bluuebunny/crossref_metadata_2025 huggingface dataset:
Eigenvalue behavior in FH signal rejection in DS spread spectrum systems using complex adaptive filters
Authors: Pajkovié Miodrag Dj.
Published: September 2008

Eigenvalue behavior of direct sequence (DS) QPSK spread spectrum (SS) receiver using adaptive filters in presence of frequency hopped (FH) interference is analyzed. The analysis is valid both for the adaptive prediction error filters and for transversal filters with two‐sided taps. The improvement factor G depends on filter adaptation rate μ and on transient response of the filter. Thansient responses of the filters using eigenvalue behavior method are analyzed. Presented analysis and results show that slow FH jammer suppression in DS system can be obtained using complex adaptive filters. The adaptation rate dependance on different communication parameters and on discrete time is presented.
A new data structure for variable bit rate broadcast video transmission on ATM network
Authors: Modena Marco , Parladori Giorgio , Vecchietti Giovanna
Published: September 2008

The asynchronous transfer mode (ATM) technique will probably increase the demand for sophisticated video services. The availability of wide bandwidth and fast rerouting at affordable rates will influence the design of new video codecs. Firstly, variable bit rate coding algorithms can efficiently be employed in order to achieve a uniform picture quality at the receiver. Secondly, the impairment due to cell loss that may occur in the ATM environment demands specialized error concealment strategy. In this paper the segmentation and reassembling of the bit stream generated by a hybrid DCT broadcast quality video codec is addressed. A VIDEO PACKET (V.P.), composed of a variable number of ATM cells, is associated to a defined portion of the television signal. Predefined patterns and layered protection included in the V.P. allow the detection of lost cells and consequently the application of a simple error concealment technique.
Throughput analysis of nonpersistent inhibit sense multiple access in multipath fading and shadowing channels
Authors: Prasad Ramjee
Published: September 2008

The capacity of packet radio channels is investigated using the interference model for the coherent and incoherent cumulations in the presence of Rayleigh fading and log‐normal shadowing, assuming a nonpersistent multiple access protocol with inhibit bits to avoid collisions. Expressions for the throughput are derived for uncorrelated packet signals. The combined propagation effects yield higher channel capacity than each individual effect.
Single‐mode optical fibers with geometrical birefringence: Analysis of the propagation by means of finite element method
Authors: Cancellieri Giovanni , Chiaraluce Franco , Checchia Andrea
Published: September 2008

This work presents the results of an analysis regarding propagation in single‐mode fibers conducted by means of finite element method. A particular form of the functional is taken, in order to avoid the presence of nonphysical spurious solutions. Special attention is then given to the choice of the mesh when profile geometry is not circularly simmetric, like in the case of Fibers able to preserve the state of polarization or nominally single‐polarization. This situation has been carefully analysed, showing that particular new kinds of index profiles, such as elliptical azimuthally modulated W profiles, are able to produce extended intervals of single‐polarization operation, to the point where their practical use appears feasible.
A new electronically tunable integrable CCII‐OTA‐based active‐C oscillator
Authors: Abuelma'atti Muhammad Taher
Published: September 2008

A new electronically tunable oscillator circuit is proposed. The circuit uses a single current‐conveyor, three operational transconductance amplifiers and two capacitors. The circuit enjoys low sensitivity characteristics and has a high potential for integration in addition to its wide range of electronic tunability.
A methodology for buffer design in ATM switches
Authors: Bernabei Francesco , Ferretti Roberto , Listanti Marco , Zingrillo Giuseppe
Published: September 2008

This paper deals with a general method for buffer design in an ATM system in which the target loss probability should be very low (e.g. less than 10‐9).

This method is based on the application of the Generalized Extreme Value Theory (GEVT) on results arising from simulation runs. This theory allows the estimation of very small probabilities which would not be evaluable with traditional Montecarlo approach. An advantage of 4/5 decades with respect to Montecarlo limits can be obtained utilizing the same sample set.

The extension of the theory to the case of distribution functions of discrete random variables is here discussed. The applicability of the method is here demonstrated with reference to known probability distribution functions (Exponential, Normal, Weibull, Iperexponential, Geometric, Bernoulli and Poissonian). Moreover, the GEVT is applied in the cases of classical queueing systems, i.e. M/D/l, Geo/D/1 and MMPP/D/1. Finally, the general criteria for the evaluation of the basic GEVT parameters are discussed.
Sinusoidal oscillators with slew‐rate type nonlinearity
Authors: Borys Andrzej
Published: September 2008

