Improved space-time codes for wireless communications /

The rapid growth of demand for wireless communications has called for an effective usage of the scarce spectrum of radio frequencies. The capacity and performance of a wireless link can be greatly improved by utilizing multiple transmit/receive antennas. This dissertation presents a new view of performance analysis and improved code designs for this diversity strategy. Firstly, we develop a new view of performance analysis for diversity schemes in Rayleigh fading channels. The PWEP is found to be a Function of the eigenvalues of a certain signal-only matrix which is formed by codeword difference and the covariance matrix of channel. The exact computation of the PWEP often requires evaluating a multi-order derivative of a complicated rational function when poles of the signal matrix are repeated. For the moderate multiplicity case, we present a simple tech­ nique to approximate the PWEP. In addition, a new simple bound is proposed which is asymptotically tighter than the standard Chemoff bound and converges to the true probability at high SNR. Secondly, we propose a new class of improved high-rate space-time codes for slow fading channels based on the concatenated expanded STBC-MTCM construction which significantly outperform other existing designs of similar complexity. Unlike the conventional STBC-MTCM designs, the proposed construction yields a high-rate space-time code by expanding the cardinality of STBC before concatenating it with ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. an outer MTCM encoder. A simple design rule is imposed on the MTCM encoder to guarantee full diversity advantage. The proposed codes considerably outperform the easting designs. For example, the proposed 4-state 2-bits/symbol QPSK STBCMTCM code for the 2-transmit antenna case already outperforms the pioneering 32state ST-TCM design. Moreover, decoding complexity of the proposed STBC-MTCM constructions is made practically low by exploiting signal orthogonality. Thirdly, we propose a provably robust space-time coding scheme which achieves good performance in a wide range of correlated fading conditions. The proposed robust design requires no feedback of channel state information or statistics to the encoder. The key to achieve robust performance is to formulate code design criteria that are not channel-dependent. A coding structure that enables this idea of channelindependent design criteria is formulated by concatenating a full-rank STBC with an outer encoder.