bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum and suboptimum detection of weak signals in cyclostationary non‐gaussian noise
Authors: Izzo Luciano , Paura Luigi , Tanda Mario
Published: September 2008

The paper deals with the detection of a signal in additive non‐Gaussian nonstationary noise, with reference to the case where the time‐varying noise intensity exhibits ciclostationarity. The locally optimum noise‐synchronized detector is shown to be the locally oprimum detector for stationary noise preceded by a time‐varying invertible transformation. Since the implementation of such detector is quite involved owing to the requirements that the exact waveform of the noise intensity variations is known and a perfect synchronization of the receiver to such variations is available, the paper proposes also two suboptimum detection structures. The former is the locally optimum detector for the stationary white noise, designed with reference to the time‐averaged value of the periodic noise intensity; the latter performs at the same time an estimate (achieved by two different algorithms) of the noise intensity and the signal detection. The performances of all considered detectors are evaluated and a comparison among them is made via computer simulations.
Implementation of multirate systems by digital signal processors
Authors: Wintermantel Jörg
Published: September 2008

The progress in the field of digital signal processing leads to the development of digital multirate techniques. Due to the fact that every single part of the whole system is processed with a minimum sample rate these techniques result in a very advantageous realization of a digital system with respect to the required processing time. In this paper a systematic procedure is shown leading to an efficient implementation of such multirate systems by digital signal processors. With the introduction of appropriate measures it is possible to make statements about the efficiency of the implementation with respect to the available arithmetical capacity of the signal processor. The presented method is demonstrated by the example of the implementation of a voice frequency telegraph FSK‐modem by a digital signal processor.
A collisionless tree LAN with simultaneous transmission and high throughput: A performance study
Authors: Marano Salvatore
Published: September 2008

Recently, some local area networks have been proposed where collision avoidance switches are connected in a rooted tree with stations at its leaves and a communication protocol witch makes possible multiple concurrent transmissions. These avoidance collision switches allow the implementation of random access protocol without having to pay the penalty of packet collisions. The collision avoidance LANS presented are the broadcast Star, the Hubnet rooted tree, the Tinker‐Tree and the Alberonet. In this paper a modified version of station and switch protocols is proposed in order to improve Alberonet performances. In particular, simulation results about performances of new protocols are compared with those obtained previously for Alberonet protocol and for different traffic distributions and network characteristics (size, packet length, etc.,). These results show that Alberonet performances are particularly improved with local traffic distribution. Moreover, improvements are more pronounced when modified station and switch protocols are combined. Finally, some considerations are provided which partially justify why new protocols work better than Alberonet protocols.
From R&D laboratories reduction of the chip area of MMIC distributed amplifiers
Authors: Øifot Anton M. , Pedersen Øystein
Published: September 2008

This paper presents a principle for reduction of the chip area of MMlC distributed amplifiers. It is based upon analysis of the attenuation on the drain line, and results in partly circular gate and drain lines as the basic configuration. Measurements show that s21of an MMlC realization of this principle is approximately 1 dB better thans21of a constant‐kreference amplifier. However, s22and the noise figure are not as good. The achieved reduction of the chip area is approximately 36.5%.
Latch‐up in CMOS circuits: A review
Authors: Sangiorgi Enrico
Published: September 2008

In CMOS technologies, rapidly becoming the most important ones for VLSI microelectronics, the inherent phenomenon of latch‐up, represents one of the most serious limitations for further dimension scaling in the deep sub‐micron range. For this reason latch‐up has attracted a lot of attention in the last decade and a deep understanding of its essential features has been achieved, although a few specific problems are still to be satisfactorily solved.
A new test structure for recombination measurements in thin si layers for VLSI structures
Authors: Bellone Salvatore , Spirito Paolo
Published: September 2008

The capability of two recently proposed measurements methods to evaluate recombination properties of thin layers is discussed. Both methods make use of a novel test structure which allows one to evaluate a) the lifetime profile along submicron epilayers and b) the recombination velocity set by a generic heavily doped layer. Measurements performed on 1 μm thick epilayers demonstrate that the recombination lifetime in these layers is not correlated with the doping level and it has values lower than those reported in thicker layers. Moreover, experimental data collected n+ layers of different technology suggest a phonon‐assisted lifetime value much lower than that reported in literature for uniformly doped bulk material.
Simulation of surface effects in planar GaAs MESFET structures by use of a quasi‐2D model
Authors: Brockerhoff Wolfgang , Versteegen Michael , Bertenburg Ralf , Seiler Ulrich , Heime Klaus
Published: September 2008

Surface effects in planar submicron GaAs MESFET are investigated in detail by use of a quasi twodimensional model taking into account the nonstationary transport effects in the channel which are very important for simulation of submicron structures. The model explains the transconductance compression in submicron MESFET due to the influence of the free surface in the parasitic gate‐source and gate‐drain region. The dependence of device performance on the surface potential is shown.
Simulation of surface state dynamics on GaAs MESFETs
Authors: Barton Trevor M.
Published: September 2008

