Organizational Unit: Electrical & Electronics Engineering
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Conference paperPublication Metadata only LIG at MediaEval 2015 multimodal person discovery in broadcast TV task(CEUR-WS, 2015) Budnik, M.; Safadi, B.; Besacier, L.; Quénot, G.; Khodabakhsh, Ali; Demiroğlu, Cenk; Electrical & Electronics Engineering; DEMİROĞLU, Cenk; Khodabakhsh, AliIn this working notes paper the contribution of the LIG team (partnership between Univ. Grenoble Alpes and Ozyegin University) to the Multimodal Person Discovery in Broadcast TV task in MediaEval 2015 is presented. The task focused on unsupervised learning techniques. Two different approaches were submitted by the team. In the first one, new features for face and speech modalities were tested. In the second one, an alternative way to calculate the distance between face tracks and speech segments is presented. It also had a competitive MAP score and was able to beat the baseline.Conference paperPublication Metadata only Experimental evaluation of a software defined visible light communication system(IEEE, 2020) Mohamed, Bassam Aly Abdelrahman; Elamassie, Mohammed; Kebapçı, Burak; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Mohamed, Bassam Aly Abdelrahman; Kebapçı, BurakVisible light communication (VLC) allows the dual use of light-emitting diodes (LEDs) for illumination and communication purposes. With its large bandwidth and immunity to electromagnetic interference, VLC can be used as complementary and/or alternative to radio communications. In this paper, we present a comprehensive experimental evaluation of a software-defined VLC system with on-off keying for both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios. The experimental set-up is based on a pair of modified National Instruments USRPs coupled with a custom design front-end. In the measurement campaign, we vary the distance between 1 to 3 meters with a step size of 0.5 m. For each point in this LOS scenario, we measure signal-to-noise ratio (SNR) and bit error rate (BER) with and without a lens. We also evaluate the effect of the reception angle (i.e, no strict alignment) on system performance. We further evaluate the SNR performance for NLOS scenarios and demonstrate a robust performance due to the wide field-of-view of the front-end.Conference paperPublication Metadata only Rate-adaptive OFDM MIMO VLC system(IEEE, 2018-01-19) Narmanlıoğlu, Ömer; Kızılırmak, R. Ç.; Miramirkhani, Farshad; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Miramirkhani, Farshad; Narmanlıoğlu, ÖmerIn this paper, we investigate link adaptation for an orthogonal frequency division multiplexing (OFDM)-based multiple-input multiple-output (MIMO) visible light communication (VLC) system. The MIMO system under consideration employs repetition coding, therefore all the transmitters emit the same information. We propose a rate adaptation algorithm where the modulation size is selected among the available constellation sets. The receiver first calculates the instantaneous signal-to-noise ratio per subcarrier, then determines the maximum constellation size on each subcarrier that can be supported while satisfying a predefined target bit error rate. Our numerical results reveal that a peak data rate of more than 1.14 Gbits/sec can be achieved using LEDs with cut-off frequency of 10 MHz in typical office spaces.Conference paperPublication Metadata only Effect of partial coherence on MISO FSO systems(IEEE, 2015) Gökçe, M. C.; Baykal, Y.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratMultiple-input single-output (MISO) techniques are employed in free space optical (FSO) systems to mitigate the degrading effects of atmospheric turbulence and therefore the link reliability is improved. In this paper, we consider an incoherent radial array beams and a finite sized slow detector for MISO FSO systems. We have derived the average power and power correlation formulas on the finite sized slow detector using the Huygens Fresnel principle in weak atmospheric turbulence. This helps us to find the system performance, such as power scintillation and aperture averaging factor. Effect of system parameters such as the source size, the ring radius, the degree of coherence, the link distance, the structure constant and the receiver aperture radius are analyzed on the performance of MISO FSO systems.Conference paperPublication Metadata only Recovery of temporal synchronization error through online 3D tracking with two cameras(ACM, 2014) Topçu, O.; Ercan, Ali Özer; Alatan, A. A.; Electrical & Electronics Engineering; ERCAN, Ali ÖzerMultiple object tracking within a network of cameras with overlapping fields of views has gained interest. The acquisition of images in an asynchronous manner hinders the practical implementation of such systems. Most of the previous work reported tests over short intervals, leaving the performance degradation due to asynchronous image acquisition unknown. In this work, we propose an online method to recover the synchronization error while tracking objects. The recovered error is fed back to trackers so as to restore their performance. The time synchronization error is measured by the mismatch in the epipolar constraint between the two cameras. We show that successful recovery of the synchronization error is possible when its product with the object motion speeds are within some limits.Conference paperPublication Metadata only Outage performance of multi-hop hybrid FSO/RF communication systems(IEEE, 2015) Kazemi, H.; Uysal, Murat; Touati, F.; Haas, H.; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, five scenarios are considered for the realization of a multi-hop hybrid free-space optical/radio frequency (FSO/RF) communication system with decode-and-forward (DF) relaying, and analytical outage probability expressions are derived. The scenarios have a different number of FSO and RF links. The aim is to identify an optimum scenario to effectively improve the end-to-end reliability of the multi-hop hybrid FSO/RF system. Outage performance is investigated for the scenarios under various weather conditions