Exploiting algebraic structure in space-time coding for broadband wireless access

In wireless mobile radio communication, there is an endless quest for increased capacity and improved quality through available limited bandwidths. In recent years, communication engineers around the world have been working relentlessly to offer a mobile alternative to wired access networks, such as fibre optic and digital subscriber line (DSL) links. In this endeavor to provide high information rate with reliability, space-time block codes (STBC), an elegant yet simple class of Multiple Input Multiple Output (MIMO) systems for wireless communications have opened new and exciting opportunities for research. The IEEE 802.16 family of standards and its associated industry consortium, WiMAX, has adopted STBC as an enabling technology to deliver the promised broadband connectivity with a data rate up to 75 Mbps over a 20 MHz bandwidth and a coverage range up to 30 miles.; In this dissertation, we first present a novel full-rate full-diversity orthogonal STBC for 4 transmit antennas based on quaternionic algebra. The code does not result in constellation expansion for PSK modulation. The quaternionic structure of the code is exploited to reduce the complexity of maximum likelihood (ML) coherent decoding from a size-256 search to a size-16 search for QPSK modulation. Simulation results in a WiMAX 802.16 broadband wireless access environment demonstrate that the proposed code increases the cell coverage area by 1.5 and 2.6 folds compared to single-antenna transmission.; Rate and diversity impose a fundamental trade-off in space-time coding. In this dissertation, we also propose a different point of view where we design novel high-rate (> 1) space-time codes that have a high-diversity code embedded within them. This allows a form of communication where the high-rate code opportunistically takes advantage of good channel realizations whereas the embedded high-diversity code ensures that at least part of the information is received reliably. Finally, we design a new rate- 54 full-diversity orthogonal STBC for QPSK and 2 transmit antennas by enlarging the signalling set from the set of quaternions. Selective optimum power scaling of information symbols is used to guarantee full-diversity while maximizing the coding gain and minimizing the transmitted signal peak-to-minimum power ratio. We also extend our designs to the case of 4 TX by enlarging the set of Quasi-Orthogonal STBC with power scaling.