Space-time codes and protocols for point-to-point and multi-hop wireless communications

The presence of random fading in wireless channels constitutes one of the most challenging problems for achieving reliable digital communications. At the same time, fading also offers opportunities for improved performance via multi-dimensional communications, also known as multiple-input/multiple-output (MIMO) signaling. Given the ever increasing demand for high data rate in real-time applications involving transmission of voice, data and multimedia content, modern communication networks need be properly designed in order to fully extract the potential gains offered by MIMO schemes. In point-to-point communications, the use of multiple antennas at the transmitter and/or receiver constitutes one of the standard approaches to MIMO signaling, through the use of Space-Time Codes. Such codes enable dramatic performance improvement over single-antenna systems.; More recently, techniques for multi-hop distributed communications have also attracted considerable interest. An application where multi-hopping is necessary, for example, are the so called ad-hoc and sensor networks and the 802.16j (Multi-hop Relay) standard currently under development. Theoretical results have shown that, besides the power savings achieved by communicating over shorter distances, distributed communication can also achieve a significant portion of the MIMO gains via cooperation between terminals.; This thesis discusses new approaches for performance analysis of Space-Time Block Codes (STBCs). For point-to-point communication, besides yielding significantly tighter performance criteria in terms of the error-rate characterization, the new bounds are also used to design better codes. For multi-hop communication, cooperative distributed protocols based on distributed STBCs (DSTBCs) are proposed and analyzed; upper and lower bounds on the performance are also developed for this scenario, and the diversity gain is characterized for several multi-hop communication strategies. The impact of asynchronous communication across the terminals on the performance is also investigated. Techniques for cooperative communication in the presence of multipath and intersymbol interference (ISI) environments are also proposed and investigated. In particular, time reversal DSTBCs (TR-STBCs) are considered. Due to the orthogonal properties of the code, it is shown that maximum likelihood detection can be performed at the receiver with a standard scalar Viterbi-type detector. Experimental results of the proposed scheme are reported and confirm the potential gains predicted in the analysis. Finally, the achievable rates of several half-duplex cooperation strategies are investigated. Upper and lower bounds on the achievable outage mutual information (OMI), outage probability and throughput are developed. Interestingly, it is shown that multi-hop communication is not always superior to single-hop communication from an achievable rate perspective; while at low transmit energy multi-hop transmission is superior, at high energy it appears that the opposite is true.