Joint Chromatic Dispersion and Frequency Offset Estimation in Optical Transceivers
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Solution Overview
Problem
Long-haul optical communication systems face performance limitations due to fiber optic impairments like chromatic dispersion (CD) and local oscillator frequency offset (LOFO), which can hinder data transmission, especially in multiple-subcarrier-based transmission methods where timely compensation is crucial but challenging.
Innovation Solution
An optical transceiver with a processor that uses a two-dimensional measurement grid to jointly estimate CD and LOFO values, processing the optical signal in both time and frequency domains, and applies these estimates for compensation before transmission, facilitating accurate and rapid correction of impairments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple-subcarrier-based transmission (e.g., OFDM) is used to increase data rates, then bandwidth and data transmission capacity are improved, but the time available for determining compensation for CD and LOFO is reduced, making accurate compensation more difficult
Solution Approach 1:
The patent applies preliminary action by performing joint CD and LOFO estimation using training sequences before the actual data transmission. The estimation is conducted in advance during the preamble period, allowing the system to prepare compensation parameters beforehand. This enables rapid compensation during data transmission without consuming additional time from the payload, thus resolving the contradiction between high data rates and sufficient compensation time.
2Device complexity
If traditional separate estimation methods are used for CD and LOFO, then the estimation process is simpler, but the accuracy and effectiveness of compensation are reduced, especially in multiple-subcarrier systems
Solution Approach 1:
The patent merges the separate CD estimation and LOFO estimation processes into a single joint estimation operation. By combining both estimations using the same training sequences and processing framework, the system achieves improved accuracy for both parameters simultaneously. The joint estimation leverages the relationship between CD and LOFO effects on the signal, allowing more precise compensation than separate methods, while maintaining reasonable computational complexity through efficient algorithm design.
3Object-affected harmful factors
If chromatic dispersion causes different spectral components to travel at different speeds, then signal broadening and ISI occur, but the fundamental physics of light propagation cannot be changed
Solution Approach 1:
The patent converts the harmful effects of CD and LOFO into beneficial information for compensation. By deliberately allowing the signal to experience these impairments during transmission through the fiber, the system obtains measurable effects in the received training sequences. These measured effects are then used to calculate precise compensation parameters that are applied to correct the data transmission. The harmful physical phenomena become the basis for determining the exact compensation needed, transforming the problem into a solution.
Data Source
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AI summary
An optical transceiver in an optical communications network, comprising a receiver configured to receive an optical signal comprising an X-polarization component and a Y-polarization component. The optical transceiver further comprises a processor coupled to the receiver and configured to determine a chromatic dispersion (CD) estimate and a local oscillator frequency offset (LOFO) estimate based on a relationship between a plurality of CD values and a plurality of LOFO values. The optical transceiver further comprises a transmitter coupled to the processor and configured to transmit the CD estimate, the LOFO estimate, and the optical signal to a downstream component in the optical communications network.