This paper describes a model for surface states on GaAs MESFETs which is used to characterise the dynamic behaviour of these traps under pulsed operating conditions. The surface charge due to trap filling is shown to be highly non‐uniform between the gate and the drain, and the form of the surface charge distribution is found to depend on the current‐voltage characteristics of the gate Schottky contact. The trap filling is calculated in a self‐consistent manner within the framework of a two‐dimensional unipolar physical simulation. The resulting model is used to investigate some anomalous features of the behaviour of the MESFET. In particular, time dependence of the gate‐drain breakdown voltage under transient conditions is explained in terms of a reduction on the gate edge electric fields as surface states near the drain end of the gate fill with excess electrons and thus become more negatively charged at high values of the drain‐gate voltage. This excess surface charge modifies the electric fields near the drain end of the gate. These calculations are supported by experimental measurements on a real device.
Simulation of short‐channel and surface effects in submicron GaAs MESFETs
Authors: Makowitz Rainer , Brockerhoff Wolfgang
Published: September 2008

A transient two‐dimensional hydrodynamic device simulator is presented that allows an accurate modelling of charge transport in unipolar devices made of multiple valley semiconductor material. Carrier energy balance is included to account fon non‐equilibrium transport with emphasis on heat transport by convection, which is normally not considered by GaAs device simulators. The transport model allows investigation of realistic GaAs MESFET's fabricated by ion‐implantation with gate lengths down to 0.2 μm and high channel doping.

The causes of various short channel effects, namely threshold voltage variation and trans‐conductance compression are examined. It is shown that poor pinch‐off behaviour of devices with short gates has its origins much more in drain induced barrier lowering than in substrate conduction. As drain current increases with shorter gate length it could be expected that trans‐conductance would also be higher because of the larger amount of current that can be controlled by the gate. Instead, lower transconductance at zero gate bias is observed experimentally. It is known that this phenomenon can be attributed to surface depletion effects. TO test this hypothesis, a simple model for a uniform surface charge density has been included in the sirnulator. First results are in good agreement to measured dc‐parameters. Simulation also indicates that the channel narrowing due to surface depletion leads to travelling domain oscillations that are visible in the terminal currents.
Structural optimization of millimeter‐wave subhalf‐micron gate MODFETs
Authors: Shawki Tarek , Salmer Georges
Published: September 2008

A study of the variations of the small signal parameters of subhalf‐micron‐gate Het‐erostructure Field Effect Transistors HFETs with device scaling (aspect ratio), gate offset in the recessed zone and hot‐carrier confinement by buffer barriers is carried out for the sake of optimizing sumicron HFET structures for 40–100 GHz applications. We discuss the performance limits of existing structures and investigate new concepts and approaches to circumvent these limitations based on thorough understanding of device physics gained from 2D energy modeling. We project a net improvement in HFET millimetric performance using subhalf‐micron‐gate pseudomorphic structures which we expect to have maximum oscillation frequencies in excess of 400 GHz in the near future.
Harmonic distortion in nearly sinusoidal oscillators
Authors: Borys Andrzej
Published: September 2008

An approach for calculation of harmonic content (h) in nearly sinusoidal oscillators is presented. It uses Volterra series to develop explicit expressions, which are then used to discuss the dependence of h and the dependence of amplitudes of harmonics upon the feedback and upon the oscillation‐amplitude. Finally, the oscillator determining equation is written for two different fictitious points of cutting of the loop to illustrate uniqueness of this equation. Moreover, it is shown that the harmonic content h is generally different at different points in the oscillator‐loop.
Multi‐threshold and signal trend forecasting algorithms for hand‐off in cellular communications
Authors: Muñoz‐Rodríguez David , Lara‐Rodríguez Domingo
Published: September 2008

In this paper field strength profiles are considered as time series and the use of some prediction techniques in the hand‐off process is examined in order to have meaningful handovers. Different forecasting methods are here considered taking into account parameters as memory size requirements, weighting factors and its effect on the mean square error as well as method applicability. A forecasting method is selected and the obtained results are used in novel handover procedures. This procedures use multiple threshold and take into account trend variation. Application results including effect on number of hand‐offs are here presented and it was observed a reduction on number of hand offs for the examined profiles respect to methods that rely only on current field strenght measurements.
From R&D laboratories: A microprocessor controlled dual‐input integrator
Authors: Nandi Rabindranath , Sanyal Salil Kumar
Published: September 2008

A grounded capacitor dual‐input active integrator network configuration is presented. For the digital control of the time constant of the integrator, an array of binary weighted switched resistors has been used. The switch activation is done by a digital code generated by a microprocessor. Experimental results on such a digitally programmable integrator design are included.
The microstrip spiral antenna
Authors: Cerri Graziano
Published: September 2008

The Archimedean printed spiral antenna is investigated by numerical methods, usjng the Green's function for stratified media.