This paper is a continuation of [1] and deals with a class of single‐op‐amp sinusoidal oscillators working under the amplitude limiting regime of a slew‐rate nonlinearity. The Wien‐bridge oscillator example is chosen for a detailed analysis. It is shown, using the first‐order determining equation, that the oscillation‐frequency (f0) depends upon the passive elements of the oscillator structure only; it is independent of the op‐amp gain‐bandwidth product (Gfl)! Moreover, the oscillation‐amplitude (A0) is a function of the oscillation‐frequency, of the op‐amp parameters: slew‐rate factor (SR), and GB and finally, of the attenuation of the Wien‐bridge resistive branch (k). Notable is the high sensitivity of the amplitude A0 with respect to the changes in the factor k. Furthermore, an upper bound for the realizable oscillation‐frequency is developed and verified on the experimental data. Finally, the harmonic content (A) is computed for different fo's and compared with those values obtained by means of the describing‐function method.
Performance of heterodyne optical OOK systems with coding
Authors: Majumder Satya Prasad , Gangopadhyay R.
Published: September 2008

The performance degradation of heterodyne optical OOK systems caused by additive receiver noise and phase noise can be substantially overcome by using coding techniques. Using two statistical descriptions of the filtered phase noise process, performance of the coded optical OOK system is evaluated. The results indicate that predictions based on the two phase models closely agree only for sufficiently small ratios of the overall laser linewidth β to the bit rate, namely when βT/M < 2 × 10−2, with T being the bit duration and M the IF bandwidth expansion factor. The analysis further shows that the coded OOK system can attain substantial coding gains; for instance, a coding gain of 10.5 dB is achieved for a rate‐1/2 convolutional code of constraint length K = 7 with βT= 0.64 and M= 10.
Bistatic scattering on a monostatic radar range
Authors: Herdeg Wolfgang F. , Wendel Horst
Published: September 2008

Suitable combination of monostatic radar range and reflector plate allows to study bistatic scattering while varying only the aspect angle. We exemplify the scheme by measuring the scattering from an isolated rectangular metal edge. The various scattering contributions are discriminated by high resolution imaging.
Site diversity in land‐mobile cellular telephony network with discontinuous voice transmission
Authors: Linnartz Jean‐Paul M. G.
Published: September 2008

Cellular radio channels suffer from signal outages due to multipath fading and shadowing. Analytical expressions are given for the probability that the instantaneous C/I‐ratio drops below a required protection ratio. A radio signal from a mobile subscriber exhibits outages at different base station sites with relatively low correlation. The quality of communication over a mobile telephone circuit can be improved by appropriately combining voice segments received at various base stations. The probability of dropping a voice segment for an end‐to‐end «up‐link» circuit (mobile‐to‐PSTN) in an interference‐limited cellular network with discontinuous voice transmission and macro diversity is evaluated mathematically. Asymptotic expressions of the signal outage probability for high average C/I‐ratios are presented in closed form.
Surface acoustic wave resonators
Authors: Avitabile Gianfranco , Roselli Luca , Atzeni Carlo , Manes Gianfranco
Published: September 2008

Surface Acoustic Wave (SAW) resonators are implemented by creating a planar resonant cavity, delimited by two distributed, rather than concentrated, mirrors, consisting of arrays of reflecting metal strips. SAW resonators permit to achieve higher frequencies than their bulk‐wave acoustic counterparts with comparable spectral purity and very high Q, while, due to the planar nature, they result of small size and rugged construction.

The basic SAW resonator operation, with emphasis on design parameters and device configuration, is presented. A complex simulation package for Computer‐Aided Design of SAW resonators has been developed. Several resonators in the VHF‐UHF frequency band have been designed and tested, exhibiting good agreement with the simulation forecast and state‐of‐the‐art performances.

This paper summarizes a three years work conducted under support of the Progetto Finaliz‐zato MADESS, CNR.
Techniques in processing multi‐frequency multi‐polarization spaceborne SAR data
Authors: Curlander John C. , Chang C. Y.
Published: September 2008

This paper presents the algorithm design of the SIR‐C ground data processor, with emphasis on the unique elements involved in the production of registered multi‐frequency polari‐metric data products. A quick‐look processing algorithm used for generation of low‐resolution browse image products and estimation of echo signal parameters is also presented. Specifically, we will discuss the following: 1) Azimuth reference function generation to produce registered polarimetric imagery; 2) Geometric rectification to accommodate cross‐track and along‐track Doppler drifts; 3) Multi‐look filtering designed to generate output imagery with a uniform resolution; and 4): Efficient coding to compress the polarimetric image data for distribution.
Parallel/pipeline multiprocessor architectures for SAR data processing
Authors: Albrizio Rosa , Mazzone Albino , Veneziani Nicola , Aloisio Giovanni
Published: September 2008

In SAR digital data processing, using the range‐Doppler approach, the main computational load occurs in the range and azimuth compressions, for which one‐dimensional circular convolutions in the Fourier domain are used. In the paper it is shown how the intrinsic degrees of parallelism of the process can be efficiently exploited to design a flexible parallel/pipeline multiprocessor architecture, based on advanced components with interconnection capabilities and capable to perform up to the real‐time SAR data focusing. In the proposed architecture, an efficient line compression can be achieved by means of pipelined processors for the range and the azimuth compressions and many of these structures, each performing the compression of a line or its section, can be used to sustain the computational load and the data rate requirements. In the paper, we also show how the data communication between the range and the azimuth processors can be solved when a maximum of eight of these line compressors are used.

