18 research outputs found
IST-2000-30148 I-METRA: D3.1 Design, analysis and selection of suitable algorithms
This deliverable contains a description of the space-time coding algorithms to be simulated within the I-METRA project. Different families of algorithms have been selected and described in this document with the objective of evaluating their performance. One of the main objectives of the I-METRA project is to impact into the current standardisation efforts related to the introduction of Multiple Input Multiple Output (MIMO) configurations into the High Speed Downlink and Uplink Packet Access concepts of UMTS (HSDPA and HSUPA). This required a review of the current specifications for these systems and the analysis of the impact of the potential incorporation of the selected MIMO schemes.Preprin
IST-2000-30148 I-METRA: D4 Performance evaluation
This document considers the performance of multiantenna transmit/receive techniques in high-speed downlink and uplink packet access. The evaluation is done using both link and system level simulations by taking into account link adaptation and packet retransmissions. The document is based on the initial studies carried out in deliverables D3.1 and D3.2.Preprin
Handoff issues in a transmit diversity system
This thesis addresses handoff issues in a WCDMA system with space-time block coded transmit antenna diversity. Soft handoff has traditionally been used in CDMA systems because of its ability to provide an improved link performance due to the inherent macro diversity. Next generation systems will incorporate transmit diversity schemes employing several transmit antennas at the base station. These schemes have been shown to improve downlink transmission performance especially capacity and quality. This research investigates the possibility that the diversity obtained through soft handoff can be compensated for by the diversity obtained in a transmit diversity system with hard handoff. We analyze the system for two performance measures, namely, the probability of bit error and the outage probability, in order to determine whether the improvement in link performance, as a result of transmit diversity in a system with hard handoffs obviates the need for soft handoffs
On-chip cross-talk analysis for multiple RF front ends of a wireless gigabit LAN system
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (leaves 169-173).In the Wireless-Gigabit-Local-Area-Network (WiGLAN) project, we proposes a system architecture that adopts multiple antennas [1, 2, 3, 4] to control the trade-off between data rate and transmission quality [5, 6] through Space-Time Coding (STC) [7, 8, 9] and Orthogonal Frequency Division Multiplexing (OFDM). However, along the multiple RF front-ends, there are multiple nodes that signal cross-talk can occur. Such signal cross-talk occurring on a silicon chip becomes more and more significant as the integration level and operating radio frequency rise, seriously degrading the system performance, the data rate and transmission quality. Most of the literature about on-chip crosstalk suppression have been focusing on adopting various process-technology techniques, such as using guard ring structures to separate the parallel RF front ends or inserting a ground plane to shield the cross-talk. In this study, we will take a different approach. We will investigate the effects of on-chip cross-talk upon the operations of the coding and modulation schemes adopted in the WiGLAN system and explore methods, other than those mentioned, to counteract them.by Jie De Jacky Liang.S.M
MIMO Systems
In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity
Mitigation techniques through spatial diversity combining and relay-assisted technology in a turbulence impaired and misaligned free space optical channel.
Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban, 2018.In recent times, spectrum resource scarcity in Radio Frequency (RF) systems is one of the
biggest and prime issues in the area of wireless communications. Owing to the cost of
spectrum, increase in the bandwidth allocation as alternative solution, employed in the recent
past, does no longer offer an effective means to fulfilling high demand in higher data rates.
Consequently, Free Space Optical (FSO) communication systems has received considerable
attention in the research community as an attractive means among other popular solutions to
offering high bandwidth and high capacity compared to conventional RF systems. In
addition, FSO systems have positive features which include license-free operation, cheap and
ease of deployment, immunity to interference, high security, etc. Thus, FSO systems have
been favoured in many areas especially, as a viable solution for the last-mile connectivity
problem and a potential candidate for heterogeneous wireless backhaul network. With these
attractive features, however, FSO systems are weather-dependent wireless channels.
Therefore, it is usually susceptible to atmospheric induced turbulence, pointing error and
attenuation under adverse weather conditions which impose severe challenges on the system
performance and transmission reliability. Thus, before widespread deployment of the system
will be possible, promising mitigation techniques need to be found to address these problems.
In this thesis, the performance of spatial diversity combining and relay-assisted techniques
with Spatial Modulation (SM) as viable mitigating tools to overcome the problem of
atmospheric channel impairments along the FSO communication system link is studied.
