bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast computation of outage probability for cellular mobile radio systems
Authors: Zorzi Michele 
Published: September 2008

AbstractIn this paper a new approximate method for the computation of outage probabilities in a mobile radio environment is proposed. It allows one to evaluate the performance of a mobile radio system in the presence of fading, in a very fast and accurate way, while maintaining a very good flexibility as to the application to different network environments. Coding is also considered as a possible choice, in order to increase the spectral efficiency of the system, which represents a major concern for the designers of cellular networks.
Timing jitter and its impact on a self‐synchronised optical fibre PPM system
Authors: Elmirghani Jaafar M. H. , Cryan Robert A. 
Published: September 2008

AbstractAn original spectral characterisation for the jitter in optical fibre pulse position modulation (PPM) is developed. The characterisation is used to examine the problem of slot synchronisation in PPM under two distinct cases. First when the PPM system is dominated by the self modulation noise namely the pattern‐dependent jitter. Then when both pattern and receiver‐generated jitter accumulate to impair the PPM system. We present a thorough performance analysis of the system under jitter impairment. Original results are obtained for the slot timing variance and the wrong slot error probability (WSE) in terms of the PPM number of slots, the phase lock loop (PLL) bandwidth and the normalised fibre bandwidth. The results indicate that with proper selection of the system parameters the slot jitter impairment can be minimised and maintained within prespecified levels. Frame synchronisation robustness is examined for a novel class of frame synchronisers previously proposed. Original results are presented for the extracted frame clock timing variance and the system WSE probability due to frame clock jitter when the system is dominated by its self noise. The frame synchronisers performance is shown to be optimisable through proper selection of the PLL bandwidth and the number of natural sequences tracked.
Evaluation of the constant modulus algorithm in blind equalization of three ray multipath fading channels
Authors: Cusani Roberto , Laurenti Alberto 
Published: September 2008

AbstractA QAM data transmission system operating over a band‐limited simplified three‐ray multipath fading channel can be equalized by the constant modulus algorithm. A systematic study of the convergence of this blind equalizer is performed in terms of the channel parameters by adopting an analytical model. The convergence behaviour is expressed in terms of the dispersion pattern of the equalized samples around the true symbols of the constellation.
A fast method for the NLMS algorithm with time‐variant decorrelation filters
Authors: Poltmann Rainer D. 
Published: September 2008

AbstractFor many applications, such as the cancellation of room echoes, the NLMS algorithm converges too slowly because of the correlatedness of the adjustment signals. Therefore, it was repeatedly proposed to increase the convergence speed by means of decorrelation filters. In the present contribution a well‐known structure based on the use of time‐variant decorrelation filters is replaced by an alternative one which supplies exactly the same results but allows the computational efforts to be reduced considerably.
Intelligent image interpretation for high‐compression high‐quality sequence coding
Authors: Bedini Gianfranco , Favalli Lorenzo , Marazzi Andrea , Mecocci Alessandro , Zanardi Carletto 
Published: September 2008

AbstractVideo transmission at very low bit rate has got growing attention in recent years. In this paper we propose an approach for the compression of 144 x 176 pixels Q‐CIF video conference sequences. The compression ratio well exceeds 200 : 1 (thus leading to bit‐rates under 10 kbit/s for 10 frames/s) with very good psycovisual quality of the reconstructed images. The algorithm integrates and improves different feature extraction and image coding techniques. At first the speaker's head is detected by means of active snakes. A new form of internal energy is defined that allows a very robust and fast head tracking. After head detection, internal facial features (i.e., eyes, nose, and mouth) are located by means of a new algorithm. The image is decomposed into different parts with different psicovisual relevance. This information is used to guide in an intelligent way the subsequent processing of the motion compensated difference image. The important areas are coded more accurately while the less relevant areas are coded in a coarser way. This approach grants very high compression while the image quality remains high. Subpixel block matching is used to obtain a motion compensated difference image. This image is segmented into homogeneous regions that are then coded by means of a technique based on differential chain code.
Spectral and rank order approaches to texture analysis
Authors: Fioravanti Stefano , Fioravanti Roberto , De Natale Francesco G. B. , Marik Radek , Mirmehdi Majid , Kittler J. , Petrou M. 
Published: September 2008

