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S/MIMO MC-CDMA Heuristic Multiuser Detectors Based on Single-Objective Optimization

ABRAO, Taufik; OLIVEIRA, Leonardo D. de; CIRIACO, Fernando; Angelico, Bruno Augusto; Jeszensky, Paul Jean Etienne; PALACIO, Fernando Jose Casadevall
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
Português
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This paper analyzes the complexity-performance trade-off of several heuristic near-optimum multiuser detection (MuD) approaches applied to the uplink of synchronous single/multiple-input multiple-output multicarrier code division multiple access (S/MIMO MC-CDMA) systems. Genetic algorithm (GA), short term tabu search (STTS) and reactive tabu search (RTS), simulated annealing (SA), particle swarm optimization (PSO), and 1-opt local search (1-LS) heuristic multiuser detection algorithms (Heur-MuDs) are analyzed in details, using a single-objective antenna-diversity-aided optimization approach. Monte- Carlo simulations show that, after convergence, the performances reached by all near-optimum Heur-MuDs are similar. However, the computational complexities may differ substantially, depending on the system operation conditions. Their complexities are carefully analyzed in order to obtain a general complexity-performance framework comparison and to show that unitary Hamming distance search MuD (uH-ds) approaches (1-LS, SA, RTS and STTS) reach the best convergence rates, and among them, the 1-LS-MuD provides the best trade-off between implementation complexity and bit error rate (BER) performance.; Brazilian CAPES Agency[BEX0556/07-6]

Algoritmo de escolha de sequencias de espalhamento em sistemas CDMA considerando a interferencia de celulas adjacentes; Spreading sequences selection algorithm for CDMA systems considering the interference from adjacent cells

Paulo Marcelo Perez Rodrigues de Britto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/12/2006 Português
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O desempenho de sistemas de comunicações sem fio que utilizam técnicas de espalhamento espectral e múltiplo acesso por divisão de código (CDMA) é limitado pela interferência. Nesta dissertação, analisamos o desempenho de um algoritmo de seleção de seqüências de espalhamento de comprimento fixo, que busca a minimização dos efeitos de interferência em sistemas CDMA operando em canais com desvanecimento seletivo em freqüência e possuindo células adjacentes interferentes. Analisamos o desempenho deste sistema no qual o espalhamento espectral é feito usando duas seqüências: seqüências do usuário e seqüências identificadoras de células. Dentre as seqüências analisadas, podemos citar as Walsh, a Gold, as de comprimento máximo e também um tipo de seqüência de espalhamento baseado nas seqüências de comprimento máximo; The performance of wireless communication systems using spread spectrum techniques and code division multiple access (CDMA) is interference-limited. In this dissertation, we evaluate the performance of a selection algorithm for fixed-length spreading sequences, aimed on minimizing the interference effects in CDMA systems operating in frequency selective fading channels and having adjacent interfering cells. We check the performance of this system where the spread spectrum operation is performed using two sequences: user sequences and cell identification sequences. Among the sequences considered...

Controle de congestionamento do protocolo TCP em sistemas de comunicação sem fio CDMA usando estrategia de detecção multiusuario, arranjo de antenas e correção de erro FEC; A new TCP congestioned window algorithm for wireless CDMA system using multiuser decorrelating detection, antenna array and FEC

Gonzalo Fernando Olmedo Cifuentes
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/11/2008 Português
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Neste trabalho foi proposto um novo algoritmo para o controle da janela de congestionamento do protocolo TCP, que melhora o desempenho da vazão de dados em redes sem fio. A estimação da banda disponível responsável pela melhoria do sistema, se dá pois os segmentos TCP com erro produzidos pelo canal sem fio são reconhecidos por uma confirmação negativa NACK, ou quando o buffer do sistema enche. Para o mecanismo proposto, uma expressão analítica da vazão de dados em função da probabilidade de erro de segmentos TCP no canal sem fio é obtida. No sistema sem fio é analisado o enlace reverso de sistemas CDMA de sequencia direta, tanto síncrono, como assíncrono, considerando um canal seletivo em frequencia com desvanecimento do tipo Rayleigh e modulação BPSK. São comparados diferentes tipos de receptores, que usam detecção multiusuário descorrelacionadora, arranjo de antenas e codificação de canal do tipo convolucional ou turbo. Foram obtidas expressões simples e precisas, antes não encontradas na literatura da eficincia assintotica média e da probabilidade de erro de bit que foram comparadas com resultados de simulação. Foram comparadas tres estratégias propostas de decodificação iterativa turbo. Expressões de complexidade computacional do receptor também foram elaboradas.; In this work...

