Design of TwoDimensional Nonuniform Constellations with Better Performance Modern communication systems adopt nonuniform constellations (NUCs) to approach Shannon limit. Generally, the design process of NUCs is based on maximizing bitinterleaved coded modulation (BICM) capacity for given channel conditions. However, the traditional Monte Carlo methods for computing BICM capacity cannot ensure the accuracy of NUC optimization with low complexity. This paper proposes a new design method including the derivation of a computable expression about BICM capacity and a new optimization scheme with simplified calculation of gradient in the algorithm. In this way, we obtain a set of 2DNUCs with low complexity and better performance than those adopted by ATSC 3.0.

BitLevel Capacity analysis on NonUniform Constellations The aim of this paper is to present a bitlevel capacity analysis of the nonuniform constellations (NUC) and to evaluate the reasons of their outperformance over a long time used uniform constellations (UC). The analysis is performed for QAM constellations order of 16 and 64, however, the results and conclusions can be extended for biggest orders. PerSNR optimized 2D NUC are analyzed in the full SNR range of operation, from rectangular Shape like UC at high SNR to total converged NUC, like 4QAM. The NUC are designed based on the optimization of the BICM capacity equation by mean of a Particle Swarm Optimization Algorithm. The different simulations and the validation of the results were carried out through the evaluation of the different perSNR NUC in the BICM capacity equation. No simulations were performed in any codingdecoding chain. In these conditions, it is presented that the total condensed NUC for 64QAM and others with different convergences levels around the 4QAM shape has capacity gain over the 2D NUC64QAM presented in ATSC 3.0 with a code rate of 215 for SNR values lowers than 1.6 dB. A capacity gain of up to 0.022 bitsHz was achieved over the ATSC 3.0 NUC.