bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intact versus fractional switching in SONET/SDH cross—connects
Authors: Park Won Bae , Owen Henry L. , Zegura Ellen Witte 
Published: September 2008

AbstractSynchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) cross connect switching structures may be made non—blocking by providing sufficient hardware resources. For example, in a three—stage Clos switching structure this is accomplished by providing a sufficient number of middle stage switches to allow connections to be made without blocking. Nonblocking SONET/SDH cross—connects are more expensive than architectures which reduce the hardware complexity in their implementations at the expense of increased blocking probability. Under certain circumstances, initially unsuccessful new connections may still be connected if rearrangement of existing connections is possible. Factors which make rearranging connections difficult in a SONET/SDH signal environment is the multirate and multicast nature of the traffic, the requirement that any rearrangements must not interrupt existing sessions, and subnetwork connection protection. Cross—connects with this subnetwork connection protection capability must provide hardware and software functionality that selects between two independent copies of a signal and passes the error—free copy through the matrix. We explain how subnetwork protection introduces a requirement for intact switching of SONET/SDH signals. We also present a comparison of intact and fractional SONET/SDH connection and rearrangement algorithms in the context of subnetwork connection protection requirements. We demonstrate the blocking probability impact of introducing subnetwork protection connections into cross—connects.
Availability and performance of single/multiple site diversity satellite systems under rain fades
Authors: Livieratos Spiros N. , Corns Panayotis G. 
Published: September 2008

AbstractAn analysis is presented for the evaluation of the probability of error achieved by single/multiple site diversity systems taking into account rain attenuation. A systematic method is proposed relating rain attenuation statistics to BER performance masks recommended by ITU for satellite links. The efficiency of site diversity as a countermeasure against severe rain attenuation is investigated for various frequency bands and climatic regions. Single site systems are compared to double and triple site diversity systems.
Broadband capacity upgrade strategies in residential areas: An investment cost analysis
Authors: Ims Leif Aarthun , Myhre Dagfinn , Olsen Borgar Torre 
Published: September 2008

AbstractThe paper presents an analysis of the investment costs associated with broadband' upgrades in various residential areas in which there is an existing twisted pair infrastructure. Upgrade strategies— based on a combination of optical fibre systems and digital subscriber line (DSL) technologies are examined. The analysis highlights the significant differences in investment levels expected in downtown, urban, suburban and rural areas for the ranges of DSL capacities from 2 Mbit/s to 26 Mbit/s. The paper reports work performed in the EURESCOM2 project P614, Implementation Strategies for Advanced Access Networks*. The methodology and tool initially developed by the RACE3 2087/TITAN4 project, and now under further development in the ACTS5 226 OPTIMUM6 project has been applied in the techno—economic analysis.
Performance of a baseband adaptive predistorter in presence of orthogonal multicarrier modulation
Authors: Santella Giovanni , Mazzenga Franco 
Published: September 2008

AbstractThe performance of a baseband adaptive predistortion system to linearize memoryless high power amplifier (HPA) are analyzed in the presence of an Orthogonal Frequency Division Multiplexing (OFDM) signal. The predistortion scheme adopted is based on a digital signal processing microprocessor and a memory look—up table to predistort the baseband drive signal. Stability of the adaptation algorithm, rate of convergence and effect of quantization are assessed through simulation. The curves of Total Degradation versus the Output Back—off have been calculated for QPSK, 16QAM and 64QAM constellations. Starting from these results, the improvement brought by the use of the predistorter and the degradation caused by the quantization has been assessed.
Prioritisation of data partitioned MPEG—4 video over mobile networks
Authors: Worrall Stewart T. , Fabri Simon N. , Sadka Abdul H. , Kondoz Ahmet M. 
Published: September 2008

AbstractDespite much research in the field of mobile multimedia, delivery of real—time—interactive video over noisy wireless channels remains a challenging problem. Two of the major issues in providing true end—to—end mobile multimedia capability are interoperability between platforms and networks and the poor performance of video compression algorithms in error—prone environments. This paper presents a method for prioritising data partitioned MPEG—4 video in a way suitable for transmission over a mobile network. The effectiveness of the technique is demonstrated by examining the performance when transmitted using the Real—Time Transport protocol over GPRS (General Packet Radio Service) data channels under varying channel conditions.
Hierarchical transmission of MPEG—2 sequences in noisy environments
Authors: Favalli Lorenzo 
Published: September 2008

