Probabilistic Phase Error Carrier Recovery for Optical Symbols
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Solution Overview
Problem
Coherent optical communication systems face challenges in accurately recovering data symbols due to unbounded phase errors caused by frequency mismatches and phase non-linearities, leading to symbol errors and cycle slips, which existing techniques struggle to compensate effectively without increasing overhead through strong Forward Error Correction (FEC) schemes.
Innovation Solution
A method is introduced that calculates a probabilistic phase error for each data symbol estimate, using a filter function to compute a phase rotation, which is applied to generate rotated symbol estimates, thereby improving symbol detection accuracy by modeling the statistical performance of the optical communication system within the carrier recovery algorithm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional carrier recovery techniques are used to compensate for phase errors, then frequency offset compensation is achieved, but unbounded phase errors from laser line width and XPM cause cycle slips and symbol errors
Solution Approach 1:
The patent transforms the unbounded phase error parameter into a bounded probabilistic phase error parameter by modeling the statistical distribution of phase errors. Instead of directly compensating the raw phase error which grows unbounded, the invention calculates probability values based on the statistical characteristics of phase errors, thereby bounding the parameter space and enabling reliable symbol detection even in the presence of laser line width and XPM effects
Solution Approach 2:
The patent introduces probabilistic phase error values as an intermediary between the raw unbounded phase error and the symbol detection process. These probabilistic values serve as a mediator that captures the statistical essence of phase errors without inheriting the unbounded growth problem, allowing the system to make reliable detection decisions based on probability rather than absolute phase values
2Reliability
If strong Forward Error Correction (FEC) schemes are used to correct symbol errors, then symbol error rate is reduced, but system overhead increases
Solution Approach 1:
The patent performs preliminary action by calculating probabilistic phase error values before symbol detection occurs. By pre-characterizing the phase error statistics and incorporating this information into the detection process, the system proactively prevents symbol errors rather than relying on post-detection correction through FEC, thereby reducing the need for heavy forward error correction overhead
3Stability of the object's composition
If bounded filtering functions are used to compensate phase errors, then filtering stability is maintained, but unbounded phase errors cannot be effectively compensated
Solution Approach 1:
The patent resolves this contradiction by changing the parameter being filtered from the unbounded phase error to the bounded probabilistic phase error. The bounded filtering function maintains its stability properties while now operating on a parameter (probabilistic phase error) that is inherently bounded, thereby achieving both filtering stability and effective phase error compensation simultaneously
Data Source
AI summary
Methods and systems of data symbol recovery in a coherent optical receiver of an optical communications system. A respective probabilistic phase error is calculated for each of a plurality of data symbol estimates. A phase rotation is calculated based on the probabilistic phase error estimates, using a filter function, and the phase rotation applied to at least one data symbol estimate to generate a corresponding rotated symbol estimate. Each rotated symbol estimate is processed to generate corresponding decision values of each data symbol.