Browsing by Subject "Estimation"

Now showing 1 - 20 of 73

Open Access
Adaptive tracking of narrowband HF channel response
(Wiley-Blackwell Publishing, 2003) Arikan, F.; Arıkan, Orhan
Estimation of channel impulse response constitutes a first step in computation of scattering function, channel equalization, elimination of multipath, and optimum detection and identification of transmitted signals through the HF channel. Due to spatial and temporal variations, HF channel impulse response has to be estimated adaptively. Based on developed state-space and measurement models, an adaptive Kalman filter is proposed to track the HF channel variation in time. Robust methods of initialization and adaptively adjusting the noise covariance in the system dynamics are proposed. In simulated examples under good, moderate and poor ionospheric conditions, it is observed that the adaptive Kalman filter based channel estimator provides reliable channel estimates and can track the variation of the channel in time with high accuracy.
Open Access
Anchor placement in TOA based wireless localization networks via convex relaxation
(IEEE, 2021-09-06) Öztürk, Cuneyd; Gezici, Sinan
A wireless source localization network consisting of synchronized target and anchor nodes is considered. An anchor placement problem is formulated to minimize the Cramér-Rao lower bound (CRLB) on estimation of target node positions by anchor nodes. First, it is shown that the anchor placement problem can be approximated as a minimization problem of the ratio of two supermodular functions. Due to the lack of a polynomial time algorithm for such problems, an anchor selection problem is proposed to solve the anchor placement problem. Via relaxation of integer constraints, the anchor selection problem is approximated by a convex optimization problem, which is used to propose two algorithms for anchor selection. Furthermore, extensions to quasi-synchronous wireless localization networks are discussed. To examine the performance of the proposed algorithms, various simulation results are presented.
Open Access
Average distance estimation in randomly deployed wireless sensor networks (WSNs): an analytical study
(Inderscience Enterprises, 2019) Sevgi, Cüneyt
A wireless sensor network (WSN) is an energy-scarce network in which the energy is primarily dissipated by the nodes during data transmission to the base station (BS). The location of the BS dramatically affects the energy dissipation, the throughput, and the lifetime. While in certain studies the optimal positioning of a BS is considered, the system parameters are optimized when the BS location is known in advance in many others. Herein, we provide a general-purpose mathematical framework to find the expected distance value between every point within any n-sided simple polygon shaped sensing field and an arbitrarily located BS. Knowing this value is imperative particularly in random deployment as it is used for energy-efficient clustering. Although similar derivations appear in the related literature, to the best of our knowledge, this study departs from them, since our derivations do not depend on the shape of the field and the orientation of BS relative to it.
Open Access
Birleşik sezim ve kestirim sistemlerinin gürültü ile geliştirilmesi
(IEEE, 2014-04) Akbay, Abdullah Başar; Gezici, Sinan
Belirli koşullar altında, optimal olmayan bazı sezici ve kestiricilerin performansını girdilerine gürültü ekleyerek geliştirmek mümkündür. Bu çalışmada, birleşik bir sezim ve kestirim sisteminin gürültü eklenerek geliştirilmesi incelenmektedir. Sistem performansının maksimizasyonu bir optimizasyon problemi olarak tanımlanmaktadır. Optimal toplanır gürültü dağılımının istatiksel özellikleri belirlenmektedir. Sistem performansının gürültü ile iyileştirilemeyeceği bir koşul elde edilmektedir.Önerilen optimizasyon probleminin, bir doğrusal programlama (DP) problemi olarak yaklaşımı sunulmaktadır. Bir sayısal örnek üzerinde, kuramsal bulguları desteklemek amacıyla, gürültü eklenmiş sistem ile orijinal sistemin performansları karşılaştırılmaktadır.
