bluuebunny/crossref_metadata_2025 huggingface dataset:
Letter: Cross Section Computation of Trihedral Corner Reflectors with the Geometrical Optics Approximation
Authors: Groot Jos
Published: September 2008

A Monte Carlo type numerical method based upon the geometrical optics (GO) approximation to compute the monostatic radar cross section of trihedral corner reflectors is introduced. Advantages of the method are its simplicity and the possibility to use it for the most complex reflector shapes. Disadvantage is its slow convergence as a function of the number N of rays involved, and hence the amount of computer time needed. Comparison of numerical with experimental and GO analytical results for the often used triangular and square‐based reflectors confirm the validity of the numerical method. The analytical results presented are valid for a wider angular range than those given in the most commonly used literature.

The method was utilized in the problem of finding a reflector shape exhibiting a relatively flat angular RCS pattern. The pattern of the resulting optimal reflector varies less than approximately I dBm2 within a region of about ±25° ‐ 30° around boresight. For the most commonly used triangular reflector this region is only about ±10° ‐ 15° wide.
Noise Prediction Equalizer and Decision Feedback Equalizer for High Speed Digital Subscriber Line Transmission ‐ A Comparison of Performance
Authors: Ernst Detlef
Published: September 2008

A new equalizer structure, the noise prediction equalizer, was recently proposed in the literature, especially for applications in high speed digital subscriber line transmission systems. It consists of a decision feedback equalizer and an additional noise prediction filter. The calculation of its optimum tap weights in the mean square error sense yields a nonlinear system of equations, that can be solved by approximation in two different ways. The characteristics of the transmission channel and the additive noise determine which method yields the smaller mean square error. Even without approximations the minimum mean square error of the noise prediction equalizer exceeds that of a decision feedback equalizer with filters of equivalent lengths. In addition the noise prediction equalizer offers almost no advantage in comparison with the decision feedback equalizer for the adaptive filter adjustment.
Distributed Routing Techniques for Internally Unbuffered Interconnection Networks
Authors: Ferrari Gianfranco , Lenti Marco , Pattavina Achille
Published: September 2008

This paper deals with techniques for improving the performance of unbuffered banyan networks adopted in a switching fabric of a broadband packet switching network. We propose an arrangement of parallel banyan networks provided with output buffers that enables more than one packet to reach an output interface of the switch. Different solutions for the packet distribution to the banyan networks of the stack are investigated and the corresponding traffic performance is evaluated. Two types of packet addressing patterns are considered, depending on how many packets are allowed to address each switch outlet. The results obtained prove that a significant reduction in packet loss probability is possible with respect to a simple banyan network.
Input/Output Buffered Replicated Banyan Networks for Broadband Switching Applications
Authors: Corazza Giorgio , Raffaelli Carla
Published: September 2008

A switching architecture suitable for broadband applications, employingR‐replicated Banyan interconnection networks with input and output buffering, is presented. Various solutions for traffic management among the replicated networks and buffer allocation are considered and their performances evaluated by means of an analytical model based on Markov chain representations of input and output buffers. The main results regard evaluation of maximum throughput, delay and packet loss probability by varying operating and design parameters. It has been shown that our architecture satisfies broadband switching operating requirements, with a suitable choice of design parameters, and also performs better than other architectures presented in literature. These considerations suggest that the investigated architecture is very interesting for the implementation of a broadband switch and should be compared with other solutions in an economic perspective.
Analysis of Global‐List Decoding for Convolutional Codes
Authors: Zigangirov Kamil , Osthoff Harro
Published: September 2008

Department of Information Theory University of Lund Box 118 S‐ 221 00 Lund ‐ Sweden

In this paper we consider the global‐list decoding algorithm for convolutional codes. We introduce the notion of the L‐list minimum distance and prove lower and upper bounds for if. Furthermore, we derive lower and upper bounds for the decoding error probability of the global‐' list decoding.
ISCP (ISDN Signalling Control Part): the Best Candidate for the Target Broadband‐ISDN Signalling Protocol
Authors: Paglialunga Alberto , Siviero Maurizio
Published: September 2008

This article is focused on the signalling protocol for future Broadband ISDN (B‐ISDN). A brief description of the current ISDN signalling system is given, highlighting some of its limits which make this system unsuitable to be applied in a B‐ISDN environment. The paper recalls the advantages of the Call Control and Bearer Control functional separation which is needed to handle complex telecommunication services as those offered by a broadband network. The main requirements of the future B‐ISDN are presented as far as network signalling is concerned and an hypothesis of protocol is outlined. The best protocol candidate to satisfy the B‐ISDN requirements is the ISDN Signalling Control Part (ISCP). It is based on the Application Layer Structure (OSI layer 7) principles, which are briefly described. Furhermore, the alternative use of TCAP and S‐ACSE to handle establishment and control of associations is outlined. Finally, an example of procedure to establish Call Control and Bearer Control associations in an ISCP environment is provided.
Data Flow Through a Double Process System
Authors: Burton Fraser , Gell Michael
Published: September 2008

