Parallel Channel Skew for Stronger FEC Burst Error Correction
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Solution Overview
Problem
As data rates increase beyond 50 Gbps with PAM4 or larger signal constellations, existing Ethernet standards face challenges in providing affordable, mass-manufactured network hardware with consistently robust performance due to increased channel attenuation and dispersion, making it difficult to maintain reliable data transmission over extended cable lengths.
Innovation Solution
The introduction of skew into parallel transmission channels through a block code encoder, demultiplexer, skewer, and drivers in transceivers enhances the performance of forward error correction (FEC) decoders by buffering lanes with differing delays, ensuring robust data transfer across multiple lanes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data transmission rate is increased beyond 50 Gbps with PAM4 or larger signal constellations, then productivity is improved, but channel attenuation and dispersion increase causing performance degradation
Solution Approach 1:
The transmitted data stream is divided into multiple parallel channels (e.g., 4 lanes for 200 Gbps transmission). Each lane carries a portion of the data at a lower individual rate, which reduces the impact of attenuation and dispersion on any single channel while maintaining high aggregate throughput.
Solution Approach 2:
The system transitions from single-lane high-rate transmission to multi-lane lower-rate transmission. By changing the transmission parameters (number of lanes, symbols per lane), the system achieves high productivity while maintaining reliability through reduced per-channel attenuation and dispersion effects.
2Productivity
If equalizers operate at faster symbol rates to support higher data rates, then productivity is improved, but manufacturing cost and complexity increase
Solution Approach 1:
Instead of using a single complex equalizer operating at high symbol rates, the system segments the equalization function across multiple parallel channels operating at lower symbol rates. This reduces the complexity of each individual equalizer while maintaining overall system performance.
3Reliability
If skew is introduced into parallel transmission channels, then error correction capability is improved, but device complexity increases due to buffering requirements
Solution Approach 1:
The system deliberately introduces skew (delay) in certain parallel channels before transmission. This preliminary action redistributes burst errors across multiple code blocks, enabling the FEC decoder to correct errors more effectively. The buffering required for skew introduction is managed as part of the overall transmission protocol.
Data Source
AI summary
Digital communication transmitters, systems, and methods can introduce skew into parallel transmission channels to enhance the performance of forward error correction (FEC) decoders. One illustrative serializer-deserializer (SerDes) transmitter embodiment includes: a block code encoder configured to convert a sequence of input data blocks into a sequence of encoded data blocks; a demultiplexer configured to distribute code symbols from the sequence of encoded data blocks to multiple lanes in a cyclical fashion, the multiple lanes corresponding to parallel transmission channels; a skewer configured to buffer the multiple lanes to provide respective lane delays, the lane delays differing from each other by no less than half an encoded data block period; and multiple drivers, each driver configured to transmit code symbols from one of said multiple lanes on a respective one of said parallel transmission channels.