Statistical-dynamical channel modeling of outdoor optical wireless links

The growing need for Earth observation and monitoring systems has stimulated considerable interest in free-space optical wireless (FSO) systems because of the huge bandwidth requirements. However, terrestrial FSO links are severely impacted by weather conditions especially dense fog to a larger extent while, rain and snow to a lesser extent. For the proper deployment of FSO technology requires a better understanding of the free-space channel transmission characteristics as they have major influence on the transmission link properties like link availability, reliability and quality of service. This thesis provides new insight on the fog microphysics, its characterization and the fog attenuation modeling. A comprehensive analysis of the measured fog attenuations is presented by building the discussion through comparison of recorded attenuations at Graz (Austria), Milan (Italy), Nice (France) and Prague (Czech Republic). It was observed that fog attenuations in radiation fog ...

Awan, Muhammad Saleem — Graz University of Technology


UWB Channel Fading Statistics and Transmitted-Reference Communication

It is well known that Ultra WideBand (UWB) transmission is inherently robust against small-scale-fading (SSF) that arises in multipath scattering environments, due to its large signal bandwidth. However, no model with a physical interpretation exists that relates the variations of received signal strength to the signal bandwidth and general channel parameters, like e.g. the average channel power delay profile. Such a model would be of relevance for e.g. system designers, who have to make tradeoffs between system aspects, like complexity and energy efficiency on one hand, and robustness against small-scale fading on the other hand. In this thesis, a model is presented that allows for such a tradeoff analysis, relating the average power delay profile parameters and signal bandwidth to the statistical properties of the SSF. Additionally, it is shown how the uncoded and coded BER of BPSK modulation can ...

Romme, Jac — Graz University of Technology


Factor Graph Based Detection Schemes for Mobile Terrestrial DVB Systems with Long OFDM Blocks

This PhD dissertation analyzes the performance of second generation digital video broadcasting (DVB) systems in mobile terrestrial environments and proposes an iterative detection algorithm based on factor graphs (FG) to reduce the distortion caused by the time variation of the channel, providing error-free communication in very severe mobile conditions. The research work focuses on mobile scenarios where the intercarrier interference (ICI) is very high: high vehicular speeds when long orthogonal frequency-division multiplexing (OFDM) blocks are used. As a starting point, we provide the theoretical background on the main topics behind the transmission and reception of terrestrial digital television signals in mobile environments, long with a general overview of the main signal processing techniques included in last generation terrestrial DVB systems. The proposed FG-based detector design is then assessed over a simpli ed bit-interleaved coded modulation (BICM)-OFDM communication scheme for a ...

Ochandiano, Pello — University of Mondragon


MIMO Designs for filter bank multicarrier and multiantenna systems based on OQAM

From the perspective of increasingly data rate requirements in mobile communications, it is deemed necessary to do further research so that the future goals can be reached. To that end, the radio-based communications are resorting to multicarrier modulations and spatial diversity. Until today, the orthogonal frequency division multiplexing (OFDM) modulation is regarded as the dominant technology. On one hand, the OFDM modulation is able to accommodate multiantenna configurations in a very straightforward manner. On the other hand, the poor stopband attenuation exhibited by the OFDM modulation, highlights that a definitely tight synchronization is required. In addition, the cyclic prefix (CP) has to be sufficiently long to avoid inter-block interference, which may substantially reduce the spectral efficiency. In order to overcome the OFDM drawbacks, the filter bank multicarrier modulation based on OQAM (FBMC/OQAM) is introduced. This modulation does not need any ...

López, Màrius Caus — Universitat Politècnica de Catalunya (UPC)


OFDM Multi-User Communication Over Time-Variant Channels

Wireless broadband communications for users moving at vehicular speed is a cor- nerstone of future fourth generation (4G) mobile communication systems. We inves- tigate a multi-carrier (MC) code division multiple access (CDMA) system which is based on orthogonal frequency division multiplexing (OFDM). A spreading sequence is used in the frequency domain in order to distinguish individual users and to take advantage of the multipath diversity of the wireless channel. The transmission is block oriented. A block consists of OFDM pilot and OFDM data symbols. At pedestrian velocities the channel can be modelled as block fading. We ap- ply iterative multi-user detection and channel estimation. In iterative receivers soft symbols are derived from the output of an soft-input soft-output decoder. These soft symbols are used in order to reduce the interference from other users and to enhance the channel estimates. We ...