The integral equation for the current distribution is obtained by imposing the condition of vanishing total electric field tangential to the conducting strip and solved by application of the method of moments.

Knowledge of the current on the arms of the antenna allows the evaluation of input impedance and radiation characteristics of the spiral.
High speed and coherent transmission components
Authors: Speier P. , Wünstel K. , Hildebrand O.
Published: September 2008

This paper focusses on research and development activities for discrete components used either in high speed direct modulation or coherent systems, respectively. By taking full benefit of highly advanced epitaxial growth techniques like LPMOVPE and GSMBE new device structures have been realized.

On the transmitter side a SIBH laser structure is reported which is especially designed for extremely low parasitics allowing for a transmission speed in excess of 10 Gbit/s. Results on DFB‐MQW lasers are presented. By making use of two dimensional effects these lasers have shown low threshold currents, high output power as well as narrow linewidth, which is of strong interest for both high bit rate and coherent transmission, Wavelength tunable lasers, such as multisection DFB or DBR lasers as well as a YCC‐I3 laser, are investigated. With 3 section DFB‐lasers a linewidth of 3.5 MHz has been obtained. A 4‐channel FSK transmission experiment at 565 Mbit./s has been successfully performed. The passiv DBR lasers have shown a tuning range of 4.2 nm. With the novel YCC‐I3 laser structure an enormous total tuning range of 22 nm together with a continuous tuning range of 1.15 nm with 20 dB sidemode suppression and a linewidth of 35 MHz has been achieved. Semiconductor travelling wave amplifiers are reported with high average internal gain of 28 dB at bias current of 50 mA. Using 4 cascaded amplifiers a 591 Mbit/s direct detection experiment of 279 km has been performed.

Results on pin‐photodiodes and APD's are presented. Optimized pin‐detectors have been used to detect 20 Gbit/s pattern in a system experiment. Specially designed APD's are reported with a gain‐bandwidth product of 70 GHz.
Analysis of the influence of spatially localized oxide traps on the capacitance of MIS tunnel diodes
Authors: Nannini Andrea , Bagnoli Paolo Emilio
Published: September 2008

A method is proposed to calculate the capacitance of conducting MIS diodes based on a proper solution of the Poisson equation, which holds for any type of trap distribution in the oxide layer. This approach allows us to calculate the electric field and the voltage drop along the whole MIS structure, thus arriving at a general expression of its capacitance. By using these results, we obtain, as a special case, the usual expression for MIS diode capacitance in the presence of interfacial states. The theoretical l/Cz vs reverse voltage characteristics of junctions with spatially distributed oxide traps present different slopes and voltage axis intercepts in comparison with those calculated by localizing interfacial states at the insulator/ semiconductor interface only.
Improving the performances of a radiopaging system by means of a new demodulation procedure
Authors: Ettorre Giuseppe , Marietti Piero
Published: September 2008

This work deals with the problems encountered in radiopaging systems employing the POCSAG code. In order to integrate the receiver's components, a Direct Conversion Receiver (DCR) should be used. When a simple demodulation procedure is employed problems due to the unacceptably high BER arise. The paper describes two solutions of the problem and gives experimental results showing how they reduce the BER in a common RF environment.
Custom integrated circuits for audio processing and signalling in vehicular units
Authors: Chiappano Giovanni , Colamonico Armando , Donati Marcello , Maloberti Franco , Montecchi Federico , Palmisano Giuseppe
Published: September 2008

The circuitry for the audio signal and subaudio signalling processing on the new vehicular unit for Italian Mobile Radio System is described. The overall system was realized with two different kinds of CMOS custom circuits and a few other discrete components. The two chips were designed with the switched capacitor (SC) technique and integrated in a 3u double poly CMOS technology. The system is fed by a 5V single power supply and dissipates about 140 mW.
An example of a new VLSI design style based on systolic macrocells: A high‐speed single‐chip transversal filter for signal processing applications
Authors: Roncella Roberto , Saletti Roberto , Terreni Pierangelo
Published: September 2008

This paper describes the VLSI design of a high‐speed single‐chip FIR filter for data with a limited number of bits. A new design style that allows easy design of high speed VLSI systems was used. This style is based on the extensive use of systolic arrays and it is well suited to VLSI system realizations for digital signal processing (DSP) applications. This realization shows that high performance systems can be obtained with a systolic approach, using a few main building blocks called macrocells, systolic at the bit‐level, of general use and easily interconnected.
A new ARQ scheme using a go‐back‐N protocol
Authors: Benelli Giuliano
Published: September 2008

