Browsing by Subject "Telecommunication"

Now showing 1 - 10 of 10

Open Access
Client-server synchronization and buffering for variable rate multimedia retrievals
(1996) Hui J.Y.; Karasan, E.; Li J.; Zhang, J.
We consider the use of large buffers and feedback as a mechanism to maintain loosely coupled synchronization between a multimedia server and a client. The multimedia stream is modeled as a fluid flow through rate controlled valves and buffers with multiple thresholds. These thresholds are used to control the rates upstream. The quality of service for the multimedia connection is characterized in terms of the jitter in the received media stream due to buffer underflow and overflow. This quality of service is used to exercise rate and admission control in the presence of congestion. The feedback mechanism is, implemented in GRAMS, an adaptive multimedia client-server system. Experimental statistics are gathered for the purpose of traffic engineering. We employ a fluid flow and first passage time analysis to understand the traffic process through the pipelines and the buffers and to estimate the amount of signaling required by the feedback mechanism.
Open Access
Model-free adaptive hysteresis for dynamic bandwidth reservation
(IEEE, 2007-10) Akar, Nail
Dynamic bandwidth reservation refers to the process of dynamically updating the bandwidth allocation to a connection between two network end points on the basis of actual aggregate traffic demand of the connection. We assume a scenario in which bandwidth updates for the connection should not be performed too frequently and the frequency of updates are thus limited to a so-called desired update rate. We propose an asynchronous model-free adaptive hysteresis algorithm for dynamic bandwidth reservations with such update frequency constraints. We validate the effectiveness of the proposed approach by comparing its bandwidth efficiency with that of a synchronous model-based dynamic bandwidth reservation mechanism from the existing literature.
Open Access
Optimum power randomization for the minimization of outage probability
(IEEE, 2013) Dulek, B.; Vanli, N. D.; Gezici, Sinan; Varshney P. K.
The optimum power randomization problem is studied to minimize outage probability in flat block-fading Gaussian channels under an average transmit power constraint and in the presence of channel distribution information at the transmitter. When the probability density function of the channel power gain is continuously differentiable with a finite second moment, it is shown that the outage probability curve is a nonincreasing function of the normalized transmit power with at least one inflection point and the total number of inflection points is odd. Based on this result, it is proved that the optimum power transmission strategy involves randomization between at most two power levels. In the case of a single inflection point, the optimum strategy simplifies to on-off signaling for weak transmitters. Through analytical and numerical discussions, it is shown that the proposed framework can be adapted to a wide variety of scenarios including log-normal shadowing, diversity combining over Rayleigh fading channels, Nakagami-m fading, spectrum sharing, and jamming applications. We also show that power randomization does not necessarily improve the outage performance when the finite second moment assumption is violated by the power distribution of the fading. © 2013 IEEE.
Open Access
Spectrum sensing via restricted neyman-pearson approach in the presence of non-Gaussian noise
(IEEE, 2013) Turgut, Esma; Gezici, Sinan
In this paper, spectrum sensing in cognitive radio systems is studied for non-Gaussian channels in the presence of prior distribution uncertainty. In most practical cases, some amount of prior information about signals of primary users is available to secondary users but that information is never perfect. In order to design optimal spectrum sensing algorithms in such cases, we propose to employ the restricted Neyman-Pearson (NP) approach, which maximizes the average detection probability under constraints on the worst-case detection and false-alarm probabilities. We derive a restricted NP based spectrum sensing algorithm for additive Gaussian mixture noise channels, and compare its performance against the generalized likelihood ratio test (GLRT) and the energy detector. Simulation results show that the proposed spectrum sensing algorithm provides improvements over the other approaches in terms of minimum (worst-case) and/or average detection probabilities. © 2013 IEEE.
Open Access
Survivability in hierarchical telecommunications networks under dual homing
(Institute for Operations Research and the Management Sciences (I N F O R M S), 2014) Karaşan, O. E.; Mahjoub, A. R.; Özkök, O.; Yaman, H.
The motivation behind this study is the essential need for survivability in the telecommunications networks. An optical signal should find its destination even if the network experiences an occasional fiber cut. We consider the design of a two-level survivable telecommunications network. Terminals compiling the access layer communicate through hubs forming the backbone layer. To hedge against single link failures in the network, we require the backbone subgraph to be two-edge connected and the terminal nodes to connect to the backbone layer in a dual-homed fashion, i.e., at two distinct hubs. The underlying design problem partitions a given set of nodes into hubs and terminals, chooses a set of connections between the hubs such that the resulting backbone network is two-edge connected, and for each terminal chooses two hubs to provide the dual-homing backbone access. All of these decisions are jointly made based on some cost considerations. We give alternative formulations using cut inequalities, compare these formulations, provide a polyhedral analysis of the smallsized formulation, describe valid inequalities, study the associated separation problems, and design variable fixing rules. All of these findings are then utilized in devising an efficient branch-and-cut algorithm to solve this network design problem.
Open Access
Telecommunications policy reform in Turkey
(Wiley-Blackwell Publishing Ltd., 2007) Akdemir, E.; Başçı, E.; Togan, S.
