A design for Turbo trellis-coded modulation (TCM) systems is proposed with nearly half of the encoding delay caused by the conventional scheme.An introduction is also given to the associated constraint that the interleaver has to satisfy.An estimate of channel values in decoding is suggested so as to improve the accuracy of extrinsic information calculations and thus the decoding performance.The proposed iterative decoding algorithm

a natural extension of the standard decoding algorithm for TCM

is similar to the bit-wise one for binary turbo codes with the BPSK modulation.The bit error rate 10

-5

of this scheme needs signal-to-noise ratios within 0.4dB from the Shannon limit 2.85dB for the throughput 2bits/s/Hz with the 8PSK modulation.