The present invention performs decoding of trellis coded modulated data using a conventional decoder by splitting up the tasks of estimating the uncoded portion and estimating the coded portion into separate tasks. The task of estimating the coded portion is performed based on a transformation on the input symbols and by taking advantage of the symmetry of the constellation associated with the modulated data when referencing a lookup table. The lookup table may also be designed to be smaller than a straight forward implementation by taking advantage of the same symmetry of the constellation.The alteration of the data is then corrected for, resulting in a smaller constellation (Bi Phase Shift Key for 1 coded bit per symbol systems, Quadrature Phase Shift Key for 2 coded bits per symbol systems) mapping only the coded portion of the data. This allows a conventional Viterbi decoder to estimate the coded portion. The task of estimating the uncoded portion of the data is then performed by using information about the sector of the constellation of the original data along with a re-encoded version of the estimated coded portion.