AbstractThere are two major approaches to texture analysis, both supported by physiological evidence: those based on the spatial statistics, and those based on its spectral properties. One of the most sophisticated spectral approaches to texture is that based on the Wigner distribution where the attributes computed for each pixel encapsulate both the local spectral and phase properties of the local Fourier transform in a unique real spectrum. On the other hand, some of the most efficient methods which operate in the spatial domain alone, are those based on rank order functions. Before one embarks on the use of the sophisticated methods, it is worth exploring the efficient ones to the limit of their performance. In this paper we investigate these two major approaches and compare their performance both in terms of quality of results and efficiency. The problem we consider is that of detecting defective blobs and cracks on complex textural backgrounds. We show that in most cases rank order approaches can perform well, although no unique method can be employed for both types of defects. On the other hand, the Wigner approach with a very small modification can cope with both types of defects and handle even the identification of very subtle cracks. Thus, it seems that for any real time performance inspection system, the rank order approaches should form the front end with the more sophisticated methods coming in play when necessary.
Content‐driven pyramid compression of medical images for error‐free archival and progressive transmission
Authors: Lotti Franco , Aiazzi Bruno , Baronti Stefano , Casini Andrea , Alparone Luciano 
Published: September 2008

AbstractAn efficient encoding scheme based on an improved Laplacian pyramid is proposed for lossless/lossy compression aimed at archival and progressive transmission of grayscale medical images. The major assets are: pyramid entropy is decreased by adopting two different filters for reduction and expansion; encoding priority is given to major details through a hierarchical content‐driven decision rule; the binary quad‐tree of split/unsplit nodes is blockwise zig‐zag scanned and run‐length encoded. Error feedback along the levels of the Laplacian pyramid ensures control of the maximum absolute error, up to fully reversible reconstruction capability, and enhances the efficiency and the robustness of the whole scheme. While coding results on the standard greyscale image Lena are pretty competitive with the most recent literature, reversible compression of scanned RX images achieves ratios of about 1:5, establishing improvements over DPCM schemes; high‐quality lossy versions at 0.15 bit/pel outperform JPEG both visually and quantitatively. Moreover, no floating‐point computation is required in the algorithm, and on‐line compression and reconstruction are feasible on general‐purpose terminals.
Ungerboeck DPSK codes do not shape the signal spectrum
Authors: Ramésh R. 
Published: September 2008

AbstractWe consider the power spectrum of trellis codes in conjunction with a differential encoder. We present a closed form expression for the power spectrum of PSK trellis codes that are subjected to differential encoding. Using this expression, we show that when the trellis code in question is defined by the Ungerboeck rules, the power spectrum of the resulting differentially encoded sequence is a constant; in other words, Ungerboeck DPSK codes do not shape the signal spectrum.
Applicability of four‐dimensional modulations to digital satellites: a simulation study
Authors: Taricco Giorgio , Biglieri Ezio , Castellani Valentino 
Published: September 2008

AbstractWe examine multidimensional modulation schemes in view of their application to digital satellite communications systems. In particular, we focus our attention on four‐dimensional signals and describe the applicability of several coded constellations based on Q2PSK with optimum selection of baseband signals. Equal‐energy signal sets, signals carved from lattices, convo‐lutionally‐encoded and trellis‐encoded schemes are compared by evaluating their performance by computer simulation in a channel model that includes the effects of linear filters, nonlinear amplifiers, and carrier and timing recovery circuits. Among the schemes considered here, trellis‐coded modulation seems to offer the best tradeoff between performance and complexity.
A new selective ARQ scheme with a finite buffer
Authors: Benelli Giuliano , Garzelli Andrea 
Published: September 2008

