Science Spin January 2009

Making best use of radio spectrum

By Sean Duke

Once upon a time, a telephone was only a telephone, a radio was only a radio, a game was only a game and a TV was only a TV. Those days are gone, and today's devices are no longer just one thing. The modern device is very complex, capable, and can be used in different ways. A phone can be a radio, a TV, a game and a phone all at the same time.

Multi-purpose devices today communicate using the frequencies that are available in the 'radio spectrum'. The spectrum is regarded by the telecommunications industry as a precious finite resource, and it is managed at the moment as such. The national or international telecommunications regulators around the world typically allocate certain frequencies for phone, for example, while other frequencies are earmarked for TV. This is a very rigid, non-dynamic system that has, up to now, worked reasonably well for all.

The CTVR is an SFI supported CSET (Centre for Science, Engineering and Technology) headquartered at TCD. It is multi-disciplinary, involving researchers from a number of different fields and a number of third level institutions. There are also several committed industry partners. The overarching goal is for those involved to tackle the engineering and scientific challenges involved in creating a future, more dynamic telecom world.

Dr Linda Doyle is one of the key researchers at the CTVR. During her talk at the recent SFI Science Summit, held in Kilkenny, she said that tight regulation of radio spectrum up to now is understandable given that radio frequencies are difficult, imperfect entities to deal with. This imperfection, she explained, is why state bodies around the world, such as ComReg in Ireland, have sought to closely regulate how radio frequencies are used.

Predictable

"A radio signal in reality is like a bit splat of paint," said Dr Doyle, "frequencies leak from one band into another, distortion occurs, signals get corrupted and it becomes very difficult to receive the signals that you want to do." The current regulatory system, she added, manages such chaos, so that services don't encroach too much on one another.

"So life is somewhat predictable," continued Dr Doyle, "and you have some kind of level of insurance that I understand the system in which I must operate, I understand the conditions in which I must operate. The services don't encroach on each other in an unreasonable way, and you always know who your neighbour is."

This has been the system up to now, but telecommunications researchers have been challenging this rigid way of organising radio spectrum. One of main reasons to challenge the current set up, said Dr Doyle, is that it doesn't encourage innovation. Innovation requires available spectrum, but often that spectrum is not available.

The regulator, a national body, or an international body, is extremely powerful in this sphere, and they can essentially decide - not the market - what kind of technologies are going to dominate into the future. They decide whom the 'winners' will be. This is not ideal, said Dr Doyle, as, for example, in the past it has been seen that mistakes have been made where ideas or concepts supported by the regulator have failed, and never taken off.

Dynamic

Researchers at the CTVR, such as Dr Doyle, have been asking themselves in recent years how a better, more flexible system of utilising spectrum resources can be put in place? Why does the management of spectrum have to be so rigid? Why can't spectrum be used in a dynamic fashion? Why can't systems be created, for example, that allow devices to hop into available spectrum space, and then hop out again when that licensee returns?

The hop in, and hop out again system is called 'dynamic spectrum access'. The way it works - in theory at least - is that a device searches around its environment to see what spectrum is available, what is not being used at that time. The device then, intelligently, decides to move into the available space until the owner comes back. It is something akin to using a parking space that is unoccupied while the owner of that space is not there, and being able to immediately vacate the space when the owner returns, and needs to use it.

The concept at CTVR is that spectrum consumers of all kinds should be allowed to co-exist. Dr Doyle and her colleagues want to push the existing systems so that more interesting and dynamic things can be done, and in the longer term to challenge the existing system completely. The push is, thus, towards a world where the market, not regulators, will determine what kind of technologies will be successful. "This is very much the kind of fluid spectrum world that we in CTVR envisage," said Dr Doyle.

Smart

In the future, devices and networks will be 'smart'. The old rigid rules will go out the window, and a new generation of radio devices will be designed so that it can search for a wide space, move into that wide space, and move out again as required. The key to all of this, on the radio, and network side, is flexibility. This will enable telecommunications to move away from the static world that has existed up to now. It will require, however, a new generation of smart radios to be built, and tested in the field, to see what will work.

Dr Doyle said that Ireland is ideally placed for spectrum experimentation, primarily because there are spectrum frequencies available for experimentation here. The CTVR has given its own testing frequencies to use by ComReg. That's very impressive given its location in Dublin City Centre, at TCD, as spectrum is usually even harder to get in urban centres. This enabled CTVR to get the first experimental license for a smart, software radio, in the world, and such experiments could not have happened anywhere else.

The availability of test spectrum has helped to attract a range of industry and academic collaborations, said Dr Doyle. This all means that in the radio experimentation 'space', she said, the CTVR has a very central role to play in terms of what technologies get used in Ireland, how that technology is used, and what kind of innovation is encouraged.