In this paper a new protocol suitable for communication systems using error detecting codes is described. This scheme is similar to a Go‐Back‐N protocol, but it presents higher performance. The throughput of the protocol is determined through a theoretical analysis. The results show that the proposed protocol maintains, as the Go‐Back‐N schemes, a simple implementation structure, but at the same time permits to achieve high throughput values. In particular, for high error rates in the communication channel the described protocol achieves performance comparable with that of the selective protocol with infinite buffer.
Impact of long periods of identical bits on the choice of a scrambler for SDH
Authors: Brugia Odoardo , Carbonelli Marco , Perucchini Daniele
Published: September 2008

The statistical properties of sequences of consecutive identical bits at the output of various scrambler types are analyzed and discussed in order to provide designers of Synchronous Digital Hierarchy systems with a wide range of choices for scrambling implementation.
A unified analysis for the multiple‐site diversity outage performance of single/dual ‐ polarized communication systems
Authors: Kanellopoulos John , Ventouras Spyros
Published: September 2008

Multiple site diversity systems are foreseen for earth to satellite paths operating at frequencies above 10 GHz in localities with high rain‐induced attenuation. A recently suggested model for the prediction of diversity performance is properly modified to include also the double polarized systems. The unified method for single/double polarized earth‐space paths uses the assumption of lognormal unconditional distribution of rainfall for the location under consideration. Numerical results are presented corresponding to several operating systems under the hypothesis of using both single and double polarization. Some useful conclusions are deduced.
New technologies for physically disabled individuals
Authors: Tronconi Alberto , Billi Marco
Published: September 2008

Often, physical impairments due to congenital conditions, acquired disabilities, progressive neurological diseases, and temporary conditions, do not allow the processes by which information is exchanged between people through verbal and non‐verbal behaviours. Furthermore some physically handicapped, encounter insurmountable obstacles with computer access. These impediments also prevent many possibilities in the use of electronic communication systems.

In this paper we present some notes on the use of the new technology to realize communication aids for physically disabled persons. We supply some information on the devices which are commercially available and on the systems that we are developing.
Multimedia services and applications
Authors: Barbosa Luis Orozco , Georganas Nicolas D.
Published: September 2008

Multimedia communications is the field referring to the representation, storage, retrieval and dissemination of machine‐processable information expressed in multiple media, such as text, voice, graphics, image, audio and video. With the advent of high capacity storage devices powerful and yet economical computer workstations and high‐speed integrated services digital networks providing a variety of multimedia communications services are becoming not only technically but also economically feasible. Applications in medicine, education, travel, real‐estate, banking, insurance, administration and publishing and advertising are emerging at a fast pace. These applications are characterized by large multimedia documents that have to be communicated within very short delays. Computer‐controlled cooperative work, whereby a group of users can jointly view, create, edit and discuss multimedia documents is going to be characteristic of many transactions in the year 2000. In this paper, we review the activity in Multimedia Communications, Services and Applications.
Evolution of LANs and MANs towards high speeds: Gigabits per second and beyond
Authors: Gerla Mario , Fratta Luigi , Bannister Joseph
Published: September 2008

This paper traces the evolution of LANs ad MANs from the early Ethernet days to recent Gigabit per second prototypes. Three generation are identified. The first generation includes Ethernets, Token Rings and Token Busses, and has a speed upper limit in the order of lOMbit/s. The second generation consists of architectures which have evolved from the first generation exploiting the fiber optics technology and properly modifying the access protocols. Higher speeds (in the order of hundreds of Mbit/s) and larger distances are thus achieved. Typical examples are FDDI and DQDB. The third generation represents a further step in the direction of higher speeds (hundreds of Gigabit per second). The key elements to achieve such high speeds are passive optic components and wavelength division.

The paper consists of two parts. In the first part, the evolution of topologies and access protocols from generation to generation is described. In the second part, two representative examples of third generation networks, namely, Tree Net and WON, are presented.
Structure of broadband communication network
Authors: Mossotto Cesare
Published: September 2008

The present telecommunication evolution is driven by a very complex relationship between market forces and new advanced technologies. This process is accelerated, among other things, by regulation actions and, more important, by the availability for end users of competing alternative solutions. Aim of the paper is first to discuss some of the major requirements/opportunities ‐ from standard to business user needs, from intelligence to decentralization, from mobile to image communications. This allows setting a rationale and an overall consistent framework for the three‐yearSubproject 1: Structure of Broadband Communication Network.After a brief introduction about the innovation process in complex systems, the paper clarifies the role and the time scale for the service offering of broadband structures in telecommunication networks. The main research topics are then summarized thereby giving an introduction to the three more focused Conference papers, which consider specific relevant issues, broadband network evolution, metropolitan area networks, and satellite systems for high‐definition television (HDTV). Finally, the subproject organization, work progress and major achievements obtained in the first‐year activity are outlined.
Technologies for broadband optical communications
Authors: Daino Benedetto
Published: September 2008

