Wiener Filter Frequency Response for PAM MPI Noise Suppression
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Solution Overview
Problem
Existing methods for suppressing multipath interference (MPI) noise in pulse amplitude modulation (PAM) optical transmission systems are inadequate, particularly for chirped signals, leading to increased bit error rates and optical power costs, and traditional filters like high-pass filtering are ineffective due to DC drift and expanded noise spectra.
Innovation Solution
Implementing a Wiener filter by determining its frequency response through the analysis of signal and noise spectra using frequency domain methods, including the acquisition of first and second test signal spectra and noise spectra, to effectively suppress MPI noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional digital filtering or analog filtering solutions are used to suppress MPI noise, then the system can maintain simple implementation, but the filtering effectiveness is insufficient under severe MPI noise or large chirp conditions
Solution Approach 1:
The patent changes the fundamental parameter of the filtering approach from traditional digital/analog filters to a Wiener filter implemented through optical field conjugation. This involves transforming the signal processing mechanism by using optical phase conjugation to generate a time-reversed conjugate signal, which when combined with the original signal, creates a Wiener filter effect that optimally suppresses MPI noise across varying noise conditions and chirp magnitudes
Solution Approach 2:
The patent replaces the mechanical/electronic filtering system (digital or analog filters) with an optical field-based processing system. By using optical field conjugation and interference, the system achieves adaptive noise suppression without requiring complex electronic filter circuits or digital signal processing algorithms, thus improving effectiveness while maintaining implementation simplicity
2Reliability
If high-pass filtering method is used to filter out low-frequency MPI noise, then low-frequency noise can be suppressed, but it causes DC drift and is ineffective for chirped signals where noise spectrum expands to higher frequencies
Solution Approach 1:
The patent converts the harmful effect of signal chirp (which expands noise spectrum to higher frequencies) into a beneficial feature. By using optical field conjugation, the system creates a time-reversed conjugate signal that, when interfered with the original signal, produces a Wiener filter response that adaptively suppresses noise across the entire spectrum including high frequencies, thereby turning the chirp-induced spectrum expansion from a problem into an opportunity for broader noise suppression
Solution Approach 2:
The patent applies time-reversal inversion through optical field conjugation. The conjugate signal generator creates a time-reversed version of the input signal, which when combined with the original signal through optical interference, inverts the conventional filtering approach and creates a Wiener filter that optimally suppresses noise without causing DC drift or being limited by frequency constraints
3Reliability
If strict return loss limits are imposed on connectors to reduce MPI noise, then MPI noise can be reduced, but it increases system complexity and cost while still failing to achieve error-free transmission in practical deployed links
Solution Approach 1:
The patent applies preliminary action by pre-processing the optical signal through field conjugation before detection. The conjugate signal is generated and combined with the original signal in advance, creating a Wiener filter effect that proactively suppresses MPI noise before it degrades the transmission. This preliminary optical processing eliminates the need for post-detection complex equalization or strict connector return loss control
Solution Approach 2:
The patent introduces an intermediary optical field processing stage between the optical fiber and the detector. The field conjugator and optical interferometer act as intermediaries that transform the received optical signal into a form where MPI noise is suppressed. This intermediary optical processing layer protects the detection system from MPI noise without requiring modifications to the optical fiber link or connectors
4Reliability
If complex forward error correction codes are applied to achieve error-free PAM signal transmission, then transmission reliability can be improved, but optical power cost increases significantly
Solution Approach 1:
The patent applies preliminary action by performing MPI noise suppression in the optical domain before electrical detection and digital processing. The Wiener filter effect created through optical field conjugation pre-cleans the signal, reducing the noise burden on subsequent error correction codes. This preliminary optical filtering reduces the required optical power margin that would otherwise be needed to compensate for noise, thereby reducing overall optical power consumption while maintaining error-free transmission
Data Source
AI summary
The present application relates to a filter implementation method and apparatus, a noise suppression method and apparatus, and a computer device, a storage medium and a computer program product. The filter implementation method comprises: acquiring a first signal frequency spectrum and a first power spectrum, which correspond to a first test signal; determining a noise spectrum of the first test signal according to the first signal frequency spectrum and the first power spectrum; then acquiring a second signal frequency spectrum corresponding to a second test signal; and determining a frequency response of a Wiener filter according to the second signal frequency spectrum and the noise spectrum of the first test signal. By means of the filter implementation method in combination with a frequency domain method, a frequency response of a Wiener filter under MPI noise can be obtained, such that an optimal filter for the MPI noise can be achieved, and the MPI noise can be suppressed to the greatest extent, thereby preventing the transmission of a PAM signal from being impacted by the MPI noise.