A Signal demodulation algorithm for high-speed inter-satellite link based on double closed-loop structure

The inter-satellite link plays an important role in the process of realizing global connection, which is expected to be fast, efficient and seamless. It also builds an integrated communication network between space and earth. Since the inter-satellites are generally far away from each other, and they move relatively at high speed in their own respective orbits, which will bring large path loss and Doppler shift. When using high-frequency communication, the Doppler shift is more obvious, which has a serious impact on the data recovery at the receiver and cannot meet the reliability requirements for communication. Aiming at the above problems, this paper proposes a new demodulation algorithm based on double closed-loop structure. The Walker inter-satellite link is adopted firstly, then we designed the transmission frame structure. Finally we propose a complete modulation and demodulation scheme. In the demodulation scheme, We use the Delayed Auto Correlation (DAC) method for the super-frame header to improve the capture performance when the signal to noise ratio (SNR) is low. Then, for the spread spectrum signal, an improved timing error detection method is proposed. It reduces the processing bandwidth, and improves the accuracy of timing error detection under the condition of low SNR. What's more, it is easy to implement. The simulation results show that when the SNR is greater than 13dB, the proposed algorithm can quickly complete the synchronization, and the bit error rate (BER) is less than 10-6, which meets the requirements of the received signal level of the inter-satellite link.