Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12469/47

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Citation - WoS: 21
Citation - Scopus: 22
Design of Practical Broadband Matching Networks With Lumped Elements
(IEEE-INST Electrical Electronics Engineers Inc, 2013) Şengül, Metin Y.
It is always preferable to use commercially available software tools to design broadband matching networks for microwave communication systems. However for these tools the matching network topology and element values must be selected properly. Therefore in this paper a practical method is presented to generate matching networks with good initial element values. Eventually the performance of the designed matching network is optimized by employing the commercially available computer-aided design (CAD) tools. An example is given to illustrate the utilization of the proposed method. It is shown that the proposed method provides very good initials for CAD tools.
Citation - Scopus: 1
Ieee 802.15.4a Based Ultra Wideband Systems for Coexistence With Primary Users
(IEEE, 2015) Fındıklı, Çağlar; Erküçük, Serhat; Çelebi, Mehmet Ertuğrul
Peaceful coexistence is a major implementation issue for both cognitive radios and ultra wideband (UWB) systems. Accordingly the UWB impulse radio (UWB-IR) based Wireless Personal Area Network (WPAN) standard IEEE 802.15.4a has suggested using linear combination of pulses to limit interference to coexisting primary systems. In this paper motivated by implementing the IEEE 802.15.4a based UWB-IR systems for peaceful coexistence we consider the implementation of linear combination of pulses as suggested by the standard. Accordingly we (I) design linearly combined pulses that conform to the standard requirements and (ii) study the UWB-IR system performance in the presence of orthogonal frequency division multiplexing (OFDM) based wideband primary systems with various bandwidths and subcarriers. The study shows that the UWB-IR system performance can be significantly improved by selecting suitable pulses for transmission and employing appropriate filtering techniques at the receiver when the primary system is active. The results are important for the practical implementation of IEEE 802.15.4a based UWB systems coexisting with licensed systems.
Citation - WoS: 37
Citation - Scopus: 40
Joint Optimization of Wireless Network Energy Consumption and Control System Performance in Wireless Networked Control Systems
(IEEE-INST Electrical Electronics Engineers Inc, 2017) Şadi, Yalçın; Ergen, Sinem Coleri
Communication system design for wireless networked control systems requires satisfying the high reliability and strict delay constraints of control systems for guaranteed stability with the limited battery resources of sensor nodes despite the wireless networking induced non-idealities. These include non-zero packet error probability caused by the unreliability of wireless transmissions and non-zero delay resulting from packet transmission and shared wireless medium. In this paper we study the joint optimization of control and communication systems incorporating their efficient abstractions practically used in real-world scenarios. The proposed framework allows including any non-decreasing function of the power consumption of the nodes as the objective any modulation scheme and any scheduling algorithm. We first introduce an exact solution method based on the analysis of the optimality conditions and smart enumeration techniques. Then we propose two polynomial-time heuristic algorithms based on intelligent search space reduction and smart searching techniques. Extensive simulations demonstrate that the proposed algorithms perform very close to optimal and much better than previous algorithms at much smaller runtime for various scenarios.
Citation - WoS: 25
Citation - Scopus: 28
Low-Complexity Map-Based Successive Data Detection for Coded Ofdm Systems Over Highly Mobile Wireless Channels
(IEEE-INST Electrical Electronics Engineers Inc, 2011) Panayırcı, Erdal; Dogan, Hakan; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of data detection for coded orthogonal frequency-division multiplexing (OFDM) systems in the presence of frequency-selective and very rapidly time varying channels. New low-complexity maximum a posteriori probability (MAP) data detection algorithms are proposed based on sequential detection with optimal ordering (SDOO) and sequential detection with successive cancellation (SDSC). The received signal vector is optimally decomposed into reduced dimensional subobservations by exploiting the banded structure of the frequency-domain channel matrix whose bandwidth is a parameter to be adjusted according to the speed of the mobile terminal. The data symbols are then detected by the proposed algorithms in a computationally efficient way by means of the Markov chain Monte Carlo (MCMC) technique with Gibbs sampling. The impact of the imperfect channel state information (CSI) on the bit error rate (BER) performance of these algorithms is investigated analytically and by computer simulations. A detailed computational complexity investigation and simulation results indicate that particularly the algorithm based on SDSC has significant performance and complexity advantages and is very robust against channel estimation errors compared with existing suboptimal detection and equalization algorithms proposed earlier in the literature.
Broadband Microwave Amplifier Design With Lumped Elements
(Walter De Gruyter Gmbh, 2016) Şengül, Metin Y.
