m psk and m qam ber computation using signal space concepts in this paper we introduce a simple geometric approach that is based on signal space concepts to efficiently evaluate the performance of m ary phase shift keying m psk and m ary quadrature amplitude modulation m qam schemes over an additive white gaussian noise channel in particular new bit error rate approximations are derived and shown to be in excellent agreement with monte carlo simulation results

cancellation and direct summands in dimension 1 abstract let be a module finite algebra over a commutative noetherian ring of krull dimension 1 we extend roiter s direct summand theorem to arbitrary finitely generated modules obtaining a sharpened form of serre s direct summand theorem in this setting we also extend drozd s cancellation theorem to arbitrary finitely generated modules obtaining a sharpened form of bass s cancellation theorem in this setting a corollary is that over commutative reduced noetherian rings of dimension 1 direct sum cancellation holds in every genus of finitely generated modules this becomes false if the ring has nilpotent elements another corollary is that if direct sum cancellation holds in the genera of modules m and n then it holds in the genus of m n this seems to be new even for the modules that occur in integral representation theory the main thrust of this paper is to close the gap between integral representation theory and the rest of module theory by eliminating hypotheses concerning the existence of maximal orders of finite normalization in the commutative case and allowing our rings to have nilpotent ideals

on the general ber expression of one and two dimensional amplitude modulations quadrature amplitude modulation qam is an attractive technique to achieve high rate transmission without increasing the bandwidth a great deal of attention has been devoted to the study of bit error rate ber performance of qam and approximate expressions for the bit error probability of qam have been developed in many places in the literature however the exact and general ber expression of qam with an arbitrary constellation size has not been derived yet we provide an exact and general closed form expression of the ber for one dimensional and two dimensional amplitude modulations i e pam and qam under an additive white gaussian noise awgn channel when gray code bit mapping is employed the provided ber expressions offer a convenient way to evaluate the performance of pam and qam systems for various cases of practical interest moreover simple approximations can be found from our expressions which are the same as the well known approximations if only the dominant terms are considered

on the accuracy of gaussian approximations in the error analysis of ds cdma with oqpsk modulation this paper considers the bit error probability analysis of direct sequence code division multiple access with offset quadrature phase shift keying oqpsk modulation and random signature sequences a statistical characterization of the decision variable at the output of the correlation receiver is obtained and several techniques for evaluating the error performance previously derived for binary phase shift keying bpsk modulated systems are then extended to the case of oqpsk this includes exact bit error evaluation as well as various approximation methods based on gaussian modeling of the multiple access interference terms these techniques known as the standard and improved gaussian approximations have increasing complexity depending on the level of accuracy required for bpsk the standard approximation is typically found to be inaccurate unless the number of users becomes large and only the improved approximation yields sufficient accuracy in general but for the case of oqpsk the relative performance comparison developed in this paper shows that for all practical purposes the simple standard approximation is surprisingly very accurate even with a small number of users

a fast encoding method for lattice codes and quantizers in an earlier paper the authors described a very fast method which for the root lattices a n d n e n their duals and certain other lattices finds the closest lattice point to an arbitrary point of the underlying space if the lattices are used as codes for a gaussian channel the algorithm provides a fast decoding procedure or if they are used as vector quantizers the algorithm performs the analog to digital conversion efficiently the present paper offers a solution to the inverse problem for the same lattices the encoding problem for channel codes or the digital to analog part of quantizing namely given an integer k to find the kth code vector and to the closely related problem of finding the index k of a given code vector

exact image theory for the sommerfeld half space problem part iii general formulation the general sommerfeld problem with both epsilon and mu discontinuous and a source consisting of arbitrarily oriented electric and or magnetic dipoles at the same location is considered in terms of image theory the problem is formulated with electric and magnetic fields instead of potential quantities resulting in a vector transmission line interpretation of the fourier transformed problem the image sources are seen to be located in complex space expressable in terms of a certain basic image current function which was encountered in part ii of this paper on the vertical electric dipole problem the horizontal electric magnetic dipole image is solved and found to consist of both vertical and horizontal current components the image concept is generalized to the most general three dimensional sources as a check the well known reflection coefficient method is obtained as the far field approximation of the present theory

