Space-time coding schemes for wireless communications over flat fading channels

The increasing demand for higher data rates and higher quality in wireless communications has motivated the use of multiple antenna elements at both the transmitter and the receiver sides in a wireless link. The problem discussed in our research is the development of fundamental space-time (ST) coding and modulation methods to achieve the gains provided by multiple antennas, in terms of both improved robustness of the link and a higher spectral efficiency. We focus on a point-to-point wireless environment, in which the channel is modeled as flat fading, and channel knowledge is not available at the transmitter. Several new and improved schemes tailored for different applications are proposed.; We first consider the design of ST trellis codes that reduce the probability of error without loss of spectral efficiency. It is found that the typical assumption of high signal-to-noise ratio (SNR) and, consequently, traditional design criteria are invalid in certain situations. Analyzing pair-wise error probability, we derive two sets of tighter design criteria for low and moderate SNR regions, respectively. New ST trellis codes optimized for moderate SNR are provided via a computer search. To avoid the prohibitively high complexity of searching for good codes with a larger number of transmit antennas and higher-level modulation, we introduce a novel systematic code construction method, diagonal block ST coding. This two-step approach demonstrates promising results at the commonly assumed high SNR.; We then conduct an intensive study into generalized layered ST architecture that allows a tradeoff between error probability and spectral efficiency. Our goal is to enhance the tradeoff by further reducing the error probability. Techniques with no or little increase in receiver complexity, such as optimal power allocation and optimal decoding order, are introduced. A hard-decision iterative decoding algorithm that significantly enhances the system performance is also proposed.; Finally, we consider the design of ST techniques that avoid channel estimation at the receiver, but with minimal loss in error performance. A new differential ST modulation scheme based on orthogonal ST block codes with square codeword matrices is introduced. The important difference from previous differential ST modulation schemes is the use of multiple amplitudes. This makes our scheme more power efficient. We then introduce a joint design of channel coding and general differential ST modulation, called trellis-coded differential unitary space-time modulation. Several examples that offer a good tradeoff between the coding advantage and trellis complexity are presented.