175 research outputs found

    Mitigating PAPR in cooperative wireless networks with frequency selective channels and relay selection

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    The focus of this thesis is peak-to-average power ratio (PAPR) reduction in cooperative wireless networks which exploit orthogonal frequency division multiplexing in transmission. To reduce the PAPR clipping is employed at the source node. The first contribution focuses upon an amplify-and-forward (AF) type network with four relay nodes which exploits distributed closed loop extended orthogonal space frequency block coding to improve end-to-end performance. Oversampling and filtering are used at the source node to reduce out-of-band interference and the iterative amplitude reconstruction decoding technique is used at the destination node to mitigate in-band distortion which is introduced by the clipping process. In addition, by exploiting quantized group feedback and phase rotation at two of the relay nodes, the system achieves full cooperative diversity in addition to array gain. The second contribution area is outage probability analysis in the context of multi-relay selection in a cooperative AF network with frequency selective fading channels. The gains of time domain multi-path fading channels with L paths are modeled with an Erlang distribution. General closed form expressions for the lower and upper bounds of outage probability are derived for arbitrary channel length L as a function of end-to-end signal to noise ratio. This analysis is then extended for the case when single relay selection from an arbitrary number of relay nodes M is performed. The spatial and temporal cooperative diversity gain is then analysed. In addition, exact form of outage probability for multi-path channel length L = 2 and selecting the best single relay from an arbitrary number of relay nodes M is obtained. Moreover, selecting a pair of relays when L = 2 or 3 is additionally analysed. Finally, the third contribution context is outage probability analysis of a cooperative AF network with single and two relay pair selection from M available relay nodes together with clipping at the source node, which is explicitly modelled. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of algorithms and methods

    Predictive resource allocation for URLLC using empirical mode decomposition

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    Abstract. Empirical mode decomposition (EMD) based hybrid prediction methods can be an efficient way to allocate resources for ultra reliable low latency communication (URLLC). In this thesis, we have considered efficient resource allocation for the downlink channel at the presence of several interferers. Initially, we have generated desired signal that we need to transmit in downlink and total interference signal that will affect the desired signal transmission. Then, we used EMD to decompose the total interference signal power into intrinsic mode functions (IMFs) and residual. Due to the properties of EMD, decomposed IMFs become less random as IMF number increases. As a result of that property, prediction model training process become less complex and prediction accuracy also increases as randomness of signal decreases. Long short term memory (LSTM) deep neural network method and auto regressive integrated moving average (ARIMA) time series method are deployed to predict future interference power values based on historical values. For each decomposed component (IMFs and residual), two prediction models have been trained using LSTM and ARIMA methods. Finally, predicted components of IMFs and residual are added together to form total predicted interference power. According to the predicted interference power, resources are allocated for downlink transmission of the signal and evaluated it with the baseline estimation techniques. The research demonstrates that the suggested method achieves near optimal resource allocation for URLLC

