Cycle Slip Detection in Phase-Modulated Optical Signals
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Solution Overview
Problem
Conventional coherent communications systems face challenges in correcting phase mismatches between transmitter and receiver local oscillators, particularly in optical systems, where phase-locked loops can be complex, expensive, and unreliable, and existing digital signal processing methods do not effectively address cycle slips that occur during phase error correction.
Innovation Solution
A method and apparatus for detecting and removing cycle slips in phase-modulated signals using digital signal processing downstream of the local oscillator, employing coarse and fine phase-error estimation, conditional phase unwrapping, and cycle slip detection and removal blocks to adjust phase errors without adjusting the local oscillator, thereby avoiding the need for phase-locked loops and reducing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase-locked loop is used to correct phase mismatch between transmitter and receiver local oscillators, then phase matching accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces the phase-locked loop (a hardware-based feedback control system) with digital signal processing algorithms that operate on the received signal. Specifically, the system uses digital phase error estimation and correction techniques to achieve phase synchronization without requiring a phase-locked loop, thereby reducing hardware complexity while maintaining phase matching accuracy.
Solution Approach 2:
The patent uses pilot symbols that are inserted into the transmitted signal to carry phase reference information. The receiver copies the expected pilot symbol phases and compares them with the received pilot symbols to estimate phase errors, enabling accurate phase correction without complex hardware.
2Device complexity
If digital signal processing is used to estimate and correct phase errors without adjusting the local oscillator, then device complexity is reduced, but cycle slips may occur that degrade signal quality
Solution Approach 1:
The patent performs preliminary phase error estimation using pilot symbols before processing data symbols. By establishing an accurate phase reference from the pilot symbols first, the system prepares the phase correction parameters in advance, which helps prevent cycle slips during subsequent data symbol processing.
Solution Approach 2:
The patent implements a feedback mechanism where phase error estimates are continuously calculated from received symbols (both pilot and data symbols) and used to correct phase mismatches. This ongoing feedback process allows the system to detect and correct phase errors dynamically, reducing the likelihood of cycle slips and improving overall signal reliability.
Data Source
AI summary
Embodiments of the disclosure include a method and apparatus for detecting and removing cycle slip. A phase-modulated signal having a plurality of phase-modulated symbols is received at an optical receiver, and, for each phase-modulated symbol, a phase-error estimate of a phase error of the phase-modulated symbol is generated. The presence of a cycle slip is then detected based on the phase-error estimates, and, a phase of each of one or more of the received phase-modulated symbols is adjusted to remove the detected cycle slip without adjusting a local oscillator.