159 results on '"Khalighi, Mohammad-Ali"'
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152. Efficient channel coding for multipulse pulse position modulation in terrestrial FSO systems.
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Xu, Fang, Khalighi, Mohammad-Ali, and Bourennane, Salah
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- 2009
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153. Performance evaluation of receive-diversity free-space optical communications over correlated Gamma-Gamma fading channels.
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Guowei Yang, Khalighi, Mohammad-Ali, Ghassemlooy, Zabih, and Bourennane, Salah
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- 2013
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154. Monte-Carlo-based channel characterization for underwater optical communication systems.
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Gabriel, Chadi, Khalighi, Mohammad-Ali, Bourennane, Salah, Leon, Pierre, and Rigaud, Vincent
- Abstract
We consider channel characterization for underwater wireless optical communication (UWOC) systems. We focus on the channel impulse response and, in particular, quantify the channel time dispersion for different water types, link distances, and transmitter/receiver characteristics, taking into account realistic parameters. We use the Monte Carlo approach to simulate the trajectories of emitted photons propagating in water from the transmitter towards the receiver. During their propagation, photons are absorbed or scattered as a result of their interaction with different particles present in water. To model angle scattering, we use the two-term Henyey–Greenstein model in our channel simulator. We show that this model is more accurate than the commonly used Henyey–Greenstein model, especially in pure sea waters. Through the numerical results that we present, we show that, except for highly turbid waters, the channel time dispersion can be neglected when working over moderate distances. In other words, under such conditions, we do not suffer from any inter-symbol interference in the received signal. Lastly, we study the performance of a typical UWOC system in terms of bit-error-rate using the simple on–off-keying modulation. The presented results give insight into the design of UWOC systems. [ABSTRACT FROM PUBLISHER]
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- 2013
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155. Coded PPM and Multipulse PPM and Iterative Detection for Free-Space Optical Links.
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Fang Xu, Khalighi, Mohammad-Ali, and Bourennane, Salah
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- 2009
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156. Optimization of Receivers' Field of Views in Multi-User VLC Networks: A Bio-inspired Approach
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Eltokhey, Mahmoud Wafik, Khalighi, Mohammad Ali, and Ghassemlooy, Fary
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H600 ,Electrical and Electronic Engineering ,Computer Science Applications - Abstract
Visible light communication is a well-known emerging technology that enables high data rate wireless access in indoor environments by making dual-us e of light-emitting diode luminaires for providing lighting and communication. Managing multiple access and addressing the user's mobility are among the current challenges of this technology. To manage multiple access interference arising from unintended received signals of other users, different approaches have been proposed so far, including zero-forcing precoding and broadcasting of the users' signals. However, by this approach, the network performance is sensitive to the users' locations, since they affect the correlation properties of the network channel matrix. A higher correlation (e.g., for the case of users getting closer together) results in a performance degradation. To mitigate this, we propose a novel approach of optimizing the receivers field-of-views based on the bio-inspired particle swarm optimization in order to adapt to the users' location, and hence, improve the network's robustness. The efficiency of the proposed method is demonstrated through numerical simulations.
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157. Joint optimization of a partially coherent Gaussian beam for free-space optical communication over turbulent channels with pointing errors.
