Optical Receiver Noise Tolerance via Forward-Backward Error Processing
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Solution Overview
Problem
Optical receivers configured to receive differential signals, such as DPSK and DQPSK, face challenges in maintaining signal-to-noise ratio (SNR) performance due to optical noise, particularly in wavelength-division multiplexed (WDM) optical telecommunication systems, which affects the system's reach and reliability.
Innovation Solution
The proposed solution involves processing differential signals to consider both forward-looking and backward-looking errors on a symbol-by-symbol basis, generating error correction signals to mitigate noise, and adjusting gain elements for optimal performance, thereby enhancing noise tolerance and SNR. This includes calculating correlated errors over specific time periods to improve the receiver's noise handling capabilities, particularly in relation to chromatic dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If differential modulation schemes (DPSK, DQPSK) are used to simplify receiver implementation, then ease of manufacture is improved, but signal-to-noise ratio performance deteriorates
Solution Approach 1:
The patent applies preliminary action by estimating correlated noise from adjacent symbols before final demodulation. The receiver calculates noise estimates from forward and backward adjacent symbols, combines these estimates, and uses the combined estimate to correct the current symbol before determining the final demodulated value. This preliminary noise correction improves SNR performance while maintaining the simplicity of differential modulation schemes.
2Device complexity
If optical noise on delayed reference signal is present, then measurement precision deteriorates, but device complexity remains unchanged
Solution Approach 1:
The patent implements feedback by using information from adjacent symbols to correct the current symbol. The receiver calculates correlated noise estimates from forward and backward adjacent symbols, feeds this noise estimate back into the demodulation process, and uses it to correct the current symbol's phase errors. This feedback mechanism improves measurement precision without adding significant device complexity.
3Reliability
If error correction processing is added to mitigate optical noise, then signal-to-noise ratio performance is improved, but device complexity increases
Solution Approach 1:
The patent applies partial action by focusing error correction only on the specific problem of correlated noise from adjacent symbols, rather than implementing comprehensive error correction for all possible error sources. The receiver calculates noise estimates from adjacent symbols and applies correction in a targeted manner, improving SNR performance without the full complexity of general error correction codes.
4Reliability
If correlated error correction from adjacent symbols is implemented, then reliability is improved, but loss of time increases
Solution Approach 1:
The patent implements continuity of useful action by processing adjacent symbols continuously as they arrive, rather than buffering and processing them in batches. The receiver calculates correlated noise estimates from forward and backward adjacent symbols in real-time and applies corrections continuously to the current symbol, improving noise tolerance without significant time loss.
Data Source
AI summary
The present invention provides a system, apparatus and method to improve the signal-to-noise ratio performance in receivers configured to receive differential data signals. According to various embodiments of the invention, a received differential signal is processed to consider both forward-looking and backward-looking error components to improve SNR performance, and ultimately the reach of the optical line system. Additional processing is provided to further enhance noise tolerance related to chromatic dispersion.