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: Evandro Conforti / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-23T23:28:57Z (GMT). No. of bitstreams: 1 Ribeiro_AntonioMarceloOliveira_D.pdf: 6175407 bytes, checksum: 03c529ed2452256d1369e23e047687ec (MD5) Previous issue date: 2013 / Resumo: Os efeitos provocados pelo ambiente de propagação sobre o sinal transmitido, assim como as condições impostas pela mobilidade do receptor, afetam diretamente a qualidade de serviço em sistemas de comunicação sem fios. Portanto, é necessário compreender e analisar os efeitos de degradação que o canal terá sobre um dado sistema de comunicação de dados e, dessa forma, avaliar a necessidade de medidas para mitigar os eventuais efeitos prejudiciais do canal. Neste trabalho, apresenta-se uma caracterização estatística do canal de rádio móvel, a partir de medições em campo nas bandas de 1800, 2500 e 3500 MHz, através de uma técnica simples de aquisição da envoltória do sinal. Em particular, são calculadas, para a envoltória, funções de distribuição de probabilidade, taxas de cruzamentos, duração de desvanecimento e sua distribuição, funções de correlação espacial e em frequência, tempo de coerência e largura de banda de coerência. Realiza-se, igualmente, uma análise comparativa destes resultados com os seguintes modelos estatísticos: Rayleigh, Nakagami, Rice, Weibull, Hoyt (Nakagami-q) e ?-?. Além disso, é dada ênfase à estimação de parâmetros dos modelos de canal de rádio, através de dois métodos: momentos (MoM) e máxima verossimilhança (ML). Neste contexto, obtém-se expressões para a variância e o intervalo de confiança, assintóticos, de estimadores ML, baseadas na informação de Fisher que uma amostra aleatória contém a respeito do parâmetro a ser estimado. De forma geral, foi observado um bom ajuste entre as medidas em campo e correspondentes curvas teóricas, para estatísticas de primeira e segunda ordem da envoltória. As medições em campo deste trabalho mostraram que os estimadores ML agruparam mais as curvas teóricas, em torno da curva experimental, quando comparados aos estimadores MoM. Adicionalmente, a matriz de covariância dos estimadores ML para ? e ?, obtida a partir das medições em campo, mostrou que a variância do estimador de ? é, pelo menos, dez vezes maior que aquela do estimador de ?. Igualmente, valores medidos de correlação espacial apresentaram bom ajuste aos modelos teóricos, em termos de uma tendência geral de variação. Em particular, curvas de distribuição cumulativa do tempo de coerência, , para medidas em campo em 3500MHz, mostraram que é maior que 1,7 ms, para 90% do tempo, quando o receptor se move a 30 km/h. Por fim, medidas em campo da largura de banda de coerência, em 1800MHz, revelaram que um valor de ?f < 60 kHz irá garantir um nível de correlação da envoltória maior que 0,9, para 90% do tempo / Abstract: The propagation environment effects on the transmitted signal as well as the conditions imposed by the receiver mobility directly affect the quality of service (QoS) in wireless communication systems. Therefore, it is necessary to understand and analyze the degradation effects inflicted by the channel on a given data communication system, in order to evaluate the measures to mitigate these deleterious effects. In this thesis, we present a statistical characterization of the mobile radio channel based on field measurements performed over the 1800, 2500, and 3500 MHz bands, using a simple technique for acquiring the signal envelope. In particular, envelope statistics for probability distribution functions were calculated, as well as the crossing rates, duration of fading and its distribution, spatial and frequency correlation functions, coherence time, and coherence bandwidth. A comparative analysis of these results was also carried out against the following statistical models: Rayleigh, Nakagami, Rice, Weibull, Hoyt (Nakagami-q), and ?-?. Also, emphasis is given to the parameter estimation of radio channel models using two methods: moments (MoM) and maximum likelihood (ML). In this context, expressions for the asymptotic variance and confidence interval of ML estimators were obtained, based on the Fisher information a random sample contains over the parameter to be estimated. In general, there was a good fit between the field measurements and corresponding theoretical curves for envelope statistics of first and second order. Field measurements of this work have shown that ML estimators grouped more the theoretical curves around the experimental one, when compared to MoM estimators. Additionally, the covariance matrix of ML estimators for ? and ?, obtained from field measurements, showed that the variance of ? estimator is at least ten times greater than the one of ? estimator. Moreover, measured values of spatial correlation showed a good .t to the theoretical models, in terms of a general tendency of variation. Particularly, cumulative distribution curves of the coherence time , for field measurements at 3500MHz, showed that is greater than 1,7 ms for 90% of time when the receiver is moving at 30 km/h. Finally, 1800- MHz field measurements of coherence bandwidth revealed that a value of ?f < 60 kHz will ensure a level of envelope correlation greater than 0.9 for 90% of time / Doutorado / Telecomunicações e Telemática / Doutor 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

