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[pt] Este trabalho considera o uso de um protocolo determinístico de acesso ao meio para transmissão eficiente de tráfegos assimétricos, através de um modo de operação TDD. Este modo é uma das opções selecionadas para adoção em sistemas celulares de terceira geração. São apresentados e analisados diferentes protocolos de acesso ao meio sendo um destes escolhido para ser implementado e ter o seu desempenho estudado. Diferentes modelos estatísticos para diversos tipos de tráfego assimétricos são considerados. Em seguida são discutidos os conceitos de qualidade de serviço (QoS) e os parâmetros que devem ser controlados.Continuando o trabalho são analisados detalhadamente: o protocolo escolhido, a maneira como este foi adaptado para aquele modo de operação e as medidas de desempenho que devem ser realizadas. Finalmente os resultados para cada tipo de tráfego individualmente e em conjunto são apresentados. / [en] This work has the objective of adapting a deterministic access protocol to the TDD mode of operation adopted as one of the third generation technologies in order to provide transmission of asymmetric traffic in a more efficient way. Different access methods are presented and analyzed and one of them is selected to be simulated and have its performance verified. Realistic asymmetric traffic models are discussed and actually implemented. Minimum requirements for Quality of Service for different traffics considered are introduced. The Quality of Service analysis made is focused on the minimum requirements of those traffic models. Detailed analysis of the chosen protocol is made in addition to its adaptation to the proposed situation. Finally, the results are presented showing the response of the protocol to each one of the traffic models considered and also to the situation when they are present simultaneously.

One of the most important components of any wireless network is the medium access control protocol. This research deals with wireless ATM (WATM) medium access control (MAC) protocol. Conventional studies concerning WATM have focused mainly on variations of the time-division-multiple-access (TDMA) method for the wireless aspect of WATM networks. However, there are many advantages that the direct-sequence code-division-multiple-access (DS-CDMA) air-interface method has, such as inherent robustness against multipath fading, better resilience against security infringement attempts, and greater overall capacity compared to the TDMA method as proven in the cellular telephone industry. The main reason behind the relatively broader support for the TDMA method is that the source bit rate is generally higher compared to the DS-CDMA method since the maximum data rate per mobile unit is limited by the processing gain of a traditional DS-CDMA method. In this research, the problem of limited data rate often associated with a DS-CDMA air-interface is alleviated by employing the recently conceived multi-coded DS-CDMA as the primary air-interface, which is known to achieve maximum data rate per mobile unit comparable to applications employing TDMA. The focus of this research is on overcoming periods of significant deterioration of the wireless channel by adaptively employing bit combining. A MAC protocol called Adaptive Parallel Multiple Sub-stream CDMA (APMS-CDMA) is proposed to alternate between normal and ¡°rake-in¡± mode to deal with the often hostile environment of a WATM network. Although the context in which this research effort was conducted was a wireless ATM network environment, the protocol and techniques developed here can be applied to other infrastructure wireless systems using multi-code CDMA as their air-interface. Further, independent of the air-interface technique employed, other wireless systems can benefit from the channel estimation and the traffic management techniques used in this research effort. / Ph. D.

[pt] Neste trabalho realizamos um estudo sobre a capacidade de tráfego em sistemas CDMA para comunicações móveis celulares, com ênfase na capacidade segundo a metodologia de Erlang. É feita inicialmente uma breve análise da capacidade de sistemas celulares tradicionais FDMA/TDMA para efeitos de comparação. Em seguida procuramos fazer uma análise básica da capacidade de tráfego em sistemas CDMA, reunindo os modelos e resultados de diversos trabalhos encontrados na literatura. Para finalizar nós verificamos o efeito de diversos aspectos de sistemas CDMA na capacidade do sistema, aspectos estes cujas análises detalhadas não são encontradas na literatura, como a limitação no número de canais, a possibilidade de uma fila de espera, o comportamento temporal da interferência, o aumento de capacidade realmente obtido com setorização e o efeito do soft-handoff na capacidade. / [en] In this work we present an investigation on the traffic capacity of CDMA systems for cellular mobile communication, with emphasis on the Erlang capacity. It is mitially made a brief analysis of the capacity in traditional FDMA/TDMA cellular systems. We then present a basic analysis of the traffic capacity in CDMA systems, assembling the models and results from several works found in the literature. Finally, we investigate the effect in the system capacity of several aspects of CDMA systems, that had not been previously addressed. We have thoroughly examinated the limitation in the number of available channels, the possibility of a waiting queue, the temporal behaviour of the interference, the actual increase in capacity obtained through sectorization and the effect of soft-handoff in the capacity.

Wideband Code Division Multiple Access (WCDMA) is one of the main technologies for the implementation of third-generation (3G) cellular systems. It is based on radio access technique proposed by ETSI Alpha group and the specifications was finalised 1999. WCDMA is also known as UMTS and has been adopted as a standard by the ITU under the name “IMT-2000 direct spread”. The implementation of WCDMA will be a technical challenge because of its complexity and versatility. The complexity of WCDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. In WCDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. WCDMA increases data transmission rates in GSM systems by using the CDMA air interface instead of TDMA. WCDMA is based on CDMA and is the technology used in UMTS. WCDMA is the dominating 3G technology, providing higher capacity for voice and data and higher data rates. The gradual evolution from today's systems is driven by demand for capacity, which is required by new and faster data based mobile services. WCDMA enables better use of available spectrum and more cost-efficient network solutions. The operator can gradually evolve from GSM to WCDMA, protecting investments by re-using the GSM core network and 2G/2.5G services. Orthogonal Frequency Division Multiplexing (OFDM) - technique for increasing the amount of information that can be carried over a wireless network uses an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. 802.11a WLAN, 802.16 and WiMAX technologies use OFDM. It's also used in the ETSI's HiperLAN/2 standard. In addition, Japan's Mobile Multimedia Access Communications (MMAC) WLAN broadband mobile technology uses OFDM. In frequency-division multiplexing, multiple signals, or carriers, are sent simultaneously over different frequencies between two points. However, FDM has an inherent problem: Wireless signals can travel multiple paths from transmitter to receiver (by bouncing off buildings, mountains and even passing airplanes); receivers can have trouble sorting all the resulting data out. Orthogonal FDM deals with this multipath problem by splitting carriers into smaller subcarriers, and then broadcasting those simultaneously. This reduces multipath distortion and reduces RF interference allowing for greater throughput. In this paper we have discussed about these two methods of third generation radio transmission system which are WCDMA and OFDM with various aspects. In between these two radio transmission technique, a better choice will be investigated.