In the Research Project on Telecommunications of the National Research Council, the area of the «Technologies for broadband optical communications» was individuated as one of the key areas for the promotion of advanced research activities and the formation of highly specialized competences in a field which will be determinant for the development of future communication networks. The subproject 2 was established on this view, and a detailed plan for researches on some relevant topics, namely the coherent techniques, the optical switching and the optoelectronic components, has been defined. In the following, the objectives and the research activities included in the project are illustrated in detail.
Experimental realizations of broadband communication networks
Authors: Cappellini Vito
Published: September 2008

The advantages of broadband communication networks are outlined. The activities developed in the framework of the Sub‐Project 5 of the C.N.R. Telecommunications Project are presented: the study and implementation of LANs and MANs using different communication links (optical fibres, satellite systems and also, for urban areas, microwave systems); the study of high speed optical communication networks (deflection networks and multi‐hop networks); the experiments on advanced services, carried out mainly for the scientific users. Two services are in particular outlined, teleeducation and telemedicine, on which experiments are planned with the aim of exploiting the capabilities of the broadband communication networks. Some indications are also given on the geographical areas, that are candidate for LANs‐MANs implementation and experiments performance.
Evolving system architecture towards B‐ISDN
Authors: Di Pino Duccio , Forcina Alessandro , Dogliotti Renato , Casale Salvatore , Maggi Wolfango , Berrini Alberto
Published: September 2008

The paper aims at describing a possible evolution strategy of a telecommunication network architecture which should provide users with a wide range of broadband services in a relatively short term. The discussion reflects the work carried out within the Italian «Progetto Finalizzato Telecomunicazioni» and it assumes, as starting points, the deployment of a digital network structure, together with the first introduction of the new Synchronous Digital Hierarchy (SDH) equipment.

On the basis of the mentioned hypotheses, the exploitation in the network of the SDH capabilities, the role of Metropolitan Area Networks (MANs) and the issues related to the deployment of optical fibres in the distribution network are discussed with the target to provide a «grace‐ful» evolution path towards the future ATM‐based Broadband ISDN (B‐ISDN).
Metropolitan area networks: Standards, services and performance
Authors: Coronaro Massimo , Freschi Giuseppe , Iudica Melchiorre , Pavanelli Claudio , Roffinella Daniele
Published: September 2008

The paper, after a general survey of Metropolitan Area Network (MAN) issues, in which the market demand and recent trends in MAN concepts (e.g. relationship with Broadband Integrated Services Digital Network, B‐ISDN) are considered, examines the ongoing MAN related activities inside standard‐setting bodies such as IEEE (Institute of Electrical and Electronic Engineers) and ETSI (European Telecommunications Standards Institute). Emerging trends in architecture, protocols and services are reviewed.

A more detailed characterization of the bearer services MANs are required to provide (i.e. connectionless, non isochronous connection oriented and isochronous) is then given, emphasizing their broadband nature and the related applications; the functions providing these services within the Distributed Queue Dual Bus (DQDB) framework are briefly described.

The last section is devoted to a discussion of MAN performance. specifically in terms of fairness, focusing again on the DQDB protocol, which appears to be the most promising solution for MANs, and on possible improvements of its characteristics.
Digital transmission of HDTV on satellite channels
Authors: Cominetti Mario , Morello Alberto , Castellani Valentino , Visintin Monica , Casoria Atanasio , Losquadro Giacinto , Puccio Antonio
Published: September 2008

The perspectives for digital HDTV on satellite channels are examined at the light of the recent progress on bit‐rate reduction algorithms and on modulation and channel coding techniques. The experimental HDTV transmissions at 70 Mbit/s carried out by the RAI during the «1990 Football Worldcup» are shortly described. A preliminary configuration of the future HDTV network architecture has been identified, including terrestrial and satellite links. Two advanced modulation and coding systems, suitable for operating in the 30/20 GHz frequency range, have been studied by computer simulations: a) QPSK modulation and concatenated convolutional and Reed‐Solomon coding, and b) Trellis‐coded 8‐PSK modulation and concatenated Reed‐Solomon coding. The satellite channel has been optimized as regards the transmitting and receiving filters partitioning and the TWTA operating point. An example of design of a complete satellite chain at 30/20 GHz shows the feasibility of a 140 Mbit/s HDTV transmission system based on the described techniques.
Optical coherent systems in optical fibre LAN's and MAN's
Authors: De Marchis Giancarlo , Antodicola Claudio , Betti Silvello , Curti Franco , Grosso Guido , Iannone Eugenio , Matera Francesco
Published: September 2008

A review of the potentialities offered by optical coherent techniques in LAN's and MAN's applications is presented. Some aspects concerning both topology and access techniques have been briefly discussed. The optical coherent systems and their technological requirements have been analyzed in order to show the advantages offered both in networking and broadcasting.
Semiconductor devices for photonic switching
Authors: Costa Bruno , Cocito Marco
Published: September 2008

