Yazar "Ayvaz, Elif Nur" seçeneğine göre listele

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    A Fast Start-Up Modified LMS Algorithm
    (IEEE, 2018) Ayvaz, Elif Nur; Maraş, Meryem; Özen, Ali
    Due to the time-delay spread of the channel, the equalizers for high data rate mobile communication systems has critical importance in mitigation of inter-symbol interference (ISI). One of the most important channel equalization algorithms is the least mean squares (LMS) algorithm. However, the slow convergence rate and the need for long training sequences are the major disadvantages of the LMS algorithm. In this paper, a fast-start-up modified LMS (FSU-M-LMS) algorithm based on channel matched filter (CMF) has been proposed to increase the convergence speed and performance of the LMS algorithm. In order to prove the performance of the proposed method, computer simulations are performed on stationary and nonstationary frequency selective Rayleigh fading channels. The obtained simulation results illustrate that the proposed FSU-M-LMS algorithm has better mean square error (MSE), bit error rate (BER) and channel tracking performances than the conventional LMS, modified LMS (M-LMS), normalized LMS (N-LMS) and conventional RLS algorithm.
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    A New Fast Walsh Hadamard Transform Spread UW-Optical-OFDM Waveform
    (Institute of Electrical and Electronics Engineers Inc., 2022) Tekel, Buse Nur; Ayvaz, Elif Nur; Özen, Ali
    In this study, it is recommended to apply the UW-OFDM waveform, which is offered as an alternative to classical OFDM in 5G and beyond waveform design research and development studies used in radio frequency (RF) communication, in optical OFDM systems. However, it is recommended to combine the proposed UW-O-OFDM waveform with fast Walsh Hadamard transform (FWHT) to improve its performance in this study. In the present study, the PAPR gains on the transmit and receive side of the classical O-OFDM, UW-O-OFDM and proposed UW-FWHT-O-OFDM waveforms are analyzed comparatively. From the obtained numerical results, it is understood that PAPR performance on the transmit side of the proposed UW-FWHT-O-OFDM waveform is approximately 5 dB better than the classical O-OFDM waveform and the proposed UW-O-OFDM waveform is approximately 3.5 dB better than the classical O-OFDM waveform. In addition, with the suggested waveform at 30 dB SNR on the receiver side, approximately 0.8 dB PAPR gain against the UW-O-OFDM waveform and approximately 4.2 dB PAPR improvement against the classical O-OFDM waveform is observed. © 2022 IEEE.
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    A novel adaptive blind channel equalizer for chaotic communication systems
    (Institute of Electrical and Electronics Engineers Inc., 2019) Gomec, Meltem; Maraş, Meryem; Ayvaz, Elif Nur; Özen, Ali
    In this paper, a new blind channel equalizer based on fuzzy logic is proposed for chaotic communication systems. Inverse filtering criteria (IFC) based algorithm, super exponential algorithm (SEA) and constant modulus algorithm (CMA) are the most popular three-blind channel equalization algorithm for classical communication systems. However, these algorithms are not sufficient for the desired performance values for chaotic communication systems and need to be developed. In this study, the normalized CMA algorithm based on fuzzy logic (Fuzzy Logic Normalized CMA, F-N-CMA) is proposed for chaotic communication systems. Computer simulation studies are performed to test the accuracy of the proposed method and to compare with the classical CMA, modified CMA (Modified CMA, M-CMA) and normalized CMA (Normalized CMA, NCMA) algorithms. It is observed that the best MSE-Iteration Number, MSE-SNR, ISI-Iteration Number and ISI-SNR achievements are obtained with the proposed method from the simulation results. © 2019 IEEE.
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    A Novel Adaptive Variable Forgetting Factor RLS Algorithm
    (IEEE, 2018) Maraş, Meryem; Ayvaz, Elif Nur; Özen, Ali
    As the demand for higher data rates increases steadily, there will always be a need to develop more efficient wireless communication systems. Adaptive channel equalizers need to be used to correct the disturbing effects of the channel resulting from the time-varying mobile communication channel. One of the most popular channel equalization algorithms is the recursive least squares (RLS) algorithm. However, the performance of the fixed forgetting factor RLS algorithm is falling in the time-varying channel environment. In this paper, a new adaptive variable forgetting factor RLS (AVFF-RLS) algorithm based on the autocorrelation of the error signal has been proposed to increase the convergence speed and performance of the RLS algorithm. In order to test the performance of the proposed method, computer simulations are performed on frequency selective Rayleigh fading channels. It is observed that the proposed AVFF-RLS algorithm has better mean square error (MSE), bit error rate (BER) and channel tracking performances than the conventional RLS, conventional LMS, modified LMS (M-LMS) and normalized LMS (N-LMS) algorithms from the obtained simulation results.