Open Access
Capacity bounds for an ultra-wideband channel model
(IEEE, 2004-10) Arıkan, Erdal
There is an ongoing effort by the IEEE 802.15.3a subcommittee to reach a UWB personal area network standard. We estimate the achievable rates for such networks using a channel model specified by the same group. The analysis of this channel model is of interest in light of recent information-theoretic work on multipath fading channels which show that in order to take full advantage of such channels' capacity the transmitted signals have to be "peaky" in a certain sense. The immense bandwidth of the UWB channel also suggests at first that peaky signals should be used. However, unlike the many other wireless systems where the transmitter energy is limited, in the UWB channel only the power spectral density of the transmitted signal is constrained. As a result, the signal power can grow in proportion to the utilized bandwidth and peaky signals are not needed. © 2004 IEEE.
Open Access
Çokyollu kanal parametre kestirimi için yeni bir dizilim sinyal işleme tekniği
(IEEE, 2007-06) Güldoǧan, Mehmet Burak; Arıkan, Orhan
Bu bildiride, çarpraz belirsizlik işlevinin kullanıldığı yeni bir dizilim sinyal işleme tekniği önerilmektedir. Geliştirilen teknik bir algılayıcı dizilimine gelen sinyallerden herbirinin geliş yönünü (GY), zaman gecikmesini Doppler kaymasını ve genliğini dürümlü bir sekilde kestirir. Önerilen Çarpraz Belirsizlik İşlevi - Yön Bulma (ÇBI-YB) tekniği ile Çoklu Sinyal Sınıflandırması (MUSIC) algoritmasının performansları sentetik sinyaller kullanılarak kök Ortalama Karesel Hata (kOKH) cinsinden değişik işaret Gürültü Oranı (İGO) değerleri için karşılaştırılmıştır. Önerilen tekniğin başarımı kayıt edilmiş çokyollu yüksek-enlem iyonosfer verileri üzerinde irdelenmiştir. Elde edilen sonuçlar, düşük İGO değerlerinde dahi çokyollu sinyal kaynaklarını ayırmada önerilen ÇBİ-YB tekniğinin ciddi başarım artışı sağladığını göstermektedir.
Open Access
Comparative theoretical analysis of distance estimation in visible light positioning systems
(Institute of Electrical and Electronics Engineers Inc., 2016) Keskin, M. F.; Gezici, Sinan
In this paper, theoretical limits and estimators are studied for synchronous and asynchronous visible light positioning (VLP) systems. Specifically, the Cramér-Rao lower bounds (CRLBs) and maximum likelihood estimators are investigated for distance estimation based on time-of-arrival (TOA) and/or received signal strength (RSS) parameters. Hybrid TOA/RSS-based distance estimation is proposed for VLP systems, and its CRLB is compared analytically against the CRLBs of TOA-based and RSS-based distance estimation. In addition, to investigate the effects of sampling, asymptotic performance results are obtained under sampling rate limitations as the noise variance converges to zero. A modified hybrid TOA/RSS-based distance estimator is proposed to provide performance improvements in the presence of sampling rate limitations. Numerical examples are presented to illustrate the theoretical results. © 2015 IEEE.
Open Access
Comparison of low complexity UWB range estimators based on experimental data
(IEEE, 2012) Soğancı, Hamza; Gezici, Sinan; Tan, A.S.
In this paper, performances of low complexity time based range estimators that are employed for ultra wide-band (UWB) systems are compared using experimental data. These estimators are widely used in practical applications due to their low complexity. However, performances of these estimators vary depending on the choice of certain parameters such as the threshold value and window size. The optimal values for these parameters are investigated for several situations using the data acquired in the experiments. © 2012 IEEE.
