COVERT COMMUNICATIONS SYSTEM

THIS PROPOSAL IS FOR THE DESIGN OF A COVERT COMMUNICATIONS SYSTEM BASED ON ACOUSTIC CHARGE TRANSPORT (ACT) FILTER TECHNOLOGY. THIS SYSTEM IS COVERT IN THAT A NEARBY UNFRIENDLY RECEIVER WILL BE UNLIKELY TO DISCOVER THE PRESENCE OF THE TRANSMITTED SIGNAL, WHILE A MORE-DISTANT FRIENDLY RECEIVER WILL ONLY DETECTS THE SIGNAL, BUT ALSO MAINTAINS AN ADEQUATE SIGNAL-TO-NOISE RATIO. THE TECHNICAL APPROACH CHOSEN FOR THIS SYSTEM IS TO EMPLOY VERY LARGE PROCESSING GAIN IN THE RECEIVER SO THAT THE TRANSMITTED SIGNAL POWER DENSITY IS WELL BELOW THERMAL NOISE. ONE METHOD OF ACHIEVING RECEIVER PROCESSING GAIN IS TO ENCODE THE TRANSMITTED SIGNAL (VOICE OR DATA) WITH A CODE WHICH SPREADS THE SIGNAL ACROSS A WIDER BANDWIDTH THAN WOULD BE NEEDED TO SEND THE DESIRED INFORMATION. THE RESULTING "SPREAD SPECTRUM" IS TRANSMITTED TO A RECEIVER WHICH DECODES OR "COMPRESSES" THE SIGNAL INTO ITS ORIGINAL FORM; THE AMOUNT OF COMPRESSION DETERMINES THE PROCESSING GAIN. THE PROPOSED SYSTEM UTILIZES A CIRCULATING INTEGRATOR APPROACH TO ACHIEVE PROCESSING GAINS OF 45 TO 50 DB, WITH SYNCHRONIZATION TIMES OF LESS THAN 1 SECOND, AND TOTAL RECEIVER VOLUME APPROXIMATELY EQUAL TO THAT OF A CIGARETTE PACK.