Dissertations / Theses on the topic 'Spatial diversity'
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1
Suard, Bruno P. (Bruno Pierre). "Spatial diversity in cellular networks." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12757.
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García, Molina José Antonio. "GNSS Signal processing and spatial diversity exploitation." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/668852.
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Global Navigation Satellite Systems (GNSS) signals are broadly used for positioning, navigation and timing (PNT) in many different applications and use cases, Athough different PNT technologies are available, GNSS is expected to be a key player in the derivation of positioning and timing for many future applications, including those in the context of the Internet of Things (IOT) or autonomous vehicles, since it has the imponant advantage of being open access and worldwide available. Indeed, GNSS is performing very well in mild propagation conditions, achieving position and time synchronization accuracies down to the cm and ns levels, respectively. Nevertheless, the exploitation of GNSS in harsh propagation conditions typical of urban and indoor scenarios is very challenging, resulting in position errors of up to tens or even hundreds of meters, and timing accuracies of hundreds of ns.
This thesis deals with the processing of GNSS signals for positioning and timing in harsh propagation conditions. In particular, the focus is on signal processing techniques exploiting the spatial diversities present both at transmission and reception levels when multiple GNSS satellites are in view by multiple receiver antennas, which form a multiple-input multiple-output (MIMO) system. In this context, three problems or research areas open in the GNSS literature are targeted. The first research area is the unambiguous estimation of and positioning with high-order binary offset carrier (BOC) signals. The second research area is the time synchronization in indoor conditions. And the third research area is the positioning with co-located and distributed receiver antennas.
In the first research area, this thesis shows that the robust unambiguous positioning with high-order BOC signals in harsh propagation conditions is possible when jointly exploiting these signals in the position domain and taking advantage of the spatial diversity introduced by arrays of antennas. The proposed estimators introduce an important benefit with respect to singlesatellite-based unambiguous techniques (operating at pseudorange level) thanks to the processing gain introduced by the MIMO-GNSS system formed. Indeed, when multiple antennas are featured by the receiver, the proposed approach allows the exploitation of high-order BOC signals even in indoor conditions, achieving positioning accuracies of few meters in propagation conditions for which BPSK(I) signals can only achieve accuracies of tens of meters.
In the second research area, this thesis proposes a joint time and channel estimation approach for static indoor GNSS receivers featuring an array of antennas in order to improve the timing accuracy in indoor propagation conditions. This approach exploits both the structure of the diffuse multipath components of the indoor channel and the MIMO system formed by all the GNSS signals received via an array of antennas, Simulation results with a wideband satellite-to-indoor channel model show that the proposed timing estimators allow an important mitigation of the dominant indoor multipath conditions.
Finally, in the third research area, this thesis proposes the exploitation of co-located and distributed receiver antennas for positioning in harsh propagation conditions. In order to improve the performance achieved with co-located antennas, a distributed array processing approach for collaborative GNSS-based snapshot positioning is proposed in the MIMO-GNSS framework. In this solution, one of the receivers is used as anchor and a distributed array is formed, allowing to transform the positioning problem into an angle estimation problem in order to reduce the computational burden.La señales transmitidas por los sistemas globales de navegación por satélite (Global Navigation Satellite Systems, GNSS) son comúnmente utilizadas para posicionamiento y sincronización en muchas y diversas aplicaciones. De hecho, se espera que los sistemas GNSS sean clave en futuras aplicaciones como el Internet de las cosas o los vehículos autónomos, ya que su uso es abierto, gratuito y global. No obstante, aunque las prestaciones que se pueden obtener con las señales GNSS son excelentes en condiciones de propagación favorables, la explotación de estas señales en condiciones más adversas típicas de entornos urbanos o de interior sigue siendo un problema complejo en la actualidad, Esta tesis aborda el procesado de señales GNSS para posicionamiento y sincronización en condiciones de propagación adversas, centrándose en la explotación de la diversidad espacial disponible cuando un array de antenas es utilizado para recibir las señales de varios satélites GNSS en vista. En concreto, esta tesis tiene como objetivo tres problemas o áreas de investigación abiertas en la literatura. La primera área de investigación trata la estimación no ambigua de la posición con señales BOC (Binary Offset Carrier) de alto orden. La segunda área de investigación se centra en el problema de sincronización basado en GNSS en entornos de interior. Y la tercera área de investigación aborda el problema de posicionamiento con arrays de antenas y arrays de receptores distribuidos.
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Ardrey, David, Gregory Gimler, and Mark Pippitt. "Spatial Diversity Combining Using Blind Estimation Techniques." International Foundation for Telemetering, 2015. http://hdl.handle.net/10150/596413.
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ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NVThis paper proposes a spatial diversity combining approach by which spatially diverse telemetry signals from multiple antennas are combined before they are demodulated. The combined signal is guaranteed to at least replicate and in many cases improve upon the performance of any single antenna. By taking advantage of blind channel estimation, the combined signal can be computed as a time varying weighted sum of digital I and Q samples from multiple antennas. Multiple antenna combining is enabled by improved computation capability, high speed network connectivity, and accurate clock synchronization. The algorithm will be demonstrated at the Reagan Test Site (RTS), whose modernization program encompasses multiple antenna sites with network capability and a state of the art software defined radio back end. This paper details the spatial diversity combining algorithm and discusses its merits and challenges. Index Terms - Telemetry, Reagan Test Site, blind estimation, multiple antenna combining, best source selection, spatial diversity combining.
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Jones, Haley M., and Haley Jones@anu edu au. "On multipath spatial diversity in wireless multiuser communications." The Australian National University. Research School of Information Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20050202.152811.
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The study of the spatial aspects of multipath in wireless communications environments
is an increasingly important addition to the study of the temporal aspects
in the search for ways to increase the utilization of the available wireless channel
capacity. Traditionally, multipath has been viewed as an encumbrance in wireless
communications, two of the major impairments being signal fading and intersymbol
interference. However, recently the potential advantages of the diversity offered by
multipath rich environments in multiuser communications have been recognised.
Space time coding, for example, is a recent technique which relies on a rich scattering
environment to create many practically uncorrelated signal transmission
channels. Most often, statistical models have been used to describe the multipath
environments in such applications. This approach has met with reasonable success
but is limited when the statistical nature of a field is not easily determined or is
not readily described by a known distribution.¶
Our primary aim in this thesis is to probe further into the nature of multipath
environments in order to gain a greater understanding of their characteristics and
diversity potential. We highlight the shortcomings of beamforming in a multipath
multiuser access environment. We show that the ability of a beamformer to resolve
two or more signals in angle directly limits its achievable capacity.¶
We test the probity of multipath as a source of spatial diversity, the limiting
case of which is co-located users. We introduce the concept of separability to define
the fundamental limits of a receiver to extract the signal of a desired user from
interfering users signals and noise. We consider the separability performances of
the minimum mean square error (MMSE), decorrelating (DEC) and matched filter
(MF) detectors as we bring the positions of a desired and an interfering user closer
together. We show that both the MMSE and DEC detectors are able to achieve
acceptable levels of separability with the users as close as λ/10.¶
In seeking a better understanding of the nature of multipath fields themselves,
we take two approaches. In the first we take a path oriented approach. The
effects on the variation of the field power of the relative values of parameters such
as amplitude and propagation direction are considered for a two path field. The
results are applied to a theoretical analysis of the behaviour of linear detectors
in multipath fields. This approach is insightful for fields with small numbers of
multipaths, but quickly becomes mathematically complex.¶
In a more general approach, we take a field oriented view, seeking to quantify
the complexity of arbitrary fields. We find that a multipath field has an intrinsic
dimensionality of (πe)R/λ≈8.54R/λ, for a field in a two dimensional circular region, increasing only linearly with the radius R of the region. This result implies that there is no such thing as an arbitrarily complicated multipath field. That is, a field generated by any number of nearfield and farfield, specular and diffuse
multipath reflections is no more complicated than a field generated by a limited
number of plane waves. As such, there are limits on how rich multipath can
be. This result has significant implications including means: i) to determine a
parsimonious parameterization for arbitrary multipath fields and ii) of synthesizing
arbitrary multipath fields with arbitrarily located nearfield or farfield, spatially
discrete or continuous sources. The theoretical results are corroborated by examples
of multipath field analysis and synthesis.
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Baik, Eugene. "Iterative detection for overloaded OFDMA with spatial diversity." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41254.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 81-85).