A simple model of an element in a data communications network has been investigated. It is shown that the system exhibits a rich dynamical behaviour which under certain conditions may lead to a substantial and sometimes persistent degradation in its performance. Simple guidelines are established for specifying the conditions under which such exotic behaviour, eg: periodic and aperiodic oscillations, can be avoided in order to guarantee reliable and optimal operation of the system. The model is extended to consider multi‐process/processor systems.
A Multicarrier El‐HDSL Transceiver System with Coded Modulation
Authors: Chow Peter S. , Al‐Dhahir Naofal , Cioffi John M. , Bingham John A. C.
Published: September 2008

In this paper, we present a trellis‐coded multicarrier transceiver system, known as Discrete Multitone modulation, for the application of transmitting digital data at the El rate of 2.048 Mbit/s over existing copper telephone lines. The service of El‐HDSL (El‐rate High‐speed Digital Subscriber Lines) is currently being studied by ETSI for future deployment in Europe. Because of severe crosstalk and additive white Gaussian noise (AWGN) encountered in El‐HDSL, the application of a powerful trellis code is highly desirable to ensure reliable system performance, with a required bit‐error‐rate (BER) of no more than 10−7, at the desired El data rate. Detailed descriptions of the DMT transmitter and receiver structures are given, and projected performance results, both with and without the addition of a trellis code, are presented. Because of the different transmission environments encountered in the various countries in Europe, we have performed our computer simulation on both British and German (1) copper twisted‐pairs. We find that with the addition of Wei's powerful 4‐D 16‐state trellis code, we can achieve the El rate with a positive margin over all loops tested using either one or two sets of twisted‐pairs only, depending on the particular transmission scenario.
Block‐Coded Modulation Using Reed‐Muller Component Codes and Multistage Decoding
Authors: Karam Georges , Paxal Vendela , Sari Hikmet
Published: September 2008

Using a 2‐step partitioning of the signal constellation and Reed‐Muller component codes, we construct block‐coded modulation (BCM) schemes that achieve an asymptotic coding gain close to 6 dB. The component code associated to the first partitioning step is a distance‐4 or a distance‐8 Reed‐Muller code, and the code associated to the second partitioning step is a simple parity‐check code. We investigate BCM schemes with square signal constellations and a fractional number of information bits per symbol as well as BCM schemes with circular signal constellations and an integer number of information bits per symbol. We use multistage decoding with a Viterbi algorithm for the first component code using the trellis description given by Forney. Our results indicate that with short block lengdis, these BCM schemes compare favorably with trellis coded modulation (TCM) of similar complexity. Due to the rapid increase of the error coefficient, however, they lose their advantage as the block length increases.
Trellis Coded 16‐QAM for Fading Channels
Authors: Du Jun , Vucetic Branka
Published: September 2008

Fast growth in digital communications leads to increasing needs for high data transmission rates. Such needs can be met by bandwidth efficient modulation schemes. In this paper, a trellis coded. 16‐QAM scheme over flat fading channels is considered. Through analysis, new bounds on error rate performance of the scheme are derived. A set of new criteria for code design based on these bounds are formulated and used to construct new trellis 16‐QAM codes for fading channels. One of the key parameters in code design is the minimum product distance. An algorithm for computing the minimum product distance and its multiplicity is proposed. The algorithm is applied in search for optimum trellis codes. The performance of 16‐QAM TCM schemes with ideal channel state information (CSI) on Rayleigh fading channels is evaluated by simulation. The results show the proposed codes achieve significant improvements relative to the best known 16‐QAM modulation codes as well as 16‐PSK codes.
Millimetre Wave Short Range Communications for Advanced Transport Telematics
Authors: Andrisano Oreste , Chiani Marco , Tralli Velio , Frullone Mario , Moss Colin R.
Published: September 2008

This paper presents the results of a research programme to investigate short range millimetre wave communications links for road transport telematics applications. The work was carried out by the University of Bologna, the Fondazione U. Bordoni and Marconi Radar and Control Systems Limited. Financial support was provided by PROMETHEUS programme, which is itself a EUREKA research project and the ECC DRIVE programme.

