1,720,993 research outputs found
Görünür ışık haberleşmesi ağları için hareketlilik yönetimi ve kaynak atama stratejileri
No full textThere has been a growing interest in Visible Light Communications (VLC) in recent years. The existing works in the literature on point-to-point VLC systems are well established, and especially the studies on physical layer aspects demonstrate the po tential of VLC. However, to transform VLC into a multi-user, multi-cell, scalable, and fully networked wireless technology, significant further efforts for upper layer issues are needed. This dissertation focuses on mobility management and resource allocation techniques for indoor and vehicular VLC systems. In the first part of this thesis, we consider a centralized Direct Current biased Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM) based VLC network and formulate a subcarrier resource allocation problem to maximize the user satisfaction index. We have used the Particle Swarm Optimization (PSO) method for the solution to the resulting problem. The superiority of the proposed algorithm is demonstrated through an extensive simula tion study. In the second part of the thesis, we propose an energy-efficient dynamic resource management framework for indoor OFDM-based VLC networks. Specifi cally, we formulate and investigate a stochastic cross-layer optimization problem to optimize the network resources under the constraints of queue stability and power to maximize the average system throughput. In the last part of the thesis, we pro pose handover algorithms for indoor and outdoor VLC networks. First, we propose a handover algorithm for indoor VLC networks with Coordinated Multipoint (CoMP) transmission and evaluate its performance in physical channel settings based on ray tracing. Then, we present a novel dynamic handover algorithm for outdoor vehicular VLC networks. The proposed algorithm dynamically revises the handover parameters by considering the vehicle speed without requiring additional feedback information.G¨or¨un¨ur ı¸sık haberle¸smesi (VLC) sistemlerine son yıllarda giderek artan bir ilgi mev cuttur. Literat¨urdeki noktadan noktaya VLC sistemlerini inceleyen ¸calı¸smalar yeterli olgunluk seviyesindedir ve ¨ozellikle fiziksel katman ile ilgili ¸calı¸smalar VLC’nin potan siyelini ortaya koymaktadır. Fakat, VLC sistemlerini ¸cok kullanıcılı, ¸cok h¨ucreli ve a˘g tabanlı bir kablosuz a˘g teknolojisine d¨on¨u¸st¨urmek i¸cin ¨ust katman konularını inceleyen ¨onemli yeni ¸calı¸smalara ihtiya¸c vardır. Bu tez i¸c mekan ve ta¸sıtlara ili¸skin VLC sistem lerinde kaynak ataması ve hareketlilik y¨onetimi tekniklerine odaklanır. Bu tezin ilk kısmında, do˘gru akım e¸sikli optik ortogonal frekans b¨olmeli ¸co˘gullama (DCO-OFDM) tekni˘gine dayalı merkezi bir VLC a˘gı i¸cin kullanıcı memnuniyet indeksini maksimize eden bir alt ta¸sıyıcı atama problemi form¨ule edilmi¸stir. Bu problemin ¸c¨oz¨um¨u i¸cin biyolojiden ilham alan par¸cacık s¨ur¨u optimizasyonu (PSO) kullanılmı¸stır. Onerilen ¨ algoritmanın ¨ust¨unl¨u˘g¨u kapsamlı bir sim¨ulasyon ¸calı¸smasıyla g¨osterilmi¸stir. Tezin ikinci kısmında, OFDM temelli i¸c mekan VLC a˘gları i¸cin enerji tasarruflu dinamik kaynak y¨onetimi yapısı ¨onerilmi¸stir. Spesifik olarak, kuyruk kararlılı˘gı ve g¨u¸c kısıtları altında ortalama sistem ¸cıktısını maksimize etmek i¸cin a˘g kaynaklarının kullanımını en iyileyen stokastik katmanlar arası optimizasyon problemi form¨ule edilmi¸s ve ince lenmi¸stir. Tezin son kısmında, i¸c ve dı¸s mekan VLC a˘gları i¸cin el de˘gi¸stirme y¨ontemleri ¨onerilmi¸stir. ˙Ilk olarak, i¸c mekan VLC a˘gları i¸cin koordineli ¸cok-noktalı (CoMP) ile timli bir el de˘gi¸stirme algoritması ¨onerilmi¸s ve ¨onerilen algoritmanın performansı ı¸sın takibine dayalı fiziksel kanal kullanılarak de˘gerlendirilmi¸stir. Sonrasında, ta¸sıtlara ili¸skin VLC a˘gları i¸cin hıza duyarlı dinamik bir el de˘gi¸stirme y¨ontemi g¨osterilmi¸stir. Onerilen algoritma, ek geri bildirim bilgisi gerektirmeden ara¸c hızını dikkate alarak ¨ el de˘gi¸stirme parametrelerini dinamik olarak revize eder
A cross-layer design for dynamic resource management of VLC networks
No full textIn this article, we propose a cross-layer resource management mechanism for an indoor multiuser visible light communication (VLC) access network. The physical layer builds upon DC-biased orthogonal frequency division multiple access. Channel state information at the physical layer serves as a performance indicator for better data rate opportunity while queue state information at medium access control layer provides the information about packet urgency. A packet based traffic arrival model is considered such that incoming packets with random inter arrival times join a separate queue dedicated to each user if the admission control accepts them, otherwise packets are dropped. We formulate and solve a stochastic cross-layer optimization problem to optimize the network resources under the constraints of queue stability and power to maximize the average system throughput. By using the Lyapunov optimization technique, we convert the long term time-Average optimization problem into series of single time slot online problem. Then, we decompose the problem into independent sub problems and propose packet admission, resource (access point and subcarrier) allocation and power control solutions. We present simulation results to demonstrate the superiority of proposed scheme over existing solutions in the literature.TÜBİTA