Open Access
Comparison of the CAF-DF and sage algorithms in multipath channel parameter estimation
(IEEE, 2008-07) Güldoğan, M. Burak; Arıkan, Orhan
In this paper, performance of the recently proposed Cross Ambiguity Function - Direction Finding (CAF-DF) technique is compared with the Space Alternating Generalized Expectation Maximization (SAGE) technique. The CAF-DF, iteratively estimates direction of arrival (DOA), time-delay, Doppler shift and amplitude corresponding to each impinging signal onto an antenna array by utilizing the cross ambiguity function. On synthetic signals, based on Monte Carlo trials, performances of the algoritms are tested in terms of root Mean Squared Error (rMSE) at different Signal-to-Noise Ratios (SNR). Cramer-Rao lower bound is included for statistical comparisons. Simulation results indicate the superior performance of the CAF-DF technique over SAGE technique for low and medium SNR values. © 2008 IEEE.
Open Access
Compressive sampling and adaptive multipath estimation
(IEEE, 2010) Pilancı, Mert; Arıkan, Orhan
In many signal processing problems such as channel estimation and equalization, the problem reduces to a linear system of equations. In this proceeding we formulate and investigate linear equations systems with sparse perturbations on the coefficient matrix. In a large class of matrices, it is possible to recover the unknowns exactly even if all the data, including the coefficient matrix and observation vector is corrupted. For this aim, we propose an optimization problem and derive its convex relaxation. The numerical results agree with the previous theoretical findings of the authors. The technique is applied to adaptive multipath estimation in cognitive radios and a significant performance improvement is obtained. The fact that rapidly varying channels are sparse in delay and doppler domain enables our technique to maintain reliable communication even far from the channel training intervals. ©2010 IEEE.
Open Access
Cooperative visible light positioning systems
(2017-12) Erdem, Osman
Light emitting diode (LED) based visible light positioning (VLP) systems o er an alternative approach to commonly used radio frequency (RF) based positioning systems. In the literature, VLP studies are performed only for noncooperative systems. In this thesis, received signal strength (RSS) based cooperative localization is proposed for visible light systems. The e ects of cooperation on the localization accuracy of visible light positioning systems are illustrated based on a Cram er-Rao lower bound expression. The obtained expression is generic for any three-dimensional con guration and covers all possible cooperation scenarios via de nitions of connectivity sets. In addition, a low-complexity positioning algorithm is proposed for cooperative location estimation. Numerical results are presented to investigate the signi cance of cooperation and to evaluate performance of the proposed algorithm in various scenarios.
Open Access
Counting surrounding nodes using DS-SS signals and de Bruijn sequences in blind environment
(IEEE, 2013-03) Warty, C.; Seçer, Görkem; Yu, R.W.; Spinsante, S.
In recent years the technological development has encouraged several applications based on node to node communications without any fixed infrastructure. This paper presents preliminary evaluation of popular estimating techniques to populate active nodes in the neighborhood using De Bruijn sequences. They have much higher cardinality compared to any other family of binary sequences at a parity of length. This characteristic of De Bruijn sequences can be exploited to identify the presence of an active node in a dense surrounding, to assist the primary node in making intelligent decisions in a blind or foggy environment. The simulation model in this paper evaluates the use of eigenvalue estimation to estimate the spreading sequence among noisy signals, based on eigenvalues analysis techniques. The received signal is divided into windows, from which a covariance matrix is computed; the sequence can be reconstructed from the two first eigenvectors of this matrix, and that useful information, such as the desynchronization time, can be extracted from the eigenvalues. © 2013 IEEE.
Open Access
CRLB based optimal noise enhanced parameter estimation using quantized observations
(IEEE, 2010-02-22) Balkan, G. O.; Gezici, Sinan
In this letter, optimal additive noise is characterized for parameter estimation based on quantized observations. First, optimal probability distribution of noise that should be added to observations is formulated in terms of a CramerRao lower bound (CRLB) minimization problem. Then, it is proven that optimal additive noise can be represented by a constant signal level, which means that randomization of additive signal levels is not needed for CRLB minimization. In addition, the results are extended to the cases in which there exists prior information about the unknown parameter and the aim is to minimize the Bayesian CRLB (BCRLB). Finally, a numerical example is presented to explain the theoretical results.