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It Ee Lee, Ghassemlooy, Zabih, Wai Pang Ng, and Khalighi, Mohammad-Ali
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- 2013
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158. Lösungen für die drahtlose Übergabe im Fahrzeugbereich Kommunikation mit sichtbarem Licht
- Author
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Alizadeh Jarchlo, Elnaz, Dressler, Falko, Technische Universität Berlin, Caire, Giuseppe, and Khalighi, Mohammad-Ali
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ddc:004 - Abstract
A vast number of research works demonstrated the high potential of Visible Light Communications (VLC) as a complementary wireless communication technology that can be widely used in vehicular VLC (V-VLC) networks. V-VLC utilizes visible light spectrum to provide communication connections among vehicles. To guarantee coverage in V-VLC networks many Access Points (AP) can be used, which can result in intermittent connectivity between vehicles as the clients and their associated AP and lead to many handovers. In VLC-based vehicular communications the link may experience regular link failures due to shadowing, obstacle, and mobility in contrast to RF-based networks. Therefore, one of the main challenges of V-VLC is the frequent handover which causes outages and network disruption, evidently. In this thesis I introduce V-VLC network scenarios, where there are Automated Guided Vehicles (AGV) moving linearly and in two dimensional (2D) around the warehouse in an indoor environment and each AGV is equipped with several Light Clients (LC). The installed LC stablish VLC link connections with their corresponding Light Access points (LAP) which are installed on ceiling. Each pair of LC and LAP is assigned to non-overlapped frequency bands using Frequency Division Multiple Access (FDMA) technique. Therefore, each LC can establish a VLC link with its corresponding LAP. This Ph.D. thesis aims enhancing the reliability and robustness of the indoor vehicular network communications by reducing the handover latency in the vehicular network. In this thesis, I propose handover solutions at different network layers using different wireless technologies. Note, in all proposed solutions, VLC acts as a primary connection link. To address the frequent link failures during handover in the V-VLC network, I propose Flexible Light Communications (Flight) and Frequency Diversity and Link Aggregation (FDLA) architectures which make use of link aggregation method and FDMA in data link layer to switch between available LAP in case of handover during mobility or the link blockage in linear and 2D movements, respectively. Applying Flight and FDLA solutions decrease the handover delay from 15 s to 0.3, and 0.2 s, respectively compared with no handover technique. Moreover, in the transport layer I utilize the advantage of Multipath-Transmission Control Protocol (MPTCP) to provide network redundancy and load balancing during handover and minimize the number of packet lost caused by connection lose. This solution minimizes the handover delay up to 0.02 s. Additionally, to add robustness and increase network reliability and coverage, I propose Li-Wi, a system which utilizes the benefits of high data rates and link availability of VLC and Wireless Fidelity (WiFi), respectively. Li- Wi solution minimizes the handover latency significantly up to 0.03 s. The main contributions of this thesis can be summarized as (i) Developed several upper layer handover solutions for indoor V-VLC networks,(ii) Assessed the effect of link aggregation and MPTCP methods in the data link and transport layers, respectively separately and together as a combined architecture in a hybrid vehicular network where VLC and WiFi act as a primary and backup links, respectively, and (iii) Demonstrated how applying proposed solutions decrease network latency in both horizontal and vertical handovers in a V-VLC network, which lead to provide an improved network in terms of coverage, reliability and robustness. Eine erhebliche Anzahl von Forschungsarbeiten hat das hohe Potenzial von Visible Light Communications (VLC) als komplementäre drahtlose Kommunikationstechnologie aufgezeigt, die in Fahrzeug-VLC-Netzwerken (V-VLC) breit eingesetzt werden kann. V-VLC nutzt das sichtbare Lichtspektrum, um Kommunikationsverbindungen zwischen Fahrzeugen herzustellen. Um die Abdeckung in V-VLC-Netzwerken zu gewährleisten, müssen viele Access Points (AP) verwendet werden, was zu einer intermittierenden Konnektivität zwischen den Fahrzeugen als Client und ihren zugehörigen AP‘s führt und viele Handover zur Folge hat. In der VLC-basierten Fahrzeugkommunikation kann es, im Gegensatz zu RF-basierten Netzwerken, zu regelmäßigen