Joint FEC and Space-Time Coding for Multi-Mode Fiber MDL Mitigation
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Solution Overview
Problem
Existing coding solutions for optical fiber transmission systems using multi-mode fibers are inadequate in completely mitigating mode-dependent loss (MDL) effects, which impair the capacity and performance of these systems.
Innovation Solution
The implementation of a joint Forward Error Correction (FEC) coding and Space-Time coding solution, specifically adapted to the number of selected propagation modes, to optimize transmission power usage and reduce complexity, thereby effectively mitigating MDL effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mode scrambling or strong mode coupling is used to reduce MDL effects, then the impact of mode-dependent loss is reduced, but the implementation complexity increases due to the high number of scramblers required
Solution Approach 1:
The patent combines Forward Error Correction (FEC) coding with Space-Time (ST) coding into a joint coding scheme. The FEC encoder processes data symbols to generate coded symbols, which are then encoded by the ST encoder to produce transmission symbols. This merging of two coding functions into a unified system achieves MDL mitigation while avoiding the complexity of multiple optical scramblers.
Solution Approach 2:
The patent replaces optical-domain mode scrambling mechanisms with digital-domain joint FEC-ST coding. Instead of using physical optical scramblers that require precise alignment and multiple components, the solution uses digital signal processing algorithms that operate on the data symbols, achieving equivalent or superior MDL mitigation with reduced implementation complexity.
2Productivity
If multiple propagation modes are used to multiplex and transmit larger amount of data symbols, then the transmission capacity increases, but the performance deteriorates due to non-unitary impairments and crosstalk effects between modes
Solution Approach 1:
The patent changes the coding parameters by using joint FEC-ST coding with specific code rates and coding schemes adapted to the number of selected propagation modes. The system determines optimal coding parameters based on the MDL value and the number of modes, allowing it to achieve both high transmission capacity and reliable performance by tuning the coding parameters to match the channel conditions.
3Device complexity
If existing Space-Time codes are used for MDL mitigation, then the implementation cost is reduced, but the MDL effects are not completely mitigated
Solution Approach 1:
The patent creates a composite coding scheme by combining FEC coding and ST coding into a unified joint coding system. This composite approach leverages the error correction capabilities of FEC and the spatial-temporal diversity of ST coding, achieving complete MDL mitigation while maintaining implementation efficiency. The joint coding structure allows the system to benefit from both coding paradigms simultaneously.
Data Source
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AI summary
Embodiments of the invention provide an optical transmitter configured to transmit a data sequence over at least two spatial propagation modes through an optical transmission channel in a multi-mode optical fiber transmission system, the transmission system being associated with a predefined value of a mode-dependent loss, wherein the optical transmitter comprises: - a forward error correcting code encoder (22) configured to encode said data sequence into a codeword vector by applying at least one error correcting code; - a modulator (23) configured to determine a set of modulated symbols by applying a modulation scheme to said codeword vector; and - a Space-Time encoder (24) configured to determine a codeword matrix by applying a Space-Time code to said set of modulated symbols.