frame based approach for peak to average power ratio reduction in ofdm a new method for reducing the peak to average power ratio papr in orthogonal frequency division multiplexing is proposed the new method called erasure pattern selection eps is based on the use of frame expansion for adding redundancy to the data part of the redundancy is removed by examining several patterns for erasing subcarriers and selecting the pattern that produces the lowest papr for transmission the residual redundancy in the data is exploited at the receiver to aid both the reconstruction of the erased data and correction of errors the implementation is aided with the incorporation of a projection onto convex sets pocs method in eps in order to select and assign the best values to the unused subcarriers and further reduce the papr complexity analysis and simulation results show that the pocs based eps method outperforms existing probabilistic methods while requiring lower overall complexity

aspects of three dimensional constrained delaunay meshing presented in this paper are the theoretical aspects of node addition to a non convex multiboundary mesh of tetrahedral elements as used in finite element modelling the method used is derived from watson1 and shenton and cendes2 and is extended to deal with node addition on inter material boundaries several situations are identified that result in an illegal insertion polyhedron ip these could be caused by the constrained nature of the mesh adjacent objects with different material properties or degenerate node configurations a new delaunay algorithm is described that checks for illegal cases of the ip and then corrects them this checking relies on the consistent ordering of the element nodes it is shown that a particular type of illegal ip can easily be identified and corrected using this technique the delaunay algorithm is then applied to automatic mesh generation and modification to the basic delaunay algorithm is described so that previously meshed edges and faces of the current object being meshed are not deleted during the addition of subsequent nodes this protection method only becomes viable by recognizing the node ordering sense of the ip faces

delaunay versus max min solid angle triangulations for three dimensional mesh generation the delaunay triangulation has been used in several methods for generating finite element tetrahedral meshes in three dimensional polyhedral regions other types of three dimensional triangulations are possible such as a triangulation satisfying a local max min solid angle criterion in this paper we present experimental results to show that max min solid angle triangulations are better than delaunay triangulations for finite element tetrahedral meshes since the former type of triangulations contains tetrahedra of better shape than the latter type we also describe how mesh points are generated and triangulated in our tetrahedral mesh generation method

theoretical analysis and performance of ofdm signals in nonlinear awgn channels orthogonal frequency division multiplexing ofdm baseband signals may be modeled by complex gaussian processes with rayleigh envelope distribution and uniform phase distribution if the number of carriers is sufficiently large the output correlation function of instantaneous nonlinear amplifiers and the signal to distortion ratio can be derived and expressed in an easy way as a consequence the output spectrum and the bit error rate ber performance of ofdm systems in nonlinear additive white gaussian noise channels are predictable both for uncompensated amplitude modulation amplitude modulation am am and amplitude modulation pulse modulation am pm distortions and for ideal predistortion the aim of this work is to obtain the analytical expressions for the output correlation function of a nonlinear device and for the ber performance the results in closed form solutions are derived for am am and am pm curves approximated by bessel series expansion and for the ideal predistortion case

a general framework for transmission with transceiver distortion and some applications a general theoretical framework is presented for analyzing information transmission over gaussian channels with memoryless transceiver distortion which encompasses various nonlinear distortion models including transmit side clipping receive side analog to digital conversion and others the framework is based on the so called generalized mutual information gmi and the analysis in particular benefits from the setup of gaussian codebook ensemble and nearest neighbor decoding for which it is established that the gmi takes a general form analogous to the channel capacity of undistorted gaussian channels with a reduced effective signal to noise ratio snr that depends on the nominal snr and the distortion model when applied to specific distortion models an array of results of engineering relevance is obtained for channels with transmit side distortion only it is shown that a conventional approach which treats the distorted signal as the sum of the original signal part and a uncorrelated distortion part achieves the gmi for channels with output quantization closed form expressions are obtained for the effective snr and the gmi and related optimization problems are formulated and solved for quantizer design finally super nyquist sampling is analyzed within the general framework and it is shown that sampling beyond the nyquist rate increases the gmi for all snr values for example with binary symmetric output quantization information rates exceeding one bit per channel use are achievable by sampling the output at four times the nyquist rate

on the distribution of the peak to average power ratio in ofdm signals the distribution of the peak to average power ratio papr in strictly band limited orthogonal frequency division multiplexing ofdm signals is studied assuming that the base band ofdm signal is characterized as a band limited complex gaussian process we first attempt to derive the exact distribution of the papr in the band limited ofdm signals since this distribution cannot be expressed in a closed form we further develop a simple closed form approximation based on the level crossing rate analysis comparisons of the proposed distributions with those obtained by computer simulations show good agreement and convergence with an increase in the number of subcarriers

predistorter for mimo system with nonlinear power amplifiers a multiple input multiple output mimo system with nonlinear power amplifiers pas is considered the nonlinear pas distort the transmitted signal causing performance degradation the common approach for the mitigation of nonlinear distortions is the linearization of each one of the pas in the mimo system separately we propose to apply a more generic approach in the form of a global linearization of the entire nonlinear mimo channel the aim of the global linearization is to reduce the nonlinear distortions seen at the receiver an iterative technique is proposed for the implementation of such a linearization the proposed technique improves the system performance including 1 power efficiency of the pas 2 quality of the received signal measured in terms of symbol error rate and 3 spectral purity of the transmitted signals

voronoi delaunay analysis of voids in systems of nonspherical particles the voronoi network is known to be a useful tool for the structural description of voids in the packings of spheres produced by computer simulations in this article we extend the voronoi delaunay analysis to packings of nonspherical convex objects main properties of the voronoi network which are known for systems of spheres are valid for systems of any convex objects a general numerical algorithm for calculation of the voronoi network in three dimensions is proposed it is based on the calculation of the trajectory of the imaginary empty sphere of variable size moving inside a system the delaunay empty sphere method analysis of voids is presented for an ensemble of random straight lines and for a molecular dynamics model of liquid crystal the spatial distribution of voids and a simple percolation analysis are obtained the distributions of the bottleneck radii and the radii of spheres inscribed in the voids are calculated

iterative soft compensation for ofdm systems with clipping and superposition coded modulation this paper deals with the clipping method used in orthogonal frequency division multiplexing ofdm systems to reduce the peak to average power ratio papr an iterative soft compensation method is proposed to mitigate the clipping distortion which can outperform conventional treatments the impact of signaling schemes on the residual clipping noise power is studied via the symbol variance analysis it is found that superposition coded modulation scm can minimize the residual clipping noise power among all possible signaling schemes this indicates that scm based ofdm systems are more robust to clipping effect than other alternatives when soft compensation is applied it is also shown that a multi code scm scheme can further reduce the clipping effect and its overall performance can be quickly evaluated using a semi analytical evolution method numerical examples are provided to verify the analysis

