研究目的
To improve the bandwidth efficiency of free-space optical systems and to reduce the impact of the background noise by proposing a differential M-ary pulse-amplitude modulation (M-PAM) signalling scheme that uses two laser transmitters.
研究成果
The proposed differential M-PAM signalling scheme improves bandwidth efficiency and reduces the impact of background noise in free-space optical systems. It allows for efficient channel estimation without requiring pilot symbol transmission, achieving performance close to the perfect channel knowledge case with a sufficiently large observation window.
研究不足
The proposed channel estimator requires a slight increase in system implementation complexity due to the need for a second photodetector and corresponding electronics. The method's efficiency is limited by the background radiation level, as too high levels can saturate the A/D input for the S-branch.
1：Experimental Design and Method Selection:
The study proposes a differential M-PAM signalling scheme using two laser transmitters for free-space optical communications. The methodology includes comparing the performance of the proposed differential PAM with conventional PAM signalling under perfect and imperfect channel state information (CSI) conditions.
2：Sample Selection and Data Sources:
The analysis is based on theoretical models and simulations, considering atmospheric turbulence channels and background noise effects.
3：List of Experimental Equipment and Materials:
The proposed system includes two laser diodes, optical filters, photodetectors, and electronic components for signal processing.
4：Experimental Procedures and Operational Workflow:
The study involves signal transmission using differential PAM, channel estimation without pilot symbols, and performance evaluation through BER analysis.
5：Data Analysis Methods:
The performance is evaluated using bit error rate (BER) analysis under different conditions of channel knowledge and background noise levels.
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