Browsing by Author "Karaşan, Ezhan"
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Item Open Access Capacity of noisy, discrete memoryless channels under input constraints(1990) Karaşan, EzhanIn this thesis work, we examine the capacity of discrete memoryless channels under input constraints. We consider a certain class of input-restricted channels for which constrained sequences can be modeled as outputs of a finite-state machine(FSM). No efficient algorithm is known for computing the capacity of such a channel. For the noiseless case, i.e., when the channel input letter and the corresponding output letter are identical, it is shown that [1] the channel capacity is the logarithm of the largest eigenvalue of the adjacency matrix of the state-transition diagram of the FSM generating the allowed channel input sequences. Furthermore, the probability distribution on the input sequences achieving the channel capacity is first-order markovian. Here, we discuss the noisy case. For a specific input-restricted channel, we show that unlike the noiseless case, the capacity is no longer achieved by a first-order distribution. We derive upper and lower bounds on the maximum rate achievable by a K-th order markovian distribution on the allowed input sequences. The computational results show that the second-order distribution does strictly better than the first-order distribution for this particular channel. A sequence of upper bounds on the capacity of an input-restricted channel is also given. We show that this sequence converges to the channel capacity. The numerical results clarify that markovian distribution may achieve rates close to the capacity for the channel considered in this work.Item Open Access Downlink data rate, energy and spectral efficiency distribution in heterogeneous networks with cell-edge located small cells(Springer, 2020) Yenihayat, Güven; Karaşan, EzhanIn this paper, the probability distributions of per user downlink data rate, spectral efficiency (SE) and energy efficiency (EE) are analytically derived for a heterogeneous network model with cell-edge located small cells. The high accuracies of analytically derived cumulative distribution functions (CDF) are verified using distributions obtained via simulations. CDF expressions are then used in order to optimize key performance indicators (KPI) which are selected here as 10th percentile downlink data rate (R10), spectral efficiency (SE10) and energy efficiency (EE10). In addition to optimizing KPIs separately, we also investigate the variation of the KPIs with respect to each other employing the analytically derived distributions. The results show that the resource allocation parameter values maximizing R10 are very close to the values that maximize EE10. However, the values that are optimal for EE10 and R10 are not optimal for SE10, which demonstrates the EE and SE trade-off in HetNets.Item Open Access Is proportional fair scheduling suitable for age-sensitive traffic?(Elsevier, 2023-05) Akar, Nail; Karaşan, EzhanProportional Fair (PF) scheduling with successful deployments in various cellular wireless networks and wireless LANs, aims at maximizing the sum of the logarithms of user throughputs. PF scheduling is known to strike an appropriate balance between fairness and throughput, for conventional data traffic. On the other hand, there has recently been a surge of interest in status update networks carrying age-sensitive traffic for which information freshness is crucial and therefore network performance metrics driven by Age of Information (AoI) are instrumental, as opposed to conventional performance metrics such as delay, loss, or throughput, used for conventional data traffic. This paper studies the scheduling problem for the downlink of a cellular wireless network with a transmitter sending age-sensitive status update packets from multiple information sources to users with the goal of keeping the information as fresh as possible for the users. For this purpose, under the generate-at-will