Radio spectrum is a vital national asset; proper management of this finite resource is essential to the operation and development of telecommunications, radio-navigation, radio astronomy, and passive remote sensing services. To maximize the utility of the radio spectrum, knowledge of its current usage is beneficial. As a result, several spectrum studies have been conducted in urban Atlanta, suburban Atlanta, and rural North Carolina. These studies improve upon past spectrum studies by resolving spectrum usage by nearly all its possible parameters: frequency, time, polarization, azimuth, and location type. The continuous frequency range from 400MHz to 7.2 GHz was measured with a custom-designed system. More than 8 billion spectrum measurements were taken over several months of observation. A multi-parameter spectrum usage detection method was developed and analyzed with data from the spectrum studies. This method was designed to exploit all the characteristics of spectral information that was available from the spectrum studies. Analysis of the spectrum studies showed significant levels of underuse. The level of spectrum usage in time and azimuthal space was determined to be only 6.5 % for the urban Atlanta, 5.3 % for suburban Atlanta, and 0.8 % for the rural North Carolina spectrum studies. Most of the frequencies measured never experienced usage. Interference was detected in several protected radio astronomy and sensitive radio navigation bands. A cognitive radio network architecture to share spectrum with fixed microwave systems was developed. The architecture uses a broker-based sharing method to control spectrum access and investigate interference issues.

The area of deterministic noise cancellation in mobile radio communication systems is investigated and analyzed. Several interoperation problems in the mobile wireless radio space are identified and interference concerns for the Bluetooth - WLAN networks are characterized and quantified in the physical layer. A mathematical framework has been created for describing interference in the 2.4 GHz band. An adaptive noise suppression system has been developed that is able to alleviate the encroachment of the aggressor signal on the victim without sacrificing any of the original signal. This system is demonstrated to improve the victim SNR in a spread spectrum communication scenario. The research is extended to construct an interference canceller that is easy to assimilate into existing RF front-ends. A low-power small form-factor analog active canceller has been designed in 0.18-ìm Si-CMOS IC technology that delivers adequate noise suppression performance while operating in the RF domain. This includes novel implementations of phase rotator circuits based on delay interpolation and an integrated low-current quadrature modulator-based continuously variable analog phase shifter. This canceller is capable of up to 30 dB of in-band cancellation for the Bluetooth - WLAN problem. Other versions of the canceller are configured to protect GPS and DVB-H receivers from unintentional radiators transmitting in the vicinity. These demonstrate noise mitigation of at least 15 dB in their respective bands while generating very low broadband noise at the output. A simple low-power mixed-signal automatic control mechanism is also developed to operate the canceller adaptively. The work described in this dissertation advances the state-of-the-art in the area of mobile wireless radio coexistence.

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Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The extension of the Karoo Array Telescope (KAT), MeerKAT, will be the most sensitive radio telescope in the southern hemisphere until it is superseded by the completion of the Square Kilometre Array (SKA). These instruments are to be constructed in the Karoo which is an area in South-Africa that is protected against Radio Frequency Interference (RFI) by the Astronomy Geographical Advantage (AGA) act. However, the telescope is also vulnerable to self-generated interference and specialised measurement systems are required to monitor RFI levels. The development of a ReAl Time Transient AnalYser (RATTY) is described and two Experimental Development Models (XDM) are compared. The first uses a mixing philosophy, and the second direct-sampling. The selection of these models was based on the evaluation of several analogue Front-End (FE) designs. A stripline-filter design process is presented along with the results obtained for custom filters developed for the FEs. Several analyses were compared to measurements performed with one of the devices and good agreement