High-Order Modulation Techniques for AWGN Interference Resistance

Abstract

High-order modulation is widely used when a communication system needs higher spectral efficiency, but its performance is still strongly affected by additive white Gaussian noise (AWGN). When the constellation becomes denser, the distance between signal points becomes smaller, so the system usually needs a higher SNR to keep the error rate at an acceptable level. This paper reviews the AWGN channel as a common benchmark and then discusses the main ideas used in high-order modulation research. The review mainly focuses on two parts: traditional high-order rectangular modulation such as Quadrature Amplitude Modulation (QAM), and newer constellation design methods such as Amplitude Phase Shift Keying (APSK), geometric shaping, and probabilistic shaping. It also points out several common problems in current studies, including overly ideal assumptions, limited system-level discussion, and increased implementation complexity. Finally, possible future directions are summarised, such as combining modulation design with coding, receiver structure, and hardware constraints. In general, research on high-order modulation under the AWGN model is still important because it helps explain both the basic theory and the practical design of high-rate communication systems.