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Dissertations / Theses on the topic 'MIMO systems'
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Sörman, Simon. "System Information Distribution in Massive MIMO Systems." Thesis, Linköpings universitet, Kommunikationssystem, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-129294.
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The 5th generation mobile telecommunication system (5G) is currently being specified and developed, with large expectations on throughput and efficiency. While 4G and more specifically LTE might constitute a basis of the design of the network, there are some parts that should be improved. One thing to improve is the static signalling that occurs very frequently in a 4G network, of which system information such as synchronization signals, detection of network frequencies, operators, configurations etc. is a part. It has been shown that the static signalling requires both much energy and time-frequency resources. Since the system information is not intended for a single user it is always broadcast so that any user, and any amount of users can read it when needed. 5G will use a technique called massive MIMO, where the base station is equipped with a large number of antennas which can be used to direct signals in space, called beamforming. This thesis presents a new method for distribution of system information that can utilize the beamforming capabilities of massive MIMO. A simple model together with simulated user channel statistics from urban 4G scenarios are used to show that the new method outperforms the classical method of only broadcasting the information, with respect to time-frequency resources. Especially if there are high requirements on the latency of the system information, the new method results in a large gain.
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Chen, Danshan. "Precoding for MIMO systems." Thesis, University of York, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535046.
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Bennia, Abdelhak. "Mimo systems parameters identification." Thesis, Virginia Tech, 1986. http://hdl.handle.net/10919/41579.
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In this thesis, a presentation of a new canonical representation of multi-input multioutput systems is given. The new characterization covers the full range of practical situations in linear systems according to the structural properties and model of the perturbations which are known. Its direct link to ARMA processes as well as to classical state space representation ls also given.
The importance of the new representation lies in the fact that all unknown parameters and state variables appear linearly multlplied by either external variables (inputs and outputs) that appear in the data record, or by matrices that are only composed of ieroes and ones. This property enables us to perform a joint state and parameters estimation. Moreover, if the noises are gaussian and their statistics are known, an on-line algorithm that involves a standard dlscrete-time time-varying Kalman filter is proposed and used successfully in the estimation of unknown parameters for simulated examples.
Master of Science
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Rashid, Imran. "MIMO multi-hop relay systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/mimo-multihop-relay-systems(f8d60fed-c19c-419d-b14f-7defc4721bc3).html.
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Multiple Input Multiple Output (MIMO) systems use multiple transmit and receive antennas to achieve higher data rates by transmitting multiple independent data systems. Transmission errors can be reduced by using Hybrid Automatic Repeat request (HARQ) combining techniques with MIMO systems. In this thesis, the use of HARQ for MIMO multi-hop communication is studied. We propose two MIMO HARQ combining methods which are based on using pre-combiningonly and a joint pre and post combining techniques. In addition to conventional single-hop transmission, HARQ schemes for MIMO multi-hop relay systems are also investigated. A novel approach is proposed to deal with the parallel HARQ processes in MIMO relay scenario. An information theoretic throughput analysis is performed to evaluate the performance of the relay system by employing various transmission techniques for relay-destination link. Evaluation is carried out on the delay involved while employing the relay systems as compared to single hop systems. Simulation results show that the proposed system can enhance the overall throughput performance of MIMO single-hop and multi-hop relay systems. Considering the recent research interest in green radio and requirements of reduced energy consumption by the wireless networks, we evaluated the energy efficiency of existing and proposed MIMO HARQ techniques for sensor and cellular networks. The results show that the proposed scheme is more energy efficient compared to other schemes in single-hop as well as multi-hop scenarios.
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Ma, Shaodan. "Semi-blind signal detection for MIMO and MIMO-OFDM systems." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36846569.
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Ma, Shaodan, and 馬少丹. "Semi-blind signal detection for MIMO and MIMO-OFDM systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B36846569.
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Negrão, João Lucas. "Efficient detection : from conventional Mimo to massive Mimo communication systems." Universidade Estadual de Londrina. Centro de Tecnologia e Urbanismo. Programa de Pós-Graduação em Engenharia Elétrica, 2018. http://www.bibliotecadigital.uel.br/document/?code=vtls000218370.
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Ao longo deste trabalho, problemas relacionados aos sistemas de comunicação equipados com múltiplas antenas no transmissor e receptor (MIMO - Multiple- Input Multiple-Output) são analisados sob o ponto de vista de detecção clássica, da otimização não-linear, bem como da pré-codificação linear, desde MIMO convencional (algumas antenas no Tx e Rx) até sistemas MIMO de larga-escala (massivo). Inicialmente, a eficiência de detecção de vários detectores MIMO foi analisada sob a prerrogativa de canais altamente correlacionados, situação em que sistemas MIMO apresentam elevada perda de desempenho, além de, em alguns casos, uma crescente complexidade. Diante deste cenário, foi estudado especificamente o comportamento em termos do compromisso complexidade x taxa de erro de bits (BER - Bit Error Rate), para diferentes técnicas de detecção, como o cancelamento de interferências sucessivo (SIC), redução treliça (LR), bem como a combinação de cada uma destas às técnicas lineares de detecção. Nessa análise, também foram considerados diferentes estruturas de antenas uniformes com arranjos geométricos lineares (ULA - uniform linear array) e de arranjo planar (UPA - uniform planar array) em ambos transmissor e receptor. Além disso, também foram considerados diferentes número de antenas e ordem de modulação. Em seguida, o problema de detecção MIMO foi estudado sob uma perspectiva de otimização não-linear, visando especificamente alcançar o desempenho ótimo. Foi analisada a solução de detecção com relaxação semi-definida (SDR - semi- definite relaxation). O detector SDR-MIMO é uma abordagem eficiente capaz de atingir o desempenho muito próximo ao ótimo, especialmente para baixas e médias ordens de modulação. Concentramos nossos esforços no desenvolvimento de uma aproximação computacionalmente eficiente para o algoritmo de detecção de máxima verossimilhança (ML - Maximum Likelihood) MIMO baseado na programação semi-definida (SDP - Semidefinite Programming) para as constelações M-QAM. Finalmente, estuda-se um problema de alocação de potência com o objetivo de maximizar a capacidade de um canal de broadcasting MIMO massivo em uma única célula equipada com pré-codificação forçagem à zero (ZFBF - zero-forcing beamforming) e inversão de canal regularizado (RCI - regularized channel inversion) na estação rádio base (BS). Nosso objetivo é investigar esse problema considerando um sistema massivo no limite, ou seja, quando o número de usuários, K, e antenas na BS, M, tendem ao infinito porém com uma razão constante, β = K M . Primeiramente deriva-se a relação sinal-interferência mais ruído (SINR) para ambos os pré-codificadores escolhidos. Em seguida, investiga-se um esquemas de alocação de potência ótimo que maximiza a soma das capacidades por antena sob uma restrição de potência máxima disponível, conclui-se que o problema é convexo e que a alocação de potência ótima segue a estratégia de watter-filling (WF). Também estudou-se o problema relacionado à alocação de potência em um grupo finito de usuários separados em grupos e determinou-se o impacto desse esquema na capacidade total do sistema.Throughout this work, problems related to communication systems equipped with multiple antennas in the transmitter and receiver (MIMO - Multiple-Input Multiple-Output) are analyzed from the point of view of classical detection, nonlinear optimization, as well as linear pre-coding, from conventional MIMO (some Tx and Rx antennas) to large-scale (massive) MIMO systems. Initially, the detection efficiency of several MIMO detectors were analyzed under the prerogative of highly correlated channels, in which situation, MIMO systems present a high loss of performance, and, in some cases, an increasing complexity. Considering this scenario, we have specifically studied the behavior in terms of compromise complexity x bit error rate (BER), for different detection techniques, such as the successive interference cancellation (SIC), lattice reduction (LR), as well as the combination of each of these with linear detection techniques. In this analysis, different uniform antenna structures with uniform linear array (ULA) and planar array array (UPA) were also considered in both transmitter and receiver side. In addition, different number of antennas and order of modulation were also considered. Next, the MIMO detection problem was studied from a nonlinear optimization perspective, specifically aiming to achieve optimum performance. The detection solution with semi-defined relaxation (SDR - it semidefinite relaxation) were analyzed. The SDR-MIMO detector is an efficient approach capable of achieving near-optimal performance, especially for low and medium modulation orders. We focused our efforts on developing a computationally efficient approach for the maximum likelihood (ML) MIMO detection algorithm based on semi-definite programming (SDP) for M-QAM constellations. Finally, we study an optimal power allocation problem aiming to maximizes the sum-rate capacity of a single cell massive MIMO broadcast channel equipped with zero-forcing beamforming (ZFBF) and regularized channel inversion (RCI) precoding at the base station (BS). Our purpose is to investigate this problem in the large-scale system limit, i.e, when the number of users, K, and antennas at the BS, M, tend to infinity with a ratio β = K/M being held constant. We first derive the signal to interference plus noise (SINR) ratio for both chosen precoders. Then we investigate optimal power allocation schemes that maximize the sum-rate per antenna under an average power constraint and we show that the problem is convex and the power allocation follows the well-known Water-Filling strategy. We also studied a problem related to an optimal power allocation at a finite group of clustered users and determine the impact of this scheme in the ergodic sum-rate capacity.
