886 research outputs found
Hybrid Free-Space Optical and Visible Light Communication Link
V součastnosti bezdrátové optické komunikace (optical wireless communication, OWC) získávají širokou pozornost jako vhodný doplněk ke komunikačním přenosům v rádiovém pásmu. OWC nabízejí několik výhod včetně větší šířky přenosového pásma, neregulovaného frekvenčního pásma či odolnosti vůči elektromagnetickému rušení. Tato práce se zabývá návrhem OWC systémů pro připojení koncových uživatelů. Samotná realizace spojení může být provedena za pomoci různých variant bezdrátových technologií, například pomocí OWC, kombinací různých OWC technologií nebo hybridním rádio-optickým spojem. Za účelem propojení tzv. poslední míle je analyzován optický bezvláknový spoj (free space optics, FSO). Tato práce se dále zabývá analýzou přenosových vlastností celo-optického více skokového spoje s důrazem na vliv atmosférických podmínek. V dnešní době mnoho uživatelů tráví čas ve vnitřních prostorech kanceláří či doma, kde komunikace ve viditelném spektru (visible light communication, VLC) poskytuje lepší přenosové parametry pokrytí než úzce směrové FSO. V rámci této práce byla odvozena a experimentálně ověřena závislost pro bitovou chybovost přesměrovaného (relaying) spoje ve VLC. Pro propojení poskytovatele datavých služeb s koncovým uživatelem může být výhodné zkombinovat více přenosových technologií. Proto je navržen a analyzovám systém pro překonání tzv. problému poslední míle a posledního metru kombinující hybridní FSO a VLC technologie.The field of optical wireless communications (OWC) has recently attracted significant attention as a complementary technology to radio frequency (RF). OWC systems offer several advantages including higher bandwidth, an unregulated spectrum, resistance to electromagnetic interference and a high order of reusability. The thesis focuses on the deployment and analyses of end-user interconnections using the OWC systems. Interconnection can be established by many wireless technologies, for instance, by a single OWC technology, a combination of OWC technologies, or by hybrid OWC/RF links. In order to establish last mile outdoor interconnection, a free-space optical (FSO) has to be investigated. In this thesis, the performance of all-optical multi-hop scenarios is analyzed under atmospheric conditions. However, nowadays, many end users spend much time in indoor environments where visible light communication (VLC) technology can provide better transmission parameters and, significantly, better coverage. An analytical description of bit error rate for relaying VLC schemes is derived and experimentally verified. Nonetheless, for the last mile, interconnection of a provider and end users (joint outdoor and indoor connection) can be advantageous when combining multiple technologies. Therefore, a hybrid FSO/VLC system is proposed and analyzed for the interconnection of the last mile and last meter bottleneck
Propagation measurement based study on relay networks
Von der nächsten Generation von Mobilfunksystemen erwartet man eine
umfassende Versorgung mit breitbandigen Multimediadiensten. Um die dafür
erforderliche flächendeckende Versorgung mit hohen Datenraten zu
gewährleisten, können Relay-Netzwerke einen wesentlichen Beitrag liefern.
Hierbei werden Netzwerkstationen mit Relay-Funktionalität in zellulare
Netzwerke integriert.
Diese Dissertation befasst sich mit der Untersuchung Relay-basierter
Netzwerke unter Verwendung von Ausbreitungsmessungen. Die Arbeit deckt
Fragen zur Kanalmodellierung, Systemevaluierung bis hin zur
Systemverifikation ab. - Zunächst wird ein auf Funkkanalmessungen
beruhendes experimentelles Kanalmodell für Relay-Netzwerke vorgestellt. Im
Weiteren werden technische Verfahren für Mehrfachzugriffs-Relay-Netzwerke
MARN diskutiert. Die erreichbare Systemleistung wurde unter Verwendung von
Rayleigh-Kanälen innerhalb einer Systemsimulation bestimmt und im Anschluss
mit realen Kanälen, die sowohl direkt aus Funkkanalmessungen als auch
indirekt aus dem bereits erwähnten Kanalmodell abgeleitet wurden,
verifiziert.
