Differential space time block codes using QAM constellations

The propose differential space time block codes (STBC) using quadrature amplitude modulation (QAM), which can not be utilized in the conventional differential STBC. Since QAM constellations have a larger minimum distance compared with phase shift keying (PSK), the proposed method has the advantage of SNR gain compared with conventional differential STBC. The QAM signals are encoded in a manner similar to that of conventional differential STBCs. To decode QAM signals, the signals received are normalized by the channel power estimated forgoing training symbols, and then decoded with a conventional QAM decoder. When the transmission rate is more than 3 bits/channel use in time varying channels, the simulation results demonstrate that the proposed method with the channel power estimation outperforms the conventional differential STBC.