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Studies of a Variable Voltage PEM Fuel Cell StackSu, You-Min 13 October 2009 (has links)
In this paper a proton exchange membrane fuel cell (called PEMFC)
stack was developed to power or charge 3C products without any voltage
transformer. PEMFC stacks made with traditional bipolar plates to
generate a high voltage are usually by accumulating multiple single fuel
cells together. The design with traditional heavy and large bipolar plates
is inconvenient for 3C products to generate a high voltage in a finite
volume. To solve this problem, a heterogeneous carbon fiber bunch
unipolar plate is adopted to replace traditional bipolar plates, and a
special membrane electrode assembly (called MEA) with multiple sets of
banded electrodes is used to replace a traditional MEA that is made with
only a set electrodes. With this new design, the fuel cell voltage can
easily increase in a layer. The designed stack can provide multiple
voltages and currents by proper series and/or parallel connections.
The variable voltage 16-cell fuel cell is composed of 4-layer
4-banded type MEAs and 5 heterogeneous carbon fiber bunch bipolar
plates. The 16-cell stack is divided into 4 sets. Each set of 4 series
connection cell is arranged in a line in 4 different layers. The 4-cell sets
can connect by series/parallel on the two ends of the stack. The total
volume of the 16-cell stack is 385cm3 and its weight is 365g. The new
design can power or charge certain 3C products directly.
If 2 sets of 4-cell fuel cells are connected in series, the stack can
provide 2A at 3.6V. With the above 2 sets of 2*4-cell connected in
parallel, the stack can provide 3.5A at 3.6V. If the 4 sets of 4-cell are all
connected in series, the stack can provide 1.8 A at 7.2V. These voltages
and currents derived from these stacks can power or charge a mobile
phone, a photo camera and a video camera directly. If a higher voltage or
current are needed, two or more 16-cell stacks can be connected in series
XI
or parallel. Then notebooks or any other 3C products in which higher
power are needed can be driven.
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Pomidorų kekerinio puvinio ir maro išplitimo dinamika uždaro grunto sąlygomis / The purpose of research - the investigation of impact fungi (Phytophthora infestans) and (Botrytis aclada) exert on tomato under the growing conditions of closed soilMačiulaitienė, Laura 08 August 2007 (has links)
Darbo tikslas – ištirti pomidorų kekerinio puvinio – (Botrytis cinerea) ir maro (Phytophthora infestans) išplitimą uždaro grunto sąlygomis. Stebėjimai buvo atliekami 2006 metais Kėdainių rajone, Žiogaičių kaime, ūkininko Aurelijaus Bieliausko ūkyje. Šiltnamio plotas 1026,6 m2 . Pomidorai- viena svarbiausių ir populiariausių šiltnamių daržovių. Pastaruoju metu daugiausia žalos padaro šios pomidorų ligos: šiltnamiuose – kekerinis puvinys; lauke ir šiltnamiuose – maras. Dėl nepalankių augalams augti sąlygų, kurios sukelia fiziologines ligas, lapai gelsta, susisuka, lapai ir viršūnės nyksta, vaisių viršus gali pradėti pūti, trūkinėti, deformuotis, ant jų paviršiaus atsiranda dėmių. Dėl įvairių priežasčių, tai drėgmės perteklius arba stygius, blogai vėdinami šiltnamiai, netinkamai tręšiami augalai, per aukšta ar per žema oro temperatūra, dideli jos svyravimai, bloga žemės aeracija, šviesos trūkumas, mechaniniai augalų sužalojimai – tai dažnos įvairių ligų plitimo priežastys. Mažėja augalų produktyvumas, nukenčia derliaus kokybė. Kai ligoms plisti sąlygos palankios, sutrumpėja vegetacija ir augalai masiškai žūsta. Pirmieji ligų požymiai pastebėti birželio mėn. 03 d. Daugiausiai augalų buvo pažeista 06 16 ir pažeidimai, įvairiu intensyvumu, siekė net 50% visų stebimų augalų. 2006 m birželio 29 dieną, buvo atliekamas pomidorų stebėjimas ir nustatyta, jog abiejų veislių kontroliniai variantai visiškai sunykę. / The purpose of research - the investigation of impact fungi (Phytophthora infestans) and (Botrytis aclada) exert on tomato under the growing conditions of closed soil. Observation was made in 2006 in Kėdainiai disrtict, village of Žiogaičiai, in farmer Aurelijus Bieliauskas farm. Size of the greenhause shed is 1026.6 square metres. Recently most dangerous tomato dieseases are: in a warm shed - (Botrytis cinerea), Outside and in the warm shed – (Botrytis aclada). Plague, in an old warm sheds, where soil hasn‘t been changed for a while: - root decay and wilt . In case of negative growing conditions, which causes physiological disease, leaves gets yellow, twists, leaves falls down from the top , decay of the top part of fruit, they