The paper provides a theoretical assessment of the effects of multipath as applied to millimetre wave vehicle‐to‐vehicle and vehicle‐to‐roadside communications links. A digital link, based on phase shift keying, is assumed. Performance improvements resulting from the use of both antenna diversity and coding are assessed.
Address‐Predictive Vector Quantization of Images by Topology‐Preserving Codebook Ordering
Authors: Poggi Giovanni
Published: September 2008

Address vector quantization is a recently proposed image coding technique based on vector quantization (VQ) which exploits the interblock dependence by jointly encoding groups of VQ addresses. In this paper, by further developing the idea of address encoding, a new image coding technique is proposed. It is based upon the design of an ordered VQ codebook such that co‐devectors which are similar to each other have close addresses. As a result, the performance in terms of bit‐rate is very close to that of Address VQ, but much lower computational complexity and memory storage are required.
Letter: PLL Bandwidth Impact on Slave Clock Output Short Term Stability
Authors: Brugia Odoardo , Carbonelli Marco , Seta Domenico De , Perucchini Daniele
Published: September 2008

Starting from a fairly general slave clock reference model, a relationship between phase noise power spectral density and output stability expressed in terms of TIE, is used to evaluate. via numerical integration, actual clock behaviour in the case of SDH equipment clocks. This approach may prove very useful in designing synchronization for SDH based transport networks.
Timing Considerations for Optical Fibre PPM
Authors: Cryan Robert A. , Elmirghani Jaafar M. H. , Clayton F. Mike
Published: September 2008

Digital pulse position modulation (PPM) has been shown to be an effective modulation format for the optical fibre channel. It is paricularly attractive as it can exploit the abundant mono‐mode optical fibre bandwidth to offer improved performance. The format is a discrete time modulation format wherein synchronisation at both the slot and the frame levels is vital. In this paper we derive an original analytic expression that predicts the spectral properties of optical fibre digital PPM on the basis of its cyclostationary random properties. We establish the conditions required to achieve both slot and frame synchronisation and further, we show that the system synchronisability can be optimised in terms of its parameters. In particular, we consider die effect of the pulse shape, modulation index and the data probability distribution on the spectral properties. Finally, we present original practical results measured on a 128‐ary PPM system and show that they are within 1 dB of those predicted by our analytic model. We conclude that optical fibre digital PPM synchronisation can be achieved and further, optimised, in terms of the major system parameters.
Status of Glass and Silicon‐Based Technologies for Passive Components
Authors: Mccourt Martin
Published: September 2008

Passive integrated optic fabrication technologies are reviewed and compared with respect to the component requirements of Fiber in the Loop. At this time, ion‐exchange in glass is the most industrialised process, with two companies already in production.
Letter: High Capacity Digital Radio With Trellis Coding
Authors: Baccetti Baccio , Taverna Marcello , Bellini Sandro , Saivini Giorgio
Published: September 2008

In this paper we analyze the performance of Trellis Coded Modulation (TCM) for high capacity digital radio. Some error correcting code is needed to comply with the low background bit error rates prescribed for this application, despite practical imperfections unavoidable in modems and nonlinear distortion of high power amplifiers. The redundancy that can be accepted is very limited, however, due to the strict bandwidth constraints.

TCM schemes are very effective in conserving bandwidth. Therefore, they look very promising for digital radio applications.

We analyze many aspects of TCM, including multidimensional schemes. We consider the performance of TCM in the AWGN channel and in multipath fading channels, and we evaluate the effect of nonlinear amplification. Finally, we consider decoder complexity.

Significant coding gains can be obtained from codes of acceptable complexity. A good compromise between performance and complexity turn out to be 8‐state codes. The complete Viterbi decoder for these codes can be fully integrated on just one chip.

As a typical application, a system transporting the first level of the Synchronous Digital Hierarchy (STM ‐ 1; 155.52 Mbit/s) operating on 30 MHz interleaved crosspolarized frequency arrangements is analyzed in detail.
Letter
Authors: Costamagna Eugenio , Fanni Alessandra , Maestrini Raoul
Published: September 2008

In this letter, we examine how the reliability of a telecommunication network depends on the redundancy of the number of edges, with respect to the minimum number of edges required to connect all the nodes,varying the failure probabilities associated with each edge. Typical reliability patterns can be recognized, which depend substantially on the network redundancy and on the mean value of the assumed probabilities, and simple heuristic strategies allow to obtain good reliability results by insertion of very small numbers of redundant edges. The main results are well represented in graphical form in Figs. 2 and 3, where network reliabilities are computed from randomly assigned link reliabilities, assuming gaussian and uniform distributions. Reliabilities performances can be easily lower and upper bounded, as a function of network .redundancy and link reliability distributions.
Integrated receiver structure of staged decoder and CCI canceller for CDMA with multilevel coded modulation
Authors: Saifuddin Ahmed , Kohno Ryuji , Imai Hideki
Published: September 2008

This work presents a direct sequence spread‐spectrum multiaccess (DS/CDMA) receiver that employs integrated structure of staged decoder and CCI (co‐channel interference) canceller, when multilevel coded modulation is used and the system undergoes fading channel. We exploit the attractive multistage decoding method of multilevel coding. Each stage decoding is jointly done with the data estimation process and thus replicas of CCI can be formed with high precision, which ultimately results in performance improvement without any additional decoding delay or circuit complexity. We have chosen appropriate multilevel 8‐PSK coded modulation schemes for the integrated receiver of staged decoder and CCI canceller in fading channels. Computer simulation results show the significant coding gain that can be achieved by the proposed scheme in comparison with the conventional scheme. The effect of estimation error as well as unequal power is also investigated.
Linear adaptive transmitter‐receiver structures for asynchronous CDMA systems
Authors: Rapajic Predrag B. , Vucetic Branka S.
Published: September 2008

