in a spread spectrum communications system employing cyclic code shift keying as its primary modulation , the transmission waveform is spread for transmission security by modulo - 2 adding a pseudo - noise sequence to the ccsk data symbols prior to phase modulating onto a carrier signal for transmission . if the transmission modulation is minimum shift keying the two components of the data stream are applied to the carrier with a differential encoding step implicit in the modulation scheme . this differential encoding characteristic makes stripping of the pn spread function prior to ccsk demodulation difficult at the receiving end . in order to demodulate this waveform in an optimum manner , an array correlator , the adjacent correlator stages of which have one chip relative time displacements of their ccsk reference waveform , is employed . in effect the array correlator becomes a parallel array of matched filters matched to each cyclic shift of the incoming waveform . by modulo - 2 addition of the pn spreading waveform with the time displaced ccsk reference waveform in each stage of the correlator , the correlator can be made to match all versions of the spread symbol being received .