The performance evaluation of the proposed architecture is made referring to real spaceborne SAR sensors.
On the use of joint time‐frequency representations in SAR signal processing
Authors: Barbarossa Sergio , Gregori Carlo , Nicastro Giuseppe
Published: September 2008

The aim of this paper is to show that some of the open problems in Synthetic Aperture Radar signal processing can be seen in a new and advantageous perspective if the received signals are represented in the time‐frequency domain. The joint time‐frequency representation makes easier the extraction of the information necessary for the formation of the synthetic aperture, responsible for the high cross‐range resolution. The proposed approach is applied to the imaging of moving objects and to the focusing of extended scenes, in presence of instabilities of the radar platform such that the conventional estimation techniques become insufficient. In particular, the time‐frequency analysis allows the estimation of the useful signal parameters even in case of undersampling. This allows the use of relatively low Pulse Repetition Frequencies(PRF), avoiding then the shortcomings due to highPRFs, like the reduction of the sizes of the monitorable areas or the data rate increase.
Prediction of the outage performance of an orbital diversity earth‐space system
Authors: Kanellopoulos John D. , Reppas Adrianos
Published: September 2008

Diversity systems are foreseen for earth to satellite links operating at frequencies above 10 GHz in localities with high rain‐induced attenuation. The paper discusses orbital diversity, which uses two satellites and an earth receiving site. A recently suggested model for the prediction of site diversity performance is properly modified by considering the particular geometry of the present problem. Both types of rain (stratified and convective raincells) are also examined. Numerical results are compared with experimental data taken from a simulated earth‐space system located in Italy. The agreement was found to be quite encouraging.
Signal detection in cyclostationary generalized gaussian noise with unknown parameters
Authors: Napolitano Antonio , Paura Luigi , Tanda Mario
Published: September 2008

The paper deals with the detection of a known signal embedded in cyclostationary white generalized Gaussian noise. Two cases are considered: the former assumes unknown (but nonrandom) the periodic noise intensity, the latter considers unknown also the noise‐shape parameter. Since for these detection problems non uniformly most powerful test exists, the generalized log‐likelihood ratio test (GLLRT) is considered because of its asymptotic optimality properties. The GLLRT‐based detectors for both cases are synthesized and their asymptotic (i.e., for large sample size) performances are analytically evaluated. Moreover, for finite sample size, the performances, carried out via computer Monte Carlo simulations, are compared with that of the optimum detector, whose synthesis is based on a complete noise characterization.
TCP/IP measured performance over an ethernet local network
Authors: Braccini Alessandro , Bimbo Alberto Del , Vicario Enrico , Cappellini Vito
Published: September 2008

Both a reliable transfer and a datagram transmission protocol are provided at the transport level of the Internet protocol suite. In this paper, an evaluation of the performance of these different protocols in the presence of background load is presented. The experimental analysis was carried out on an Ethernet Local Area Network with PC‐type workstations. The loading conditions were established by means of an artificial traffic generator. A reproducible experimental environment and a methodology to achieve accuracy in measurements were developed.
Signal processing for broadband communications
Authors: Bellanger Maurice
Published: September 2008

Signal processing affects all aspects of broadband communications: terminals, transmission media and networking techniques. In this context, the paper provides a review of several basic signal processing concepts, which can now be implemented and exploited, with the present technological capabilities: perfect filter banks, fast adaptive filtering and code representation. These are key elements for a smooth introduction and evolution of the broadband communication network.
ASIC‐based acoustic echo‐canceller board for VME bus
Authors: Maloberti Franco , Torelli Guido , Panini Claudio , Troiani Mauro , Roncella Roberto , Terreni Pierangelo , Toncelli Cristiano , Saletti Roberto
Published: September 2008

This paper deals with the design and realization of an echo‐canceller board for a VME bus. The work has been carried out by integrating the abilities and the competences of some academic and industrial research groups within the framework of Subproject 3.1 of the Italian National Research Council «Telecommunication Project». The board implements an efficient algorithm for the cancellation of acoustic echoes and is to be used in a video‐conference terminal. It employes application specific integrated circuits (ASIC), in order to obtain a compact realization of the system, as required in present inter‐personal terminal systems. The board consists of a DSP processor which computes the algorithm, a high‐performance interface with the analog world, and a finite impulse response filter (FIR) which emulates the response of the acoustic channel. The design and the performance of the integrated circuits for the A/D and D/A conversion and the FIR filter are reported.
VQ coding for videophone applications adopting knowledge‐based techniques: Implementation on parallel architectures
Authors: Braccini Carlo , Grattarola Aldo , Lavagetto Fabio , Zappatore Sandro
Published: September 2008