Open Access
Differentiation and localization of target primitives using infrared sensors
(IEEE, 2002-09-10) Aytaç, Tayfun; Barshan, Billur
This study investigates the use of low-cost infrared sensors in the differentiation and localization of commonly encountered target primitives in indoor environments, such as planes, corners, edges, and cylinders. The intensity readings from such sensors are highly dependent on target location and properties in a way which cannot be represented in a simple manner, making the differentiation and localization process difficult. In this paper, we propose the use of angular intensity scans and present an algorithm to process them. This approach can determine the target type independent of its position. Once the target type is identified, its position can also be estimated. The method is verified experimentally. An average correct classification rate of 97% over all target types is achieved and targets are localized within absolute range and azimuth errors of 0.8 cm and 1.6°, respectively. The proposed method should facilitate the use of infrared sensors in mobile robot applications for differentiation and localization beyond their common usage as simple proximity sensors for object detection and collision avoidance.
Open Access
Direct and two-step positioning in visible light systems
(IEEE, 2018) Keskin, Musa Furkan; Gezici, Sinan; Arıkan, Orhan
Visible light positioning (VLP) systems based on light emitting diodes can facilitate high accuracy localization services for indoor scenarios. In this paper, direct and two-step positioning approaches are investigated for both synchronous and asynchronous VLP systems. First, the Cramér-Rao lower bound (CRLB) and the direct positioning-based maximum likelihood estimator are derived for 3-D localization of a visible light communication receiver in a synchronous scenario by utilizing information from both time delay parameters and channel attenuation factors. Then, a two-step position estimator is designed for synchronous VLP systems by exploiting the asymptotic properties of time-of-arrival and received signal strength estimates. The proposed two-step estimator is shown to be asymptotically optimal, i.e., converges to the direct estimator at high signal-to-noise ratios. In addition, the CRLB and the direct and two-step estimators are obtained for positioning in asynchronous VLP systems. It is proved that the two-step position estimation is optimal in asynchronous VLP systems for practical pulse shapes. Various numerical examples are provided to illustrate the improved performance of the proposed estimators with respect to the current state-of-the-art and to investigate their robustness against model uncertainties in VLP systems.
Open Access
Direct positioning in synchronous and asynchronous visible light systems
(IEEE, 2018) Keskin, Musa Furkan; Gezici, Sinan; Arıkan, Orhan
In this paper, direct positioning approaches are investigated for both synchronous and asynchronous visible light systems. First, the maximum likelihood estimator (MLE) and the Cramér-Rao lower bound (CRLB) are derived for the synchronous scenario by considering the information from both channel attenuation factors and time delay parameters. Then, asynchronous visible light positioning (VLP) systems are investigated and the corresponding CRLBs and MLEs are obtained based on received signal strength (RSS) information. It is shown that the direct and two-step position estimators are equivalent in the asynchronous scenario under mild conditions. Numerical examples are provided to illustrate the theoretical results.
Open Access
Distributed MIMO radar signal processing
(2022-07) Ercan, Mahmut Kemal
Radar systems are remote sensing tools that generate electromagnetic waves and extract information by receiving altered versions of these waves. Nowadays, many radar types are being used in speciﬁc areas such as weather prediction, automobiles, and the military. One type of radar employed in military applica-tions is called the multistatic radar system. Multistatic radar systems consist of multiple transmitters and receivers widely separated from each other. Although multistatic radar systems have not been invented recently, one type of multistatic radar has recently taken the attention of the literature, the multiple input mul-tiple output (MIMO) radar system. In this thesis, we analyze the performance of some techniques presented in the MIMO radar literature, make improvements, and propose new methods. First, we review the literature for MIMO radar waveform generation. Then, we propose a parameter estimation technique for multiple target cases using the polyphased-piecewise linear frequency modulated (PPLFM) waveform. Secondly, we propose a detection algorithm in which each receiver preprocesses received sig-nals and extracts bistatic range and Doppler for each transmitter. A grid of points in the region of interest (ROI) is generated, and by using a weighting function, a weight for each plot is calculated, and detection is performed via thresholding. Third, we propose a policy-iteration-based position and velocity estimation algo-rithm. We deﬁne a cost function using bistatic range and Doppler measurements for the proposed estimation algorithm. To perform estimation in the presence of multiple targets, we conduct data association by weighting the bistatic measure-ments. Fourth, a tracking algorithm that uses the Generalized Multi Bernoulli Filter is proposed. Lastly, we investigate the alternative MIMO antenna struc-tures and analyze the detection and tracking performance of the Electromagnetic Vector Sensor (EMVS). At the end of the thesis, it is demonstrated that the performance of the proposed algorithms is promising. Additionally, we show that the detection and tracking performance of the EMVS-based MIMO radar system is better than the performance of the MIMO radar system with dipole antennas.
