Optical Carrier Modulation via Constant Composition Codes
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Solution Overview
Problem
Conventional methods for modulating digital input signals onto optical carriers, such as probabilistic and geometrical power shaping, face challenges like performance loss, costly iterative processing, and high computational complexity, particularly in constructing distribution matchers and implementing non-binary forward error correction.
Innovation Solution
The method involves using a constant composition code to modulate a digital data stream onto an optical carrier by selecting codewords that map bits to constellation points, enabling low complexity geometric shaping and efficient encoding, with a multi-ring constellation allowing separate coding of radii and phases, and employing a digital signal processor to decode these symbols effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If probabilistic power shaping is used to achieve longer transmission reach, then transmission distance is improved, but distribution matcher construction complexity increases and performance loss occurs
Solution Approach 1:
The patent segments the digital input stream into first segments and second segments, applying different encoding schemes to each. The first segments are encoded using constant composition codes for geometric shaping, while the second segments are encoded using conventional schemes, thereby simplifying the overall system while maintaining transmission distance improvements.
Solution Approach 2:
The patent replaces complex probabilistic distribution matchers with simpler constant composition codes that achieve similar power shaping effects. This substitution uses less computationally intensive coding structures that are easier to implement and decode, reducing system complexity while maintaining the transmission distance benefits.
2Reliability
If many-to-one mapping is used for distribution matching, then power shaping is achieved, but performance loss occurs and iterative receiver processing becomes costly
Solution Approach 1:
Instead of using many-to-one mapping that requires complex iterative decoding, the patent inverts the approach by using one-to-one mapping with constant composition codes. Each codeword directly maps to a unique constellation point sequence, eliminating the need for iterative receiver processing while maintaining power shaping performance.
3Reliability
If geometrical power shaping is applied to optimize constellation geometry, then transmission performance is improved, but computational complexity increases due to non-binary FEC requirements
Solution Approach 1:
The patent extracts the geometric shaping function from complex non-binary FEC schemes and implements it separately using constant composition codes. This separation allows the geometric optimization to be achieved independently with lower computational complexity, while conventional binary FEC handles the error correction, reducing overall system complexity.
4Ease of manufacture
If conventional QAM modulation is used, then implementation is simple, but transmission reach is limited compared to power-shaped formats
Solution Approach 1:
The patent merges conventional QAM modulation simplicity with power shaping benefits by combining constant composition coding with QAM constellation mapping. The result is a hybrid scheme that maintains the implementation simplicity of conventional QAM while achieving the extended transmission reach of power-shaped formats through optimized constellation point distribution.
Data Source
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AI summary
Method of modulating an optical carrier according to a constellation of symbols to carry a digital data stream formed of first segments of a same length and second segments, said method comprising: for each one of the first segments, selecting a codeword of a constant composition code, the selected codeword having a value corresponding to a value of said one of the first segments, and for each selected codeword, modulating a sequence of the symbols of the constellation onto the optical carrier based on one of the second segments, each symbol of the sequence being located from a center of the constellation at a distance defined by a value of a corresponding letter of the selected codeword.