Multilevel block coded modulation (BCM) schemes with unequal error protection (UEP) are investigated. These schemes are based on unconventional set partitions that greatly reduce the error coefficients associated with multi-stage decoding of conventional BCM, at the expense of smaller intra-set distances.
Morelos-Zaragoza, Robert H.; Fossorier, Marc P. C.; Lin, Shu; and Imai, Hideki, "Multilevel Block Coded Modulation with Unequal Error Protection" (1997). Faculty Publications. Paper 12.