  In this letter, we propose a trellis-coded nonorthogonal multiple access
(NOMA) scheme. The signals for different users are produced by trellis coded
modulation (TCM) and then superimposed on different power levels. By
interpreting the encoding process via the tensor product of trellises, we
introduce a joint detection method based on the Viterbi algorithm. Then, we
determine the optimal power allocation between the two users by maximizing the
free distance of the tensor product trellis. Finally, we manifest that the
trellis-coded NOMA outperforms the uncoded NOMA at high signal-to-noise ratio
(SNR).
