Transmission strategies for broadband wireless systems with MMSE turbo equalization

This monograph details efficient transmission strategies for single-carrier wireless broadband communication systems employing iterative (turbo) equalization. In particular, the first part focuses on the design and analysis of low complexity and robust MMSE-based turbo equalizers operating in the frequency domain. Accordingly, several novel receiver schemes are presented which improve the convergence properties and error performance over the existing turbo equalizers. The second part discusses concepts and algorithms that aim to increase the power and spectral efficiency of the communication system by efficiently exploiting the available resources at the transmitter side based upon the channel conditions. The challenging issue encountered in this context is how the transmission rate and power can be optimized, while a specific convergence constraint of the turbo equalizer is guaranteed.Die vorliegende Arbeit beschäftigt sich mit dem Entwurf und der Analyse von effizienten Übertragungs-konzepten für drahtlose, breitbandige Einträger-Kommunikationssysteme mit iterativer (Turbo-) Entzerrung und Kanaldekodierung. Dies beinhaltet einerseits die Entwicklung von empfängerseitigen Frequenzbereichs-entzerrern mit geringer Komplexität basierend auf dem Prinzip der Soft Interference Cancellation Minimum-Mean Squared-Error (SC-MMSE) Filterung und andererseits den Entwurf von senderseitigen Algorithmen, die durch Ausnutzung von Kanalzustandsinformationen die Bandbreiten- und Leistungseffizienz in Ein- und Mehrnutzersystemen mit Mehrfachantennen (sog. Multiple-Input Multiple-Output (MIMO)) verbessern. Im ersten Teil dieser Arbeit wird ein allgemeiner Ansatz für Verfahren zur Turbo-Entzerrung nach dem Prinzip der linearen MMSE-Schätzung, der nichtlinearen MMSE-Schätzung sowie der kombinierten MMSE- und Maximum-a-Posteriori (MAP)-Schätzung vorgestellt. In diesem Zusammenhang werden zwei neue Empfängerkonzepte, die eine Steigerung der Leistungsfähigkeit und Verbesserung der Konvergenz in Bezug auf existierende SC-MMSE Turbo-Entzerrer in verschiedenen Kanalumgebungen erzielen, eingeführt. Der erste Empfänger - PDA SC-MMSE - stellt eine Kombination aus dem Probabilistic-Data-Association (PDA) Ansatz und dem bekannten SC-MMSE Entzerrer dar. Im Gegensatz zum SC-MMSE nutzt der PDA SC-MMSE eine interne Entscheidungsrückführung, so dass zur Unterdrückung von Interferenzen neben den a priori Informationen der Kanaldekodierung auch weiche Entscheidungen der vorherigen Detektions-schritte berücksichtigt werden. Durch die zusätzlich interne Entscheidungsrückführung erzielt der PDA SC-MMSE einen wesentlichen Gewinn an Performance in räumlich unkorrelierten MIMO-Kanälen gegenüber dem SC-MMSE, ohne dabei die Komplexität des Entzerrers wesentlich zu erhöhen. Der zweite Empfänger - hybrid SC-MMSE - bildet eine Verknüpfung von gruppenbasierter SC-MMSE Frequenzbereichsfilterung und MAP-Detektion. Dieser Empfänger besitzt eine skalierbare Berechnungskomplexität und weist eine hohe Robustheit gegenüber räumlichen Korrelationen in MIMO-Kanälen auf. Die numerischen Ergebnisse von Simulationen basierend auf Messungen mit einem Channel-Sounder in Mehrnutzerkanälen mit starken räumlichen Korrelationen zeigen eindrucksvoll die Überlegenheit des hybriden SC-MMSE-Ansatzes gegenüber dem konventionellen SC-MMSE-basiertem Empfänger. Im zweiten Teil wird der Einfluss von System- und Kanalmodellparametern auf die Konvergenzeigenschaften der vorgestellten iterativen Empfänger mit Hilfe sogenannter Korrelationsdiagramme untersucht. Durch semi-analytische Berechnungen der Entzerrer- und Kanaldecoder-Korrelationsfunktionen wird eine einfache Berechnungsvorschrift zur Vorhersage der Bitfehlerwahrscheinlichkeit von SC-MMSE und PDA SC-MMSE Turbo Entzerrern für MIMO-Fadingkanäle entwickelt. Des Weiteren werden zwei Fehlerschranken für die Ausfallwahrscheinlichkeit der Empfänger vorgestellt. Die semi-analytische Methode und die abgeleiteten Fehlerschranken ermöglichen eine aufwandsgeringe Abschätzung sowie Optimierung der Leistungsfähigkeit des iterativen Systems. Im dritten und abschließenden Teil werden Strategien zur Raten- und Leistungszuweisung in Kommunikationssystemen mit konventionellen iterativen SC-MMSE Empfängern untersucht. Zunächst wird das Problem der Maximierung der instantanen Summendatenrate unter der Berücksichtigung der Konvergenz des iterativen Empfängers für einen Zweinutzerkanal mit fester Leistungsallokation betrachtet. Mit Hilfe des Flächentheorems von Extrinsic-Information-Transfer (EXIT)-Funktionen wird eine obere Schranke für die erreichbare Ratenregion hergeleitet. Auf Grundlage dieser Schranke wird ein einfacher Algorithmus entwickelt, der für jeden Nutzer aus einer Menge von vorgegebenen Kanalcodes mit verschiedenen Codierraten denjenigen auswählt, der den instantanen Datendurchsatz des Mehrnutzersystems verbessert. Neben der instantanen Ratenzuweisung wird auch ein ausfallbasierter Ansatz zur Ratenzuweisung entwickelt. Hierbei erfolgt die Auswahl der Kanalcodes für die Nutzer unter Berücksichtigung der Einhaltung einer bestimmten Ausfallwahrscheinlichkeit (outage probability) des iterativen Empfängers. Des Weiteren wird ein neues Entwurfskriterium für irreguläre Faltungscodes hergeleitet, das die Ausfallwahrscheinlichkeit von Turbo SC-MMSE Systemen verringert und somit die Zuverlässigkeit der Datenübertragung erhöht. Eine Reihe von Simulationsergebnissen von Kapazitäts- und Durchsatzberechnungen werden vorgestellt, die die Wirksamkeit der vorgeschlagenen Algorithmen und Optimierungsverfahren in Mehrnutzerkanälen belegen. Abschließend werden außerdem verschiedene Maßnahmen zur Minimierung der Sendeleistung in Einnutzersystemen mit senderseitiger Singular-Value-Decomposition (SVD)-basierter Vorcodierung untersucht. Es wird gezeigt, dass eine Methode, welche die Leistungspegel des Senders hinsichtlich der Bitfehlerrate des iterativen Empfängers optimiert, den konventionellen Verfahren zur Leistungszuweisung überlegen ist