This study introduces a broadband microwave amplifier design that utilizes the measured scattering parameters of active devices without assuming an initial topology for the matching networks or an analytic form of the system transfer function. The algorithm can be extended to design multistage broadband microwave amplifiers. An example is given to illustrate the application of the proposed method. It was found that the proposed method provides very good initials for CAD tools to further improve amplifier performance by working on the element values.
Citation - WoS: 81
Citation - Scopus: 92
New Trellis Code Design for Spatial Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2011) Basar, Ertugrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Spatial modulation (SM) in which multiple antennas are used to convey information besides the conventional M-ary signal constellations is a new multiple-input multiple-output (MIMO) transmission technique which has recently been proposed as an alternative to V-BLAST (vertical Bell Labs layered space-time). In this paper a novel MIMO transmission scheme called spatial modulation with trellis coding (SM-TC) is proposed. Similar to the conventional trellis coded modulation (TCM) in this scheme a trellis encoder and an SM mapper are jointly designed to take advantage of the benefits of both. A soft decision Viterbi decoder which is fed with the soft information supplied by the optimal SM decoder is used at the receiver. A pairwise error probability (PEP) upper bound is derived for the SM-TC scheme in uncorrelated quasi-static Rayleigh fading channels. From the PEP upper bound code design criteria are given and then used to obtain new 4- 8- and 16-state SM-TC schemes using quadrature phase-shift keying (QPSK) and 8-ary phase-shift keying (8-PSK) modulations for 2 3 and 4 bits/s/Hz spectral efficiencies. It is shown via computer simulations and also supported by a theoretical error performance analysis that the proposed SM-TC schemes achieve significantly better error performance than the classical space-time trellis codes and coded V-BLAST systems at the same spectral efficiency yet with reduced decoding complexity.
Citation - WoS: 1
Support Vector Machines Based Target Tracking Techniques
(IEEE, 2006) Özer, Sedat; Çırpan, Hakan Ali; Kabaoğlu, Nihat
This paper addresses the problem of aplying powerful statistical pattern classification algorithms based on kernels to target tracking. Rather than directly adapting a recognizer we develop a localizer directly using the regression form of the Support Vector Machines (SVM). The proposed approach considers using dynamic model together as feature vectors and makes the hyperplane and the support vectors follow the changes in these features. The performance of the tracker is demostrated in a sensor network scenario with a moving target in a polynomial route.
Citation - WoS: 4
Citation - Scopus: 4
Channel Estimation for Spatial Modulation Orthogonal Frequency Division Multiplexing Systems
(IEEE, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
A combination of spatial modulation and orthogonal frequency division multiplexing (SM-OFDM) has been recently proposed for multicarrier systems while assuming the perfect channel state information (P-CSI) available at the receiver. But in practical scenarios the estimation of CSI is crucial in order to detect the transmitted data coherently. In this work(1) a new frame structure and pilot symbol aided channel estimation (PSA-CE) technique with a piecewise linear interpolation is proposed for the SM-OFDM systems operating in the presence of frequency selective channel. Bit error rate (BER) performance of the proposed channel estimation technique is then investigated with different channel models such as Typical Urban ( TU) and Rural Urban (RU) for 4-quadrature amplitude modulation (QAM). In particular it is shown that the performance with estimated channel came close to that with known channel within 2.3 dB in SNR for BER = 10(-4) for TU channels.
Citation - WoS: 1
Beacons for Indoor Positioning
(IEEE, 2017) Cay, Elif; Mert, Yeliz; Bahcetepe, Ali; Akyazi, Bugra Kagan; Öğrenci, Arif Selçuk
This work aims to develop a system for the tracking and control of elderly or handicapped people in an indoor environment. We have developed both a special box using an Arduino board and a mobile application on Android to determine the location of the target based on the Bluetooth Low Energy signals transmitted by special Beacons which are placed in the area of interest. Both systems are used to determine the position of the person and to monitor any event that would cause an alert. Those events can be a long stay in a fixed position or the entry into pre-defined forbidden zones. The location data will be stored in a database for further processing. Alerts can trigger messages to be sent to local authorities and/or relatives of the people. Measurements and test results are discussed regarding their performance. It is clear that more research and development is necessary for obtaining reliable products.
