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Quartile: search.filters.quartile.Q2Subject: search.filters.subject.Telecommunication

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Now showing 1 - 4 of 4
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    A limited memory BFGS based unimodular sequence design algorithm for spectrum-aware sensing systems
    (IEEE-inst Electrical Electronics Engineers inc, 2022) N/A; Savcı, Kubilay; PhD Student; Graduate School of Sciences and Engineering; N/A
    Unimodular sequences with good correlation and spectral properties are desirable in numerous applications such as active remote sensing and communication systems. therefore, designing sequences with stopband and correlation sidelobe constraints has gained a lot of attention in the last few decades. in this paper, we propose a fast and efficient iterative algorithm to design unimodular and sparse frequency waveforms with low aperiodic/periodic autocorrelation sidelobes and desired stopband properties. in our approach, the bi-objective optimization problem which minimizes both the integrated sidelobe level (ISL) of the autocorrelation function and the power density in the spectral stopbands is first turned into an unconstrained single objective optimization problem and then is treated as a nonlinear large-scale problem. for the solution of the problem, we develop an algorithm based on Limited Memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) Quasi-Newton optimization method. Unlike most gradient based algorithms which employ line searches to deduce the step length, owing to L-BFGS method, unit step length is taken as a general rule to avoid the cost of computation at every iteration with very few exceptions. the calculation of gradient is based on Fast Fourier Transform and Hadamard product operations and thus the algorithm is fast and computationally efficient. Moreover, the algorithm is space efficient and its low-memory feature makes it possible to generate long sequences. Several numerical examples are presented to validate the efficacy of the proposed method and to show its superiority over other state-of-art algorithms.
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    Lifetime analysis of wireless sensor nodes in different smart grid environments
    (Springer, 2014) Eriş, Çiğdem; Güngör, Vehbi Çağrı; Fadel, Etimad; Akyıldız, Ian F.; Saimler, Merve; PhD Student; Graduate School of Sciences and Engineering; N/A
    Wireless sensor networks (WSNs) can help the realization of low-cost power grid automation systems where multi-functional sensor nodes can be used to monitor the critical parameters of smart grid components. The WSN-based smart grid applications include but not limited to load control, power system monitoring and control, fault diagnostics, power fraud detection, demand response, and distribution automation. However, the design and implementation of WSNs are constrained by energy resources. Sensor nodes have limited battery energy supply and accordingly, power aware communication protocols have been developed in order to address the energy consumption and prolong their lifetime. In this paper, the lifetime of wireless sensor nodes has been analyzed under different smart grid radio propagation environments, such as 500 kV substation, main power control room, and underground network transformer vaults. In particular, the effects of smart grid channel characteristics and radio parameters, such as path loss, shadowing, frame length and distance, on a wireless sensor node lifetime have been evaluated. Overall, the main objective of this paper is to help network designers quantifying the impact of the smart grid propagation environment and sensor radio characteristics on node lifetime in harsh smart grid environments.
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    Multi-layered video broadcasting over 1xEV-DO using multiple objective optimization
    (Institute of Electrical and Electronics Engineers (IEEE), 2006) N/A; Department of Electrical and Electronics Engineering; Atıcı, Çağdaş; Sunay, Mehmet Oğuz; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A: N/A
    In cellular environments video broadcasting is a challenging problem in which the number of users receiving the service and the average QoS has to be intelligently optimized. For video broadcasting in a 1xEV-DO system, the orthogonal Walsh codes may be distributed among the multiple layers of the scalable coded video stream. In this paper, we propose a novel, multiple objective optimized, multi-layered video broadcasting scheme for the 1xEV-DO system. With this scheme, the average observed service quality is maximized while minimizing the total number of time slots in which individual mobile subscribers experience outages. Simulations done for the ITU Pedestrian A and Vehicular B channels show that our proposed scenario provide significant increase to the average service quality while maintaining the total number of slots receiving no service as small as in original scenario.
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    Reclaimer scheduling in dry bulk terminals
    (IEEE-inst Electrical Electronics Engineers inc, 2020) Ünsal, Özgür; PhD Student; Graduate School of Sciences and Engineering; N/A
    This paper studies a complex parallel scheduling problem with non-crossing constraint, sequence dependent setup times, eligibility restrictions, and precedence relationships motivated by reclaimer scheduling in dry bulk terminals. in a stockyard of any dry bulk terminal, stockpiles are handled by reclaimers. therefore, improving the operational efficiency of reclaimers is critical for the overall performance of these terminals which are struggling with increasing workload. We study the variants of this problem with and without stacking operations. for each variant, we present a lower and an upper bound. a strong lower bound is obtained by relaxing the non-crossing constraint and solving the resulting problem to the optimality. While this relaxation still addresses a challenging scheduling problem, proposed arc-time-indexed formulation copes with the instances of practical size. We develop a novel constraint programming formulation to provide an upper bound for the problem. Computational experiments show this robust approach is able to generate near-optimal schedules for different stockyard configurations within a minute.