BICM Transmission Using Non-Uniform QAM Constellations: Performance Analysis and Design

In this paper we study bit-interleaved coded modulation (BICM) transmission using non-uniform (NU) quadrature amplitude modulation (QAM) constellations. For such a NUQAM-BICM transmission, we develop closed-form approximations for the probability density function of the L-values, and we use them to predict the coded bit error rate (BER)performance of the system in the AWGN channel. We then numerically optimize NU-QAM-BICM based on convolutional codes. Compared to uniform QAM-based BICM transmission, and for a target BER of 10^-7, we reach gains up to 1 dB. When the design is applied to turbo codes a decrease in the error floor can be obtained.