Device for the transmission of digital data with at least two levels of protection and corresponding reception device

A device for transmitting digital data in the form of a series of data elements, the device employing a plurality of orthogonal frequency carriers, said device comprising:

• distributing means for distributing said digital data into at least two sets of data elements, a first of the sets of data elements requiring a first level of protection and at least one second set of data elements requiring a second level of protection;
• first modulation means, coupled to the distributing means to receive the first set of data elements, for associating the first set of data elements with a first series of modulation symbols selected according to a first modulation symbol alphabet corresponding to a first type of modulation providing for said first level of protection;
• first interleaving means, coupled to the first modulation means to supply each frequency carrier of a first selected set of said plurality of orthogonal frequency carriers with a distinct succession of modulation symbols picked out of said first series of modulation symbols, for interleaving in both time and frequency all of the first series of modulation symbols so that no two successive modulation symbols is supplied to the same frequency carrier;
• at least one second modulation means, coupled to the distributing means to receive a different set of data elements from said at least one second set of data elements, for separately associating with each different set of data elements a separate series of modulation symbols selected from distinct modulation symbol alphabets corresponding to at least a second type of modulation providing for said second level of protection;
• a separate second interleaving means, coupled to each second modulation means to supply each frequency carrier of a separate set of said orthogonal frequency carriers with a distinct succession of modulation symbols picked up out of one of said separate series of modulation symbols, for interleaving in both time and frequency all of the modulation symbols of each series is supplied to the same frequency carrier;
• processing means coupled to all of the interleaving means for procession the interleaved signals to form an output signal suitable for transmission incorporating said sets of data elements in a form including differing levels of protection;
• and
• transmitting means coupled to the processing means for transmitting said output signal.