asymptotical performance of m ary and binary signals over multipath multichannel rayleigh and rician fading this paper presents a general framework for computing the asymptotic error probability i e at high average snrs of m ary and binary signaling schemes over rician and rayleigh fading diversity channels a general theorem theorem 1 relates the asymptotic error rate of multipath and multichannel receivers over awgn isi free channels to the multidimensional integral of the conditional error probability two other theorems are presented for the particular cases where the conditional error probability is a function of the sum of received snrs theorem 2 or received amplitudes theorem 3 theorems 2 and 3 are related for linear coherent systems and closed form expressions are obtained for equal gain combining systems detection structures for typical diversity schemes coherent noncoherent maximal ratio and equal gain combining and quadratic noncoherent combining are considered we analyze the asymptotic error rates of some m ary signaling schemes mpsk mpam with kth order diversity and orthogonal signals with k 1 and with coherent and noncoherent detection binary signaling is also considered in our study

a technique for approximating the location of surface and leaky wave poles for a lossy dielectric slab an approximation technique for locating the surface and leaky wave poles for a lossy dielectric slab is presented the problem is reduced to the simultaneous solution of two transcendental equations for each of the perfect magnetic conductor pmc and perfect electric conductor pec cases which is shown to yield a simple approximate solution for the poles and which can subsequently be refined using numerical optimization the technique yields both surface wave and leaky wave poles and results are presented for a typical example to demonstrate the approach the greatest approximation accuracy was observed for surface wave and leaky wave poles well removed from the spectral gap for poles either within or in close proximity to the spectral gap an alternative iterative technique is proposed expressions for the number of proper plus improper surface wave poles in a given problem are also derived

pseudosimilarity and cancellation of modules abstract two square matrices a and b over a ring are pseudosimilar if there exist x y and z satisfying xay b zbx a and xyx xzx x hartwig and hall showed this is equivalent to similarity over a field this result is extended to rings where free modules satisfy a cancellation property these include rings r with r rad r artinian or more generally rings with one in the stable range and polynomial rings over dedekind domains furthermore it is shown for commutative rings that if a and b are pseudosimilar then diag a o m and diag b o m are similar for some m

a homotopy method for locating all the poles of a parallel plate waveguide with the pml in this paper a homotopy method for locating all the poles of a parallel plate waveguide with the perfectly matched layer is proposed as is well known the green s functions for an open multilayered medium can be approximated by those for a parallel plate waveguide with the perfectly matched layer while the latter green s functions can be theoretically expressed into series expansions of their own eigenmodes without involving any numerical integrations the homotopy method here is applied for finding the desired mode poles in this method the newton raphson iteration is employed to solve every node equation except the start node equation while the dichotomy method is used to solve the start node equation the roots of the end node equation are just the desired mode poles with the proposed method the green s functions for a lossy or lossless multilayered medium can be efficiently calculated by the corresponding series expansions some numerical examples are provided to examine the robustness and accuracy of the proposed method

electromagnetic modeling of three dimensional bodies in layered earths using integral equations we have developed an algorithm based on the method of integral equations to simulate the electromagnetic responses of three dimensional bodies in layered earths the inhomogeneities are replaced by an equivalent current distribution which is approximated by pulse basis functions a matrix equation is constructed using the electric tensor green s function appropriate to a layered earth and it is solved for the vector current in each cell subsequently scattered fields are found by integrating electric and magnetic tensor green s functions over the scattering currents efficient evaluation of the tensor green s functions is a major consideration in reducing computation time we find that tabulation and interpolation of the six electric and five magnetic hankel transforms defining the secondary green s functions is preferable to any direct hankel transform calculation using linear filters a comparison of responses over elongate three dimensional 3 d bodies with responses over two dimensional 2 d bodie

