bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Analysis of new Techniques of Predistortion with Memory in Digital Radio Links
Authors: Bernardini Angelo , Fina Silvia De
Published: September 2008

This paper presents an efficient data predistortion technique with memory applied to digital transmissions over nonlinear channels, specifically satellite links, employing QAM signal formats. The proposed technique is aimed at reducing the high complexity of a conventional pre‐distorter with memory by splitting the function to be realised into simpler blocks. This approach has been suggested by the circumstance that the numerical channel is constituted, in this case, by a nonlinear memoryless block and by two linear blocks with memory so that the predistorter itself can be realised by two FIR filters separated by a memoryless nonlinear element. As for the nonlinear block, we propose the employment of a neural net performing a typical surface reconstruction task, that is the approximation of the function inverting the nonlinearity source (in this case the high power amplifier). Performance analysis has shown a significant improvement with respect to memoryless predistortion (up to 4.5 dB); our proposal, moreover, outperforms conventional 3‐stage‐memory predistortion as the modulation levels increase and as the spectral shaping gets narrower.
Letter: Prediction of the Outage Performance of an Unbalanced Orbital Diversity Earth‐Space System (Log‐Normal Case)
Authors: Kanellopoulos John D. , Ventouras Spiros
Published: September 2008

Diversity schemes are foreseen for earth to satellite links operating at frequencies above 10 GHz to overcome the high rain induced attenuation. In this paper, the orbital diversity configuration, which uses two satellites and an earth receiving site, is discussed.

For this reason, a recently suggested model for the prediction of the outage performance of a balanced orbital diversity system is extended to include the more complicated but practical unbalanced case. The lognormal distribution and the convective raincells are assumed to be representative of the point rainfall statistics and the spatial structure of the rainfall, respectively. Numerical results are compared with experimental data of this kind, taken from an operated unbalanced system located at Fucino, Italy. The agreement was found to be quite encouraging.
Performance Study of an ATM Self‐Routing Multistage Switch with Bursty Traffic: Simulation and Analytic Approximation
Authors: Xiong Yijun , Petit Guido , Bruneel Herwig
Published: September 2008

AnNxNself‐routing multistage switching network with bursty and uniform traffic, which is composed ofSx 5 switching elements with output queueing and hasK= logSNstages, is considered in this paper. The input traffic is modelled by a two‐state (active/silent) Markov chain. Each arriving cell selects one of theNoutlets as its destination independently and with equal probability I/N.The performance of the switching network is studied by means of a simulation method. An approximate traffic model of a four‐state Markov chain is proposed to characterize the cell arrival processes to further stages and its related switching element performance is analyzed. Comparison with the simulation results shows that the proposed traffic model gives a good approximation, which implies that the performance of the switching element mainly depends on the first two moments of the active and silent periods and is not sensitive to the shapes of their distributions. The influence of bursty traffic on the performance of the switching network is discussed and illustrated by some numerical examples. The impact of traffic randomization on the performance of the switching network is also investigated.
Multiplexers ΣD/D/1 with Service in Cyclic Order and Service in the Order of Arrival
Authors: Petersen Joachim , Gillen Thomas
Published: September 2008

In future Broadband Integrated Services Digital Networks, information will be transferred in the form of small fixed sized data units called cells. Stations making use of constant bit rate services generate cells at regular intervals. The waiting times experienced by cells if such cell streams are multiplexed and the properties of the cell stream outgoing from the multiplexer are of high interest. They are analyzed here for time continuous, time slotted and time discrete operation, comparing service in cyclic order to service in the order of arrival. Results are given in closed form.
Nonlinear Distortion and Intensity Noise Induced by Laser Frequency Chirping and Fiber Dispersion in Multichannel Intensity Modulation Systems
Authors: Gao Yu , Leich Martin
Published: September 2008

