Analysis of Demmapping for Hierarchical 16QAM

A hierarchical modulation scheme is presented to upgrade an existing digital broadcast system by adding more data stream in its transmissions. The hierarchical modulation is composed of a basic constellation, which is the same as in the original system, and a secondary constellation, which carries the additional data for the upgraded system. The upgraded system with the hierarchical modulation is backward compatible (BC mode) in the sense that receivers that have been deployed in the original system can continue receiving data in the basic constellation. Hierarchical receivers can be designed to receive data carried in the secondary constellation, as well as those in the basic constellation. Two independent streams can be detected by applying to LLR (log likelihood ratio) but in this paper we propose the robust demapping algorithm with same performance of LLR