This thesis paper proposes a Medium Access Control (MAC) protocol for wireless networks, termed as CD-MMAC that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis. / sabbir@linuxmail.org

With the rapid development and the increasing use of wireless devices, spectrum scarcity has become a problem. The higher frequencies have bad propagation characteristics and the lower frequencies have low data rates, therefore the radio spectrum that is available for efficient wireless transmission is a limited resource. One of the proposed solutions for this problem is cognitive relay networks (CRNs), where cognitive radio is combined with a cooperative spectrum sharing system to increase the spectrum utilization. In this thesis, the outage probability performances of underlay CRNs with interference power constraints from the primary network over Weibull fading channels have been investigated for three different scenarios. The maximum transmit power of the secondary network is governed by the maximum interference power that the primary network&apos;s receiver can tolerate. The first scenario is a cognitive dual-hop decode-and-forward (DF) relay network over independent non-identically distributed (i.n.i.d.) Weibull fading channels. In the second scenario, the CRN consists of a DF relay plus the direct link transmission with a selection combining receiver at the destination over i.n.i.d. Weibull fading channels. The third CRN considered has multiple DF relays where the best relay selection scheme is employed over independent identically distributed (i.i.d.) Weibull fading channels. The analytical results have been derived using the statistical characteristics of end-to-end signal-to-noise ratios, and have been verified by Monte-Carlo simulations.

