Multiple-symbol differential space-time OFDM over frequency-selective channels

Unlike most differential space-time (DST) block coding methods, which use phase shift keying (PSK) constellations, we propose a scheme utilizing quadrature amplitude modulation (QAM) signals, which can provide better spectral and power efficiencies. Meanwhile, we extend the number of symbol observation intervals (SOI) from two to three, and thus better performance is obtained. Due to the increasing complexity caused by the larger SOI, we also provide a sub-optimal maximum likelihood (ML) approach by decomposing the dimension of the QAM constellations. The proposed method uses orthogonal frequency division multiplexing (OFDM) to transform a frequency-selective channel into multiple flat fading sub-channels, along which the DST coding is applied.