Lattice-Superposition NOMA for Near-Far Users

A novel non-orthogonal multiple access scheme based on lattice superposition is proposed. Sixteen points from the D-4 lattice are picked as the signal constellation in the four-dimensional real space. Superposition coding for two users is applied at the downlink of the communication system. While the far user detects its intended signal directly, the near user performs interference cancellation before detects its own intended signal. The performance of our proposed scheme is compared with a benchmark orthogonal scheme using 16-QAM. When the link gain difference between the two users is large, our proposed lattice superposition scheme outperforms the benchmark significantly. In particular, when the link gain of the far user is 20 dB smaller than that of the near user, with a word error probability of 10(-3), an energy gain of 6 dB can be obtained.