The last few years witnessed a dramatic increase in the demand on high-rate reliable wireless communications. In order to meet these new requirements, resorting to Multiple-Input Multiple-Output (MIMO) techniques was inevitable as they may offer high-rate reliable wireless communications without any additional bandwidth. In the case where the transmitter does not have any prior knowledge about the channel state information, space-time coding techniques have proved to efficiently exploit the MIMO channel degrees of freedom while taking advantage of the maximum diversity gain. On the other hand, the ML decoding complexity of Space-Time Codes (STCs) generally increases exponentially with the rate which imposes an important challenge to their incorporation in recent communications standards. Recognizing the importance of the low-complexity criterion in the STC design for practical considerations, this thesis focuses on the design of new low-complexity Space-Time Block Codes (STBCs) where the transmitted code matrix can be expressed as a weighted linear combination of information symbols and we propose new codes that are decoded with a lower complexity than that of their rivals in the literature while providing better or slightly lower performance.
