Canbey H.H.,ASELSAN Inc.
IEEE International Symposium on Phased Array Systems and Technology | Year: 2017
Phased array receive/transmit systems are widely used in radar and electronic warfare applications. A low noise receive module for a phased array system operating at 3-6GHz band is designed, produced and validated. The measurement results are compared to the numerical results obtained from AWR Design Environment simulations. © 2016 IEEE.
Selcuk G.,ASELSAN Inc.
Proceedings - SIMS 2016: 2nd International Conference on Systems Informatics, Modelling and Simulation | Year: 2016
In this study, the degradation of adjacent channel power ratio (ACPR) performance in personal mobile radio (PMR) systems, which use two-point modulation in their phase locked loops (PLLs) is investigated. First an expression for the widths of charge pump pulses, which arise due to imbalanced modulation are found by also taking into account the low pass filtering of the loop. Then the frequency domain representation of charge pump pulses is obtained by Fourier transform. Using this representation and the loop filter response, the spurious signals in the spectrum of the voltage controlled oscillator (VCO) is calculated by using narrowband FM assumption. Evaluating the power of the spectrum within the bandwidth of the adjacent channel, ACPR performance is obtained. A practical setup is constructed to validate the proposed method. Coherence is observed between the measurements of the test setup and expressions obtained in this study. © 2016 IEEE.
Laz E.,ASELSAN Inc.
2017 IEEE Radar Conference, RadarConf 2017 | Year: 2017
The optimal measurement cost allocation problem is investigated for both centralized and decentralized detection systems in the presence of cost constrained measurements. The aim is to obtain optimum detection performance for a given multistatic sensor system under a total cost constraint. For the evaluation of detection performance, Bhattacharyya distance criterion is considered. The main goal for this criterion is to maximize the Bhattacharyya distance between the distributions of the decision statistics under different hypotheses subject to a total cost constraint. The Bhattacharyya distance expressions are obtained for both detection systems and the optimization problems are proposed. The solutions of the proposed problems indicate how to allocate the cost budget among the measurement devices in order to achieve the optimum performance. Numerical examples are presented to discuss the implications of the results. © 2017 IEEE.
Dursun T.,ASELSAN Inc. |
Soutis C.,University of Manchester
Materials and Design | Year: 2014
Aluminium alloys have been the primary material for the structural parts of aircraft for more than 80. years because of their well known performance, well established design methods, manufacturing and reliable inspection techniques. Nearly for a decade composites have started to be used more widely in large commercial jet airliners for the fuselage, wing as well as other structural components in place of aluminium alloys due their high specific properties, reduced weight, fatigue performance and corrosion resistance. Although the increased use of composite materials reduced the role of aluminium up to some extent, high strength aluminium alloys remain important in airframe construction. Aluminium is a relatively low cost, light weight metal that can be heat treated and loaded to relatively high level of stresses, and it is one of the most easily produced of the high performance materials, which results in lower manufacturing and maintenance costs. There have been important recent advances in aluminium aircraft alloys that can effectively compete with modern composite materials. This study covers latest developments in enhanced mechanical properties of aluminium alloys, and high performance joining techniques. The mechanical properties on newly developed 2000, 7000 series aluminium alloys and new generation Al-Li alloys are compared with the traditional aluminium alloys. The advantages and disadvantages of the joining methods, laser beam welding and friction stir welding, are also discussed. © 2013 Elsevier Ltd.
Yavuz E.,ASELSAN Inc. |
Telatar Z.,Ankara University
Digital Signal Processing: A Review Journal | Year: 2013
In this paper, it is shown that there is a fundamental flaw in the paper [Chih-Chin Lai, A digital watermarking scheme based on singular value decomposition and tiny genetic algorithm, Digital Signal Processing 21 (2011) 522-527]. The method has watermark ambiguity problem at detector and could not be used as a proof of ownership as stated in the paper. © 2013 Elsevier Inc. All rights reserved.