Verbindungsausfällen aufgrund von Abschattungen, Hindernissen und Mobilität kommen. Daher ist eine der größten Herausforderungen von V-VLC der häufige Handover, das zu Ausfällen und Netzwerkstörungen führt. In dieser Arbeit stelle ich V-VLC-Netzwerk-Szenarien vor, in denen es Automated Guided Vehicles (AGV) gibt, die sich linear und in 2D im Inneren einer Lagerhalle bewegen und jedes AGV mit mehreren Light Clients (LC) ausgestattet ist. Die installierten LCs stellen VLC-Link-Verbindungen mit ihren entsprechenden LAPs her, die an der Decke installiert sind. Jedes Paar von LC und LAP wird unter Verwendung der FDMA-Technik nicht überlappenden Frequenzbändern zugeordnet. Daher kann jeder LC eine VLC-Verbindung mit seinem entsprechenden LAP herstellen. Diese Doktorarbeit zielt darauf ab, die Zuverlässigkeit und Robustheit der Kommunikation in Indoor-Fahrzeugnetzen zu verbessern, indem die Handover Latenzzeit im Netzwerk reduziert wird. In dieser Arbeit schlage ich Handover-Lösungen auf verschiedenen Netzwerkschichten unter Verwendung verschiedener drahtloser Technologien vor. Dabei ist zu beachten, dass in allen vorgeschlagenen Lösungen VLC als primärer Verbindungslink fungiert. Umdie häufigen Verbindungsausfälle während des Handovers im V-VLC-Netzwerk zu adressieren, schlage ich Flexible Light Communications (Flight) und Frequency Diversity and Link Aggregation (FDLA) Architekturen vor, die die Link Aggregation Methode und Frequency Division Multiple Access (FDMA) in der Datenverbin dungsschicht nutzen, um zwischen verfügbaren Light Access Points (LAP) im Falle eines Handovers während der Mobilität oder der Verbindungsblockade in linearen und zweidimensionalen (2D) Bewegungen zu wechseln. Die Anwendung der Flightund FDLA-Lösungen verringert die Handover-Verzögerung von 15 s um 0,3 bzw. 0,2 s im Vergleich zu keiner Handover-Technik. Darüber hinaus nutze ich in der Transportschicht den Vorteil des Multipath-Transmission Control Protocol (MPTCP), um Netzwerk-Redundanz und Lastausgleich während des Handovers zu gewährleisten und die Anzahl der Paketverluste aufgrund von Verbindungsverlusten zu minimieren. Diese Lösung minimiert die Handover-Verzögerung um bis zu 0,02 s. Um zusätzlich die Stabilität hinsichtlich Netzwerkzuverlässigkeit und –abdeckung zu erhöhen, , schlage ich die Verwendung von Li-Wi vor. Li-Wi ist ein System, das die Vorteile der hohen Datenraten und Link-Verfügbarkeit von VLC bzw. Wireless Fidelity (WiFi) nutzt. Die Li-Wi-Lösung minimiert die Handover-Latenzzeit signifikant um bis zu 0,03 s.Die Hauptbeiträge dieser Arbeit lassen sich wie folgt zusammenfassen: (i) Entwicklung verschiedener Handover-Lösungen für V-VLC-Netzwerke in Innenräumen, (ii) Bewertung der Auswirkungen von Link-Aggregation und MPTCP-Methoden in den Datenverbindungs- und Transportschichten, jeweils separat und zusammen als kombinierte Architektur in einem hybriden Fahrzeugnetzwerk, in dem VLC und Wi-Fi als primäre bzw. Backup-Links fungieren, und (iii) Demonstration, wie die Anwendung der vorgeschlagenen Lösungen die Netzwerk-Latenz sowohl bei horizontalen als auch bei vertikalen Handovern in einem V-VLC-Netzwerk verringert, was zu einem verbesserten Netzwerk in Bezug auf Abdeckung, Zuverlässigkeit und Stabilität führt.
- Published
- 2021
159. Performance evaluation of receive-diversity free-space optical communications over correlated Gamma-Gamma fading channels.
- Author
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Yang G, Khalighi MA, Ghassemlooy Z, and Bourennane S
- Abstract
The efficacy of spatial diversity in practical free-space optical communication systems is impaired by the fading correlation among the underlying subchannels. We consider in this paper the generation of correlated Gamma-Gamma random variables in view of evaluating the system outage probability and bit-error-rate under the condition of correlated fading. Considering the case of receive-diversity systems with intensity modulation and direct detection, we propose a set of criteria for setting the correlation coefficients on the small- and large-scale fading components based on scintillation theory. We verify these criteria using wave-optics simulations and further show through Monte Carlo simulations that we can effectively neglect the correlation corresponding to the small-scale turbulence in most practical systems, irrespective of the specific turbulence conditions. This has not been clarified before, to the best of our knowledge. We then present some numerical results to illustrate the effect of fading correlation on the system performance. Our conclusions can be generalized to the cases of multiple-beam and multiple-beam multiple-aperture systems.
- Published
- 2013
- Full Text
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