AbstractAutomatic repeat request (ARQ) techniques with error‐detecting codes are commonly used in communication systems. Of these, selective protocols, while the most efficient, have the notable drawback of requiring large buffers at the receiver side. A new selective ARQ protocol with a finite‐length buffer is described in this paper. If A' is the number of codewords transmit‐table in the round‐trip delay, the described protocol requires a buffer having length equal to N + Na Na≥2 being an integer. A lower bound on the throughput of the described ARQ protocol is derived. The proposed protocol achieves higher throughputs than similar schemes, giving comparable results to selective protocols with infinite‐length buffers for high error rates in the communication channel.
Iterative correction of intersymbol interference: Turbo‐equalization
Authors: Douillard Catherine , Jézéquel Michel , Berrou Claude , Electronique Département , Picart Annie , Didier Pierre , Glavieux Alain 
Published: September 2008

AbstractThis paper presents a receiving scheme intended to combat the detrimental effects of intersymbol interference for digital transmissions protected by convolutional codes. The receiver performs two successive soft‐output decisions, achieved by a symbol detector and a channel decoder, through an iterative process. At each iteration, extrinsic information is extracted from the detection and decoding steps and is then used at the next iteration as in turbo‐decoding. From the implementation point of view, the receiver can be structured in a modular way and its performance, in bit error rate terms, is directly related to the number of modules used. Simulation results are presented for transmissions on Gauss and Rayleigh channels. The results obtained show that turbo‐equalization manages to overcome multipath effects, totally on Gauss channels, and partially but still satisfactorily on Rayleigh channels.
Interative (“turbo”) decoding of threshold decodable codes
Authors: Riedel Sven , Svirid Yuri V. 
Published: September 2008

AbstractIn this paper we extend the idea of iterative decoding of two‐dimensional systematic convolutional codes ‐ so‐called “turbo” codes ‐ to threshold decoding. A threshold decoding algorithm is presented which uses soft information from the channel and a priori values in order to generate soft outputs. A soft output value can be split into three terms. The first two terms represent the soft input including the a priori value, while the third is called extrinsic value. The extrinsic value is passed on as a priori information to the following decoder. Surprisingly good simulation results were obtained for the Gaussian channel and the fully interleaved slowly Rayleigh fading channel.
Analysis of the m and m2routings in circuit‐switched networks
Authors: Wong Eric W. M. , Yum Tak‐Shing P. , Chan Kit‐Man 
Published: September 2008

AbstractIn nonhierarchical circuit‐switched networks, calls can be routed to alternate paths if the direct path is blocked. In this paper, we analyze two alternate‐path routing rules called theMaximum Free Circuitrouting and theMaximum Free Circuit with Minimum Occupied channelrouting. For convenience, we shall call them theMandM2routings respectively. In the use ofMrouting, a call is routed to an alternate path that has the maximum number of free circuits when the direct path is blocked. TheM2routing is an improvement of theMrouting in that when multiple alternate paths have the same number of free circuits, the path with the smallest total occupied channels is chosen. Analytical results show thatM2routing provides additional improvement overMrouting when the number of alternate paths is large and/or the trunk group size is small. These results are verified by simulation. As the implementation ofM2routing is no more complicated thanMrouting (both require the same channel occupancy information) and its performance is always better thanMrouting,M2routing is deemed a better rule to use.
Generalized chirp modulation technique
Authors: Wysocki Tadeusz 
Published: September 2008

