Digital Predistortion Circuit for Frequency-Selective Coaxial Channels
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional systems face challenges in effectively compensating for nonlinear distortion and frequency selectivity in hybrid fiber-coaxial networks, leading to suboptimal signal transmission quality due to the non-flat channel response of coaxial cables and nonlinearities introduced by power amplifiers.
Innovation Solution
A transmitter system is designed with digital predistortion circuitry and tilt filters to adjust signal spectra, combined with a wideband equalizer to compensate for nonlinear and linear distortions, ensuring a flat frequency response across the frequency-selective channel, thereby improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transmission systems are used without predistortion, then device complexity is low, but signal transmission quality deteriorates due to nonlinear distortion and frequency selectivity
Solution Approach 1:
The patent applies predistortion filtering before signal transmission to pre-compensate for nonlinear distortion and frequency selectivity effects. The transmit filter modifies the signal spectrum in advance to counteract expected channel impairments, ensuring improved signal quality at the receiver without requiring complex adaptive equalization
Solution Approach 2:
The patent changes the spectral parameters of the transmitted signal by applying frequency-dependent gain adjustments through the predistortion filter. This modifies the signal's frequency distribution to compensate for the frequency-selective nature of the coaxial cable channel, transforming the signal characteristics to match the channel response
2Use of energy by moving object
If power amplifiers operate at high efficiency, then energy consumption is reduced, but nonlinear distortion increases degrading signal quality
Solution Approach 1:
The patent applies predistortion to the signal before amplification to pre-counteract the nonlinear distortion that will be generated by the power amplifier. By modifying the signal spectrum in advance with opposite-phase distortion components, the system enables high-power amplifier operation while canceling out harmful nonlinear effects at the receiver
3Reliability
If the channel response is non-flat, then frequency-selective fading occurs, but equalization complexity increases
Solution Approach 1:
The patent applies predistortion filtering at the transmitter to pre-compensate for frequency-selective fading before signal transmission. By adjusting the signal spectrum in advance to counteract expected channel frequency response variations, the system simplifies receiver equalization requirements while improving signal reception reliability across the frequency band
Data Source
AI summary
A transmitter is configured to generate a DOCSIS signal for transmission onto a frequency-selective coaxial cable. The transmitter comprises a first reverse tilt filter circuit, a digital predistortion circuit, a forward tilt filter, a wideband equalizer, a second reverse tilt filter, and a power amplifier. The responses of the tilt filters may be set based on the frequency response of the frequency-selective coaxial cable to which the transmitter is intended to be coupled. The predistortion circuit may compensate for distortion introduced by circuitry of the transmitter. The equalizer circuit may be operable to compensate for undesired linear response of other circuitry of the transmitter.