Emprego de antenas adaptativas para a estimação de dados em ambiente CDMA; Applying adaptive antennas for data estimation in CDMA medium

Puttini, Saulo Benigno
Fonte: Universidade de Brasília Publicador: Universidade de Brasília
Tipo: Dissertação
Português
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2006.; Este trabalho fundamenta-se em propor e avaliar o desempenho de um modelo receptor adaptativo, com utilização de arranjo de sensores, a ser empregado em meios de multiplicidade de acesso via divisão por códigos (CDMA) para fins de estimação de dados. Inicialmente é apresentado um estudo sobre arranjos de antenas, desenvolvendo-se o equacionamento de um arranjo linear e uniforme (ULA). Enfatiza-se o emprego deste para fins de separação espacial de usuários, sendo relatadas e ilustradas algumas formas de conformação de feixe. A seguir, o trabalho aborda o emprego de algoritmos adaptativos, especialmente o método de Wiener e filtro de Mínima Média Quadrática (LMS), para arranjos de sensores, originando os tão conhecidos arranjos adaptativos. Prosseguindo, aborda-se o problema de estimação da direção de chegada (DOA), sendo ilustrados alguns métodos amplamente difundidos na literatura especializada. Algumas simulações de espectro espacial de potência são realizadas, visando a avaliar, principalmente, a capacidade de resolução e a imunidade em relação ao ruído. É apresentado, então...

Comparison of single and multi-user pre-filtering techniques using different chip mapping for DL MC-CDMA systems

Silva, Adão; Gameiro, Atílio
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
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In this paper we compare the performance of the joint space-frequency single and multi-user pre-filtering techniques that have been proposed recently for DL MC-CDMA systems. We consider the use of antenna arrays at the base station and a single antenna at the mobile terminal (MT). We investigate how the chip mapping strategy impacts on the performance of the pre-filtering approaches. Thus, practical combinations of prefiltering and chip mapping are discussed. The performance is evaluated for different chip mapping strategies, considering typical indoor and pedestrian scenarios and both uncoded data and channel turbo coding based on UMTS specifications. © 2007 IEEE.; European WISQUAS Celtic project CP2-035; FCT FFTXXI project POSI/CPS/4670/2002

Iterative frequency-domain detection for IA-precoded MC-CDMA systems

Silva, Adão; Teodoro, Sara; Dinis, Rui; Gameiro, Atílio
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica
Português
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Interference alignment (IA) is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative frequency-domain detection receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization) can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In this paper we combine iterative IA precoding at the transmitter with IB-DFE based processing at the receiver for MC-CDMA systems. The receiver is designed in two steps: first a linear filter is used to mitigate the inter-user aligned interference, and then an iterative frequency-domain receiver is designed to efficiently separate the spatial streams in the presence of residual inter-user aligned interference at the output of the filter. The matrices for this non- linear space-frequency equalizer are obtained by minimizing the overall mean square error (MSE) of all data streams at each subcarrier. Our receiver structure is explicitly designed taking into account the residual inter-user interference, allowing both an efficient separation of the spatial streams and a reduction in the number of iterations of the IA procedure. We also propose a simple, yet accurate analytical approach for obtaining the performance of the proposed receiver structure. Our scheme achieves the maximum degrees of freedom provided by the IA precoding...

