Blind Frequency Recovery in Optical Systems
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Solution Overview
Problem
Conventional digital PLL-based blind carrier recovery algorithms are ineffective for high-speed optical systems due to intrinsic feedback delay and require extensive parallel processing, which degrades performance, and existing methods are not suitable for high-order QAM systems with low tolerance to frequency and phase noise.
Innovation Solution
A multi-stage blind frequency search method using a combination of parallel and sequential processing architectures to accurately estimate and remove carrier frequency offset in optical systems, employing a two-stage frequency search process with coarse and fine frequency resolution to minimize the number of required symbols and hardware complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional digital PLL-based blind carrier recovery algorithms are used, then carrier phase and frequency can be recovered simultaneously, but the system becomes too complex and performs poorly in high-speed optical systems due to feedback delay
Solution Approach 1:
The patent divides the frequency recovery process into two distinct stages: a coarse frequency search stage that quickly identifies the approximate frequency offset range, and a fine frequency search stage that precisely determines the actual frequency offset. This segmentation eliminates the need for complex PLL feedback mechanisms while achieving accurate carrier recovery in high-speed optical systems.
2Speed
If heavily parallel processing is used in optical systems, then processing speed is maintained, but the performance of PLL-based algorithms degrades due to feedback delay
Solution Approach 1:
The patent performs preliminary frequency offset estimation in the coarse search stage using a limited set of test frequencies, establishing an approximate offset range before proceeding to the fine search stage. This preliminary action reduces the search space for subsequent processing, enabling accurate frequency recovery without requiring extensive parallel computation or suffering from feedback delay issues.
3Measurement precision
If the number of frequency test points is increased to improve frequency offset estimation accuracy, then measurement precision improves, but the number of required symbols and processing complexity increase
Solution Approach 1:
The patent segments the frequency search process into coarse and fine stages, using a small number of test frequencies in the coarse stage to identify the offset range, then using fewer test frequencies in the fine stage to precisely determine the actual offset. This two-stage approach achieves high measurement precision while minimizing the total number of required symbols and processing operations.
Data Source
AI summary
Described herein are systems and methods for accurately estimating and removing a carrier frequency offset. One exemplary embodiment relates to a system comprising a frequency offset detection circuit detecting a carrier frequency offset in an optical signal, and a frequency testing circuit calculating an estimated frequency offset value of the carrier frequency offset, wherein the frequency testing circuit removes a carrier phase based on the estimated frequency offset value and recovers the optical signal. Another exemplary embodiment relates to a method comprising detecting a carrier frequency offset in an optical signal, calculating an estimated frequency offset value of the carrier frequency offset, removing a carrier phase based on the estimated frequency offset value, and recovering the optical signal.