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.

In the direct sequence-code division multiple access (DS-CDMA) system, which uses direct sequence spread spectrum (DSSS) technique to perform multiple-access, the major limitation of the system capacity is the capability of interference rejection. In this system, multiuser receivers usually divided into two groups, the first group is called the ¡§centralized receiver,¡¨ because it must know the information of total users, including the spreading sequence of each user, channel response, etc. Due to the complexity of computation, this kind of receivers is suitable for the base station. The second group is called the ¡§decentralized receiver,¡¨ because it only needs to know the information of desired user, therefore, it is very suitable for mobile station. The decentralized receiver can be further separate into two kinds: data-aided and non-data-aided receivers. Usually, the non-data-aided receiver is also called the blind receiver; our proposed interference cancellator belongs to this blind one. This thesis mainly discusses the performance of our proposed interference cancellator in different conditions. There is a novel interference detector which can efficiently detect strong interferers in our proposed interference cancellator. When strong interferers exist, the received signal will be passed through the interference-blocking transformer, which exploits the subspace approach to block strong interference. After interference cancelled, conventional de-spreading technique is used to obtain the desired data. In this thesis, besides the complete mathematical analysis of our proposed interference cancellator, computer simulations are also used to observe its performance behavior in different conditions. The simulation results exhibit that this interference cancellator has good performance in different conditions, and due to have the property of low complexity, our proposed interference cancellator is very suitable for the mobile station. Finally, we make a conclusion for this blind interference cancellator, and expect to realize a mature multiuser receiver based on this technique in the future.

Intersymbol interference(ISI) is an important factor which affects the performance of communication systems. To achieve highspeed digital transmission and reliable communication, an equalizer can effectively eliminate ISI caused by band-limited channel or multipath. In this paper, we introduce an adaptive H¡Û equalizing algorithm. Different form conventional recursive least square filtering algorithm, the adaptive H¡Û filtering algorithm is a worst case optimization. It can minimize the effect of the worst disturbances (including input noise and modeling error) on the equalization error. It has been proven that the adaptive H¡Û filtering algorithm has the advantage of reduction of sensitivity to modeling error and suitability for arbitrary ambient noise over RLS algorithm. However, the computational burden of the H¡Û algorithm is enormous. To reduce the computational complexity, the subweight partition technique is employed to the H¡Û algorithm. Computer simulation also shows that the H¡Û algorithm can reduce the dynamic estimation error resulting from subweight partition. Finally, in order to overcome multiple access interference, interchip interference, time-varying effects from the channel and computational complexity, the H¡Û algorithm with subweight partition (termed H¡Û-based) is then further extended to the multiuser detection in code division multiple access (CDMA) system. Simulation results are presented to demonstrate the advantage of the H¡Û-based equalizing algorithm.

In mobile radio systems, the bandwidth of spread spectrum signals for CDMA system is very wide. If the bandwidth exceeds the coherence bandwidth of the channel, the signal is seriously distorted by the multiple propagation paths. The available bandwidth is divided into a lot of small parts in Multi-carrier-CDMA system. Selecting the number of subcarriers according to the environment of channel will make the bandwidth of spread spectrum signals smaller than the coherence bandwidth of channel. And then the system can overcome the question of multiple propagation paths. The performance of Multi-carrier CDMA system is sensitive to frequency offset. Frequency offset results from Doppler shift due to mobile movement, as well as from a mismatch between the carrier frequency of local oscillators at the transmitter and receiver. Consequently, the subcarriers¡¦ orthogonality are lost, causing Inter-carrier Interference (ICI). The interference of other subcarriers will make the error of estimated channel coefficients. Effect of frequency offset will lower the performance of the combing detector that needing channel estimated. In this thesis, we propose a method to correct the frequency offset. Using the relation of two continuous received signals to estimate the frequency and compensate it. We will analysis and compare this method in different condition. Simulation results will demonstrate the performance of this proposed method.

In this thesis, an improved genetic algorithm (GA) for multi-user detectors is investigated in synchronous and asynchronous DS-CDMA systems. Although the embedded GA and multistage detector (E-GA/MSD) can also improve the conventional GA performance for multiuser detection, the MSD incurs high computational consumption when the users are growing. To eliminate the MSD operation at each generation, an improved GA with adjustable parent size and enlarged sampling space is developed. The proposed GA with much less complexity can achieve almost the same BER performance as the E-GA/MSD. Simulation results demonstrate that the proposed GA is near to an optimum detector. Additionally, we apply the proposed GA to a spatial diversity reception assisted multiuser detector over uncorrelated flat Rayleigh fading channels in synchronous CDMA systems. As expected, computer simulations also show that the proposed GA can achieve the lower BER performance than conventional GA.