Person: UYSAL, Murat
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Murat
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UYSAL
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ArticlePublication Open Access Performance and optimization of network-coded cooperative diversity systems(IEEE, 2013-03) Nasri, A.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, we study network–coded cooperative diversity (NCCD) systems comprising multiple sources, one relay, and one destination, where the relay detects the packets received from all sources and performs Galois field (GF) network coding over GF(2m) before forwarding a single packet to the destination. Assuming independent Rayleigh fading for all links of the network, we derive simple and accurate closed–formapproximations for the asymptotic symbol and bit error rates of NCCD systems. The derived error rate expressions are valid for arbitrary numbers of sources, arbitrary modulation schemes, and arbitrary constellation mappings and provide significantinsight into the impact of various system and channel parameters on performance. Moreover, these expressions can be exploited for optimization of the constellation mapping as well as for formulation of various NCCD system optimization problemsincluding optimal power allocation, relay selection, and relay placement.
ArticlePublication Metadata only High-rate distributed space-time-frequency coding for wireless cooperative networks(IEEE, 2011-02) Wu, J.; Hu, H.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, we propose high-rate distributed space-time-frequency codes (DSTFCs) to exploit maximum achievable diversity gains over frequency-selective fading channels. The proposed designs achieve full-rate for any number of cooperative nodes, and allow channel variations over multiple OFDM blocks within one DSTFC codeword. We analyze diversity gains of DSTFCs through both conditional and average pairwise error probability (PEP), and we proposes better design criteria based on one-side channel conditional PEP. We show that the difference between the frequency-selective channel orders of source-to-relay and relay-to-destination links may provide extra diversity advantages, thus additional performance gains. Through Monte-Carlo simulations, we demonstrate that proposed high-rate DSTFCs provide notable diversity advantages over existing designs.ArticlePublication Open Access Performance evaluation of LOS and NLOS vertical inhomogeneous links in underwater visible light communications(IEEE, 2018-03-22) Anous, N.; Abdallah, M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, underwater visible light communication (UWVLC) vertical links are modeled and evaluated, taking account of the inhomogeneous nature of underwater (UW) environment. An equivalent simplified model of stratified N layers is employed in which variations in refractive index and attenuation profiles across UW depth are considered. A generalized path loss expression is deduced which allows estimation of the vertical link loss prior to link design. Mathematical expressions of the received power for line-of-sight (LOS) and non-line-of-sight (NLOS) links between transmitters (Tx) and receivers are deduced. We evaluate the performance by computing the received power and bit error rate for inhomogeneous underwater links. Numerical examples are used to illustrate the proposed models. Deviations from expected results when considering a homogeneous underwater model are discussed. A simple underwater bilayer model is then introduced, which is considered a rough approximate model in comparison to the stratified N layers model. This model assists in estimating the UW link behavior without extensive calculations. The conditions necessary for applying this model are discussed and justified. Moreover, the effects of Tx orientation along with narrowing the transmitted light cone on LOS and NLOS vertical links are examined. A Tx power saving of 30%-50% in UWVLC links is proved to be achieved by rotating the Tx and narrowing its emitted light cone.ArticlePublication Metadata only Ultraviolet communications for unmanned aerial vehicle networks(IEEE, 2022) Tadayyoni, Hamed; Ardakani, M. H.; Heidarpour, A. R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Tadayyoni, HamedDue to the strong scattering, ultraviolet (UV) communication links enable non-line-of-sight (NLOS) outdoor connectivity and relax the pointing, acquisition, and tracking requirements encountered in infrared links. This feature makes the UV communications attractive, in particular, for unmanned aerial vehicle (UAV) networks where link alignment is hard to realize. In this letter, we study the performance of the uplink of a ground sensor network where a UAV periodically visits the area to receive the data from serial sensor nodes. The transmission from the closest sensor to the flying UAV is the desired signal while the received signals from other nodes are treated as interference. We derive the bit error rate for the uplink airborne UV in the presence of interference. Numerical results are provided to validate our theoretical analysis and investigate the effect of interferers on the system performance.ArticlePublication Open Access Unified resource allocation and mobility management technique using particle swarm optimization for VLC networks(IEEE, 2018-12) Demir, Muhammet Selim; Sait, S. M.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Demir, Muhammet SelimIn this paper, we present a unified resource allocation and mobility management algorithm based on particle swarm optimization (PSO) for indoor visible light communication (VLC) networks. We consider a VLC network where multiple LEDs serve as access points (APs). A centralized controller collects channel state information, quality of service requirements of the users, and the overload status of the APs. Based on the available information, in each time interval, the controller decides which user is served by which AP and assigns subcarriers to the users with the objective of maximizing both the system throughput and user satisfaction. We formulate the resource allocation problem as a constrained nonlinear integer programming problem and solve it using meta-heuristic PSO. Through an extensive simulation study, the superiority of the proposed algorithm in terms of system throughput and user satisfaction over round robin, best channel quality information, and genetic algorithms is demonstrated.ArticlePublication Metadata only Low complexity least minimum symbol error rate based post-distortion for vehicular VLC(IEEE, 2020-10) Mitra, R.; Miramirkhani, F.; Bhatia, V.