Coherent Optical Channel Labeling With PN Codes for Polarization Swaps
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Solution Overview
Problem
In coherent optical transmission systems, existing methods struggle to accurately identify and descramble polarization channels due to phase and polarization rotations caused by transmitter, receiver, and optical fiber imperfections, leading to data ambiguity and potential signal loss.
Innovation Solution
The use of relatively long binary PN codes is introduced to serve as alignment codes, which are combined with data signals and encoded with phase shifts to label and identify the independent polarization/phase channels, enabling reliable identification and correction of phase rotations and channel swaps through correlation peak detection and remapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pilot tones are added to aid channel identification, then channel identification accuracy is improved, but signal interference increases and polarity ambiguity remains
Solution Approach 1:
The patent extracts the identification function from the data signal by adding separate pilot symbols at known positions. These pilot symbols carry only identification information and are separated from the data-bearing components, allowing channel identification without the polarity ambiguity that plagues pure data signal analysis.
Solution Approach 2:
The patent introduces pilot symbols as intermediary elements that mediate between the transmitted signal and the identification process. These pilots serve as reference markers that explicitly indicate channel mappings and polarities, eliminating the need to infer channel information from the data signal itself.
2Measurement precision
If pilot tones are used for channel identification, then channel mapping is improved, but data loss increases due to interference with other signals
Solution Approach 1:
The patent segments the transmitted signal into distinct components: data symbols and pilot symbols. The pilots are placed at specific, known positions within the signal frame, separating the identification function from the data transmission function. This segmentation allows pilots to provide channel mapping information without interfering with data integrity.
Solution Approach 2:
The patent performs preliminary identification using the known pilot symbols before processing the data signal. By establishing channel mappings and polarities in advance based on the pilots, the system can then correctly interpret the data symbols without confusion about channel assignments, preventing data loss from misinterpretation.
3Stability of the object's composition
If conventional signal processing is applied to unmix channels, then orthogonality is improved, but channel identification ambiguity remains
Solution Approach 1:
The patent uses the known pilot symbols as feedback references that explicitly tell the receiver which channels correspond to which polarities and phases. This feedback information is embedded in the signal structure itself, allowing the receiver to resolve the identification ambiguity that would otherwise persist after signal mixing.
Solution Approach 2:
The patent introduces asymmetric marker patterns through the pilot symbols that break the symmetry of the signal space. These asymmetric pilots create unique signatures for each channel configuration, allowing the receiver to distinguish between different channel mappings and polarities that would otherwise appear symmetric and indistinguishable.
Data Source
AI summary
Described are systems and methods for identifying the phase and polarization of independent modulation streams in quadrature channels of a coherent transmission system by using digital code. As a result, phase rotation and polarization of streams that during transmission may have become rotated and swapped around in the channel are correctly labeled and depermuted according to a known and predictable order.