bluuebunny/crossref_metadata_2025 huggingface dataset:
Supervised fuzzy contextual segmentation of polarimetric SAR images
Authors: Dellepiane Silvana , Fontana Franco
Published: September 2008

In the Remote Sensing application domain, especially for SAR (Synthetic Aperture Radar) images characterized by notable textural properties, the use of context and the integration of multipolarimetric data appear essential to improving the accuracy of classification. Methods based on the MRF approach have recently yielded good results, as they allow the development of robust processing algorithms. Unfortunately, these methods are not free of drawbacks. For instance, they suffer from high computational complexity. Given these conditions, this paper proposes the Fuzzy Contextual Segmentation (FCS) method, which integrates uncertainty and contextual information in a smgle framework through a fuzzified k‐NN approach. The membership value assigned to every site is updated by taking into account the information related to the steps of model‐matching, propagation of global context, and decision on local context. An application of the method to real SAR images is reported. Two fully polarimetric data sets were utilized to assess the performance of our algorithm. Results and error evaluation is supporting evidence for the practical effectiveness of the method.
Letter: A new stop‐and‐wait type‐II hybrid ARQ scheme using rate‐compatible convolutional codes
Authors: Taspinar Necmi
Published: September 2008

In this letter, a new stop‐and‐wait type‐II hybrid ARQ scheme is proposed. This scheme is obtained by using the RCC (rate‐ compatible convolutional) codes and the scheme proposed by Moeneclaey et al. A substantial throughput improvement is obtained over the generalized type‐II hybrid ARQ scheme proposed by Kallel and Haccoun for SW mode. The improvement in the throughput efficiency becomes much better for high values of h incremental coded bits especially when Es/N0 is between 3.5 dB and ‐2 dB. The proposed scheme also yields better throughput efficiency than the type‐II hybrid SW ARQ scheme proposed by Kallel when Es/N0, > 3.5 dB and Es/N0< 0.5 dB for h = 8. Moreover the throughput improvement includes all values of Es/N0 under 10 dB when h = 1. 2 and 4.
Charging and rate control for elastic traffic
Authors: Kelly Frank
Published: September 2008

This paper addresses the issues of charging, rate control and routing for a communication network carrying elastic traffic, such as an ATM network offering an available bit rate service. A model is described from which max‐min fairness of rates emerges as a limiting special case; more generally, the charges users are prepared to pay influence their allocated rates. In the preferred version of the model, a user chooses the charge per unit time that the user will pay; thereafter the user's rate is determined by the network according to a proportional fairness criterion applied to the rate per unit charge. A system optimum is achieved when users' choices of charges and the network's choice of allocated rates are in equilibrium.
Improved WDM packet switch architectures with output channel grouping
Authors: Binh Le Nguyen , Chong Hock Choong
Published: September 2008

We present two switching schemes for routing optical information signals that are transported by wavelength division multiplexed (WDM) networks with and without grouping of optical channels of different wavelength allocations. A brief account of two WDM packet switches without channel grouping are briefly described with the use of a neural network controller for routing control to illustrate the necessity for grouping wavelength channels. This leads to designs of improved WDM packet switch architectures which are described in details for wavelength routing, broadcasting and selecting wavelength channels. Optical channels with different wavelength allocations are grouped and appropriate routing algorithms are designed to enhance the throughput efficiency of the packet switch. Computer simulation is carried out to evaluate the performance of a WDM packet switching system with output channel grouping which exhibits only single intermediate stage architecture.
Letter: Neural classifiers as optimal decision devices for warped M‐QAM signal formats
Authors: Bernardini Angelo , Fina Silvia De
Published: September 2008

The paper is focused on the application of perceptron‐based neural networks to optimal decision for M‐QAM signals transmitted over nonlinear channels. The decision is performed by two cascaded blocks: the first denotes one of the 4 quadrants and the second selects one of the M/4 symbols. A specific initialization procedure has been adopted in order to avoid local minima. The classifier performance, for the specific application, has been evaluated by the CNR (Carrier to Noise Ratio) degradation due to nonlinearity (δCIN) for a target error rate Pe = 10−3. The results, obtained by Monte Carlo simulations, denote optimal matching with respect to upper bounds obtained with some minor simplifying hypothesis, even if the overall method's effectiveness can be adequate only for mild nonlinearity conditions.
Letter: A predictive analysis of differential attenuation on adjacent satellite paths including rain height effects
Authors: Kanellopoulos John D. , Margetis Dionysios
Published: September 2008