cracks, deforms and spots appears. In many cases its to much or not enough rain, bad airing in a warm shed, wrong manure , to high or to low temperature, high temperature fluctuation, bad ground airing, not enough light, mechanical damage – they all are common reasons which causes plant diseases. It decreases plat productivity, looses yield quality. When conditions are good for disease spreading, vegetation gets shorter and plants dies. First signs of disease were noticed on the third of June. More plant were affected on the 16th of June and signs were various and reached over 50% researched plants. On the 29th of June 2006, was made tomato research and stated that both breed checkpoints was totally decadent.
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Caracterização de variedades de amendoim cultivadas em diferentes populações /Bulgarelli, Elisangela Maria Bernal. January 2008 (has links)
Resumo: Para obtenção de bons resultados de produtividade com menor custo, o uso do espaçamento entrelinhas e densidades de plantas na linha devem ser adequados, pois, a população de plantas é um dos fatores que se destacam por afetar diretamente os componentes de produção. Tendo em vista a escassez de informações relacionadas ao comportamento de variedades de amendoim, principalmente as rasteiras, cultivadas em diferentes populações, propôs-se no presente trabalho estudar os efeitos da densidade de plantas no desenvolvimento e produtividade do amendoim. Foram conduzidos três experimentos envolvendo três cultivares, sendo duas rasteiras Runner IAC 886 e IAC Caiapó e uma ereta IAC Tatu ST. Foram estudadas quatro densidades de plantas (22, 18, 12 e 6 plantas/m) mantendo-se o espaçamento entrelinhas em 0,90 m. Utilizou-se o delineamento em blocos ao acaso com quatro repetições, sendo a parcela experimental constituída de 7 linhas de 5 m de comprimento. Os resultados foram submetidos à análise de variância pelo teste F e as médias foram comparadas pelo teste de Tukey a 5% de probabilidade. As características relacionadas ao crescimento vegetativo foram pouco influenciadas pelas densidades de plantas. A cultivar Runner IAC 886 apresentou maior número de ramificações na menor densidade de plantas e a IAC Caiapó, apresentou maior comprimento de ramificações na maior densidade de plantas. Dentre as características relacionadas à produtividade, a mais afetada pela densidade de plantas foi o número de vagens por planta. A cultivar IAC Caiapó apresentou maior número de vagens por planta na menor densidade testada. As cultivares rasteiras Runner IAC 886 e IAC Caiapó apresentaram produtividades semelhantes nas diferentes densidades testadas e a ereta IAC Tatu ST, maiores produtividades nas maiores densidades de plantas. / Abstract: The row spacing and plants density must be adequate for obtaining yield increases with lower costs, since the plants population is one of the main factors directly affecting the yield components. Once the information related to peanut varieties behavior in different populations is scarce, the aim of the present work was to study the effect of plants density on peanut yield and development. Experiments were carried out using three cultivars, the runner type ones Runner IAC 886 and IAC Caiapó and the bunch type IAC Tatu ST. Four plants density (22, 18, 12 and 6 plants per meter of row) were evaluated in 0.90 m row spacing. The randomized block design was used with four replicates, being the experimental plots composed by 7 rows of 5 m length each. Data were submitted to the variance analysis by the F test and means were compared by the Tukey test (5% probability). Traits related to vegetative growth were lightly affected by the different plants density. The higher plant branching was observed at the lower density for the Runner IAC 886 cultivar, while the IAC Caiapó showed higher plant branching at the higher density. Among the yield components, the number of pods per plant was the most affected trait by the plants density change. The IAC Caiapó cultivar showed the higher number of pods per plant at the lower tested density. Otherwise, the runner type cultivars Runner IAC 886 and IAC Caiapó showed similar results for yield at the different tested densities, whereas the bunch type IAC Tatu ST had higher yield at higher plants density. / Orientadora: Maria Aparecida Pessôa da Cruz Centurion / Coorientadora: Fabíola Vitti Moro / Banca: João Carlos de Oliveira / Banca: Ivana Marino Bárbaro / Mestre
