Multiple-input/multiple-output (MIMO) systems with the adaptive array processing technique, also referred to as smart antennas, have received extensive attention in wireless communications due to their ability to combat multipath fading and co-channel interference, two major channel impairments that degrade system performance. However, when smart antennas are deployed in wireless networks, careful attention is required since any defective or imperfect operation of smart antennas can severely degrade the performance of the entire network. Therefore, the evaluation of network performance under ideal and imperfect conditions is critical in the process of system design and should precede deploying smart antennas on the wireless network. This work focuses on the development of an analytical framework to evaluate the performance of wireless networks based on popular DS/CDMA cellular systems equipped with antenna arrays. Spatial diversity at both the base station (BS) and the mobile station (MS) is investigated through both analytical analysis and simulation. The main contribution of this research is to provide a comprehensive analytical framework for examining the system level performance with multiple antennas at both the BS and the MS. Using the framework developed in this research, system capacity and coverage of the uplink (or reverse link) are investigated when antenna arrays are implemented at both the BS and the MS. In addition, the system capacity and soft handoff capability of the downlink (or forward link) are examined taking into account MIMO. Furthermore, various physical and upper layer parameters that can affect the system level performance are taken into account in the analytical framework and their combined impact is evaluated. Finally, to validate the analytical analysis results, a system level simulator is developed and selective results are provided. / Ph. D.

Ever since the FCC allocated 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) technology, interest has been renewed in both academic and industrial circles to exploit this vast spectrum for short range, high data rate wireless applications. The great potential of UWB lies in the fact that it can co-exist with the already licensed spectrum users and can still pave the way for a wide range of applications. However, this wide bandwidth complicates the circuit level implementation of key RF blocks like the power amplifier (PA), transmit/receive switch, low noise amplifier (LNA) and mixers in an UWB transceiver. Though expensive technologies like SiGe or GaAs have been used for transceiver realizations, the ultimate goal is to have a single-chip, low-cost solution which can only be achieved by using CMOS technology. Nevertheless, some of the inherent limitations of CMOS like lower fT of transistors make the design of UWB circuits in CMOS an extremely challenging task. Two proposals- Multi-Band OFDM and Direct-Sequence CDMA have been put before the IEEE 802.15.3a task group to decide on the industry standard for the commercial deployment of this technology. Though the debate on which standard is better has not been resolved, proponents of both the groups have already begun to develop prototypes of their respective proposals. This thesis describes the design of a key RF block in the UWB transceiver - the Power Amplifier. For the first part of this work, a PA suitable for MB-OFDM specifications was designed and fabricated in TSMC 0.18um CMOS technology. The class-AB PA is able to cover the lower UWB frequency band from 3.1 GHz to 4.75 GHz and delivers an output power of -2 dBm at 4 GHz. Simulated results show a gain of 19±2 dB achieved over the entire band and the PA consumes 36.54 mW from a 1.8V supply. In the second part of this work, a PA that meets the DS-CDMA specifications was designed and fabricated. This PA operates in the class-AB regime, delivering an output power of -4.2 dBm with input-1dB compression point at -22 dBm. Complete design and implementation was done using TSMC 0.18um CMOS technology and it consumes a very low power of 25 mW, while realizing a flat gain of 19±1 dB across the whole band of operation. All the above mentioned results are from simulations in SpectreRF and measurements are yet to be taken. Additional features like power ON/OFF scheme and output impedance control has also been incorporated in the design. / Master of Science