Interference between adjacent Earth‐space paths can be caused by propagation effects due to differential rain attenuation. In the present paper, a modification of an existing method to predict the rain differential attenuation statistics is proposed. The modified method takes into account a more complicated but realistic model for the description of the rain height. The present results are compared with the available simulation data for the differential attenuation over pairs of paths in the Montreal area. The difference between the existing predictive results and the deduced ones after use of the modified procedure, for various geographic latitudes and climatic zones, is also examined.
Letter: Cyclical coincidence arrays and exact pdfs representing interference for some CDMA systems
Authors: Kostić Zoran , Pavlović Gordana , Titlebaum Edward L.
Published: September 2008

A new class of coincidence (hit) arrays called cyclical hit arrays is defined. Cyclical hit arrays give insight into previously unknown properties of several sets of number theoretic frequency‐hop patterns, based on Welch‐Costas and Quadratic Congruence codes. Three theorems related to cyclical hit arrays are proved. The theorems are used to determine exact probability distribution functions of random variables which represent the number of coincidences between two arbitrary patterns from the same set of codes. The number of coincidences expresses interference levels between two users of code‐division multiple‐access (CDMA) systems which utilize the considered patterns. The obtained results can be used for computing the exact expressions for the total interference and for error probabilities in several CDMA systems.
Synchronous all‐optical code‐division multiple‐access networks
Authors: Zhang Jian‐Guo , Kwong Wing C. , Chen Lian‐Kuan , Cheung Kwok‐Wai
Published: September 2008

A feasible architecture is proposed for implementing synchronous all‐optical code‐division multiple‐access (CDMA) networks with full channel tunability. The proposed network uses fastly programmable all‐optical CDMA encoders and decoders which are based on tunable optical delay‐lines and require only a small number of electro‐optic switches. Coding and decoding algorithms for “synchronous” prime‐sequence codes that can be rapidly performed in the optical domain are described. Moreover, a two‐wavelength scheme is presented to effectively solve the problems associated with clock distribution and frame synchronization in large‐scale synchronous CDMA networks. By using the proposed technique, all‐optical CDMA transmitters and receivers can be constructed with integrated optics and can achieve a very high processing speed.
A novel procedure for jones' parameters estimation for M‐4QAM optical systems
Authors: Cusani Roberto , Baccarelli Enzo , Galli Stefano
Published: September 2008

A new procedure is proposed for estimating the State‐of‐Polarisation of the received optical signal in Four‐Quadrature Amplitude Modulation systems. The proposed solution, which is obtained on the basis of the Maximum Likelihood criterion, is merely electronic and operates in the presence of laser phase noise, photodetection noise and cross‐polarisation interference. It employs a suitably designed training sequence to estimate Jones' parameters in the data‐aided training mode. A proper decision‐directed procedure is then activated to lock‐in the estimated parameters in the operative mode. The variances of the resulting estimation errors are evaluated and the overall system performance is given in terms of Bit Error Probability versus signal‐to‐noise ratio. The theoretical analysis and the computer simulations show the superiority of the proposed recovery procedure with respect to alternative solutions recently proposed in literature.
Performance analysis of modified/quadrature partial response‐trellis coded modulation (M/QPR‐TCM) systems
Authors: Nuri Uçan Osman
Published: September 2008

In this paper, to improve bandwidth efficiency and error performance partial response signalling and trellis coded modulation is considered together of M‐QAM systems. The new system proposal is denoted as Modified/Quadrature Partial Response‐Trellis Coded Modulation (M/QPR‐TCM). Two new non‐catastrophic schemes M/6QPR‐TCM and M/9QPR‐TCM are investigated for 4QAM. Error event lower bounds of the considered schemes are analyzed in AWGN and colored noise. Analytical upper bounds for the mobile fading channel with ideal channel state information (CSI) and infinite interleaving/deinterleaving are derived. The interesting result is that, the bit error probability upper bounds of the proposed M/QPR‐TCM systems are better than the related QAM‐TCM schemes forSNRvalues greater than a threshold.
Letter: Evaluation of total radiowave attenuation statistics for slant path links from phenomenon‐based attenuation distributions
Authors: Pozhidayev Victor , Dintelmann Fritz
Published: September 2008

