bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mutual clock synchronization in global digital communication networks
Authors: Lindsey William C. , Chen Jeng‐Hong 
Published: September 2008

AbstractThere 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

AbstractSDH 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

AbstractFull 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

AbstractThis 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

AbstractIn 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

AbstractIn 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

AbstractThis 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

AbstractThe 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

AbstractA 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

AbstractGeneralized 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

AbstractIn 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

AbstractMedium 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

AbstractTwo 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

AbstractA 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

AbstractAn 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

AbstractOver 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

AbstractThe 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

AbstractIn 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.
Optimal and sub‐optimal maximum a posteriori algorithms suitable for turbo decoding
Authors: Robertson Patrick , Hoeher Peter , Villebrun Emmanuelle 
Published: September 2008

AbstractFor estimating the states or outputs of a Markov process, the symbol‐by‐symbol maximum a posteriori (MAP) algorithm is optimal. However, this algorithm, even in its recursive form, poses technical difficulties because of numerical representation problems, the necessity of non‐linear functions and a high number of additions and multiplications. MAP like algorithms operating in the logarithmic domain presented in the past solve the numerical problem and reduce the computational complexity, but are suboptimal especially at lowSNR(a common example is the Max‐Log‐MAP because of its use of the max function). A further simplification yields the soft‐output Viterbi algorithm (SOVA). In this paper, we present a Log‐MAP algorithm that avoids the approximations in the Max‐Log‐MAP algorithm and hence is equivalent to the true MAP, but without its major disadvantages. We compare the (Log‐)MAP, Max‐Log‐MAP and SOVA from a theoretical point of view to illuminate their commonalities and differences. As a practical example, we consider Turbo decoding, and we also demonstrate the practical suitability of the Log‐MAP by including quantization effects. The SOVA is, at 10−4, approximately 0.7 dB inferior to the (Log‐)MAP, the Max‐Log‐MAP lying roughly in between. The channel capacities of the three algorithms ‐when employed in a Turbo decoder‐ are evaluated numerically.
Computation of the outage probability in rice fading radio channels
Authors: Tomba Luciano 
Published: September 2008

AbstractMethods for the evaluation of the outage probability in mobile radio systems have been widely investigated, but analytical results have been published only for Rayleigh fading radio channels. For the case of Rice fading, only approximated results have been found. In this paper, an exact expression of the outage probability for a subscriber of a CDMA cellular mobile radio system, with the radio channel impaired by Rice fading and log‐normal shadowing superimposed is given.