IB-DFE with interference alignment precoding scheme for MC-CDMA systems; Esquemas de pré-codificação IA com IB-DFE para sistemas MC-CDMA

Moreira, José Eduardo Leal
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
Português
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To achieve high bit rates, needed to meet the quality of service requirements of future multimedia applications, multi-carrier code division multiple access (MC-CDMA) has been considered as a candidate air-interface. Interference alignment (IA) is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative block decision feedback equalization (IB-DFE) based receivers can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In this thesis we proposed an IA precoding at the transmitter with IB-DFE based processing at the receiver for MC-CDMA systems. The IA precoding is applied at chip level instead of the data symbols level, as in the conventional IA based systems. The receiver is designed in two steps: first the equalizers based on zero forcing (ZF) or minimum mean square error (MMSE) are used to remove the aligned users´ interference. Then and after a whitening noise process, an IB-DFE based equalizer is designed to remove both the residual inter-user aligned and inter-carrier interferences. The results have shown that the obtained performance is very close to the one obtained by the optimal matched filter, with few iterations at the receiver side.; Para atingir maiores ritmos de transmissão...

Equalization and precoding techniques for future MC-CDMA systems; Técnicas de equalização e pré-codificação para sistemas MC-CDMA

João, Alícia Mafalda de Figueiredo Paiva
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
Português
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O número de dispositivos com ligações e aplicações sem fios está a aumentar exponencialmente, causando problemas de interferência e diminuindo a capacidade do sistema. Isto desencadeou uma procura por uma eficiência espectral superior e, consequentemente, tornou-se necessário desenvolver novas arquitecturas celulares que suportem estas novas exigências. Coordenação ou cooperação multicelular é uma arquitectura promissora para sistemas celulares sem fios. Esta ajuda a mitigar a interferência entre células, melhorando a equidade e a capacidade do sistema. É, portanto, uma arquitectura já em estudo ao abrigo da tecnologia LTE-Advanced sob o conceito de coordenação multiponto (CoMP). Nesta dissertação, considerámos um sistema coordenado MC-CDMA com pré-codificação e equalização iterativas. Uma das técnicas mais eficientes de pré-codificação é o alinhamento de interferências (IA). Este é um conceito relativamente novo que permite aumentar a capacidade do sistema em canais de elevada interferência. Sabe-se que, para os sistemas MC-CDMA, os equalizadores lineares convencionais não são os mais eficientes, devido à interferência residual entre portadoras (ICI). No entanto, a equalização iterativa no domínio da frequência (FDE) foi identificada como sendo uma das técnicas mais eficientes para lidar com ICI e explorar a diversidade oferecida pelos sistemas MIMO MC-CDMA. Esta técnica é baseada no conceito Iterative Block Decision Feedback Equalization (IB-DFE). Nesta dissertação...

Análise de desempenho de sistemas CDMA, utilizando multi-portadoras e multi-códigos; Performance analysis of CDMA systems, using multi carriers and multi codes

Araújo, Alessandra Sousa
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
Português
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O avanço tecnológico em telecomunicações mostra que inúmeros e dife- rentes sistemas vêm surgindo a cada dia. Estes sistemas se adequam às necessidades do mercado, pela sua evolução. A grande variedade de serviços oferecidos a cada dia pelos sistemas de comunicação movel é o reflexo da necessidade de acesso e de sua utilização. Este trabalho analisa o desempenho de tres sistemas: Multi-portadora CDMA, Multi-códigos CDMA e Multi-portadora e Multi-códigos CDMA com multi-taxas de serviços utilizando-se a modulação BPSK. O modelo desses sis- temas consiste no transmissor e receptor, com análise da relação sinal/ruí³do mais interferência (SNIR) e a probabilidade média de erro do bit (Pe médio). O desempenho desses sistemas e apresentado pela comparação ao do número de sub-rajadas, do número de portadoras, do número de usuários, dos diferen- tes parâmetros de fading, da ordem da diversidade e das propriedades multi trajetos de propagação. O sistema Multi-portadoras e Multi-codigos CDMA em termos de SNIR e da probabilidade media de erro do bit quando comparado os sistemas Multi- portadoras CDMA e Multi-códigos CDMA apresentou uma melhora de per- formance. ______________________________________________________________________________ ABSTRACT; The technology advance in telecommunication systems shows that un- countable and di®erent systems have been raised every day. These systems suit to the market needs in terms of evolution. The wide variety of services o®ered every day by the mobile communication systems is response of the need for access and their utilization. This work analyzes the performance of three systems: Multi-Carrier CDMA...