Orthogonal Frequency Division Multiple Access (OFDMA) systems have built-in mechanisms to mitigate the effects of the wireless multipath channel but are limited in system capacity to available bandwidth. This shortcoming can be worked around through the process of "overloading," where users are additionally multiplexed in the spatial domain to each frequency resource. To efficiently resolve non-orthogonally multiplexed users within the system, sophisticated multiple antenna receivers with multiuser detection methods are necessary. The focus of this thesis will be the formulation of an iterative multiple antenna receiver framework for overloaded uplink OFDMA systems. Specifically, we formulate optimal MAP and reduced complexity MMSE symbol detection algorithms for the multiuser detection and single user decoding turbo loop. We verify the performance of each algorithm through Monte Carlo simulation with randomly generated multipath MIMO channels. From the results we determine the tradeoffs of algorithm complexity with performance and the effect of channel correlation on the supportable user load. Our MMSE algorithm with soft interference cancellation is observed to closely approach single user performance in low to moderately correlated MIMO channels after turbo loop iteration. Additionally, we observe that increasing the number of antennas relative to the number of overloaded users can mitigate the effects of moderate correlation to provide acceptable error performance.
by Eugene Baik.
M.Eng.
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Holter, Bengt. "Adaptive coded modulation in spatial and multiuser diversity systems." Doctoral thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2005. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1724.
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This thesis consists of five included papers plus an introduction. The majority of the papers are devoted to performance analysis of an adaptive coded modulation (ACM) scheme based on multidimensional trellis codes. Primarily, single-user systems exploiting spatial diversity are analysed, but results are also presented for a multiuser system exploiting multiuser diversity.
The performance of the ACMscheme is evaluated for slowly flat-fading channels. When spatial diversity is exploited at the receiver end only, the analysis is focused on two different combining techniques: maximum ratio combining (MRC) and switched combining. Amultiple-inputmultiple-output (MIMO) diversity system is also considered, in which case the combined effect of both transmit and receive diversity is realized by using space-time block coding at the transmitter.
For wireless systems using spatial diversity, it is of interest to employ measures which can capture and quantify the performance improvement related to a reduced fading level. In this thesis, ameasure called the amount of fading (AF) is used to characterize the behavior of the error rate curve at a high signal-to-noise ratio (SNR). In particular, closed-form expressions for the AF at the output of a MIMO diversity system are provided, and it is shown that for a constant correlation model, the average symbol error probability at high SNRs may be expressed in terms of the AF.
Finally, a set of switched multiuser access schemes are proposed based on switched diversity algorithms originally devised to select between antennas in a spatial diversity system. ACM is used on each selected link to ensure a high spectral efficiency of the system.
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Kisel, Yael. "The spatial scale of speciation and patterns of diversity." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528297.
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Williams, Ian E. "Channel Equalization and Spatial Diversity for Aeronautical Telemetry Applications." International Foundation for Telemetering, 2010. http://hdl.handle.net/10150/605946.
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ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, CaliforniaThis work explores aeronautical telemetry communication performance with the SOQPSK- TG ARTM waveforms when frequency-selective multipath corrupts received information symbols. A multi-antenna equalization scheme is presented where each antenna's unique multipath channel is equalized using a pilot-aided optimal linear minimum mean-square error filter. Following independent channel equalization, a maximal ratio combining technique is used to generate a single receiver output for detection. This multi-antenna equalization process is shown to improve detection performance over maximal ratio combining alone.
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McInnes, Lynsey. "Spatial and temporal signatures of ecological constraints on diversity." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7081.
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Broad-scale diversity patterns are the outcome of ecological and evolutionary processes that permit different numbers of species to coexist in a region. Many studies have focused on understanding the factors that allow a region to contain more species or a clade to diversify more rapidly. In this thesis, I shift focus to instead explore the constraints that prevent biodiversity increasing unbounded, using a combination of phylogenetic and biogeographical approaches across a range of temporal and spatial scales. In chapter two, I investigate conservatism (i.e., the tendency for more closely related species to be more similar) in the extremes of climate tolerated by a species, assessing the hypothesis that tightly-conserved tolerances are influential in determining the range extents of the species. By using global data from two vertebrate classes and a range of climatic variables, I assess the taxonomic generality of this hypothesis and identify the most strongly conserved variables. In chapters three and four, I develop novel macroecological analyses of factors that may limit the extent of geographic ranges and apply them to Afrotropical birds (chapter three) and all continental mammals (chapter four). Chapter five assesses how the spatial distribution of range limits can be used to compare species’ relative abilities to occupy available landscape. In chapter six, I present new methods to detect signals of past changes to diversity limits in phylogenies, using simulations to explore the power of phylogenies to reveal such patterns of diversity-dependent cladogenesis. In addition to the main research chapters, I append a synthetic review, of which I am joint first author, exploring the evolutionary underpinnings of large-scale species-area relationships. This thesis builds links between the macroecology of species’ distributions with the dynamics of clades over macroevolutionary timescales to determine how geography, phylogeny and history interact in the generation and maintenance of large-scale biodiversity.
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Cumanan, Kanapathippillai. "Spatial diversity and optimization techniques for cognitive radio networks." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/10698.
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The explosive growth of wireless applications and high demand for wireless resources have created spectruIIl crisis. Many spectrnm occupancy measurements have shown that most of the allocated spectrum experiences inefficient utilization. Hence radically new approaches arc required for better utilization of spectrum. This has motivated the concept of opportunistic spectrum access in the licensed bands namely cogni ti ve radio technology. This intelligent wireless system has the potential to improve the spectrum utilization by enabling unlicensed users to access the licensed bands without disturbing the licensed users. In this thesis, spatial multiplexing techniques are studied for underlay cognitive radio networks where transmit beamformers arc designed to satisfy quality of service and interference constraints using convex optimization techniques. Robust schemes arc also proposed in the presence of imperfect channel state information at the basestation. To overcome the infeasibility issues encountered in the beamformer design, a joint resource allocation and admission control technique is proposed using the branch and bound optimi7, ation method. Finally, signal-to-interference and noise ratio (SINR) balancing techniques are developed for different types of interference constraints on the primary users using a max-min fairness approach. These SINR balancing techniques also solve the problem of infeasibility. The performance of all these new schemes has been verified using MATLAB simulation results.
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Sharma, Vimal. "Multi-user spatial diversity techniques for wireless communication systems." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/34905.
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Multiple antennas at the transmitter and receiver, formally known as multiple-input multiple-output (MIMO) systems have the potential to either increase the data rates through spatial multiplexing or enhance the quality of services through exploitation of diversity. In this thesis, the problem of downlink spatial multiplexing, where a base station (BS) serves multiple users simultaneously in the same frequency band is addressed. Spatial multiplexing techniques have the potential to make huge saving in the bandwidth utilization. We propose spatial diversity techniques with and without the assumption of perfect channel state information (CSI) at the transmitter. We start with proposing improvement to signal-to-leakage ratio (SLR) maximization based spatial multiplexing techniques for both fiat fading and frequency selective channels.
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Karaminas, Panagiotis D. "Array processing in mobile radio networks." Thesis, Imperial College London, 2001. http://hdl.handle.net/10044/1/11483.
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Graham, Richard A. Jr. "An Examination of Spatial Diversity Combining Using Commercial Off the Shelf Equipment in Missile Telemetry." International Foundation for Telemetering, 2014. http://hdl.handle.net/10150/577331.
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ITC/USA 2014 Conference Proceedings / The Fiftieth Annual International Telemetering Conference and Technical Exhibition / October 20-23, 2014 / Town and Country Resort & Convention Center, San Diego, CAThis experiment has two purposes. One, to determine if a modern diversity combiner normally used in missile telemetry for polarization diversity can be used for spatial diversity to obtain a gain in the signal quality. Two, to determine if a simple test can be designed such that a non-laboratory test can be performed by the average telemetry operator in order to assess the first purpose.
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Chan, Ivis Julieta. "Modelling spatial turnover patterns in tree species diversity for conservation." Thesis, Bournemouth University, 2015. http://eprints.bournemouth.ac.uk/24394/.
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The planet’s biodiversity is increasingly threatened by the effects of rapid environmental change. Biodiversity loss led by expanding anthropogenic activity, combined with the effects of changing climatic regimes, pose a threat to natural communities and the ecosystem services that they underpin. Understanding how communities of species vary across space and the factors that drive such variation is essential to predicting the impacts of human and climate-induced changes on biodiversity and ecosystem services. This knowledge can be used to plan conservation areas that effectively represent the underlying ecological processes that maintain biodiversity and ensure the provision of ecosystem services crucial to human wellbeing. Beta diversity has been variably defined since the concept was first introduced as a measure of variation in species assemblages. This has given rise to the development of different measures of beta diversity, and to varying conclusions regarding the variation of species composition across space. In this thesis, I aimed to investigate the spatial structuring of tree species turnover patterns (beta diversity) and the potential drivers of these patterns, within the highly environmentally heterogeneous Mesoamerican region. In addition, the effect of habitat loss on tree diversity up to the year 2000 was estimated, and the representativeness of the protected area system was assessed in an effort to highlight potential areas of conservation concern across the region. The efficacy of ecoregions in representing turnover patterns was also assessed. The spatial structuring of areas of low similarity (high beta diversity) was clustered in the north and south of the study region, as well as within the Central American mountainous regions. Areas of low similarity mostly fell within dry, pine-oak, and montane ecoregions. Moist forests were indicated as having high similarity. The congruence of the modelled pattern of beta diversity in trees with patterns of high beta diversity in other taxa provides insights into areas of potential conservation efforts. Habitat loss in the past decade was high in the southern areas of the isthmus indicating that countries like Nicaragua, Costa Rica, and Panama had lost high proportions of their original habitat and species. However, habitat loss was intensive throughout the region, and areas of high beta diversity were found to be among the least represented in the current protected areas system. Classification based on beta diversity broadly resembled the WWF ecoregional classification for the region. This suggests that models based on broad climatic variables can help elucidate beta diversity patterns at broad spatial scales, although conservation planning also requires robust information at finer scales.
