Generation of soft bit metrics for differentially encoded quadrature phase shift keying (QPSK)

A computer implemented method for generating soft bit metrics in a telecommunications system employing modulation with differential encoding comprising the steps of:

• a) identifying, from the signs of received coordinates, a subset of coordinates that significantly contribute to a logarithmic likelihood ratio (LLR) of each bit;
• b) determining dominant terms of the LLR;
• and
• c) outputting an indicia of the soft bit metrics;
• wherein the subsets so identified are represented by (x1, x2), (y1, y2), (x1,y2), and (x2, Y1), with the coordinates x1, x2, y1 and y2 corresponding to in-phase and quadrature components of two successively received symbols produced by a modulator performing the differential encoding;
• wherein the identification step includes comparing coordinate magnitudes within a subset to generate a magnitude of the LLR.