Zemen, T. — Vienna University of Technology


Design and implementation of low complexity adaptive optical OFDM systems for software-defined transmission in elastic optical networks

Due to the increasing global IP traffic and the exponential growing demand for broadband services, optical networks are experimenting significant changes. Advanced modulation formats are being implemented at the Digital Signal Processing (DSP) level as key enablers for high data rate transmission. Whereas in the network layer, flexi Dense Wavelength-Division Multiplexing (DWDM) grids are being investigated in order to efficiently use the optical spectrum according to the traffic demand. Enabling these capabilities makes high data rate transmission more feasible. Hence, introducing flexibility in the system is one of the main goals of this thesis. Furthermore, minimizing the cost and enhancing the Spectral Efficiency (SE) of the system are two crucial issues to consider in the transceiver design. This dissertation investigates the use of Optical Orthogonal Frequency Division Multiplexing (O-OFDM) based either on the Fast Fourier Transform (FFT) or the Fast ...

Reixats, Laia Nadal — Universitat Politecnica de Catalunya (UPC)


Detection and Decoding Algorithms of Multi-Antenna Diversity Techniques for Terrestrial DVB Systems

This PhD dissertation analyzes the behavior of multi-antenna diversity techniques in broadcasting scenarios of TDT (terrestrial digital television) systems and proposes a low-complexity detection and decoding design for their practical implementation. For that purpose, the transmission-reception chains of the European DVB-T (Digital Video Broadcasting - Terrestrial) and DVB-T2 standards have been implemented over which diversity and MIMO (multiple-input multiple-output) techniques have been assessed through Monte Carlo simulations. On one hand, the most important multi-antenna diversity techniques such as CDD (cyclic delay diversity), Alamouti code-based SFBC (space-frequency block coding) and MRC (maximum ratio combining), have been evaluated in a DVB-T system over both fixed and mobile Rayleigh and Ricean channels. With the DVB-T2 standard release, multi-antenna processing has actually been introduced in digital television systems. The distributed SFBC configuration proposed in DVB-T2 is analyzed from a performance point of view considering ...

Sobron, Iker — University of Mondragon


On MIMO Systems and Adaptive Arrays for Wireless Communication. Analysis and Practical Aspects

This thesis is concerned with the use of multiple antenna elements in wireless communication over frequency non-selective radio channels. Both measurement results and theoretical analysis are presented. New transmit strategies are derived and compared to existing transmit strategies, such as beamforming and space time block coding (STBC). It is found that the best transmission algorithm is largely dependent on the channel characteristics, such as the number of transmit and receive antennas and the existence of a line of sight component. Rayleigh fading multiple input multiple output (MIMO) channels are studied using an eigenvalue analysis and exact expressions for the bit error rates and outage capacities for beamforming and STBC is found. In general are MIMO fading channels correlated and there exists a mutual coupling between antenna elements. These findings are supported by indoor MIMO measurements. It is found that the ...

Wennstram, Mattias — Uppsala University


Study of the Effects Produced by Time Modulation Applied to an Antenna Array in Digital Transmission Systems

An ever-increasing demand for higher mobility, capacity and reliability, together with a definitive compromise with sustainability, are the hallmarks of mobile and wireless communications systems nowadays. Under these premises, smart antenna devices -capable of sensing the electromagnetic environment and suitably adapting its radiation features- are correspondingly called to play a crucial role. In this sense, today's wireless standards consider multiple-antenna techniques in order to exploit space diversity, spatial multiplexing and beamforming to achieve better levels of reliability and capacity. Such advantages, however, are obtained at the expense of increased system complexity which may be unaffordable in terms of size and energy efficiency. Consequently, some technical challenges remain to develop the adequate antenna technologies capable of supporting the aforementioned features in a limited physical space that the mobility demand dictates. The concept of time-modulated array (TMA) is a feasible multi-antenna technique ...

