RF Interferer Detection via Time-Frequency Variance Ratio
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Solution Overview
Problem
Existing communication systems, particularly in noise- and interference-rich environments, face challenges in detecting radio frequency (RF) interferers due to heavily filtered Phase Shift Keyed (PSK) waveforms, which are difficult to distinguish from background noise, leading to signal collisions and failure in simultaneous transmissions, especially in satellite and line-of-sight communications.
Innovation Solution
A communications technique that calculates the variance in both the time and frequency domains and determines the ratio of these variances to identify a 'channel busy condition', indicating the presence of an RF interferer, thereby preventing signal collisions by not transmitting over a busy channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If heavily filtered Phase Shift Keyed (PSK) waveforms are used for communication, then the communication system can operate in filtered channels, but the waveforms become difficult to distinguish from background noise and interference
Solution Approach 1:
The patent transitions from time-domain only analysis to frequency-domain analysis by applying Fast Fourier Transform (FFT) to the received signal samples. This dimensional change allows the system to detect PSK signals by examining their spectral characteristics, where the cyclic nature of PSK waveforms produces distinctive frequency domain patterns that are easily distinguishable from noise and interference.
2Reliability
If Carrier Sense Multiple Access (CSMA) is used to detect channel usage, then the system can avoid simultaneous transmissions, but it does not work well in noise- and interference-rich environments
Solution Approach 1:
The patent changes the detection parameter from simple energy detection (time-domain power measurement) to spectral analysis (frequency-domain characteristic detection). By computing the FFT of received samples and analyzing the spectral magnitude distribution, the system can reliably distinguish PSK signals from noise and interference, enabling accurate channel sensing even in challenging environments.
3Device complexity
If signal detection is performed without a training sequence, then the communication protocol is simplified, but the ability to determine the presence or absence of PSK waveforms is hampered
Solution Approach 1:
The patent enables PSK signals to self-identify through their inherent cyclic structure. By analyzing the frequency domain characteristics of the received signal, the system can detect the presence of PSK waveforms without requiring external training sequences or synchronization signals. The periodic nature of PSK modulation creates distinctive spectral patterns that automatically reveal the signal's presence.
Data Source
AI summary
A communications device includes a demodulator configured to demodulate a received communications signal into complex time domain samples. A processor is coupled to the demodulator and configured to determine the variance over time domain magnitude samples, perform a complex Fast Fourier Transform (cFFT) on the complex time domain samples as magnitude and phase to obtain frequency domain samples and determine the variance over the frequency domain samples. A comparator compares a variance ratio of the time domain magnitude samples and the frequency domain samples with a threshold to determine if a RF interferer is present, indicative that the communications channel is busy.