Hadamard Encoding for Optical Channel Quality Uniformity
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Solution Overview
Problem
In optical transmission systems, especially for future 1 Tbps data transmission using the 1.3 μm band, wavelength dispersion causes significant waveform degradation, leading to variations in signal quality among channels, particularly due to the immature technology required for short-wave channels, resulting in lower reception power and poorer signal quality compared to long-wave channels.
Innovation Solution
An encoding device and decoding device are developed, utilizing Walsh encoding and adaptive digital filters to equalize signal quality across channels by performing an encoding process that adjusts intensity signals using a Hadamard matrix and wavelength multiplexing, and a decoding process that compensates for waveform degradation through adaptive filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wavelength multiplexing with multiple channels is used to increase transmission capacity, then data transmission rate is improved, but signal quality variation among channels increases due to wavelength dispersion
Solution Approach 1:
The patent applies Walsh-Hadamard transform encoding to change the signal parameters before transmission. By transforming the original signal into an encoded form with specific correlation properties, the system achieves more uniform signal quality across channels with different wavelength dispersions, resolving the contradiction between high transmission capacity and signal quality uniformity
Solution Approach 2:
The patent employs maximum likelihood sequence estimation (MLSE) at the receiver end, which uses feedback from the received signal to estimate and compensate for channel effects. This feedback mechanism allows the system to adapt to varying wavelength dispersion conditions and maintain consistent signal quality across all channels
2Productivity
If short-wave channels are used to increase the number of channels, then transmission capacity is improved, but reception power decreases leading to poorer signal quality
Solution Approach 1:
The Walsh-Hadamard transform encoding changes the signal structure to have better correlation properties. This parameter transformation ensures that even channels with lower reception power (short-wave channels) maintain adequate signal quality through the inherent noise resistance of the encoded signal structure
Solution Approach 2:
The patent applies channel-specific processing where each channel's signal is independently encoded and decoded with consideration for its specific characteristics (including reception power level). This local optimization ensures that short-wave channels with lower power receive appropriate signal processing to maintain quality
3Device complexity
If intensity modulation is used to reduce cost, then device complexity is reduced, but waveform degradation increases due to wavelength dispersion
Solution Approach 1:
The patent converts the harmful effect of wavelength dispersion into a manageable problem by using Walsh-Hadamard transform encoding. The encoding structure allows the system to tolerate and compensate for waveform degradation, effectively converting the harmful dispersion effect into a condition that can be handled through signal processing
Solution Approach 2:
The patent introduces an intermediary processing stage (Walsh-Hadamard transform encoding and MLSE decoding) between the simple intensity modulation and the final signal recovery. This intermediary layer protects the simple modulation scheme from waveform degradation by adding error resilience without increasing the complexity of the modulation itself
Data Source
AI summary
An encoding device includes an encoding unit, DA converters, light sources, intensity modulators, and wavelength multiplexers. The encoding unit adds (NM/2) to an encoded signal having a negative minimum value in a range of the encoded signal among encoded signals of N channels of (NM+1) values obtained by calculating an inner product of a Hadamard matrix of N rows and N columns and a matrix having elements of N intensity signals of (M+1) values. The DA converters of the channels convert the encoded signals of the channels from digital signals into electrical analog signals. The light sources output light of wavelengths for use in the channels. The light intensity modulators of the channels intensity-modulate the light output from the light sources with the encoded signals converted into the electrical analog signals by the DA converters. The wavelength multiplexer outputs a wavelength-multiplexed signal obtained by wavelength-multiplexing the light intensity-modulated by the light intensity modulators.