Novel Capture Algorithm Framework for Spread Spectrum Systems Under Noise and Interference

In high-speed moving environments, the Doppler effect severely impacts the frequency hopping synchronization of MSK modulated signals. Accurate frequency point estimation and Doppler frequency offset compensation are crucial for ensuring effective frequency hopping synchronization in highdynamic scenarios. To address this challenge, this paper proposes a dual-channel two-stage capture algorithm. The algorithm first establishes an initial capture threshold using the PMF-FFT method, then explores the selection of the sliding window size for two down-converted signals, aiming to find the peak corresponding to the frequency point within one frequency hopping period, while ensuring performance, complexity, and frame header capture time. In the tracking stage, adaptive threshold setting for frequency points within a hopping period is achieved using a correlation synchronization algorithm to correct Doppler frequency offset and bit shifts caused by down-sampling. In the data processing phase, the input signal is demodulated and de-spread in segments at a specified sampling rate and sample size. After LDPC decoding and CRC verification, the received data is obtained. Experimental results show that at an information rate of 300 k and a carrier-to-noise ratio of 40 dB, the system achieves a bit error rate that meets the communication system requirements with an SNR of −8dB.