[pt] Este trabalho apresenta uma análise detalhada de uma recente proposta de combinação da transmissão em blocos com portadora única e a técnica CDMA, referida como CS-CDMA (Chip Spread CDMA). Uma característica marcante desta técnica de transmissão é que diferentemente do que ocorre nos sistemas DS-CDMA, a ortogonalidade entre os códigos dos diferentes usuários é mantida mesmo quando a transmissão é feita através de um canal multipercurso seletivo em frequência, suposto invariante no tempo, permitindo assim que os usuários possam ser identicamente desacoplados na recepção. Além desta vantagem, resultados de desempenho indicaram uma significativa superioridade deste sistema sobre o tradicional DS-CDMA. Entretanto comparações existentes, consideraram apenas o up-link, do sistema e adotaram algumas premissas, que incluem, a utilização de códigos ortogonais pelos diversos usuários e a suposição de canais de transmissão invariantes no tempo. O presente trabalho apresenta uma análise detalhada da técnica (CS-CDMA e uma análise comparativa dos sistemas em condições menos favoráveis. Os sistemas operam em ambientes invariante e variante no tempo, com códigos ortogonais e não ortogonais e em dois cenários diferentes, down- link e up-link. Os resultados consideram recepção com equalização no domínio da frequência utilizando equalizadores do tipo ZF (Zero Forcing) e MMSE (Minimum Mean Squared Error). Simulações foram realizadas no intuito de se avaliar o desempenho dos dois sistemas considerados. Curvas de probabilidade de erro foram obtidas e ilustram e comparam tais desempenhos em diferentes situações e cenários de interesse. / [en] This dissertation proposes detailed analysis of a recent combined mechanism for transmission in blocks with a single carrier and CDMA technique known as Chip Spread CDMA (CS-CDMA). An important feature of this transmission technique is that unlike what happens in Direct Sequence (DS-CDMA) systems, the orthogonality between codes of different users is maintained even when the transmission, considered time-invariant, is made through a selective multipath channel frequency, which ideally allows users to be uncoupled in reception. However, existing comparisons only consider the up-link transmission and adopt certain assumptions, which include orthogonal codes for different users and time invariant channels. This technique have shown a significant superiority as compared with the traditional DS-CDMA. A comparison of (CS-CDMA systems in more realistic conditions are presented in this work. Various environments were tested in the presence of BPSK modulation systems, as well as invariant and time-varying transmission. Comparison between scenarios down-link and up-link are also presented. The results consider equalized reception in the frequency domain using the ZF (Zero Forcing) equalizers and MMSE (Minimum Mean Squared Error). Simulations were carried out in order to evaluate the performance of the two systems considered. Error probability curves were obtained to illustrate and compare the performances in different situations and scenarios.

[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.

Les systèmes numériques de communications connaissent un essor considérable sous l'impulsion d'une demande de plus en plus pressante de mobilité, de diversité des services et d'intégration des applications multimédia les plus récentes. Les recherches présentées dans ce mémoire de thèse ont pour but l'étude de nouveaux systèmes de communications qui pourront s'appliquer aussi bien aux systèmes de radiocommunications mobiles qu'aux systèmes de communications à l'intérieur des bâtiments. L'élément nouveau est ici la combinaison de deux techniques : l'étalement de spectre permettant la mise en oeuvre d'un accès multiple à répartition de codes (AMRC) et les modulations à porteuses multiples (OFDM). Cette<br />combinaison permet de tirer partie de la robustesse et de l'efficacité spectrale de l'OFDM, et de la capacité d'accès multiple des techniques AMRC. Deux techniques associant l'OFDM et l'AMRC sont plus particulièrement analysées.<br /><br />La première technique, l'AMRC à porteuses multiples est étudiée sur un canal de Rayleigh à trajets multiples. En réception, plusieurs techniques d'égalisation ou de traitement de diversité sont mises en oeuvre et une approche plus globale de la détection est proposée. Elle consiste à intégrer la fonction de désétalement dans le processus d'égalisation, permettant ainsi d'améliorer la fiabilité de la détection. Ces techniques d'égalisation sont insérées et combinées de différentes façons dans des structures d'annulation d'interférences.<br /><br />Si le système AMRC à porteuses multiples est généralement proposé pour des liaisons synchrones ou quasi-synchrones, le système AMRC<br />multipilote peut être utilisé dans un contexte asynchrone. Les performances théoriques de ce système sont développées et comparées aux performances des systèmes AMRC à porteuse unique.

Direct sequence code division multiple access (DS-CDMA) technique is one of the significant multiplexing technologies used in wireless communication services. In the DS-CDMA framework, all users have been assigned distinct signature code sequence to achieve multiple accesses within the same frequency band, and allow signal separating at the receiver. Under multipath fading environment with near-far effect, the current CDMA systems employed the RAKE receiver, to enhance the system performance. It is known that if training data is available the minimum mean squares error (MMSE) multiuser receiver, in which the average power of the receiver output is minimized subject to appropriate constraints, could be obtained by solving directly by the constrained Wiener estimation solution. However, if this is not the case, the blind multiuser receiver is an alternative approach to achieve desired performance closed to the one with the MMSE approach. In this thesis, based on the max/min criterion, the blind multiuser receiver, with linear constraints, is devised. Here constraint equations are written in parametric forms, which depend on the multipath structure of the signal of interest. Constraint parameters are jointly optimized with the parameters of the linear receiver to obtain the optimal parameters. In consequence, the sliding window linearly constrained RLS (SW-LC-RLS) algorithm is employed to implement the optimal blind receiver, with max/min approach. This new proposed scheme can be used to deal with multiple access interference (MAI) suppression for the environments, in which the narrow band interference (NBI) due to other systems is joined suddenly to the DS-CDMA systems, and having serious near-far effect. Under such circumstance, the channel character due to the NBI and near-far effect will become violent time varying, such that the conventional LC-RLS algorithm as well as LC-LMS algorithms could not perform well. Via computer simulation it confirms that our proposed scheme has better capability for MAI suppression in DS-CDMA systems than other existing schemes, and is more robust against the NBI and near-far problems.

