OFDM Waveform Randomization for LPD/LPI Communications
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Solution Overview
Problem
Traditional OFDM techniques are susceptible to detection and jamming due to embedded cyclo-stationary features and large power fluctuations, making them unsuitable for covert communications like LPD/LPI (Low Probability of Detection/Low Probability of Intercept) applications.
Innovation Solution
A multi-node communication network using modified OFDM techniques that suppress cyclic prefixes, randomize sub-carriers and pilot symbol values, and correct distortions via direct sequence spreading, generating featureless Gaussian noise waveforms to mimic Gaussian noise statistics, thereby making signals harder to detect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional OFDM techniques are used, then spectral efficiency is improved, but detection and jamming susceptibility increases
Solution Approach 1:
The patent changes key parameters of the OFDM signal by removing cyclic prefixes, randomizing subcarrier frequencies and pilot symbol values, and applying phase rotations to transform the signal into featureless Gaussian noise waveform statistics, thereby eliminating detectable cyclo-stationary features while maintaining spectral efficiency
Solution Approach 2:
The patent applies different processing to different parts of the OFDM signal: cyclic prefixes are removed entirely, subcarriers are selectively randomized, pilot symbols have their values randomized, and phase rotation is applied specifically to compensate for frequency offsets, creating localized modifications that collectively achieve LPD/LPI properties
2Productivity
If traditional OFDM techniques are used, then data transmission capability is improved, but power fluctuation increases
Solution Approach 1:
The patent changes the power characteristics by removing cyclic prefixes and applying phase rotation, which transforms the signal into Gaussian noise waveform statistics with reduced peak-to-average power ratio, thereby reducing power fluctuations while maintaining data transmission capability
3Reliability
If cyclic prefixes are included in OFDM signals, then multipath interference resistance is improved, but signal detectability increases
Solution Approach 1:
The patent extracts and removes the cyclic prefix component from the OFDM signal structure, eliminating the source of cyclo-stationary features that make signals detectable, while compensating for the loss of multipath resistance through frequency domain equalization and phase rotation techniques
4Measurement precision
If pilot symbols are used for synchronization, then timing and frequency synchronization is improved, but cyclic features are introduced
Solution Approach 1:
The patent changes the pilot symbol values by applying randomization, transforming them from fixed known sequences into random values that maintain synchronization capability through statistical properties while eliminating detectable cyclo-stationary features associated with traditional pilot structures
Data Source
AI summary
In embodiments, a communication node of a multi-node communication network includes a controller communicatively coupled to a communication interface, wherein the controller is configured to: acquire a data payload to be transmitted based on a randomized transmission interval; duplicate a bit sequence of the data payload with a selected spreading pattern; perform bit-to-symbol mapping of the bit sequence based on a selected M-ary number to generate a data payload symbol sequence; randomize a location or value of one or more pilot symbols and one or more data carriers of the data payload symbol sequence; transform frequency-domain symbols of the data payload symbol sequence into time-domain symbols to generate a time-domain data payload signal; remove amplitude fluctuation of the data payload signal to generate a phasor data payload signal; and transmit the phasor data payload signal to at least one additional communication node of the multi-node communication network.