An innovative algorithm is presented for the design and implementation of a self‐adaptive vector quantizer for videophone coding. The codebook is organized in a binary tree structure capable to modify its topology and content in order to adaptively track the input varying statistics. The resulting tree structure is unbalanced, in the sense that some branches are extended more than others, depending on the input vector distribution, and therefore the suboptimality of tree structured VQ with respect to the full‐search approach is greatly reduced. As it is known a priori that the class of input video data consists of a human head slowly moving against a static background, knowledge based segmentation of incoming frames can be efficiently performed. Exhaustive simulations have shown the effectiveness of the algorithm in standard CIF videophone sequences. Some procedures have been parallelized and implemented on a AT&T Pixel Machine for frame‐rate coding. Results and comments on both the algorithm and the parallel implementation are presented.
Signalling protocols for multimedia application: Prototype for an ATM test‐bed
Authors: Contini Enzo , Piovano Luciano , Ravera Mauro
Published: September 2008

Currently under study as part of the future ATM based communication network definition is the development of a flexible signalling system. This document shows how the signalling protocol prototype at the User to Network Interface was defined in an ATM test‐bed. Taking Rec.Q.931 as a starting point, we introduced into the new signalling protocol structure the concept of Call Control and Bearer Control separation thus making it possible to handle multiconnection and multiparty call configurations in an easy way.

To satisfy the new signalling requirements, a flexible description of the telecommunication service is proposed. Each information type is described individually and the relationships among them is outlined. In addition this paper proposes a matrix‐based description of the call model, particularly useful for the introduction of multiparty configurations.

The paper then recalls the advantages of the Call Control and Bearer Control separation concept, and goes on to analyze a number of identifiers whose function, in this context, is to correlate the Call Control entity with those of Bearer Control. As an example, we give various messages of this signalling prototype protocol: their structure is based on the tools and identifiers described above.
Deflection network: Principles, implementation, services
Authors: Albertengo Guido , Civera Pier Luigi , Cigno Renato Lo , Piccinini Gianluca , Zamboni Maurizio , Borgonovo Flaminio , Fratta Luigi , Panizzardi Giuseppe
Published: September 2008

This paper deals with slotted data networks routing packets with a deflection technique. In particular regular mesh topologies that can be mapped on toroidal surfaces are analyzed. First an introduction to the concept of deflection routing is given, then many routing algorithms are considered and compared by means of their performance in terms of maximum attainable throughput and efficiency. Afterwards the architecture of a node currently under development, which implements one of the described algorithms, is described and analyzed; the switching fabric, a full custom VLSI, the interface of the node towards LANs and workstations, and the network management algorithm are described in detail. Finally the possibility of providing special services, like guaranteed bandwidth, circuit oriented connections, etc. is taken into account.
Guaranteed bandwidth transport service in multihop networks
Authors: Bernabei Francesco , Gratta Laura , Listanti Marco
Published: September 2008

This paper deals with the feasibility of a Guaranteed Bandwidth Transport Service (GBTS), usually employed for the handling of isochronous and/or data services with real time requirements, on Multihop Networks (MHNs). A Resource Allocation Protocol (RAP) for the set‐up of GB calls is proposed. This protocol allows the low cost requirements of a LAN/MAN node to be satisfied, together with a high flexibility in bandwidth allocation. In the paper a performance study is carried out to verify the response of the MHNs to GB traffic. In particular, the path blocking probability has been evaluated by means of an analytical model in the cases of balanced and unbalanced loads. Moreover, a comparison with the performance of similar LAN/MAN structures, i.e. simple ring and ring with spatial reuse is carried out. Finally, a methodology to manage the resources in order to make the grade of service independent of the physical location of the network nodes is proposed and its impact on the network performance is evaluated.
Bit error probability of a digital mobile radio cellular system in presence of co‐channel interference, thermal and impulsive noise
Authors: Prasad Ramjee , Hollemans Willem , Kegel Adriaan
Published: September 2008

The bit error probability is derived for a mobile cellular radio network in the presence of co‐channel interference, Gaussian noise and narrow‐band impulsive noise (Middleton's class A noise) using DPSK (differential phase shift keying) modulation and 4‐QAM (quadrature amplitude modulation). The spectrum efficiency of the mobile radio system is also evaluated. The influence of reuse distance, i.e. cluster size, and traffic intensity on the performance parameters is investigated. The mobile environment is considered as a (fast) Rayleigh fading channel.

The UHF groundwave propagation law is introduced by considering the local mean power to be inversely propotional to the fourth power of the propagation distance.

It is found that the bit error probability is more vulnerable to Gaussian white noise than to narrow‐band impulsive noise.
Orthogonal multiple carrier data transmission
Authors: Fliege Norbert J.
Published: September 2008

In this paper, the idea of data transmission by essentially using the discrete Fourier transform (DFT) algorithm, the idea of overlapped but orthogonally sampled multiple data transmission channels, and the idea of subband signal processing by means of DFT polyphase filter banks are combined. The main result in a novel orthogonal multiple carrier (OMC) data transmission system with high computational efficiency and high bandwidth efficiency.

