bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐Linear Optical Transmission Systems
Authors: O'Mahony Michael J.
Published: September 2008

In recent years much research has focussed on the development of high capacity optical transmission systems for terrestrial and undersea application. The development of optical amplifier repeaters has led to the situation where multigigabit transmission is required over very large distances. In this situation the effects of fibre dispersion pose a serious limitation to performance. This paper considers the effects of fibre dispersion and discusses the technique of non‐linear propagation which has been proposed to overcome the problem. The main design equations for a soli‐ton system are presented and discussed.
Applications of Coherent Techniques to Optical Transmission: State of the Art and Perspectives
Authors: Betti Silvello , Marchis Giancarlo De , Iannone Eugenio
Published: September 2008

The state of the art and the perspectives of application of coherent techniques to optical‐transmission systems are discussed. After a review of the performance achieved with point‐to‐point single channel transmission systems, different frequency‐division‐multiplexed systems are analyzed for both point‐to‐point transmission and local area network applications. Attention has been devoted to possible applications of coherent optical systems in broadcast and local area networks exploiting both subcarrier and frequency division multiplexing techniques. In conclusion the potentials offered by these systems are considered relatively to space intersatellite optical links.
Future Scenarios for Telecommunications Networks
Authors: Hawker Ian , Cochrane Peter
Published: September 2008

To maintain the pace of progress the future development of telecoms networks should reduce the cost per connection, improve quality of service and increase network functionality and intelligence. In this paper we examine some .of the longer term network options including optical networking to create bandwidth transparency in order to reduce costs and enable new networking approaches (eg where bandwidth is traded for simpler control). We also discuss the reliability threat from the growth of ‘software mountains’ associated with increased network intelligence and functionality, and suggest self organization as a viable alternative.
Performance Calculations of Optically Preamplified IM‐DD Receivers
Authors: Gaibazzi Alberto , Ghiggino Pierpaolo , Shamir Netta
Published: September 2008

The performance of optically preamplified IM‐DD receivers is investigated, in terms of Sensitivity and BER, employing a statistic model which is more accurate than the customary Gaussian approximation.

A comparison between the two statistics' predictions is presented.

The implications of practical receivers on the performance of the system have been analysed in detail. Particular care has been taken to investigate the penalties arising from a non‐optimum threshold setting of the comparator.
Optical Fiber Buffer for High‐Performance Broadband Switching
Authors: Masetti Francesco , Gavignet‐Morin Paulette
Published: September 2008

This paper presents an optical buffer shift register based on a set of fiber delay lines electrically‐controlled, to provide cell storage and queueing capabilities in high‐performance broadband switches satisfying ATM service requirements. The concept of multi‐wavelength cell buffering is adopted, to realise a partially shared buffer with a storage capacity equivalent to a set of single shift registers. The final system is well‐suited for photonic switches adopting time‐ and wavelength‐division multiplexing techniques to perform the routing functions inside the switching matrix.

We have demonstrated both the suitability of optical fibers as signal delay lines and the use of semiconductor optical amplifiers as gates associated to passive splitters, to realise cell buffering and time‐switching. An experimental set‐up has been implemented at 600 Mbit/s, operating without guardbands between packets. Good performances were obtained in terms of gain and speed of the whole system: the slight penalty and time shifts observed show that the system synchronisation is very good, thus capable of allowing higher operating bit‐rates.
Passive Optical Networks ‐ Deployment and Evolutionary Potential
Authors: Faulkner David , Stern Jeff , Frost Peter , Cook Andrew
Published: September 2008

This paper gives insight into the ways in which Passive optical networks may be economically deployed in a well‐established copper infrastructure.