When a chirped intensity‐modulated light signal is transmitted through a dispersive optical fiber, substantial nonlinear distortion and intensity noise are generated due to the laser frequency chirping and the FM‐AM conversion. This paper presents a new theoretical analysis of these effects. Based on a concise system input‐output representation, the intensity noise and the nonlinear distortion after fiber transmission are determined and given by simple analytical expressions. The classical Volterra‐Wiener theory is applied to ascertain the system dynamic nonlinea‐rity. It is shown how the laser intensity and phase noise, the fiber length and dispersion as well as the intensity modulation, affect the overall system performance. In particular, their impact on multichannel analog TV transmission systems is investigated.
Diversity Combiner for a Limiter‐Discriminator‐Integrator Receiver for Coded CPFSK
Authors: Goldman Haim
Published: September 2008

The paper describes the operation and analyses the performance of a diversity combiner for a limiter‐discriminator‐integrator receiver for coded continuous‐phase frequency‐shift‐keying (CPFSK). The plane of received signals is optimally partitioned using the generalized cut‐off rate as the optimization criterion. Each received symbol is assigned a weight used for soft decision decoding. If estimates of SNR on the diversity branches are available, the combiner utilizes either both branches or just the branch with the largest SNR, depending on the relative magnitudes of the SNRs. In the large effective range, in which it is advantageous to use both branches, the performance of the analysed combiner is better than that of the selection combiner. The combiner can also operate with no SNR estimates. The paper presents results for optimal partition parameters of the signal plane for various modes of operation, criteria for choosing the optimal mode and an upper bound on the probability‐of‐error for operation with a rate 0.5 convolutional code.
Performance of Interpulse Signal Coding in Interleaved‐Pulse Polarimetric SAR
Authors: Giuli Dino , Facheris Luca
Published: September 2008

Fully polarimetric Synthetic Aperture Radars (SAR) provide a complete measurement of the scattering matrix of the imaged target by alternately transmitting two pulses at orthogonal polarizations, while processing echoes simultaneously received on two orthogonal polarization channels. Due to this procedure of performing measurements, the problem of interference caused by range ambiguities is of greater concern than in conventional non‐polarimetric SAR. Such interference is made up by signals of different nature, depending on the order (even or odd) of the range ambiguity. In particular, odd‐order range ambiguities generate an interference on crosspolar terms of the matrix, proportional to one of the copolar terms, which have typically a much greater magnitude. This drawback, that never occurs in non‐polarimetric SAR systems, is a major source of measurement contamination, in particular in the presence of range ambiguous echoes from areas which are illuminated at low incidence angles.

In this paper, after discussing the influence of range ambiguities on the accuracy of scattering matrix measurement as performed by interleaved‐pulse SAR, we examine the utility of appropriate interpulse phase coding strategies, to be devised and utilized with the purpose to reduce the interference due to range ambiguities and affecting those target scattering matrix elements, whose measurement is expected to be most critical.
Laser Diodes and Integrated Optoelectronic Circuits for Fiber Optical Applications
Authors: Wolf Thomas , Amann Markus Christian , Albrecht Helmut
Published: September 2008

The development of high performance semiconductor laser diodes has played a key role in the rapid deployment of optical fiber communications, and the realisation of advanced system concepts strongly depends on the further improvement of the laser diodes. This includes the demand for wavelength tunable single frequency laser diodes as well as the need for optoelectronic integration. The different laser structures in the 1.3 and 1.5 μ m wavelength regions, their relevant parameters and applications are described in this paper. The impact of recent progresses in the material technology on the device performance is particularly investigated. It is further shown that the availability of low‐cost, highly complex integrated optoelectronic components represents a prerequisite for the introduction of optical communication systems in the subscriber area. The photonic and optoelectronic integrated circuits presented so far for bidirectional transmission, photonic switching and optical distribution are presented and the challenges for the future development are discussed.
Recent Results on Fatigue and Dispersion Modification in Optical Fibers
Authors: Antos A. Joseph , Glaesemann G. Scott , Vandewoestine Robert V.
Published: September 2008

