Method and system for applying Viterbi type PSK demodulation for optimum correlation of GPS signals

A receiver for improving the sensitivity in the demodulation of a received direct sequence spread spectrum signal, said 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 to convert the downconverted signal to a digital signal;
• a despreader 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 a trellis created for the despread signal, the processor:
• breaking the despread signal into time intervals;
• creating the trellis of evenly distributed phase state nodes at each time interval by:
• defining a plurality of phase states representing the phases evenly quantized over 0 to 360 degrees;
• defining possible state transitions from and to each phase state node;
• creating paths between phase state nodes in one time interval and phase state nodes in another time interval according to said possible state transitions;
• assigning a transition probability to each path;
• and
• creating a likelihood metric for each path based on a measured phase of said despread signal and the transition probability for the path, the measured phase of the despread signal having a random process approximated by a Markov process;
• and
• utilizing the Viterbi algorithm on said trellis to perform a maximum likelihood estimation of a phase trajectory of the despread signal with said quantized resolution of phase states over 0 to 360° throughout the time interval.