Intersymbol interference is avoided by choosing each channel as a Nyquist system. The problem of unavoidable crosstalk between adjacent channels is solved by sampling the equally spaced zeros of the crosstalk impulse response. It is shown that in a critically sampled DFT filter bank the space between the zeros exactly equals one symbol period. The time offset of half a symbol period between the zeros of the real part and the zeros of the imaginary part of the crosstalk impulse response leads to a special staggering technique with time offset. Finally the structure of the polyphase filter banks is optimized resulting in fast Fourier transforms of half of the original length.
Image compression by the wavelet decomposition
Authors: Albanesi M. G. , De Lotto I. , Carrioli L.
Published: September 2008

Decomposition of images with the Haar orthonormal basis which is an important member of compactly supported Wavelets and a quadtree structured hierarchical coding technique are used in this work to obtain high image compression efficiency and time complexity linear in the number of pixels. An exhaustive testing of the algorithm has been performed on images of different complexity and typical of some application environment (image transmission and storing, remote control of intelligent robots). The results of the experiments arc presented and discussed. Finally, a comparison of quality performance of these techniques with the JPEG (Block Cosine Transform coding) compression technique is presented.
Further applications of the optimal strategy srpt to media access protocols in local area networks
Authors: Schmickler Leonhard
Published: September 2008

After a recently reported application of the SRPT principle to the Ethernet LAN based on the CSMA/CD access protocol we present in this paper further SRPT applications to the token passing LANs Token Bus, Token Ring and the FDDI high speed LAN. Messages are sorted in the station transmit queues according to their length and transmitted over the network using the standardized priority classes to prefer short messages. It will be shown that under a typical user scenario the mean value as well as the standard deviation and the correlation of the transfer time are remarkably reduced compared to FIFO operation.
Performance analysis of differential chain coding
Authors: Liu Kun , Prasad Ramjee
Published: September 2008

Chain coding of hardwritten line drawings for digital transmission is considered in this paper. A line drawing is considered to be composed of unconstrained two‐dimensional open and closed thin curves. Each curve is quantized in line‐following fashion into a sequence of discrete links, i.e., the chain‐code representation. Chain quantization based on grid‐intersect quantization (GIQ) and object boundary quantization (OBQ) is considered. Their performance in terms of the quantization distortion is quantitatively analyzed. To reduce the amount of data required to represent a line drawing, differential chain coding (DCC) is used to convert the chain code of a line drawing into binary data. The performance of DCC in terms of the number of bits required per unit length of curve is analyzed. The tradeoff between quantization distortion and coding efficiency for DCC is determined.
A comparison of coherent digital PPM with PCM
Authors: Cryan Robert A. , Unwin Rodney T. , Massarella Alistair J. , Sibley Martin J. N. , Garrett Ian
Published: September 2008

Digital pulse position modulation (PPM) is a preferred modulation format for the ideal photon counting channel and optical intersateilite links. Here we examine its potential for the coherent optical fibre communications channel. We present a thorough performance and optimisation analysis. Comparisons, at a wavelength of 1.5 μm, are made with shot‐noise limited coherent PCM (homodyne and heterodyne ASK, FSK and PSK) over a range of fibre band‐widths and varying PPM word size. We conclude that for moderate to high fibre bandwidths homodyne digital PPM should achieve an improvement in sensitivity of typically 5 dB over homo‐dyne PSK PCM.
Adaptive DCT for image‐data compression
Authors: De Natale Francesco G. B. , Desoli Giuseppe S. , Giusto Daniele D. , Vernazza Gianni
Published: September 2008

This paper deals with the development of a coding system for image data compression based on the Discrete Cosine Transform (DCT). The aim is to integrate several methods into a single approach in order to obtain an adaptive coder characterized by higher performances. In particular, a variable blocksize scheme is used, which is based on quadtree segmentation driven by edge information. To improve data compression, DCT coefficients are then coded by a vector quantizer.

Experiments have shown that the values of compression factors can be notably increased, while maintaining a good reconstruction quality.
An abstract representation of the scalar wave equation of optics
Authors: Kragl Hans
Published: September 2008

Based on the time ‐ dependent, lossless scalar wave equation interior losses and radiation losses are introduced by a dissipation function. This method is well ‐ known from classical mechanics. To illustrate the mathematical procedure all aspects are studied by a mechanical system analogous to the optical wave field. Finally, the results are transferred to optics. By this means the physical meaning of the lossy operators that correspond to the operators E and HF of the lossless wave equation, becomes clear. These lossy operators are no longer self ‐ adjoint and as a consequence, there is no action integral for the lossy equation but only a more general variational functional. Three examples and a discussion of the necessary approximations to be made conclude the subject.
A calculated distribution for attenuation due to atmospheric absorption in the millimeter wave range
Authors: Bernardini Angelo , Pattuelli Riccardo , Pescosolido Luca , Boumis Marina
Published: September 2008

