Joint design for modulation and constellation labels in non-orthogonal 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 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 user by means of the mutual information. 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, we propose a fairness balanced criterion for HM system by considering both power constraints and user QoS constraints. Multi-start interior-point algorithm is proposed to deal with the constellation optimization problems. Numerical results show that the proposed HM verify the performance gains of optimized HM compared with the optimized quadrature amplitude modulation (QAM) based HM and other orthogonal transmission methods.