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.

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Dans un contexte de besoins croissants de moyens de communication pour augmenter la sécurité des vols et répondre aux attentes des compagnies et des passagers, le monde de l'aviation civile cherche de nouveaux systèmes de communication pouvant répondre à ces objectifs. Les systèmes de communication sol-bord existants, que ce soit les solutions par satellites en bande L (SATCOM, ...) ou les solutions cellulaires par liaison directe avec le sol (HF, VHF, ...), présentent des limites en terme de capacité, de couverture et de coût.La proposition avancée dans le cadre de cette thèse est d'utiliser les avions comme relais afin de propager les données jusqu'à une station sol. Ce système peut être vu comme un réseau ad hoc mobile dont les nœuds sont les avions civils en vol. Grâce à plusieurs sauts successifs au travers d'avions relais, chaque avion doit pouvoir joindre le sol sans être à portée directe d'une station. Le réseau ad hoc ainsi formé peut ensuite être utilisé pour différentes classes de communications : contrôle aérien, services pour les compagnies aériennes ou pour les passagers. Une telle solution permettrait d'améliorer la couverture des solutions cellulaires classiques en zone continentale. Elle est également applicable en zone océanique où les seuls moyens disponibles sont actuellement le satellite et la HF. On peut imaginer que les coûts de déploiement et de maintenance seraient relativement bas puisque l'infrastructure sol est limitée.Dans cette thèse, nous avons étudié la faisabilité puis les performances qui peuvent être attendues pour ce système de communication aéronautique innovant.

In a multihop cellular network, mobile terminals have the capability to transmit directly to other mobile terminals enabling them to use other terminals as relays to forward traffic towards the base station. Previous studies of networks consisting of a single cell found that the SINR in a multihop cellular network is slightly lower than in a traditional cellular network. However, multihop cellular networks may have a higher capacity than traditional cellular networks due to their potential for lower intercell interference. For this reason, the effects of intercell interference are investigated in this thesis. Our simulations of a network with many cells show that multihop cellular networks have a higher SINR than traditional cellular networks due to the near elimination of intercell interference. However, multihop cellular networks still suffer from large amounts of interference surrounding the base station because all traffic either emanates or is destined to the base station making it the capacity bottleneck. To resolve this problem, we propose a novel architecture called the autonomous infrastructure multihop cellular network where users can connect their mobile terminals to the backbone network giving them the functionality of an access point. Access points receive traffic from other terminals and send it directly onto the backbone, as would a base station. This reduces the traffic handled by the base station and increases network capacity. Our analysis and simulations show that in autonomous infrastructure multihop cellular networks, the SINR at the base station is higher, the power consumption is lower and the coverage is better than in normal multihop cellular networks. Access points require parameters like their transmission range to be adjusted autonomously to optimal levels. In this thesis, we propose an autonomous pilot power protocol. Our results show that by adjusting a parameter within the protocol, a required coverage level of terminals can be specified and achieved without knowledge of the location or density of mobile terminals. Furthermore, we show that the protocol determines the transmission range that is optimal in terms of SINR and power consumption that achieves the required coverage while effectively eliminating the bottleneck that existed at the base station.

In a multihop cellular network, mobile terminals have the capability to transmit directly to other mobile terminals enabling them to use other terminals as relays to forward traffic towards the base station. Previous studies of networks consisting of a single cell found that the SINR in a multihop cellular network is slightly lower than in a traditional cellular network. However, multihop cellular networks may have a higher capacity than traditional cellular networks due to their potential for lower intercell interference. For this reason, the effects of intercell interference are investigated in this thesis. Our simulations of a network with many cells show that multihop cellular networks have a higher SINR than traditional cellular networks due to the near elimination of intercell interference. However, multihop cellular networks still suffer from large amounts of interference surrounding the base station because all traffic either emanates or is destined to the base station making it the capacity bottleneck. To resolve this problem, we propose a novel architecture called the autonomous infrastructure multihop cellular network where users can connect their mobile terminals to the backbone network giving them the functionality of an access point. Access points receive traffic from other terminals and send it directly onto the backbone, as would a base station. This reduces the traffic handled by the base station and increases network capacity. Our analysis and simulations show that in autonomous infrastructure multihop cellular networks, the SINR at the base station is higher, the power consumption is lower and the coverage is better than in normal multihop cellular networks. Access points require parameters like their transmission range to be adjusted autonomously to optimal levels. In this thesis, we propose an autonomous pilot power protocol. Our results show that by adjusting a parameter within the protocol, a required coverage level of terminals can be specified and achieved without knowledge of the location or density of mobile terminals. Furthermore, we show that the protocol determines the transmission range that is optimal in terms of SINR and power consumption that achieves the required coverage while effectively eliminating the bottleneck that existed at the base station.

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