Acousto-optic system for automatic identification and decoding of digitally modulated signals

University of PlymouthSchool of Electronic Communication andElectrical EngineeringDrake CircusPlymouth, PL4 8AAUnited KingdomE-mail: creeve@plymouth.ac.ukAbstract. A simple acousto-optic system is described that is capable ofdemodulating frequency- and phase-modulated signals using a bicellphotodetector. A summary of an analytical study of the system is pro-vided, describing its main performance characteristics. Results from aMathcad model of the system are presented showing that, by taking thesum and difference of the outputs from the two bicell elements, it ispossible to identify and demodulate a wide range of different types ofmodulation without any a prioriinformation. Thus the technique is wellsuited for surveillance receiver and electronic support measures (ESM)applications. In particular, it is shown that biphase shift keying (BPSK),quaternary phase shift keying (QPSK), offset-keyed QPSK, differentialQPSK, continuous phase frequency shift keying (FSK) [including mini-mum shift keying (MSK)], and ordinary FSK all give unique and easilyidentifiable signatures. Experimental results are presented, which are ingood agreement with both theoretical and modeled results.