New full-diversity high-rate space-time block codes based on selective power scaling

We design a new rate-5/4 full-diversity orthogonal STBC for QPSK and 2 transmit antennas by enlarging the signalling set from the set of quaternions used in the Alamouti [1] code. Selective power scaling of information symbols is used to guarantee full-diversity while maximizing the coding gain and minimizing the transmitted signal peak-to-minimum power ratio. The optimum power scaling factor is derived using two equivalent criteria and shown to outperform schemes based on only constellation rotation while still enjoying a low-complexity ML decoding algorithm. Extensions to the case of 4 transmit antennas are reported in [4].