An asynchronous code‐division multiple access (CDMA) system with adaptive transmitters and receivers is considered. It is assumed that the adaptive receiver and transmitter have no knowledge of the signature waveforms and timing of other users. The concept of adaptive transmitter is based on feedback information from the corresponding receiver. The information obtained from the receiver is used to calculate the optimum transmitter signature. The signatures are adaptively adjusted according to the MSE criterion during the training period as well as during data transmission. CDMA systems employing the adaptive transmitters in the presence of multiple access interference achieve the matched filter bound with no interference. The proposed CDMA system are tested by simulation over a channel with multiple access interference and additive white gaussian noise.
The performance of diversity combining for fast frequency hopped NCMFSK in rayleigh fading
Authors: Aaron Gulliver T. , Ezers Rolands E. , Barry Feistead E. , Wight James S.
Published: September 2008

Frequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.
Realization of a passive broadband‐network termination 1 (B‐NT1) for the optical user‐network interface
Authors: Jahreis Oliver , Möller Olaf , Derr Frowin
Published: September 2008

A new passive Broadband Network Termination 1 (B‐NT1) as an alternative to the active B‐NT1 for B‐ISDN is described which supervises the UB interface between B‐LT and B‐NT1. For this purpose, the B‐LT generates an additional pseudo noise (PN‐)signal which is reflected at the passive B‐NT1 and analysed by a correlation method in the B‐LT. The alarm flow between B‐LT and the B‐NT2 remains unchanged by introducing a new reflection alarm REFL in the B‐LT which is based on the evaluation of the correlation signal and describes the condition of the UB interface. The passive B‐NT1 concept offers a more economical alternative for the network operator to provide Operation and Maintenance (OAM) on the TB and UB interface.
Power and bandwidth efficient digital communication using turbo codes in multilevel codes
Authors: Wachsmann Udo , Huber Johannes
Published: September 2008

The recently proposed Turbo codes are applied to bandwidth efficient modulation schemes via multilevel coding. For this purpose, Turbo codes are extended for a wide range of fine tunable rates by puncturing. A straightforward derivation of iterative Turbo decoding and the concept of extrinsic information is presented. New design rules for multilevel codes with arbitrary component codes and codeword lengths are derived from information theory. Simulation results show that application of Turbo codes to properly designed multilevel coding schemes leads to digital transmission schemes with high power and bandwidth efficiency.
Capacity of channels with uncoded side information
Authors: Shamai Shlomo , Verdú Sergio
Published: September 2008

Parallel independent channels where no encoding is allowed for one of the channels are studied. The Slepian‐Wolf theorem on source coding of correlated sources is used to show that any information source whose entropy rate is below the sum of the capacity of the coded channel and the input/output mutual information of the uncoded channel is transmissible with arbitrary reliability. The converse is also shown. Thus, coding of the side information channel is unnecessary when its mutual information is maximized by the source distribution. Applications to superposed coded/uncoded transmission on Gaussian channels are studied and an information‐theoretic interpretation of Parallel‐Concatenated channel codes and, in particular. Turbo codes is put forth.
Small scale site diversity for satellite communications: 11.5 GHz propagation measurements and system applications
Authors: Lombardi Paolo
Published: September 2008

“Small scale site diversity”, a well known antifading technique for satellite communications above 10 GHz, is considered in the paper. This technique takes advantage of the limited extension of heavy rain cells by replacing each earth station in a rainy area with two, or more, interconnected stations and using the earth‐satellite path less affected by fading.The statistical results are presented of a three years( 1986‐88) propagation experiment. The EUTELSAT‐I 11.5 GHz beacon signal rain attenuations on the diversity paths between the satellite and two earth stations located in the Rome area about 16 km apart were measured. The experiment results are synthetically expressed in terms of the “diversity gain”, showing that, with an ideal diversity switching system, the fade margin can be reduced by an amount equal to 65‐80% of the margin needed in the single station case. On the ground of these results, reasonably extended to a different situation, an example is given of an underdimensioned link which can be made compliant to high availability requirements enabled by the use of the small scale site diversity technique.
Learning the compatibility matrix for adaptive resource management in cellular radio networks
Authors: Duque‐Anón Manuel , Koch Patrik , Kunz Dietmar , Rüber Bemhard , Ullrich Meinhard
Published: September 2008