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Richard, Monique. "Fern species diversity in relation to spatial scale and structure." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0002/MQ44258.pdf.
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Richard, Monique 1972. "Fern species diversity in relation to spatial scale and structure." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20850.
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Species with different requirements can coexist if the environment varies in space; we therefore expect a positive relationship between species diversity and environmental heterogeneity. In this thesis I examine the influence of environmental structure on patterns of fern diversity in one hectare of old-growth forest and compare these patterns to other surveys covering a broad range of scales. The nineteen species recorded in the hectare had non-random spatial distributions and differed in their soil preferences. Diversity was positively related to soil moisture and negatively related to soil fertility, but there was no relationship with environmental variance. The counteracting influence of dispersal may predominate over selection processes at the hectare scale. Both species-area curves and the decreasing correlation of species composition with distance had very similar slopes over quadrat sizes ranging from 1 x 1 m to 50 x 50 km, suggesting that some diversity patterns may be independent of scale.
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Sutton, D. J. "Diversity and spatial distribution of carabid beetles in Bernwood forest." Thesis, Oxford Brookes University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379683.
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Green, Jennifer. "Genetic diversity in annual weed species at different spatial scales." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394431.
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Mokise, Kealeboga. "Spatial diversity in a SIMO-OFDM hybrid powerline-wireless system." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/75857.
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Spatial diversity is an effective diversity technique used in multiple antenna wireless systems.
It requires that antenna elements be sufficiently distributed by at least ten times the signal
wavelength (10λ). Sufficient spatial distribution of antenna elements renders performance
improvements through diversity gain. In consumer electronics, antenna elements are often
located in close proximity, < λ, due to form size constraints. Therefore performance improvement through spatial diversity is limited even though multiple antenna systems are employed.
The work in this dissertation addresses the use of power line communication as a method to
spatially distribute antenna elements of a multiple antenna wireless system. Addressing this
problem requires the cooperative use of both wireless and powerline channels to form a hybrid
channel.
A hybrid powerline-wireless channel is defined as the concatenation of a powerline channel and
a wireless channel to establish a unified channel. A sequence-based channel sounding approach
using maximum length sequences and software-defined radio was designed, implemented andapplied to attain channel transfer characteristics of the hybrid channel. The measurement
campaign was carried out for an indoor low-voltage level powerline network. The attained
results include the channel impulse responses, frequency responses and power delay profiles.
Coherence bandwidth, average channel attenuation and power delay profile timing delays
are channel parameters that were extracted from the measurements. The extracted channel
parameters reveal that the hybrid channel is a challenging medium for data transfer and
communication applications.
Based on the attained hybrid channel characterisation parameters, a physical layer structure
for a 1 × 2 single-input multiple-output orthogonal frequency division multiplexing (SIMOOFDM) hybrid powerline-wireless system was designed and implemented. An investigation of
the bit-error-rate performance of single-carrier and multi-carrier modulation for a multipath
powerline channel was carried out in simulation. Using OFDM as a suitable candidate for
multi-carrier modulation, it was found to outperform single-carrier modulation. OFDM was
used as the channel access method for the hybrid channel. Source encoding and decoding of
the physical layer structure was designed to be robust against inherent interferences of the
hybrid channel. Selection combining, equal gain combining and maximal ratio combining
methods were designed and implemented. Estimation methods for error rate, data transfer
rate and SNR of the SIMO-OFDM system were designed and implemented. Capacitive signal
coupling was used to interface the powerline channel to the wireless propagation environment,
hence establishing the hybrid channel. This method also allowed powerline transmission to be
performed at a much lower frequency than wireless transmission.
An experiment was conducted to investigate the effect of spatial distribution on the 1 × 2
SIMO-OFDM hybrid powerline-wireless system for indoor environments. The results of the
experiment were error rate curves produced for different spatial distribution lengths through a
powerline channel for each signal combining method. Error rate performance improvements in
the SIMO-OFDM system were achieved with an increase of antenna element spatial distribution
due to lowered signal envelope correlation. Small but yet notable diversity gains were observed
by the increase in the slope of the produced error rate and signal-to-noise ratio curves for each
signal combining method. Experimental parameters and apparatus placed a limitation on
the achievable spatial distribution of diversity branches, hence the achievable diversity gains.
This was a result of overwhelming inherent interferences of the hybrid channelDissertation (MEng)--University of Pretoria, 2020.
CeTEIS
Electrical, Electronic and Computer Engineering
MEng
Unrestricted
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Feinstein, Larry M. "Microbial Functional Activity and Diversity Patterns at Multiple Spatial Scales." Kent State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=kent1341967745.
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Parameswaran, Rajaraman. "Effects of user and spatial diversity on high data rate wireless systems." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/35621.
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A novel design paradigm for wireless data delivery involves use of a scheduler at a base station to schedule users awaiting transmission and send downlink data to these users with all available cell power. This is unlike previous systems that share the available downlink power between users and trade off interference with capacity. The concept is used in 3G wireless standards like 1xEVDO and HSDPA. The scheduler is designed to exploit the peaks in channels seen by different users and transmit data to the user that can support the best rate. In contrast, antenna diversity, where multiple antennas are deployed at the receiver or transmitter; has the effect of improving received signal fidelity by averaging the channel variation.
In this thesis, we evaluate the joint effect of user diversity and antenna diversity for various scheduling algorithms. The system is first studied with a single user to calculate theoretical throughput values. A loaded system is then simulated and throughput trends are plotted for each user. Total system capacity is evaluated in terms of served bytes for various combinations of scheduling algorithm, diversity type and channel quality. Multi-user scheduling diversity is studied using the same system simulation model via Tomlinson Harashima precoding. Results are generated for various cell powers. Single-user and multi-user scheduling cases are compared to understand the pros and cons of each approach.Master of Science
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Solé-Senan, Xavier Oriol. "Plant diversity and ecosystem services in agricultural landscapes along different spatial scales." Doctoral thesis, Universitat de Lleida, 2017. http://hdl.handle.net/10803/406287.
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Aquesta tesi té com a objectiu escatir fins quin punt les diversitats d'espècies i funcional de les comunitats de flora arvense canvien a escala de camp i de paisatge. A escala de camp, l'estudi s'ha focalitzat en l'anàlisi de l'efecte de la intensificació agrícola, depenent de la posició dins del camp i en funció del nivell de pertorbació en cada hàbitat que forma part del tradicional paisatge en mosaic en els ambients mediterranis. A escala de paisatge, hem analitzat els canvis en la diversitat al llarg de gradients d'heterogeneïtat en el paisatge, tenint en compte d'una banda l'heterogeneïtat composicional i per l'altra l'heterogeneïtat configuracional. L'aproximació basada en atributs biològics ens ha permès dirigir l'estudi a analitzar de quina manera afecten els canvis a la composició florística d'aquestes comunitats a la provisió dels serveis ecosistèmics que els agroecosistemes aporten a altres organismes.La presente tesis tiene como objetivo dilucidar hasta qué punto la riqueza en especies y la diversidad funcional de las comunidades de flora arvense cambian a escala de campo y de paisaje. A escala de campo, el estudio se ha enfocado en el análisis del efecto de la intensificación agrícola, en cuanto a la posición en el campo y al nivel de perturbación en cada hábitat en la diversidad y funcionalidad de las comunidades de flora arvense. A escala de paisaje, hemos analizado los cambios en la diversidad a lo largo de gradientes de heterogeneidad en el paisaje, teniendo en cuenta por un lado la heterogeneidad composicional y por el otro la heterogeneidad configuracional. La aproximación basada en atributos biológicos nos ha permitido enfocar el estudio en cómo afectan los cambios en la composición florística de dichas comunidades a la provisión de los servicios ecosistémicos que los agroecosistemas aportan a otros organismos.
