2-Tap Precoder Equalizer for ISI Mitigation in Optical Links
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Solution Overview
Problem
High-speed data transmission in short-distance optical links faces Inter-symbol Interference (ISI) due to bandwidth limitations, leading to signal distortion and error propagation issues, which are challenging to address with existing equalizers like Decision Feedback Equalizers and Tomlinson-Harashima Precoding, especially in hardware implementation.
Innovation Solution
A method utilizing a 2-tap Tomlinson-Harashima Precoder at the transmitter and a decision feedback equalizer with adaptive auxiliary coefficients at the receiver, which generates pre-equalization and equalization signals to mitigate ISI, allowing for high-speed processing by simplifying hardware configuration and optimizing filter coefficients based on approximate channel response characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a Decision Feedback Equalizer (DFE) is used to reduce ISI, then signal distortion is compensated, but error propagation occurs causing BER degradation
Solution Approach 1:
The equalization function is divided into two independent parts: a transmitter precoder that processes only past symbols (no feedback) and a receiver equalizer that processes current and future symbols. This segmentation eliminates the error propagation problem inherent in feedback-based DFE while maintaining ISI compensation capability.
Solution Approach 2:
The transmitter precoder performs preliminary equalization by applying the inverse channel response to past symbols before transmission. This pre-compensation removes ISI caused by past symbols, allowing the receiver to focus only on removing residual ISI from current and future symbols without feedback loops.
2Manufacturing precision
If multi-tap filter coefficients are used in THP or DFE, then ISI is removed effectively, but hardware implementation becomes complex and high-speed processing becomes difficult
Solution Approach 1:
Instead of using multiple tap coefficients (excessive action), the invention uses a single tap coefficient in the precoder and a single tap coefficient in the equalizer. This partial action approach provides sufficient ISI compensation for the given bandwidth constraint while dramatically simplifying hardware implementation and enabling high-speed processing.
3Manufacturing precision
If adaptive filter coefficients are updated frequently in THP, then channel response is optimized, but information transmission overhead increases
Solution Approach 1:
The system uses fixed filter coefficients that are pre-optimized for the given bandwidth constraint. The precoder and equalizer operate independently without requiring frequent updates of filter coefficient information between transmitter and receiver, eliminating the information overhead associated with adaptive coefficient updates while maintaining effective channel response optimization.
Data Source
AI summary
A method of equalization for high-speed processing and an equalizer thereof are proposed. The method of equalization includes determining a filter coefficient applied to a transmitter equalizer provided with a 2-tap precoder according to an approximate channel response characteristic, generating a pre-equalization signal by removing precursor ISI of a transmission feedback signal by the precoder to which the filter coefficient is applied, so as to output the pre-equalization signal as a transmitting signal, and receiving a transmission signal and generating an equalization signal by removing postcursor ISI of the received transmission signal by a receiver equalizer provided with a feedback filter having auxiliary coefficients for compensating for a difference between an overall channel response of the transmission signal and a channel response based on the precoder.