bluuebunny/crossref_metadata_2025 huggingface dataset:
Joint evaluation of time and frequency selective fading effects in CPM systems with LDI detection
Authors: Verdone Roberto
Published: September 2008

Limiter ‐ discriminator ‐ integrator (LDI) detection of binary full and partial response continuous‐phase modulation (CPM) in a channel characterised by Rayleigh fading, time and frequency selectivity, is investigated. An analytical approach able to take into account the presence of any number of delayed paths in the channel is presented. The narrowband bandpass filter effects and the role of the post‐detection integration time and other system parameters are evaluated. The numerical results show that full‐response schemes perform better than partial‐response modulation formats as regards the error floor due to the Doppler effect or the presence of a delayed version of the received signal.
Image processing activities in RACE projects: An overview
Authors: Badiqué Eric
Published: September 2008

Image Processing (IP) activities within the European Union RACE (Research in Advanced Communications in Europe) Programme are primarily oriented towards image coding which can be duly considered as the most striking success of IP yet. But other IP‐related areas essential to the deployment of advanced communications are equally well covered such as image generation, manipulation, segmentation, interpretation and modelling. Intelligent IP techniques, which can range from a simple signal‐adaptive filter to a complete scene analysis prior to model‐based coding, are increasingly being introduced and their potential recognised. Within the emerging ACTS (Advanced Communications Technology and Services) Programme, they will become common place and contribute to achieving high‐quality, flexible and ubiquitous communications evolving towards full virtual presence services.
Performance of phase‐detector receivers for coded BPSK and QPSK communication
Authors: Goldman Haim
Published: September 2008

The paper analyses the performance of phase‐detector receivers for soft decision demodulation of coded BPSK and QPSK communication. In these receivers the received signal is passed through a hard limiter and the information is extracted from the signal's phase only. The performance criteria are cutoff rates that are computed for both maximum likelihood receivers and practical receivers that use a finite set of integer metrics. For the latter type, the optimal partition parameters of the phase circle are computed. The performance of the analysed receivers is compared with the performance of the optimal coherent BPSK receiver. It is found that the reliance on the phase only for extraction of information induces a small performance degradation in BPSK and a considerable degradation in QPSK. It is also found that the performance of the phase‐detector QPSK receiver that demodulates the two quadrature branches independently is similar to the performance of the optimal phase‐detector QPSK receiv2r.
Fast small‐kernel K‐nearest neighbour noise‐smoothing algorithm
Authors: Mitchell Harvey B.
Published: September 2008

A basic operation in image processing is the removal of noise from a noise‐corrupted input picture. The Af‐nearest neighbour (KNN) is a very effective noise‐smoothing filter: it removes both additive and multiplicative noise without blurring the edges and lines in the input picture. The main drawback to this filter is its high computational complexity. In this paper, the author describes a fast algorithm specifically designed for the small‐kernel KNN filter. The computational complexity of the new algorithm is sufficiently low to facilitate real‐time noise‐smoothing.
Electronic simulation of phase noise
Authors: Kreß Dieter , Ziemann Olaf , Dietzel Ralf
Published: September 2008

Theoretical considerations show how to simulate lorentzian shaped phase noise of optical or microwave carrier signals by means of bandlimited noise frequency modulation. An experimental setup is presented which realizes the predicted behaviour concerning spectral bandwidth and shape.
The adoption of optical systems: An econometric cost model of the european telecommunications carriers
Authors: Garrone Paola
Published: September 2008

Following the mainstream applied economic literature on the production structure of the telecommunications (TLC) carriers, the paper provides an econometric estimation of the overall effects of the adoption of optical systems in junction and trunk network on the aggregate long‐run costs of the existing TLC European carriers. The analysis uses data from 16 European carriers over the 1980–'92 period. The optical systems are shown to have significantly reduced the costs of the European carriers. Firms operating non‐rural and high density areas have benefited especially from the adoption of optical systems. In addition, the efficiency gain related to fibre optic lines turns out to be cumulative.
FH‐SSMA with Band‐efficient modulations over cellular fading channels
Authors: Correia Americo M. C. , Albuquerque Augusto A.
Published: September 2008

We present frequency hopped spread‐spectrum multiple‐access (FH‐SSMA) employing bandwidth‐efficient modulations that are phase‐continuous during each hop. The particular cases of minimum‐shift keying (MSK), and Gaussian minimum‐shift keying (GMSK) are studied in detail. Noncoherent sequence estimation on a hop‐by‐hop basis is considered. System performance has been evaluated in selective Rayleigh fading with additive white Gaussian noise (AWGN) and the presence of multiple‐access cellular interference. This system performance is better than the performance of FH‐SSMA with noncoherent binary FSK modulation. The effects of power control, different fading covariance functions and different power bandwidth definitions are investigated.
DS‐SSMA capacity for a mobile satellite system
Authors: Bartucca Francesco , Biglieri Ezio
Published: September 2008

