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Jointly multi-user detection and channel estimation with genetic algorithm

Neto, Fernando Ciriaco Dias; ABRAO, Taufik; Toledo, Antonio Fischer de; Jeszensky, Paul Jean Etienne
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
48.817896%
This work aims at proposing the use of the evolutionary computation methodology in order to jointly solve the multiuser channel estimation (MuChE) and detection problems at its maximum-likelihood, both related to the direct sequence code division multiple access (DS/CDMA). The effectiveness of the proposed heuristic approach is proven by comparing performance and complexity merit figures with that obtained by traditional methods found in literature. Simulation results considering genetic algorithm (GA) applied to multipath, DS/CDMA and MuChE and multi-user detection (MuD) show that the proposed genetic algorithm multi-user channel estimation (GAMuChE) yields a normalized mean square error estimation (nMSE) inferior to 11%, under slowly varying multipath fading channels, large range of Doppler frequencies and medium system load, it exhibits lower complexity when compared to both maximum likelihood multi-user channel estimation (MLMuChE) and gradient descent method (GrdDsc). A near-optimum multi-user detector (MuD) based on the genetic algorithm (GAMuD), also proposed in this work, provides a significant reduction in the computational complexity when compared to the optimum multi-user detector (OMuD). In addition, the complexity of the GAMuChE and GAMuD algorithms were (jointly) analyzed in terms of number of operations necessary to reach the convergence...

Esquemas de codificação para um sistema DS-CDMA com portadoras ortogonais

Dayani Adionel Guimarães
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/06/1998 Português
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Nessa dissertação é apresentado um estudo de um sistema de acesso múltiplo DS-CDMA com portadoras ortogonais. O desempenho do sistema em um canal com desvanecimento Rayleigh multipercurso foi analisado através de simulação computacional. Os ganhos de desempenho através do uso de informação de estado de canal no sistema foram obtidos. Dois esquemas de codificação de canal para o sistema estudado foram sugeridos. Os esquemas proporcionam ganhos de desempenho consideráveis, sem a necessidade de redução da taxa de transmissão de informação ou aumento da largura de faixa do sinal transmitido; In this dissertation, a study of an orthogonal multicarrier DS-CDMA multiple access system is presented lhe performance of the system in a multipath Rayleigh fading channel was analyzed through computer simulation. The performance gains through the use of channel state information in the system were obtained Two channel coding schemes for the studied system were suggested. The schemes provide considerable gain of performance, without reducing the transmission rate of information or increasing the transmitted signal bandwidth

An iterative detection technique for DS-CDMA signals with strong nonlinear distortion effects

Dinis, Rui; Silva, Paulo
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2006 Português
Relevância na Pesquisa
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Whenever a DS-CDMA signal (direct sequence code division multiple access) is the sum of several components associated to different spreading codes (e.g., the DS-CDMA signal to be transmitted by the BS (Base Station) in the downlink, or any multicode DS- CDMA signal), it has high envelope fluctuations, and a high PMEPR (Peak-to-Mean Envelope Power Ratio) setting strong linearity requirements for the power amplifiers. For this reason, it is desirable to reduce the envelope fluctuations of the transmitted signals. A promising class of nonlinear signal processing schemes, combining a nonlinear operation in the time- domain with a linear, frequency-domain filtering operation, was recently proposed for reducing the envelope fluctuations (and, inherently, the PMEPR) of DS-CDMA signals, while maintaining the spectral occupation of the corresponding conventional DS-CDMA signals. However, the performance degradation due to the nonlinear distortion effects on the transmitted signals can be relatively high, especially when a low PMEPR is intended. This can be especially serious if different powers are assigned to different spreading codes. To avoid significant performance degradation in these situations, we consider improved receiver where there is an iterative estimation and cancelation of nonlinear distortion effects. Our performance results show that the proposed receiver allows significant performance improvements after just a few iterations...

A Charrelation Matrix-Based Blind Adaptive Detector for DS-CDMA Systems

Luo, Zhongqiang; Zhu, Lidong
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 14/08/2015 Português
Relevância na Pesquisa
49.128984%
In this paper, a blind adaptive detector is proposed for blind separation of user signals and blind estimation of spreading sequences in DS-CDMA systems. The blind separation scheme exploits a charrelation matrix for simple computation and effective extraction of information from observation signal samples. The system model of DS-CDMA signals is modeled as a blind separation framework. The unknown user information and spreading sequence of DS-CDMA systems can be estimated only from the sampled observation signals. Theoretical analysis and simulation results show that the improved performance of the proposed algorithm in comparison with the existing conventional algorithms used in DS-CDMA systems. Especially, the proposed scheme is suitable for when the number of observation samples is less and the signal to noise ratio (SNR) is low.