This contribution suggests a method how to combine effect‐specific cumulative distributions of attenuation to a total‐attenuation distribution as required e.g. in long‐term frequency scaling applications. The method is believed to be applicable for frequencies up to about 40 GHz. It has been tested with 20 GHz radiometric data collected near Moscow and the agreement found between our measurements and the results of this procedure is remarkably good.
Letter: Cell level modelling of H.261 coded video sequences at different bit rates
Authors: Dagiuklas Anastasios , Ghanbari Mohammed
Published: September 2008

A video source, with a low to medium activity, coded with an H.261 type video codec can be modelled at the frame level as an M state Markov chain. For cell level modelling, the generated cells within the frame are distributed using a modulated Poisson process with interarrivals of Gamma function. Sequences with scene cuts use an. additional state in the Markov chain to represent the scene cut bit rate. The multiplexed model of N homogeneous sources is represented by a linear Markov model of N × M states. The transition probabilities in the multiplexed model are approximated by a truncated discrete normal distribution bounded within ±N states. The proposed single and multiplexed models exhibit similar cell loss performance with the real coded data at both cell and burst scale levels. The multiplexed model is then generalised to represent the aggregate traffic of several homogeneous sources at different bit rates.
RACE “MARS” project for the experimentation of multimedia interactive services: Architecture solutions and results
Authors: Bertin Christian , De Sousa Amaro F. , Figuera Gonzalo , Friedrich Manuel , Guglielmo Mario
Published: September 2008

This paper describes the architecture implemented in five different countries to validate, by means of tests carried out with expert users, a service architecture for the interactive retrieval of multimedia information. The service architecture definition (which corresponds to the DA VIC 1.0 Specifications) and all activities for the set‐up and running of the experiments, have been carried out within the RACE R2120 “Multimedia Audiovisual Retrieval Services” (MARS) project. A unique server and terminal architecture has been developed and put in operation at each site, while a combination of different public network solutions were used for the terminal access side. All national experiments made use of an ATM‐based transport network. The interconnections between the five countries were provided by the European ATM Pilot (EAP). The minimal testbed configuration implemented in each country consisted of one server and two terminals. After the integration and test phases, this configuration was extensively tested within the national environment to obtain the users' perception of the service.
Diamond project: Video‐on‐demand system, and trials
Authors: Van De Haar Peter G. , Schoenmakers Arno F. , Eilley Edward S. , Tedd Douglas N. , Tickell Stephen A. , Lloyd Phil R. , Badham Mark , O'Brien Steve , Poole Robin , Sampson Paul , Harding Jon , Simula Timo , Varonen Teema , Sauvala Seppo
Published: September 2008

The DIAMOND project (Domestic IBC Applications for Multimedia on Demand; IBC = Integrated Broadband Communications), sponsored by the EC (RACE R2105), had the objective of exploring and demonstrating the technical feasibility of providing Video On Demand (VOD) to the home, with an acceptable quality of service at an acceptable cost level. Within Philips, a Video Server (VS) and Set Top Box (STB) were developed, while Octacon developed a Service Gateway (SGW). The system was tested on both a public switched network using ADSL (Helsinki, Finland) and on a CATV network (Sligo, Ireland); both trials were of a small scale and free of charge. The purpose of this paper is to present an overview of the overall system as developed for the DIAMOND trials, together with user evaluation results from the Helsinki trial.
HD‐SAT: Digital HDTV‐broadcasting by satellite and cable networks with commonality for terrestrial broadcasting
Authors: Dosch Christoph , Lavan Ethan
Published: September 2008

