Optical technique for identification and decoding of digitally modulated signals in surveillance receivers

An acousto-optic technique for identifying and decoding various unknown types of digitally modulated signals is described. The performance of the system, which uses a bicell photodiode detector assembly, is modelled. It is shown that the output of the system, which consists of the sum and difference of the signals from the two bicell elements, is different and easily identifiable for each of the following modulation types: BPSK, QPSK, offset-keyed QPSK, differential QPSK, continuous-phase FSK (including MSK) and non continuous-phase FSK. Preliminary experimental results from an optical breadboard system are presented which are in good agreement with the modelled results.