A group of transmitters all working on the same frequency within range of each other. Usually these will interfere causing serious problems with reception. However with DVB-T2 transmission, and the TV channels all running on the same locked frequencies over all transmitters, any interference is constructive, adding to the quality of the received signal. SFN’s are very efficient with radio frequency spectrum use as, for example, all transmissions of a group of TV channels around a country can use the same channel frequency throughout a network. Also the constructive interference makes it easier to get good reception, sometimes even with a modest antenna.