We consider a cellular satellite system conceived to enhance the capabilities of the pan‐European terrestrial system (GSM). This adopts EHF band and highly‐inclined orbits. We present a preliminary assessment of system capacity based on asynchronous direct‐sequence spread‐spectrum multiple access (DS‐SSMA). Performance is measured in terms of error probability achieved by K users simultaneously accessing the system with a given signal‐to‐noise ratio.
Suboptimal, partially coherent detection over multipath/multichannel rayleigh fading
Authors: Abdel‐Ghaffar Hisham S. , Pasupathy Subbarayan
Published: September 2008

Partially coherent detection is studied as a problem of detection over diversity channels with unknown amplitudes, and known or perfectly estimated phases. The optimum composite hypothesis receiver is derived for binary, uniformly orthogonal signaling. Because of the high corn plexity of this optimum receiver, two suboptimal structures are considered a Linear equal gain combiner (LEGC) receiver and a quadratic coherent combiner, which is also a generalized likelihood ratio test (GLRT) receiver for this case. We examine the combiner output signal‐to‐noise ratio (SNR) for the two suboptimal receivers and show that this measure cannot be a performance comparison criterion for receivers of different orders. The exact performance of the GLRT receiver is evaluated in terms of the conditional, average and asymptotic bit error rates (BER), and graphical results are presented. An interesting result is that these BER expressions are obtained, for even and odd diversity orders, via different routes and that quadratic noncoherent detection represents a degenerate case of quadratic coherent detection with even diversity. The average BER of LEGC is exactly evaluated for dual diversity. LEGC and quadratic coherent combining are compared with respect to the asymptotic BEA and the exact BER for dual diversity. It is shown that LEGC is better in terms of the average BER in fading, while quadratic coherent combining is conditionally better whenever the signals received over different links have significantly different strengths.
Letter: On the capacity of the binary input gaussian and rayleigh fading channels
Authors: Taricco Giorgio
Published: September 2008

A class of binary‐input discrete‐time channels with symmetric distribution of the output with respect to the input is considered and the channel capacity is analytically evaluated. The Gaussian and Rayleigh fading channel belong to this class and their capacities are numerically obtained for different quantization of the output. The asymptotic capacities for low signal‐to‐noise ratio (SNR) are compared and it is shown that the Rayleigh fading channel loses about 1 dB.
Feasability of AM‐VSB CATV optical networks using semiconductor laser diodes
Authors: Froidure Jean‐Christophe , Jaunart Emmanuel , Mégret Patrice , Lamquin Michel , Blondel Michel
Published: September 2008

In the past five years practical multi‐channel AM‐VSB optical fibre links have moved from the R&D labs into real world applications. In this paper, we focus on the design and performance capabilities of current commercialized systems using distributed feedback lasers (DFB), single mode optical fibres and PIN optical receivers. We first discuss fundamental concepts used in IM‐DD communication links. The noise and distortions sources are identified and their influence on the systems performances are presented. The use of Erbium Doped Fibre Amplifiers (EDFA) at 1550 nm is envisaged and their influence on the power budget of the CATV network is analyzed.
Letter: New statistical model for burst error distribution
Authors: Cornaglia Bruno , Spini Marco
Published: September 2008

Due to the adoption in high capacity Digital Radio Relay Systems of transmission techniques such as low redundancy error‐correcting codes, trellis coded modulations, Viterbi receivers, etc., the errors tend to be clustered in bursts. Up to now, a model used to describe the burst error distribution was the Neyman‐A contagious model. This model was conceived to be applied in entomology and bacteriology, but it is also used in telecommunications. So, according to this model, the bursts and the number of errors in bursts are both supposed to be Poisson distributed. However, this distribution does not represent accurately the real situation, so, in order to derive a new probability distribution function, that improves the accuracy of the description of a burst error distribution a new model is required. In this paper a new model based on Erlang distribution for the number of errors in bursts, is described by using the Neyman approach.
Orthogonal short codes for code division multiple access networks
Authors: Kanj Khalil , Elhakeem Ahmed K. , Le‐Ngoc Tho
Published: September 2008

Short codes are known to have better balance and spectral characteristics than their long counterparts. In this work we show by simulations that for certain users loads their bit error performance are excellent. A CDMA network performance is investigated under different load and fading situations. We also investigate the effects of using orthogonal codewords in conjunction with concatenated short codes to further reduce the multi‐user interference in these networks.
Narrowband characterisation of the land mobile satellite channel: A comparison of empirical models
Authors: Kanatas Athanasios G. , Constantinou Philip
Published: September 2008

Land Mobile Satellite Systems (LMSS) are subject to severe signal degradation due to. blockage of the line‐of‐sight (LOS) path as well as multipath propagation phenomena. A thorough understanding of the fading effects is of great importance to the design of such a system. This paper reviews and compares ‐ where appropriate ‐ the empirical narrowband models reported in literature. The observation and comparison of these models leads us to the conclusion that this type of channel is strongly dependent on the frequency used For the link, the elevation angle, and the characteristics of the environment in the vicinity of the mobile. The values included clearly indicate the behaviour of the original models and their modifications under different conditions. A table including expected values for the required link margin is presented for the system engineers.
The EXPLOIT testbed
Authors: Potts Martin
Published: September 2008

