bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automatic 3D model building from video sequences
Authors: Gool Luc Van , Zisserman Andrew 
Published: September 2008

AbstractWe describe progress on automating the construction of 3D geometric models from video sequences. The system we are developing allows a person to walk around a room with a video camera, and from the video sequence alone extract a 3D model of the room. The room can then be graphically rendered together with possible arrangements of previously modelled objects, e.g. CAD models of furniture. The system is designed to ease model acquisition for virtual reality and telepresence applications, however the approach also has application in model based image coding. The approach is based on recent work in computer vision where image primitives are extracted and matched through an image sequence. For example, the simultaneous estimation of epipolar geometry and image corner correspondences. The matching techniques are both robust (detecting and discarding mismatches) and fully automatic. No knowledge of the camera (e.g. its focal length) or motion is required. 3D structure is computed from the matched image primitives (corners, lines and texture). The structure is then triangulated and texture is mapped onto the triangles from intensities in the images. Experimental results are provided for a variety of scenes, including isolated objects acquired with a standard CCD camera, and outdoor scenes acquired with a hand‐held camcorder.
An advanced satellite system to provide interactive multimedia mobile services
Authors: Losquadro Giacinto , Luglio Michele , Vatalaro Francesco , Paraboni Aldo 
Published: September 2008

AbstractProvision of wideband services up to the final user anywhere is a challenging task for terrestrial technologies unless the satellite is included as an essential system component. This objective is even more difficult to be met if at least a limited degree of user interactivity and mobility is required. Satellite multimedia applications will require wide bandwidths, high degree of flexibility on‐board and intelligence at terminal level. The combined use of Ka band (20‐30 GHz) and EHF (in the range 40‐45 GHz) can extend interactive multimedia and personal services to ubiquitous and mobile users. This paper discusses the main interactive multimedia services and applications that may be provided via satellite. Particularly, it describes a new project, the “SECOMS project”, that is under way in the framework of a programme of the European Union. The paper provides some indications on the main SECOMS assumptions and requirements, and system design elements.
Transport‐independent group and session management for group communications platforms
Authors: Wilde Erik , Plattner Bernhard 
Published: September 2008

AbstractWith more and more computers gradually changing from isolated, personal tools to networked workstations, group communications is an area of research which has received much attention recently. This paper focuses on a model and the architecture of a system which supports group communications by providing group and session management functionality. The system architecture is related to DNS or ×.500, however avoids their complexity by focusing on group and session management and adding functionality where necessary. New functionality is needed for the dynamics of group communications (members of a connection may change over the lifetime of the connection) and increased complexity of relations which may be established between objects. A model is described which defines six object types which represent the relevant objects. Users and groups represent real world users and their relations. Sessions and flows describe ongoing group communications. Flow templates and certificates provide mechanisms for management and security issues. The architecture presented in this paper can be used for group and session management support within different group communications platforms. A description of the implementation as well as implementation results are given in the last section.
Differential cryptanalysis of RC5
Authors: Knudsen Lars R. , Meier Willi 
Published: September 2008

AbstractIn this paper we investigate the strength of the secret‐key algorithm RC5 proposed by Ron Rivest. The target version of RC5 works on words of 32 bits, has 12 rounds and a user‐selected key of 128 bits. Kaliski and Yin estimated the strength of RC5 by differential and linear cryptanalysis. They conjectured that their linear analysis is optimal and that the use of 12 rounds for RC5 is sufficient to make both differential and linear cryptanalysis impractical. In this paper we show that the differential analysis made by Kaliski and Yin is not optimal. We give differential attacks better by up to a factor of 512. Also we show that RC5 has many weak keys with respect to differential attacks. This weakness relies on the structure of the cipher and not on the key schedule. Finally we discuss some possible extensions of our attacks and some modifications of RC5 in order to improve the resistance against our differential attacks.
A realistic security analysis of identification schemes based on combinatorial problems
Authors: Poupard Guillaume 
Published: September 2008