Firstly, the performance analysis of a heterodyne FSO-SM system with different diversity
combiners such as Maximum Ratio Combining (MRC), Equal Gain Combining (EGC) and
Selection Combining (SC) under the influence of lognormal and Gamma-Gamma
atmospheric-induced turbulence fading is presented. A theoretical framework for the system
error is provided by deriving the Average Pairwise Error Probability (APEP) expression for
each diversity scheme under study and union bounding technique is applied to obtain their
Average Bit Error Rate (ABER). Under the influence of Gamma-Gamma turbulence, an
APEP expression is obtained through a generalized infinite power series expansion approach
and the system performance is further enhanced by convolutional coding technique.
Furthermore, the performance of proposed system under the combined effect of misalignment
and Gamma-Gamma turbulence fading is also studied using the same mathematical approach.
Moreover, the performance analysis of relay-assisted dual-hop heterodyne FSO-SM system
with diversity combiners over a Gamma-Gamma atmospheric turbulence channel using
Decode-and-Forward (DF) relay and Amplify-and-Forward (AF) relay protocols also is
presented. Under DF dual-hop FSO system, power series expansion of the modified Bessel
function is used to derive the closed-form expression for the end-to-end APEP expressions
for each of the combiners under study over Gamma-Gamma channel, and a tight upper bound
on the ABER per hop is given. Thus, the overall end-to-end ABER for the dual-hop FSO
system is then evaluated. Under AF dual-hop FSO system, the statistical characteristics of AF
relay in terms of Moment Generating Function (MGF), Probability Density Function (PDF)
and Cumulative Distribution Function (CDF) are derived for the combined Gamma-Gamma
turbulence and/or pointing error distributions channel in terms of Meijer-G function. Based
on these expressions, the APEP for each of the under studied combiners is determined and the
ABER for the system is given by using union bounding technique. By utilizing the derived
ABER expressions, the effective capacity for the considered system is then obtained.
Furthermore, the performance of a dual-hop heterodyne FSO-SM asymmetric RF/FSO
relaying system with MRC as mitigation tools at the destination is evaluated. The RF link
experiences Nakagami-m distribution and FSO link is subjected to Gamma-Gamma
distribution with and/or without pointing error. The MGF of the system equivalent SNR is
derived using the CDF of the system equivalent SNR. Utilizing the MGF, the APEP for the
system is then obtained and the ABER for the system is determined.
Finally, owing to the slow nature of the FSO channel, the Block Error Rate (BLER)
performance of FSO Subcarrier Intensity Modulation (SIM) system with spatial diversity
combiners employing Binary Phase Shift Keying (BPSK) modulation over Gamma-Gamma
atmospheric turbulence with and without pointing error is studied. The channel PDF for MRC
and EGC by using power series expansion of the modified Bessel function is derived.
Through this, the BLER closed-form expressions for the combiners under study are obtained
Advanced Algebraic Concepts for Efficient Multi-Channel Signal Processing
Unsere moderne Gesellschaft ist Zeuge eines fundamentalen Wandels in der Art und Weise
wie wir mit Technologie interagieren. Geräte werden zunehmend intelligenter - sie verfügen
über mehr und mehr Rechenleistung und häufiger über eigene Kommunikationsschnittstellen.
Das beginnt bei einfachen Haushaltsgeräten und reicht über Transportmittel bis zu großen
ĂĽberregionalen Systemen wie etwa dem Stromnetz. Die Erfassung, die Verarbeitung und der
Austausch digitaler Informationen gewinnt daher immer mehr an Bedeutung. Die Tatsache,
dass ein wachsender Anteil der Geräte heutzutage mobil und deshalb batteriebetrieben ist,
begrĂĽndet den Anspruch, digitale Signalverarbeitungsalgorithmen besonders effizient zu gestalten.
Dies kommt auch dem Wunsch nach einer Echtzeitverarbeitung der groĂźen anfallenden
Datenmengen zugute.
