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Energy Efficient Cloud Computing Based Radio Access Networks in 5G. Design and evaluation of an energy aware 5G cloud radio access networks framework using base station sleeping, cloud computing based workload consolidation and mobile edge computingSigwele, Tshiamo January 2017 (has links)
Fifth Generation (5G) cellular networks will experience a thousand-fold increase in data traffic with over 100 billion connected devices by 2020. In order to support this skyrocketing traffic demand, smaller base stations (BSs) are deployed to increase capacity. However, more BSs increase energy consumption which contributes to operational expenditure (OPEX) and CO2 emissions. Also, an introduction of a plethora of 5G applications running in the mobile devices cause a significant amount of energy consumption in the mobile devices. This thesis presents a novel framework for energy efficiency in 5G cloud radio access networks (C-RAN) by leveraging cloud computing technology. Energy efficiency is achieved in three ways; (i) at the radio side of H-C-RAN (Heterogeneous C-RAN), a dynamic BS switching off algorithm is proposed to minimise energy consumption while maintaining Quality of Service (QoS), (ii) in the BS cloud, baseband workload consolidation schemes are proposed based on simulated annealing and genetic algorithms to minimise energy consumption in the cloud, where also advanced fuzzy based admission control with pre-emption is implemented to improve QoS and resource utilisation (iii) at the mobile device side, Mobile Edge Computing (MEC) is used where computer intensive tasks from the mobile device are executed in the MEC server in the cloud. The simulation results show that the proposed framework effectively reduced energy consumption by up to 48% within RAN and 57% in the mobile devices, and improved network energy efficiency by a factor of 10, network throughput by a factor of 2.7 and resource utilisation by 54% while maintaining QoS.
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[en] SIMULATION OF RADIO ACCESS NETWORKS: BASE STATIONS POSITIONING AND RESOURCE ALLOCATION USING UTILITY CRITERIA / [pt] SIMULAÇÃO DE REDES DE ACESSO RÁDIO: POSICIONAMENTO DE ESTAÇÕES BASE E ALOCAÇÃO DE RECURSOS USANDO UM CRITÉRIO DE UTILIDADECHRISTIAN FRAGOAS F RODRIGUES 06 July 2023 (has links)
[pt] Esta tese apresenta um simulador para avaliação de desempenho de uma
rede de acesso por rádio 5G. O simulador, Sama (1), permite definir os modelos
de equipamentos das estações base com múltiplos setores e conformação de
feixes (beamforming), os arranjos de estações base da rede, os equipamentos
dos usuários, a distribuição de usuários na área de serviço, e pode empregar
diferentes algoritmos de alocação dos recursos tempo-frequenciais, dentre
outro parâmetros customizáveis. O simulador produz diversos indicadores de
desempenho da rede de acesso, como condições de canal, taxas/capacidades
de dados, latências, e satisfação dos usuários, em diversos níveis hierárquicos
(por estações base, seus setores, ou feixes). As funcionalidades do simulador
são demonstradas considerando diversos casos de uso de redes 5G. Propõe-se
metodologias para alocação de posições de estações base, isto é, para encontrar
bons arranjos de estações base. Propõe-se uma metodologia heurística baseada
em critérios de projeto para redes de radiodifusão. Para redes de acesso
celular apresenta-se uma metodologia baseada em agrupamentos (clusters) das
posições dos UEs. Por fim, nesta tese, apresenta-se um algoritmo de alocação de
recursos de tempo-frequência baseado em um critério de utilidade para alocar
recursos tempo-frequenciais em redes de acesso por rádio 5G considerando as
demandas de capacidade dos usuários. A partir da demanda individual de um
terminal, estima-se qual a utilidade em servi-lo e, a partir disso, ordenam-se os terminais em um setor e alocam-se os recursos de tempo-frequência. O
algoritmo de alocação de recursos apresentado obtém resultados competitivos
e muitas vezes melhores que algoritmos de alocação conhecidos. / [en] This thesis presents a simulator for evaluating the performance of a 5G radio access network. The simulator, called Sama(2), allows for defining the equipment models of base stations with multiple sectors and beam forming,the arrangement of base stations in the network, the user equipment, the distribution of users in the service area, and can employ different algorithms for allocating time-frequency resources, among other customizable parameters. The simulator produces various performance indicators for the access network, such as channel conditions, data rates/capacities, latencies, and users satisfaction, at different hierarchical levels (per base stations, their sectors, or beams).The functionalities of the simulator are demonstrated considering different use cases for 5G networks. Methodologies are proposed for allocating base station positions, that is, finding good base station arrangements. A heuristic methodology based on design criteria (such as elevation, coverage of the region of interest, and interference between stations) is proposed for broadcasting networks. Meanwhile, for cellular access networks, a methodology based on clustering of UE positions is presented. Finally, this thesis presents a resource allocation algorithm based on a utility criterion to allocate time-frequency resources in 5G radio access networks considering the users capacity demands. Based on the individual demand of a terminal, the algorithm estimates its utility and orders the terminals in a sector to allocate the time-frequency resources accordingly. The presented resource allocation algorithm obtains competitive results and often out performs known allocation algorithms.