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
Relevância na Pesquisa
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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.

Handset Detector Architectures for DS-CDMA Wireless Systems

Livingston, Frank; Chandrasekhar, Vikram; Vaya, Mani; Cavallaro, Joseph R.; Livingston, Frank; Chandrasekhar, Vikram; Vaya, Mani; Cavallaro, Joseph R.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
Relevância na Pesquisa
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Conference Paper; This paper investigates detector architectures for wireless handsets employing DS-CDMA. The code-matched filter (MF) and minimum output energy (MOE) detectors are analyzed with respect to fixed-point arithmetic behavior. Architectures employing fixed-point arithmetic are then proposed for these detectors. The maximum throughput of these architectures and the associated costs in terms of area usage and power consumption are evaluated. Results of the fixed-point analysis indicate that the MOE detector is more susceptible to quantization than the MF detector. Results of implementation indicate that the superior performance of the MOE detector is achieved at a considerably higher cost in terms of area usage and power consumption. Finally, comparison of hardware implementation with software-based DSP implementation indicates that software approaches result in considerably lower throughputs.

Channel Estimation for Multirate DS-CDMA Systems

Sabharwal, Ashutosh; Mitra, Urbashi; Bhashyam, Srikrishna; Sabharwal, Ashutosh; Mitra, Urbashi; Bhashyam, Srikrishna
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
Português
Relevância na Pesquisa
68.6571%
Conference paper; The problem of channel estimation for multiple data rate Direct-Sequence Code-Division Multiple-Acess (DS-CDMA) systems is addressed. The derived algorithms are suitable for both variable chipping rate and/or variable spreading multirate systems. Furthermore, methods for uplink and downlink channel estimation are investigated. It is observed that direct exploitation of the multirate nature of the signal yields improved performance. The algorithms are evaluated via simulation.

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
Relevância na Pesquisa
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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.

Reducing dynamic power consumption in next generation DS-CDMA mobile communication receivers

Chandrasekhar, Vikram
Fonte: Universidade Rice Publicador: Universidade Rice
Português
Relevância na Pesquisa
49.128984%
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 high-lighting 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.

Reducing dynamic power consumption in next generation DS-CDMA mobile communication receivers

Chandrasekhar, Vikram; Livingston, Frank; Cavallaro, Joseph R.
Fonte: Inderscience Enterprises Ltd. Publicador: Inderscience Enterprises Ltd.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
68.6571%
Reduction of the power consumption in portable wireless receivers is important for cellular systems, including UMTS and IMT2000. This paper explores the architectural design-space and methodologies for reducing the dynamic power dissipation in the Direct Sequence Code Division Multiple Access (DS-CDMA) downlink RAKE receiver. At the algorithm level, we investigate the tradeoffs of reduced precision and arithmetic complexity on the receiver performance. We then present and analyse two architectures for implementing the reference and reduced complexity receivers, with respect to dynamic power dissipation. The combined effect of reduced precision and complexity reduction leads to a 37.44% power savings.

Smart antenna application in DS-CDMA mobile communication system

Ng, Kok Keng.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
48.93842%
This thesis examine the use of an equally- spaced linear adaptive antenna array at the mobile station for a typical Direct Sequence Code Division Multiple Access (DS-CDMA) cellular mobile communications system with forward error correction, with soft decision decoding is studied. We analyze the performance of a randomly positioned mobile terminal with a randomly orientated adaptive antenna array in the forward channel (base-station to mobile) of a multi-cell DS-CDMA system and established four performance boundaries. Using the more conservative optimized array antenna performance boundary for the 2-, 3- and 4-element linear array, we compare the capacity and the performance of different cellular systems under a range of shadowing conditions, with and without antenna sectoring at the base-station, and for various user capacities, using Monte Carlo simulation. We further apply tapped-delay line (transversal filter) to each antenna element channel, to allow frequency dependent amplitude and phase adjustment for broadband signals. The performance of a DS-CDMA cellular system with a mobile terminal equipped with a linear array and a tapped-delay line is analyzed. It has been demonstrated that the optimization process has been extremely computationally expensive and hence minimum taps should be used for practical consideration. The results illustrated that...

