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Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
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Publication Metadata only A fundamental experimental approach for optimal design of speed bumps(Elsevier, 2018) Bilgin, Ertuğrul; Lav, Abdullah Hilmi; N/A; Lav, Ahmet Hakan; Undergraduate student; School of MedicineSpeed bumps and humps are utilized as means of calming traffic and controlling vehicular speed. Needless to say, bumps and humps of large dimensions in length and width force drivers to significantly reduce their driving speeds so as to avoid significant vehicle vertical acceleration. It is thus that this experimental study was conducted with the aim of determining a speed bump design that performs optimally when leading drivers to reduce the speed of their vehicles to safe levels. The first step of the investigation starts off by considering the following question: "What is the optimal design of a speed bump that will - at the same time - reduce the velocity of an incoming vehicle significantly and to a speed that resulting vertical acceleration does not jeopardize road safety? The experiment has been designed to study the dependent variables and collect data in order to propose an optimal design for a speed bump. To achieve this, a scaled model of 1:6 to real life was created to simulate the interaction between a car wheel and a speed bump. During the course of the experiment, a wheel was accelerated down an inclined plane onto a horizontal plane of motion where it was allowed to collide with a speed bump. The speed of the wheel and the vertical acceleration at the speed bump were captured by means of a Vernier Motion Detector.Publication Metadata only An online optimization approach to post-disaster road restoration(Pergamon-Elsevier Science Ltd, 2021) Akbari, Vahid; Shiri, Davood; Department of Industrial Engineering; Salman, Fatma Sibel; Faculty Member; Department of Industrial Engineering; College of Engineering; 178838Natural disasters impact transportation networks adversely and cause road sections to be damaged or blocked. The road network may even become disconnected, impeding accessibility between disaster-stricken areas and critical locations such as hospitals, relief aid depots and transportation hubs. In the immediate response phase, a set of blocked edges should be selected and restored to reconnect the transportation network. While locations of the disrupted roads can be identified using drone or satellite images, an accurate estimation of time to restore a road segment can be carried out only after expert observations on the field. In this article, we study a post-disaster road restoration problem modeled on an undirected edge-weighted graph with k blocked edges, where the unblocking time of a blocked edge is revealed online once the road restoration team visits an end-node of that blocked edge. The objective is to minimize the time at which the road network is reconnected. We first investigate the worst-case performance of online algorithms against offline optimal solutions by means of the competitive ratio. We prove that any online deterministic algorithm cannot achieve a competitive ratio better than 2k-1. We also provide an optimal online algorithm that is proven to achieve this lower bound. In addition, to achieve good performance on realistic instances, we implement an algorithm that solves a mixed integer programming model each time new information is revealed. Since model solution is prohibitively time-consuming, we also propose a novel polynomial time online algorithm. We compare these two algorithms with two other benchmark online algorithms on both Istanbul road network instances and several other city instances from the literature. Our experiments show that the proposed polynomial time online algorithm performs superior to the benchmark ones and obtains solutions close to the offline optimum on all the tested instances.Publication Open Access Coordinate interleaved orthogonal design with media-based modulation(Institute of Electrical and Electronics Engineers (IEEE), 2021) Yldırım, İbrahim; Altunbaş, İbrahim; Department of Chemical and Biological Engineering; Başar, Ertuğrul; Faculty Member; Department of Chemical and Biological Engineering; College of Engineering; 149116In this work, we propose a new multiple-input multiple-output (MIMO) concept, which is called coordinate interleaved orthogonal design with media-based modulation (CIOD-MBM). The proposed two novel CIOD-MBM schemes provide improved data rates as well as diversity gain while enabling hardware simplicity using a single radio frequency (RF) chain. Moreover, using the equivalent channel model, a reduced complexity can be obtained for maximum likelihood (ML) detection of the proposed system. Using computer simulations, it is