25 research outputs found

    Адаптивная идентификация и интерпретация результатов газогидродинамических исследований скважин

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    Настоящая научно-квалификационная работа посвящена актуальной задаче разработки и исследованию новых моделей и алгоритмов адаптивной идентификации газогидродинамических параметров, позволяющих в процессе проведения газогидродинамических исследований скважин (ГГДИС) в промысловых условиях определять параметры газовых пластов и время завершения испытаний скважин.This scientific and qualification work is devoted to the urgent task of developing and researching new models and algorithms for the adaptive identification of gas-hydrodynamic parameters that allow the process of conducting gas hydrodynamic studies of wells (GGDIS) in field conditions to determine the parameters of gas reservoirs and the time for completion of well tests

    Design Method for Wideband Circularly Polarized Slot Antennas

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    A compact ultrawideband (UWB) circularly polarized (CP) slot antenna is proposed with a methodology for automated reoptimization for packaging with proprietary devices. The slot structure employs a dual-feed with an integrated compact UWB phase shifter. The design process involves an advanced optimization algorithm and demonstrates the use of spline curves for generation of CP signals. These allow easy optimization, while preserving phase coherency across a wideband. The prototyped antennahas a CP bandwidth of 54% (from 3.2 to 6.1 GHz)

    Footwear-Centric Body Area Network with Directional UWB Antenna

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    A footwear-centric body area network employing a directional antenna is compared with waist-centric systems using omnidirectional and directional antennas. The impact of body movements on path gain is analysed for two bands at 3.99 GHz and 7.99 GHz. The path gain and data rate results demonstrate that footwear-centric configurations are equivalent or better than waist-centric body area networks

    Impact of the wireless channels on the performance of ultrawideband communication systems

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    Ultrawideband (UWB) wireless systems employ signals with bandwidths in excess of 500 MHz or with relative bandwidth more than 20%. The radiated signals have low power spectral density. A decade ago, UWB wireless systems were deemed to be the technology that will deliver 'Gigabit-wireless' for short range communications. However, the performance of current systems is significantly below the initial expectations. This thesis explores the UWB wireless channel and shows how its properties limit the performance of current UWB systems. Furthermore, it is shown that if the knowledge of the channel is fully exploited a significant performance improvement of UWB systems can be achieved. The thesis begins with exploration of the channel properties. Unlike previous work, that has investigated either the 'classical narrowband' channel with bandwidth 1 GHz, this work studies the transition between the narrowband channels with bandwidth of 1 MHz to the extremely wide band channels with bandwidths of up to 10 GHz. The thesis concludes that for signals with bandwidth 100 MHz has properties 'like UWB channels' with bandwidths in the GHz range. Additionally, the thesis suggests a correction to the IEEE802.15.4a model for channel impulse response because as will be shown in the thesis many multi paths in the model are manifes- tations of the antenna impulse response. Hence multiple multipaths in the IEEE802.15.4a model actually represent a single multipath component. This reduces the number of multipath components in the model by approximately factor of five. The understanding of the transition between narrowband and ultrawideband channel is used to improve the spectral efficiency of impulse radio systems which traditionally use signals with bandwidth> 1 GHz. It is shown that the optimum signal bandwidth for impulse radio systems is in the range 150-450 MHz. Such systems balance the robustness against frequency selective fading with the reduction of duty cycle. Hence, the data-rate of impulse radio systems can be significantly improved. The frequency selective fading is shown to be the main limiting factor for the performance of the commercial UWB WiMedia systems with OFDM. It is shown that adaptive loading of OFDM sub carriers , which is compatible with the frequency selectivity of the channel, is more suitable for UWB OFDM systems than the use of strong Forward-Error-Correction measures. The introduction of the adaptive OFDM is not a significant change to the design of the scheme because the commercial WiMedia standard already foresees pilot OFDM symbols for channel estimation. The adaptive OFDM for UWB has already been considered by some authors. Unlike previous works, this thesis explores the performance of such a system in a large number of measured wireless channels. Finally, the thesis studies the MIMO techniques for UWB systems. Suitable schemes for fixed and adaptive OFDM are discussed. A realistic simulation using measured wireless channel shows that a 4x 1 system with a low complexity beam-steering and adaptive OFDM can deliver a data-rate of 400 Mbps over a range of 9 m. This performance is for a system with bandwidth 528 MHz (like in the WiMedia standard). A further increase can be achieved with the increase of the system's bandwidth.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