representations under ring extensions latimer macduffee and taussky correspondences c g latimer and c c macduffee defined in 8 a bijective correspondence between similarity classes of nonsingular rational integral n x n matrices having a common separable characteristic polynomialf x and the classes of faithful ideals in the ring z x f x z x z the ring of rational integers several authors have used this simple duality with the ideas indigenous to one theory to obtain valuable consequences in the other see 14 and 15 f or a survey thereby motivating further analysis of the correspondence as in 1 2 4 17 and 181 nevertheless the theory has generally been catagorized as a subset of module theory of orders in semisimple algebras following zassenhaus s proof of jordan s theorem on the finiteness of such similarity classes see 7 14 and 21 i the purpose of this note is to replace the semisimple assumption present in these previous studies with the weaker condition that the modules considered become trivial under a suitable extension of the base ring the ease in which matrix and ideal theory are transferable under the latimer macduffee duality prompted our adherence to their approach when possible in this development over arbitrary commutative rings we review prior matrix ideal correspondences in section 2 preliminary to the general framework in section 3 there an n x ii matrix class is replaced by the isomorphism class of a rank n projective r module m which is also a faithful module over a rank n projective r algebra a the ideal theory is obtained by extending the base ring r of scalars to a commutative ring s for which m becomes trivial s ll mn s or a as s or a modules and m is then identified with a fractional a ideal in s or a in the classical case s is the field of quotients of a domain r theorem 1 reduces to the latimer macduffee duality in the latter case theorem 2 shows that the theory is equally adaptable to any commutative rank iz projective r algebra a which is isomorphic to its dual over a suitable extension of r as an application we show that a nonderogatory matrix is similar to the companion matrix of its

log concavity property of the error probability with application to local bounds for wireless communications a clear understanding of the behavior of error probability ep as a function of signal to noise ratio snr and other system parameters is fundamental for assessing the design of digital wireless communication systems we propose an analytical framework based on the log concavity property of the ep which we prove for a wide family of multidimensional modulation formats in the presence of gaussian disturbances and fading based on this property we construct a class of local bounds for the ep that improve known generic bounds in a given region of the snr and are invertible as well as easily tractable for further analysis this concept is motivated by the fact that communication systems often operate with performance in a certain region of interest roi and thus it may be advantageous to have tighter bounds within this region instead of generic bounds valid for all snrs we present a possible application of these local bounds but their relevance is beyond the example made in this paper

multidimensional modulation and coding for band limited digital channels a class of multidimensional signals based on generalized group alphabets is introduced and its basic properties are derived the combination of generalized group alphabets and coding is also examined two coding schemes are considered g ungerboeck s scheme 1982 for combination with convolutional codes and v v ginzburg s 1984 scheme for combination with block codes it is concluded that the performance of these schemes makes them attractive for transmission over band limited digital channels

error probabilities of two dimensional m ary signaling in fading a new exact method for computing the average symbol error probability of two dimensional m ary signaling in slow fading is presented the method is generally applicable to polygonal decision regions the exact average symbol error rate of coherent 16 star qam is obtained and compared to that of 16 rectangular qam new results for optimum ring ratios of 16 star qam in additive white gaussian noise awgn and in slow fading are also given

secure diversity multiplexing tradeoff of zero forcing transmit scheme at finite snr in this paper we address the finite signal to noise ratio snr diversity multiplexing tradeoff dmt of the multiple input multiple output mimo wiretap channel where a zero forcing zf transmit scheme that intends to send the secret information in the orthogonal space of the eavesdropper channel is used first we introduce the secrecy multiplexing gain at finite snr that generalizes the definition at high snr then we provide upper and lower bounds on the outage probability under secrecy constraint from which secrecy diversity gain estimates of zf are derived through asymptotic analysis we show that the upper bound underestimates the secrecy diversity gain whereas the lower bound is tight at high snr and thus its related diversity gain estimate is equal to the actual asymptotic secrecy diversity gain of the mimo wiretap channel

direct sum cancellation of submodule systems abstract we consider a category whose objects consist of a module together with a finite family of submodules thus extending the scope of elementary divisor theory the rings considered are module finite algebras over a commutative noetherian ring of krull dimension 1 and the property we focus on is direct summand cancellation extending results of d zelinsky

application of dcim to mpie mom analysis of 3d pec objects in multilayered media the formulation c green s functions for multilayered media are reformulated in this paper to extract z dependent part when the source and observation points are in different layers the discrete complex image method dcim is applied to obtain complex images independent on z but dependent on z spl acute for simulation of three dimensional 3 d perfectly electrical conduction pec objects penetrating two or more layers tables of complex images are built in a z spl acute grid during the matrix filling stage of the mixed potential integral equation together with method of moments mpie mom the spatial domain green s functions are interpolated from values in the z spl acute grid while these values are calculated from complex images in the z spl acute grid this interpolation scheme is more efficient than those directly storing the spatial domain green s functions numerical examples are given for analyzing a dipole in a two layered media