was shown between the system characteristics. Issues regarding the Spurious Free Dynamic Range (SFDR) of the FE designs were identified in the process and measurement-corrected simulations used to predict the achievable ranges. The outcome of the XDM comparison promotes the continued development of a direct-sampling strategy to fulfil the short-term goals of the project. A static calibration procedure is demonstrated for the mixing system and implemented to account for different FE configurations. An overview of the digital and software components of the RATTY system is given and Electromagnetic Compatibility (EMC) principles are applied during the construction of both systems. / AFRIKAANSE OPSOMMING: Die finale fase van die Karoo Reeks Teleskoop (KAT), MeerKAT, sal die sensitiefste radio teleskoop in die suidelike halfrond wees. Dit sal egter oortref word deur die vierkante kilometer reeks, wat die sensitiefste radio teleskoop ter wêreld sal word. Beide instrumente sal vatbaar wees vir radiofrekwensie steurings en sal opgerig word in ‘n wet-beskermde omgewing. Die teleskope is ook vatbaar vir radiofrekwensie steurings wat deur interne stelsels opgewek kan word. Dus word gespesialiseerde meetapparate benodig om die betrokke area en substelsels van die teleskope te monitor. Die ontwikkeling van ‘n meetinstrument vir die ontleding van kort-durasie tydseine (RATTY) word beskryf en twee eksperimentele ontwikkelings modelle word vergelyk. Hierdie modelle is gebaseer op die verfyning van voorafgaande ontwerpe vir die analoog substelsel van die instrument en hierdie proses word verduidelik. Die eerste model volg ‘n menger strategie waar die tweede model direkte-monstering implementeer. ‘n Dubbel-laag, mikrostrookfilter ontwerpsproses word beskryf en die gemete resultate vir die ontwikkelde filters word bespreek. Verskeie ontledings is aangewend en vergelyk met die gemete resultate van die stelsels. Hieruit word bevredigende ooreenkomste getref. Die beperkings van die modelle, weens interne distorsie, word geïdentifiseer in dié proses en verdere skattings word gemaak d.m.v. simulasies. Die eksperimentele modelle word vergelyk en die voorkeur van ‘n direkte-monsterings stelsel word gemotiveer. Die digitale en sagteware komponente word oorsigtelik behandel. Tydens die konstruksie van die modelle word die toepassing van elektromagnetiese verenigbaarheids beginsels verduidelik. Laastens word ‘n eenvoudige kalibrasie toegepas op die menger stelsel en ‘n toepassing daarvan word behandel.

Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T09:28:35Z (GMT). No. of bitstreams: 1 MinangoNegrete_JuanCarlos_M.pdf: 1358924 bytes, checksum: 0b87bf307832cb8c65d04765674c0306 (MD5) Previous issue date: 2014 / Resumo: O uso da técnica de multiplex espacial, transmissão de feixes de símbolos independentes usando múltiplas antenas de transmissão, tem sido proposta para atingir a exigência de taxas de dados maiores dos futuros sistemas de comunicações sem fio de banda larga. No entanto, quando a técnica de multiplex espacial é aplicada a uma rede celular, seu desempenho é afetado pela interferência de co-canal. Este trabalho avalia e compara os efeitos da interferência de co-canal na taxa de erro de bit média, BER, entre sistemas de transmissão digital com multiplex espacial e sistemas de transmissão digital com uma única antena de transmissão, onde os parâmetros da potência de transmissão e eficiência espectral são levados em consideração, a fim de se fazer comparações justas entre os dois sistemas. O enlace direto em um ambiente com desvanecimento plano e lento do tipo Rayleigh na presença de um interferente de co-canal dominante foi considerado. Além disso, o uso do detector ótimo, MV, no receptor e os esquemas de modulação BPSK, QPSK e M-QAM foram também considerados. Simulações de Monte Carlo foram feitas para a obtenção dos desempenhos em termos da BER como uma função da relação sinal-ruído por bit, Eb/N0, e da relação sinal-interferência, SIR. Os resultados da avaliação e comparação de desempenho entre os sistemas com multiplex espacial e com uma única antena de transmissão apresentados neste trabalho, constituem uma ferramenta importante a fim de se conhecer os benefícios reais da técnica de multiplex espacial aplicada a uma rede celular, como por exemplo nos padrões WiMAX ou LTE / Abstract: Spatial multiplexing technique, consisting of independent symbol transmission on multiple transmission antennas, has been proposed to meet the requirement for higher data rates of future wireless broadband communication systems. However, when spatial multiplexing technique is applied to a cellular network, the