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Statistical analysis and reduction of multiple access interference in MC-CDMA systemsLi, Xuan January 2008 (has links)
Multicarrier code division multiple access (MC-CDMA) is a very promising candidate for the multiple access scheme in fourth generation wireless communi- cation systems. During asynchronous transmission, multiple access interference (MAI) is a major challenge for MC-CDMA systems and significantly affects their performance. The main objectives of this thesis are to analyze the MAI in asyn- chronous MC-CDMA, and to develop robust techniques to reduce the MAI effect. Focus is first on the statistical analysis of MAI in asynchronous MC-CDMA. A new statistical model of MAI is developed. In the new model, the derivation of MAI can be applied to different distributions of timing offset, and the MAI power is modelled as a Gamma distributed random variable. By applying the new statistical model of MAI, a new computer simulation model is proposed. This model is based on the modelling of a multiuser system as a single user system followed by an additive noise component representing the MAI, which enables the new simulation model to significantly reduce the computation load during computer simulations. MAI reduction using slow frequency hopping (SFH) technique is the topic of the second part of the thesis. Two subsystems are considered. The first sub- system involves subcarrier frequency hopping as a group, which is referred to as GSFH/MC-CDMA. In the second subsystem, the condition of group hopping is dropped, resulting in a more general system, namely individual subcarrier frequency hopping MC-CDMA (ISFH/MC-CDMA). This research found that with the introduction of SFH, both of GSFH/MC-CDMA and ISFH/MC-CDMA sys- tems generate less MAI power than the basic MC-CDMA system during asyn- chronous transmission. Because of this, both SFH systems are shown to outper- form MC-CDMA in terms of BER. This improvement, however, is at the expense of spectral widening. In the third part of this thesis, base station polarization diversity, as another MAI reduction technique, is introduced to asynchronous MC-CDMA. The com- bined system is referred to as Pol/MC-CDMA. In this part a new optimum com- bining technique namely maximal signal-to-MAI ratio combining (MSMAIRC) is proposed to combine the signals in two base station antennas. With the applica- tion of MSMAIRC and in the absents of additive white Gaussian noise (AWGN), the resulting signal-to-MAI ratio (SMAIR) is not only maximized but also in- dependent of cross polarization discrimination (XPD) and antenna angle. In the case when AWGN is present, the performance of MSMAIRC is still affected by the XPD and antenna angle, but to a much lesser degree than the traditional maximal ratio combining (MRC). Furthermore, this research found that the BER performance for Pol/MC-CDMA can be further improved by changing the angle between the two receiving antennas. Hence the optimum antenna angles for both MSMAIRC and MRC are derived and their effects on the BER performance are compared. With the derived optimum antenna angle, the Pol/MC-CDMA system is able to obtain the lowest BER for a given XPD.
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Outside cell Interference Computations for Cellular Code Division Multiple AccessThakur, Anuja 10 December 2003 (has links)
No description available.
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Performance Analysis Of Multicarrier DS-CDMA SystemsShankar Kumar, K R 04 1900 (has links) (PDF)
No description available.
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Development and Analysis of Adaptive Interference Rejection Techniques for Direct Sequence Code Division Multiple Access SystemsMangalvedhe, Nitin R. 30 July 1999 (has links)
The inadequacy of conventional CDMA receivers in a multiple access interference-limited mobile radio environment has spurred research on advanced receiver technologies. This research investigates the use of adaptive receivers for single user demodulation to overcome some of the deficiencies of a conventional receiver and, hence, enhance the system capacity. Several new adaptive techniques are proposed. The new techniques and some existing schemes are analyzed. The limitation of existing blind algorithms in multipath channels is analyzed and a new blind algorithm is proposed that overcomes this limitation. The optimal receiver structure for multi-rate spread spectrum systems is derived and the performance of this receiver in various propagation channels is investigated. The application of coherent and differentially coherent implementations of the adaptive receiver in the presence of carrier frequency offsets is analyzed. The performance of several new adaptive receiver structures for frequency offset compensation is also studied in this research. Analysis of the minimum mean-squared error receiver is carried out to provide a better understanding of the dependence of its performance on channel parameters and to explain the near-far resilience of the receiver. Complex differentially coherent versions of the sign algorithm and the signed regressor algorithm, algorithms that have a much lower computational complexity than the least-means square algorithm, are proposed and applied for CDMA interference rejection. / Ph. D.
