The phase synchronization accuracy of modulated baseband signal in high-speed space optical communication directly affects the error rate and ranging performance of the communication system. At present, high-speed modulation baseband signal have problems such as low phase synchronization accuracy and complex hardware implementation. This paper proposes a high-speed modulation baseband signal phase synchronization algorithm based on FPGA. The phase of high-speed baseband signal transmission clock is adjusted in real time through closed-loop control to realize the phase synchronization of I and Q high-speed signals. The experimental results show that the phase synchronization accuracy of the high-speed optical modulation baseband signal with code rate of 5Gbps is less than 5ps; The communication sensitivity is better than -46dBm, and the ranging accuracy is better than 3mm. Compared with traditional methods, synchronization accuracy, communication sensitivity and ranging accuracy have been significantly improved, and low hardware complexity.
Feed-forward timing recovery scheme has the advantage of fast estimation without acquisition time, but it is rarely used in resource-constrained spaceborne applications because of the computational complexity required to achieve highperformance estimation. In view of the limited resources and weak receiving power of the inter-satellite optical communication system, a low-complexity and parallelized feedforward timing recovery scheme is presented in this paper. Low-pass filtering based on Kalman filter is introduced to estimate the timing offset accurately. Phase jump detector is added to avoid the timing phase slip at 0/π that traditional feedforward timing recovery faces in low SNR. The corresponding experiment results show that the proposed scheme can achieve stable estimation and correction of clock bias under the condition of low signal-to-noise ratio with low implementation complexity.
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