Nouvelles méthodes de traitement d’antenne en émission alliant diversité et formation de voie

This work deals with the use of an antenna array at the base station of a mobile communication system for transmission. In reception, solutions that exploit the antenna array are now well established. In transmission, however, the problem remains open. Two approaches are possible : exploit the array by using beamforming techniques or by using diversity techniques. These two approaches are based on opposite assumptions about the channels correlation, which implies a greater or smaller distance between antennas, depending on the environment. In practice, these assumptions are not verified. Here, we aim to deal with the problem as a whole for better exploiting the antenna array. This work treats the mono-user case, as well as the multi-user scenario. In the mono-user case, we propose a transmission scheme composed of a classical transmit diversity technique applied to virtual antennas, which are ...

Zanatta Filho, Danilo — Conservatoire National des Arts et Métiers


Digital design and experimental validation of high-performance real-time OFDM systems

The goal of this Ph.D. dissertation is to address a number of challenges encountered in the digital baseband design of modern and future wireless communication systems. The fast and continuous evolution of wireless communications has been driven by the ambitious goal of providing ubiquitous services that could guarantee high throughput, reliability of the communication link and satisfy the increasing demand for efficient re-utilization of the heavily populated wireless spectrum. To cope with these ever-growing performance requirements, researchers around the world have introduced sophisticated broadband physical (PHY)-layer communication schemes able to accommodate higher bandwidth, which indicatively include multiple antennas at the transmitter and receiver and are capable of delivering improved spectral efficiency by applying interference management policies. The merging of Multiple Input Multiple Output (MIMO) schemes with the Orthogonal Frequency Division Multiplexing (OFDM) offers a flexible signal processing substrate to implement ...

Font-Bach, Oriol — Centre Tecnològic de Telecomunicacions de Catalunya (CTTC)


Transmission Strategies for Interfering Networks with Finite Rate and Outdated Channel Feedback

The emergence of very capable mobile terminals, e.g. smartphones or tablets, has dramatically increased the demand of wireless data traffic in recent years. Current growth forecasts elucidate that wireless communication standards will not be able to afford future traffic demands, thus many research efforts have been oriented towards increasing the efficiency of wireless networks. Wireless communications introduce many issues not present in wired systems, e.g. multipath effects or interference. Some of these issues may be tackled by the use of multiple antennas, i.e. MIMO technologies. This solution allows increasing not only the reliability and robustness of the communications, i.e. the diversity gain, but also its efficiency, i.e. the multiplexing gain or degrees of freedom (DoF). The DoF describe the slope of channel capacity at very high signal-to-noise-ratio (SNR) regime. For a point-to-point (P2P) communication, assuming that the wireless channel response ...

Torrellas, Marc — Universitat Politècnica de Catalunya


Advanced Multi-Dimensional Signal Processing for Wireless Systems

The thriving development of wireless communications calls for innovative and advanced signal processing techniques targeting at an enhanced performance in terms of reliability, throughput, robustness, efficiency, flexibility, etc.. This thesis addresses such a compelling demand and presents new and intriguing progress towards fulfilling it. We mainly concentrate on two advanced multi-dimensional signal processing challenges for wireless systems that have attracted tremendous research attention in recent years, multi-carrier Multiple-Input Multiple-Output (MIMO) systems and multi-dimensional harmonic retrieval. As the key technologies of wireless communications, the numerous benefits of MIMO and multi-carrier modulation, e.g., boosting the data rate and improving the link reliability, have long been identified and have ignited great research interest. In particular, the Orthogonal Frequency Division Multiplexing (OFDM)-based multi-user MIMO downlink with Space-Division Multiple Access (SDMA) combines the twofold advantages of MIMO and multi-carrier modulation. It is the essential element ...

Cheng, Yao — Ilmenau University of Technology


A Unified Framework for Communications through MIMO Channels

MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) CHANNELS constitute a unified way of modeling a wide range of different physical communication channels, which can then be handled with a compact and elegant vector-matrix notation. The two paradigmatic examples are wireless multi-antenna channels and wireline Digital Subscriber Line (DSL) channels. Research in antenna arrays (also known as smart antennas) dates back to the 1960s. However, the use of multiples antennas at both the transmitter and the receiver, which can be naturally modeled as a MIMO channel, has been recently shown to offer a significant potential increase in capacity. DSL has gained popularity as a broadband access technology capable of reliably delivering high data rates over telephone subscriber lines. A DSL system can be modeled as a communication through a MIMO channel by considering all the copper twisted pairs within a binder as a whole rather ...

