FM Demodulator IBOC Interference Mitigation

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Solution Overview

Problem

FM analog demodulators face interference from in-band on-channel (IBOC) digital signals, which can degrade analog service quality and stereo separation, especially with increased digital signal injection power.

Innovation Solution

The implementation of a method and apparatus that digitally samples FM radio signals to compute a signal quality metric, detects sum and difference components of the baseband multiplex signal, and blends the output from stereo to monaural when the signal quality falls below a threshold, effectively mitigating interference from IBOC signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If IBOC digital signal injection power is increased, then digital audio quality is improved, but analog FM reception quality deteriorates due to increased digital sideband interference

Engineering Contradiction:

Improvedigital audio qualityVSAvoidanalog FM reception quality

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent detects digital sideband interference components in the FM signal and actively subtracts them from the received signal. By identifying the harmful digital interference and removing it through signal processing, the system converts the problematic co-channel transmission into a beneficial situation where both digital and analog services can coexist at high power levels without mutual degradation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Productivity

If digital signal power is increased from 20 dB below analog to 10 dB below analog, then digital service coverage is improved, but analog service degradation becomes more severe

Engineering Contradiction:

Improvedigital service coverageVSAvoidanalog service reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The interference cancellation mechanism enables the system to tolerate higher digital signal power levels by actively removing digital sideband components from the analog FM signal. This allows digital service coverage to be expanded while maintaining analog service reliability, as the harmful digital interference is converted into a removable component rather than permanent degradation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If FM demodulator is designed for high performance with DSP algorithms, then analog reception quality is improved, but susceptibility to digital sideband interference increases

Engineering Contradiction:

Improveanalog reception qualityVSAvoidsusceptibility to digital interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes the digital sideband interference components from the FM signal before demodulation. By separating the harmful digital components from the analog FM signal, the high-performance DSP demodulator can process only the clean analog signal, maintaining its superior performance characteristics while eliminating susceptibility to digital interference

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS9184961B2FM analog demodulator compatible with IBOC signals

Publication Date: 2015.11.10 IBIQUITY DIGITAL CORP

AI summary

A method includes: receiving an FM radio signal including an analog-modulated portion; digitally sampling an analog-modulated portion of the radio signal to produce a plurality of samples; using a ratio between an average magnitude and an RMS magnitude of a block of the samples to compute a signal quality metric; detecting sum and difference components of the baseband multiplex signal content; using the baseband content to produce an output signal; and blending the output signal from stereo to monaural as the signal quality metric falls below a threshold value.