Harmonic Signal Frequency Extension via Non-Linear Spectrum Convolution
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Solution Overview
Problem
Existing communication systems, particularly wireless communication systems, face bandwidth limitations that result in the loss of high-frequency speech information, leading to reduced intelligibility and quality, especially in noisy environments, and current harmonic extension methods suffer from inaccuracies in pitch estimation and aliasing artifacts.
Innovation Solution
A system and method that perform a non-linear transformation on the complex spectrum of band-limited harmonic signals in the frequency domain using linear convolution to extend harmonics outside the original frequency band, eliminating aliasing artifacts and allowing controlled harmonic generation across desired frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bandpass filtering is applied to limit bandwidth, then communication system complexity is reduced and transmission efficiency is improved, but high-frequency speech information is lost leading to reduced intelligibility and quality
Solution Approach 1:
The patent applies preliminary action by compressing high-frequency components into lower frequency ranges before transmission through the narrowband channel. This pre-processing step ensures that the essential speech information is preserved in a format that can pass through the limited bandwidth channel, preventing information loss during transmission.
Solution Approach 2:
The patent transforms the frequency domain representation by compressing high-frequency components into lower frequency ranges. This dimensional transformation allows the signal to fit within the limited passband while preserving the information content, effectively mapping the signal into a compatible frequency dimension for the communication channel.
2Reliability
If frequency compression is applied to reintroduce harmonics, then speech quality and intelligibility are improved, but aliasing artifacts are introduced in higher frequencies
Solution Approach 1:
The patent extracts and removes the problematic aliasing artifacts that are generated during frequency compression. By identifying and eliminating these harmful components, the patent preserves the beneficial frequency compression effects while preventing the degradation caused by aliasing, thus maintaining speech quality without the harmful artifacts.
3Manufacturing precision
If pitch estimation methods are used for spectral copying, then proper placement of transposed harmonics is achieved, but performance degrades severely when pitch estimate is inaccurate
Solution Approach 1:
The patent employs self-service by using the signal's own spectral characteristics to guide the harmonic extension process. Instead of relying on external pitch estimation, the method uses autocorrelation and spectral analysis of the compressed signal itself to accurately determine harmonic placements, making the system self-sufficient and robust to pitch estimation errors.
4Ease of operation
If non-linear transformation is applied to generate harmonics, then harmonics are generated at multiples of fundamental frequency without pitch estimation, but bandwidth control is difficult and harmonics are generated across all frequencies
Solution Approach 1:
The patent applies local quality by selectively generating harmonics only in specific frequency ranges rather than across the entire spectrum. The method uses frequency-selective filtering and targeted harmonic synthesis to place harmonics only where needed, providing localized control over the spectral content while maintaining the simplicity of non-linear transformation.
Data Source
AI summary
A system and methods are provided for extending the frequency bandwidth of a harmonic signal. Harmonic content of a band-limited signal is extended to frequencies outside the signal's passband by performing a non-linear transformation on the complex spectrum of the band-limited signal in the frequency domain. The non-linear transformation may be accomplishes by a linear convolution of the complex spectrum with itself. A system for extending the frequency bandwidth of a harmonic signal includes a signal processor with a forward transform module for transforming a time domain signal into the frequency domain, a non-linear transform module for performing the non-linear transformation on the complex spectrum of the harmonic signal, and a reverse transform module for transforming the extended spectrum of the harmonic signal back into the time domain.