This paper reports recent results on two areas of optical fiber technology that, while unrelated, are of current interest. The first topic addresses dispersion limitation of transmission rates in optical fibers. This topic has increased in visibility in the last two years as optical amplification has minimized the importance of attenuation limits in the design of long transmission distance systems. Methods to minimize the dispersion limitation, such as dispersion shifted fiber, distributed amplification and dispersion compensating fiber, will be discussed. The second topic, that of the mechanical fatigue in optical fibers, has been a topic of research for many years, but new data continues to be gathered that is useful for cable design and system reliability calculations. Data is presented for two static fatigue tests of 3 years and 15 years duration.
Performance of coded direct‐sequence systems with rake reception in a multipath fading environment
Authors: Goeckel Dennis , Stark Wayne
Published: September 2008

The probability of error is determined for an uncoded coherent direct‐sequence spread‐spectrum system with rake reception operating in a specular multipath fading environment. Bounds on the probability of error for a convolutionally‐coded system are also calculated through the use of the union bound. The model that is utilized contains a large number of paths divided into groups across the signalling interval. The rake is assumed to be locked onto the direct path and one strong path from each of a subset of the other groups. The probability of error is calculated using the characteristic function to determine the effect of various system parameters such as the processing gain and the number of rake branches. Comparisons are made with results obtained through the standard Gaussian assumption. Finally, further analytic results are presented for the rake receiver in the low signal‐to‐noise ratio limit.
Performance evaluation of multi‐cell direct‐sequence microcellular systems
Authors: Sun Chung‐Ming , Polydoros Andreas
Published: September 2008

The performance of an asynchronous multi‐cell Direct‐Sequence Spread Spectrum Multiple‐Access (DS/SSMA) system is evaluated in lineal microcells with flat Rician fading and shadowing. Both the Bit Error Rate(BER)of the uplink (i.e., the user to the base station) and the downlink (i.e., the base station to the user) are evaluated. We develop a new analytical model to evaluate the uplink performance which accounts for the user's spatial distribution, the chip waveform, the power control, and macro‐selection diversity. On the downlink, since no power control is used, the desired signal follows a composite log‐normal noncentral chi‐square distribution. We propose an approximation method to reduce the computational complexity while still providing satisfactory precision. The analysis results show that the macro‐selection diversity can reduce the other‐cell interference effectively even for a channel with heavy shadowing. The Rician factor, the standard deviation of the shadowing, and the chip waveform have significant influence on the performance.
Fast computation of outage probability for cellular mobile radio systems
Authors: Zorzi Michele
Published: September 2008

In 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

An 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

A 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

For 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

Video 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

There 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

An 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

We 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

We 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

Automatic 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

This 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

In 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

In 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

Chirp 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

Recent 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

The 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

Network 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

A 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

An 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

The 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

The 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

This 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

This 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.
Letter: All digital spread spectrum modems for power line communications
Authors: Dostert Klaus M.
Published: September 2008

Through the use of band‐spreading techniques electrical power distribution networks become reliable and universal data links. For cost and performance reasons all digital solutions for the. construction of modems are paramount. The use of general purpose digital signal processors (DSP) is neither feasible nor cost‐effective. After a review of appropriate signalling schemes the key components for integration into an ASIC will be outlined. Within the transmitter section of the ASIC a programmable address counter together with a sample memory provides precise and fast signal synthesis. In the receiver section a fast front‐end is needed for correlation operations. Furthermore essential steps towards bit decision are performed. A typical ASIC, representing the heart of a power line modem, finally contains the following functional blocks: An 8 bit correlator with a minimum of four separate accumulators, a squarer with at least two additional accumulators forming the decision logic, and a programmable 10 bit address counter. VHDL‐based ASIC design was performed and fabrication took place in October 1994 within the EUROCHIP project. An ASIC incorporates 5250 gates with a power consumption below 50 mW. Modems have been built with different signalling schemes for data rates up to 2400 bits/s. Measurements revealed typical bit error rates below 10−‐6.
Measurement‐based flow control for ABR services in ATM networks
Authors: Ghani Nasir , Mark Jon W.
Published: September 2008

