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Tesis sobre el tema "Channel adaptation"

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Publicado: 25 de mayo de 2024

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1

Choi, Jihwan Patrick 1975. "Channel prediction and adaptation over satellite channels with weather-induced impairments". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9070.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.
Includes bibliographical references (leaves 85-87).
Title as it appears in MIT commencement exercises program, June 2000: Satellite channels with weather-induced impairments.
Bad weather conditions, especially due to rain, cause satellites operating at high frequencies (above 10 GHz) to have significant link attenuation. Usually extra link margins are used to assure link availability. These margins cause inefficient use of precious satellite and terminal power, and unnecessarily limit data throughputs. Efficiency improvements using channel prediction and adaptation over satellite channels with weather-induced impairments are considered in this thesis. First, we consider scintillation and rain attenuation as two dominant factors for signal fading over satellite-earth paths above 10 GHz, and explore physical and mathematical modeling of the two processes. Statistical and spectral analyses of these processes using one or two pole autoregressive (AR) models yield simple linear estimators for the received signal attenuation. Using these estimators, we present results where we can predict the received signal attenuation within ±0.5 dB 1 second ahead and within ± 1.0 dB 4 seconds ahead. For adaptation, we change the signal transmission power, the modulation symbol size, and the code rate adaptively. In particular, we suggest a continuous power control and discrete rate control strategy, through which we build a set of modulation/code states, and discretely change the modulation symbol size and the code rate from state to state. Within each state, continuous power control is implemented. Several examples that use this technique and quantitative analyses of power increase and capacity are provided. The analyses indicate that there is a substantial gain in performance either in capacity and/or power consumption with the adaptive schemes.
by Jihwan Patrick Choi.
S.M.
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2

Qela, Blerim. "The 8-channel dynamic channel equalizer and its adaptation as a "smart amplifier solution"". Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/27013.

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In this thesis, design of the 8-channel DCE (Dynamic Channel Equalizer) for use in WDM (Wavelength Division Multiplexing) systems in general and in particular its adaptation as a "Smart Amplifier Solution" is presented. The innovative Optimized C-band Gain Flattened EDFA (Erbium Doped Fiber Amplifier) design without GFF (Gain Flattening Filter) and its integration with the DCE and embedded control electronics into a Smart Amplifier is proposed. Further improvement of the Smart Amplifier is suggested. The systems design approach, where all subsystems are taken into account to optimize the WDM network was adopted. Hence, the Post and In-Line Amplifiers with APC (Automatic Power Control) are also considered and designed accordingly to achieve the optimized amplification and equalization results for the dynamic WDM networks. The experimental results and discussion for each design are presented and simulation data are provided for comparison and confirmation of the proposed Smart Amplifier design. In addition, simulation results with respect to feasibility of the Optimized C+L band EDFA and conditions under which it can be used as a broadband ASE source are discussed.
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3

Ran, Jianjun. "Signal processing, channel estimation and link adaptation in MIMO-OFDM systems". Göttingen Cuvillier, 2008. http://d-nb.info/989862291/04.

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4

Du, Jinfeng. "Pulse Shape Adaptation and Channel Estimation in Generalised Frequency Division Multiplexing Systems". Licentiate thesis, Stockholm : Informations- och kommunikationsteknik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9457.

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Ogino, Tetsuya. "Environmental adaptation mechanism in marine annelids". Kyoto University, 2019. http://hdl.handle.net/2433/242707.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第21830号
農博第2343号
新制||農||1068(附属図書館)
学位論文||H31||N5202(農学部図書室)
京都大学大学院農学研究科応用生物科学専攻
(主査)教授 佐藤 健司, 教授 澤山 茂樹, 准教授 豊原 治彦
学位規則第4条第1項該当
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6

El, Yakzan Adnan. "Performance prediction, parameter selection, and channel adaptation in the line-of-sight outdoors optical wireless channels using intelligent systems". Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/59682/.

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With the increased usage of optical wireless communication, finding appropriate parameters for reliable transmission and providing efficient channel performance have become of challenging interest in research and industry. This has been a strong motivation to examine and develop methods and techniques to find suitable link parameters to increase the channel availability. This thesis is mainly concerned with designing, implementing and adapting intelligent algorithms to solve for parameter selection, channel prediction, and channel adaptation in dynamic optical wireless channels. The problem could be solved with other methods such as binary and sequential search; however, intelligent systems have the ability to find optimal results with more reliability, time efficiency and increased flexibility. The research focuses on single and multi-objective selection techniques using application-specific genetic algorithm (ASGA) in the outdoors line-of-sight (LOS) optical wireless channel where parameters have different effects on the channel performance and may affect the behaviour of other channel parameters. The technique is well-established at pre-installation stages of the channel, and could be also applied at run-time if a reconfigurable hardware is installed. An intelligent system, which uses a genetic algorithm predicted and optimized optical wireless channel in the (LOS) field, is presented. The prediction technique is proposed to estimate the bit error rate (BER) at the receiver, and suggests appropriate selection of link parameters. In this research, the work is developed based on on-off keying (OOK) modulation, and makes use of different weather conditions for channel modeling. A first attempt is made with a GA-based selection for transmission wavelengths (700nm to 1600nm), the overall deterministic attenuations being estimated by a visibility model, where the changes in visibility decide about the wavelength control margin. The research is then extended to consider various external link parameters scaled by look-up tables that meet the optical wireless industry. It shows that the transmission power should not always be the only costin the channel, and there are other parameters worthy of control. Principal Component Analysis is applied targeting the ASGA selected datasets to extract the contribution of each parameter to the output, and the implicit relations that exist among data sets to achieve a certain bit-error-rate. An Artificial Neural Network (ANN) is then applied to the channel for BER prediction; this may also validate the pre-installation advice done by PCA. Finally, a two-stage modelling using a neuro-fuzzy hybrid algorithm used for adapting the channel by monitoring the link range and total attenuations in the channel. Through analysing the simulation results using these intelligent systems algorithms, the thesis aims at providing maximum utilization of channel parameters for achieving optimum channel performance and increased availability under the application of various intelligent systems, which demonstrate their efficiency and effectiveness as compared with other techniques.
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7

Huusko, J. (Jarkko). "Communication performance prediction and link adaptation based on a statistical radio channel model". Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526211473.

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Abstract This thesis seeks to develop a robust semi-analytical performance prediction method for an advanced iterative receiver that processes spatially multiplexed signals that have propagated through frequency-selective receive correlated multiple-input multiple-output (MIMO) wireless communication channels. In a change of perspective, the proposed performance prediction methods are applied at the transmitter, which seeks to attain a target frame error rate (FER) either by adaptive power control or by adaptive modulation and coding (AMC). The performance prediction scheme utilises the statistical properties of the channel—namely noise variance, number of separable propagation paths and the eigenvalues of the receive correlation matrix—to predict the signal-to-interference-plus-noise ratio (SINR) at the output of a frequency domain soft interference cancellation minimum mean square error equaliser. The SINR distribution is used to derive the distribution of the variance of the log-likelihood ratios (LLRs) at the output of a soft symbol-to-bit demapper. Mutual information transfer charts establish a bijective relationship between the variance of the LLRs and mutual information. A 3rd Generation Partnership Project compliant turbo code is assumed. Since the decoder operates independently from the channel, its extrinsic information transfer (EXIT) charts can be simulated in advance. By utilising the approximate LLR variance distribution of the demapped equaliser output, it is possible to evaluate the probability of an intersection between an equaliser chart associated with a random channel realisation and a fixed decoder chart. This probability provides the FER. Since the proposed performance prediction method does not require any instantaneous channel state information, it can be applied at the transmitter side as a robust link adaptation scheme. In adaptive transmission power control, the modulation order and code rate are fixed. By iteratively adjusting transmission power, the transmitter attempts to find an equaliser output LLR variance distribution that reaches a specified target FER. In AMC, transmission power is fixed. The equaliser output's LLR variance distribution is determined by the modulation order, while the decoder chart's position is determined by the code rate. The transmitter iteratively adjusts the code rate and attempts to find a modulation order and code rate pairing that reaches the target FER. For vertically encoded spatially multiplexed systems, the adaptive transmission power control and AMC schemes are complemented by adaptive repeat redundancy and incremental redundancy hybrid automatic repeat request (HARQ) techniques, respectively
Tiivistelmä Työn tavoitteena on kehittää luotettava semianalyyttinen suorituskyvyn ennustusmenetelmä tehokkaalle iteratiiviselle vastaanottimelle, joka käsittelee taajuusselektiivisen, vastaanotinpäässä tilakorreloituneen moniantennikanavan kautta kulkeneita tilakanavoituja signaaleja. Toisessa vaiheessa esitettyjä ennustusmenetelmiä hyödynnetään mukauttamalla lähetystehoa tai modulaatioastetta ja koodisuhdetta (adaptive modulation and coding [AMC]), samalla säilyttäen tavoitteeksi asetetun kehysvirhesuhteen (frame error rate [FER]). Suorituskyvyn ennustusmenetelmä hyödyntää kanavan tilastollisia ominaisuuksia – kohinan varianssia, eroteltavien etenemispolkujen lukumäärää sekä vastaanottimen korrelaatiomatriisin ominaisarvoja – ennustaakseen signaali–kohina-plus-interferenssisuhteen (signal-to-interference-plus-noise ratio [SINR]) jakauman taajuustasossa toimivan, häiriötä poistavan pienimmän keskineliösumman kanavakorjaimen lähdössä. SINR-jakaumasta johdetaan pehmän symboleista biteiksi -muunnoksen jälkeisten logaritmisten bittitodennäköisyyksien suhdelukujen (log-likelihood ratio [LLR]) jakauma. Keskinäisinformaation siirroskartat perustuvat LLR:ien varianssin sekä keskinäisinformaation väliseen bijektiivisyyteen. Informaatio on kanavakoodattu 3rd Generation Partnership Project -standardin mukaisella turbokoodilla. Turbodekooderin toiminta on kanavasta riippumatonta, joten dekooderin lisäinformaation siirroskartat (extrinsic information transfer [EXIT] charts) voidaan simuloida itsenäisesti. Hyödyntämällä kanavakorjaimen lähdön pehmeiden bittipäätösten LLR:ien varianssin jakaumaa, on mahdollista arvioida millä todennäköisyydellä korjaimen satunnaisen kanavarealisaation siirroskartta leikkaa dekooderin siirroskartan. Tämä todennäköisyys voidaan tulkita kehysvirhesuhteeksi. Koska suorituskyvyn ennustusmenetelmä ei vaadi hetkellistä tietoa kanavan tilasta, sitä voidaan hyödyntää lähetyksen mukautuksessa. Mukautuvassa tehonsäädössä modulaatio ja koodisuhde eivät muutu. Lähetin pyrkii iteratiivisella tehonsäädöllä löytämään korjaimen lähdölle LLR-jakauman, joka tuottaa halutun kehysvirhesuhteen. Mukautuvassa modulaation ja koodisuhteen valinnassa lähetysteho säilyy vakiona. Modulaatioaste vaikuttaa korjaimen lähdön LLR-jakaumaan ja koodisuhde dekooderin siirroskartan muotoon. Iteratiivisesti koodisuhdetta säätämällä lähetin pyrkii löytämään modulaation ja koodisuhteen yhdistelmän, joka saavuttaa tavoitellun kehysvirhesuhteen. Vertikaalisesti tilakanavoiduissa järjestelmissä mukautuvaa tehonsäätöä täydennetään lähetystehoa mukauttavilla uudellenlähetyksillä, kun taas mukautuvaa modulaation ja koodisuhteen valintaa täydennetään puolestaan koodisuhdetta pienentävillä automattisilla uudelleenlähetyspyynnöillä (hybrid automatic repeat request [HARQ])
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8

Huang, Jinliang. "Adaptation in multiple input multiple output systems with channel state information at transmitter". Licentiate thesis, Stockholm : Institutionen för elektronik, dator- och programvarusystem, Kungliga tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4443.

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9

FALCÃO, Marcos Rocha de Moraes. "Channel reservation and spectrum adaptation strategies in a multi-level prioritized cognitive radio network". Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/21070.

