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Publication Open Access A cross-layer design for QoS support in cognitive radio sensor networks for smart grid applications(Institute of Electrical and Electronics Engineers (IEEE), 2012) Güngör, Vehbi C.; Shah, Ghalib Asadullah; Akan, Özgür Barış; Faculty Member; College of EngineeringIn this paper, we propose a cross-layer design to meet the QoS requirements for smart grids employing the cognitive radio sensor networks for their control and monitoring operations. Existing routing protocols pertaining to QoS support are not able to simultaneously handle traffic of different characteristics present in smart grids. Therefore, considering the traffic heterogeneity of smart grid applications exhibiting diverse QoS requirements, a set of priority classes is defined in order to differentiate the traffic for the respective service. Specifically, the problem is formulated as a weighted network utility maximization (WNUM) whose objective is to maximize the weighted sum of flows service. A cross-layer heuristic solution is provided to solve the utility optimization problem by performing joint routing, dynamic spectrum allocation and medium access. Performance of the proposed protocol is evaluated using ns-2, which shows that the number of flows belonging to each class are served according to their weight fraction with their respective data rate, latency and reliability requirement.
Publication Metadata only A dual-mode quadruple precision floating-point divider(IEEE, 2006) N/A; N/A; N/A; İşseven, Aytunç; Akkaş, Ahmet; Master Student; Faculty Member; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/AMany scientific applications require more accurate computations than double precision or double-extended precision floating-point arithmetic. This paper presents the design of a dual-mode quadruple precision floating-point divider that also supports two parallel double precision division. A radix- 4 SRT division algorithm with minimal redundancy is used to implement the dual-mode quadruple precision floating-point divider. To estimate area and worst case delay, a double, a quadruple, a dual-mode double, and a dual-mode quadruple precision floating-point division units are implemented in VHDL and synthesized. The synthesis results show that the dual-mode quadruple precision divider requires 22% more area than the quadruple precision divider and the worst case delay is 1% longer. A quadruple precision division takes fifty nine cycles and two parallel double precision division take twenty nine cycles.Publication Open Access A hybrid architecture for federated and centralized learning(Institute of Electrical and Electronics Engineers (IEEE), 2022) Elbir, Ahmet M.; Papazafeiropoulos, Anastasios K.; Kourtessis, Pandelis; Chatzinotas, Symeon; Department of Electrical and Electronics Engineering; Ergen, Sinem Çöleri; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 7211Many of the machine learning tasks rely on centralized learning (CL), which requires the transmission of local datasets from the clients to a parameter server (PS) entailing huge communication overhead. To overcome this, federated learning (FL) has been suggested as a promising tool, wherein the clients send only the model updates to the PS instead of the whole dataset. However, FL demands powerful computational resources from the clients. In practice, not all the clients have sufficient computational resources to participate in training. To address this common scenario, we propose a more efficient approach called hybrid federated and centralized learning (HFCL), wherein only the clients with sufficient resources employ FL, while the remaining ones send their datasets to the PS, which computes the model on behalf of them. Then, the model parameters are aggregated at the PS. To improve the efficiency of dataset transmission, we propose two different techniques: i) increased computation-per-client and ii) sequential data transmission. Notably, the HFCL frameworks outperform FL with up to 20% improvement in the learning accuracy when only half of the clients perform FL while having 50% less communication overhead than CL since all the clients collaborate on the learning process with their datasets.Publication Metadata only A novel reconfigurable intelligent surface-supported code index modulation-based receive spatial modulation system(IEEE-Institute of Electrical and Electronics Engineers, 2024) Ozden, Burak Ahmet; Cogen, Fatih; Aydin, Erdogan; Ilhan, Haci; Wen, Miaowen; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; College of EngineeringToday's wireless communication networks have many requirements such as high data rate, high reliability, low latency, low error data transmission, and high energy efficiency. High-performance index modulation (IM) techniques and reconfigurable