Yazar "Karabulut, Muhammet Ali" seçeneğine göre listele

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    IEEE 802.11 MAC Protokolünün VANET ağlardaki performans modellemesi ve analizi
    (Oğuzhan Yılmaz, 2020) Karabulut, Muhammet Ali; Shah, A. F. M. Shahen; İlhan, Hacı
    IEEE 802.11 standardı, araçsal tasarsız ağlar (Vehicular Ad Hoc Networks, VANETs) için ortam erişim kontrolü (Medium Access Control, MAC) ve fiziksel (PHY) katmanının özelliklerini tanımlamaktadır. IEEE 802.11 standardında, dağıtılmış koordinasyon işlevi (Distributed Coordination Function, DCF) MAC katmanında kullanılan bir tekniktir. DCF, ortama erişmek için çarpışmadan kaçınma ile taşıyıcı duyarlı çoklu erişim (Carrier Sense Multiple Access with Collision Avoidance, CSMA/CA) tekniğini kullanmaktadır. Ayrıca, gönderim isteği (Request To Send, RTS)/ gönderime uygun (Clear To Send, CTS) mekanizması gizli araç düğümleri problemlerinin üstesinden gelmek için kullanılır. CSMA/CA ve RTS/CTS mekanizmalarının algoritmaları sunulmuştur. Markov zincir modeline dayalı analitik analiz, performansı araştırmak için sunulmuştur. Araç hızı, araç yoğunluğu, çekişme penceresi (Contention Window) ve yeniden iletim limiti (Maximum Retransmision Limit) gibi performansı etkileyebilecek parametreler göz önünde bulundurulmuştur. Performans ölçüleri ve parametreleri arasındaki ilişki incelenmiştir. Veri hızı, paket bırakma oranı (Packet Dropping Rate, PDR) ve gecikme ifadeleri elde edilmiştir. Ayrıca, benzetim sonuçları ile performans analizi doğrulanmıştır. CSMA/CA ve RTS/CTS mekanizmalarının karşılaştırılması sunulmuştur.
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    Improvement of performance with MIMO Enabled MAC Protocol for VANETs
    (Institute of Electrical and Electronics Engineers Inc., 2020) Karabulut, Muhammet Ali; Shahen Shah, A.F.M.; Ilhan, Haci
    Multiple inputs multiple outputs (MIMO) techniques are considered important methods as they significantly increase the capacity of wireless networks without additional bandwidth or transmission power. A MIMO system acquires a physical layer (PHY) and a transmission channel layered structure. As a result, support from higher layers can significantly improve the system-level performance of the network, with an inter-layer approach that enables effective management of the spatial layers of the channel. In this study, a high capacity medium access control (MAC) protocol is presented for MIMO support. The proposed protocol is based on the IEEE 802.11 standard and provides flexible and scalable support for multiple antenna terminals backwards compatible with vehicular nodes. © 2020 IEEE.
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    OEC-MAC: A Novel OFDMA Based Efficient Cooperative MAC Protocol for VANETS
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA, 2020) Karabulut, Muhammet Ali; Shah, A. F. M. Shahen; İlhan, Hacı
    In vehicular ad hoc networks (VANETs), mobility between vehicles can cause rapid topology changes with frequent disconnections, which result in collisions and packet losses that make communications unstable. Alternatively, cooperative transmission can increase the reliability of communication by eliminating these problems in VANETS. In heavy traffic conditions, carrier sense multiple access with collision avoidance (CSMA/CA) suffers from collision, and it is not effective when high data rate is required. Therefore, orthogonal frequency division multiple access (OFDMA) is proposed. With the use of OFDMA, throughput is increased and delay is decreased by reducing the probability of collision in high traffic scenario. In this study, a novel OFDMA based efficient cooperative MAC protocol (OEC-MAC) is proposed for VANETs. Subcarrier channels assignment and access mechanisms are provided. The mechanism is presented not only for choosing the appropriate transmission mode but also for selecting the optimum relay. New control messages are defined to support cooperative communication. The performance of OEC-MAC protocol is examined by providing analytical analysis based on Markov chain model. Numerical results are demonstrated, which reveal that OEC-MAC protocol ensures a remarkable increase in throughput and also satisfies the strict delay requirement of 100 ms in VANETs for safety messages (sm). In addition, communication reliability is increased by reducing the packet dropping rate (PDR). Numerical results are compared with existing protocols, and a quantitative comparison is provided. It has been seen form results that proposed OEC-MAC protocol is better than existing schemes, especially under heavy traffic scenarios.
