DAB is the satillite radio service. One of the provider is I think worldspace. FM you get it for free whereas you pay a monthly fee for DAB. Mostly its without any of the annoying ads. They have different channels for different kinds of music. Folks, correct me if I'm wrong.
DAB is compressed digital audio transmission with fairly poor bitrates. Worldspace in India is a good example of this. On a good set of speakers it reveals its limitations. No idea if the new DAB+ (which uses AAC encoding) is available in India.
I have a DAB/FM tuner and when i connected the DAB aerial and did an autoscan it picked up no DAB broadcasts. There are no broadcasts in DAB at least for now in mumbai. Wonder if and when they will introduce DAB in India as i believe its hiss free radio.
worldspace is a radio service which uses digital transmission/compression, but it is not really DAB as the world knows it. India has chosen DAB as the standard format over Digital FM used in the US, but the service is yet to start. I was told that AIR was doing some trial transmission in Delhi. So I am not surprised that you did not get any signals in mumbai