Potential benefits of hierarchical modes of the DVB-T specification

Many engineers and broadcasters are very familiar with the concept of digital terrestrial television (DTT), and hopefully will all have seen live reception of the signals at some time. However a number of those people will not have encountered the idea of hierarchical modulation, which is a part of the ETSI standard-the definition of the RF transmission standard for DVB-T signals. This paper introduces the ideas behind the hierarchical modes, and shows one of the ways in which they could be used at some time in the future, or perhaps by countries still in the process of planning their DTT services at the moment. This paper is not intended to suggest that the existing UK DTT services should be replaced by hierarchical services, but instead it points out a potential way in which the DTT system could be used, if additional frequencies become available in the future