bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strategies and Algorithms for Routing both Unicast and Multicast Paths in WDM Networks
Authors: Listanti Marco , Cervelli Andrea , Sabella Roberto 
Published: September 2008

AbstractThis paper introduces the concept of the multicast optical path in WDM networks, and treats the strategies and the algorithms, which allow the routing of plural multicast paths together with unicast paths. This analysis was motivated by the possibility of exploit the optical layer facilities in the transport network, to carry distributive services, such as video channels (e.g. CATV), without the need of dedicated transmission networks. The strategies and algorithms reported in this paper arise from a generalisation of those ones, which have been previously reported in literature. They are wavelength path (WP: which does not make use of wavelength conversion), virtual wavelength path (VWP: which make full use of wavelength conversion), and partial virtual wavelength path (PVWP: making a parsimonious use of wavelength conversion). The analysis shows the characteristics and performance of those strategies and algorithms considering, as a figure of merit, either the number of wavelengths or the system scale (dimensions of the optical nodes), and compare one to each other in order to point out advantages and disadvantages. The main result is that multicast optical paths can favourably be accommodated in a WDM network, and the strategy we propose, making a parsimonious use of wavelength conversion, allows the lowest system scale to be obtained with a very low number of wavelength converters.
Routing and Wavelength Assignment in All‐Optical Networks with Multicast Traffic
Authors: Sahin GÖKhan , Azizǒlu Murat 
Published: September 2008

AbstractThis paper considers multicast routing and wavelength assignment (MCRWA) in a wide area all‐optical network. We present static and dynamic MCRWA algorithms, and evaluate their blocking performance under various fanout splitting policies. Through simulations and comparisons with a lower bound, we demonstrate that dynamic MCRWA can perform significantly better than its static counterparts. We then quantify the throughput gain due to link sharing in multicasting, and the performance penalty that would be suffered by considering each multicast request as multiple unicast connection requests. We also present an analytical model for estimating the blocking performance of the static MCRWA algorithms. The performance improvement with multifiber networks and with wavelength conversion are also investigated.
A Hybrid Interference Cancellation Scheme for Multiuser Systems in Multipath Fading Channels
Authors: Johansson Ann‐Louise , Svensson Arne 
Published: September 2008

AbstractA new hybrid interference cancellation (IC) scheme is proposed for the uplink of multirate direct‐sequence code division multiple access (DS‐CDMA) systems communicating over mobile radio channels. The hybrid IC scheme includes both non‐decision directed and decision directed IC, together with a modified RAKE combiner to utilize the diversity in a frequency‐selective channel. The performance is evaluated via computer simulations for the two multiple data rate schemes, mixed modulation and multicode, in a multipath environment. Both known channel parameters and channel estimation using pilot symbols are considered. The results show that rnulticode or a combination of multicode and mixed modulation are preferable when handling multirate system and the loss in performance compared to the single‐user bound is small.
Accurate Recovery of Dense Depth Map for 3D Motion Based Coding
Authors: Georgis Nikos , Kittler Josef , Bober Mirek 
Published: September 2008

AbstractThe problem of scene structure recovery from image motion is considered in the context of motion compensated video coding. In order to compensate for full 3D motion of the camera, the scene depth map together with camera egomotion need to be estimated from the image sequence. An important prerequisite of the shape and motion recovery is the establishment of correspondences between the points in two successive frames of a video sequence. In the paper we abandon the traditional feature based approach and develop a correspondence analysis technique based on robust matching of local image intensities under affine transformation. We show that the technique not only establishes true correspondences, but the resulting field of corresponding points is dense, and their displacement is obtained with a subpixel accuracy and free of bias. We demonstrate that these dense high quality matches yield accurate estimates of the imaging geometry which are several orders of magnitude better than estimates obtained with feature based methods. This accuracy is reflected in a superior quality of estimates of the scene structure. The experiments are performed with images of a scene with known geometry, obtained using a calibrated camera. The obtained depth estimates are dense, with error of the order of 1% which contrasts with the sparse depth map and greater than 10% errors offered by a typical feature based approach. The technique is also applied to coding. Preliminary results indicate that significant improvement of the predicted image can be achieved by using accurate dense depth cstimates.
New Channel Assignment Methods for Hot‐Spot Overlaying CDMA Cellular Systems
Authors: Jung‐Shyr Wu 
Published: September 2008