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CAPES
Wireless technologies have dominated the communication's market by offering reasonable speeds and convenience at low deployment costs. However, due to the significant growth of mobile computing devices and their bandwidth demands, together with the paradigm shift brought by the Internet of things, future wireless networks should become highly dense and heterogeneous, which will hardly cope with the traditional fixed spectrum allocation policy. Some standards such as the Long Term Evolution – Advanced (LTE-A), have already set the precedent for carrier aggregation (CA), aiming at scaling up bitrates, which partially helps solving the problem. However, cognitive radio (CR) has been put forward as the most promising solution to handle this complex ecosystem since it may provide better spectrum utilization and user coordination through non-traditional mechanisms. Among other features, it allows non-licensed users, known as secondary users (SUs) to opportunistically use temporarily idle licensed bands that are used by licensed clients called primary users (PUs). Once PUs and SUs are expected to share the same spectrum bands, a critical issue is to concomitantly avoid primary interference while supporting QoS for the secondary services. This dissertation studies the synergistic integration of cognitive radio networks (CRNs), Dynamic Spectrum Access DSA techniques and resource allocation strategies (e.g., CA) that combined, should improve the overall system’s performance. We have proposed a layered M/M/N/N queue-based model that addresses three user priorities, flexible bandwidth choices, multi-level channel reservation and two channel aggregation strategies. Different network load conditions for each feature were evaluated in terms of four performance metrics: blocking probability, forced termination probability, spectrum utilization and throughput. Such study is particularly useful for understanding the effects of each of these approaches in the secondary network. To the best of our knowledge, our model fulfills almost completely the user bandwidth’s possibilities, improves the existing channel reservation formulation and demonstrates that our proposed dynamic channel aggregation strategy performs similarly to a more complex simultaneous channel aggregation and fragmentation approach, but can be technically more feasible.
Tecnologias sem fio têm dominado o mercado das comunicações, oferecendo velocidades razoáveis e conveniência a um baixo custo de implantação. No entanto, devido ao crescimento significativo do número de plataformas computacionais móveis e de suas demandas por largura de banda, acrescido do advento da Internet das Coisas, as redes sem fio do futuro devem passar a ser muito mais densas e heterogêneas, sendo difíceis de se adequar a política tradicional de alocação espectral fixa. Recentemente, o método de agregação de portadora (AP) fora proposto no padrão Long Term Evolution – Advanced (LTE-A), com o propósito de aumentar as taxas de bit, mitigando assim parte do problema. Todavia, rádio cognitivo (RC) foi apresentada como a solução mais promissora para lidar com este ecossistema complexo, uma vez que pode proporcionar uma melhor utilização do espectro e coordenação de usuários através de mecanismos não-tradicionais. Entre outras características, isso permite que usuários não-licenciados também conhecidos como usuários secundários (USs) utilizem de forma oportunista bandas licenciadas temporariamente ociosas, cujos clientes licenciados são também chamados de usuários primários (UPs). Como os UPs e os USs devem compartilhar as mesmas bandas, uma questão crítica é evitar interferência primária e concomitantemente apoiar a qualidade de serviço prestada aos USs. Esta dissertação estuda a integração sinérgica das redes de rádio cognitivas, técnicas de acesso dinâmico ao espectro e estratégias de alocação de recursos (AP), que combinados, devem melhorar o desempenho do sistema. Neste trabalho, propomos um modelo baseado em filas do tipo M/M/N/N, que inclui três prioridades de usuário, opções de largura de banda, reserva de canal multi-nível e duas estratégias de agregação de canal. Para cada recurso estudado, empregamos diferentes condições de carga de rede e avaliamos os resultados em termos de quatro métricas: probabilidade de bloqueio, a probabilidade de terminação forçada, utilização espectral e vazão. Este estudo é particularmente útil para compreender os efeitos de cada uma destas abordagens em relação à rede secundária. O modelo fornecido cumpre quase completamente as possibilidades do largura de banda de cada nível de usuário, melhora a formulação de reserva de canal existente e demonstra que estratégia de agregação de canais proposta possui performance similar a uma abordagem mais complexa de agregação e fragmentação simultânea, mas que seria tecnicamente mais viável.
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10

Pollitte, Wesley Alan. "The effect of vertical networks on channel governance adaptation a transaction cost economics approach /". Diss., Connect to online resource - MSU authorized users, 2008.

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11

Palapelas, Kantola Philip. "Extreme Quantile Estimation of Downlink Radio Channel Quality". Thesis, Linköpings universitet, Artificiell intelligens och integrerade datorsystem, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-177657.

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The application area of Fifth Generation New Radio (5G-NR) called Ultra-Reliable and Low-Latency Communication (URLLC) requires a reliability, the probability of receiving and decoding a data packet correctly, of 1 - 10^5. For this requirement to be fulfilled in a resource-efficient manner, it is necessary to have a good estimation of extremely low quan- tiles of the channel quality distribution, so that appropriate resources can be distributed to users of the network system.  This study proposes and evaluates two methods for estimating extreme quantiles of the downlink channel quality distribution, linear quantile regression and Quantile Regression Neural Network (QRNN). The models were trained on data from Ericsson’s system-level radio network simulator, and evaluated on goodness of fit and resourcefulness. The focus of this study was to estimate the quantiles 10^2, 10^3 and 10^4 of the distribution.  The results show that QRNN generally performs better than linear quantile regression in terms of pseudoR2, which indicates goodness of fit, when the sample size is larger. How- ever, linear quantile regression was more effective for smaller sample sizes. Both models showed difficulty estimating the most extreme quantiles. The less extreme quantile to esti- mate, the better was the resulting pseudoR2-score. For the largest sample size, the resulting pseudoR2-scores of the QRNN was 0.20, 0.12 and 0.07, and the scores of linear quantile regression was 0.16, 0.10 and 0.07 for the respective quantiles 10^2, 10^3 and 10^4.  It was shown that both evaluated models were significantly more resourceful than us- ing the average of the 50 last measures of channel quality subtracted with a fixed back-off value as a predictor. QRNN had the most optimistic predictions. If using the QRNN, theo- retically, on average 43% more data could be transmitted while fulfilling the same reliability requirement than by using the fixed back-off value.
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12

ITAKURA, Fumitada, Kazuya TAKEDA, Katsunobu ITOU y Weifeng LI. "Single-Channel Multiple Regression for In-Car Speech Enhancement". Institute of Electronics, Information and Communication Engineers, 2006. http://hdl.handle.net/2237/15051.

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Yücek, Tevfik. "Channel, spectrum, and waveform awareness in OFDM-based cognitive radio systems". Scholar Commons, 2007. http://scholarcommons.usf.edu/etd/2425.

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The radio spectrum is becoming increasingly congested everyday with emerging technologies and with the increasing number of wireless devices. Considering the limited bandwidth availability, accommodating the demand for higher capacity and data rates is a challenging task, requiring innovative technologies that can offer new ways of exploiting the available radio spectrum. Cognitive radio arises to be a tempting solution to the spectral crowding problem by introducing the notion of opportunistic spectrum usage. Because of its attractive features, orthogonal frequency division multiplexing (OFDM) has been successfully used in numerous wireless standards and technologies. We believe that OFDM will play an important role in realizing the cognitive radio concept as well by providing a proven, scalable, and adaptive technology for air interface. The goal of this dissertation is to identify and address some of the challenges that arise from the introduction of cognitive radio. Specifically, we propose methods for obtaining awareness about channel, spectrum, and waveform in OFDM-based cognitive radio systems in this dissertation. Parameter estimation for enabling adaptation, spectrum sensing, and OFDM system identification are the three main topics discussed. OFDM technique is investigated as a candidate for cognitive radio systems. Cognitive radio features and requirements are discussed in detail, and OFDM's ability to satisfy these requirements is explained. In addition, we identify the challenges that arise from employing OFDM technology in cognitive radio. Algorithms for estimating various channel related parameters are presented. These parameters are vital for enabling adaptive system design, which is a key requirement for cognitive radio. We develop methods for estimating root-mean-square (RMS) delay spread, Doppler spread, and noise variance. The spectrum opportunity and spectrum sensing concepts are re-evaluated by considering different dimensions of the spectrum which is known as multi-dimensional spectrum space. Spectrum sensing problem in a multi-dimensional space is addressed by developing a new sensing algorithm termed as partial match filtering (PMF). Cognitive radios are expected to recognize different wireless networks and have capability of communicating with them. Algorithms for identification of multi-carrier transmissions are developed. Within the same work, methods for blindly detecting transmission parameters of an OFDM based system are developed. Blind detection is also very helpful in reducing system signaling overhead in the case of adaptive transmission where transmission parameters are changed depending on the environmental characteristics or spectrum availability.
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14

Cavalcanti, de Castro Marcel. "Enhancing P2P Systems over Wireless Mesh Networks". Doctoral thesis, Karlstads universitet, Avdelningen för datavetenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-8691.

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Due to its ability to deliver scalable and fault-tolerant solutions, applications based on the peer-to-peer (P2P) paradigm are used by millions of users on the internet. Recently, wireless mesh networks (WMNs) have attracted a lot of interest from both academia and industry, because of their potential to provide flexible and alternative broadband wireless internet connectivity. However, due to various reasons such as unstable wireless link characteristics and multi-hop forwarding operation, the performance of current P2P systems is rather low in WMNs. This dissertation studies the technological challenges involved while deploying P2P systems over WMNs. We study the benefits of location-awareness and resource replication to the P2P overlay while targeting efficient resource lookup in WMNs. We further propose a cross-layer information exchange between the P2P overlay and the WMN in order to reduce resource lookup delay by augmenting the overlay routing table with physical neighborhood and resource lookup history information. Aiming to achieve throughput maximization and fairness in P2P systems, we model the peer selection problem as a mathematical optimization problem by using a set of mixed integer linear equations. A study of the model reveals the relationship between peer selection, resource replication and channel assignment on the performance of P2P systems over WMNs. We extend the model by formulating the P2P download problem as chunk scheduling problem. As a novelty, we introduce constraints to model the capacity limitations of the network due to the given routing and channel assignment strategy. Based on the analysis of the model, we propose a new peer selection algorithm which incorporates network load information and multi-path routing capability. By conducting testbed experiments, we evaluate the achievable throughput in multi-channel multi-radio WMNs. We show that the adjacent channel interference (ACI) problem in multi-radio systems can be mitigated, making better use of the available spectrum. Important lessons learned are also outlined in order to design practical channel and channel bandwidth assignment algorithms in multi-channel multi-radio WMNs.
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Perez, Moreno Kevin. "A study of the system impact from different approaches to link adaptation in WLAN". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200124.

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The IEEE 802.11 standards define several transmission rates that can be used at the physical layer to adapt the transmission rate to channel conditions. This dynamic adaptation attempts to improve the performance in Wireless LAN (WLAN) and hence can have impact on the Quality of Service (QoS) perceived by the users. In this work we present the design and implementation of several new link adaptation (LA) algorithms. The performance of the developed algorithms is tested and compared against some existing algorithms such as Minstrel as well as an ideal LA. The evaluation is carried out in a network system simulator that models all the pro- cedures needed for the exchange of data frames according to the 802.11 standards. Different scenarios are used to simulate various realistic conditions. In particular, the Clear Channel Assessment Threshold (CCAT) is modified in the scenarios and the impact of its modification is also assessed. The algorithms are tested under identical environments to ensure that the experiments are controllable and repeatable. For each algorithm the mean and 5th percentile throughput are measured under different traffic loads to evaluate and compare the performance of the different algorithms. The tradeoff between signaling overhead and performance is also evaluated. It was found that the proposed link adaptation schemes achieved higher mean through- put than the Minstrel algorithm. We also found that the performance of some of the proposed schemes is close to that of the ideal LA.
IEEE 802.11-standarderna definierar flera överföringshastigheter som kan användas vid det fysiska skiktet för att anpassa överföringshastigheten till kanal förhållanden. Denna dynamiska anpassning försöker förbättra prestandan i wireless LAN (WLAN) och därmed kan ha inverkan på Quality of Service (QoS) uppfattas av användarna. I detta examensarbete presenterar vi utformningen och genomförandet av flera ny link adaptation (LA) algoritmer. Prestandan hos de utvecklade algoritmer testas och jämförs med vissa befintliga algoritmer så som Minstrel liksom en ideal LA. Utvärderingen genomförs i ett nätverkssystem simulator som ger alla de förfaranden som behövs för utbyte av dataramar enligt 802.11-standarderna. Olika scenarier används för att simulera olika realistiska förhå llanden. Algoritmerna är testade under identiska miljöer för att experimenten är styrbar och repeterbar. För varje algoritm genomströmningen mättes under olika trafikbelastningar för att utvärdera och jämföra resultaten för de olika algoritmer. Den avvägning mellan signalering overhead och prestanda utvärderas också . Det konstaterades att de system som föreslå s link adaptation uppnå s högre genom- snittlig throughput än Minstrel algoritm. Vi fann också att utförandet av vissa av de föreslagna systemen är nära den av ideal LA.
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Minack, Enrico. "Evaluation of the influence of channel conditions on Car2X Communication". Master's thesis, Universitätsbibliothek Chemnitz, 2005. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200501571.

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The C2X Communication is of high interest to the automotive industry. Ongoing research on this topic mainly bases on the simulation of Vehicular Ad Hoc Networks. In order to estimate the necessary level of simulation details their impact on the results needs to be examined. This thesis focuses on different channel models as the freespace, shadowing, and Ricean model, along with varying parameters. For these simulations the network simulator ns-2 is extended to provide IEEE 802.11p compliance. However, the WAVE mode is not considered since it is still under development and not finally approved. Besides a more sophisticated packet error model than the existing implementation, as well as a link adaptation algorithm, is added. In this thesis several simulations examine specific details of wireless communication systems such as fairness of multiple access, interferences, throughput, and variability. Furthermore, the simulation points out some unexpected phenomena as starving nodes and saturation effects in multi hop networks. Those led to the conclusion that the IEEE 802.11 draft amendment does not solve known problems of the original IEEE 802.11 standard.
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17

McClintick, Kyle W. "Training Data Generation Framework For Machine-Learning Based Classifiers". Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-theses/1276.