Based on the Liebe's model for the atmospheric absorption dependance on temperature, relative humidity and pressure, a statistical distribution of absorption for seven Italian cities is calculated from data collected over a six years period. Results are statistically analyzed and relevant issues such as climatic dependence and time variability are investigated.
On the need for integrated approaches to image understanding
Authors: Moneta Carlo , Vernazza Gianni , Zunino Rodolfo
Published: September 2008

Knowledge‐Based (K‐B) approaches to Computer Vision seem to have come to a stalemate, due to difficulties inherent in performing crucial activities, e.g., autonomous refinement of the embedded high‐level knowledge and time‐consuming low‐level processing. In the paper, the problem is related to a broader class of issues, and the conclusion is drawn that no individual method can be regarded as a unique and comprehensive paradigm for Computer Vision. A possible solution to this problem might lie in combining different methodologies to enhance mutual advantages and to balance individual shortcomings; K‐B vision approaches are reviewed here from this integration‐oriented perspective. Higher‐level integration should aim at improving 'intelligent' activities of K‐B systems; Machine Learning approaches to Vision are discussed from this point of view, Lower‐level integration should provide K‐B systems with the fast number‐crunching capability and robustness required; the use of neural networks and of associative memories is evaluated for this purpose. All such methodologies are reviewed, taking into account both their intrinsic peculiarities and the specific problems that may arise from coupling them with K‐B vision systems. The paper aims at providing an updated and critical picture of some lines of research that are currently being pursued to achieve an efficient integration of K‐B techniques into complex vision systems.
Comparison of TP4, TCP and XTP Part 1: Connection management mechanisms
Authors: Baguette Yves , Danthine André
Published: September 2008

This paper is the first part of a comparative study of the transport mechanisms of three protocols: ISO TP4, XTP and, to a lesser extent, DARPA TCP. This first part focuses exclusively on the connection management (i.e. connection set‐up and release) mechanisms. The mechanisms used during the phase of data transfer over a connection will be analysed in the companion paper. The goal of the comparison of the connection management mechanisms is to determine the suitability of each of the three protocols assuming that they operate in HSLANs environments characterized by high performance but also, possibly, by a wide range of application requirements as regards the types of communications to provide. This paper takes account of the very last Revision 3.6 of XTP and of the upgraded version of the ISO Transport Protocol which has been circulated for ballot as Draft International Standard (DIS) 8073.
Towards Full Communication Through Multimedia Personal Terminals
Authors: Abdat Mourad , Bellanger Maurice
Published: September 2008

Multimedia personal terminals are key elements in the full communication process. Basically, they have to efficiently encode multimedia signals and interconnect through transmission networks. The paper gives an up‐to‐date overview of the standards which are involved in both functions, emphasizing the still and moving picture standards, JPEG, JBIG, MPEG, and networks with a definite multimedia orientation, ISDN and IVDLAN. Finally, several issues are raised, which are important for the future impact of multimedia personal terminals.
Multisensor High‐Performance Terminal for Indoor Infrared Cellular Network
Authors: Castanié Francis , Roviras Daniel , Sala Alain , Ayache Alain , Carmona Cesar , Puech Philippe
Published: September 2008

This communication describes the High‐Performance Terminal of the ESPRIT II Factory Customer Premise Network project. In the first section, a brief description of the network architecture is given, showing the function of this terminal. It is shown that it is expected to integrate Audio‐Signal Processing up to the level of the automatic recognition of acoustic signatures, and Image processing up to feature extraction and image compression. The second section is devoted to the description of the signal processing algorithms, together with some relevant results of the recognition procedure. The third section gives an insight of the image processing algorithms, with a special attention paid to their 3‐D capability.
A Portable Parallel Toolkit for 3D Image Processing
Authors: Charles Henri‐Pierre , Li Jian‐Jin , Miguet Serge
Published: September 2008

Three dimensional image processing algorithms are highly time consuming. For the study of different algorithms on different parallecomputers, we need a common, portable programming model. This article describe our common programming model and the results we obtain on two volumic image processing algorithms.
An Optical Flow Algorithm Preserving Motion Boundaries and its Parallel Implementation
Authors: Bartolini Franco , Cappellini Vito , Mecocci Alessandro
Published: September 2008

One of the main techniques for the analysis of image sequences is the optical flow computation. The optical flow is a vector field representing the apparent motion, on the image, of the projected points of the objects in the scene. Many algorithms have been developed to compute the optical flow. In this paper one of these algorithms is reviewed, the performance enhanced and a possible parallel implementation presented. The main advantage of the resulting algorithm is its good behavior in presence of noise or motion boundaries; this is obtained by means of a local technique which doesn't require global optimization and by applying a median filter to restore the vector field. Furthermore a pyramidal approach is used to increase the range of interframe displacements computable by the algorithm. To enhance the time performance a parallel implementation on a network of transputers has been studied; a theoretical analysis of the efficiency of the implemented architecture is discussed and its agreement with the experimental results is reported.
Autoassociative Neural Networks for Image Compression
Authors: Basso Andrea , Kunt Murat
Published: September 2008

