A 32QAM Super-Quasi-Orthogonal Space-Time Trellis Code for Four Transmit Antennas

Abstract

We demonstrate a super-quasi-orthogonal space- time (ST) trellis code for four transmit antennas with rectangular signal constellations for wireless communications with a spectral efficiency of 5bits/s/Hz, thus larger than only 4 bits/s/Hz as shown in our previous conference paper. Considering a mobile wireless communications system with four transmit antennas, we form an 8D signal constellation as Cartesian product of four 2D rectangular signal sets, an 8D point being transmitted by the first antenna as four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted by the other three antennas are not independent, but so chosen as to form, together with the symbols transmitted by the first antenna, the entries of a 4times4 quasi-orthogonal matrix. The union of two sets of quasi-orthogonal matrices forms a super-quasi-orthogonal signal set. With 4x4 quasi-orthogonal matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The frame error rate (FER) and the bit error rate (BER) performance results show an excellent behavior of our proposed super-quasi-orthogonal ST trellis codes.