This paper introduces the HD‐SAT project, describes its main characteristics as well as the results of the system demonstration which was performed jointly with the dTTb project, (digital terrestrial television broadcasting) during the Montreux International Television Exhibition in June, 1995. The HD‐SAT system exploits the 20 GHz frequency band as the basis of a complete broadcast system delivering very high quality High‐Definition TV (HDTV) services over a variety of media. The satellite segment implements graceful degradation to assure the required service continuity. MPEG‐2 transmultiplexing is performed at the cable head‐end to provide an optimised transport stream for the cable channel. Maximising compliance to MPEG‐2 standards for the picture coding and DVB standards for the transmission segments results in a system open to interworking with other media and other services. This was demonstrated at the Montreux event, where the HD‐SAT system was demonstrated over live satellite and standard cable networks, and where common HD‐SAT coding and receiver hardware was used for the dTTb terrestrial and cable transmission within the joint demonstration.
Automatic 3D model building from video sequences
Authors: Gool Luc Van , Zisserman Andrew
Published: September 2008

We 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

Provision 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

With 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

In 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

In 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

In 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

The 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

This 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

A 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

We 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

This 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

In 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

In 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

In 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

The 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

Equalisation 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

Soft‐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

Deeper 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

In 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

The 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

This 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.
Subspace‐based tracking of multipath channel parameters for CDMA systems
Authors: Sengupta Chaitali , Cavallaro Joseph R. , Aazhang Behnaam
Published: September 2008

In this paper, we evaluate several issues in the application of subspace‐based methods to tracking channel parameters in Code Division Multiple Access (CDMA) communication systems, in the presence of multipath fading. We focus on two aspects of the problem – the performance of Singular Value Decomposition (SVD) based schemes while tracking the time variations in the signal subspace, due to fading, and, the performance tradeoff involved in using several complexity reducing approximate schemes. The performance benefits to be obtained from application of subspace‐based methods to channel estimation has been well studied. The aim of this work is to lay the groundwork for real time implementation of this computationally complex problem.
Comments on “Orthogonal multiple carrier data transmission”
Authors: Fliege N. J. , Vangelista Lorenzo , Laurenti Nicola
Published: September 2008

In a paper from 1992, Fliege introduced a novel multicarrier modulation scheme claiming to obtain an implementation that is computationally more efficient and has a simpler filter bank structure with respect to those previously presented in the literature. Being understood the correctness and valuability of the ideas expressed in that paper, nevertheless we would like to point out that an implementation with the same computational complexity had already been presented by Hirosaki in 1981, and that the optimization of the filter bank structure is based on an incorrect step.
Effects of Multiple Node Crossing on ATM Traffic Performance
Authors: Bianchi Giuseppe , Melen Riccardo
Published: September 2008

It is commonly recognized that traffic statistics change when a stream of ATM cells crosses several network nodes. In particular, some cells may experience a shorter delay than the previous ones, and thus the peak rate of the traffic stream may increase. In order to control this “cell clumping” effect, on one side spacing techniques have been proposed to restore the original peak rate of the sources at the outlets of each network node, while on the other side bounds to keep into account the peak rate increase have been suggested. Although some contributes have evaluated the effects of multiple node crossing on the distribution of the cell interarrival time, little attention has been paid to the effect of these modifications in terms of cell loss probability. Scope of this paper is to show, by adopting a realistic simulation model, that multiple node crossing produces a negligible effect on cell loss probability, when the admitted traffic is suitably regulated by a connection admission control rule. Moreover, a notable result is that, in the case of large buffers at the network nodes and traffic loads well over the limits imposed by the CAC rule, the per node cell loss probability eventually reduces as network nodes are crossed.
On Coded and Interleaved Noncoherent Multiple Symbol Detected MPSK
Authors: Peleg Michael , Shitz Shlomo Shamai
Published: September 2008

The performance of multiple symbol noncoherent detection of MPSK combined with coding and interleaving is examined in terms of the cut‐off rate bound. It is shown that, within this approach, inner modulation coding improves on standard DPSK when both are combined with an external error correcting code, such as the industry standard,K= 7R= 1/2 convolutional code. Some modulation codes over BPSK and QPSK are examined and a reduced complexity decoder is presented. The results and conclusions are verified by some simulations.
Load Profiling Based Routing for Guaranteed Bandwidth Flows
Authors: Matta Ibrahim , Bestavros Azer , Krunz Marwan
Published: September 2008

