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Yayın On the extraction of the channel allocation information in spectrum pooling systems(IEEE, 2007-04) Öner, Mustafa Mengüç; Jondral, Friedrich K.The spectrum pooling strategy allows a license owner to share a part of his licensed spectrum with a secondary wireless system (the rental system, RS) during its idle times. The coexistence of two mobile systems on the same frequency band poses many new challenges, one of which is the reliable extraction of the channel allocation information (CAI), i.e. the channel occupation of the licensed system (LS). This paper presents a strategy for the extraction of the CAI based on exploiting the distinct cyclostationary characteristics of the LS and RS signals and demonstrates, via simulations, its application on a specific spectrum pooling scenario, where the LS is a GSM network and the RS is an OFDM based WLAN system.Yayın On the effect of random sampling jitter on cyclostationarity based spectrum sensing algorithms for cognitive radio(IEEE, 2009) Öner, Mustafa MengüçCognitive radio is an enabling technology, which is expected to lead to a more efficient utilization of the available spectral resources due to its flexibility and its ability to sense its spectral environment. Recently, spectrum sensing methods based on exploiting the cyclostationary characteristics of communication signals have been drawing considerable interest. Imperfections in the cognitive radio receiver that affect the cyclic statistics of a signal of interest may lead to a degradation in the performance of spectrum sensing algorithms based on cyclostationarity. One such typical source of imperfection is random timing jitter in the sampling process. In this work, we explore the effect of random sampling jitter on the second order cyclostationary statistics of wide sense cyclostationary signals. General analytical expressions are derived for the cyclic statistics of sampled signals in the presence of sampling jitter and specific results are provided for two cases of interest. Subsequently, the effect of the jitter on a spectrum sensing algorithm is investigated via simulations.Yayın EEG signal compression based on classified signature and envelope vector sets(Wiley, 2009-03) Gürkan, Hakan; Güz, Ümit; Yarman, Bekir Sıddık BinboğaIn this paper, a novel method to compress electroencephalogram (EEG) signal is proposed. The proposed method is based on the generation process of the classified signature and envelope vector sets (CSEVS), which employs an effective k-means clustering algorithm. It is assumed that both the transmitter and the receiver units have the same CSEVS. In this work, on a frame basis, EEG signals are modeled by multiplying only three factors called as classified signature vector, classified envelope vector, and gain coefficient (GC), respectively. In other words, every frame of an EEG signal is represented by two indices R and K of CSEVS and the GC. EEG signals are reconstructed frame by frame using these numbers in the receiver unit by employing the CSEVS. The proposed method is evaluated by using some evaluation metrics that are commonly used in this area such as root-mean-square error, percentage root-mean-square difference, and measuring with visual inspection. The performance of the proposed method is also compared with the other methods. It is observed that the proposed method achieves high compression ratios with low-level reconstruction error while preserving diagnostic information in the reconstructed EEG signal.Yayın Cognitive cooperative MAC with one primary and two secondary users: achievable rates and optimal power control(IEEE-INST Electrical Electronics Engineers Inc, 2014-11) Edemen, Çağatay; Kaya, OnurWe consider a three-user fading cognitive cooperative multiple access channel (MAC) with one primary and two secondary transmitters. We propose two encoding/decoding strategies with varying levels of cooperation, based on block Markov superposition encoding and backward decoding. The first is an overlay model, where the secondary users (SUs) aid the transmission of the primary user (PU) by causally decoding the PU message and forwarding it while also cooperating among each other. The second is an underlay model, where the SUs cooperate by decoding and forwarding each other's messages while treating the signal received from the PU as noise. In either case, the PU is guaranteed to operate at its maximum achievable single user rate. We characterize the achievable SU rate region for both models and maximize this region as a function of the transmit powers. The simulation results show that the SU rate region can be significantly enlarged, particularly using the overlay model.Yayın Equilibrium and stability analysis of delayed neural networks under parameter uncertainties(Elsevier Science Inc, 2012-02-15) Faydasıçok, Özlem; Arik, SabriThis paper proposes new results for the existence, uniqueness and global asymptotic stability of the equilibrium point for neural networks with multiple time delays under parameter uncertainties. By using Lyapunov stability theorem and applying homeomorphism mapping theorem, new delay-independent stability criteria are obtained. The obtained results are in terms of network parameters of the neural system only and therefore they can be easily checked. We also present some illustrative numerical examples to demonstrate that our result are new and improve corresponding results derived in the previous literature.Yayın Mülteci barınaklarının uydu görüntülerinden çoklu-sınıflı çizge-kesme bölütleme ve gölge bilgisi kullanılarak otomatik sezimi(IEEE, 2014-04-23) Kucur Ergünay, Şerife Seda; Kahraman, Fatih; Ateş, Hasan FehmiBu çalışmada, mülteci kamplarında bulunan yaşam alanlarının/barınakların (çadır, konteynır vb.) uydu ve hava görüntülerinden otomatik olarak sezimi ve sayımına yönelik bir yöntem tanıtılmaktadır. Mülteci kamplarındaki barınakların çok yüksek çözünürlüklü (VHR) görüntülerde dahi çok küçük