This thesis is aimed at disentangling the extent at which species richness and functional diversity of plant species from arable communities change at field and landscape scale. At field scale, the study was focused on the effects of agricultural intensification regarding field position and the level of disturbance at which such habitat is subjected on the diversity and functionality of arable plants community. At landscape scale, we assessed the diversity changes along gradients of landscape heterogeneity, taking into account on the one hand the surrounding compositional landscape heterogeneity and on the other hand the configurational landscape heterogeneity. The trait-based approach conducted allows us to focus on how shifts in species composition in such arable plant communities are expected to affect the delivery of the ecosystem services that these agroecosystems provide to other organisms.
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Lominé, Jimmy. "Étude d’une antenne vectorielle UHF multibande appliquée à la goniométrie 3D." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0096/document.
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De nos jours, il existe de nombreuses antennes de radiogoniométrie UHF large bande ou multibandes, néanmoins très peu d’entre elles permettent une couverture angulaire 3D. A notre connaissance, la première antenne de radiogoniométrie 3D fût étudiée dans les années 1960, par une équipe de l’université du Michigan. Composée de 17 capteurs positionnés sur une surface hémisphérique, sa taille et son nombre d’éléments en font un dispositif encombrant et complexe à utiliser. De récentes études ont proposé une autre approche basée sur la mesure multicomposante du champ électromagnétique, permettant de réduire la taille des antennes et le nombre d’éléments tout en conservant une couverture angulaire 3D. Cependant, à ce jours, seul des systèmes HF (3MHz-30MHz) ou bande étroite ont été abordés. Cette thèse porte donc sur l’étude et le développement d’une antenne vectorielle UHF multibande appliquée à la radiogoniométrie 3D pour des ondes transverses magnétiques. Tout d’abord, deux techniques de goniométrie adaptées à cette approche sont confrontées : une nouvelle technique basée sur la décomposition en harmonique sphérique du rayonnement de l’antenne qui permet de recomposer le champ électromagnétique reçu à partir d’échantillons mesurés et un algorithme bien connu, MUSIC. Une méthodologie de conception est proposée, en identifiant les critères physiques des antennes vectorielles qui influent sur leurs performances à savoir la précision d’estimation, la sensibilité, le nombre d’éléments et l’encombrement. Cette méthode est utilisée pour développer et réaliser une première antenne vectorielle monobande. La caractérisation de cette antenne réaliste permet d’écarter la première technique de traitement dont les performances sont trop sensibles aux perturbations de rayonnement. Une antenne vectorielle bibande compacte, d’un rayon de λ/4 et d’une hauteur de λ/5.5 à la fréquence la plus basse, composée de seulement six éléments rayonnants couvrant chacun les bandes de fréquences GSM [890MHz-960MHz] et [1710MHZ-1880MHz] est ensuite développée en se basant sur cette méthode de conception. Les capteurs électriques et magnétiques constituant l’antenne sont étudiés séparément puis assemblés selon une répartition spatiale planaire pour restreindre l’encombrement. Les structures rayonnantes sont communes pour les deux bandes de fréquences ce qui permet réduire le nombre d’éléments ainsi que les éventuelles perturbations de rayonnement. Après la caractérisation de l’antenne bibande au travers de simulations numériques, un prototype est réalisé et ses performances d’estimation sont mesurées en chambre anéchoïque afin de valider l’approche par simulation. La sensibilité obtenue est de -110dBW/m² (85μV/m) pour une précision de 5° RMS. Enfin l’étude est élargie au cas général d’antennes multibandes en illustrant le processus d’extension de la couverture fréquentielle par l’ajout d’une troisième bande, [400MHz-430MHz]. Six nouveaux éléments sont donc développés et intégrés aux capteurs GSM existants afin d’obtenir une antenne tribande d’un rayon de λ/3.2 et d’une hauteur de λ/12.5 à 400MHz. Malgré une légère augmentation de l’erreur d’estimation, causée par la présence de ces nouveaux éléments, la caractérisation de cette nouvelle antenne tribande montre de bonnes performances d’estimation avec une sensibilité de -105dBW/m² (155μV/m) pour une précision de 5° RMSNowadays, a lot of wideband or multiband direction finding antennas operating in the UHF band exist. Nevertheless, only few of them allow to estimate the direction of arrival in the full 3D space. At the author’s knowledge, the first 3D direction finding antenna was studied in the 1960s, at the University of Michigan. Composed of 17 sensors, located on a large hemispherical surface, this antenna is bulky and complex to use. Recently, some studies have proposed another approach based on the multicomponent measurement of the electromagnetic field that allows to decrease the antennas size and the number of radiating elements without reducing the 3D angular coverage. However, only HF (3-30MHz) or narrowband systems have been reported. The objective of this PhD is to study and to develop an UHF multiband vector sensor applied to the estimation of the direction of arrival of transverse magnetic waves in the full 3D space. Firstly, two signal processing techniques adapted to this approach are compared : a new technique based on the spherical harmonic decomposition of the antenna radiation which allows to recompose the received electromagnetic field from the measured samples and a well-known high resolution algorithm called MUSIC. A design methodology allowing to identify the physical criteria of vector sensors related to the antenna performances such as the estimation accuracy, the sensitivity, the number of elements and the antenna size is proposed. This method is used for developing and designing a first single-band vector sensor. The results obtained from numerical simulations allow to rule out the first signal processing technique which is too sensitive to the radiation perturbations. Then, a compact dual-band vector sensor operating in the GSM frequency band, [890MHz-960MHz] and [1710MHZ-1880MHz], is developed by using the same design methodology. The antenna size is λ/4 in radius and λ/5.5 in height at the lowest frequency. The electric and magnetic elements which compose the vector sensors are designed separately and then combined according to a planar spatial distribution to retain a compact antenna size. The same radiating structures are used for operating in the two frequency bands in order to reduce the number of elements and the eventual radiation perturbations. After the performances assessment through numerical simulations in each band, a prototype is manufactured and its estimation performances are measured for a validation purpose. The sensitivity is -110dBW.m−2 (85μV.m−1) for a 5◦ RMS angular accuracy. Finally, the study is extended to the general case of multiband antennas by adding a third band, [400MHz-430MHz]. New elements are developed and incorporated into the dual-band GSM sensors to obtain a tri-band vector sensor. The size of this new antenna is λ/3.2 in radius and λ/12.5 in height at 400MHz. Despite a slight increase of the angular errors in the estimation of the direction of arrival caused by the presence of the new antenna elements, the characterization of the tri-band sensor performances by simulation show a good accuracy with a sensitivity valued at -105dBW.m−2 (155μV.m−1) for a 5◦ RMS angular accuracy
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Sykes, Olivier John. "Diversity and context dependency in European spatial planning : investigating the application of the European spatial development perspective." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417298.
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Forman, Michael A., Ken Condreva, Gary Kirchner, and Kevin Lam. "Quantifying Coding Gain from Telemetry Data Combining." International Foundation for Telemetering, 2008. http://hdl.handle.net/10150/606214.
Full textAbstract:
ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, CaliforniaA method for combining telemetry data and quantifying the resulting coding gain for a ballistic missile test flight is presented. Data received from five ground stations in 54 data files with 18 million intermittent frames is combined, to create a single file with 1.5 million continuous frames. Coding gain provided by data combining is as high as 30 dB, with a useful improvement of 5 dB at boost and terminal stages. With frame reconstruction techniques, erroneous words in a frame are reduced from 2.1% to 0.12 %.
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Smith, Victoria Clare. "Invertebrate response to weed diversity and spatial arrangement within arable fields." Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494233.
Full textAbstract:
Weeds play a vital role in supporting arable biodiversity by providing both food and shelter to invertebrates and their predators. A better understanding of the relationship between weeds and invertebrates will form a necessary first step towards balancing the needs of both weed control and biodiversity in order to achieve a more sustainable system of crop production. Analysis of data from the FSEs (Farm Scale Evaluations) showed that no standard composition of weeds or invertebrates exists across all arable fields. Both weed and invertebrate species compositions varied according to the crop sown and, in the case of weeds, herbicide management applied. Variation in invertebrate composition was partially explained by variation in weed composition. This suggests that manipulating the composition of weeds within a crop may influence invertebrate composition.
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Magani, Musa Gayaunan. "Improved ultra wideband communication system through adaptive modulation and spatial diversity." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8567.