Several articles in this special issue of the ETT journal, entitled “ATM Field Trials and Experiments”, refer to specific traffic experiments performed on the “EXPLOIT” ATM testbed in Basel, Switzerland. This paper is intended to give the reader a general introduction to this testbed, background information about the project in which it has been supported and extended, and an in; sight into the range of areas in which traffic experiments have been performed. The testbed currently comprises 6 ATM switches, interworking capabilities to N‐ISDN and Frame Relay, broadband signalling and traffic control features which, combined with access to the European ATM network, form a unique platform for the testing of new broadband terminals and applications. Sophisticated traffic generation and analysis equipment is also being used to undertake traffic experiments, mainly in the ATM‐sensitive areas of traffic control, resource management and network performance.
Experimental evaluation of CDV impact on ATM resource management
Authors: Jaussi Laurent , Barcelo Jose‐Maria , Louis Stephane , Casals Olga
Published: September 2008

Measurements of the CDV that a CBR connection accumulates through an ATM network that consists of several switches are presented in this paper. Combining network segments on the EXPLOIT testbed, the Swiss ATM pilot network and the ATM Local Area Network at the Swiss Federal Institute of Technology, an extended test platform could be constructed to evaluate the magnitude of CDV accumulated in a real network. The measurement results are compared to simple tractable models that can be used to dimension the CDV tolerance for UPC/NPC functions along the network. Finally, an estimation of the impact of CDV on resource allocation is carried out using so‐called Worst Case Traffic models to estimate the maximum amount of CDV tolerated to guarantee the proper operation of multiplexing functions.
The validation and integration of the TRIBUNE test‐bed
Authors: Doelman Arie
Published: September 2008

The RACE project TRIBUNE is focused on a number of issues pertaining to the introduction of the Integrated Broadband Communication. The project has implemented a broadband test‐bed with a fully standardized Broadband User Network Interface (B‐UNI) according to the latest ITU‐T recommendations. A lot of effort was therefore spent on the specification, implementation and verification of the B‐UNI and the integration of the test‐bed. This paper is intended to focus on the evaluation of the innovative methods used and experience gained during the three year period of specification, implementation and verification. In this paper we will start with focusing on the specification of the B‐UNI. Particularly the decision to use formal specification languages (‐SDL 88) will be evaluated. The actual implementation of the B‐UNI is discussed in the second part, specially the experience and result of the use of automatic code generation modules. We will elaborate on how the verification of the implementation of the B‐UNI was managed in the third part of this document. Specially the use of the Ferry Clip method and the automatic generation of test suites will be focused upon. Finally, we will show that the taken steps in the previous phases have led to relatively short and easy integration phase of a complex test‐bed around a B‐UNI.
Behaviour of XTPX in the European ATM pilot
Authors: Klovning Espen , Bonaventure Olivier
Published: September 2008

We present and discuss measurements performed with XTPX over the European ATM Pilot. The main characteristic of this wide area ATM network is that the traffic contract is enforced by a Usage Parameter Control (UPC) mechanism. When the ATM traffic is compliant with the traffic contract, XTPX achieves a good utilisation of the link. However, when the ATM traffic is not entirely compliant, the UPC discards cells and the link utilisation becomes very low.
On the effects of workstation scheduling on ATM cell output
Authors: Lin Eric C. , Karlsson Gunnar
Published: September 2008

In this paper, we report on how System V UNIX scheduling can affect the way a workstation outputs ATM cell traffic under various process loads. Whenever multiple processes run concurrently, process contention occurs that creates burstiness and affects a workstation's traffic output. Experiments using a generic sending process and an FTP file transfer were performed that reveal the scheduling contention effects on traffic flow. Our results show that contention can introduce significant cell delay which can be on the order of hundreds of milliseconds. In addition, burstiness occurs where cells are “clumped” together in a variable manner. The average cell output rate decreases with increasing process load, but there is a preference given to a process that transmits cells as opposed to CPU‐intensive programs. The impact of scheduling on traffic shaping based on a leaky bucket is also examined. We show that improper selection of the shaping parameters can occur if change in the process load is ignored and if the initial transient associated with process start‐up is not accounted for. Lastly, we make some comparisons between the scheduling algorithms of System V and 4.3 BSD UNIX.
ATM block transfer capability vs. available bit rate service
Authors: Guillemin Fabrice
Published: September 2008