AbstractThe MPEG—2 standard, describes several options to split the video stream in sub—streams conveying information at different detail level. This fact can be exploited to generate a low quality stream with all what is necessary for a basic service while all other sub—streams carry “detail” information to improve the quality of the reconstructed signal. In a mixed network environment this can be exploited to allow the stream to be decoded by different terminals. Another use is to provide flexibility in tough transmission systems where either traffic or noise can give rise to severe impairments. In this paper signal—to—noise—ratio scalability is used in a radio transmission system targeted as the DVB—S (Digital Video Broadcasting — Satellite) to investigate the eventual gains. It is shown that for a given target rate, differentiated coding allows the received signal to be decoded at a channel Signal to Noise Ratio which is 3 dB lower than the one necessary for a single—stream coded sequence.
Rate—distortion optimal fast thresholding for MPEG—2 image sequence coding
Authors: Tzovaras Dlmitrios , Boulgouris Nlkolaos V. , Argyraki Katerina , Strintzis Michael G. 
Published: September 2008

AbstractA new Rate—Distortion (R—D) optimized image sequence encoding scheme is introduced, fully compatible with the standard MPEG—2 decoder. R—D optimal DCT coefficient thresholding is used, so that best image reproduction quality is achieved under the constraint of a “local” target bit rate for every image. The proposed technique combines R—D optimal coefficient thresholding and some elements of the MPEG—2 rate control model “Test Model 5” and results in a new video encoding scheme, which offers in most cases a higher representation quality than “Test Model 5”. The performance of the proposed technique is experimentally evaluated for the coding of standard test image sequences.
Error concealment in the transformed domain for DCT—coded picture transmission over Noisy Channels
Authors: Ancis Marcella , Giusto Daniele D. , Perra Cristina 
Published: September 2008

AbstractIn this paper, the problem of DCT information loss in the transmission of coded pictures over unreliable packet networks is studied. Due to the use of variable length coding, packet losses can make impossible the reconstruction of large areas, causing annoying artifacts in the decoded image. Here, different methods of error concealment directly working in the transformed domain are described and their performance are compared with reference to the results of an extensive testing phase. Our analysis spans from very simple interpolation algorithms, which require only minor computational resources, even if at expense of a limited reconstruction quality, to more complex techniques, based on the use of Artificial Neural Networks, which yield good results even in very detailed areas, but require longer computational time.
Dynamic QoS mapping control for streaming video in relative service differentiation networks
Authors: Shin Jitae , Kim Jin‐Gyeong , Kim Jongwon , Jay Kuo C.‐C. 
Published: September 2008

AbstractA dynamic quality of service (QoS) mapping control scheme, which includes feedforward and feedback QoS control, is proposed for the differentiated services (DiffServ) networks in this work. To achieve reliable and consistent end—to—end video streaming with relative service differentiation, the proposed solution consists of two parts: (1) relative priority—based indexing and categorization of streaming video content at the sending end—system and (2) dynamic and aggregate QoS mapping control with packet, session, and class—based granularity level for categorized packets at the edge of the DiffServ domain, called the video gateway (VG), based upon the load variation of the network. In particular, we focus on dynamic solutions to handle QoS demand variations of continuous media applications (e. g. varying priorities from aggregated/categorized packets) and QoS supply variations of the DiffServ network (e. g. varying loss/delay due to fluctuating network loads). Thus, with the proposed dynamic QoS mapping control, video streaming with enhanced quality is demonstrated under a pricing model.
Data transfer statistics in internet dial—up sessions
Authors: Naldi Maurizio 
Published: September 2008

AbstractThis letter reports the results of a measurement campaign aimed at characterizing the traffic in Internet dial—up sessions. This is done at the data transfer level, i. e. considering the average data rate and the volume of data transferred during calls to Internet service providers. Major statistics (mean and two percentile values) are provided for both quantities with a hourly time resolution together with the empirical probability density functions relative to the peak hour.
The capacity of the noncoherent channel
Authors: Colavolpe Giulio , Raheli Riccardo 
Published: September 2008

AbstractThe capacity of a random—phase additive white Gaussian noise (AWGN) channel, referred to as noncoherent channel, is investigated in the case of a transmission of N information symbols. The non—Gaussianity of die capacity—achieving distribution is shown and a lower bound on the channel capacity is derived. For increasing values of the number of transmitted symbols N, the capacity of a noncoherent channel is shown to asymptotically approach that of a coherent channel, i. e., a known—phase AWGN channel. The asymptotical Gaussianity of the capacity—achieving distribution is also shown. Based on the derived lower bound, the inherent capacity loss of a noncoherent channel, as compared to a coherent one, may be considered very limited for all but very small values of N. This result may be viewed as the information theoretic counterpart of a similar conclusion derived by many authors with reference to the probability of detection error.
On the capacity of cellular CDMA and TDMA over nondispersive channels
Authors: Sari Hikmet , Steendam Heidi , Moeneclaey Marc 
Published: September 2008