AbstractThe CDMA cellular system can provide more capacity than AMPS systems. To deploy microcells overlaying in macrocells to provide more capacity is also attractive. However, system performance and capacity degrade due to the co‐channel interference among microcells and macrocells if a single channel is used. Based on a hot‐spot overlaying environment. we propose three multi‐channel schemes where different channels can be assigned for hot spot and macrocell. Performance measures in terms of capacity, service hole, blocking probability and blocking ratio in uplink and downlink are evaluated. It shows that the schemes with channel selection based on SIR and active users gain more benefits than the scheme with separate channels assigned for macrocells and hot‐spot. Using the proposed multi‐channel access schemes, we can avoid the co‐channel interference among macrocells and hot‐spot and provide more capacities than Baier's suggestion [1]. In addition, the proposed schemes make soft handoff workable and improve the system performance.
Letter: On the Identifiability of a Channel Transfer Function from Cyclic and Conjugate Cyclic Statistics
Authors: Mazzenga Franco 
Published: September 2008

AbstractThe problem of blind identification of digital communication channels from the second order cyclic and conjugate cyclic moments of the received signal is addressed. A novel condition for blind identification is obtained when both second order cyclic and conjugate cyclic moments of the received signal are available. In particular it is shown that the class of the identifable transmission channels is extended with respect to the case where only one of the two statistics is used.
Dynamic Rate Shaping on MPEG‐2 Video Streams for Bandwidth Saving on a Faded Satellite Channel
Authors: Celandroni Nedo , Ferro Erina , Potort Francesco , Chimienti Antonio , Lucenteforte Maurizio 
Published: September 2008

AbstractIn a previous work, we studied how to send a video stream over a noisy satellite channel using the scalability features of the MPEG‐2 standard. The base and the enhancemcnt tlows were sent with different levels of protection (bit and coding rates) in order to deal with the channel degradation. In this paper, we add Dynamic Rate Shaping (DRS), thus obtaining a greater flexibility in the choice of transmission parameters. In fact, it is possible to trim the required bandwidth in continuous mode in the working range, thus saving some bandwidth when keeping the video quality constant during changing fade conditions. The performances of DRS applied to both the non‐scalable and the scalable MPEG‐2 coded video streams are shown separately. An application of thc techniques presented is discussed, and some criteria are given for choosing the most suitable pammcters, according to the service quality requirements.
Channel Allocation with Recovery Strategy in Wireless Networks
Authors: Ma Yue , Han James J. , Trivedx Kishor S. 
Published: September 2008

AbstractWith the increasing penetration of wireless communications systems, customers are expecting the same level of service, reliability and performance from the wireless communication systems as the traditional wire‐line networks. Due to the dynamic environment, such as the roaming of mobile subscribers, maintaining a high radio frequency (RF) availability is one of the most challenging aspects in wireless network management. To date, in wireless network management, a call is dropped when the channel it uses goes down. In order to increase system end‐to‐end availability, an RF channel recovery scheme is proposed in this paper. When an RF channcl Pds, the channcl is replaced by another working channel and the call continues. The methods to replace failed RF channels of ongoing calls and to handle channel failures of handoR and new calls are investigatcd. Markov reward models are developed to compare system availability and performance. Automated generation and solution of Markov reward modcls is facilitatcd by a version of stochastic Petri nets that we call stochastic reward nets. The results show that the rccovcry schcme reduces the dropped calls and the blocked calls significantly under both light and normal trarffics.
A QoS‐Based Handover Initiation Algorithm for Wireless Systems
Authors: Graziosi Fabio , Santucci Fortunato 
Published: September 2008

