Time Dilation Waveform Dithering for LPI Signal Suppression
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Solution Overview
Problem
Existing digital communications systems are vulnerable to cyclostationary detection techniques, which can identify transmitted signals due to their constant symbol rate or carrier frequency, requiring costly and complex modifications to vary frequency and symbol rate, and existing methods are not fully effective in preventing detection.
Innovation Solution
A time dilation function is applied to dither the samples of a transmitted waveform in a pseudo-random manner, altering their occurrence times, making the signal undetectable by cyclostationary methods, and this can be reversed at the receiver to maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frequency hopping or symbol rate variation is used to prevent cyclostationary detection, then signal detectability is reduced, but device complexity and cost increase due to hardware modifications
Solution Approach 1:
The patent applies time dilation to the transmitted waveform samples, transforming them from a constant time grid to a pseudo-randomly distorted time grid. This parameter transformation of the time domain structure eliminates cyclostationary features without requiring hardware modifications, as it can be implemented through digital signal processing of the waveform samples before transmission.
Solution Approach 2:
The patent replaces physical hardware modifications (frequency hopping synthesizers, variable symbol rate generators) with a mathematical transformation applied to the waveform samples. The time dilation function operates on the digital representation of the signal, substituting mechanical/electrical system changes with algorithmic processing that achieves the same LPI/LPD effect without increasing hardware complexity.
2Object-affected harmful factors
If existing cyclostationary suppression techniques are used, then some detection resistance is achieved, but they only vary symbol rate over finite values and remain detectable
Solution Approach 1:
Instead of varying symbol rate over a finite set of discrete values, the patent applies continuous time dilation transformation to the waveform samples. The time dilation function creates a pseudo-random time distortion that continuously varies the apparent symbol timing, eliminating the discrete nature of traditional methods and providing more effective suppression of cyclostationary features.
Solution Approach 2:
The patent transforms the static symbol rate into a dynamic, pseudo-randomly varying time structure through time dilation. Rather than switching between fixed symbol rates, the system creates a continuously evolving time grid that adapts pseudo-randomly, making the signal structure more unpredictable and更难 to detect using cyclostationary analysis.
3Reliability
If constant symbol rate and carrier frequency are used, then communication reliability is maintained, but cyclostationary detection becomes easy
Solution Approach 1:
The patent applies time dilation transformation to the waveform samples before transmission, preparing the signal in advance to have suppressed cyclostationary features. This preliminary processing of the waveform samples ensures that when the signal is transmitted with constant symbol rate and carrier frequency, it already possesses LPI/LPD properties without requiring real-time modulation changes.
Solution Approach 2:
The patent introduces time dilation as an intermediary transformation layer between the conventional modulator and the transmission medium. This intermediate processing step modifies the waveform sample timing structure without changing the underlying symbol rate or carrier frequency, allowing the signal to maintain communication reliability while gaining detection resistance through the time domain transformation.
Data Source
AI summary
A communications system including a transmitter having a modulator that converts information bits to samples, a transmitter pseudo random number generator that generates a sequence of transmitter random numbers defining a time dilation function, and a transmitter time varying delay processor responsive to the samples and the time dilation function, where the transmitter time varying delay processor dithers the samples in time based on the time dilation function. The system also includes a receiver responsive to the dithered samples from the transmitter, where the receiver includes a receiver pseudo random number generator that generates a sequence of receiver random numbers in sync with the transmitter random numbers, a receiver time varying delay processor responsive to the receiver random numbers and the dithered samples, where the receiver time varying delay processor removes the dithering of the samples, and a demodulator for demodulating the samples to recover the information bits.