θ qam a parametric quadrature amplitude modulation family and its performance in awgn and fading channels we study a parametric quadrature amplitude modulation qam family called qam which includes other known constellations such as square qam sqam and triangular qam tqam as special cases the versatile structure of the qam signal constellation which occurs from the varying angle between the signal points results in achieving the minimum symbol error rate ser or bit error rate ber under an average power constraint the theoretical study aims at providing insight into the trade off between error performance and complexity of this parametric modulation scheme exact analytical expressions are obtained for the ser in additive white gaussian noise awgn and nakagami m fading channels while highly accurate ber approximations are presented finally we find the optimum angles in a minimal ser or ber sense for a specific signal to noise ratio snr and modulation order m this serves as an indicator for the appropriate constellation with respect to channel conditions and ser or ber requirements the presented theoretical analysis is validated via extensive computer simulations

matrix equivalence and isomorphism of modules abstract it is well known that if a and b are n m matrices over a ring r then coker a coker b does not imply a and b are equivalent an elementary proof is given that the implication does hold if 1 is in the stable range of r furthermore for certain r including commutative rings if a is block diagonal and b is block upper triangular with the same diagonal blocks as a then coker a coker b implies a and b are equivalent under a special equivalence this extends results of roth and gustafson as a corollary a theorem on decomposition of modules is obtained

on convexity of error rates in digital communications convexity properties of error rates of a class of decoders including the maximum likelihood min distance one as a special case are studied for arbitrary constellations bit mapping and coding earlier results obtained for the additive white gaussian noise channel are extended to a wide class of noise densities including unimodal and spherically invariant noise under these broad conditions symbol and bit error rates are shown to be convex functions of the signal to noise ratio snr in the high snr regime with an explicitly determined threshold which depends only on the constellation dimensionality and minimum distance thus enabling an application of the powerful tools of convex optimization to such digital communication systems in a rigorous way it is the decreasing nature of the noise power density around the decision region boundaries that ensures the convexity of symbol error rates in the general case the known high low snr bounds of the convexity concavity regions are tightened and no further improvement is shown to be possible in general the high snr bound fits closely into the channel coding theorem all codes including capacity achieving ones whose decision regions include the hardened noise spheres from the noise sphere hardening argument in the channel coding theorem satisfy this high snr requirement and thus has convex error rates in both snr and noise power we conjecture that all capacity achieving codes have convex error rates convexity properties in signal amplitude and noise power are also investigated some applications of the results are discussed in particular it is shown that fading is convexity preserving and is never good in low dimensions under spherically invariant noise which may also include any linear diversity combining

clarification of issues on the closed form green s functions in stratified media the closed form green s functions cfgf derived for the vector and scalar potentials in planar multilayer media have been revisited to clarify some issues and misunderstandings on the derivation of these green s functions in addition the range of validity of these green s functions is assessed with and without explicit evaluation of the surface wave contributions as it is well known the derivation of the cfgf begins with the approximation of the spectral domain green s functions by complex exponentials and continues with applying the sommerfeld identity to cast these approximated spectral domain green s functions into the space domain in closed forms questions and misunderstandings of this derivation which have mainly originated from the approximation process of the spectral domain green s functions in terms of complex exponentials can be categorized and discussed under the topics of 1 branch point contributions 2 surface wave pole contributions and 3 the accuracy of the obtained cfgf when these issues are clarified the region of validity of the cfgf so obtained may be defined better therefore in this paper these issues will be addressed first and then their origins and possible remedies will be provided with solid analysis and numerical demonstrations

multilayered media green s functions in integral equation formulations a compact representation is given of the electric and magnetic type dyadic green s functions for plane stratified multilayered uniaxial media based on the transmission line network analog along the aids normal to the stratification furthermore mixed potential integral equations are derived within the framework of this transmission line formalism for arbitrarily shaped conducting or penetrable objects embedded in the multilayered medium the development emphasizes laterally unbounded environments but an extension to the case of a medium enclosed by a rectangular shield is also included

similarity of holomorphic matrices abstract let be a noncompact riemann surface e g the complex plane the main result is that if a and b are two square holomorphic matrices on such that for any z in there is a neighborhood of z with a and b holomorphically similar on the neighborhood then a and b are holomorphically similar on this is then applied to extend results of wasow on pointwise similarity we actually prove these results for bezout domains satisfying certain conditions and then observe that these conditions are satisfied by the ring of holomorphic functions on

