Multifrequency modem using trellis-coded modulation.

摘要

Multifrequency modem in which the serial bit string received from the DTE (10) is divided into groups of bits the number m of which is determined by the characteristics of a sub-channel of the passband of a telephone line (22). A convolutional coding means delivers m+1 bits in response to the m bits of each group, these m+1 bits being converted into a complex symbol of a constellation with 2<m+1> points, the inverse discrete Fourier transform then being performed (16) on the sequence of symbols X(k) so as to obtain a sequence of digital samples over time (18) to be transmitted over the telephone line after conversion to analog signals. On reception, the sequence of digital samples over time (26) is transformed into a sequence of complex symbols (30) by a discrete Fourier transform (28), a Viterbi algorithm weighted as a function of the relevant constellation then being applied (32) to the symbols so as to obtain the data bits. <IMAGE>