Automatic Repeat-reQuest (ARQ) schemes are extensively used in communication systems and computer networks to achieve reliable transmission. Using space-time codes (STCs) with multiple input multiple output (MIMO) or multiple input single output (MISO) systems is an effective way to combat multipath fading, which is the most severe impairment for wireless communication systems. STCs are designed to use the rich scattering multipath environment provided by using multiple transmit antennas. The work done in this thesis focuses on the use of ARQ schemes with non-orthogonal space-time block codes (NOSTBCs) based on Reed Solomon codes. The truncated-selective ARQ (TS-ARQ) scheme is considered and three novel hybrid ARQ (HARQ) schemes are proposed. Simulation results reveal that, compared to using TS-ARQ with orthogonal space-time block codes (OSTBCs), using NOSTBCs with any of the three proposed HARQ schemes can provide significant gains in terms of dropped packet rate and spectral efficiency at the cost of increased decoding complexity. The performance can be further improved by using the water filling principle to adaptively allocate transmit power among transmit antennas.

No description available.

No description available.

No description available.

No description available.

Evidentials are expressions used to indicate the source of evidence and strength of speaker commitment to information conveyed. They include sentence adverbials such as 'obviously', parenthetical constructions such as 'I think', and hearsay expressions such as 'allegedly'. This thesis argues against the speech-act and Gricean accounts of evidentials and defends a Relevance-theoretic account Chapter 1 surveys general linguistic work on evidentials, with particular reference to their semantic and pragmatic status, and raises the following issues: for linguistically encoded evidentials, are they truth-conditional or non-truth-conditional, and do they contribute to explicit or implicit communication. For pragmatically inferred evidentials, is there a pragmatic framework in which they can be adequately accounted for? Chapters 2-4 survey the three main semantic/pragmatic frameworks for the study of evidentials. Chapter 2 argues that speech-act theory fails to give an adequate account of pragmatic inference processes. Chapter 3 argues that while Grice's theory of meaning and communication addresses all the central issues raised in the first chapter, evidentials fall outside Grice's basic categories of meaning and communication. Chapter 4 outlines the assumptions of Relevance Theory that bear on the study of evidentials. I sketch an account of pragmatically inferred evidentials, and introduce three central distinctions: between explicit and implicit communication, truth-conditional and non-truth-conditional meaning, and conceptual and procedural meaning. These distinctions are applied to a variety of linguistically encoded evidentials in chapters 5-7. Chapter 5 deals with sentence adverbials, chapter 6 focuses on parenthetical constructions, and chapter 7 looks at hearsay particles. My main concern is with how these expressions pattern with respect to the three distinctions developed in chapter 4. 1 show that although all three types of expression contribute to explicit rather than implicit communication, they exhibit important differences with respect to both the truth conditional/ non-truth-conditional and the conceptual/procedural distinctions. Chapter 8 is a brief conclusion.

Frequency scaling in traditional computing systems has hit the power wall and multicore computing is here to stay. Unlike homogeneous multicores which have uniform architecture and instruction set across cores, heterogenous multicores have differentially capable cores to provide optimal performance for specialized functionality. However, this heterogeneity also translates into difficult programming models, and extracting its potential is not trivial. The Cell Broadband Engine by the Sony Toshiba IBM(STI) consortium was amongst the first heterogenous multicore systems with a single Power Processing Unit(PPU) and 8 Synergistic Processor Units (SPUs). We address the issue of porting an existing sequential C/C++ codebase on to the Cell BE through compiler driven program analysis and profiling. Until parallel programming models evolve, the "interim" solution to performance involves speeding up legacy code by offloading computationally intense parts of a sequential thread to the co-processor; thus using it as an accelerator. Unique architectural characteristics of an accelerator makes this problem quite challenging. On the Cell, these characteristics include limited local store of the SPU, high latency of data transfer between PPU and SPU, lack of branch prediction unit, limited SIMDizability, expensive scalar code etc. In particular, the designers of the Cell have opted for software controlled memory on its SPUs to reduce power consumption and to give programmers more control over the predictability of latency. The lack of a hardware cache on the SPU can create performance bottlenecks because any data that needs to be brought in to the SPU must be brought in using a DMA call. The need for supporting a software controlled cache is thus evident for irregular memory accesses on the SPU. For such a cache to result in improved performance, the amount of time spent in book-keeping and tracking at run-time should be minimal. Traditional algorithms like LRU, when implemented in software incur overheads on every cache hit because appropriate data structures need to be updated. Such overheads are on off critical path for traditional hardware cache but on the critical path for a software controlled cache. Thus there is a need for better management of "data movement" for the code that is offloaded on to the SPU. This thesis addresses the "code partitioning" problem as well as the "data movement" problem. We present GLIMPSES - a compiler driven profiling tool that analyzes existing C/C++ code for its suitability for porting to the Cell, and presents its results in an interactive visualizer. Software Controlled Cache - an improved eviction policy that exploits information gleaned from memory traces generated through offline profiling. The trace is analyzed to provide guidance for a run-time state machine within the cache manager; resulting in reduced run-time overhead and better performance. The design tradeoffs and several pros and cons of this approach are brought forth as well. It is shown that with just about the right amount of runtime book-keeping and decision making, one can get to the difficult solution space of the right balance to achieve high performance.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 214-215) / Microfiche. / xv, 215 leaves, bound ill. 29 cm

The main focus of this thesis is the investigation of a number of different space-time coding scenarios based on predominately the application of turbo codes and low density parity check (LDPC) codes to a multi-antenna system. Both codes structures make use of the BPSK stacking construction that readily applies binary linear codes to the space-time channel while also providing a check on the suitability of the resulting code in order to achieve maximum diversity advantage. The turbo-like codes investigated are based upon the application of a parallel concatenated scheme to directly map the data and parity bits generated by the encoder to one of three possible antennas outputs. It is further highlighted in this case how the interleaver plays a crucial role in determining overall performance as this determines whether the resulting space-time codes achieve maximum diversity advantage or otherwise. Performance results are presented for a number of different constituent codes and interleaver design. The LDPC space-time codes considered herein again are based on satisfying the BPSK stacking construction to ensure full diversity advantage is achieved. The code design is based on a recursive application of the Shur complement in order to devise block based codes that have a resulting parity check matrix that is relatively sparse. A number of various code constructions that satisfy the conditions are then simulated in order to determine performance in both slow and fast fading channel conditions. This thesis also investigates the use of certain non-linear codes termed “chaotic codes” and their application as constituent codes within a parallel concatenated (turbo-like) coding scheme. Performance of such codes is shown to be readily analysed via the use extrinsic information transfer (EXIT) techniques. The modified codes are simulated over an AWGN channel using BPSK modulation for a number of different block lengths. / Thesis (PhDTelecommunications)--University of South Australia, 2006.

Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 38-40)