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As the research on beyond 5G heats up, we survey and explore power andbandwidth efficient modulation schemes in details. In the existing publicationsand in various communication standards, initially square quadrature amplitudemodulation (SQAM) constellations (even power of 2) were considered. However,only the square constellations are not efficient for varying channel conditionsand rate requirements, and hence, odd power of 2 constellations wereintroduced. For odd power of 2 constellations, rectangular QAM (RQAM) iscommonly used. However, RQAM is not a good choice due to its lower powerefficiency, and a modified cross QAM (XQAM) constellation is preferred as itprovides improved power efficiency over RQAM due to its energy efficient twodimensional (2D) structure. The increasing demand for high data-rates hasfurther encouraged the research towards more compact 2D constellations whichlead to hexagonal lattice structure based constellations, referred to ashexagonal QAM (HQAM). In this work, various QAM constellations are discussedand detailed study of star QAM, XQAM, and HQAM constellations is presented.Generation, peak and average energies, peak-to-average-power ratio,symbol-error-rate, decision boundaries, bit mapping, Gray code penalty, andbit-error-rate of star QAM, XQAM, and HQAM constellations with differentconstellation orders are presented. Finally, a comparative study of various QAMconstellations is presented which justifies the supremacy of HQAM over otherQAM constellations. With this, it can be claimed that the use of the HQAM invarious wireless communication systems and standards can further improve theperformance targeted for beyond 5G wireless communication systems.

A Survey on Design and Performance of Higher-Order QAM Constellations