The concept of all optical networks and the motivations for investigating them are briefly mentioned. Photonic switching is specifically considered and reasons for carrying out research on semiconductor based materials and devices for the implementation of optical switching functions are given. Afterwards the main physical properties that may find applications in photonic devices made of semiconductor materials are reviewed, with emphasis on QW structures and the associated important phenomena of Quantum Confined Stark Effect and Optical Stark Effect. The state of the art is then presented regarding the various devices needed in a photonic switching node: space/time switches and switching matrices (both of the electro‐optical and opto‐optical type), frequency switches, frequency converters and filters, digital memory elements made by optical bistable devices, logic optical devices.
Transputer based videocoders: Requirements and architectures
Authors: Brofferio Sergio , Mastronardi Giuseppe , Rampa Vittorio
Published: September 2008

Videocoding algorithms possess a high degree of computation concurrency that can be exploited by parallel architectures. This paper presents the status of an applied research aimed at the implementation of a Transputer based videocoder for professional workstations. Basic algorithms are reviewed in terms of computation requirements and the ones specifically developed for ATM systems up to 2Mbit/s are quantitatively analyzed. Architectural tradeoffs are presented so that the demonstrator architecture can be defined in its hardware and software aspects. A video transputer module is defined and designed down to the logical level. Different partitioning of the algorithm execution is possible using a newly proposed «Farmer» Operating System.
Image coding with block DCT and motion compensation. Iwo different approaches
Authors: Bellifemine Fabio , Chimienti Antonio , Picco Romualdo , Muratori Mario , Stroppiana Mario
Published: September 2008

Many approaches have been used to the purpose of image data compression. Each of them combines various techniques to exploit the redundancy of the image signal.

In this paper two different approaches will be presented, analysed and compared. They have been developed by the CNR‐CSTV and the RAI Research Centre(1) respectively, in the framework of subproject 3.2 of the CNR «Telecomunicazioni» project. The goal is to define a coding scheme suitable for the bit‐rate compression of digital HDTV signals in order to cope with the characteristics of two kinds of channels: a synchronous channel at 70 Mbit/s and an asynchronous one with peak bit‐rate of 140 Mbit/s. The coded images must have a good quality for distribution networks.

Both algorithms are based on the hybrid transform image coding using the 2D‐DCT to reduce the spatial correlation. In order to further decrease die temporal correlation a motion compensation technique is also applied. The aim of this paper is to describe the two algorithms and to investigate the main differences.
A new coding diversity technique
Authors: Benelli Giuliano
Published: September 2008

Diversity techniques are widely used when the communication channel is affected.by heavy noise and disturbances. In the diversity techniques the same information is transmitted over m >1 channels. At the receiver side, the signals are combined together in order to reduce the bit error probability. In this paper a new diversity technique, using a suitable channel coding algorithm, is described. In this technique the information transmitted differs from one channel to the other one. The performance of this technique is obtained through a theoretical analysis. The application both to forward error correcting codes and automatic repeat request systems is described. The proposed technique is applied also to automatic repeat request schemes without diversity. The proposed technique permits to achieve in many cases higher performance than the classical diversity schemes.
Doppler correction for scattering matrix measurements of random targets
Authors: Tragi Karl
Published: September 2008

A central topic in active microwave remote sensing is the measurement of polarimet‐ric scattering matrix time series. At least two successive measurements, employing orthogonal transmitter polarisations, are necessary to determine the full S‐matrix of an object. In many remote sensing applications, however, the observed targets experience small but non‐negligible variations even in the small time interval which is required to perform the S‐matrix measurement. In order to cope with this problem, a Doppler phase correction scheme can be applied which compensates for the deterministic mean target motion. The possible internal variation of a composite target due to the random motion of the target's individual scattering centres of particles, however, results in decorrelation of the consecutively measured S‐matrix columns and leaves significant statistical errors uncorrected. In the present paper the mean Doppler phase correction method and the related estimation errors are studied in greater detail, employing a quite general model of time‐variant random targets. It turns out that the critical quantity which determines the statistical accuracy of the Doppler correction is given by the ratio of the pulse repetition interval and the decorrelation time of the observed random target. The pulse repetition frequency of the radar measurement, hence, has to be chosen carefully in order to avoid large estimation errors in the S‐matrix determination. Matching the pulse repetition frequency properly to the decorrelation time of the observed target, on the other hand, allows the measurement and processing of polarimetric S‐matrix series with maximum information content on the target. The present statistical studies, this way, are of fundamental interest in many polarimetric remote sensing applications.
Signalling for B‐ISDN communications
Authors: Biocca Alfredo , Contini Enzo , Fioretto Giorgio , Piovano Luciano
Published: September 2008

The ATM based B‐ISDN offering a multiplicity of services in an integrated way represents the future communication network. One of the major points relates the signalling system to be adopted in order to fulfil the high flexibility the B‐ISDN requires.

