bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inter‐Block Redundancy Reduction in Vector‐Quantized Images by a Neural Predictor
Authors: Fioravanti Stefano , Giusto Daniele D. 
Published: September 2008

AbstractA 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

AbstractThis 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

AbstractSpread 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

AbstractThe 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

AbstractThe 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

AbstractWe 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

AbstractOptimum 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

AbstractIt 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

AbstractTransmission 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.
Performance Analysis of new Techniques of Predistortion with Memory in Digital Radio Links
Authors: Bernardini Angelo , Fina Silvia De 
Published: September 2008

AbstractThis paper presents an efficient data predistortion technique with memory applied to digital transmissions over nonlinear channels, specifically satellite links, employing QAM signal formats. The proposed technique is aimed at reducing the high complexity of a conventional pre‐distorter with memory by splitting the function to be realised into simpler blocks. This approach has been suggested by the circumstance that the numerical channel is constituted, in this case, by a nonlinear memoryless block and by two linear blocks with memory so that the predistorter itself can be realised by two FIR filters separated by a memoryless nonlinear element. As for the nonlinear block, we propose the employment of a neural net performing a typical surface reconstruction task, that is the approximation of the function inverting the nonlinearity source (in this case the high power amplifier). Performance analysis has shown a significant improvement with respect to memoryless predistortion (up to 4.5 dB); our proposal, moreover, outperforms conventional 3‐stage‐memory predistortion as the modulation levels increase and as the spectral shaping gets narrower.
Letter: Prediction of the Outage Performance of an Unbalanced Orbital Diversity Earth‐Space System (Log‐Normal Case)
Authors: Kanellopoulos John D. , Ventouras Spiros 
Published: September 2008

AbstractDiversity schemes are foreseen for earth to satellite links operating at frequencies above 10 GHz to overcome the high rain induced attenuation. In this paper, the orbital diversity configuration, which uses two satellites and an earth receiving site, is discussed.For this reason, a recently suggested model for the prediction of the outage performance of a balanced orbital diversity system is extended to include the more complicated but practical unbalanced case. The lognormal distribution and the convective raincells are assumed to be representative of the point rainfall statistics and the spatial structure of the rainfall, respectively. Numerical results are compared with experimental data of this kind, taken from an operated unbalanced system located at Fucino, Italy. The agreement was found to be quite encouraging.
Performance Study of an ATM Self‐Routing Multistage Switch with Bursty Traffic: Simulation and Analytic Approximation
Authors: Xiong Yijun , Petit Guido , Bruneel Herwig 
Published: September 2008

AbstractAnNxNself‐routing multistage switching network with bursty and uniform traffic, which is composed ofSx 5 switching elements with output queueing and hasK= logSNstages, is considered in this paper. The input traffic is modelled by a two‐state (active/silent) Markov chain. Each arriving cell selects one of theNoutlets as its destination independently and with equal probability I/N.The performance of the switching network is studied by means of a simulation method. An approximate traffic model of a four‐state Markov chain is proposed to characterize the cell arrival processes to further stages and its related switching element performance is analyzed. Comparison with the simulation results shows that the proposed traffic model gives a good approximation, which implies that the performance of the switching element mainly depends on the first two moments of the active and silent periods and is not sensitive to the shapes of their distributions. The influence of bursty traffic on the performance of the switching network is discussed and illustrated by some numerical examples. The impact of traffic randomization on the performance of the switching network is also investigated.
Multiplexers ΣD/D/1 with Service in Cyclic Order and Service in the Order of Arrival
Authors: Petersen Joachim , Gillen Thomas 
Published: September 2008

AbstractIn future Broadband Integrated Services Digital Networks, information will be transferred in the form of small fixed sized data units called cells. Stations making use of constant bit rate services generate cells at regular intervals. The waiting times experienced by cells if such cell streams are multiplexed and the properties of the cell stream outgoing from the multiplexer are of high interest. They are analyzed here for time continuous, time slotted and time discrete operation, comparing service in cyclic order to service in the order of arrival. Results are given in closed form.
Nonlinear Distortion and Intensity Noise Induced by Laser Frequency Chirping and Fiber Dispersion in Multichannel Intensity Modulation Systems
Authors: Gao Yu , Leich Martin 
Published: September 2008

AbstractWhen a chirped intensity‐modulated light signal is transmitted through a dispersive optical fiber, substantial nonlinear distortion and intensity noise are generated due to the laser frequency chirping and the FM‐AM conversion. This paper presents a new theoretical analysis of these effects. Based on a concise system input‐output representation, the intensity noise and the nonlinear distortion after fiber transmission are determined and given by simple analytical expressions. The classical Volterra‐Wiener theory is applied to ascertain the system dynamic nonlinea‐rity. It is shown how the laser intensity and phase noise, the fiber length and dispersion as well as the intensity modulation, affect the overall system performance. In particular, their impact on multichannel analog TV transmission systems is investigated.
Diversity Combiner for a Limiter‐Discriminator‐Integrator Receiver for Coded CPFSK
Authors: Goldman Haim 
Published: September 2008