    Impact of the wireless channel on the performance of ultrawideband communication systems

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    Ultrawideband (UWB) wireless systems employ signals with bandwidths in excess of 500 MHz or with relative bandwidth more than 20&amp;percnt;. The radiated signals have low power spectral density. A decade ago, UWB wireless systems were deemed to be the technology that will deliver 'Gigabit-wireless' for short range communications. However, the performance of current systems is significantly below the initial expectations. This thesis explores the UWB wireless channel and shows how its properties limit the performance of current UWB systems. Furthermore, it is shown that if the knowledge of the channel is fully exploited a significant performance improvement of UWB systems can be achieved. The thesis begins with exploration of the channel properties. Unlike previous work, that has investigated either the 'classical narrowband' channel with bandwidth &lt;100 MHz or the UWB channel with bandwidth &gt;1 GHz, this work studies the transition between the narrowband channels with bandwidth of 1 MHz to the extremely wideband channels with bandwidths of up to 10 GHz. The thesis concludes that for signals with bandwidth &lt;1 GHz UWB antennas and antenna arrays can be described by the classical means of gain and array factor, i.e. they treat such signals as 'narrowband'. In contrast, wireless propagation for signals with bandwidth &gt;100 MHz has properties 'like UWB channels' with bandwidths in the GHz range. Additionally, the thesis suggests a correction to the IEEE802.15.4a model for channel impulse response because as will be shown in the thesis many multipaths in the model are manifestations of the antenna impulse response. Hence multiple multipaths in the IEEE802.15.4a model actually represent a single multipath component. This reduces the number of multipath components in the model by approximately factor of five. The understanding of the transition between narrowband and ultrawideband channel is used to improve the spectral efficiency of impulse radio systems which traditionally use signals with bandwidth &gt;1 GHz. It is shown that the optimum signal bandwidth for impulse radio systems is in the range 150-450 MHz. Such systems balance the robustness against frequency selective fading with the reduction of duty cycle. Hence, the data-rate of impulse radio systems can be significantly improved. The frequency selective fading is shown to be the main limiting factor for the performance of the commercial UWB WiMedia systems with OFDM. It is shown that adaptive loading of OFDM subcarriers, which is compatible with the frequency selectivity of the channel, is more suitable for UWB OFDM systems than the use of strong Forward-Error-Correction measures. The introduction of the adaptive OFDM is not a significant change to the design of the scheme because the commercial WiMedia standard already foresees pilot OFDM symbols for channel estimation. The adaptive OFDM for UWB has already been considered by some authors. Unlike previous works, this thesis explores the performance of such a system in a large number of measured wireless channels. Finally, the thesis studies the MIMO techniques for UWB systems. Suitable schemes for fixed and adaptive OFDM are discussed. A realistic simulation using measured wireless channel shows that a 4×1 system with a low complexity beam-steering and adaptive OFDM can deliver a data-rate of 400 Mbps over a range of 9 m. This performance is for a system with bandwidth 528 MHz (like in the WiMedia standard). A further increase can be achieved with the increase of the system’s bandwidth.</p

    Impact of the Wireless Channel on the Performance of Ultrawideband Communication Systems

