23 research outputs found

    Direct Antenna Modulation using Frequency Selective Surfaces

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    In the coming years, the number of connected wireless devices will increase dramatically, expanding the Internet of Things (IoT). It is likely that much of this capacity will come from network densification. However, base stations are inefficient and expensive, particularly the downlink transmitters. The main cause of this is the power amplifier (PA), which must amplify complex signals, so are expensive and often only 30% efficient. As such, the cost of densifying cellular networks is high. This thesis aims to overcome this problem through codesign of a low complexity, energy efficient transmitter through electromagnetic design; and a waveform which leverages the advantages and mitigates the disadvantages of the new technology, while being suitable for supporting IoT devices. Direct Antenna Modulation (DAM) is a low complexity transmitter architecture, where modulation occurs at the antenna at transmit power. This means a non-linear PA can efficiently amplify the carrier wave without added distortion. Frequency Selective Surfaces (FSS) are presented here as potential phase modulators for DAM transmitters. The theory of operation is discussed, and a prototype DAM for QPSK modulation is simulated, designed and tested. Next, the design process for a continuous phase modulating antenna is explored. Simulations and measurement are used to fully characterise a prototype, and it is implemented in a line-of-sight end-to-end communications system, demonstrating BPSK, QPSK and 8-PSK. Due to the favourable effects of spread spectrum signalling on FSS DAM performance, Cyclic Prefix Direct Sequence Spread Spectrum (CPDSSS) is developed. Conventional spreading techniques are extended using a cyclic prefix, making multipath interference entirely defined by the periodic autocorrelation of the sequence used. This is demonstrated analytically, through simulation and with experiments. Finally, CPDSSS is implemented using FSS DAM, demonstrating the potential of this new low cost, low complexity transmitter with CPDSSS as a scalable solution to IoT connectivity

    A guide to the methodology

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    Corpora are widely used in linguistics, but not always wisely. This book attempts to frame corpus linguistics systematically as a variant of the observational method. The first part introduces the reader to the general methodological discussions surrounding corpus data as well as the practice of doing corpus linguistics, including issues such as the scientific research cycle, research design, extraction of corpus data and statistical evaluation. The second part consists of a number of case studies from the main areas of corpus linguistics (lexical associations, morphology, grammar, text and metaphor), surveying the range of issues studied in corpus linguistics while at the same time showing how they fit into the methodology outlined in the first part

    Corpus linguistics: A guide to the methodology

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    Corpora are widely used in linguistics, but not always wisely. This book attempts to frame corpus linguistics systematically as a variant of the observational method. The first part introduces the reader to the general methodological discussions surrounding corpus data as well as the practice of doing corpus linguistics, including issues such as the scientific research cycle, research design, extraction of corpus data and statistical evaluation. The second part consists of a number of case studies from the main areas of corpus linguistics (lexical associations, morphology, grammar, text and metaphor), surveying the range of issues studied in corpus linguistics while at the same time showing how they fit into the methodology outlined in the first part

    Corpus linguistics: A guide to the methodology

    Get PDF
    Corpora are widely used in linguistics, but not always wisely. This book attempts to frame corpus linguistics systematically as a variant of the observational method. The first part introduces the reader to the general methodological discussions surrounding corpus data as well as the practice of doing corpus linguistics, including issues such as the scientific research cycle, research design, extraction of corpus data and statistical evaluation. The second part consists of a number of case studies from the main areas of corpus linguistics (lexical associations, morphology, grammar, text and metaphor), surveying the range of issues studied in corpus linguistics while at the same time showing how they fit into the methodology outlined in the first part

    Corpus linguistics: A guide to the methodology

    Get PDF
    Corpora are widely used in linguistics, but not always wisely. This book attempts to frame corpus linguistics systematically as a variant of the observational method. The first part introduces the reader to the general methodological discussions surrounding corpus data as well as the practice of doing corpus linguistics, including issues such as the scientific research cycle, research design, extraction of corpus data and statistical evaluation. The second part consists of a number of case studies from the main areas of corpus linguistics (lexical associations, morphology, grammar, text and metaphor), surveying the range of issues studied in corpus linguistics while at the same time showing how they fit into the methodology outlined in the first part

    Corpus linguistics: A guide to the methodology

    Get PDF
    Corpora are widely used in linguistics, but not always wisely. This book attempts to frame corpus linguistics systematically as a variant of the observational method. The first part introduces the reader to the general methodological discussions surrounding corpus data as well as the practice of doing corpus linguistics, including issues such as the scientific research cycle, research design, extraction of corpus data and statistical evaluation. The second part consists of a number of case studies from the main areas of corpus linguistics (lexical associations, morphology, grammar, text and metaphor), surveying the range of issues studied in corpus linguistics while at the same time showing how they fit into the methodology outlined in the first part
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