AbstractIn this paper, we analyze the security of two zero‐knowledge identification schemes based on combinatorial NP‐complete problems, PKP (Shamir [3]) and CLE (Stem [5]). We use two different approaches in order to determine, on the one hand, the theoretical limit to the efficiency of the known attacks and, on the other hand, the practical results they permit. Accordingly, we obtain a precise evaluation of which parameters should be chosen today for a secure use of these protocols.
Cell delay variation in an ATM multiplexer
Authors: Molnár Sándor , Blaabjerg Søren 
Published: September 2008

AbstractIn this paper Cell Delay Variation (CDV) in an ATM multiplexer is investigated in the case where a Constant Bit Rate (CBR) traffic stream is mixed with a background traffic stream that arrives in the form of independent and identically distributed batches with general batch size distribution (Batch Bernoulli process). An exact Markovian solution approach is presented which gives the entries in the underlying transition matrix in closed form. In addition an approximate diffusion approach that is both computational simple and provides insight into the point process properties of theCBRstream after passing through the multiplexer is presented. It is demonstrated that the diffusion approximation has nice properties: it is second order exact in the heavy traffic case, and it provides fast and reasonable accuracy results over a wide range of system parameters.
Optimal chip waveforms for DS‐CDMA with generalized OQPSK modulation
Authors: Landolsi Mohamed A. , Stark Wayne E. 
Published: September 2008

AbstractThe effect of chip waveform shaping on both the error and spectral performance of DS‐CDMA communication systems using generalized offset quadrature modulation formats is investigated. A solution to the problem of optimizing the chip waveform shape to achieve minimum multiple access interference variance at a given in‐band power bandwidth occupation and with a continuous phase constraint is presented. Several design examples with various bandwidth occupancies are used to illustrate the gains achieved by the optimized chip waveforms over other conventional modulation schemes such as OQPSK and MSK.
Letter non‐linear equalization for incoherent radiomobile channel
Authors: Abrardo Andrea , Benelli Giuliano 
Published: September 2008

AbstractThis paper presents the simulation study of a multiple‐symbols differential demodulator for Gaussian Minimum Shift Keying (GMSK) which compensates for the heavy selective distortions caused by multipath propagation. The receiver includes a channel estimator operating in a training mode at the beginning of each burst, and a multiple‐symbols differential processor which has been demonstrated in the literature to be optimum over non‐coherent AWGN channels. The combination of channel estimation and differential demodulation makes the receiver robust to fast Doppler shifts and to wide time‐spread. Simulation results are presented which show the performance in different multipath environments based on the recommendations established by the GSM system. Comparisons with a coherent receiver including a matched filter, an adaptive channel estimator and a Viterbi processor show that the detector proposed in this correspondence is quite attractive.
Fixed‐rate video codecs for mobile radio systems
Authors: Streit Jurgen , Hanzo Lajos 
Published: September 2008

AbstractA comparative study of arbitrarily programmable, but fixed‐rate videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s is offered. In contrast to existing and forthcoming standard schemes, such as the H.261, H.263 and MPEG2, MPEG4 codecs, which rely on bandwidth‐efficient but error‐sensitive variable‐length coding techniques combined with a complex self‐descriptive bitstream structure, the proposed codecs exhibit a more robust, regular bitstream and a constant bitrate. Clearly, their philosophy is different from the above error‐sensitive and variable‐rate standard schemes, since these constant‐rate codecs were designed to allow direct replacement of mobile radio voice codecs in second generation wireless systems, such as the Pan‐European GSM, the American IS‐54 and IS‐95 as well as the Japanese systems, operating at 13, 8, 9.6 and 6.7 kbit/s, respectively. This philosophy can, however, be adopted to higher‐rate systems, such as the Digital European Cordless Telecommunications (DECT) and the Universal Mobile Telecommunications System (UMTS). The Type 1 codecs proposed benefit from invoking sophisticated compression techniques in order to achieve best video quality at a given bitrate. In contrast, the Type 2 schemes introduced maximise the codecs' error resilience at the cost of slightly reduced video quality under error‐free conditions. Gain‐cost quantised, fixed but arbitrarily programmable rate discrete cosine transformed (DCT) video codecs, vector‐quantised (VQ) and quad‐tree (QT) coded algorithms are proposed and their video quality, complexity, compression ratio and error resilience trade‐offs are comparatively analysed under identical conditions. Finally, our candidate codecs are compared to the standard H261, H.263 and MPEG2 benchmark codecs.
Future airborne optical fiber communication networks with single‐wavelength and multi‐wavelength code‐division multiple access techniques
Authors: Zhang Jian‐Guo 
Published: September 2008