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Simulation of Third Generation CDMA SystemsAlam, Fakhrul 31 December 1999 (has links)
The goal for the next generation of mobile communications system is to seamlessly integrate a wide variety of communication services such as high speed data, video and multimedia traffic as well as voice signals. The technology needed to tackle the challenges to make these services available is popularly known as the Third Generation (3G) Cellular Systems. One of the most promising approaches to 3G is to combine a Wideband Code Division Multiple Access (WCDMA) air interface with the fixed network of Global System for Mobile communications (GSM). In this thesis a signal simulator was implemented according to the physical layer specification of the IMT-2000 WCDMA system. The data is transmitted in a frame by frame basis through a time varying channel. The transmitted signal is corrupted by multiple access interference which is generated in a structured way rather than treating it as Additive White Gaussian Noise (AWGN). The signal is further corrupted by AWGN at the front end of the receiver. Simple rake diversity combining is employed at the receiver. We investigate the bit error rate at both uplink and downlink for different channel conditions. Performance improvement due to error correction coding scheme is shown. The simulator developed can be an invaluable tool for investigating the design and implementation of WCDMA systems. / Master of Science
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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 cellsBritto, Paulo Marcelo Perez Rodrigues de 12 November 2006 (has links)
Orientador: Celso de Almeida, Rodrigo Pereira Ramos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T10:36:25Z (GMT). No. of bitstreams: 1
Britto_PauloMarceloPerezRodriguesde_M.pdf: 4780408 bytes, checksum: c3b152e041128b5d94429d8b87c0068c (MD5)
Previous issue date: 2006 / Resumo: 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 / Abstract: 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, we use Walsh, Gold, maximum length and a type of spreading sequence based on the maximum length class / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica
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Avaliação do algoritmo de busca de sequencias de espalhamento em canais com desvanecimento seletivo em frequencia com codigos corretores de erros / Evaluation of the spread sequences selection algorithm over frequency selective fading channels with error correcting codesMataveli, Luis Otavio, 1983- 08 April 2008 (has links)
Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T06:34:19Z (GMT). No. of bitstreams: 1
Mataveli_LuisOtavio_M.pdf: 877476 bytes, checksum: afc5fb9153e7311af03669d45d798a73 (MD5)
Previous issue date: 2008 / Resumo: O desempenho dos sistemas de comunicação sem fio que utilizam a técnica de múltiplo acesso CDMA é limitado pela interferência. A proposição de um algoritmo de escolha de seqüências de espalhamento foi feita para buscar uma diminuição na interferência média do sistema. Nos padrões atuais, como CDMA2000 e WCDMA, não são definidos nenhum critério para escolha das seqüências. Por isso, nesta dissertação será analisado o desempenho do algoritmo de escolha de seqüências de espalhamento proposto anteriormente juntamente com o uso de códigos corretores de erro em canais com desvanecimento seletivo em freqüência. Será analisado o comportamento das seqüências Walsh, Gold e m-deslocadas. O algoritmo analisado apresenta bons resultados sem o uso de codificação, mas, como maneira de analisar um sistema mais próximo do real, serão utilizados os códigos convolucionais e turbo. Palavras-chave: Algoritmo de busca, sistemas CDMA, espalhamento espectral, códigos convolucionais, códigos turbo. / Abstract: The performance of wireless communication systems that use the multiple access code division technique, CDMA, is interference-limited. A sequence selection algorithm allows a reduction in the mean interference of the system. In the standards like CDMA2000 and WCDMA no algorithm is defined for choosing the sequences. For this reason, in this dissertation we evaluate the performance of the proposed spread sequences selection algorithm together with error correcting codes over frequency selective fading channels. It is analyzed the behavior of Walsh, Gold, and shifted-m sequences. The algorithm had shown good results without channel coding, but to analyze a system similar to a real one, convolutional and turbo codes are going to be used. Key words: Selection algorithm, CDMA systems, spread spectrum, convolutional codes, turbo codes. / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica
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[en] STRUCTURES AND ALGORITHMS FOR MULTIUSER DETECTION AND INTERFERENCE SUPRESSION IN DS-CDMA SYSTEMS / [pt] ESTRUTURAS E ALGORITMOS PARA DETECÇÃO MULTIUSUÁRIO E SUPRESSÃO DE INTERFERÊNCIA EM SISTEMAS DS-CDMARODRIGO CAIADO DE LAMARE 26 January 2005 (has links)
[pt] Esta tese apresenta novas estruturas e algoritmos para
detecção multiusuário e supressão de interferência em
sistemas DS-CDMA. São investigadas estruturas baseadas em
redes neurais recorrentes para projeto de receptores com
decisão realimentada e desenvolvidos algoritmos adaptativos
para combater a interferência de múltiplo acesso e a
interferência entre símbolos. Novos algoritmos baseados na
minimização da taxa de erro de bits são examinados e
generalizados para esquemas de detecção com cancelamento de
interferência. Para situações onde uma seqüência de
treinamento não é disponibilizada, é considerado um novo
critério de projeto às cegas de receptores com restrições
lineares baseado na função custo módulo constante.