Multiuser Channel Estimation and Tracking for Long Code CDMA Systems

Bhashyam, Srikrishna; Aazhang, Behnaam; Bhashyam, Srikrishna; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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Journal Paper; Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next generation wireless systems use long spreading codes whose period is much larger than the symbol duration. In this paper, we derive the maximum likelihood channel estimate for long code CDMA systems over multipath channels using training sequences and approximate it using an iterative alogrithm to reduce the computational complexity in each symbol duration. The iterative channel estimate is also shown to be asymptotically unbiased. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. The effect of error in decision feedback from the multistage detector (used in the absence of training sequences) is also shown to be neglible for reasonable feedback error rates using simulations. The proposed iterative channel estimation technique is also extended to track slowly varying multipath fading channels using decision feedback. Thus...

Multiuser Channel Estimation for Long Code CDMA Systems

Bhashyam, Srikrishna; Aazhang, Behnaam; Bhashyam, Srikrishna; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
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Conference Paper; Channel estimation techniques for code-division multiple access (CDMA) systems need to combat multiple access interference (MAI) effectively. Most existing estimation techniques are designed for CDMA systems with short repetitive spreading codes. However, current and next generation wireless systems use long spreading codes whose period is much larger than the symbol duration. In this paper, we derive the maximum likelihood channel estimate for long code CDMA systems over multipath channels using training sequences and approximate it using an iterative algorithm to reduce the computational complexity in each processing window. The asymptotic convergence of the mean of the iterative estimate to the actual channel is also shown. The effectiveness of the iterative channel estimator is demonstrated in terms of squared error in estimation as well as the bit error rate performance of a multistage detector based on the channel estimates. Finally, the proposed iterative channel estimation technique is extended to track slowly varying multipath fading channels using decision feedback. Thus, an MAI resistant multiuser channel estimate with reasonable computational complexity is derived for long code CDMA systems over multipath fading channels.

Reducing Dynamic Power Consumption in Next Generation DS-CDMA Mobile Communication Receivers

Chandrasekhar, Vikram; Chandrasekhar, Vikram
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
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Masters Thesis; Reduction of the power consumption in portable wireless receivers is an important consideration for next-generation cellular systems specified by standards such as the UMTS, IMT2000. This thesis explores the design-space for reducing the dynamic power dissipation in a RAKE receiver for the Direct Sequence Code Division Multiple Access (DS-CDMA) downlink. Starting with a reference implementation of the DS-CDMA RAKE receiver, we demonstrate design methodologies for achieving significant power reduction, while highlighting the corresponding performance trade-offs. At the algorithm level, we investigate the impact of reduced precision and arithmetic complexity on the performance of the DS-CDMA RAKE receiver. We then present architectures for implementing the reference and reduced complexity DS-CDMA RAKE receivers, and analyze these architectures with respect to their dynamic power dissipation. Finally, we analyze clock-gating techniques for reducing the activity rate in both the architectures to achieve further power reduction.

Advanced MIMO-CDMA Receiver for Interference Suppression: Algorithms, System-on-Chip Architectures and Design Methodology

Guo, Yuanbin; Guo, Yuanbin
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
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PhD Thesis; MIMO (Multiple Input Multiple Output) technology is proposed in CDMA systems for much higher rate packet services. The receiver architecture is essential for the mobile devices to support high speed multimedia service. The design challenges come from both detection algorithms and hardware architectures. Much more complicated algorithms are required to suppress various interferences. However, the current hardware design archi-tecture and methodology is falling far behind the requirements of small size, low cost and power consumption. System-On-Chip (SoC) architectures are a major revolution taking place in the design of integrated circuits due to many advantages in the power consumption and compact size. The VLSI-oriented complexity reduction of the numerical algorithms plays an essential role to design efficient real-time architectures. Thus, the thesis contributes to three major as-pects: to propose high performance algorithms with realistic complexity in different chan-nel conditions; to propose real-time SoC architectures with area/speed/power efficiency; and to propose an efficient design methodology for modelling, partitioning/binding, verifi-cation and synthesis of the wireless systems. Specifically, to cut the design cycle and enable extensive architecture tradeoff study...

