Research on Optimization of Transmission Schemes for Satellite Communications under Low Signal-to-Noise Ratio Conditions

To address the performance bottlenecks of convolutional coding and π/4-DQPSK modulation in satellite communications, this paper proposes an optimized scheme employing Turbo codes combined with QPSK modulation. By redesigning the frame structure, implementing Turbo encoding, and adopting QPSK coherent demodulation, the link performance is significantly enhanced while maintaining compatibility with existing interfaces. MATLAB-based simulations demonstrate that the optimized system achieves a 4.8 dB reduction in required signal-to-noise ratio (SNR) at equivalent bit error rate (BER), validating the superiority of Turbo and QPSK integration. This solution effectively meets low-rate service communication requirements under low-SNR conditions, providing technical guidelines for optimizing FDMA-based satellite voice services.