Joint Design for Modulation and Constellation Labels in Multiuser Superposition Transmission

Abstract

Hierarchical modulation (HM), a promising non-orthogonal multiple access scheme, is able to provide different levels of protection for data streams and achieve a larger rate region that cannot be realized by traditional orthogonal schemes. In this paper, we propose a novel HM system with non-uniform constellation inputs and analytically derive the bit-interleaved coded modulation (BICM)-capacity for each hierarchical layer. Different from the power optimization method for the superimposed uniform constellation, we directly optimize the constellation positions in conjunction with the optimal binary labels design for HM in additive white Gaussian noise channels. For maximizing the BICM-capacity, a fairness balanced criteria is developed for the HM system by considering both power constraints and QoS constraints. Multi-start interior-point algorithm is then proposed to carry out the constellation optimization problems, and the corresponding methods are also proposed to reduce optimization complexity. Numerical results verify the performance gains of optimized HM compared with the optimized quadrature amplitude modulation based HM and other orthogonal transmission methods.