shown that CIOD-MBM schemes provide remarkably better performance against the conventional MBM and CIOD systems.Publication Metadata only Hub network design problem with capacity, congestion, and stochastic demand considerations(Informs, 2023) Bayram, Vedat; Farham, M. Saleh; Department of Industrial Engineering; Yıldız, Barış; Department of Industrial Engineering; College of EngineeringOur study introduces the hub network design problem with congestion, capacity, and stochastic demand considerations (HNDC), which generalizes the classical hub location problem in several directions. In particular, we extend state-of-the-art by integrating capacity acquisition decisions and congestion cost effect into the problem and allowing dynamic routing for origin-destination (OD) pairs. Connecting strategic and operational level decisions, HNDC jointly decides hub locations and capacity acquisitions by considering the expected routing and congestion costs. A path-based mixed-integer second-order cone programming (SOCP) formulation of the HNDC is proposed. We exploit SOCP duality results and propose an exact algorithm based on Benders decomposition and column generation to solve this challenging problem. We use a specific characterization of the capacity-feasible solutions to speed up the solution procedure and develop an efficient branch-and-cut algorithm to solve the master problem. We conduct extensive computational experiments to test the proposed approach's performance and derive managerial insights based on realistic problem instances adapted from the literature. In particular, we found that including hub congestion costs, accounting for the uncertainty in demand, and whether the underlying network is complete or incomplete have a significant impact on hub network design and the resulting performance of the system.Publication Open Access Index modulation based coordinate interleaved orthogonal design for secure communications(Institute of Electrical and Electronics Engineers (IEEE), 2021) Yıldırım, İbrahim; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Özpoyraz, Burak; Faculty Member; Master Student; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 149116; N/AIn this paper, we propose a physical layer security scheme that exploits a novel index modulation (IM) technique for coordinate interleaved orthogonal designs (CIOD). Utilizing the diversity gain of CIOD transmission, the proposed scheme, named CIOD-IM, provides an improved spectral efficiency by means of IM. In order to provide a satisfactory secrecy rate, we design a particular artificial noise matrix, which does not affect the performance of the legitimate receiver, while deteriorating the performance of the eavesdropper. We derive expressions of the ergodic secrecy rate and the theoretical bit error rate upper bound. In addition, we analyze the case of imperfect channel estimation by taking practical concerns into consideration. It is shown via computer simulations that the proposed scheme outperforms the existing IM-based schemes and might be a candidate for future secure communication systems.Publication Open Access Machine learning based channel modeling for Vehicular Visible Light Communication(Institute of Electrical and Electronics Engineers (IEEE), 2021) Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Turan, Buğra; Faculty Member; Other; PhD Student; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 7211; N/AVehicular Visible Light Communication (VVLC) is preferred as a vehicle-to-everything (V2X) communications scheme due to its highly secure, low complexity and radio frequency (RF) interference free characteristics, exploiting the line-of-sight (LoS) propagation of visible light and usage of already existing vehicle light emitting diodes (LEDs). Current VVLC channel models based on deterministic and stochastic methods provide limited accuracy for path loss prediction since deterministic methods heavily depend on site-specific geometry and stochastic models average out the model parameters without considering environmental effects. Moreover, there exists no wireless channel model that can be adopted for channel frequency response (CFR) prediction. In this paper, we propose novel framework for the machine learning (ML) based channel modeling of the VVLC with the goal of improving the model accuracy for path loss and building the CFR model through the consideration of multiple input variables related to vehicle mobility and environmental effects. The proposed framework incorporates multiple measurable input variables, e.g., distance, ambient light, receiver inclination angle, and optical turbulence, with the exploitation of feed forward neural network based multilayer perceptron neural network (MLP-NN), radial basis function neural network (RBF-NN) and decision tree based Random Forest learning methods. The