Die vorliegende Arbeit demonstriert Methoden zum Finden effizienter algebraischer Lösungen
für eine Vielzahl von Anwendungen mehrkanaliger digitaler Signalverarbeitung. Solche Ansätze
liefern nicht immer unbedingt die bestmögliche Lösung, kommen dieser jedoch häufig recht
nahe und sind gleichzeitig bedeutend einfacher zu beschreiben und umzusetzen. Die einfache
Beschreibungsform ermöglicht eine tiefgehende Analyse ihrer Leistungsfähigkeit, was für den
Entwurf eines robusten und zuverlässigen Systems unabdingbar ist. Die Tatsache, dass sie nur
gebräuchliche algebraische Hilfsmittel benötigen, erlaubt ihre direkte und zügige Umsetzung
und den Test unter realen Bedingungen.
Diese Grundidee wird anhand von drei verschiedenen Anwendungsgebieten demonstriert.
Zunächst wird ein semi-algebraisches Framework zur Berechnung der kanonisch polyadischen
(CP) Zerlegung mehrdimensionaler Signale vorgestellt. Dabei handelt es sich um ein sehr
grundlegendes Werkzeug der multilinearen Algebra mit einem breiten Anwendungsspektrum
von Mobilkommunikation ĂĽber Chemie bis zur Bildverarbeitung. Verglichen mit existierenden
iterativen Lösungsverfahren bietet das neue Framework die Möglichkeit, den Rechenaufwand
und damit die Güte der erzielten Lösung zu steuern. Es ist außerdem weniger anfällig gegen eine
schlechte Konditionierung der Ausgangsdaten. Das zweite Gebiet, das in der Arbeit besprochen
wird, ist die unterraumbasierte hochauflösende Parameterschätzung für mehrdimensionale Signale,
mit Anwendungsgebieten im RADAR, der Modellierung von Wellenausbreitung, oder
bildgebenden Verfahren in der Medizin. Es wird gezeigt, dass sich derartige mehrdimensionale
Signale mit Tensoren darstellen lassen. Dies erlaubt eine natĂĽrlichere Beschreibung und eine
bessere Ausnutzung ihrer Struktur als das mit Matrizen möglich ist. Basierend auf dieser Idee
entwickeln wir eine tensor-basierte Schätzung des Signalraums, welche genutzt werden kann
um beliebige existierende Matrix-basierte Verfahren zu verbessern. Dies wird im Anschluss
exemplarisch am Beispiel der ESPRIT-artigen Verfahren gezeigt, fĂĽr die verbesserte Versionen
vorgeschlagen werden, die die mehrdimensionale Struktur der Daten (Tensor-ESPRIT),
nichzirkuläre Quellsymbole (NC ESPRIT), sowie beides gleichzeitig (NC Tensor-ESPRIT) ausnutzen.
Um die endgültige Schätzgenauigkeit objektiv einschätzen zu können wird dann ein
Framework für die analytische Beschreibung der Leistungsfähigkeit beliebiger ESPRIT-artiger
Algorithmen diskutiert. Verglichen mit existierenden analytischen AusdrĂĽcken ist unser Ansatz
allgemeiner, da keine Annahmen ĂĽber die statistische Verteilung von Nutzsignal und
Rauschen benötigt werden und die Anzahl der zur Verfügung stehenden Schnappschüsse beliebig
klein sein kann. Dies fĂĽhrt auf vereinfachte AusdrĂĽcke fĂĽr den mittleren quadratischen
Schätzfehler, die Schlussfolgerungen über die Effizienz der Verfahren unter verschiedenen Bedingungen
zulassen. Das dritte Anwendungsgebiet ist der bidirektionale Datenaustausch mit
Hilfe von Relay-Stationen. Insbesondere liegt hier der Fokus auf Zwei-Wege-Relaying mit Hilfe
von Amplify-and-Forward-Relays mit mehreren Antennen, da dieser Ansatz ein besonders gutes
Kosten-Nutzen-Verhältnis verspricht. Es wird gezeigt, dass sich die nötige Kanalkenntnis
mit einem einfachen algebraischen Tensor-basierten Schätzverfahren gewinnen lässt. Außerdem
werden Verfahren zum Finden einer günstigen Relay-Verstärkungs-Strategie diskutiert. Bestehende
Ansätze basieren entweder auf komplexen numerischen Optimierungsverfahren oder auf
Ad-Hoc-Ansätzen die keine zufriedenstellende Bitfehlerrate oder Summenrate liefern. Deshalb
schlagen wir algebraische Ansätze zum Finden der Relayverstärkungsmatrix vor, die von relevanten
Systemmetriken inspiriert sind und doch einfach zu berechnen sind. Wir zeigen das
algebraische ANOMAX-Verfahren zum Erreichen einer niedrigen Bitfehlerrate und seine Modifikation
RR-ANOMAX zum Erreichen einer hohen Summenrate. FĂĽr den Spezialfall, in dem
die Endgeräte nur eine Antenne verwenden, leiten wir eine semi-algebraische Lösung zum
Finden der Summenraten-optimalen Strategie (RAGES) her. Anhand von numerischen Simulationen
wird die Leistungsfähigkeit dieser Verfahren bezüglich Bitfehlerrate und erreichbarer
Datenrate bewertet und ihre Effektivität gezeigt.Modern society is undergoing a fundamental change in the way we interact with technology.
