Free Space Optical Signal Processor for Phase Synchronization
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Solution Overview
Problem
In free space optical communication systems, particularly from artificial satellites to Earth, accurately calculating the effect of atmospheric fluctuations and Doppler shifts on optical signals is challenging, leading to difficulties in maintaining phase synchronization and resulting in incorrect signal demodulation due to relative phase error compensation.
Innovation Solution
A received signal processor that estimates signal-to-noise ratios, performs symbol decisions, determines phase rotation amounts, and rotates phases of digital signal sequences to correct relative phase errors, ensuring accurate phase synchronization and signal alignment for maximal ratio combining.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If digital coherent technologies are applied to free space optical communication to increase transmission capacity, then transmission capacity is improved, but phase synchronization becomes difficult due to atmospheric fluctuations
Solution Approach 1:
The received signal is segmented into multiple propagation modes using mode separating means. By processing each mode independently through dedicated single-mode fibers and detecting them separately, the system can handle atmospheric fluctuations mode-by-mode, maintaining phase synchronization reliability while preserving high transmission capacity through parallel mode processing
Solution Approach 2:
The system changes the parameter of signal representation by transforming the received optical signal from a single composite mode into multiple distinct propagation modes. This parameter transformation allows each mode to be processed with appropriate phase compensation, resolving the phase synchronization issue while maintaining high data throughput through multi-mode parallel processing
2Productivity
If laser beam is coupled to single-mode fiber with small core diameter to enable digital coherent technologies, then transmission capacity is improved, but coupling efficiency decreases due to atmospheric fluctuations
Solution Approach 1:
The coupling process is segmented by first coupling the received multi-mode signal into a multimode fiber, then using mode converting means to transform it into multiple single-mode signals that can be efficiently coupled into individual single-mode fibers. This segmentation approach maintains high coupling efficiency by matching modes at each stage while enabling digital coherent processing
Solution Approach 2:
A multimode fiber acts as an intermediary between the free-space optical channel and the single-mode fibers required for digital coherent detection. This intermediary allows efficient coupling from the atmospheric channel while enabling subsequent mode conversion and separation to achieve compatible signals for single-mode fiber input
Data Source
AI summary
An appropriate synthesized signal cannot be obtained by only correcting relative phase errors of a plurality of received signals; therefore, a received signal processor according to an exemplary aspect of the present invention includes a plurality of signal-to-noise ratio estimation means for estimating respective signal-to-noise ratios of a plurality of digital signal sequences in which relative phase errors of a plurality of received signal sequences having been corrected; a plurality of temporary decision means for performing symbol decisions of the plurality of digital signal sequences and outputting symbol signal sequences; symbol-map-rotation determination means for determining respective phase rotation amounts of the plurality of digital signal sequences from the plurality of symbol signal sequences and the respective signal-to-noise ratios of the plurality of digital signal sequences; and a plurality of phase rotation means for rotating phases of the plurality of digital signal sequences respectively based on the phase rotation amounts.