A distributedexplicit‐rate (ER)capacity allocation algorithm for handlingavailable‐bit rate (ABR)services in ATM networks is described. The algorithm uses a measurement‐based approach to achieve max‐min bandwidth fairness and to provide priority service mechanisms for heterogeneous traffic, e.g.,constant‐bit rate (CBR), variable‐bit rate (VBR), ABR, etc. Explicit provisions are made for handlingminimum cell rate (MCR)guarantees forABRconnections and minimizing RM cell buffering delays at the network switches. It is also proposed that the sources measure their average rates to properly handle variability and to improve bandwidth utilization. An extensive simulation study for a number of network scenarios, which shows that the proposed scheme adapts well to network dynamics and converges to max‐min fairness, is presented.
Spectrum shaping for land mobile radio systems
Authors: Ramésh R. , Chennakeshu Sandeep , Hassan Amer A. , Anderson John B.
Published: September 2008

Spectral efficiency for land mobile radio channels is primarily limited by adjacent channel interference. Conventional digital modulation schemes do not achieve current specifications for adjacent channel interference at high data rates. The adjacent channel interference can be mitigated by the intelligent choice of transmitter components such as the modulation scheme and the transmit filter. We present a trellis coded modulation (TCM) scheme that can provide high data rates and at the same time reduce adjacent channel interference. We present methods to choose an appropriate TCM scheme under constraints of Euclidean distance and peak‐to‐average power. We also present methods to optimize transmit filters to minimize adjacent channel interference under various constraints. Examples are provided to illustrate the gains that can be obtained.
The influence of signal quantization on the performance of digital receivers for CDMA radio networks
Authors: Gaudenzi Riccardo De , Giannetti Filippo , Luise Marco
Published: September 2008

In an all‐digital implementation of a data modem for Direct‐Sequence Spread Spectrum (DS/SS) Code‐Division Multiple Access (CDMA) systems, the in‐phase and quadrature components of the received signal are customarily digitized just after IF matched filtering and baseband conversion. To reduce the processing effort in the data demodulator, it is of interest to represent the signals in the digital domain with as little a number of bits as possible. On the other hand, coarse signal quantization (down to 2‐3 bits/sample) causes a non‐negligible performance degradation as far as the receiverBERis concerned. The aim of this paper is thus the investigation of the impact of signal quantization on theBERperformance of a DS/SS CDMA receiver in the presence of Gaussian noise and co‐channel interference. Based on a general theoretical analysis, a few multiple access strategies are taken into consideration, and the theoretical findings are also checked by computer simulation. For all those systems, a four‐bit ADC, yielding less than 0.5 dB signal‐to‐noise ratio degradation at aBER= 10−3appears to provide a good trade‐off between performance loss and demodulator complexity.
Viterbi detection for the double differential MPSK modulation
Authors: Papproth Eckhard , Kaleh Ghassan Kawas
Published: September 2008

A double differential encoding technique for phase shift keying symbols and its detection using the Viterbi algorithm to counteract channel phase and frequency uncertainties are presented. After deriving the detector structure from a maximum‐likelihood sequence detection approach we examine its performance and complexity and compare it to those of conventional and block detection techniques. For moderate complexity we attain the performance of the conventional single differential detector.
MDPSK on frequency‐selective ricean channels with diversity and cochannel interference
Authors: Abu‐Dayya Adnan A. , Beaulieu Norman C.
Published: September 2008

Precise average bit error rate (BER) results forM‐ary differential phase shift keying (MDPSK) on slow frequency‐selective Ricean fading and microcellular cochannel interference channels are presented. The microcellular fading environment is modeled by a Ricean fading desired signal and Rayleigh fading interferers. Equal gain postdetection microdiversity combining to mitigate the effects of fading is investigated. Nyquist pulse shaping is used and differential detection is employed at the receiver. The performance of the Gaussian interference model is also assessed. In this model, the interference contribution is represented by a Gaussian noise whose mean and variance are equal to the mean and variance of die sum of the interfering signals. The accuracy of the Gaussian model is assessed by comparing itsBERperformance with preciseBERresults. The preciseBERresults are obtained by using a combination of analysis and simulation. The effects of the Ricean AT‐factor, the number of diversity branches,L, and the level of modulation,M, on the averageBERare investigated in detail.
Authenticated key‐exchange in a mobile radio network
Authors: Hwang Min‐Shiang , Lee Chii‐Hwa
Published: September 2008

