Butterfly FIR Filter Phase Sum Control for BPSK Demultiplexing
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Solution Overview
Problem
The existing coherent optical receiving systems using Constant Modulus Algorithm (CMA) struggle to appropriately demultiplex polarization multiplexed BPSK signals, leading to incorrect convergence of tap coefficients and increased bit error rates, and existing solutions either require a training sequence or reduce resistance to frequency offset.
Innovation Solution
An optical receiver with a butterfly FIR filter and coefficient control mechanism that adapts tap coefficients to ensure the phase sum of output signals is 0 or π, allowing for proper demultiplexing of BPSK signals without a training sequence and maintaining resistance to frequency offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Constant Modulus Algorithm (CMA) is used for polarization demultiplexing, then the system can operate without a training sequence, but it fails to appropriately demultiplex BPSK signals leading to incorrect convergence of tap coefficients
Solution Approach 1:
The patent changes the control parameter from constant modulus (CMA) to constant phase sum (a new criterion). Instead of minimizing the deviation from constant modulus, the system now controls the tap coefficients to maintain a constant phase sum between the X and Y polarization components. This parameter change enables appropriate convergence for BPSK signals while maintaining operation without training sequences.
Solution Approach 2:
The patent introduces a feedback mechanism where the phase sum of the output signals from the butterfly FIR filter is continuously calculated and used to adjust the tap coefficients. The coefficient control unit monitors the phase sum and adaptively updates the tap coefficients to maintain the phase sum at a predetermined value (0 or π), creating a closed-loop control system that ensures accurate demultiplexing.
2Measurement precision
If existing solutions are used to fix BPSK demultiplexing, then demultiplexing accuracy may improve, but a training sequence is required or resistance to frequency offset is reduced
Solution Approach 1:
The system performs self-adjustment through the constant phase sum control mechanism. The coefficient control unit automatically adjusts the tap coefficients based on the phase sum feedback without requiring external training sequences or manual intervention. The system serves itself by using the phase relationship between polarization components as an intrinsic reference for adaptation.
Solution Approach 2:
The constant phase sum control mechanism serves multiple functions simultaneously: it enables accurate BPSK demultiplexing, maintains frequency offset resistance, and operates without training sequences. This single control approach universally addresses multiple requirements that previously required separate solutions or compromises.
3Measurement precision
If tap coefficients are adaptively controlled to maintain constant phase sum, then BPSK signal demultiplexing accuracy is improved, but the control mechanism complexity increases
Solution Approach 1:
The patent merges the phase calculation and tap coefficient control functions into an integrated coefficient control unit. The phase sum calculation, feedback processing, and tap coefficient adjustment are combined in a single control module that works in conjunction with the existing butterfly FIR filter structure. This merging reduces the need for separate complex control mechanisms while achieving accurate phase demultiplexing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate demultiplexing of polarization multiplexed BPSK signals, reducing bit error rates and avoiding the need for a training sequence, while maintaining robustness against frequency offset.
Implementation Method 1
a coherent optical detection means receiving an optical signal in which a plurality of BPSK modulated carrier waves are polarization-multiplexed, performing coherent detection by mixing the received optical signal with local light
Data Source
AI summary
In order to appropriately demultiplex the polarization multiplexed BPSK signal without using a training sequence and decreasing the resistance to a frequency offset, an optical receiver includes a coherent optical detection unit receiving an optical signal in which BPSK modulated carrier waves are polarization-multiplexed, performing coherent detection by mixing the received optical signal with local light, and outputting first electrical signals corresponding to the carrier waves; a butterfly FIR filter receiving the first electrical signals and extracting second electrical signals corresponding to each of the carrier waves from the first electrical signals; and a coefficient control unit for calculating a sum of respective phases of the second electrical signals output from the butterfly FIR filter, adaptively controlling tap coefficients of the butterfly FIR filter so that the calculated phase sum may become equal to 0 or π, and outputting tap coefficients after being controlled to the butterfly FIR filter.