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Dual-polarized fully-metallic Vivaldi antenna array in a triangular lattice / Dubbelpolariserad helmetallisk Vivaldi-antennuppsättning i ett triangulärt gitterOrgeira Alvarez, Omar January 2022 (has links)
New mobile communication generations need electromagnetic sensors capable of steering their high-directive beams towards the users. Conventional base stations use square lattice phased arrays to accomplish this task. These arrays are composed of a large number of radiating elements to achieve the required high directivity and scanning capabilities. These systems are of high complexity and cost because after each element there is a large electronic chain. Therefore, it is of high interest to reduce the element count in the aperture of the array while maintaining its performance. Instead of using a square lattice to place the radiating elements, a triangular lattice can be used. It is proven that a triangular lattice optimally samples the aperture and reduces the element count by up to a 15.5%, hence reducing the cost and complexity of the complete antenna system. However, dual-polarized Vivaldi elements do not conform naturally to this kind of lattice and, consequently, they have not been thoroughly studied in the literature despite this well-known advantage. In this work, a novel dual-polarized fully-metallic Vivaldi element is presented. Also, the feeding network for this element is designed in the form of a suspended stripline. This technology presents low loss in comparison with a conventional stripline or microstrip. The radiating elements can be manufactured in a single piece, and they are easily integrated with the stripline feeding by just placing one on top of the other. An infinite array analysis, i.e. unit cell analysis, was performed to show the correct performance of the triangular lattice array and the proposed dual-polarized Vivaldi antenna design. A good matching was achieved over the entire band from 6 to 15 GHz for all the scanning planes and up to 60◦ scanning angle. The active element patterns show the good behaviour of the array, i.e. the absence of scan blindness and grating lobes. Finally, the unit cell analysis is compared to a finite 11×11 array for verification. / Nya generationer av mobilkommunikation behöver elektromagnetiska sensorer som kan styra sin högriktade signalenergi mot användarna. Konventionella basstationer använder kvadratiska gitterfasuppsättningar. Dessa arrayer är sammansatta av ett stort antal strålningselement för att uppnå den erforderliga höga riktningsförmågan och avsökningskapaciteten. Dessa system är av hög komplexitet och kostnad eftersom det efter varje element finns en lång elektronisk kedja. Därför är det av stort intresse att minska antalet element i arrayens apertur samtidigt som dess prestanda bibehålls. Istället för att använda ett kvadratiskt gitter för att placera de strålande elementen, kan ett triangulärt gitter användas. Det är bevisat att ett triangulärt gitter optimalt samplar aperturen och minskar elementantalet med upp till 15.5%, vilket minskar kostnaden och komplexiteten för hela antennsystemet. Dubbelpolariserade Vivaldi-element överensstämmer dock inte naturligt med denna typ av triangulära symmetri och följaktligen har de inte studerats grundligt i litteraturen trots denna välkända fördel. I detta arbete presenteras ett nytt dubbelpolariserat fullt metalliskt Vivaldi-element. Matningsnätverket för detta element är också utformat i form av en upphängd stripline. Denna metod ger låga förluster i jämförelse med en konventionell stripline eller mikrostrip. En oändlig array-analys, d.v.s. enhetscell, utfördes för att visa den korrekta prestandan för den triangulära gittermatrisen. En bra matchning uppnåddes över hela bandet från 6 till 15 GHz för alla skanningsplan och upp till 60° utstyrningsvinkel. Aktiva elementstrålnings diagrammet visar konfigurationens lovande egenskaper, d.v.s. ingen skanningsblindhet eller gallerlober. Slutligen jämförs enhetscellanalysen med en ändlig 11x11 array för verifiering.
