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Ofcom Offers U.K. Spectrum Blueprint

Last week, United Kingdom's telecom regulator Ofcom published its spectrum blueprint for the next decade. It identified the second of six priorities for spectrum management:

"The future of the 700MHz band and free-to-view TV: Ofcom is investigating the potential to rearrange the bands used for digital terrestrial TV [DTT]. This could release more of this prime spectrum for mobile broadband use sometime after 2018, while ensuring that viewers would continue to benefit from digital terrestrial TV."

The document notes that "As there is no unused spectrum across many frequencies, the growth in competing spectrum demands will need to be addressed by a mix of spectrum re-purposing to higher value uses and greater use of spectrum sharing." Ofcom recognized the challenges in spectrum management, noting that "we are not able to rely on market forces in all circumstances given the complex nature of spectrum interactions."

One major factor cited is "the scale and complexity of the coexistence challenges and their mitigation that can arise in case of major change of use. This can form a major obstacle for markets to overcome due to the co-ordination problems that can result, for example where there are many thousands of light-licensed users or potentially millions of license exempt users (e.g. households receiving DTT transmissions)."

Ofcom stated: "In addition, there may be circumstances where a potential use of spectrum creates wider social value which, by definition, cannot be reflected in pure market-led activity (although in such cases it is important that decisions take account of the opportunity cost of spectrum allocations that are designed to access this wider social value)."

The regulatory organization is looking at ways to more efficiently use spectrum by more accurately predicting coverage. The coexistence issues it tends to address include emphasis on the development of additional theoretical modeling capability:

"For example, we are exploring the potential to procure new DTT planning models and coexistence tools for the UHF and VHF bands. In parallel, we will work closely with industry stakeholders to review the planning assumptions used in our present and future models. This will allow more accurate DTT coverage predictions, which will also be used as inputs into other computer simulation tools which are better able to predict, for example, coexistence with other services including mobile, white space devices and PMSE; and making greater use of empirical testing where complements to theoretical models are justified."

Ofcom noted that "depending on the stage of development of relevant technologies, we will use testing rigs at our facility at Baldock, or we will consider testing commercially available consumer equipment out in the field in a more 'real world' environment."

Another area where Ofcom sees potential for increasing spectrum availability is through improvements in RF performance standards, including those dealing with out-of-band emissions and the ability of receivers to reject signals transmitted in adjacent bands.

Ofcom recognized a trend I've observed--a move to higher and higher frequencies. The organization cites as an example that fixed wireless services are now beginning to use spectrum above 60 GHz, and that commercial satellite services that historically used spectrum below 12 GHz have now expanded their use into 28 GHz.

Ofcom states: "This effect could also extend the range of the 'sweet spot', where demand for spectrum is greatest, up to perhaps 6GHz, providing some level of mitigation for forecast increases in demand."

Many of the issues and solutions are similar to those under consideration at the FCC. Broadcasters world-wide are likely to see increasing pressure on their UHF broadcast spectrum as well as auxiliary broadcast spectrum such as the 2 GHz used for news gathering and "vacant" broadcast TV spectrum currently used for wireless microphones.

The 60 page Ofcom Spectrum management strategy provides an excellent evaluation of the challenges broadcasters and other spectrum incumbents are likely to face.

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.