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Gonzalez, Perez Miryam Guadalupe. "Scaling up virtual MIMO systems." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31321.
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Multiple-input multiple-output (MIMO) systems are a mature technology that has been incorporated into current wireless broadband standards to improve the channel capacity and link reliability. Nevertheless, due to the continuous increasing demand for wireless data traffic new strategies are to be adopted. Very large MIMO antenna arrays represents a paradigm shift in terms of theory and implementation, where the use of tens or hundreds of antennas provides significant improvements in throughput and radiated energy efficiency compared to single antennas setups. Since design constraints limit the number of usable antennas, virtual systems can be seen as a promising technique due to their ability to mimic and exploit the gains of multi-antenna systems by means of wireless cooperation. Considering these arguments, in this work, energy efficient coding and network design for large virtual MIMO systems are presented. Firstly, a cooperative virtual MIMO (V-MIMO) system that uses a large multi-antenna transmitter and implements compress-and-forward (CF) relay cooperation is investigated. Since constructing a reliable codebook is the most computationally complex task performed by the relay nodes in CF cooperation, reduced complexity quantisation techniques are introduced. The analysis is focused on the block error probability (BLER) and the computational complexity for the uniform scalar quantiser (U-SQ) and the Lloyd-Max algorithm (LM-SQ). Numerical results show that the LM-SQ is simpler to design and can achieve a BLER performance comparable to the optimal vector quantiser. Furthermore, due to its low complexity, U-SQ could be consider particularly suitable for very large wireless systems. Even though very large MIMO systems enhance the spectral efficiency of wireless networks, this comes at the expense of linearly increasing the power consumption due to the use of multiple radio frequency chains to support the antennas. Thus, the energy efficiency and throughput of the cooperative V-MIMO system are analysed and the impact of the imperfect channel state information (CSI) on the system's performance is studied. Finally, a power allocation algorithm is implemented to reduce the total power consumption. Simulation results show that wireless cooperation between users is more energy efficient than using a high modulation order transmission and that the larger the number of transmit antennas the lower the impact of the imperfect CSI on the system's performance. Finally, the application of cooperative systems is extended to wireless self-backhauling heterogeneous networks, where the decode-and-forward (DF) protocol is employed to provide a cost-effective and reliable backhaul. The associated trade-offs for a heterogeneous network with inhomogeneous user distributions are investigated through the use of sleeping strategies. Three different policies for switching-off base stations are considered: random, load-based and greedy algorithms. The probability of coverage for the random and load-based sleeping policies is derived. Moreover, an energy efficient base station deployment and operation approach is presented. Numerical results show that the average number of base stations required to support the traffic load at peak-time can be reduced by using the greedy algorithm for base station deployment and that highly clustered networks exhibit a smaller average serving distance and thus, a better probability of coverage.
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Liu, Di. "Tensor precoding for MIMO systems." Thesis, University of York, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546819.
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Wu, Zhuo. "MIMO techniques in cellular systems." Thesis, University of York, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423603.
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Singh, Parth Raj. "Source localization with MIMO systems." Thesis, Nantes, 2017. http://www.theses.fr/2017NANT4043/document.
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Dans cette thèse, nous considérons la dernière génération du radar. Il s’agit d’un radar MIMO bistatique qui est composé de plusieurs antennes d’émission et de réception. Pour ce système, les antennes émettrices transmettent des signaux linéairement indépendants afin qu’ils puissent être identifiés à l’aide d’un banc de filtres adaptés au niveau des antennes de réception. Les signaux filtrés sont alors traités pour extraire les paramètres des cibles, tels que les DOA, DOD, vitesse, etc. Un radar MIMO bistatique offre une grande diversité spatiale et une excellente identifiabilité des paramètres, etc., ce qui nous a incités à l’utiliser dans ce travail. La situation en champ lointain d’un radar MIMO bistatique est largement traitée dans la littérature. Mais, peu de travaux existe sur la situation en champ proche, c’est ce qui a motivé le travail de cette thèse. La localisation de cibles en champ proche est importante en raison de nombreuses applications à l’intérieur des constructions. A ce sujet, la plupart des méthodes actuelles utilisent l’approximation de Fresnel dans laquelle le front d’onde sphérique des signaux reçus est supposé quadrique plutôt que planaire comme en champ lointain. Dans ce travail de thèse, nous avons proposé une nouvelle méthode de localisation des cibles en champ proche qui utilise l’approximation de Fresnel. Celle-ci conduit à une estimation biaisée des paramètres de localisation car en réalité le front d’onde est sphérique. Nous avons proposé alors deux méthodes de correction pour réduire les effets de l’approximation de Fresnel et deux autres méthodes qui utilisent directement le modèle exacte basé sur le front d’onde sphériqueSources localization is used in radar, sonar, and telecommunication. Radar has numerous civilian and military applications. Radar system has gone through many developments over the last few decades and reached the latest version known as MIMO radar. A MIMO radar is composed of multiple transmitting and receiving antennas like a conventional phased array radar. However, its transmitting antennas transmit linearly independent signals so that they can be easily identified by the matched filters bank at its receiving end. The matched filtered signals are then processed to extract the ranges, DOAs, DODs, velocities, etc. of the targets. A bistatic MIMO radar system provides high resolution, spatial diversity, parameter identifiability, etc. which inspired us to use it in this work. There are many existing methods to deal with the far field region of MIMO radar system. However, little work can be found on the near field region of a bistatic MIMO radar which motivated the work in this thesis. Near field targets localization is also important because of many indoor applications. Most of the existing near field sources localization techniques use Fresnel approximation in which the real spherical wavefront is assumed quadric unlike planar in far field situation. In this work we have proposed a novel near field targets localization method using Fresnel approximation. The Fresnel approximation leads to a biased estimation of the location parameters because the true wavefront is spherical. Consequently, we have proposed two correction methods to reduce the effects of Fresnel approximation and other two methods which directly use the exact signal model based on spherical wavefront
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Mota, Susana de Jesus. "Channel modelling for MIMO systems." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14961.
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Doutoramento em Engenharia ElectrotécnicaSystems equipped with multiple antennas at the transmitter and at the receiver, known as MIMO (Multiple Input Multiple Output) systems, offer higher capacities, allowing an efficient exploitation of the available spectrum and/or the employment of more demanding applications. It is well known that the radio channel is characterized by multipath propagation, a phenomenon deemed problematic and whose mitigation has been achieved through techniques such as diversity, beamforming or adaptive antennas. By exploring conveniently the spatial domain MIMO systems turn the characteristics of the multipath channel into an advantage and allow creating multiple parallel and independent virtual channels. However, the achievable benefits are constrained by the propagation channel’s characteristics, which may not always be ideal. This work focuses on the characterization of the MIMO radio channel. It begins with the presentation of the fundamental results from information theory that triggered the interest on these systems, including the discussion of some of their potential benefits and a review of the existing channel models for MIMO systems. The characterization of the MIMO channel developed in this work is based on experimental measurements of the double-directional channel. The measurement system is based on a vector network analyzer and a two-dimensional positioning platform, both controlled by a computer, allowing the measurement of the channel’s frequency response at the locations of a synthetic array. Data is then processed using the SAGE (Space-Alternating Expectation-Maximization) algorithm to obtain the parameters (delay, direction of arrival and complex amplitude) of the channel’s most relevant multipath components. Afterwards, using a clustering algorithm these data are grouped into clusters. Finally, statistical information is extracted allowing the characterization of the channel’s multipath components. The information about the multipath characteristics of the channel, induced by existing scatterers in the propagation scenario, enables the characterization of MIMO channel and thus to evaluate its performance. The method was finally validated using MIMO measurements.
