Chaotic Spread Spectrum Signal Artifact Suppression
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Solution Overview
Problem
Existing communications systems using chaotic signals suffer from detectable artifacts in waveforms, making them vulnerable to signal detection.
Innovation Solution
A method employing direct sequence spread spectrum signals modulated with chaotic sequences and filtered using a pulse-shaped filter to suppress blind detection features, creating a waveform with no detectable artifacts, combined with forward error correction and chaotic phase scrambling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chaotic signals are used for communication, then security and reliability are improved, but detectable artifacts appear in the waveform
Solution Approach 1:
The patent extracts and removes the detectable artifacts from the chaotic signal waveform through careful design of the modulation and filtering processes, leaving only the essential communication information while eliminating the harmful detectable components
Solution Approach 2:
The patent changes key parameters of the chaotic signal including phase modulation depth, filtering characteristics, and spectral distribution to transform the waveform from one with detectable artifacts to one that is indistinguishable from background noise
2Difficulty of detecting and measuring
If spread spectrum is used to spread transmitted power below noise floor, then detectability is reduced, but signal-to-noise ratio decreases
Solution Approach 1:
The patent applies pulse shaping filtering and phase modulation in advance before transmission to pre-condition the signal, ensuring that when the power is spread below the noise floor, the signal maintains its integrity and can be properly recovered despite the low signal-to-noise ratio
3Object-generated harmful factors
If pulse shaped filter is used to suppress blind detection features, then artifact detection is suppressed, but signal processing complexity increases
Solution Approach 1:
The pulse shaped filter is designed to perform multiple functions simultaneously: it shapes the signal spectrum, suppresses blind detection features, and maintains signal integrity for coherent detection, thereby achieving artifact suppression without proportionally increasing processing complexity
Data Source
AI summary
A method for transmitting covertly employs three features in a novel combination to create a transmission waveform that has no detectable artifacts. First, the method employs spread spectrum, such as a direct sequence spread spectrum signal, to transmit the power level below the noise floor. Second, the method modulates the phase of each chip in the spread spectrum signal using a chaotic sequence. Third, the method filters the transmission signal using a pulse shaped filter to depress blind detection features in the amplitude modulation and higher order power spectral densities. The novel combination of these features results in a practically invisible and undetectable transmission waveform. Many other features are disclosed herein to optimize this combination.