through numerical examples. It is identified that for a given link distance the end-to-end outage probability is minimized when using a hybrid FSO/RF link between every two successive nodes of the multi-hop system, and this requires the maximum number of FSO and RF links to be deployed.Conference paperPublication Metadata only Performance analysis of cooperative diversity networks with imperfect channel estimation over Rician fading channels(IEEE, 2010) Ikki, S. S.; Feteiha, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, we examine the effect of channel estimation error on the error and outage probabilities of a multi-relay system with amplify-and-forward relaying over frequency-flat Rician fading channel. We consider orthogonal relaying and study both conventional cooperative systems (i.e., all relays participate in the relaying phase) and opportunistic cooperative systems (i.e., only the best relay participates in the relaying phase). Based on the derivation of effective signal-to-ratio (SNR) at the receiver taking into account channel estimation error, we obtain closed-form expressions for error and outage probabilities in high SNR regime. Such closed form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Computer simulations are used to validate our analytical results.ArticlePublication Metadata only Defect-aware nanocrossbar logic mapping through matrix canonization using two-dimensional radix sort(ACM, 2011-08) Gören, S.; Uğurdağ, Hasan Fatih; Palaz, O.; Electrical & Electronics Engineering; UĞURDAĞ, Hasan FatihNanocrossbars (i.e., nanowire crossbars) offer extreme logic densities but come with very high defect rates; stuck-open/closed, broken nanowires. Achieving reasonable yield and utilization requires logic mapping that is defect-aware even at the crosspoint level. Such logic mapping works with a defect map per each manufactured chip. The problem can be expressed as matching of two bipartite graphs; one for the logic to be implemented and other for the nanocrossbar. This article shows that the problem becomes a Bipartite SubGraph Isomorphism (BSGI) problem within sub-nanocrossbars free of stuck-closed faults. Our heuristic KNS-2DS is an iterative rough canonizer with approximately O(N2) complexity followed by an O(N3) matching algorithm. Canonization brings a partial or full order to graph nodes. It is normally used for solving the regular Graph Isomorphism (GI) problem, while we apply it to BSGI. KNS stands for K-Neighbor Sort and is used for initializing our main contribution 2-Dimensional-Sort (2DS). 2DS operates on the adjacency matrix of a bipartite graph. Radix-2 2DS solves the problem in the absence of stuck-closed faults. With the addition of Radix-3 and our novel Radix-2.5 sort, we solve problems that also have stuck-closed faults. We offer very short runtimes (due to canonization) compared to previous work and have success on all benchmarks. KNS-2DS is also novel from the perspective of BSGI problem as it is based on canonization but not on a search tree with backtracking.ArticlePublication Metadata only Cryptographic security concerns on timestamp sharing via a public channel in quantum-key-distribution systems(American Physical Society, 2022-07) Pahalı, Melis; Durak, Kadir; Tefek, U.; Electrical & Electronics Engineering; DURAK, Kadir; Pahalı, MelisQuantum-key-distribution protocols are known to be vulnerable against a side channel attack that exploits the time difference in detectors' responses used to obtain key bits. The recommended solution against this timing side channel attack is to use a large time bin width instead of high-resolution timing information. A common notion is that using a large bin width reduces the resolution of detectors' responses, hence supposedly minimizes the information leakage to an eavesdropper. We challenge this conventional wisdom and demonstrate that increasing the bin width does not monotonically reduce the mutual information between the key bits and the eavesdropper's observation of detectors' responses. Instead of randomly increasing the bin width, it should be carefully chosen because the mutual information fluctuates with respect to the bin width. We also examine the effect of full width half maximums (FWHMs) of the detectors' responses on the mutual information and show that decreasing the FWHM increases the mutual information. Lastly, the start time of binning is also shown to be important in the binning process and the mutual information fluctuates periodically with respect to it.ArticlePublication Metadata only Effect of sea waves on vertical underwater visible light communication links(IEEE, 2023-04) Elamassie, Mohammed; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; ELAMASSIE, Mohammed; UYSAL, MuratUnderwater visible light communication (VLC) has been proposed to deal with emerging high bandwidth underwater applications. Initial research works on underwater VLC are based on the assumption that both transmitter and receiver are submerged, creating a horizontal link. In most of the vertical communication links, one of the transceiver nodes takes the form of a buoy and requires taking into the effect of the sea surface, which is inherently unsteady due to wind and waves. In this article, we consider a vertical underwater VLC link where the transmitter is in the form of a buoy at the sea surface, and the receiver is a submerged node at a certain depth. We assume sinusoidal waves and consider the fact that the buoy will fluctuate and oscillate, during drifting up and down, around its vertical axis. This effectively results in a 3-D displacement at the suspended transmitter. Building upon these assumptions of practical relevance, we propose an aggregate channel model, which includes a random path loss due to periodic changes of the transmission distance and a fading term induced by pointing errors with periodic changes of relative movement. Based on the proposed statistical model, we derive closed-form expressions for the exact and asymptotic bit error ratio and investigate the achievable diversity orders. We further present numerical results to confirm the analytical findings.