The first part of this document deals with the general requirements of the B‐ISDN signalling system, analyzing the new call and connection control concepts and giving some guide‐lines for a modelling activity. Considerations for a long‐term signalling system, which will have to handle a multiplicity of services, are also presented: multimedia services, complex call configurations, transitions among them during the lifetime of a call, and re‐configurations of attributes values for a connection are described.

The second part proposes some basic issues for a preliminary example of signalling system which handles ATM point‐to‐point connections between two users or between a user and a specialized node, supporting services which require centralized resources within the network, such as connectionless or multimedia services.
An ATM switching testbed
Authors: Balboni Gian Paolo , Chiarottino Wolmer , Demichelis Carlo , Melen Riccardo , Pelizza Maurizio , Ravera Mauro
Published: September 2008

An experimental ATM switching node being developed by CSELT in the framework of CNR PFT is described.

The node is built around a self‐routing buffered multistage switching network based oh a single type of integrated component. Each port of the network is connected to a packet processor which is in charge of interfacing with external ATM flows at 150 Mbit/s and of dealing with the ATM layer protocols.

A distributed control structure is implemented, together with a software architecture which permits a rapid and easy introduction and testing of new services by abstracting system resources and defining a formal interface to application software.

The access network developed within the ATM testbed is based on an active star shaped B‐NT which controls the access of the customer equipment to the local exchange and performs statistical multiplexing of the generated information flows.

The terminals and interworking unit being provided in the ATM testbed have also been described, to give a picture of the services which will be considered in the experimentations.
A comprehensive analysis of DQDB
Authors: Conti Marco , Gregori Enrico , Lenzini Luciano
Published: September 2008

This paper reports on an extended simulation analysis of the asynchronous part of the DQDB MAC protocol. The analysis is divided into three parts. The first and second part deal with one priority level, while in the third part we analyze DQDB behavior with multiple priority level. In the first part we study DQDB inunderload conditionsi.e., when the offered load is lower than the medium capacity. Our results show that in underload, the access delay is not always as low as expected. In the second part we study DQDB inoverload conditions, i.e., when the offered load is higher than the medium capacity. Our results show that DQDB without the Bandwidth Balancing mechanism(BWB)is unfair and that the unfairness is dependent on the medium capacity and the bus length. When the BWB is enabled, DQDB fairness and performance, in the steady state, improve significantly. However, DQDB takes some time (depending on the BWB‐MOD value) to achieve the steady state during which the node quality of service is degraded. In the third part we show that the DQDB priority mechanism is not always effective.
User oriented satellite networks: Studies on utilization of transmission capacity in TDMA and TDMA/FDMA systems
Authors: Celandroni Nedo , Ferro Erina , Dossi Laura , Tartara Guido
Published: September 2008

The project to interconnect, in the C.N.R. environment, local area networks via satellite links at high speed, presents the problem of an efficient utilization of the transmit capacity of the satellite channel, as well as problems related to the terminal design. In particular, referring to satellite access schemes in FDMA and/or TDMA, the optimization of the transmission capacity utilization, according to the traffic requirements, is analyzed. Two systems, based on hybrid MF‐TDMA, are presented and synchronization problems are analyzed.
Users, services and traffic modelling for broadband telecommunications planning
Authors: Capurro Mario , Ravaglia Renzo , Giuli Dino
Published: September 2008

The emergent broadband networks represent the hub of the research and marketing activities in the telecommunications world. A rigorous network planning methodology is necessary in order to identify the most profitable introduction strategies of broadband telecommunications services and in order to determine the best network solutions according to users needs and fixed requirements, such as usually cost and performance requirements.

The first step of such a methodology must deal with users and services analysis in the environment of interest.

In this paper a proposal of users, services and traffic modelling is presented, which constitutes the first fundamental stage of a general broadband network planning theory. The analysis of these factors is performed, with particular focus on traffic characterization.
Design and verification of A CMOS transconductance cell with extended linearity
Authors: Gatti Umberto , Maloberti Franco , Torelli Guido
Published: September 2008

A fully CMOS tunable transconductance cell is presented. The key element of the circuit is an MOS transistor operated in the triode region with an adjustable constant drain‐to‐source voltage. The cell can be used in both single‐ended‐input and differential‐input configurations. Both design considerations and measurements performed on integrated test structures are presented. The cell shows a very good linearity over a large dynamic range. For the cell used in the differential configuration, the measured total harmonic distortion is as good as −53 dB and ‐ 43 dB with a differential input signal peak amplitude of 3 V and 6 V, respectively, when the supply voltage is equal to ±5 V. The cell also shows very good performance up to several megahertz.
Effect of the transmission impairments on the performance of packet radio networks
Authors: Immovilli Gianni , Merani Maria Luisa
Published: September 2008

Packet radio has recently gained great interest in the wider context of mobile communications. In this scenario, the signal worsening due to real transmission conditions (linear and nonlinear distortion, fading, interferences, noise) deeply affect the network performance. It is then necessary to verify whether it is feasible, and if so, how to dimension the transmission system supporting the network itself, in order to respect a fixed quality condition.