AbstractWe investigate the interuser interference in cellular code—division multiple access (CDMA) and timedivision multiple access (TDMA) systems and compare the two multiple access techniques at different levels of user density per cell. The study includes the interference both on the downstream channel (from base station to users) and on the upstream channel (from users to base station). The purpose is to compare the two multiple access techniques when the total bandwidth occupancy and the maximum number of users per cell are the same. The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA. The implication of this result, which holds for both the downstream and the upstream channels, is that for the same total bandwidth and number of users per cell, TDMA gives substantially superior bit error rate (BER) performance. This is confirmed by our numerical results evaluated for both additive white Gaussian noise (AWGN) channels and memoryless flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth to achieve the same signal—to—interference (S/I) ratio, a result which may seem surprising, because the fact that CDMA employs a frequency reuse factor of 1 is often given as an evidence that this technique can support a higher number of users than TDMA in a given geographic area and frequency bandwidth.
Adaptive radio resource management in F/TDMA cellular networks using smart antennas
Authors: Hartmann Christian , Eberspächer Jörg 
Published: September 2008

AbstractIn this paper we discuss different Radio Resource Management (RRM) strategies for smart antenna cellular networks. The focus is on adaptive strategies which combine spatial channel reuse within the cell with dynamic inter—cell channel allocation. In particular, three different SDMA channel allocation strategies are described and compared in terms of complexity as well as traffic capacity. The comparison is done by means of system simulations of a multi—cellular environment. We show that with a growing degree of freedom the RRM strategies yield better results in terms of traffic capacity while the number of handoffs per call increases and the complexity grows.
Adaptive soft—decision decoding for array codes
Authors: Peng Xiao‐Hong , Farrell Paddy G. 
Published: September 2008

AbstractAn adaptive decoding scheme is introduced that achieves efficient soft—decision decoding for row—and—column parity array codes. The special structure of array codes is exploited to make effective use of hard—decision methods to realize soft—decision decoding. This leads to considerable reduction in decoding complexity as the amount of soft—decision computation varies with channel conditions. It is shown that the new decoding algorithm guarantees bounded distance performance. Simulation results indicate that the actual improvement of decoding performance over uncoded systems and previous decoding methods is significant.
Paging area planning in future cellular systems
Authors: Kazantzakis M. , Demestichas P. , Demesticha V. , Tzifa E. , Kazantzakis J. 
Published: September 2008

AbstractEfficient resource utilisation in future cellular systems is related to the control of the signalling load imposed by the paging operations. This relies on the application of efficient paging schemes, and on the “proper” planning of paging areas. In this paper we define and solve a version of the paging area planning problem. In particular, we provide a low complexity algorithm, under the assumption that the scheme applied falls within the last interaction based paging (LIBP) category.
A large hierarchical network star—star topology design algorithm
Authors: Petrek Jozef , Sledt Volker 
Published: September 2008

AbstractThe hierarchical communication network design includes solving problems like the concentrator quantity problem, the concentrator location problem and the assignment problem. Many algorithms have been proposed to solve these particular problems. The two latter problems are NP—hard and no optimal solution of these problems has been found for large networks. In this paper we present a high complexity algorithm for star—star network topology design which solves all three problems for several hierarchy levels simultaneously and finds a superior solution in a reasonable time even for large networks with a few thousand terminals due to a new and quick assignment algorithm. The computational results showed that our assignment algorithm is superior to “Simulated annealing” and “Tabu search”.
Implications of Interdomain Traffic Characteristics on Traffic Engineering
Authors: Uhlig Steve , Bonaventure Olivier 
Published: September 2008

AbstractWe study the interdomain traffic as seen by a non‐transit ISP, based on a six days trace covering all the interdomain links of this ISP. Our analysis considers the relationships between the interdomain traffic and the interdomain topology. We first discuss the day‐to‐day stability of the interdomain traffic matrix to evaluate the feasibility of interdomain traffic engineering. Then, we study the variability of the interdomain flows for several aggregation levels (prefix, AS and sink tree) and with respect to the interdomain topology seen by BGP. We show that despite the important variability of interdomain flows, it would be useful for a non‐transit ISP to traffic engineer its access traffic by relying on a sink tree aggregation level.
Partitioned residual echo power estimation for frequency‐domain acoustic echo cancellation and postfiltering
Authors: Enzner Gerald , Martin Rainer , Vary Peter , Enzner G. , Martin R. , Vary P. 
Published: September 2008

