Digital Optical Link Compression Using Nonuniform Quantizers
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Solution Overview
Problem
Conventional optical communication networks face challenges in meeting the growing demand for high-speed data and video services due to limitations in spectral efficiency and bandwidth, particularly with the introduction of advanced modulation formats like 5G new-radio (NR) and high-resolution multimedia, which lead to increased sensitivity to nonlinear distortions and requirements for high-resolution converters.
Innovation Solution
The implementation of non-uniform quantization algorithms, such as the K-law and relaxed Lloyd algorithms, for analog-to-digital and digital-to-analog converters, which optimize quantization levels to reduce quantization noise and improve compression efficiency, enabling efficient transmission of high-order modulated signals over digital optical links.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional uniform quantization is used in analog-to-digital converters, then the implementation is simple, but the quantization noise is high and compression efficiency is poor
Solution Approach 1:
The patent applies non-uniform quantization where different quantization step sizes are used for different amplitude ranges of the signal. Small amplitude signals use smaller step sizes to reduce quantization noise, while large amplitude signals use larger step sizes. This local adaptation of quantization quality resolves the contradiction by optimizing precision where needed without uniformly increasing complexity across all signal levels.
Solution Approach 2:
The patent changes the quantization parameter (step size) based on the signal characteristics. By using variable step sizes instead of fixed uniform steps, the system adapts the quantization resolution to match the signal's probability distribution, thereby suppressing quantization noise while managing complexity through algorithmic optimization.
2Productivity
If high-order modulation formats are deployed to increase data capacity, then the spectral efficiency improves, but the sensitivity to nonlinear distortions increases and requires high-resolution converters
Solution Approach 1:
The patent replaces analog signal processing with digital signal processing. By digitizing the optical signals and using digital modulation formats, the system achieves high data capacity while being less sensitive to nonlinear distortions that affect analog systems. The digital domain allows for error correction and signal regeneration that mitigates the effects of nonlinearities in the optical fiber.
Solution Approach 2:
The patent employs advanced digital modulation formats with optimized constellation mappings and adaptive equalization parameters to maintain signal integrity at high data rates. By dynamically adjusting transmission parameters and using digital signal processing algorithms, the system achieves high capacity while compensating for nonlinear distortions through electronic rather than optical means.
3Productivity
If the number of quantization digits is reduced to improve compression efficiency, then the bandwidth utilization improves, but the quantization noise increases
Solution Approach 1:
The patent uses non-uniform quantization with variable step sizes that are smaller for low-amplitude signals and larger for high-amplitude signals. This allows the system to maintain low quantization noise for the most frequently occurring small signals while using fewer bits overall, thereby achieving good compression efficiency without excessive quantization noise in the critical low-level signal regions.
Solution Approach 2:
The patent implements dynamic quantization where the quantization parameters are adjusted based on the signal statistics and channel conditions. This dynamic adaptation allows the system to optimize the balance between compression efficiency and quantization noise suppression in real-time, rather than using fixed uniform quantization that cannot adapt to varying signal characteristics.
4Ease of manufacture
If legacy D/A or A/D converters with 8-10 digit resolution are used, then the cost is low, but the carrier-to-noise ratio requirement cannot be met for high-order modulations
Solution Approach 1:
The patent replaces the need for high-resolution analog converters with digital signal processing techniques. By performing quantization, modulation, and signal processing in the digital domain, the system achieves the required carrier-to-noise ratio performance without relying on expensive high-resolution analog-to-digital or digital-to-analog converters, thereby maintaining low cost while meeting performance requirements.
Data Source
AI summary
An optical network includes a transmitting portion configured to (i) encode an input digitized sequence of data samples into a quantized sequence of data samples having a first number of digits per sample, (ii) map the quantized sequence of data samples into a compressed sequence of data samples having a second number of digits per sample, the second number being lower than the first number, and (iii) modulate the compressed sequence of data samples and transmit the modulated sequence over a digital optical link. The optical network further includes a receiving portion configured to (i) receive and demodulate the modulated sequence from the digital optical link, (ii) map the demodulated sequence from the second number of digits per sample into a decompressed sequence having the first number of digits per sample, and (iii) decode the decompressed sequence.