenze sono una risorsa in via di esaurimento. Il Guardian si occupa indirettamente di cognitive radio con un pezzo che riporta il discorso sull'uso della risorsa-spettro in un contesto meno scientifico e più economico e sociale. L'articolo cita un documento dell'Associazione dei CEO americani che invoca l'allocazione di un maggior numero di frequenze a operatori commerciali non pubblici, per uno sfruttamento più efficiente di un bene così prezioso. Ma il Guardian si concentra piuttosto sulle sperimentazioni di tecniche di frequency hopping e uso dinamico delle spettro in corso in Irlanda, dove certi studi sono resi più facili da una maggiore disponibilità di frequenze non assegnate ai militari. Oltre al frequency hopping il pezzo menziona l'Ultra Wideband, che invece di selezionare al momento una frequenza libera (come farebbe la cognitive radio, che da questo punto di vista non è poi così radicalmente nuova), spezza un segnale in un gran numero di piccole frazioni a bassissima potenza, in uno spettro estremamente diffuso. Con l'occasione riporto anche il link a un recente articolo di Scientific American, citato da DXLD, che si occupa appunto di radio cognitiva.

Overcrowded airwaves mean it's time to hop ahead

An increasing number of technologies rely on radio spectrum. Before it runs out, an Irish research group suggests we get used to sharing what we have left

Karlin Lillington - The Guardian
Thursday March 2, 2006

Like oil, radio spectrum is one of the world's dwindling resources. Why else would five mobile operators have paid that infamous £22.5bn for 3G licences in the UK in 2000, if they didn't think it was a rarity? Tightly controlled by regulators in each country, spectrum is required by radio and television broadcasts and mobile phone networks, microwave ovens, home wireless networks, hospital x-ray machines, satellites, cordless phones, Bluetooth computer keyboards and garage door-openers. And, as Mark Twain said of land, they're not building any more of it. The explosion in wireless computing and mobile devices has placed even greater strain on this scarce natural resource - so much so that last week, the US-based Tech CEO Council issued a report, stating: "There are few more important natural resources than our radio spectrum. An increasingly essential platform for how we work, live, play and learn, radio spectrum may be the most critical infrastructure element of 21st century economies."
The council's idea of a solution to scarcity in the US is for the government there to give up some government-held spectrum to private companies, which, they argue, will use it more productively. But across the Atlantic, a research group based at Trinity College Dublin, partnering with Bell Labs, has a different approach: spectrum-hopping, or dynamic spectrum allocation. Operators could hop across the frequencies, utilising unused or underused spectrum.

Scarce resource

"Spectrum is considered a scarce resource," notes Dr Linda Doyle, who leads the spectrum research group within TCD's Centre for Telecommunications Value-chain Research (CTVR). "But some of that scarcity is actually a false scarcity, because spectrum isn't efficiently used." She displays a chart of spectrum use in London over a 24-hour period, with heavy use marked in red bands, and blue bands indicating no activity. Perhaps 70% of the chart is blue. The US Federal Communication Commission (FCC) has stated that about 90% of spectrum is underutilised, she adds. Most of the congested areas indicate usage in the more desirable spectrum bands. Certain frequencies are valued by some industries because they enable better signal quality or strength - mobile and television operators - or conversely, enable a signal to be received over a longer distance - shortwave radio broadcasts - where distance is valued. But even within the very congested bands, not all are used at capacity all the time, and spectrum-hopping is seen as a possible solution as more devices and services clamour for a slice of spectrum.

The central piece of virtual equipment needed for the experiment is what Doyle calls a software radio - "a bucket of software components that can be put together in many different ways," says Doyle. This makes the software element highly flexible. For example, it would enable a single device using the software to be marketed in multiple geographies. Now, devices such as mobile phones generally have to be manufactured separately for each region, at greater cost and lower efficiency. The software could be used in any device that uses spectrum, whether passively (to receive) or actively (sending and/or receiving), from handhelds to mobiles to radios to television sets. What makes the TCD-Bell Labs collaboration unusual is that, in a unique arrangement with Irish communications regulator ComReg, their researchers have been granted a 50MHz swath of spectrum for an experimental software radio licence to conduct live experiments. By contrast, the entire FM radio broadcast band in Ireland is 20MHz.
Until now, nobody has been able to experiment with live spectrum, says TCD Professor Donal O'Mahony, director of CTVR. Research groups worldwide have been working in the area of spectrum-hopping for some time, but have had to use computer simulations. Doyle says there isn't another regulator in the world that has been willing (or able) to grant spectrum for this kind of use. When, at a recent conference, she mentioned the grant to Michael Gallagher, the assistant secretary for communications and information of the US National Telecommunications and Information Administration, "he nearly fell off his chair," she says.
Isolde Goggin, the chair of ComReg, says it was able to offer the spectrum under its "test and trial" research and development programme because Ireland "is in a fairly fortunate position": a low population density means there is a lot of uncongested spectrum, and being an island on the western edge of Europe means the spectrum is cleanly isolated from neighbouring countries and the experiments are unlikely to cause interference. And it's not a Nato member, so the military won't complain.

New approach

For the same reason, Ireland has more spectrum available than countries with a large military. Goggin says that ComReg made the decision "to turn spectrum allocation around from a restrictive approach, to saying if we can do it, we will". Doyle says spectrum-hopping would require a complete rethink of how commercial-use spectrum is allocated and paid for. Rather than a licensing system that lets operators control a fiefdom of spectrum - the current model, which the Tech CEO Council would like to see expanded - spectrum-hopping would be more like a frequency timeshare. One aspect of the research will be to consider the issue of management as well as potential business models, she says. Goggin notes that hopping is only one possibility for the way spectrum management might develop. However, "The consensus is that the current model has to change." Regulators worldwide are moving away from the notion that the regulator's role is to imagine what future uses of spectrum might be, and then reserve chunks for those uses. "That approach is not very well able to cope with unpredictable fluctuations in demand".
Other options for better spectrum management include: ultrawideband (UWB) technology where, rather than hopping around, a signal is broken into incredibly short pieces and simultaneously spread over an enormously wide frequency band, allowing numerous signals to share the same bandwidth at slightly different times; mesh networks, where numerous individual devices form large, ad hoc networks for passing signals around; and new technologies that minimise interference. Goggin says she imagines a mix of these approaches are likely. The Irish hope their ability to give researchers access to spectrum will attract investment as well as create opportunities for local companies. "Because Ireland is an island, it can be a playground for spectrum," says Doyle.
But Goggin has even bigger dreams. "This could be Ireland's oil," she muses.

Tags: radioascolto, radiofonia, radio, dxing.