Estudo do efeito de dipolos em arranjos de antenas adaptativas de sistemas de comunicação DS-CDMA

Torquato, Ciro Augusto Paula
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
69.313687%
This master dissertation introduces a study about some aspects that determine the aplication of adaptative arrays in DS-CDMA cellular systems. Some basics concepts and your evolution in the time about celular systems was detailed here, meanly the CDMA tecnique, specialy about spread-codes and funtionaly principies. Since this, the mobile radio enviroment, with your own caracteristcs, and the basics concepts about adaptive arrays, as powerfull spacial filter was aborded. Some adaptative algorithms was introduced too, these are integrants of the signals processing, and are answerable for weights update that influency directly in the radiation pattern of array. This study is based in a numerical analysis of adaptative array system behaviors related to the used antenna and array geometry types. All the simulations was done by Mathematica 4.0 software. The results for weights convergency, square mean error, gain, array pattern and supression capacity based the analisis made here, using RLS (supervisioned) and LSDRMTA (blind) algorithms.; Esta dissertação de mestrado vem trazer um estudo sobre alguns aspectos que influenciam na aplicação de antenas adaptativas em sistemas celulares DS-CDMA (ou simplesmente CDMA). Foram detalhados alguns conceitos básicos a respeito do sistema celular e em geral...

Estudo do efeito de dipolos em arranjos de antenas adaptativas de sistemas de comunicação DS-CDMA

Torquato, Ciro Augusto Paula
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
49.005493%
This master dissertation introduces a study about some aspects that determine the aplication of adaptative arrays in DS-CDMA cellular systems. Some basics concepts and your evolution in the time about celular systems was detailed here, meanly the CDMA tecnique, specialy about spread-codes and funtionaly principies. Since this, the mobile radio enviroment, with your own caracteristcs, and the basics concepts about adaptive arrays, as powerfull spacial filter was aborded. Some adaptative algorithms was introduced too, these are integrants of the signals processing, and are answerable for weights update that influency directly in the radiation pattern of array. This study is based in a numerical analysis of adaptative array system behaviors related to the used antenna and array geometry types. All the simulations was done by Mathematica 4.0 software. The results for weights convergency, square mean error, gain, array pattern and supression capacity based the analisis made here, using RLS (supervisioned) and LSDRMTA (blind) algorithms; Esta dissertação de mestrado vem trazer um estudo sobre alguns aspectos que influenciam na aplicação de antenas adaptativas em sistemas celulares DS-CDMA (ou simplesmente CDMA). Foram detalhados alguns conceitos básicos a respeito do sistema celular e em geral...

Return-Link code Acquisition for 1-d and 2-D With DS-CDMA for High-Capacity Multiuser Systems

Reed, Mark; Hanlen, Leif; Corazza, Giovanni E
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
58.46126%
Acquisition of the code timing in a direct-sequence code-division multiple-access (DS-CDMA) system at the base station must take place before signal detection and decoding is possible. Code acquisition under severe multiple-accessinterference (MAI) condit

Blind Adaptive Successive Interference Cancellation for Multicarrier DS-CDMA

Shakya, Indu; Ali, Falah H.; Stipidis, Elias
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/02/2011 Português
Relevância na Pesquisa
49.047344%
A new adaptive receiver design for the Multicarrier (MC) DS-CDMA is proposed employing successive interference cancellation (SIC) architecture. One of the main problems limiting the performance of SIC in MC DS-CDMA is the imperfect estimation of multiple access interference (MAI), and hence, the limited frequency diversity gain achieved in multipath fading channels. In this paper, we design a blind adaptive SIC with new multiple access interference suppression capability implemented within despreading process to improve both detection and cancellation processes. Furthermore, dynamic scaling factors derived from the despreader weights are used for interference cancellation process. This method applied on each subcarrier is followed by maximum ratio or equal gain combining to fully exploit the frequency diversity inherent in the multicarrier CDMA systems. It is shown that this way of MAI estimation on individual subcarrier provides significantly improved performance for a MC DS-CDMA system compared to that with conventional matched filter (MF) and SIC techniques at a little added complexity. Performance evaluation under severe nearfar, fading correlation and system loading conditions are carried out to affirm the gain of the proposed adaptive receiver design approach.

Coded DS-CDMA Systems with Iterative Channel Estimation and no Pilot Symbols

Torrieri, Don; Mukherjee, Amitav; Kwon, Hyuck
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/08/2010 Português
Relevância na Pesquisa
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In this paper, we describe direct-sequence code-division multiple-access (DS-CDMA) systems with quadriphase-shift keying in which channel estimation, coherent demodulation, and decoding are iteratively performed without the use of any training or pilot symbols. An expectation-maximization channel-estimation algorithm for the fading amplitude, phase, and the interference power spectral density (PSD) due to the combined interference and thermal noise is proposed for DS-CDMA systems with irregular repeat-accumulate codes. After initial estimates of the fading amplitude, phase, and interference PSD are obtained from the received symbols, subsequent values of these parameters are iteratively updated by using the soft feedback from the channel decoder. The updated estimates are combined with the received symbols and iteratively passed to the decoder. The elimination of pilot symbols simplifies the system design and allows either an enhanced information throughput, an improved bit error rate, or greater spectral efficiency. The interference-PSD estimation enables DS-CDMA systems to significantly suppress interference.; Comment: To appear, IEEE Transactions on Wireless Communications