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    A Novel Concatenated LWT and WHT Based UFMC Waveform Design for the Next Generation Wireless Communication Systems
    (Wiley, 2021) Ayvaz, Elif Nur; Maraş, Meryem; Gomec, Meltem; Savaşçıhabeş, Asuman; Özen, Ali
    A novel concatenated Lifting Wavelet Transform (LWT) and Walsh Hadamard Transform (WHT) with Universal Filtered Multi Carrier (UFMC) waveform is suggested as an alternative to Orthogonal Frequency Division Multiplexing (OFDM) waveform for the next generation wireless telecommunication systems in this paper. The suggested waveform is composed of LWT and WHT with UFMC waveform. Both the elimination the disadvantages of OFDM and the improvement the achievement of UFMC waveform, from the fifth generation waveform candidates, has been aimed with the suggested waveform. In order to verify the performance of the suggested waveform and compare with the traditional OFDM, UFMC, and LWT-UFMC waveform computer simulation studies are performed in additive white Gaussian noise and flat Rayleigh fading channel environments. The acquired computer simulation results exhibit that the achievement of the suggested waveform has better than the achievement of the traditional OFDM, UFMC, and LWT-UFMC waveform. (c) 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.
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    A novel gfdm waveform design based on cascaded wht-lwt transform for the beyond 5g wireless communications
    (MDPI AG, 2021) Maraş, Meryem; Ayvaz, Elif Nur; Gömeç, Meltem; Savaşcıhabeş, Asuman; Özen, Ali
    In this paper, a new WHT-LWT-GFDM waveform obtained by combining Walsh–Hada-mard Transform (WHT), Lifting Wavelet Transform (LWT), and Generalized Frequency Division Multiplexing (GFDM) is presented for use in next-generation wireless communication systems. The proposed approach meets the requirement of 5th-generation (5G) and beyond communication schemes in terms of low latency, low peak-to-average-power ratio (PAPR), and low bit-error rate (BER). To verify the performance of the presented waveform, PAPR and BER simulation results were obtained in additive white Gaussian noise (AWGN) and flat Rayleigh fading channels, and the performance of the proposed system was compared with conventional Orthogonal Frequency Division Multiplexing (OFDM), GFDM, and Walsh–Hadamard transform-based GFDM (WHT-GFDM). Simulation results show that the proposed waveform achieves the best BER and PAPR performances and it provides considerable performance gains over the conventional waveforms. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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    A novel waveform design based on lifting wavelet transform for the 5G beyond
    (Institute of Electrical and Electronics Engineers Inc., 2019) Ayvaz, Elif Nur; Maraş, Meryem; Gomec, Meltem; Özen, Ali
    In this paper, a new waveform design based on Lifting Wavelet Transform (LWT) is proposed for next generation wireless communication systems. The proposed waveform design (LWT-UFMC) consists of combination of the LWT and universal filtered multi carrier (UFMC) waveform. It is aimed to improve the performance of the UFMC waveform, which is from the 5th Generation (5G) waveform candidates, with the proposed LWT-UFMC waveform. Computer simulation studies are performed to test the achievement of the recommended waveform and to compare with the classical OFDM and UFMC in AWGN and flat Rayleigh fading channels. It is seen that the proposed waveform from the obtained simulation results has the best and highly satisfactory performance. © 2019 IEEE.
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    Artificial Intelligence Based Under Water Acoustic Channel Equalizer Design
    (Institute of Electrical and Electronics Engineers Inc., 2022) Yucel, Fatma Ceren; Maraş, Meryem; Kepezkaya, Talat; Ayvaz, Elif Nur; Özen, Ali
    In this study, it is suggested to use artificial intelligence assisted fuzzy logic based LMS (F-LMS) algorithm to improve the performance of single carrier (SC) underwater acoustic communication (UWAC) systems in multipath underwater acoustic channel environments. Numerical simulation studies are carried out to compare the proposed F-LMS algorithm with the bit error rate (BER) and mean square error (MSE) performance measures over decision feedback equalizer (DFE) and channel matched filter DFE (CMF-DFE). From the produced numerical results, it is understood that the best gains are achieved in both MSE and BER simulations with the proposed F-LMS algorithm. In addition to these, the most important contribution of the proposed study is to eliminate the error floor that occurs in DFE equalizers in BER simulations with CMF-DFE equalizers. © 2022 IEEE.
