Browsing by Subject "Air traffic control"

Now showing 1 - 4 of 4

Open Access
Efficient transport of time-varying IP traffic in flexi-grid optical networks
(IEEE, 2014) Tunc, Çağlar; Akar, Nail
Frequency slot width selection in flexi-grid optical networks refers to the process of online update of the slot width of the channel, according to time-varying traffic demands. Since slot width updates are associated with signaling costs, it is common to limit the rate of updates. In this article, we propose a model-free hysteresis-based slot width selection algorithm for flexi-grid optical networks. © 2014 IEEE.
Open Access
Exact and heuristic approaches based on noninterfering transmissions for joint gateway selection, time slot allocation, routing and power control for wireless mesh networks
(Elsevier, 2017) Gokbayrak, K.; Yıldırım, E. A.
Wireless mesh networks (WMNs) provide cost-effective alternatives for extending wireless communication over larger geographical areas. In this paper, given a WMN with its nodes and possible wireless links, we consider the problem of gateway node selection for connecting the network to the Internet along with operational problems such as routing, wireless transmission capacity allocation, and transmission power control for efficient use of wired and wireless resources. Under the assumption that each node of the WMN has a fixed traffic rate, our goal is to allocate capacities to the nodes in proportion to their traffic rates so as to maximize the minimum capacity-to-demand ratio, referred to as the service level. We adopt a time division multiple access (TDMA) scheme, in which a time frame on the same frequency channel is divided into several time slots and each node can transmit in one or more time slots. We propose two mixed integer linear programming formulations. The first formulation, which is based on individual transmissions in each time slot, is a straightforward extension of a previous formulation developed by the authors for a related problem under a different set of assumptions. The alternative formulation, on the other hand, is based on sets of noninterfering wireless transmissions. In contrast with the first formulation, the size of the alternative formulation is independent of the number of time slots in a frame. We identify simple necessary and sufficient conditions for simultaneous transmissions on different links of the network in the same time slot without any significant interference. Our characterization, as a byproduct, prescribes a power level for each of the transmitting nodes. Motivated by this characterization, we propose a simple scheme to enumerate all sets of noninterfering transmissions, which is used as an input for the alternative formulation. We also introduce a set of valid inequalities for both formulations. For large instances, we propose a three-stage heuristic approach. In the first stage, we solve a partial relaxation of our alternative optimization model and determine the gateway locations. This stage also provides an upper bound on the optimal service level. In the second stage, a routing tree is constructed for each gateway node computed in the first stage. Finally, in the third stage, the alternative optimization model is solved by fixing the resulting gateway locations and the routing trees from the previous two stages. For even larger networks, we propose a heuristic approach for solving the partial relaxation in the first stage using a neighborhood search on gateway locations. Our computational results demonstrate the promising performance of our exact and heuristic approaches and the valid inequalities
Open Access
A survey on scheduling in IEEE 802.16 mesh mode
(Institute of Electrical and Electronics Engineers, 2010) Kas, M.; Yargicoglu, B.; Korpeoglu, I.; Karasan, E.
IEEE 802.16 standard (also known as WiMAX) defines the wireless broadband network technology which aims to solve the so called last mile problem via providing high bandwidth Internet even to the rural areas for which the cable deployment is very costly. The standard mainly focuses on the MAC and PHY layer issues, supporting two transmission modes: PMP (Point-to-Multipoint) and mesh modes. Mesh mode is an optional mode developed as an extension to PMP mode and it has the advantage of having an improving performance as more subscribers are added to the system using multi-hop routes. In 802.16 MAC protocol, mesh mode slot allocation and reservation mechanisms are left open which makes this topic a hot research area. Hence, the focus of this survey will mostly be on the mesh mode, and the proposed scheduling algorithms and performance evaluation methods. © 2010 IEEE.
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Türk havacılığına adanmış 50 sene: Hasan Nur Kıvanç
(Bilkent University, 2021) Çakırcık, Çağla Su; Aksu, İzzet Cem; Bodur, Müberra Nur; Özdel, Özgür Boran; Bilge, Tarık Berkan
Türkiye’de havacılığın başlangıcı 1900’lü yılların başlarına dayanır. Türkiye Cumhuriyeti, kurucularının muasır medeniyetlere ulaşma hedefinin gerekliliği olarak havacılık alanında gerek askeri gerekse sivil havacılık açısından kendi kendine yetebilen bir yapı kurmayı amaçlamıştır. Havacılığın gelişimi, ilgili personellerin yetiştirilmesi ve bu kişilerin eğitimi amaçlanarak planlamalar yapılmıştır. Bu planlamaların sonucu olarak Türk Hava Kurumu, Türkkuşu gibi kurumlar kurulmuştur. Bu kurumların yetiştirdiği bir havacı personel olan Hasan Nur Kıvanç, Türk havacılığına planör pilotu, planör eğitmeni, hava trafik kontrolörü, meteoroloji uzmanı olarak hizmet etmiştir. Hasan Nur Kıvanç, İnönü Hava Okulunda gerek öğrenci olarak gerekse eğitmen olarak Türk havacılığına katkı sağlamıştır. 1960’tan bu yana yüzü aşkın pilot yetiştiren Hasan Nur Kıvanç, havacılık bakımından oldukça tecrübelidir.