Multilevel coded modulation for unequal error protection and multistage decoding - Part II: Asymmetric constellations

In this paper, multilevel coded asymmetric modulation with multistage decod ing and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings are more pr omising than traditional (Ungerboeck-type) partitionings, to achieve UEP ca pabilities with multilevel coding and multistage decoding. Three types of u nconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM co nstellations over the additive white Gaussian noise channel to introduce de sign guidelines. Generalizations to other PSK and QAM type constellations f ollow the same lines. Upper bounds on the bit-error probability based on un ion bound arguments are first derived. In some cases, these bounds become l oose due to the large overlappings of decision regions associated with asym metric constellations and unconventional partitionings. To overcome this pr oblem, simpler and tighter approximated bounds are derived. Based on these hounds, it is shown that additional refinements can be achieved in the cons truction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations.