Researcher:
Pehlivan, İbrahim

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İbrahim

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Pehlivan

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Pehlivan, İbrahim

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2019 - 201912020 - 20212

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Researcher Of Publications: search.filters.isAuthorOfPublication.f487e648-b981-437c-a9b5-512041010ebf

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    PublicationOpen Access
    Scheduling of energy harvesting for MIMO wireless powered communication networks
    (Institute of Electrical and Electronics Engineers (IEEE), 2019) Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Pehlivan, İbrahim; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 7211; N/A
    Radio frequency (RF) energy harvesting has the potential to provide perpetual energy to the nodes in communication networks. In this letter, we study the optimization problem for the scheduling of the RF energy harvesting to satisfy the energy demands of the links in a wireless powered network containing a multi-antenna hybrid beamforming base station and multi-antenna users: The time is divided into multiple slots, where different beamforming weights are assigned to each slot. Upon formulation of the problem as a non-convex quadratically constrained linear program, we propose a solution method based on alternating minimization algorithm. We demonstrate via simulations that the additional degrees of freedom introduced by the scheduling algorithm can reduce the number of required RF chains in the hybrid beamforming structure for a certain delay performance, resulting in significant cost savings.
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    PublicationOpen Access
    Joint optimization of energy transfer scheduling and power control in MIMO wireless powered communication networks
    (Institute of Electrical and Electronics Engineers (IEEE), 2020) Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Pehlivan, İbrahim; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 7211; N/A
    Hybrid beamforming is a low-cost alternative to digital beamforming with its capability to operate with fewer radio frequency (RF) chains than antennas. However, the diminishing degree of freedom from utilizing fewer RF chains results in considerable performance degradation. To circumvent this setback, scheduling of energy harvesting (SEH) has been recently proposed to provide an additional degree of freedom. In this letter, we study the optimization of SEH together with the beamforming weights, energy and data transfer intervals, and uplink transmit power. The objective is minimizing the total duration of uplink and downlink transmission, whereas the constraints include minimum data transfer, maximum allowed transmit power and hybrid beamforming requirements. We formulate the non-convex optimization problem and convert it to the equivalent rank constrained semidefinite programming problem. We then propose efficient solution methodologies based on iteratively moving the rank constraints to the objective function as a penalty. Extensive simulations demonstrate that SEH is an effective circumvention to the RF chain scarcity, culminating in up to 26% delay performance gain.
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    PublicationOpen Access
    Effect of downlink energy transfer scheduling on SDMA and TDMA uplink transmission
    (Institute of Electrical and Electronics Engineers (IEEE), 2021) Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Pehlivan, İbrahim; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; 7211; N/A
    The high cost and power consumption of digital beamforming, as a result of the high number of RF chains, has overshadowed its performance on multi-antenna wireless powered communication networks (WPCNs). This setback forced researchers to low-cost alternatives such as hybrid beamforming, which decreases the number of expensive RF chains by utilizing cheaper phase shifters. This cost-cutting, however, comes with reduced control over beamforming weights and compromise performance. To circumvent this deficiency, scheduling of energy harvesting (SEH), utilizing the degree of freedom in the time domain, has been proposed. In SEH, the downlink slot is subdivided into multiple variable-length subslots with different beamforming weights. In this paper, we examine the effect of SEH on the optimization of minimum length scheduling for space division multiple access (SDMA) uplink transmission compared to time division multiple access (TDMA) uplink transmission. Via simulations, we demonstrate that SDMA benefits more from the additional degree of freedom provided by the usage of SEH for any number of nodes. However, SDMA yields inferior delay performance compared to TDMA as the number of nodes increases, which restricts the application of SDMA with SEH, making it impractical.