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Iterative low-complexity multiuser detection and decoding for coded UWB systemsSathish, Arun D. 07 1900 (has links)
In general, ultra wideband (UWB) signals are transmitted using ~'eIYshort pulses m tiIae
domain, thus promising very high data rates. In this thesis, a recei'ler structure is proposed for
decoding multiuser information data in a convolutionally coded UWB system. The proposed
iterative receiver has three stages: a pulse detector, a symbol detector, and a channel decoder.
Each of these stages outputs soft values, which are used as a priori information in the next
iteration. Simulation results show that the proposed system can provide performance very close
to a single-user system. / Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical and Computer Engineering. / "July 2006." / Incluldes bibliographic references (leaves 29-31)
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Transmission of vector quantization over a frequency-selective Rayleigh fading CDMA channelNguyen, Son Xuan 19 December 2005
Recently, the transmission of vector quantization (VQ) over a code-division multiple access (CDMA) channel has received a considerable attention in research community. The complexity of the optimal decoding for VQ in CDMA communications is prohibitive for implementation, especially for systems with a medium or large number of users. A suboptimal approach to VQ decoding over a CDMA channel, disturbed by additive white Gaussian noise (AWGN), was recently developed. Such a suboptimal decoder is built from a soft-output multiuser detector (MUD), a soft bit estimator and the optimal soft VQ decoders of individual users. <p>Due to its lower complexity and good performance, such a decoding scheme is an attractive alternative to the complicated optimal decoder. It is necessary to extend this decoding scheme for a frequency-selective Rayleigh fading CDMA channel, a channel model typically seen in mobile wireless communications. This is precisely the objective of this thesis. <p>Furthermore, the suboptimal decoders are obtained not only for binary phase shift keying (BPSK), but also for M-ary pulse amplitude modulation (M-PAM). This extension offers a flexible trade-off between spectrum efficiency and performance of the systems. In addition, two algorithms based on distance measure and reliability processing are
introduced as other alternatives to the suboptimal decoder. <p>Simulation results indicate that the suboptimal decoders studied in this thesis also performs very well over a frequency-selective Rayleigh fading CDMA channel.
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Transmission of vector quantization over a frequency-selective Rayleigh fading CDMA channelNguyen, Son Xuan 19 December 2005 (has links)
Recently, the transmission of vector quantization (VQ) over a code-division multiple access (CDMA) channel has received a considerable attention in research community. The complexity of the optimal decoding for VQ in CDMA communications is prohibitive for implementation, especially for systems with a medium or large number of users. A suboptimal approach to VQ decoding over a CDMA channel, disturbed by additive white Gaussian noise (AWGN), was recently developed. Such a suboptimal decoder is built from a soft-output multiuser detector (MUD), a soft bit estimator and the optimal soft VQ decoders of individual users. <p>Due to its lower complexity and good performance, such a decoding scheme is an attractive alternative to the complicated optimal decoder. It is necessary to extend this decoding scheme for a frequency-selective Rayleigh fading CDMA channel, a channel model typically seen in mobile wireless communications. This is precisely the objective of this thesis. <p>Furthermore, the suboptimal decoders are obtained not only for binary phase shift keying (BPSK), but also for M-ary pulse amplitude modulation (M-PAM). This extension offers a flexible trade-off between spectrum efficiency and performance of the systems. In addition, two algorithms based on distance measure and reliability processing are
introduced as other alternatives to the suboptimal decoder. <p>Simulation results indicate that the suboptimal decoders studied in this thesis also performs very well over a frequency-selective Rayleigh fading CDMA channel.
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Application of Array Processing Techniques to CDMA Multiuser Detection SystemsChang, Ann-Chen 11 May 2000 (has links)
Several issues on the problems of the adaptive array beamforming and code-division multiple access (CDMA) multiuser detection are investigated in this dissertation. Recently, based on the decomposition of observation vector space into two orthogonal eigenspace, the eigenspace-based (ESB) and the generalized eigenspace-based (GEIB) array signal processing techniques have been widely discussed due to their superior performance over conventional techniques. At first, the purpose of this dissertation is mainly to present robust and efficient algorithms for further enhancing the performance of ESB and GEIB techniques under imperfect and practical operation environments. We also propose a method of corrected steering angles to combat the supersensitivity of eigenanalysis interference canceler (EIC) to source number overestimation and steering angle errors.
We analyze the performance of several ESB multiuser detectors, including conventional direct-form detector and generalized sidelobe canceler (GSC) for synchronous CDMA system with and without desired user code mismatch. We also present a way of resolving spreading code mismatch in blind multiuser detection with subspace-based technique. Furthermore, the structure of GSC can be utilized to deal with the case of the desired user's SNR < 0 dB.
