Patent ID: 7315582

Claim:
A transmitter comprising: a primary encoder (CODER 1 ) for receiving a primary stream containing data and for supplying a primary encoded stream, a secondary encoder (CODER 2 ) for encoding a secondary stream containing additional data and for supplying a secondary encoded stream, a hybrid modulator ( 40 ) for receiving either the primary encoded stream or both primary and secondary encoded streams, and for generating either n-bit symbols of a first constellation or n+m-bit symbols of a second constellation in accordance with a predetermined pattern indicating, for each symbol duration, which constellation is to be applied; wherein the hybrid modulator ( 40 ) comprises: switching means ( 42 ) allowing selection of n-bit sequences from the primary encoded stream and/or m-bit sequences from the secondary encoded stream, with respect to a predetermined pattern, a first modulator (QPSK) for receiving said n-bit sequences from the switching means ( 42 ) and for generating n-bit symbols of the first constellation, a second modulator for receiving both n-bit sequences and m-bit signals from the switching means ( 42 ) and for generating n+m-bit symbols of the second constellation, a de-multiplexer (DEMUX) for de-multiplexing the symbols generated by said first and second modulators, control means for controlling the switching means and the de-multiplexer with respect to the predetermined pattern, in order that: if the predetermined pattern indicates that the first constellation is to be applied, an n-bit sequence is passed from the switching means ( 42 ) to the first modulator for generating an n-bit symbol to be supplied at the output of the de-multiplexer (DEMUX), if the predetermined pattern indicates that the second constellation is to be applied, an n-bit sequence and an m-bit sequence are passed from the switching means ( 42 ) to the second modulator for generating an n+m-bit symbol to be supplied at the output of the de-multiplexer (DEMUX).