Space time transceiver design over multipath fading channels

Imperial Users onl

Técnicas de cooperação entre estações base para sistemas celulares

Mestrado em Engenharia Electrónica e TelecomunicaçõesA cooperação entre células é uma das áreas de pesquisa em maior crescimento, sendo uma solução promissora para sistemas celulares sem fio, por forma a amenizar a interferência entre as células, melhorar a equidade do sistema e aumentar a capacidade nos anos vindouros. Esta tecnologia já está em estudo no LTE-Advanced sob o conceito de coordenação multiponto (CoOMP). Esta dissertação insere-se na área de comunicações sem fios e tem como principal objectivo, estudar, implementar e avaliar o desempenho de esquemas de cooperação entre estações base, projectados para os futuros sistemas de comunicações móveis de portadora múltipla (OFDM/A). Especificamente, o sistema cooperativo estudado é constituído por duas estações base equipadas com um agregado de antenas, ligadas a uma unidade de processamento central, e dois terminais móveis equipados cada um com apenas uma antena. O sistema referido foi implementado de acordo com as especificações do LTE e avaliado em diversos cenários de propagação. As técnicas desenvolvidas permitem contornar os problemas relacionados com a má qualidade de canal entre emissor e receptor, melhorando o seu desempenho, especificamente ao nível da taxa de erros de transmissão.Multicell cooperation is one of the fastest growing areas of research, and it is a promising solution for cellular wireless systems to mitigate intercell interference, improve system fairness and increase capacity in the years to come. This technology is already under study in LTE-Advanced under the coordinated multipoint (CoOMP) concept. This dissertation is inserted in the wireless communications area, with its main objective being the study, implementation and evaluation of the performance of cooperative schemes between base stations designed for the future mobile communication multiple carrier systems (OFDM/A). Specifically, the cooperative system studied consists of two base stations, each with multiple antenna, connected to a central processing unit, and two mobile terminals, each equipped with only one antenna. The system referred to was implemented in accordance with the specifications of LTE and was tested in various different propagation situations. The developed techniques ensure the mitigation of problems related to interference between the portable terminals namely at the cell edges, improving specifically the bit error rate performance

Signal processing techniques for mobile multimedia systems

Recent trends in wireless communication systems show a significant demand for the delivery of multimedia services and applications over mobile networks - mobile multimedia - like video telephony, multimedia messaging, mobile gaming, interactive and streaming video, etc. However, despite the ongoing development of key communication technologies that support these applications, the communication resources and bandwidth available to wireless/mobile radio systems are often severely limited. It is well known, that these bottlenecks are inherently due to the processing capabilities of mobile transmission systems, and the time-varying nature of wireless channel conditions and propagation environments. Therefore, new ways of processing and transmitting multimedia data over mobile radio channels have become essential which is the principal focus of this thesis. In this work, the performance and suitability of various signal processing techniques and transmission strategies in the application of multimedia data over wireless/mobile radio links are investigated. The proposed transmission systems for multimedia communication employ different data encoding schemes which include source coding in the wavelet domain, transmit diversity coding (space-time coding), and adaptive antenna beamforming (eigenbeamforming). By integrating these techniques into a robust communication system, the quality (SNR, etc) of multimedia signals received on mobile devices is maximised while mitigating the fast fading and multi-path effects of mobile channels. To support the transmission of high data-rate multimedia applications, a well known multi-carrier transmission technology known as Orthogonal Frequency Division Multiplexing (OFDM) has been implemented. As shown in this study, this results in significant performance gains when combined with other signal-processing techniques such as spa ce-time block coding (STBC). To optimise signal transmission, a novel unequal adaptive modulation scheme for the communication of multimedia data over MIMO-OFDM systems has been proposed. In this system, discrete wavelet transform/subband coding is used to compress data into their respective low-frequency and high-frequency components. Unlike traditional methods, however, data representing the low-frequency data are processed and modulated separately as they are more sensitive to the distortion effects of mobile radio channels. To make use of a desirable subchannel state, such that the quality (SNR) of the multimedia data recovered at the receiver is optimized, we employ a lookup matrix-adaptive bit and power allocation (LM-ABPA) algorithm. Apart from improving the spectral efficiency of OFDM, the modified LM-ABPA scheme, sorts and allocates subcarriers with the highest SNR to low-frequency data and the remaining to the least important data. To maintain a target system SNR, the LM-ABPA loading scheme assigns appropriate signal constella tion sizes and transmit power levels (modulation type) across all subcarriers and is adapted to the varying channel conditions such that the average system error-rate (SER/BER) is minimised. When configured for a constant data-rate load, simulation results show significant performance gains over non-adaptive systems. In addition to the above studies, the simulation framework developed in this work is applied to investigate the performance of other signal processing techniques for multimedia communication such as blind channel equalization, and to examine the effectiveness of a secure communication system based on a logistic chaotic generator (LCG) for chaos shift-keying (CSK)