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Sensor technology to assess grape bunch temperature variability in Vitis vinifera L. cv. ShirazMoffat, Tessa 03 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The microclimate environment around the bunch is complex. The spatial distribution of leaves as well as bunch position and morphology impact on the path of direct radiation received by the berries. Canopy microclimate is largely determined by the meteorological conditions (air temperature, solar radiation, wind speed and direction, relative humidity, and precipitation) as well as management practices (trellis/training system, canopy height, vine spacing, row orientation, canopy management practices, irrigation and soil variability and management). The fact that the grapevine continuously responds to its environment, adds to the complexity and dynamic nature of the microclimate that the bunches experience. Field studies involving the effect of the natural bunch environment (i.e. light and temperature conditions) on berry composition, are therefore a challenge, due to the difficulties in quantifying meteorological elements such as temperature and light, which can be hugely variable.
There are different sensors available to assess bunch and berry temperature and it can be deployed in different ways within the grapevine canopy, but the difficulty remains in studying the variability that exists within a bunch. This study investigated the value of available sensor technology to measure bunch/berry temperature as well as the spatial and temporal variability on a bunch. Differences in temperature on an intra-berry level were assessed whereas the impact of canopy configuration and bunch orientation on the different sensor levels was also investigated. The contribution of macro- and mesoclimate on bunch and berry temperature was addressed by measuring at two locations (Robertson and Stellenbosch). The potential long term differences in temperature within a bunch with regard to thermal accumulation are discussed. Issues around sensor placement and some technical difficulties related to the sensors are discussed. The results indicated how the effects of mesoclimate were transferred through to the different sensors. A dominating effect of the sea breeze in Stellenbosch was found. Canopy configuration/architecture affected the light regime in the canopy, consequently impacting on bunch temperature variability, specifically in Stellenbosch where a "Ballerina" trellising system was used. Bunch orientation resulted in differences in the temporal variability of bunch/berry temperature and little variability was observed in temperature within the berry. Temperatures of berries situated at the back of the bunch were judged more optimal compared to exposed berries. Direct radiation caused extreme temperatures in exposed berries, which may be detrimental to berry composition and wine quality. This emphasized the importance of the canopy (trellis/training system and management practices) in protecting the bunch from extreme conditions. The large on-bunch spatial variability, observed from measurements with the thermal imager, demonstrated the importance of sensor placement in quantifying the bunch temperature regime; this is also relevant for the future development of berry temperature modelling. Thermal accumulation through the season also illustrated the variability that existed within a bunch, suggesting a potential long term effect on the berry composition. This study proved, in conditions similar to those that may prevail in the South African wine industry, that sensor type and positioning need to be carefully considered in any viticultural/oenological study where bunch microclimate and grape temperatures are assessed. / AFRIKAANSE OPSOMMING: Die mikroklimaat omgewing rondom die tros is kompleks. Die ruimtelike verspreiding van blare sowel as trosposisie en -morfologie het 'n impak op die pad waarlangs direkte straling ontvang word deur die korrels. Lowermikroklimaat word grootliks bepaal deur die meteorologiese kondisies (lugtemperatuur, sonstraling, windspoed en -rigting, relatiewe humiditeit en reënval) sowel as bestuurspraktyke (prieel/opleistelsel, lowerhoogte, wingerdstokspasiëring, ry-oriëntasie, lowerbestuurspraktyke, besproeiing asook grondvariasie en bestuur). Die feit dat die wingerdstok voortdurend reageer op sy omgewing dra by tot die kompleksiteit en dinamiese aard van die mikroklimaat wat die trosse ervaar. Veldstudies gemoeid met die effek van die natuurlike trosomgewing (d.w.s. lig- en temperatuurkondisies) op korrelsamestelling is daarom 'n uitdaging. Die rede hiervoor is dat dit problematies is om meteorologiese elemente soos temperatuur en lig, wat baie veranderlik kan wees, te kwantifiseer.