Single- versus Multi-Carrier Terahertz-Band Communications: A Comparative Study

The prospects of utilizing single-carrier (SC) and multi-carrier (MC) waveforms in future terahertz (THz)-band communication systems remain unresolved. On the one hand, the limited multi-path components at high frequencies result in frequency-flat channels that favor low-complexity wideband SC systems. On the other hand, frequency-dependent molecular absorption and transceiver characteristics and the existence of multi-path components in indoor sub-THz systems can still result in frequency-selective channels, favoring off-the-shelf MC schemes such as orthogonal frequency-division multiplexing (OFDM). Variations of SC/MC designs result in different THz spectrum utilization, but spectral efficiency is not the primary concern with substantial available bandwidths; baseband complexity, power efficiency, and hardware impairment constraints are predominant. This paper presents a comprehensive study of SC/MC modulations for THz communications, utilizing an accurate wideband THz channel model and highlighting the various performance and complexity trade-offs of the candidate schemes. Simulations demonstrate that discrete-Fourier-transform spread orthogonal time-frequency space (DFT-s-OTFS) achieves a lower peak-to-average power ratio (PAPR) than OFDM and OTFS and enhances immunity to THz impairments and Doppler spreads, but at an increased complexity cost. Moreover, DFT-s-OFDM is a promising candidate that increases robustness to THz impairments and phase noise (PHN) at a low PAPR and overall complexity.Comment: 18 pages, 12 figures, journa

Técnicas de igualização adaptativas com estimativas imperfeitas do canal para os futuros sistemas 5G

