Multicarrier CDMA systems with MIMO technology

The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

Cooperative diversity schemes for wireless communication systems

Mestrado em Engenharia Electrónica e TelecomunicaçõesA presente dissertação insere-se na área das comunicações sem fios, ou mais especificamente na temática da diversidade cooperativa. Neste trabalho é feito o estudo, implementação e avaliação do desempenho de esquemas de diversidade cooperativa de baixa complexidade para sistemas de comunicação móvel. Estes esquemas são mapeados em modelos de simulação baseados em OFDMA e são completamente simulados em CoCentric System Studio. Os resultados obtidos com os modelos desenvolvidos mostram que os esquemas de diversidade cooperativa atenuam os efeitos do desvanecimento induzido pela propagação multipercurso, aumentando desta forma a capacidade e cobertura dos sistemas wireless. Os ganhos são particularmente altos quando as perdas de percurso são consideráveis, como é o caso das zonas urbanas densas. ABSTRACT: This dissertation is inserted into the wireless communication, or more specifically, into the cooperative diversity field. within this thesis, the performance of low-complexity cooperative diversity schemes projected for mobile communication systems are studied, implemented and evaluated. These schemes are mapped into simulation models based on OFDMA and are fully simulated in the CoCentric System Studio environment. The obtained results show that the proposed cooperative schemes for the uplink communication mitigate fading induced by multipath propagation, thereby increasing the capacity and coverage of wireless systems. Cooperation gains are particularly high when multipath losses are considerable, as is the case for dense urban regions

Multi-user MIMO wireless communications

Mehrantennensysteme sind auf Grund der erhöhten Bandbreiteneffizienz und Leistung eine Schlüsselkomponente von Mobilfunksystemen der Zukunft. Diese ermöglichen das gleichzeitige Senden von mehreren, räumlich getrennten Datenströmen zu verschiedenen Nutzern. Die zentrale Fragestellung in der Praxis ist, ob der ursprünglich vorausgesagte Kapazitätsgewinn in realistischen Szenarios erreicht wird und welche spezifischen Gewinne durch zusätzliche Antennen und das Ausnutzen von Kanalkenntnis am Sender und Empfänger erzielt werden, was andererseits einen Zuwachs an Overhead oder nötiger Rechenleistung bedeutet. In dieser Arbeit werden neue lineare und nicht-lineare MU-MIMO Precoding- Verfahren vorgestellt. Der verfolgte Ansatz zur Bestimmung der Precoding- Matrizen ist allgemein anwendbar und die entstandenen Algorithmen können zur Optimierung von verschiedenen Kriterien mit beliebig vielen Antennen an der Mobilstation eingesetzt werden. Das wurde durch die Berechnung der Precoding- Matrix in zwei Schritten erreicht. Im ersten Schritt wird die Überschneidung der Zeilenräume minimiert, die durch die effektiven Kanalmatrizen verschiedener Nutzer aufgespannt werden. Basierend auf mehreren parallelen Einzelnutzer-MIMO- Kanälen wird im zweiten Schritt die Systemperformanz bezüglich bestimmter Kriterien optimiert. Aus der gängigen Literatur ist bereits bekannt, dass für Nutzer mit nur einer Antenne das MMSE Kriterium beim precoding optimal aber nicht bei Nutzern mit mehreren Antennen. Deshalb werden in dieser Arbeit zwei neue Mehrnutzer MIMO Strategien vorgestellt, die vom MSE Kriterium abgeleitet sind, nämlich sukzessives MMSE und RBD. Bei der sukzessiven Verarbeitung mit einer entsprechenden Anpassung der Sendeleistungsverteilung kann die volle Diversität des Systems ausgeschöpft werden. Die Kapazität nähert sich dabei der maximalen Summenrate des Systems an. Bei gemeinsamer Verarbeitung der MIMO Kanäle wird unabhängig vom Grad der Mehrnutzerinterferenz die maximale Diversität erreicht. Die genannten Techniken setzen entweder eine aktuelle oder eine über einen längeren Zeitraum gemittelte Kanalkenntnis voraus. Aus diesem Grund müssen die Auswirkungen von Kanal-Schätzfehlern und Einflüsse des Transceiver Front-Ends auf die Verfahren näher untersucht werden. Für eine weitergehende Abschätzung der Mehrantennensysteme muss die Performanz des Gesamtsystems untersucht werden, da viele Einflüsse auf die räumliche Signalverarbeitung bei Betrachtung eines einzelnen Links nicht erkennbar sind. Es wurde gezeigt, dass mit MIMO Precoding Strategien ein Vielfaches der Datenrate eines Systems mit nur einer Antenne erzielt werden kann, während der Overhead durch Pilotsymbole und Steuersignale nur geringfügig zunimmt.Multiple-input, multiple-output (MIMO) systems are a key component of future wireless communication systems, because of their promising improvement in terms of performance and bandwidth efficiency. An important research topic is the study of multi-user (MU) MIMO systems. Such systems have the potential to combine the high throughput achievable with MIMO processing with the benefits of space division multiple access (SDMA). The main question from a practical standpoint is whether the initially predicted capacity gains can be obtained in more realistic scenarios and what specific gains result from adding more antennas and overhead or computational power to obtain channel state information (CSI) at the transceivers. In this thesis we introduce new linear and non-linear MU MIMO processing techniques. The approach used for the design of the precoding matrix is general and the resulting algorithms can address several optimization criteria with an arbitrary number of antennas at the user terminals (UTs). This is achieved by designing the precoding matrices in two steps. In the first step we minimize the overlap of the row spaces spanned by the effective channel matrices of different users. In the next step, we optimize the system performance with respect to the specific optimization criterion assuming a set of parallel single-user MIMO channels. As it was previously reported in the literature, minimum mean-squared-error (MMSE) processing is optimum for single-antenna UTs. However, MMSE suffers from a performance loss when users are equipped with more than one antenna. The two MU MIMO processing techniques that result from the two different MSE criteria that are proposed in this thesis are successive MMSE and regularized block diagonalization. By iterating the closed form solution with appropriate power loading we are able to extract the full diversity in the system and empirically approach the maximum sum-rate capacity in case of high multi-user interference. Joint processing of MIMO channels yields maximum diversity regardless of the level of multi-user interference. As these techniques rely on the fact that there is either instantaneous or long- term CSI available at the base station to perform precoding and decoding, it was very important to investigate the influence of the transceiver front-end imperfections and channel estimation errors on their performance. For a comprehensive assessment of multi-antenna techniques, it is mandatory to consider the performance at system level, since many effects of spatial processing are not tractable at the link level. System level investigations have shown that MU MIMO precoding techniques provide several times higher data rates than single-input single-output systems with only slightly increased pilot and control overhead