scenario, an age-agnostic model-free scheduler is proposed with the goal of minimizing the weighted sum peak AoI of the network, which is the performance metric used in this paper for quantifying information freshness. With numerical examples, the proposed scheduler is compared and contrasted with weighted PF scheduling in terms of implementation and performance, in both non-opportunistic and opportunistic scenarios.Item Open Access Mikrodalga karasal radyo link analiz ve simülasyonlarının Rec. ITU-R P.530 tavsiyesine uygun olarak gerçeklenmesi(URSI, 2014) Göktaş, Polat; Topçu, Satılmış; Karaşan, Ezhan; Altıntaş, AyhanBu çalışmada, NATO Band 3+ (1350 – 2690 MHz) ve NATO Band 4 (4400 – 5000 MHz) frekanslarında çalışan karasal mikrodalga radyo linklerin analizi için gerekli olan yansıma noktası hesabının iyileştirilmesi ve yansımadan dolayı oluşan çok yollu sönümlenme yayılım mekanizmasının en kötü aydaki link kullanılabilirliğinin hesaplanması ele alınmıştır. TX (verici) ve RX (alıcı) istasyonlarının koordinat bilgileri, radyo linkin TX ve RX istasyonları arasındaki mesafesi, TX ve RX antenlerinin yerden yükseklikleri ve kazançları, polarizasyon tipi, radyo kırılma indisi, zamanın yüzdesi, SNR, sayısal arazi yükseklik haritası ve iklimsel veriler gibi yayılım parametreleri kullanılarak çeşitli linkler için analizler yapılmıştır. Yağmur ve atmosferik gazlardan kaynaklanan zayıflamayı dikkate alarak alıcıdaki güç seviyesi hesaplanmıştır ve yansımadan kaynaklanan çok yollu sönümlenmenin en kötü aydaki link kullanılabilirliği üzerindeki etkileri incelenmiştir.Item Open Access Modeling age of information in a cooperative slotted Aloha network(Springer, 2023-03-28) Vaezi, Kaveh; Akar, Nail; Karaşan, EzhanIn this paper, we study a slotted Aloha cooperative network where a source node and a relay node send status updates of two underlying stochastic processes to a common destination. Additionally, the relay node cooperates with the source by accepting its packets for further re-transmissions using probabilistic acceptance and relaying. We obtain the exact steady state distributions of Age of Information (AoI) and Peak AoI sequences of both nodes using Quasi-Birth-Death Markov chains. The analytical model is first validated by simulations and then used to obtain optimal cooperation policies when transmission probabilities are fixed. Subsequently, we study the more general problem of joint optimization of the transmission probabilities and cooperation level between the source and relay, with detailed numerical examples.Item Open Access Radio Communications Interdiction Problem under deterministic and probabilistic jamming(Elsevier, 2019) Tanergüçlü, Türker; Karaşan, Oya Ekin; Akgün, I.; Karaşan, EzhanThe Radio Communications Interdiction Problem (RCIP) seeks to identify the locations of transmitters on the battlefield that will lead to a robust radio communications network by anticipating the effects of intentional radio jamming attacks used by an adversary during electronic warfare. RCIP is a sequential game defined between two opponents that target each other’s military units in a conventional warfare. First, a defender locates a limited number of transmitters on the defender’s side of the battlefield to optimize the relay of information among its units. After observing the locations of radio transmitters, an attacker locates a limited number of radio jammers on the attacker’s side to disrupt the communication network of the defender. We formulate RCIP as a binary bilevel (max–min) programming problem, present the equivalent single level formulation, and propose an exact solution method using a decomposition scheme. We enhance the performance of the algorithm by utilizing dominance relations, preprocessing, and initial starting heuristics. To reflect a more realistic jamming representation, we also introduce the probabilistic version of RCIP where a jamming probability is associated at each receiver site as a function of the prevalent jamming to signal ratios leading to an