Unified Constellation Design Using Projection Over QAM: Concept and Examples

Beyond fifth generation (B5G) / sixth generation (6G) wireless systems require full utilization of all spectrums. However, hardware devices operating in the high-frequency bands bring a series of non-ideal behaviors, including nonlinear distortion caused by high-power amplifiers and phase noise generated by radio-frequency oscillators, which will lead to performance degradation of traditional signal modulation technology. To this end, this paper proposes a 5G new radio-compatible constellation design method using projection over quadrature amplitude modulation (QAM). First, to address the nonlinear distortion caused by power amplifiers, the pseudo-amplitude-phase-shift keying (APSK) constellation with a low peak-to-average power ratio is proposed. The signal points are selected from QAM by minimum Euclidean distance with APSK. Second, for a phase noise channel, the pseudo-spiral constellation is designed with the projection of Spiral constellation points onto QAM by the proposed minimum radial-angular weighted distance. Simulation results show that the proposed pseudo-APSK modulation outperforms traditional QAM at medium and high code rates considering nonlinear distortion produced by a power amplifier. Besides, the proposed pseudo-spiral modulation exhibits significant performance gain and improved robustness compared to QAM under phase noise-affected channels, particularly in medium-high signal-to-noise ratio conditions.