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Advances in Multimedia communications have shown the need for high data rate wireless links over short distances. This is to enhance flexibility, accessibility, portability and mobility of devices in home and enterprise environment thereby making users more productive. In 2004, the WiMedia group proposed the Multiband Orthogonal Frequency Division Multiplex Ultra Wideband (MB-OFDM UWB) system with a target of delivering data rate of 480Mbps over 3 metres. However, by now no existing commercial UWB product can meet this proposed specification. The project aims to investigate the reason why UWB technology has failed to realise its potential by carrying out detailed analysis and to seek ways of solving the technical problems. Detailed system analyses were carried out on the UWB technology using a commercial UWB product and a MB-OFDM UWB Evaluation kit. UWB channel measurements of different scenarios were carried out in order to characterise both time varying and time invariant channels. The scenarios are the realistic environments where UWB devices are operating with human subjects in various movement patterns. It gives insight into the effects of human object blocking on the MB-OFDM system performance and estimates an acceptable feedback rate in a UWB time varying channel when implementing an adaptive modulation. The adaptive modulation was proposed and implemented in the MB-OFDM system model to demonstrate the improved Bit Error Rate (BER) performance. Modulating bits are varied across the sub-channels depending on the signal to noise ratio (SNR). Sub-channels experiencing severe fading employ lower or no bit-loading while sub-channels with little or no fading utilise higher bit-loading to maintain a constant system data rate. Spatial diversity was employed to exploit different properties of the radio channel to improve performance. Good diversity gain of two receiving diversity systems using maximal ratio combining and antenna selection techniques is demonstrated in the measurements with the different antenna orientations. An antenna selection circuit is designed and implemented working together with AT90CAP9 UWB Evaluation kit, verifying an improved performance of the UWB system in an indoor environment. The maximal ratio combining technique is also implemented and demonstrated to give a better system performance on a test bed after post-processing.
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Alabed, Samer. "Computationally Efficient Spatial and Cooperative Diversity Techniques for Wireless Communication Networks." Phd thesis, TU Darmstadt, 2012. https://tuprints.ulb.tu-darmstadt.de/2984/1/Samer_Alabed_Computationally_Efficient_Spatial_and_Cooperative_Diversity_Techniques_for_Wireless_Communication_Networks.pdf.
Full textAbstract:
Several techniques are recently proposed to improve the robustness of wireless communication systems, increase the throughput, and overcome channel impairments such as multi-user interference and multi-path fading. Among them, using multiple-antennas is one of the most remarkable techniques as it allows to improve the error performance and the data rate without an increase in the frequency bandwidth or transmitted power. However, multiple-antenna techniques are not applicable in all ad-hoc networks due to hardware constraints. As an alternative, cooperative diversity techniques have been proposed to achieve gains similar to that of multiple-antenna techniques.
In this thesis, we develop computationally efficient multiple-antenna and cooperative diversity techniques for wireless communication networks which offer an improved tradeoff between computational complexity, error performance, and data rate. We first consider space-time block coding for conventional multiple antenna systems. We propose a low complexity decoder for quasi-orthogonal space-time block codes. Both the coherent and non-coherent implementations of this decoder are developed. The proposed decoder can provide a substantially improved tradeoff between the complexity and performance as compared to state-of-the-art decoding techniques. The proposed decoder enjoys a nearly linear decoding complexity and it approximately achieves the optimal performance of the maximum-likelihood decoder.
Recently, cooperative diversity strategies for two-way wireless relay networks have been proposed using the amplify-and-forward and the decode-and-forward
protocols. Although the simultaneous bidirectional decode and-forward transmission has been shown to outperform other decode-and-forward strategies, it has mainly two disadvantages: high relay decoding complexity and the impossibility to use the direct link between the communicating terminals. In this thesis, we propose novel coherent and non-coherent simultaneous bidirectional decode-and-forward distributed space-time coding strategies that provide a higher coding gain and enjoy a substantially lower relay decoding complexity than the state-of-the-art strategies at the same symbol rate. In the proposed strategies, the communicating terminals can benefit from the direct link which is not exploited by other existing simultaneous bidirectional transmission strategies.
Various differential distributed space-time coding strategies for two-way relay networks using the amplify-and-forward protocol which do not require channel
state information either at the relays or at the terminals have been proposed. The simultaneous two-way differential distributed space-time coding strategy
using the amplify-and-forward protocol has been shown to outperform the conventional differential four-phase strategy in the low to medium signal-to-noise ratio region. However, there are mainly three disadvantages associated with it: I) the relay power wasted for transmitting redundant information at either side, ii) the direct link between the communicating terminals can not be used and iii) the considerable bias at high signal-to-noise ratio. In this work, amplify-and-forward differential distributed space-time coding strategies for two-way wireless relay networks are developed, that provide a higher coding gain than the state-of-the art strategies. In the proposed strategies, the relays do not waste power to transmit redundant information at either side and the communicating terminals can fully use the direct link between them.
Although differential distributed space-time coding strategies do not require channel state information at the relays, they are associated with a low error
performance, a high latency, and decoding complexity. Another strategy used in relay networks relies on coherent processing of the relay signals using distributed beamforming techniques. This strategy enjoys a good error performance and low decoding complexity while offering an optimal decoding delay. However, a common requirement in distributed beamforming is the availability of perfect channel state information at all nodes. To avoid this requirement, we introduce a distributed differential beamforming strategy that combines the differential diversity and the distributed beamforming strategy while retaining the benefits of both approaches. The proposed strategy does not require channel state information at any node and enjoys a good error performance, optimal delay, and low decoding complexity.
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Boonchaiyapruek, P. "Spatial culture and spatial capital in Bangkok : a study of adaptability and diversity in the urban transformation process." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1566916/.
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In the last half-century urbanisation in Thailand has dramatically accelerated as its economy has globalised. The rapid growth of Bangkok since the 1970s initiated a transformation of its urban fabric from a relatively compact area to an unplanned sprawl. Whilst some areas of Bangkok have been demolished and filled in by new compound buildings others have undergone a transformation associated with craft consumption tastes, international mainstream culture and other qualities characteristic of ‘gentrification’. This thesis approaches the transformation of Bangkok's built environment in the half-decade 2008 to 2014 in the context of a critical examination of these gentrification processes. It explores gentrification from a 'bottom-up' perspective addressing changes in land-use and building stock at the scale of the building plot, street, neighbourhood and city. This approach enables it to be precise about what 'gentrification' means in a Thai context. Employing integrated space syntax and GIS analysis of contemporary and historical datasets derived from a combination of official sources and extensive original fieldwork, this thesis reflects on the issue of gentrification as a global phenomenon experienced locally. Yet if global processes are largely responsible for the gentrification of the urban landscape in terms of consumption practice, in Bangkok it is the local sociospatial processes that are responsible for how these processes are negotiated and realized in concrete terms. This thesis therefore, seeks to articulate a crucial link between the flows of economic capital associated with globalisation, the cultural capital of elite consumption patterns and what Marcus (2010) calls the 'spatial capital' of urban public space. It is proposed that the particular qualities of Bangkok's urban space are key indicators of 'being global', implicated in formulating the ‘sense of distinction’ that characterises the local sub-cultures of its transnational and local elites in which crystallises the sense of place and the land-use pattern of the neighbourhoods in gentrfying areas. It also suggests that complex metric distance scales performance is a critical syntactic concept of urban space that appropriates gentrification process in Bangkok.
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Dembele, Sidi. "Structuration spatiale de la biodiversité agricole dans la zone cotonnière du Mali." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC046.