AbstractChirp modulation is one of the proposed digital phase modulation schemes where positive and negative data are represented, respectively, by increasing and decreasing of the instantaneous frequency. Chirp modulation is resistive to Doppler effect while its error performance, due to the phase characteristics, is quite poor. The paper deals with a generalization of the Chirp technique leading to new classes of signal formats for digital communications with improved spectral efficiency and good error performance. To achieve this task, the second time derivative of an information carrying phase component of a modulated signal is set to be proportional to an information carrying data signal. Further, for a generation of specific signal formats, the alternate mark inversion encoding of data to be transmitted is applied.
Volterra adaptive prediction of speech with application to waveform coding
Authors: Mumolo Enzo , Carini Alberto 
Published: September 2008

AbstractRecent studies have shown that the airflow in the vocal tract is highly unstable and oscillates between its walls. Therefore linear prediction speech analysis, which is based on laminar airflow hypothesis, leads to approximate representations. This paper deals with nonlinear speech modeling and its exploitation to high quality medium‐rate coding. We first give evidence that the nonlinearities in speech can be described by a second‐order finite memory Volterra operator. An algorithm for performing adaptive nonlinear prediction is described. Application of the algorithm to speech coding is then reported and stability and computational issues are discussed. Performance evaluations and comparisons with linear predictive speech coding are reported and show that improvements in coding performances can be obtained.
Characterization of timing signals and clocks
Authors: Carbonelli Marco , De Seta Domenico , Perucchini Daniele 
Published: September 2008

AbstractThe characteristics of timing signals at the output of autonomous and slave clocks are thoroughly investigated: first, a mathematical model of timing signals is introduced, then models for describing autonomous and slave clocks are presented whereby an analysis of their behaviour in a synchronization network is carried out. Further, two commonly used measurement configurations are described in order to identify the measurement set‐ups more useful for telecommunication applications; the most frequently used quantities for characterizing time and frequency stability are introduced and deeply investigated. Finally, the stability quantities behaviour both for autonomous and slave clocks is studied, with the aim at providing synchronization network designers with powerful tools for network planning and for assessing network performance.
Design aspects and analysis of SDH equipment clocks
Authors: Urbansky Ralph , Sturm Wolfram 
Published: September 2008

AbstractNetwork synchronization has gained increasing attention since the introduction of the Synchronous Digital Hierarchy (SDH), as network synchronization performance due to the SDH‐internal bit rate adaptation technique have a major impact on the phase transfer characteristic of SDH‐based networks. Excessive jitter or wander may result in bit errors or frame slips within digital exchanges. This paper discusses the requirements with respect to SDH Equipment Clocks (SEC), which are the basis for improved network synchronization. Two parameters have a significant impact on the phase error generated by the clock: the oscillator performance and the phase detector characteristic. This paper proposes a synthesizer‐based PLL structure employing a fixed frequency highly stable oscillator. A novel approach for an all‐digital phase detector provides enhanced resolution, thereby reducing the phase error. Analytical and simulation results demonstrate the feasibility of this approach.
Application of transition place coding in asynchronous time‐division multiplexing
Authors: Smiljanic Mirko N. , Temerinac Miodrag R. 
Published: September 2008

AbstractA new concept of asynchronous multiplexing of digital signals has been recently proposed by authors. The concept is based on a new format called “Transition Place Coding” (TPC). In this paper the TPC principle has been outlined and the transmission efficiency, the jitter and the error multiplication of the TPC format are analyzed in details. It is shown that the TPC format can be used as an optical line code. Two modifications of the TPC format are presented: a format without transition bit (TPC1) and a format with sliding frame (TPC2). An extensive analysis of the above mentioned characteristics of both TPC1 and TPC2 format was performed. A new asynchronous time‐division multiplexing method based on the TPC formats has been proposed and analyzed with emphasis on an adaptive multiplexing. The TPC multiplex is verified by a computer simulation and by several experimental realizations. Finally, a comprehensive comparison of the TPC multiplex is performed and conditions where their applications appear most desirable are defined. It is shown that the TPC multiplex is attractive for optical fibre communications.
Simultaneous frame and bit synchronization of HF receivers by constant false alarm methods
Authors: De Fina Silvia 
Published: September 2008