Abstract In this thesis, novel data and channel estimation methods are proposed and analyzed for low-complexity short-range communication (SRC) radios. Low complexity is challenging to achieve especially in very wideband or millimeter-wave SRC radios where phase recovery and energy capture from numerous multipaths easily become a bottleneck for system design. A specific type of transceiver is selected using pulse amplitude modulation (PAM) at the transmitter and energy detection (ED) at the receiver, and it is thus called an ED-PAM system. Nonnegative PAM alphabets allow using an ED structure which enables a phase-unaware detection method for avoiding complicated phase recovery at the receiver. Moreover, the ED-PAM approach results in a simple multipath energy capture, and only one real decision variable, whose dimension is independent of the symbol alphabet size, is needed. In comparison with optimal phase-aware detection, the appealing simplicity of suboptimal ED-PAM systems is achieved at the cost of the need for a higher transmitted signal energy or shorter link distance for obtaining a sufficient signal-to-noise ratio (SNR) at the receiver, as ED-PAM systems are more vulnerable to the effects of noise and interference. On the other hand, the consequences of requiring a higher SNR may not be severe in the type of SRC scenarios where a sufficient received SNR is readily available due to a short link distance. Furthermore, significant interference can be avoided by signal design. However, what has slowed down the development of ED-PAM systems is that efficient symbol decision threshold estimation and related error probability analysis in multipath fading channels have remained as unsolved problems. Based on the above observations, this thesis contributes to the state-of-the-art of the design and analysis for ED-PAM systems as follows. Firstly, a closed-form near-optimal decision threshold selection method, which adapts to a time-varying channel gain and enables an arbitrary choice of the PAM alphabet size and an integer time-bandwidth product of the receiver filters, is proposed. Secondly, two blind estimation schemes of the parameters for the threshold estimation are introduced. Thirdly, analytical error probability evaluation in frequency-selective multipath fading channels is addressed. Special attention is given to lognormal fading channels, which are typically used to model very wideband SRC multipath channels. Finally, analytical error probability evaluation with nonideal parameter estimation is presented. The results can be used in designing low-complexity transceivers for very wideband and millimeter-wave wireless SRC devices of the future. / Tiivistelmä Tässä työssä esitetään ja analysoidaan uusia data- ja kanavaestimointimenetelmiä, joiden tavoitteena on yksinkertaistaa lähikommunikaatiota (short-range communication, SRC) langattomien laitteiden välillä. SRC-radioiden yksinkertainen toteutus on poikkeuksellisen haasteellista silloin, kun käytetään erittäin suurta kaistanleveyttä tai millimetriaaltoalueen tiedonsiirtoa. Tällöin vastaanottimen yksinkertaisen toteutuksen voivat estää esimerkiksi kantoaallon vaiheen estimointi ja signaalienergian kerääminen lukuisilta kanavan monitiekomponenteilta. Näistä lähtökohdista valitaan SRC-radion järjestelmämalliksi positiiviseen pulssiamplitudimodulaatioon (pulse amplitude modulation, PAM) perustuva lähetin ja energiailmaisimeen (energy detection, ED) perustuva vastaanotin. ED-PAM-järjestelmän ei tarvitse tietää vastaanotetun signaalin vaihetta ja signaalienergian kerääminen tapahtuu yksinkertaisen diversiteettiyhdistelytekniikan avulla. Lisäksi ilmaisuun tarvitaan vain yksi reaalinen päätösmuuttuja, jonka dimensio on riippumaton PAM-tasojen määrästä. ED-PAM-tekniikan yksinkertaisuutta optimaaliseen vaihetietoiseen ilmaisuun verrattuna ei saavuteta ilmaiseksi. Yhtenä rajoituksena on alioptimaalisen ED-PAM-tekniikan luontainen taipumus vahvistaa kohinan ja häiriöiden vaikutusta symbolin päätöksenteossa. Kohinan vahvistus ei välttämättä ole suuri ongelma niissä SRC-radioissa, joissa pienen linkkietäisyyden johdosta riittävä signaali-kohinasuhde vastaanottimessa voidaan kohinan vahvistuksesta huolimatta saavuttaa. Myös häiriöiden vahvistuksen vaikutusta voidaan tehokkaasti vähentää signaalisuunnittelulla. Joka tapauksessa ED-PAM-tekniikan käyttöönottoa on hidastanut tehokkaiden symbolipäätöskynnysten estimointi- ja analysointimenetelmien puuttuminen. Edellä mainitut havainnot ovat motivoineet löytämään uusia suunnittelu- ja analyysimenetelmiä ED-PAM-järjestelmille seuraavasti. Symbolipäätöskynnysten estimointiin johdetaan lähes optimaalinen suljetun muodon menetelmä, joka kykenee adaptoitumaan muuttuvassa kanavassa ja valitsemaan mielivaltaisen kokonaisluvun sekä PAM-tasojen määrälle että vastaanottimen aika-kaistanleveystulolle. Lisäksi esitetään kaksi sokeaa päätöskynnysten estimointimenetelmää, jotka eivät tarvitse redundanttista opetussignaalia. Työn toisessa osassa ED-PAM-järjestelmän symbolivirhesuhdetta analysoidaan taajuusselektiivisessä monitiekanavassa. Analyysissä keskitytään log-normaalijakauman mukaan häipyvään kanavaan. Seuraavaksi analyysia laajennetaan ottamalla mukaan epäideaalisten kynnysarvojen estimoinnin vaikutus. Saavutettuja tuloksia voidaan hyödyntää erittäin laajakaistaisten ja millimetriaaltoalueen SRC-laitteiden suunnittelussa.

Narrowband Internet-of-Things (NB-IoT) is a new wireless technology designed to support cellular networks with wide coverage for a massive number of very cheap low power user devices. Studies have been initiated for deployment of NB-IoT in unlicensed frequency bands, some of which demand the use of a frequency-hopping scheme with a short channel dwell time. In order for a device to connect to a cell, it must synchronize well within the dwell time in order to decode the frequency-hopping pattern. Due to the significant path loss, the narrow bandwidth and the device characteristics, decreasing the synchronization time is a challenge. This thesis studies different methods to decrease the synchronization time for NB-IoT without increasing the demands on the user device. The study shows how artificial fast fading can be combined with denser reference signalling in order to achieve improvements to the cell acquisition and synchronization procedure sufficient for enabling unlicensed operation of NB-IoT. / Narrowband Internet-of-Things (NB-IoT) är en ny trådlös teknik som är designad för att hantera mobilnät med vidsträckt täckning för ett massivt antal mycket billiga och strömsnåla användarenheter. Studier har inletts för att operera NB-IoT i olicensierade frekvensband, varav några kräver att frekvenshoppande spridningsspektrum, med kort uppehållstid per kanal, används. För att en användarenhet ska kunna ansluta till en basstation måste den slutföra synkronisingsfasen inom uppehållstiden, så att basstationens hoppmönster kan avkodas. På grund utav den stora signalförsvagningen, den smala bandbredden och användarenhetens egenskaper är det en stor utmaning att förkorta synkroniseringstiden. Detta examensarbete studerar olika metoder för att förkorta synkroniseringstiden i NB-IoT utan att öka kraven på användarenheten. Arbetet visar att artificiell snabb-fädning kan kombineras med tätare referenssignalering för att uppnå förbättringar i synkroniseringsprocessen som är tillräckliga för att möjliggöra operation av NB-IoT i olicensierade frekvensband.

