High-Entropy Continuous Phase Modulation for LPD
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Solution Overview
Problem
Conventional low probability of detection (LPD) communication systems, such as those using Quadrature Phase Shift Keying (QPSK) and Binary Phase Shift Keying (BPSK), are susceptible to adversarial detection due to their cyclostationary features, making them inefficient and detectable by unauthorized receivers.
Innovation Solution
A high-entropy continuous phase modulation communication system with constant envelope modulation, utilizing a smaller, lighter, and more efficient power amplifier, which mimics Gaussian distributed thermal noise, thereby suppressing structural features and forcing adversarial detectors to use less effective energy detection techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional modulation types such as QPSK and BPSK are used, then communication structure is simple and easy to implement, but the signal exhibits cyclostationary features that make it susceptible to adversarial detection
Solution Approach 1:
The patent applies parameter changes by transitioning from conventional modulation schemes (QPSK, BPSK) to high-entropy continuous phase modulation with constant envelope. This changes the fundamental parameters of the signal structure, eliminating cyclostationary features while maintaining communication functionality. The high-entropy randomization transforms the signal statistics to mimic Gaussian distributed thermal noise, making it undetectable by traditional spectral analysis methods.
2Difficulty of detecting and measuring
If signals are designed to mimic Gaussian distributed thermal noise for LPD, then detectability is reduced, but high peak-to-average-power ratio is required which produces large peaks
Solution Approach 1:
The patent resolves this contradiction by changing the envelope parameter from variable to constant. The constant envelope modulation scheme maintains the high-entropy randomization needed to mimic Gaussian noise while constraining the amplitude to a constant value. This eliminates large peaks and allows operation with smaller, more efficient power amplifiers while maintaining LPD characteristics.
3Productivity
If a high output linear power amplifier is used to produce useful communication links, then communication distance and jamming margin are improved, but the amplifier becomes large, heavy, and inefficient
Solution Approach 1:
The patent changes the operating parameter of the power amplifier from linear mode to saturation mode. By using constant envelope modulation, the amplifier can be operated at saturation without waveform distortion, achieving high efficiency. The constant envelope ensures that even though the amplifier operates non-linearly at saturation, the signal integrity is preserved, enabling long-range communication without requiring large, heavy linear amplifiers.
4Weight of moving object
If constant envelope modulation is used with smaller power amplifiers, then SWaP-C criteria are met and efficiency is improved, but maintaining long-range communication capability becomes challenging
Solution Approach 1:
The patent applies continuity of useful action through high-entropy continuous phase modulation. The continuous phase property ensures uninterrupted signal transmission with smooth transitions, while the high-entropy randomization maintains signal energy distribution that resists detection and jamming. This continuous, randomized signal structure allows smaller amplifiers to achieve long-range communication by preventing energy concentration that would otherwise require high-power linear amplifiers.
Data Source
AI summary
System for generating a constant envelope and suppressed cyclic feature signal may include a transmission security (TRANSEC) function, a spread spectrum chip, an M-ary continuous phase modulator, and a pulse-shaped filter. The TRANSEC may generate a pseudorandom symbol by M-ary symbol generation selects a symbol with a signal phase, and the spread spectrum chip corresponding to the generated pseudorandom symbol or a phase rotation of the pseudorandom symbol. The M-ary continuous phase modulator with a delta-phase mapper maps the signal phase based at least in part on the selected symbol. The pulse-shaped filter of the M-ary modulator introduces inter-symbol interference from a previous and a subsequent symbol into a current symbol; the inter-symbol interference may be introduced by the main lobe of the signal phase being contained within a bandwidth of a chip rate of the spread spectrum chip for frequency modulation signal transmission of information by the generated signal.