reduction of peak factor in orthogonal multicarrier modulation by amplitude limiting and coding a main disadvantage of orthogonal multicarrier modulation is that it exhibits a high peak to average power ratio papr because of this all circuits between the output of the modulator and the input of the demodulator must be linear within a large dynamic range to avoid distortions and spectral spreading it is therefore desirable to limit the papr of the multicarrier signal a method based on amplitude limiting and forward error correcting al fec coding is proposed for reduction of the papr the performance of the al fec is compared to two methods based on block coding specially constructed to reduce the papr the al fec is superior as compared to the existing methods moreover its practical realization is very simple for any number of carriers

localisation in a cosserat continuum under static and dynamic loading conditions abstract localisation studies have been carried out for an unconstrained elasto plastic strain softening cosserat continuum because of the presence of an internal length scale in this continuum model a perfect convergence is found upon mesh refinement a finite constant width of the localisation zone and a finite energy dissipation are computed under static as well as under transient loading conditions because of the existence of rotational degrees of freedom in a cosserat continuum additional wave types arise and wave propagation becomes dispersive this has been investigated analytically and numerically for an elastic cosserat continuum and an excellent agreement has been found between both solutions

theoretical characterization of nonlinear clipping effects in im dd optical ofdm systems this paper looks at the problem of theoretically characterizing the nonlinear biasing and clipping bac effects on an optical orthogonal frequency division multiplexing ofdm signal in intensity modulated direct detected im dd optical systems due to the unipolarity of the im dd optical channel a large dc bias and associated nonlinear clipping distortion nlcd is inevitable resulting in a significant performance penalty this nlcd can be well modelled as a linear deterministic attenuation plus an uncorrelated random additive clipping noise in the time domain in the frequency domain the nlcd results in an additive or impulsive noise on the received ofdm constellation a total effective signal to noise ratio snr formula is then presented which is a function of biasing power modulation constellation and receiver snr figure this suggests that rather than eliminating all clippings the system performance is indeed optimized with some deliberately introduced nlcd as a result of higher power efficiency analytical results are in agreement with simulations for various cases which help us to accurately and efficiently evaluate the performance of such systems

an adaptive strategy for elliptic problems including a posteriori controlled boundary approximation we derive a posteriori error estimates for the approximation of linear elliptic problems on domains with piecewise smooth boundary the numerical solution is assumed to be defined on a finite element mesh whose boundary vertices are located on the boundary of the continuous problem no assumption is made on a geometrically fitting shape a posteriori error estimates are given in the energy norm and the l 2 norm and efficiency of the adaptive algorithm is proved in the case of a saturated boundary approximation furthermore a strategy is presented to compute the effect of the non discretized part of the domain on the error starting from a coarse mesh this especially implies that parts of the domain where the measured error is small stay non discretized the presented algorithm includes a stable path following to supply a sufficient polygonal approximation of the boundary the reliable computation of the a posteriori estimates and a mesh adaptation based on delaunay techniques numerical examples illustrate that errors outside the initial discretization will be detected

tetrahedral mesh generation based on node insertion in crystal lattice arrangements and advancing front delaunay triangulation a method of unstructured technical mesh generation for general three dimensional domains is presented a conventional boundary representation is adopted as the basis for the description of solids with evolving geometry and topology the geometry of the surfaces is represented either analytically or by piecewise polynominal interpolation a preliminary surface mesh is generated by an advancing front method with the nodes inserted by hard sphere packing in physical space in accordance with a prescribed mesh density interior nodes are inserted in a face centered cubic fcc crystal lattice arrangements coupled to octree spatial subdivision with the local lattice parameter determined by a prespecified nodal density function prior to triangulation of the volume the preliminary surface mesh is preprocessed by a combination of local transformations and subdivisions in order to guarantee that the surface triangulation be a subcomplex of the volume delaunay triangulation a joint delaunay triangulation of the interior and boundary nodes which preserves the modified surface mesh is then constructed via an advancing front approach the resulting mesh is finally improved upon by the application of local transformations the overall time complexity of the mesher is o n log n the robustness and versatility of the approach as well as the good quality of the resulting meshes is demostrated with the aid of selected examples

solution of two dimensional vorticity equation on a lagrangian mesh anovel vorticity basedsolutionmethodologyhasbeendevelopedtocomputeunsteadye owpastbodies vorticity is evolved on a set of points and the vorticity in the remainder of the e eld is determined by linear interpolation interpolationisaccomplished bydelaunaytriangularizationofthepointsin the e eld triangulationofthevorticity e eldprovidesabasistointegratethevorticitytocomputethevelocity nodalconnectivityfromthetriangularization also provides a list of the neighboring points that are used to construct a second order least squares e t of the vorticity first and second order spatial derivatives can then be computed based on this polynomial e t surface vorticity on the body is computed to satisfy the no slip boundary condition and is introduced into the e ow via diffusion a diffusion transport velocity was derived to account for spatial movementof the vorticity dueto viscous diffusion the points are advected by the sum of the induced velocity computed from the biot savart integral and the diffusion velocity the remaining diffusion term includes a form of the laplacian and is computed directly this solution scheme was found to be stable as applied to the problem of impulsively started e ow about a circular cylinder and e at plate comparisons with experimental and the blasius boundary layer solution for a e at plate were used to demonstrate the effectiveness of this method

structure of void space in polymer solutions the structure of void space in two and three dimensional 3d polymer solutions is studied using voronoi tessellation and percolation theory the polymer molecules are modeled as freely jointed chains of n tangent hard disks two dimensions or spheres three dimensions polymer chains are equilibrated via monte carlo simulations and the pore space in configurations of equilibrated chains is mapped using voronoi tessellation in d dimensions a voronoi vertex is the center of the sphere tangent to the d 1 nearest monomers an edge of the voronoi diagram is the shortest route between two neighboring vertices the edge is considered connected if a monomer can pass through and disconnected otherwise the voronoi construction is used to calculate the percolation threshold of the void space the most interesting result is that the polymer area fraction at the percolation threshold is a nonmonotonic function of n in two dimensions but monotonically reaches a constant value in three dimensions the crossover behavior of the percolation threshold is also observed in pseudo 3d the pore size distribution decreases monotonically with increasing pore size this is markedly different from that in configurations of hard disks monomeric fluid where the pore size distribution is peaked at finite size

an analysis of band limited communication systems from amplifier efficiency and distortion perspective considering growing concerns toward green communications not only their bandwidth efficiency but also their power consumption is expected to gain increasing importance for future communication systems a power amplifier pa is one of the most power consuming analog devices at the transmitter in communication systems and a precise estimation of the power consumption at the transmitter circuit requires the knowledge of its efficiency that depends on the distribution of input signal envelope and the amount of input back off in this paper we develop a simple analytical model that can be used for estimating achievable efficiency of a linear pa as well as the amount of resulting nonlinear distortion for a given modulated signal exclusively from its envelope distribution based on this model the trade off relationships between the efficiency and signal to distortion power ratio for several spectrally efficient linear modulations are examined it is also shown that in some special cases of gaussian input and memoryless nonlinearity pa models the results can be represented in simple closed form expressions

