Browsing by Subject "Measurement errors"

Now showing 1 - 7 of 7

Open Access
Comparisons of FMM implementations employing different formulations and iterative solvers
(IEEE, 2003-06) Gürel, Levent; Ergül, Özgür
The implementation of multi-level fast multipole algorithm (MLFMA) requires the consideration of several parameters. The preferred combination of the parameters given is not trivially obvious and requires a careful investigation. This paper extensively investigates such parameters by using a series of scattering problems of various sizes containing different numbers of unknowns as a testbed.
Open Access
Kesirli fourier dönüşümü genliklerinden karmaşık sinyallerin geri kazanımı
(IEEE, 2004-04) Ertosun, M. Günhan; Atlı, Haluk; Özaktaş, Haldun M.; Barshan, Billur
Bu makalede kesirli Fourier dönüşümü genlikleri kullanılarak karmaşık sinyallerin evrelerinin bulunması üzerinde durulmuştur. Bu aynı zamanda optik eksende enine boyuna rastgele iki yerde yapılan genlik ölçümlerinden evre bilgisinin bulunmasına karşılık gelmektedir. İteratif algoritmanın yakınsaklığı, gürültü ve ölçüm hatalarının etkisi ve bunların dönüşümün kesir değerine olan bağlılığı incelenmiştir. Genel olarak, kesir değerinin ünitere yakın olduğu durumlarda, sıfıra yakın olduğu durumlara göre daha iyi sonuçlar elde edilmiştir. Buna göre, en iyi sonuçları elde etmek için, iki ölçüm düzlemi arasındaki kesir değeri ünitere olabildiğince yakın seçilmelidir.
Open Access
Location and curvature estimation of spherical targets using multiple sonar time-of-flight measurements
(Institute of Electrical and Electronics Engineers, 1999-12) Barshan, B.
A novel, flexible, three-dimensional multisensor sonar system is described to localize the center of a generalized spherical target and estimate its radius of curvature. Point, line, and planar targets are included as limiting cases which are important for the characterization of a mobile robot's environment. Sensitivity analysis of the curvature estimate with respect to measurement errors and some of the system parameters is provided. The analysis is verified experimentally for specularly reflecting cylindrical and planar targets. Typical accuracies in range and azimuth are 0.17 mm and 0.1°, respectively. Accuracy of the curvature estimate depends on the target type and system parameters such as transducer separation and operating range.
Open Access
Radius of curvature estimation and localization of targets using multiple sonar sensors
(A I P Publishing LLC, 1999-04) Barshan, B.; Sekmen, A. S.
Acoustic sensors have been widely used in time-of-flight ranging systems since they are inexpensive and convenient to use. One of the most important limitations of these sensors is their low angular resolution. To improve the angular resolution and the accuracy, a novel, flexible, and adaptive three- dimensional (3-D) multi-sensor sonar system is described for estimating the radius of curvature and location of cylindrical and spherical targets. Point, line, and planar targets are included as limiting cases which are important for the characterization of typical environments. Sensitivity analysis of the curvature estimate with respect to measurement errors and certain system parameters is provided. The analysis and the simulations are verified by experiments in 2-D with specularly reflecting cylindrical and planar targets, using a real sonar system. Typical accuracies in range and azimuth are 0.18 mm and 0.1°, respectively. Accuracy of the curvature estimation depends on the target type and system parameters such as transducer separation and operating range. The adaptive configuration brings an improvement varying between 35% and 45% in the accuracy of the curvature estimate. The presented results are useful for target differentiation and tracking applications.A flexible and adaptive three-dimensional multisensor sonar system capable of estimating the location and radius of curvature of spherical and cylindrical targets is presented. The performance radius of curvature estimation is analyzed to provide information for differentiating reflectors with different radii. Results showed that the adaptive configuration improved the accuracy of the curvature estimate between 35% and 45%.
Open Access
Simultaneous extraction of geometry and surface properties of targets using infrared intensity signals
(IEEE, 2005) Aytaç, Tayfun; Barshan, Billur
We propose the use of angular intensity signals obtained with low-cost infrared sensors and present an algorithm to simultaneously extract the geometry and surface properties of commonly encountered targets in indoor environments. The method is verified experimentally with planes, 90° corners, and 90° edges covered with aluminum, white cloth, and Styrofoam packaging material. An average correct classification rate of 80% of both geometry and surface over all target types is achieved and targets are localized within absolute range and azimuth errors of 1.5 cm and 1.1°, respectively. Taken separately, the geometry and surface type of targets can be correctly classified with rates of 99% and 81%, respectively, indicating that the geometrical properties of the targets are more distinctive than their surface properties, and surface determination is the limiting factor. The method demonstrated shows that simple infrared sensors, when coupled with appropriate signal processing, can be used to extract substantially more information than such devices are commonly employed for.
Open Access
Structured least squares problems and robust estimators
(IEEE, 2010-10-22) Pilanci, M.; Arıkan, Orhan; Pinar, M. C.
A novel approach is proposed to provide robust and accurate estimates for linear regression problems when both the measurement vector and the coefficient matrix are structured and subject to errors or uncertainty. A new analytic formulation is developed in terms of the gradient flow of the residual norm to analyze and provide estimates to the regression. The presented analysis enables us to establish theoretical performance guarantees to compare with existing methods and also offers a criterion to choose the regularization parameter autonomously. Theoretical results and simulations in applications such as blind identification, multiple frequency estimation and deconvolution show that the proposed technique outperforms alternative methods in mean-squared error for a significant range of signal-to-noise ratio values.
Open Access
Upper bounds on position error of a single location estimate in wireless sensor networks
(Hindawi Publishing Corporation, 2014) Gholami, M. R.; Ström, E. G.; Wymeersch, H.; Gezici, Sinan
This paper studies upper bounds on the position error for a single estimate of an unknown target node position based on distance estimates in wireless sensor networks. In this study, we investigate a number of approaches to confine the target node position to bounded sets for different scenarios. Firstly, if at least one distance estimate error is positive, we derive a simple, but potentially loose upper bound, which is always valid. In addition assuming that the probability density of measurement noise is nonzero for positive values and a sufficiently large number of distance estimates are available, we propose an upper bound, which is valid with high probability. Secondly, if a reasonable lower bound on negative measurement errors is known a priori, we manipulate the distance estimates to obtain a new set with positive measurement errors. In general, we formulate bounds as nonconvex optimization problems. To solve the problems, we employ a relaxation technique and obtain semidefinite programs. We also propose a simple approach to find the bounds in closed forms. Simulation results show reasonable tightness for different bounds in various situations.