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In this thesis, we propose a new framework for the generation of training data for machine learning techniques used for classification in communications applications. Machine learning-based signal classifiers do not generalize well when training data does not describe the underlying probability distribution of real signals. The simplest way to accomplish statistical similarity between training and testing data is to synthesize training data passed through a permutation of plausible forms of noise. To accomplish this, a framework is proposed that implements arbitrary channel conditions and baseband signals. A dataset generated using the framework is considered, and is shown to be appropriately sized by having $11\%$ lower entropy than state-of-the-art datasets. Furthermore, unsupervised domain adaptation can allow for powerful generalized training via deep feature transforms on unlabeled evaluation-time signals. A novel Deep Reconstruction-Classification Network (DRCN) application is introduced, which attempts to maintain near-peak signal classification accuracy despite dataset bias, or perturbations on testing data unforeseen in training. Together, feature transforms and diverse training data generated from the proposed framework, teaching a range of plausible noise, can train a deep neural net to classify signals well in many real-world scenarios despite unforeseen perturbations.
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18

Feldman, Chris R. "Evolutionary Genetics of Tetrodotoxin (TTX) Resistance in Snakes: Tracking a Feeding Adaptation from Populations Through Clades". DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/159.

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Understanding the nature of adaptive evolution has been the recent focus of research detailing the genetic basis of adaptation and theoretical work describing the mechanics of adaptive evolution. Nevertheless, key questions regarding the process of adaptive evolution remain. Ultimately, a detailed description of the ecological context, evolutionary history, and genetic basis of adaptations is required to advance our understanding of adaptive evolution. To address some of the contemporary issues surrounding adaptive evolution, I examine phenotypic and genotypic changes in a snake feeding adaptation. Adaptations can arise through fixation of novel mutations or recruitment of existing variation. Some populations of the garter snakes Thamnophis sirtalis, T. couchii, and T. atratus possess elevated resistance to tetrodotoxin (TTX), the lethal toxin of their newt prey. I show that TTX resistance has evolved independently through amino acid changes at critical sites in a voltage-gated sodium channel protein (Nav1.4) targeted by TTX. Thus, adaptive evolution has occurred multiple times in garter snakes via de novo acquisition of beneficial mutations. Detailing the genetic basis of adaptive variation in natural populations is the first step towards understanding the tempo and mode of adaptive evolution. I evaluate the contribution of Nav1.4 alleles to TTX resistance in two garter snake species from central coastal California. Allelic variation in Nav1.4 explains 29% and 98% of the variation in TTX resistance in T. atratus and T. sirtalis, respectively, demonstrating that Nav1.4 is a major effect locus. The simple genetic architecture of TTX resistance in garter snakes may significantly impact the dynamics of trait change and coevolution. Patterns of convergent evolution are cited as some of the most compelling examples of the strength of natural selection in shaping organismal diversity. Yet repeated patterns may tell us as much about the constraints that restrict evolution as about the importance of natural selection. I present data on convergent molecular adaptations in parallel arms races between diverse snakes and amphibians from across the globe. Six snake species that prey on TTX bearing amphibians have independently acquired amino acid changes in Nav1.4. The derived mutations are clustered in two portions of the gene, often involving the same sites and substitutions. While a number of amino acid changes can make Nav1.4 insensitive to TTX, most of these negatively impact or abolish the ion-conducting function of the protein. Thus, intramolecular pleiotropy likely prevents most replacements from becoming fixed and imposes limits on protein evolution.
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19

Moreira, Darlan Cavalcante. "EstratÃgias de EstimaÃÃo de Canal para AdaptaÃÃo de Enlace em Sistemas MIMO-OFDM". Universidade Federal do CearÃ, 2006. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=2095.

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FundaÃÃo de Amparo à Pesquisa do Estado do CearÃ
Atualmente a internet à uma ferramenta largamente utilizada e o grande desenvolvimentoe popularidade de tecnologias de acesso sem-fio (wireless) nos levam a um futuro no qual uma conexÃo caracterizada por estar disponÃvel âanytime, anywhereâ, ou seja, a qualquer hora e em qualquer lugar, serà essencial. Tal caracterÃstica à considerada obrigatÃria em sistemas4G (quarta geraÃÃo), mas para uma experiÃncia satisfatÃria para o usuÃrio à necessÃrio que uma conexÃo segura e eficiente esteja disponÃvel. A fim de obter tal eficiÃncia, a comunidade de pesquisa tem gerado algumas soluÃÃes promissoras que obtÃm ganhos significativos no desempenho do sistema, tais como modulaÃÃo e codificaÃÃo adaptativas, codificaÃÃo espaÃo-temporal, mÃltiplas antenas e canais MIMO (Multiple Input Multiple Output ), modulaÃÃo multiportadora, detecÃÃo multiusuÃrio, etc. [1]. Dentre essas soluÃÃes, destaca-se a adaptaÃÃo do sistema, ou seja, o sistema deve estar em constante adaptaÃÃo para obter sempre o melhor desempenho possÃvel para cada situaÃÃo em que se encontra. No entanto, uma importante premissa para a adaptaÃÃo do sistema consiste em conhecer o estado atual em que o sistema se encontra (informaÃÃo sobre o canal de comunicaÃÃo). Para isso diversas tÃcnicas de estimaÃÃo de canal sÃo propostas na literatura, cada uma possuindo vantagens e desvantagens. Nesse trabalho o impacto da estimaÃÃo de canal na adaptaÃÃo de enlace à analisado atravÃs de simulaÃÃes computacionais1. Em particular, duas tÃcnicas de estimaÃÃo de canal com caracterÃsticas diferentes sÃo analisadas, para alguns cenÃrios especÃficos em um sistema MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ), atravÃs de uma mÃtrica que considera tanto a redundÃncia introduzida para estimar o canal quanto o erro de estimaÃÃo de canal de cada tÃcnica. Os resultados encontrados constituem curvas que podem ser utilizadas para efetuar a adaptaÃÃo de enlace do sistema de maneira mais realista, ou seja, considerando o efeito da estimaÃÃo de canal, alÃm de incluir a prÃpria tÃcnica de estimaÃÃo de canal como um parÃmetro a ser adaptado.
Atualmente a internet à uma ferramenta largamente utilizada e o grande desenvolvimentoe popularidade de tecnologias de acesso sem-fio (wireless) nos levam a um futuro no qual uma conexÃo caracterizada por estar disponÃvel âanytime, anywhereâ, ou seja, a qualquer hora e em qualquer lugar, serà essencial. Tal caracterÃstica à considerada obrigatÃria em sistemas4G (quarta geraÃÃo), mas para uma experiÃncia satisfatÃria para o usuÃrio à necessÃrio que uma conexÃo segura e eficiente esteja disponÃvel. A fim de obter tal eficiÃncia, a comunidade de pesquisa tem gerado algumas soluÃÃes promissoras que obtÃm ganhos significativos no desempenho do sistema, tais como modulaÃÃo e codificaÃÃo adaptativas, codificaÃÃo espaÃo-temporal, mÃltiplas antenas e canais MIMO (Multiple Input Multiple Output ), modulaÃÃo multiportadora, detecÃÃo multiusuÃrio, etc. [1]. Dentre essas soluÃÃes, destaca-se a adaptaÃÃo do sistema, ou seja, o sistema deve estar em constante adaptaÃÃo para obter sempre o melhor desempenho possÃvel para cada situaÃÃo em que se encontra. No entanto, uma importante premissa para a adaptaÃÃo do sistema consiste em conhecer o estado atual em que o sistema se encontra (informaÃÃo sobre o canal de comunicaÃÃo). Para isso diversas tÃcnicas de estimaÃÃo de canal sÃo propostas na literatura, cada uma possuindo vantagens e desvantagens. Nesse trabalho o impacto da estimaÃÃo de canal na adaptaÃÃo de enlace à analisado atravÃs de simulaÃÃes computacionais1. Em particular, duas tÃcnicas de estimaÃÃo de canal com caracterÃsticas diferentes sÃo analisadas, para alguns cenÃrios especÃficos em um sistema MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ), atravÃs de uma mÃtrica que considera tanto a redundÃncia introduzida para estimar o canal quanto o erro de estimaÃÃo de canal de cada tÃcnica. Os resultados encontrados constituem curvas que podem ser utilizadas para efetuar a adaptaÃÃo de enlace do sistema de maneira mais realista, ou seja, considerando o efeito da estimaÃÃo de canal, alÃm de incluir a prÃpria tÃcnica de estimaÃÃo de canal como um parÃmetro a ser adaptado.
Nowadays the internet is a widely used tool and the great development and popularity of wireless technologies leads us to a future where the connectivity will be characterized as âanywhere, anytimeâ. Such characteristic is considered essential in 4G systems. However, for a satisfactory user experience a secure and efficient connectivity has to be always available. To obtain such efficiency, the research community has generated a number of promising solutions that achieve significative improvements in system performance, such as adaptive modulation and coding, space-time coding, multiple antennas and MIMO (Multiple Input Multiple Output ) channels, multicarrier modulation, multiuser detection, etc. [1]. Among these solutions, the system adaptation is a particularly interesting one, there is, the system must constantly adapt itself to achieve the best performance for each situation. However, one important premise for the system adaptation is the knowledge of the channel state information (CSI). To obtain this knowledge, several channel estimation strategies were proposed in the literature, each one with advantages and disadvantages. In this work we analyze the impact of channel estimation in the link adaptation through computer simulations1. Two channel estimation techniques with different characteristics were analyzed for some specific scenarios in a MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ) system. To perform the analysis it was used a metric that consider the redundancy introduced to estimate the channel and the channel estimation error of each technique. The obtained results constitute curves that can be used to perform link adaptation in a more realistic way, that is, considering the effect of channel estimation. Besides, it is shown that even the choice of the channel estimation strategy can be an adaptable parameter so that the most adequate channel estimation strategy for each system state is used.
Nowadays the internet is a widely used tool and the great development and popularity of wireless technologies leads us to a future where the connectivity will be characterized as âanywhere, anytimeâ. Such characteristic is considered essential in 4G systems. However, for a satisfactory user experience a secure and efficient connectivity has to be always available. To obtain such efficiency, the research community has generated a number of promising solutions that achieve significative improvements in system performance, such as adaptive modulation and coding, space-time coding, multiple antennas and MIMO (Multiple Input Multiple Output ) channels, multicarrier modulation, multiuser detection, etc. [1]. Among these solutions, the system adaptation is a particularly interesting one, there is, the system must constantly adapt itself to achieve the best performance for each situation. However, one important premise for the system adaptation is the knowledge of the channel state information (CSI). To obtain this knowledge, several channel estimation strategies were proposed in the literature, each one with advantages and disadvantages. In this work we analyze the impact of channel estimation in the link adaptation through computer simulations1. Two channel estimation techniques with different characteristics were analyzed for some specific scenarios in a MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing ) system. To perform the analysis it was used a metric that consider the redundancy introduced to estimate the channel and the channel estimation error of each technique. The obtained results constitute curves that can be used to perform link adaptation in a more realistic way, that is, considering the effect of channel estimation. Besides, it is shown that even the choice of the channel estimation strategy can be an adaptable parameter so that the most adequate channel estimation strategy for each system state is used.
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20

Güvenç, İsmail. "Towards practical design of impulse radio ultrawideband systems: Parameter estimation and adaptation, interference mitigation, and performance analysis". Scholar Commons, 2006. http://scholarcommons.usf.edu/etd/2541.

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Ultrawideband (UWB) is one of the promising technologies for future short-range high data rate communications (e.g. for wireless personal area networks) and longer range low data rate communications (e.g. wireless sensor networks).Despite its various advantages and potentials (e.g. low-cost circuitry, unlicensed reuse of licensed spectrum, precision ranging capability etc.), UWB also has its own challenges. The goal of this dissertation is to identify and address some of those challenges, and provide a framework for practical UWB transceiver design.In this dissertation, various modulation options for UWB systems are reviewed in terms of their bit error rate (BER) performances, spectral characteristics, modem and hardware complexities, and data rates. Time hopping (TH) code designs for both synchronous (introduced an adaptive code assignment technique) and asynchronous UWB impulse radio (IR) systems are studied. An adaptive assignment of two different multiple access parame ters (number of pulses per symbol and number of pulse positions per frame)is investigated again considering both synchronous and asynchronous scenarios, and a mathematical framework is developed using Gaussian approximations of interference statistics for different scenarios. Channel estimation algorithms for multiuser UWB communication systems using symbol-spaced (proposed a technique that decreases the training size), frame-spaced (proposed a pulse-discarding algorithm for enhanced estimationperformance), and chip-spaced (using least squares (LS) estimation) sampling are analyzed.A comprehensive review on multiple accessing andinterference avoidance/cancellation for IR-UWB systems is presented.BER performances of different UWB modulation schemes in the presence of timing jitter are evaluated and compared in static and multipath fading channels, and finger estimation error, effects of jitter distribution, and effects of pulse shape are investigated. A unified performance analysis app roach for different IR-UWB transceiver types (stored-reference, transmitted-reference, and energy detector) employing various modulation options and operating at sub-Nyquist sampling rates is presented. The time-of-arrival (TOA) estimation performance of different searchback schemesunder optimal and suboptimal threshold settings are analyzed both for additive white Gaussian noise (AWGN) and multipath channels.
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21

Nellis, Shelley. "EFFECTS OF ALTERNATIVE PREY AS A BUFFER TO PREDATION OF CHANNEL CATFISH (ICTALURUS PUNCTATUS) BY LARGEMOUTH BASS (MICROPTERUS SALMOIDES)". VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/129.

