bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of time‐differential GCRA enforcer and shaper in multi‐service ATM networks
Authors: Wu Jung‐Shyr , Kuo Fang‐Jang
Published: September 2008

According to the ITU‐T Recommendation 1.371, the Generic Cell Rate Algorithm (GCRA) is used to define Peak Cell Rate for the ATM network. It is further applied by the ATM Forum to define Sustainable Cell Rate and Burst Tolerance so as to facilitate Usage Parameter Control and Network Parameter Control. To check the validity of a cell according to the declared traffic parameters, the enforcer must read die clock time when a cell arrives. However, the clock of the enforcer would roll over frequently and thus makes wrong judgment. On the other hand, for a shaper in a customer premise node to dispatch cells conforming to the declared parameters, the clock would also roll over and the cell would not be dispatched correctly. To overcome the problems introduced by clock roll‐over, we propose two modifiedGCRAsfor the enforcer and the shaper, respectively. According to the proposed algorithms, we design new architectures for multi‐connection shapers and enforcers in which a cell's priority is also considered. We also prove that the proposed algorithms are justified for the proposed architectures.
Letter: Exact formulas for computing the energy of “square” and “cross” two‐dimensional rectangular signal constellations
Authors: Sterian Corneliu‐Eugen D.
Published: September 2008

A rigorous construction of “cross” constellations is given and the exact formulas for calculating the average norm of rectangular signal sets is derived. Using these formulas, the increase of the average norm when doubling the size of the constellation is evaluated.
Impact of the time error sampling period on telecommunications clock stability measures
Authors: Bregni Stefano , Carbonelli Marco , De Seta Domenico , Perucchini Daniele
Published: September 2008

Five stability quantities have been considered in the new telecommunications international standards for clock specification: the Allan Deviation, the Modified Allan Deviation, the Time Deviation, the root mean square of the Time Interval Error and the Maximum Time Interval Error. A key issue to consider carefully ‐ but sometimes overlooked ‐ when performing stability measurements, in order to draw meaningful conclusions from the measurement data, is the impact of the TE sampling period on the behaviour of the stability quantities. Such a dependence, for some of the quantities above, has been already pointed out in different reference papers, which studied in depth the behaviour of the stability quantities analytically and under various aspects. In order to provide further, sourly information on the impact that the TE sampling period may have in practice on the measured stability quantities, this paper reports a broad set of simulation results, under the presence of all the power‐law clock noises and for all the stability quantities, together with some experimental results. The results obtained confirm, in excellent agreement with the theoretical analyses, that the behaviour of the Modified Allan Deviation and of the Time Deviation is substantially dependent on the chosen measurement sampling period in the observation intervals where white and flicker phase noises dominate.
Performance of joint diversity and equalization techniques in an indoor radio environment
Authors: Dossi Laura , Tartara Guido
Published: September 2008

The measured wideband complex impulse response profiles from eight different indoor areas are used to evaluate the performance of joint diversity and equalization techniques in the presence of flat fading and frequency selective fading. The error probabilities of a joint two‐branch diversity receiver with an adaptive finite‐length equalizer on each branch, whose taps are jointly optimized according to the minimum mean square error criterion, are computed for different data rates using the measured channel responses.
Multicarrier modulation system with erasures‐correcting decoding for nakagami fading channels
Authors: Goldfeld Lev , Wulich Dov
Published: September 2008

The Multi Carrier Modulation (MCM) system with soft decision erasures correcting decoding based on a block code applied for Nakagami fading channel is considered. Upper and lower estimations of the Bit Error Rate (BER) have been found. Good agreement between simulated and theoretical results has been obtained. It is shown that for low SNR the proposed system has lowerBERthan MCM with Trellis Code Modulation (TCM). Moreover the decision delay needed for the proposed system is much lower than for the TCM based system.
Performance comparison of different dynamic channel allocation techniques for mobile satellite systems
Authors: Re Enrico Del , Fantacci Romano , Giambene Giovanni
Published: September 2008

Dynamic Channel Allocation (DCA) techniques permit a high resource utilization in cellular networks and are able to adapt themselves in the presence of rapid variations of traffic loads offered to the cells. Therefore, they are particularly suitable for Mobile Satellite Systems (MSSs). This paper compares the performance of several DCA solutions that are based on the evaluation of a cost function in terms of both quality of service parameters (i.e., blocking probabilities) and signaling load to be supported by the system. Both GEostationary Orbit (GEO) and Low Earth Orbit (LEO) MSSs have been considered. A particularly interesting DCA solution is proposed that tries to serve a new call attempt in a cell where no channel is available by means of a channel reconfiguration in an interfering cell. Handover requests that do not attain immediately service can be queued for a maximum time in order to enhance system performance.
Computing error probabilities over fading channels: A unified approach
Authors: Biglieri Ezio , Caire Giuseppe , Taricco Giorgio , Ventura‐Traveset Javier
Published: September 2008

