Low-complexity APSK demodulation algorithm based on K-means clustering in LEO satellite communication systems

Amplitude Phase Shift Keying (APSK) is more suitable for the nonlinear channels of Low Earth Orbit (LEO) satellite communication systems compared to Quadrature Amplitude Modulation (QAM). To tackle challenges posed by Direct Current (DC) interference and high demodulation complexity, we propose an APSK demodulation algorithm based on K-means clustering. Initially, static DC components are calculated and removed from the received APSK signals. Subsequently, the estimated APSK constellation points serve as initial centers for K-means clustering. These centers are refined through the K-means process and act as theoretical APSK constellation points for the Max-Log-MAP demodulation algorithm, effectively eliminating residual DC. We then introduce a low-complexity APSK demodulation algorithm that utilizes the symmetry of constellation points along with the Euclidean distance between DC-eliminated signals and these constellation points to minimize the set of constellation points. Simulation results indicate that for 32-APSK, our proposed demodulation submodule reduces computational complexity to approximately one-third that of the Max-Log-MAP algorithm while improving Bit Error Rate (BER) performance by about 0.23 dB. Furthermore, end-to-end simulation experiments conducted within LEO satellite communication systems demonstrate that our approach not only maintains this complexity advantage but also enhances BER performance by approximately 1.1 dB.