The authors use binary linear UEP (LUEP) codes, in combination with a QPSK signal set and Gray mapping, to obtain new efficient block QPSK modulation codes with unequal minimum squared Euclidean distances. They give several examples of codes that have the same minimum squared Euclidean distance as the best QPSK modulation codes of the same rate and length. A new suboptimal two-stage soft-decision decoding is applied to LUEP QPSK modulation codes.
Robert H. Morelos-Zaragoza and Shu Lin. "Unequal Error Protection QPSK Modulation Codes" Faculty Publications (1992): 1121-1125. https://doi.org/10.1109/ICCS.1992.255087