Os sistemas equipados com múltiplas antenas no emissor e no recetor, conhecidos como sistemas MIMO (Multiple Input Multiple Output), oferecem capacidades mais elevadas, permitindo melhor rentabilização do espectro e/ou utilização de aplicações mais exigentes. É sobejamente sabido que o canal rádio é caracterizado por propagação multipercurso, fenómeno considerado problemático e cuja mitigação tem sido conseguida através de técnicas como diversidade, formatação de feixe ou antenas adaptativas. Explorando convenientemente o domínio espacial os sistemas MIMO transformam as características multipercurso do canal numa mais-valia e permitem criar vários canais virtuais, paralelos e independentes. Contudo, os benefícios atingíveis são condicionados pelas características do canal de propagação, que poderão não ser sempre as ideais. Este trabalho centra-se na caracterização do canal rádio para sistemas MIMO. Inicia-se com a apresentação dos resultados fundamentais da teoria da informação que despoletaram todo o entusiamo em torno deste tipo de sistemas, sendo discutidas algumas das suas potencialidades e uma revisão dos modelos existentes para sistemas MIMO. A caracterização do canal MIMO desenvolvida neste trabalho assenta em medidas experimentais do canal direcional adquiridas em dupla via. O sistema de medida é baseado num analisador de redes vetorial e numa plataforma de posicionamento bidimensional, ambos controlados por um computador, permitindo obter a resposta em frequência do canal rádio nos vários pontos correspondentes à localização dos elementos de um agregado virtual. As medidas são posteriormente processadas com o algoritmo SAGE (Space-Alternating Expectation-Maximization), de forma a obter os parâmetros (atraso, direção de chegada e amplitude complexa) das componentes multipercurso mais significativas. Seguidamente, estes dados são tratados com um algoritmo de classificação (clustering) e organizados em grupos. Finalmente é extraída informação estatística que permite caracterizar o comportamento das componentes multipercurso do canal. A informação acerca das características multipercurso do canal, induzidas pelos espalhadores (scatterers) existentes no cenário de propagação, possibilita a caracterização do canal MIMO e assim avaliar o seu desempenho. O método foi por fim validado com medidas MIMO.
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Choi, Lai U. "Multi-user MISO and MIMO transmit signal processing for wireless communication /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20CHOI.
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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 167-170). Also available in electronic version. Access restricted to campus users.
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Karlsson, Marcus. "Aspects of Massive MIMO." Licentiate thesis, Linköpings universitet, Kommunikationssystem, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-132718.
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Next generation cellular wireless technology faces tough demands: increasing the throughput and reliability without consuming more resources, be it spectrum or energy. Massive mimo (Multiple-Input Multiple-Output) has proven, both in theory and practice, that it is up for the challenge. Massive mimo can offer uniformly good service to many users using low-end hardware, simultaneously, without increasing the radiated power compared to contemporary system. In Massive mimo, the base stations are equipped with hundreds of antennas. This abundance of antennas brings many new, interesting aspects compared to single-user mimo and multi-user mimo. Some issues of older technologies are nonexistent in massive mimo, while new issues in need of solutions arise. This thesis considers two aspects, and how these aspects differ in a massive mimo context: physical layer security and transmission of system information. First, it is shown that a jammer with a large number of antennas can outperform a traditional, single-antenna jammer in degrading the legitimate link. The excess of antennas gives the jammer opportunity to find and exploit structure in signals to improve its jamming capability. Second, for transmission of system information, the vast number of antennas prove useful even when the base station does not have any channel state information, because of the increased availability of space-time coding. We show how transmission without channel state information can be done in massive mimo by using a fixed precoding matrix to reduce the pilot overhead and simultaneously apply space-time block coding to use the excess of antennas for spatial diversity.Det ställs hårda krav på nästa generations cellulära trådlösa system: att simultant öka datatakten på kommunikationen och dess tillförlitlighet utan att konsumera mer resurser, oavsett om det spektrum eller energi. Massiv mimo (eng: Multiple-Input Multiple-Output) har visat, både i teori och praktik, att tekniken är redo att tackla utmaningen. Massiv mimo kan betjäna många användare samtidigt, med god service, utan att öka den utstrålade effekten jämfört med nuvarande system. Massiv mimo, där basstationerna är utrustade med hundratals antenner, skiljer sig från dagens system vilket gör att många nya problem dyker upp och nya infallsvinklar på befintliga problem krävs. Denna avhandling analyserar två problem, och hur dessa förändras i ett massiv mimo sammanhang: säkerhet för fysiska lagret och överföring av systeminformation. Särskiljt visas att en störsändare med ett stort antal antenner kan överträffa en traditionell störsändare med en enda antenn. Antalet antenner ger störsändaren möjlighet att hitta strukturer i signaler och utnyttja detta för att förbättra störningens effekt. Det stora antalet antenner visar sig vara användbart även för överföring av systeminformation, där basstationen inte har någon kanalkännedom. Antennerna ger möjligheten att tillämpa spatial kodning (eng: space-time block coding). Vi visar hur överföringen utan kanalkännedom kan göras i massiv mimo genom att använda en fix förkodningsmatris för att reducera antalet pilotsymboler. Samtidigt kodar vi spatiellt över antennerna för att tillhandahålla spatiell diversitet.
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Zheng, Gan. "Optimization in linear multiuser MIMO systems." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557923.
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Zheng, Gan, and 鄭淦. "Optimization in linear multiuser MIMO systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557923.
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Stimming, Christian. "Multiple antenna concepts in OFDM transmission systems." Göttingen Cuvillier, 2009. http://d-nb.info/995846030/04.
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Phasouliotis, Antonis. "Multicarrier CDMA systems with MIMO technology." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/multicarrier-cdma-systems-with-mimo-technology(87853579-fae7-45cb-b243-abe731f2c786).html.
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The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.
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Quitin, François. "Channel modeling for polarized MIMO systems." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209951.
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This thesis treats of channel models for polarized multi-antenna wireless systems. Polarized multi-antenna systems are systems that use perpendicularly polarized, co-located antennas at the base station and at the mobile terminal, in order to benefit from the so-called polarization diversity. Such systems benefit from the advantages of MIMO systems while still maintaining a compact equipment size. Two models will be presented in this thesis. The first one is the Polarized-Input Polarized-Output (PIPO) channel model, the second one is the Polarized-Diffuse-Directional channel model. The PIPO model is a statistical channel model for tri-polarized to tri-polarized communication systems. A tri-polarized antenna system is a tranceiver using three perpendicular antennas. The aim of the PIPO channel model is to have a model that has a simple mathematical structure, so it can be used for solving precoding equations or capacity calculations. Although the PIPO model has a very simple structure, it takes the following parameters into account: coherent channel component, cross-polar channel power imbalance, inter-channel correlation, short- and long-scale time variance.
Experimental measurements are used to parameterize the model. It is shown how the model parameters are extracted from experimental measurements, and the results are analyzed to allow further simplification of the model.
The PDD model, on the other hand, is a geometry-based stochastic channel model. It models the channel as a sum of clusters, where each cluster consists of groups of multipath components (MPCs). The PDD model includes two novelties that will be developed in detail in this thesis.
- The model considers polarization on a per-cluster basis. This permits to have a more accurate description of the polar-angular spectrum.
- The diffuse multipath component (DMC) is included by considering a diffuse component for each cluster. The diffuse cluster component is then modeled as the sum of a set of diffuse MPCs.
The model is specified in detail, and it is shown how the model can be generated.
Experimental measurements were carried out to parameterize the model. A new extraction technique for extracting the specular-diffuse clusters from the measurements is proposed. This technique is based on joint clustering of the specular MPCs and the bins of the diffuse component. The experimental results are analyzed, and superimposed with environment information to gain further insight into the physical aspects of clustered propagation.
Finally, both models are validated. Several validation metrics are introduced, and their pertinence in the context of polarized MIMO systems is highlighted. Both models are successfully validated, and the advantages and limitations of each models are investigated.
Cette thèse traite des modèles de canal pour systèmes sans-fils multi-antennes polarisés. Des systèmes multi-antennes polarisés sont des systèmes qui utilisent des antennes polarisées perpendiculairement co-localisées à la station de base et au terminal mobile, dans le but de bénéficier de la diversité de polarisation. De tels systèmes peuvent bénéficier des avantages des systèmes MIMO tout en diminuant l'encombrement des équipements. Deux modèles seront présentés dans cette thèse. Le premier est le modèle Polarized-Input Polarized-Output (PIPO), le second est le modèle Polarized-Diffuse-Directional (PDD).
Le modèle PIPO est un modèle statistique pour des systèmes de communication tri-polaire à tri-polaire. Un système tri-polaire est un émetteur ou un récepteur qui utilise trois antennes perpendiculaires. Le but du modèle de canal PIPO est d'avoir un modèle qui a une structure mathématique simple, afin qu'il puisse être utilisé pour résoudre des équations de précodage ou des calculs de capacité. Malgré la structure simple du modèle PIPO, il tient compte des paramètres suivants: la composante cohérente du canal, les différences de puissance entre canaux cross-polaires, la corrélation entre canaux, les variations à courte et à longue échelle de temps. Des mesures expérimentales ont été réalisées afin de paramétriser le modèle. Les techniques pour extraire les paramètres du modèle des mesures expérimentales sont présentées, et les résultats sont analysés afin de permettre une simplification supplémentaire du modèle.