To support the stringent Quality of Service (QoS) requirements of real‐time (e.g. audio/video) applications in integrated services networks, several routing algorithms that allow for the reservation of the needed bandwidth over a Virtual Circuit (VC), established on one of several candidate routes, have been proposed. Traditionally, such routing is done using the least‐loaded concept, and thus results in balancing the load across the set of candidate routes. In this paper, we propose the use ofload profilingas an attractive alternative to load balancing for routing guaranteed bandwidth VCs (flows). Load profiling techniques allow the distribution of “available” bandwidth across a set of candidate routes to match the characteristics of incoming VC QoS requests. We thoroughly characterize the performance of VC routing using load profiling and contrast it to routing using load balancing and load packing. We do so both analytically and via extensive simulations of multi‐class traffic routing in Virtual Path (VP) based networks. Our findings show that for routing guaranteed bandwidth flows in VP networks, load profiling is desirable as it reduces VP bandwidth fragmentation, which increases the likelihood of accepting new VC requests. This fragmentation could be particularly harmful when the granularity of VC requests is large. Typically, this occurs when a common VC is established to carry theaggregatetraffic flow of many high‐bandwidth real‐time sources. For VP‐based networks, our simulation results show that our load‐profiling VC routing scheme performs better or as well as the traditional load‐balancing VC routing in terms of revenue under both skewed and uniform workloads. Furthermore, load‐profiling routing improves routing fairness by proactively increasing the chances of admitting high‐bandwidth Hows.
Optimal Routing for Dynamic Multipoint Connection
Authors: Chakraborty Debasish , Shiratori Norio , Chakraborty Goutam , Pornavalai Chotipat
Published: September 2008

Multimedia applications are becoming increasingly important as networks are now capable to carry continuous media traffic, such as voice and video, to the end user. Most of the multimedia applications need multicast support too. In dynamic multicasting, destination nodes can join and leave the group during the communication period. Total or partial rerouting can optimize the tree cost to some extent. But rerouting for optimization is complex as cell‐ordering at ATM switches has to be preserved. Optimum Steiner tree is NP‐complete and therefore the present problem too. We propose a heuristic centralized routing algorithm, which optimize the total cost of the Steiner tree over the whole session period, where information about the joining and leaving of participants are available, at the time s/he actually joins. With this algorithm, the average hop‐length from source to destination has also reduced considerably. The efficiency of our algorithm and comparison with other proposed algorithms is shown by various simulation results.
On‐Line Learning and Dynamic Capacity Allocation in the Traffic Management of Integrated Services Networks
Authors: Burrell Anthony T. , Papantoni‐Kazakos P.
Published: September 2008

A Traffic Monitoring Algorithm (TMA) is utilized to allocate channel capacities dynamically to heterogeneous traffics with time‐varying characteristics. The threshold parameters that characterize the operational characteristics of the TMA control the overall system performance, including traffic rejection rates and wasted capacity rates. In this paper an on‐line learning algorithm is introduced, to dynamically adapt the threshold parameters of the TMA for attaining a prespecified upper bound on the traffic rejection rate, at minimal cost in wasted capacity rate. The learning algorithm is analyzed and evaluated to expose its superior convergence characteristics.
A Self‐Adaptive Load Balanced Internet Multicast Routing Protocol
Authors: Lin Jhyda , Chang Ruay‐Shiung
Published: September 2008

The prevailing Internet has brought many novel network applications. These applications often involve the interactions among multiple members in a single session. For example, the images and voices of the lecturer in distance learning must be transmitted to multiple destinations at the same time on demand. The status and opinions of any participant should also be transmitted to each other in a video conferencing for the interactivity of conversations. Without suitable protocol supports from the underlying networks, these applications may be costly and infeasible. One of the important protocol supports is the capability of multicasting, sending a single data packet to a set of receivers that are members of a multicast group. In the past, there are four well‐known Internet multicast routing protocols: DVMRP (Distance Vector Multicast Routing Protocol), MOSPF (Multicast extensions to Open Shortest Path First), CBT (Core‐Based Tree), and PIM (Protocol Independent Multicast). In this paper, based on PIM, we propose a new multicast routing protocol called SEAL‐PIM (SElf‐Adaptive and Load balanced PIM). The new protocol reduces the PIM message and resource overhead and balances the traffic load in the network by rearranging the links of routing and the locations of the group rendezvous points to adapt to the current distribution of group members. Finally, simulations are done to compare our algorithm with the original PIM scheme. The results indicate that the performance improvement is good.