Citation - WoS: 14
Citation - Scopus: 16
Bayesian Compressive Sensing for Primary User Detection
(Inst Engineering Technology-IET, 2016) Başaran, Mehmet; Erküçük, Serhat; Cirpan, Hakan Ali
In compressive sensing (CS)-based spectrum sensing literature most studies consider accurate reconstruction of the primary user signal rather than detection of the signal. Furthermore possible absence of the signal is not taken into account while evaluating the spectrum sensing performance. In this study Bayesian CS is studied in detail for primary user detection. In addition to assessing the signal reconstruction performance and comparing it with the conventional basis pursuit approach and the corresponding lower bounds signal detection performance is also considered both analytically and through simulation studies. In the absence of a primary user signal the trade-off between probabilities of detection and false alarm is studied as it is equally important to determine the performance of a CS approach when there is no active primary user. To reduce the computation time and yet achieve a similar detection performance finally the effect of number of iterations is studied for various systems parameters including signal-to-noise-ratio compression ratio mean value of accumulated energy and threshold values. The presented framework in this study is important in the overall implementation of CS-based approaches for primary user detection in practical realisations such as LTE downlink OFDMA as it considers both signal reconstruction and detection.
Citation - WoS: 4
Citation - Scopus: 5
Analysis of Extended Busy Tone Performance for Coexistence Between Wran and Wlan Tvws Networks
(IEEE, 2015) Karatalay, Onur; Erküçük, Serhat; Baykaş, Tunçer
TV White Spaces indicate spectrum bands which were reserved for licensed terrestrial TV broadcasting and opened to unlicensed use under regulatory conditions. One important regulation which is common in all regulatory domains is no harmful interference is created to licensed devices. On the other hand interference between unlicensed devices is not regulated. As a result system designers developed new methods to improve coexistence between TVWS networks. Extended busy tone one of such methods is designed for coexistence between wireless regional area and wireless local area networks based on IEEE 802.22 and 802.11af standards respectively. In this paper we analyse the performance of extended busy tone at different range conditions and verify via simulations under realistic conditions. Our results indicate that the method can reduce interference considerably at intermediate distances and enable networks to operate without a significant reduction in throughput.
Citation - Scopus: 5
Iterative channel estimation techniques for uplink MC-CDMA systems
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali
In this work maximum likelihood (ML) channel estimation for uplink multicarrier code-division multiple-access (MC-CDMA) systems is considered in the presence of frequency fading channel. The expectation-maximization (EM)- and a space-alternating generalized expectation-maximization (SAGE) algorithm are introduced to avoid matrix inversion for the ML channel estimation problem. We compare the both algorithms in terms of the number of used iteration and show that the proposed algorithms converge the same performance of the ML estimator as the increasing number of iterations.
Citation - WoS: 1
Busy Tone Based Power Control for Coordination of Iffy 802.11af and 802.22 System
(IEEE, 2017) Ülgen, Oğuz; Erküçük, Serhat; Karatalay, Onur; Baykas, Tuncer
In this paper, a new power control algorithm based on busy tone approach has been proposed for the coordination of IEEE 802.22 and IEEE 802.11af systems in TV white space. Different from the earlier studies, in addition to both 802.11af access point and clients listening to the busy tone, they also adjust their communication power according to the location information and use hopping for communication, if needed Acccordingly, interference caused to 802.22 systems has been reduced while the 802.11af systems are still able to communicate. This study quantifies the 802.11af and 802.22 system performances in terms of interfering packet rate and succesful packet transmission rate for different scenarios considering the communication parameters and channel models adapted for the standards.
Citation - WoS: 3
Citation - Scopus: 4
Design of Broadband Microwave Amplifiers With Mixed-Elements Via Reflectance Data Modeling
(Elsevier GMBH Urban & Fischer Verlag, 2008) Şengül, Metin Y.; Yarman, Sıddık Binboğa
A practical method is introduced to design single-stage broadband microwave amplifiers with mixed lumped and distributed elements via modeling the reflectance data obtained from lumped-element input and output matching network prototypes. The same transducer power gain level is obtained by using less number of lumped-elements in the mixed-element amplifier than that of the lumped-element amplifier prototype. A mixed-element amplifier design is presented to exhibit the utilization of the method. It is expected that the method will be employed to design microwave amplifiers for broadband communication systems. (C) 2007 Elsevier GmbH. All rights reserved.
Design of Phase Shifters With Ladder Stubs Via Real Frequency Technique
(World Scientific, 2020) Şengül, Metin Y.
Generally at high frequencies, lumped-elements are not preferred because of their limited range of values. Therefore, in this work, a kind of phase shifter formed with ladder stubs is studied and a new approach to design phase shifter's low pass and high pass sections which are composed of series or shunt connected open-ended or short-ended stubs is proposed. In the approach, since the main focus is to form low pass and high pass two-port sections, switching process is not considered. First, the designer selects the section type and the total number of stubs in the sections; it is not necessary to fix the two-port section topologies and not necessary to derive the characteristic impedance and delay expressions for the stubs. In the example, 5-stub two-port sections of a 180∘ phase shifter are designed by means of the proposed approach.
