Erküçük, Serhat

Erküçük, Serhat

Name Variants

Erküçük, Serhat
S.,Erküçük
S. Erküçük
Serhat, Erküçük
Erkucuk, Serhat
S.,Erkucuk
S. Erkucuk
Serhat, Erkucuk
Erküçük, S.
Erküçük,S.

Job Title

Prof. Dr.

Email Address

Serkucuk@khas.edu.tr

Main Affiliation

Electrical-Electronics Engineering

Status

Former Staff

Full item page

Scholarly Output

67

Articles

19

Citation Count

0

Supervised Theses

9 Scholarly Output Search Results

Now showing 1 - 9 of 9

Coexistence of Cognitive Radio Based Networks in Tv White Space
(Kadir Has Üniversitesi, 2016) Karatalay, Onur; Erküçük, Serhat; Erküçük, Serhat
Due to increasing data rates in enhancing wireless communications RF spectrum which is one of the most crucial natural sources has become more valuable. in order to utilize the limited spectrum e_ciently and solve the scarcity problem regulatory agencies granted unlicensed networks or secondary users (SUs) access to licensed bands for wireless communication with the condition that they should not cause harmful interference to primary users (SUs). Cognitive radio (CR) technology enables devices to access the spectrum opportunistically. Using CR based networks licensed bands can be utilized more e_ectively for wireless communications. TV White Space (TVWS) refers to portions of the RF spectrum that was reserved only for licensed terrestrial TV broadcasting and is opened to unlicensed use under regulatory conditions. While regulations protect licensed systems in TVWS from harmful interference interference prevention among unlicensed systems is left mainly to manufacturers. Consequently there is a need to develop new coexistence approaches between TVWS networks. Busy tone broadcasting is a coexistence method which can be used by TVWS networks to announce that the selected frequency band is occupied. in this dissertation a busy tone based coexistence algorithm is proposed for wireless local area networks (WLANs) operating in TVWS (i.e. iEEE 802.11af based networks) where wireless regional area network (WRAN) (i.e. iEEE 802.22 based network) is assumed to be the busy tone broadcaster. The proposed algorithm is analyzed in detail considering the e_ects of log-normal shadowing client distribution around the access point and the number of clients where exact interfering packet rate and successful packet transmission rate expressions are obtained and validated by simulations for di_erent scenarios. The results show that with the proposed coexistence approach a WLAN can reliably detect the busy tone signal to change its frequency band and can reduce interference to WRAN. Even if there is no available frequency band for the WLAN the WRAN still maintains its enhanced successful packet transmission performance. The deployment of the proposed algorithm is important for successful coexistence between cognitive wireless regional and local area networks where interference among networks is not regulated such as in TVWS bands.
Realistic Performance Considerations for Combinational Cooperative Detection Method
(Kadir Has Üniversitesi, 2016) Samo, Rameez Ahmed; Erküçük, Serhat; Erküçük, Serhat
Combinational cooperative detection (CCD) method is different from the conventional cooperative detection method in the sense that each user may reach a different decision for the activity of the primary user. in the CCD method the locations of the secondary users (SUs) were fixed and selected near the border points of the communication area. The detection performance for SUs at random locations was not considered earlier. The CCD method’s practical implementation was explained with observing different system parameter’s effects on the detection performance for those fixed locations. Carrying previous work done forward in this thesis some realistic performance considerations for the CCD method are assessed. in accordance with that firstly the effect of SUs random locations on the detection performance is considered and compared with the performance for fixed locations. Secondly the effect of distance variations between master and primary user is tested. Finally the effect of different propagation environments on the detection performance of CCD is examined. The results are important to assess the realistic performance of the CCD method.
SCMA codebook design approaches
(Kadir Has Üniversitesi, 2020) Kiracı, Furkan; Erküçük, Serhat; Erküçük, Serhat
In 4G systems, Orthogonal Frequency-Division Multiple Access (OFDMA) has been used conventionally for multiple access purposes. This technique has low spectral efficiency since it allocates the resources orthogonally to each user. As an alternative to this technique, Non-orthogonal Multiple Access (NOMA) has been proposed for new generation 5G systems as it allows different users to use the same resources and therefore, increases spectral efficiency. Sparse Code Multiple Access (SCMA) is a code-based NOMA technique and its performance depends on codebook design. In this thesis, four different approaches are proposed by examining the design of the conventional codebook, which is widely used in SCMA studies in the literature. In the first approach, the distances between the constellation set points have been increased while the total energy remains constant. In the second approach, the angle between the constellation set points on the sub-carriers in the codebook has been equally set. In the third approach, by applying the permutation method, it has been aimed to reduce the complexity in the codebook by multiplying the constellation set points on the first and second sub-carriers with the halfangle formula. In the fourth approach, a new constellation set points with the energy remaining constant has been designed. Considering the four different design approaches, the conventional codebook has been modified. Simulation results have shown that 1-2dB gain can be achieved using different design approaches in the high signal-to-noise-ratio (SNR) region.
Primary User Detection in Ultrawide-Band Based Wireless Sensor Networks
(Kadir Has Üniversitesi, 2013) Sabucu, Yağmur; Erküçük, Serhat; Erküçük, Serhat
In this thesis ultra-wideband (UWB) based wireless sensor networks (WSNs) are considered for the detection of a primary user. Different from earlier works (i) both uplink and downlink information of the primary user are assessed for the primary user detection and (ii) iEEE 802.15.4a standard is considered for the implementation of each secondary user. Specifically the worked focused on the comparison of the two iEEE 802.15.4a based signalling namely binary pulse position modulation (BPPM) and combined BPPM/ binary phase shift keying (BPPM/BPSK) and the implementation of noncoherent receivers at the fusion center for reduced complexity. Accordingly the sensor-fusion center link is investigated in detail considering practical implementation conditions. Some suggestions have been provided based on the primary user detection performance results of the UWB based WSNs. -- Abstract'tan.
