Communication system’s performance is sensitive to bandwidth, power, cost etc. There have been various solutions to improve the performance, out of them, one of the fundamental solutions over the years is design of optimum modulation schemes. As the research on beyond 5G heats up, we survey and explore power and bandwidth efficient modulation schemes for the next generation communication systems in details. In the existing literature, initially square quadrature amplitude modulation (SQAM) was considered. However, only square constellations are not sufficient for varying channel conditions and rate requirements, thus, efficient odd power of 2 constellations were introduced. For odd power of 2 constellations, rectangular QAM (RQAM) is most commonly used. However, RQAM is not a good choice and modified cross QAM (XQAM) constellation is preferred which provides improved power efficiency over RQAM due to its energy efficient two dimensional (2D) structure. The increasing demand for high data-rates has further encouraged research towards more compact 2D constellations which leads to hexagonal lattice structure based hexagonal QAM (HQAM) constellations. In this work, various QAM constellations are discussed and detailed study of star QAM, XQAM, and HQAM is presented. Generation, peak and average energies, peak-to-average-power ratio, symbol-error-rate, decision boundaries, bit mapping, Gray code penalty, and bit-error-rate of star QAM, XQAM, and HQAM constellations for different constellation orders are presented. Finally, a comparative study of various QAM constellations is presented which justifies the supremacy of HQAM over other QAM constellations for various wireless communication systems and a potential modulation scheme for future standards.

中文翻译：

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高阶QAM星座调查：技术挑战，最新进展和未来趋势

通信系统的性能对带宽，功率，成本等敏感。有多种解决方案可提高性能，其中，多年来的基本解决方案之一是设计最佳调制方案。随着对超越5G的研究不断升温，我们将详细研究和探索下一代通信系统的功率和带宽高效调制方案。在现有文献中，最初考虑了平方正交幅度调制（SQAM）。然而，仅正方形星座不足以改变信道条件和速率要求，因此，引入了两个星座的有效奇数功率。对于2个星座的奇数功率，最常用的是矩形QAM（RQAM）。然而，RQAM不是一个很好的选择，并且由于它具有高能效的二维（2D）结构，因此经过修改的交叉QAM（XQAM）星座图比RQAM具有更高的功率效率，因此是首选。对高数据速率的日益增长的需求进一步鼓励了对更紧凑的2D星座的研究，这导致了基于六边形晶格结构的六边形QAM（HQAM）星座。在这项工作中，讨论了各种QAM星座，并对星型QAM，XQAM和HQAM进行了详细研究。不同星座的星型QAM，XQAM和HQAM星座图的生成，峰值和平均能量，峰均功率比，符号错误率，决策边界，位映射，格雷码罚分和误码率订单被提出。最后，