a novel trellis shaping design with both peak and average power reduction for ofdm systems a new trellis shaping design is proposed for reducing the peak to average power ratio of the bandlimited orthogonal frequency division multiplexing ofdm signals the approach is based on recursive minimization of the autocorrelation sidelobes of an ofdm data sequence a novel metric in conjunction with the viterbi algorithm is devised the performance of the trellis shaping depends on signal mapping strategy and the two types of mapping referred to as type i and type ii are proposed the type i mapping has no capability of reducing the average power but it can achieve a significant reduction of the peak to average power ratio on the other hand the type ii mapping is designed to achieve both peak and average power reduction the bit error probability of the system over an awgn channel is evaluated based on the simulations which confirms the effectiveness of the proposed scheme

papr problem for walsh systems and related problems high peak values of transmission signals in wireless communication systems lead to wasteful energy consumption and degradation of several transmission performances we continue the theoretical contributions made by boche and farell toward the understanding of peak value reduction using the strategy known as tone reservation for orthogonal transmission schemes there it was shown that for orthogonal frequency division multiplexing ofdm systems the combinatorial object called arithmetic progression plays an important role in setting limitations for the applicability of the tone reservation method in this paper we show that the combinatorial object introduced as perfect walsh sum pws plays a similar role for code division multiple access cdma systems as arithmetic progression for ofdm systems by specific construction we show that for a chosen numbers m and n all subsets mathcal i of the set n of the first n 2 n natural numbers which has the density in n larger than a given delta in 0 1 i e left mathcal i right n geq delta and which is sufficiently large enough in the sense that left i right geq 2 2 delta 2 m 1 contains a pws of size 2 m by means of this result and motivated by the previously mentioned connection between arithmetic progression and pws we show results for the pws which are analogous to the famous szemeredi theorem on arithmetic progressions conlon gower s theorem on probabilistic construction of sparse sets containing an arithmetic progression and even a solution of an analogon to the erd s conjecture on arithmetic progressions those results give in particular an insight into the asymptotic limitations of tone reservation method for the cdma systems besides we show that a subset i of n is a pws if and only if the embedding inequality of the subspace of l 1 0 1 containing linear combinations of walsh functions indexed by elements of mathcal i holds with the minimum possible embedding constant sqrt left mathcal i right the corresponding approach based in particular by the fact that the pwss are the only walsh sums having unit l 1 norm proven in this paper by means of that results we show that the minimum possible threshold constant for which the tone reservation method is applicable yields sqrt left mathcal i right if and only if the information set mathcal i is a pws

fast and robust delaunay tessellation in periodic domains an algorithm is presented for constructing three dimensional delaunay tessellations in periodic domains applications include mesh generation for periodic transport problems and geometric decomposition for modelling particulate structures the algorithm is a point insertion technique and although the general framework is similar to point insertion in a convex hull a number of new issues are introduced by periodicity these issues are discussed in detail in the context of the computational algorithm examples are given for the tessellation of random points and random sphere packings performance data for the algorithm are also presented these data show an empirical scaling of the computation time with size of o n1 11 and tessellation rates of 7000 14000 tetrahedrons per second for the problems studied up to 105 points a breakdown of the performance is given which shows the computational load is shared most heavily by two specific parts of the point insertion procedure copyright 2002 john wiley sons ltd

generation of tetrahedral mesh of variable element size by sphere packing over an unbounded 3d domain this paper describes an algorithm for the generation of tetrahedral mesh of specified element size over an unbounded three dimensional domain starting from an arbitrary point in space defined as the origin and guided by the concept of advancing front spheres of size compatible with the specified element size are packed tightly together one by one to form a cluster of spheres of different sizes the compactness of the cluster of spheres is achieved by packing spheres at a site closest to the origin in a densest manner with tangent but no overlapping with as many other spheres as possible in view of these criteria a rotational mechanism between spheres is innovated which allows the newly inserted sphere to follow the path by rotation between existing spheres until the lowest point is reached the centres of the packing spheres provide ideal locations for delaunay point insertion to form a triangulation of tetrahedral elements of size compatible with the specified value spheres of random size distribution or of size specified by a node spacing function are packed by the proposed algorithm in all test examples high quality tetrahedral elements of size consistent with the specified node spacing are generated the process is fast and robust and the time complexity for mesh generation is expected to be almost linear however in the present implementation a quasi linear time relationship is observed as a search for the nearest node on the front is proposed in the sphere packing process the memory requirement has been kept to a minimum as no additional data structure other than the adjacency relationship of the tetrahedral elements as required by the delaunay triangulation is stored the structure of the advancing frontal surface needs not be explicitly constructed nor updated as it is simply not required in the sphere packing process

error performance of generalised space shift keying for indoor visible light communications in this paper the error performance analysis of a low complexity multiple transmitter generalised space shift keying gssk signalling technique for short range indoor visible light communications is presented in an n t transmitter system this signalling technique is capable of achieving a spectral efficiency of n t bits s hz the gssk system has a higher spectral efficiency than the conventional on off keying ook and pulse position modulation ppm techniques the gssk transmitter is much simpler than that of an equivalent regular pulse amplitude modulation pam system with similar spectral efficiency an analytical expression for the symbol error rate ser is presented and verified using simulations the receiver is based on the maximum likelihood criterion and using multiple photodetectors pds in the receiver improves the error performance within the room and the transmitter receiver configuration under consideration with four pds a gain of 6 db is attainable over the single pd system for the case of 2 and 3 bits s hz considering a fixed link range with n t 2 and at a symbol error rate of 10 6 using wide half angle leds with 1 2 60 requires about 12 db less in electrical signal to noise ratio compared with 1 2 30 the beam directivity is however of much lower effect when the room under consideration is equiped with sufficient leds to provide full coverage the gssk technique can also support dimming control by using different pulse widths this however is at a price of reduced spectral efficiency

three dimensional unstructured mesh generation part 1 fundamental aspects of triangulation and point creation abstract the present paper introduces an alternative approach for delaunay triangulation in which the triangulation is mapped from an equivalent convex hull in a higher dimension furthermore some fundamental aspects of a point creation algorithm for unstructured mesh generation have been addressed based on numerical experiments a point spacing tensor and point insertion criterion have been introduced aiming to deal with anisotropic meshes

recursive clipping and filtering with bounded distortion for papr reduction repeated clipping and filtering rcf is a simple method for reducing the peak to average power ratio papr of the signal in the orthogonal frequency division modulation ofdm system we propose to modify rcf by limiting the distortion on each tone of the ofdm so that both low papr and low error can be achieved

