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Subsequent Iterations (subsequent + iteration)
Selected AbstractsApplication of a three-dimensional ray-tracing technique to global P, PP and Pdiff traveltime tomographyGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001A. Gorbatov Summary A 3-D ray-path tracing algorithm was successfully applied to global P -wave traveltime tomography. The inversion was conducted iteratively using the resultant P -wave velocity model as the initial model for the subsequent iteration. The LSQR method was adopted to solve a large and sparse system of equations. This iteratively linearized inversion with 3-D ray tracing increased wave-speed anomalies, located heterogeneities better and reduced smearing as compared to those derived from a conventional one-step inversion using 1-D ray tracing, although the general pattern of velocity anomalies was similar. A major difference was found in the lowermost mantle, where the departure of a ray path from the great circle path tends to be in general greatest. In particular, a pronounced high-velocity anomaly develops beneath the Indian Ocean, a feature not obvious in the result of 1-D inversion. The final P -wave velocity model was obtained by including reported PP and Pdiff traveltime data. The addition of the PP data sharpened the images and enhanced velocity anomalies in the upper mantle, especially at latitudes above 45° of the Northern Hemisphere. The addition of the Pdiff data sharpened and amplified velocity anomalies in the lowermost mantle in general. [source] Iterative channel estimation and data detection in frequency-selective fading MIMO channels,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2004Maja Lon Signals transmitted through multiple-input multiple-output (MIMO) wireless channels suffer from multiple-access interference (MAI), multipath propagation and additive noise. Iterative multiuser receiver algorithms mitigate these signal impairments, while offering a good tradeoff between performance and complexity. The receiver presented in this paper performs channel estimation, multiuser detection and decoding in an iterative manner. The estimation of the frequency selective, block-fading channel is initiated with the pilot symbols. In subsequent iterations, soft decisions of all the data symbols are used in an appropriate way to improve the channel estimates. This approach leads to significant improvement of the overall receiver performance, compared to other schemes. The bit-error-rate (BER) performance of the receiver is evaluated by simulations for different parameter setups. Copyright © 2004 AEI. [source] Insights on a sign-preserving numerical method for the advection,diffusion equationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2009E. SousaArticle first published online: 17 DEC 200 Abstract In this paper we explore theoretically and numerically the application of the advection transport algorithm introduced by Smolarkiewicz to the one-dimensional unsteady advection,diffusion equation. The scheme consists of a sequence of upwind iterations, where the initial iteration is the first-order accurate upwind scheme, while the subsequent iterations are designed to compensate for the truncation error of the preceding step. Two versions of the method are discussed. One, the classical version of the method, regards the second-order terms of the truncation error and the other considers additionally the third-order terms. Stability and convergence are discussed and the theoretical considerations are illustrated through numerical tests. The numerical tests will also indicate in which situations are advantageous to use the numerical methods presented. Copyright © 2008 John Wiley & Sons, Ltd. [source] Model reference adaptive iterative learning control for linear systemsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2006A. Tayebi Abstract In this paper, we propose a model reference adaptive control (MRAC) strategy for continuous-time single-input single-output (SISO) linear time-invariant (LTI) systems with unknown parameters, performing repetitive tasks. This is achieved through the introduction of a discrete-type parametric adaptation law in the ,iteration domain', which is directly obtained from the continuous-time parametric adaptation law used in standard MRAC schemes. In fact, at the first iteration, we apply a standard MRAC to the system under consideration, while for the subsequent iterations, the parameters are appropriately updated along the iteration-axis, in order to enhance the tracking performance from iteration to iteration. This approach is referred to as the model reference adaptive iterative learning control (MRAILC). In the case of systems with relative degree one, we obtain a pointwise convergence of the tracking error to zero, over the whole finite time interval, when the number of iterations tends to infinity. In the general case, i.e. systems with arbitrary relative degree, we show that the tracking error converges to a prescribed small domain around zero, over the whole finite time interval, when the number of iterations tends to infinity. It is worth noting that this approach allows: (1) to extend existing MRAC schemes, in a straightforward manner, to repetitive systems; (2) to avoid the use of the output time derivatives, which are generally required in traditional iterative learning control (ILC) strategies dealing with systems with high relative degree; (3) to handle systems with multiple tracking objectives (i.e. the desired trajectory can be iteration-varying). Finally, simulation results are carried out to support the theoretical development. Copyright © 2006 John Wiley & Sons, Ltd. 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