Bisherige Arbeiten zur Modellierung breitbandiger Multiple-Input
Multiple-Output (MIMO) Kanäle berücksichtigen nicht oder nur sehr stark
vereinfacht die Langzeitkorrelationseigenschaften zwischen den Links und
werden damit der vermaschten und räumlich weit verteilten Topologie von
Relay-Netzwerken gerecht. In der vorliegenden Dissertation erfolgte daher
eine experimentelle Untersuchung zu den Korrelationseigenschaften von
Large-Scale-Parametern LSP, die unter Verwendung von Funkkanalmessdaten aus
urbanen Umgebungen und aus Innenräumen abgeleitet wurden. Die Ergebnisse
hierzu fanden Eingang in das vom WINNER-Projekt entwickelte Kanalmodell.
Sie erlauben damit eine realistischere Simulation von Relay-unterstützten
Netzen.
Einen weiteren Schwerpunkt dieser Arbeit stellen technische Verfahren dar,
die eine Erhöhung der Systemleistung in MARN mit unbekannter Interferenz
UKIF versprechen. Im Einzelnen handelt es sich um die
Mehrfachzugriffs-Kodierung MAC - die eine verbesserte Signaltrennung auf
der Empfängerseite und eine Erhöhung des Datendurchsatzes erlaubt, den
Entwurf eines Relay-Protokolls zur Erhöhung der Systemeffizienz, einen
Minimum Mean Square Error (MMSE) Algorithmus zur Unterdrückung unbekannter
Interferenzen bei Erhaltung der MAC-Signalstruktur mehrerer Mobilstationen
MS, und ein fehlererkennungsbasiertes Signalauswahlverfahren zur
Diversitätserhöhung.
Die vorgenannten Verfahren werden in einer Systemsimulation zunächst mit
Rayleigh-Kanälen evaluiert und demonstrieren die erzielbare theoretische
Leistungssteigerung. Die Berücksichtigung realer Funkkanäle innerhalb der
Systemsimulation zeigt allerdings, dass die theoretische Systemleistung so
in der Realität nicht erreichbar ist. Die Ursache hierfür ist in den
idealisierten Annahmen theoretischer Kanäle zu suchen.
Für die Entwicklung künftiger Relay-Netzwerke bieten die in dieser Arbeit
aufbereiteten Erkenntnisse hinsichtlich der
Langzeitkorrelationseigenschaften zwischen den Links einen wertvollen
Beitrag für die Abschätzung ihrer Systemleistung auf der Basis eines
verbesserten Kanalmodells.Considering technological bases of next generation wireless systems, it is
expected that systems can provide a variety of coverage requirements to
support ubiquitous communications. To satisfy the requirements, an
innovative idea, integrating network elements with a relaying capability
into cellular networks, is one of the most promising solutions.
The main topic of this dissertation is a propagation measurement based
study on relay networks. The study includes three parts: channel modeling,
performance evaluation, and verification. First of all, an empirical
channel model for relay networks is proposed based on statistical analyses
of measurement data. Then, advanced techniques for the throughput
improvement and interference cancellation are proposed for Multiple Access
Relay Networks (MARN) which are used as an example of relay networks. The
performance of the considered MARN is evaluated for Rayleigh channels, and
then verified for realistic channels, obtained from measurement data and
from the experimental relay channel model as well.
For relay channel modeling, the long-term correlation properties between
links are of crucial importance due to the meshed-network topology.
Although, there is a wide variety of research results for Multiple-Input
Multiple-Output (MIMO) channel modeling available, the characterization of
correlation properties has been significantly simplified or even completely
ignored which motivates this research to be performed. In this
dissertation, the experimental results of the correlation properties of
Large Scale Parameters (LSP) are presented through the analysis on the
real-field measurement data for both the urban and indoor scenarios.
furthermore, the correlation properties have been fully introduced into the
WINNER channel Model (WIM) for realistic relay channel simulations.
As a further contribution of this dissertation, various advanced techniques
are proposed for MARN in the presence of Unknown Interference (UKIF).
Multiple Access Coding (MAC) is introduced as a multiple access technique.
The use of MAC provides the signal separability at the receiver and
improves throughput. Thereafter, high system resource efficiency can be
achieved through relay protocol design. At the receiver, Minimum Mean
Square Error (MMSE)-based spatial filtering is used to suppress UKIF while
preserving multiple Mobile Station (MS)s’ MAC-encoded signal structure.