To satisfy the growing demand for mobile communications micro‐cellular systems are expected to be introduced in the near future. For these, effective procedures not only for channel allocation but also for load balancing and call admission control still have to be developed. Here, the knowledge of the actual interference relations between radio cells is a key issue for both the more traditional channelized systems and the recently proposed spread spectrum techniques. Realizing that the interference relations among the cells are only slowly varying, the authors generalize the existing local and short term approaches to interference detection by including a memory trace in the evaluation procedure. A compatibility matrix for the cells is learned by statistically correlating carrier and interference power levels with call activities. In this paper, the overall system design is presented along with the detailed description of the learning procedure which is thought of as both an integrated component of future radio network management systems as well as a possible enhancement of already existing radio network planning methods. Simulations show that the adaptive strategy offers a considerable capacity increase that results from an increased spectrum efficiency.
New IIR echo canceller using a dual error criterion and lattice structures
Authors: Gerald Jose A. B. , Esteves Nelson L. , Silva Manuel M.
Published: September 2008

An adaptive IIR echo canceller for data transmission is presented, where the output‐error criterion and the equation‐error criterion are used simultaneously. The combined use of these two error criteria provides a fast initial convergence and leads to unbiased parameter estimates, even in the presence of noise. The poles of the echo path transfer function are modelled by means of lattice structures, which greatly simplifies the stability monitoring. The performance of the proposed echo canceller, as updated by LMS‐type algorithms, is evaluated by computer simulation.
Performance of a traffic smoothing switching element
Authors: Schmidt Kai , Killat Ulrich
Published: September 2008

This paper investigates a switching element which transforms a non‐uniform traffic distribution over the inputs of a switch into a uniform one. The switching element consists of an output buffered matrix switch equipped with non synchronized counters at the input lines for output selection. By means of a combinatorial analysis the desired property of the component is proved. Moreover, it is shown that no losses occur if the number of buffer places equals the number of input lines. Simulation results reveal the excellent performance of the device under various traffic conditions.
Mutual clock synchronization in global digital communication networks
Authors: Lindsey William C. , Chen Jeng‐Hong
Published: September 2008

There are numerous synchronization methodologies available for consideration in solving the problem of network synchronization in digital communication networks [1, 2]. They include: independent clocks, pulse stuffing, elastic stores, master‐slave hierarchical, time reference distribution, mutual synchronization, etc. This paper considers the network synchronization performance achievable using the method of mutual clock synchronization observed first by Christiaan Huygens in 1665 [3]. Network synchronization performance metrics studied include: nodal timing accuracy, timing jitter, slip rate, time interval between slips, probability of loss of synchronization. These metrics are shown to depend upon the distance (range) between clocks, ranging error, clock stability, nodal phase error processing bandwidth, data rate, signal‐to‐noise ratio and network connectivity. In this regard, the mutual synchronization performance achievable with long wavelength biological rhythms and electric power system rhythms is compared with the performance achievable using short wavelength rhythms required in wideband and broadband digital communications networks. The results are further applied to the problem of synchronizing a satellite communications network. When intrasatellite communication crosslinks (links between satellites in the same orbital plane) are used in a constellation of communication satellites, it is shown that the maximum data rate, the network connectivity and the constellation altitude drive the achievable network synchronization performance; the latter is set by technological limitations due to clock frequency stability, the maximum range between satellites and the minimum ranging error achievable by the ranging system. In this sense, low Earth orbits (LEO) are preferred over geosynchronous (GEO)Earth orbits. The theory is also applied to the Teledesic and Iridium networks.
Effects of fixed frequency clock offsets in synchronous digital hierarchy networks
Authors: Sholander Peter E. , Autry Chris B. , Owen Henry L.
Published: September 2008

SDH networks require synchronous clocking in order to minimize network wander and jitter. In practice, the clocks in SDH networks are not ideal and thus are not all perfectly synchronous. The operation of SDH networks with non‐ideal clocks results in undesirable wander and jitter effects. Two different philosophies are being used to minimize these undesirable synchronization effects in SDH networks. In Europe, where it is difficult to tighten clock specifications due to the multinational synchronization environment, desynchronizer designs are made more robust. In North America, where Synchronous Optical Network (SONET) is used, the specifications of both the clocks and the synchronization distribution are being tightened. Even with these different approaches, non‐ideal synchronization effects still exist in SDH networks. In particular, the STM‐N. AU, and TU overhead bytes cause gapped pointer effects when traditional fixed threshold pointer processors are used. Another type of pointer processor, a uniform pointer processor, can remove the gapped pointer effects caused by the STM‐N, AU, and TU overhead bytes. Additionally, a compensating desynchronizer may be used to remove the gapped effects caused by the VC overhead bytes. If these gapped effects are not removed. then they cause jitter and wander in a reconstructed PDH signal. This paper focuses on the case where the SDH network clocks have fixed frequency offsets. An El‐rate (2048 kbit/s) payload, which is transported over a network consisting of SDH and PDH islands, is used to show the effects of this non‐ideal clocking in SDH networks. In theory, clock frequency differences in SDH networks are accommodated by the pointer processor mechanism without slips (i.e. losing or repeating data). In practice, non‐ideal synchronization may still cause slips.
Letter: Design and implementation of a fiber delay line optical buffer for multi gigabit photonic switching fabrics
Authors: Gavignet Paulette , Chiaroni Dominique , Masetti Francesco , Jacob Jean‐Baptiste
Published: September 2008

