Coherent Receiver Signal Processing for BER Reduction
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Solution Overview
Problem
The existing methods for coherent optical communication systems, particularly those using Quadrature Phase Shift Keying (QPSK), suffer from performance loss due to differential encoding when combined with Forward Error Correction (FEC), especially in terms of bit error rate (BER), and require complex iterative decoding or expensive stable lasers to mitigate cycle slips.
Innovation Solution
A signal processing method that involves clipping and quantizing orthogonal signal components independently, optimized for a forward error correction algorithm, followed by soft differential decoding and application of FEC, which reduces noise and minimizes differential decoding penalties without requiring iterative decoding or complex computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential encoding is used to combat cycle slips, then system reliability improves, but bit error rate performance deteriorates due to differential decoding penalties
Solution Approach 1:
The patent segments the signal processing into independent in-phase and quadrature components, applying clipping and quantization separately to each component. This segmentation allows optimized processing that maintains differential encoding benefits while minimizing decoding penalties through component-independent optimization
Solution Approach 2:
The patent applies clipping levels and quantization bits as adjustable parameters to optimize the balance between cycle slip resistance and bit error rate performance. By tuning these parameters, the system achieves improved reliability while controlling the differential decoding penalty
2Measurement precision
If optimal soft differential decoding with FEC is applied, then bit error rate performance improves, but device complexity increases due to complex computations
Solution Approach 1:
The patent divides the complex decoding task into separate processing of in-phase and quadrature components, where each component undergoes independent clipping and quantization. This segmentation simplifies the overall computational complexity while maintaining performance through component-wise optimization
Solution Approach 2:
The patent uses simple clipping and quantization operations that are computationally inexpensive compared to full soft differential decoding. These simplified operations provide adequate performance with significantly reduced computational complexity and implementation cost
3Device complexity
If clipping and quantization are applied to orthogonal signal components, then noise is reduced and implementation becomes simpler, but signal precision may be lost
Solution Approach 1:
The patent uses clipping levels and quantization bit depths as tunable parameters to control the trade-off between noise reduction and signal precision. By optimizing these parameters, the system achieves simplified implementation while preserving sufficient signal precision for reliable communication
Solution Approach 2:
The patent applies different clipping levels and quantization parameters to the in-phase and quadrature components based on their specific characteristics. This local optimization ensures that each component is processed with appropriate precision, minimizing overall signal precision loss while maintaining implementation simplicity
Data Source
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AI summary
A signal processing method and a signal processing arrangement for coherent receivers are provided, the method comprising the steps of receiving a coherent complex signal, extracting orthogonal in-phase and quadrature signal components from the coherent complex signal, quantizing the orthogonal signal components independently, combining the quantized orthogonal signal components as real and imaginary part of a complex number obtaining a first signal, and soft differential decoding the first signal obtaining a second signal.