AbstractIn this paper a novel handover initiation algorithm is proposed for next generation wireless systems, in the presence of a generic packet access protocol. By proper monitoring of the sequence of packets that may be lost due to channel impairments, handover triggering can bc strictly related to the Quality of Service (QoS) parameter of the source, In particular, a threshold length of the sequence of lost packets is used as a handover criterion for delay sensitive sources. In a log‐normal shadowing environmcnt, the algorithm pcrformance is derived analytically. Simulation is also used to validate the approximations introduced in the analysis. From numerical rcsults it is sccn that the novel algorithm can provide better performance than typical signal strcngth nlgorithnls used in second gcncrution mobile radio systems. Moreover, the proposed approach is rather general and may apply 10 a large class of sourecs and acccss protocols.
Efficient Communication Over the Discrete‐Time Memoryless Rayleigh Fading Channel with Turbo Coding/Decoding
Authors: Peleg Michael , Shamai(Shitz) Shlomo 
Published: September 2008

AbstractCommunication over the discrete time memoryless Rayleigh fading channel is investigated. Codes achieving bit error rate (BER) lower than 10‐4at bit energy over the noise spectral density ratio (Eb/No) of 1 to 2dB from the channel capacity limit were found with coding rates of 0.05 to 0.36 bits per channel use. Similar codes with rates of up to 0.57 also performed reasonably close to the capacity limit. The codes are serial concatenation of turbo code and a modulation code such as Pulse Position Modulation (PPM). The receiver is based on joint iterative decoding of the turbo code and the modulation code. Information theoretic arguments are used to form guidelines for code design and to estimate performance of the iterative decoder.
Load‐Adaptive MUI/ISI‐Resilient Generalized Multi‐Carrier CDMA with Linear and DF Receivers
Authors: Giannakis Georgios B. , Stamoulis Anastasios , Wang Zhengdao , Anghel Paul A. 
Published: September 2008

AbstractA plethora of single‐carrier and multi‐carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all‐digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner‐code/outer‐code principle, which guarantees MUI/ISI‐elimination regardless of the frequency‐selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels.
Comparison of Time and Frequency Domain Processing of a Multi‐Carrier Spread‐Spectrum System
Authors: Kühne Jörg , Nahler Achim , Fettweis Gerhard P. 
Published: September 2008

AbstractMulti‐camer spread‐spectrum (MC‐SS) modulation is a new kind of spread‐spectrum modulation[1],[2]. The spreading code is designed in the frequency domain. Hence, the system is dual to a direct‐sequence spread‐system (DS‐SS) where the spreading code is given in the time domain. There exist two different views: the OFDM view and the DS‐SS view. Many publications deal with the frequency domain processing. Transmitter and receiver structures are similar to OFDM. Therefore all these implementations use a guard interval to avoid ISI. The disadvantage of this guard interval is the higher hardware complexity and the waste of symbol energy. In the following paper the effect of ISI on a MC‐SS system is investigated. Both types of implementation (time or frequency domain) are compared and the dependencies of the performance from the spreading code are demonstrated. It is shown that with proper code selection and a time domain implementation without guard interval (RAKE receiver) it is possible to outperform equivalent frequency domain receivers with guard interval (MRC).
SS‐MC‐MA Systems with Pilot Symbol Aided Channel Estimation in the Asynchronous Uplink
Authors: Kaiser Stefan , Krzymien Witold A. , Fazel Khaled 
Published: September 2008