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Channel catfish have pectoral spines that lock to defend against gape-limited predators such as largemouth bass. Previous work indicated that spines increase survival of channel catfish exposed to bass but did not determine whether bass avoid catfish if less dangerous species are available. We presented bass with channel catfish and two alternatives, bluegill and goldfish, and compared order of ingestion, ingestion time, percent of successful strikes, and time spent chasing each prey species. We also presented the three species in a jar study that standardized position in the water column as well as in a net-pen study. The order of ingestion was suggestive of a preference for goldfish, then bluegill and finally channel catfish. Handling time was greater for channel catfish, less for bluegill, and the least for goldfish. Fewer catfish were eaten when other prey were available. Bass appear to avoid channel catfish if alternative prey is available.
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22

Tran, Tuyen X. "Achievable Rate and Capacity of Amplify-and-Forward Multi-Relay Networks with Channel State Information". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1376743091.

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23

Atzori, Pamela. "Crossing the channel(s) : adaptation, national identity and public service broadcasting in the work of Charles Dickens on Spanish, French and Italian television, 1962-1970". Thesis, Aberystwyth University, 2011. http://hdl.handle.net/2160/72e8d458-8aaa-4e3f-8904-087df34ae35c.

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This thesis presents a cross-national comparison of Charles Dickens’s television adaptations produced across Western Europe (specifically by national broadcasters in France, Italy and Spain) with particular reference to the Public Service Broadcasting era. This was an important period for the development of European television and the reaffirmation of values linked to national identity after the events of World War Two. The thesis suggests that television adaptations contributed to the consolidation of forms of national identity in Western Europe, with each country applying its own version of the Public Service Broadcasting ethos. By focusing on the years 1962-1970 - when European TV networks produced many transpositions inspired by Charles Dickens’s writings - this work discusses how these adaptations contributed to the establishment of certain forms of national identity in the countries chosen for analysis. By doing do, it also aims to reinforce the importance of cross-national comparisons of European television histories, while arguing the necessity of expanding those analyses to use specific genres and broadcasts (in this case, adaptations) to illustrate the development of national broadcasters throughout the monopoly era. By using academic materials, newspaper and magazine reviews, television listings, and textual and contextual analysis, this work discusses how Spain, France and Italy, through the development of the adaptation genre and television itself, attempted to consolidate and reaffirm their own particular forms of national identity. I use Dickens’s adaptations as an example of how adaptations contributed to the dominance of PSB (and its frequently centralised notion of nationalism) in the countries selected for analysis. Rather than carrying out traditional ‘literary’ analysis of the adaptations, the thesis, therefore, examines them as television works, taking particular care to highlight how they reflect a specific nation, society and socio-political culture. In doing so, it attempts to provide the field of European TV studies - particularly in relation to that of adaptation history and Dickensian studies - with some much needed cross-national case-studies from a hugely important period of television history.
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24

Rao, Raghunandan M. "Perspectives of Jamming, Mitigation and Pattern Adaptation of OFDM Pilot Signals for the Evolution of Wireless Networks". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/77485.

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Wireless communication networks have evolved continuously over the last four decades in order to meet the traffic and security requirements due to the ever-increasing amount of traffic. However this increase is projected to be massive for the fifth generation of wireless networks (5G), with a targeted capacity enhancement of 1000× w.r.t. 4G networks. This enhanced capacity is possible by a combination of major approaches (a) overhaul of some parts and (b) elimination of overhead and redundancies of the current 4G. In this work we focus on OFDM reference signal or pilot tones, which are used for channel estimation, link adaptation and other crucial functions in Long-Term Evolution (LTE). We investigate two aspects of pilot signals pertaining to its evolution - (a) impact of targeted interference on pilots and its mitigation and (b) adaptation of pilot patterns to match the channel conditions of the user. We develop theoretical models that accurately quantify the performance degradation at the user’s receiver in the presence of a multi-tone pilot jammer. We develop and evaluate mitigation algorithms to mitigate power constrained multi-tone pilot jammers in SISO- and full rank spatial multiplexing MIMO-OFDM systems. Our results show that the channel estimation performance can be restored even in the presence of a strong pilot jammer. We also show that full rank spatial multiplexing in the presence of a synchronized pilot jammer (transmitting on pilot locations only) is possible when the channel is flat between two pilot locations in either time or frequency. We also present experimental results of multi-tone broadcast pilot jamming (Jamming of Cell Specific Reference Signal) in the LTE downlink. Our results show that full-band jamming of pilots needs 5 dB less power than jamming the entire downlink signal, in order to cause Denial of Service (DoS) to the users. In addition to this, we have identified and demonstrated a previously unreported issue with LTE termed ‘Channel Quality Indicator (CQI) Spoofing’. In this scenario, the attacker tricks the user terminal into thinking that the channel quality is good, by transmitting interference transmission only on the data locations, while deliberately avoiding the pilots. This jamming strategy leverages the dependence of the adaptive modulation and coding (AMC) schemes on the CQI estimate in LTE. Lastly, we investigate the idea of pilot pattern adaptation for SISO- and spatial multiplexing MIMO-OFDM systems. We present a generic heuristic algorithm to predict the optimal pilot spacing and power in a nonstationary doubly selective channel (channel fading in both time and frequency). The algorithm fits estimated channel statistics to stored codebook channel profiles and uses it to maximize the upper bound on the constrained capacity. We demonstrate up to a 30% improvement in ergodic capacity using our algorithm and describe ways to minimize feedback requirements while adapting pilot patterns in multi-band carrier aggregation systems. We conclude this work by identifying scenarios where pilot adaptation can be implemented in current wireless networks and provide some guidelines to adapt pilots for 5G.
Master of Science
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25

Rao, Raghunandan M. "Enhancing Performance of Next-Generation Vehicular and Spectrum Sharing Wireless Networks: Practical Algorithms and Fundamental Limits". Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/99796.

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Over the last few decades, wireless networks have morphed from traditional cellular/wireless local area networks (WLAN), into a wide range of applications, such as the Internet-of-Things (IoT), vehicular-to-everything (V2X), and smart grid communication networks. This transition has been facilitated by research and development efforts in academia and industry, which has resulted in the standardization of fifth-generation (5G) wireless networks. To meet the performance requirements of these diverse use-cases, 5G networks demand higher performance in terms of data rate, latency, security, and reliability, etc. At the physical layer, these performance enhancements are achieved by (a) optimizing spectrum utilization shared amongst multiple technologies (termed as spectrum sharing), and (b) leveraging advanced spatial signal processing techniques using large antenna arrays (termed as massive MIMO). In this dissertation, we focus on enhancing the performance of next-generation vehicular communication and spectrum sharing systems. In the first contribution, we present a novel pilot configuration design and adaptation mechanism for cellular vehicular-to-everything (C-V2X) networks. Drawing inspiration from 4G and 5G standards, the proposed approach is based on limited feedback of indices from a codebook comprised of quantized channel statistics information. We demonstrate significant rate improvements using our proposed approach in terrestrial and air-to-ground (A2G) vehicular channels. In the second contribution, we demonstrate the occurrence of cellular link adaptation failure due to channel state information (CSI) contamination, because of coexisting pulsed radar signals that act as non-pilot interference. To mitigate this problem, we propose a low-complexity semi-blind SINR estimation scheme that is robust and accurate in a wide range of interference and noise conditions. We also propose a novel dual CSI feedback mechanism for cellular systems and demonstrate significant improvements in throughput, block error rate, and latency, when sharing spectrum with a pulsed radar. In the third contribution, we develop fundamental insights on underlay radar-massive MIMO spectrum sharing, using mathematical tools from stochastic geometry. We consider a multi-antenna radar system, sharing spectrum with a network of massive MIMO base stations distributed as a homogeneous Poisson Point Process (PPP) outside a circular exclusion zone centered around the radar. We propose a tractable analytical framework, and characterize the impact of worst-case downlink cellular interference on radar performance, as a function of key system parameters. The analytical formulation enables network designers to systematically isolate and evaluate the impact of each parameter on the worst-case radar performance and complements industry-standard simulation methodologies by establishing a baseline performance for each set of system parameters, for current and future radar-cellular spectrum sharing deployments. Finally, we highlight directions for future work to advance the research presented in this dissertation and discuss its broader impacts across the wireless industry, and policy-making.
Doctor of Philosophy
The impact of today's technologies has been magnified by wireless networks, due to the standardization and deployment of fifth-generation (5G) cellular networks. 5G promises faster data speeds, lower latency and higher user security, among other desirable features. This has made it capable of meeting the performance requirements of key infrastructure such as smart grid and mission-critical networks, and novel consumer applications such as smart home appliances, smart vehicles, and augmented/virtual reality. In part, these capabilities have been achieved by (a) better spectrum utilization among various wireless technologies (called spectrum sharing), and (b) serving multiple users on the same resource using large multi-antenna systems (called massive MIMO). In this dissertation, we make three contributions that enhance the performance of vehicular communications and spectrum sharing systems. In the first contribution, we present a novel scheme wherein a vehicular communication link adapts to the channel conditions by controlling the resource overhead in real-time, to improve spectral utilization of data resources. The proposed scheme enhances those of current 4G and 5G networks, which are based on limited feedback of quantized channel statistics, fed back from the receiver to the transmitter. In the second contribution, we show that conventional link adaptation methods fail when 4G/5G networks share spectrum with pulsed radars. To mitigate this problem, we develop a comprehensive signal processing framework, consisting of a hybrid SINR estimation method that is robust and accurate in a wide range of interference and noise conditions. Concurrently, we also propose a scheme to pass additional information that captures the channel conditions in the presence of radar interference, and analyze its performance in detail. In the third contribution, we focus on characterizing the impact of 5G cellular interference on a radar system in shared spectrum, using mathematical tools from stochastic geometry. We model the worst-case interference scenario, and study the impact of the system parameters on the worst-case radar performance. In summary, this dissertation advances the state-of-the-art in vehicular communications and spectrum sharing, through (a) novel contributions in protocol design and (b) development of mathematical tools for performance characterization.
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26

Ning, Baozhu. "Performance Analysis of Iterative Soft Interference Cancellation Algorithms and New Link Adaptation Strategies for Coded MIMO Systems". Thesis, Supélec, 2013. http://www.theses.fr/2013SUPL0034/document.

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Les systèmes de communication sans fil actuels évoluent vers un renforcement des réactivités des protocles de la gestion des ressources radio (RRM) et adaptation du lien radipe (FLA) afin d'optimiser conjointement les couches MAC et PHY. En parallèle, la technologie d'antenne multiples et turbo récepteurs avancés ont un grand potentiel pour augmenter l’efficacité spectrale dans les futurs systèmes de communication sans fil. Ces deux tendances, à savoir, l'optimisation inter couche et le traitement de turbo, nécessitent le développement de nouvelles abstractions de la couche PHY (aussi appelée méthode de prédiction de la performance) qui peuvent capturer les performances du récepteur itératif par itération pour permettre l'introduction en douceur de ces récepteurs avancés dans FLA et RRM.La thèse de doctorat revisite en détail l'architecture du turbo récepteur, plus particulièrement, la classe d'algorithme itératif effectuant la détection linéaire par minimisation d’erreur quadratique moyenne avec l'annulation d’interférence (LMMSE-IC). Ensuite, une méthode semi-analytique de prédiction de la performance est proposée pour analyser son l'évolution par la modélisation stochastique de chacun des composants. Intrinsèquement, la méthode de prédiction de la performance est subordonnée à la disposition de connaissance d’information d’état du canal au niveau du récepteur (CSIR), le type de codage de canal (code convolutif ou un code turbo), le nombre de mots de code ainsi que le type d’information probabilistic sur les bits codés réinjectée par le décodeur pour la reconstruction et l'annulation d'interférence à l'intérieur d’algorithme de LMMSE -IC itératif.Dans la deuxième partie, l’adaptation du lien en boucle fermée dans les systèmes MIMO codés basés sur les abstractions de la couche PHY proposées pour les récepteurs LMMSE -IC itératifs ont été abordés. Le schéma proposé d'adaptation de liaison repose sur un faible taux de rétroaction et exploite la sélection du précodeur spatiale (par exemple, la sélection d'antennes) et du schéma de modulation et de codage (MCS) de façon à maximiser le taux moyen soumis à une contrainte de taux d'erreur de bloc. Différents schémas de codage sont testés, tels qu’un codage parcourant tous les antennes où un codage par antenne. Les simulations montrent bien le gain important obtenu avec les turbo récepteurs comparée à celui d’un récepteur MMSE classique
Current wireless communication systems evolve toward an enhanced reactivity of Radio Resource Management (RRM) and Fast Link Adaptation (FLA) protocols in order to jointly optimize the Media Access Control (MAC) and Physical (PHY) layers. In parallel, multiple antenna technology and advanced turbo receivers have a large potential to increase the spectral efficiency of future wireless communication system. These two trends, namely, cross layer optimization and turbo processing, call for the development of new PHY-layer abstractions (also called performance prediction method) that can capture the iterative receiver performance per iteration to enable the smooth introduction of such advanced receivers within FLA and RRM. The PhD thesis first revisits in detail the architecture of the turbo receiver, more particularly, the class of iterative Linear Minimum Mean-Square Error (soft) Interference Cancellation (LMMSE-IC) algorithms. Then, a semi-analytical performance prediction method is proposed to analyze its evolution through the stochastic modeling of each of the components. Intrinsically, the performance prediction method is conditional on the available Channel State Information at Receiver (CSIR), the type of channel coding (convolutional code or turbo code), the number of codewords and the type of Log Likelihood Ratios (LLR) on coded bits fed back from the decoder for interference reconstruction and cancellation inside the iterative LMMSE-IC algorithms. In the second part, closed-loop FLA in coded MIMO systems based on the proposed PHY-layer abstractions for iterative LMMSE-IC receiver have been tackled. The proposed link adaptation scheme relies on a low rate feedback and operates joint spatial precoder selection (e.g., antenna selection) and Modulation and Coding Scheme (MCS) selection so as to maximize the average rate subject to a target block error rate constraint. The cross antenna coding (the transmitter employs a Space-Time Bit-Interleaved Coded Modulation (STBICM) ) and per antenna coding (Each antenna employs an independent Bit-Interleaved Coded Modulation(BICM)) cases are both considered. The simulations clearly show the significant gain obtained with turbo receivers compared to that of a conventional MMSE receiver
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27

Abdeddaim, Mohamed Nazim. "Analyse des performances d'un réseau de capteurs exploitant le standard IEEE 802.15.4". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENM067/document.