VLSI implementation of the multistage detector for next generation wideband CDMA receivers

Xu, Gang; Rajagopal, Sridhar; Cavallaro, Joseph R.; Aazhang, Behnaam; Xu, Gang; Rajagopal, Sridhar; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Kluwer Academic Publishers Publicador: Kluwer Academic Publishers
Tipo: Artigo de Revista Científica
Português
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Journal Paper; The multistage detection algorithm has been proposed as an effective interference cancellation scheme for next generation Wideband Code Division Multiple Access (W-CDMA) base stations. In this paper, we propose a real-time VLSI implementation of this detection algorithm in the uplink system, where we have achieved both high performance in interference cancellation and computational efficiency. When interference cancellation converges, the difference of the detection vectors between two consecutive stages is mostly zero. Under the assumption of BPSK modulation, the differences between the bit estimates from consecutive stages are 0 and ±2. Bypassing the zero terms saves computations. Multiplication by ±2 can be easily implemented in hardware as arithmetic shifts. However, the convergence of the algorithm is dependent on the number of users, the interference and the signal to noise ratio and hence, the detection has a variable execution time. By using just two stages of the differencing detector, we achieve predictable execution time with performance equivalent to at least eight stages of the regular multistage detector. A VLSI implementation of the differencing multistage detector is built to demonstrate the computational savings and the real-time performance potential. The detector...

Fixed Point Error Analysis Of Multiuser Detection and Synchronization Algorithms For CDMA Communication Systems

Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam; Sengupta, Chaitali; Das, Suman; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
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Conference Paper; Conventional correlation based single-user techniques for Direct Sequence Code Division Multiple Access (DS-CDMA) wireless communication systems are susceptible to performance degradation due to interference from other users. Recent research has focused on development of several multiuser techniques where information about multiple users is used to improve performance for each individual user. Due to performance benefits of these methods, they are attractive candidates for implementation in future cellular systems. In this paper we present an error analysis of fixed point implementation of some of these techniques.

Subspace-based Tracking of Multipath Channel Parameters for CDMA Systems

Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam; Sengupta, Chaitali; Cavallaro, Joseph R.; Aazhang, Behnaam
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
Português
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Journal Paper; In this paper, we evaluate several issues in the application of subspace based methods to tracking channel parameters in Code Division Multiple Access (CDMA) communication systems, in the presence of multipath fading. We focus on two aspects of the problem - the performance of Singular Value Decomposition (SVD) based schemes while tracking the time variations in the signal subspace, due to fading, and, the performance trades involved in using several complexity reducing approximate schemes. The performance benefits to be obtained from application of subspace based methods to channel estimation has been well studied. The aim of this work is to lay the groundwork for real time implementation of this computationally complex problem.

A Software Simulation Testbed for CDMA Wireless Communication Systems

Sundaramurthy, Vishwas; Sundaramurthy, Vishwas
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
38.232727%
Masters Thesis; This thesis develops a software wireless communication testbed which simulates a Code Division Multiple Access(CDMA) link. CDMA is a popular technology in cellular systems due to its superior capacity and performance. The designer of CDMA systems has a wide array of signal processing algorithms to choose from and a variety of operating environments to deal with. The testbed is a tool to evaluate these design options and trade-offs in different scenarios. The backbone of this system is a wireless CDMA multiuser link built using Simulink and Matlab. An efficient method of system modeling is used to speed up the simulations. This testbed can be used to study the performance of a CDMA wireless link with variation in system parameters and channel conditions. The use of Real-Time Workshop for DSP code generation is studied. This method is useful for rapid prototyping of algorithms and in DSP-based simulation acceleration of the testbed.