Le modèle PDD, quant à lui, est un modèle de canal stochasique-géométrique. Il modélise le canal comme une somme de clusters, où chaque clusters est composé d'un groupe de chemins multi-trajets. Le modèle PDD inclut les deux nouveautés suivantes qui seront développées en détail dans cette thèse.
- Le modèle considère une polarisation par cluster. Ceci permet d'avoir une description plus exacte du spectre angulaire-polaire.
- La composante diffuse est prise en compte en incluant une composante diffuse pour chaque cluster. La composante diffuse d'un cluster est alors modelisée comme une somme de multi-trajets diffus.
Le modèle est spécifié en détail, et il est présenté comment le modèle peut être généré. Des mesures expérimentales ont été faites afin de paramétriser le modèle. Une nouvelle technique d'extraction est proposée pour extraire les clusters spéculaires-diffus. Cette technique est basée sur le clustering conjoint des multi-trajets spéculaires et des "bins" de la composante diffuse. Les résultats expérimentaux sont analysés, et superposés avec l'information de l'environnement de mesure afin d'avoir une connaissance accrue des aspects physiques de la propagation par clusters.
Finalement, les deux modèles sont validés. Plusieurs métriques de validations sont introduites, et leur pertinence dans le cadre des systèmes MIMO polarisés est mis en avant. Les deux modèles sont validés avec succès, et les avantages et limitations de chaque modèle sont investigués.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Krishnan, Praveen G. "Fast sphere decoder for MIMO systems." Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.umr.edu/thesis/pdf/umrthes_09007dcc80318823.pdf.
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Thesis (M.S.)--University of Missouri--Rolla, 2007.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 16, 2007) Includes bibliographical references (p. 38).
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Ding, Zhihong. "ARQ Techniques for MIMO Communication Systems." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1385.pdf.
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Chen, Harry Zhi Bing. "Signal design for MIMO-OFDM systems." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23907.
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Orthogonal frequency division multiplexing (OFDM) combined with multiple-input multiple-output (MIMO) wireless technology is an attractive air-interface solution for wireless systems. The time-selective and dispersive nature of the wireless channel, however, poses challenges for signal design. To address these challenges, this dissertation investigates several physical layer aspects of signal design for MIMO-OFDM systems.
To improve the information outage rate of certain MIMO systems with low-rank channel matrices, we propose two novel channel augmentation schemes, namely, the complex virtual antenna (CVA) and the real virtual antenna (RVA) schemes. For Bell labs space-time (BLAST) type architectures, both the CVA and the RVA schemes are more robust to channel correlations than a previously proposed scheme.
For performance enhancement of coded MIMO-OFDM, we consider wrapped space-frequency coding (WSFC) and coded vertical BLAST (V-BLAST) with adaptive bit loading (ABL) and optimize both schemes. We show that bit-loaded WSFC and V-BLAST optimized for coded MIMO-OFDM can achieve error rate performances close to that of quasi-optimal MIMO-OFDM based on single value decomposition (SVD) of the channel, while their feedback requirements for loading are low.
To exploit the spatial and frequency diversity in coded MIMO-OFDM systems, we propose cyclic space-frequency (CSF) filtering, which is applicable to both traditional MIMO systems with co-located transmit antennas and cooperative diversity systems with distributed transmit antennas. We further propose a robust CSF filtering scheme, which exploits imperfect channel state information at the transmitter (CSIT) and takes into account the reliability of the CSIT. To further improve robustness, we combine CSF filtering with space-time block coding (STBC) in the frequency domain. We also propose a linear prediction method for improving the quality of the CSIT via post-processing. For these CSF filtering schemes, design criteria are derived, closed-form solutions are given for certain special cases, and various design methods are provided for the general case. Simulation results confirm that robust CSF filtering is a promising solution for wireless communication systems.
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Rico, Ulises Pineda. "Link Optimisation for MIMO Communication Systems." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503000.
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Cox, David Alexander. "Capacity Considerations of Mimo Antenna Systems." Thesis, University of York, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503315.
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Wei, Chun-Yi. "Iterative downlink multi-user MIMO systems." Thesis, University of Southampton, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485522.
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In this treatise, we explore diverse multi-user transmission techniques and joint detection-decoding schemes designed for downlink multi-user transmissions, while maintaining a low complexity, a high throughput and a high integrity. More specifically, in Chapter 2 we will introduce various Multi-User Transmission (MUT) techniques for the Space Division Multiple Access Down-Link (DL-SDMA) employing the sophisticated linear SpatioTemporal Pre-processing (STP) schemes, which are capable of eliminating the multi-user interference at the Base Station (BS) and increase the transmission integrity at the Mobile Sta,ions (MS). Additionally, we will design signal detection techniques for the DL-SDMA system, which achieves a near-Maximum Likelihood (ML) performance at a fraction of the ML detector's complexity. In Chapter 3 we extend our research to a joint iterative detection and decoding based DL-SDMA system. We will introduce a precoder aided iterative DL-SDMA system, which is designed with the aid of Extrinsic Information Transfer (EXIT) charts and has an improved iterative decoding gain. Finally, we will characterize the impact of imperfect Channel State Information (CSI) on the proposed iterative DL-SDMA and introduce sophisticated IrRegular Convolutional Codes (IRCC) for improving the integrity of the iterative DL-SDMA system. In order to reduce the complexity of the iterative receivers, in Chapter 4 we will introduce a novel detection algorithm, which is referred to as the Irregular Generic Detection (IrGD) algorithm. The IrGD has a tunable • complexity and it was particularly designed for redUcing the complexity of the iterative decoding aided system. Furthermore, we will demonstrate the impact of imperfect CSI with the aid of EXIT charts. In addition, we will introduce an EXIT-Chart Optimized CSI Quantizer (ECO-CQ) for the iterative DL-SDMA system, which is capable of reducing CSI-related feedback overhead. In Chapter 5 we will introduce an advanced space-time signaling technique aided MUT designed for the DL-SDMA system, which results in an improved capacity. Furthermore, we will propose a low-complexity Irregular Sphere Detection (IrSD) scheme designed for approaching the capacity DL-SDMA systems, which is capable of maintaining a near-ML performance. Additionally, we will characterize our pilot assisted channel prediction aided DL-SDMA system using limited CSI feedback.
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Yao, Yao, and 姚瑤. "Carrier synchronization techniques in MIMO systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B31246230.
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Daoud, Omar Rawhi. "MIMO-OFDM for beyond 3G systems." Thesis, De Montfort University, 2006. http://hdl.handle.net/2086/4106.
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ORTEGA, ALVARO JAVIER. "SIGNAL DETECTION IN MASSIVE MIMO SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=26176@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
Este trabalho de dissertação de mestrado apresenta uma comparação de algumas das técnicas de detecção de sinais mais promissoras para a viabilização de sistemas MIMO de grande porte em termos de desempenho, taxa de erro de bit e complexidade, número médio de flops requeridos por vetor de símbolos recebido. Com este objetivo foram também consideradas as técnicas de detecção clássicas, visando assim ressaltar o desempenho das novas técnicas com relação as antigas. Além disso foram propostas e investigadas novas estruturas para detectores SIC baseados em lista (i.e., com múltiplos ramos) que resultaram em melhor desempenho com menor complexidade quando comparados aos detectores deste tipo já propostos. Na comparação dos algoritmos, foram considerados três cenários diferentes: (i ) monousuário, com ganhos de canal gaussianos complexos independentes e identicamente distribuídos, ou seja, uma propagação que só considera a presença de desvanecimento de Rayleigh; (ii ) múltiplos usuários com canais correlatados e que considera as perdas de propagação de pequena e larga escala num sistema com antena centralizada; e (iii ) múltiplos usuários com canais correlatados e que considera as perdas de propagação de pequena e larga escala num sistema com antena distribuída.
This work dissertation presents a comparison of some of the signal detection techniques most promising for the viability of large MIMO systems in terms of performance, bit error rate, and complexity, average number of flops required by transmitted symbol vector. For this purpose it was also considered classical detection techniques, thus aiming to highlight the performance of new techniques with respect the old. Also it has been proposed and investigated new structures to SIC detectors based on list (i.e., with multiple branches) resulting in better performance with less complexity compared to detectors of this kind already proposed. In the comparison of algorithms, three different scenarios were used: (i ) single user, with channel gains independent and distributed identically complex Gaussian, that is, a spread that only considers the presence of Rayleigh fading; (ii ) multiple users, with correlated channels, and considers the short and large scale path loss in a system with centralized antenna; e (iii ) multiple users, with correlated channels, and considers the short and large scale path loss in a system with distributed antenna.