Performance evaluation of OFDM based wireless communication systems using Graphics Processing Unit (GPU) based high performance computing

Wireless communication is one of the fastest developing technologies of current decade. Achieving high data rate under constrained condition demand sophisticated signal processing algorithms which in turn demand complex computational processing. Modern wireless communication techniques using OFDM demand substantial computational resources for implementation. An OFDM system with 2048 subcarriers typically requires a 2048 point IFFT for transmission and 2048 point FFT for reception. When signal processing techniques like PAPR, pre-equalization, equalization, pilot carrier insertion are implemented, the complexity increases considerably. This large complexity demands use of high performance computing systems for efficient implementation. This primary aim of this project was to take up this investigation. Rapid growth in computing and communications technology has led to the proliferation of powerful parallel and distributed computing paradigm leading to innovation in high performance computing and communications (HPCC). In this project, the performance of advanced wireless communication algorithms on Graphics Processing Unit (GPU) based high performance computing hardware has been evaluated. The computationally expensive multi-carrier wireless communication systems along with associated signal processing techniques have been implemented on GPU with an aim to reduce computation time. This project proposes the use of GPU architecture for efficient implementation of Long Term Evolution (LTE) Physical Layer, Multiple Input Multiple Output (MIMO) OFDM system and Partial Transmit sequence (PTS) technique for Peak-to-Average Power Ratio (PAPR) reduction in OFDM system. The implementation of this new method is expected to provide promising ways to implement complex wireless communication systems using GPU based computing hardware

LTE performance study

Long Term Evolution (LTE) has been designed with new architecture and features to meet user’s high data rates demand for a longer term in the future. 3rd Generation Part-nership Project (3GPP) has set the goals and targets for LTE with better performance and data rates close to fixed networks. In this thesis outdoor measurements have been conducted in three different environ-ments macro/rural, urban and suburban. This thesis study has been done with single user measurements and performance analysis scenario. The idea of measurements was to analyze LTE performance in three different types of environments. Performance analysis has been done using few key performance indicators and parameters including RSRP, RS SNR, MAC downlink throughput, timing advance and CQI. Vendor/operator specific key performance indicators and parameters were unknown. The results and analysis of this thesis give an idea about LTE performance in three dif-ferent outdoor environments. The output of this thesis study can be beneficial in under-standing LTE behavior and performance in different environments, which can be further useful in planning and deployment phases for LTE

