High Order Signal Constellations Research Articles

Constrained Interleaved Coded Modulation

Constrained interleaved coded modulation (CICM) is introduced to map coded bits onto higher order signal constellations. A reverse Gray coding (RGC) constellation mapping policy is introduced to map groups of bits onto a selected signal constellation. Then, a CICM interleaver is designed to jointly achieve both the highest possible minimum symbol Hamming distance (MSHD) and the highest possible minimum squared Euclidean distance (MSED) for use with the selected RGC-encoded constellation. It is demonstrated that CICM schemes constructed with simple block codes can be decoded with reduced coding complexity while performing better than more-complicated TCM and BICM-ID schemes known in the literature.

Approximate ML detection for MIMO systems using multistage sphere decoding

We derive a new multistage sphere decoding (MSD) algorithm, which is a generalization of the conventional sphere decoder (SD). This new MSD exploits that many higher order signal constellations can naturally be decomposed into several lower order constellations. We develop a two-stage SD for a 16-ary quadrature amplitude modulation (16QAM) multi-input multi-output (MIMO) system by decomposing 16QAM into two 4QAM constellations. The first stage generates a list of 4QAM vectors. For each of these, the second stage computes an optimal 4QAM vector. In the low signal-to-noise ratio (SNR) region, our MSD performs close to the original (single-stage) SD, but it has a lower complexity. In the high SNR region, our MSD is not suitable for reaching near maximum likelihood (ML) performance.

Optimization of symbol mappings for bit-interleaved coded Modulation with iterative decoding

We investigate bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth efficient transmission, where the bit error rate is reduced through iterations between a multilevel demapper and a simple channel decoder. In order to achieve a significant turbo-gain, the assignment strategy of the binary indices to signal points is crucial. We address the problem of finding the most suitable index assignments to arbitrary, high order signal constellations. A new method based on the binary switching algorithm is proposed that finds optimized mappings outperforming previously known ones.