ATM Block Transfer is an ATM transfer capability, which has been standardized in the May 1996 version of ITU‐T Recommendation 1.371. Two transmission modes for ABT exist, namely the delayed and immediate transmission modes, giving rise to ABT/DT and ABT/IT, respectively, which can run in the elastic or rigid modes. The Available Bit Rate (ABR) service is an ATM layer service, which has been worked by the ATM Forum and specified in the UNI Spec. 4.0 voted in June 1996. The aim of this paper is to give the high level description of ABT and ABR and to draw attention to their common features and their differences. It turns out that the service offered by ABR is much more sophisticated but also more fragile than that offered by elastic ABT/DT. Since the implementation of ABR requires a deeper modification of the existing ATM switches and cross‐connects than elastic ABT/DT, an interworking scenario between these two capabilities, compatible with the cross‐connects used in the current ATM networks, is proposed.
Letter: Output slave clock short term stability on SDH equipment
Authors: Ricchiuti Vlttorio , Ciammaichella Pietro
Published: September 2008

In the modern synchronous telecommunication networks the quality of distributed clock is of primary importance. Instabilities of slave clocks due to their internal noise sources introduce jitter on transported tributaries. Several parameters can be used to characterize the short term stability of a slave clock. In this paper we use the Time Deviation (TDEV (τ)) to characterize the short term stability of a slave clock based on Phase Locked Loop (PLL), locked to an ideal input reference signal. Different PLL bandwidth values are considered and the possibility to discriminate between the PLL internal noise types is also emphasized, analysing its output TDEV (τ) curves only.
Letter: Impact of double cavity FP demultiplexers on the performance of WDM dispersion supported transmission
Authors: Freire Mário M. , De Carvalho José A. R. Pacheco , De Carvalho Álvaro M. F. , Da Silva Henrique J. A.
Published: September 2008

This paper discusses the impact of double cavity Fabry‐Perot demultiplexers on the performance of wavelength division multiplexing (WDM) systems with dispersion supported transmission (DST) of three 10 Gbit/s channels separated 1 nm. For performance assessment, a suitable simulation methodology has been used which combines signal simulation with noise analysis in optically amplified multichannel direct detection systems. Simulation results show an improved system performance if a double cavity Fabry‐Perot filter is used as demultiplexer, resulting in WDM transmission with a crosstalk penalty less than 1 dB in the region of small linear increase of dispersion penalty of the DST method. The robustness of the multichannel DST method against data pattern dependencies is investigated.
Letter: Frame alignment design for HF receivers
Authors: Fina Silvia De , Lombardo Filippo Maria
Published: September 2008

In this letter the feasibility of the application of a frame alignment system based on a CFAR detection scheme over HF radio channels is investigated. The system performance is analyzed in terms of average holding time, average time for the detection of synchronization loss and average synchronization recovery time. The interdependence among the various parameters of the frame alignment scheme is investigated on a simulation basis.
SMATV networks ready for the introduction of digital TV
Authors: Seseña Julian , Prieto Héctor , Molina Ana
Published: September 2008

This paper describes the architectures for the reception of Digital TV in SMATV systems as well as the RF performance of the typical SMATV channel. Based on theoretical analysis, simulation and measurements campaigns performed within the DIGISMATV RACE Project, this paper presents the Reference Channel Model of SMATV systems which characterises the channel behaviour as the typical echoes performance in the coaxial distribution network. This network characterisation has been a key tool for designing and testing equalisers to be used in the QAM IRD's intended for SMATV. The interactive possibilities of SMATV systems using low cost satellite terminals are also addressed in this paper. Thanks to the achievements of the DIGISMATV RACE project it can be concluded that SMATV networks are compatible and ready for the new era of digital TV.
Security analysis of the message authenticator algorithm (MAA)
Authors: Preneel Bart , Rumen Vincent , Van Oorschot Paul C.
Published: September 2008

The security of the ISO banking standard Message Authenticator Algorithm (ISO 8731‐2), also known as MAA, is considered. The attacks presented herein, which exploit the internal structure of the algorithm, are the first computationally feasible attacks on MAA. First a MAC forgery attack is presented that requires 217 messages of 256 kbytes or 224 messages of 1 kbyte; the latter circumvents the special MAA mode for long messages defined in the standard. Next a key recovery attack on MAA is described which requires 232 chosen texts consisting of a single message block. The number of off‐line multiplications for this attack varies between 244 for one key in 1000 to about 251 for one key in 50. This should be compared to about 3 265multiplications for an exhaustive key search. Finally it is shown that MAA has 233 keys for which it is rather easy to create a large cluster of collisions. These keys can be detected and recovered with 227 chosen texts. From these attacks follows me identification of several classes of weak keys for MAA.
Managing trust in an information‐labeling system
Authors: Blaze Matt , Feigenbaum Joan , Resnick Paul , Strauss Martin
Published: September 2008

