With the current pressure of UHF spectrum for mobile services, broadcasters are often (wrongly!) accused of not using spectrum efficiently and that further use of Single Frequency Networks (SFN) could highly reduce the spectrum needed for Digital Terrestrial Television (DTT).
Certainly, SFNs can easily be used if service areas are large, of similar shape and size and do not overlap. In that case, the use of a single frequency channel to cover a large area shows a great advantage compared to Multiple Frequency Networks (MFN) which would require several frequency channels to cover the same large area.
But in reality, service areas are not homogeneous and they differ in shape and size and often overlap. This is because service areas are defined by editorial requirements and take into account topography, infrastructure, population distribution and regionality. When covering service areas which are small and which differ significantly in shape and size, the use of SFNs do not represent an advantage as the same frequency channel cannot be used in adjacent service areas with different content.
SFNs also suffer from self-interference. There are different options to overcome self-interference. The most common are adopting a more robust transmission mode or increasing the guard interval. Both options reduce the capacity of the DTT multiplex which in turn increases the number of multiplexes to transmit the services required and therefore the spectrum needed.
Overall, SFN have advantages over MFN but those advantages have associated technical and non-technical constraints. Broadcasters are already making heavy use of SFNs in their T-DAB and DTT networks and know well those constraints. The recently published Fact Sheet ‘SFN - Myths and reality’ and the Technical Report 29 ‘DVB-T2 SFN & Spectrum Efficiency’ tells you why not of the advantages of SFNs can be maximized at the same time.