1. A method for demodulating at a receiver, a transmitted message intended for a user, the transmitted message comprised of message symbols transmitted with synchronization ("sync") symbols, being the same as sync symbols prestored in the receiver, differentially encoded in phases and amplitudes of a radiowave signal transmitted as symbol s from an even symbol constellation during even symbol periods, and as s from an odd symbol constellation during odd symbol periods, comprising the steps of: a) sensing the phases and amplitudes of the radiowave signal at a down converter; b) digitizing the sensed phases and amplitudes into received samples at an analog to digital (A/D) converter; c) extracting received message samples at a sync unit; d) calculating estimated received symbol constellation {Z} comprised of estimated received symbols Z.sub.ji which is an estimate of a symbol s.sub.i being transmitted during even time periods through a channel with intersymbol interference from a previously transmitted symbol s.sub.j at an initial reference symbol unit; e) calculating estimated received symbol constellation {Z} comprised of estimated received symbols Z.sub.ji which is an estimate of a symbol s.sub.i being transmitted during odd time periods through a channel with intersymbol interference from a previously transmitted symbol s.sub.j at an initial reference symbol unit; f) determining a set of reference constellation points {Z.sup.ref } and {Z.sup.ref } being a subset of estimated received symbol constellations {Z}, {Z} that when rotated, provide received symbol constellations {Z}, {Z}; g) determining a demodulated symbol sequence at a MLSE decoder which would minimize a total deviation, being a sum of branch metrics, d.sub.ji, each branch metric, d.sub.ji, being a deviation from a received message sample to a closest estimated symbol constellation point Z.sub.ij, Z.sub.ji and is calculated from reference constellation points {Z.sup.ref } and {Z.sup.ref } for even and odd symbol periods, respectively; h) adjusting the estimated symbol constellation points Z.sub.ji, Z.sub.ji to compensate for a change in the channel over time at a reference symbol update unit; i) converting the demodulated symbol sequence to a bit sequence at an output means; j) creating a message from the bit sequence; and k) providing the message to said user.