Multilevel Coded Modulation for Unequal Error Protection and Multistage Decoding | Part II: Asymmetric Constellations

In this paper, multilevel coded asymmetric modulation with multistage decoding and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings with asymmetric constellations are more promising than traditional (Ungerboeck-type) partitionings, to achieve unequal error protection capabilities with multilevel coding and multistage decoding. Three types of unconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM constellations over the AWGN channel to introduce design guidelines. Generalizations to other PSK and This work was supported in part by TAO (Telecommunications Advancement Organization of Japan) International Collaborative Research Grant No. 8048, the National Science Foundation under Grant No. CCR-97-32959, and by LSI Logic Corp. This paper was presented in part at IEEE International Symposium on Information Theory (ISIT98), Cambridge, MA, August 1998, and at IEEE Global Telecommunications Conference (GLOBECOM98), Sydney, Australia, November 1998. QAM type constellations follow the same lines. Upper bounds on the bit error probability based on union bound arguments are rst derived. In some cases, these bounds become loose due to the large overlappings of decision regions associated with asymmetric constellations and unconventional partitionings. To overcome this problem, simpler and tighter approximated bounds are derived. Based on these bounds, it is shown that additional re nements can be achieved in the construction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations.