Delta-Sigma RF Digitization for Nonlinear-Noise-Limited HFC Links
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Solution Overview
Problem
Conventional hybrid fiber-coaxial (HFC) networks face limitations in achieving high data rates due to link loss and nonlinear noise, especially with high-order modulation formats, which are not adequately addressed by existing analog optics technology, making it difficult to support increasing data demands without expensive infrastructure replacements.
Innovation Solution
The implementation of a digital optical network using delta-sigma modulation and demodulation techniques, which convert analog signals into digitized bit streams for transmission over digital optical links, effectively separating noise from the signal and allowing for higher modulation orders and longer distances, while reducing latency and data requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional analog optics technology is used in HFC networks, then the existing infrastructure can be maintained, but the data rates are limited due to link loss and nonlinear noise
Solution Approach 1:
The patent changes the fundamental parameter of signal representation from analog to digital domain. By converting analog RF signals to digital bit streams using delta-sigma modulation, the system transforms how signals are processed and transmitted, thereby changing the relationship between signal quality and noise tolerance. This parameter change enables higher data rates while maintaining robustness against nonlinear noise in the analog portion of the HFC network.
2Productivity
If high-order modulation formats are used to increase data rates, then bandwidth efficiency improves, but tolerance to nonlinear noise deteriorates
Solution Approach 1:
The patent introduces a digital intermediary layer between the analog signal source and the transmission medium. The analog RF signal is converted to a digital bit stream that acts as an intermediary representation, which can then be transmitted over the analog HFC infrastructure with improved noise tolerance. This intermediary digital representation allows high-order modulation equivalent performance while maintaining robustness against nonlinear noise through the inherent error correction capabilities of digital signaling.
3Length of stationary object
If analog signals are transmitted over long distances in HFC networks, then coverage area increases, but signal quality deteriorates due to link loss
Solution Approach 1:
The patent replaces the mechanical/analog signal transmission system with a digital optical transmission system for the fiber portion of the HFC network. By substituting analog RF over fiber with digital optical signals, the system eliminates the accumulation of nonlinear noise and link loss issues that plague long-distance analog transmission. The digital signals can be regenerated at optical nodes, effectively resetting the signal quality and enabling extended coverage areas.
4Object-affected harmful factors
If fiber deep architecture is implemented to reduce coaxial cable distances, then nonlinear noise is reduced, but device complexity increases
Solution Approach 1:
The patent extracts the digital-to-analog conversion function from the optical domain and places it at the fiber node where it can serve multiple coaxial segments. By taking out the A/D and D/A conversion operations and positioning them strategically in the network architecture, the system achieves fiber deep benefits with reduced nonlinear noise while managing device complexity through functional consolidation at the node level rather than distributing complexity throughout the network.
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
This approach enhances the tolerance to nonlinear noise, supports higher modulation formats, and extends transmission distances, enabling more efficient use of existing fiber infrastructure without significant hardware modifications, thus addressing the limitations of conventional HFC networks.
Implementation Method 1
filter, in the frequency domain, a received time domain analog signal into a low-frequency end of a corresponding frequency spectrum
Implementation Method 2
shape the spread quantization noise out of the low-frequency end of the corresponding frequency spectrum such that the filtered analog signal and the shaped quantization noise are substantially separated in the frequency domain
Implementation Method 3
An optical fiber carries optical analog signals and connects the link between master headend, hub, and fiber node
Implementation Method 4
fiber node converts the optical analog signals from optical fiber into the RF modulated electrical signals
Data Source
AI summary
An analog signal processor includes a sampling unit configured to (i) filter, in the frequency domain, a received time domain analog signal into a low-frequency end of a corresponding frequency spectrum, (ii) sample the filtered analog signal at a frequency substantially higher than the low-frequency end, and (iii) spread quantization noise over an expanded Nyquist zone of the corresponding frequency spectrum. The processor further includes a noise shaping unit configured to shape the spread quantization noise out of the low-frequency end of the corresponding frequency spectrum such that the filtered analog signal and the shaped quantization noise are substantially separated in the frequency domain, and a quantization unit configured to apply delta-sigma modulation to the filtered analog signal using at least one quantization bit, and output a digitized bit stream that substantially follows the amplitude of the received time domain analog signal.