Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu

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

Browse

Now showing 1 - 20 of 90

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: 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: 2
Power Control and Resource Allocation in Tdd-Ofdm Based Femtocell Networks With Interference
(IEEE, 2017) Altabbaa, Mhd Tahssin; Arsan, Taner; Panayırcı, Erdal
Femtocell technology is a promising solution for different dilemmas in cellular networks. In femtocell power control the interference experienced by the network is divided into two main tiers according to the type of network whose signal is interfering with another network. In utilizing the functionality of a two-tier network where femtocell technology is deployed a major challenge is in sharing the frequency resource of a macrocell. This paper proposes an enhanced dynamic algorithm bounded by two constraints to optimize the transmission powers of femtocell users in TDD-OFDM based femtocell networks taking into consideration rate enhancement of femtocell mobile stations. We compare our algorithm with the macrocell guard system which allows femtocells to occupy only the subchannels unoccupied by the macrocell.
Citation - WoS: 4
Performance Investigation of Ieee 802.11af Systems Under Realistic Channel Conditions
(IEEE, 2015) Macit, Mustafa Can; Şenol, Habib; Erküçük, Serhat
As the analog TV broadcasting channels have become less frequently used in the last decade there has been a great interest in these frequency bands for the deployment of metropolitan local and personal area networks. Among them the local area network standard IEEE 802.11af defines PHY and MAC layer implementation of such networks in these unused frequency bands also named television white space (TVWS). According to the standard the systems may use contiguous or non-contiguous channels during their operation depending on the channel availability. In this paper we investigate in detail the performance of different operation modes of these systems under realistic channel conditions. While the perfect knowledge of channel would result in similar system performances as the number of in-between-bands occupying the non-contiguous modes is increased the channel estimation performance degrades drastically which is quantified in this study. In addition it is shown that determining the true locations of multipaths heavily relies on the selected channel resolution and has a significant effect on the system performance. Numerical examples are given to demonstrate the effects of both the non-contiguous operation modes and the selected channel resolution.
Mp-Sage Based Channel Estimation for Underwater Cooperative Ofdm Systems
(IEEE, 2013) Erdoğan, Mustafa; Şenol, Habib; Panayırcı, Erdal; Uysal, Murat
In this paper an efficient channel estimation algorithm is proposed for amplify-and-forward (AF) cooperative relay based orthogonal frequency division multiplexing (OFDM) system in the presence of sparse underwater acoustic channels and of the correlative non-Gaussian noise The algorithm is based on the combinations of the matching pursuit (MP) and the space-alternating generalized expectation-maximization (SAGE) technique to improve the estimates of the channel taps and their location as well as the Gaussian mixture noise distribution parameters in an iterative way Computer simulations show that underwater acoustic channel is estimated very effectively and the proposed algorithm has excellent symbol error rate (SER) and channel estimation performance as compared to the existing ones
Em-Based Joint Data Detection and Channel Estimation for Uplink Mc-Cdma Systems Over Frequency Selective Channels
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali; Fleury, Bernard Henri
This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency fading channel. The detection and estimation algorithm implemented at the receiver is based on a version of the expectation maximization (EM) technique which is very suitable for the multicarrier signal formats. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance.
Complex Event Post Processing for Traffic Accidents
(IEEE, 2012) Öğrenci, Arif Selçuk; Öğrenci, Arif Selçuk
In this paper we describe a framework for an expert system that tries to predict effects of an accident based on past data using supervised learning employing artificial neural networks. For this purpose sensory data events are post processed in order to generate a reasonable mapping between input and output parameters in case an event is detected automatically or manually. The framework is intended to be used to take actions for reducing the effects of the accident on traffic congestion and to inform necessary parties to intervene in a timely fashion.
Citation - WoS: 28
Citation - Scopus: 34
Design of Practical Matching Networks With Lumped Elements Via Modeling
(IEEE, 2007) Yarman, Sıddık Binboğa; Şengül, Metin Y.; Kılınç, Ali
It is a common practice to utilize commercially available software tools to design matching networks for wireless communication systems. Most of these tools require a properly selected matching network topology with good initial element values. Therefore in this paper a practical method is presented to generate matching networks with initial element values. In the implementation process of the proposed method first the driving point immitance data for the matching network is obtained in a straight forward manner without optimization. Then it is modeled as a realizable bounded-real input reflection coefficient which in turn yields the desired matching network with reasonable element values. Eventually the initial design is improved by optimizing the performance of the matched system employing the commercially available computer-aided design (CAD) packages. An example is given to illustrate the utilization of the proposed method. It is shown that new method provides excellent results as a front-end when utilized together with CAD tools.
Pilot Symbol Assisted Channel Estimation for 4x4 Space Time Block Coded Spatial Modulation Systems
(IEEE, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Recently spatial modulation (SM) and space-time block coding (STBC) are combined to take advantage of the benefits of both while avoiding their drawbacks for multiple-input and multiple-output (MIMO) systems. The pioneering works on STBC-SM assume that perfect knowledge of the channel fading coefficients is available at the receiver. This work(1) addresses the challenging and timely problem of channel estimation for 4 x 4 STBC-SM systems in the presence of time-varying channels. In this paper the estimation of channel at pilot durations is done by least square (LS) method and then the channel interpolation is performed by linear interpolation or nearest neighbor interpolation algorithms. Simulation results have demonstrated that the proposed channel estimation based on the linear interpolation offer substantial performance gains over the channel estimation based on the nearest neighbor interpolation. In particular a savings of about 5dB is obtained at BER = 10(-5) as compared with the nearest interpolation based receiver at 120km/h for 4 x 4 STBC-SM systems with the binary phase shift keying (BPSK) modulation.
Citation - Scopus: 2
The Effect Of Secondary User Locations On The Cooperative Detection Performance [iki?nci?l Kullanıcı Konumlarının İ?şbi?rli?kli? Algılama Yöntemi? Performansına Etki?si?]
(IEEE, 2012) Çatak, Evren; Erküçük, Serhat
In conventional cooperative detection a fusion center decides on the presence or absence of the primary user by gathering all the information from secondary users and conveys this decision to all users. This approach does not take into account the locations of the secondary users where a user far from the primary user may also have to keep silent. In a recent work there has been a new detection method based on combining received signals from more than two users obtaining decision tables and deciding individually for each user. While the proposed method showed promising results for the secondary users the effect of the user distribution was not investigated. In this study we consider the effect of secondary user location and number on the detection performance. We show that (i) the evaluation of the conventional method in the proposed method is not accurate and (ii) depending on the user location the detection performance may be better or worse compared to the conventional detection. © 2012 IEEE.
Citation - WoS: 1
Citation - Scopus: 2
Power Transfer Networks at Rf Frequencies "new Design Procedures With Implementation Roadmap"
(IEEE, 2006) Şengül, Metin Y.; Trabert, Johannes; Blau, Kurt; Yarman, B. Sıddık; Hein, Matthias
The purpose of this work is to provide the necessary background to design wide-band power transfer two-ports, or so-called broadband matching networks, at radio frequencies for wireless communication systems. The importance of the topic stems from the recent advances in the conceptual design and manufacturing technologies of the next-generation wireless and mobile communication systems, which will operate over ultra-wide frequency bands. In fact, for all communication systems, construction of wide-band power transfer networks is essential. Therefore, in this manuscript, new procedures to design broadband matching network are covered, and a design roadmap is given with relevant recommendations. As an example, the design of a compensation network for a RF switch matrix covering the band 17...23 GHz is presented, which employs the roadmap described in this work.
Citation - Scopus: 5
Sparse Channel Estimation With Clipping Noise in Dco-Ofdm Based Vlc Systems
(IEEE, 2020) Bektaş, Ekin Başak; Panayırcı, Erdal