Verskillende sensors is beskikbaar waarmee tros- en korreltemperatuur bepaal kan word en dit kan op verskillende wyses binne die wingerdstoklower aangewend word. Die bestudering van die variasie wat bestaan binne 'n tros is egter steeds problematies. Hierdie studie het die waarde ondersoek van die beskikbare sensortegnologie vir die meting van tros/korreltemperatuur en die ruimtelike en tydsvariasie op 'n tros. Verskille in temperatuur op 'n intra-korrelvlak is bepaal terwyl die impak van lowerkonfigurasie en trosoriëntasie op die verskillende sensorvlakke ook ondersoek is. Die bydrae van makro- en mesoklimaat tot tros- en korreltemperatuur is ondersoek deur te meet by twee verskillende liggings (Robertson en Stellenbosch). Die potensiële langtermyn verskille in temperatuur binne-in 'n tros met betrekking tot temperatuur akkumulasie word bespreek. Kwessies rakende sensorplasing en sommige tegniese probleme wat verband hou met sensors word bespreek. Die resultate het aangedui hoedat die effekte van mesoklimaat oorgedra is na die verskillende sensors. 'n Dominerende effek van die seebries is waargeneem in Stellenbosch. Lowerkonfigurasie/argitektuur het die ligregime in die lower beïnvloed en gevolglik 'n invloed gehad op die trostemperatuur veranderlikheid. Dit was veral die geval in Stellenbosch waar 'n "Ballerina" opleistelsel gebruik is. Trosoriëntasie het gelei tot verskille in tydsvariasie van tros/ korreltemperatuur en min variasie is waargeneem in temperatuur binne die korrel. Temperature van korrels wat voorkom aan die agterkant van die tros is beoordeel as meer optimaal vergeleke met blootgestelde korrels. Direkte straling het uiterste temperature in blootgestelde korrels veroorsaak wat nadelig kan wees vir korrelsamestelling en wynkwaliteit. Hierdeur is die belang van die lower (prieel/opleistelsel en bestuurspraktyke) om die tros te beskerm teen uiterste kondisies beklemtoon. Die groot ruimtelike variasie op 'n tros, soos waargeneem in metings met die termiese kamera, het die belangrikheid van sensorplasing in die kwantifisering van die trostemperatuur regime beklemtoon. Dit is ook relevant vir die toekomstige ontwikkeling van korreltemperatuur modellering. Termiese akkumulasie gedurende die seisoen is ook geïllustreer deur die veranderlikheid wat voorkom binne 'n tros, wat dui op 'n potensiële langtermyn effek op die korrelsamestelling. Hierdie studie het bewys, in kondisies wat algemeen voorkom in die Suid-Afrikaanse wynbedryf, dat sensortipe en -plasing sorgvuldig in ag geneem moet word in enige wingerd/wynkundige studie waar trosmikroklimaat en druiftemperature bepaal word. / Winetech and the National Research Foundation for their financial support of the project
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Radio resource management for wireless indoor communication systems : performance and implementation aspectsPettersson, Stefan January 2004 (has links)
In this thesis, we investigate several radio resourcemanagement (RRM) techniques and concepts in an indoorenvironment with a dense infrastructure. Future wireless indoorcommunication networks will very likely be implemented atplaces where the user concentration is very high. At these hotspots, the radio resources must be used efficiently. The goalis to identify efficient RRM techniques and concepts that aresuitable for implementation in an indoor environment. Handling the high level of co-channel interference is shownto be of paramount importance. Several investigations in thethesis point this out to be the key problem in an indoorenvironment with a dense infrastructure. We show that a locallycentralized radio resource management concept, the bunchconcept, can give a very high performance compared to othercommonly used RRM concepts. Comparisons are made withdistributed systems and systems using channel selection schemeslike CSMA/CA. The comparisons are primarily made by capacityand throughput analysis which are made by system levelsimulations. Results show that the centralized concept can give85 percent higher capacity and 70 percent higher throughputthan any of the compared systems. We