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    Dual tree complex wavelet transform based multi carrier communication systems
    (Institute of Electrical and Electronics Engineers Inc., 2019) Gomec, Meltem; Maraş, Meryem; Ayvaz, Elif Nur; Özen, Ali
    In this paper, DT-CWT-OFDM waveform based on dual tree complex wavelet conversion (DT-CWT) is introduced to enhance the achievement of the classical OFDM waveform. IFFT/FFT blocks used in the classical OFDM waveform are replaced with IDTCWT/DTCWT blocks in the DT-CWT-OFDM waveform. In order to confirm the achievement of the investigated waveform and compare it with the waveforms of classical OFDM and discrete wavelet conversion based OFDM (DWT-OFDM), computer simulation studies are carried out on AWGN, flat Rayleigh damping and frequency-selective Rayleigh damping channels. It is seen from the attained simulation outcomes that the DT-CWT-OFDM waveform has better achievement than the classical OFDM and DWT-OFDM waveforms and also provides approximately 6 dB SNR gain against the classical OFDM and approximately 1.5 dB SNR gain against the DWT-OFDM for a BER value of lE-4. © 2019 IEEE.
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    Görünür ışık haberleşme sistemleri için ortogonal dönüşüm tabanlı yeni bir DC eklemesiz optik OFDM tasarımı
    (Nuh Naci Yazgan Üniversitesi, 2023) Ayvaz, Elif Nur; Özen, Ali
    Gelişmekte olan teknolojiler ve bilgiye hızlı erişim ihtiyacı sebebiyle kablosuz mobil haberleşmeye ayrılan radyo frekans (radio-frequency) bantları hemen dolmakta ve RF bandının üst sınırlarına yaklaşmaktadır. Dolayısıyla, 5G sistemleri için ayarlanacak olası frekans bantlarının üzerinde daha yüksek frekans bantlarında çalışmanın fazlasıyla güç veya olanaksız hale gelmesi kaçınılmaz olacaktır. Bu durumda yeni bir teknolojiye ihtiyaç vardır. Radyo frekans teknolojisine dikgen (ortogonal) bir haberleşme sistemi olan görünür ışık haberleşme (Visible Light Communication, VLC) sistemleri alternatif olarak tercih edilebilmektedir. Görünür ışık haberleşmesinde, veri transferi ve oda aydınlatması için ışık saçan diyotlar (Light Emitting Diode, LED) tercih edilir. Işık bağlantısı (Light Fidelity, LiFi) olarak adlandırılan VLC'nin tamamen ağ bağlantılı versiyonu, RF tabanlı kablosuz bağlantı (Wireless Fidelity, WiFi) için tamamlayıcı bir çözüm olarak kabul edilir. VLC'deki verileri kodlamak için, dikgen frekans bölmeli çoğullama (Orthogonal Frequency Division Multiplexing, OFDM) kullanılır. OFDM yüksek veri hızları sağlar ve sembollerarası girişime (Intersymbol Interference, ISI) dayanıklıdır. OFDM sembolleri iki kutupludur. Bu nedenle, OFDM yoğunluk modülasyonu ve doğrudan sezim (Intensity Modulation/Direct Detection, IM/DD) için kullanılabilir hale getirmek için tek kutuplu hale dönüştürülmelidir. OFDM'nin tek kutuplu formlarından bazıları doğru akım (Direct Current, DC) eklemeli optik OFDM (DCO-OFDM), asimetrik olarak kırpılmış optik OFDM (ACO-OFDM), DC eklemeli olmayan optik OFDM (NDC-OFDM),dir. Bu yüksek lisans tez çalışmasında, MIMO ve VLC-OFDM tabanlı özgün iletim tekniklerinin başarımlarını iyileştirmek üzerine yapılan çalışmalarda, NDC-O-OFDM sisteminin performansını daha da yukarılara çıkartabilmek için maliyeti fazla olmayan ortogonal dönüşümlerden olan Lifting dalgacık dönüşümü tabanlı yeni bir DC eklemesiz optik OFDM (LWT-NDC-O-OFDM) sistemi önerilmektedir. Önerilen bu sistemde MIMO teknolojisi kullanılmış ve karmaşık OFDM işaretleri pozitif-negatif ve gerçel-sanal kısımlarına ayrılarak işaretlerin MIMO-VLC kanal üzerinden iletilmesi gerçekleştirilmiştir. Önerilen sistemin literatürdeki mevcut sistemlere kıyasla daha başarılı sonuçlar verdiği görülmüştür.
