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( Birkan Aksan ),( Sümeyye Gür Mazlum ) 호남수학회 2023 호남수학학술지 Vol.45 No.3
In this paper, we calculate Frenet frames, Frenet derivative formulas, curvatures, arc lengths, geodesic curvatures according to the Lorentzian 3-space R<sup>3</sup><sub>1</sub> , Lorentzian sphere S<sup>2</sup><sub>1</sub> and hyperbolic sphere H<sup>2</sup><sub>0</sub> of the spherical indicatrix curves of the spacelike Salkowski curve with the timelike principal normal in R<sup>3</sup><sub>1</sub> and draw the graphs of these indicatrix curves on the spheres.
Frequency Assignment Problem with Net Filter Discrimination Constraints
H. Birkan Yilmaz,구본홍,박성호,박휘성,함재현,채찬병 한국통신학회 2017 Journal of communications and networks Vol.19 No.4
Managing radio spectrum resources is a crucial issue. The frequency assignment problem (FAP) basically aims to allocatelimited number of frequencies to communication links in an efficientmanner. Geographically close links, however, cause interference,which complicates the assignment, imposing frequency separationconstraints. The FAP is closely related to the graph-coloringproblem and it is an NP-hard problem. In this paper, we proposeto incorporate the randomization into greedy and fast heuristics. As far as being implemented, the proposed algorithms are quitestraight forward and are unencumbered by system parameters thatneed to be tuned whenever the system changes. The proposed algorithmssignificantly improve, quickly and effectively, the solutionsobtained by greedy algorithms in terms of the number of assignedfrequencies and the range. The enhanced versions of the proposedalgorithms perform close to the lower bounds while running in areasonable duration. Another novelty of our study is its considerationof the net filter discrimination effects in the communicationmodel. Performance analysis is done by synthetic and measureddata, where the measurement data includes the effect of the real3-dimensional (3D) geographical features in the Daejeon region inKorea. In both cases, we observe a significant improvement by employingrandomized heuristics.
Service Class Differentiation in Scheduling of Electrical Vehicle Recharging
H. Birkan Yilmaz,Sukru Kuran,Salim Eryigit 에스케이텔레콤 (주) 2015 Telecommunications Review Vol.25 No.4
In this paper we discuss the service class differentiation in scheduling of the electrical vehicle recharging process. Electrical vehicles, by their design, require significant amount of time for the charging process. Therefore, utilization of parking lots is proposed for recharging due to vast amount of time spent in the parking lots. These recharging opportunities should be optimized and requires a vehicles’ mobility/parking pattern. Where to charge, when to charge, and how much to charge are at the focus for the future smart city paradigm. In this study, service class differentiation is integrated into the system for overcoming rush hour congestion. Two different subscription classes are proposed: Gold class with higher priority and an expensive subscription fee; Regular class with lower priority and cheaper subscription fee. The system takes these different service classes into consideration when recharging electrical vehicles and prioritizes the Gold class electrical vehicles over Regular classes during times of heavy load. Similar to our previous work, we also utilize a realistic 24-hour trace-based vehicular mobility model that is conducted in Zurich. To the best of our knowledge, this is the first EV recharging study that considers different service classes for electrical vehicles.