performance is affected by co-channel interference. This work evaluates and compares the effects of co-channel interference on the mean bit error rate, BER, of spatial multiplexing systems and single transmission antenna systems, where transmit power and spectral efficiency parameters are taken into consideration, in order to make a fair comparison between both systems. The downlink of a cellular network in slowly-varying flat Rayleigh fading environment and in the presence of a dominant co-channel interferer is considered. Furthermore, the use of Optimum Detector on the receiver and BPSK, QPSK and M-QAM modulations is also considered. Monte Carlo simulations are realized for obtaining the performance in terms of the BER as a function of per-bit signal-to-noise ratio, Eb/N0, and signal-to-interference ratio, SIR. The evaluation and comparison performance results between spatial multiplexing and a single transmission antenna systems presented in this work, are important tools in order to know the real benefits of spatial multiplexing technique applied to a cellular network, as the standards WiMAX or LTE / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-19T05:03:35Z (GMT). No. of bitstreams: 1 BenitezOlivo_EdgarEduardo_M.pdf: 1173114 bytes, checksum: 1fc0181244059954a5184599ee11635c (MD5) Previous issue date: 2011 / Resumo: A análise da eficiência espectral de uma rede celular é fundamental para se otimizar o aproveitamento da banda com cobertura na célula. Neste trabalho, o desempenho do enlace reverso de redes celulares é obtido em termos de sua eficiência espectral média. O cenário estudado considera um canal com perda de propagação exponencial, desvanecimento plano e lento Rayleigh e interferência de co-canal (ICC). A modelagem matemática do sistema leva em consideração vários parâmetros de planejamento, incluindo o fator de reuso de frequência, arranjo de antenas na estação rádio base (ERB), esquema de combinação por diversidade do tipoMRC (maximal ratio combining), modulação adaptativa e controle de potência. Neste contexto, uma expressão analítica da probabilidade de erro de bit (PEB) para o esquema de modulação M-QAM (multilevel quadrature amplitude modulation) é obtida em função da relação sinal-ruído por bit (Eb/N0) e da relação sinal-interferência (SIR, do inglês signal-to-interference power ratio), considerando a presença de um interferente dominante. Esta expressão constitui uma ferramenta importante para a avaliação correta do desempenho de sistemas digitais celulares. Os resultados mostram que utilizar um fator de reuso de 1, conjuntamente com controle de potência, em geral, é a maneira mais eficiente de se usar o espectro, garantindo cobertura total na célula / Abstract: The analysis of the spectral efficiency of a cellular network is essential to optimize the bandwidth usage with coverage, which is one of the major limitations on network planning. In this work, the performance of the uplink of cellular networks in terms of the mean spectral efficiency is obtained. The studied scenario considers a channel with exponential path-loss, slowly-varying flat Rayleigh fading and co-channel interference (CCI). The mathematical modeling of the system takes in consideration many parameters, including frequency reuse factor, antenna array at the base station, maximal ratio combining (MRC) diversity scheme, adaptive modulation and power control. In this context, an analytical expression of the bit error probability for the M-QAM (multilevel quadrature amplitude modulation) scheme as a function of the signal-to-noise ratio per bit (Eb/N0) and the signal-tointerference power ratio (SIR) is obtained, by considering the presence of a single dominant interferer. This expression is an important tool for the correct evaluation of the performance of digital cellular systems. The results show that using a frequency reuse of 1, jointly with power control, in general, is the most efficient way to use the spectrum, by ensuring full coverage in the cell / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

