DEVELOPMENT OF LOW PROBABILITY OF INTERCEPT/ANTIJAM (LPI/AJ) MODEM

AN INNOVATIVE LPI/AJ (LOW PROBABILITY OF INTERCEPT/ANTI-JAM) MODEM IS PROPOSED FOR THE SECURED COMMUNICATION LINK BETWEEN U.S. MILITARY AIRCRAFTS. THIS MODEM UTILIZES SPECTRAL SHAPING AND DECEPTION (SSHADE) TECHNIQUE WHICH IS CAPABLE OF PROVIDING COVERT VOICE/DATA COMMUNICATIONS IN A HOSTILE JAMMING ENVIRONMENT. THE PROPOSED TECHNIQUE GIVE 40 DB OF PROCESSING GAIN BY SPREADING THE ENERGY OVER A 40 MHZ BANDWIDTH WHEN NARROWBAND (2.4 KBPS) DIGITAL VOICE ENCODING (LPC-10E) IS USED. PRELIMINARY TRADOFF STUDY SHOWS THAT LPC-10E PROVIDES LONGER CODE LENGTH THAN CVSD (CONTINUOUS VARIABLE SLOPE DELTA). THIS MODEM HAS THE POTENTIAL OF PERFORMING IN A -30 DB SIGNAL-TO-NOISE ENVIRONMENT. JAM RESISTANT CAPABILITY IS PROVIDED BY THE AVAILABLE 40 DB PROCESSING GAIN DUE TO SPECTRUM SPREADING. ANOTHER INNOVATION IS THE USE OF SURFACE-ACOUSTIC-WAVE (SAW) CONVOLVER FOR DESPREADING THE RECEIVED SIGNAL WITHOUT THE NEED FOR COMPLEX CODE SYNCHRONIZATION PROCESS.