  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.