Open Access
A distributed positioning algorithm for cooperative active and passive sensors
(IEEE, 2010) Gholami, M.R.; Gezici, Sinan; Rydström, M.; Ström, E.G.
The problem of positioning a target node is studied for wireless sensor networks with cooperative active and passive sensors. Two-way time-of-arrival and time-difference-of-arrival measurements made by both active and passive nodes are used to estimate the position of the target node. A maximum likelihood estimator (MLE) can be employed to solve the problem. Due to the nonlinear nature of the cost function in the MLE, an iterative search might converge to local minima which often results in large estimation errors. To avoid this drawback, we instead formulate the problem of positioning as finding the intersection of a number of convex sets derived from measurements. To obtain this intersection, we apply the projection onto convex sets approach, which is robust and can be implemented in a distributed manner. Simulations are performed to compare the performance of the MLE and the proposed method. ©2010 IEEE.
Open Access
Eavesdropper and jammer selection in wireless source localization networks
(IEEE, 2021-07-26) Öztürk, Cüneyd; Gezici, Sinan
We consider a wireless source localization network in which a target node emits localization signals that are used by anchor nodes to estimate the target node position. In addition to target and anchor nodes, there can also exist eavesdropper nodes and jammer nodes which aim to estimate the position of the target node and to degrade the accuracy of localization, respectively. We first propose the problem of eavesdropper selection with the goal of optimally placing a given number of eavesdropper nodes to a subset of possible positions to estimate the target node position as accurately as possible. As the performance metric, the Cramér-Rao lower bound (CRLB) related to the estimation of the target node position by eavesdropper nodes is derived, and its convexity and monotonicity properties are investigated. By relaxing the integer constraints, the eavesdropper selection problem is approximated by a convex optimization problem and algorithms are proposed for eavesdropper selection. Then, the problem of jammer selection is proposed where the aim is to optimally place a given number of jammer nodes to a subset of possible positions for degrading the localization accuracy of the network as much as possible. A CRLB expression from the literature is used as the performance metric, and its concavity and monotonicity properties are derived. Also, a convex optimization problem is derived after relaxation. Finally, the joint eavesdropper and jammer selection problem is proposed with the goal of placing certain numbers of eavesdropper and jammer nodes to a subset of possible positions.
Open Access
Eavesdropper selection strategies in wireless source localization networks
(IEEE, 2020) Öztürk, Cüneyd; Gezici, Sinan
We consider a wireless source localization network in which eavesdropper nodes aim to estimate the position of a target node. We formulate the problem of selecting a set of N E positions out of N possible positions for placing eavesdropper nodes in order to estimate the target node position as accurately as possible. The Cramér-Rao lower bound related to the estimation of the target node position by eavesdropper nodes is derived, and its monotonicity and convexity properties are investigated. Via relaxation of the integer constraints, the eavesdropper selection problem is approximated by a convex optimization problem, which is used to propose two algorithms for eavesdropper selection. Moreover, in the presence of parameter uncertainty, a robust version of the eavesdropper selection problem is investigated. Simulation results are presented to examine performance of the proposed algorithms.