Many network services need to make “trust management” decisions; in particular, processing users' requests for action often requires using labels and credentials that may not be authentic or trustworthy. In this paper, we address the problem of trust management in information labeling. The Platform for Internet Content Selection (PICS), proposed by Resnick and Miller [13], establishes a flexible way to label documents according to various aspects of their contents, thus permitting a large and diverse group of potential viewers to make (automated) informed judgments about whether or not to view them. For some viewers, the relevant aspects may be quantity or quality of material in certain topical areas, and, for others, they may be the presence or absence of potentially offensive language or images. Thus PICS users need a language in which to specify their PICS profiles, i.e., the aspects according to which they want documents to be labeled, the acceptable values of those labels, and the parties whom they trust to do the labeling. Furthermore, PICS‐compliant client software (e.g., a web browser) needs a mechanism for checking whether a document meets the requirements set forth in a viewer's profile. A trust management solution for the PICS information‐labeling system must provide both a language for specifying profiles and a mechanism for checking whether a document meets the requirements given in a profile. This paper describes our design and implementation of a PICS profile language and our experience integrating the Policy Maker trust management engine with a PICS‐compliant browser to provide a checking mechanism. Policy Maker was originally designed to address trust management problems in network services that process signed requests for action and use public‐key cryptography [2]. Because information labeling is not inherently a cryptographically based service and thus is outside the original scope of the Policy Maker framework, our work on information labeling is evidence of Policy Maker's power and adaptability.
A mesh‐interpolation scheme for very‐low bitrate coding of video sequences
Authors: De Natale Francesco G. B. , Giusto Daniele D.
Published: September 2008

A very‐low bitrate video codec is proposed that processes an image sequence as a two‐component information source. The main difference from state‐of‐the‐art approaches lies in the use of a 3D spatio‐temporal interpolation; it is based on a non‐uniform sampling where frames are processed as 3D blocks, so achieving an adaptive allocation for the information to be transmitted. Residuals are then compressed through a transform coder. Such a method allows for a concurrent and efficient exploitation of intra‐ and inter‐frame correlations; experimental results show a good fidelity in decoded sequences, both in terms of subjective and objective quality.
Adaptive identification and equalization of magnetic recording channels
Authors: Tahir Özden M. , Kayran Ahmet H. , Panayirci Erdal
Published: September 2008

A new RLS adaptive Volterra filter is presented. The nonlinear filtering problem is transformed into an equivalent multichannel, but linear, filtering problem. The multichannel input signal is completely orthogonalized using sequential processing multichannel lattice stages. Thus, a fast convergent, highly modular and, simple filter with good numerical properties is designed. In the identification of magnetic recording channels, the filter identifies the channels directly and parameters for the channel nonlinearity are quantified simultaneously. In the equalization of magnetic channels, the most effective equalizer length can be assigned dynamically.
On recursive optimal detection of linear modulations in the presence of random fading
Authors: Castoldi Piero , Raheli Riccardo
Published: September 2008

In this paper, the problem of optimal detection of a linearly modulated digital signal transmitted over a fading channel is addressed. First, the issue of preliminary front‐end processing in order to extract a sufficient statistics for information sequence detection from the continuous‐time received signal is considered. Then, recursive algorithms are derived, which approximate optimal detection under the assumption of a linear and noisy channel modeled by a stochastic time‐varying impulse response with arbitrary known statistics. Specific solutions are proposed for the Rayleigh fading channel typical of mobile radio communications. The information symbols are assumed to be grouped into blocks which are preceded and followed by known preamble and postamble, respectively This model encompasses both Time Division Multiple Access (TDMA) schemes and pilot symbol assisted transmission. Two detection schemes are considered and relevant recursive formulations proposed. More specifically, optimal detection in complete absence of Channel State Information (CSI) (blind detection) or in presence of perfect CSI at the beginning of the data block (trained detection) are investigated. It is shown that optimal detection performance may be practically attained by sampling the received signal with few samples per symbol interval and searching a trellis diagram of adequate size by means of a Viterbi algorithm. State‐complexity reduction techniques based on Per‐Survivor Processing (PSP) for both types of detection schemes are also considered.
Eavesdropper performance in cellular CDMA
Authors: McKellips Andrew , Verdú Sergio
Published: September 2008

We study eavesdropper performance in power‐controlled cellular CDMA systems. A significant hindrance to eavesdropping in the reverse channel is the wide range of potential received powers from active users; although power control insures that all users are received with approximately equal power at the base station, it does not concern itself with the rest of the cell. Susceptibility to the near‐far problem is demonstrated, and performance sensitivity to eavesdropper location is shown to depend on a single off‐centered‐ness parameter. Both circular and linear cell geometries are considered, with log‐distance and log‐normal shadowing models adopted for signal path loss. A comparison of several eavesdropper detection strategies is performed, demonstrating a potential for significant performance improvement through the use of multiuser detection techniques.
Letter fade countermeasures and adaptive resource sharing for an experimental TDMA satellite communications system operating at Ka‐band
Authors: Schnell Michael , Hugo Dirk Von
Published: September 2008