channels with block interference a new class of channel models with memory is presented in order to study various kinds of interference phenomena it is shown among other things that when all other parameters are held fixed channel capacity c is an em increasing function of the memory length while the cutoff rate r 0 generally is a em decreasing function calculations with various explicit coding schemes indicate that c is better than r 0 as a performance measure for these channel models as a partial resolution of this c versus r 0 paradox the conjecture is offered that r 0 is more properly a measure of coding delay rather than of coding complexity

generalized pencil of function method for extracting poles of an em system from its transient response a generalized pencil of function gpof method is developed for extracting the poles of an electromagnetic system from its transient response the gpof method needs the solution of a generalized eigenvalue problem to find the poles subspace decomposition is also used to optimize the performance of the gpof method the gpof method has advantages over the prony method in both computation and noise sensitivity and approaches the cramer rao bound when the signal to noise ratio snr is above threshold an application of the gpof method to a thin wire target is presented

error rates of the maximum likelihood detector for arbitrary constellations convex concave behavior and applications motivated by a recent surge of interest in convex optimization techniques convexity concavity properties of error rates of the maximum likelihood detector operating in the awgn channel are studied and extended to frequency flat slow fading channels generic conditions are identified under which the symbol error rate ser is convex concave for arbitrary multidimensional constellations in particular the ser is convex in snr for any one and two dimensional constellation and also in higher dimensions at high snr pairwise error probability and bit error rate are shown to be convex at high snr for arbitrary constellations and bit mapping universal bounds for the ser first and second derivatives are obtained which hold for arbitrary constellations and are tight for some of them applications of the results are discussed which include optimum power allocation in spatial multiplexing systems optimum power time sharing to decrease or increase jamming problem error rate an implication for fading channels fading is never good in low dimensions and optimization of a unitary precoded ofdm system for example the error rate bounds of a unitary precoded ofdm system with qpsk modulation which reveal the best and worst precoding are extended to arbitrary constellations which may also include coding the reported results also apply to the interference channel under gaussian approximation to the bit error rate when it can be expressed or approximated as a nonnegative linear combination of individual symbol error rates and to coded systems

strong feedback cyclization for systems over rings abstract for nonnecessarily reachable systems over a commutative ring r we define a strong form of feedback cyclization fc with this natural generalization of the fc property we obtain a feedback reduced form for systems over strong fc rings i e rings for which every system verifies the fc property in the particular case of reachable single input systems this gives the usual control canonical form of bumby et al remarks on the pole shifting problem over rings j pure appl algebra 20 1981 113 127 also it is proved that a commutative ring with 1 in its stable range has the strong fc property if and only if it has the ucu property which is the natural parallel form of the result given by brewer et al pole assignability in polynomial rings power series rings and prufer domains j algebra 106 1987 265 286 for the reachable case many classes of rings which were known to be fc rings are in fact strong fc rings but there are fc rings which are not strong fc rings

trellis coded modulation with multidimensional constellations trellis coded modulation schemes using four eight or 16 dimensional constellations have a number of potential advantages over the usual two dimensional schemes a smaller constituent two dimensional constellation easier tolerance to phase ambiguities and a better trade off between complexity and coding gain a number of such schemes are presented and evaluated starting with a variety of multidimensional lattices we show how to select multidimensional constellations how to partition them into subsets how to construct trellis codes using those subsets and how to map hits to constellation points simplifications of the viterbi decoding algorithm are presented we conclude that there are multidimensional trellis coded modulation schemes that perform better for the same complexity than do two dimensional schemes

on the inverse symbol error probability for diversity reception this paper addresses the problem of finding the inverse symbol error probability sep expression for coherent detection of m ary phase shift keying with multichannel reception and maximal ratio combining in rayleigh fading to this aim we derive upper and lower bounds on sep that are simply invertible and uniformly tight for all values of signal to noise ratio this enables us to obtain tight bounds on the inverse sep and on the symbol error outage seo i e sep based outage probability as an example of application to digital mobile radio the seo in a log normal shadowing environment is analyzed