This paper is a tutorial on the calculation of error probabilities for fading channels. The method we advocate is centered on the evaluation of the Laplace transform Φδ(s) of the probability density function of the difference A between the metrics of two competing signal sequences. In some cases, knowledge of the function Φδ (s) allows one to determine error probabilities exactly in closed form, or asymptotically as the signal‐to‐noise ratio grows to infinity. The general technique t hat we describe here allows their computation in numerical form to any desired degree of accuracy. Coded as well as uncoded transmission can be considered in this unified framework. For illustration's sake, some examples of calculations are provided for frequency‐flat slow‐fading channels in which coherent detection is used, and the channel state information is perfect, or unavailable, or obtained from a noisy pilot tone.
Still picture compression based on psychovisual image‐pattern coding
Authors: Favalli Lorenzo , Mecocci Alessandro , Poli Andrea
Published: September 2008

In this paper, an approach that integrates different compression techniques is presented. The goal is to reach high compression rates for still pictures without introducing relevant visual distortions in the images. This is obtained by using a “second generation” compression scheme which adaptively uses different psychovisual techniques to reduce the image bitrate. Each image is analysed on a block by block basis and the most appropriate coding strategy is selected according to the characteristics of the current block and of surrounding blocks. Taking into account surrounding blocks leads to improved visual image quality. Another important feature of the proposed approach is that part of the approximation job is done at the receiver thus further reducing the bit rte needed for transmission.
Adaptive antennas in microwave‐PCS coexisting systems
Authors: Muñoz‐Rodriguez David , Mazlum ‐Revueltas Abdo
Published: September 2008

In this paper, mutual interference in PCS and microwave systems in a spectrum sharing scenario is analyzed. Typical values for operating MW links and cellular systems are used for evaluation. The use of adaptable smart antenna systems as a mean to reduce intersystem interference is proposed. The access techniques for PCS considered are: TDMA, FDMA and CDMA. Carrier to Interference ratio is adopted as performance criterion. Geographical separation required between both systems for their operation in terms of antennas separation is studied for different scenarios. The impact of proposed strategies in PCS system capacity for CDMA is also reported.
The VDSL transmission challenge
Authors: Cheong Kok‐Wui , Kim Joonsuk , Cioffi John M. , Kwon Ho‐Yeol , Chun You‐Sik , Yoo Kyung‐Hyun
Published: September 2008

Demand for high speed digital transmission on ordinary phone lines motivates the introduction of VDSL. This paper investigates the VDSL transmission environment. The channel is shown to be difficult for high speed digital transmission and sophisticated signal processing methods are required for reliable transmission. This paper also describes various transmission schemes that are proposed to support high data rates in the difficult transmission environment. Two schemes, SDMT and QAM/CAP, are compared in terms of SNR margins and computational complexity.
Adaptive soft‐decision algorithms for mobile fading channels
Authors: Anastasopoulos Achilleas , Polydoros Andreas
Published: September 2008

This paper addresses the task of joint symbol‐by‐symbol decisions and channel estimation in a coded/interleaved/frequency‐selective fading channel. Based on two popular soft‐decision algorithms, namely OSA and SSA, which have an inherent trellis structure, several adaptive derivatives are proposed. In particular, by extending the concept of Conventional Adaptive MLSE (CA‐MLSE) receiver to the soft‐decision case, the CA‐OSA and CA‐SSA algorithms are derived. Moreover, using the Per‐Survivor Processing (PSP) concept, two new adaptive extensions are presented, namely PSP‐OSA and PSP‐SSA. The latter of these algorithms (PSP‐SSA) has a simplified form with complexity comparable to PSP‐MLSE. Simulation results show a significant improvement of the suggested adaptive soft‐decision algorithms over the standard configuration, which consists of a hard‐decision channel equalizer followed by a convolutional decoder.
Interference mitigation in spread spectrum systems by wavelet coefficients thresholding
Authors: Landry René J. R. , Mouyon Philippe , Lekaïm David
Published: September 2008

This paper studies a potential EMI (Electro Magnetic Interference) rejection technique for the GPS Standard Positioning Service in an avionics environment. Its generalisation to any Direct Sequence Spread Spectrum (DSSS) Systems is also considered. The paper gives a brief overview of Wavelet Theory, which is well established for noise reduction but which is applied here to Continuous Wave Interference (CWI) and narrowband interference. The originality of this work lies in a method for signal rejection, taking into account features in both time and frequency domains to account for the non‐stationary characteristics of the interference. Because the software‐based receiver is more flexible, less expensive and more accurate compared with typical hardware receivers, a Generic GPS Receiver has been implemented in software [1] to validate the antijamming technique developed in this paper. The aim of the Monte Carlo simulations is to get a good idea of the Performances of the Wavelet Filter against a various types of Interferences and to compare the results with traditional processing.
Performance of cell loss priority management schemes in shared buffers with poisson arrivals
Authors: Van Mieghem Piet , David Johan , Petit Guido H.
Published: September 2008