Satellite communications systems operating at Ka‐band suffer from severe rain fading. Thus, in order to achieve an acceptable availability fade countermeasures have to be applied which are efficiently implemented using adaptive resource sharing. In this letter, the results from a measurement campaign during which an experimental time‐division multiple‐access satellite communications system applying fade countermeasures has been operated at Ka‐band are reported and discussed. The results show that fade countermeasures can be used efficiently leading to a considerable improvement in performance and/or availability.
Letter on the integral frequency‐domain/time‐domain relationship of MTIE (τ, β)
Authors: Tavella Patrizia
Published: September 2008

The range spanned by a clock time error is a random quantity that can be statistically characterised. The paper considers the case of clock affected by white phase noise and the range probability laws are inferred. From the probability distribution, the percentile Maximum Time Interval Error, MTIE(τ, β), can be estimated and the relationship between frequency domain and time domain are discussed.
Estimating Cell Transfer Delay and Cell Delay Variation in ATM Networks: Measurement Techniques and Results
Authors: Roppel Carsten
Published: September 2008

Performance parameters of the ATM layer related to delay are the cell transfer delay (CTD) and cell delay variation (CDV). Monitoring CTD and CDV is important for the operator of an ATM network, in order to guarantee the quality of service expected by the user. This paper discusses basic properties of CTD and CDV, the latter one being defined in terms of 2‐‐point CDV and 1‐‐point CDV. It outlines fundamental measurement techniques and methods for estimating CTD and 2‐‐point CDV, which do not rely on the availability of synchronized clocks at the measurement points. Finally, measurement results obtained from the ATM network operated by Deutsche Telekom are presented.
Shaping Aggregate LAN Flows for Transmission over ABR Connections
Authors: Pippas John B. , Venieris Iakovos S. , Sancjez‐P Jorge‐A.
Published: September 2008

In the current recommendations on Internetworking over Non Broadcasting Medium Access and Multi‐Protocol Over ATM, the issues of ATM bandwidth allocation and flow control for best effort external LAN flows, forwarded to ATM connections, have not been adequately addressed. In this paper, we integrate the above features in the Access Units (i.e., bridges and routers) to smooth the bursty aggregate LAN traffic, to minimize losses due to congestion and consequently to achieve high end‐to‐end performance. The proposed flow control mechanism is based on the knowledge of the bandwidth available in the backbone network. Bandwidth advertising and explicit congestion notification mechanisms are provided by several network technologies such as Frame Relay and ATM. In the latter case the corresponding transfer capability is the Available Bit Rate (ABR). The proposed flow control mechanism, counts the frame delay in the Access Unit, and sends explicit feedback (backpressure) to neighboring legacy LAN sources. Explicit feedback partially absorbs the self‐similar features of the LAN traffic and can extend the ABR flow control to the non‐ATM legacy LAN stations. The shaping performed by the AU can be considered independent to the specific bandwidth advertising mechanism of the backbone network; in our case the ABR. In the performance results, the mechanism is shown to be efficient and adaptive to changes in the ATM available bandwidth and to a variety of LAN traffic characteristics. It is also shown that the flow control mechanism can be easily integrated in the protocol stacks currently met by today's LANs.
Letter Modified Three‐Level Code Acquisition Scheme for Frequency Hopping Radio in Channels with Fading
Authors: Todorovic Branislav , Sunjevaric Milan , Lepir Dragan
Published: September 2008

Modified three‐level code acquisition scheme for frequency hopping (FH) signals, suitable for operation in a fading environment, is presented and analyzed in this letter. This scheme uses a set of passive correlators, a message demodulator and a bank of active correlators. The multiple sync prefixes reduce the probability of missing the signal in a fading environment. The effects of two the most important acquisition parameters (number of passive correlators and number of active correlators) on acquisition performances are analyzed.
Holding Time of a Frame Alignment System Operating Over Time Variant Channels
Authors: De Fina Silvia , Lombardo Filippo Maria
Published: September 2008

In this work, a complete analysis of the average holding time in a frame alignment system operating over time variant channels is developed. In these cases the probability of miss is time variant as well, so that the statistics of the underlying process has to be investigated for properly approaching the system design. In a common frame synchronization strategy, involving a certain number α‐1 of pre‐alarm states, the probability of miss has to be calculated for α consecutive frames so that any time correlation in the propagation conditions has to be properly reflected in the statistical model of the miss process. The derived expression of the average holding time can be used for designing the alignment strategy for any time variant medium, under the sole hypothesis that the probability of miss can be fully characterized by its second order statistic and that it can be assumed to hold constant for the preamble duration. Sensitivity results for a sample application in a typical system operating in the HF band are also given: the dependence of the average holding time from some parameters related to frequency selectivity (the delay spread) and time selectivity (the frequency spread s) of the propagation medium can be clearly envisaged.
Multi‐Period Planning of Survivable WDM Networks
Authors: Pickavet Mario , Demeester Piet
Published: September 2008

