The 2NQAM modulations of rate (N-1)/N

The use of error-correcting codes leads to efficient M-ary modulations by increasing their noise immunity. The results of the Ungerboeck approach concerning the optimal design of coding by taking account of the modulation are summarized. The method used by Calderbank allows the global definition of families of coded modulations using the same convolutional code. For the 2^NQAM (quadrature amplitude modulation) modulations with rate (N-1)/ N, the maximum attainable coding gain is related to the trellis complexity, exactly to the number of states in the Viterbi decoder and is nearly independent of the number of states of the modulation. OQAM with rate 2/3 gives the performances and the optimal receiver structure for all the modulations of the family. The results shows that the receiver can be implemented in two circuits, a preprocessor and a Viterbi decoder, this structure being suited to the reception of modulations with different rates and using the same convolutional code