More and more devices are becoming "smart" by gaining advanced computation capabilities
and communication interfaces, from household appliances over transportation systems to large-scale
networks like the power grid. Recording, processing, and exchanging digital information
is thus becoming increasingly important. As a growing share of devices is nowadays mobile
and hence battery-powered, a particular interest in efficient digital signal processing techniques
emerges.
This thesis contributes to this goal by demonstrating methods for finding efficient algebraic
solutions to various applications of multi-channel digital signal processing. These may not
always result in the best possible system performance. However, they often come close while
being significantly simpler to describe and to implement. The simpler description facilitates a
thorough analysis of their performance which is crucial to design robust and reliable systems.
The fact that they rely on standard algebraic methods only allows their rapid implementation
and test under real-world conditions.
We demonstrate this concept in three different application areas. First, we present a semi-algebraic
framework to compute the Canonical Polyadic (CP) decompositions of multidimensional
signals, a very fundamental tool in multilinear algebra with applications ranging from
chemistry over communications to image compression. Compared to state-of-the art iterative
solutions, our framework offers a flexible control of the complexity-accuracy trade-off and
is less sensitive to badly conditioned data. The second application area is multidimensional
subspace-based high-resolution parameter estimation with applications in RADAR, wave propagation
modeling, or biomedical imaging. We demonstrate that multidimensional signals can
be represented by tensors, providing a convenient description and allowing to exploit the
multidimensional structure in a better way than using matrices only. Based on this idea,
we introduce the tensor-based subspace estimate which can be applied to enhance existing
matrix-based parameter estimation schemes significantly. We demonstrate the enhancements
by choosing the family of ESPRIT-type algorithms as an example and introducing enhanced
versions that exploit the multidimensional structure (Tensor-ESPRIT), non-circular source
amplitudes (NC ESPRIT), and both jointly (NC Tensor-ESPRIT). To objectively judge the
resulting estimation accuracy, we derive a framework for the analytical performance assessment
of arbitrary ESPRIT-type algorithms by virtue of an asymptotical first order perturbation
expansion. Our results are more general than existing analytical results since we do not need
any assumptions about the distribution of the desired signal and the noise and we do not
require the number of samples to be large. At the end, we obtain simplified expressions for the
mean square estimation error that provide insights into efficiency of the methods under various
conditions. The third application area is bidirectional relay-assisted communications. Due to
its particularly low complexity and its efficient use of the radio resources we choose two-way
relaying with a MIMO amplify and forward relay. We demonstrate that the required channel
knowledge can be obtained by a simple algebraic tensor-based channel estimation scheme. We
also discuss the design of the relay amplification matrix in such a setting. Existing approaches
are either based on complicated numerical optimization procedures or on ad-hoc solutions
that to not perform well in terms of the bit error rate or the sum-rate. Therefore, we propose
algebraic solutions that are inspired by these performance metrics and therefore perform well
while being easy to compute. For the MIMO case, we introduce the algebraic norm maximizing
(ANOMAX) scheme, which achieves a very low bit error rate, and its extension Rank-Restored
ANOMAX (RR-ANOMAX) that achieves a sum-rate close to an upper bound. Moreover, for
the special case of single antenna terminals we derive the semi-algebraic RAGES scheme which
finds the sum-rate optimal relay amplification matrix based on generalized eigenvectors. Numerical
simulations evaluate the resulting system performance in terms of bit error rate and
system sum rate which demonstrates the effectiveness of the proposed algebraic solutions
Optimization of communication data rates under fading conditions
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