framework also includes data pre-processing step, with synthetic minority over-sampling technique (SMOTE) data balancing, and hyper-parameter tuning based on iterative grid search, to further improve the accuracy. The accuracy of the proposed ML based channel modeling is demonstrated on the real-world VVLC vehicle-to-vehicle (V2V) communication channel data. The proposed MLP-NN, RBF-NN, and Random Forest based channel models generate highly accurate path loss predictions with 3.53 dB, 3.81 dB, 3.95 dB root mean square error(RMSE), whereas the best performing stochastic model based on two-term exponential fitting provides prediction accuracy of 7 dB RMSE. Moreover, MLP-NN and RBF-NN models are demonstrated to predict VVLC CFR with 3.78 dB and 3.60 dB RMSE, respectively.Publication Metadata only Multihop-cluster-based IEEE 802.11p and LTE hybrid architecture for VANET safety message dissemination(Institute of Electrical and Electronics Engineers (IEEE), 2016) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Computer Engineering; Uçar, Seyhan; Ergen, Sinem Çöleri; Özkasap, Öznur; PhD Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; 7211; 113507Several vehicular ad hoc network (VANET) studies have focused on communication methods based on IEEE 802.11p, which forms the standard for wireless access for vehicular environments. In networks employing IEEE 802.11p only, the broadcast storm and disconnected network problems at high and low vehicle densities, respectively, degrade the delay and delivery ratio of safety message dissemination. Recently, as an alternative to the IEEE 802.11p-based VANET, the usage of cellular technologies has been investigated due to their low latency and wide-range communication. However, a pure cellular-based VANET communication is not feasible due to the high cost of communication between the vehicles and the base stations and the high number of handoff occurrences at the base station, considering the high mobility of the vehicles. This paper proposes a hybrid architecture, namely, VMaSC-LTE, combining IEEE 802.11p-based multihop clustering and the fourth-generation (4G) cellular system, i.e., Long-Term Evolution (LTE), with the goal of achieving a high data packet delivery ratio (DPDR) and low delay while keeping the usage of the cellular architecture at a minimum level. In VMaSC-LTE, vehicles are clustered based on a novel approach named Vehicular Multihop algorithm for Stable Clustering (VMaSC). The features of VMaSC are cluster head (CH) selection using the relative mobility metric calculated as the average relative speed with respect to the neighboring vehicles, cluster connection with minimum overhead by introducing a direct connection to the neighbor that is already a head or a member of a cluster instead of connecting to the CH in multiple hops, disseminating cluster member information within periodic hello packets, reactive clustering to maintain the cluster structure without excessive consumption of network resources, and efficient size-and hop-limited cluster merging mechanism based on the exchange of cluster information among CHs. These features decrease the number of CHs while increasing their stability, therefore minimizing the usage of the cellular architecture. From the clustered topology, elected CHs operate as dual-interface nodes with the functionality of the IEEE 802.11p and LTE interface to link the VANET to the LTE network. Using various key metrics of interest, including DPDR, delay, control overhead, and clustering stability, we demonstrate the superior performance of the proposed architecture compared with both previously proposed hybrid architectures and alternative routing mechanisms, including flooding and cluster-based routing via extensive simulations in ns-3 with the vehicle mobility input from the Simulation of Urban Mobility. The proposed architecture also allows achieving higher required reliability of the application quantified by the DPDR at the cost of higher LTE usage measured by the number of CHs in the network.Publication Metadata only Optimal locations of electric public charging stations using real world vehicle travel patterns(Pergamon-Elsevier Science Ltd, 2015) Cai, Hua; Xu, Ming; N/A; Department of Industrial Engineering; Shahraki, Narges; Türkay, Metin; PhD Student; Faculty Member; Department of Industrial Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 24956We propose an optimization model based on vehicle travel patterns to capture public charging demand and select the locations of public charging stations to maximize the amount of vehicle-miles-traveled (VMT) being electrified. The formulated model is applied to Beijing, China as a case study using vehicle trajectory data of 11,880 taxis over a period of three weeks. The mathematical problem is formulated in GAMS modeling environment and Cplex optimizer