SIGNAL PROCESSING FOR THROUGH-THE-EARTH COMMUNICATIONS

RELIABLE THROUGH-THE-EARTH COMMUNICATIONS (TEC) ARE NEEDED FOR COMMAND AND CONTROL OF DEEP-BASED ICBM SITES. THE REQUIRED DATA RATES CAN BE ACHIEVED BY USING BOTH SIGNAL CODING AND SIGNAL-TONOISE-RATIO (SNR) ENHANCEMENT TECHNIQUES. THE KEY SIGNAL-PROCESSING ELEMENTS OFJSUCHASYSTEM ARE: NOLINEAR PROCESSING (NLP), ADAPTIVE NOISE CANCELLATION (ANC), QUADRATURE-AMPLITUDE MOUDLATION (QAM), ERROR-CORRECTING CODING (ECC), AND DECISION-AIDED FEEDBACK (DAFB). NONLINEAR PROCESSING BY AN ADAPTIVE CLIPPER REMOVES MOST THE POWER CONCENTRATED IN THE IMPULSIVE SPIKES OF VLF NOISE. ADAPTIVE NOISE CANCELLATION COMBINES CORRELATED ELECTRIC-AND MAGNETIC-FIELD INPUTS TO MAXMIZE THE SNR. QAM AND ECC MATCH THE REQUIRED DATA RATE TO THE CHARACTERISTICS OF THE COMMUNICATION CHANNEL. DECISION-AIDED FEEDBACK ALLOWS THE OTHER THREE SYSTEMS TO OPERATE TOGETHER IN A NEARLY OPTIMAL MANNER. THE PROPOSED PROGRAM WILL DEVELOP A PRACTICAL AND NEARLY OPTIMAL TEC SYSTEM CONCEPT THROUGH ANALYSIS AND SIMULATION OF EACH OF THE SYSTEM ELEMENTS AND THEIR INTERACTIONS.