Wireless communication networks have been continuously experiencing an exponential growth since their inception. The overwhelming demand for high data rates, support of a large number of users while mitigating disruptive interference are the constant research focus and it has led to the creation of new technologies and efficient techniques. Orthogonal frequency division multiplexing (OFDM) is the most common example of a technology that has come to the fore in this past decade as it provided a simple and generally ideal platform for wireless data transmission. It’s drawback of a rather high peak-to-average power ratio (PAPR) and sensitivity to phase noise, which in turn led to the adoption of alternative techniques, such as the single carrier systems with frequency domain equalization (SC-FDE) or the multi carrier systems with code division multiple access (MC-CDMA), but the nonlinear Frequency Domain Equalizers (FDE) have been of special note due to their improved performance. From these, the Iterative Block Decision Feedback Equalizer (IB-DFE) has proven itself especially promising due to its compatibility with space diversity, MIMO systems and CDMA schemes. However, the IB-DFE requires the system to have constant knowledge of the communication channel properties, that is, to have constantly perfect Channel State Information (CSI), which is both unrealistic and impractical to implement. In this dissertation we shall design an altered IB-DFE receiver that is able to properly detect signals from SC-FDMA based transmitters, even with constantly erroneous channel states. The results shall demonstrate that the proposed equalization scheme is robust to imperfect CSI (I-CSI) situations, since its performance is constantly close to the perfect CSI case, within just a few iterations.Redes sem fios têm crescido de maneira contínua e exponencial desde a sua incepção. A tremenda exigência para altas taxas de dados e o suporte para um elevado número de utilizadores sem aumentar a interferência disruptiva originada por estes são alguns dos focos que levaram ao desenvolvimento de técnicas de compensação e novas tecnologias. “Orthogonal frequency division multiplexing” (OFDM) é um dos exemplos de tecnologias que se destacaram nesta última década, visto ter fornecido uma plataforma para transmissão de dados sem-fio eficaz e simples. O seu maior problema é a alta “peak-to-average power ratio” (PAPR) e a sua sensibilidade a ruído de fase que deram motivo à adoção de técnicas alternativas, tais como os sistemas “single carrier” com “frequency domain equalization” (SC-FDE) ou os sistemas “multi-carrier” com “code division multiple access” (MC-CDMA), mas equalizadores não lineares no domínio de frequência têm sido alvo de especial atenção devido ao seu melhor desempenho. Destes, o “iterative block decision feedback equalizer” (IB-DFE) tem-se provado especialmente promissor devido à sua compatibilidade com técnicas de diversidade no espaço, sistemas MIMO e esquemas CDMA. No entanto, IB-DFE requer que o sistema tenha constante conhecimento das propriedades dos canais usados, ou seja, necessita de ter perfeito “channel state information” (CSI) constantemente, o que é tanto irrealista como impossível de implementar. Nesta dissertação iremos projetar um recetor IB-DFE alterado de forma a conseguir detetar sinais dum transmissor baseado em tecnologia SC-FDMA, mesmo com a informação de estado de canal errada. Os resultados irão então demonstrar que o novo esquema de equalização proposto é robusto para situações de CSI imperfeito (I-CSI), visto que o seu desempenho se mantém próximo dos valores esperados para CSI perfeito, em apenas algumas iterações.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Multi-carrier transmission techniques toward flexible and efficient wireless communication systems

制度:新 ; 文部省報告番号:甲2562号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2008/3/15 ; 早大学位記番号:新470

Towards a new cloud-based planning and optimization methodology for mobile communication networks

