A method and system of improving sensitivity in the demodulation of a received signal over an arbitrary measurement time epoch, the method comprising the steps of: correlating the received signal in a coherent fashion; and utilizing a Viterbi phase state keying trellis demodulation with a variable resolution of phase states over 360.degree. to demodulate the radio frequency phase trajectory of the signal throughout the measurement time epoch; and the system comprising a receiver for receiving a direct sequence spread spectrum signal, the receiver comprising: an antenna for receiving the direct sequence spread spectrum signal; a downconverter for downconverting the received signal, producing a downconverted signal; an analog to digital converter (60) to convert the downconverted signal to a digital signal; a despreader (80) for despreading and coherently correlating the digital signal to a known signal, creating a despread signal; and a processor for applying a Viterbi algorithm to the despread signal.