Algoritmos adaptativos às cegas baseados neste novo
critério são usados para estimar os parâmetros de um
receptor linear e do canal de
comunicações. São também desenvolvidos novos mecanismos às
cegas de ajuste do passo para algoritmos do tipo gradiente
estocástico em receptores lineares com base no critério de
mínima variância com restrições. Com base nos critérios de
mínima variância e módulo constante com restrições, são
desenvolvidos critérios de projeto às cegas para receptores
com decisão realimentada e propostos algoritmos adaptativos
para essas estruturas. Um novo esquema de cancelamento
sucessivo de interferência baseado no conceito de
arbitragem é proposto e incorporado a uma estrutura de
recepção com decisão realimentada para o enlace reverso. Em
seguida, o novo esquema de
cancelamento de interferência é combinado com uma estrutura
iterativa que
emprega múltiplos estágios, resultando em melhores
estimativas do receptor
e um desempenho uniforme para os usuários. Finalmente, são
apresentadas
novas estruturas de recepção com posto reduzido, baseadas
em filtros FIR
interpolados e interpoladores variantes no tempo, e
desenvolvidos algoritmos
adaptativos às cegas e supervisionados para o novo esquema. / [en] This thesis presents new structures and algorithms for
multiuser detection
and interference suppression in DS-CDMA systems. Structures
based on
recurrent neural networks are investigated for decision
feedback receivers
and adaptive algorithms are developed for combatting
multiple access
interference and intersymbol interference. New algorithms
based on the
minimization of the bit error rate are examined and
generalized for detection
schemes with interference cancellation. For situations
where a training
sequence is not available, a new blind criterion, based on
the constant
modulus cost function with linear constraints is
considered. Based on
this novel criterion, blind adaptive algorithms are used
for estimating
the parameters of linear receivers and the channel. New
blind adaptive
mechanisms for adjusting the step size of stochastic
gradient algorithms,
using the constrained minimum variance criterion, are also
presented for
estimating the parameters of linear receivers and the
channel. Based on
constrained minimum variance and constrained constant
modulus criteria,
the blind design of decision feedback structures is
considered and blind
adaptive algorithms are derived. A new successive
interference cancellation
scheme using the concept of arbitration is proposed and
incorporated
within a decision feedback structure for uplink scenarios.
Then, the new
interference cancellation scheme is combined with an
iterative structure
that employs multiple stages, resulting in improved
receiver estimates and
providing uniform performance over the users. Finally,
novel reduced-rank
receiver structures, based on interpolated FIR filters with
time-varying
interpolators, are presented and blind and supervised
adaptive algorithms
are developed for this new scheme.
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[en] USE OF ADAPTIVE ARRAYS IN CDMA SYSTEMS / [es] UTIZACIÓN DE ANTENAS ADAPTATIVAS EN SISTEMAS CDMA / [pt] UTILIZAÇÃO DE ANTENAS ADAPTATIVAS EM SISTEMAS CDMAMAURICIO VILELA GUERRA 23 October 2001 (has links)
[pt] Este trabalho tem como objetivo avaliar alguns aspectos da
utilização de antenas adaptativas em um sistema celular
digital CDMA. Uma das razões para isto é que as antenas
adaptativas reduzem a interferência que no sistema CDMA
influencia direta e fortemente a capacidade do sistema.
Inicialmente foi feito um resumo dos princípios gerais dos
arranjos de antenas de sistemas celulares digitais e de
algoritmos de adaptação. Com base nestes princípios, é
analisada a aplicação específica a sistemas CDMA,
estabelecendo-se uma modelagem do receptor incluindo o
receptor Rake. É avaliado então através de simulação o
comportamento de dois importantes métodos de filtragem
espacial adaptativa para sistemas CDMA. / [en] This work aims to evaluate some aspects of the use of
adaptive arrays in digital celular CDMA systems. One reason
for that is that adaptive arrays reduce the interference
which strongly affects the performance of the system. First
the general principles of adaptive antennas, digital
cellular systems and adaptation algorithm are sumarized.
Based on that principles, the application to CDMA systems
is addressed, and a receiver model is developed, including
the Rake receiver. Then the behavior of two filtering
techniques is evaluated through computer simulation. / [es] Este trabajo tiene como objetivo evaluar algunos aspectos
de la utilización de antenas adaptativas en un sistema
celular digital CDMA. Una de las razones para esto es que
las antenas adaptativas reducen la interferencia, que en el
sistema CDMA influeye directa y fuertemente em la capacidad
del sistema. Inicialmente se realizó un resumen de los
principios generales de los arranjos de antenas de sistemas
celulares digitales y de algoritmos de adaptación. Con base
en estos princípios, se analiza la aplicación específica a
sistemas CDMA, estableciendo una modelaje del receptor
incluindo el receptor Rake. Se evalúa a través de
simulación el comportamiento de dos importantes métodos de
filtraje espacial adaptativa para sistemas CDMA.
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