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La diversité des systèmes de culture et des variétés joue un rôle important dans la capacité des agricultures familiales à résister aux chocs socio-économiques et environnementaux. Pour une meilleure conservation, cette diversité agricole doit d’être caractérisée et suivie dans l’espace et le temps. Tandis qu’ils étaient dominés par des éléments sur le prix, les surfaces et les productions jusqu’à récemment, les systèmes de suivi agricole commencent à intégrer les questions de diversité. Alors que jusqu’à la fin des années 1990 elle était considérée comme un facteur limitant dans l’amélioration de la productivité des systèmes d’exploitations dans le processus de sélection variétale. Or dans une situation d’incertitude pluviométrique, pour réduire le risque de cet aléa, les agriculteurs ont recours à plusieurs espèces et variétés pour survivre et produire au travers de tous les aléas rencontrés. La stratégie paysanne consiste à cultiver à la fois plusieurs variétés présentant diverses caractéristiques agronomiques (précocité, rendement, résistance aux pathologies, aux parasites, à la sécheresse, etc.) et culinaires dans un même champ ou dans des champs différents. Cette stratégie permet aux paysans de cultiver les variétés s’adaptant le mieux aux conditions pédologiques de leurs champs et répondant à la fois à leurs divers besoins.C’est dans ce contexte que se situe la présente thèse qui vise principalement à analyser la structuration spatiale de l’agrobiodiversité dans la zone cotonnière. Pour atteindre cet objectif, plusieurs méthodes et approches ont été utilisées. L’approche adoptée combine l’analyse numérique d’images satellitaires et l’utilisation de données issues d’enquêtes de terrain. L’analyse de ces données s’appuie sur la distribution spatiale de la biodiversité et sa corrélation avec les pratiques et les conditions agro-écologiques, les résultats et les performances agronomiques.Les principaux résultats issus de l’analyse des données de l’étude sont :a) On observe une grande hétérogénéité et une diversité des paysages dans la zone cotonnière du Mali-Sud avec au total, onze (11) unités de paysages ;b) On constate une grande diversité au niveau spécifique et des systèmes de culture. Les valeurs moyennes de l’indicateur de diversités spécifiques les plus sont enregistrées dans les villages où la moyenne pluviométrique est comprise entre 700 à 1000 mm d’eau suivis par des villages de moins de 700 mm ;c) L’indicateur de pression spécifique montrant une répartition géographique des pressions des différentes espèces culturales. En effet dans les villages où le coton est en tête de rotation, il exerce une forte pression sur les autres espèces. Dans ces villages, la surface en coton est beaucoup plus importante que celle des autres espèces ;d) Le rendement fait constater que la plupart des villages ont des moyens de coton au-dessus de la moyenne nationale en 2015. En analysant son évolution entre 2013 et 2015, on constate une baisse de rendement dans la plupart des villages même si cette baisse est très souvent en dent de scie avec des hausses en 2013 et 2014.e) L’indicateur de stabilité du rendement montrant que les rendements sont stables avec toutes les espèces sauf le maïs.f) Ces résultats ouvrent la voie à une plus grande contribution de la géographie dans l’analyse agronomiqueThe diversity of cropping systems and varieties plays an important role in the ability of family farms to withstand socio-economic and environmental shocks. For better conservation, this agricultural diversity needs to be characterized and monitored in space and time. While they were dominated by elements of price, area and production until recently, agricultural monitoring systems are beginning to integrate diversity issues. The diversity of cropping systems and varieties plays an important role in the ability of family farms to resist socio-economic and environmental shocks, whereas until the end of the 1990s it was considered as a limiting factor in improving the productivity of farming systems in varietal selection processes. In a situation of uncertain rainfall, to reduce the risk of this hazard, farmers use several species and varieties to survive and produce through all the hazards encountered. The peasant strategy consists in cultivating several varieties with different agronomic characteristics (early maturity, yield, resistance to diseases, parasites and drought, etc.) and culinary in the same field or in different fields. This strategy allows farmers to cultivate the varieties best suited to the soil conditions of their fields and to meet their diverse needs.It is in this context that this thesis focuses on the spatial structuring of agrobiodiversity in the cotton zone. To achieve this objective, several methods and approaches have been used. The approach adopted combines the digital analysis of satellite imagery and the use of data from field surveys. The analysis of these data is based on the spatial distribution of biodiversity and its correlation with agro-ecological practices and conditions, agronomic performance and performance.The main results from the analysis of the study data are:a) There is a great heterogeneity and diversity of landscapes in the cotton zone of Mali-Sud with a total of eleven (11) landscape units;b) There is great diversity at the specific level and in cropping systems. The mean values of the most specific indicator of diversity are recorded in villages where the mean rainfall is between 700 and 1000 mm of water followed by villages of less than 700 mm;c) The specific pressure indicator shows a geographical distribution of the pressures of the different crop species. Indeed, in villages where cotton is at the head of rotation, it exerts strong pressure on other species. In these villages, the cotton area is much larger than for the other species;d) For yield, most villages have average yields of cotton above the national average in 2015. Analyzing its evolution between 2013 and 2015, there is a decline in yield in most villages if this decline is very often sawtooth with increases in 2013 and 2014.e) The yield stability indicator shows that yields are stable with all species except maize.These results open the way for a greater contribution of geography in agronomic analysis
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Hutchinson, William Francis. "Temporal and spatial genetic diversity in the North Sea cod (Gadus morhua)." Thesis, University of Hull, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396054.
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Al-Sabouni, Nadia. "Spatial and temporal size and diversity patterns in neogene-recent planktonic foraminifera." Thesis, Royal Holloway, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498251.
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Adeane, Jaime. "Spatial diversity in wireless communications : multiple antenna systems and virtual antenna arrays." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613069.
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Tan, Hwa Sin. "Spatial multiplexing transmit diversity hybrid schemes for future wireless local area network." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/13077.
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Pillay, Kerry-Anne. "Diversity and spatial distribution of fungal endophytes in a Eucalyptus grandis tree." Diss., University of Pretoria, 2012. http://hdl.handle.net/2263/31514.
Full textAbstract:
Endophytic fungi of most woody trees are poorly studied due to their cryptic existence, the
complexity of the community and the poor ability of traditional tools to characterize them.
This study characterised the endophytic community present in commercially important
Eucalyptus grandis trees in South Africa. Two different experimental approaches were used.
Firstly environmental bar-coding, or metagenetics, was done using 454-pyrosequencing
parallel sequencing of the barcode amplicons of all the fungal isolates present in the plants
from the total DNA of the plant. Secondly, conventional DNA bar-coding of was done of
fungal endophyte isolates. Isolates of the Botryosphaeriaceae family of latent endophytic
pathogens were further characterised using a multi-gene phylogenetic approach from both
E. grandis and related native S. cordatum that grew in close proximity.
The endophytes within the three E. grandis trees were hyper diverse. A total of 1 281
Molecular Operational Taxonomic Units (MOTU) was identified based on 454-
pyrosequencing of the E. grandis fungal endophyte infections. Only 85 fungal endophytic
species were identified amongst isolates from one of these trees, using the conventional
DNA bar-coding approach. Fifteen times more species/MOTU was thus recovered using a
metagenetics compared to an isolation approach. Despite this high diversity the species
accumulation curves indicate that more endophytic diversity is to be discovered. The multigene
analysis of Botryosphaeriaceae isolates obtained from the E. grandis and S. cordatum
trees show that three species co-infect both these hosts. Two novel host associations are
also reported. This approach of verifying identities of cryptic species with appropriate multigene
analyses is most likely needed for other diverse species complexes associated with
these trees.
A very thorough sampling strategy is required to adequately characterize the endophyte
diversity in trees. The experimental approach, the 454-pyrosequening identification workflow
and database described in this study will be useful to study these endophyte communities
over time and space in future. Using these techniques and workflows described, questions
related to host association, diversity and spatial distribution within hosts, and geographical
delimitation of endophytes can be addressed.Dissertation (MSc)--University of Pretoria, 2012.
Genetics
MSc
Unrestricted
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García, Ordoñez Luis. "Perfomance limits of spatial multiplexing mimo systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/22735.
Full textAbstract:
Los canales multiple-input multiple-output (MIMO) proporcionan una forma abstracta y general de modelar un gran número de sistemas de comunicaciones. Los canales MIMO inalámbricos, en concreto, han despertado un gran interés en la comunidad investigadora durante la última década, puesto que aportan mejoras significativas en términos de eficiencia espectral y fiabilidad frente a los sistemas single-input single-output (SISO) tradicionales.
Esta tesis se concentra en sistemas MIMO de multiplexado espacial con conocimiento perfecto de canal (CSI) en ambos lados del enlace de comunicaciones. Las técnicas de multiplexado espacial engloban a todos aquellos sistemas de transmisión MIMO que dividen el flujo de datos de entrada en múltiples subflujos independientes para transmitirlos después de forma simultánea. Cuando se posee CSI perfecto en transmisión, la adaptación de dichos subflujos al estado del canal resulta en notables mejoras de las prestaciones del sistema de comunicaciones. Dentro de esta filosofía destacan los transceptores MIMO lineales por su gran relevancia práctica.
El diseño de transceptores MIMO lineales se ha abordado extensivamente en la literatura durante las tres últimas décadas bajo una gran variedad de criterios de optimización. Las prestaciones de estos esquemas, en cambio, no se han investigado analíticamente, de forma que medidas de rendimiento tales como la probabilidad de error de bit promedio (BER) y la probabilidad de outage se han evaluado mediante simulaciones numéricas, las cuales no proporcionan una visión intuitiva del comportamiento del sistema. Los análisis teóricos, en cambio, ayudan a identificar los grados de libertad en el diseño y a comprender mejor su impacto en las prestaciones obtenidas. La presente tesis parte de esta necesidad y proporciona una caracterización analítica de la BER promedio y la probabilidad de outage bajo diferentes modelos de canal. El régimen de alta relación señal a ruido (SNR) ha recibido una atención especial y las prestaciones del sistema se han investigado desde dos puntos de vista diferentes. En primer lugar, adoptando una perspectiva más práctica, hemos caracterizado las curvas de BER promedio y probabilidad de outage en términos de dos parámetros clave: la ganancia en diversidad y la ganancia de agrupación. A continuación nos hemos centrado en el marco del diversity and multiplexing tradeoff.
De esta forma, hemos podido analizar conjuntamente la capacidad del sistema para tratar con la naturaleza aleatoria del canal pero, también, la capacidad de acomodar una tasa de transmisión superior cuando la SNR crece.
