Organizational Unit: Electrical & Electronics Engineering
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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 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 Fast multiplier generator for FPGAs with LUT based partial product generation and column/row compression(Elsevier, 2017) Kakacak, Ahmet; Guzel, Aydın Emre; Cihangir, Ozan; Gören, S.; Uğurdağ, Hasan Fatih; Electrical & Electronics Engineering; UĞURDAĞ, Hasan Fatih; Kakacak, Ahmet; Guzel, Aydın Emre; Cihangir, OzanWe present a new parallel integer multiplier generator for FPGAs. It combines (i) a new Generalized Parallel Counter (GPC) grouping algorithm for column compression with (ii) a LUT based partial product generation, is (iii) unique as it automatically generates placement pragmas, (iv) uses a ternary adder as a final adder to exploit FPGA's internal carry-chains, and (v) employs a novel GPC based row compression, which aims to reduce the width of the final adder. We wrote Verilog generators for our method as well as one leading work in the literature. For synthesis, we wrote a script that can do “binary search” for the optimum latency. Our extensive implementation results on Xilinx Virtex-6 FPGAs show that we almost always produce circuits with smaller latency (i.e., timing) and Area-Timing Product (ATP) compared to the state-of-the-art in the literature, by 18% and 12% (on the average), respectively. We also offer smaller latency compared to the HDL * operator by 9% on the average at a cost of 12% larger ATP on the average. We are worse in latency in 6 cases out of 33, in all of which synthesis maps * to DSP slices. We also include area and energy results on Virtex-6 as well as a limited amount of latency, area, and ATP results on Virtex-5 and Altera Stratix III.ArticlePublication Metadata only Energy harvesting and magneto-inductive communications with molecular magnets on vibrating graphene and biomedical applications in the kilohertz to terahertz band(IEEE, 2017-09) Gülbahar, Burhan; Electrical & Electronics Engineering; GÜLBAHAR, Burhan CahitMagneto-inductive (MI) Terahertz (THz) wireless channels provide significant theoretical performances for MI communications (MIC) and wireless power transmission (WPT) in nanoscale networks. Energy harvesting (EH) and signal generation are critical for autonomous operation in challenging mediums including biomedical channels. State of the art electromagnetic vibrational devices have millimeter dimensions while targeting low frequency EH without any real-time communications. In this paper, graphene resonators are combined with single molecule magnets (SMMs) to realize nanoscale EH, MIC, and WPT with novel modulation methods achieving simultaneous wireless information and PT. The unique advantages of graphene including atomic thickness, ultra-low weight, high strain, and resonance frequencies in the Kilohertz to THz band are combined with high and stable magnetic moments of Terbium (III) bis (phthalocyanine) SMMs. Numerical analyses provide tens of nanowatts powers and efficiencies of 10 4W/m3 in acoustic and ultrasound frequencies comparable with vibrational EH devices while millimeter wave carrier generation is numerically analyzed. Proposed model and communication theoretical analysis present a practical framework for challenging applications in the near future by promising simple mechanical design. Applications include nanoscale biomedical tagging including human cells, sensing and communication for diagnosis and treatment, EH and modulation for autonomous nano-robotics, and magnetic particle imaging.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 Open Access 3D neuromorphic wireless power transfer and energy transmission based synaptic plasticity(IEEE, 2019) Gülbahar, Burhan; Electrical & Electronics Engineering; GÜLBAHAR, Burhan CahitEnergy consumption combined with scalability and 3D architecture is a fundamental constraint for brain-inspired computing. Neuromorphic architectures including memristive, spintronic, and floating gate metal-oxide-semiconductors achieve energy efficiency while having challenges of 3D design and integration, wiring and energy consumption problems for architectures with massive numbers of neurons and synapses. There are bottlenecks due to the integration of communication, memory, and computation tasks while keeping ultra-low energy consumption. In this paper, wireless power transmission (WPT)-based neuromorphic design and theoretical modeling are proposed to solve bottlenecks and challenges. Neuron functionalities with nonlinear activation functions and spiking, synaptic channels, and plasticity rules are designed with magneto-inductive WPT systems. Tasks of communication, computation, memory, and WPT are combined as an all-in-one solution. Numerical analysis is provided for microscale graphene coils in sub-terahertz frequencies with unique neuron design of coils on 2D circular and 3D Goldberg polyhedron substrates as a proof-of-concept satisfying nonlinear activation mechanisms and synaptic weight adaptation. Layered neuromorphic WPT network is utilized to theoretically model and numerically simulate pattern recognition solutions as a simple application of the proposed system design. Finally, open issues and challenges for realizing WPT-based neuromorphic system design are presented including experimental implementations.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.