Automotive industry products portfolio includes a wide variety of complex‐shaped cast iron products, such as truck engine components, that need to withstand a constant trend of higher demands, especially urged by stricter environmental regulations on emissions. Combined with this continued demand on properties improvement, cast iron industry faces a process problem related to the lack of understanding of solidification and mechanisms behind defect formation. Casting products are highly affected by the product design and the manufacturing method itself, which governs the final microstructure and hence the final mechanical properties. Wall thickness of the moulding material strongly influences the solidification time, varying the microstructural coarseness, resulting in a component with different properties depending on the local shape of the casting. The main objective of this work is the characterization of the primary austenite microstructure and its coarsening process, which has been poorly documented in cast iron literature, to allow the prediction and control of these microstructural features present in the casting. The microstructural evolution of the primary austenite in hypoeutectic lamellar graphite iron (LGI) is studied under isothermal coarsening conditions. The dendritic microstructure suffered major morphological changes that included dendrite fragmentation, globularization, and coalescence. Empirical relations based on morphological parameters are introduced to predict the microstructural evolution of primary austenite. A novel technique for colour‐etching and semi‐automatic image analysis for the characterization of quenched dendritic microstructures in cast iron is presented. A new experimental technique for production of graphitic iron with varying nodularity is presented as a solution to control the production of compacted (CGI) and spheroidal graphite iron (SGI) under laboratory conditions. The nodularity evolution is controlled as a function of the holding time and the residual Mg, allowing the study of the primary solidification and primary microstructures of hypoeutectic CGI and SGI in future investigations.

No description available.

A Broadcast Channel is a communication path between a single source and two or more receivers or users. The source intends to communicate independent information to the users. A particular case of interest is the Gaussian Broadcast Channel (GBC) where the noise at each user is additive white Gaussian noise (AWGN). The capacity region of GBC is well known and the input to the channel is distributed as Gaussian. The capacity region of another special case of GBC namely Fading Broadcast Channel (FBC)was given in [Li and Goldsmith, 2001]and was shown that superposition of Gaussian codes is optimal for the FBC (treated as a vector degraded Broadcast Channel). The capacity region obtained when the input to the channel is distributed uniformly over a finite alphabet(Constellation)is termed as Constellation Constrained(CC) capacity region [Biglieri 2005]. In this thesis the CC capacity region for two-user GBC and the FBC are obtained. In case of GBC the idea of superposition coding with input from finite alphabet and CC capacity was explored in [Hupert and Bossert, 2007]but with some limitations. When the participating individual signal sets are nearly equal i.e., given total average power constraint P the rate reward α (also the power sharing parameter) is approximately equal to 0.5, we show via simulation that with rotation of one of the signal sets by an appropriate angle the CC capacity region is maximally enlarged. We analytically derive the expression for optimal angle of rotation. In case of FBC a heuristic power allocation procedure called finite-constellation power allocation procedure is provided through which it is shown (via simulation)that the ergodic CC capacity region thus obtained completely subsumes the ergodic CC capacity region obtained by allocating power using the procedure given in[Li and Goldsmith, 2001].It is shown through simulations that rotating one of the signal sets by an optimal angle (obtained by trial and error method)for a given α maximally enlarges the ergodic CC capacity region when finite-constellation power allocation is used. An expression for determining the optimal angle of rotation for the given fading state, is obtained. And the effect of rotation is maximum around the region corresponding to α =0.5. For both GBC and FBC superposition coding is done at the transmitter and successive decoding is carried out at the receivers.