voronoi regions of lattices second moments of polytopes and quantization if a point is picked at random inside a regular simplex octahedron 600 cell or other polytope what is its average squared distance from the centroid in n dimensional space what is the average squared distance of a random point from the closest point of the lattice a n or d n e n a n ast or d n ast the answers are given here together with a description of the voronoi or nearest neighbor regions of these lattices the results have applications to quantization and to the design of signals for the gaussian channel for example a quantizer based on the eight dimensional lattice e8 has a mean squared error per symbol of 0 0717 cdots when applied to uniformly distributed data compared with 0 08333 cdots for the best one dimensional quantizer

on girth conditioning for low density parity check codes low density parity check ldpc codes are gaining interest for high data rate applications in both terrestrial and spatial communications they can be designed and studied through a bipartite graph whose characteristics affect the performance this paper proposes a low complexity method to improve the performance of ldpc codes by selectively removing some cycles from the associated bipartite graph the method is based on a modified version of the breadth first search bfs algorithm that we call modified bfs mbfs which is applied to find cycles and a greedy procedure to eliminate them throughout the paper we will give a detailed description of the algorithm proposed and analytically study its complexity simulation results show that this girth conditioning method applied to some classes of codes whose structure allows further optimization can lead to a significative complexity reduction and a performance improvements with respect to other methods

on the snr penalties of ideal and non ideal subset diversity systems subset diversity ssd techniques which select and combine the signals from a subset of the available diversity branches are important for practical wireless systems this paper characterizes the performance loss or signal to noise ratio snr penalty of one ssd system with respect to another both ideal and non ideal channel estimation are considered and the analysis is valid for the important case of arbitrary two dimensional signal constellations expressions are given for the asymptotic snr penalty for both small and large snr for all the comparisons considered additionally we develop bounds and approximations to quantify the performance of one system in terms of another for all snrs of interest furthermore for some signal constellations we derive the exact snr penalty of a non ideal system with respect to an ideal system as well as the exact penalty associated with two non ideal systems with varying degrees of estimation energy the snr penalty enables the assessment of system sensitivity to channel estimation energy combining architecture and signal constellation

similarity of matrices over commutative rings abstract a canonical form is given for nilpotent matrices which have constant rational canonical form on the spectrum of a commutative ring the similarity class of a matrix with constant rational or jordan canonical form is considered

exact image theory for the sommerfeld half space problem part ii vertical electrical dipole applying the laplace transform the exact distributed image current function is obtained for the classical sommerfeld half space problem with vertical magnetic current source the resulting field integral is well behaved when the image current is situated in complex space unlike previous approximate images the present theory is valid for any distance height of the source frequency and half space parameters it is demonstrated that the present image theory reduces to the well known dipole image at complex depth for large dielectric parameters of the half space also the reflection coefficient method is obtained as a farfield approximation calculation of fields through exact image integration is seen to be simple and accurate and require modest computer capacity and time in an appendix some properties of the multivalued green s function arising from a dipole source in complex space are also studied

degrees of freedom in adaptive modulation a unified view we examine adaptive modulation schemes for flat fading channels where the data rate transmit power and instantaneous ber are varied to maximize spectral efficiency subject to an average power and ber constraint both continuous rate and discrete rate adaptation are considered as well as average and instantaneous ber constraints we find the general form of power ber and data rate adaptation that maximizes spectral efficiency for a large class of modulation techniques and fading distributions the optimal adaptation of these parameters is to increase the power and data rate and decrease the ber as the channel quality improves surprisingly little spectral efficiency is lost when the power or rate is constrained to be constant hence the spectral efficiency of adaptive modulation is relatively insensitive to which degrees of freedom are adapted

convexity properties in binary detection problems the author investigates the convexity properties of error probability in the detection of binary valued scalar signals corrupted by additive noise it is shown that the error probability of the maximum likelihood receiver is a convex function of the signal power when the noise has a unimodal distribution based on this property the results of the optimal time sharing strategies of transmitters and jammers and of the optimal use of multiple channels are obtained

the primitive topology of a scheme abstract we define a grothendieck topology on the category of schemes whose associated sheaf theory coincides in many cases with that of the zariski topology we also give some indications of possible advantages this new topology has over the zariski topology

new trellis codes based on lattices and cosets a new technique is proposed for constructing trellis codes which provides an alternative to ungerboeck s method of set partitioning the new codes use a signal constellation consisting of points from an n dimensional lattice lambda with an equal number of points from each coset of a sublattice lambda one part of the input stream drives a generalized convolutional code whose outputs are cosets of lambda while the other part selects points from these cosets several of the new codes are better than those previously known

