Todays analog radio system still follows the basic principle of frequency modulation invented back in 1993.In addition to audio transmission ,very limited information such as the station identification can accompany the programs.Transmission quality varies greatly depending on multi-path effects and the interferance.The fully digital DAB systems doen not only offer sound in a CD like quality ,it is immune to interferance and multipath propagation.
DAB systems can use single frequency network(sfn) i.e all the senders transmitting the same radio program operate at same frequency .Today ,different senders have to use different frequencies to avoid inteferance although they are transmitting the same radio program.Using an SFN is very frequency efficient , as a single radio station only needs one frequency throughout the whole country.Additionally , DAB transmission power per antenna is orders of magnitude lower compared to traditional FM stations.DAB uses VHF and UHF frequency bands(depending on national regulations) e.g:- the terrestial tv channels 5 to 12 (175- 230 Mhz ) or the L-band .The modulation with 192 to 1536 carriers so called ensemble within DAB channel of 1.5 Mhz.

Let us assume that the broadcast sender is a radio station transmitting information about the radio conditions (block A ),the weather report (block B),the latest events in town and the menu to access these and other topics in addition to music.The sender can now assume ,knowing something about the importance of the data blocks,the block D is the most important to enable access to the other information.The second important block is A ,then B and finally C.A possible broadcast disk for this scenario could now look as follows.

DADBDADBADADDDDBDC............

It is now the receiver's task to cache the data blocks to minimize access delay as soon as a user needs a specific type of information.Again ,the receiver can only optimize caching if it knows something about the content of the data blocks.The receiver can store typical access patterns of a user to be able to guess which blocks the user will access with a high probability.Caching generally follows a cost-based strategy: what are costs for user? if if the data block has been requested but is currently not available in the cache.