AbstractAn application to HF radio links of the constant false alarm rate synchronization method based on both preamble detection and over sampling at the receiver is proposed and discussed. The method provides both frame and bit synchronization: the former is achieved by correlating the received samples with a reference preamble pattern; the latter by over sampling the incoming signal. A closed form expression of the probability of miss is derived for the general case and a statistical analysis of the synchronization method applied to HF transmissions is carried out on a simulation basis. Several curves which show the distributions of probability of miss for different propagation conditions and different fade margins are included. Inspection of these results shows that the reliability of the synchronization method has to be improved through the introduction of a suitable synchronization strategy involving a certain number of pre‐alarm states.
Letter: Linear adaptive prediction using LMS algorithm over rician fading channels
Authors: Trabelsi Chokd 
Published: September 2008

AbstractThe performance of a receiver which uses fading prediction technique in conjunction. with a channel coding/interleaving scheme is determined for Ridan non‐selective fading channels., The essence of the proposed technique is based on predicting the fading process and designing the receiver accordingly. The novel receiver employs a combination of a prediction technique and Reed Solomon (RS) codes/interleaving scheme using phase shift keying (PSK) modulation scheme. The obtained computer simulation results of the bit error rate (BER) performance show that the proposed prediction/coding/interleaving technique greatly reduces theBERdegradation caused by the multi path fading.
Upper bounds on the size of error‐correcting runlength‐limited codes
Authors: Winick Kim A. , Yang Shih‐Hsuan 
Published: September 2008

AbstractThe maximum achievable rate of an error‐correcting runlength‐limited code is considered. Runlength‐limited codes find wide applications in magnetic and optical recording, baseband. pulse transmission, and fiber optic communications. When a runlength‐limited code is used on a noisy channel, error‐correction control is often needed in order to obtain the desired system reliability. It is well‐known that the error‐correcting capability of a code is closely related to its distance properties. In this paper, asymptotic upper bounds for the maximum achievable rate of a runlength‐limited code are derived as a function of the code's minimum Hamming distance.
Performance and dimensioning of a hierarchical video storage network for interactive video services
Authors: Bianchi Giuseppe , Melen Riccardo 
Published: September 2008

AbstractThis paper examines a network architecture designed to offer interactive video services to residential subscribers. Its main feature consists in the possibility of storing heavily requested material in video “cache” locations at the local switch level. Various policies for the management of the resulting hierarchical storage system are defined and their effectiveness, in terms of success ratio of the local accesses, is evaluated via simulation. A simple evaluation of the cost trade‐off between distributing video programs in local memories and keeping them in a centralized video server is carried out as well, considering both leased line and switched line solutions for long distance transmission. The difference due to the non stationary behaviour of the user requests is also evaluated.
Experimental validation of an ATM traffic control framework in the EXPLOIT testbed
Authors: Renger Thomas , Aarstad Egil , Pettersen Harald , Kroeze John 
Published: September 2008

AbstractThis paper deals with the experimental investigation of a preventive traffic control framework for ATM networks as implemented in the EXPLOIT Testbed. This framework comprises a Usage Parameter Control (UPC) function and a Connection Admission Control (CAC) function. The obtained measurement results are complemented and compared with simulation studies and analytical results. For several On/Off traffic types it is shown that the implemented UPC function enforces both the Peak Cell Rate (PCR) and the Sustainable Cell Rate (SCR) simultaneously. By measuring the cell loss ratio as a function of the number of multiplexed sources, admission boundaries for a given network performance objective can be found and compared with the implemented CAC function based on the convolution algorithm. It appears that network performance objectives can be guaranteed, while exploiting most of the possible multiplexing gain in a network with small buffers like the EXPLOIT Testbed. Finally, it is shown that the two co‐operating functions constitute a traffic control framework which is robust against traffic contract violations as well as worst case traffic utilising the contracted UPC function tolerances maximally at both the cell level and the burst level.