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Payami, Sohail. "Hybrid beamforming for massive MIMO systems." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/842311/.
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Massive multiple-input multiple-output (MIMO) technology is considered as one of the enabling technologies to scale up the data rates for the future communication systems. Traditional MIMO systems employ digital beamforming where each antenna element is equipped with one radio frequency (RF) chain. When the number of the antennas are scaled up, the cost and power consumption of massive MIMO systems also increase significantly. Recently, hybrid analog-and-digital beamformers have attracted a lot of attention as a cost effective approach to benefit from the advantages of massive MIMO. In hybrid structure, a small number of RF chains are connected to a large number of antennas through a network of phase shifters. The optimal hybrid beamforming problem is a complex nonconvex optimization due to the nonconvex constraint imposed by phase shifters. The overall objective of this thesis is to provide simple and effective hybrid beamforming solutions for narrowband point-to-point and multiuser massive MIMO scenarios. Firstly, hybrid beamforming problem for a point-to-point communication system with perfect channel state information (CSI) is investigated, and an effective codebook based hybrid beamforming with low resolution phase shifters is proposed which is suitable for sparse scattering channels. Then, by leveraging the properties of massive MIMO, an asymptotically optimal hybrid beamforming solution as well as its closed-form formula will be presented. It will be shown that the proposed method is effective in both sparse and rich scattering propagation environments. In addition, the closed-form expression and lower-bounds for the achievable rates are derived when analog and digital phase shifters are employed. Secondly, hybrid beamforming problem to maximise the total sum-rate for the downlink of multiuser MIMO is investigated, and an effective solution as well as its closed-form expression for this system is proposed. The presented solutions for the single-antenna and multiantenna scenarios are shown to be effective as they can achieve a similar sum-rate as digital beamforming can reach. In addition, it is shown that the proposed technique with low-cost low resolution phase shifters at the RF beamformer demonstrates a comparable performance to that of a hybrid beamformer with an expensive analog beamformer. Finally, two novel hybrid beamforming techniques are proposed to reduce the power consumption at the RF beamformer. Defining a threshold level, it is shown that half of the phase shifters could be turned off without a performance loss when the wireless channel matrix is modeled by Rayleigh fading. Then, we reduce the number of the phase shifters by using a combination of phase shifters and switches at the RF beamformer. The proposed methods can significantly reduce the power consumption as switches, in general, have lower power consumption compared to phase shifters. It is noted that the presented algorithms and the closed-form expressions of their performance are derived by using the asymptotic properties of the elements of the singular vectors for the rich scattering channel matrix.
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Zhang, Fan. "Diversity strategies for MIMO communication systems." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:530327bb-e4d9-4ce2-8140-312e7d175c05.
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This thesis proposes a joint spatial diversity scheme in MIMO systems in order to improve the transmission reliability of the wireless links, thereby to extend the transmission range and increase the information throughput. Cyclic delay diversity (CDD) and antenna selection are employed here for their low complexity, high flexibility, no spectrum efficiency reduction and high compatibility with many existing standards. A bit error performance bound for CDD system with orthogonal frequency division multiplexing and convolutional coding in multipath Rayleigh fading channel is generated, which renders a fundamental understanding of the mechanism of CDD and can be used instructively for CDD system design. A transmit cyclic delay diversity and receive antenna selection (TCDD/RAS) system is proposed here to achieve a performance gain with lower additional complexity and no data rate reduction compared with a transmit orthogonal space-time block coding (OSTBC) system, which is combined with the optimum receive antenna selection scheme. A hybrid system with both OSTBC and CDD in the transmitter and antenna selection in the receiver is also derived to avoid the high complexity requirement and data rate degradation of the OSTBC system as well as the performance loss of the CDD system. A receive antenna selection criterion for the TCDD/RAS system based on the previous performance analysis results is defined, however it demands high computational complexity. Therefore a much simpler and faster selection rule, named maximum minimum post-processing SNR criterion, is generated for the TCDD/RAS system in flat fading channels and another maximum group minimum post-processing SNR selection principle is developed in frequency selective channels. Both of these two selection rules achieve higher diversity gains with lower additional complexity compared with the traditional norm and capacity selection rules. Two relay systems embedded with the TCDD/RAS scheme are also constructed: the MIMO relay system and the cooperative relay system. The joint diversity scheme in the MIMO relay system obtains a higher diversity gain than in the cooperative relay system. Moreover, these two relay systems could be combined to a system with multiple cooperative relay nodes on which multiple antennas are deployed depending on the practical requirement in the future wireless communication systems.
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Praveen, Vunnam. "Maximizing LTE performance with MIMO Systems." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-58272.
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The project explains Long Term Evolution (LTE) systems when used with Multiple-Input, MultipleOutput (MIMO) fulfill the growing demands in throughput and system robustness for the user. This is investigated by understanding the throughput capacity of LTE down-links in both spatial multiplexing and transmission diversity mode. The performance downgrades in LTE frame is analyzed. All the simulations are done in MATLAB. The simulations include Bit Error Rate (BER) being verified for values of Signal to Noise Ratio (SNR). MIMO systems use more than one antenna configuration for sending and receiving radio signals of the same frequency. The concept of beam forming may be utilized by MIMO systems. This is done by employing more than one antenna at both the ends namely transmitter (Tx) and receiver (Rx). The use of multiple antennas will achieve higher capacity and better cell coverage. MIMO technologies, when used in LTE, provide better down-link peak rates, cell coverage, and enhanced average cell throughput. LTE offers increased capacity while using standard antenna technique. This technique provides two vital aspects namely, spatial multiplexing (SM) and transmits diversity (TD). The project also explores the effect of different parameters namely, the speed of mobile station, the number of Multipath, Rician factor (K) on throughput is discussed and reported. The report evaluates the performance of LTE using MIMO in order to explain LTE system capacity, average cell throughput of LTE at different bandwidths and BER performance against SNR. The simulation outputs are shown as graphs and discussed.
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Anjos, Gustavo Miranda Castilho dos. "MIMO processing techniques for 4G systems." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12768.
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Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe theme of this dissertation work is focused in one of the key technologies specified in the last 4G cellular standards, which are the MIMO systems. In this context, the MIMO (Multiple Input Multiple Output) acronym is used to define a communication system where multiple antennas are used, therefore using this type of systems jointly with specific signal processing techniques, we can use the spatial dimension in order to generate multiplexing, diversity and beamforming gains. The aim of this work is to show the type of signal processing techniques that must be applied in order to achieve the gains referenced above, as well the optimal channel conditions in which these gains are maximized.Therefore, beyond the presentation of the theoretical background related with these type of techniques, we will present the MIMO transmission modes specified on 4G-LTE, having not only the aiming of show the type of practical constraints verified in a practical implementation, but also present the solutions used to solve that kind of constraints. In the last part of this work is presented a simulation platform implemented for one of the spatial multiplexing modes specified on LTE, which is the mode 4. The numerical results obtained allowed to see the advantage in the use of SIC (Successive Interference Cancelation) equalizers for multi-layer transmission modes, as well as the performance limitations related with the transmission through a channel where high spatial correlation conditions are verified. With the use of multiple precoding matrices, we understand the importance of perform a correct precoding selection in order to improve the transmission through a channel with this type of conditions.Beyond the observations referred above, we also saw the diversity cost related with the increase of spatial multiplexing gain.
O tema deste trabalho de dissertação visa uma das tecnologias chave especificada nos últimos standards 4G para o sector das comunicações móveis, que são os sistemas MIMO. Neste contexto, o acrónimo MIMO é usado para referenciar um sistema de comunicação que faz uso de múltiplas antenas, assim, usando este tipo de sistemas conjuntamente com técnicas de processamento de sinal apropriadas, podemos usar a dimensão espacial de forma a gerar ganhos de multiplexagem, diversidade e beamforming. O objetivo deste trabalho é mostrar que tipo de processamento de sinal deve ser feito de forma a gerar cada um dos ganhos acima referidos, assim como as condições de canal em que estes podem ser maximizados. Para além da apresentação dos fundamentos teóricos relacionados com este tipo de técnicas, iremos apresentar os modos de transmissão MIMO especificados para o 4GLTE, tendo não só como objectivo observar o tipo de constrangimentos prácticos inerentes a uma implementação real, mas também observar o tipo de soluções usadas para fazer face a esses mesmos constrangimentos. Na parte final do trabalho é apresentada uma plataforma de simulação implementada para um dos modos de multiplexagem espacial especificados no LTE, ou seja o modo 4. Os resultados numéricos obtidos permitiram constatar a vantagem em usar equalizadores SIC em modos de transmissão multi-camada, assim como também nos permitiu observar as limitações de performance inerentes á transmissão através de um canal com elevada correlação espacial. Usando várias matrizes de pré-codificação especificadas no LTE para este modo, conseguimos perceber a importância que a escolha de uma correcta précodificação tem no melhoramento de desempenho da transmissão neste tipo de canais. Para além das observações referidas acima, também podemos verificar o custo em termos de diversidade inerente ao aumento do ganho de multiplexagem.