an approach to refining three dimensional tetrahedral meshes based on delaunay transformations a technique for refining three dimensional tetrahedral meshes is proposed in this paper the proposed technique is capable of treating arbitrary unstructured tetrahedral meshes convex or non convex with multiple regions resulting in high quality constrained delaunay triangulations the tetrahedra generated are of high quality nearly equilateral sliver tetrahedra which present a real problem to many algorithms are not produced with the new method the key to the generation of high quality tetrahedra is the iterative application of a set of topological transformations based on the voronoi delaunay theory and a reposition of nodes technique the computational requirements of the proposed technique are in linear relationship with the number of nodes and tetrahedra making it ideal for direct employment in a fully automatic finite element analysis system for 3 d adaptive mesh refinement application to some test problems is presented to show the effectiveness and applicability of the new method

clipping noise in ofdm based optical wireless communication systems in this paper the impact of clipping noise on optical wireless communication owc systems employing orthogonal frequency division multiplexing ofdm is investigated the two existing optical ofdm o ofdm transmission schemes asymmetrically clipped optical ofdm aco ofdm and direct current biased optical ofdm dco ofdm are studied time domain signal clipping generally results from direct current dc biasing and or from physical limitations of the transmitter front end these include insufficient forward biasing and the maximum power driving limit of the emitter the clipping noise can be modeled according to the bussgang theorem and the central limit theorem clt as attenuation of the data carrying subcarriers at the receiver and addition of zero mean complex valued gaussian noise analytical expressions for the attenuation factor and the clipping noise variance are determined in closed form and employed in the derivation of the electrical signal to noise ratio snr the validity of the model is verified through a monte carlo bit error ratio ber simulation finally the ber performance of aco ofdm with dco ofdm is compared for different clipping levels and multi level quadrature amplitude modulation m qam schemes

analytical modeling of mimo ofdm system in the presence of nonlinear power amplifier with memory in this paper the effects of nonlinear high power amplifier hpa with memory on multi input multi output mimo orthogonal frequency division multiplexing ofdm system are analyzed and a theoretical framework is proposed the memory effects are represented by generalized memory polynomial gmp model moreover we derive an analytical formulation with infinite nonlinearity order and infinite memory length the channel is assumed mimo frequency selective and it is modeled as a linear dispersive channel with uniform power profile we show that the decision variables of the nonlinearity distortion can be modeled by the complex attenuation and zero mean additive noise model the analytical expressions for complex attenuation mean and variance of nonlinear noise are derived and ser of mimo ofdm system using hpa with memory is presented excellent agreement between the analytical results and numerical simulations is observed that verifies the accuracy and efficiency of the proposed method

on the accuracy of the gaussian approximation for the evaluation of nonlinear effects in ofdm signals the almost gaussian nature of ofdm orthogonal frequency division multiplexing signals with high number of subcarriers n is widely employed to characterize nonlinearly distorted ofdm signals and to evaluate the corresponding performance in this paper we study the accuracy of the gaussian approach when evaluating nonlinear effects in ofdm signals with finite number of subcarriers showing the strengths and limitations of this approach it is shown that the decomposition in useful and self interference components is valid even for a reduced number of subcarriers the gaussian approximation of the nonlinear self interference at the subcarrier level is very accurate provided that n2 is high however the nonlinear distortion levels slightly lower than the ones obtained with the gaussian approximation with relative errors dropping with 1 n leading to somewhat pessimistic sir levels signal to interference ratio

reed solomon and simplex codes for peak to average power ratio reduction in ofdm new schemes for peak to average power ratio reduction in orthogonal frequency division multiplexing ofdm systems are proposed reed solomon rs and simplex codes are employed to create a number of candidates from which the best are selected thereby in contrast to existing approaches the codes are arranged over a number of ofdm frames rather than over the carriers hence a combination of the principles of multiple signal representation with selection as done in selected mapping and the use of channel coding is present in particular in multiple antenna transmission the proposed schemes do not cause any additional delay but due to the utilization of the dimension space additional gains can be achieved moreover the schemes are very flexible due to the selection step any criterion of optimality can be taken into account besides multiple antenna transmission packet transmission is briefly considered which moreover covers the appealing similarities with incremental redundancy check schemes in automatic repeat request arq applications and with decoding of codes transmitted over the erasure channel the performance of the schemes is using some approximations derived analytically and is covered by numerical results that are in very good agreement with the theory significant gains can be achieved with these very flexible and versatile methods

frequency independent and frequency dependent nonlinear models of twt amplifiers simple two parameter formulas are presented for the functions involved in the amplitude phase and the quadrature nonlinear models of a twt amplifier and are shown to fit measured data very well also a closed form expression is derived for the output signal of a twt amplifier excited by two phase modulated carriers and an expression containing a single integral is given when more than two such earriers are involved finally a frequencydependent quadrature model is proposed whose parameters are obtainable from single tone measurements

generalized bounds on the crest factor distribution of ofdm signals with applications to code design in this paper generalized bounds on the crest factor cf distribution in orthogonal frequency division multiplexing ofdm transmission for both independent and dependent subcarriers are derived here the latter situation represents the coded case for independent subcarriers a general path for bounding practical constellations is provided moreover a complete characterization of their asymptotic behavior is devised and discussed the results are shown to carry over to the spherical constellations improving on recent results for dependent subcarriers the focus is mainly on binary codes where bounds on the cf distribution are obtained in terms of the distance distributions and their duals the asymptotic behavior of codes is analyzed and it is shown that the upper bound on the effective crest factor of a large class of bose chaudhuri hocquenghem bch codes behaves asymptotically as radiclogn finally two applications of the results to code design are presented first fixed phase shifts on the subcarriers for all codewords are used and an algorithm to calculate the phase shifts is designed that way it is proved that the effective cf of any binary code can be scaled to be of order radiclogn for large n without sacrificing on rate furthermore the same approach is applied to calculation of the phases of redundant subcarriers for each codeword it is shown by simulations that the values can be effectively chosen so that the cf is significantly reduced with nonexponential complexity

optimization of sndr for amplitude limited nonlinearities many components used in communication systems are nonlinear and have a peak power or peak amplitude constraint nonlinearity generates distortions and thus signal to noise and distortion ratio sndr is an appropriate performance measure in this paper we are interested in finding the nonlinear mapping that maximizes the sndr subject to the peak amplitude constraint the answer is a soft limiter with gain calculated based on the noise power and the probability density function of the input amplitude we also investigate a bounding relationship between the sndr and capacity of the nonlinear channel the results of this paper can be applied for efficient transmission of high peak to average power ratio signals or for optimal linearization of nonlinear devices

robust blind learning algorithm for nonlinear equalization using input decision information in this paper we propose a new blind learning algorithm namely the benveniste goursat input output decision bg iod to enhance the convergence performance of neural network based equalizers for nonlinear channel equalization in contrast to conventional blind learning algorithms where only the output of the equalizer is employed for updating system parameters the bg iod exploits a new type of extra information the input decision information obtained from the input of the equalizer to mitigate the influence of the nonlinear equalizer structure on parameters learning thereby leading to improved convergence performance we prove that with the input decision information a desirable convergence capability that the output symbol error rate ser is always less than the input ser if the input ser is below a threshold can be achieved then the bg soft switching technique is employed to combine the merits of both input and output decision information where the former is used to guarantee ser convergence and the latter is to improve ser performance simulation results show that the proposed algorithm outperforms conventional blind learning algorithms such as stochastic quadratic distance and dual mode constant modulus algorithm in terms of both convergence performance and ser performance for nonlinear equalization