AbstractThe paper describes the operation and analyses the performance of a diversity combiner for a limiter‐discriminator‐integrator receiver for coded continuous‐phase frequency‐shift‐keying (CPFSK). The plane of received signals is optimally partitioned using the generalized cut‐off rate as the optimization criterion. Each received symbol is assigned a weight used for soft decision decoding. If estimates of SNR on the diversity branches are available, the combiner utilizes either both branches or just the branch with the largest SNR, depending on the relative magnitudes of the SNRs. In the large effective range, in which it is advantageous to use both branches, the performance of the analysed combiner is better than that of the selection combiner. The combiner can also operate with no SNR estimates. The paper presents results for optimal partition parameters of the signal plane for various modes of operation, criteria for choosing the optimal mode and an upper bound on the probability‐of‐error for operation with a rate 0.5 convolutional code.
Performance of Interpulse Signal Coding in Interleaved‐Pulse Polarimetric SAR
Authors: Giuli Dino , Facheris Luca 
Published: September 2008

AbstractFully polarimetric Synthetic Aperture Radars (SAR) provide a complete measurement of the scattering matrix of the imaged target by alternately transmitting two pulses at orthogonal polarizations, while processing echoes simultaneously received on two orthogonal polarization channels. Due to this procedure of performing measurements, the problem of interference caused by range ambiguities is of greater concern than in conventional non‐polarimetric SAR. Such interference is made up by signals of different nature, depending on the order (even or odd) of the range ambiguity. In particular, odd‐order range ambiguities generate an interference on crosspolar terms of the matrix, proportional to one of the copolar terms, which have typically a much greater magnitude. This drawback, that never occurs in non‐polarimetric SAR systems, is a major source of measurement contamination, in particular in the presence of range ambiguous echoes from areas which are illuminated at low incidence angles.In this paper, after discussing the influence of range ambiguities on the accuracy of scattering matrix measurement as performed by interleaved‐pulse SAR, we examine the utility of appropriate interpulse phase coding strategies, to be devised and utilized with the purpose to reduce the interference due to range ambiguities and affecting those target scattering matrix elements, whose measurement is expected to be most critical.
Laser Diodes and Integrated Optoelectronic Circuits for Fiber Optical Applications
Authors: Wolf Thomas , Amann Markus Christian , Albrecht Helmut 
Published: September 2008

AbstractThe development of high performance semiconductor laser diodes has played a key role in the rapid deployment of optical fiber communications, and the realisation of advanced system concepts strongly depends on the further improvement of the laser diodes. This includes the demand for wavelength tunable single frequency laser diodes as well as the need for optoelectronic integration. The different laser structures in the 1.3 and 1.5 μ m wavelength regions, their relevant parameters and applications are described in this paper. The impact of recent progresses in the material technology on the device performance is particularly investigated. It is further shown that the availability of low‐cost, highly complex integrated optoelectronic components represents a prerequisite for the introduction of optical communication systems in the subscriber area. The photonic and optoelectronic integrated circuits presented so far for bidirectional transmission, photonic switching and optical distribution are presented and the challenges for the future development are discussed.
Recent Results on Fatigue and Dispersion Modification in Optical Fibers
Authors: Antos A. Joseph , Glaesemann G. Scott , Vandewoestine Robert V. 
Published: September 2008

AbstractThis paper reports recent results on two areas of optical fiber technology that, while unrelated, are of current interest. The first topic addresses dispersion limitation of transmission rates in optical fibers. This topic has increased in visibility in the last two years as optical amplification has minimized the importance of attenuation limits in the design of long transmission distance systems. Methods to minimize the dispersion limitation, such as dispersion shifted fiber, distributed amplification and dispersion compensating fiber, will be discussed. The second topic, that of the mechanical fatigue in optical fibers, has been a topic of research for many years, but new data continues to be gathered that is useful for cable design and system reliability calculations. Data is presented for two static fatigue tests of 3 years and 15 years duration.
Performance of coded direct‐sequence systems with rake reception in a multipath fading environment
Authors: Goeckel Dennis , Stark Wayne 
Published: September 2008

AbstractThe probability of error is determined for an uncoded coherent direct‐sequence spread‐spectrum system with rake reception operating in a specular multipath fading environment. Bounds on the probability of error for a convolutionally‐coded system are also calculated through the use of the union bound. The model that is utilized contains a large number of paths divided into groups across the signalling interval. The rake is assumed to be locked onto the direct path and one strong path from each of a subset of the other groups. The probability of error is calculated using the characteristic function to determine the effect of various system parameters such as the processing gain and the number of rake branches. Comparisons are made with results obtained through the standard Gaussian assumption. Finally, further analytic results are presented for the rake receiver in the low signal‐to‐noise ratio limit.
Performance evaluation of multi‐cell direct‐sequence microcellular systems
Authors: Sun Chung‐Ming , Polydoros Andreas 
Published: September 2008

AbstractThe performance of an asynchronous multi‐cell Direct‐Sequence Spread Spectrum Multiple‐Access (DS/SSMA) system is evaluated in lineal microcells with flat Rician fading and shadowing. Both the Bit Error Rate(BER)of the uplink (i.e., the user to the base station) and the downlink (i.e., the base station to the user) are evaluated. We develop a new analytical model to evaluate the uplink performance which accounts for the user's spatial distribution, the chip waveform, the power control, and macro‐selection diversity. On the downlink, since no power control is used, the desired signal follows a composite log‐normal noncentral chi‐square distribution. We propose an approximation method to reduce the computational complexity while still providing satisfactory precision. The analysis results show that the macro‐selection diversity can reduce the other‐cell interference effectively even for a channel with heavy shadowing. The Rician factor, the standard deviation of the shadowing, and the chip waveform have significant influence on the performance.