    Space-Time Codes for MIMO systems : Quasi-Orthogonal design and concatenation

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    Der Nachfrage an Mobilfunksystemen mit hoher Datenrate und ÜbertragungsqualitĂ€t fĂŒr eine Vielfalt von Anwendungen ist in den letzten Jahren dramatisch gestiegen. Zur Deckung des hohen Bedarfs werden jedoch neue Konzepte und Technologien benötigt, die den BeeintrĂ€chtigungen des Mobilfunkkanals entgegenwirken oder sich diese zu Nutze machen und die knappen Ressourcen wie Bandbreite und Leistung optimal ausnutzen. Eine effiziente Maßnahme zur Erhöhung der Performanz stellen Mehrantennensysteme dar. Um das große Potenzial von solchen Mehrantennensystemen auszunutzen, wurden neue Sendestrategien, so genannte Raum-Zeit Codes entworfen und analysiert, die neben der zeitlichen und spektralen auch die rĂ€umliche Komponente ausnutzen sollen. In dieser Arbeit wird die LeistungsfĂ€higkeit solcher Raum-Zeit Codes zunĂ€chst isoliert und spĂ€ter, im zweiten Teil der Arbeit, in Kombination mit herkömmlichen Kanalcodierungsverfahren untersucht. Im ersten Abschnitt, d.h. im Fall ohne herkömmliche Kanalcodierung liegt der Fokus auf diversitĂ€ts-orientierten Raum-Zeit Codes. ZunĂ€chst werden basierend auf den Raum-Zeit Codes mit orthogonaler Struktur (OSTBC) Raum-Zeit Codes mit quasi-orthogonaler Struktur fĂŒr eine beliebige Anzahl von Sende-und Empfangsantennen entworfen. Aus der Konstruktion resultieren dann zwei Gruppen von Codes. Die wesentliche Charakteristik der ersten Gruppe ist es, dass sie Verbindungen mit hoher QualitĂ€t gewĂ€hrleistet. Dies wird erreicht, indem rĂ€umliche und zeitliche Redundanz eingebracht wird und daraus die volle DiversitĂ€t (entspricht dem maximalen Abfall der Bitfehlerratenkurve) resultiert. Volle DiversitĂ€t wird auch von den OSTBC erreicht, die aufgrund ihrer Struktur den matrix-wertigen Kanal fĂŒr Mehrantennensysteme, so genannte Multiple-Input-Multiple-Output (MIMO)-KanĂ€le in parallele skalare ErsatzkanĂ€le, so genannte Single-Input-Single-Output (SISO)-KanĂ€le, transformieren. Die Anzahl der parallelen ErsatzkanĂ€le entspricht dabei der Anzahl der Sendeantennen. Diese Erkenntnis und die Einsicht in die Eigenschaften dieser ErsatzkanĂ€le waren ein wichtiger Meilenstein und ermöglichten es, die LeistungsfĂ€higkeit der OSTBC zu analysieren. Die Bestimmung der Ersatzkanalstuktur ist daher auch hier von zentraler Bedeutung. Im Falle von Raum-Zeit Codes mit quasi-orthogonaler Struktur wird in dieser Arbeit gezeigt, dass der MIMO-Kanal in einen block-diagonalen MIMO-Kanal zerlegt wird, dessen Eigenvektoren konstant und Blöcke identisch sind. Weiterhin konnte gezeigt werden, dass die Eigenwerte von jedem Block voneinander unabhĂ€ngig sind und einer nichtzentralen Chi-Quadrat-Verteilung mit einer Anzahl von Freiheitsgraden, die dem Vierfachen der Anzahl der Empfangsantennen entspricht, folgen. Durch Lockerung der Anforderung von voller DiversitĂ€t an die zu entwerfenden Codes gelangt man zu der zweiten Gruppe der Raum-Zeit Codes mit quasi-orthogonaler Stuktur, welche eine Verallgemeinerung der OSTBC darstellen. Insbesondere wird in dieser Arbeit gezeigt, dass nicht nur das Alamouti-Schema, ein OSTBC fĂŒr zwei Sendeantennen, sondern auch eine verallgemeinerte Version dieses Alamouti-Schemas, die KapazitĂ€t im Falle einer Empfangsantenne erreicht. Die in dieser Arbeit entworfenen Raum-Zeit Codes werden schließlich hinsichtlich ihrer Fehlerraten-Performanz und ihrer spektralen Effizienz mit optimalen als auch mit suboptimalen EmpfĂ€ngerstrukturen analysiert. Im zweiten Teil dieser Arbeit werden verschiedene Raum-Zeit Codes mit herkömmlichen Kanalcodierungsverfahren kombiniert. Dabei werden neue EmpfĂ€ngerstrukturen vorgestellt und die LeistungsfĂ€higkeit der Raum-Zeit Codes mit iterativen Algorithmen zur so genannten Soft-Input-Soft-Output-Decodierung mit Hilfe von neuen Analysetechniken, den so genannten EXIT-Charts, untersucht und optimiert. Im Falle von OSTBC werden zusĂ€tzlich Kriterien fĂŒr die optimale Abbildung von Bitsequenzen auf Sendesymbole hergeleitet.The demand for mobile communication systems with high data rates and improved link quality for a variety of applications has dramatically increased in recent years. New concepts and methods are necessary in order to cover this huge demand, which counteract or take advantage of the impairments of the mobile communication channel and optimally exploit the limited resources such as bandwidth and power. Multiple antenna systems are an efficient means for increasing the performance. In order to utilize the huge potential of multiple antenna concepts, it is necessary to resort to new transmit strategies, referred to as Space-Time Codes, which, in addition to the time and spectral domain, also use the spatial domain. The performance of such Space-Time Codes is analyzed in this thesis with and without conventional channel coding strategies. In case without conventional channel codes, the focus is on diversity-oriented Space-Time Codes. Based on Space-Time Block Codes from orthogonal designs (OSTBC), the Space-Time Block Codes from quasi-orthogonal designs are developed for any number of transmit and receive antennas. The outcome of this construction are two groups of codes. The main property of the first group is the support of links with high quality. This is achieved by incorporating spatial and temporal redundancy, which results in full diversity or in other words, in the maximum decay of the bit error rate curves. Full diversity is also achieved by OSTBC, which due to their structure transform the matrix-valued channel for multi-antenna systems, so called multiple-input-multiple-output (MIMO)-channels, into several parallel, scalar single-input-single-output (SISO)-channels. This insight and the understanding of the properties of the equivalent SISO-channels were the key results in order to analyze the performance of the OSTBC. The determination of the structure of the equivalent channel is also a matter of vital importance in this work. To this end, we show that the MIMO-channel in the case of Space-Time Codes from quasi-orthogonal designs is transformed into an equivalent block-diagonal MIMO-channel with identical blocks having constant eigenvectors, independent of the channel realization. Furthermore, we show that the eigenvalues of each block are pairwise independent and follow a non-central chi-square distribution, where the number of degrees of freedom equals four times the number of receive antennas. By relaxing the requirement of full diversity one arrives at the second group of Space-Time Codes from quasi-orthogonal designs. These codes represent a generalization of Space-Time Codes from orthogonal designs. Particularly, we show in this work, that not only the Alamouti-scheme, a OSTBC for two transmit antennas, but also its generalized version achieves capacity in the case of one receive antenna. The drafted codes are then analyzed with respect to the error rate performance and the spectral efficiency with optimal as well as suboptimal receiver structures. In the second part of this work the combination of Space-Time Codes with conventional channel coding techniques is considered. New receiver structures are presented and the performance of Space-Time Codes with iterative algorithms for soft-input-soft-output-decoding is analyzed and optimized with the help of new analytical tools, the so called EXIT-charts. Furthermore, some criteria for the optimal mapping strategy are derived in the case of OSTBC

