Clock Recovery in Multi-Channel Optical Receivers
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Solution Overview
Problem
Multi-channel receivers face challenges in clock recovery and equalizer convergence due to severe inter-symbol interference (ISI) in signals transmitted through different channels on a multi-mode fiber link, making it difficult to detect signals, especially those with severe ISI.
Innovation Solution
The solution involves utilizing the dependence between neighbor channels on a multi-mode fiber link for reliable clock recovery and equalizer convergence at a wavelength division multiplexing receiver. This is achieved by initially recovering a clock signal and estimating equalizer coefficients for a first channel, then using these as references to recover clock signals and estimate coefficients for subsequent channels, leveraging the similarity of fiber channel responses between neighbor channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional independent clock recovery and equalizer estimation is used for each channel, then each channel can be processed separately, but channels with severe ISI cannot be reliably detected and converged
Solution Approach 1:
The patent uses channel response copying by estimating the channel response for a first channel and then copying this estimate to the second channel. This allows the receiver to leverage the easier-to-detect first channel information to assist in detecting the harder-to-detect second channel, thereby improving reliability without requiring completely independent processing of each channel
Solution Approach 2:
The patent introduces an intermediary approach where the first channel's clock signal and equalizer coefficients serve as reference or seed values for the second channel. This intermediary information acts as a bridge that enables reliable detection in channels with severe ISI by using information from channels with better signal quality
2Productivity
If separate processing is applied to each channel, then processing complexity is distributed, but convergence of equalizer coefficients becomes difficult for channels with severe ISI
Solution Approach 1:
The patent applies preliminary action by first estimating the equalizer coefficients for the first channel, then using these pre-computed coefficients as initial values or seeds for estimating coefficients for the second channel. This preliminary estimation on the easier channel provides a good starting point that accelerates convergence and improves accuracy for the harder channel
Solution Approach 2:
The patent merges the processing of multiple channels by combining the clock recovery and equalizer estimation operations. Instead of completely independent processing, the patent combines information from the first channel (clock signal and coefficients) with the second channel processing, creating a unified approach that improves overall productivity while maintaining precision
3Device complexity
If independent equalizer estimation is used for each channel, then implementation is simpler, but channels with severe ISI experience closed eye diagrams and poor detection
Solution Approach 1:
The patent applies universality by creating a multi-functional receiver architecture where the first channel serves multiple purposes: it provides clock recovery for the second channel, provides equalizer coefficient estimates for the second channel, and acts as a reference for signal quality assessment. This universal use of the first channel's information improves detection reliability without proportionally increasing complexity
Data Source
AI summary
A multi-channel receiver that includes a first clock recovery unit configured to recover a first clock signal associated with a first optical channel is disclosed. A first coefficient estimation unit estimates a first set of coefficients using the first clock signal. A second clock recovery unit configured to recover a second clock signal associated with a second optical channel using the first clock signal as a reference clock signal. A second coefficient estimation unit estimates a second set of coefficients using the first set of coefficients.