AbstractWe design optical fiber code‐division multiple‐access (CDMA) networks to support future airborne high‐speed communication services (e.g., real‐time command and control communications). The proposed airborne communication networks have a full tunability and a fast reconfiguration time. This can support real‐time sensor data distribution and computer interconnects. Architectures for fastly tunable optical CDMA encoders and correlators using prime codes are presented, and their simple delay control logic is described, which can be easily performed by using optical fiber delay lines. Moreover, multi‐wavelength optical CDMA networks using a multi‐star topology are designed. It is shown that the use of multi‐wavelength OCDMA not only can reduce the power loss of encoders/correlators and the bandwidth expansion of optical CDMA, but also can separate avionics subsystems into groups according to different traffic requirements and data rates. This in turn can efficiently integrate several networks with different data rates and number of users into a single‐fiber network by using wavelength‐division multiplexing scheme, and new avionics subsystems can be feasibly added to such a single‐fiber network by assigning, for example, new wavelengths or additional optical CDMA codewords to facilitate future aircraft applications.
Letter: The noise behaviour of a DQPSK demodulator employing a PLL
Authors: Laute Andreas 
Published: September 2008

AbstractThis paper deals with the noise analysis of a special type of differential quadrature phase shift keying (QPSK) demodulator. The general principle of operation of this demodulator is discussed in a previous publication. The underlying assumptions are as follows: 1) the noise at the output of the phase‐locked loop (PLL), which is part of the demodulator, can be regarded as Gaussian‐distributed, 2) the four possible phase transitions of a QPSK‐modulated signal are equally likely and 3) the signal processing circuit following the demodulator allows perfect synchronization by means of the output symbol streams. The theoretical approach makes use of a generalized Taylor series representation that yields the output signal of a noise‐corrupted PLL. The known probabilities of error for the individual PLL output impulses allows the demodulator's symbol error rates to be determined. In order to verify the theoretical results, a hardware implementation intended for the reception with an intermediate frequency of 479.5 MHz was realized. The measurements performed on this setup are then compared with theory.
SONET/SDH traffic generation models
Authors: Park Won‐Bae , Owen Henry L. , Zegura Ellen Witte 
Published: September 2008

AbstractIn a SONET/SDH transmission environment, switching systems must accommodate a hierarchy of traffic and bandwidth. In the design of SONET/SDH cross‐connect switching hardware and switching algorithms, it is necessary to evaluate the switching system performance on this hierarchy through simulations. These simulations require the generation of realistic connection requests so that the switching system performance may be evaluated. Parameters which are required in such a model include the total load on the switching system, the mix of the various traffic types involved in the connection requests, as well as the active and idle times for each of the connections. This paper presents two connection request models that meet these goals in a SONET/SDH environment. Both achieve target values with high accuracy; the second is also capable of representing complex traffic types including bidirectional, multicast and protected connections.
Blind multipath channel identification for wideband communications systems based on cyclostationary statistics
Authors: Mazzenga Franco 
Published: September 2008