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Wang, Xiao Lei. "Signal Processing in Arrayed MIMO Systems." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/4644.
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Multiple-Input Multiple-Output (MIMO) systems, using antenna arrays at bothreceiver and transmitter, have shown great potential to provide high bandwidthutilization efficiency. Unlike other reported research on MIMO systems whichoften assumes independent antennas, in this thesis an arrayed MIMO systemframework is proposed, which provides a richer description of the channel charac-teristics and additional degrees of freedom in designing communication systems. Firstly, the spatial correlated MIMO system is studied as an array-to-arraysystem with each array (Tx or Rx) having predefined constrained aperture. TheMIMO system is completely characterized by its transmit and receive array man-ifolds and a new spatial correlation model other than Kronecker-based model isproposed. As this model is based on array manifolds, it enables the study of theeffect of array geometry on the capacity of correlated MIMO channels. Secondly, to generalize the proposed arrayed MIMO model to a frequencyselective fading scenario, the framework of uplink MIMO DS-CDMA (Direct-Sequence Code Division Multiple Access) systems is developed. DOD estimationis developed based on transmit beamrotation. A subspace-based joint DOA/TOAestimation scheme as well as various spatial temporal reception algorithms is alsoproposed. Finally, the downlink MIMO-CDMA systems in multiple-access multipath fading channels are investigated. Linear precoder and decoder optimization problemsare studied under different criterions. Optimization approaches with differentpower allocation schemes are investigated. Sub-optimization approaches withclose-form solution and thus less computation complexity are also proposed.
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Ximenes, Leandro Ronchini. "Tensor-based MIMO relaying communication systems." reponame:Repositório Institucional da UFC, 2015. http://www.repositorio.ufc.br/handle/riufc/12931.
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XIMENES, L. R. Tensor-based MIMO relaying communication systems. 2015. 134 f. Tese (Doutorado em Engenharia de Teleinformática) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2015.Submitted by Marlene Sousa (mmarlene@ufc.br) on 2015-06-24T12:23:49Z No. of bitstreams: 1 2015_tese_lrximenes.pdf: 22186309 bytes, checksum: b90a5d56afa23e69c67413686ac097d4 (MD5)
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In cooperative communication systems, two or more transmitting terminals are combined to increase the diversity and/or the power of the signals arriving at a particular receiver. Therefore, even if the devices do not have more than one antenna, or if a significant propaga- tion loss is present between the two communicating nodes, the various transmitting elements can act as a virtual antenna array, thus obtaining the benefits of the multiple antenna (MIMO) systems, especially the increase in the capacity. Recently, tensor decompositions have been introduced as an efficient approach for channel estimation in cooperative com- munication systems. However, among the few works devoted to this task, the utilization of the PARAFAC tensor decomposition for modeling the received signals did not allow the development of techniques for joint symbol and channel estimation. Aiming to avoid the use of pilot sequences, which limits the overall spectral efficiency by dedicating a portion of the bandwidth only for the channel estimation task, the objective of this thesis is to provide new tensor-based strategies, including transmission systems and semi-blind receivers, for one-way two-hop MIMO relaying systems. Based on a Khatri-Rao space-time coding at the source and two different Amplify-and-Forward (AF) relaying strategies, two transmission schemes are proposed. For these systems, named PT2-AF and NP-AF, the received signals at the destination node follow respectively a PARATUCK2 and a nested PARAFAC tensor model. Exploiting uniqueness properties of these tensor models which are established in the thesis, several semi-blind receivers are derived. Some of these receivers are of iterative form us- ing an ALS algorithm, whereas some other ones have closed-form solutions associated with Khatri-Rao factorizations. Some simulation results are finally presented to illustrate the per- formance of the proposed receivers which are compared to some state-of-the-art supervised techniques
Em comunicações cooperativas, dois ou mais terminais de transmissão são combinados para aumentar a diversidade e/ou a potencia dos sinais que chegam a um determinado receptor. Portanto, mesmo que os dispositivos não disponham de mais de uma antena, ou que então haja uma grande perda por propagação entre dois pontos comunicantes, os diversos elementos transmissores podem atuar como um arranjo virtual de antenas, obtendo-se assim vantagens dos sistemas de múltiplas antenas (MIMO), sobretudo o aumento da capacidade de transmissão. Recentemente, a chamada analise tensorial tem se mostrado uma abordagem eficiente então para a estimação de canais em sistemas com diversidade cooperativa. Contudo, nos poucos trabalhos dedicados a essa tarefa, a utilização da decomposição tensorial PARAFAC para a modelagem dos sinais recebidos não possibilitou o desenvolvimento de técnicas de estimação conjunta de canais e símbolos. Com a idéia de se evitar o uso de sequencias de treinamento, que limita a eficiência espectral da transmissão por dedicar uma parte da largura de banda apenas para a tarefa de estimação dos canais, o objetivo desta tese é prover novas estratégias de comunicação, em termos de sistemas de transmissão e receptores semi-cegos, baseados em tensores adaptados a sistemas cooperativos MIMO unidirecionais de dois saltos. Dois sistemas de transmissão são propostos utilizando uma codificação espaço-temporal do tipo Khatri-Rao na fonte e duas estrategias de processamento Amplify-and-Forward (AF) no relay. Para estes sistemas, nomeados PT2-AF e NP-AF, os sinais recebidos no chamado nó de destino satisfazem os modelos tensoriais do tipo PARATUCK2 e Nested PARAFAC. Explorando as propriedades de unicidade destes modelos tensoriais estabelecidas nesta tese, vários receptores semi-cegos são derivados. Alguns destes receptores são do tipo ALS, enquanto outros são de soluções baseadas na factorização de produtos de Khatri-Rao. Resultados de simulação são apresentados para ilustrar os desempenhos dos receptores propostos em comparação a alguns estimadores supervisionados
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KULSOOM, FARZANA. "DSP algorithms for MIMO based Systems." Doctoral thesis, Università degli studi di Pavia, 2020. http://hdl.handle.net/11571/1325948.
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Multiple Input Multiple Output (MIMO) systems are an emerging wireless communication technology that gained popularity due to its capability to enhance spectral efficiency and reliability. Although MIMO enhances system capacity and performance, it could be challenging due to the high number of antennas at both the transmitter and receiver. It has been therefore one of the popular research areas during the last decade, meeting ever-increasing demands of data rates. Nevertheless, serving multiple terminals simultaneously is challenging due to interference among them. The main goal of this research is to mitigate interference among users, gain better energy and spectral efficiency by employing different digital signal processing (DSP) based algorithms in the multi-user MIMO communication paradigm.
Moreover, we have investigated novel algorithms in order to mitigate inter-terminal interference by employing directional beams. In order to do so, it is imperative to perform channel estimation, which can be obtained by using time or frequency duplexing, although, with an increased number of antennas in large scale MIMO (massive MIMO), the problem becomes very complicated in both types of duplexing schemes. The research problem of reducing training and feedback overhead can be addressed properly if high dimensional signals are reduced to low dimensional, by taking the compressive sensing (CS) paradigm into account. A framework is proposed to reduce training and feedback overhead by considering the MIMO channel as sparse in mobile communication. Another important issue in modern MIMO communication systems is related to phase recovery. For this purpose, a reduced complexity Kalman filtering based solution is proposed to address phase recovery problem in cross-polar interference cancellation (XPIC) system, which can be viewed as MIMO 2 x 2 channels. Another interesting application of MIMO based systems is presented for multiple implants in the intra-body network, which utilized beamforming techniques to communicate in an energy-efficient manner.
