FM Baseband Precompensation for Bandwidth Reduction and Low Distortion
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Solution Overview
Problem
Existing FM radio broadcasting systems face challenges in reducing the bandwidth of FM analog signals to accommodate digital subcarriers without introducing significant distortion to the demodulated audio, especially when using constant-envelope high power amplifiers.
Innovation Solution
A method and apparatus that process the baseband multiplex signal through frequency modulation, filtering, demodulation, correction, and re-frequency modulation to reduce bandwidth while minimizing distortion, using an iterative process to achieve acceptable bandwidth reduction and distortion control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bandwidth of FM analog signal is reduced to accommodate digital subcarriers, then the spectral efficiency is improved, but the audio quality deteriorates due to distortion
Solution Approach 1:
The patent applies preliminary action by pre-compensating the baseband multiplex signal before FM modulation. The system predicts and corrects distortion in the baseband signal prior to modulation, preventing distortion from occurring in the final transmitted signal. This allows bandwidth reduction while maintaining audio quality by addressing the distortion issue before it affects the audio output.
2Use of energy by moving object
If constant-envelope high power amplifiers are used for IBOC transmission, then the power efficiency is improved, but the signal distortion increases due to non-linear amplification
Solution Approach 1:
The patent applies preliminary anti-action by pre-distorting the baseband signal in the opposite direction of the expected HPA distortion. The system calculates compensation filters that counteract the non-linear effects of constant-envelope HPAs before the signal is amplified. This allows the use of power-efficient HPAs while maintaining signal integrity by pre-canceling the distortion they would introduce.
3Quantity of substance
If digital subcarriers are placed closer to the FM host signal, then the digital capacity is increased, but the analog and digital interference increases
Solution Approach 1:
The patent applies local quality by applying different filtering and compensation techniques to different frequency regions of the baseband signal. The system selectively manages spectral components in different frequency ranges, allowing digital subcarriers to be placed closer to the FM host while minimizing interference through localized signal processing in specific frequency bands.
Data Source
AI summary
A method of processing a baseband multiplex signal comprises the steps of frequency modulating the baseband multiplex signal to produce a first modulated signal, filtering the first modulated signal to produce a first filtered signal, demodulating the filtered signal to produce a demodulated baseband multiplex signal, correcting the demodulated baseband multiplex signal to reduce or eliminate distortion in a predetermined frequency range of the demodulated baseband multiplex signal to produce a corrected signal, and frequency modulating the corrected signal to produce a second modulated signal. An apparatus that operates in accordance with the method is also provided.