SBIR-STTR Award

Spread spectrum and related low probability of intercept (lpi) radar and communications signals present an extreme challenge to intercept or esm receivers by virtue of their broad bandwidth, below-noiselevel spectral density, noise-like spectral shape, and unknown code, making it impossible for the interceptor to despread the signal and recover the pure data signal embedded therein. Despite these formidable obstacles, certain receiver techniques exist that make it possible to detect the presence and determine some of the characteristics of spread spectrum and other lpi signals. Accordingly, a phase i study is proposed to investigate alternative spread-spectrum detection techniques and use the best combination thereof to configure an optimum spread spectrum detector (ssd) subsystem (and associated signal simulator) design. The proposed ssd will use an optimum combination of radiometric, scanning, compressive and multiplicative "feature" detection techniques to provide automatic "real time" detection of the presence of various spread spectrum signals and to determine their key parameters, e.g. chip rate, hop rate, frequency, prf, pulse width and/or frequency deviation, all with sufficient sensitivity and dynamic range.

Spread spectrum and related low probability of intercept (lpi) radar and communications signals, by virtue of their broad bandwidth, below-noise-level spectral density, noise-like spectral shape, and unknown code, are impossible for an intercept or esm receiver to despread and recover the pure information bearing signal embedded therein. However, as demonstrated in a recently-completed phase i study an lpi receiver subsystem can utilize an optimum combination of delay/multiplicative feature detection, compressive spectrum analysis and postdetection integration to detect the presence of and extract the key parameters of such lpi signals as frequency-hop, chirp, direct sequence (pn/bpsk) etc.. Feature detection converts a broadband noise-like lpi signal spectrum to a series of discrete spectral lines which are detected and analyzed with high sensitivity by the compressive downconverter and postdetection integrator. Accordingly, a phase ii follow-on implementation program is proposed to develop, fabricate and test in detail a "flyable brassboard" embodiment of the foregoing lpi receiver as an "add on" to existing or developmental esm receiving systems