In this paper a new computationally efficient and high performance channel estimation algorithm is proposed for DC-biased optical OFDM (DCO-OFDM) systems in indoor visible light communications (VLC) in the presence of a clipping noise. The sparse structure of the channel is taken into consideration in the channel estimation algorithm. The algorithm has an iterative structure and aims at reducing the effect of the clipping noise, inevitably generated by the DCO-OFDM systems. In te algorithm, the clipping noise is estimated in the time-domain and compensated for its effect in the frequency-domain. The initial values of the channel, including sparse channel path gains and the path delays, are determined by the least-squares (LS) and the ESPRIT algorithms, respectively, by making use of the pilots. Computer simulations indicate that the proposed algorithm converge in 3 iterations at most and yields excellent bit error rate (BER) and mean-square error (MSE) performances for DC-biased optical OFDM (DCO-OFDM) based systems.
Citation - Scopus: 1
Detection of Jointly Active Primary Systems
(IEEE, 2012) Yılmaz, Burak Alptug; Erküçük, Serhat
Recent studies in cognitive radios consider the detection of multiple bands for a better utilization of the spectrum. If the cognitive radio (CR) is an ultra wideband (UWB) or a wideband system then the CR should ensure all the coexisting primary systems in these bands are detected before the CR can start data transmission. In this work we study the primary system detection performance of a wideband CR assuming that there are multiple coexisting primary systems and that these primary systems may be jointly active. Accordingly we consider the implementation of (i) a maximum a posteriori (MAP) based detection (i.e. joint detection) that takes into account the statistics of simultaneously operating systems in independent bands and (ii) a Neyman-Pearson (NP) test based detection that optimizes the threshold values independently in each band (i.e. independent detection). In addition to obtaining the probabilities of false alarm and detection expressions for these two methods we use the threshold values obtained from joint detection so as to achieve the optimum NP test based independent detection results with a simpler implementation. We also provide the performance comparison of joint and independent detection for various practical scenarios when there are multiple active primary systems. © 2012 IIMC Ltd.
Citation - WoS: 5
Citation - Scopus: 5
Relay-Aided Secure Broadcasting for Vlc
(IEEE, 2018) Arafa, Ahmed; Panayırcı, Erdal; Poor, H. Vincent
A visible light communication (VLC) broadcast channel is considered in which a transmitter communicates with two receivers in the presence of an external eavesdropper. Trusted cooperative half-duplex relays are deployed to aid with securing the transmitted data. Transmission is amplitude-constrained to maintain operation within the light emitting diodes (LEDs) dynamic range. Achievable secrecy rate regions are derived under such amplitude constraints for this multi receiver wiretap channel first for direct transmission without the relays and then for cooperative jamming decode-and-forward and amplify-and-forward relaying schemes. Superposition coding with uniform signaling is used for transmission along with secure beamforming at the relays. Superiority of the secure relaying schemes over direct transmission is shown with performance depending on how far the eavesdropper is from the transmitter and the relays.
Rgb Color Based Occupancy Rate Detection of Indoor Spaces
(IEEE, 2018) Gilik, Ayşenur; Demir, Kubilay; Özmen, Atilla
In this study, a system has been developed to detect the human density of indoor spaces such as libraries, banks, shopping malls. The RGB images used in this work was obtained from the real-life space. First and second order color moments were used as feature extractor.
Citation - Scopus: 1
Channel Estimation for Sm Systems Over Time-Varying Rayleigh Fading Channels
(IEEE, 2014) Acar, Yusuf; Dogan, Hakan; Panayırcı, Erdal
This paper is concerned with the challenging and timely problem of channel estimation for spatial modulated systems in the presence of time varying channels. Recently estimation of channel state information for SM systems is investigated by the recursive least square (RLS) algorithm for slow fading channels. However it is clear that the RLS based receiver will have a performance degradation for fast fading channels. Therefore we developed iterative channel estimation based on detected symbols and curve fitting to track the channel variations for SM systems. Simulation results have demonstrated that the proposed iterative channel estimation offer substantial performance gains over the RLS channel estimation. In particular a savings of about 4dB is obtained at BER = 10(-7) as compared with RLS based receiver at 150km/h for 2 x 4 single carrier SM systems.
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.

Browse

Browsing Elektrik - Elektronik Mühendisliği Bölümü Koleksiyonu by Publisher "IEEE"