In this work we suggest the introduction of a quality criterion which seems particularly suitable to set up a relationship between transmission and network parameters, and therefore to solve the problem previously submitted. We determine this relationship with reference to a star topology network, where the slotted Aloha protocol is employed in conjunction with a narrowband modulation scheme; independent, non‐selective and slowly varying fading conditions on every link of the network are also assumed.

The treatment developed is then applied to a significant example of packet radio network, and many numerical results are reported.
Speech packet dropping probability for speech/data transmission using packet reservation multiple access
Authors: Sastry Kasibhatia , Prasad Ramjee
Published: September 2008

The Packet Reservation Multiple Access (PRMA) is analysed using a Markov chain model for speech/data transmission to a central base station. The effect of the number of users on the speech packet dropping probability is investigated including consideration of transmission permission probability.
An accuracy measure for DFT‐based analog filter simulation techniques
Authors: Presti Letizia Lo
Published: September 2008

It is well‐known that the simulation of analog filters must be based on the simulation theorem, which refers to a digital model of the filter to be simulated. Here we show the relationships between the DFT simulation techniques and this theorem, and how to extract the digital model implicitly contained in a filtering process based on DFT. As the simulation results depend on the quality of the digital model, we propose to introduce a parameter able to measure the difference between the actual model and the ideal one. Here we define a quality coefficient, related to the mean square error between the actual model and the ideal one, with some interesting characteristics: it can be very easily software implemented, depends only on the digital model, can be evaluated at the beggining of the simulation process (before filtering), gives the user a very simple criterion to estimate the quality of the digital model.
Classification of Ortho‐mode transducers
Authors: Bøifot Anton M.
Published: September 2008

This paper presents a classification of ortho‐mode transducers (OMTs). The OMTs are classified into five main groups. The first four contain OMTs based on waveguide‐to‐waveguide transitions. The basis for this classification is symmetrical properties which affect both the isolation and the matching capacities. A systematic analysis of the generation of symmetrical and odd symmetrical higher‐order modes including their influence on the isolation and matching conditions is also included. The last group of OMTs consists of devices with waveguide‐to‐coax transitions. These are denoted hybrid OMTs.
An abstract representation of the scalar wave equation of optics. Part 3
Authors: Kragl Hans
Published: September 2008

The abstract representation of the scalar wave equation of optics is extended from the time‐dependent wave equation to the stationary wave equation via the fundamental action integral. It is demonstrated that the stationary wave equation together with general initial conditions is not equivalent with the corresponding time‐dependent equation, because with the transition one has lost physical information. The consequences thereof are discussed. Subsequently the modes of the stationary wave equation are defined and their attributes, which follow from missing losses of the physical system, are given. Finally the mode coupling method for the stationary wave equation is derived by geometrical reflections. Two examples illustrate the considerations.
On the definition of forced‐response stability
Authors: Fettweis Alfred
Published: September 2008

The purpose of this note is to establish the equivalence of two distinct definitions of forced‐response stability used in the literature.
Loss formula for burst transmission spread spectrum systems
Authors: Kleinhempel Werner , Baier Paul Walter
Published: September 2008

In burst transmission spread spectrum systems it is advantageous to effect receiver synchronization by passive correlation, i.e. by matched filtering, and to detect the message by active correlation which means multiplication by a reference signal and integration in the time domain. If the number of available active correlation circuits is limited, a certain percentage of the arriving telegrams cannot be processed and will be lost. In conventional analog burst spread spectrum systems the loss can be calculated with the Erlang loss formula. For modern digital burst spread spectrum systems the Erlang loss formula is only an approximation which maiy give unaccurate results. In this paper an exact loss formula for digital spread spectrum systems will be presented and compared with the Erlang loss formula. The formula will be applied to minimize the loss of a practical system.
A new general procedure to extract the noise parameters of microwave gaAs mesfets
Authors: Armenise Mario Nicola , Perri Anna Gina
Published: September 2008

In this paper a generalized procedure to extract the noise parameters of GaAs MESFETs is presented. The average quadratic error between the measured values of optimum noise figure and the calculated ones is minimized in order to obtain the optimum admittance value at the amplifier input. The hypothesis of device unilaterality is assumed. A comparison between the proposed method and the previous ones has been carried out. A consequent more simplified analytical approach to evaluate the optimum noise source impedance of a GaAs MESFET amplifier allows the proposed procedure to be easly implemented in the most popular CAD tools.