constant envelope ofdm this paper describes a transformation technique aimed at solving the peak to average power ratio papr problem associated with ofdm orthogonal frequency division multiplexing constant envelope ofdm ce ofdm transforms the ofdm signal by way of phase modulation to a signal designed for efficient power amplification at the receiver the inverse transformation phase demodulation is applied prior to the conventional ofdm demodulator the performance of ce ofdm is analyzed in additive white gaussian noise awgn and fading channels ce ofdm is shown to achieve good performance in dense multipath with the use of cyclic prefix transmission in conjunction with a frequency domain equalizer fde by way of computer simulation and hardware realization ce ofdm is shown to compare favorably to conventional ofdm

inclusion of microscopic rotation of powder particles during compaction in finite element method using cosserat continuum theory the effect of microscopic rotation of powder particles in compaction is included in the rigid plastic finite element method on the basis of the cosserat continuum theory in the cosserat continuum theory couple stress induced from the microscopic rotation is introduced and the equilibrium equations of moment for the couple stress are solved simultaneously with those of force a yield criterion for the cosserat porous continuum is proposed by taking the effect of the couple stress into consideration and constitutive equations for the rigid plastic porous material are derived from the yield criterion on the basis of the associated flow rule the equilibrium equations of force and moment for the cosserat continuum are formulated by the use of the galerkin method the effect of microscopic rotation of powder particles in plane strain closed die compaction is examined in addition the calculated result is compared with that for the conventional continuum without the microscopic rotation 1998 john wiley sons ltd

performance analysis of deliberately clipped ofdm signals we analyze the performance of the clipped orthogonal frequency division multiplexing ofdm system in terms of peak power reduction capability and degradation of channel capacity the clipping is performed on the baseband ofdm signals with and without oversampling followed by the ideal low pass filter first the effect of the envelope clipping on the peak to average power ratio papr and the instantaneous power of the band limited ofdm signal is studied we then discuss the channel capacity of the oversampled and clipped ofdm signals over the additive white gaussian noise and ideally interleaved rayleigh fading channels the capacity is calculated based on the assumption that the distortion terms caused by the clipping are gaussian it is shown that the snr penalty due to the clipping can be considerably alleviated by using optimal coding and reducing the information data rate the results are justified by the simulation results using near optimal turbo codes

anisotropic centroidal voronoi tessellations and their applications in this paper we introduce a novel definition of the anisotropic centroidal voronoi tessellation acvt corresponding to a given riemann metric tensor a directional distance function is used in the definition to simplify the computation we provide algorithms to approximate the acvt using the lloyd iteration and the construction of anisotropic delaunay triangulation under the given riemannian metric the acvt is applied to the optimization of two dimensional anisotropic delaunay triangulation to the generation of surface cvt and high quality triangular mesh on general surfaces various numerical examples demonstrating the effectiveness of the proposed method are presented

channel coding with multilevel phase signals a coding technique is described which improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth this is achieved by channel coding with expanded sets of multilevel phase signals in a manner which increases free euclidean distance soft maximum likelihood ml decoding using the viterbi algorithm is assumed following a discussion of channel capacity simple hand designed trellis codes are presented for 8 phase shift keying psk and 16 quadrature amplitude shift keying qask modulation these simple codes achieve coding gains in the order of 3 4 db it is then shown that the codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals which we call mapping by set partitioning based on a new distance measure between binary code sequences which efficiently lower bounds the euclidean distance between the corresponding channel signal sequences a search procedure for more powerful codes is developed codes with coding gains up to 6 db are obtained for a variety of multilevel phase modulation schemes simulation results are presented and an example of carrier phase tracking is discussed

the advancing front mesh generation method revisited this paper presents a mesh generation method of the advancing front type which is designed in such a way that the well known difficulties of the classical advancing front method are not present the retained solution consists of using the first steps of a voronoi delaunay method to construct a background mesh which is then used to govern the algorithm the two dimensional case is considered in detail and possible extensions to adaption problems and three dimensions are indicated

tetrahedral mesh generation in convex primitives this paper presents a method for generating tetrahedral meshes in three dimensional primitives given a set of closed and convex polyhedra having non zero volume and some mesh controlling parameters the polyhedra are automatically split to tetrahedra satisfying the criteria of standard finite element meshes the algorithm tries to generate elements close to regular tetrahedra by maximizing locally the minimum solid angles associated to a set of a few neighbouring tetrahedra the input parameters define the size of the tetrahedra and they can be used to increase or decrease the discretization locally all the new nodes which are not needed to describe the geometry are generated automatically

equivalence of the void percolation problem for overlapping spheres and a network problem the percolation problem for the complement of the union of randomly located overlapping spheres is shown to be equivalent to a bond percolation problem on the edges of the voronoi tesselation of the sphere centres this result provides a convenient definition of cluster size and therefore of the critical exponents for this problem it also provides an efficient algorithm for monte carlo computation of the percolation threshold and the critical exponents

performance analysis for ofdm signals with peak cancellation peak cancellation pc is known as one of the simplest peak to average power ratio papr reduction techniques that are applicable to various communications standards the salient advantage of pc is its ease of hardware implementation but it induces in band distortion and out of band radiation in order to restrict the amount of distortion within an acceptable level it is critical to carefully design the cancelling pulses as well as the envelope threshold over which pc is applied in most studies however they are determined empirically through computer simulations this paper thus focuses on a rigorous theoretical analysis of pc applied to band limited orthogonal frequency division multiplexing ofdm signals and discusses its validity and limitation for practical applications based on the level crossing rate approximation of the peak distribution we derive a closed form expression for the achievable signal to distortion power ratio sdr we also analyze the adjacent channel leakage ratio aclr as well as error vector magnitude evm with which the symbol error rate ser over an additive white gaussian noise awgn channel is obtained all the theoretical results developed in this work are compared with those based on the corresponding computer simulations to justify our analytical approach it thus serves as a useful and accurate tool for designing cancelling pulses as well as the threshold level for given specific system requirements such as sdr or evm and aclr

integer based constellation shaping method for papr reduction in ofdm systems in this paper the problem of reducing the peak to average power ratio papr in an orthogonal frequency division multiplexing system is considered we design a cubic constellation called the hadamard constellation whose boundary is along the bases defined by the hadamard matrix in the transform domain then we further reduce the papr by applying the selective mapping technique the encoding method following the method introduced in the work of kwok is derived from a decomposition known as the smith normal form this new technique offers a papr that is significantly lower than those of the best known techniques without any loss in terms of energy and or spectral efficiency and without any side information being transmitted moreover it has a low computational complexity

