| Teletar, Foschini and Gans showed that there is a huge potential capacity of multi-antenna systems. To approach the potential huge capacity, new codes and modulations, which are called space-time codes, have attracted much attention lately. One attractive approach is to construct space-time block codes (STBC) from orthogonal designs proposed by Alamouti, Tarokh, Jafarkhani and Calderbank. These codes achieve full diversity and have fast maximum-likelihood (ML) decoding.; In this dissertation, we first provide a tutorial review of STBC from complex orthogonal designs (COD), in particularly, the Hurwitz theorem on COD and its realizations. We then present a simple and intuitive interpretation of the realization. We show that for some special COD without linear processing, the symbol transmission rate can not be greater than 3/4 for more than two transmit antennas. Furthermore, we construct two STBC with symbol transmission rates 7/11 and 3/5 from COD for five and six transmit antennas, respectively.; In the second part of the dissertation, we focus on STBC from quasi-orthogonal designs. Recently, Jafarkhani, Tirkkonen, Boariu and Hottinen proposed quasi-orthogonal STBC, where the orthogonality is relaxed to provide higher rate. These codes still have fast ML decoding, but do not have full diversity. Based on these codes, we introduce a new modulation scheme by properly choosing the signal constellations. In particular, we propose that half of the symbols in a quasi-orthogonal design are from a signal constellation set and another half of them are from the rotated constellation . The resulting STBC may have both full diversity and fast ML decoding. We also obtain some upper bounds for the diversity product. We show that the optimal rotation angles for signal constellations from a square lattice and a lattice of equilateral triangles are π/4 and π/6, respectively. |