The performances of two important cell loss priority mechanisms (CLPM) in shared buffers withNservers, Partial Buffer Sharing (N‐PBS) and Push‐Out Buffer (JV‐POB), are compared. Each arriving flowiis guided to a shared queue of sizeKwhere it is served by the correspondingi‐th server. Further, these flows are Poissonean, independent of each other and consist of a uniformly distributed mix of high (H) and low (L) priorities. Subject to the required cell loss ratios for both priorities,clr*Landclr*H, we determine the maximum allowable traffic intensity λmaxfor each incoming traffic flow as a function of the global priority mix in the buffer of sizeK.For an arbitrary CLPM, the maximum allowable load is achieved in the symmetrical traffic situation where allNlinks carry the same load. Only when N> 1, theN‐POB scheme is found to be superior in performance toN‐PBSover the whole priority mix range and for realistic cell loss ratio requirements. Moreover, the difference in performance betweenN‐POB andN‐PBS increases with increasingN, but decreases with increasingK.Finally, a methodology based on buffer size scaling has enabled the computation of the performance of theN‐POB.
Performance of a fixed‐beam system in the is‐95 CDMA forward link
Authors: Moorti Tushar , Paulraj Arogyaswami , Stützle Rupert
Published: September 2008

We study the performance of a fixed‐beam system in the forward link of IS‐95 CDMA systems by means of Monte Carlo simulations. The simulations are performed using a comprehensive model of the forward link which includes correlated shadowing, soft and softer handoff, and transmit power allocation. The effects of user distribution, soft/softer handoff threshold, and multipath diversity are examined. We find that the availability of signal diversity plays an important role in the system performance. When the soft handoff threshold is decreased from ‐12 dB to ‐18 dB, capacity increases by 15%, but handoff overhead more than doubles. When fifty percent of users have 2‐ray multipath, capacity increases by 18%. Thus, the availability of multipath in the system has a dramatic influence on forward link capacity. A non‐uniform distribution using a “highways” model reduces capacity by more than a half. This shows that for successful implementation of a fixed‐beam system, it is important to plan cell sites in a way that keeps loading uniformly distributed in azimuth.
MC‐CDMA with quadrature spreading for wireless communication systems
Authors: Slimane Slimane Ben
Published: September 2008

Multi‐Carrier CDMA (MC‐CDMA) systems using the Orthogonal Frequency Division Division Multiple Access (OFDM) technique resolve the frequency selectivity in multipath fading channels and have good spectral properties. The addition of a spread spectrum component to the OFDM introduces a frequency diversity gain that can combat deep multipath fading situations. In this paper a MC‐CDMA system operating over frequency selective, slowly fading channels is considered and its performance is studied analytically and by computer simulations. We consider the downlink of a cellular radio system where for each user a BPSK modulation and a quadrature (complex) spreading code is used. The spreading codes are arranged in a way that reduces the effect of the multipath fading channel and restores some of the orthogonality losses between users. The obtained results show considerable performance improvement compared to conventional OFDM and to MC‐CDMA that uses single spreading codes. The effect of frequency offsets on the system performance is also addressed in this paper. Its superior performance and low complexity receiver make MC‐CDMA with quadrature spreading codes suitable for future wireless communication systems to achieve the requirements of high quality services, high speed, and low cost‐receiver.
Efficient implementation of linear multiuser detectors for asynchronous CDMA systems by linear interference cancellation
Authors: Elders‐Boll Harald , Schotten Hans Dieter , Busboom Axel
Published: September 2008

The decorrelating and the linear, minimum mean‐squared error (MMSE) detector for asynchronous code‐division multiple‐access communications are ideally infinite memory‐length detectors. Finite memory approximations of these detectors require the inversion of a correlation matrix whose dimension is given by the product of the number of active users and the length of the processing window. With increasing number of active users or increasing length of the processing window, the calculation of the inverse may soon become numerically very expensive. In this paper, we prove that the decorrelating and the linear MMSE detector can both be realized by linear multistage interference cancellation algorithms with ideally an infinite number of stages. It will be shown that depending on the signal‐to‐noise ratio, the number of active users, and the choice of the cancellation algorithm, only a few stages are necessary to obtain the sameBERperformance as with the ideal detectors. The computational costs for one stage of a linear interference cancellation algorithm are essentially given by one matrix‐vector multiplication. Thus, the computational complexity can be reduced considerably. Since each stage introduces a time delay equivalent to the bit duration, the number of stages also determines the detection delay. Because a few stages are sufficient, this approach can also be used to obtain receiver structures with low memory consumption and detection delay.
A lower bound on the bit‐error‐rate resulting from mismatched viterbi decoding
Authors: Lapidoth Amos , Shamai (Shitz) Shlomo
Published: September 2008