boyuta sahip, belli bir alanda çok sık ve bazen karmaşık şekilde yerleştirilmiş ve arkaplan ile ayrıştırılması zor nesnelere denk geliyor olması otomatik barınak/çadır sezim ve sayımını zorlaştırmaktadır. Bahsedilen problemin çözümüne yönelik olarak çok sınıflı çizge-kesme (graph-cut) bölütlemesi ve gölge bilgisinin kullanıldığı özgün bir yöntem çalışma kapsamında önerilmektedir. Buna göre, ilk adımda çizge-kesme bölütleme yöntemi ve morfoloji işlemleri uygulanarak çadır sezimi yapılmıştır. Bu adımda sezilememiş çadırların bulunabilmesi için ikinci bir adımda çadırların gölge bilgisinden faydalanılmıştır. En son adımda gradyan-tabanlı eşikleme yöntemi ile yanlış tespitlerin elenmesi amaçlanmıştır. Önerilen yöntem, özellikle karmaşık yerleşim düzenine sahip mülteci kampları (çadırkent) üzerinde test edilmiştir. Yöntemin başarımı kesinlik (precision) ve geri getirme (recall) kriterlerine göre belirlenmiştir. Elde edilen ortalama kesinlik ve geri getirme başarımları sırasıyla %91.9 ve %90.0 olup problemin zorluğu göz önünde bulundurulduğunda umut vadedici bir sonuçtur.Yayın Phased subarray imaging for low-cost, wideband coherent array imaging(IEEE, 2003) Johnson, Jeremy A.; Oralkan, Ömer; Ergün, Arif Sanlı; Demirci, Utkan; Karaman, Mustafa; Khuri-Yakub, Butrus ThomasThe front-end hardware complexity of conventional full phased array (FPA) imaging is proportional to the number of array elements. Phased subarray (PSA) imaging has been proposed as a method of reducing the hardware complexity-and therefore system cost and size-while achieving near-FPA image quality. A new method is presented for designing the subarray-dependent interpolation filters suitable for wideband PSA imaging. The method was tested experimentally using pulse-echo data of a wire target phantom acquired using a 3.2-cm. 128-element capacitive micromachined ultrasonic transducer (CMUT) array with 85% fractional bandwidth at 3 MHz. A specific PSA configuration using seven 32-element subarrays was compared to FPA imaging, representing a 4-fold reduction in front-end hardware complexity and a 43% decrease in frame rate. For targets near the fixed transmit focal distance, the mean 6-dB lateral resolution was identical to that of FPA, the axial resolution improved by 4%, and the SNR decreased by 5 dB. Measurements were repeated for 10 different PSA configurations with subarray sizes ranging from 4 to 60. The lateral and axial resolutions did not vary significantly with subarray size; both the SNR and contrast-to-noise ratio (CNR) improved with increased subarray size.Yayın Generic BER analysis of VLC channels impaired by 3D user-mobility and imperfect CSI(Institute of Electrical and Electronics Engineers Inc., 2021-07) Reddy Sekhar, K.; Miramirkhani, Farshad; Mitra, Rangeet; Turlapaty, Anish ChandVisible light communications (VLC) has emerged as a high-speed, low-cost, and green supplement for the existing radio frequency (RF) based infrastructures. However, the performance of VLC based systems is found to degrade significantly due to detrimental outages caused by non-negligible variations in the VLC channel-gain, that are jointly induced by radial user-mobility and random photodetector-orientation (together designated as 3D mobility in this letter). In addition to the 3D user-mobility mentioned above, the performance of VLC based systems is further limited by imperfect channel-state information (CSI). Such degradations in the VLC-link caused by the aforementioned factors necessitate the quantification of performance-metrics for further benchmarking/receiver-design. In this work, an analytical expression for bit-error rate (BER) is derived for a single LED indoor VLC system considering the radial user-mobility, random receiver orientation, and imperfect CSI altogether. Further, the derived BER expressions are validated using computer-simulations using typical VLC channel models from the literature. A close agreement between the analytical and the simulated BER is observed, which verifies the accuracy of the presented analysis.Yayın A New speech coding algorithm using zero cross and phoneme based SYMPES(IEEE, 2013-07-11) Şişman, Burak; Güz, Ümit; Gürkan, Hakan; Yarman, Bekir Sıddık BinboğaIn this work, a new low bit rate hybrid speech coding approach which combines the benefits of the SYMPES (Systematic Procedure for Predefined Envelope and Signature Sequences) and zero cross and phoneme based segmentation is proposed. In the new approach, the SYMPES structure is developed in the phoneme based fashion. In order to achieve lower bit rates, some drawbacks such as computational complexity, relatively high encoding times etc. of the SYMPES are also eliminated in the new version. Experimental results show that in almost same bit rates very promising speech quality is obtained compared to the other conventional methods such as CELP (Code Excited Linear Predictive) coding algorithm.Yayın 2W wideband microwave PA design for 824-2170 MHz band using normalized gain function method(IEEE, 2013) Köprü, Ramazan; Kuntman, Hulusi Hakan; Yarman, Bekir Sıddık BinboğaIn this work, we present the design of a 2W linear wideband microwave PA (power amplifier) targeted to operate in 824-2170 MHz mobile frequency range covering GSM850, EGSM, DCS, PCS and WCDMA. The design is basically based on the NGF (Normalized Gain Function) method which is very recently introduced into the literature. NGF is defined as the ratio of T and |S-21|(2), i.e. T-NGF= T/|S-21|(2), shape of the gain function of the amplifier to be designed and the shape of the transistor forward gain function, respectively. Synthesis of input/output matching networks (IMN/OMN) of the amplifier requires target gain functions, which are mathematically generated in terms of TNGF. The particular transistor used in the design is FP31QF, a 2W HFET from TriQuint Semiconductor. Theoretical PA performance obtained in Matlab is shown to be in a very high agreement with the simulated performance in MWO (Microwave Office) of AWR Inc.
