OSNR Measurement via BER Curves in Coherent Optical Links
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Solution Overview
Problem
Current optical communication networks face challenges in accurately measuring the optical signal-to-noise ratio (OSNR) in coherent optical systems, especially with the presence of ROADMs, which leads to underestimation of noise levels and misinterpretation of OSNR values, making it difficult to determine the performance of optical communications links.
Innovation Solution
A method involving the determination of OSNR-BER relationships using a plurality of transponder modulation formats, where the bit error rate is measured across different modulation formats, and an averaged OSNR value is derived to select optimal modulation formats and transmission parameters for improved link performance, employing a measurement apparatus that generates pre-FEC BER vs OSNR curves to accurately assess the OSNR in coherent optical systems without ROADMs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OSNR measurement methods are used in coherent optical systems with ROADMs, then measurement simplicity is maintained, but OSNR measurement precision deteriorates due to underestimation of noise levels
Solution Approach 1:
The patent introduces an intermediary measurement approach by using BER measurements as a mediator to indirectly determine OSNR values. Instead of directly measuring OSNR which is problematic in ROADM networks, the system measures BER performance and uses pre-determined OSNR-BER relationships to derive accurate OSNR values, thus resolving the measurement precision issue without requiring complex direct OSNR measurement equipment
Solution Approach 2:
The patent replaces the conventional direct OSNR measurement mechanism with an alternative measurement mechanism based on BER performance testing. By substituting the direct physical OSNR measurement with BER-based indirect measurement and lookup table methodology, the system achieves accurate OSNR determination in ROADM networks where conventional measurement methods fail
2Measurement precision
If a single modulation format is used for OSNR determination, then measurement simplicity is maintained, but determination accuracy deteriorates due to transponder variations
Solution Approach 1:
The patent applies preliminary action by pre-determining OSNR-BER relationships for multiple modulation formats before actual deployment. The system pre-generates lookup tables containing OSNR-BER characteristics for various modulation formats (QPSK, 16-QAM, 64-QAM, etc.), so that during operation, accurate OSNR determination can be quickly achieved by selecting the appropriate pre-characterized modulation format without time-consuming real-time analysis
Solution Approach 2:
The patent utilizes parameter changes by varying the modulation format parameter to determine OSNR. By testing different modulation formats (changing the modulation parameter) and observing BER performance, the system can accurately determine OSNR values that account for transponder variations. The methodology changes the modulation parameter systematically to extract precise OSNR information
3Productivity
If fixed grid DWDM is used, then network compatibility is maintained, but spectral efficiency deteriorates for high data rate transmissions
Solution Approach 1:
The patent applies dynamics by enabling dynamic adjustment of wavelength allocation and modulation format selection based on actual link conditions and data rate requirements. The system dynamically adapts the optical signal parameters (wavelength, modulation format, baud rate) to optimize spectral efficiency for each specific transmission scenario, moving away from static fixed grid assignments while maintaining compatibility through standardized interfaces
4Reliability
If dispersion compensating modules are installed to mitigate chromatic dispersion, then signal transmission quality is improved, but network cost and complexity increase
Solution Approach 1:
The patent replaces the mechanical/optical dispersion compensation approach (using physical DCM modules) with an electronic/digital compensation methodology. By using DSP-based digital signal processing in the receiver, the system electronically compensates for chromatic dispersion effects, thereby maintaining signal transmission quality while eliminating the need for additional physical dispersion compensating modules in the optical path
Data Source
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AI summary
The present invention provides a method of indirectly determining the optical signal-noise ratio of an optical fibre communications link. In a test environment, the relationship between OSNR and pre-FEC BER (forward error-corrected bit error rate) is determined for a particular type of optical transponder. When a transponder of that type is connected to an optical communications link then the pre-FEC BER can be measured and the OSNR inferred from the pre-determined OSNR-BER relationship. The OSNR value can then be used to select a transponder modulation format or other transmission parameters.