A lower bound is derived on the bit error rate that results when a rate l/nconvolutionally encoded binary data stream is transmitted over a noisy symmetric channel, and is then decoded using a mismatched Viterbi decoder, i.e., a Viterbi decoder that performs maximum‐likelihood sequence estimation using possibly incorrect branch metrics. The branch metrics are assumed to be symmetric, but are generally differrent from the log‐likelihood function. The proposed bound is expressed in terms of the pairwise error probability for a given error event normalized by the sum of the events length and the code's memory. While the bound can be somewhat loose for medium signal‐to‐noise ratios, it is usually asymptotically tight at high signal‐to‐noise ratios. For the special case where the branch metrics employed are equal to the log‐likelihood function our lower bound does not coincide with the standard bound that was derived by Forney and Mazo. It falls short by a multiplicative constant that depends on the code's memory and the shortest error event of minimum Hamming weight. We apply our lower bound to the study of convolutionally encoded direct‐sequence spread‐spectrum communication with Laplacian noise and show that nearest‐neighbor decoding, which is optimal for Gaussian noise, is sub‐optimal and asymptotically (for high processing gain) results in a 3 dB loss in performance when compared with the optimal maximum‐likelihood decoder. Extensions to ratec/nconvolutional encoders, general trellis encoders and to symmetric channels with memory are also presented.
On the optimisation of a noncoherent CDMA system based onM‐ary orthogonal modulation
Authors: Benthin Marcus , Pelz Rodolfo Mann , Kammeyer Karl‐Dirk , Nikolai Dirk
Published: September 2008

This paper concerns the optimisation of a DS‐CDMA based mobile communication system with respect to the transmission quality in the case of data and video services respectively. For combatting transmission errors, forward error protection based on convolutional codes and interleaving in connection with soft decision maximum‐likelihood (ML) decoding through the Viterbi algorithm is applied. In this context, a technique to generate post‐decision reliability information in the case of a noncoherent DS‐CDMA receiver for a given ML metric is presented. The proposed error control strategy involves the application of equal error protection for raw data transmission with the average post‐decodingBERas an optimisation criterion. In the case of a video transmission, a‐priori knowledge regarding the error sensitivity of individual parameter sets suggests an unequal error protection strategy based on punctured convolutional codes, where the segmentalSNRat the source codec output represents the optimisation criterion. Due to the high complexity of the system under investigation, corresponding results are obtained through simulation of the point‐to‐point transmission link. A significant gain regarding the achievable transmission quality with respect to conventional approaches can be achieved in connection with a compound design of source coding, channel coding and spectral spreading.
Performance of residue number system based DS‐CDMA over multipath fading channels using orthogonal sequences
Authors: Yang Lie‐Lung , Hanzo Lajos
Published: September 2008

This paper is concerned with a new direct‐sequence spread‐spectrum multiple‐access communication system based on the so‐called residue number system (RNS) or redundant residue number system (RRNS). The system operates in a multi‐path fading environment, and a RAKE receiver structure with maximum ratio combining is used for demodulation. Approximations to the error probabilities are given by using Gaussian statistics for the multiple‐access and the multipath interference. Concatenated codes employing residue number system product codes (RNS‐PC) as the inner codes and nonbinary Reed‐Solomon (RS) codes as the outer codes are adopted to improve the system performance. The performance of the system is determined for a range of different length RNS‐PC schemes. The results show that, for a given outer RS code and a given number of moduli of the inner RNS‐PC, the performance of the system can be optimized by varying the relative number of information moduli and redundant moduli of the inner RNS‐PC and the moduli's values.
Analytical computation of the error probability of (G)MSK with adaptive sampling in mobile radio channels
Authors: Molisch Andreas F. , Paier Mario , Bonek Ernst
Published: September 2008

We extend the analytical computation of the error probability of (Gauss‐filtered) Minimum Shift Keying (G)MSK with adaptive determination of the sampling time in mobile radio channels. We present a new method that allows to include i) anN‐path fading channel (withST, whereSis the rms delay spread, andT” the bit length) and ii) noise. We show that the errors due to ISI go likeK(SIT)2, where the proportionality constantKdepends on the Gaussian filtering, the receiver filtering, and the sampling time. The chosen sampling instants for large group delays depend on the signal‐to‐noise ratios: for lowSNR, sampling times near the average mean delay are optimum, while at highSNR, sampling times that are shifted by approximatelyT/2 are optimum.
Evolutionary Searching in Cellular Radio Systems Planning
Authors: Jaimes‐Romero Fernando , Muñoz‐Rodriguez David
Published: September 2008

In this paper the suitability of genetic algorithms (GA) as an alternative tool to cope with some design problems in cellular radio is studied. We particularly studied the channel assignment problem for wich two algorithms are examined: a Simple GA and a Hybridized GA where a local search algorithm is incorporated into the search process as a mutation operator.
On the Behavior of Input Queuing Switch Architectures
Authors: Marsan Marco Ajmone , Bianco Andrea , Giaccone Paolo , Leonardi Emilio , Neri Fabio , Filippi Enrica
Published: September 2008