To solve the spectrum scarcity problem caused by the high number of wireless applications and users, the concept of cognitive radio (CR) was proposed in the past few years. Cognitive radio networks (CRNs) provide dynamic spectrum access (DSA), where the unlicensed users can access the spectrum without causing unacceptable level of interference to the primary user (PU). DSA was based on conventional spectrum sensing information or geolocation databases. Later, radio environment map (REM) as an improved geolocation database was introduced to enhance the DSA process. It is a comprehensive map consists of different integrated databases, and the interference field information is one of its databases. In this thesis, a description of the REM concept and its construction methods will be presented. The focus will be for the indirect methods for constructing interference map, which represents a layer of the REM. Indirect method refers to the methods that utilize known model information, to first estimate the primary transmitter parameters and then generate REM. Two indirect methods under lognormal shadowing were presented and compared. The better of these two methods is further investigated in different scenarios. These scenarios include different number of sensors, varied size of measurements, several shadowing spread values, different percentages of error in path-loss exponent, and the effect of the number of moving sensors and their speeds to the REM quality. The performance is evaluated using these metrics: “localization error, signal power error and correct detection zone ratio (CDZR). The results show that performance is enhanced as the number of sensors and the size of measurements increase, whereas clear degradation in REM quality is shown when shadowing spread increases or the model parameters are not well calibrated. Also, as the number of moving sensors or their speeds increase, the REM performance becomes less effective

Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T13:51:01Z (GMT). No. of bitstreams: 1 OrozcoGarzon_NathalyVeronica_M.pdf: 2420238 bytes, checksum: 44b2e62e1f4262ea3a2a169999209c79 (MD5) Previous issue date: 2014 / Resumo: A principal contribuição desta tese é a proposta de um mecanismo com transmissão oportunista. Este método de transmissão é realizado apenas quando o desvanecimento no receptor estiver acima de um certo limiar. Neste sistema oportunista o transmissor e o receptor estão em constante comunicação através de um canal de realimentação e o receptor indica ao transmissor quando ele deve transmitir. Para a análise de desempenho do sistema oportunista vamos considerar um canal com ruído e desvanecimento plano e lento Rayleigh e também interferência de co-canal (CCI) vamos também considerar diferentes esquemas de modulação (BPSK, QPSK, 4-QAM, 16-QAM e 64-QAM). A análise de desempenho do sistema proposto baseia-se na probabilidade de erro de bit média (BER), para a qual expressões analíticas foram obtidas. Estas expressões foram verificadas usando o método de simulação de Monte Carlo, com excelente concordância entre os dois resultados. Além disso, foram consideradas a eficiência espectral e a potência de transmissão do sistema. Os resultados obtidos mostram que a transmissão oportunista pode combater o desvanecimento de forma eficiente, pois o sistema oportunista elimina os efeitos do desvanecimento quase em sua totalidade. Foi feita também uma comparação entre o sistema oportunista e um sistema ordinário para a comparação de desempenho. Além disso, a transmissão oportunista é menos sensível à interferência de co-canal. Várias curvas são apresentadas ilustrando a eficiência do mecanismo oportunista proposto em termos da probabilidade de erro de bit média / Abstract: This thesis proposes, as the main contribution, a new mechanism with an opportunistic transmission. This transmission method is realized just when the fading at receiver is above a threshold value. In this opportunistic system the transmitter and the receiver are in constant communication through a feedback link and the receiver indicates when the transmitter should transmit. To analyze the performance of the opportunistic system we consider a noise channel and a flat and slow Rayleigh fading channel in the presence of co-channel interference (ICC). We also consider different modulation schemes (BPSK, QPSK, 4-QAM, 16-QAM e 64-QAM). The performance analysis of the proposed system is based on the mean bit error probability (BER), for which analytical expressions are established. These expressions are verified using Monte-Carlo simulation method with excellent agreement between both results. Furthermore, we consider the spectral efficiency and the power transmission of this system. The opportunistic transmission can combat the fading efficiently. That is, once it eliminates the fading effects almost entirely. Moreover, it is made a comparison between the opportunistic system and the ordinary system performance. Furthermore, the opportunistic transmission is less sensitive to co-channel interference. Several figures are presented illustrating the efficiency of the proposed mechanism in terms of mean bit error probability / Mestrado / Telecomunicações e Telemática / Mestra em Engenharia Elétrica