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Les réseaux de capteurs suscitent un engouement croissant du fait du grand nombre d'applications mais également des défis inhérents à ce genre de réseaux. Le standard IEEE 802.15.4 a été proposé afin de standardiser les couches physique et MAC. Dans ce travail nous avons dans un premier temps proposé une variante multi-canal pour le standard 802.15.4 permettant de résoudre le problème de collisions de supertrames. Pour cela nous proposons de construire un réseau en arbre avec la particularité que chaque cellule du réseau utilise un canal différent permettant ainsi une réduction conséquente des interférences et augmente la capacité du réseau. Nous avons également introduit un nouveau mécanisme de construction de topologie, d'allocation de canal et d'ordonnancement de supertrames nécessaire au bon fonctionnement d'une telle solution. Dans un deuxième temps nous avons analysé l'impact des différents paramètres de la méthode d'accès du standard. Nous avons mis en exergue les faiblesses de la méthode d'accès dont les performances baissent drastiquement pour des réseaux trop importants. Partant de ce constat, nous avons proposé des mécanismes d'auto-adaptation pour la méthode d'accès du standard. Ces derniers permettent d'adapter dynamiquement la taille des fenêtres de contention en fonction des conditions de trafic observées sur le canal. Le calcul des valeurs optimales est exécuté par chaque coordinateur pour résoudre le problème de surdité. Ces mécanismes sont distribués et convergent rapidement même en cas de trafic en rafales
An increasing interest has been observed in Wirless Sensor Network that can be explained by wide range of WSN applications as well as by the challenges involving the constraints of this type of networks. The IEEE 802.15.4 standard has been proposed with the objective of standardizing the physical and MAC layers. In this work, we have firstly proposed an alternative multichannel scheme for the IEEE 802.15.4 standard. It is able to solve the problem of superframe collisions based on a cluster-tree topology approach in which each cluster uses a different channel allowing the reduction of the interference and increased network capacity. We have also difined a novel mechanism for topology construction, channel allocation, and superframe scheduling. Secondly, we have analyzed the impact of different parameters on the medium access control. We have shown the weakness of the medium access method proposed in the standard. For instance, we have observed a decrease in performance when the standard is applied in large networks. Motivated by the analysis and its results we have then proposed auto-adaptive mechanisms for the medium access control. They allow to dynamically adapt the size of the contention window according to the observed traffic conditions. Each coordinator computes the optimal values to avoid deafness. The proposed mechanisms rapidly converge even in the case of bursty traffic
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28

Cui, DongBo. "Muscarinic Cholinergic Modulation of Neuronal Excitability and Dynamics via Ether-a-go-go-Related Gene Potassium Channel in Rodent Neocortical Pyramidal Cells". Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1559904265174505.

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29

Banerjee, Debashis. "Intelligent real-time environment and process adaptive radio frequency front-ends for ultra low power applications". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53882.

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In the thesis the design of process tolerant, use-aware radio-frequency front-ends were explored. First, the design of fuzzy logic and equation based controllers, which can adapt to multi-dimensional channel conditions, are proposed. Secondly, the thesis proves that adaptive systems can have multiple modes of operation depending upon the throughput requirements of the system. Two such modes were demonstrated: one optimizing the energy-per-bit (energy priority mode) and another achieving the lowest power consumption at the highest throughput (data priority mode). Finally, to achieve process tolerant channel adaptive operation a self-learning methodology is proposed which learns the optimal re-configuration setting for the system on-the-fly. Implications of the research are discussed and future avenues of further research are proposed.
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30

Mhamdi, Maroua. "Méthodes de transmission d'images optimisées utilisant des techniques de communication numériques avancées pour les systèmes multi-antennes". Thesis, Poitiers, 2017. http://www.theses.fr/2017POIT2281/document.

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Cette thèse est consacrée à l'amélioration des performances de codage/décodage de systèmes de transmission d'images fixes sur des canaux bruités et réalistes. Nous proposons, à cet effet, le développement de méthodes de transmission d'images optimisées en se focalisant sur les deux couches application et physique des réseaux sans fil. Au niveau de la couche application et afin d'assurer une bonne qualité de service, on utilise des algorithmes de compression efficaces permettant au récepteur de reconstruire l'image avec un maximum de fidélité (JPEG2000 et JPWL). Afin d'assurer une transmission sur des canaux sans fil avec un minimum de TEB à la réception, des techniques de transmission, de codage et de modulation avancées sont utilisées au niveau de la couche physique (système MIMO-OFDM, modulation adaptative, CCE, etc). Dans un premier temps, nous proposons un système de transmission robuste d'images codées JPWL intégrant un schéma de décodage conjoint source-canal basé sur des techniques de décodage à entrées pondérées. On considère, ensuite, l'optimisation d'une chaîne de transmission d'images sur un canal MIMO-OFDM sans fil réaliste. La stratégie de transmission d'images optimisée s'appuie sur des techniques de décodage à entrées pondérées et une approche d'adaptation de lien. Ainsi, le schéma de transmission proposé offre la possibilité de mettre en oeuvre conjointement de l'UEP, de l'UPA, de la modulation adaptative, du codage de source adaptatif et de décodage conjoint pour améliorer la qualité de l'image à la réception. Dans une seconde partie, nous proposons un système robuste de transmission de flux progressifs basé sur le principe de turbo décodage itératif de codes concaténés offrant une stratégie de protection inégale de données. Ainsi, l'originalité de cette étude consiste à proposer des solutions performantes d'optimisation globale d'une chaîne de communication numérique pour améliorer la qualité de transmission
This work is devoted to improve the coding/ decoding performance of a transmission scheme over noisy and realistic channels. For this purpose, we propose the development of optimized image transmission methods by focusing on both application and physical layers of wireless networks. In order to ensure a better quality of services, efficient compression algorithms (JPEG2000 and JPWL) are used in terms of the application layer enabling the receiver to reconstruct the images with maximum fidelity. Furthermore, to insure a transmission on wireless channels with a minimum BER at reception, some transmission, coding and advanced modulation techniques are used in the physical layer (MIMO-OFDM system, adaptive modulation, FEC, etc). First, we propose a robust transmission system of JPWL encoded images integrating a joint source-channel decoding scheme based on soft input decoding techniques. Next, the optimization of an image transmission scheme on a realistic MIMO-OFDM channel is considered. The optimized image transmission strategy is based on soft input decoding techniques and a link adaptation approach. The proposed transmission scheme offers the possibility of jointly implementing, UEP, UPA, adaptive modulation, adaptive source coding and joint decoding strategies, in order to improve the image visual quality at the reception. Then, we propose a robust transmission system for embedded bit streams based on concatenated block coding mechanism offering an unequal error protection strategy. Thus, the novelty of this study consists in proposing efficient solutions for the global optimization of wireless communication system to improve transmission quality
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31

Spires, Meggan Hazel. "Barriers to and enablers of climate change adaptation in four South African municipalities, and implications for community based adaptation". Thesis, Rhodes University, 2015. http://hdl.handle.net/10962/d1018913.

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The focus of this study is on understanding the multiple and interacting factors that hinder or enable municipal planned climate change adaptation, here called barriers and enablers respectively, and their implications for community based adaptation. To do this I developed a conceptual framework of barriers to and enablers of planned climate change adaptation, which informed a systematic literature review of barriers to planned community based adaptation in developing countries. In this framework barriers were grouped into resource, social and physical barriers. I then conducted empirical case study analysis using qualitative research methods in four South African municipalities to understand what barriers and enablers manifested in these contexts. In light of the reflexive nature of my methodology, my framework was adjusted based on my empirical findings, where contextual barriers were found to better represent the empirical results and subsumed physical barriers. I found my framework useful for analysis, but in the empirical cases, barriers and enablers overlaid and interacted so significantly that in reality it was often difficult to separate them. A key finding was that enablers tended to be more about the way things are done, as opposed to direct opposites of barriers. Comparison of barriers and enablers across the case studies revealed a number of key themes. Municipalities struggle to implement climate change adaptation and community based adaptation within contexts of significant social, economic and ecological challenges. These contextual barriers, when combined with certain cognitive barriers, lead to reactive responses. Existing municipal systems and structures make it difficult to enable climate change adaptation, which is inherently cross‐sectoral and messy, and especially community based adaptation that is bottom‐up and participatory. Lack of locally applicable knowledge, funding and human resources were found to be significant resource barriers, and were often underlain by social barriers relating to perceptions, norms, discourses and governance challenges. Enablers of engaged officials, operating within enabling organisational environments and drawing on partnerships and networks, were able to overcome or circumvent these barriers. When these enablers coincided with windows of opportunity that increased the prioritisation of climate change within the municipality, projects with ancillary benefits were often implemented. Analysis of the barriers and enablers identified in the literature and case studies, informed discussion on whether municipalities are able to implement community based adaptation as defined in the literature, as well as the development of recommendations for how municipal planned climate change adaptation and community based adaptation can be further understood and enabled in the future. These recommendations for practice and research include: (a) To acknowledge and understand the conceptual framings of municipal climate change work, as these framings inform the climate change agenda that is pursued, and hence what municipal climate change adaptation work is done and how it was done. (b) The need for further research into the social barriers that influence the vital enablers of engaged officials, enabling organisational environments, and partnerships and networks. (c) To learn from pilot community‐level interventions that have been implemented by municipalities, as well as from other disciplines and municipalities. (d) To develop top‐down/bottom‐up approaches to enable municipal planned climate change adaptation and community based adaptation, that benefits from high level support and guidance, as well as local level flexibility and learning‐by‐doing. (e) To develop viable mechanisms for municipalities to better engage with the communities they serve.
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32

Lamire, Mohammed. "Adaptation de groupements tetraedriques xo4 aux edifices octaedriques : etude structurale des deformations de la charpente et des possibilites d'insertion cationique". Caen, 1987. http://www.theses.fr/1987CAEN2035.

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Plusieurs types structuraux ont servi de base aux investigations. Dans chaque cas, un compose nouveau a ete synthetise et sa structure etablie par diffraction rx : pwo::(5), bronze monophosphate a tunnels pentagonaux; na::(x)p::(4)w::(14)o::(50), bronze monophosphate a tunnels hexagonaux; ba::(2)p::(8)w::(32)o::(112), bronze diphosphate a tunnels hexagonaux; rb::(x)p::(8)w::(8)o::(40), bronze diphosphate a tunnels octagonaux et deux formes de mo::(4)p::(6)si::(2)o::(25), silicophosphate. La description des coordinences, les calculs de potentiels de sites et l'ecoulement de ces proprietes au sein des cages et des tunnels permettent de prevoir les possibilites d'accueil par insertion cationique
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33

Rey, Micolau Francesc. "Feedback-Channel and adaptative mimo coded-modulations". Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6899.

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En els sistemes de comunicacions on el transmissor disposa de certa informació sobre l'estat del canal (CSI), es possible dissenyar esquemes lineals de precodificació que assignin la potència de manera òptima induint guanys considerables, sigui en termes de capacitat, sigui en termes de la fiabilitat de l'enllaç de comunicacions. A la pràctica, aquest coneixement del canal mai és perfecte i, per tant, el senyal transmès es veurà degradat degut al desajust entre la informació que el transmissor disposi del canal i el seu estat real.