Palomar, Daniel Perez — Technical University of Catalonia (UPC)


A multimicrophone approach to speech processing in a smart-room environment

Recent advances in computer technology and speech and language processing have made possible that some new ways of person-machine communication and computer assistance to human activities start to appear feasible. Concretely, the interest on the development of new challenging applications in indoor environments equipped with multiple multimodal sensors, also known as smart-rooms, has considerably grown. In general, it is well-known that the quality of speech signals captured by microphones that can be located several meters away from the speakers is severely distorted by acoustic noise and room reverberation. In the context of the development of hands-free speech applications in smart-room environments, the use of obtrusive sensors like close-talking microphones is usually not allowed, and consequently, speech technologies must operate on the basis of distant-talking recordings. In such conditions, speech technologies that usually perform reasonably well in free of noise and ...

Abad, Alberto — Universitat Politecnica de Catalunya


Analog Joint Source Channel Coding for Wireless Communications

In 1948, the Shannon’s work titled ”A mathematical theory of communication” completely revolutionized the way to understand the problem of the reliable communications. He showed that any communications system is able to transmit with an arbitrarily low error probability as long as the transmission rate is kept below a certain limit. The separation between the source and channel coding was also shown as the optimal strategy to achieve the theoretical limits. Those ideas inspire the development of a whole digital communication theory focused on building more and more sophisticated coding schemes. It leads to most of communication systems were designed according to a digital approach and the separation principle from that moment, whereas other alternatives were set aside. However, in the last years, communication systems based on a jointly optimization of the source and channel encoder has aroused the interest ...

Fresnedo Arias, Óscar — University of A Coruña


Stochastic Schemes for Dynamic Network Resource Allocation

Wireless networks and power distribution grids are experiencing increasing demands on their efficiency and reliability. Judicious methods for allocating scarce resources such as power and bandwidth are of paramount importance. As a result, nonlinear optimization and signal processing tools have been incorporated into the design of contemporary networks. This thesis develops schemes for efficient resource allocation (RA) in such dynamic networks, with an emphasis in stochasticity, which is accounted for in the problem formulation as well as in the algorithms and schemes to solve those problems. Stochastic optimization and decomposition techniques are investigated to develop low-complexity algorithms with specific applications in cross-layer design of wireless communications, cognitive radio (CR) networks and smart power distribution systems. The costs and constraints on the availability of network resources, together with diverse quality of service (QoS) requirements, render network design, management, and operation challenging ...

Lopez Ramos, Luis Miguel — King Juan Carlos University


Algorithms and architectures for adaptive array signal processing

Antenna arrays sample propagating waves at multiple locations. They are employed e.g. in radar, sonar and wireless communication systems because of their capacity of spatial selectivity and localization of radiating sources. Current model-based algorithms make use of computationally demanding orthogonal matrix decompositions such as the singular value decomposition (SVD). On the other hand the data rates are often extremely high. Therefore, real-time execution of complex algorithms often requires parallel computing. We study the simultaneous design of new algorithms and parallel architectures for subspace tracking, for robust adaptive beamforming and for direction finding of narrow-band and wide-band sources. By structuring all recursive algorithms in a similar way, they can be mapped efficiently onto the Jacobi architecture, which was originally developed for SVD updating. The numerical and architectural aspects of this algorithm are improved by the use of a minimal parameterziation of ...

Vanpoucke, Filiep — Katholieke Universiteit Leuven


Advanced Signal Processing Techniques for Global Navigation Satellite Systems

This Dissertation addresses the synchronization problem using an array of antennas in the general framework of Global Navigation Satellite Systems (GNSS) receivers. Positioning systems are based on time delay and frequency-shift estimation of the incoming signals in the receiver side, in order to compute the user's location. Sources of accuracy degradation in satellite-based navigation systems are well-known, and their mitigation has deserved the attention of a number of researchers in latter times. While atmospheric-dependant sources (delays that depend on the ionosphere and troposphere conditions) can be greatly mitigated by differential systems external to the receiver's operation, the multipath effect is location-dependant and remains as the most important cause of accuracy degradation in time delay estimation, and consequently in position estimation, becoming a signal processing challenge. Traditional approaches to time delay estimation are often embodied in a communication systems framework. Indeed, ...