The comparison with state of the art methods is also exhibited. The research work conducted in this thesis addresses theoretical, methodological and empirical contributions to MIMO based system research problem and attempted to achieve better performance by employing different DSP based algorithms.Multiple Input Multiple Output (MIMO) systems are an emerging wireless communication technology that gained popularity due to its capability to enhance spectral efficiency and reliability. Although MIMO enhances system capacity and performance, it could be challenging due to the high number of antennas at both the transmitter and receiver. It has been therefore one of the popular research areas during the last decade, meeting ever-increasing demands of data rates. Nevertheless, serving multiple terminals simultaneously is challenging due to interference among them. The main goal of this research is to mitigate interference among users, gain better energy and spectral efficiency by employing different digital signal processing (DSP) based algorithms in the multi-user MIMO communication paradigm. Moreover, we have investigated novel algorithms in order to mitigate inter-terminal interference by employing directional beams. In order to do so, it is imperative to perform channel estimation, which can be obtained by using time or frequency duplexing, although, with an increased number of antennas in large scale MIMO (massive MIMO), the problem becomes very complicated in both types of duplexing schemes. The research problem of reducing training and feedback overhead can be addressed properly if high dimensional signals are reduced to low dimensional, by taking the compressive sensing (CS) paradigm into account. A framework is proposed to reduce training and feedback overhead by considering the MIMO channel as sparse in mobile communication. Another important issue in modern MIMO communication systems is related to phase recovery. For this purpose, a reduced complexity Kalman filtering based solution is proposed to address the phase recovery problem in cross-polar interference cancellation (XPIC) system, which can be viewed as MIMO 2 x 2 channels. Another interesting application of MIMO based systems is presented for multiple implants in the intra-body network which utilized beamforming techniques to communicate in an energy-efficient manner. The comparison with state of the art methods is also exhibited. The research work conducted in this thesis addresses theoretical, methodological and empirical contributions to MIMO based system research problem and attempted to achieve better performance by employing different DSP based algorithms.
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Li, Yabo. "Space-time encoding and decoding for MIMO systems and cooperative communication systems." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 0.82 Mb., 155 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3205421.
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Wu, Xiaoting. "Array signal processing for MIMO radar /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?ECED%202009%20WU.
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Lessa, Carmen Lúcia Avelar. "Esquema para transmissão utilizando MIMO com cooperação de usuários." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261418.
Full textAbstract:
Orientador: Gustavo FraidenraichDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-19T21:07:30Z (GMT). No. of bitstreams: 1 Lessa_CarmenLuciaAvelar_M.pdf: 2504273 bytes, checksum: 47a502a9d17e8b31113225b0cb9926c3 (MD5) Previous issue date: 2011
Resumo: Neste trabalho é proposta uma estratégia para transmissão digital utilizando cooperação de usuários em conjunto com a tecnologia de múltiplas antenas (MIMO - do inglês. Multiple Input Multiple Output). Em um primeiro modelo de sistema foi utilizada a tecnologia CDMA (do inglês, Code Division Multiple Access) para distinção entre as mensagens dos usuários. Já em um segundo modelo sugerido foram utilizadas as técnicas do Descorrelacionador e a Decomposição em Valores Singulares (SVD - do inglês, Singular Value Decomposition) para permitir a cooperação entre os usuários sem a necessidade de multiplexação por código. Neste trabalho é apresentado como a cooperação entre os usuários pode ser feita utilizando várias antenas. Como exemplo foi considerado um regime de cooperação para o canal MIMO com dois usuários com uma única antena e o receptor com duas antenas. O cálculo da probabilidade de erro para este caso foi desenvolvido
Abstract: This work proposes user cooperation strategy using multiple antennas technology (MIMO). In a first model it was used a Code Division Multiple Access (CDMA) system and in a second model was applied the techniqucs of the Decorrclator and Singular Value Decomposition (SVD) to allow cooperation of users. It is show how cooperation using different numbers of antennas can be accomplished. It was considered a cooperation scheme for MIMO MAC channel with two users having single antenna and the reciver with two antennas. The results show that user cooperation with multiple antennas reduces the bit error probability
Mestrado
Telecomunicações e Telemática
Mestre em Engenharia Elétrica
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Luo, Tuo. "Performance enhancements in practical MIMO communications systems /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20LUO.
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Shao, Lei. "Code design for MIMO-OFDM(A) systems /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/5859.
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Piazza, Daniele Dandekar Kapil. "Reconfigurable antennas for adaptive MIMO communication systems /." Philadelphia, Pa. : Drexel University, 2009. http://hdl.handle.net/1860/3037.
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Turpin, Michael J. "An investigation of a multiple-input-multiple-output communication system with the Alamouti Space-time code." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FTurpin.pdf.
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Fozooni, Milad. "Low-cost architectures for future MIMO systems." Thesis, Queen's University Belfast, 2017. https://pure.qub.ac.uk/portal/en/theses/lowcost-architectures-for-future-mimo-systems(ca73fe96-9ebb-4eb9-94cb-acbb11137bde).html.
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Massive multiple-input multiple-output is a promising technique for the next generation of wireless communication systems which addresses most of the critical challenges associated with concurrent relaying systems, such as digital signal processing complexity, long processing delay, and low latency wireless communications. However, the deployment of conventional fully digital beamforming methods, dedicates one radio frequency (RF) chain to each antenna, is not viable enough due to the high fabrication/implementation cost and power consumption. In this thesis, we envision to address this critical issue by reducing the number of RF chains in a viable analog/digital configuration paradigm which is usually referred to hybrid structure. From another viewpoint, the development of fifth generation enabling technologies brings new challenges to the design of power amplifiers (PAs). In particular, there is a strong demand for low-cost, nonlinear PAs which, however, introduce nonlinear distortions. On the other hand, contemporary expensive PAs show great power efficiency in their nonlinear region. Inspired by this trade-off between nonlinearity distortions and efficiency, finding an optimal operating point is highly desirable, and this is the second key contribution of this thesis.
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Sobhanmanesh, Fariborz School of Electrical Engineering And Telecommunications UNSW. "Hardware implementation of V-BLAST MIMO." Awarded by:University of New South Wales. School of Electrical Engineering And Telecommunications, 2006. http://handle.unsw.edu.au/1959.4/24198.
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The exploitation of the theoretically enormous capacity achieved by the multiple transmit and receive antennas systems (MIMO) in a rich scattering communication channel has been the subject of vast body of research on the field of MIMO. In particular, the Vertically-layered Bell Laboratories Layered Space-Time (V-BLAST) is a well known MIMO architecture which has demonstrated the enormous capacity of 20-40 bit/s/Hz in an indoor propagation environment with realistic SNR and error rates. However, due to the intensive computation involved, it would be difficult to implement this architecture for high data rate communication systems. Some works have been done to improve the receiver complexity and performance by coding techniques, by different detection architectures. In this thesis, we have focused on QR-based decoders for V-BLAST MIMO. For a suitable V-BLAST detection implementation, we need to carefully consider the problem from algorithmic, arithmetic and architectural aspects. At the algorithmic level, the numerical stability and robustness should be considered. At the arithmetic level, signal quantization is important, and, at the architectural level, parallelism and pipelining require attention. We have performed the above mentioned optimization on the 1-pass QR factorization with back substitution SIC (Symbol Interference Cancellation) decoder in chapter 3. At first optimizations are made on the proposed algorithm and architecture using MATLAB simulations. Then a new architecture for the QR-factorizer as the core processor of the V-BLAST decoder is developed in chapter 4. This architecture uses only two low complexity CORDIC (Coordinate rotation digital computer) processors. The parameterized feature of the controller and address generator blocks of this architecture has provided a scalable architecture for the implementation of QR factorization for square matrix of any dimension. The reduced hardware complexity of the processors and its simple parameterized controller are two outstanding features of the architecture, resulting in a more suitable alternative architecture for QR factorization than traditional triangular systolic arrays. In the next phase of the research, new hardware architectures of the back substitution SIC decoder was developed for a 4 X 4 MIMO system with 16-QAM constellation scheme in chapter 5. The division operation for back substitution needs a complex hardware, and results in the numerical instability. In the proposed hardware the elimination of division and modification of multiplier has reduced the hardware complexity and led to numerical stability. In addition the pre decoding block was designed and optimized in terms of number of the pipeline registers and CORDIC rotator processors. The developed hardware is capable of processing 20 vectors data burst and results in a throughput of 149 Mb/s. The FPGA (Field Programmable Gate Array) and ASIC (Application specific Integrated Circuit) implementations of the proposed optimized architecture are presented in Chapter 5. We found that the equivalent gates and the core area in our design is less than 30% of other designs and the maximum clock frequency and the throughput is higher (175 %) than other works. Finally the improvements of the BER performance using the branching method and parallel architectures are presented in chapter 6. In this supplementary part to back substitution OSIC decoder, the final symbol vector is selected from 2 or 8 potential candidates based on the minimum Euclidean norm, which improves the BER between 3 to 7 db and gives a very close match to the original V-BLAST performance.