investigate several RRM techniques to deal with thechannel interference problem and show that beamforming cangreatly reduce the interference and improve the systemperformance. Beamforming, especially sector antennas, alsoreduce the transmitter powers and the necessary dynamic range.A comparison is made between the use of TD/CDMA and pure TDMAwhich clearly shows the performance benefits of usingorthogonal channels that separates the users and reduces theco-channel interference. Different channel selection strategiesare studied and evaluated along with various methods to improvethe capability of system co-existence. We also investigate several practical measures to facilitatesystem implementation. Centralized RRM is suitable forguaranteeing QoS but is often considered too complex. With thestudied centralized concept the computational complexity can bereduced by splitting the coverage area into smaller pieces andcover them with one centralized system each. This reduces thecomplexity at the prize of lost capacity due to theuncontrolled interference that the different systems produce.Our investigations show that sector antennas can be used toregain this capacity loss while maintaining high reduction incomplexity. Without capacity loss, the computational complexitycan be reduced by a factor of 40 with sectoring. Theimplementation aspects also include installation sensitivity ofthe indoor architecture and the effect of measurement errors inthe link gains. The robustness against installation errors ishigh but the bunch concept is quite sensitive to largemeasurement errors in the studied indoor environment. Thiseffect can be reduced by additional SIR-margins of the radiolinks. The studied bunch concept is shown to be promising for usein future wireless indoor communication systems. It provideshigh performance and is feasible to implement. Keywords:Radio resource management, indoorcommunication, the bunch concept, centralized RRM, dynamicchannel allocation, channel selection, co-channel interference,power control, feasibility check, capacity, throughput, qualityof service, beamforming, downtilting, sector antennas,co-existence, computational complexity, sensitivity analysis,measurement errors, infrastructure, system implementation,WLAN, HiperLAN/2, IEEE 802.11.
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Electro-optic diagnostic techniques for the CLIC Linear ColliderPan, Rui January 2015 (has links)
One of the most promising devices to provide accurate measurement of the longitudinal bunch profile at the tens of femtosecond level is based on electro-optic techniques. In this thesis, a bunch profile monitor, based on electro-optic spectral decoding (EOSD), is currently developed for the CLIC Test Facility 3 at CERN. The monitor is optimised for bunch lengths over 3.5 ps with effective window of 16 ps, and sub-picosecond resolution. The measurement results from the EO monitor are compared with measurements by coherent transition radiation on a streak camera. The measurement on bunch charge dependence is studied. Timing resolution of the bunch profile monitor is studied in both theory and numerical calculation. This thesis summarises a frequency analysis approach of electro-optic effect based on $\chi^{(2)}$ frequency mixing process. From the theory analysed in frequency domain, a non-crossed polarization measurement includes all three of the probe laser background term, the linear term to Coulomb field and the quadratic term to Coulomb field. Three methods are induced based on this frequency analysis result to retrieve Coulomb field value which is emitted from electron beam. The measured 1.3 MV/m field strength agrees with calculation result. An experiment is designed to study the role of incident beam sizes and non-collinear incident beams in EO technique. Due to the phase matching process, the non-collinear angle of the incident beams induces a frequency dependent angular chirp in the beams emitted after the EO crystal. This frequency offset may lead to frequency loss in fibre coupling, and thus lead to bunch length broadening in a measurement for short electron bunch.
