Transmit Sub-Sample Dithering for Cyclostationary Feature Elimination
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Solution Overview
Problem
Existing communication systems face challenges in reducing cyclostationary features of transmitted waveforms, which can lead to detection by adversaries, compromising Low Probability of Detection (LPD) and Low Probability of Intercept (LPI) without degrading demodulation performance.
Innovation Solution
The implementation of sub-sample dithering processing using polyphase resampling filters at the transmitter to modify sample timing, reducing cyclostationary features by varying symbol rate within a single burst transmission, and employing digital signal processing techniques like polyphase resampling, sample dropping/repeating, or Farrow filters to convert discrete-time IF signals into RF signals with reduced cyclostationary properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmit modulation schemes with inherent cyclostationary properties are used, then waveform detection capability is improved, but probability of detection by adversaries increases
Solution Approach 1:
The patent applies dynamics by making the sample duration variable rather than fixed. The transmitter dynamically adjusts the duration of samples within a burst transmission, changing the timing characteristics of the modulated signal. This dynamic variation eliminates the periodic cyclostationary features that adversaries use for detection, while the receiver compensates for these variations to maintain detection capability.
Solution Approach 2:
The patent changes the temporal parameter of sample duration in the discrete-time IF signal. By varying the duration of individual samples or groups of samples, the statistical properties of the transmitted waveform change over time, destroying the cyclostationary structure. This parameter modification allows the signal to maintain detectability through controlled variations while preventing adversary detection by eliminating predictable periodic patterns.
2Object-affected harmful factors
If sub-sample dithering processing is applied to reduce cyclostationary features, then probability of intercept is reduced, but signal processing complexity increases
Solution Approach 1:
The patent segments the sample stream into groups and applies dithering processing to specific samples within each group. Rather than processing every sample individually, the system divides the signal into manageable segments and selectively modifies certain samples. This segmentation approach reduces the overall processing complexity while still achieving effective cyclostationary feature reduction across the transmitted burst.
Solution Approach 2:
The patent employs computationally efficient dithering techniques that use simple, lightweight processing operations. The dithering sequence is generated and applied in a manner that minimizes computational burden, using straightforward timing adjustments rather than complex signal transformations. This allows the system to achieve security benefits without requiring high-complexity processing hardware.
3Object-affected harmful factors
If sample timing is modified to eliminate cyclostationary properties, then Low Probability of Detection is enhanced, but demodulation performance may degrade
Solution Approach 1:
The patent implements feedback mechanisms where the receiver is aware of the dithering pattern used by the transmitter. The receiver uses this knowledge to compensate for the timing variations introduced by sub-sample dithering, reversing the effects of the dithering process during demodulation. This feedback loop ensures that while the transmitted signal has reduced cyclostationary properties for security, the legitimate receiver can correctly demodulate the signal by applying the inverse transformation.
Solution Approach 2:
The patent creates an asymmetric situation where the transmitter and receiver share secret knowledge about the dithering pattern, while adversaries do not. The timing modifications appear as random disturbances to anyone without knowledge of the pattern, but to the authorized receiver, these same modifications are predictable and compensatable. This asymmetry allows the system to simultaneously achieve LPD/LPI properties and maintain reliable demodulation for authorized users.
Data Source
AI summary
Systems (400) and methods for reducing a number of cyclostationary features in a transmitted signal. The methods comprise: obtaining by a transmitter a discrete-time IF signal comprising a sequence of samples all having a same sample duration; performing operations by a sub-sample dithering processing device of the transmitter to modify a sample timing of the discrete-time IF signal by decreasing or increasing a duration of at least one first sample of the sequence using a digital signal processing technique in a digital domain; converting the discrete-time IF signal to an RF signal; and transmitting the RF signal having a reduced number of cyclo stationary features.