Three-Dimensional Channel Characteristics for Molecular Communications With an Absorbing Receiver
Yilmaz, H. Birkan,Heren, Akif Cem,Tugcu, Tuna,Chan-Byoung Chae IEEE 2014 IEEE Communications Letters Vol.18 No.6
<P>Within the domain of molecular communications, researchers mimic the techniques in nature to come up with alternative communication methods for collaborating nanomachines. This letter investigates the channel transfer function for molecular communications via diffusion. In nature, information-carrying molecules are generally absorbed by the target node via receptors. Using the concentration function, without considering the absorption process, as the channel transfer function implicitly assumes that the receiver node does not affect the system. In this letter, we propose a solid analytical formulation and analyze the signal metrics (attenuation and propagation delay) for molecular communication via diffusion channel with an absorbing receiver in a 3-D environment. The proposed model and the formulation match well with the simulations without any normalization.</P>
Chemical Propagation Pattern for Molecular Communications
Yilmaz, H. Birkan,Suk, Gee-Yong,Chae, Chan-Byoung IEEE 2017 IEEE wireless communications letters Vol.6 No.2
<P>In a diffusion-based molecular communication system, molecules are employed to convey information. When we focus on absorbing receivers, we need to consider propagation and reception processes in a framework of first passage processes. For this kind of molecular communication system, the characteristics of the channel is also affected by the shape of the transmitter. In the literature, most studies focus on systems with a point transmitter due to circular symmetry. In this letter, we address the propagation and reception patterns of chemical signals emitted from a spherical transmitter. We also investigate the directivity gain achieved by the reflecting spherical transmitter. We quantify the power gain by measuring the received power at different angles on a circular region.</P>
Joint assignment of frequency and polarization to minimize the chromatic number
구본홍,H. Birkan Yilmaz,채찬병,박성호,박휘성,함재현 한국통신학회 2017 ICT Express Vol.3 No.1
In this letter, we propose graph theory-based heuristics for jointly assigning frequency and antenna polarization in a cluster-based tactical communication environment (e.g., military communications). In addition to considering the frequency assignment problem (which is an NP-hard problem), we also consider the polarization assignment issue. A practical antenna and a 3D ray tracing-based simulator are exploited to measure the interference. We show that the suggested heuristics are nearly optimal in terms of chromatics and their low complexity makes them suitable for practical usage.
Akkaya, Ali,Yilmaz, H. Birkan,Chan-Byoung Chae,Tugcu, Tuna IEEE 2015 IEEE COMMUNICATIONS LETTERS Vol.19 No.2
<P>The performance of molecular communication is significantly impacted by the reception process of the messenger molecules. The receptors' size and density, however, have yet to be investigated. In this letter, we analyze the effect of receptor density and size on the signal reception of an absorbing receiver with receptors. The results show that, when the total receptor area is the same, better hitting probability is achieved by using a higher number of relatively small receptors. In addition, deploying receptors, which cover a small percentage of the receiver surface, is able to create an effective communication channel that has a detectable signal level.</P>
Intelligent Network Data Analytics Function in 5G Cellular Networks using Machine Learning
Salih Sevgican,Meriç Turan,Kerim Gökarslan,H. Birkan Yilmaz,Tuna Tugcu 한국통신학회 2020 Journal of communications and networks Vol.22 No.3
5G cellular networks come with many new features compared to the legacy cellular networks, such as network data analytics function (NWDAF), which enables the network operatorsto either implement their own machine learning (ML) based dataanalytics methodologies or integrate third-party solutions to theirnetworks. In this paper, the structure and the protocols of NWDAFthat are defined in the 3rd Generation Partnership Project (3GPP)standard documents are first described. Then, cell-based syntheticdata set for 5G networks based on the fields defined by the 3GPPspecifications is generated. Further, some anomalies are added tothis data set (e.g., suddenly increasing traffic in a particular cell),and then these anomalies within each cell, subscriber category,and user equipment are classified. Afterward, three ML models,namely, linear regression, long-short term memory, and recursiveneural networks are implemented to study behaviour informationestimation (e.g., anomalies in the network traffic) and network loadprediction capabilities of NWDAF. For the prediction of networkload, three different models are used to minimize the mean absoluteerror, which is calculated by subtracting the actual generated datafrom the model prediction value. For the classification of anomalies, two ML models are used to increase the area under the receiver operating characteristics curve, namely, logistic regressionand extreme gradient boosting. According to the simulation results, neural network algorithms outperform linear regression innetwork load prediction, whereas the tree-based gradient boosting algorithm outperforms logistic regression in anomaly detection. These estimations are expected to increase the performance of the5G network through NWDAF.