Nonlinear Trellis Coding for Optical Transmission Bandwidth
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Solution Overview
Problem
The PAM4 method for ultra-high-speed optical transmission is affected by waveform deterioration due to bandwidth limitations of electro-optical devices, and signal quality deterioration caused by wavelength dispersion, particularly at modulation rates of 50 Gbaud or higher, which is not effectively compensated by digital signal processing.
Innovation Solution
An optical transmission system employing nonlinear trellis coding that converts m-valued transmission symbols into M-valued coded symbols, restricting transitions between coded symbols in time series, allowing for improved bandwidth limitation tolerance without increasing costs through the use of digital signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PAM4 modulation is used for ultra-high-speed optical transmission, then the transmission rate can reach 100 Gb/s or higher with simpler configuration, but the signal is much more affected by waveform deterioration due to bandwidth limitations of electro-optical devices
Solution Approach 1:
The patent changes the parameter of signal spectrum width by applying nonlinear trellis coding. The coding scheme transforms the signal representation to occupy a narrower frequency spectrum, thereby reducing the impact of bandwidth limitations on signal quality while maintaining the high transmission rate capability of PAM4 modulation
Solution Approach 2:
The patent applies coding at the transmitter side before transmission to pre-compensate for the expected waveform deterioration. By encoding the signal with nonlinear trellis coding in advance, the system prepares the signal to be more robust against bandwidth limitations and wavelength dispersion effects that will occur during transmission
2Productivity
If the modulation rate is increased to 50 Gbaud or higher for higher transmission capacity, then the transmission rate increases, but signal quality deterioration due to wavelength dispersion becomes more marked and cannot be compensated by digital signal processing
Solution Approach 1:
The patent changes the signal's spectral characteristics by applying nonlinear trellis coding, which narrows the signal spectrum. This parameter change makes the signal less susceptible to wavelength dispersion effects that worsen with higher modulation rates, thereby maintaining signal quality at 50 Gbaud and above
Solution Approach 2:
The patent converts the harmful effect of high modulation rates (which increase susceptibility to dispersion) into a benefit by using nonlinear trellis coding to create a narrower spectrum signal. The higher modulation rate is transformed into an opportunity to achieve higher transmission capacity while the coding scheme mitigates the associated dispersion penalties
3Reliability
If nonlinear trellis coding is applied to narrow the signal spectrum and improve bandwidth limitation tolerance, then signal quality improves, but the decoding process becomes more complex and computationally intensive
Solution Approach 1:
The patent applies the coding operation at the transmitter side in advance, which structures the transmitted signal with known properties. This preliminary encoding action enables the receiver to use simpler decoding operations, as the code structure is already embedded in the transmitted signal, reducing the computational burden compared to uncoded systems requiring complex equalization
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
The system narrows the signal spectrum while maintaining cost-effectiveness by reducing noise amplification during digital signal processing, thereby improving bandwidth limitation tolerance and reducing signal quality deterioration.
Implementation Method 1
a transmission unit that generates the signal light by performing optical modulation on the basis of the symbol for transmission
Implementation Method 2
The direct detection method, which demodulates data signals based on strength information of optical signals
Implementation Method 3
digital coherent technology which is a combination of coherent detection and digital signal processing techniques
Data Source
AI summary
An optical transmitter generates symbols for transmission by applying a predetermined coding method to each of m-valued transmission symbols generated from transmission data, generates signal light by performing optical modulation on the basis of the symbols for transmission, and transmits the signal light. An optical receiver generates a series of digital signals from the received signal light, detects coded symbols by applying predetermined digital signal processing to the series of digital signals, decodes the m-valued transmission symbols from the detected coded symbols, and restores the transmission data from the decoded m-valued transmission symbols. An operation based on the predetermined coding method performs nonlinear coding that generates the coded symbols by generating m-valued intermediate symbols from the m-valued transmission symbols, the nonlinear coding restricting transitions between series of the coded symbols in time series by assigning bit information to a state transition between coded symbols adjacent in time series and making a number of states that each of the coded symbols can take on greater than a number of states of the m-valued transmission symbols.