1. A method for signal analysis, executed by a decoder, the method comprising: digitizing, by the decoder, a signal modulated by a pseudo noise (PN) sequence; dividing, by the decoder, the digitized signal into a plurality of sample blocks; and estimating, by the decoder, a PN phase embedded in a sample block of the plurality of sample blocks using an iterative message passing algorithm (iMPA) executed on a primary graphical model augmented with an auxiliary model, wherein the primary graphical model and the auxiliary model are each represented by a respective generator polynomial, and wherein the primary graphical model and the auxiliary model each represent the PN sequence.