Subasi Y.,ASELSAN Inc. |
Demirekler M.,Middle East Technical University
Automatica | Year: 2014
In this study we define a new observability measure for stochastic systems: The mutual information between the state sequence and the corresponding measurement sequence for a given time horizon. Although the definition is given for a general system representation, the paper focuses on the linear time invariant Gaussian case. Some basic analytical results are derived for this special case. The measure is extended to the observability of a subspace of the state space, specifically an individual state and/or the modes of the system. A single measurement system represented in the observable canonical form is examined in detail. A recursive form of the observability measure for a finite time horizon is derived. The possibility of using this form for designing a sensor selection algorithm is demonstrated by two examples. © 2014 Elsevier Ltd. All rights reserved.
Taskin S.,ASELSAN Inc. |
Lodree Jr. E.J.,University of Alabama
International Journal of Production Economics | Year: 2010
This paper addresses a stochastic inventory control problem for manufacturing and retail firms who face challenging procurement and production decisions associated with hurricane seasons. Specifically, the paper presents a control policy in which stocking decisions are based on a hurricane forecast model that predicts the number of landfall hurricanes for an ensuing hurricane season. The multi-period inventory control problem is formulated as a stochastic programming model with recourse where demand during each pre-hurricane season period is represented as a convolution of the current period's demand and an updated estimate of demand for the ensuing hurricane season. Due to the computational challenges associated with solving stochastic programming problems, recent scenario reduction techniques are discussed and illustrated through an example problem. The proposed model specifies cost minimizing inventory strategies for simultaneously meeting stochastic demands that occur prior to the hurricane season while proactively preparing for potential demand surge during the season. © 2009 Elsevier B.V. All rights reserved.
Cigla C.,ASELSAN Inc. |
Alatan A.A.,Middle East Technical University
Signal Processing: Image Communication | Year: 2013
A novel local stereo matching algorithm is introduced to address the fundamental challenge of stereo algorithms, accuracy and computational complexity dilemma. The time consuming intensity dependent aggregation procedure of local methods is improved in terms of both speed and precision. Providing connected 2D support regions, the proposed approach exploits a new paradigm, namely separable successive weighted summation (SWS) among horizontal and vertical directions enabling constant operational complexity. The weights are determined by four-neighborhood intensity similarity of pixels and utilized to model the information transfer rate, permeability, towards the corresponding direction. The same procedure is also utilized to diffuse information through overlapped pixels during occlusion handling after detecting unreliable disparity assignments. Successive weighted summation adaptively cumulates the support data based on local characteristics, enabling disparity maps to preserve object boundaries and depth discontinuities. According to the experimental results on Middlebury stereo benchmark, the proposed method is one of the most effective local stereo algorithm providing high quality disparity models by unifying constant time filtering and weighted aggregation. Hence, the proposed algorithm provides a competitive alternative for various local methods in terms of achieving precise and consistent disparity maps from stereo video within fast execution time. © 2013 Elsevier B.V. All rights reserved.
Aytekin O.,Middle East Technical University |
Zongur U.,ASELSAN Inc. |
Halici U.,Middle East Technical University
IEEE Geoscience and Remote Sensing Letters | Year: 2013
The automatic detection of airports is essential due to the strategic importance of these targets. In this letter, a runway detection method based on textural properties is proposed since they are the most descriptive element of an airport. Since the best discriminative features for airport runways cannot be trivially predicted, the Adaboost algorithm is employed as a feature selector over a large set of features. Moreover, the selected features with corresponding weights can provide information on the hidden characteristics of runways. Thus, the Adaboost-based selected feature subset can be used for both detecting runways and identifying their textural characteristics. Thus, a coarse representation of possible runway locations is obtained. The performance of the proposed approach was validated by experiments carried on a data set of large images consisting of heavily negative samples. © 2004-2012 IEEE.
Turhan M.,ASELSAN Inc.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016
Elicitation of requirements is critical for the conformance of a system. However, collecting user information and deriving it into unambiguous and verifiable design requirements present a challenge. Therefore non-functional design requirements are usually ended up with ambiguous statements like easy to use. Within the framework of this problem, this paper presents a user research conducted at the early stage of the development process of an electronic warfare system’s hand terminal. As a result; the implicit user demands on system functions, the specifications of the hand terminal should provide to its users were collected from the stakeholders’ perspective and the research data were clarified in a way guiding designers to define design requirements and realize the final design. © Springer International Publishing Switzerland 2016.