The architecture of mobile networks has dramatically evolved in order to fulfill the growing demands on wireless services and data. The radio resources, which are used by the current mobile networks, are limited while the users demands are substantially increasing. In the future, tremendous Internet applications are expected to be served by mobile networks. Therefore, increasing the capacity of mobile networks has become a vital issue. Heterogeneous networks (HetNets) have been considered as a promising paradigm for future mobile networks. Accordingly, the concept of small cell has been introduced in order to increase the capacity of the mobile networks. A femtocell network is a kind of small cell networks. Femtocells are deployed within macrocells coverage. Femtocells cover small areas and operate with low transmission power while providing high capacity. Also, UEs can be offloaded from macrocells to femtocells. Thus, the capacity can be increased. However, this will introduce different technical challenges. The interference has become one of the key challenges for deploying femtocells within a certain macrocells coverage. Undesirable impact of the interference can degrade the performance of the mobile networks. Therefore, radio resource management mechanisms are needed in order to address key challenges of deploying femtocells. The objective of this work is to introduce radio resource control approaches, which are used to increase mobile networks' capacity and alleviate undesirable impact of the interference. In addition, proposed radio resource control approaches ensure the coexistence between macrocell and femtocells based on LTE-Advanced environment. Firstly, a novel mechanism is proposed in order to address the interference challenge. The proposed approach mitigates the impact of interference based on controlling radio sub-channels' assignment and dynamically adjusting the transmission power. Secondly, a dynamic strategy is proposed for the FFR mechanism. In the FFR mechanism, the whole spectrum is divided into four fixed sub-channels and each sub-channel is assigned for a different sub-area after splitting the macrocell coverage area into four sub-areas. The objective of the proposed scheme is to divide the spectrum dynamically based on the QoS indicators for each sub-area. Lastly, a novel packet scheduling scheme is proposed to improve the performance of femtocell networks. The proposed scheduling strategy assigns radio resources based on two objectives: increasing the network capacity and achieving better fairness among attached UEs.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Prospects of up-rating existing high voltage direct current (HVDC) transmission schemes, as well as the conversion of existing alternating current (AC) to direct current (DC) lines and the development of new HVDC schemes in sub-Saharan Africa, have led to renewed interest in DC research. The radio interference (RI), audible noise (AN) and corona loss (CL) performance of HVDC transmission lines are critical factors when assessing the reliability of the line design. The RI performance is especially important when considering the successful transmission of the carrier signal of the power line carrier (PLC) system. The PLC system is the main form of communication between teleprotection devices on the Cahora Bassa HVDC scheme. The aim of the dissertation is to devise modelling as well as metrological techniques to characterise DC conductor corona. A particle-in-cell (PIC) computational code is developed to gain a better understanding of the physical processes that occur during corona events. The numerical code makes use of the charge simulation method (CSM) and nite element method (FEM) to solve for the Laplace and Poisson eld equations. Higher-order basis functions are implemented to obtain a more accurate solution to the Poisson equation. The computational tool yields insight into the mathematical models for the various ionization, attachment and electron avalanche processes that give rise to corona currents. Together with a designed and developed electrometer-type circuit, the numerical code assists the visualisation of the space charge particle dynamics that form in the electrode gap during corona events. The metrological techniques consider the wideband time domain (TD) as well as the frequency domain (FD) information of the measured corona pulses in the presence of noise. These are then compared to the narrowband CISPR standard measurements centred around 500kHz. The importance of impedance matching when attempting to derive a wideband excitation function is