| Space-time coding is an effective approach to improve the reliability of data transmission as well as the data rates over multiple-input multiple-output (MIMO) fading wireless channels. In this thesis, space-time code designs are investigated with a view to address practical concerns such as decoding complexity and channel impairments.; We study low-decoding complexity space-time block codes (STBC), a popular subclass of space-time codes, for quasi-static frequency-flat fading MIMO channels. Therefore, the space-time code matrices are designed to allow the separation of transmitted symbols into groups for decoding; we call these codes multi-group decodable STBC. A new multi-group decodable STBC, called orthogonality-embedded space-time (OEST) codes, is then proposed. The equivalent channel, general decoder, and maximum mutual information of OEST codes are presented. The following contributions, based on OEST codes, are made: (1) It is shown that OEST codes subsume existing orthogonal, quasi-orthogonal, and circulant STBC. Therefore, the results of OEST codes can be readily applied to these codes. (2) New STBC, called semi-orthogonal algebraic space-time (SAST) codes, are derived from OEST codes. SAST codes are rate-one, full-diversity, four-group decodable, delay-optimal for even number of antennas. SAST codes nearly achieve the capacity of multiple-input single-output channels. (3) The framework of OEST codes is applied to the existing single-symbol decodable codes, like minimum decoding complexity quasi-orthogonal STBC (MDC-QSTBC) and coordinate-interleaved orthogonal designs, and 4-group quasi-orthogonal STBC. Several open problems of these codes are solved, including equivalent channel, general decoder, symbol error rate performance analysis, and optimal signal rotations. Additionally, MDC-QSTBC are shown to achieve full diversity using antenna selection with limited feedback.; We also consider the designs of space-time codes for MIMO systems, using orthogonal frequency division multiplexing (OFDM) for frequency-selective fading channels. The resulting codes are called space-frequency codes. The OFDM system performance is heavily affected by inter-carrier interference, which is caused by frequency offset between the carrier oscillators of the transmitter and receiver. We analytically quantify the performance loss of space-frequency codes clue to frequency offset. A new class space-frequency codes, called inter-carrier interference self-cancellation space-frequency (ISC-SF) codes, is proposed to effectively mitigate the effect of frequency offset. |