is used to find the optimal solutions. Formulating mathematical model properly, input data transformation, and Cplex option adjustment are considered for accommodating large-scale data. We show that, compared to the 40 existing public charging stations, the 40 optimal ones selected by the model can increase electrified fleet VMT by 59% and 88% for slow and fast charging, respectively. Charging demand for the taxi fleet concentrates in the inner city. When the total number of charging stations increase, the locations of the optimal stations expand outward from the inner city. While more charging stations increase the electrified fleet VMT, the marginal gain diminishes quicldy regardless of charging speed.Publication Metadata only Package routing problem with registered couriers and stochastic demand(Pergamon-Elsevier Science Ltd, 2021) Department of Industrial Engineering; Yıldız, Barış; Faculty Member; Department of Industrial Engineering; College of Engineering; 258791Providing the crowd-sourced delivery capacity and hence enabling the practice, occasional couriers (OC) are the most critical resource in crowd-shipping (CS). therefore, As well as establishing and retaining a solid OC base, using the OC trips efficiently is of utmost importance for the viability of the CS applications. one auspicious idea to enhance the efficiency, i.e., cover a larger demand set with the available OC trips, is to use transshipments (deliver packages with a coordinated effort of OCs) and collect OC trip information in advance to efficiently coordinate them, which gives rise to the package routing problem with registered couriers (PRP-R) we introduce in this paper. in particular, we study a CS model in which the couriers register their trips in advance while the express shipping demands arrive through a stochastic process, and the network management needs to dynamically decide package-courier assignments to carry out deliveries in the most efficient way. We develop a novel rolling horizon algorithm to solve this challenging problem in real-time, which explicitly considers the limited OC capacities and use of a back-up delivery capacity (company-owned or third party provided) to ensure the service quality. Beyond the classical rolling horizon approaches, the suggested methodology uses a novel Monte Carlo procedure to take anticipated future system conditions into account, and thus can provide package-courier assignments that have almost the same cost with the optimal solution of the static version of the problem where all demand arrivals are known a-priory. the comprehensive numerical experiments attest to the efficacy of our methodology for the real-time management of the CS operations and provide significant managerial insights about the design of CS networks.Publication Metadata only Performance analysis of OTSM under hardware impairments and imperfect CSI(IEEE-Inst Electrical Electronics Engineers Inc, 2024) Doosti-Aref, Abed; Masouros, Christos; Zhu, Xu; Arslan, Hüseyin; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Ergen, Sinem Çöleri; Department of Electrical and Electronics Engineering; College of EngineeringOrthogonal time sequency multiplexing (OTSM) has been recently proposed as a single-carrier waveform offering similar bit error rate to orthogonal time frequency space (OTFS) and outperforms orthogonal frequency division multiplexing (OFDM) in doubly-spread channels (DSCs);however, with a much lower complexity making it a potential candidate for 6G wireless networks. In this paper, the performance of OTSM is explored by considering the joint effects of multiple hardware impairments (HWIs) such as in-phase and quadrature imbalance (IQI), direct current offset (DCO), phase noise, power amplifier non-linearity, carrier frequency offset, and synchronization timing offset for the first time in the area. First, the discrete-time baseband signal model is obtained in vector form under all mentioned HWIs. Second, the system input-output relations are derived in time, delay-time, and delay-sequency (DS) domains in which the parameters of all mentioned HWIs are incorporated. Third, analytical expressions are derived for the pairwise and average bit error probability under imperfect channel state information (CSI) as a function of the parameters of all mentioned HWIs. Analytical results demonstrate that under all mentioned HWIs, noise stays additive white Gaussian, effective channel matrix is sparse, DCO appears as a DC signal at the receiver interfering with only the zero sequency, and IQI redounds to self-conjugated sequency interference in the DS domain. Simulation results reveal the fact that by considering the joint effects of all mentioned HWIs and imperfect CSI not only OTSM outperforms OFDM by 29%in terms of energy of bit per noise but it performs same as OTFS in high mobility DSCs. IEEE