AbstractIn this letter a blind channel identification algorithm for broadband signals is proposed. Although we take CDM signals into consideration for simplicity, the algorithm can be easily extended to any other wideband communication system. The algorithm is based on cyclostationary properties of the CDM signal. Moreover a brief discussion on the identifiability of a generic channel transfer function from the measured cyclic and conjugate cyclic spectra of the received signal is also presented.
Correlation branch selection for extended tracking range delay‐locked loops
Authors: Wilde Andreas 
Published: September 2008

AbstractIn spread spectrum systems the delay‐locked loop is commonly used to track the spreading code. A problem is to design the delay‐locked loop to be both accurate and robust against disturbances which normally requires a tradeoff. The use of extended tracking range delay‐locked loops increases the ability of the system to maintain lock even for large Doppler frequency offsets. The extended tracking range is achieved by using more than two correlators to form the error detector characteristic. However, the noise level in the synchronization loop is increased by every additional correlator leading to larger tracking jitter. In this paper an algorithm is proposed which reduces the noise level in the loop considerably. This is done by selecting only those correlation branches with an useful control signal. The investigated performance criteria are the tracking jitter and the mean time to loose lock. Both analytical and simulation results are presented. The extended tracking range delay‐locked loop with correlation branch selection shows very promising performance results for both criteria at medium to high signal‐to‐noise ratios. It approaches the performance of the classical delay‐locked loop for the tracking jitter and has a much larger mean time to loose lock than the classical delay‐locked loop.
Signal synchronization for direct‐sequence code‐division multiple access radio modems
Authors: De Gaudenzi Riccardo , Glannetti Fllippo , Luise Marco 
Published: September 2008

AbstractThe design of low‐complexity, ‐size, and ‐cost modems for Code‐Division Multiple Access (CDMA) radio links like those envisaged in the 21st‐century Personal Communications Network puts forth challenging issues as far as signal detection for best power efficiency is concerned. As is often the case in modem design, the “ancillary” functions of signal synchronization may reveal fundamental in such an optimum design problem. Spread‐Spectrum CDMA signals reveal particularly demanding in this respect, so that the basic issues in carrier, code and chip/data timing should be carefully re‐considered before tackling light‐heartedly the design of a Digital Signal Processing (DSP)‐based CDMA modem. It is the aim of this paper to present an overview of those code acquisition/tracking and carrier frequency/phase recovery techniques for a Direct‐Sequence Spread‐Spectrum signal, that appear particularly suited to an efficient VLSI implementation.
Wireless channel equalisation
Authors: Taylor Desmond P. , Vitetta Giorgio M. , Hart Brian D. , Mämmelä Aarne 
Published: September 2008

AbstractEqualisation techniques for wireless channels, in particular for those encountered in mobile wireless communications, are examined. Equalisation is broadly defined to include reception techniques which estimate the state or response of the channel and then attempt to compensate for its effects. The paper considers equalisation techniques for fading dispersive channels which include both time and frequency selectivity. In addition, brief consideration is given to the problems of blind equalisation, techniques for dealing with fast fading channels and to the problem of joint equalisation and decoding. The paper does not attempt to provide in‐depth analysis or performance results. Rather, the interested reader is referred to the extensive list of references.
Soft‐input soft‐output modules for the construction and distributed iterative decoding of code networks
Authors: Benedetto Sergio , Montorsi Guido , Divsalar Dariush , Pollara Fabrizio 
Published: September 2008

AbstractSoft‐input soft‐output building blocks (modules) are presented to construct and iteratively decode in a distributed fashioncode networks, a new çoncept that includes, and generalizes, various forms of concatenated coding schemes. Among the modules, a central role is played by the SISO module (and the underlying algorithm): it consists of a four‐port device performing a processing of the sequences of two input probability distributions by constraining them to the code trellis structure. The SISO and other soft‐input soft‐output modules are employed to construct and decode a variety of code networks, including “turbo codes” and serially concatenated codes with interleavers.
A modified fast buffer reservation algorithm (M‐FBR) for congestion control in ATM networks
Authors: Iera Antonio , Marano Salvatore , Beraldi Roberto 
Published: September 2008

