Optical Signal Coding for Narrower-Spectrum PAM4 Transmission
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Solution Overview
Problem
The challenge in achieving ultrahigh speed optical transmission at 100 Gb/s is exacerbated by signal quality deterioration due to band limitations and wavelength dispersion, particularly with the PAM4 method, as it results in a wider frequency spectrum and significant quality degradation, which conventional methods like probabilistic shaping cannot effectively mitigate.
Innovation Solution
An optical transmission system employing non-linear block coding that converts M-value symbol sequences into L-value symbol sequences with narrower signal spectra, using discrete Fourier transformation to calculate cost values and assign symbol sequences with minimal signal fluctuation, thereby reducing signal spectrum bandwidth and compensating for waveform deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PAM4 modulation method is used to achieve ultrahigh speed optical transmission at 100 Gb/s, then transmission speed is improved, but signal quality deteriorates due to wider frequency spectrum occupying and band limitation
Solution Approach 1:
The patent applies parameter changes by transforming the symbol sequence from time domain to frequency domain using Fourier transformation, and changes the probability distribution parameters of symbols to reshape the signal spectrum. This reduces the occupied bandwidth and mitigates band limitation effects, allowing high-speed transmission while maintaining signal quality.
Solution Approach 2:
The patent performs preliminary signal processing by pre-shaping the symbol sequence before transmission. The coding unit processes the symbol sequence in advance to control the signal spectrum characteristics, preventing waveform deterioration before it occurs during transmission through the optical fiber.
2Speed
If PAM4 modulation method is used to achieve ultrahigh speed optical transmission at 100 Gb/s, then transmission speed is improved, but signal quality deteriorates due to wavelength dispersion in transmission fibers
Solution Approach 1:
The patent changes the spectral parameters of the signal by applying Fourier transformation and probability shaping. This parameter transformation reduces the signal bandwidth and makes it less susceptible to wavelength dispersion effects, enabling high-speed transmission over longer distances without significant quality degradation.
3Reliability
If probabilistic shaping is applied to improve reception sensitivity, then reception sensitivity is improved in Gaussian noise environment, but it cannot suppress signal quality deterioration in environments with band limitation and wavelength dispersion
Solution Approach 1:
The patent segments the signal processing into distinct functional units: a coding unit that performs probability shaping and spectral control, and a decoding unit that reverses the processing. This segmentation allows the system to address multiple transmission impairments (band limitation and wavelength dispersion) simultaneously while maintaining reception sensitivity.
Solution Approach 2:
The patent creates a universal solution that handles multiple transmission impairments through a single integrated approach. The coding unit simultaneously controls signal spectrum for band limitation mitigation and reduces dispersion effects, making the system adaptable to various transmission conditions while improving reception sensitivity.
Data Source
AI summary
An optical transmission system including an optical transmitter and an optical receiver, wherein the optical transmitter includes a signal coding unit that performs non-linear block coding on an M (M is an integer greater than or equal to 1)-value symbol sequence or a bit sequence input as data information to generate an L (L is an integer greater than or equal to 2, L>M)-value symbol sequence that corresponds to the M-value symbol sequence or the bit sequence in one-to-one correspondence, a digital-to-analog conversion unit that converts the generated L-value symbol sequence to an analog signal, and a modulator that generates an optical modulation signal by performing modulation based on the analog signal, and the optical receiver includes a light receiving unit that receives the optical modulation signal transmitted from the optical transmitter and converts the optical modulation signal to an electrical signal, and a signal decoding unit that restores the M-value symbol sequence or the bit sequence by performing processing that is the reverse of processing performed by the signal coding unit, on the electrical signal.