    Optical Communication

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    Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

    MIMO communications over relay channels

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    Cellular, Wide-Area, and Non-Terrestrial IoT: A Survey on 5G Advances and the Road Towards 6G

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    The next wave of wireless technologies is proliferating in connecting things among themselves as well as to humans. In the era of the Internet of things (IoT), billions of sensors, machines, vehicles, drones, and robots will be connected, making the world around us smarter. The IoT will encompass devices that must wirelessly communicate a diverse set of data gathered from the environment for myriad new applications. The ultimate goal is to extract insights from this data and develop solutions that improve quality of life and generate new revenue. Providing large-scale, long-lasting, reliable, and near real-time connectivity is the major challenge in enabling a smart connected world. This paper provides a comprehensive survey on existing and emerging communication solutions for serving IoT applications in the context of cellular, wide-area, as well as non-terrestrial networks. Specifically, wireless technology enhancements for providing IoT access in fifth-generation (5G) and beyond cellular networks, and communication networks over the unlicensed spectrum are presented. Aligned with the main key performance indicators of 5G and beyond 5G networks, we investigate solutions and standards that enable energy efficiency, reliability, low latency, and scalability (connection density) of current and future IoT networks. The solutions include grant-free access and channel coding for short-packet communications, non-orthogonal multiple access, and on-device intelligence. Further, a vision of new paradigm shifts in communication networks in the 2030s is provided, and the integration of the associated new technologies like artificial intelligence, non-terrestrial networks, and new spectra is elaborated. Finally, future research directions toward beyond 5G IoT networks are pointed out.Comment: Submitted for review to IEEE CS&

    Design of large polyphase filters in the Quadratic Residue Number System

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    Packet Scheduling and Quality of Service in HSDPA

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    Advances in Multi-User Scheduling and Turbo Equalization for Wireless MIMO Systems