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Energy efficient cloud computing based radio access networks in 5G: Design and evaluation of an energy aware 5G cloud radio access networks framework using base station sleeping, cloud computing based workload consolidation and mobile edge computingSigwele, Tshiamo January 2017 (has links)
Fifth Generation (5G) cellular networks will experience a thousand-fold increase in data traffic with over 100 billion connected devices by 2020. In order to support this skyrocketing traffic demand, smaller base stations (BSs) are deployed to increase capacity. However, more BSs increases energy consumption which contributes to operational expenditure (OPEX) and CO2 emissions. Also, an introduction of a plethora of 5G applications running in the mobile devices causes a significant amount of energy consumption in the mobile devices.
This thesis presents a novel framework for energy efficiency in 5G cloud radio access networks (C-RAN) by leveraging cloud computing technology. Energy efficiency is achieved in three ways; (i) at the radio side of H-C-RAN (Heterogeneous C-RAN), a dynamic BS switching off algorithm is proposed to minimise energy consumption while maintaining Quality of Service (QoS), (ii) in the BS cloud, baseband workload consolidation schemes are proposed based on simulated annealing and genetic algorithms to minimise energy consumption in the cloud, where also advanced fuzzy based admission control with pre-emption is implemented to improve QoS and resource utilisation (iii) at the mobile device side, Mobile Edge Computing (MEC) is used where computer intensive tasks from the mobile device are executed in the MEC server in the cloud. The simulation results show that the proposed framework effectively reduced energy consumption by up to 48% within RAN and 57% in the mobile devices, and improved network energy efficiency by a factor of 10, network throughput by a factor of 2.7 and resource utilisation by 54% while maintaining QoS.
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DECENTRALIZED KEY GENERATION SCHEME FOR CELLULAR-BASED HETEROGENEOUS WIRELESS Ad Hoc NETWORKSGUPTA, ANANYA 02 October 2006 (has links)
No description available.
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Computation of Specific Absorption Rate in the Human Body due to Base-Station Antennas using a Hybrid FormulationAbd-Alhameed, Raed, Excell, Peter S., Mangoud, Mohab A. January 2005 (has links)
A procedure for computational dosimetry to verify safety standards compliance of mobile communications base stations is presented. Compared with the traditional power density method, a procedure based on more rigorous physics was devised, requiring computation or measurement of the specific absorption rate (SAR) within the biological tissue of a person at an arbitrary distance. This uses a hybrid methd of moments/finite difference time domain (MoM/FDTD) numerical method in order to determine the field or SAR distribution in complex penetrable media, without the computational penalties that would result from a wholly FDTD simulation. It is shown that the transmitted power allowed by the more precise SAR method is, in many cases, between two and five times greater than that allowed by standards implementing the power flux density method.
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利用全國性e-GPS衛星定位基準網辦理土地複丈精度之研究-以鶯歌地區為例詹君正 Unknown Date (has links)
內政部土地測量局為擴大RTK有效作業範圍,同時降低主站布設密度,已規劃透過網際網路高速、寬頻之數據傳輸技術,預定於九十五年度前完成建置全國性電子化GPS(e-GPS)衛星定位測量基準網,就其連續定位觀測資料,建構區域性定位誤差內插模式,並配合虛擬基準站(Virtual Base Station,VBS)即時動態定位技術(Real-Time Kinematic, RTK)( 簡稱VBS-RTK),獲得高精度的定位成果,提供多目標定位服務及加值應用。
本研究利用全國性e-GPS衛星定位基準站即時動態定位系統北區服務網為基準網,探討以VBS-RTK定位技術應用於圖根測量及直接辦理土地複丈之可行性。首先檢核實驗區內控制點與圖根點成果發現,縱坐標(N)較差絕對值之平均值為1.9公分,橫坐標(E)較差平均值為2.0公分。經分析後得知,本實驗區之VRS-RTK測量成果與原坐標成果間有系統誤差存在,透過六參數轉換後,其坐標較差值均能符合圖根點測量規範。其次,以VBS-RTK直接辦理土地複丈,其界址點坐標成果較差亦均符合界址點位置檢查與原坐標值之較差不得超過6公分之規定。 / For expanding the effective range and decreasing the density of base stations, Land Survey Bureau, Ministry of the Interior (LSB) have set up a national e-GPS base stations network in 2006. In order to obtain high precision position result and provide multi-goals positioning service with plus value application, the system will be involved regional position error interpolating mode and Virtual Base Station(VBS)technique.
