Optical Variants for BER Reduction in Transport Systems
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Solution Overview
Problem
Optical communication systems face limitations in reducing bit-error rate (BER) due to the constraints of forward error correction (FEC) coding, particularly in noisy channels, where the coding-gain differences among FEC codes are limited, necessitating additional performance-enhancement techniques.
Innovation Solution
The implementation of optical variants, which are different in parameters such as time of transmission, spatial localization, polarization, and carrier wavelength, that are detected and processed coherently to average out noise and distortions in optical transport links, complementing or replacing FEC coding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If FEC coding is used to reduce bit-error rate in noisy optical channels, then the bit-error rate is reduced, but the required forward-channel bandwidth increases
Solution Approach 1:
The patent introduces spatial diversity by transmitting multiple optical variants of the same data through different spatial paths (different cores in a multi-core fiber). This adds a spatial dimension to the transmission, allowing the receiver to combine signals from multiple paths to achieve error reduction without increasing the bandwidth of individual channels.
Solution Approach 2:
The patent creates multiple copies of the same data encoded in different optical variants (different spatial, spectral, or temporal characteristics). These copies are transmitted through different channels and then combined at the receiver, allowing error reduction through diversity combining without requiring additional bandwidth beyond what is needed for the original signal.
2Reliability
If FEC coding with lower payload data rate is used for noisier channels, then the bit-error rate is reduced, but the data rate decreases
Solution Approach 1:
The patent merges multiple optical variants carrying the same data through different spatial, spectral, or temporal dimensions. By coherently combining these variants at the receiver, the system achieves error reduction through diversity gain while maintaining the original data rate, avoiding the need for lower-rate FEC codes.
Solution Approach 2:
The patent creates a composite transmission signal by combining multiple optical variants with different characteristics (spatial, spectral, temporal). This composite approach provides robustness against channel impairments while maintaining high data rates, as the combining process exploits the diversity of the different variants to suppress errors.
3Reliability
If multiple optical variants per bit-word are transmitted with different parameters, then the bit-error rate is reduced through coherent summation, but the device complexity increases
Solution Approach 1:
The patent employs a universal framework where optical variants can differ in multiple dimensions (spatial, spectral, temporal) but are processed through a unified coherent combining mechanism. This multi-functional approach allows the same system architecture to handle various types of diversity without requiring separate processing paths for each variant type.
Solution Approach 2:
The patent changes physical parameters of the optical signal (spatial mode, wavelength, time slot) to create diverse transmission paths. By systematically varying these parameters, the system generates multiple variants that can be combined to reduce errors, while the underlying processing remains relatively simple and unified.
Data Source
AI summary
An optical transport system configured to transmit a set of two or more optical variants per bit-word, with the optical variants in the set being different from one another in one or more of the time of transmission, spatial localization, polarization of light, carrier wavelength, and subcarrier frequency. Differences between the optical variants may also be due to different respective constellation mapping. The optical variants of each set are detected and processed at the receiver in a manner that enables coherent summation of the corresponding electrical signals prior to constellation de-mapping. The coherent summation tends to average out the deleterious effects of linear and nonlinear noise/distortions imparted on the individual optical variants in the optical transport link because said noise/distortions are incoherent in nature. A BER reduction enabled by the use of optical variants may be implemented in addition to or instead of that provided by FEC coding.