Flexible Wi-Fi communication among mobile robots in Indoor industrial environments

In order to speed up industrial processes and to improve logistics, mobile robots are getting important in industry. In this paper, we propose a flexible and configurable architecture for the mobile node that is able to operate in different network topology scenarios. The proposed solution is able to operate in presence of network infrastructure, in ad hoc mode only, or to use both possibilities. In case of mixed architecture, mesh capabilities will enable coverage problem detection and overcoming. The solution is based on real requirements from an automated guided vehicle producer. First, we evaluate the overhead introduced by our solution. Since the mobile robot communication relies in broadcast traffic, the broadcast scalability in mesh network is evaluated too. Finally, through experiments on a wireless testbed for a variety of scenarios, we analyze the impact of roaming, mobility and traffic separation, and demonstrate the advantage of our approach in handling coverage problems

Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights

In this paper, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles

A Flexible Transport Layer Protocol Architecture for Handover in a Vehicular VLC Network

Recent research works have focused on the feasibility of using the multipath-transmission control protocol (MPTCP) in order to optimize network throughput and latency. In this work, we propose a novel architecture using MPTCP for a vehicular visible light communications (VLC) network to improve the performance in terms of network outage duration and throughout. Two relevant MPTCP schedulers and an MPTCP tool are selected to analyze VLC performance during the handover. The results show that the proposed system offers low-outage duration handover of 24 ms and high data throughput of 125 Mbps using "Redundant"and "Default"schedulers, respectively

FDLA: A Novel Frequency Diversity and Link Aggregation Solution for Handover in an Indoor Vehicular VLC Network

VLC (VLC) has been introduced as a complementary wireless technology that can be widely used in industrial indoor environments where automated guided vehicles aim to ease and accelerate logistics. Despite its advantages, there is one significant drawback of using an indoor () network that is there is a high handover outage duration. In line-of-sight VLC links, such handovers are frequently due to mobility, shadowing, and obstacles. In this paper, we propose a frequency diversity and link aggregation solution, which is a novel technique in Data link layer to tackle handover challenge in indoor networks. We have developed a small-scale prototype and experimentally evaluated its performance for a variety of scenarios and compared the results with other handover techniques. We also assessed the configuration options in more detail, in particular focusing on different network traffic types and various address resolution protocol intervals. The measurement results demonstrate the advantages of our approach for low-outage duration handovers in. The proposed idea is able to decrease the handover outage duration in a two-dimensional network to about 0.2 s, which is considerably lower compared to previous solutions

Analyzing Interface Bonding Schemes for VLC with Mobility and Shadowing

Node mobility and shadowing are the most common reasons requiring a handover in vehicular visible light communications (VVLC). In order to provide seamless mobility during the handover, it is required to decrease the network outage duration. This paper aims to improve the outage duration in handover caused by mobility and shadow for VLC networks. We analyze interface bonding schemes using two different primary interface reselection methods. The results show that using "failure"interface selection method instead of "always"method reduces the VLC handover outage duration by 62% and 44% in bonding schemes for transmission control protocol (TCP) and user datagram protocol (UDP) network traffic, respectively

Lösungen für die drahtlose Übergabe im Fahrzeugbereich Kommunikation mit sichtbarem Licht

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.EC/H2020/764461/EU/European Training Network on Visible light based Interoperability and Networking/VisIo

Kablosuz duyarga ağlarında yaşam süresine duyarlı ağırlıklı kümeleme.

Wireless Sensor Networks typically include wireless sensor nodes with limited energy. Network lifetime and scalability are considered as two significant requirements for sensor network applications. In order to decrease energy consumption and increase network lifetime one can apply an efficient clustering method. The application of the clustering method proposed in this thesis (LTS-WCA) leads to reducing the energy cost and the transmission distance of each node by grouping the nodes in several clusters and assigning specific cluster heads for each group. This study aims to compare existing clustering algorithms and make modifications to enhance their performance. The study includes the implementation of LTS-WCA, which is proposed within the scope of this work, in a simulation environment and its evaluation in order to demonstrate its effectiveness.M.S. - Master of Scienc

A polynomial analog baseband predistorter for compensation of wireless amplifier’s distortion

This paper presents a new analog polynomial pre-distortion circuit using 350nm CMOS technology to reduce the distortion of the power amplifier in wireless communication systems. The proposed pre-distortion circuit uses the polynomial approach. The coefficients of the polynomial are controlled by multiplying them with sufficient digit defined through the indirect learning process to provide best practice linearization. Circuit level simulation of the proposed circuit is using Cadence DFW II is used as proof of concept. The simulation set-up comprises a power amplifier, excited with a four carrier GSM signal, pre-distorted by the proposed circuit. Simulation results show that using the pre-distortion circuit the 3rd order intermodulation distortion is reduced on average by 12 and 16 dB.publishe