The research area is located within the north service net of the national e-GPS base stations network, feasible discussion of using to Supplementary control survey and direct to transact the land resurvey with the VBS-RTK technique. Firstly, The 4th and the higher order control points and the traverse points located at the research area were examined with the VRS-RTK. Compared with the original data, the results have shown that the average of the absolute value of errors is 1.9 cm at the N-axis, 2.0 cm at the E-axis. After transformations either by affine-6-parameters, the result shows that all of the errors are satisfy the stipulation of rules.Secondly, using the VBS-RTK technique to undertake land survey correction, the all errors are satisfy the stipulation of rules.( less than 6 cm )
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Integrated silicon technology and hardware design techniques for ultra-wideband and next generation wireless systemsHuo, Yiming 18 May 2017 (has links)
The last two decades have witnessed the CMOS processes and design techniques develop and prosper with unprecedented speed. They have been widely employed in contemporary integrated circuit (IC) commercial products resulting in highly added value. Tremendous e orts have been devoted to extend and optimize the CMOS process and its application for future wireless communication systems. Meanwhile, the last twenty years have also seen the fast booming of the wireless communication technology typically characterized by the mobile communication technology, WLAN technology, WPAN technology, etc.
Nowadays, the spectral resource is getting increasingly scarce, particularly over the frequency from 0.7 to 6 GHz, whether the employed frequency band is licensed or not. To combat this dilemma, the ultra wideband (UWB) technology emerges to
provide a promising solution for short-range wireless communication while using an unlicensed wide band in an overlay manner. Another trend of obtaining more spectrum is moving upwards to higher frequency bands. The WiFi-Alliance has already developed a certi cation program of the 60-GHz band. On the other side, millimeterwave (mmWave) frequency bands such as 28-GHz, 38-GHz, and 71-GHz are likely to be licensed for next generation wireless communication networks. This new trend poses both a challenge and opportunity for the mmWave integrated circuits design.
This thesis combines the state-of-the-art IC and hardware technologies and design
techniques to implement and propose UWB and 5G prototyping systems. First of
all, by giving a thorough analysis of a transmitted reference pulse cluster (TRPC)
scheme and mathematical modeling, a TRPC-UWB transceiver structure is proposed
and its features and speci cations are derived. Following that, the detailed design,
fabrication and veri cation of the TRPC-UWB transmitter front end and wideband
voltage-controlled oscillators (VCOs) in CMOS process is presented. The TRPCUWB
transmitter demonstrates a state-of-the-art energy e ciency of 38.4 pJ/pulse.
Secondly, a novel system architecture named distributed phased array based MIMO
(DPA-MIMO) is proposed as a solution to overcome design challenges for the future
5G cellular user equipment (UE) design. In addition, a prototyping design of on-chip
mmWave antenna with radiation e ciency enhancement is presented for the IEEE
802.11ad application.
Furthermore, two wideband K-band VCO prototypes based on two di erent topologies
are designed and fabricated in a standard CMOS process. They both show good
performance at center frequencies of 22.3 and 26.1 GHz. Finally, two CMOS mmWave
VCO prototypes working at the potential future 5G frequency bands are presented
with measurement results. / Graduate / 2018-04-30 / amenghym@gmail.com
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Avalia??o dos modelos de predi??o de propaga??o para telefonia m?vel celular na cidade do NatalPinheiro, Fred Sizenando Rossiter 17 February 2006 (has links)
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FredSRP.pdf: 1871145 bytes, checksum: 9d94e1a0030a3d2f8d2aa6aaa2df93bd (MD5)
Previous issue date: 2006-02-17 / The development of wireless telecommunication in the last years has been great. It has been taking academics to conceive new ideas and techniques. Their aims are to increase the capacity and the quality of the system s services. Cells that are smaller every time, frequencies that are every time higher and environments that get more and more complex, all those facts deserve more accurate models the propagation prediction techniques are inserted in this context and results with a merger of error that is compatible with the next generations of communication systems. The objective of this Work is to present results of a propagation measurement campaign, aiming at pointing the characteristics of the mobile systems covering in the city of Natal (state of Rio Grande do Norte, Brazil). A mobile laboratory was set up, using the infra-structure available and frequently used by ANATEL. The measures were taken in three different areas: one characterized by high buildings, high relief, presence of trees and towers of different highs. These areas covered the city s central zone, a suburban / rural zone and a section of coast surrounded by sand dunes.
