TCM-NOMA: Joint Multi-User Codeword Design and Detection in Trellis-Coded Modulation-Based NOMA for Beyond 5G

In this paper, we propose a novel non-orthogonal multiple access (NOMA) scheme based on trellis-coded modulation (TCM) techniques. Unlike the traditional code-domain NOMA scheme, we consider to jointly map the incoming data streams of multiple users to a superposed codeword so as to improve the coding gain of the system without any bandwidth extension. Both codeword design and multi-user detection are considered to optimize the TCM for NOMA. For the NOMA encoder, the multi-dimensional (MD) constellation is carefully selected and a new set partitioning algorithm is developed for MD signal set labeling. For joint decoding, a suboptimal two-layer Viterbi algorithm is developed where the non-orthogonal nature is utilized to reduce the complexity. Numerical evaluations have been performed to show that our proposed TCM-based NOMA scheme is superior to the traditional code-domain NOMA and orthogonal frequency division multiple access schemes with high E
_b
/N
₀
in terms of the BER performance under the same channel conditions.