DETAILED DESCRIPTION OF THE DRAWING In the subject system, the information necessary to select a given television program is not fixedly-programmed into each receiver but is rather is down-loaded from the satellite continually on each transponder.
The television program selection information comprises a set of data known as a Master Program Guide (MPG), which relates television program titles, their start and end times, a virtual channel number to be displayed to the user, and information allocating virtual channels to transponder frequencies and to a position in the time-multiplexed data stream transmitted by the particular transponder.
In a system according to the subject invention, it is not possible to tune any channel until the first master program guide is received from the satellite, because the receiver literally does not know where any channel is located in terms of frequency and position (i.
e.
data time slot) within the data stream of any transponder.
The concept of virtual channels allows allocation of virtual channel numbers by category, such as, sports, movies, news.
This realization, in turn, allows for active and inactive virtual channels.
That is, ten virtual channels assigned to sporting events on a Saturday afternoon, may be inactivated after the games and may provide enough bandwidth to support, for example, twenty movie channels.
Thus, the user has the perception that he has many more channels than, in fact, could be supported simultaneously, by the available bandwidth.
Another words, the concept of virtual channels allows time-multiplexing of the system bandwidth.
Moreover, it allows a television program requiring greater bandwidth (such as a sporting event) to "borrow" bits from a second television program on the same transponder which does not require as great a bandwidth (such as a "talk show").
Thus, the available bandwidth of a given transponder can be reallocated, as needed, from one virtual channel to another.
Advantageously, the system is totally flexible in that any program may be assigned, or reassigned at any master program guide transmission time, to any transponder or data time slot, in a fashion which is completely transparent to the user, who sees only the unchanged program title and virtual channel
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Television 
