Browsing by Author "Demir, Muhammet Selim"

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CoMP-based dynamic handover for vehicular VLC networks
(IEEE, 2020-09) Demir, Muhammet Selim; Eldeeb, Hossıen Badr; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; ELDEEB, Hossien Badr Hossien; Demir, Muhammet Selim
Visible light communication (VLC) has emerged as a potential wireless connectivity solution for infrastructure-to-vehicle networks where street lights can be configured to serve as access points. In this letter, we propose dynamic soft handover algorithm based on coordinated multipoint (CoMP) transmission. The proposed algorithm takes the rate of change in the received power as an input and accordingly revises the handover margin and time-to-trigger value without explicit information of the vehicle velocity. Our simulation results demonstrate that the proposed algorithm outperforms conventional CoMP and hard handover and maintains a stable signal quality regardless of vehicle velocity.
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A cross-layer design for dynamic resource management of VLC networks
(IEEE, 2021-03) Demir, Muhammet Selim; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim
In 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.
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Handover in VLC networks with coordinated multipoint transmission
(IEEE, 2018-01-31) Demir, Muhammet Selim; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim; Miramirkhani, Farshad
In 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.
Open Access
Resource allocation for visible light communication systems using simulated annealing based on a problem-specific neighbor function
(IEEE, 2019) Siddiqi, U. F.; Sait, S. M.; Demir, Muhammet Selim; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim
In 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.
Open Access
Unified resource allocation and mobility management technique using particle swarm optimization for VLC networks
(IEEE, 2018-12) Demir, Muhammet Selim; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim
In 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.
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VLC ağları için genetik algoritma temelli kaynak atama tekniği
(IEEE, 2017) Demir, Muhammet Selim; Gemici, Ö. F.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet Selim
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.