Next, algorithm for adaptive H¡Û filter has demonstrated the advantage of reduction of sensitivity to modeling error (due to finite tap number) and suitability for arbitrary ambient noise over recursive least squares (RLS) algorithm. However, the computational burden of the H¡Û algorithm is enormous. In order to reduce the computational complexity, subweight partition scheme is employed to an H¡Û-based algorithm. The computation burden of the conventional adaptive H¡Û algorithm can be mitigated with slight performance degradation. The H¡Û-based algorithm is then further extended to the adaptive beamformer and blind multiuser detector.
Finally, we present new diversity techniques for multiuser detection under multipath fading channels in asynchronous CDMA systems. The enhanced capacity of diversity for multipath channels can be achieved by appropriately utilizing the constraint matrix and the response vector in multiple constraint minimum variance (MCMV) algorithm. Moreover, the proposed techniques offer gratifying multiple access interference (MAI) suppression. We also incorporate the signal subspace-based projection into MCMV detector, so that the noise enhancement in the MCMV criterion can be reduced.
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Code optimization and analysis for multiple-input and multiple-output communication systemsYue, Guosen 01 November 2005 (has links)
Design and analysis of random-like codes for various multiple-input and multiple-output communication systems are addressed in this work. Random-like codes have drawn significant interest because they offer capacity-achieving performance. We first consider the analysis and design of low-density parity-check (LDPC) codes for turbo multiuser detection in multipath CDMA channels. We develop techniques for computing the probability density function (pdf) of the extrinsic messages at the output of the soft-input soft-output (SISO) multiuser detectors as a function of the pdf of input extrinsic messages, user spreading codes, channel impulse responses, and signal-to-noise ratios. Using these techniques, we are able to accurately compute the thresholds for LDPC codes and design good irregular LDPC codes. We then apply the tools of density evolution with mixture Gaussian approximations to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations which include different number of antennas, different channel models and different demodulation schemes. We also study the coding-spreading tradeoff in LDPC coded CDMA systems employing multiuser joint decoding. We solve the coding-spreading optimization based on the extrinsic information SNR evolution curves for the SISO multiuser detectors and the SISO LDPC decoders. Both single-cell and multi-cell scenarios will be considered. For each of these cases, we will characterize the extrinsic information for both finite-size systems and the so-called large systems where asymptotic performance results must be evoked. Finally, we consider the design optimization of irregular repeat accumulate (IRA) codes for MIMO communication systems employing iterative receivers. We present the density evolution-based procedure with Gaussian approximation for optimizing the IRA code ensemble. We adopt an approximation method based on linear programming to design an IRA code with the extrinsic information transfer (EXIT) chart matched to that of the soft MIMO demodulator.
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Multiuser detection in TH-UWB communication systemsHosseini, Iraj Unknown Date
No description available.
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Signal Detection for Overloaded ReceiversKrause, Michael January 2009 (has links)
In this work wireless communication systems with multiple co-channel signals present at the receiver are considered. One of the major challenges in the development of such systems is the computational complexity required for the detection of the transmitted signals. This thesis addresses this problem and develops reduced complexity algorithms for the detection of multiple co-channel signals in receivers with multiple antennas. The signals are transmitted from either a single user employing multiple transmit antennas, from multiple users or in the most general case by a mixture of the two. The receiver is assumed to be overloaded in that the number of transmitted signals exceeds the number of receive antennas. Joint Maximum Likelihood (JML) is the optimum detection algorithm which has exponential complexity in the number of signals. As a result, detection of the signals of interest at the receiver is challenging and infeasible in most practical systems.
The thesis presents a framework for the detection of multiple co-channel signals in overloaded receivers. It proposes receiver structures and two list-based signal detection algorithms that allow for complexity reduction compared to the optimum detector while being able to maintain near optimum performance. Complexity savings are achieved by first employing a linear preprocessor at the receiver to reduce the effect of Co-Channel Interference (CCI) and second, by using a detection algorithm that searches only over a subspace of the transmitted symbols. Both algorithms use iterative processing to extract ordered lists of the most likely transmit symbols. Soft information can be obtained from the detector output list and can then be used by error control decoders.
The first algorithm named Parallel Detection with Interference Estimation (PD-IE) considers the Additive White Gaussian Noise (AWGN) channel. It relies on a spatially reduced search over subsets of the transmitted symbols in combination with CCI estimation. Computational complexity under overload is lower than that of JML. Performance results show that PD-IE achieves near optimum performance in receivers with Uniform Circular Array (UCA) and Uniform Linear Array (ULA) antenna geometries.
The second algorithm is referred to as List Group Search (LGS) detection. It is applied to overloaded receivers that operate in frequency-flat multipath fading channels. The List Group Search (LGS) detection algorithm forms multiple groups of the transmitted symbols over which an exhaustive search is performed. Simulation results show that LGS detection provides good complexity-performance tradeoffs under overload.
A union bound for group-wise and list-based group-wise symbol detectors is also derived. It provides an approximation to the error performance of such detectors without the need for simulation. Moreover, the bound can be used to determine some detection parameters and tradeoffs. Results show that the bound is tight in the high Signal to Interference and Noise Ratio (SINR) region.