A new method is proposed in this study for implementation of secure digital mobile communication systems. Two requirements for the systems must be considered, i.e., privacy and authentication. Privacy ensures that an eavesdropper cannot intercept conversations between two parties. Authentication ensures that service is not obtained fraudulently in order to avoid charge for usage. Additionally, a new key distribution scheme is designed for practical implementation in a low‐cost and low‐power digital mobile communication system.
Robust sequential projection algorithm: Teletraffic applications
Authors: Ursini Edson Luiz , Yacoub Michel Daoud , Amaral Wanger Caradori Do , Girolami Alessandro
Published: September 2008

Ann‐step ahead Robust Sequential Projection Algorithm ‐ Robust SPA ‐, used for traffic forecast as well as for long term network planning is proposed. The algorithm uses the State Space Model with the state transition matrix being estimated by a relaxation technique. This lightly increases its complexity, as compared to a similar algorithm proposed in the literature, but renders the Robust SPA a better performance. The algorithm is also compared with the Expectation‐Maximization technique and, in general, the Robust SPA yields a slightly poorer performance as far as the mean square error between projected and observed data is concerned. On the other hand, it is more robust and requires far less computational effort. Moreover, due to its simplicity, an automated version of the algorithm can be easily implemented for applications in which a great deal of data is to be forecasted.
Heuristic algorithms for reliable multiplexed network design
Authors: Costamagna Eugenio , Fanni Alessandra
Published: September 2008

A heuristic optimization algorithm is presented for topological optimization of wideband communication networks whose structure is based on a single central office and on a number of multiplexing centres. The reliability problem is discussed in detail introducing in the objective function a cost term related to the probability of failures. Optimization is performed in two steps. In the first step a tree non redundant network is determined, providing the starting configuration for the second step, in which redundant edges are introduced. Cross‐connect devices replace multiplexers when suitable, and a very general mesh topology is created. Statistics on a large number of test networks are reported. Network costs and reliability performances are deeply investigated.
On the use of dispersity routing for fault tolerant realtime channels
Authors: Banerjea Anindo
Published: September 2008

This paper presents a taxonomy of dispersity routing schemes designed to provide fault‐tolerant realtime communication. Our model involves the provision of dispersity at the application level, rather than in the physical layer as in traditional uses of dispersity. We assume a connection oriented realtime communication service such as that provided by the Tenet Suite 1 or Asynchronous Transfer Mode (ATM) networks. We use the ideas of dispersity routing, redundancy, disjoint paths, and hot and cold standbys to design and classify a set of schemes that can provide a range of fault‐tolerant realtime services. The classification provides a convenient framework, which we use to discuss the properties of the schemes and to conduct simulation experiments. We compare the service provided and the costs of our schemes to other approaches to fault‐tolerant realtime communication, such as the Internet approach. We conclude that dispersity routing is a flexible approach to increasing the fault tolerance of realtime connections, which can provide a range of improvements in service with a corresponding range of costs.
A secure and optimally efficient multi‐authority election scheme
Authors: Cramer Ronald , Gennaro Rosario , Schoenmakers Berry
Published: September 2008

In this paper we present a new multi‐authority secret‐ballot election scheme that guarantees privacy, universal veriability, and robustness. It is the first scheme for which the performance is optimal in the sense that time and communication complexity is minimal both for the individual voters and the authorities. An interesting property of the scheme is that the t and communication complexity for the voter is independent of the number of authorities. A voter simply posts a single encrypted message accompanied by a compact proof that it contains a valid vote. Our result is complementary to the result by Cramer, Franklin, Schoenmakers, and Yung in the sense that in their scheme the work for voters is linear in the number of authorities but can be instantiated to yield information‐theoretic privacy, while in our scheme the voter's effort is independent of the number of authorities but always provides computational privacy‐protection. We will also point out that the majority proposed voting schemes provide computational privacy only (often without even considering the lack of information‐theoretic privacy), and that our new scheme is by far superior to those schemes.