fast delaunay triangulation in three dimensions abstract an efficient algorithm for delaunay triangulation of a given set of points in three dimensions based on the point insertion technique is presented various steps of the triangulation algorithm are reviewed and many acceleration procedures are devised to speed up the triangulation process new features include the search of a neighbouring point by the layering scheme locating the containing tetrahedron by random walk formulas of important geometrical quantities of a new tetrahedron based on those of an existing one a novel approach in establishing the adjacency relationship the use of adjacency table and the management of memory the resulting scheme is one of the fastest triangulation algorithms known to the authors which is able to generate tetrahedra generation rate of 15 000 tetrahedra per second for randomly generated points on a hp 735 machine

geometry based fully automatic mesh generation and the delaunay triangulation one approach to fully automatic mesh generation in two and three dimensions is to generate and triangulate a set of points within and on the boundary of a geometry using the properties of the delaunay triangulation because the point data generate mesh topology of greater dimension it is necessary to insure topological compatibility and perform classification of the resulting mesh with respect to the original geometry necessary and sufficient conditions for classification of mesh topology on three dimensional planar geometry are given as well as a discussion of the more complex case of curved geometry this paper also presents conditions to insure topological compatibility along with techniques for identifying and resolving cases of incompatibility

statistical geometry of particle packings i algorithm for exact determination of connectivity volume and surface areas of void space in monodisperse and polydisperse sphere packings packings of spheres serve as useful models of the geometry of many physical systems in particular the description of the void region in such packings the region not occupied by the spheres is crucial in many studies the void region is in general composed of disconnected cavities we present an algorithm for decomposing void space into cavities and determining the exact volumes and surface areas of such cavities in three dimensional packings of monodisperse and polydisperse spheres

a finite volume method for approximating 3d diffusion operators on general meshes a finite volume method is presented for discretizing 3d diffusion operators with variable full tensor coefficients this method handles anisotropic non symmetric or discontinuous variable tensor coefficients while distorted non matching or non convex n faced polyhedron meshes can be used for meshes of polyhedra whose faces have not more than four edges the associated matrix is positive definite and symmetric if the diffusion tensor is symmetric a second order resp first order accuracy is numerically observed for the solution resp gradient of the solution

an analytical approach to the calculation of evm in clipped multi carrier signals error vector magnitude evm is an important figure of merit in many communication systems in this work an analytical approach to the calculation of evm in clipped multi carrier signals is proposed in contrast to previous work the evm in this work is calculated with no simplifying model e g a gaussian assumption the expression is given in a form of a power series based on the derived expressions for evm bounds on the maximal achievable rate are derived

a finite volume method for the approximation of maxwell s equations in two space dimensions on arbitrary meshes a new finite volume method is presented for discretizing the two dimensional maxwell equations this method may be seen as an extension of the covolume type methods to arbitrary possibly non conforming or even non convex n sided polygonal meshes thanks to an appropriate choice of degrees of freedom an equivalent formulation of the scheme is given in terms of discrete differential operators obeying discrete duality principles the main properties of the scheme are its energy conservation its stability under a cfl like condition and the fact that it preserves gauss law and divergence free magnetic fields second order convergence is demonstrated numerically on non conforming and distorted meshes

delaunay triangulation of non convex planar domains this paper investigates the possibility of integrating the two currently most popular mesh generation techniques namely the method of advancing front and the delaunay triangulation algorithm the merits of the resulting scheme are its simplicity efficiency and versatility with the introduction of non delaunay line segments the concept of using delaunay triangulation as a means of mesh generation is clarified an efficient algorithm is proposed for the construction of delaunay triangulations over non convex planar domains interior nodes are first generated within the planar domain these interior nodes and the boundary nodes are then linked up together to produce a valid triangulation in the mesh generation process the delaunay property of each triangle is ensured by selecting a node having the smallest associated circumcircle in contrast to convex domains intersection between the proposed triangle and the domain boundary has to be checked this can be simply done by considering only the non delaunay segments on the generation front through the study of numerous examples of various characteristics it is found that high quality triangular element meshes are obtained by the proposed algorithm and the mesh generation time bears a linear relationship with the number of elements nodes of the triangulation

generalization of voronoi diagrams in the plane in this paper we study the voronoi diagram for a set of n line segments and circles in the euclidean plane the diagram is a generalization of the voronoi diagram for a set of points in the plane and has applications in wire layout facility location clustering and contouring problems we present an o n log n 2 algorithm for constructing the diagram it is an improvement of a previous known result which takes o nc sqrt log n time the algorithm described in this paper is also shown to be applicable under a more general metric if certain conditions are satisfied

superposition coded modulation with peak power limitation we apply clipping to superposition coded modulation scm systems to reduce the peak to average power ratio papr of the transmitted signal the impact on performance is investigated by evaluating the mutual information driven by the induced peak power limited input signals it is shown that the rate loss is marginal for moderate clipping thresholds if optimal encoding decoding is used this fact is confirmed in examples where capacity approaching component codes are used together with the maximum a posteriori probability map detection in order to reduce the detection complexity of scm with a large number of layers we develop a suboptimal soft compensation sc method that is combined with soft input soft output siso decoding algorithms in an iterative manner a variety of simulation results for additive white gaussian noise awgn and fading channels are presented it is shown that with the proposed method the effect of clipping can be efficiently compensated and a good tradeoff between papr and bit error rate ber can be achieved comparisons with other coded modulation schemes demonstrate that scm offers significant advantages for high rate transmissions over fading channels

the role of am to pm conversion in memoryless nonlinear systems a generalized proof is presented that am to pm conversion can only degrade never improve the intermodulation noise performance of memoryless nonlinear systems with random input signals having even probability density functions and a measure of degradation is defined it is also shown for such signals that am to pm conversion causes a deterministic constant phase shift to be added to the argument of the signal component at the output but has no other effect on its phase this class of inputs includes one or the sum of several psk signals as well as large ensembles that can be modeled as gaussian noise the latter are dealt with by using bussgang s theorem on input output cross correlation in the proof bussgang s theorem is extended to the complex case to include phase as well as amplitude nonlinearities yielding a complex version of the theorem for gaussian inputs it is shown that the undistorted signal and the intermodulation noise at the output of such systems are uncorrelated

a combined octree delaunay method for fully automatic 3 d mesh generation fully automatic three dimensional mesh generation is a fundamental requirement for automating the numerical solution of partial differential equations two techniques in particular the octree and delaunay approaches have been used towards this end a method that combines both approaches to fully automatic mesh generation is presented here the resulting algorithm provides the linear growth rate and divide and conquer approach of the octree method with the simplicity and optimal properties of the delaunay triangulation

adaptivity techniques for compressible inviscid flows abstract to enhance the resolution of numerically simulated flowfields grid adaptivity is vitally important further to afford complete flexibility in the spatial discretisation of the flow domain both structured unstructured and combinations of grid types are likely to be required hence the development of grid adaptivity techniques for general grids is important this paper discusses adaptivity achieved through point enrichment point derefinement and point movement applied on general grids a flexible data structure is described together with suitable strategies for adaptively refining a computational grid applications are presented of adaptive grid refinement for two dimensional compressible flow simulation