intelligent surface (RIS) technology, which has recently attracted the attention of researchers, are strong candidates to meet these requirements. This paper introduces a novel RIS-supported code IM-based receive spatial modulation (RIS-CIM-RSM) system. The proposed RIS-CIM-RSM system uses quadrature amplitude modulation (QAM) symbols, receive antenna indices, and spreading code indices for wireless data transmission. In the proposed system, an RIS applies a phase rotation that maximizes signal-to-noise ratio (SNR) to the signals coming to the reflecting elements and directs them to the selected receive antenna. Performance analyses of the proposed RIS-CIM-RSM system such as data rate, throughput, and energy saving are obtained. The results obtained show that the proposed RIS-CIM-RSM system is superior to the counterpart RIS-based IM systems in the literature in terms of data rate, throughput, energy saving, and error performance.Publication Open Access A queueing-theoretical delay analysis for intra-body nervous nanonetwork(Elsevier, 2015) Department of Electrical and Electronics Engineering; Abbasi, Naveed Ahmed; Akan, Özgür Barış; Faculty Member; Department of Electrical and Electronics Engineering; College of EngineeringNanonetworks is an emerging field of study where nanomachines communicate to work beyond their individual limited processing capabilities and perform complicated tasks. The human body is an example of a very large nanoscale communication network, where individual constituents communicate by means of molecular nanonetworks. Amongst the various intra-body networks, the nervous system forms the largest and the most complex network. In this paper, we introduce a queueing theory based delay analysis model for neuro-spike communication between two neurons. Using standard queueing model blocks such as servers, queues and fork-join networks, impulse reception and processing through the nervous system is modeled as arrival and service processes in queues. Simulations show that the response time characteristics of the model are comparable to those of the biological neurons.Publication Metadata only A supervised learning-assisted partitioning solution for ris-aided noma systems(IEEE-Inst Electrical Electronics Engineers Inc, 2024) ; Department of Electrical and Electronics Engineering; Gevez, Yarkın; Arslan, Emre; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; ; Graduate School of Sciences and Engineering; College of Engineering;Thanks to its capacity for producing intelligent radio environments that are both efficient and affordable, reconfigurable intelligent surfaces technology is gaining recognition as a potential solution for advanced communication systems. Efficient information processing is crucial for smart surfaces to effectively respond to electromagnetic signals, however achieving this requires additional resources such as computing time, storage, energy, and bandwidth. To address these challenges, model-agnostic methods such as machine learning can be an effective solution, as ML employs trainable variables to examine raw data and generate valuable outcomes. This study introduces a novel approach that integrates a hybrid RIS and utilizes an uplink non-orthogonal multiple access transmission from the users to the base-station. The proposed scheme utilizes supervised learning for RIS partitioning to optimize RIS element distribution that minimizes interference between users situated in the RIS's non-line-of-sight. The proposed system achieves similar achievable rates and fairness among users as the current advanced iterative algorithm described in existing literature, while significantly reducing the time and complexity involved. A theoretical outage probability formulation is derived along with computer simulations and comparisons presented to assess system outage and bit error probability results for varying quality-of-service conditions and successive interference cancellation scenarios.Publication Open Access A theoretical modeling and analysis communication via heat flow at nanoscale(Institute of Electrical and Electronics Engineers (IEEE), 2014) Kılınç, Deniz; Akan, Özgür Barış; College of EngineeringNanonetworks constructed by interconnecting nanodevices using wireless communication allow the nanodevices to perform more complex functions by means of cooperation between them. For the first time in the literature, a novel and physically realizable nanoscale communication technique is introduced: Nanoscale Heat Communication (NHC) in which the heat transfer is used for communication at the nanoscale. The transmitted information is encoded in temperature signals using Magneto-Caloric Effect (MCE) which is the change in temperature of a magnetic material exposed to a varying magnetic field. Thermal energy emitted or absorbed by a transmitter nanodevice