A 16QAM super-orthogonal space-frequency code for broadband mobile communication systems with two transmit antennas

We combine our previously designed 32-state super-orthogonal space-time trellis code (SOSTTC) with orthogonal frequency division multiplexing (OFDM) to build a broadband mobile communication system having a spectral efficiency that amounts to 4 bits/s/Hz depending on the length of the cyclic prefix used to avoid interframe interference. The transmitter is equipped with two antennas, where the OFDM frames they transmit are not independent, as they carry the same information in an orthogonal form. The 2N OFDM tones are grouped in N pairs of tones. Each group of two tones transmits the entries of a 2×2 orthogonal matrix. In our case, the entries are symbols taken from the rectangular 16-point quadrature-amplitude modulation (QAM) signal constellation. At the receiver end, each OFDM aggregate frame transmitted by both transmit antennas is independently decoded using the Viterbi algorithm. We perform system simulations using a frequency-selective multiple-input multiple-output (MIMO) fading channel model. We also study the effect of the antenna spacing at the base station (BS) and the mobile station (MS). We have determined the antenna spacing ranges that are very helpful for designing antenna arrays.