expected coverage of receivers as an objective function. We approximate the nonlinearity in the jamming probability function using a piecewise linear convex function and solve this version by adapting the decomposition algorithm constructed for RCIP. Our extensive computational results on realistic scenarios show the efficacy of the solution approaches and provide valuable tactical insights.Item Open Access Sabit karasal mikrodalga LOS/NLOS radyo linklerin enterferans analizi(IEEE, 2015-05) Göktaş, Polat; Topcu, Satılmış; Karaşan, Ezhan; Altıntaş, AyhanBu çalışmada, NATO Band 3+ (1350-2690 MHz) ve NATO Band 4 (4400-5000 MHz) frekans bantlarında çalışan sabit karasal mikrodalga LOS (karasal görüş çizgisi)/ NLOS (ufuk ötesi) radyo linkleri için enterferans modellenmesi ele alınmıştır. Sabit karasal noktadan-noktaya haberleşme sistemlerinde enterferansa maruz kalan istasyonlardaki hem açık havadaki hem de yağmurdaki saçılmadan kaynaklanan enterferansın hesaplanması yapılmıştır. Ayrıca, ITU-R P.452 Tavsiyesinde bahsedilen açık havadaki enterferans kaybının hesabındaki enterferans yayılım mekanizmaları incelenmiştir. Enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların koordinat bilgileri, enterferansa neden olan verici ve enterferansa maruz kalan alıcı istasyonların antenlerinin yerden yükseklikleri, anten ayrımcılıgı, ˘ polarizasyon tipi, radyo kırılma indeksi, deniz seviyesinden ortalama kırıcılık, zaman yüzdesi, yığın kategorisi, sayısal arazi yükseklik haritası ve iklimsel veriler gibi enterferans yayılım parametreleri kullanılarak çeşitli mikrodalga radyo linkler için enterferans analizleri yapılmıştır.Item Open Access Sabit karasal noktadan-noktaya haberleşme sistemlerinin analizi(2015) Göktaş, P.; Topçu, Satılmış; Karaşan, Ezhan; Altıntaş, AyhanItem Open Access Sabit karasal noktadan-noktaya sistemlerin çok yollu sönümlenmesini azaltmak için uzaysal çeşitleme tekniğini değerlendirme(IEEE, 2015-05) Göktaş, Polat; Topcu, Satılmış; Karaşan, Ezhan; Altıntaş, AyhanÇok yollu sönümlenme mekanizması, 10 GHz altındaki frekanslarda çalışan sabit karasal mikrodalga görüş çizgisi radyo linkleri için belirleyici yayılım faktörüdür. Çok yollu yayılımdan dolayı sönümlenme karasal görüş çizgisi linklerdeki alınan sinyalleri zayıflamakta ve dolayısıyla noktadan-noktaya sistemlerin performasını bozmaktadır. Çeşitli metodlar; çeşitleme ile yada çeşitleme tekniği olmadan çok yollu sönümlenmenin etkilerini azaltmak için kullanılır. Uzay çeşitlemede dikey aralık çok yollu sönümlenmeyi azaltmanın en etkili metodlarından biridir. Bu makalede, sabit karasal mikrodalga görüş çizgisi radyo linkleri için iki anten uzay çeşitleme konfigürasyonu konseptinin değerlendirilmesi yapılmıştır. Arazi hat profili boyunca yerden yansıma noktalarından kaynaklanan çok yolluluktan dolayı çok yollu sönümlenme olayları analiz edilmiştir. Örnek sabit karasal mikrodalga görüş çizgisi radyo linklerindeki farklı anten yerden yüksekliklerinde iki anten konfigürasyonu ile uzaysal çeşitleme benzetim çalışması yapılmıştır. Benzetim sonuçları alıcıdaki güç seviyesine göre degerlendirilmiştir.Item Open Access SF-Devil: Distributed Bluetooth scatternet formation algorithm based on device and link characteristics(IEEE, 2003-06-07) Pamuk, Canan; Karaşan, EzhanBluetooth has become very popular owing to the fact that it is a promising ad-hoc networking technology for short ranges. Although construction and operation of piconets is well defined in Bluetooth specifications, there is no unique standard for scatternet formation and operation. In this paper, we propose a distributed Bluetooth scatternet formation algorithm based on device and link characteristics (SF-DeviL). SF-DeviL handles energy efficiency using class devices and the received signal strength. SF-DeviL forms scatternets that are robust to position changes and battery depletions. © 2003 IEEE.Item Open Access Traffic engineering in case of interconnected and integrated layers(IEEE, 2008-09-10) Hegyi P.; Cinkler, T.; Şengezer, Namık; Karaşan, Ezhan