TV white spaces: approach to coexistence

Executive summary

1.1 Citizens and consumers in the UK continue to increase their use of wireless data devices such as smartphones and tablets. At the same time, there is substantial innovation worldwide in applications, services and devices that use wireless data. As a result, demand for wireless data has grown rapidly, and continues to do so.

1.2 Wireless data communications require access to radio waves, known as spectrum. Spectrum is divided into different frequency bands and allocated for particular types of use. The majority of spectrum is allocated using licences, for instance licences to operate mobile phone services. Other spectrum use is made licence exempt, such as that for Wi-Fi.

1.3 However in some areas, allocated spectrum is not used in all locations and/or at all times. This is referred to as "white spaces" and it can be used by other devices and services. A new way to access spectrum, known as dynamic spectrum access, provides a means to use this spectrum. Under this approach, white space devices can change their spectrum use in response, for example, to the needs of other spectrum users. This is a form of spectrum sharing, and provides a way to use spectrum that would otherwise lie fallow.

1.4 Growth in demand for wireless data makes a strong case for increasing the efficiency of spectrum use through these sorts of techniques. This consultation focuses on white spaces in the frequencies from 470 MHz to 790 MHz (the UHF TV band) which are currently used for Digital Terrestrial Television and by Programme Making and Special Events users.

1.5 This is the first set of frequencies in which we have decided to authorise dynamic spectrum access. However, we see significant scope to enable it more widely and are currently consulting on the future role of spectrum sharing for mobile and wireless data services .

Our proposals

1.6 We have previously decided that white space devices should be permitted to access the UHF TV band subject to ensuring that there is a low probability of harmful interference to other services in and adjacent to the UHF TV band . We will achieve this objective by restricting the power and frequencies at which white space devices can transmit at a given time and location based on calculations of the amount of available white space in each location.

1.7 There is uncertainty about the risk of harmful interference from white space devices. If we allow white space devices to operate at power levels that are too high, we will fail in our overall objective of ensuring a low probability of harmful interference to other services in and adjacent to the UHF TV band. However, if we restrict white space devices too tightly we may sterilise large amounts of spectrum for very little benefit, because only a tiny minority of users would be adversely affected if white space devices were allowed to operate at somewhat higher power levels.

1.8 Our overall approach to ensuring a low probability of harmful interference to other services in and adjacent to the UHF TV band is to err on the side of caution at this early stage, setting parameters that we believe we may be able to relax in the future in the light of more experience. Later this year, we will test our proposals to the extent practicable in a pilot programme comprising a number of trials around the UK by a range of service providers. As part of the pilot we will allow increased power levels to be used for limited time periods to assist with this testing. We will refine our coexistence proposals in light of evidence both from the pilot and from stakeholders with a view to finalising them in the summer of next year ahead of the launch of a full, nationwide solution in the third quarter of 2014.

1.9 Against this background, we propose in this document a set of parameters and algorithms with the objective of ensuring a low probability of harmful interference from white space devices to:

  • Digital Terrestrial Television services;
  • licensed users of equipment for Programme Making and Special Events; and
  • services above and below the UHF TV band.

1.10 We also set out our proposed approach for how we will avoid causing harmful interference from white space devices to services used by our international neighbours.

White Space availability

1.11 We have carried out detailed initial modelling of the potential effects of our coexistence proposals on the amount of white space spectrum that will be available for white space devices. The analysis shows white space availability for four different scenarios that vary by device category and antenna height. This analysis suggests that:

  • The constraints required for DTT mean that the best performing white space devices can radiate at the maximum permitted power level in three or more 8 MHz channels at around 90% of households in the UK. This figure falls to around 70% for less well-performing devices. However, at lower power levels, devices can access considerably more channels and do so from a larger number of locations;
  • The configuration of the DTT network means that there is considerable geographic variability in white space availability. For example, DTT constraints are substantially less severe in London than they are in Glasgow. In Central London, the best performing devices would be able to access nine or more channels at maximum power at 100% of households, while in Glasgow (where the DTT environment is more challenging), these types of device would only have access to three or more channels at around 60% of households; and
  • PMSE use is only likely to impose material additional constraints on white space availability in some locations. We estimate, for example, that PMSE constraints (when combined with DTT constraints) reduce the availability of white space in Central London so that better-performing devices would only be able to operate at maximum power in nine or more channels at around 90% of households. In Glasgow, by contrast, PMSE would impose almost no additional constraint on availability.