AbstractSpread spectrum multi‐carrier multiple access (SS‐MC‐MA) systems exploit in a similar manner as MC‐CDMA systems the advantages of the diversity gain due to the spread spectrum technique and the high bandwidth efficiency due to the orthogonal multi‐carrier modulation. However, the main difference is that SS‐MC‐MA systems use FDMA for the user separation and therefore are less vulnerable to multiple access interference, and thus are especially of interest for the uplink of mobile radio systems. They allow asynchronism between the mobile users. In this paper we investigate the effects of ISIand ICI due to asynchronism in the uplink of an SS‐MC‐MA system on the performance of pilot symbol aided channel estimation. Moreover, we consider the suitability of power boosting of the pilot symbols to improve the link performance.
Non—data—aided ML carrier frequency and phase synchronization in OFDM systems
Authors: Panayirci Erdal , Georghiades Costas N. , Huq Ayesha T. 
Published: September 2008

AbstractIn this paper non—data—aided(NDA), maximum likelihood(ML) algorithms are derived for the carrier frequency and phase offset, separately, for OFDM systems employing M—PSK modulation scheme. NDA ML estimation algorithm for frequency offset estimation exploits the redundant information contained in the cyclic prefix proceeding the OFDM symbols, thus reducing the need for pilots. Its mean—squared performance is obtained analytically and compared with simulation results. It is observed that the resulting algorithm generates very accurate estimation even when the offset is high. It is also shown that the frequency estimator may be used in a tracking mode. The ML algorithm derived for the carrier phase estimation is also a non—data—aided(NDA) and maximizes the lowSNRlimit of the likelihood function averaged over M—PSK signal constellation. It is shown that for sufficiently smallSNRthe ML phase estimator obtained reduces to the familiar M/th order power synchronizer which belongs to the class of NDA feedforward carrier synchronizers introduced earlier in the literature. Its mean—squared performance is obtained analytically and compared with simulation results. We observe that the resulting algorithm generates very accurate estimation even when the phase offset is high, that the self noise is absent and the performance of the algorithm is basically the same as die Cramer—Rao bound for moderate to highSNR.Finally we note mat me error variance derived for the mean—squared performance of this NDA ML synchronizer is an extension of the approximate variance formula appeared in Reference 20,equation(14) for M—PSK.
On the transmission of an analog wideband signal through a narrowband channel
Authors: Wulich Dov , Goldfeld Lev 
Published: September 2008

AbstractThe problem of transmitting a wideband signal through a narrowband channel is considered. A new solution to this problem is proposed in which the wideband signal is divided into two parts: a first part which occupies exactly the spectrum that the channel can carry and a second— the rest of the signal. It is proposed to transmit the first part without any coding (in analog form) while the second part is sampled and quantized and the resulting data stream is transmitted simultaneously with the first part via the same channel. An alternative approach, based on the separation theorem, is to optimally quantize the whole signal using an optimal source encoder at the rate equal to the channel capacity and then to transmit the signal (digitally) using an optimal channel encoder. Such double optimality yields the best achievable MSE performance. It is shown that if the double optimality assumptions are applied to the second part of the signal, in the proposed case, than the MSE performance equals that which follows from the separation theorem. If, however at least one of these optimal encoders can not be achieved, the proposed method has a better MSE performance than that based on the separation theorem when applied to the whole signal.
A markov—based algorithm for the generation of MPEG sequences matching intra— and inter—GoP correlation
Authors: Lombardo Alfio , Palazzo Sergio , Schembra Giovanni , Morabito Glacomo 
Published: September 2008

AbstractThe development of sophisticated multimedia applications requires accurate performance evaluation tools to efficiently design and manage future high bandwidth networks. These tools have to be accurate, in order to closely match the statistical characteristics of network traffic, easy to implement, and efficient. VBR compressed video traffic is expected to represent most of the multimedia traffic loading networks in the immediate future, and the MPEG coding scheme will be the most widely used standard for many types of applications. Although many works in literature present models of video traffic, little effort has been devoted up to now to capturing one of the most important characteristics of MPEG video traffic: intra—GoP correlation. In this paper, after demonstrating that this correlation strongly affects the performance of a network loaded by MPEG video traffic, an accurate, fast and easy generation algorithm is proposed. The algorithm allows a sequence to be generated, imposing the Short Range Dependence (SRD), the Long Range Dependence (LRD) behavior and the probability density function of any given MPEG video sequence.
QoS degradation in cellular systems due to H/O hysteresis
Authors: Hernández Raúl E. Díaz , Rodríguez David Muñoz , Molina Ramírez Carlos A. 
Published: September 2008