AbstractResidual echo arises in hands‐free telephony equipment due to insufficient echo canceler convergence, but can be suppressed using a postfilter. The residual echo power spectral density is the most crucial control parameter for both frequency‐domain acoustic echo cancellation and combined residual echo and noise postfiltering. In this contribution we present and compare residual echo power spectral estimation techniques. We introduce a new partitioned block‐adaptive estimation technique delivering considerably improved residual echo estimates in strongly reverberant and noisy acoustic environments. We show that the adaptation loop of the frequency‐domain adaptive filter (FDAF) can be used simultaneously for residual echo power estimation and tracking of the echo path impulse response. In this way, the FDAF and the postfilter concept supplement each other in a true synergy with low complexity. The resulting echo and noise control system proves to be robust in double talk situations as well.
Most probable paths and performance formulae for buffers with gaussian input traffic
Authors: Addie Ron , Mannersalo Petteri , Norros Ilkka 
Published: September 2008

AbstractIn this paper, performance formulae for a queue serving Gaussian traffic are presented. The main technique employed is motivated by a general form of Schilder's theorem, the large deviation result for Gaussian processes. Most probable paths leading to a given buffer occupancy are identified. Special attention is given to the case where the sample pams of die Gaussian process are smooth. The performance approximations are compared with known analytical results or by means of simulation. The approximations appear to be surprisingly accurate.
Radial basis function receiver for DS‐CDMA
Authors: Tanner Rudolf , Cruickshank David G. M. 
Published: September 2008

AbstractThis paper presents a nonlinear sub‐optimum receiver structure for DS‐CDMA. We also draw attention to the nonlinear separation problem in a DS‐CDMA system and suggest me use of ideas known in the field of partem recognition. We visualise the separation problem and the decision boundaries of different receiver structures, which in return give reasons for each receiver's performance. The proposed receiver structure is based upon the radial basis function (RBF) network. Techniques from pattern recognition are exploited to reduce the RBF complexity for mulupath scenarios, for example the use of the Mahalanobis distance measure. The presented RBF receiver has significantly less complexity (in terms of centres or neurons) than the optimum RBF receiver through the use of super centres, and outperforms Verdu's detector.
Adaptive state‐ dependent importance sampling simulation of markovian queueing networks
Authors: Boer Pieter‐Tjerk De , Nicola Victor F. 
Published: September 2008

AbstractIn this paper, a method is presented for the efficient estimation of rare‐event (buffer overflow) probabilities in queueing networks using importance sampling. Unlike previously proposed change of measures, the one used here is not static, i.e., it depends on the buffer contents at each of the network nodes. The ‘optimal’ state‐dependent change of measure is determined adaptively during the simulation, using the cross‐entropy method. The adaptive state‐dependent importance sampling algorithm proposed in this paper yields asymptotically efficient simulation of models for which it is shown (formally or otherwise) that no effective static change of measure exists. Simulation results for queueing models of communication systems are presented to demonstrate the effectiveness of the method.
An adaptive importance sampling approach for the transient analysis of markovian queueing networks
Authors: Buchholz Peter 
Published: September 2008

AbstractWe present a new method for the efficient estimation of rare events and smart probabilities in Markovian queueing networks. The method uses importance sampling to modify the probability distribution of the events to be observed. In contrast to most other importance sampling approaches, transient instead of steady state analysis is considered and the change of the measure is computed adaptively. The whole approach is based on the combination of discrete event simulation and randomization, a technique to transform a continuous time Markov chain into a discrete time chain and an associated Poisson process. By means of randomization it is possible to derive a simple model describing me relation between me occurrence of the rare event and the probability of different transition types. This model can be used to compute adaptively the change of transition probabilities to make the rare event less rare depending on the observed behavior in some replications and the time horizon of transient analysis. If the time horizon increases, the method is extended by introducing regeneration points in the analysis. By means of small examples it is shown that the method yields satisfactory results even for more complex queueing networks for which optimal or approximatively optimal importance sampling parameters are not known from the theory.
Adaptive importance sampling in routing and wavelength assignment problem
Authors: Hyytiä Esa , Virtamo Jorma 
Published: September 2008

AbstractDynamic routing and wavelength assignment in all‐optical networks is a well‐known problem for which many reasonably well working heuristic algorithms have been proposed in the literature. The problem can be also approached in the Markov decision process (MDP) framework. Due to the huge size of the state space only heuristic algorithms are viable in practice. However, so called first policy iteration can be used to enhance the performance of any given (standard) policy. In some cases the improvement can be considerable. For the first policy iteration one needs to estimate so called relative values of states, which are defined as the expected difference in future rewards/costs between two states. The relative values can be estimated by short simulations starting the system from a given state. As the blocking probability in network is usually very low this leads to a problem where rare events must be estimated. Also, depending on the system's current state some arrival realisations are more likely to cause blockings than others. An adaptive importance sampling method is proposed to overcome these difficulties.