It is important to highlight that the analysis was made taking into consideration the actual reality of cellular systems with covering ranges by reduced cells, with the intent of causing greater re-use of frequencies and greater capacity of telephone traffic. The predominance of telephone traffic by cell in the city of Natal occurs within a range inferior to 3 (three) km from the Radio-Base Station. The frequency band used was 800 MHz, corresponding to the control channels of the respective sites, which adopt the FSK modulation technique. This Dissertation starts by presenting a general vision of the models used for predicting propagation. Then, there is a description of the methodology used in the measuring, which were done using the same channels of control of the cellular system. The results obtained were compared with many existing prediction models, and some adaptations were developed by using regression techniques trying to obtain the most optimized solutions.
Furthermore, according to regulations from the old Brazilian Holding Telebr?s, a minimum covering of 90% of a determined previously area, in 90% of the time, must be obeyed when implanting cellular systems. For such value to be reached, considerations and studies involving the specific environment that is being covered are important. The objective of this work is contribute to this aspect / O enorme desenvolvimento das comunica??es sem fio tem levado estudiosos a conceber novas id?ias e t?cnicas visando aumentar a capacidade e melhorar a qualidade de servi?o dos sistemas de comunica??o m?vel. C?lulas cada vez menores, freq??ncias cada vez mais altas e ambientes cada vez mais complexos est?o a merecer modelamentos mais acurados e as t?cnicas de predi??o de propaga??o se inserem neste contexto, estando ainda a merecer resultados com margem de erro compat?vel com as pr?ximas gera??es de sistemas de comunica??o. Este trabalho tem por finalidade apresentar os resultados de uma campanha de medidas de propaga??o visando caracterizar a cobertura de sistemas m?veis celulares na cidade do Natal, RN. Um laborat?rio m?vel foi montado aproveitando a estrutura dispon?vel e utilizada rotineiramente pela ANATEL. As medi??es foram efetuadas em ?reas com caracter?sticas de edifica??es, relevo, arboriza??o e alturas de torres diversificadas, abrangendo a zona central da cidade, uma zona de caracter?stica suburbana / rural e trecho litor?neo circundado por dunas. ? importante destacar que a an?lise foi feita considerando a realidade atual dos sistemas celulares com raios de cobertura por c?lula reduzidos visando proporcionar maior reuso de freq??ncias e maior capacidade de tr?fego telef?nico. A predomin?ncia do tr?fego telef?nico por c?lula na cidade do Natal ocorre dentro de um raio inferior a 3 (tr?s) km em rela??o a Esta??o R?dio-Base. A faixa de freq??ncia utilizada foi de 800 MHz, correspondendo aos canais de controle dos respectivos sites, os quais adotam a t?cnica de modula??o FSK. Neste trabalho, apresenta-se inicialmente uma vis?o geral dos modelos utilizados para predi??o de propaga??o. Em seguida, descreve-se a metodologia utilizada nas medi??es, as quais foram efetuadas aproveitando os pr?prios canais de controle do sistema celular. Os resultados obtidos foram comparados com diversos modelos de predi??o existentes e foram desenvolvidas adapta??es utilizando t?cnicas de regress?o na tentativa de obten??o de solu??es mais otimizadas. Al?m disso, ? importante observar que, de acordo com norma da antiga holding brasileira Telebr?s, uma cobertura m?nima de 90% de uma ?rea pr?-estabelecida em 90% do tempo deve ser obedecida em implanta??es de sistemas celulares. Para que tal ?ndice seja obtido, considera??es e estudos envolvendo o ambiente espec?fico de atendimento s?o importantes. Este trabalho apresenta uma contribui??o nesse sentido
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Simulador das interferências de campos elétrico e magnético em função da potência para estação rádio base de "Acesso Múltiplo por Divisão de Código - CDMA" na faixa de frequência de 800 MHzKiszka Júnior, Pedro 02 April 2011 (has links)