hypersurfaces in projective schemes and a moving lemma let x s be a quasi projective morphism over an affine base we develop in this article a technique for proving the existence of closed subschemes h s of x s with various favorable properties we offer several applications of this technique including the existence of finite quasi sections in certain projective morphisms and the existence of hypersurfaces in x s containing a given closed subscheme c and intersecting properly a closed set f assume now that the base s is the spectrum of a ring r such that for any finite morphism z s pic z is a torsion group this condition is satisfied if r is the ring of integers of a number field or the ring of functions of a smooth affine curve over a finite field we prove in this context a moving lemma pertaining to horizontal 1 cycles on a regular scheme x quasi projective and flat over s we also show the existence of a finite surjective s morphism to psd for any scheme x projective over s when x s has all its fibers of a fixed dimension d

pragmatic space time trellis codes gtf based design for block fading channels the pragmatic approach for the construction of space time codes over block fading channels leads to low complexity encoders decoders making them suitable for various applications including cooperative communications we propose a design methodology for pragmatic space time codes which is based on an extension of the concept of generalized transfer function our search algorithm provides code generators for arbitrary number of states antennas and fading rates numerical results show that the performance of the pragmatic space time codes obtained by our design methodology is generally better than that of previously known space time trellis codes in block fading channels

fast quantizing and decoding and algorithms for lattice quantizers and codes for each of the lattices a n n geq 1 d n n geq 2 e 6 e 7 e 8 and their duals a very fast algorithm is given for finding the closest lattice point to an arbitrary point if these lattices are used for vector quantizing of uniformly distributed data the algorithm finds the minimum distortion lattice point if the lattices are used as codes for a gaussian channel the algorithm performs maximum likelihood decoding

pole assignability in polynomial rings power series rings and prufer domains the topics treated in this paper have their origins in the area of algebraic systems theory however the paper itself should be classified as pure commutative algebra and we shall present it as such in the body of the text still it is appropriate to give a brief paragraph of motivation if a physical system is governed by a pair f g of matrices then the stability of the system can be determined by examining the eigenvalues of the matrix f if the system is unstable a feedback matrix k can sometimes be employed in such a way that the eigenvalues of the matrix f gk measure the stability of the modified system f gk g in this manner an unstable system can be rendered stable the pole assignability problem over commutative rings is one method of attacking the problem of finding such matrices k the paper is divided into four sections section 1 is given over almost entirely to defining the properties in which we shall be interested it concludes with a theorem about residuating and lifting the properties section 2 is concerned with the preservation of the properties under polynomial ring and power series ring formation section 3 is concerned with feedback cyclization a strong form of pole assignability section 4 is concerned with pole assignability over priifer domains a complete elaboration of our results must await the introduction of the necessary terminology for now we mention the following results in somewhat vague language if r is a zero dimensional ring then the pole assignability problem is solvable in r x and in r xl from a ringtheoretic standpoint almost any class of commutative rings contains members for which the feedback cyclization problem is solvable on the other hand if r is a ring with 1 in its stable range then the feedback cyclization problem is solvable in r if and only if a certain nice matricial property

on the location of proper and improper surface wave poles for the grounded dielectric slab microstrip antennas a recently obtained closed form asymptotic representation due to s barkeshli 1988 of the microstrip surface green s function is known to provide an efficient moment method analysis of microstrip problems however in order to make this closed form expression accurate even for very small separation of source and field points to within a few tenths of a wavelength both the proper and improper surface wave transition effects must be included in the solution this requires finding the location of the corresponding proper and improper poles a good initial estimate that allows the poles to be located rapidly by using an iterative procedure is presented the number of proper and improper surface wave poles that have to be considered and their values are tabulated

locating all the modes of green s function for a three layered medium based on the path tracking algorithm through a mathematical analysis on the relationship between the characteristic equations of the microstrip geometry and a configuration with a three layered medium a method based on the path tracking algorithm is proposed for precisely locating all the modes for a three layered medium with moderate thickness including surface wave modes leaky wave modes and improper real modes with this method the difficulty caused by branch points and cuts in the contour integral method could be avoided this method can be applied not only in the discrete complex image method dcim but also in the steepest descent path sdp method the proposed method can be extended to more complicated configurations