In this paper a neural autoassociative technique applied to image compression is presented. Particular attention is devoted to the preprocessing stage. The validity of some of the already established theoretical results is discussed and an experimental study of the mapping capabilities of the network based on a nonlinear parametrized activation function is presented. In order to test the image reconstruction capabilities of the neural technique, comparisons with more traditional image processing tools such as Karhunen‐Loeve Transform (KLT) are shown. A massively parallel implementation of a linear version of the neural technique on the Associative String Processor (ASP) machine is presented. Despite the linear structure of the ASP and the use of fixed arithmetic for the implementation, promising results are shown in terms of learning speed (of the order of 109connections per second) and quality of the reconstructed images.
Inter‐Block Redundancy Reduction in Vector‐Quantized Images by a Neural Predictor
Authors: Fioravanti Stefano , Giusto Daniele D.
Published: September 2008

A prediction scheme is proposed, which allows one to exploit residual interblock correlation after vector quantization (VQ), without loss in the quality of reconstructed images.

Such a scheme is based on a Perceptron neural network, whose goal is to produce an estimation of a block, once the neighboring blocks have already been coded. The network is trained on a set of images by means of the classical back‐propagation algorithm. The error to be minimized is the Euclidean distance (i.e., the mean square error, MSE) between the block generated by the network (using the four previously‐coded neighboring blocks as input) and the current block.

During the encoding phase, for each block vector‐quantized, the block produced by the network is used to generate a reduced codebook that, in the case of a correct prediction, allows one to use a smaller number of bits for the transmission of the block.

Experimental results show that the probability of a correct prediction ranges from 60 to 75 %, thus producing an increase in compression by a factor of 1.3 to 1.6. The main advantages of the presented approach lie in the efficiency of the neural predictor (even for images not included in the training set), and in reduced memory requirements in comparison with other methods previously proposed.
Comparison of TP4, TCP and XTP Part. 2: Data Transfer Mechanisms
Authors: Baguette Yves , Danthine André
Published: September 2008

This paper is the second part of a comparative study of the transport mechanisms of three protocols: ISO TP4, XTP and, to a lesser extent, DARPA TCP. Whereas the first partis entirely dedicated to the connection management mechanisms, the mechanisms compared in this second part are those used during the phase of data transmission over a connection. The comparison aims at highlighting the limitations and drawbacks of the data transfer mechanisms of the existing TP4 and TCP protocols as regards their applicability in HSLANs environments characterized by a high bandwidth and a low error rate. It also aims at clearly identifying the area where the emerging XTP contributes to the improvement of the past situation. Like its companion paper, this paper takes account of the last Revision 3.6 of XTP and of the upgraded version of the ISO Transport Protocol which has been circulated for ballot as Draft International Standard (DIS) 8073.
An All‐Digital Receiver for Satellite Audio Broadcasting Signals Using Trellis Coded Quasi‐Orthogonal Code‐Division Multiplexing
Authors: Braun Walter , Eglin Peter , Abello Ricard
Published: September 2008

Spread Spectrum Code Division Multiplex is an attractive scheme for the transmission of multiple signals over a satellite transponder. By using orthogonal or quasi‐orthogonal spreading codes the interference between the users can be virtually eliminated. However, the acquisition and tracking of the spreading code phase can not take advantage of the code orthogonality since sequential acquisition and Delay‐Locked loop tracking depend on correlation with code phases other than the optimal despreading phase. Hence, synchronization is a critical issue in such a system.

A demonstration hardware for the verification of the orthogonal CDM synchronization and data transmission concept is being designed and implemented. The system concept, the synchronization scheme, and the implementation are described. The performance of the system is discussed based on computer simulations.
Implementation of a Spread Spectrum Receiver and Modem for the Data‐Relay System Using Digital Signal Processing
Authors: Aftelak Andrew John , Fielding S. J. , Maguire Paul , Ward Anthony Kim , Madde Roberto
Published: September 2008

The ESA Data‐Relay System (DRS) is a space‐borne communications system which provides communications between ground stations and satellites in low Earth orbits (LEOs) with inter‐orbit links giving a data‐relay facility. The system requires a ground based receiver and modem and this paper describes the implementation of such a receiver relying heavily on Digital Signal Processing Techniques. The spread spectrum receiver and modem is presently under development by Satellites International Limited under contract to the European Space Agency (ESA). The specification requirement for the demodulator is severe, with low signal‐to‐noise ratios and high Doppler shifts. The demodulator is very flexible in terms of the types of signal it can receive, which include spread spectrum signals. The demodulator is implemented almost completely using digital techniques. Such an approach leads to potentially low implementation losses and allows the use of novel techniques in the receiver's sub‐systems.
Adaptive UPPC System for High Frequency Satellite Communications
Authors: Cacopardi Saverio , Reali Gianluca , Martinino Francesco
Published: September 2008

