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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Microfluidic pulse shaping methods for molecular communications(Elsevier, 2023) Department of Electrical and Electronics Engineering; Kahvazi Zadeh, Maryam; Bolhassan, Iman Mokari; Kuşcu, Murat; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of EngineeringMolecular Communication (MC) is a bio-inspired communication modality that utilizes chemical signals in the form of molecules to exchange information between spatially separated entities. Pulse shaping is an important process in all communication systems, as it modifies the waveform of transmitted signals to match the characteristics of the communication channel for reliable and high-speed information transfer. In MC systems, the unconventional architectures of components, such as transmitters and receivers, and the complex, nonlinear, and time-varying nature of MC channels make pulse shaping even more important. While several pulse shaping methods have been theoretically proposed for MC, their practicality and performance are still uncertain. Moreover, the majority of recently proposed experimental MC testbeds that rely on microfluidics technology lack the incorporation of programmable pulse shaping methods, which hinders the accurate evaluation of MC techniques in practical settings. To address the challenges associated with pulse shaping in microfluidic MC systems, we provide a comprehensive overview of practical microfluidic chemical waveform generation techniques that have been experimentally validated and whose architectures can inform the design of pulse shaping methods for microfluidic MC systems and testbeds. These techniques include those based on hydrodynamic and acoustofluidic force fields, as well as electrochemical reactions. We also discuss the fundamental working mechanisms and system architectures of these techniques, and compare their performances in terms of spatiotemporal resolution, selectivity, system complexity, and other performance metrics relevant to MC applications, as well as their feasibility for practical MC applications.Publication Metadata only Ris-aided angular-based hybrid beamforming design in mmwave massive mimo systems(IEEE, 2022) Koc, Asil; Tho Le-Ngoc; Department of Electrical and Electronics Engineering; Yıldırım, İbrahim; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of EngineeringThis paper proposes a reconfigurable intelligent surface (RIS)-aided and angular-based hybrid beamforming (AB-HBF) technique for the millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems. The proposed RIS-AB-HBF architecture consists of three stages: (i) RF beam-former, (ii) baseband (BB) precoder/combiner, and (iii) RIS phase shift design. First, in order to reduce the number of RF chains and the channel estimation overhead, RF beamformers are designed based on the 3D geometry-based mmWave channel model using slow time-varying angular parameters of the channel. Second, a BB precoder/combiner is designed by exploiting the reduced-size effective channel seen from the BB stages. Then, the phase shifts of the RIS are adjusted to maximize the achievable rate of the system via the nature-inspired particle swarm optimization (PSO) algorithm. Illustrative simulation results demonstrate that the use of RISs in the AB-HBF systems has the potential to provide more promising advantages in terms of reliability and flexibility in system design.Publication Metadata only IDE-integrated microneedle arrays as fully biodegradable platforms for wearable/implantable capacitive biosensing(Institute of Electrical and Electronics Engineers Inc., 2023) Department of Electrical and Electronics Engineering; Ürey, Hakan; Mirzajani, Hadi; Department of Electrical and Electronics Engineering; Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); College of EngineeringMicroneedle biosensors have emerged as a promising tool for in situ biomarker detection due to their minimally invasive nature and ability to interface with interstitial fluid (ISF). However, most previously demonstrated ones are limited to in situ detection of small molecules and ions, employing amperometry or potentiometry measurement techniques with electrical current or voltage output metrics, respectively, which may not be suitable for detecting large molecules, such as proteins. This letter presents an innovative approach utilizing a microneedle array integrated with an interdigitated electrode (MAIDE), enabling in situ capacitive detection and quantification of protein biomarkers. Following microneedle penetration, the interdigitated electrode array establishes direct contact with the solution, enabling real-time monitoring of interfacial capacitance modulations as the result of the binding reaction, leading to the acquisition of rich molecular data. Equivalent circuit model extraction followed by impedance spectroscopy for different concentrations of bovine serum albumin (BSA) indicated the suitability of the proposed platform in tracking the interfacial capacitance variations with respect to different BSA concentrations of 100, 10, and 1 μg/mL with a detection limit of 21 ng/mL. Furthermore, the device showed satisfactory results for biodegradability experiments where it disintegrated for a duration of 10 h. In addition, in vivo experiments show stable capacitance readings with (dC/C)% deviations less than 0.5%, indicating its potential for biodegradable wearable/implantable capacitive biosensing applicationsPublication Metadata only On the performance of OFDM-IM systems in the presence of CFO effects(Elsevier Inc., 2024) Besseghier, Mokhtar; Ghouali, Samir; Djebbar, Ahmed Bouzidi; Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; ; College of Engineering;This study presents a comprehensive analysis of the performance degradation effects of carrier frequency offset (CFO) on orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems operating over frequency-selective multipath fading channels. CFO is an impairing factor that degrades the signal-to-noise ratio (SNR) through signal attenuation and inter-carrier interference (ICI). We derive a closed-form expression to quantify the SNR degradation under CFO for OFDM-IM systems. Additionally, we formulate a very tight upper bound for the bit error rate (BER), accounting for index modulation errors, CFO distortion, and multipath fading. The presented analytical formulations capture the unique characteristics of OFDM-IM systems and facilitate precise performance evaluation. The findings yield valuable insights into mitigating CFO-induced BER degradation through appropriate system parameter selection and CFO compensation techniques. Moreover, this investigation makes significant contributions towards designing reliable OFDM-IM communication links resilient to the combined effects of index modulation, frequency offsets, and dispersive channel conditions.