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    Nach einer Einleitung behandelt Teil 2 Mehrbenutzer-Scheduling fĂŒr die AbwĂ€rtsstrecke von drahtlosen MIMO Systemen mit einer Sendestation und kanaladaptivem precoding: In jeder Zeit- oder Frequenzressource kann eine andere Nutzergruppe gleichzeitig bedient werden, rĂ€umlich getrennt durch unterschiedliche Antennengewichte. Nutzer mit korrelierten KanĂ€len sollten nicht gleichzeitig bedient werden, da dies die rĂ€umliche Trennbarkeit erschwert. Die Summenrate einer Nutzermenge hĂ€ngt von den Antennengewichten ab, die wiederum von der Nutzerauswahl abhĂ€ngen. Zur Entkopplung des Problems schlĂ€gt diese Arbeit Metriken vor basierend auf einer geschĂ€tzten Rate mit ZF precoding. Diese lĂ€sst sich mit Hilfe von wiederholten orthogonalen Projektionen abschĂ€tzen, wodurch die Berechnung von Antennengewichten beim Scheduling entfĂ€llt. Die RatenschĂ€tzung kann basierend auf momentanen Kanalmessungen oder auf gemittelter Kanalkenntnis berechnet werden und es können Datenraten- und Fairness-Kriterien berĂŒcksichtig werden. Effiziente Suchalgorithmen werden vorgestellt, die die gesamte Systembandbreite auf einmal bearbeiten können und zur KomplexitĂ€tsreduktion die Lösung in Zeit- und Frequenz nachfĂŒhren können. Teil 3 zeigt wie mehrere Sendestationen koordiniertes Scheduling und kooperative Signalverarbeitung einsetzen können. Mittels orthogonalen Projektionen ist es möglich, Inter-Site Interferenz zu schĂ€tzen, ohne Antennengewichte berechnen zu mĂŒssen. Durch ein Konzept virtueller Nutzer kann der obige Scheduling-Ansatz auf mehrere Sendestationen und sogar Relays mit SDMA erweitert werden. Auf den benötigten Signalisierungsaufwand wird kurz eingegangen und eine Methode zur SchĂ€tzung der Summenrate eines Systems ohne Koordination besprochen. Teil4 entwickelt Optimierungen fĂŒr Turbo Entzerrer. Diese Nutzen Signalkorrelation als Quelle von Redundanz. Trotzdem kann eine Kombination mit MIMO precoding sinnvoll sein, da bei Annahme realistischer Fehler in der Kanalkenntnis am Sender keine optimale InterferenzunterdrĂŒckung möglich ist. Mit Hilfe von EXIT Charts wird eine neuartige Methode zur adaptiven Nutzung von a-priori-Information zwischen Iterationen entwickelt, die die Konvergenz verbessert. Dabei wird gezeigt, wie man semi-blinde KanalschĂ€tzung im EXIT chart berĂŒcksichtigen kann. In Computersimulationen werden alle Verfahren basierend auf 4G-Systemparametern ĂŒberprĂŒft.After an introduction, part 2 of this thesis deals with downlink multi-user scheduling for wireless MIMO systems with one transmitting station performing channel adaptive precoding:Different user subsets can be served in each time or frequency resource by separating them in space with different antenna weight vectors. Users with correlated channel matrices should not be served jointly since correlation impairs the spatial separability.The resulting sum rate for each user subset depends on the precoding weights, which in turn depend on the user subset. This thesis manages to decouple this problem by proposing a scheduling metric based on the rate with ZF precoding such as BD, written with the help of orthogonal projection matrices. It allows estimating rates without computing any antenna weights by using a repeated projection approximation.This rate estimate allows considering user rate requirements and fairness criteria and can work with either instantaneous or long term averaged channel knowledge.Search algorithms are presented to efficiently solve user grouping or selection problems jointly for the entire system bandwidth while being able to track the solution in time and frequency for complexity reduction. Part 3 shows how multiple transmitting stations can benefit from cooperative scheduling or joint signal processing. An orthogonal projection based estimate of the inter-site interference power, again without computing any antenna weights, and a virtual user concept extends the scheduling approach to cooperative base stations and finally included SDMA half-duplex relays in the scheduling.Signalling overhead is discussed and a method to estimate the sum rate without coordination. Part 4 presents optimizations for Turbo Equalizers. There, correlation between user signals can be exploited as a source of redundancy. Nevertheless a combination with transmit precoding which aims at reducing correlation can be beneficial when the channel knowledge at the transmitter contains a realistic error, leading to increased correlation. A novel method for adaptive re-use of a-priori information between is developed to increase convergence by tracking the iterations online with EXIT charts.A method is proposed to model semi-blind channel estimation updates in an EXIT chart. Computer simulations with 4G system parameters illustrate the methods using realistic channel models.Im Buchhandel erhĂ€ltlich: Advances in Multi-User Scheduling and Turbo Equalization for Wireless MIMO Systems / Fuchs-Lautensack,Martin Ilmenau: ISLE, 2009,116 S. ISBN 978-3-938843-43-
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