This paper presents a new heuristic algorithm useful for long‐term planning of survivable WDM networks. A multi‐period model is formulated that combines network topology design and capacity expansion. The ability to determine network expansion schedules of this type becomes increasingly important to the telecommunications industry and to its customers. The solution technique consists of a Genetic Algorithm that allows to generate several network alternatives for each time period simultaneously and shortest‐path techniques to deduce from these alternatives a least‐cost network expansion plan over all time periods. The multi‐period planning approach is illustrated on a realistic network example. Extensive simulations on a wide range of problem instances are carried out to assess the cost savings that can be expected by choosing a multi‐period planning approach instead of an iterative network expansion design method.
PCS Subscribers Mobility Modeling Using Fractional Brownian Motion (FBM)
Authors: Aleman‐Llanes Enrique , Munoz‐Rodriguez David , Molina Carlos
Published: September 2008

The growth of PCS systems demands better resource management algorithms. Reduction of the cell size has been a common point that many solutions propose. As a result of cell reduction, the importance of finer mobility descriptions increases, such that it is necessary to look for improved analytical tools to model mobility. In this paper, a mobility model based on Fractional Brownian Motion (FBM) is presented. The proposed model represents a wide variety of mobility scenarios, removing the unrealistic constraints of previous models. The suitability and flexibility of the proposed methodology is discussed through the analysis of different scenarios.
Convolutional Encoders to Minimize Bit‐Error‐Rate
Authors: Lapidoth Amos , Sallaway Peter J.
Published: September 2008

The results of a computer search for convolutional encoders for the binary symmetric channel and the additive white Gaussian noise channel are reported. Both feed‐forward and feedback encoders are considered. It is shown that, when bit error rate is the design criterion. feedback encoders may outperform the best feed‐forward encoders at no additional complexity.
Fundamental Properties of the Low Voltage Power Distribution Grid Used as a Data Channel
Authors: Dostert Klaus , Zimmermann Manfred , Waldeck Torsten , Arzberger Michael
Published: September 2008

Recently a steadily increasing interest towards usink the low voltage power distribution grid for various communication purposes is noticed. For the construction of appropriate equipment, being able to cope with the properties of such an unusual channel, a thorough understanding of physics is paramount. The work presented in the following describes essential contributions towards modelling basic properties of low voltage energy distribution networks as data channels. New and important measurement results of parameters significantly influencing the performance of communication systems are outlined. covering typical values and properties of network access impedance, propagation characteristics as well as different kinds of interference in the frequency range 20kHz to 150kHz. Furthermore channel model approaches based on the results are discussed.
Design of a Multistage Optical Packet Switch
Authors: Raffaelli Carla
Published: September 2008

Optical packet switching is considered as a means to achieve high speed networking in future optical multi‐service networks, Optical switches of limited size are feasible with present‐day photonic technology, so solutions for the design and implementation of large switches are proposed here. They are based on a multistage architecture built using small switching modules with output queuing, organised according to a Clos topology. Many degrees of freedom are available for switch design and they are exploited to achieve performance optimisation in relation to packet loss. Simulation and analytical tools are developed to evaluate switch architecture performance. Results and application examples are given to show the feasibility of the multistage architecture for optical networking.
Stochastic channel allocation in non—linear environments
Authors: Baruffa Giuseppe , Cacopardi Saverio , Frescura Fabrizio , Reali Gianluca
Published: September 2008

In this paper new techniques able to solve the problem of frequency assignment in satellite communications are proposed. Their performance is evaluated in a non—linear environment that models the satellite channel behaviour. The stochastic approach consists in the exploration and validation of new load configurations for the downlink channel. Since the carriers have different powers, the complexity of the problem is high. An analytical approach is used for calculating the number and the power of 3rd order inter—modulation products, which may also be used for higher order contributions. After this, comparisons between classic and stochastic techniques, in terms of computational time and allocation quality, are shown.
Synchronized data services over MPEG—2 digital television broadcast systems
Authors: Brunheroto J. , Chernock R. , Dettori P. , Paraszczak J. , Schaffa F. , Seidman D. , Dong X.
Published: September 2008

Until the present, the digital television (DTV) industry has focused providing high—quality basic video and audio services. With advancements in the underlying technologies, digital television is likely to evolve into a much more interactive medium, involving advanced data services and applications which are both integrated with and synchronized to the video/audio content of the broadcast. We present our approach for the implementation of these synchronized data services, with emphasis on the issues of content synchronization and the optimization of data placement in the broadcast stream.
Geographical and temporal characteristics of inter‐POP flows: View from a single pop
Authors: Bhattacharyya Supratik , Diot Christophe , Taft Nina , Jetcheva Jorjeta
Published: September 2008