Asymptotic Analysis of General Multiuser Detectors in MIMO DS-CDMA Channels

Takeuchi, Keigo; Tanaka, Toshiyuki; Yano, Toru
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/06/2007 Português
Relevância na Pesquisa
49.266616%
We analyze a MIMO DS-CDMA channel with a general multiuser detector including a nonlinear multiuser detector, using the replica method. In the many-user, limit the MIMO DS-CDMA channel with the multiuser detector is decoupled into a bank of single-user SIMO Gaussian channels if a spatial spreading scheme is employed. On the other hand, it is decoupled into a bank of single-user MIMO Gaussian channels if a spatial spreading scheme is not employed. The spectral efficiency of the MIMO DS-CDMA channel with the spatial spreading scheme is comparable with that of the MIMO DS-CDMA channel using an optimal space-time block code without the spatial spreading scheme. In the case of the QPSK data modulation scheme the spectral efficiency of the MIMO DS-CDMA channel with the MMSE detector shows {\it waterfall} behavior and is very close to the corresponding sum capacity when the system load is just below the transition point of the {\it waterfall} behavior. Our result implies that the performance of a multiuser detector taking the data modulation scheme into consideration can be far superior to that of linear multiuser detectors.; Comment: Submitted to IEEE Journal on Selected Areas in Communications

Performance Comparisions of ICA Algorithms to DS-CDMA Detection

Parmar, Sargam; Unhelkar, Bhuvan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/02/2010 Português
Relevância na Pesquisa
48.817896%
Commercial cellular networks, like the systems based on DS-CDMA, face many types of interferences such as multi-user interference inside each sector in a cell to interoperate interference. Independent Component Analysis (ICA) has been used as an advanced preprocessing tool for blind suppression of interfering signals in DS-CDMA communication systems. The role of ICA is to provide an interference-mitigated signal to the conventional detection. This paper evaluates the performance of some major ICA algorithms like Cardoso's joint approximate diagonalization of eigen matrices (JADE), Hyvarinen's fixed point algorithm and Comon's algorithm to solve the symbol estimation problem of the multi users in a DSCDMA communication system. The main focus is on blind separation of convolved CDMA mixture and the improvement of the downlink symbol estimation. The results of numerical experiment are compared with those obtained by the Single User Detection (SUD) receiver, ICA detector and combined SUD-ICA detector.; Comment: Journal of Telecommunications,Volume 1, Issue 1, pp52-56, February 2010

Guard Zones and the Near-Far Problem in DS-CDMA Ad Hoc Networks

Torrieri, Don; Valenti, Matthew C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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The central issue in direct-sequence code-division multiple-access (DS-CDMA) ad hoc networks is the prevention of a near-far problem. This paper considers two types of guard zones that may be used to control the near-far problem: a fundamental exclusion zone and an additional CSMA guard zone that may be established by the carrier-sense multiple-access (CSMA) protocol. In the exclusion zone, no mobiles are physically present, modeling the minimum physical separation among mobiles that is always present in actual networks. Potentially interfering mobiles beyond a transmitting mobile's exclusion zone, but within its CSMA guard zone, are deactivated by the protocol. This paper provides an analysis of DS-CSMA networks with either or both types of guard zones. A network of finite extent with a finite number of mobiles is modeled as a uniform clustering process. The analysis uses a closed-form expression for the outage probability in the presence of Nakagami fading, conditioned on the network geometry. By using the analysis developed in this paper, the tradeoffs between exclusion zones and CSMA guard zones are explored for DS-CDMA and unspread networks.; Comment: to appear at Milcom-2012

Digital DS-CDMA detection in impulsive noise: base-band vs. band-pass nonlinear processing

Roncagliolo,P.A.; Muravchik,C.H.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 Português
Relevância na Pesquisa
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In the context of DS-CDMA detection, a digital base-band model for the received signal after chip-matched filtering, is often adopted. Nonlinear treatment of these samples for robust detection in impulsive environments has been already proposed. In this paper we study the advantages of band-pass non-linear detection schemes for DS-CDMA receivers, over those in base-band. We consider for both schemes i) an impulsive noise model with independent a-stable distributed sequences and ii) a hard-limiter as memoryless nonlinearity. Probability of error and asymptotic relative efficiency expressions are given, with simulations that validate them. Results shown that band-pass non-linear detection is preferable.