AbstractWhile hysteresis alleviates the ping—pong effect in a cellullar handoff, it also introduces severe outage degradation. In this letter, the handoff triggering condition as well as the unavailability to handoff completion are studied in terms of mobile location and hysteresis factor. It is shown how hysteresis favors high dropped—call probability zones within the service area. The proposed methodology is applicable to both forward and reverse channel analysis. Numerical results are presented and discussed.
Video Talks: A comprehensive multimedia conferencing system
Authors: Cash Glenn L. , Civanlar M. Reha , Haskell Barry G , Kapilow David A. , Kollarits Richard V. , Paul Baldine B. , Swain Cassandra T. 
Published: September 2008

AbstractA multimedia conferencing system, dubbed AT&T VideoTalks™, has been designed and constructed at AT&T Labs—Research. It allows presentations generated in one conference room to be received in other conference rooms and at desktop computers. Real—time interaction is provided between the conference rooms. Desktop viewers can submit audio or text based questions. Interconnection is accomplished entirely via the corporate IP intranet. Multimedia presentations, including audio, video and graphics, are also digitally recorded for later re—multicasts or on—demand viewing using indexes based on viewgraphs. Network congestion is prevented by restricting the total number of presentations and playbacks. VideoTalks is a prototype system that can be retrofitted to provide for a variety of Internet services, such as remote learning, narrowcasting to niche audiences, video telephony, video conferencing, low cost video—on—demand, etc.
Interference susceptibility of selected bandwidth—efficient modulation schemes
Authors: Povero Gabriella , Vassallo Enrico , Visintin Monica 
Published: September 2008

AbstractButterworth and Square—Root—Raised—Cosine (SRRC) filtered OQPSK, and GMSK with BT = 0. 5 and BT = 1 are compared in the presence of narrow band and wide band interferers, over AWGN and nonlinear channels. The purpose of this work is to help finding out the most suitable modulation scheme for the increasingly crowded frequency bands available for space research missions.
Secure access schemes in mobile database systems
Authors: Hwang Min‐Shiang , Lee Chii‐Hwa 
Published: September 2008

AbstractMobile computing is a newly emerging computing paradigm. Whether using the term mobile database system or some other form, the database concept is essential to the mobile computing environment. This work employs a more thorough yet general means of defining the mobile database system, along with several application scenarios. Possible secure access schemes are also presented for databases in a mobile computing environment. The tradeoffs of these schemes are also analyzed. Moreover, the feasibility of applying some possible secure access methods is explored, along with the potential difficulties and unresolved issues. Finally, concluding remarks and recommendations for future works are made.
Using array signal processing to improve rural area coverage for satellite communications services
Authors: Blostein Steven D. , Karimi Joubin 
Published: September 2008

AbstractWe address wide—area coverage for hand—held portables using an on—board signal processing satellite in geostationary (GEO) orbit at minimum payload cost. A GEO link, being power—limited, differs from terrestrial mobile communications systems that use direct radiating antennas by requiring a focal—fed parabolic reflector, which acts as a fixed analog beamformer. We propose to cascade a high—gain parabolic reflector and a digital maximum signal—to—interference—plus—noise ratio (SINR) multi—beamformer for spatial multi—user interference suppression to achieve coverage extension. This involves on—board antenna array signal processing of multiple feeds. It is shown that nearly uniform coverage of an area the size of Canada can be provided using only five parbolic reflector apertures. Compared to conventional focussed multibeam system, link margins are typically increased from a minimum requirement of 5. 25 dB to 7. 5 dB in border areas. The more uniform coverage reduces dynamic power control requirements.