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Interference management in MIMO networksGaur, Sudhanshu 19 May 2008 (has links)
Several efficient low complexity interference management techniques were developed for improving the performance of multiple-input multiple-output (MIMO) networks. Sub-optimal techniques involving optimal antenna selection-aided stream control were proposed for joint optimization of co-channel MIMO links in a space division multiple access (SDMA) network. Results indicated that the use of the SDMA scheme along with partial channel state information at the transmitters significantly reduces the signaling overhead with minimal loss in throughput performance. Next, a mean squared error (MSE) based antenna selection framework was presented for developing low complexity algorithms for finite complexity receivers. These selection algorithms were shown to provide reasonable bit-error rate performance while keeping the overall system complexity low. Furthermore, some new algebraic properties of linear orthogonal space-time block codes (OSTBCs) were utilized to develop a single-stage and minimum MSE optimal detector for two co-channel users employing unity rate real and derived rate-1/2 complex OSTBCs. A sub-optimal space-time interference cancellation (IC) technique was also developed for a spatial-multiplexing link subjected to Alamouti interference. The performance of proposed interference management techniques and their implications for future research are discussed.
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Multiuser detection in TH-UWB communication systemsHosseini, Iraj. January 2009 (has links)
Thesis (M. Sc.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Aug. 14, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Communications, Department of Electrical and Computer Engineering, University of Alberta." Includes bibliographical references.
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[en] MULTIUSER RECEIVERS WITH OPTIMAL GROUP DETECTION FOR CODE-DIVISION MULTIPLE-ACCESS CHANNELS / [pt] RECEPÇÃO MULTIUSUÁRIO COM DETECÇÃO ÓTIMA POR GRUPOS EM SISTEMAS COM MÚLTIPLO ACESSO CDMAMARCELO FREITAS MARCAL 05 August 2002 (has links)
[pt] As técnicas de múltiplo acesso mais cogitadas nas
propostas para padrões de 3 geração de sistemas celulares
envolvem alguma forma de CDMA ( Code Division Multiple
Access)na qual os usuários podem transmitir
simultaneamente na mesma faixa de freqüência sendo
separáveis no receptor pela ortogonalidade, ou quase
ortogonalidade, entre os sinais utilizados pelos
diferentes usuários para transmissão de informação.Os
receptores multiusuário, propostos para uso na 3 geração
de sistemas celulares, realizam a detecção do sinal do
usuário desejado conjuntamente com os sinais
interferentes, resultando em um ganho de desempenho em
relação aos receptores CDMA convencionais, que tratam os
sinais interferentes como um simples ruído de fundo.Este
trabalho tem por objetivo estudar a viabilidade de um
receptor CDMA multiusuário hpibrido síncrono, que combina
a eficiência do recepor Decorrelator no combate a
interferência de múltiplo acesso (IMA) e sua simpicidade
de implementação com a robustez e alto desempenho do
receptor ótimo. Para evitar a complexidade inerente a
estrutura de detecção ótima é sugerido que o conjunto de
sinais na saída do estágio Decorrelator seja particionado
em grupos e detectados de forma paralela e ótima. Esta
técnica é conhecida como detecção ótima por grupos.
Também é proposto e explorada a utilização de uma métrica
para a formação dos grupos, baseada na minimização da
probabilidade de erro de bit do usuário com pior
desenpenho no sistema. Ao longo deste trabalho são
exibidos resultados analíticos e de simulação, que
comprovam a utilidade e exelente relação entre desempenho
e complexidade da estrutura proposta em canais AWGN. Por
fim, a estrutura proposta é avaliada para um canal com
desvanecimento de Rayleigh plano. / [en] The most discussed multiple access techiniques for the 3G
of mobile wireless systems involve some form of CDMA - Code
Division Multiple Access- where the users can transmit
simultaneously their signals in the same frequency band
separable in the receiver by the orthogonality or, quasi-
orthogonality, properties of the transmitted signals.
Multiuser detectors MUD perform the detection of the
desired user signal jointly with the signals transmitted by
the remaining users, resulting in a better performance than
the conventional CDMA receivers, that treat the
interference created by the signals of other users simply
as background noise.This work has the objective of
investigating the viability of syncrhronous hybrid
multiuser detector, wich combines the implementation
simplicity and efficiency of the decorrelating multiuser
detector in mitigating the multiple access interference
with the robustness and high performance of the optimum
multiuser detector.In order to avoid the complexity of the
optimum multiuser detection scheme it is proposed to
combine the signals from the decorrelator output into
groups and perform optimal detection of the signals in each
group. This approach is known as optimal group detection.
Also in this work, a strategy on how to perform the
grouping is proposed and explored. This strategy is based
on the minimization the bit error probability of the user
with the worst performance.Simulation and analytical
results show the excellent trade-off between performance
and complexity of the proposed optimum multiuser group
detector in AWGN channels. The receiver performance is also
evaluated in Rayleigh flat fading channels.
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