PAM4 Error Correction with LLR-Guided Erasure Decoding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current error correction methods in PCIe systems are limited in correcting burst errors and require high retransmission rates due to the inability to effectively handle errors occurring in multiple symbols within an ECC group.
Innovation Solution
An electronic device with an ECC decoder, CRC decoder, and erasure decoding unit that performs LLR calculations to identify error symbol candidates and re-performs ECC decoding after erasing these candidates, reducing retransmission requests by selectively correcting errors in PCIe systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ECC decoding is used on PAM-4 symbols, then the circuit complexity is reduced, but the error correction capability is insufficient for burst errors affecting multiple symbols
Solution Approach 1:
The patent performs preliminary actions by calculating LLR values for all PAM-4 symbols before ECC decoding, identifying error-prone symbols in advance. This allows the system to prepare erasure information beforehand, enabling more effective error correction when burst errors occur across multiple symbols without requiring overly complex circuitry.
Solution Approach 2:
The patent introduces an intermediary mechanism by using LLR (Log-Likelihood Ratio) calculations as a mediator between signal reception and ECC decoding. The LLR values serve as intermediate information that helps identify which symbols are likely to contain errors, allowing the ECC decoder to focus correction efforts on specific symbols rather than treating all symbols equally, thus improving burst error correction without proportionally increasing complexity.
2Reliability
If retransmission is used to handle uncorrectable errors, then error correction reliability is maintained, but system productivity decreases due to bandwidth degradation
Solution Approach 1:
The patent extracts error-prone symbols from the data stream by calculating LLR values and identifying symbols with high error probability. By separating and flagging these problematic symbols for erasure decoding, the system can correct errors within the current transmission rather than requiring retransmission, thus maintaining reliability while preserving system throughput and reducing bandwidth degradation.
3Device complexity
If PAM-4 modulation is used instead of NRZ, then circuit complexity is reduced, but error correction becomes more challenging due to lower BER margin
Solution Approach 1:
The patent performs preliminary LLR calculations on all PAM-4 symbols before ECC decoding to identify which symbols are most likely to contain errors. This preliminary assessment allows the system to prepare erasure information in advance, making the subsequent error correction process more efficient and reliable, thereby offsetting the inherently lower BER margin of PAM-4 modulation without requiring complex transmission circuits.
Data Source
AI summary
Disclosed is an electronic device, which includes an ECC decoder that performs ECC decoding on a flit including a plurality of PAM-4 symbols for each of a plurality of ECC groups, a CRC decoder that performs CRC decoding on the ECC decoded flit to obtain data, and an erasure decoding unit that calculates an LLR for each of the PAM-4 symbols when the CRC decoding fails, extracts an error symbol candidate from among the plurality of PAM-4 symbols for each of the plurality of ECC groups based on the LLR, and performs the ECC decoding again after erasing the error symbol candidate.