Browsing by Subject "Algorithm design and analysis"

Now showing 1 - 6 of 6

Open Access
CiSE: a circular spring embedder layout algorithm
(Institute of Electrical and Electronics Engineers, 2013) Dogrusoz, U.; Belviranli, M. E.; Dilek, A.
We present a new algorithm for automatic layout of clustered graphs using a circular style. The algorithm tries to determine optimal location and orientation of individual clusters intrinsically within a modified spring embedder. Heuristics such as reversal of the order of nodes in a cluster and swap of neighboring node pairs in the same cluster are employed intermittently to further relax the spring embedder system, resulting in reduced inter-cluster edge crossings. Unlike other algorithms generating circular drawings, our algorithm does not require the quotient graph to be acyclic, nor does it sacrifice the edge crossing number of individual clusters to improve respective positioning of the clusters. Moreover, it reduces the total area required by a cluster by using the space inside the associated circle. Experimental results show that the execution time and quality of the produced drawings with respect to commonly accepted layout criteria are quite satisfactory, surpassing previous algorithms. The algorithm has also been successfully implemented and made publicly available as part of a compound and clustered graph editing and layout tool named Chisio. © 1995-2012 IEEE.
Open Access
Closed-form Green's functions for general sources and stratified media
(Institute of Electrical and Electronics Engineers, 1995-07) Dural, G.; Aksun, M. I.
The closed-form Green's functions of the vector and scalar potentials in the spatial domain are presented for the sources of horizontal electric, magnetic, and vertical electric, magnetic dipoles embedded in general, multilayer, planar media. First, the spectral domain Green's functions in an arbitrary layer are derived analytically from the Green's functions in the source layer by using a recursive algorithm. Then, the spatial domain Green's functions are obtained by adding the contributions of the direct terms, surface waves, and complex images approximated by the Generalized Pencil of Functions Method (GPOF). In the derivations, the main emphasis is to put these closed-form representations in a suitable form for the solution of the mixed potential integral equation (MPIE) by the method of moments in a general three-dimensional geometry. The contributions of this paper are: 1) providing the complete set of closed-form Green's functions in spectral and spatial domains for general stratified media; 2) using the GPOF method, which is more robust and less noise sensitive, in the derivation of the closed-form spatial domain Green's functions; and 3) casting the closed-form Green's functions in a form to provide efficient applications of the method of moments.
Open Access
Design of application specific processors for the cached FFT algorithm
(IEEE, 2006-05) Atak, Oğuzhan; Atalar, Abdullah; Arıkan, Erdal; Ishebabi, H.; Kammler, D.; Ascheid, G.; Meyr, H.; Nicola, M.; Masera, G.
Orthogonal frequency division multiplexing (OFDM) is a data transmission technique which is used in wired and wireless digital communication systems. In this technique, fast Fourier transformation (FFT) and inverse FFT (IFFT) are kernel processing blocks in an OFDM system, and are used for data (de)modulation. OFDM systems are increasingly required to be flexible to accommodate different standards and operation modes, in addition to being energy-efficient. A trade-off between these two conflicting requirements can be achieved by employing application-specific instruction-set processors (ASIPs). In this paper, two ASIP design concepts for the cached FFT algorithm (CFFT) are presented. A reduction in energy dissipation of up to 25% is achieved compared to an ASIP for the widely used Cooley-Tukey FFT algorithm, which was designed by using the same design methodology and technology. Further, a modified CFFT algorithm which enables a better cache utilization is presented. This modification reduces the energy dissipation by up to 10% compared to the original CFFT implementation.
Open Access
An information-theoretic analysis of Grover's algorithm
(IEEE, 2003-06-07) Arıkan, Erdal
Grover discovered a quantum algorithm for identifying a target element in an unstructured search universe of N items in approximately 1r/4VN queries to a quantum oracle. For classical search using a classical oracle, the search complexity is of order N /2 queries since on average half of the items must be searched. In work preceding Grover's, Bennett et al. had shown that no quantum algorithm can solve the search problem in fewer than D(VN) queries. Thus, Grover's algorithm has optimal order of complexity. Here, we present an informationtheoretic analysis of Grover's algorithm and show that the square-root speed-up by Grover's algorithm is the best possible by any algorithm using the same quantum oracle.
Open Access
Simulating a wavelength-size 2-D lens with an accurate numerical method
(IEEE, 2001) Boriskin, A. V.; Nosich, A. I.; Altıntaş, Ayhan
The effect of a localized light source directivity improvement due to an arbitrarily shaped dielectric cylinder taken as a 2-D model of a dielectric lens is studied. The source is simulated by the field of a complex source-point (CSP). An efficient algorithm for the solution of 2-D problem of wave scattering by a smooth dielectric cylinder is developed, based on the concept of analytical regularization. The basic properties of the algorithm are studied. Numerical results for the accuracy of the algorithm and sample far-field characteristics such as the total radiated power, directivity and radiation patterns for various lens parameters are presented.
Open Access
Special Issue on Advances in Channel Coding
(Korean Institute of Communication Sciences, 2015) Arikan, E.; Lentmaier, M.; Montorsi, G.
Since the invention of turbo codes in 1993 there has been an enormous interest and progress in the field of capacity approaching code constructions. Many classical constructions have been replaced by newer, better performing codes with feasible decoding complexity. Most of these modern code constructions, such as turbo codes, Gallager's low-density parity-check (LDPC) codes and their generalizations, can be modeled by sparse graphical models. Spatial coupling of sparse graphical models has in the last years attracted a lot of interest due to the threshold saturation phenomenon, which leads to capacity achieving performance with iterative message passing decoding. Polar codes are a recently discovered class of capacity achieving codes that are formed by an explicit construction based on a phenomenon called channel polarization. These codes, too, have various low-complexity decoding algorithms based on message passing on a sparse graph that has a recursive structure similar to that of fast transforms in signal processing.