AbstractDeeper investigation is needed for several open issues related to congestion and admission control within the field of the high speed B‐ISDN network with ATM protocol. The system must be more effective in resource management and robust enough to cope with changes in traffic environment, which nowadays is characterised by sophisticated multimedia services. In this paper a new admission and congestion control strategy is proposed. It originates from the Fast Buffer Reservation (FBR) scheme, a virtual circuit acceptance algorithm proposed by Prof. Turner, and enhances its effectiveness, thus resulting in a complete approach for bandwidth management. The scheme is called Modified FBR (M‐FBR). The use of the FBR method, in fact, when based on the powerful Excess Probability Criterion (EPC), seemed to be impeded by the occurrence of lock out problems. By adopting a new kind of service at the buffer exit, the new mechanism offers the required flexibility and robustness, as well as ease of control, while preserving burst integrity and exhibiting a high burst‐served to burst‐sent ratio.
Letter soft‐decision decoding of linear block codes as optimization problem
Authors: Breitbach Markus , Bossert Martin , Lucas Rainer , Kempter Christian 
Published: September 2008

AbstractIn this contribution the problem of channel decoding is considered from the viewpoint of optimization theory. The decoding problem is at first denoted as integer optimization problem. To solve this problem, well‐known methods from optimization theory are suitable. Two examples are presented: First, an Omura‐type algorithm from [13] can be derived from the Simplex algorithm. Second, the decoding problem is reformulated such that it can be solved by a Branch‐and‐Bound algorithm. By simulation results, questions concerning bit error rate and complexity will be discussed.
Frames FMA2 wideband‐CDMA for UMTS
Authors: Toskala Antti , Castro Jonathan P. , Dahlman Erik , Latva‐Aho Matti , Ojanperä Tero 
Published: September 2008

AbstractThe basic principles of the physical layer of the FRAMES (Future Radio Wideband Multiple Access System) FMA2 (FRAMES Multiple Access) wideband CDMA system are described in this paper. The FMA2 is part of the FRAMES dual mode platform designed as UMTS air interface, where the harmonisation with GSM is also taken into account. The main characteristics features in the FMA2 are the asynchronous network operation and flexible layer 1 support for the variable rate transmission needs. This paper presents also performance results, which allow to conclude that the FMA2 meets UMTS air interface requirements. The FMA2 concept was a major part of the ETSI (European Telecommunications Standards Institute) wideband CDMA concept group, selected by ETSI as a basis for UMTS air interface for the paired frequency band.
A high capacity third‐generation mobile satellite system design
Authors: Lyons Bob , Mazur Brian , Lodge John , Moher Michael , Crosier Stewart , Erup Lars 
Published: September 2008

AbstractThis paper describes a CDM/CDMA based approach for a 3‐rd generation multi‐beam satellite mobile and personal communications system using Highly Elliptical Orbit (HEO) satellites. The forward link uses a synchronous CDM intra‐beam/asynchronous CDM inter‐beam approach, while the return link uses a quasi‐synchronous CDMA intra‐beam/asynchronous CDMA inter‐beam approach. Using probabilistic analysis, these approaches are shown to provide higher forward and return link capacities than equivalently synchronized FDM/FDMA approaches. Forward link transmissions are modulated using QPSK. Return link transmissions are modulated using either ϕ/4‐QPSK or precompensated frequency modulation (PFM4). PFM4 is intended for use with a saturated amplifier in low‐cost/power‐efficient, e.g. hand‐held, terminals, and can be demodulated using a ϕ/4‐QPSK receiver. All forward and return link transmissions are coded using a rate 1/2, constraint length 9, convolutional code. The paper summarizes several key tradeoffs and the resulting system design.