is subject to the laws of thermal diffusion which changes the temperature of the communication medium. The transmitted information is decoded by a receiver nanodevice that senses the temperature variations. Using information theoretical analysis, a closed-form expression for the channel capacity is obtained. According to the performance evaluation of the channel capacity, NHC provides a significantly higher capacity communication compared with the existing molecular communication techniques. Therefore, NHC stands as a promising solution to nanoscale communication between nanomachines based on its channel capacity performance, advantages, and possible applications for the emerging field of nanonetworks.Publication Open Access Adaptive unipolar MIMO-OFDM for visible light communications(Institute of Electrical and Electronics Engineers (IEEE), 2019) Al-Nahhal, Mohamed; Uysal, Murat; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Faculty Member; Department of Electrical and Electronics Engineering; College of Sciences; 149116Unipolar orthogonal frequency division multiplexing (U-OFDM) appears as an attractive optical OFDM solution for emerging visible light communication (VLC) systems. This paper proposes spectral efficiency improvement for U-OFDM systems by applying adaptive transmission over realistic VLC links. This adaptive transmission includes switching among a number of multiple-input multiple-output (MIMO) modes combined with appropriate modulation size selection. The considered MIMO modes are repetition coding, spatial modulation, and spatial multiplexing, where each mode supports different modulation sizes. The selection of the corresponding MIMO mode and its modulation size is based on the received signal-to-noise ratio and target bit error rate. The proposed U-OFDM system is applied over different VLC MIMO setups with realistic channel models for 8 x 8, 4 x 4 and 2 x 2 MIMO systems. Our simulation results show that the proposed adaptive system provides a significant spectral efficiency improvement over stand-alone U-OFDM MIMO modes/setups.Publication Open Access An information theoretical analysis of broadcast networks and channel routing for FRET-based nanoscale communications(Institute of Electrical and Electronics Engineers (IEEE), 2012) Kuşcu, Murat; Malak, Derya; Akan, Özgür Barış; Faculty Member; College of EngineeringNanoscale communication based on Forster Resonance Energy Transfer (FRET) enables nanomachines to communicate with each other using the excited state of the fluorescent molecules as the information conveyer. In this study, FRET-based nanoscale communication is further extended to realize FRET-based nanoscale broadcast communication with one transmitter and many receiver nanomachines, and the performance of the broadcast channel is analyzed information theoretically. Furthermore, an electrically controllable routing mechanism is proposed exploiting the Quantum Confined Stark Effect (QCSE) observed in quantum dots. It is shown that by appropriately selecting the employed molecules on the communicating nanomachines, it is possible to control the route of the information flow by externally applying electric field in FRET-based nanonetworks.Publication Open Access An information theoretical analysis of nanoscale molecular gap junction communication channel between cardiomyocytes(Institute of Electrical and Electronics Engineers (IEEE), 2013) Kılınç, Deniz; Akan, Özgür Barış; College of EngineeringMolecular communication (MC) is a promising paradigm to communicate at nanoscale and it is inspired by nature. One of the MC methods in nature is the gap junction (GJ) communication between cardiomyocytes. The GJ communication is achieved by diffusion of ions through GJ channels between the cells. The transmission of the information is realized by means of the propagation of the action potential (AP) signal. The probabilities of both the AP propagation failure and the spontaneous AP initiation are obtained. For the first time in the literature, the GJ communication channel is modeled and analyzed from the information theoretical perspective to find the communication channel capacity. A closed-form expression is derived for the capacity of the GJ communication channel. The channel capacity, propagation delay, and information transmission rate are analyzed numerically for a three-cell network. The results of the numerical analyses point out a correlation between an increase in the incidence of several cardiac diseases and a decrease in the channel capacity, an increase in the propagation delay, and either an increase or a decrease in the transmission rate. The method that we use and results that are presented may help in the investigation, diagnosis, and treatment of cardiac diseases as well as help in the design of nanodevices communicating via GJ channels.