On the Behavior of Input Queuing Switch Architectures

Many proposals of input queuing cell switch architectures have recently appeared in the literature. Some have found application in commercial very high speed IP routers. In this paper we discuss the pros and cons of input and output queuing switch architectures, we provide a taxonomy of scheduling algorithms for input queuing switches, and we present comparative performance results for some of the recent proposals of input queuing cell switches. Performance is measured in terms of cell loss probability, as well as average, standard deviation, and 99‐‐th quantile of the cell delay with different traffic patterns. The complexity of the algorithms, and the amount of control information to be exchanged inside the switch for their execution, are also discussed.
On the Integration of Best‐Effort and Guaranteed Performance Services
Authors: Altman Eitan , Artiges Damien , Traore Karim
Published: September 2008

One of the main challenges of emerging high speed telecommunication networks is the integration of services. Both ATM as well as the Internet have been evolving so as to accommodate both best‐effort type traffic (such as file transfer) as well as real time traffic requiring guaranteed performance. The co‐existence of these two service types on the same network carries important benefits such as resource sharing between service classes, and the ability of the user to easily select an appropriate service class according to requirements and preferences. These benefits depend on efficient network management and resource sharing strategies. The aim of this paper is twofold. First, we study the performance measures of both service types, as a function of the network management strategy. This study allows us at a second phase to design efficient network management schemes. This includes questions such as whether best‐effort traffic should use only bandwidth left‐over by the guaranteed performance ones, or whether (and how much) bandwidth needs to be reserved to best‐effort traffic. Another management issue that we study is the pricing. We allow for different classes of guaranteed‐performance traffic to have different priorities with respect to the rejection probabilities.
Scheduling Algorithms for Application‐Level QoS Support of Continuous Media Streams
Authors: Antoniou Zoe , Stavrakakis Ioannis
Published: September 2008

The Quality of Service (QoS) of real time applications is affected in a rather direct manner by the timely delivery of Application‐level Data Units (ADUs) which are typically mapped into several Network‐level Data Units (NDUs). As a consequence, it would be reasonable to associate a common deadline with all the NDUs in one ADU and develop a scheduling policy that aims to maximise the number of ADUs that are delivered by their respective deadlines. In the first part of the paper, an ADU‐based Earliest Due First (EDF) scheduling policy is investigated under periodic ADU arrival processes which are typical of continuous media streams. The proposed policy can be implemented in terms of a simple First ADU In – First ADU Out (FAI‐FAO) policy and it is shown to improve on the ADU dropping rate induced by FIFO policies of comparable complexity. In the second part of the paper, the more complex and effective Size‐Deadline Sensitive(SDS) scheduling policy is proposed and investigated under general ADU arrival processes. This policy is shown to be optimal in the sense that it maximises the number of complete ADUs scheduled for transmission at any point in time, by taking into consideration the associated diverse deadlines and the ADU sizes and combining the principles of two well known scheduling algorithms, the Earliest Due First (EDF) and the Shortest Job First (SJF). It is argued and illustrated that the proposed optimal scheduling leads in efficient actual service which under certain arrival processes is shown to be the optimal. Numerical results are presented and the induced ADU and NDU loss rates under the proposed policy are compared against those induced by the standard EDF and SJF policies.
Active Networking: A New Paradigm for Next Generation Networks?
Authors: Fan Zhong , Mehaoua Ahmed
Published: September 2008

Traditional data networkspassivelytransport bits from one end system to another and the role of computation within such networks is extremely limited. In contrast,activenetworks allow their users to inject customized programs into network nodes. Also, switches of active networks perform customized computations on the messages flowing through them. In this paper, we discuss the active networking concepts and different approaches to the realization of active networks. We outline potential applications of this novel technology to some difficult problems in current networks and related issues. Since the term “active networking” was first proposed in 1996, there have been considerable research activities at a number of sites. The focus of this paper is therefore put on some recent developments in this area. Possible directions for future research are also identified.
Using Active Networks to Enable Universal Personal Computing
Authors: Törö Maria , Leung Victor C. M.
Published: September 2008

Active networking is an emerging research area aimed at providing flexible and user definable services by employing switches and routers capable of executing user supplied programs and performing computations on user data in transit. This networking environment can be customized on a per user application basis. As the use of network computing applications becomes globally pervasive, users will demand new services which allow network access by nomadic users not only using their own portable computers, but using also any locally available networked computers or workstations, while providing each user with a personalized computing environment regardless of access location or computing equipment. This form of service, called universal personal computing, is also an emerging research area. In this paper, we review the capabilities of active networks as proposed in recent papers, and discuss the issues of implementing universal personal computing. By examining how these issues are addressed by active networks, we propose that active networks present an excellent platform for realizing universal personal computing service.
A new OFDM‐CDMA Uplink Concept withM‐ary Orthogonal Modulation
Authors: Dekorsy Armin , Kammeyer Karl‐Dirk
Published: September 2008