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Feedback Systems for Control of Coupled-bunch Instabilities in the Duke Storage RingWu, Wenzhong January 2012 (has links)
<p>The Duke storage has been developed as a dedicated driver for the storage ring based free-electron lasers (FEL) and a high flux Compton gamma-ray source, the High Intensity Gamma-ray Source. The storage ring can be operated from about 250 MeV to 1.2 GeV, which can produces FEL lasers over a wide range of wavelengths and gamma-rays with a tunable energy from 1 MeV to 100 MeV. The Duke light source facility conducts world-class researches across a wide range of scientific disciplines and technological applications.</p><p> In a storage ring, beam instabilities can cause a signifcant degradation in machine performance. In the Duke storage ring, coupled-bunch instabilities (CBIs) are the main source which limit ultimately achievable beam current in multi-bunch operations. In order to to suppress CBIs in the Duke storage, we developed a bunch-bybunch longitudinal feedback (LFB) system which is based on a field programmable gate array (FPGA) embedded system. During the design and implementation of the LFB system, several novel methods and techniques are developed in numerical analysis of feedback control and kicker cavity design/fabrication. High current are realized at low energies by using the LFB system. In addition, after the successful commissioning of the LFB system, a analog transverse feedback (TFB) system has been upgraded to a digital one using the same technique as the LFB system. </p><p>The LFB system has been routinely operated for HIGS. Additional,the LFB and TFB feedback systems become an useful diagnostic tools in researches of electron beam dynamics, FEL lasing process, and background of HIGS. The control of CIBs in different operation modes are studied using the feedback system. Furthermore, based on the TFB system, a novel bunch cleaning method has been developed to reduce the background of gamma-ray.</p> / Dissertation
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Studies and Development of Self-humidifying PEM Fuel CellChen, Chun-Yu 05 September 2011 (has links)
¡@¡@In this thesis, we develop a self-humidifying PEMFC. The humidifying effects on the stability and impedance of the fuel cell are studied. A portable and passive PEMFC stack usually exposes in the ambient no matter that it works or not. However, the ambient is far from saturated. The water within MEA will diffuse to the membrane¡¦s surface and evaporate continuously. The membrane will be short in water without water supplying. Because the conductivity of H+ of the membrane is highly dependent on water content, the dehydration of the membrane will reduce the interconnected passageway of H+ and affect the performance of fuel cell directly. And because of the different expansion rate the electrode of MEA is also possible to separate from its membrane when it operates repeatedly. This separation will make the performance of fuel cell an unrecovered decay.
¡@¡@At first, the hydration status of the dry membrane is observed. We measure the addition weight of water into membrane by using cotton thread humidifying, and estimate the water permeation distances. The maximum water supply rate of cotton thread is 4.26mg/min, and the permeation rate of water through membrane where is 2.5cm from water surface is 0.15mg/cm¡Dmin. Then we design the self-humidifying devices of PEMFC stack. The humidifying effects on performance and stability of the fuel cell are studied.
¡@¡@When the active area is 0.7¡Ñ4.5cm2 and the cotton thread is 5mm from the center of electrode the supplying water can arrive at the reaction area under the electrode through the membrane in one minute. The difference of the supplying water between the bottom and top is 7% by using 6cm cotton thread. Therefore water can hydrate the membrane and the difference of the supplying water between bottom and top is not oversize. The higher current load, the voltage efficiency is lower. The increasing heat generation rate results in the water evaporation rate would be greater than the water generation rate. So the drop of voltage under higher current is greater than lower current. By comparing with the difference of high frequency impedance the change of humidifying is smaller between 1hr operating. It indicates that humidifying by cotton thread keeps the membrane hydration.
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Manufacture and performance of the MEA of a 500W Proton exchange membrane fuel cell (PEMFC)Tsai, Po-feng 09 March 2012 (has links)
This study has two purposes: First, the catalyst-coated membrane (CCM) method to produce high performance and high utilization of electrode, and the other is to enhance the fuel cell performance with the heterogeneous carbon fiber bunch framework of stack.