Furthermore, an error detection aided signal selection technique is
proposed for diversity increasing.
The theoretical system performance with aforementioned techniques is
simulated for Rayleigh channels. Thereafter, realistic channels are
exploited for the performance verification. The gap between the theoretical
performance and the realistic performance indicates that the assumptions
made to the simplified Rayleigh-channels do not fully hold in reality.
For the future relay system design, this work provides valuable information
about the performance evaluation of relay networks in consideration of the
correlation properties between links
Characterization of the on-body path Loss at 2.45 GHz and energy efficient WBAN design for dairy cows
Wireless body area networks (WBANs) provide promising applications in the healthcare monitoring of dairy cows. The characterization of the path loss (PL) between on-body nodes constitutes an important step in the deployment of a WBAN. In this paper, the PL between nodes placed on the body of a dairy cow was determined at 2.45 GHz. Finite-difference time domain simulations with two half-wavelength dipoles placed 20 mm above a cow model were performed using a 3-D electromagnetic solver. Measurements were conducted on a live cow to validate the simulation results. Excellent agreement between measurements and simulations was achieved and the obtained PL values as a function of the transmitter-receiver separation were well fitted by a lognormal PL model with a PL exponent of 3.1 and a PL at reference distance ( 10 cm) of 44 dB. As an application, the packet error rate ( PER) and the energy efficiency of different WBAN topologies for dairy cows (i.e., single-hop, multihop, and cooperative networks) were investigated. The analysis results revealed that exploiting multihop and cooperative communication schemes decrease the PER and increase the optimal payload packet size. The analysis results revealed that exploiting multihop and cooperative communication schemes increase the optimal payload packet size and improve the energy efficiency by 30%
Outage Probability Analysis of Full-Duplex Amplify-and-Forward MIMO Relay Systems
abstract: Multiple-input multiple-output systems have gained focus in the last decade due to the benefits they provide in enhancing the quality of communications. On the other hand, full-duplex communication has attracted remarkable attention due to its ability to improve the spectral efficiency compared to the existing half-duplex systems. Using full-duplex communications on MIMO co-operative networks can provide us solutions that can completely outperform existing systems with simultaneous transmission and reception at high data rates.
This thesis considers a full-duplex MIMO relay which amplifies and forwards the received signals, between a source and a destination that do not a have line of sight. Full-duplex mode raises the problem of self-interference. Though all the links in the system undergo frequency flat fading, the end-to-end effective channel is frequency selective. This is due to the imperfect cancellation of the self-interference at the relay and this residual self-interference acts as intersymbol interference at the destination which is treated by equalization. This also leads to complications in form of recursive equations to determine the input-output relationship of the system. This also leads to complications in the form of recursive equations to determine the input-output relationship of the system.
To overcome this, a signal flow graph approach using Mason's gain formula is proposed, where the effective channel is analyzed with keen notice to every loop and path the signal traverses. This gives a clear understanding and awareness about the orders of the polynomials involved in the transfer function, from which desired conclusions can be drawn. But the complexity of Mason's gain formula increases with the number of antennas at relay which can be overcome by the proposed linear algebraic method. Input-output relationship derived using simple concepts of linear algebra can be generalized to any number of antennas and the computation complexity is comparatively very low.
For a full-duplex amplify-and-forward MIMO relay system, assuming equalization at the destination, new mechanisms have been implemented at the relay that can compensate the effect of residual self-interference namely equal-gain transmission and antenna selection. Though equal-gain transmission does not perform better than the maximal ratio transmission, a trade-off can be made between performance and implementation complexity. Using the proposed antenna selection strategy, one pair of transmit-receive antennas at the relay is selected based on four selection criteria discussed. Outage probability analysis is performed for all the strategies presented and detailed comparison has been established. Considering minimum mean-squared error decision feedback equalizer at the destination, a bound on the outage probability has been obtained for the antenna selection case and is used for comparisons. A cross-over point is observed while comparing the outage probabilities of equal-gain transmission and antenna selection techniques, as the signal-to-noise ratio increases and from that point antenna selection outperforms equal-gain transmission and this is explained by the fact of reduced residual self-interference in antenna selection method.Dissertation/ThesisMasters Thesis Electrical Engineering 201
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