This paper, considering the economic effects of liberalisation in the telecommunications sector on the Turkish economy, makes use of the empirical studies on the linkages between regulatory regimes and telecommunications prices. Since Turkey is trying to liberalise the telecommunications sector by following the EU approach to liberalisation, the paper considers briefly the regulatory regimes in the telecommunications sectors of the EU and Turkey, determines the ad valorem equivalent of barriers to the telecommunications services sector in Turkey, and derives estimates of the welfare effects of adopting the EU rules and regulations in the Turkish telecommunications sector. It shows that there is tremendous scope for Turkey to benefit from adopting and implementing the legislative, regulatory and institutional framework of the EU telecommunications sector. © 2007 The Authors Journal compilation © 2007 Blackwell Publishing Ltd.
Restricted
Türk Telekom tarihi
(Bilkent University, 2020) Gözdemir, Almina; Gedik, Berkan; Tütüncü, Can; Kaymak, Cemre; Çelik, Ekim
Bu çalışmada, Türkiye’nin telekomünikasyon sektöründeki en önemli temsilcilerinden biri olan Türk Telekom’un, 1980li yıllardan itibaren telekomünikasyondaki modernleşme çalışmaları ile başlayıp PTT bünyesinden ayrılması ve daha sonra özelleştirilmesi ile biten süreç ele alınmıştır. Bu araştırmada Türk Telekom A.Ş.’nin Türkiye telekomünikasyon alanına olan katkıları ve bu alanın gelişimindeki rolü incelenmiştir.
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Turkcell firmasının 1994-2000 yılları arasında Türkiye’deki telekomünikasyon sektörünün gelişimine etkisi
(Bilkent University, 2023) Kılyar, Ahmet Derin; Özaydın, Ahmet; Söylemez, Hazal Nisan; Özdemir, Enes; Özkan, Kemal Onur
Bu makalede Turkcell’in, 1994’ten 2000 yılına kadarki süreçte Türkiye’deki telekomünikasyon sektörüne ekonomik ve teknolojik etkileri araştırılacaktır. Bunun için önce Turkcell’den önce Türkiye’deki telekomünikasyon sektörünün kamu otoritesi ağır basan ve tekel niteliğindeki yapısının, buna karşılık küresel çapta telekomünikasyonaki liberalizasyon trendinin, Turkcell’in kuruluş amacının ve sürecinin açıklanması gerekmektedir. Türkiye’nin öncü ve piyasada birinci GSM operatörünün 2000 yılına kadarki süre içerisindeki santral kurmak, kapsama alanını yurt dışına genişletmek, müşteri memnuniyetini arttırmak için çeşitli politikalar uygulamak vb. sektörel faaliyetleri incelenecektir. Hem dönemin gazete haberleri gibi birincil kaynaklardan hem de makale vb. ikincil kaynaklardan yararlanılacaktır. Sonuç olarak Turkcell’in sektördeki başarısı somutlaştırılacaktır.
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Türkiye’de ilklerin şirketi Netaş: Kuruluşu, gelişimi ve Ar-Ge tarihi
(Bilkent University, 2021) Aktaş, Betül Hilal; Yıldız, Mehmet Kaan; Yüksek, Ümit; Coşar, Ömer Faruk; Başer, Umut
Bu proje kapsamında 20. yüzyılın ikinci yarısında doğan Türkiye’deki önemli özel telekomünikasyon şirketlerinden NETAŞ ele alınmıştır. Proje konu seçimini etkileyen önemli hususlardan bir tanesi NETAŞ’ın diğer Türk telekomünikasyon şirketlerine kıyasla Türkiye’de ve yurt dışında çeşitli stratejik planlarla daha uygun eylemler gerçekleştirmesidir. Bununla birlikte NETAŞ, Türkiye’nin ilk yerli telekomünikasyon cihazlarını üretmesi ve Türkiye’nin ilk yazılım ihracatını gerçekleştirmesi sebebiyle, Türkiye’nin telekomünikasyon ve bilgi işlem geçmişi açısından önemli bir yere sahip olmasıdır. Proje sürecinde NETAŞ Ar-Ge eski yöneticilerinden Ali Akurgal ile röportaj yapılmıştır ve geçmişteki önemli NETAŞ projeleri hakkında bilgi edinilmiştir.
Open Access
Wide area telecommunication network design: Application to the Alberta SuperNet
(2008) Cabral, E.A.; Erkut, E.; Laporte G.; Patterson, R.A.
This article proposes a solution methodology for the design of a wide area telecommunication network. This study is motivated by the Alberta SuperNet project, which provides broadband Internet access to 422 communities across Alberta. There are two components to this problem: the network design itself, consisting of selecting which links will be part of the solution and which nodes should house shelters; and the loading problem which consists of determining which signal transport technology should be installed on the selected edges of the network. Mathematical models are described for these two subproblems. A tabu search algorithm heuristic is developed and tested on randomly generated instances and on Alberta SuperNet data. © 2008 Operational Research Society Ltd. All rights reserved.