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Maharaj, Bodhaswar Tikanath Jugpershad. "MIMO channel modelling for indoor wireless communications /." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-07292008-130655/.
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Chan, Wing Chau. "Performance limits of MIMO wireless communications /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20CHANW.
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Srinivasan, Ramya. "Throughput optimization in MIMO networks." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42735.
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Enabling multi-hop wireless mesh networks with multi-input multi-output (MIMO) functionality boosts network throughput by transmitting over multiple orthogonal
spatial channels (spatial multiplexing) and by performing interference cancellation,
to allow links within interference range to be concurrently active. Furthermore,
if the channel is in a deep fade, then multiple antenna elements at the
transmitter and/or receiver can be used to transmit a single stream, thereby improving
signal quality (diversity gain).
However, there is a fundamental trade-off between boosting individual link performance
and reducing interference, which must be modeled in the process of optimizing
network throughput. This is called the diversity-multiplexing-interference suppression
trade-off. Optimizing network throughput therefore, requires optimizing the trade-off
between the amounts of diversity employed on each link, the number of streams multiplexed
on each link and the number of interfering links allowed to be simultaneously
active in the network.
We present a set of efficient heuristics for one-shot link scheduling and stream
allocation that approximately solve the problem of optimizing network throughput
in a single time slot. We identify the fundamental problem of verifying the feasibility
of a given stream allocation. The problems of general link scheduling and stream
allocation are very closely related to the problem of verifying feasibility.
We present a set of efficient heuristic feasibility tests which can be easily incorporated
into practical scheduling schemes. We show for some special MIMO network
scenarios that feasibility is of polynomial complexity. However, we conjecture that in
general, this problem, which is a variation of Boolean Satisablility, is NP-Complete.
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García, Ordoñez Luis. "Perfomance limits of spatial multiplexing mimo systems." Doctoral thesis, Universitat Politècnica de Catalunya, 2009. http://hdl.handle.net/10803/22735.
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Los canales multiple-input multiple-output (MIMO) proporcionan una forma abstracta y general de modelar un gran número de sistemas de comunicaciones. Los canales MIMO inalámbricos, en concreto, han despertado un gran interés en la comunidad investigadora durante la última década, puesto que aportan mejoras significativas en términos de eficiencia espectral y fiabilidad frente a los sistemas single-input single-output (SISO) tradicionales.
Esta tesis se concentra en sistemas MIMO de multiplexado espacial con conocimiento perfecto de canal (CSI) en ambos lados del enlace de comunicaciones. Las técnicas de multiplexado espacial engloban a todos aquellos sistemas de transmisión MIMO que dividen el flujo de datos de entrada en múltiples subflujos independientes para transmitirlos después de forma simultánea. Cuando se posee CSI perfecto en transmisión, la adaptación de dichos subflujos al estado del canal resulta en notables mejoras de las prestaciones del sistema de comunicaciones. Dentro de esta filosofía destacan los transceptores MIMO lineales por su gran relevancia práctica.
El diseño de transceptores MIMO lineales se ha abordado extensivamente en la literatura durante las tres últimas décadas bajo una gran variedad de criterios de optimización. Las prestaciones de estos esquemas, en cambio, no se han investigado analíticamente, de forma que medidas de rendimiento tales como la probabilidad de error de bit promedio (BER) y la probabilidad de outage se han evaluado mediante simulaciones numéricas, las cuales no proporcionan una visión intuitiva del comportamiento del sistema. Los análisis teóricos, en cambio, ayudan a identificar los grados de libertad en el diseño y a comprender mejor su impacto en las prestaciones obtenidas. La presente tesis parte de esta necesidad y proporciona una caracterización analítica de la BER promedio y la probabilidad de outage bajo diferentes modelos de canal. El régimen de alta relación señal a ruido (SNR) ha recibido una atención especial y las prestaciones del sistema se han investigado desde dos puntos de vista diferentes. En primer lugar, adoptando una perspectiva más práctica, hemos caracterizado las curvas de BER promedio y probabilidad de outage en términos de dos parámetros clave: la ganancia en diversidad y la ganancia de agrupación. A continuación nos hemos centrado en el marco del diversity and multiplexing tradeoff.
De esta forma, hemos podido analizar conjuntamente la capacidad del sistema para tratar con la naturaleza aleatoria del canal pero, también, la capacidad de acomodar una tasa de transmisión superior cuando la SNR crece.
En esta tesis se han evaluado las prestaciones de los transceptores MIMO lineales analíticamente y de forma simultánea para los modelos de canal MIMO inalámbricos más comunes, tales como el canal Rayleigh incorrelado o semicorrelado, o el canal Ricean incorrelado. Para alcanzar este objetivo, hemos obtenido una formulación general que unifica la caracterización probabilística de los autovalores de matrices aleatorias Hermíticas con una determinada estructura, que incluye los modelos de canal anteriores como casos particulares. En efecto, la formulación propuesta y los resultados obtenidos proporcionan un marco sólido para el análisis de las prestaciones de los sistemas MIMO, pero también pueden ser muy útiles en otras áreas del procesado estadístico de la señal y las comunicaciones.
Finalmente, como conclusión al análisis realizado en esta tesis, se han evidenciado las limitaciones inherentes a los sistemas prácticos de multiplexado espacial con conocimiento de canal estudiados. En consecuencia, se han propuesto esquemas alternativos que tratan dichas limitaciones y superan las prestaciones de los diseños prácticos disponibles en la literatura.Multiple-input multiple-output (MIMO) channels are an abstract and general way to model many different communication systems of diverse physical nature. In particular, wireless MIMO channels have been attracting a great interest in the last decade, since they provide significant improvements in terms of spectral efficiency and reliability with respect to single-input single-output (SISO) channels. In this thesis we concentrate on spatial multiplexing MIMO systems with perfect channel state information (CSI) at both sides of the link. Spatial multiplexing is a simple MIMO transmit technique that does not require CSI at the transmitter and allows a high spectral efficiency by dividing the incoming data into multiple independent substreams and transmitting each substream on a different antenna. When perfect CSI is available at the transmitter, channel-dependent linear precoding of the data substreams can further improve performance by adapting the transmitted signal to the instantaneous channel eigen-structure. An example of practical relevance of this concept is given by linear MIMO transceivers, composed of a linear precoder at the transmitter and a linear equalizer at the receiver. The design of linear MIMO transceivers has been extensively studied in the literature for the past three decades under a variety of optimization criteria. However, the performance of these schemes has not been analytically investigated and key performance measures such as the average bit error rate (BER) or the outage probability have been obtained through time-comsuming Monte Carlo simulations. In contrast to numerical simulations, which do not provide any insight on the system behavior, analytical performance expressions help the system designer to identify the degrees of freedom and better understand their influence on the system performance. This thesis attempts to fill this gap by providing analytical average and outage performance characterizations in some common MIMO channel models. More exactly, we derive exact expressions or bounds (depending on the case) for the average BER and the outage probability of linear MIMO transceivers designed under a variety of design criteria. Special attention is given to the high signal-to-noise ratio (SNR) regime, where the system performance is investigated under two different perspectives. First, from a more practical point-of-view, we characterize the average BER and outage probability versus SNR curves in terms of two key parameters: the diversity gain and the array gain. Then, we focus on the diversity and multiplexing tradeoff framework in order to take into consideration the capability of the system to deal with the fading nature of the channel, but also its ability to accommodate higher data rates as the SNR increases. The performance of linear MIMO transceivers is simultaneously analyzed for the most common wireless MIMO channel models such as the uncorrelated and semicorrelated Rayleigh, and the uncorrelated Rician MIMO fading channels. For this purpose, we have obtained a general formulation that unifies the probabilistic characterisation of the eigenvalues of Hermitian random matrices with a specific structure, which includes the previous channel distributions as particular cases, i.e., the uncorrelated and semicorrelated central Wishart, the uncorrelated noncentral Wishart, and the semicorrelated central Pseudo-Wishart distributions. Indeed, the proposed formulation and derived results provide a solid framework for the analytical performance evaluation of MIMO systems, but it could also find numerous applications in other fields of statistical signal processing and communications. Finally, and as a consequence of our performance analysis, limitations inherent to all practical linear MIMO transceiver designs have been enlightened. Accordingly, new schemes have been proposed which achieve considerable performance enhancements with respect to classical linear MIMO transceivers.
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Zhang, Yan. "Link adaptation schemes for MIMO wireless systems." Diss., Connected to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3190136.
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Thesis (Ph. D.)--University of California, San Diego, 2005.Title from first page of PDF file (viewed March 15, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 86-90).
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Benjebbour, Anass. "Efficient Signal Processing Techniques for MIMO Systems." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147580.
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