Algorithms and Architectures for Channel Estimation in Wireless CDMA Communication Systems

Sengupta, Chaitali; Sengupta, Chaitali
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text; Text
Português
Relevância na Pesquisa
37.97293%
PhD Thesis; Wireless cellular communication is witnessing a rapid growth in markets, technology, and range of services. An attractive approach for economical, spectrally efficient, and high quality digital cellular and personal communication services is the use of code division multiple access (CDMA) technology. The estimation of channel delays along with channel attenuation and phases of different users constitutes the first stage in the detection process at the receiving base station in a CDMA communication system. This stage, called channel parameter estimation, forms the bottleneck for the detection of users' bitstreams; both in terms of accuracy as well as execution time. In this thesis, we develop new algorithms and architectures to solve the CDMA channel estimation problem. We have first developed a framework that facilitates a computationally efficient solution to the combined problem of channel estimation and detection in a scenario involving multiple users, multiple paths, and multiple sensors at the receiver. The channel estimation approaches presented in this thesis, consist of two categories: (1) maximum likelihood based schemes, and (2) signal and noise subspace based schemes. The maximum likelihood approach is used to solve the complex multidimensional problem of channel estimation in the presence of multipath effects and concurrently using an antenna array at the base station receiver. Once the composite channel impulse response of each user is estimated...

W-CDMA capacity analysis using GIS based planning tools and MATLAB simulation

Navarro Cadavid, Andrés; Cardona Marcet, Narcís
Fonte: 3G Mobile Communication Technologies, 2000 Publicador: 3G Mobile Communication Technologies, 2000
Tipo: article; Artículo Formato: PDF; Electrónico
Português
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The evolution of cellular systems towards third generation (3G) or IMT-2000 seems to have a tendency to use W-CDMA as the standard access method, as ETSI decisions have showed. However, there is a question about the improvements in capacity and the wellness of this access method. One of the aspects that worry developers and researchers planning the third generation is the extended use of the Internet and more and more bandwidth hungry applications. This work shows the performance of a W-CDMA system simulated in a PC using cover maps generated with DC-Cell, a GIS based planning tool developed by the Technical University of Valencia, Spain. The maps are exported to MATLAB and used in the model. The system used consists of several microcells in a downtown area. We analyse the interference from users in the same cell and in adjacent cells and the effect in the system, assuming perfect control for each cell. The traffic generated by the simulator is voice and data. This model allows us to work with coverage that is more accurate and is a good approach to analyse the multiple access interference (MAI) problem in microcellular systems with irregular coverage. Finally, we compare the results obtained, with the performance of a similar system using TDMA.

Ordered Hunt Schemes for Overlaid CDMA Cellular Systems

Castañeda-Camacho,J.; Lara-Rodríguez,D.
Fonte: Facultad de Ingeniería, UNAM Publicador: Facultad de Ingeniería, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2010 Português
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48.232725%
The CDMA overlay concept, has been proposed as one alternative to take advantage of the bandwidth available in narrowband systems. In fact, the basic idea of the CDMA overlay is to allow to wideband CDMA wave forms, to share a common spectrum with narrowband conventional wave forms. In this work, we have focused in the analysis of the performance of the forward link of the CDMA and TDMA systems when they are overlaid. In our model, in order to limit the interference into the CDMA layer caused by the TDMA system, the use of notch filters has been considered. However, one drawback of the filters is that it rejects only one part of the interference generated by the TDMA system. Therefore, we have proposed two new ideas of reduction of the interference which can not be eliminated by filters; ordered hunt and real location of the slots. Finally, we present an analytical evaluation of the forward link capacity of the systems involved in the overlaid process, due to this is the limiting link and as a function of the outage probabilities. Practical considerations such as power requirements, power control, handoff, the offered load for different services and scenarios are also addressed.