This paper proposes the application ofM‐ary orthogonal Walsh modulation for an OFDM‐CDMA uplink transmission. Beside the examination of general system properties, it is shown that decision‐directed phase estimation represents a channel estimation concept suitable for the new system. The Walsh modulation can also be interpreted as a linear block code with low decoding complexity, and the paper concerns the serial concatenation of convolutional codes (CC) with Walsh modulation. New aspects arise since the CC mainly operates in time domain, and the Walsh modulation is merely arranged in frequency domain. In this context, we derive the bit specific reliability information for maximum likelihood (ML) soft decoding of the CC and discuss the trade‐off between coding and spreading in case of sufficient and non‐sufficient frequency interleaving. Throughout the discussions, the results are always compared with BPSK modulation performance, and it can clearly be demonstrated thatM‐ary Walsh modulation significantly outperforms BPSK modulation in all aspects considered in this work.
Estimation of Point‐to‐Point Traffic in Circuit‐Switched Networks
Authors: Buttò Milena , Conversi Pietro Giulio , Naldi Maurizio
Published: September 2008

The paper addresses the problem of estimating the traffic demand between any pair of nodes in a circuit‐switched network on the basis of trunk group measurements (carried load and blocking probability on a link) and the routing plan. Two methods – a closed form one based on the use of the pseudo‐inverse matrix and an iterative one – are examined in network scenarios of varied size and connectivity under different congestion levels. In addition, a criterion based on a Bayesian approach is proposed for initializing the iterative method. It is shown that the iterative method is affected by lower estimation errors than the pseudo‐inverse method, and that the iterative method's performance is further enhanced by the employment of the Bayesian initialization criterion. Some tentative relationships are provided between the estimation accuracy and the network size and connectivity. The improvement in the estimation accuracy is accompanied by an even more pronounced reduction in the computational load. The use of the iterative method with Bayesian initialization requires in fact running times even two orders of magnitude lower than those needed by the pseudo‐inverse method, the gap being larger the larger the network and the higher the connectivity.
Letter Computation of Constrained Multicast Trees Using a Genetic Algorithm
Authors: Sun Quan , Langendoerfer Horst
Published: September 2008

This paper shows that the genetic algorithm can be used to solve the delay‐constrained least‐cost least‐inter‐destination‐delay‐variation multicast problem efficiently. The proposed genetic algorithm performs well when the number of destination nodes is small relative to the size of the network.
Survey of Architectures and Performance of ATM Switches Based on Deflection Routing
Authors: Pattavina Achille
Published: September 2008

ATM switch architectures based on deflection routing are here examined, described in terms of a general switch model and compared with regards to their internal operations. Their common feature is the availability of multiple I/O paths through a multistage unbuffered interconnection network where conflicts for the same interstage link are dealt with by deflecting packets onto the wrong path. The main engineering parameter of the architecture, that is the number of network stages that provides a given packet loss performance is studied in depth. In particular it is found that basically all the examined architectures have a complexity on the order ofNlog2Nin the range of switch size of usual interest. Furthermore it has been possible to rank the architectures with comparable complexity based on the loss performance they provide. The Shuffleout switch turns out to behave better than other architectures previously known as providing an optimal performance.
Polymorphic Control for Cost‐Effective Design of Optical Networks
Authors: Chunming Qiao , Yousong Mei , Myungsik Yoo , Xijun Zhang
Published: September 2008

A WDM optical layer can provide differentiated services to various upper layer protocols by forming many virtual optical networks (VONs). Polymorphic control of an optical layer in the form of On‐demand‐reconfiguration in some VONs and Self‐reconfiguration in other VONs is proposed. The former is suitable for bursty traffic and short‐lived connections, and the latter is for steady traffic and long‐lived connections. In respect to On‐demand‐reconfiguration, efficient distributed wavelength reservation protocols, and in particular optical burst switching (OBS) protocols supporting bursty traffic (eg. Internet traffic) are described. In respect to Self‐reconfiguration, optimal algorithms to schedule all‐to‐all personalized communications (AAPC) in WDM rings and its extensions are described.
On the Support of Bandwidth on Demand Service over Wide‐Area WDM Optical Networks
Authors: Nen‐Fu Huang , Yao‐Tzung Wang , Bo Li , Te‐Lung Liu
Published: September 2008