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    Performance modeling and analysis of the IEEE 802.11 MAC protocol for VANETs
    (GAZI UNIV, FAC ENGINEERING ARCHITECTURE, BAYAR BULVARI, MALTEPE, ANKARA, 06570, TURKEY, 2020) Karabulut, Muhammet Ali; Shah, A. F. M. Shahen; İlhan, Hacı
    The IEEE 802.11 standard defines the specifications of the media access control (MAC) and physical (PHY) layers for vehicular ad hoc networks (VANETs). In IEEE 802.11, distributed coordination function (DCF) is the fundamental access technique, which employs a carrier sense multiple access with collision avoidance (CSMA/CA) mechanism to access the medium. In addition, request to send (RTS)/clear to send (CTS) mechanism is used to overcome hidden vehicular nodes problem. In this paper, an analytical model is developed to evaluate the performance of the IEEE 802.11 MAC for VANETs. The algorithm of CSMA/CA and RTS/CTS mechanism are presented. Markov chain model based analytical analysis is presented to investigate the performance. Parameters that can influence the performance such as vehicles velocity, vehicle density, contention window size, maximum retransmission limit etc. are considered. The relationship between the performance metrics and parameters are derived. Throughput, packet dropping rate (PDR) and delay expressions are obtained. Moreover, numerical results are demonstrated to verify the analysis. The comparison between CSMA/CA and RTS/CTS access mechanisms is presented.
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    Performance Optimization of Cluster-Based MAC Protocol for VANETs
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141, 2020) Shah, A. F. M. Shahen; Karabulut, Muhammet Ali; İlhan, Hacı; Türeli, Ufuk
    Recently, a novel cluster-based medium access control (CB-MAC) protocol has been proposed for vehicular ad hoc networks (VANETs). Though performance of CB-MAC protocol is affected by cluster size, no mechanism is provided to manage cluster size efficiently. In this paper, the performance of CB-MAC protocol is optimized for VANETs by optimizing transmission probability with cluster size. Each vehicle should adopt the optimum transmission probability in the cluster which can be obtained by tuning the number of clusters in VANET. Therefore, optimum number of clusters is defined based on the number of vehicles in VANETs. An analytical study based on Markov chain model is provided. Optimum transmission probability, and optimum number of clusters expressions are derived. The microscopic mobility model is generated in SUMO for practical scenario. Simulation results are presented which verify analytical (theoretical) analysis and show that the performance of CB-MAC protocol is maximized in terms of throughput, packet dropping rate (PDR), and delay. Throughput is remarkably increased, whereas PDR and delay are decreased.
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    Survey and Performance Evaluation of Multiple Access Schemes for Next-Generation Wireless Communication Systems
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141, 2021) Shah, A. F. M. Shahen; Qasim, Ahmed Nidham; Karabulut, Muhammet Ali; İlhan, Hacı; Islam, Md. Baharul
    Mobile communication systems are always in continuous evolution due to the demands of the end-users using this technology. Therefore, before the possible launch of 5G, some technologies have opened the way to the new mobile communication system. The need for technologies that provide more comfort to users has led to the construction of complex communication systems that were only science fiction decades ago. The information society in which we are now immersed has been the result of constant progress over time. In this paper, a survey of multiple access schemes for next-generation wireless communication systems is presented. Multiple access schemes are reviewed for possible use in next-generation wireless communication systems such as orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA), and delta-orthogonal multiple access (D-OMA), etc. General comparisons of 1G to 6G are presented. Different types of OMA are explained, and then orthogonal frequency division multiple access (OFDMA) is chosen as an example of the OMA scheme to compare with NOMA and D-OMA. There are two types of NOMA: power-domain and code-domain, which are discussed and compared. Simulation results are presented, and a comparison among different access schemes is provided.