En esta tesis se han evaluado las prestaciones de los transceptores MIMO lineales analíticamente y de forma simultánea para los modelos de canal MIMO inalámbricos más comunes, tales como el canal Rayleigh incorrelado o semicorrelado, o el canal Ricean incorrelado. Para alcanzar este objetivo, hemos obtenido una formulación general que unifica la caracterización probabilística de los autovalores de matrices aleatorias Hermíticas con una determinada estructura, que incluye los modelos de canal anteriores como casos particulares. En efecto, la formulación propuesta y los resultados obtenidos proporcionan un marco sólido para el análisis de las prestaciones de los sistemas MIMO, pero también pueden ser muy útiles en otras áreas del procesado estadístico de la señal y las comunicaciones.
Finalmente, como conclusión al análisis realizado en esta tesis, se han evidenciado las limitaciones inherentes a los sistemas prácticos de multiplexado espacial con conocimiento de canal estudiados. En consecuencia, se han propuesto esquemas alternativos que tratan dichas limitaciones y superan las prestaciones de los diseños prácticos disponibles en la literatura.Multiple-input multiple-output (MIMO) channels are an abstract and general way to model many different communication systems of diverse physical nature. In particular, wireless MIMO channels have been attracting a great interest in the last decade, since they provide significant improvements in terms of spectral efficiency and reliability with respect to single-input single-output (SISO) channels. In this thesis we concentrate on spatial multiplexing MIMO systems with perfect channel state information (CSI) at both sides of the link. Spatial multiplexing is a simple MIMO transmit technique that does not require CSI at the transmitter and allows a high spectral efficiency by dividing the incoming data into multiple independent substreams and transmitting each substream on a different antenna. When perfect CSI is available at the transmitter, channel-dependent linear precoding of the data substreams can further improve performance by adapting the transmitted signal to the instantaneous channel eigen-structure. An example of practical relevance of this concept is given by linear MIMO transceivers, composed of a linear precoder at the transmitter and a linear equalizer at the receiver. The design of linear MIMO transceivers has been extensively studied in the literature for the past three decades under a variety of optimization criteria. However, the performance of these schemes has not been analytically investigated and key performance measures such as the average bit error rate (BER) or the outage probability have been obtained through time-comsuming Monte Carlo simulations. In contrast to numerical simulations, which do not provide any insight on the system behavior, analytical performance expressions help the system designer to identify the degrees of freedom and better understand their influence on the system performance. This thesis attempts to fill this gap by providing analytical average and outage performance characterizations in some common MIMO channel models. More exactly, we derive exact expressions or bounds (depending on the case) for the average BER and the outage probability of linear MIMO transceivers designed under a variety of design criteria. Special attention is given to the high signal-to-noise ratio (SNR) regime, where the system performance is investigated under two different perspectives. First, from a more practical point-of-view, we characterize the average BER and outage probability versus SNR curves in terms of two key parameters: the diversity gain and the array gain. Then, we focus on the diversity and multiplexing tradeoff framework in order to take into consideration the capability of the system to deal with the fading nature of the channel, but also its ability to accommodate higher data rates as the SNR increases. The performance of linear MIMO transceivers is simultaneously analyzed for the most common wireless MIMO channel models such as the uncorrelated and semicorrelated Rayleigh, and the uncorrelated Rician MIMO fading channels. For this purpose, we have obtained a general formulation that unifies the probabilistic characterisation of the eigenvalues of Hermitian random matrices with a specific structure, which includes the previous channel distributions as particular cases, i.e., the uncorrelated and semicorrelated central Wishart, the uncorrelated noncentral Wishart, and the semicorrelated central Pseudo-Wishart distributions. Indeed, the proposed formulation and derived results provide a solid framework for the analytical performance evaluation of MIMO systems, but it could also find numerous applications in other fields of statistical signal processing and communications. Finally, and as a consequence of our performance analysis, limitations inherent to all practical linear MIMO transceiver designs have been enlightened. Accordingly, new schemes have been proposed which achieve considerable performance enhancements with respect to classical linear MIMO transceivers.
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Forien, Raphael. "The spatial structure of genetic diversity under natural selection and in heterogeneous environments." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX082/document.
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Cette thèse porte sur la structure spatiale de la diversité génétique. Dans un premier temps, nous étudions un processus à valeurs mesure décrivant l'évolution de la composition génétique d'une population soumise à la sélection naturelle. Nous montrons que ce processus satisfait un théorème de la limite centrale, et que ses fluctuations sont données par la solution d'une équation aux dérivées partielles stochastique. Nous utilisons ce résultat pour donner une estimation du fardeau de dérive au sein d'une population structurée en espace.Dans un deuxième temps, nous nous intéressons à la composition génétique d'une population lorsque les individus se déplacent plus facilement dans une région de l'espace que dans l'autre (on parle alors de dispersion hétérogène). Nous démontrons dans ce cas la convergence des fréquences alléliques via la convergence des lignées ancestrales vers un système de mouvements browniens de Walsh.Nous détaillons également l'impact d'une barrière géographique traversant l'habitat d'une population sur sa diversité génétique. Nous montrons que les lignées ancestrales décrivent dans ce cas des mouvements browniens partiellement réfléchis, dont nous donnons plusieurs constructions.Dans le but d'appliquer ces travaux, nous adaptons une méthode d'inférence démographique au cas de la dispersion hétérogène. Cette méthode utilise les blocs continus de génome hérités d'un même ancêtre entre les paires d'individus dans l'échantillon et permet d'estimer les caractéristiques démographiques d'une population lorsque celles-ci varient dans l'espace. Pour terminer nous démontrons l'efficacité de notre méthode sur des données simuléesThis thesis deals with the spatial structure of genetic diversity. We first study a measure-valued process describing the evolution of the genetic composition of a population subject to natural selection. We show that this process satisfies a central limit theorem and that its fluctuations are given by the solution to a stochastic partial differential equation. We then use this result to obtain an estimate of the drift load in spatially structured populations.Next we investigate the genetic composition of a populations whose individuals move more freely in one part of space than in the other (a situation called dispersal heterogeneity). We show in this case the convergence of allele frequencies via the convergence of ancestral lineages to a system of skew Brownian motions.We then detail the effect of a barrier to gene flow dividing the habitat of a population. We show that ancestral lineages follow partially reflected Brownian motions, of whom we give several constructions.To apply these results, we adapt a method for demographic inference to the setting of dispersal heterogeneity. This method makes use of long blocks of genome along which pairs of individuals share a common ancestry, and allows to estimate several demographic parameters when they vary accross space. To conclude, we demonstrate the accuracy of our method on simulated datasets
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Anderson, T. Michael McNaughton Samuel J. "Determinants of plant species diversity across spatial scales in Serengeti National Park, Tanzania." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2004. http://wwwlib.umi.com/cr/syr/main.
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Ilmonen, J. (Jari). "Benthic macroinvertebrate and bryophyte assemblages in boreal springs: diversity, spatial patterns and conservation." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514290633.
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In this thesis, I studied the patterns in the assemblage composition as well as the biogeography and ecology of spring macroinvertebrates and bryophytes in Finland. My main objectives were to assess the importance environmental variables to macroinvertebrate and bryophyte assemblage composition in springs at the level of multiple spatial scales. In addition, I assessed the importance of springs in the boreal mire landscape, and sought the ecological and environmental determinants of a key species in boreal springs. In a large-scale study, I also examined the concordance between macroinvertebrates and bryophytes across boreal ecoregions, and assessed how macroinvertebrate assemblage variation corresponds to terrestrially-based ecoregions.
Locally, spring macroinvertebrate assemblage structure displays high variation between different kinds of mesohabitats within springs, highlighting the importance of careful sampling of all habitat types in spring surveys. Helocrenes and other aquatic-terrestrial ecotone habitats harbour the highest species diversity and most spring-dependent species among spring habitat types. Further, spring-influenced mire patches were shown to have distinct cranefly assemblages in the mire landscape and to harbour higher cranefly diversity than mire types with lower trophic status, emphasising the importance of springs for mire biodiversity. Regionally, a red-listed spring-dependent caddisfly species appeared to be a surrogate for a high spring conservation value, indicating high overall species diversity and the occurrence of additional red-listed species.
On a large geographical scale, intersecting the boreal ecoregions, a pattern of gradual change of benthic macroinvertebrate assemblage composition from south to north was detected, largely corresponding to terrestrially-derived ecoregions. However, the physical attributes of springs also need to be taken into account in bioassessment studies. Macroinvertebrate assemblage variation also correlated with physical habitat-scale variables, but not with changes in water chemistry. In contrast, spring bryophyte assemblages showed a distinct response to variation in water chemistry, but not to variation in physical habitat characteristics. Bryophytes and insect assemblages were concordant with each other on the large geographical scale, although the concordance was rather weak. Because of their different kind of responses to the physical and chemical variables, insects and bryophytes of springs are poor surrogates for each other in boreal springs.
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Sarker, Swapan Kumar. "Spatial and temporal patterns of mangrove abundance, diversity and functions in the Sundarbans." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8499/.
