Differential space time block codes using QAM constellations

Chan-Soo Hwang, Seung Hoon Nam, Jaehak Chung, Vahid Tarokh

Abstract: 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.