Symbol-Based Randomized OFDM Subcarrier Control
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Solution Overview
Problem
OFDM communications systems are susceptible to Inter-Carrier Interference (ICI), Inter-Symbol Interference (ISI), and frequency selective fading, which affect signal quality and increase the probability of detection and interception due to their high peak-to-average power ratio and requirement for minimum signal-to-noise ratio per subcarrier.
Innovation Solution
The system employs Symbol-Based Randomization (SBR) and a frequency-domain spreading function like the Walsh transform to dynamically turn subcarriers on or off, reduce peak-to-average power ratio, and vary subcarrier frequencies based on encryption algorithms, thereby reducing ICI, ISI, and frequency selective fading, while maintaining instantaneous signal-to-noise ratio and enhancing Low Probability of Interception (LPI) and Low Probability of Detection (LPD characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM transmits multiple subcarriers simultaneously to increase data rate, then productivity is improved, but peak-to-average power ratio increases causing susceptibility to interference and detection
Solution Approach 1:
The patent applies periodic frequency hopping where subcarriers are turned on and off in periodic patterns determined by encryption algorithms. This creates time-varying transmission where the same data can be transmitted across different subcarrier sets at different times, reducing peak power concentration while maintaining data rate through repeated transmissions and combining at the receiver.
Solution Approach 2:
The system dynamically selects and activates specific subcarriers based on encryption algorithms and channel conditions rather than using all subcarriers continuously. This dynamic subcarrier selection reduces the peak-to-average power ratio by activating only necessary subcarriers at any given time, while maintaining high data rate through efficient resource allocation and frequency diversity.
2Reliability
If OFDM uses fixed subcarrier frequencies to maintain orthogonality, then reliability is improved, but susceptibility to frequency selective fading and jamming increases
Solution Approach 1:
The patent implements dynamic frequency hopping where subcarrier frequencies change over time according to encryption algorithms. This transforms the static OFDM system into a dynamic one that can adapt to fading conditions and avoid jamming frequencies, maintaining reliability through frequency diversity while preserving orthogonality within each transmission symbol period.
Solution Approach 2:
The system changes the frequency parameter of subcarriers dynamically based on encryption keys and channel conditions. By varying subcarrier frequencies according to predetermined hopping patterns, the system avoids persistent frequency selective fading and jamming while maintaining the orthogonality required for reliable OFDM operation within each symbol period.
3Productivity
If OFDM transmits continuous signals to maintain data flow, then productivity is improved, but probability of detection and interception increases
Solution Approach 1:
The patent employs periodic transmission patterns where data is transmitted in bursts across different frequency sets determined by encryption algorithms. This creates gaps in continuous transmission that reduce detectability while maintaining data flow continuity through repeated transmissions and combining at the receiver, effectively hiding the communication from interceptors.
Solution Approach 2:
The system transmits multiple copies of the same data across different subcarrier sets at different times according to encryption patterns. This redundant transmission approach ensures data flow continuity while reducing detection probability, as interceptors would need to capture and correlate multiple encrypted copies across different frequencies to successfully intercept the communication.
4Productivity
If OFDM activates all subcarriers to maximize data rate, then productivity is improved, but power consumption increases
Solution Approach 1:
The patent implements dynamic subcarrier activation where only necessary subcarriers are activated at any given time based on encryption algorithms and channel conditions. This reduces power consumption by avoiding transmission on all subcarriers continuously, while maintaining high data rate through efficient selection of active subcarriers and utilization of frequency diversity over time.
Solution Approach 2:
The system dynamically changes the activation state parameter of subcarriers, switching between active and inactive states according to encryption patterns and channel quality. This parameter modulation reduces average power consumption while maintaining productivity by concentrating transmission power on selected subcarriers that provide the best data rate per unit power.
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A
AI summary
A device and system communicates data and includes a modulation and mapping circuit that modulates and maps data symbols into a plurality of multiple subcarrier frequencies that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexed (OFDM) communications signal based on a fixed or variable OFDM symbol rate. A pseudo-random signal generator is operative with the modulation and mapping circuit and generates pseudo-random signals to the modulation and mapping circuit based on an encryption algorithm for frequency hopping each subcarrier at an OFDM symbol rate to lower any probability of interception and detection, reduce power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio, wherein selected subcarriers are turned ON or OFF to increase the transmit power and signal-to-noise ratio and reduce the Inter-Carrier Interference (ICI) and adverse effects of frequency selective fading.