Is it time to junk spectrum licences?
How about a TCP/IP for radio...
By Peter Judge, Techworld | Published: 01:00, 04 May 2005
For 100 years, access to the airwaves has been managed by bodies like the UK's Ofcom and the US Federal Communications Commission. New technologies could make them redundant.
Because radio signals interfere with each other, bodies were set up to arbitrate who should have the right to transmit on any given frequency. In the UK, the responsibility rests with Ofcom, and the radio spectrum is sliced up something like this. None of the spectrum is "owned", but Ofcom decides who has the right to use it.
Spectrum feels scarce at the moment. Phone operators paid heavily for access to spectrum where they are permitted to use 3G mobile technology, and Wi-Fi systems have to manage spectrum carefully to create coverage.
However, about half the spectrum is more or less unoccupied, according to research by Ofcom - so the scarcity is clearly artificial. Much of the "wasted" spectrum was bagged by the military a long while ago, or was licensed and not yet used by broadcasters.
What do we do with UWB?
Ultra-wide band has tossed the regulators an even trickier problem. The technology uses very low power signals, across a broad range of spectrum, something regulators have trouble allowing. In the US, the FCC has allowed it, provided it uses power levels lower than those allowed to leak from non-radio equipment like CD players.
Ofcom supports UWB and clearly wants to allow it in Europe on the same basis as the FCC allows it in the US, but the mobile operators seem likely to oppose it. Having paid so much for their 3G licences, they don't want anything else in that spectrum - even if it's at a level that has absolutely no effect on them.
"The UK could consume billions of UWB chips a year, creating £10 billion for the UK economy," said David Cleevely, director of the Communications Research Network (CRN), formerly known as the Communications Innovation Institute, at Cambridge University. He is concerned that objections from the mobile operators may stall that, and keep the UK out of a lucrative worldwide market.
Enter market forces
Ofcom is considering three different methods to license spectrum:
- Right now virtually all spectrum is managed by Ofcom, in a command and control fashion. Ofcom decides what can be done with a given piece of spectrum, and issues the licence to a named operator. Neither the operator, nor the technology they use can be changed, except by Ofcom.
- Ofcom wants to introduce market management, where operators can resell their licences at a market rate, and where spectrum can be re-used for different purposes, without reference to Ofcom. This would, for instance, make it possible for broadcasters to sell spectrum to mobile operators, or allow network operators to phase in new technologies.
- Some spectrum is currently essentially umnanaged. Anyone can use the licence-exempt spectrum at 2.4GHz and 5.8GHz, for anything provided they keep within power limits intended to reduce interference.
While some have expressed fears that market forces will fragment the spectrum, Ofcom is convinced it will do the opposite - allowing operators to use the best technology available, and not wait for the go-ahead. "Some people say liberalisation will lead to fragmentation of the spectrum, but I have the opposite view," says Graham Louth, Ofcom's director of spectrum trading.
What about a commons?
Spectrum trading will only help where a single technology and a single operator control a piece of spectrum. It won't help ultra-wide band, and is completely irrelevant to licence-exempt technologies like Wi-Fi and Bluetooth.
It is astonishing just how much has been achieved by Wi-Fi, using what commentators call "junk spectrum". At this point, virtually all Wi-Fi activity is in one single unlicensed band, at 2.4GHz, which allows only three non-interfering channels.
Many people want to increase the size of the "spectrum commons", allowing free use of more spectrum, so more can be achieved.
"We want to look at the possibility of release or sharing of spectrum," says William Webb, head of research and development of Ofcom. Ofcom plans to double the licence-exempt bands to around seven percent of the available spectrum. This sounds small, but more license-exempt spectrum is only useful if it is available worldwide (as 2.5GHz and 5.8GHz are), so a global market can develop.
The proposals to allow UWB would provide a commons in "underlay" spectrum, below the noise floor in other spectrum.
Between these to, however, it is difficult to build a big enough commons in spectrum that is not yet spoken for.
Enter cognitive radio
Fortunately, developments in radio look like saving the day - and were aired at a recent conference at the CRN in Cambridge. Just as ultra-wide band uses spectrum more intelligently, software defined radio could allow one radio to function in many different ways, communicating on different frequencies, using different protocols as required (for instance, connecting by Bluetooth, Wi-Fi or GPRS according to what is available).
Beyond that, cognitive radio could allow systems to use spectrum even more intelligently - listening to determine whether spectrum is being used, before sending short messages, and backing off if someone else is talking.
The idea could work alongside the command and control method, creating more capacity without disturbing existing users, much as the Internet routes around difficulties on global communications networks.
"A framework analogous to TCP/IP might be developed for radio, which would enable individual radios to obtain short-term access to spectrum resources," said Will Stewart, a former chief scientist at Marconi, who is now chairman of silicon research company Innos.
Cognitive radios could create a gigantic "virtual spectrum commons", made up of all the spectrum that no-one else is using at any given time.
According to Stewart, the idea could even be commercialised, by allowing users to buy and sell elements of capacity, (called "capels" in his suggestion).
In the long run, trading in capels, independent of bandwidth, could replace much of the trading in spectrum, which is about to start. In the far future, spectrum licences may look old-fashioned.
Fast data by whatever means
If inefficiencies can be got rid of, we - and our devices - could all be using a lot more mobile data, and technology debates may become irrelevant.
According to calculations by Stewart, 2GHz of spectrum is enough to give 10 Mbit/s of throughput to 1000 people every square km, with a cell size of 1km.
Our devices may provide us with wireless broadband - while under the covers, without our direct awareness, the device may be negotiating whether to use WiMax, Wi-Fi, UWB, or other new technologies.