Full-Rate Orthogonal Space-Time Block Code With Pulse-Shaped Offset QAM for Four Transmit Antennas

In this paper, we show, in both theory and simulation, that by transmitting two real orthogonal space-time block codes (O-STBC) on the I- and Q-channels with pulse-shaped offset QAM, we are able to achieve full rate transmit diversity for a 4 times 1 system with very simple "half-symbol" detection, i.e., the real I- and Q-symbols can be separately decoded. For this scheme, two families of pulse shapes of the offset QAM signal are considered: i) pulse shapes with zero inter-symbol interference (ISI) and ii) pulse shapes with controlled ISI between the I- and Q-channels. In the zero ISI case, the half-symbol decoding is optimum in the maximum likelihood sense and the system is able to achieve full transmit diversity. The associated bit error probability (BEP) performance is better than that of conventional full-rate, full-diversity quasi-orthogonal space-time block codes (QO-STBC), as well as rate-1/2 and rate-3/4 complex O-STBCs. To achieve good spectral confinement while maintaining decoding simplicity, we investigate pulse shape design techniques so that some performance gains can be traded off by introducing a controlled small amount of ISI at the sampling instants. We also extend the analysis to a 4 times 4 multiple-input multiple-output (MIMO) system, and derive the design criteria on how to construct the two real O-STBCs in order to minimize the performance degradation caused by the controlled ISI