optimal delaunay point insertion summary an efficient algorithm for delaunay triangulation of a given set of points in d dimensions is presented various steps of the point insertion algorithm are reviewed and many acceleration procedures are implemented to speed up the triangulation process new features include the search for a neighbouring point by a layering scheme locating the containing simplex by a random walk formulas of important geometrical quantities of a new simplex based on those of an old one a novel approach in establishing the adjacency relationship using connection matrices the resulting scheme seems to be one of the fastest triangulation algorithms known which enables us to generate tetrahedra in r3 with a linear generation rate of 15 ooo tetrahedra per second for randomly generated points on an hp 735 workstation

boundary recovery for three dimensional conforming delaunay triangulation we present an efficient boundary recovery method for conforming delaunay triangulation of three dimensional domains our method combines local transformations like edges faces swappings and modified constrained delaunay refinement like edges faces splittings to recover the missing boundary edges and faces its convergence is theoretically proved its effectiveness is also demonstrated through some meshing examples

3d delaunay mesh generation coupled with an advancing front approach abstract this paper describes a fully automatic mesh generation method suitable for domains of any shape in r 3 initially a so called boundary mesh is generated wherein internal points are created using advancing front point placement and inserted using a delaunay method the algorithm combines the advantages of efficiency and nice mathematical properties of a delaunay approach with advancing front high quality point placement strategy several three dimensional examples are presented to demonstrate the overall efficiency and the relevance of the combined procedure the present method can be extended to isotropic or anisotropic adaptive mesh generation

uniform line fillings deterministic fabrication of random metamaterials requires filling of a space with randomly oriented and randomly positioned chords with an on average homogenous density and orientation which is a nontrivial task we describe a method to generate fillings with such chords lines that run from edge to edge of the space in any dimension we prove that the method leads to random but on average homogeneous and rotationally invariant fillings of circles balls and arbitrary dimensional hyperballs from which other shapes such as rectangles and cuboids can be cut we briefly sketch the historic context of bertrand s paradox and jaynes s solution by the principle of maximum ignorance we analyze the statistical properties of the produced fillings mapping out the density profile and the line length distribution and comparing them to analytic expressions we study the characteristic dimensions of the space between the chords by determining the largest enclosed circles and balls in this pore space finding a lognormal distribution of the pore sizes we apply the algorithm to the direct laser writing fabrication design of optical multiple scattering samples as three dimensional cubes of random but homogeneously positioned and oriented chords

a theoretical characterization of nonlinear distortion effects in ofdm systems this paper presents a theoretical characterization of nonlinear distortion effects in orthogonal frequency division multiplexing ofdm transmission systems in the theoretical framework developed it is shown that the effects on the decision variables of the in band distortion introduced by a bandpass memoryless nonlinearity can be described by means of a complex gain and an additive gaussian term with zero mean and suitable variance analytical expressions for gain and variance are given the conditions which allow this description are emphasized and discussed as a consequence a completely analytical procedure to evaluate error probability is also obtained and illustrated using ofdm discrete multitone modulation dmt systems with rectangular pulse shaping for the soft envelope limiter nonlinearity a closed form is derived a comparison with simulation results is carried out to verify the accuracy of this method

on error estimates and adaptivity in elastoplastic solids applications to the numerical simulation of strain localization in classical and cosserat continua the a posteriori error estimates based on the post processing approach are introduced for elastoplastic solids the standard energy norm error estimate established for linear elliptic problems is generalized here to account for the presence of internal variables through the norm associated with the complementary free energy this is known to represent a natural metric for the class of elastoplastic problems of evolution in addition the intrinsic dissipation functional is utilized as a basis for a complementary a posteriori error estimates a posteriori error estimates and adaptive refinement techniques are applied to the finite element analysis of a strain localization problem as a model problem the constitutive equations describing a generalization of standard j2 elastoplasticity within the cosserat continuum are used to overcome serious limitations exhibited by classical continuum models in the post instability region the proposed a posteriori error estimates are appropriately modified to account for the cosserat continuum model and linked with adaptive techniques in order to simulate strain localization problems superior behaviour of the cosserat continuum model in comparison to the classical continuum model is demonstrated through the finite element simulation of the localization in a plane strain tensile test for an elastopiastic softening material resulting in convergent solutions with an h refinement and almost uniform error distribution in all considered error norms

mimo ofdm with nonlinear power amplifiers the influence of nonlinear power amplifiers pas on the performance of multiple input multiple output mimo orthogonal frequency division multiplexing ofdm systems is investigated a full mimo scheme with transmitters tx precoding and receivers rx decoding is considered it is shown under assumption of high order ofdm and frequency selective channel that the ratio between the useful signal and the nonlinear distortions is proportional to the number of tx antennas i e the influence of the nonlinear distortions decreases as the number of tx antennas increases the distortion reduction factor drf is proposed as a performance metric for mimo ofdm systems with nonlinear pas a general formula for signal to distortion and noise ratio is obtained for the nonlinear pa with memory described by the wiener hammerstein wh model special cases of mimo such as maximum ratio transmission mrt and maximum ratio combining mrc are considered a full agreement between the theoretical and simulation results is obtained the main contribution of this paper is in a statement that tx processing reduces the effect of nonlinear distortions this is obtained by novel approach for analysis of the mimo ofdm systems with nonlinear pas with memory

compressible flowfield solutions with unstructured grids generated by delaunay triangulation a method is described that constructs three dimensional unstructured tetrahedral meshes using the delaunay triangulation criterion the approach includes an automatic point creation technique and ensures that given an initial surface triangulation which bounds a domain a valid boundary conforming assembly of tetrahedra is produced the efficiency of the proposed procedure reduces the computer time for the generation of realistic unstructured tetrahedral grids to the order of minutes on workstations of modest computational capabilities the grids generated are used with two finite element algorithms to simulate inviscid transonic compressible flows flow solutions for aerospace configurations are presented and computed results compared with experimental data

single symbol ml decoding for orthogonal and quasi orthogonal stbc in clipped mimo ofdm systems using a clipping noise model with gaussian approximation an efficient way to reduce the peak to average power ratio papr in ofdm systems is clipping after the clipping in an mimo ofdm system the additive noise may not be white in this paper we develop fast single symbol ml decoding algorithms for orthogonal space time block codes ostbc and linearly transformed quasi orthogonal space time block codes qostbc in clipped mimo ofdm systems by using a clipping noise model with gaussian approximation by using the statistics of the clipping distortions our newly developed fast ml decoding algorithms improve the performance for clipped mimo ofdm systems with ostbc and qostbc while the decoding complexities are not increased simulation results are presented to illustrate the improvement