Fernandez-Prades, Carles — Universitat Politecnica de Catalunya


Cooperative and Cognitive Communication Techniques for Wireless Networks

During the past years wireless communications have been exhibiting an increased growth rendering them the most common way for communication. The continuously increasing demand for wireless services resulted in limited availability of the wireless spectrum. To this end, Cognitive Radio (CR) techniques have been proposed in literature during the past years. The concept of CR approach is to utilize advanced radio and signal-processing technology along with novel spectrum allocation policies to enable new unlicensed wireless users to operate in the existing occupied spectrum areas without degrading the performance of the existing licensed ones. Moreover, the broadcast and fading nature of the wireless channel results in severe degradation on the performance of wireless transmissions. A solution to the problem is the use of multiple-antenna systems so as to achieve spatial diversity. However, in many cases, the communication devices' nature permit the ...

Tsinos, Christos — University of Patras


Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation ...

Gaspar, Ivan — Technische Universität Dresden


Space-Time Block Coding for Multiple Antenna Systems

The demand for mobile communication systems with high data rates has dramatically increased in recent years. New methods are necessary in order to satisfy this huge communications demand, exploiting the limited resources such as bandwidth and power as efficient as possible. MIMO systems with multiple an- tenna elements at both link ends are an efficient solution for future wireless communications systems as they provide high data rates by exploiting the spatial domain under the constraints of limited bandwidth and transmit power. Space-Time Block Coding (STBC) is a MIMO transmit strategy which exploits transmit diversity and high reliability. STBCs can be divided into two main classes, namely, Orthogonal Space-Time Block Codes (OSTBCs) and Non-Orthogonal Space-Time Block Codes (NOSTBCs). The Quasi-Orthogonal Space-Time Block Codes (QSTBCs) belong to class of NOSTBCs and have been an intensive area of research. The OSTBCs achieve full ...

Badic, B. — Vienna University of Technology


Impact of channel state information on the analysis and design of multiantenna communication systems

During the last decade, there has been a steady increase in the demand of high data rates that are to be supported by wireless communication applications. Among the different solutions that have been proposed by the research community to cope with this new demand, the utilization of multiple antennas arises as one of the best candidates due to the fact that it provides both an increase in reliability and also in information transmission rate. Although the use of multiple antennas at the receiver side dates back from the sixties, the full potential of multiple antennas at both communication ends has been both theoretically and practically recognized in the last few years. The design of proper multi-antenna communication systems to satisfy the high data rates demand depends not only on the chosen figure of merit or performance metric, but also on ...

Payaró Llisterri, Miquel — Centre Technologic de Telecomunicacions de Catalunya


Mobile Cellular Communications with Base Station Antenna Arrays: Spectrum Efficiency, Algorithms and Propagation Models

This thesis deals with the problem of increasing the spectrum efficiency of cellular systems, by the use of antenna array base stations. The focus of the thesis is on downlink transmission in frequency division duplex systems, i.e., systems with different up and downlink carrier frequency. In a short summary the thesis: * Proposes five reasonable propagation models. * Uses these models to design and analyze three different beamformers: The maximum desired power (MDP), the summed interference to carrier ratio minimizing (SCIR) and the generalized-SCIR beamformer. * Introduces three capacity enhancement approaches: same sector frequency reuse (SSFR), reduced cluster size without nulling (RCS-WON) and reduced cluster size with nulling (RCS-WIN). * Proposes channel allocation, power control, and beamforming algorithms for these approaches. * Estimates the ``outage probability'' (probability of insufficient quality), for SICR-SSFR, SICR-RCS-WON and SICR-RCS-WIN, using simulations as well as ...

Zetterberg, Per — Royal Institute of Technology, Sweden

The current layout is optimized for mobile phones. Page previews, thumbnails, and full abstracts will remain hidden until the browser window grows in width.

The current layout is optimized for tablet devices. Page previews and some thumbnails will remain hidden until the browser window grows in width.