We have developed and created a simulator for calculations and indicatios of maximum permissible values for the electric and magnetic fields as well as the power density in Rádio Base Station, with the use of CDMA technology, in the range of 800 MHz, being the values allowable were referenced and based on the International Commission on Non-ionizing radiation protection. The simulator developed allows to calculate the interference field radiated by rádio base station, with input data such as channel power rádio; Gain Antenna; Number of Rádio Channels, Frequency Operation; Losses in Cable, Attenuation of Direction; Minimum distance; Reflections. To get quickly without the need for the implementation of instruments for measurements, calculations only in that simulator, we calculated values such as: Effective Radiated Power; Density Power Sector; electric field in the Sector; Magnetic Field in the sector; Flux Density Magnetic; point of maximum permissible exposure to electric field and the power density. As results presented in graphs for clarity of visualization of power density in the industry, as well as defining the coverage area. Is also present in the simulator, folders with specifications of antennas, towers and cables used in mobile phones, whose manufacturers are: World RFS, Andrew, and Karthein Brasilsat. They are presented several "links" network access "internet" to complement the specifications of cables, antennas, etc. .. Moreover also part of the simulator to perform calculations quickly and safely assisting in obtaining results of loss of rádio signal generated by rádio base station. Where the simulator has paintings depicting the spreads, where we define propagation "A" and "B".By spreading the "A" we can get the calculations of rádio signal attenuation models in areas of urban, dense urban, suburban, and rural open. Are added in the calculations of reflection coefficients of reflection, the standing wave ratio, return loss, the ratio of reflected power, as well as losses of the signal by impedance mismatch. As for the spread "B" as we can get results in the loss calculations in the rádio signal line in sight and no sight, the effective area, the power density, the power received, the range, the level conversion and the conversion gain in radiant systems. / Neste trabalho foram desenvolvidos e criados dois simuladores para cálculos e indicações de valores Máximos Permissíveis para os campos elétricos e magnéticos, bem como as Densidades de Potência em Estações Rádio Base, com a utilização de Tecnologia CDMA, na faixa de 800 MHz. Esses valores permissíveis foram referênciados e fundamentados pela Comissão Internacional de Proteção à Radiação não Ionizante.
O simulador 1 permite calcular as interferências de campo irradiado por estação rádio base, com entrada de dados tais como: Potência do Canal de Rádio; Ganho da Antena; Número de Canais de Rádio; Frequência de Operação; Perdas no Cabo; Atenuação da Direção; Distância Mínima; Reflexões. O referido simulador permite, de maneira rápida e sem a necessidade da execução de instrumentos para medições, alcançar os seguintes valores calculados: Potência Radiada Efetiva; Densidade de Potência do Setor; Campo elétrico no Setor; Campo Magnético no Setor; Densidade de fluxo Magnético; ponto de exposição máxima permitida de campo elétrico, bem como a densidade de potência. Os resultados são apresentados em gráficos, para clareza da visualização da densidade de potência no setor, assim como para a definição da área de cobertura.
O simulador abrange também pastas com especificações de antenas, cabos e torres utilizadas na telefonia celular, dos seguintes fabricantes: RFS World, Andrew, Karthein e Brasilsat. São apresentados diversos ―links‖ de acesso à rede ―internet‖ para complemento das especificações de cabos, antenas, etc. O simulador 2 apresenta mais variáveis, procurando executar cálculos de forma rápida e segura auxiliando na obtenção de resuldados das perdas do sinal de rádio produzidas por estação rádio base. Nesse caso, o simulador apresenta telas representando as propagações denominadas ―A‖ e ―B‖.
Através da propagação ―A‖ podemos obter os cálculos de atenuação do sinal de rádio em áreas de modelos urbana, urbana densa, suburbana, aberta e rural. Nos cálculos de reflexão, adicionamos os coeficientes de reflexão, a relação de onda estacionária, a perda de retorno, a relação de potência refletida, assim como as perdas do sinal por descasamento de impedância.
Com a propagação ―B‖ podemos obter como resultados as perdas do sinal de rádio na linha visada e não visada, a área efetiva, a densidade de potência, a potência recebida, o raio de cobertura, a conversão de níveis e a conversão de ganho em sistemas irradiantes. / Mestre em Ciências
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