Optical Receiver Frequency Offset Compensation via Residual Feedback
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Solution Overview
Problem
Conventional digital coherent optical receivers face challenges in accurately compensating for frequency offsets due to increasing noise with transmission distance, leading to phase shifts and transmission errors, which limits the transmission distance and system design freedom.
Innovation Solution
An optical communication receiving device with a frequency offset compensation unit, a carrier phase recovery unit, and a residual frequency offset detection unit that calculates and corrects frequency offsets using residual frequency offset values, improving accuracy and reducing noise-induced errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the transmission distance is increased, then the transmission capability is improved, but the noise increases making frequency offset detection inaccurate
Solution Approach 1:
The patent implements a feedback mechanism where the carrier phase recovery unit outputs carrier phase information back to the frequency offset compensation unit. This feedback loop allows the system to continuously monitor and correct frequency offsets even in high-noise conditions, resolving the contradiction between extended transmission distance and maintained detection accuracy.
Solution Approach 2:
The system performs preliminary frequency offset compensation using the frequency offset compensation unit before the carrier phase recovery unit processes the signal. This preliminary action reduces the impact of noise on subsequent phase recovery operations, enabling accurate detection despite increased transmission distance.
2Device complexity
If conventional frequency offset compensation is used, then the system is simple, but residual frequency offset causes phase slips and transmission errors
Solution Approach 1:
The patent merges the frequency offset compensation function with the carrier phase recovery function into an integrated system. The frequency offset compensation unit and carrier phase recovery unit work together with shared signal processing paths, reducing overall system complexity while improving reliability through mutual support between the two functions.
Solution Approach 2:
The feedback from the carrier phase recovery unit to the frequency offset compensation unit creates a self-correcting system that eliminates residual frequency offsets. This feedback mechanism prevents phase slips and transmission errors without requiring significantly increased system complexity.
3Measurement precision
If noise is reduced by decreasing transmission distance, then frequency offset detection accuracy is improved, but system design freedom is limited
Solution Approach 1:
The feedback mechanism enables the system to maintain high frequency offset detection accuracy regardless of transmission distance. By continuously monitoring carrier phase and adjusting frequency offset compensation accordingly, the system achieves noise-resistant operation that preserves both detection accuracy and transmission distance flexibility.
Solution Approach 2:
The preliminary frequency offset compensation performed before carrier phase recovery creates a cleaner signal for phase detection. This preliminary action effectively reduces the impact of transmission distance-related noise, maintaining detection accuracy while preserving system design freedom for various transmission scenarios.
Data Source
AI summary
A receiving device that converts, to a digital signal, a signal in which signal light from an optical transmission path and local oscillation light are mixed, so as to perform digital signal processing, the optical communication receiving device comprising: a frequency offset compensation unit configured to calculate a frequency offset of the digital signal and to, based on the frequency offset, compensate for a phase of the digital signal; a carrier phase recovery unit configured to calculate a carrier phase of the digital signal whose phase is compensated for in the frequency offset compensation unit; anda residual frequency offset detection unit configured to calculate an average of differences in the carrier phase, and to output the average as a residual frequency offset, wherein the frequency offset compensation unit is configured to correct the frequency offset using the residual frequency offset output by the residual frequency offset detection unit.