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Mangroves are a group of woody plants that occur in the dynamic tropical and subtropical intertidal zones. Mangrove forests offer numerous ecosystem services (e.g. nutrient cycling, coastal protection and fisheries production) and support costal livelihoods worldwide. Rapid environmental changes and historical anthropogenic pressures have turned mangrove forests into one of the most threatened and rapidly vanishing habitats on Earth. Yet, we have a restricted understanding of how these pressures have influenced mangrove abundance, composition and functions, mostly due to limited availability of mangrove field data. Such knowledge gaps have obstructed mangrove conservation programs across the tropics. This thesis focuses on the plants of Earth’s largest continuous mangrove forest — the Sundarbans — which is under serious threat from historical and future habitat degradation, human exploitation and sea level rise. Using species, environmental, and functional trait data that I collected from a network of 110 permanent sample plots (PSPs), this thesis aims to understand habitat preferences of threatened mangroves, to explore spatial and temporal dynamics and the key drivers of mangrove diversity and composition, and to develop an integrated approach for predicting functional trait responses of plants under current and potential future environmental scenarios. I found serious detrimental effects of increasing soil salinity and historical tree harvesting on the abundance of the climax species Heritiera fomes. All species showed clear habitat preferences along the downstream-upstream gradient. The magnitude of species abundance responses to nutrients, elevation, and stem density varied between species. Species-specific density maps suggest that the existing protected area network (PAN) does not cover the density hotspots of any of the threatened mangrove species. Using tree data collected from different salinity zones in the Sundarbans (hypo-, meso-, and hypersaline) at four historical time points: 1986, 1994, 1999 and 2014, I found that the hyposaline mangrove communities were the most diverse and heterogeneous in species composition in all historical time points while the hypersaline communities were the least diverse and most homogeneous. I detected a clear trend of declining compositional heterogeneity in all ecological zones since 1986, suggesting ecosystem-wide biotic homogenization. Over the 28 years, the hypersaline communities have experienced radical shifts in species composition due to population increase and range expansion of the disturbance specialist Ceriops decandra and local extinction or range contraction of many endemics including the globally endangered H. fomes. Applying habitat-based biodiversity modelling approach, I found historical tree harvesting, siltation, disease and soil alkalinity as the key stressors that negatively influenced the diversity and distinctness of the mangrove communities. In contrast, species diversity increased along the downstream – upstream, and riverbank — forest interior gradients, suggesting late successional upstream and forest interior communities were more diverse than the early successional downstream and riverbank communities. Like the species density hotspots, the existing PAN does not cover the remaining biodiversity hotspots. Using a novel integrated Bayesian modelling approach, I was able to generate trait-based predictions through simultaneously modelling trait-environment correlations (for multiple traits such as tree canopy height, specific leaf area, wood density and leaf succulence for multiple species, and multiple environmental drivers) and trait-trait trade-offs at organismal, community and ecosystem levels, thus proposing a resolution to the ‘fourth-corner problem’ in community ecology. Applying this approach to the Sundarbans, I found substantial intraspecific trade-offs among the functional traits in many tree species, detrimental effects of increasing salinity, siltation and soil alkalinity on growth related traits and parallel plastic enhancement of traits related to stress tolerance. My model predicts an ecosystem-wide drop in total biomass productivity under all anticipated stress scenarios while the worst stress scenario (a 50% rise in salinity and siltation) is predicted to push the ecosystem to lose 30% of its current total productivity by 2050. Finally, I present an overview of the key results across the work, the study’s limitations and proposals for future work.
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Tejero, Cicuéndez Héctor 1993. "Patterns and drivers of desert reptile diversity at different phylogenetic and spatial scales." Doctoral thesis, TDX (Tesis Doctorals en Xarxa), 2021. http://hdl.handle.net/10803/672957.
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Biodiversity patterns result from the interplay of evolutionary, ecological, and environmental processes. Investigating the drivers of such patterns is central to evolutionary biology, and it is further essential to understand how the undergoing global changes will shape the future of biodiversity. This thesis explores diversity patterns and their drivers at different taxonomic and spatial scales, using reptiles from arid regions as a model of study. Specifically, this thesis analyzes the ecomorphological diversity of the Afro-Arabian geckos of the genus Pristurus in the context of island colonization and habitat specialization, the biogeographic patterns of Afro-Arabian squamates in the light of the region's geologic and climatic history, and the differences in lizard richness among the greatest deserts of the world. General processes were identified as determinant for the evolution of arid reptiles, although the results also highlight the complexity and the system-specific nature of biodiversity patterns and their driversLos patrones de biodiversidad son el resultado de múltiples procesos evolutivos, ecológicos y ambientales. Estudiar las causas de dichos patrones es fundamental en biología evolutiva, y además es clave para entender el impacto de los presentes cambios globales en la biodiversidad. Esta tesis utiliza los reptiles de las zonas áridas para explorar patrones de diversidad y sus causas a distintas escalas taxonómicas y geográficas. Concretamente, se analizan la diversidad ecomorfológica de los geckos Pristurus en el contexto de la colonización de islas y la especialización de hábitat, los patrones biogeográficos de los reptiles de Afro-Arabia a la luz de la historia geológica y climática de la región, y las diferencias en diversidad de lagartos entre los grandes desiertos del mundo. Se identificaron procesos clave en la evolución de los reptiles de zonas áridas, pero los resultados también demuestran la complejidad de los patrones de diversidad y sus causas.
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Doucet, Keith R. (Keith Raymond) Carleton University Dissertation Engineering Electrical. "Application of spatial diversity for jog detection in the presence of multipath effects." Ottawa, 1990.
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Wall, Patrick Daniel. "Incorporating spatial datasets into paleontology effects on estimates of diversity, origination, & extinction /." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2009. http://wwwlib.umi.com/cr/syr/main.
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Baessler, Cornelia. "Plant species diversity and genetic variation : temporal changes and spatial determinants in agricultural landscapes /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17734.
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Mietzner, Jan [Verfasser]. "Spatial diversity in MIMO communication systems with distributed or co-located antennas / Jan Mietzner." Kiel : Universitätsbibliothek Kiel, 2008. http://d-nb.info/1019630051/34.
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Hill, J. L. "The effect of forest spatial geometry on tree species diversity in tropical forest patches." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637276.
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Species loss in fragmented tropical forest is the greatest single threat to biodiversity. Fragmentation involves changes in the size, shape and spatial distribution of existing forest. Understanding these effects and comparing their impact with the influence of other environmental variables is of utmost importance in prioritising forest blocks for conservation. The spatial geometry of forest blocks in Ghana, West Africa, was examined with respect to tree species number and composition. Tree species number proved to be positively related to forest block area, according to laws of probability and ecological determinism. In addition, tree species composition was dictated by forest block size, with larger reserves recording significantly more rate species than smaller ones. Additional species encountered in reserves of increasing size followed a predictable pattern, which allowed the identification of species vulnerable to habitat loss. An effect of forest block shape on the structure and composition of tree species was visible using coarse spatial resolution satellite sensor imagery. Fragmentation of a previously continuous canopy led to distinct forest edge effects. This was verified by ground data, which showed an increase in the proportions of common pioneer species along reserve peripheries. Significant trends were only detected across small areas: indicating that shape is not an important consideration in the design of larger forest reserves. The effect of forest block proximity on tree species number was examined using regression analysis, but any rôle of proximity was dominated by the influence of area. The influence of climate and fire activity was strongly expressed throughout the examination of spatial geometry in the form of residual variation about the regression line. Results of multivariate analysis indicated that the management of size and disturbance should be considered in preference to shape and proximity if higher levels of diversity and bioquality are to be maintained.
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Richthofen, Aurel von Verfasser], Vanessa Miriam [Akademischer Betreuer] [Carlow, and Reinhard [Akademischer Betreuer] König. "Spatial Diversity and Sustainable Urbanisation in Oman / Aurel von Richthofen ; Miriam Carlow, Reinhard König." Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1187440671/34.
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Mietzner, Jan [Verfasser]. "Spatial Diversity in MIMO Communication Systems with Distributed or Co-located Antennas / Jan Mietzner." Aachen : Shaker, 2007. http://d-nb.info/1166509621/34.
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Mengüllüoğlu, Deniz [Verfasser]. "Foraging Ecology, Genetic Diversity and Spatial Behaviour of Caucasian Lynx in Anatolia / Deniz Mengüllüoğlu." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1219508314/34.
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Richthofen, Aurel von [Verfasser], Vanessa Miriam [Akademischer Betreuer] Carlow, and Reinhard [Akademischer Betreuer] König. "Spatial Diversity and Sustainable Urbanisation in Oman / Aurel von Richthofen ; Miriam Carlow, Reinhard König." Braunschweig : Technische Universität Braunschweig, 2019. http://nbn-resolving.de/urn:nbn:de:gbv:084-2019012209286.
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