Future broadband networks must support integrated services and offer flexible bandwidth usage. Most existing proposals for wide‐area wavelength division multiplexed (WDM) networks employ circuit switching adopting the concept of lightpath, in which each circuit or lightpath occupies an entire wavelength. This, however, is not suited for end‐to‐end transport of information streams, typically with each stream having its unique traffic characteristics such as the bandwidth needed, different traffic bursty nature, and diverse service requirements. In this paper, we explore the extensions of the functions of what we refer as the optical link control (OLC) layer, native on top of optical layer, to offer finer granularity of wavelength usage and further enable the possibility of bandwidth on‐demand (BOD) service directly over WDM networks. The objective is to facilitate the support of integrated services over WDM networks and to mitigate the changes needed in the upper layers as well. The proposed approach attempts to exploit the strengths of both optics and electronics, in which packets are either routed end‐to‐end over a lightpath transparently, or forwarded from wavelength to wavelength by electronic switching, whenever required. Furthermore, in order to establish an end‐to‐end BOD connection, the issue of how to select the best wavelength to mute the given connection is also investigated. The effectiveness of the proposal is evaluated by simulation.
Transmitter Vs. Receiver SDL Solutions for Contention Resolution in WDM Ring Networks
Authors: Chlamtac Imrich , Fumacalli Andrea , Wing Eric , Wong Ming
Published: September 2008

In a single channel ring network the maximum achievable node throughput is inversely proportional to the number of nodes. Recent progress in WDM has opened the possibility to overcome this limitation by utilizing the multiple channels for parallel transmissions. Here we present an approach to obtaining a Concurrently accessed multi‐Ring all‐Optical WDM Network (CROWN) in which in‐transit packets pass through the node (are switched) without being convened into the electronic domain. This avoids the well‐known electronic bottleneck which further reduces the throughput of conventional WDM networks. The proposed architecture is also economical by using only a single high speed transmittcr and receiver per node. To allow data to be maintained in the optical format and still benefit from the multiplicity of channcls this low‐cost node configuration introduces the use of Switched Dclay Lines (SDL) as part of either the receiver or the transmitter hardware. It is shown that in the WDM multi‐channel system the (per node) capacity is at least 50% of the capacity of a single channel optical system with equivalent total bandwidth. However, the cost of the proposcd WDM solution is greatly reduced as it does not require that nodes access the network at the network aggregate bandwidth rate.
Simple On‐Line Scheduling Algorithms for All‐Optical Broadcast‐and‐Select Networks
Authors: Marsan Marco Ajmone , Bianco Andrea , Leonardi Emilio , Neri Fabio , Nucci Antonio
Published: September 2008

This paper considers all‐optical broadcast networks providing a number of slotted WDM channels for packet communications. Each network user is equipped with one tunable transmitter and one fixed receiver, so that full connectivity can be achieved by tuning transmitters to the different wavelengths. Tuning times are not negligible with respect to the slot time. A centralized network controller allocates slots in a TDWDM frame according to (long‐term) bandwidth requests issued by users. Simple on‐line transparent scheduling strategies are proposed, which accommodate bandwidth requests when they are received (on‐line approach), with the constraint of not affecting existing allocations when a new request is served (transparency). Strategies that attempt to allocate in contiguous slots all the transmissions of each source on one wavelength reduce overheads, are simple, and provide good performance. Even better performance can be achieved, at the cost of a modest complexity increase, when the transparency constraint is not strictly imposed, i.e., when a full re‐allocation of existing connections is performed once in a while.
New Optical Amplifier Placement Schemes for Broadcast Networks
Authors: Iness Jason , Mukherjee Biswanath
Published: September 2008

WDM optical broadcast networks (based on the passive‐star coupler) may encounter large splitting and attenuation losses that need to be compensated for using optical amplifiers, such as EDFAs. However, optical amplifiers are costly, so their total count in the network should be minimized. This study will examine three different such amplifier‐placement schemes. The first approach utilize fewer amplifiers than previous schemes that do not add special hardware to avoid the near‐far effect. The second study considers a bidirectionai‐link network and it can use fewer amplifiers than a comparable unidirectional‐link network. The third study minimizes the number of amplifiers when the amplifiers are equipped with special hardware to avoid the near‐far effect, i.e., amplifiers are equipped with attenuators/filters to equalize amplifier input power on different wavelengths.
Performance Evaluation of the KEOPS Wavelength Routing Optical Packet Switch
Authors: Cadro Philippe , Gravey Annie , Guillemot Christian , Marie Raymond
Published: September 2008

This paper presents results concerning the performance evaluation of the KEOPS wavelength routing optical transparent packetswitch. This switch solves contention using optical delay lines; these delay lines are grouped in several sets, in the first stage of the switch. Each input port has access to a few of these delay lines, and each set of delay lines has access to each output port. Non‐FIFO output buffers are thus emulated using scheduling on a small number of delay lines with non‐consecutive delays. Under simplifying assumptions, analytical models are derived, and checked by simulation. These models provide efficient bounds for estimating packet loss probability, under the assumption of regular, balanced input traffic. It is shown that the proposed switch architecture achieves a good performance in terms of packet loss, with a number of delay lines significantly smaller than the ones currently used in other architectures.
Generalized Concatenation of Encoded CPFSK Modulation
Authors: Hautle Armin , Bossert Martin , Shavgulidze Sergo , Ugrelidze Nodar
Published: September 2008

