A Novel Method for Recognition of Modulation Code of LPI Radar Signals

The Low Probability of Intercept (LPI) capability of the radar defeats conventional RWR/ESM systems. The important advantage of LPI radar is to go undetected, while maintaining a strong battlefield awareness. Common Spectral analysis and conventional methods fail to detect emissions of LPI Radars and even normal radars in noisy environments. This leads to use Higher Order Spectral Analysis (HOSA) techniques enabling us to extract much more information from the same intercept and hence facilitating detection. This paper reports the results of HOSA techniques (Bi-spectrum, Bicoherence and Tri-spectrum) applied to LPI Radar signals. Bi-phase Barker coded signals of different lengths, P1, P2, P3 and P4 Poly-phase coded signals and Frank signal are analyzed using HOSA techniques to produce 2-D signatures of these signals which serve as reference for computing correlation coefficient with respect to the similar plots obtained for an unknown received signal. The system identifies the type of the signal by the maximum value of correlation coefficient obtained. The results obtained clearly indicate the promising capability of this technique to identify the type of LPI signal with SNRs as low as –3 dB and even lower.