Dual-Polarization Coherent Channel Identification Using PN Codes
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Solution Overview
Problem
In high-speed communication systems, particularly in dual-polarization coherent optical transmission, existing methods struggle to accurately identify and descramble polarization and quadrature 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 implementation of relatively long binary PN codes is used to label and identify the phase and polarization of independent modulation streams by encoding them with distinct phase shifts, allowing for reliable identification and correction of channel orientations without interfering with the data signal, using a PN code generator and correlator system within the receiver.
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 identification becomes ambiguous
Solution Approach 1:
The patent extracts the channel identification function from the data signal by using separate pilot tones in specific polarization channels. The pilot tones are added only to the X-polarization channel (and optionally Y-polarization), allowing the receiver to identify channel orientations without requiring the pilot tones to carry data information, thus reducing interference with data transmission.
Solution Approach 2:
The patent introduces pilot tones as intermediary signals that mediate between the transmitted data and the identification process. These pilot tones serve as reference markers that enable the receiver to determine polarization and quadrature channel orientations without directly interfering with the data carried in other channels, as long as proper channel separation is maintained.
2Measurement precision
If pilot tones are used for channel identification, then channel orientation can be determined, but polarity ambiguity remains without additional timing information
Solution Approach 1:
The patent performs preliminary actions by adding pilot tones with known phases to specific channels before data transmission. The pilot tones are configured with specific phase relationships (e.g., 0° and 180° for X-polarization, 90° and 270° for Y-polarization) that establish reference points before the data is transmitted, enabling the receiver to resolve polarity ambiguities without requiring additional timing information during data reception.
3Reliability
If signal processing is applied to ensure orthogonality, then data stream separation is improved, but channel identification ambiguity increases due to arbitrary permutations
Solution Approach 1:
The patent uses pilot tones as distinctive markers that change the 'color' or identity of specific channels. By adding pilot tones with specific phases to the X-polarization channel (and optionally Y-polarization), the receiver can visually distinguish and identify the correct channel orientations among the four possible permutations, resolving the ambiguity that would otherwise exist after signal processing separates the data streams.
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.