efficient three dimensional delaunay triangulation with automatic point creation and imposed boundary constraints a method is described which constructs three dimensional unstructured tetrahedral meshes using the delaunay triangulation criterion several automatic point creation techniques will be highlighted and an algorithm will be presented which can ensure that given an initial surface triangulation which bounds a domain a valid boundary conforming assembly of tetrahedra will be produced statistics of measures of grid quality are presented for several grids the efficiency of the proposed procedure reduces the computer time for the generation of realistic unstructured tetrahedral grids to the order of minutes on workstations of modest computational capabilities

on the optimum multicarrier performance with memoryless nonlinearities it is widely recognized that orthogonal frequency division multiplexing ofdm signals are very prone to nonlinear distortion effects which can lead to significant performance degradation however recent results have showed that nonlinear distortion effects do not necessarily mean performance degradation and can actually lead to performance improvements relative to conventional linear ofdm schemes in this paper we consider the effects of bandpass memoryless nonlinear devices on ofdm signals and study the optimum asymptotic performance for both nondispersive channels and severely time dispersive channels we present analytical methods for obtaining the euclidean distance between two ofdm signals that are subjected to different nonlinear characteristics these results are then employed for obtaining the average asymptotic gain relative to conventional linear ofdm schemes in nondispersive channels and the gain distribution for severely time dispersive channels with rayleigh distributed fading on the different multipath components our analytical results which are shown to be very accurate indicate that the optimum detection of ofdm schemes with strong nonlinear distortion effects allows significant gains when compared with conventional linear ofdm schemes

analysis and power diversity based cancellation of nonlinear distortions in ofdm systems one of the main drawbacks of orthogonal frequency division multiplexing ofdm systems is the high peak to average power ratio papr of the transmitted signals which can cause the introduction of intercarrier interference ici due to the presence of nonlinear power amplifiers pas in this paper a theoretical analysis of the ici in nonlinear ofdm systems with polynomial pas is made contrary to other works this analysis provides an exact description of the nonlinear ici moreover three receivers for channel estimation and ici cancellation in ofdm systems with polynomial pas are proposed based on the concept of power diversity that consists in retransmitting the information symbols several times with a different transmission power each time the transmission powers that minimize the sum of the residual mean square errors mses provided by the proposed receivers are derived in the case of a third degree polynomial pa an important advantage of the proposed receivers is that the optimal transmission powers do not depend on the channel and the pa coefficients

three dimensional unstructured mesh generation part 3 volume meshes abstract volume meshes are generated through three dimensional triangulation and interior point creation based on the surface meshes to deal with non convex geometries boundary surface conformity is gained via edge swapping boundary edge and surface recovery and the robustness of the algorithm has been discussed in terms of the accuracy of geometric judgements the performane of the mesh generator has been investigated by means of numerical experiments and examples have been tested to validate the mesh generator the possibility of extension of this mesh generator to incorporate with analysis programs in terms of adaptive analysis has been explored this paper is also designed to briefly address mesh quality measures quality statistics and mesh smoothing techniques using mesh quality metrics visual quality assessment has been discussed furthermore several general ways of visual representation of volume meshes have been introduced

nonlinear distortion noise and linear attenuation in mimo systems theory and application to multiband transmitters nonlinear static multiple input multiple output mimo systems are analyzed the matrix formulation of bussgang s theorem for complex gaussian signals is rederived and put in the context of the multivariate cumulant series expansion the attenuation matrix is a function of the input signals covariance and the covariance of the input and output signals the covariance of the distortion noise is in addition a function of the output signal s covariance the effect of the observation bandwidth is discussed models of concurrent multiband transmitters are analyzed for a transmitter with dual non contiguous bands expressions for the normalized mean square error nmse vs input signal power are derived for uncorrelated partially correlated and correlated input signals a transmitter with arbitrary number of non contiguous bands is analysed for correlated and uncorrelated signals in an example the nmse is higher when the input signals are correlated than when they are uncorrelated for the same input signal power and it increases with the number of frequency bands a concurrent dual band amplifier with contiguous bands is analyzed in this case the nmse depends on the bandwidth of the aggregated signal

a class of nonlinear signal processing schemes for bandwidth efficient ofdm transmission with low envelope fluctuation this work presents a wide class of digital signal processing schemes for orthogonal frequency division multiplexing ofdm transmission which combine a nonlinear operation in the time domain and a linear filtering operation in the frequency domain the ultimate goal of these schemes is to reduce the envelope fluctuation of ordinary ofdm while keeping its high spectral efficiency and allowing a low cost power efficient implementation an appropriate statistical model concerning the transmitted frequency domain blocks is developed which is derived from well established results on gaussian stochastic processes distorted by memoryless nonlinearities this model can be employed for performance evaluation by analytical means with highly accurate results whenever the corresponding conventional ofdm signals exhibit quasi gaussian characteristics cases where the signal processing scheme is repeatedly used in an iterative way are treated through an extension of the proposed statistical modeling a set of numerical results is presented and discussed so as to show the practical interest of both the proposed schemes and the analytical methods for evaluation of their performance for the sake of comparisons this paper includes numerical results concerning the partial transmit sequence technique which is an alternative peak to mean envelope power ratio reducing technique of higher complexity often recommended due to its distortionless nature the superior performance complexity tradeoffs through the proposed class of nonlinear signal processing schemes is emphasized

iterative cancellation of non linear distortion noise in digital communication systems in this paper an iterative receiver that performs non linear distortion noise cancellation is presented the performance is assessed for time division multiple access tdma orthogonal frequency division multiple access ofdma and single carrier frequency division multiple access sc fdma waveforms even though a return link setup is considered the receiver is equally applicable in the forward link taking into account the differences in the data multiplexing and the channel analytical modeling of the received electrical signal to noise ratio snr is carried out for ofdma with one iteration of non linear distortion noise cancellation the performance is assessed in terms of power efficiency and spectral efficiency where the total degradation td of the received snr in a non linear channel is minimized the modulation formats of the dvb rcs2 satellite return link standard and a respective non linear channel have been used ofdma shows the highest power efficiency gain of 1 1 2 5 db with 2 iterations of non linear noise cancellation across the different modulation orders in sc fdma the gain is in the range of 0 3 1 1 db while gains of 0 1 0 8 db and 0 2 1 9 db are presented in tdma with 20 roll off and 5 roll off respectively

a new algorithm for three dimensional voronoi tessellation abstract a new efficient algorithm for computing the voronoi tessellation in three dimensions is presented the voronoi tessellation is obtained by constructing delaunay tetrahedra the complete set of these tetrahedra corresponds to that of a single voronoi polyhedron

delaunay s mesh of a convex polyhedron in dimension d application to arbitrary polyhedra this paper presents a method for creating a delaunay triangulation connected to a set of specified points the theoretical aspect is recalled for an arbitrary dimension and the method is discussed in order to derive a practical approach valid for dimensions 2 and 3 which is simple robust and well adapted to computation convex polyhedral and arbitrary polyhedral situations are introduced