Using the principles of generalized concatenation we introduce a new design for coded M‐ary CPFSK systems with modulation indexh= l/M. This technique is based on a set partitioning method of inner CPFSK into nested subsystems with increasing free Euclidean distance which are combined with several outer convolutional codes having different error‐correcting capabilities. In other words, we construct multilevel codes on the basis of inner modulationwith memory, namely CPFSK. The new generalized concatenated constructions were simulated in an additive white Gaussian noise channel. The multistep decoding algoritm is described where for soft output decoding the well‐known symbol‐by‐symbol maximum aposterioriprobability (MAP) algorithm is applied to the inner CPFSK. A comparison of the generalized concatenated codes with the best known trellis‐coded CPFSK schemes is also presented.
Signal Dependence of Cross‐Phase Modulation in WDM Systems
Authors: Rapp Lutz
Published: September 2008

In intensity modulated direct detection wavelength division multiplexing (WDM) systems, the effect of cross‐phase modulation (XPM) combined with groupvelocity dispersion causes signal distortion, which depends on the transmitted signals. The influence of the mutual dependence of these signals on the resulting degradation of the system performance is investigated theoretically and by means of simulations. Considering the propagation of two digital signals, the eye‐closure penalty is determined for different bit patterns and consequences for system design are pointed out. An approximation method is described in order to provide a better understanding of the signal dependence of XPM. Finally, a technique reducing the impact of XPM on data transmission in WDM systems is proposed.
Letter: Further Results on the Computation of the Outage Probability in Mobile Radio Systems
Authors: Tomba Luciano
Published: September 2008

In this letter we present a general method for the computation of the outage probability in fading radio channels. It is based on the joint use of the saddle‐point approximation and the gaussian quadrature rules. From our numerical results we have found that this procedure is fast and accurate at the same time.
Performance Analysis of a Call Admission Control Strategy for Adaptive‐Rate Traffic in Wireless Networks
Authors: Lombardo Alfio , Palazzo Sergio , Schembra Giovanni
Published: September 2008

In the near future, the telecommunication services provided by wireless networks will be characterized by high throughput and flexibility. Today the challenge in this area is to find techniques which will make it possible to introduce multimedia capabilities into mobile communications. The application of a wireless network structure made up of pico‐cells to solve this problem will cause an increase in the handover rate. Therefore, a major requirement in a wireless environment is to design an effective call admission control (CAC) strategy to minimize the handover drop probability. Another important requirement is to maximize network utilization, in terms OF the average number of channels used. The target of the paper is to define an extension of the Guard Channel CAC strategy for adaptive‐rate traffic sources, in such a way that both the handover drop probability and network utilization are optimized. In order to assess the effectiveness of the proposed CAC strategy, two Markov models of the system are introduced: one, from the network point of view, to evaluate global system performance, and another, from the user point of view, to evaluate the performance each user is provided with by the network. Numerical examples conclude the paper to analyze which factors most affect performance when the traffic bit rate is adaptive and the proposed admission strategy is applied.
An Integrated Multiple Access and Hierarchical Coding Scheme for Video Communication on Wireless Networks
Authors: Bolla Raffaele , Iscra Alessandro , Marchese Mario , Nobile Carlo , Tore Sandro Zappa
Published: September 2008

A Medium Access Control (MAC) protocol of the Reservation Random Access (RRA) family is integrated with a hierarchical video‐coding scheme, to realize effective real‐time video services over the up‐link of a mobile wireless network. For every picture or for each group of contiguous pictures (GOP), the encoder generates an information set organized in a hierarchical layered structure. The base layer contains the information needed to a low quality video; the other layers contain data, which, if received and decoded, can enhance the video quality. The basic idea is to reserve bandwidth only to grant the transmission of base layer information, and modify the MAC scheme to manage the video enhancement data together with voice/dota streams. by adaptively transmitting the increimental video information only it the performances of other traffic classes will not drop below a certain threshold. The aim or this proposal is the improvement of the video stream quality in low load conditions, without a significant reduction of other traffic classes performance during high load periods. Several simulation results show the effectiveness of the proposed method.
Controlling QoS by Integrated Power Control and Link Adaptation in Broadband Wireless Networks
Authors: Leung Kin K. , Wang Li‐Chun
Published: September 2008

We propose and analyze the performance of an algorithm for integrated power control and adaptive, modulationkoding to achieve a specitied range of packct error rate for real‐time applications in broadband wireless packet‐switched networks. The algorithm applies the Kalman‐filter method [I] for power control, and adapts packet transmission to an appropriate modulation level, according to the packet error requirement, and the radio and interference conditions. A new criterion for maintaining stable transmission power is derived. Based on the criterion, the proposed technique performs the link adaptation and adjusts transmission power to achieve the specified packet error rate. The effectiveness of the proposed method is dcmonstratcd by several numcrical examples.