    No full text
    Ultrawideband (UWB) wireless systems employ signals with bandwidths in excess of 500 MHz or with relative bandwidth more than 20&percnt;. The radiated signals have low power spectral density. A decade ago, UWB wireless systems were deemed to be the technology that will deliver 'Gigabit-wireless' for short range communications. However, the performance of current systems is significantly below the initial expectations. This thesis explores the UWB wireless channel and shows how its properties limit the performance of current UWB systems. Furthermore, it is shown that if the knowledge of the channel is fully exploited a significant performance improvement of UWB systems can be achieved. The thesis begins with exploration of the channel properties. Unlike previous work, that has investigated either the 'classical narrowband' channel with bandwidth &lt;100 MHz or the UWB channel with bandwidth &gt;1 GHz, this work studies the transition between the narrowband channels with bandwidth of 1 MHz to the extremely wideband channels with bandwidths of up to 10 GHz. The thesis concludes that for signals with bandwidth &lt;1 GHz UWB antennas and antenna arrays can be described by the classical means of gain and array factor, i.e. they treat such signals as 'narrowband'. In contrast, wireless propagation for signals with bandwidth &gt;100 MHz has properties 'like UWB channels' with bandwidths in the GHz range. Additionally, the thesis suggests a correction to the IEEE802.15.4a model for channel impulse response because as will be shown in the thesis many multipaths in the model are manifestations of the antenna impulse response. Hence multiple multipaths in the IEEE802.15.4a model actually represent a single multipath component. This reduces the number of multipath components in the model by approximately factor of five. The understanding of the transition between narrowband and ultrawideband channel is used to improve the spectral efficiency of impulse radio systems which traditionally use signals with bandwidth &gt;1 GHz. It is shown that the optimum signal bandwidth for impulse radio systems is in the range 150-450 MHz. Such systems balance the robustness against frequency selective fading with the reduction of duty cycle. Hence, the data-rate of impulse radio systems can be significantly improved. The frequency selective fading is shown to be the main limiting factor for the performance of the commercial UWB WiMedia systems with OFDM. It is shown that adaptive loading of OFDM subcarriers, which is compatible with the frequency selectivity of the channel, is more suitable for UWB OFDM systems than the use of strong Forward-Error-Correction measures. The introduction of the adaptive OFDM is not a significant change to the design of the scheme because the commercial WiMedia standard already foresees pilot OFDM symbols for channel estimation. The adaptive OFDM for UWB has already been considered by some authors. Unlike previous works, this thesis explores the performance of such a system in a large number of measured wireless channels. Finally, the thesis studies the MIMO techniques for UWB systems. Suitable schemes for fixed and adaptive OFDM are discussed. A realistic simulation using measured wireless channel shows that a 4×1 system with a low complexity beam-steering and adaptive OFDM can deliver a data-rate of 400 Mbps over a range of 9 m. This performance is for a system with bandwidth 528 MHz (like in the WiMedia standard). A further increase can be achieved with the increase of the system’s bandwidth.</p

    Multi-tone frequency shift keying for ultrawideband wireless communications

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    This paper explores the performance of Multi-tone Frequency Shift Keying (MT-FSK) in ultrawideband wireless communications as an alternative to the standard modulation techniques. Its advantage is its ability to provide multiple user access even within the recently tightened regulations on UWB communications. Unlike previous works that discussed MT-FSK from the information theory perspective, here the possibility of practical implementation is explored. The basic system parameters such as tone bandwidth, number of frequencies and duty cycle are studied in terms of propagation characteristics, optimum data rate and system complexity. With optimum parameters, we show that a system using Multi-tone Frequency Shift Keying is capable of data transmission at a data-rate of 250 Mbps with Bit-Error-Rate below 10^-5 whilst the receiver complexity is lower than for standard methods utilising the ultrawideband spectrum by means of impulse radio or multi-band OFDM.</p

    Bandwidth requirement for suppression of grating lobes in ultrawideband antenna arrays

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    Sparse ultrawideband antenna arrays suppress the grating lobes due to the fact that the duration of pulses processed by individual antenna elements is too short to constructively superpose them in the time domain. Such arrays represent an attractive option for design of many low-comlexity low-cost ultrawideband systems, where narrow beamwidth is achieved by increase of element spacing. This paper empirically explores the minimum bandwidth required for suppression of the grating lobes. It is found that the relative bandwidth required to suppress grating lobes is independent on the centre frequency, element spacing, and number of elements. There is a weak dependency of the bandwidth on the type of the pulse used, but the general conclusion is that the relative bandwidth has to exceed 100% in order to suppress the grating lobes. It is, however, noted that whilst sparse array with a low number of antenna elements can suppress the grating lobes and posses a narrow beam, the compromise for this feature is a reduction of the level of spatial filtering between the main lobe and other directions, when compared to arrays where grating lobes are suppressed by dense spacing
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