Técnicas de processamento com múltiplas antenas para o sistema LTE

Mestrado em Engenharia Electrónica e TelecomunicaçõesPerformance, mobilidade e partilha podem ser consideras como as três palavras-chave nas comunicações móveis de hoje em dia. Uma das necessidades fundamentais do ser humano é a partilha de experiencias e informação. Com a evolução ao nível do hardware móvel, a crescente popularidade de smartphones, tablets e outros dispositivos moveis, fez com que a exigência em termos de capacidade e taxa de transferência por parte das redes móveis não parasse de crescer. As limitações das redes 3G fizeram com que não conseguissem corresponder a tais exigências e como tal, a transição para uma tecnologia mais robusta e eficiente passou a ser inevitável. A resposta escolhida como solução a longo prazo é a rede designada por LTE, desenvolvida pela organização 3GPP é assumido que será a rede de telecomunicações predominante no futuro. As vantagens mais sonantes são, naturalmente, elevadas taxas de transmissão, maior eficiência espectral, redução da latência e de custos de operação. As principais tecnologias em que o LTE se baseia, são o OFDM e sua variante para múltiplo acesso, OFDMA, usado para o downlink e o SC-FDMA para o uplink. Além disso, usa sistemas com múltiplas antenas para impulsionar a eficiência espectral. Apesar de já implementado em alguns países por diversas operadoras, constantes pesquisas continuam a ser realizadas com o intuito de melhorar a sua performance. Nesta dissertação é proposto um esquema duplo de codificação na frequência e no espaço (D-SFBC) para um cenário baseado em OFDM com 4 antenas de transmissão e duas antenas de recepção (4 × 2 D-SFBC) para o downlink. No cenário considerado, 4 símbolos de dados são transmitidos utilizando unicamente 2 sub-portadoras, fazendo com que, este sistema seja limitado pela interferência. Para de forma eficiente descodificar os símbolos de dados transmitidos, foi desenvolvido um equalizador iterativo no domínio da frequência. Duas abordagens são consideradas: cancelamento da interferência em paralelo (PIC) e sucessivo cancelamento de interferência (SIC). Uma vez que apenas 2 sub-portadoras são usadas para transmitir quatro símbolos de dados em paralelo, o esquema desenvolvido duplica a taxa de dados quando comparado com o esquema 2 × 2 SFBC, especificado no standard do LTE. Os esquemas desenvolvidos foram avaliados sob as especificações para LTE e usando codificação de canal. Os resultados mostram que os esquemas implementados neste trabalho utilizando um equalizador iterativo supera os convencionais equalizadores lineares na eliminação da interferência adicional introduzida, em apenas 2 ou 3 iterações.Performance, mobility and sharing can be assumed as the three keywords in the mobile communications nowadays. One of the fundamental needs of human beings is to share experiences and information. With the evolution of mobile hardware level, the growing popularity of smartphones, tablets and other mobile devices, has made that the demand in terms of capacity and throughput by mobile networks did not stop growing. Thus, the limitations of 3G stops it of being the answer of such demand, and a transition to a powerful technology has become unavoidable. The answer chosen is LTE, developed by the 3GPP organization is assumed to be the predominant telecommunications network in the future. The most relevant advantages are high transmission rates, higher spectral efficiency, reducing latency and operating costs. The key technologies in which LTE is based, are OFDM and its variant schemes for multiple access, OFDMA, used for downlink, and SC-FDMA for the uplink. It also uses multiple antennas systems in order to improve spectral efficiency. Although already implemented in some countries by several operators, continuous research is conducted in order to improve their performance. In this dissertation it is proposed a double space-frequency block coding (D-SFBC) scheme for an OFDM based scenario with 4 transmit antennas and 2 receive antennas (4×2 D-SFBC) for the downlink. In the considered scenario, 4 data symbols are transmitted by using only 2 subcarriers and thus the system is interference limited. To efficiently decode the transmitted data symbols an iterative equalizer designed in frequency domain is developed. Two approaches are considered: parallel interference cancellation (PIC) and successive interference cancellation (SIC). Since only 2 subcarriers are used to transmit 4 data symbols in parallel the developed scheme achieve the double data rate when compared with the 2×2 SFBC, specified in the LTE standard. The developed schemes were evaluated under the main LTE specifications and using channel coding. The results have show that the schemes implemented in this work using an interactive equalizer outperforms the conventional linear equalizers in the interference removal, just by using 2 or 3 iterations