En aquest context, aquesta tesi estudia dos problemes diferents però alhora estretament relacionats: el disseny d'un esquema pràctic de seguiment del canal en transmissió per canals variants en temps, i el disseny d'esquemes lineals de precodificació que siguin robustos a la incertesa del canal.

La primera part de la tesi proposa el disseny d'un esquema de seguiment de canal que, mitjançant un enllaç de retorn de baixa capacitat, proporcioni al transmissor una informació acurada sobre el seu estat. Històricament, aquest tipus d'esquemes han rebut fortes crítiques degut a la gran quantitat d'informació que és necessari transmetre des del receptor cap el transmissor. Aquesta tesi, doncs, posa especial èmfasi en el disseny d'aquest canal de retorn. La solució que es proposa, basada en el filtre de Kalman, utilitza un esquema que recorda al transmissor DPCM. Les variacions del canal són tractades mitjançant dos predictors lineals idèntics situats en el transmissor i en el receptor, i un canal de retorn que assisteix el transmissor amb l'error de predicció. L'interès d'aquest esquema diferencial és que permet seguir les variacions del canal amb només dos o quatre bits per coeficient complex, fins i tot en canals ràpidament variants.

La resta de la tesi cobreix el segon objectiu, l'estudi de diferents esquemes d'assignació de potències quan el coneixement del canal en transmissió no és perfecte. El problema es planteja per a un sistema MIMO OFDM com a formulació més general, incloent els casos d'una sola antena, de l'esquema beamforming i del canal multiplicatiu com a casos particulars.

Primerament s'ha plantejat l'optimització dels criteris de mínim error quadràtic mig (MMSE) i mínima BER sense codificar. La innovació en el treball presentat a la tesi, respecte a altres treballs que segueixen els mateixos criteris de disseny, ha estat la formulació Bayesiana del problema per al disseny dels algoritmes robustos.

La tesi continua amb el plantejament d'estratègies robustes d'assignació de potència destinades a minimitzar la BER codificada. Per aquesta tasca s'han utilitzat criteris de teoria de la informació. Possiblement una de les principals contribucions d'aquesta tesi ha estat el plantejament del cut-off rate com a paràmetre de disseny. Aquest criteri s'introdueix com alternativa a la capacitat de canal o a la informació mutual per al disseny del transmissor quan s'inclou codificació de canal.



La ultima part de la tesi proposa un interleaver adaptatiu de baixa complexitat que, utilitzant el coneixement del canal disponible en el transmissor, assigna estratègicament els bits no només per combatre les ràfegues d'errors, sinó també per lluitar contra els esvaïments que puguin presentar les diferents portadores del canal per a una realització concreta. El disseny d'aquest interleaver, anomenat "interleaver RCPC" està basat en els codis Rate-Compatible Punctured Convolutional Codes. Com s'il·lustra a partir del resultats numèrics, l'ús d'aquest interleaver millora les prestacions dels algoritmes quan es comparen amb les que s'obtindrien si s'utilitzes un interleaver de bloc o un interleaver pseudo-aleatori.
When the transmitter of a communication system disposes of some Channel State Information (CSI), it is possible to design linear precoders that optimally allocate the power inducing high gains either in terms of capacity or in terms of reliable communications. In practical scenarios, this channel knowledge is not perfect and thus the transmitted signal suffers from the mismatch between the CSI at the transmitter and the real channel.

In that context, this thesis deals with two different, but related, topics: the design of a feasible transmitter channel tracker for time varying channels, and the design of optimal linear precoders robust to imperfect channel estimates.

The first part of the thesis proposes the design of a channel tracker that provides an accurate CSI at the transmitter by means of a low capacity feedback link. Historically, those schemes have been criticized because of the large amount of information to be transmitted from the receiver to the transmitter. This thesis focuses, thus, the attention in an accurate design of the return link. The proposed solution is based on the Kalman filter and follows a scheme that reminds the well known DPCM transmitter. The channel variability is processed by two identical linear predictors located at the transmitter and at the receiver, and a feedback link that assists the transmitter with the prediction error. The interest of this differential scheme is that allows to track the channel variations with only two or four bits per complex channel coefficient even in fast time-varying channels.

The rest of the thesis covers the second topic, studying different robust power allocation algorithms when the CSI is not perfectly known at the transmitter. For the sake of generality, the problem is formulated for the general MIMO OFDM case, encompassing the single antenna transmission, the beamforming schemes and the frequency-flat fading channels as particular cases.

First, the minimum MSE and the minimum uncoded BER parameters are chosen to be optimized, evaluating the performance of the algorithms in terms of uncoded BER. The basic novelty with respect to previous works that considers the same strategies of design is the proposal of a Bayesian approach for the design of the robust algorithms.

Next the study is extended by proposing robust power allocation strategies focused on the minimization of the coded BER. For this purpose, information-theoretic criteria are used. Probably, one of the main contributions in the thesis is the proposal of the cut-off rate as a parameter of design whose maximization is directly related to the coded BER. This criterion is introduced as an alternative to the channel capacity and the mutual information for the design of optimal transceivers in the presence of any channel coding stage.






The last part of the thesis proposes a low complexity adaptive interleaver that, making use of the CSI available at the transmitter, reallocates the bits not only to combat the bursty channel errors but also to combat the specific distribution of the faded subcarriers as a function of the channel response. The design of this interleaver, named as "RCPC interleaver", is based on the Rate-Compatible Punctured Convolutional Codes. As shown by numerical results, the use of this interleaver improves the performance of the algorithms when they are compared with the classical block interleavers and pseudo-random interleavers.
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34

Collins, Sinead. "Microalgal adaptation to changes in carbon dioxide". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100340.

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It is generally accepted that global levels of CO2 will roughly double over the next century. Because of their large population sizes and fast generation times, microalgae may adapt to global change through novel mutations fixed by natural selection, such that future populations may be genetically different from contemporary ones. The prediction that microalgae may respond evolutionarily to rising CO2 was tested using populations of Chlamydomonas reinhardtii grown for 1000 generations at increasing CO2. Laboratory populations grown at high CO2 did not show a direct response to selection at elevated CO2, instead evolving a range of non-adaptive syndromes. In addition, populations selected at elevated CO2 often grew poorly at ambient CO2. The same evolutionary responses were seen in natural populations isolated from CO2 springs. CO2 uptake was measured in a subset of the laboratory selection lines, which were found to have cells that either leaked CO2, had lost the ability to induce high-affinity CO 2 uptake, or both. These phenotypes were tentatively attributed to the accumulation of conditionally neutral mutations in genes involved in the carbon concentrating mechanism (CCM). The high-CO2-selected phenotypes were found to be reversible in terms of fitness when populations were backselected in air, though wild-type regulation of the CCM was not regained. It has been suggested that phytoplankton adaptation to changes in CO2 levels is constrained by selective history. This was tested by culturing genetically distinct populations of Chlamydomonas at decreasing levels of CO2. In this case, divergence between lines was attributable to chance rather than selective history.
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35

Siketina, Natalya Hennadievna. "Adaptation industrial enterprises to changed competitive environment". Thesis, Science initiative "Universum", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/39997.

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Competitive environment results in positive changes in market agents' relations. At the same time, it is characterized by constant, often unpredictable, changes in the conditions of their existence, which, for one, positively affects production activity, while others have a negative impact on efficiency, often leading them to bankruptcy. These features of the competitive environment require the identification of the mechanism of adaptation of enterprises to its changes, namely, the reengineering of the internal environment of the enterprise, in accordance with the variability of external economic conditions, based on a certain production policy.
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36

BONAVENTURA, Rosario Emanuele. "NEUROPLASTIC AND BEHAVIORAL CHANGES FOLLOWING PRISM ADAPTATION". Doctoral thesis, Università degli Studi di Palermo, 2022. https://hdl.handle.net/10447/548778.

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Prismatic or Prism adaptation (PA) is a particular visuomotor procedure that through the deviation of visual field and a motor task influences brain activity (Redding & Wallace, 2006). Initially developed 1998, when Rossetti et al. study showed an improvement of neglected hemispace exploring emineglected stroke patients, the number of studies focused on PA was greatly increased. The PA effects were investigated in healthy subjects as well as in patients in different tasks targeting different cognitive functions. A large number of applications of PA procedure was developed in the different studies but the majority of the procedures includes a movement task during the wearing of lenses that deviate the visual field of the subjects. Functional magnetic resonance (fMRI) studies have showed, prevalently, a recruitment of cerebellum and parietal cortex during PA procedure. Moreover, recent evidences (Bracco et al., 2017) have shown an increase of motor cortex activity during the task. The present work presents the results of a series of experiments aimed at identifying new applications of PA. The work is structured in three chapters. In the first chapter we will present an overview of PA thought analysing the different techniques, settings, and neuro-correlates of the procedure. In the second chapter we will be present a brief analysis of the pre-existing literature about PA and postural effects, followed by an experimental work about baropodometric and hand strength changes after PA. In the third chapter we will present an experimental work about the effects of PA in Phonemic Fluency and discuss the main results with reference to pre-existing literature about PA effects in cognitive function. I declare that all the articles reported in this dissertation are reproduced according to the Creative Commons policy (CC-BY) or with the permission of the journals.
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37

Gilster, Elisabeth 1955. "Communication strategies and behavioral adaptations in intercultural channels". Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290671.

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Although international business-to-business marketing is pervasive, little systematic empirical work has been conducted on face-to-face interactions between channel members from different cultures. Greater knowledge regarding cross-cultural communication strategies (e.g. verbal and non-verbal language choices) and behavioral adaptations (e.g. rapport building, increased flexibility with timing, and contractual format) will enhance the strength, efficiency and longevity of relationships between channel partners from distinct cultures. More importantly, a lack of this knowledge seriously jeopardizes cross-cultural understanding and the ability to develop and maintain intercultural exchange relationships. This dissertation presents an empirically derived conceptual framework of cross-cultural communication and behavioral processes. This framework is drawn from extensive ethnographic fieldwork in two intercultural channels of distribution and from academic literature. Acculturation moderates the influence that culture of the producer and the power situation have on the choice of communication strategies and behaviors in interactions between intercultural channel partners. The more the choice of communication strategies and behavioral adaptations is consistent with cultural traditions of the channel members, the higher the levels of trust engendered through the relationship. Hence, trust was expected to be a critical predictor of satisfaction and performance. This was consistent in the interview data, but not in the observation data. The conceptual framework is tested using survey research in the same industries. Power and acculturation were found to have limited effects on the choice of communication strategies. Trust was shown to play a very limited role as a mediating variable. However, significant correlations between the communication strategies and behavioral adaptations and the business outcome variables were revealed. In the conclusion, implications for marketing managers are discussed, limitations of this research are outlined, and future research ideas are proposed.
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38

Nosakhare, Ehimwenma. "QT-interval adaptation to changes in autonomic balance". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84865.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 93-98).
ECG variability, as it relates to the influence of the autonomic nervous system on the heart, is primarily studied via frequency-domain and time-domain analysis of heart rate variability (HRV). HRV studies the variability of the RR intervals in the ECG; these intervals are modulated by the autonomic influence on the periodicity of the the heart's pacemaker, the sino-atrial node. The autonomic influence at this level is dominated by the parasympathetic nervous system. In order to have a robust assessment of autonomic balance, there is a need for an ECG-based approach to assess the influence of the sympathetic nervous system. In this thesis, using spectral analysis, we quantify the variability of the QT interval, which is primarily modulated by the sympathetic nervous system. We also estimate the time constant of the sympathetic nervous system by least-squares fitting of the QT time series resulting from step perturbations in autonomic balance. This study is carried out on graded head-up tilt test data. Our results demonstrate the potential of QT interval variability as a non-invasive assessment of the sympathetic nervous system activity on the heart.
by Ehimwenma Nosakhare.
S.M.
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39

MACRI', CARMELO NICODEMO. "Adaptations of plant species to environmental changes". Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1003150.

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The future climate change represents the biggest challenge for plant and animal species. The scenarios forecasted by the IPCC predict a global increase in temperatures and regional changes in rainfall during this century. Therefore, studying the relationship between climate and several traits of species is crucial in our understanding of the effects that future changes may have on plants. Species growing along a wide environmental gradient are a suitable study model to verify the relationship between intraspecific variability and both current and future climate. The aim of my PhD project is to analyse the relationship between environmental variability and variation in morphological traits, germination capacity and genetic structure of Lilium pomponium, using a multidisciplinary approach. The results of this study may enhance our understanding about the possible responses of this threatened species to environmental changes. Lilium pomponium is an endemism of the Ligurian and Maritime Alps spanning along a wide altitudinal gradient (100 and 2000 m a.s.l.), ranging from a Mediterranean to a subalpine climate. Our results show that the populations exposed to different environmental pressures have variations in floral characteristics, these variations likely play an important role in reducing among-populations variability in reproductive output. Germination tests show that the increase in temperature may negatively affect seeds germination capacity. Nevertheless, projections of thermal requirement for seed germination under future climatic conditions suggest that populations will probably respond to future temperature increase shifting their germination phenology. Moreover, in the future the species may find suitable ecological conditions for seed germination in new areas at higher altitudes. Finally, genetic analysis suggests that there is no clear pattern of diversity and differentiation between populations, which may be related to the topographic complexity of the areas and to the biogeographical history of the species. Overall, the results obtained suggest that high among-populations variability found in L. pomponium may be a bet-hedging strategy to cope with unpredictable environmental conditions occurring in Mediterranean climate and that it might also represent a successful strategy to face the future environmental change.
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40

Childs, Margaret Mary. "Teacher adaptation of a curriculum during implementation". Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/377.