Unified resource allocation and mobility management technique using particle swarm optimization for VLC networks
Full text linkIn this paper, we present a unified resource allocation and mobility management algorithm based on particle swarm optimization (PSO) for indoor visible light communication (VLC) networks. We consider a VLC network where multiple LEDs serve as access points (APs). A centralized controller collects channel state information, quality of service requirements of the users, and the overload status of the APs. Based on the available information, in each time interval, the controller decides which user is served by which AP and assigns subcarriers to the users with the objective of maximizing both the system throughput and user satisfaction. We formulate the resource allocation problem as a constrained nonlinear integer programming problem and solve it using meta-heuristic PSO. Through an extensive simulation study, the superiority of the proposed algorithm in terms of system throughput and user satisfaction over round robin, best channel quality information, and genetic algorithms is demonstrated.Council for Scientific and Industrial ResearchPublisher versio
Handover in VLC networks with coordinated multipoint transmission
No full textIn this work, we consider a cellular visible light communication (VLC) network where each ceiling luminary serves as an access point (AP). The network is assumed to support coordinated multipoint transmission (CoMP). The user is mainly served by an AP (i.e., luminary) from which he/she gets the strongest signal. When the user moves towards the cell edge, the received signal from the served AP drops. Based on the handover algorithm decision, a handover to another AP can take place or CoMP is initiated. In the case of CoMP, the user is jointly served by two coordinating APs that transmit the same information. We compare the performance of proposed joint transmission-handover algorithm with conventional hard handover and demonstrate significant performance gains in terms of user data rate
Genetic algortihm based resource allocation technique for VLC networks
No full textDue to copyright restrictions, the access to the full text of this article is only available via subscription.Bu çalışmada, görünür ışıkla haberleşme (VLC) ağları için genetik algoritma (GA) temelli kaynak atama tekniği önerilmiştir. Optik VLC agı mevcut aydınlatma altyapısının kullanıldığı iç mekanlarda çok küçük boyutlu hücrelerden oluşur. Sistem kapasitesini artırmak ve kaynakları kullanıcılar arasında daha adaletli bir şekilde dağıtmak için VLC ağlarında etkili kaynak atama mekanizmalarına gerek vardır. Bu nedenle, bu çalışmada GA temelli kaynak atama tekniği önerilerek toplam kanal kapasitesini maksimize etme amaçlanmıştır. Önerilen kaynak atama algoritması Round Robin ve Best CQI algoritmalarına göre sistem kapasitesini arttırma açısından daha iyi sonuçlar vermiştir.In this paper, we present a genetic algorithm (GA) based resource allocation technique for indoor optical visible light communication (VLC) networks. Optical VLC network using existing lighting infrastructure in an indoor environment is a cellular network with very small size cells. It is necessary to have effective resource allocation mechanisms for VLC networks to maximize system throughput and fairness among users. We propose a GA based resource allocation scheme to improve total system throughput. Our proposed scheme gives better results compared to Round Robin and Best CQI algorithms in terms of system throughput.TÜBİTA
Resource allocation for visible light communication systems using simulated annealing based on a problem-specific neighbor function
No full textIn this paper, we consider a visible light communication (VLC) system with direct current-biased orthogonal frequency division multiplexing (DC-OFDM) and investigate resource allocation for a multi-user environment. Based on the user satisfaction index as a function of data rate, we aim to optimally determine the allocation of the users to different LEDs (acting as access points) and 0I-DM subcarriers. We propose a simulated annealing-based heuristic to maximize the average user satisfaction index. In an effort to make the proposed solution practically feasible, the runtime of the proposed heuristic is kept less than the channel coherence time, whose value is in order of tens of milliseconds. We evaluate the performance of the proposed heuristic algorithm in different scenarios that vary in the number of users, the number of LEDs, and the separation between users. Our results demonstrate that the proposed heuristic outperforms other well-known heuristics (such as standard simulated annealing, iterative greedy, particle swarm optimization, and tabu search) while achieving good quality solutions within a short execution time, i.e., 40-80 ms.King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia ; TÜBİTAKPublisher versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
