DAB coverage planning: report to Government

26 April 2012

Executive summary

This report provides a technical feasibility study of a DAB coverage plan to support a potential future digital radio switchover

1.1 The Government published a Digital Radio Action Plan (DRAP) in 2010, the purpose of which is 'to provide the information to allow for a well-informed decision by Government on whether to proceed with a radio switchover'. Ofcom was asked to chair a DAB coverage and spectrum planning group to 'determine the current level of FM coverage and develop a range of options to increase DAB coverage to match FM'.

1.2 This report to Government sets out the approach and results of this planning exercise. In particular, it covers:

  • The definition of the geographical areas, based on the editorial coverage areas of existing FM radio services, within which we would aim to replicate FM coverage as far as practicable with DAB coverage (we refer to these as 'editorial areas' in this report);
  • The technical planning parameters used to predict acceptable levels of FM and DAB coverage for indoor portable and in-vehicle radio receivers;
  • The extent of existing FM coverage within each editorial area, for both indoor portable radio reception and in-vehicle radio reception on major roads; and
  • DAB transmitter network scenarios illustrating how increasing levels of DAB coverage can be achieved using increasing numbers of transmitters, replicating as far as practicable FM coverage within each editorial area.

1.3 Broadcast radio coverage is dependent on a range of different factors including the height of the transmitting antenna and the power of the transmitting station, the type of terrain and ground clutter, atmospheric weather conditions, receiver sensitivity (and aerial gain) and whether the receiver is used indoors or in vehicles.

1.4 There are also important differences between FM and DAB technologies. For FM the quality of the audio output progressively degrades with decreasing signal strength and greater interference, whilst the quality of DAB remains constant and then disappears abruptly. Therefore, comparing FM and DAB coverage requires some qualitative judgement to be exercised over when the level of user experience for FM and DAB is broadly equivalent.

1.5 The DAB network scenarios set out in this report do not constitute a definitive or final view on what the post-switchover DAB network should be, but seek to illustrate the technical feasibility of matching DAB and FM coverage to inform a Government's decision on whether to proceed with switchover. Therefore, this document does not represent a regulatory decision by Ofcom.

1.6 If Government decides to proceed with digital radio switchover a more detailed planning exercise will be needed, in collaboration with multiplex operators and other stakeholders, to optimise the exact number, location and power of additional DAB transmitters needed to replicate FM coverage in the most practical and cost effective way.

1.7 This report draws upon two previous Ofcom documents - a consultation published in July 2011 which set out our proposed approach to this radio coverage planning work, and an interim statement published in December 2011 which summarised consultation responses and set out the further work we were planning to undertake to improve the accuracy of our coverage planning predictions.