Abstract: A coded modulation scheme for concatenated simple parity-check (SPC) codes and QAM modulation is studied. By analyzing the approximate union bound on SPC codes considered QAM modulation, it is shown that in order to improve BER performance, the Euclidean distance of the parity-check bits should be enlarged. On the contrary, that of the information bits should be decreased. Finally, the optimum Euclidean distance distribution between the parity-check bits and the information bits is obtained by computing the approximate union bound. And simulation results show that after optimizing, some codes have an about 2dB BER performance gain at the high SNR region compared with the traditional scheme.

Key words: Concatenated SPC code, QAM, coded modulation, union bound