Bounded Phase Error Compensation in Optical Carrier Recovery
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Solution Overview
Problem
Optical communication systems face unbounded phase errors due to frequency mismatches and phase noise, leading to cycle slips that are difficult to correct, especially as symbol rates increase, requiring significant Forward Error Correction (FEC) resources and increasing sensitivity to noise.
Innovation Solution
The method involves processing SYNC bursts with known symbol sequences to estimate frequency offsets and apply phase rotations to data symbol estimates, allowing for the use of bounded filters to correct phase errors, thereby reducing the occurrence of cycle slips and the need for strong FEC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If unbounded filtering function is used to compensate unbounded phase error, then phase error compensation is achieved, but cycle slips occur
Solution Approach 1:
The patent changes the parameter of the filtering function from unbounded to bounded. Specifically, it uses a bounded filtering function that limits the phase error compensation to prevent cycle slips, while still effectively compensating for frequency offset and phase noise within acceptable ranges.
Solution Approach 2:
The patent implements feedback mechanisms to monitor phase error and adjust the filtering function accordingly. The system uses feedback from phase error detection to dynamically adjust the bounded filtering parameters, ensuring that phase error compensation remains within bounds while adapting to changing channel conditions.
2Reliability
If strong FEC is used to correct cycle slips, then data recovery reliability is improved, but FEC budget increases and sensitivity to noise increases
Solution Approach 1:
The patent applies preliminary anti-action by preventing cycle slips before they occur through bounded phase error compensation. By using a bounded filtering function that proactively limits phase error growth, the system reduces the need for extensive FEC to correct cycle slips, thereby lowering the FEC budget requirement.
Solution Approach 2:
The patent performs preliminary action by estimating frequency offset and applying phase rotation before data symbol processing. This preliminary frequency offset estimation and phase correction reduces the impact of phase errors on data symbols, decreasing the burden on FEC and reducing the required FEC budget.
3Reliability
If frequency offset estimation is performed continuously, then phase error compensation is improved, but processing complexity increases
Solution Approach 1:
The patent employs periodic action by performing frequency offset estimation at regular intervals rather than continuously. The system estimates frequency offset periodically using training symbols or pilot signals, then applies the estimated offset for a predetermined period, reducing processing complexity while maintaining effective phase error compensation.
Solution Approach 2:
The patent performs frequency offset estimation in advance using training sequences before data transmission begins. This preliminary estimation allows the system to prepare phase correction parameters ahead of time, reducing real-time processing complexity while maintaining reliable phase error compensation during data transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively limits phase errors to bounded values, reducing the number of errored symbols and the required FEC budget, while maintaining data recovery performance without the need for differential encoding, thus enhancing the reliability and efficiency of optical communication systems.
Implementation Method 1
the modulated optical signal received at the coherent receiver is mixed with a narrow-line-width local oscillator (LO) signal, and the combined signal is made incident on one or more photodetectors
Implementation Method 2
the combined signal is made incident on one or more photodetectors. The frequency spectrum of the electrical current appearing at the photodetector output(s) is substantially proportional to the convolution of the received optical signal and the local oscillator (LO)
Data Source
AI summary
A method of data symbol recovery in a coherent receiver of an optical communications system. Two or more SYNC bursts, having a known symbol sequence and periodicity, are processed to derive an estimate of a frequency offset ”f between a transmit laser and a Local Oscillator (LO) of the receiver. A phase rotation º(n) is computed based on the estimate of the frequency offset ”f, and applied to a plurality of data symbol estimates to generate corresponding rotated symbol estimates. The rotated symbol estimates are then filtered to generate corresponding decision values of each data symbol.