The code division multiple access (CDMA) system implemented by the direct-sequence (DS) spread spectrum (SS) technique is one of the most promising multiplexing technologies for wireless communications services. The SS communication adopts a technique of using much wider bandwidth necessary to transmit the information over the channel. In the DS-CDMA system, due to the inherent structure interference, referred to as the multiple access interference (MAI), the system performance might degrade. Next, for DS-CDMA systems over frequency-selective fading channels, the effect of inter symbol interference (ISI) will exist, such that a multiuser RAKE receiver has to be employed to combat the ISI as well as MAI. Since, in practical wireless communication environment, there may have several communication systems operated in the same area at the same time. In this thesis, we consider the environment of DS-CDMA systems, where the asynchronous narrow band interference (NBI) due to other systems is joined suddenly to the CDMA system. In general, when a system works in a stable state with adaptive detectors, a suddenly joined NBI signal will cause the system performance to be crash down. Under such circumstance, the existing conventional adaptive RAKE detectors may not be able to track well for the rapidly sudden changing NBI associated with the problems of ISI and MAI. It is known that the adaptive filtering algorithms, based on the sliding window linear constrained recursive least squares (SW LC-RLS), is very attractive to a violent changing environment. The main concern of this thesis is to propose a novel sliding window constant modulus RLS (SW CM-RLS) algorithm, based on the Min/max criterion, to deal with the NBI for DS-CDMA system over multipath channels. For simplicity and having less system complexity the generalized side-lobe canceller (GSC) structure is employed, and is referred to as the SW CM-GSC-RLS algorithm. The aim of the SW CM-GSC-RLS algorithm is used to alleviate the effect of NBI. It has the advantages of having faster convergence property and tracking ability, and can be applied to the environment in which the NBI is suddenly joined to the system under the effect of channel mismatch to achieve desired performance. At the end of this thesis, we extend the idea of the proposed algorithm to the space-time DS-CDMA RAKE receiver, in which the adaptive beamformer with temporal domain DS-CDMA receiver is employed. Via computer simulation results, we show that our new proposed schemes outperform the conventional CM GSC-RLS algorithm as well as the GSC-RLS algorithm (the so-called LCMV approach), in terms of mean square error of estimating channel impulse response, output signal to interference plus noise ratio and bit-error-rate.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

¡@¡@Pseudo-noise (PN) code synchronizer is an essential element of direct-sequence code division multiple access (DS-CDMA) system because data transmission is possible only after the receiver accurately synchronizes the locally generated PN code with the incoming PN code. The code synchronization is processed in two steps, acquisition and tracking, to estimate the delay offset between the two codes. Recently, the adaptive LMS filtering scheme has been proposed for performing both code acquisition and tracking with the identical structure, where the LMS algorithm is used to adjust the FIR filter taps to search for the value of delay-offset adaptively. A decision device is employed in the adaptive LMS filtering scheme as a decision variable to indicate code synchronization, hence it plays an important role for the performance of mean acquisition time (MAT). In this thesis, only code acquisition is considered. ¡@¡@In this thesis, a new decision device, referred to as the weight vector square norm (WVSN) test method, is devised associated with the adaptive LMS filtering scheme for code acquisition in DS-CDMA system. The system probabilities of the proposed scheme are derived for evaluating MAT. Numerical analyses and simulation results verify that the performance of the proposed scheme, in terms of detection probability and MAT, is superior to the conventional scheme with mean-squared error (MSE) test method, especially when the signal-to-interference-plus-noise ratio (SINR) is relatively low. ¡@¡@Furthermore, an efficient and joint-adaptation code acquisition scheme, i.e., a smart antenna coupled with the proposed adaptive LMS filtering scheme with the WVSN test method, is devised for applying to a base station, where all antenna elements are employed during PN code acquisition. This new scheme is a process of PN code acquisition and the weight coefficients of smart antenna jointly and adaptively. Numerical analyses and simulation results demonstrate that the performance of the proposed scheme with five antenna elements, in terms of the output SINR, the detection probability and the MAT, can be improved by around 7 dB, compared to the one with single antenna case.

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