Full photonic packet switching fabrics require memories, which are not available today in the optical domain: therefore, an alternative is the use of optical buffers based on fibers used as delay lines. This letter reports the optimised implementation of such a buffer operated in a multi‐wavelength regime and accessed by fast optical gates. The buffer operating principles and two different implementation structures are first briefly presented. Then differential delays and influence on bit error rate performance are discussed on the basis of test results within a 4 × 4 photonic packet switching matrix handling ATM cells at 2.488 Gbit/s. The results demonstrate that fiber delay lines are a simple, potentially cost‐effective solution to implement buffering within highspeed photonic packet switching systems, adopting current optical technology.
Chip shaping and channel coding for CDMA
Authors: Chaib Jean‐Paul , Leib Harry
Published: September 2008

This work considers asynchronous DS‐CDMA systems with single‐user receivers. The focus is on chip pulse shaping and combined error control/PN sequence spreading. It is shown that pulse shaping can significantly reduce the effects of cross‐talk interference. A criterion which measures the ability of a chip waveform to reduce cross‐talk interference is derived, taking into account, the signal bandwidth. This work also shows that the best performance is achieved when all the bandwidth expansion is accomplished by error control coding. instead of PN sequences. Comparisons of CDMA systems using different pulse shapes are presented, taking into account the bandwidth of each pulse. Finally CDMA is compared to orthogonal multiple access (TDMA/FDMA) in an interference free environment. It is shown that for the same bandwidth (99% energy containment bandwidth), CDMA with suitable chip waveforms and coding yields the same performance as binary orthogonal multiple access with raised cosine shaping of 70% excess bandwidth.
Continuous‐phase modulations for CDMA radio communications: Modem architecture and performance
Authors: Giannetti Filippo , Luke Marco , Reggiannini Ruggero
Published: September 2008

In this paper we analyze the structure and the performance of a digital modem for band‐limited spread‐spectrum signals to be employed in a radio communication network with asynchronous code‐division multiple access and constant‐envelope continuous‐phase modulation. After a description of the modem structure and the evaluation of its bit error rate in the presence of co‐channel interference, we tackle the key point of code synchronization. In particular, we present a detailed analysis of the code acquisition strategy, assessing its performance in terms of false alarm probability, missed detection probability and mean acquisition time. Furthermore, we address the problem of code chip timing recovery, describing the performance of three different code tracking loops in terms of the steady‐state RMS chip timing error jitter. The analytical approach we present can be applied to any Continuous Phase Modulation (CPM) format that can be approximated by an Offset‐QAM signal, such as Gaussian‐filtered Minimum‐Shift Keying (GMSK).
Effects of user mobility on the capacity of a CDMA cellular network
Authors: Baiocchi Andrea , Sestini Fabrizio , Priscoli Francesco Delli
Published: September 2008

In the recent technical literature on cellular networks Code Division Multiple Access (CDMA) has received a large attention as a promising radio interface access technique. Many studies. are devoted to the capacity evaluation of the radio interface adopting CDMA, but seemingly none of them accounts for the variability of the user spatial density due to user mobility. This should be a concern especially in a microcellular environment, where it cannot be relied upon a significant spatial average over the radio coverage area of a Base Station. The major aim of this work is a preliminary assessment of the effects of “bursty” user mobility on the capacity of the CDMA radio interface. To this end. we introduce a user mobility model apt to describe large fluctuations of the number of users in a radio cell area. A reference model of a CDMA network is used to evaluate the effects of user mobility on the capacity for a wide range of the model parameters, by means of simulations accounting for shadowing, call attempt process, voice activity and antenna directivity and assuming perfect power control. We show that user mobility can remarkably affect the CDMA capacity, mainly because of the resulting highly bursty behaviour of self‐noise. A simple traffic control scheme is devised to increase the capacity of the CDMA network, under a joint constraint on link availability, call blocking and call dropping probabilities. It is pointed out that the concepts introduced in this paper are independent of the specific CDMA implementation, i.e. they hold for any asynchronous CDMA based cellular network.
A novel carrier recovery technique for orthogonal multicarrier systems
Authors: Daffara Flavio , Adami Ottavio
Published: September 2008

This paper deals with the carrier frequency synchronization of orthogonal multicarrier systems, which are an effective transmission technique for coping with the typical channel impairments present in mobile reception. A new carrier frequency detector is introduced and its performance thoroughly analyzed in the presence of a multipath channel. In particular we have analytically derived the frequency detector characteristic curve and its noise power spectral density. We have compared the new algorithm with other known algorithms and we have shown that it permits a considerable improvement in the noise level to be achieved. Therefore the proposed algorithm seems to be a valid candidate for carrier frequency recovery in applications employing multicarrier transmission.
A study for interactive TV via satellite
Authors: Caire Giuseppe , Elia Carlo , Longo Luca , Viola Roberto
Published: September 2008