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The purpose of this study is to investigate to what extent foundation phase teachers adapt Curriculum 2005. The study was guided by two research questions: (1) What are the critical components of Curriculum 2005 (foundation phase)? (2) What are the adaptations that teachers have made in teaching this curriculum? The specific focus of this study is foundation phase teachers’ initial implementation of the revised version of Curriculum 2005, the Revised National Curriculum Statement (RNCS). An Innovation Configuration Checklist was developed identifying the critical components of the RNCS and the variations of each. Using the checklist, foundation phase teachers were surveyed to establish the adaptations being made during implementation. The findings of this study indicate that there is less active learning and more teacher directed activity than is required by the RNCS. Assessment appears to be a problem area. Most teachers understand what is expected of them in terms of assessment and attempt to put it into practice. Assessment has however, proved to be burdensome and time consuming. Teachers’ planning demonstrates a sound understanding of the procedures to be followed. Teachers do however, need support in terms of deeper pedagogical content knowledge. Although teachers comply with the technical aspects of curriculum development they neglect the emancipatory aspects of the RNCS. The situation in foundation phase classrooms might be described as one where much change is taking place, but little transformation is happening at present. Teachers are nevertheless, reflecting on how to improve their teaching and continue to explore ways to adapt and improve the RNCS.
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41

Dimou, Konstantinos. "Améliorations de l'accès paquet en sens montant du WCDMA". Phd thesis, Télécom ParisTech, 2003. http://pastel.archives-ouvertes.fr/pastel-00000671.

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Les systèmes de 3G offrent de nouveaux services support (bearer services) à plus hauts débits pour les modes de transmission "paquet". Ces services vont coexister avec la voix (ou d'autres services temps réels), des scénarios de trafic mixte, voix et données, doivent être envisagés. La norme UMTS permet effectivement aux utilisateurs d'avoir plus d'un service activé simultanément. Les différentes classes de trafic augmentent la complexité de la gestion des ressources radios. Dans ce contexte, deux types de fonctions sont étudiés: l'allocation de TFCI et l'ordonnancement de paquets. Leur impact sur la qualité de service (QoS) ainsi que sur la capacité du système est évalué. On propose des améliorations de ces mécanismes dans le but d'augmenter la capacité du système et par conséquent d'améliorer la QoS des utilisateurs. Les études se restreignent au sens montant, c'est à dire aux transmissions du mobile (User Equipment ou UE) vers le réseau. Un premier mécanisme pour lequel un effort d'amélioration est fait, est l'adaptation du lien radio par variation du débit instantané transmis. On simule le cas d'une transmission multiservice (voix et données). L'UE doit partager un débit global qui lui est alloué entre les différents services activés. Ces derniers sont véhiculés dans des radio bearers (tuyaux supports). À chaque intervalle élémentaire de transmission (Transmission Time Interval, TTI), l'UE sélectionne un sous-débit pour chaque bearer; ceci se fait par la sélection d'un "format de transport" à appliquer pendant la durée TTI. Cette procédure s'effectue dans la couche MAC (Medium Access Control); le résultat de la sélection est une combinaison de formats de transport (Transport Format Combination, TFC) que la couche physique doit utiliser. La procédure, nommée sélection de TFC, permet d'adapter la transmission des différents services aux conditions variables de la propagation radio: elle détermine notablement la performance de transmission. L'algorithme de sélection de TFC est tracé dans ses grandes lignes dans la norme. Un de ses principes est de favoriser le trafic temps réel au détriment des services de données par paquet. Cependant, le trafic temps réel peut être perturbé par le trafic de données sous certaines conditions, en particulier pour les mobiles éloignés de la station de base (Node B). On propose un algorithme de sélection de TFC qui limite ces perturbations et qui offre une plus large zone de couverture aux services temps réels. En plus, il améliore la QoS du service de données et le débit effectif de l'UE sans augmenter sa puissance de transmission. Un autre type d'études concerne l'ordonnancement de paquets entre les différents utilisateurs ou UEs. C'est une procédure qui est contrôlée par la partie fixe du réseau. Nous l'étudions principalement par simulation en considérant divers mécanismes ou variations. Un premier mécanisme est nommé fast Variable Spreading Factor (fast VSF): les UEs distants changent rapidement leur facteur d'étalement (SF) afin de conserver une puissance de transmission constante, ce qui vise à stabiliser l'interférence inter-cellulaire. Un deuxième mécanisme étudié est un accès paquet décentralisé (decentralized mode) utilisant une information en retour sur le niveau global d'interférence dans la cellule. Un troisième mécanisme nommé "fast scheduling" (ordonnancement rapide) raccourcit le cycle d'ordonnancement. Les résultats ont montré que dans le cas de faible ou moyenne charge dans la cellule, le mode décentralisé réduit le délai par paquet jusqu'à 25 %. L'ordonnancement rapide augmente la capacité du système jusqu' à 10%. En plus, il améliore la QoS perçue par les utilisateurs en terme de débit par utilisateur et délai par paquet transmis.
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42

Ajayi, Idowu Iseoluwa. "Enhanced Physical Layer Security through Frequency and Spatial Diversity". Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS227.

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La sécurité de la couche physique (PLS) est un paradigme émergent qui se concentre sur l'utilisation des propriétés de la communication sans fil, telles que le bruit, l'évanouissement, la dispersion, l'interférence, la diversité, etc. pour assurer la sécurité entre les utilisateurs légitimes en présence d'un espion. Comme le PLS utilise des techniques de traitement du signal et de codage, il intervient au niveau de la couche physique et peut donc garantir le secret quelle que soit la puissance de calcul de l'espion. Cela en fait une approche intéressante pour compléter la cryptographie traditionnelle dont le principe de sécurité est basé sur la dureté informatique de l'algorithme de cryptage qui ne peut pas être facilement cassé par un espion. En outre, les récents progrès rapides des technologies de communication sans fil ont permis l'émergence et l'adoption de technologies telles que l'internet des objets, les communications ultra-fiables et à faible latence, les communications massives de type machine, les véhicules aériens sans pilote, etc. La plupart de ces technologies sont décentralisées, limitées en ressources de calcul et de puissance, et sensibles aux délais. La plupart de ces technologies sont décentralisées, limitées en ressources de calcul et de puissance, et sensibles aux délais. Cela fait du PLS une alternative très intéressante pour assurer la sécurité dans ces technologies. À cette fin, dans cette thèse, nous étudions les limites de la mise en œuvre pratique de la PLS et proposons des solutions pour relever ces défis. Tout d'abord, nous étudions le défi de l'efficacité énergétique de la PLS par l'injection de bruit artificiel (AN) dans un contexte massif d'entrées multiples et de sorties multiples (MIMO). La grande matrice de précodage dans le contexte MIMO massif contribue également à un signal d'émission avec un rapport élevé entre la puissance de crête et la puissance moyenne (PAPR). Cela nous a incités à proposer un nouvel algorithme, appelé PAPR-Aware-Secure-mMIMO. Dans ce schéma, les informations instantanées sur l'état du canal (CSI) sont utilisées pour concevoir un AN tenant compte du PAPR qui assure simultanément la sécurité tout en réduisant le PAPR. Ensuite, nous considérons le PLS par adaptation du canal. Ces schémas PLS dépendent de la précision de la CSI instantanée et sont inefficaces lorsque la CSI est imprécise. Toutefois, la CSI peut être inexacte dans la pratique en raison de facteurs tels qu'un retour d'information bruyant, une CSI périmée, etc. Pour résoudre ce problème, nous commençons par proposer un schéma PLS qui utilise le précodage et la diversité pour fournir le PLS. Nous proposons ensuite un réseau neuronal autoencodeur peu complexe pour débruiter la CSI imparfaite et obtenir des performances PLS optimales. Les modèles d'autoencodeur proposés sont appelés respectivement DenoiseSecNet et HybDenoiseSecNet. Enfin, nous étudions les performances de la PLS dans le cas d'une signalisation à alphabet fini. Les signaux gaussiens ont une grande complexité de détection parce qu'ils prennent un continuum de valeurs et ont des amplitudes non limitées. Dans la pratique, on utilise des entrées de canal discrètes parce qu'elles permettent de maintenir une puissance de transmission de crête et une complexité de réception modérées. Cependant, elles introduisent des contraintes qui affectent de manière significative la performance du PLS, d'où la contribution de cette thèse. Nous proposons d'utiliser des clés dynamiques pour partitionner les espaces de modulation de manière à ce qu'ils profitent à un récepteur légitime et non à un espion. Ces clés sont basées sur le canal principal indépendant et leur utilisation pour la partition conduit à des régions de décision plus grandes pour le récepteur prévu et plus petites pour l'espion. Ce système est appelé modulation partitionnée par index (IPM)
Physical layer security (PLS) is an emerging paradigm that focuses on using the properties of wireless communication, such as noise, fading, dispersion, interference, diversity, etc., to provide security between legitimate users in the presence of an eavesdropper. Since PLS uses signal processing and coding techniques, it takes place at the physical layer and hence can guarantee secrecy irrespective of the computational power of the eavesdropper. This makes it an interesting approach to complement legacy cryptography whose security premise is based on the computational hardness of the encryption algorithm that cannot be easily broken by an eavesdropper. The advancements in quantum computing has however shown that attackers have access to super computers and relying on only encryption will not be enough. In addition, the recent rapid advancement in wireless communication technologies has seen the emergence and adoption of technologies such as Internet of Things, Ultra-Reliable and Low Latency Communication, massive Machine-Type Communication, Unmanned Aerial Vehicles, etc. Most of these technologies are decentralized, limited in computational and power resources, and delay sensitive. This makes PLS a very interesting alternative to provide security in such technologies. To this end, in this thesis, we study the limitations to the practical implementation of PLS and propose solutions to address these challenges. First, we investigate the energy efficiency challenge of PLS by artificial noise (AN) injection in massive Multiple-Input Multiple-Output (MIMO) context. The large precoding matrix in massive MIMO also contributes to a transmit signal with high Peak-to-Average Power Ratio (PAPR). This motivated us to proposed a novel algorithm , referred to as PAPR-Aware-Secure-mMIMO. In this scheme, instantaneous Channel State Information (CSI) is used to design a PAPR-aware AN that simultaneously provides security while reducing the PAPR. This leads to energy efficient secure massive MIMO. The performance is measured in terms of secrecy capacity, Symbol Error Rate (SER), PAPR, and Secrecy Energy Efficiency (SEE). Next, we consider PLS by channel adaptation. These PLS schemes depend on the accuracy of the instantaneous CSI and are ineffective when the CSI is inaccurate. However, CSI could be inaccurate in practice due to such factors as noisy CSI feedback, outdated CSI, etc. To address this, we commence by proposing a PLS scheme that uses precoding and diversity to provide PLS. We then study the impact of imperfect CSI on the PLS performance and conclude with a proposal of a low-complexity autoencoder neural network to denoise the imperfect CSI and give optimal PLS performance. The proposed autoencoder models are referred to as DenoiseSecNet and HybDenoiseSecNet respectively. The performance is measured in terms of secrecy capacity and Bit Error Rate (BER). Finally, we study the performance of PLS under finite-alphabet signaling. Many works model performance assuming that the channel inputs are Gaussian distributed. However, Gaussian signals have high detection complexity because they take a continuum of values and have unbounded amplitudes. In practice, discrete channel inputs are used because they help to maintain moderate peak transmission power and receiver complexity. However, they introduce constraints that significantly affect PLS performance, hence, the related contribution in this thesis. We propose the use of dynamic keys to partition modulation spaces in such a way that it benefits a legitimate receiver and not the eavesdropper. This keys are based on the independent main channel and using them to partition leads to larger decision regions for the intended receiver but smaller ones for the Eavesdropper. The scheme is referred to as Index Partitioned Modulation (IPM). The performance is measured in terms of secrecy capacity, mutual information and BER
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43

Guobaitis, Vincent Michael. "An analysis of state efforts on adaptation to climate change in the transportation sector with applications to Georgia". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42905.

