Coherence of modulated noise interference in the receiver of a radio engineering system

The issue of noise immunity in receiving paths is one of the primary challenges in designing various radio engineering systems, such as communication systems, radars, and radio navigation. One type of interference that significantly degrades the performance of such systems is active noise jamming (ANJ). The main types of active jamming include: continuous noise jamming (direct noise or modulated); pulsed noise; intermittent noise, etc. When modulated ANJ affects a radio system’s receiver (e.g., a radio station or radar), it drastically reduces the maximum communication range or maximum target detection range (in the case of pulsed radar). From a physical standpoint, when modulated ANJ is applied, the power spectral density (PSD) of the receiver’s intrinsic noise increases by an amount equal to the PSD of the ANJ. Modern radio systems employ various noise suppression techniques to counteract modulated ANJ. To address the problem of modulated interference discrimination, it is proposed to use an assessment of the process coherence level in the radio system’s receiver as an informative feature. Noise jamming can be represented as: a fluctuating process (oscillations with random amplitude and phase/frequency); the result of random superposition (summation) of deterministic signals. Analyzing the coherence level of modulated active noise jamming—based on estimating the signal energy distribution via the eigenvalues of the correlation matrix—allows the coherence properties of modulated ANJ to serve as an additional informative feature (quantitative measure). The following dependencies were obtained: entropy value vs. amplitude modulation coefficient; entropy value vs. effective frequency and phase modulation index for different bandwidths of the modulating low-frequency noise. Assessing the coherence level of modulated active noise jamming helps determine the type and operating mode relative to the radar receiver’s bandwidth: frequency targeting (spot jamming); barrage jamming (wideband noise suppression).