The great concern of telecommunication operators to offer high-quality services to their customers requires a constant care with the state of the networks. These networks can present some problems that imply that the experience offered to customers is unsatisfactory. In order to monitor these situations, operators collect, on a fairly regular basis, data, like drive tests, that allow them to monitor and correct minor issues. This thesis takes advantage of the data collected and uses it in network planning in order to precisely obtain the coverage estimation of a network. In order to automate failure correction mechanisms, a totally automatic propagation model is presented, which precisely describes the state of the network, allowing it to be used for network planning and optimisation. After its implementation, the model was compared to a second model, generated through Artificial Intelligence, which is completely agnostic to all telecommunications knowledge. These models, for the considered scenarios, reached average absolute errors between estimated and actual values of 6.1 dB with a standard deviation of 4 dB. The existence of several real telecommunication network measures and their evolution to Multiple Input, Multiple Output (MIMO) systems motivated not only the investigation on the coverage impact with the change from a Single Input, Single Output (SISO) to a MIMO system, but also the investigation on the reduction of complexity of the receivers used in MIMO systems. The closer the Bit Error Rate performance of the receiver is to the Matched Filter Bound, the smaller will be the reduction in the coverage area with the transition from a SISO system to a MIMO system.A grande preocupação dos operadores de telecomunicações em oferecerem serviços de alta qualidade aos seus clientes leva a um constante cuidado com o estado das redes. Estas redes podem apresentar alguns problemas que implicam que a experiência oferecida aos clientes seja desagradável. De forma a monitorizar estas situações, os operadores recolhem, com bastante regularidade, dados, como "drive tests", que lhes permitem avaliar e corrigir pequenos problemas. Esta tese aproveita os dados recolhidos e utiliza-os no planeamento da rede de forma a obter fielmente a estimativa de cobertura de uma rede. De forma a automatizar mecanismos de correção de falhas, é apresentado um modelo de propagação completamente automático, que descreve de forma precisa o estado da rede permitindo que seja aplicado em algoritmos de planeamento e otimização da rede. Após a sua implementação, este modelo foi comparado com um segundo modelo, gerado através de inteligência artificial, que é completamente agnóstico a todo o conhecimento de telecomunicações. Estes modelos, para os cenários estudados, atingiram erros absolutos médios entre os valores estimados e os valores reais de 6.1 dB com um desvio padrão de 4 dB. A existência de diversos dados reais das redes de telecomunicações e a evolução para os sistemas "Multiple Input", "Multiple Output" (MIMO) motivou não só a investigação no impacto da cobertura com a mudança de um sistema "Single Input", "Single Output" (SISO) para um sistema MIMO, mas também a investigação na redução de complexidade dos recetores utilizados em sistemas MIMO. Quanto mais próxima a "Bit Error Rate performance" do recetor estiver do "Matched Filter Bound", menor será a redução na área de cobertura com a transição de um sistema SISO para um sistema MIMO

A hybrid-structure offset-QAM filter-bank multi-carrier MIMO system

Offset quadrature amplitude modulation (OQAM) filter-bank multi-carrier (FBMC), has great potential for boosting the spectral efficiency (SE) and energy efficiency (EE) of future communication systems. This is due to its superior spectral localization, CP-less transmission and relaxed synchronization requirements. Our research focuses on three main OQAM/FBMC research problems: the computational complexity reduction taking equalization into consideration, its integration with multiple-input multiple-output (MIMO) and its high peak-to-average power ratio (PAPR). OQAM/FBMC systems are mainly implemented either using frequency spreading (FS) or polyphase network (PPN) techniques. The PPN technique is generally less complex, but when using frequency domain equalization (FDE) to equalize multipath channel effects at the receiver, there is a computational complexity overhead when using PPN. A novel hybrid-structure OQAM/FBMC MIMO space-frequency block coding (SFBC) system is proposed, to achieve the lowest possible overall complexity in conjunction with FDE at the receiver in frequency selective Rayleigh fading channel. The Alamouti SFBC block coding is performed on the complex-orthogonal signal before OQAM processing, which resolves the problems of intrinsic interference when integrating OQAM/FBMC with MIMO. In better multipath channel conditions with a line-of-sight (LOS) path, a zero-forcing (ZF) time domain equalization (TDE) is exploited to further reduce the computational complexity with comparable performance bit-error-rate (BER). On the other hand, to tackle the high PAPR problem of the OQAM/FBMC system in the uplink, a novel single carrier (SC)-OQAM/FBMC MIMO system is proposed. The system uses DFT-spreading applied to the OQAM modulated signal, along with interleaved subcarrier mapping to significantly reduce the PAPR and enhance the BER performance over Rayleigh fading channels, with relatively low additional computational complexity compared to the original complexity of the FBMC system and compared to other FBMC PAPR reduction techniques.The proposed hybrid-structure system has shown significant BER performance in frequency-selective Rayleigh fading channels compared to OFDM, with significantly lower OOB emissions in addition to the enhanced SE due to the absence of CP. In mild multipath fading channels with a LOS component, the PPN OQAM/FBMC MIMO using TDE has a comparable BER performance with significantly less computational complexity. As for the uplink, the SC-OQAM/FBMC MIMO system significantly reduces the PAPR and enhances the BER performance, with relatively low additional computational complexity