Performance of Orbital Angular Momentum Based Communication Systems Under Varied Atmospheric Turbulence
(Kadir Has Üniversitesi, 2016) Ashfaq Sheikh, Abdul Ahad; Erküçük, Serhat; Erküçük, Serhat
Orbital Angular Momentum is gaining a lot of attention in the past years as it is providing the means to break free from the ever increasing shortage of options when it comes to Data Rates and Effective Frequency Utilization. OAM promises to break the shackles and provide a solution where a beam which can be transformed into multiple beams within itself and become independent streams of data (pertaining to the principle of orthogonality) to be transferred when properly utilized. in this thesis the generation of these beams is discussed along with how to propagate them through free space and send and receive data. As astonishing as it seems there is a draw back in reality from theory. Free space contains Atmospheric Turbulence which interferes with the beam propagation of OAM and as a result the photons in the light beam are affected as well as the independence of each OAM mode is affected. Accordingly the data stream suffers crosstalk. in this thesis Weak and Strong Atmospheric Turbulences and how they effect a variety of OAM modes as they propagate through free space are studied a comparison between them are provided.
Siso - Mimo Applications and Analysis of Visible Light Communications Systems
(Kadir Has Üniversitesi, 2016) Yeşilkaya, Anıl; Erküçük, Serhat; Panayırcı, Erdal; Erküçük, Serhat; Başar, Ertuğrul
Rapid development in technology and increasing necessity to reach information instantaneously saturates RF bands rapidly. Because of that, it can be seen that we are gradually approaching upper limits of the band. It can said that, operating beyond that upper limit would be hard and unfeasible for 5th generation mobile systems (5G). At this point, it is needed to develop alternative telecommunication systems to RF technology. VLC could be the most appropriate and appealing solution for researchers due to its unregulated visible light band. In this context, determination of the real VLC channel models would play vital role on bit error rate performance of the communication systems. The main objective of this thesis is to introduce this novel and interesting topic to the the researchers and investigating performances of SISO and MIMO OFDM based VLC systems in realistic channel models obtained in Zemax environment. Besides, novel transmission model is proposed in the thesis and analyzed and simulated in great detail. Obtained performances of SISO-MIMO OFDM based VLC systems are compared with reference systems and conclusions are offered about the results.
Power Control and Multihop Communication Approaches for the Coexistence of Ieee 802.11af and Ieee 802.22 Networks in Tv White Space
(Kadir Has Üniversitesi, 2017) Ulgen, Oguz; Erküçük, Serhat; Erküçük, Serhat
Communication networks have been among the most important research fields of scientists in the recent years. Researches have been conducted in various different topics and contents as technology has evolved. As some new technologies become available some technologies become out of date. One of the outdated technologies in recent years is the analog TV broadcasting. With the shift from analog TV broadcasting to digital TV broadcasting the frequency bands of old analog TV broadcasting has become available for the implementation of new technologies. This spectrum is called TV White Space (TVWS). Due to wide coverage and good signal transmission properties in TVWS researchers and engineers have focused on developing standards for this valuable spectrum. Within the same period of time another new technology based on cognitive radios has been investigated and implemented. Among the standards and technologies developed for TV White Space one focus area has been to allow the access of unlicensed (secondary) users to the spectrum. Even though solutions for protecting the licensed (primary) users has been successful researches for protecting the secondary users in coexistence have not given conclusive results. Several of these researches are on the coexistence of iEEE 802.22 wireless regional area network and iEEE 802.11af wireless local area network. However due to the nature of two heterogeneous networks not communicating with each other there is a need for further coexistence mechanisms. in this thesis different from the earlier works busy tone based power control and multihop communication algorithms are implemented for different coexistence scenarios of iEEE 802.22 and iEEE 802.11af. interfering packet rate results and successful packet transmission rate results obtained via computer simulations and improved results are presented. in addition interfering packet rate results and successful packet transmission rate results are presented under realistic channel models ii and log-normal shadowing. The presented results are important to improve the results of existing busy tone based approaches.
Detection of Interdependent Multiband Systems for Cognitive Radios and Ultra-Wideband Systems
(Kadir Has Üniversitesi, 2012) Yılmaz, Burak; Erküçük, Serhat; Erküçük, Serhat
As a result of advances in the wireless technology new systems have been proposed and hence more frequency bands are occupied in the spectrum. Therefore the number ofavailable frequency bands for future wireless communication systems is decreasing and alternative communication technologies have appeared in recent years. These are cognitive radio and ultra wideband systems which use the spectrum more efficiently. -- Abstract'dan.
Performance of Ieee 802.11af Systems Under Realistic Channel Conditions
(Kadir Has Üniversitesi, 2016) Macit, Mustafa Can; Erküçük, Serhat; 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 regional local and personal area networks. Among them the local area network standard iEEE 802.11af denes 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. Unlike perfectly known channel condition of iEEE 802.11af based systems used in the literature we investigate in detail the performance of different operation modes of these systems under realistic channel conditions. Accordingly we implement and compare the performances of perfectly known channel linear minimum mean-square error (LMMSE) estimator and a matching pursuit (MP) based channel estimator. MP based estimator being the more practical estimator compared to the others we assess how its performance approaches the other methods. According to simulation results MP-based channel estimation performance is found to be only 1-2 dB inferior compared to LMMSE-based estimation with known delays in low and medium SNR regions. Also the efects of guard interval rate channel resolution and separation of in-between bands in non-contiguous modes are tested in different scenarios. The results of thesis are important for practical implementation of iEEE 802.11af based systems.