Maneiro-Catoria, Roberto — University of A Coruña


On MIMO Systems with Limited Feedback: End-to-End Distortion, Analog Channel Feedback, and Layered Multiplexing

In this thesis, we investigate the following three fields on multi-input multi-output (MIMO) systems with limited feedback. End-to-end distortion: The first part of the thesis presents the joint impact of antenna numbers, source-to-channel bandwidth ratio, spatial correlation and time diversity on the optimum expected end-to-end distortion in an outage-free MIMO system. In particular, based on the analytical expression for any signal-to-noise ratio (SNR), the closed-form expression of the asymptotic optimum expected end-to-end distortion at a high SNR is derived, comprised of the optimum distortion exponent and the optimum distortion factor. The simulation results illustrate that, at a practical high SNR, the analysis on the impacts of the optimum distortion exponent and the optimum distortion factor explains the behavior of the optimum expected end-to-end distortion. The results in this part could be the performance objectives for analog-source transmission systems as well ...

Chen, Jinhui — TELECOM ParisTech


Randomized Space-Time Block Coding for the Multiple-Relay Channel

In the last decade, cooperation among multiple terminals has been seen as one of the more promising strategies to improve transmission speed in wireless communications networks. Basically, the idea is to mimic an antenna array and apply distributed versions of well-known space-diversity techniques. In this context, the simplest cooperative scheme is the relay channel: all the terminals (relays) that overhear a point-to-point communication between a source and a destination may decide to aid the source by forwarding (relaying) its message. In a mobile system, it is common to assume that the relays do not have any information about the channel between them and the destination. Under this hypothesis, the best solution to exploit the diversity offered by multiple transmitting antennas is to use space-time coding (STC). However, classical STC's are designed for systems with a fixed and usually low number ...

Gregoratti, David — Universitat Politecnica de Catalunya (UPC)


Iterative Multi-User Receivers for CDMA Systems

Mobile communication networks of the third and future generations are designed to offer high-data rate services like video-telephony and data-transfer. The current Rake receiver architecture will create a shortage in available bandwidth offered to the users. This is not due to a shortage in spectrum but results from inefficient receiver architectures. Spectral efficiency can be increased considerably through multi-user detection techniques in the receiver algorithms. The present thesis investigates iterative re- ceivers for encoded CDMA transmission in the uplink. The iterative receiver is a suboptimal receiver algorithm with manageable complexity. It consists of an inter- ference mitigating multi-user detector, a bank of single-user decoders, and a channel estimator. Instead of deciding on the transmitted symbols right after the first decod- ing, the receiver feeds back tentative decision symbols to mitigate multiple-access interference in the next iteration. Similarly, soft decision symbols ...

Wehinger, J. — Vienna University of Technology


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


Contributions to the 3D city modeling: 3D polyhedral building model reconstruction from aerial images and 3D facade modeling from terrestrial 3D point cloud and images

The aim of this work is to develop research on 3D building modeling. In particular, the research in aerial-based 3D building reconstruction is a topic very developed since 1990. However, it is necessary to pursue the research since the actual approaches for 3D massive building reconstruction (although efficient) still encounter problems in generalization, coherency, accuracy. Besides, the recent developments of street acquisition systems such as Mobile Mapping Systems open new perspectives for improvements in building modeling in the sense that the terrestrial data (very dense and accurate) can be exploited with more performance (in comparison to the aerial investigation) to enrich the building models at facade level (e.g., geometry, texturing). Hence, aerial and terrestrial based building modeling approaches are individually proposed. At aerial level, we describe a direct and featureless approach for simple polyhedral building reconstruction from a set of ...

Hammoudi Karim — Université Paris-Est, Saint-Mandé, France


Reduced-Complexity Code Synchronization in Multipath Channels for BOC Modulated CDMA Signals with Applications in Galileo and Modernized GPS Systems

Applications for the new generations of Global Navigation Satellite Systems (GNSS) are developing rapidly and attract a great interest. Both US Global Positioning System (GPS) and European Galileo signals use Direct Sequence-Code Division Multiple Access (DS-CDMA) technology, where code and frequency synchronization are important stages at the receiver. The GNSS receivers estimate jointly the code phase and the Doppler spread through a two-dimensional searching process in time-frequency plane. Since both GPS and Galileo systems will send several signals on the same carriers, a new modulation type - the Binary Offset Carrier (BOC) modulation, has been selected. The main target of this modulation is to provide a better spectral separation with the existing BPSK-modulated GPS signals, while allowing optimal usage of the available bandwidth for different GNSS signals. The BOC modulation family includes several BOC variants, such as sine BOC (SinBOC), ...

Burian, Adina — Universitat Trier

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.