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. IEEEPublication Metadata only The effect of wearable technology on psychomotor agitation in patients with diagnostic patients with schizophrenia expansion and psychosis(Cambridge Univ Press, 2023) Aydin, P. Cetinay; Tokatlıoğlu, T. Şahin; Eser, E.; Zemen, N.; Department of Electrical and Electronics Engineering; Oflaz, Fahriye; Gürsoy, Beren Semiz; Hayırlıoğlu, Yusuf Ziya; Department of Electrical and Electronics Engineering; School of Nursing; College of Engineering; Graduate School of Sciences and EngineeringPublication Metadata only Kirchhoff meets Johnson: in pursuit of unconditionally secure communication(WILEY, 2024) Department of Electrical and Electronics Engineering; Başar, Ertuğrul; Department of Electrical and Electronics Engineering; College of EngineeringNoise: an enemy to be dealt with and a major factor limiting communication system performance. However, what if there is gold in that garbage? In conventional engineering, our focus is primarily on eliminating, suppressing, combating, or even ignoring noise and its detrimental impacts. Conversely, could we exploit it similarly to biology, which utilizes noise-alike carrier signals to convey information? In this context, the utilization of noise, or noise-alike signals in general, has been put forward as a means to realize unconditionally secure communication systems in the future. In this tutorial article, we begin by tracing the origins of thermal noise-based communication and highlighting one of its significant applications for ensuring unconditionally secure networks: the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange scheme. We then delve into the inherent challenges tied to secure communication and discuss the imperative need for physics-based key distribution schemes in pursuit of unconditional security. Concurrently, we provide a concise overview of quantum key distribution schemes and draw comparisons with their KLJN-based counterparts. Finally, extending beyond wired communication loops, we explore the transmission of noise signals over-the-air and evaluate their potential for stealth and secure wireless communication systems.Publication Metadata only Flexible-rate learned hierarchical bi-directional video compression with motion refinement and frame-level bit allocation(IEEE, 2022) Department of Electrical and Electronics Engineering; Çetin, Eren; Yılmaz, Mustafa Akın; Tekalp, Ahmet Murat; Department of Electrical and Electronics Engineering; Koç Üniversitesi İş Bankası Yapay Zeka Uygulama ve Araştırma Merkezi (KUIS AI)/ Koç University İş Bank Artificial Intelligence Center (KUIS AI); College of Engineering; Graduate School of Sciences and EngineeringThis paper presents improvements and novel additions to our recent work on end-to-end optimized hierarchical bidirectional video compression [1] to further advance the state-of-the-art in learned video compression. As an improvement, we combine motion estimation and prediction modules and compress refined residual motion vectors for improved rate-distortion performance. As novel addition, we adapted the gain unit proposed for image compression to flexible-rate video compression in two ways: first, the gain unit enables a single encoder model to operate at multiple rate-distortion operating points; second, we exploit the gain unit to control bit allocation among intra-coded vs. bi-directionally coded frames by fine tuning corresponding models for truly flexible-rate learned video coding. Experimental results demonstrate that we obtain state-of-the-art rate-distortion performance exceeding those of all prior art in learned video coding.Publication Metadata only Predicting path loss distributions of a wireless communication system for multiple base station altitudes from satellite images(IEEE, 2022) Güntürk, Bahadır K.; Ateş, Hasan F.; Baykaş, Tunçer; Department of Electrical and Electronics Engineering; Shoer, İbrahim; Department of Electrical and Electronics Engineering; College of EngineeringIt is expected that unmanned aerial vehicles (UAVs) will play a vital role in future communication systems. Optimum positioning of UAVs, serving as base stations, can be done through extensive field measurements or ray tracing simulations when the 3D model of the region of interest is available. In this paper, we present an alternative approach to optimize UAV base station altitude for a region. The approach is based on deep learning;specifically, a 2D satellite image of the target region is input to a deep neural network to predict path loss distributions for different UAV altitudes. The neural network is designed and trained to produce multiple path loss distributions in a single inference;thus, it is not necessary to train a separate network for each altitude.Publication Metadata only Comparison of convex combination and affine combination of adaptive filters(Ieee, 2009) Singer, Andrew C.; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; Kozat, Süleyman Serdar; Erdoğan, Alper Tunga; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; College of Engineering; 177972; 41624In the area of combination of adaptive filters, two main approaches, namely convex and affine combinations have been introduced. In this article, the relation between these two approaches is investigated. First, the problem of obtaining optimal convex combination coefficients is formulated as the projection of the optimal affine combination weights to the unit simplex in a weighted inner product space. Based on this formulation the closed form expressions for optimal combination weights and target MSE levels are obtained for two and three branch cases.