In this paper, we study traffic demands in an IP bacbkone, identify the routes used by these demands, and evaluate traffic granularity levels that are attractive for improving the poor load balancing that our study reveals. The data used in this study was collected at a major POP in a commercial Tier‐1 IP backbone. In the first part of this paper we ask two questions. What is the traffic demand between a pair of POPs in the backbone? How stable is this demand? We develop a methodology that combines packet‐level traces from access links in the POP and BGP routing information to build components of POP‐to‐POP traffic matrices. Our analysis shows that the geographic spread of traffic across egress POPs is far from uniform. In addition, we find that the time of day behaviors for different POPs and different access links also exhibit a high degree of heterogeneity. In the second part of this work, we examine commercial routing practices to assess how these demands are routed through the backbone. We find that traffic between a pair of POPs is engineered to be restricted to a few paths and that this contributes to widely varying link utilization levels. The natural question that follows from these findings is whether or not there is a better way to spread the traffic across backbone paths. We identify traffic aggregates based on destination address prefixes and find that this set of criteria isolates a few aggregates that account for an overwhelmingly large portion of inter‐POP traffic. We demonstrate that these aggregates exhibit stability throughout the day on per‐hour time scales, and thus form a natural basis for splitting traffic over multiple paths to improve load balancing.
An integrated approach to MPLS traffic engineering over automatically switched transport networks
Authors: Van Hoey G. , Van Bosch S. Den , De Vallée‐Poussin P. La , Degrande N. , De Neve H.
Published: September 2008

Internet traffic engineering is defined as performance evaluation and performance optimisation of operational IP networks. The definition covers both planning and routing optimisation. Planning typically optimises network topology at large time scales. Routing optimisation optimises the routing configuration in the network for a specific traffic matrix, assuming a fixed topology. With automatically switched transport networks the topology provides an additional degree of freedom at time scales on the order of magnitude of those at which traffic engineering operates. Therefore, in such a network, the decision processes should be co‐ordinated. The present contribution describes an approach and algorithms to support such co‐ordinated decisions in a centralised off‐line traffic‐engineering tool. The approach optimises the logical topology and link capacity overlaying the ASTN and the IP routing configuration. It is supported by a simulation example.
Kalman‐filters in subbands for noise reduction with enhanced pitch‐adaptive speech model estimation
Authors: Puder Henning
Published: September 2008

In this paper, we present an approach for a Kalman filter which enhances single channel speech signals disturbed by car noise. For the Kalman filters, the speech and noise signals are modelled by AR processes and the corresponding models have to be estimated, based on the noisy speech. To avoid high model orders, the filtering is performed in subbands. We especially focus on the estimation of the speech model: First, standard model estimation methods are investigated and the method giving the best stable model is then utilized as a preliminary solution. To enhance the models without generating musical tones, a new method is proposed that utilizes estimates of the speaker's pitch frequency. The algorithm we present has less than 39 ms delay and thus fulfills the ETSI requirements for mobile telephony [1].
On the importance function in splitting simulation
Authors: Garvels Marnix J. J. , Van Ommeren Jan‐Kees C. W. , Kroese Dirk P.
Published: September 2008

Thesplitting methodis a simulation technique for the estimation of very small probabilities. In this technique, the sample paths are split into multiple copies, at various stages in the simulation. Of vital importance to the efficiency of the method is theImportance Function(IF). This function governs the placement of the thresholds or surfaces at which the paths are split We derive a characterisation of the optimal IF and show that for multi‐dimensional models the “natural” choice for the IF is usually not optimal. We also show how nearly optimal splitting surfaces can be derived or simulated using reverse time analysis. Our numerical experiments illustrate that by using the optimal IF, one can obtain a significant improvement in simulation efficiency.
The spatial dimension in the case of mc‐cdma
Authors: Lindner JÜRgen , Pietsch Christian
Published: September 2008

After discussing basic possibilities to exploit the spatial dimension for wireless communications, a vector transmission model for MIMO channels is taken to investigate the potential of the spatial dimension for MC‐CDMA. For frequency‐selective channels it is shown that the spreading component of MC‐CDMA may already provide enough diversity, so that it gets more important to use the spatial component offered by MIMO channels for parallel transmissions.
Ring planning in transport networks with very high resilience requirements
Authors: Parnis Noel , Cotta Bruno , Drakopoulos Elias , Antonopoulos Andreas
Published: September 2008

In this paper we concentrate on issues relating to the planning and design of ring transport networks with stringent resilience requirements. Given the standardized and widely used ring protection schemes as well as the Single Ring Interconnection (SRI) and the Dual Node Interworking (DNI) schemes, we engage in a study to examine the issues and trade‐offs arising from the variety of architecture options when planning a network. We analyze and compare the resilience properties of the various options including the recently defined and developed DNI on protection interworking feature. We then use a case study to demonstrate the traffic carrying capabilities and the resilience properties of the various available architectures under different traffic scenarios. Trade‐offs introduced are illustrated and explained and an analysis of the modeling results allows for a better understanding of the significance of ring clustering for resilience purposes. We conclude on the penalties of DNI when MS‐SPRings and SNCP‐ring architectures are employed and we demonstrate that significant efficiencies can be achieved from the emergence of DNI on protection techniques.