A backward compatible local service insertion technique for DAB single frequency networks

Current broadcast systems make use of either single frequency networks (SFNs) or multifrequency networks (MFNs) to distribute content. However, neither of the topologies is efficient to distribute both global and local content at the same time. While SFNs are ideal for delivering global content in a frequency- and power-efficient way, MFNs are well-suited to deliver local content to the desired reception areas. This paper describes a technique to allow local service insertion (LSI) in Digital Audio Broadcasting (DAB) SFNs. DAB has been in use for several years around the world. Proposals for LSI have been made before. However, those considerations focused on the transmission modes (TMs) II and III, which are no more supported in the current version of the DAB standard. Another approach is the use of small power transmitters resulting in a limited coverage area. Differential modulation makes it difficult to introduce local services into an SFN. The technique presented in this paper uses an artificial phase reference symbol consistent with differential modulation. Furthermore, this approach is compatible with TM I and supports existing DAB receivers. The proposed LSI technique is described in this paper and analyzed in terms of requirements for the services. Signal-to-noise ratio requirements are also evaluated.