Citation - WoS: 11
Citation - Scopus: 13
Flexible Physical Layer Based Resource Allocation for Machine Type Communications Towards 6g
(Institute of Electrical and Electronics Engineers Inc., 2020) Şadi, Yalçın; Erküçük, Serhat; Panayırcı, Erdal
The exponential growth of Internet of Things applications necessitates the design of next generation cellular systems to provide native support for machine type communications (MTC). While 5G aims at providing this native support under domain of massive MTC (mMTC) as one of the three major domains it focuses; i.e., enhanced mobile broadband, ultra reliable low latency communication, and mMTC, the enabling technologies and communication architectures are still limited and incomplete considering the nearly standardized efforts under 3GPP Releases 15 and 16. Studies towards 6G should elaborate on enabling truly massive MTC flexibly to support fast growing machine-to-machine (M2M) services with massive number of devices and very diverse quality of service (QoS) requirements. In this paper, we study radio resource allocation for mMTC based on the envisioned flexible physical layer architecture for 5G and beyond, possibly including 6G. We first present an overview of the 5G New Radio physical layer aspects particularly focusing on multiple numerologies and discuss the 3GPP features in Releases 15-17 as possible enablers of a flexible radio resource allocation scheme. Then, we propose a polynomial-time persistent resource allocation scheme for M2M communications aiming at meeting diverse QoS requirements of the M2M applications while achieving spectral efficiency. Finally, we present some numerical results and discuss future research directions for access schemes to enable truly massive MTC.
Citation - Scopus: 1
Extending the Lifetime of Wsns With Maximum Energy Selection Algorithm (mesa)
(Institute of Electrical and Electronics Engineers Inc., 2017) Cengiz, Korhan; Dağ, Tamer
The limited battery supply of a sensor node is one of the most important factors that limit the lifetime of the WSNs. As a consequence increasing the lifetime of WSNs through energy efficient mechanisms has become a challenging research area. Previous studies have shown that instead of implementing direct transmission or multi-hop routing clustering can significantly improve the total energy dissipation and lifetime of a WSN. The traditional LEACH and LEACH based algorithms have evolved from this idea. In this paper we propose a fixed clustering routing algorithm for WSNs which selects the node with maximum residual energy for the following rounds according to a threshold level. The Maximum Energy Selection Algorithm (MESA) can improve the lifetime of the network and reduce the energy dissipation significantly. Our studies have shown that when compared with LEACH and LEACH based algorithms such as ModLEACH and DEEC MESA gains for the lifetime extension and energy dissipation is very important. © 2016 IEEE.
Citation - WoS: 11
Citation - Scopus: 11
Space-Time Block Coding for Spatial Modulation
(IEEE, 2010) Başar, Ertuğrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Space-time block coded spatial modulation (STBC-SM) which employs space-time block coding (STBC) for spatial modulation (SM) is proposed as a new multiple-input multiple-output (MIMO) transmission scheme. In the STBC-SM scheme the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain therefore both core STBC and antenna indices carry information. A general framework is presented for the design of the STBC-SM scheme for any number of transmit antennas. The proposed scheme is optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme. It is shown by computer simulations that STBC-SM provides approximately 3-5 dB (depending on the spectral efficiency) better error performance than SM and V-BLAST systems.
Synthesis of Lossless Ladder Networks With Simple Lumped Elements Connected Via Commensurate Transmission Lines
(AVES YAYINCILIK, 2010) Şengül, Metin Y.
An algorithm has been proposed, to synthesize low-pass, high-pass, band-pass and band-stop lossless ladder networks with simple lumped elements connected via commensurate transmission lines (Unit elements, UEs). First, the type of the element that will be extracted is determined from the given mixed-element network function. After obtaining element value, it is extracted, and the two-variable reflection function of the remaining mixed-element network is obtained. This process is repeated until extracting all the elements. For each network type, an example is included, to illustrate the implementation of the related algorithm.
Citation - WoS: 9
Citation - Scopus: 9
Synthesis of Resistively Terminated Lc Ladder Networks
(Istanbul University, 2011) Şengül, Metin Y.
In this work element value calculation algorithms have been proposed for low-pass high-pass band-pass and band-stop LC ladder networks. According to the calculated constant from the given transfer scattering matrix the element type that will be extracted is decided. After calculating the element value its transfer scattering matrix is obtained. Then transfer scattering matrix of the remaining network is calculated and the same procedure is applied until the termination resistance is reached. After explaining the algorithms four examples are given to illustrate the utilization of the proposed method.

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