The digital compression revolution will offer the possibility of receiving hundreds of TV channels from the same orbital location. Only some of them will be dedicated to traditional television services. The largest part will be utilized for specialized services that will require user interaction. Interaction requires a “reverse channel” from the user site to the service provider premises. In this paper we study the feasibility of such a reverse channel via satellite. After discussing some system options, we focus on the simplest and most attractive one: where the users have the capability of sending information back to the service provider directly through a satellite link. For this solution, we provide a system outline and we present a coding and modulation scheme based on pragmatic‐coded non‐coherent orthogonal M‐FSK concatenated with shortened Reed‐Solomon codes which is able to meet the transmission requirements. Next, we address the problem of symbol‐timing and carrier frequency offset open‐loop estimation for short burst TDMA transmission with non‐coherent M‐FSK modulation. Finally, we discuss some particular network aspects of such a reverse channel.
Experimental validation of selected results on ATM statistical multiplexing in the EXPLOIT project
Authors: Mitrou Nikolas , Lykouropoulos Nikolaos , Nellas Vassilis , Kontovasilis Kimon
Published: September 2008

A number of experiments were designed and performed on the EXPLOIT ATM testbed, aiming at validating selected results on statistical multiplexing of bursty traffic. The influence of the burst‐size and silence‐duration distributions on the multiplexer's performance, the performance experienced by the individual classes in a heterogeneous traffic environment and the performance in the case of heterogeneous traffic featuring different time scales are the main issues investigated.
Generalized concatenation of convolutional codes
Authors: Bossert Martin , Dieterich Hans , Shavgulidze Sergo
Published: September 2008

Generalized concatenation of inner and outer convolutional codes is studied. The essential problem is the partitioning of the inner code. A construction procedure to obtain a suitable equivalent description for a given code is derived, which gives the best possible distances in the partitioned subcodes. The construction rule is illustrated with two examples. A small code is studied to emphasize the ideas of the construction and a large code, namely the satellite standard code, demonstrates the considerable gains in decoding performance when using generalized concatenation. Furthermore, the possibilities for iterative decoding are pointed out.
ATM switch with multimedia traffic priority control
Authors: Ganos Peter A. , Koukias Michael N. , Kokkinakis George K.
Published: September 2008

In this paper, a novel ATM switch with a dynamic multimedia traffic priority control scheme (HQMS: Hybrid combination of Queue Length Threshold and Minimum Laxity Threshold Scheme) is proposed. The ATM switch has the same basic topology as the Knockout switch, but employs a simplerN×Lconcentration scheme, which takes into account cells belonging to different priority levels. The structure of the switch supports two priority mechanisms. The first one is calledpriority discardingand acts as a local congestion control scheme within the switch fabric satisfying different cell loss requirements of different ATM traffic classes. The second one is calledpriority schedulingand uses two priority methods: aspace priority methodused for the control of the buffer space when an overflow condition occurs andor when the expiration of the maximum admissible delay of the delay sensitive cells takes place and theservice priority methodwhich assigns transmission priorities to the buffered cells. A hardware implementation of the two priority mechanisms of the HQMS is presented. The performance of the switch has been studied by simulation, considering three ATM classes (video, data, voice) with different source models. The results have shown that for a large range of traffic load, the proposed HQMS satisfies the loss and delay requirements of the three classes.
A parallel MAC architecture for a Gigabit/s DQDB MAN suitable for multimedia applications
Authors: Casale Salvatore , Corte Aurelio La
Published: September 2008

Medium access control protocols based on a dual bus topology, such as the IEEE 802.6 Distributed Queue Dual Bus (DQDB), are usually considered to be highly satisfactory for high speed networks. But the DQDB can only partly support new sophisticated multimedia services, mainly because the increase in the channel bit rate needed to meet the greater bandwidth requirements causes an increase in unfairness in the medium access control of the nodes. In this paper the authors propose a Gigabit/s Metropolitan Area Network (MAN) based on the IEEE 802.6 DQDB protocol and multichannel connectivity on optical fiber, by means of Wavelength Division Multiplexing (WDM). They present a parallel node architecture in whichNDQDB subnodes parallelly accessNWDM channels. Channel access at each node is regulated byNfinite state machines operating independently and sharing a single MAC Convergence Functions (MCF) block for the segmentation and reassembly of user information. On the basis of the MAC architecture proposed, B network management structure is also presented, with particular reference to the Quality of Service monitoring processes. The proposed architecture is more modular than the DQDB standard; it provides greater fairness and better access delay and allows efficient management of service classes with priority.
Multichannel multiple queue protocols
Authors: Pountourakis Ioannis E. , Sykas Efstathios D.
Published: September 2008

