Space-time block codes for wireless systems: Construction, performance analysis, and trellis coded modulation

Space-time codes are effective means by which to combat fading by exploiting diversity in both spatial and temporal dimensions. In this work, code performance and design are considered in the context of Direct-Sequence Code-Division Multiple-Access (DS-CDMA) systems. The performance criteria, diversity gain and coding gain, are redefined as functions of the spreading code correlation. Uplink and downlink scenarios are both analyzed in multipath fading channels. Optimal codes are searched for both spread and non-spread systems. To reduce the decoding complexity, suboptimal linear decoders are classified and analyzed. The asymptotic achievable diversity level is derived when the number of receive antennae is large. Motivated by the structures found in computer optimized codes, via distance preserving isometries, Space-Time Block Codes (STBCs) are constructed bottom-up by optimizing the coding gain layer-by-layer and reusing the optimized structure. STBCs constructed in this way are dubbed Nonlinear Hierarchical Codes (NHCs). NHCs are essentially a generalization of Slepian's group codes for the Gaussian channel to the multiple-input multiple-output quasi-static fading channel. NHCs consistently offer comparable or significantly better performance than constrained designs (orthogonal or unitary). Systematic Regular MTCM (RMTCM) design procedures are proposed to exploit the layered structure of NHCs which leads to optimized designs for various rates/block sizes/constellation sizes. The match between the distance spectrum of NHCs to the regular trellis structure optimizes coding gain directly, and full diversity is naturally maintained given the full rank of the constituent NHCs. Several factors which affect performance in both quasi-static and fast block fading channels are analyzed and exploited to improve the overall performance. Set expansion is used to improve high rate RMTCM designs. RMTCM offers the best tradeoff between performance and complexity among STTC and (interleaved) serial concatenated system.