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratVehicular visible light communications (VLC) has emerged as a viable supplement for high speed next-generation vehicle to vehicle (V2V) communication systems. However, performance of a V2V-VLC link is impaired due to nonlinear transfer-characteristics of light emitting diodes (LEDs), and inter-symbol interference (ISI). In this article, a low-complexity least-squares based post-distortion algorithm is formulated over reproducing kernel Hilbert space (RKHS) for a multi-hop V2V-VLC link. The impairments encountered in V2V-VLC channels are mitigated in RKHS by a minimum symbol error-rate post-distorter using a low dimensional approximation of random Fourier features (RFF) (which is a soft approximation of the feature-map to RKHS), that facilitates computationally simple post-distortion under finite memory-budget. The convergence and the BER-performance of the proposed post-distorter is analyzed over realistic V2V VLC channels obtained via ray-tracing. From the analysis, and the presented computer-simulations, the proposed post-distorter is found to exhibit equivalent convergence characteristics and error-rate over reasonable distances, with much lower computational complexity.ArticlePublication Metadata only Channel estimation for amplify-and forward relaying: cascaded against disintegrated estimators(IEEE, 2010) Amin, O.; Gedik, B.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratThe authors investigate the performance of amplify-and-forward relaying with two different pilot-symbol-assisted channel estimation methods. In the first estimation method, the cascaded channel consisting of source-to-relay and relay-to-destination links is estimated at the destination terminal. No channel estimator is required at the relay terminal. In the second estimation method, the estimation of cascaded channel is disintegrated into separate estimations of source-to-relay and relay-to-destination links which are carried out at the relay and the destination terminals, respectively. The latter method involves feed-forwarding a quantised version of the source-to-relay channel estimate to the destination terminal. Through the derivation of mean squared error (MSE) diversity gain analysis and Monte-Carlo simulations, the authors investigate the performance of amplify-and-forward relaying with these channel estimation methods. Our results demonstrate that full diversity can be achieved in the presence of channel estimation. The authors further show that cascaded channel estimator outperforms its competitor with a small number of quantisation bits. As the number of employed quantisation bits increase, disintegrated channel estimator approaches to its competitor eventually outperforming it.ArticlePublication Metadata only Centralized light access network (C-LiAN): a novel paradigm for next generation indoor VLC networks(IEEE, 2017) Kizilirmak, R. Ç.; Narmanlıoğlu, Ömer; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Narmanlıoğlu, ÖmerVisible light communication (VLC) builds upon the idea of using existing lighting infrastructure for wireless data transmission. In a conventional VLC network, each light fixture acts as an access point (AP) which are connected to each other through electrical grid as well as data backbone. These VLC-enabled fixtures consist baseband unit (BBU) followed by the optical front-end (OFE). In this paper, we propose the so-called centralized light access network (C-LiAN) which aggregates all AP computational resources into a central pool that is managed by a centralized controller. Unlike the distributed architecture where each light fixture performs both baseband processing and optical transmission/reception, the centralized architecture employs “dummy”fixtures with a VLC OFE. Moving the baseband processing to a central pool reduces the associated cost and complexity of each VLC-enabled LED luminary. It further enables joint processing of signals from different APs making possible an efficient implementation of joint processing, offloading, handover, interference management, scheduling, and resource management algorithms. As an example to demonstrate the virtues of C-LiAN, we further present the performance of coordinated multipoint transmission and enhanced inter-cell interference coordination with almost blank subframe techniques originally proposed for Long Term Evolution-Advanced in the context of indoor VLC networks.ArticlePublication Metadata only Adaptive power loading for multi-relay OFDM regenerative networks with relay selection(IEEE, 2012-03) Amin, O.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, MuratIn this paper, we propose an adaptive power loading algorithm for an OFDM (orthogonal frequency division multiplexing)-based multi-relay regenerative network with relay selection. The proposed scheme is based on selecting the "best" relay(s) according to different strategies and distributing the power adaptively among the subcarriers of source and selected relay(s) as to minimize an upper bound on the bit error rate (BER). Our Monte Carlo simulation results demonstrate superior performance gains through power loading with respect to conventional equal power loading schemes. The effects of imperfect channel estimation and relay location on the BER performance are further discussed.ArticlePublication Metadata only A comparative evaluation of propagation characteristics of vehicular VLC and MMW channels(IEEE, 2023) Hosseinabadi, Fahimeh Aghaei; Eldeeb, H. B.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Hosseinabadi, Fahimeh AghaeiVehicle-to-vehicle (V2V) communication is an underlying key technology to realize future intelligent transportation systems. Both millimeter wave (MMW) communication and visible light communication (VLC) are strong candidates to address V2V connectivity. Most of the earlier literature focuses on an individual technology. In an effort to better highlight the differences and relative advantages of these two competing technologies, we provide a comprehensive one-to-one comparison between vehicular VLC and MMW channels in this paper. For this purpose, we utilize ray tracing simulations which enable the consideration of three-dimensional modeling of the propagation environment and allow the study of various system parameters and road conditions in both line-of-sight and non-line-of-sight conditions. Under the same settings, we present the received signal strengths for both systems and investigate the channel characteristics for communication between two vehicles in the same lane as well as in different lanes with a lateral shift. We also analyze the impact of low, medium, and high density of neighbor vehicles as well as partial and complete blockage.