Application of Opportunistic Bit to Multilevel Codes

In this paper, we propose a new signal organization method to work in the structure of the multi level coding (MLC). The transmit bits are divided into opportunistic bit (OB) and conventional bit (CB), which are mapped to the lower level- and higher level signal in parallel to the MLC, respectively. Because the OB's mapping does not require signal power explicitly, the energy of the CB modulated symbol can be doubled. As the result, the overall mutual information of the proposed method is found higher than that of the conventional BPSK in one dimensional case. Moreover, the extension of the method to the two-complex-dimension shows the better performance over the QPSK. The numerical results confirm this approach.