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    Improving the performance of GFDM waveform employing lifting wavelet transform
    (Institute of Electrical and Electronics Engineers Inc., 2019) Maraş, Meryem; Ayvaz, Elif Nur; Gomec, Meltem; Özen, Ali
    In this paper, it is recommended that the combination of generalized frequency division multiplexing (GFDM) structure with lifting wavelet transform (LWT) to increase the performance of GFDM waveform from waveform candidates of the next generation wireless communication systems. The proposed LWT-GFDM method is suitable for the requirements of the 5th Generation (5G) communication systems such as low latency, low PAPR (Peak to Average Power Ratio) and low OOBE (Out of Band Emission). In order to test the performance of the proposed method and compare it with classical OFDM, GFDM and GFDM using discrete wavelet transform (DWT-GFDM), computer simulation studies are performed in AWGN and flat Rayleigh fading channels. It is observed that the proposed method has the best performances from the obtained simulation results. © 2019 IEEE.
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    The effect of different curing units on the degree of polymerization of different composite resins
    (J Oral Res Rev, 2021) Karataş, Özcan; Gömeç, Meltem; Ayvaz, Elif Nur; Maraş, Meryem
    Objective: The aim of this study was to investigate the degree of polymerization of composite resins cured with different light-curing units (LCUs). Materials and Methods: Three bulk-fill composite (Beautifil Bulk-Fill Giomer, Filtek Bulk-Fill, and X-Tra Fill) and a methacrylate-based composite (Filtek Z250) were used in this study. Thirty disc-shaped specimens, 4 mm thick, were prepared from each composite resin. Specimens were divided into three groups and polymerized with light-emitting diode (LED), Plasma arch curing unit (PAC), and quartz-tungsten halogen LCU. The bottom and top surface microhardness of the specimens stored in distilled water for 24 h at 37°C after polymerization was measured with a universal test device. The hardness ratio (HR) of specimens was calculated by the bottom surface microhardness/top surface microhardness formula. Data were analyzed by two-way ANOVA and Tukey’s least significant difference post hoc tests (? = 0.05). Results: Statistically significant differences were detected between the mean HR values of the specimens polymerized with different LCUs (P < 0.05). The mean HR values of Beautifil Bulk-Fill Giomer specimens were found to be statistically significantly lower than other composites (P < 0.05). The mean HR values of the specimens polymerized with PAC LCU were found to be statistically significantly lower than other LCUs (P < 0.05). Conclusion: The degree of polymerization of the composite resin restoration may be affected by the structural properties of the resin and the type of LCU. The clinician may use alternative techniques, especially in deep cavities.
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    Turning performance and factors related to turning in mild and moderate Phase Parkinson’s Disease patients
    (International Journal of Aging Research, 2018) Soyuer, Ferhan; Cankurtaran, Feyzan; Maraş, Meryem; Ayvaz, Elif Nur
    Background/aim: The purpose of study is to determine the turning performance and other factors related to turning in mild and moderate phase Parkinson’s disease patients (PD). Methods: Ninety two patients were followed up for observation. After passing neurological examinations, the Unified Parkinson Disease Rating Scale (UPDRS), Hoehn / Yahr Scale (H&Y), Mini Mental State Examination (MMSE), Tinetti test, Berg Balance test, 6 m walking test, step count, 360° turning duration, and Functional Independence Measure (FIM) were applied. All cases were evaluated according to the “on” period. Results: Forty one females and 51 males participated in the study. The duration of time it took to turn right was 8.22 ± 6.26 seconds, and the time it took to turn from left was 8.51 ± 6.63 sec. There appeared to be no statistical difference in the turn times of patients either in terms of the socio-economic factors of gender, education level, or employment status. But, statistically significant relationships were found when it came to in both directions, age, duration of illness, UPDRS, FIM, Tinetti, the Berg Test, the walking test, and the number of steps taken. Conclusion: Our results suggest that 360 degree turning performance in mild and moderate stage PD is strongly associated with patient’s age, disease duration and disease severity.