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With climate change arising as an important issue in the 21th century, many states have been working diligently to develop climate action plans with the hopes of reducing greenhouse gas emissions and stop climate change from occurring. According to scientists' theories, however, many places across the globe are already feeling the effects of a changing climate and must therefore switch their focus from mitigation to adaptation. In the United States, there has been a focus on how climate change will impact one of the most vulnerable parts of the country, the transportation infrastructure. Many countries have already begun adapting their transportation infrastructure to climate change including the United States. This thesis focuses on how states are adapting to climate change by analyzing strategies, frameworks, and reports released by these states in order to document where they stand in regards to adaptation of the transportation network. The states that are adapting their transportation infrastructure are Washington, Oregon, California, Hawaii, Alaska, Florida, North Carolina, Maryland, Delaware, Pennsylvania, Michigan, Connecticut, Massachusetts, Vermont, and Maine. There is also a brief summary of how Canada and the United Kingdom are preparing for climate change with an analysis of frameworks and strategies used to adapt their transportation infrastructure. The ultimate goal of this thesis is to provide engineers and policymakers with evidence that several states are implementing adaptation into transportation projects and provide a variety of strategies for them to use in their own state. Specifically, this report provides applications of adaptation for Georgia to use, so that they can begin the lengthy process of adapting their transportation infrastructure to climate change.
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44

Hubeika, Valiantsina. "Intersession Variability Compensation in Language and Speaker Identification". Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2008. http://www.nusl.cz/ntk/nusl-235432.

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Variabilita kanálu a hovoru je velmi důležitým problémem v úloze rozpoznávání mluvčího. V současné době je ve velkém množství vědeckých článků uvedeno několik technik pro kompenzaci vlivu kanálu. Kompenzace vlivu kanálu může být implementována jak v doméně modelu, tak i v doménách příznaků i skóre. Relativně nová výkoná technika je takzvaná eigenchannel adaptace pro GMM (Gaussian Mixture Models). Mevýhodou této metody je nemožnost její aplikace na jiné klasifikátory, jako napřílad takzvané SVM (Support Vector Machines), GMM s různým počtem Gausových komponent nebo v rozpoznávání řeči s použitím skrytých markovových modelů (HMM). Řešením může být aproximace této metody, eigenchannel adaptace v doméně příznaků. Obě tyto techniky, eigenchannel adaptace v doméně modelu a doméně příznaků v systémech rozpoznávání mluvčího, jsou uvedeny v této práci. Po dosažení dobrých výsledků v rozpoznávání mluvčího, byl přínos těchto technik zkoumán pro akustický systém rozpoznávání jazyka zahrnující 14 jazyků. V této úloze má nežádoucí vliv nejen variabilita kanálu, ale i variabilita mluvčího. Výsledky jsou prezentovány na datech definovaných pro evaluaci rozpoznávání mluvčího z roku 2006 a evaluaci rozpoznávání jazyka v roce 2007, obě organizované Amerických Národním Institutem pro Standard a Technologie (NIST)
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45

Breslin, Catherine J. "Explorations of neurobiology with analogue integrated circuits : ion channels and intraneuronal adaptation". Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/12758.

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One method for exploring neurobiology is to build analogue integrated, circuits which are then used as models for developing and testing theories of the brain. The original motivation for the use of analogue integrated circuits was the concept of a physical equivalence between field-effect transistors operating in the weak-inversion region and ion channels permitting ion conductance through the neuronal membrane. The concept of physical equivalence is examined, with respect to both the physical processes occurring in ion channels and transistors and the equivalences that can be found between neurobiology and models of neurobiology. Changes in ion conductance are the basis for the transmission of electrical impulses in neurons and nervous systems. For the transmission to benefit, or at least not harm, the chances of survival for the organism's genetic material, it must be capable of adapting to changing environment. It has been suggested that ion channels undergoing electrokinesis along the neuronal membrane are a component of intraneuronal adaptation. Analogue integrated circuitry is built to represent the neuronal membrane, a population of dendritic N-type Ca++ channels and intraneuronal adaptation. This is used to link the electrokinesis theory with recent observations of ion channel behaviour, specifically the ion channel gating mechanism, gating modes and transitions between them. The effect of gating in ion channels on the overall output of a neuron is examined and the circuitry is shown to perform a simple adaptation task.
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46

Rodriguez, Osuna Andrea. "Adaptation Funding to Climate Changeunder the Global Environment Facility : An Analysis of Bolivia’s Adaptation Project". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-150785.

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Adaptation finance has recently become an essential component to address internationalclimate change impacts. The Global Environment Facility (GEF) is the main mechanismproviding financial adaptation assistance from developed to developing countries. Underthis mechanism, Bolivia figures as the country with more projects than any other eligiblecountry, giving the impression that Bolivia receives favourable treatment when resourcesare allocated. This study analyzes the process by which Bolivia receives funding foradaptation projects using the principle of good governance and elements of accountability,fairness and effectiveness in the allocation of resources, to understand how suchadaptation projects are granted. The analysis results showed the process in Bolivia has lowlevels of accountability, neither low or high levels of fairness and low levels ofeffectiveness and that the theories presented by the literature review reflect the resultsfound. The analyses also suggested that it is difficult to determine that Bolivia receivesfavourable treatment because all projects where Bolivia received funding are all sharedwith other countries. It was also found that two projects are currently suspended and notyet implemented.
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47

Nanduri, Chandra Sekhara Srinivas. "Platform business models : incumbent adaptation perspectives subsequent to discontinuous changes". Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/80492.

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This thesis explored the impact of platforms on South African Banking, Telecom and Media industries, studying how the industry competes or collaborates with the phenomenon. Thus far, research focuses on non-existential threats, which allowed for long-term adaptation and scant evidence about incumbent adaptation under discontinuous changes. This research looked at two key questions: (a) how discontinuous changes impact incumbents; and (b) how incumbents adapt their exploration and exploitation balance subsequent to discontinuous changes. A qualitative methodology was applied to answer these research questions. Semi-structured interviews were conducted with leaders and senior management involved in the organisational sense-making process to understand the phenomenon. Interview findings were analysed using thematic analysis to generate insights and meanings from the adaptation experiences. This study contributes to the literature by combing incumbent adaptation, discontinuous changes, and organisational design aspects based on in-depth interviews. There are four main findings: one, platforms were perceived as a threat, affirming past research; two, leadership assumes 3–5 years for full-scale adaptation before entirely disrupted, supporting past research in the domain; three, contrary to the literature, which expects increased exploration during discontinuous changes, Incumbents balancing their exploration and exploitation initiatives is a significant revelation; four, the transformation journey was mostly led by Top Management Teams (TMT), who preferred to run these initiatives as a separate organisation. However, these Incumbents are yet to achieve the much-talked-about network effects and the scale compared to digital-first ventures; whether their approach yields result or not, no Oracle can tell.
Mini Dissertation (MPhil)--University of Pretoria, 2020.
Gordon Institute of Business Science (GIBS)
MPhil
Unrestricted
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48

Gruionu, Gabriel. "Structural adaptation of arcade arteries to changes in blood flow". Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280607.

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Arcades are blood vessels that form direct connections between two arteries or arterioles. Because they are supplied with blood from two sources, arcades can function as alternative flow pathways following obstruction of arteries or arterioles, as in coronary and peripheral vascular disease and stroke. In response to changes in blood flow or metabolic conditions, vascular networks undergo structural adaptation or remodeling, which includes structural changes of the existing vessels and growth of new vessels. Following obstruction of a blood supply, arcade vessels may adjust their internal diameters chronically to convert the alternative pathways into main blood distribution vessels. The overall goal of this dissertation was to examine structural changes in the internal diameter of a single arcade artery and the arterioles of an arcade network following changes in blood flow, using experimental and theoretical approaches. Diameter changes of the mouse gracilis arcade artery were observed up to 56 days following resection of one of its two blood supplies. Overall, diameters increased to a maximum around day 21 and then declined. The diameter changes were spatially non-uniform, being largest towards the point of resection, providing transiently increased perfusion to the most affected regions. Observed diameter changes were compared with predictions of a theoretical model, in which diameter varies in response to stimuli derived from local metabolic and hemodynamic conditions. Good agreement was found when effects of a time-delayed growth stimulus in regions of reduced perfusion were included, with a delay of about 7 days. The effectiveness of arcades in maintaining perfusion both immediately following obstruction and after structural adaptation in the arteriolar arcade network between two feed artery branches of the pig triceps brachii muscle was examined. Morphometric data from vascular casting and published data were used to develop a computational model for the hemodynamics and structural adaptation of the network in response to local stimuli. The results show that the arcades provide alternative flow pathways to the region initially supplied by the obstructed branch and that structural adaptation can lead to improved flow restoration following interruption of blood flow.
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49

Simpson, James Hightower. "Leadership Adaptation to Changes in Public Funding of Community Colleges". ScholarWorks, 2017. https://scholarworks.waldenu.edu/dissertations/3369.

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Although growth in U.S. community colleges has been exponential, a major challenge accompanying that growth has been the source of funding, which has consisted of shifting proportions of tuition, local taxes, and state aid. The shift away from state aid toward fundraising, profit-oriented research, sophisticated financing, and higher tuition presents challenges and unintended consequences. This shift could threaten the community college access mission and contribute to a perception of higher education as a private good rather than a public good. With a framework of academic capitalism and resource dependency theories, the purpose of this basic qualitative interview study with 7 leaders from executive teams in community colleges was to explore strategies used in adapting to the changes in funding models. Participants were recruited using snowball sampling, and interview data were analyzed to identify recurring themes. Findings indicated a need for strategies to replace state funding; grants and fundraising were not considered sufficient. Strategies such as working cash bonds, prioritization studies, and differential tuition programs were reported to have long-term potential, but their efficacy remained to be confirmed. Restoring state funding would require that colleges align interests with legislators and donors, research and develop bold initiatives, craft successful communication and marketing strategies, and facilitate a culture shift within their institution that embraces the need for alternative revenue streams. This study raises awareness that rising tuition and education costs in general may threaten the community college mission, limiting access to higher education for students, especially for lower SES students who cannot afford the debt to fund the higher tuition.
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50

West, Crystal. "Renal Epithelial Sodium Channel (ENaC) Regulation of Pregnancy Mediated Hemodynamic Adaptations: Mechanistic Insights". VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/260.

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Pregnancy-mediated sodium (Na) retention is required to provide an increase in plasma volume for the growing fetus. The mechanisms responsible for this Na retention are not clear. In the first study, we generated a renal tubule protein profile indicating α ENaC as the only sodium transport protein upregulated in mid and late pregnancy. To determine the in vivo activity of ENaC we conducted in vivo studies in late pregnant rats (day 18-20) and virgin rats to measure the natriuretic response to ENaC blockade (with benzamil). The in vivo activity of ENaC (UNaV post benzamil - UNaV post vehicle) was markedly increased in late pregnancy and this difference was abolished by pretreatment with the mineralocorticoid receptor antagonist, eplerenone. These findings demonstrate that the increased α ENaC subunit of pregnancy is associated with a mineralocorticoid-dependent increase in ENaC activity. The plasma volume increased progressively during pregnancy with the greatest plasma volume being evident in late pregnancy. ENaC inhibition abolished the difference in plasma volume status between virgin and pregnant rats. This indicates ENaC activity is a major contributor of plasma volume status in late pregnancy. Inadequate plasma volume expansion results in complicated pregnancy with growth restricted (GR) fetus and maternal/fetal death. The second study aimed to determine the importance of renal vs extrarenal ENaC in sodium retention and blood pressure regulation during pregnancy to do so we chronically blocked ENaC with either daily subcutaneous injections of benzamil (BZ) or intrarenal transfection of αENaC shRNA. Chronic ENaC blockade with benzamil prevented normal sodium retention in the pregnant rat. Prevention of sodium retention resulted in reduced maternal serum sodium concentration, blood pressure, body weight, and fetal growth restriction. However, chronic benzamil treatment had no effect on sodium retention, body weight, or BP in virgin rats. Intrarenal transfection of a shRNA targeting αENaC successfully decreased renal αENaC mRNA expression in late pregnant rats compared to controls transfected with scrambled sRNA. Intrarenal transfection of αENaC shRNA reduced sodium retention maternal, ΔBW, and pup weight. These findings suggest that renal ENaC is necessary for maintenance of sodium balance, blood pressure regulation, and progression of a healthy pregnancy. In the third study, we performed large-scale proteomic analysis on late pregnant and virgin principal collecting duct cells, isolated by laser capture microscopy. The primary aim of this project was to identify potential proteins or signaling pathways that could account for the sodium retention occurring in pregnancy. Large-scale liquid chromatography tandem mass spectrometry (LC-MS/MS) was performed at the NIH which identified a total of 365 proteins in virgin and late pregnant collecting duct cells. We identified pregnancy associated abundance changes in six proteins related to the ubiquitin/proteasome degradation pathway. Since a major mechanism of ENaC regulation is through trafficking we focused on changes in this pathway and their implications for enhancing ENaC activity during pregnancy. The final study aimed to apply these findings to the overall theme of pregnancy as a state of arterial underfilling. We performed a Na transporter profile in kidney cortex homogenates from animals treated chronically with vasodilators (nifidipine or sodium nitrate). We found that only the abundance of transporters in the distal nephron (NCC, ENaC, AQP2) was similar to pregnancy, however differences were seen in pre-macula densa transporters (NHE3, NKCC2). The similar changes observed in the distal convoluted tubule and renal collecting duct promote Na and water retention. The changes in these transporters may explain the similar plasma volume expansions previously described in pregnant and chronically vasodilated rats, thus supporting the underfill hypothesis of pregnancy. Taken together, this project supports an important role for the collecting duct in the pregnancy mediated sodium and fluid reabsorption during pregnancy.
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