Two protocols suitable for random multiple access packet broadcast in a multichannel. communication system are proposed and analyzed. Broadcast channels are classified as retrans. mission channels devoted in collision resolution of busy stations and as contention channels for the access of free stations. The proposed protocols differ in the way that a busy station is allocated to a retransmission channel for collision resolution. Analytic Markovian models are developed so as to evaluate the system performance in terms of throughput and delay. The performance of multichannel systems is compared with the single channel system. Numerical results show performance improvement under heavy load.
System design and evaluation of a large modular photonic ATM switch
Authors: Jacob Jean‐Baptiste , Casoni Maurizio , Corazza Giorgio , Raffaelli Carla , Parmentier Pierre
Published: September 2008

A photonic ATM switching node based on the Fibre Delay Line switching element developed in the framework of the RACE project ATMOS (ATM Optical Switching) is described. The feasibility of this switching element has been proved within the physical limitation of present‐day technology to support up to 16 input and 16 output lines and a buffer capacity of at least 16 cells for each output. In this paper various interconnection options are discussed with the aim of a large, high throughput switch implementation. In particular a Clos architecture is chosen for the design of a 256 × 256 switching fabric operating at 2.5 Gbit/s and its performance is evaluated by means of simulation in a random and bursty traffic environment. It is demonstrated that a multiplane configuration of optical matrices followed by an efficient concentration strategy is capable of meeting the target ATM requirements, that is cell loss probability less than 10−‐9with load up to 0.8. A detailed design of the switch and its complexity evaluation are also given.
Letter: ATM switches with nonindependent routing
Authors: Bruneel Herwig , Wittevrongel Sabine
Published: September 2008

An N × N ATM switching element with output queueing is considered. Each inlet of the switch is fed by a bursty on/off source with geometrically distributed on/off‐periods. Cells are routed from the inputs to the outputs of the switch in a uniform but correlated manner. Specifically, for the first cell of each on‐period all the destination addresses are equiprobable. Each subsequent cell of the same on‐period has a probability R of being routed to the same destination as the previous cell, and is sent to one of the N‐ 1 other destinations with probability (1 ‐ R)/(N ‐ 1). Cells belonging to different on‐periods are routed entirely independently. By means of an approximate analytical method, the influence of the degree of burstiness of the sources and the amount of correlation in the routing mechanism on the queueing performance of the switch is investigated.
Rate control algorithms for the ATM ABR service
Authors: Hernandez‐Valencia Enrique J. , Benmohamed Lotfi , Nagarajan Ramesh , Chong Song
Published: September 2008

Over the last couple of years both the ATM Forum and ITU‐T have converged on a closed‐loop, feedback based, rate control mechanism as the framework for the Available Bit Rate ATM Transfer Capability. In this framework, anABRsource adapts its transmission rate to changing characteristics of the ATM network by either testing periodically the state of the network or through direct feedback from the network. The state of the network is conveyed to the source either as a simple binary feedback signaling congestion or no congestion, or as an explicit rate indicating the rate at which the source can transmit. In this paper we review the detailed framework for theABRservice standardized by the ATM Forum, the underlying service philosophy and protocol design goals forABRflow control, and the premises and high‐level performance characteristics for the more promisingABRrate control schemes proposed so far.
Rate based flow control with bandwidth information
Authors: Ait‐Hellal Omar , Altman Eitan , Başar Tamer
Published: September 2008

The ATM Forum has chosen the rate‐based approach for flow control ofABR(Available Bit Rate) traffic in ATM. It is based on a reactive approach whereby the transmission rate ofABRsources can be adapted to the available bandwidth at a bottleneck link. The ATM forum has specified the behavior of the source and destination, as well as the manner in which feedback information (on the available bandwidth and on the congestion state of the network) should be conveyed back to the source. The decision on the precise control mechanism, however, has been left to the designer of the switches. We propose in this paper a reactive control scheme that is based only on information on the available bandwidth. We analyze its stability, and then test its performance and fairness by simulations in the presence of other higher priorityCBRorVBRtraffic.
Decision feedback multi‐user detection for multitone CDMA
Authors: Vandendorpe Luc , Wiel Olivier Van De
Published: September 2008

In the present paper we analyze the problem of multi‐user detection for multitone CDMA systems in the presence of multipath and multiple access interferences. Two types of decision feedback structures are derived for an MSE criterion. In order to understand the potential of these detectors we study their steady‐state behaviors. The investigation is carried out for devices following a receiver made of a bank of matched filters and assuming perfect carrier phase and timing recovery. An exact expression of the bit error probability for BPSK symbols after joint detection is obtained by means of the characteristic function method. The performance of the two DF multi‐user detectors is obtained for a constrained comparison and their near‐far resistance is demonstrated in asynchronous scenarios for two types of channels.