investigated. The TD measurements are quite distinct from the well-published FD measurements, and consider the pulse shape, pulse spectrum and pulse repetition rates. The use of three possible conductor corona test methods to study direct current conductor RI performance under both positive and negative polarities is investigated at high altitude in this dissertation. These include a small corona cage, a short test line and the Eskom Megawatt Park large outdoor corona cage. Derived wideband and narrowband monopolar DC RI excitation functions at 500kHz are consolidated with existing radio noise (RN) measurement protocols and prediction methods. The use of a corona cage to derive excitation functions for monopolar RI predictions is explored and it is shown that a small corona cage, due to the build-up of space charge in the small distance between the electrodes, cannot be used to predict the RI levels on HVDC transmission lines accurately. As a consequence of the physics, computational modelling and both frequency and time domain measurements, it is now possible to explain why a small cage system prevents the accurate RI prediction on transmission lines. The large outdoor corona cage and short test line RI performance predictions agree with existing empirical prediction formulas. / AFRIKAANSE OPSOMMING: Vooruitsigte van die opgradering van bestaande hoogspanningsgelykstroom transmissielyn skemas, asook die omkering van bestaande wisselstroom na gelykstroom lyne en die ontwikkeling van nuwe hoogspanningsgelykstroom skemas in sub-Sahara Afrika, het gelei to hernude belangstelling in gelykstroomnavorsing. Die korona-werkverrigting van hoogspanningsgelykstroom oorshoofselyne in terme van radiosteuring, hoorbare-geraas en koronaverliese is kritiese faktore om in aanmerking te neem wanneer die betroubaarheid van die lynontwerp geëvalueer word. Die radiosteuring-werkverrigting is veral van belang tot die suksesvolle oordrag van die kraglyndragolf draersein wat die hoof kommunikasievorm tussen beskermingstoerusting op die Cahora Bassa transmissielyn skema is. Die doel van hierdie proefskrif is om modellering- sowel as meettegnieke te ontwerp om gelykstroomgeleierkorona te karakteriseer. 'n Partikel-in-sel numeriese kode is ontwikkel om 'n beter begrip te verkry van die siese prosesse gedurende koronagebeure. Die numeriese kode maak gebruik van die lading-simulasiemetode, sowel as die eindige element metode om die Laplace en Poisson veldvergelykings op te los. Hoër-orde basisfunksies is geimplimenteer om 'n meer akkurate oplossing vir die Poisson vergelyking te verkry. Die numeriese kode bied insig tot die wiskundige modelle vir die verskeie ionisasie-, aanhegtings- en lawineprosesse wat lei tot koronastrome in die area om die hoogspanningsgeleier. Die numeriese kode, saam met 'n elektro-meter wat ontwerp en ontwikkel is, dra by tot die begrip van die ruimtelading partikeldinamika wat onstaan in die elektrodegaping gedurende koronagebeure. Die meettegnieke neem die wyeband tydgebied- en frekwensiegebiedinformasie van die koronapulse in ag in die teenwoordigheid van geraas. Dit word dan vergelyk met die nouband CISPR meetstandaard vir 'n frekwensie van 500kHz. Die belangrikheid van impedansie-aanpassing vir wyeband metings met die doel om opwekkingsfunksies af te lei, word ondersoek. Die tydgebiedmetings verskil van die algemene frekwensiegebiedmetings, en ondersoek die pulsvorm, -spektrum en -herhalingskoers. Die gebruik van drie moontlike koronageleier-toetsmetodes om gelykstroom radiosteurings-werkverrigting vir positiewe en negatiewe polariteite te bestudeer by hoë vlakke bo seespieël word ondersoek in die proefskrif. Dit sluit in 'n klein koronakou, 'n kort toetslyn en die Eskom Megawatt Park groot buitelug-koronakou. Afgeleide wye- en nouband monopolêre gelykstroom radiosteuring opwekkingsfunksies by 500kHz word gekonsolideer met bestaande radioruis metingsprotokolle en voorspellingsmetodes. Die gebruik van 'n koronakou om opwekkingsfunksies af te lei vir monopolêre radiosteuringvoorspellings is ondersoek en daar is gevind dat 'n klein koronakou nie gebruik kan word om radiosteuringvlakke op hoogspanningsgelykstroom transmissielyne akkuraat te voorspel nie. Dit is as gevolg van die opbou van ruimtelading in die klein elektrodegaping. Met behulp van die sika, numeriese modellering en beide die frekwensie- en tydgebiedmetings, is dit nou moontlik om te verklaar waarom die klein koronakou die akkurate radiosteuringvoorspellings op transmissielyne onmoontlik maak. Die groot buitelug-koronakou en kort toetslyn radiosteuringvoorspellings stem ooreen met bestaande empiriese voorspellings formules.