The use of more and more high frequency bands is presently one of the major trends in the satellite communications field. Several important advantages can be achieved by increasing frequency against a sensible impact with atmospheric effects, in particular with the heavy fading induced by rain precipitations. In the last few years, several methods based on adaptive techniques to counteract the rain attenuation have been proposed. This paper presents a new UPPC system concept based on the idea of estimating the actual up‐link to down‐link attenuation ratio (the so‐called frequency scaling factor), by using the received satellite beacon and the earth station transmitted signal, as relayed by satellite. To this purpose, an estimation procedure based on a Parameter‐Updating Prediction Algorithm (PUPA) is proposed. Simulation results for the case of 20/30 GHz frequency bands are provided.
An Adjustable‐Rate Multilevel Coded Modulation System: Analysis and Implementation
Authors: Cremonesi Paolo , Pellizzoni Roberto , Spalvieri Arnaldo , Biglieri Ezio
Published: September 2008

We present the main results of a study devoted to efficient implementation of multilevel coded modulation schemes. The key point here is that the proposed design is flexible, in the sense that the same hardware allows for the implementation of several coded schemes. This goal is achieved by associating a two‐dimensional binary partition chain with a set of punctured convo‐lutional codes. System performance is evaluated through its error probability. This is derived from the weight enumerators of the coded modulation, and the results are confirmed by computer simulation. Hardware implementation is also described briefly.
Reduced Complexity Detectors for Continuous Phase Modulation Based on a Signal Space Approach
Authors: Palenius Torgny , Svensson Arne
Published: September 2008

Optimum detectors for CPM use in general a large number of filters in order to calculate the optimum metrics. In this paper, we propose correlation detectors that calculate its metrics in a subspace of the signal space. The subspace is selected such that the asymptotic error performance is optimized for the given dimensionality. We focus on noncoherent detectors but show also some results for coherent detectors. The subspace metric calculation is combined with previously published reduced complexity decoding algorithms such as the SAN(B) and RSSD algorithms. Optimum subspace correlation detectors with different number of filters are found for both binary and quaternary CPM schemes. Their error performance on an AWGN channel is derived analytically through the use of a minimum Euclidean distance approach and is also simulated through the symbol error probability. Comparison is done with the optimum detectors. A close agreement between minimum distance and simulated symbol error probability is found for all considered detectors. We find that in most cases only 4 to 6 matched filters are needed in order to obtain a performance that is close to optimum. This corresponds to at least a five‐fold reduction in number of filters and with the reduced complexity search algorithms for making symbol decisions this leads to a dramatic reduction in overall complexity.
Coded Modulations for Fading Channels: An Overview
Authors: Sundberg Carl‐Erik W. , Seshadri Nambi
Published: September 2008

It is by now well known that combined channel coding and digital modulation (in short coded modulation) yield power and bandwidth efficient digital transmission schemes for the Gaussian channel. These schemes perform closer to channel capacity than those where coding and modulation are treated separately. More recently, coded modulation methods have been investigated for transmission over Rayleigh fading channels. It has been discovered that systems optimized for the Gaussian channel are not optimum for fading channels. This is primarily due to the importance of built‐in time diversity of the coded modulation scheme for fading channels.

In this paper we give a brief overview of recent developments in signal design for Rayleigh fading channels. Mainly schemes based on phase shift keying are presented. Theoretical guidance for design and identification of the most important system parameters are given. A couple of detailed examples of code designs and their error probability performance are also given. Optimum and suboptimum receivers are discussed. An overview of analytical performance analysis tools, as well as code designs for both trellis coded modulation and block coded modulation is included in the paper. Methods for unequal error protection are given. Potential application areas are identified. An extensive reference list is supplied.
Matched Filter Bound for Trellis‐Coded Transmission over Frequency‐Selective Fading Channels with Diversity
Authors: Fechtel Stefan A. , Meyr Heinrich
Published: September 2008

Transmission of trellis‐coded digital information over time‐variant frequency‐selective multipath radio channels leads to receiver design considerations and bit error characteristics fundamentally different from those of links using static channels. Making use of diversity is of prime importance in a fading environment. Explicit antenna diversity, implicit time diversity from interleaved trellis‐coded modulation, and implicit multipath diversity via energy detection/equalization are three methods of transmission quality enhancement that can be jointly employed without loss of power and bandwidth.

Thematched filter bound(MFB) is a lower bound on the average bit error rate under ideal conditions, i.e. perfect channel estimation, interleaving, and equalization. In this paper, a new method of evaluating the MFB based on an eigenvalue approach is presented and the analysis extended to include transmission of trellis‐coded linearly modulated signals over selective diversity channels having arbitrary fading multipath profiles.

MFB results are generated for a number of illuminating examples (trellis codes with effective code lengths up to 5, selective two‐ray and GSM Rayleigh as well as flat Rician channels) that demonstrate the potential benefits of implicit time and multipath diversity. Some simulation results are presented giving rise to concluding remarks on the tightness of the bound.