First, to establish an ideal electrode structure, there has an intensive triple phase boundaries. We will describe how the procedure of reliable and practical electrode improved following the optimization of (1) the spray system, and (2) the catalyst dispersion. We will also focus (3) modification of the spray system, and (4) electrode performance analysis.
In addition, investigate of the single cell performance in heterogeneous carbon fiber bunch framework. We will find that: (1) Increasing the catalyst loading and concentrated the catalyst activation reaction, can be improve the electrode performance and catalyst utilization. (2) Coating a thin conductive layer onto membrane electrode (ME), be a precise hot-pressue process in the Stack and MEA or GDL and ME, can be reduce the contact resistance. Specially, reduce the carbon fiber coverage fraction with electrode area, result the activation reaction decay and ohmic loss obviously. (3) Increasing the gas flow rate, can enhance the mass transfer performance, but increase the pressure of the reaction gas, can¡¦t significant effect on performance. Besides, when the stack is anode side up, seems favorable to the exclusion the generate water of cathode.
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Radio resource management for wireless indoor communication systems : performance and implementation aspectsPettersson, Stefan January 2004 (has links)
<p>In this thesis, we investigate several radio resourcemanagement (RRM) techniques and concepts in an indoorenvironment with a dense infrastructure. Future wireless indoorcommunication networks will very likely be implemented atplaces where the user concentration is very high. At these hotspots, the radio resources must be used efficiently. The goalis to identify efficient RRM techniques and concepts that aresuitable for implementation in an indoor environment.</p><p>Handling the high level of co-channel interference is shownto be of paramount importance. Several investigations in thethesis point this out to be the key problem in an indoorenvironment with a dense infrastructure. We show that a locallycentralized radio resource management concept, the bunchconcept, can give a very high performance compared to othercommonly used RRM concepts. Comparisons are made withdistributed systems and systems using channel selection schemeslike CSMA/CA. The comparisons are primarily made by capacityand throughput analysis which are made by system levelsimulations. Results show that the centralized concept can give85 percent higher capacity and 70 percent higher throughputthan any of the compared systems.</p><p>We investigate several RRM techniques to deal with thechannel interference problem and show that beamforming cangreatly reduce the interference and improve the systemperformance. Beamforming, especially sector antennas, alsoreduce the transmitter powers and the necessary dynamic range.A comparison is made between the use of TD/CDMA and pure TDMAwhich clearly shows the performance benefits of usingorthogonal channels that separates the users and reduces theco-channel interference. Different channel selection strategiesare studied and evaluated along with various methods to improvethe capability of system co-existence.</p><p>We also investigate several practical measures to facilitatesystem implementation. Centralized RRM is suitable forguaranteeing QoS but is often considered too complex. With thestudied centralized concept the computational complexity can bereduced by splitting the coverage area into smaller pieces andcover them with one centralized system each. This reduces thecomplexity at the prize of lost capacity due to theuncontrolled interference that the different systems produce.Our investigations show that sector antennas can be used toregain this capacity loss while maintaining high reduction incomplexity. Without capacity loss, the computational complexitycan be reduced by a factor of 40 with sectoring. Theimplementation aspects also include installation sensitivity ofthe indoor architecture and the effect of measurement errors inthe link gains. The robustness against installation errors ishigh but the bunch concept is quite sensitive to largemeasurement errors in the studied indoor environment. Thiseffect can be reduced by additional SIR-margins of the radiolinks.</p><p>The studied bunch concept is shown to be promising for usein future wireless indoor communication systems. It provideshigh performance and is feasible to implement.</p><p><b>Keywords:</b>Radio resource management, indoorcommunication, the bunch concept, centralized RRM, dynamicchannel allocation, channel selection, co-channel interference,power control, feasibility check, capacity, throughput, qualityof service, beamforming, downtilting, sector antennas,co-existence, computational complexity, sensitivity analysis,measurement errors, infrastructure, system implementation,WLAN, HiperLAN/2, IEEE 802.11.</p>
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