The telecommunications market demands service flexibility coupled with high reliability, which the copper network struggles to provide. Particularly beneficial is the fibre‐to‐the‐building approach, which is being followed in certain areas in Europe. This provides the necessary service flexibility and promises huge capacity upgrades for the future. Following initial deployments the opportunity exists to broaden the deployment throughout Europe. Ubiquitous solutions will enable the benefits of fibre to be brought to smaller and smaller customers. Beyond this, the capacity and reach of fibre can be exploited more widely ‐ restructuring the network to extend broad band services to all customers.
Bandwidth Allocation in an IBCN Queueing System with Quasirandom Input
Authors: Schlott Reinhard
Published: September 2008

In this paper, we present a call admission strategy for an Integrated Broadband Communication System serving two types of customers ‐ Narrowband and Broadband. Either one or both of the customer groups are assumed to have a finite number of sources (customers). The model involves a multidimensional state space, for which balance equations are derived. Since the system employs separated queues, one for each type of customer, multiple transitions can take place within the state space. Their probabilities have been derived analytically. Finally we compute the carried load and mean queue lenghts and compare these with separated one‐dimensional models. A quasi‐separation and a bandwidth‐ratio effect appears from graphs.
Decorrelators for multi‐sensor systems in CDMA networks
Authors: Kandala Srinivas , Sousa Elvino S. , Pasupathy Subbarayan
Published: September 2008

In this paper we consider a multi‐sensor detection problem in both additive white Gaussian noise (AWGN) and fading channels with the users using the channel based on a code division multiple access (CDMA) scheme. Several multi‐sensor detectors that have been studied previously do offer good performance; however, these detectors require the knowledge of the signal energies and these have to be estimated. Such an estimation might not be feasible in fading and time‐varying channels. We show how the linear optimal detector can then be simplified to obtain a decorrelating detector which does not require the knowledge of the users' signals. We show that this decorrelating detector performs almost as well as the linear optimal detector in an AWGN channel. We further investigate its performance in single‐path and frequency‐selective slowly fading channels. In a slowly fading channel when there is multi‐user interference, the conventional detector reaches a saturation point beyond which no improvement in performance can be obtained. We show that the performance of the decorrelating detector does not depend on the other users' energies and hence on the other users' fading characteristics. We further show that a decorrelating detector can be used to obtain a Rake type of receiver in frequency‐selective fading channels.
DS‐CDMA outage performance over a mobile satellite channel
Authors: Vojcic B. R. , Pickholtz R. L. , Milstein L. B.
Published: September 2008

A DS CDMA satellite uplink with power control error is considered. CDMA system performance is normally interference limited, and, in an additive, white, Gaussian noise channel, with many users, sufficient processing gain, and effective power control, individual users typically experience the average performance over all users. In this case, the other users appear as the equivalent of additional Gaussian noise and each user experiences the same environment. An alternative measure of performance under fading conditions is the probability of outage. For coded signals, the fading must be averaged over all the symbols in the code word. For properly interleaved signals and i.i.d. Rayleigh fade statistics, the average must be performed over a chi‐squared variate. The probability of outage, defined as the probability that the decoded bit error rate exceeds a specified threshold, is monotonic with the probability that the chi‐squared variate is less than a specified threshold. We derive upper and lower bounds on the outage probability for soft decision decoding.
Dynamic code allocation for integrated voice and multi‐priority data traffic in CDMA networks
Authors: Geraniotis E. , Chang Y.‐W. , Yang W.‐B.
Published: September 2008

In the context of deriving schemes for efficient use of the spectrum by multi‐media users in direct‐sequence code‐division multiple‐access (DS/CDMA) networks we describe in this paper an optimal policy for CDMA code allocation to voice and multi‐priority data traffic We consider CDMA networks with voice traffic and two types of data traffic: high priority data traffic with the same priority as voice traffic that requires real‐time delivery and lower priority data traffic that can tolerate delay and thus can be queued. A movable boundary policy in the CDMA code domain is used for the voice and high priority data, whereas a small number of CDMA codes are reserved for the lower priority data which also utilizes any CDMA codes left unused by the other two traffic types. The optimal policy is obtained by minimizing a cost function consisting of the weighted sum of the rejection rates of voice and high priority data traffic subject to performance requirements (bit error rates or BER) on all traffic types. The queueing delay of the lower priority data traffic is also evaluated. A semi‐Markov decision process (SMDP) with guaranteed BERs for voice and data traffic is used for formulating the dynamic code assignment problem. A value‐iteration algorithm is applied to this SMDP to derive the optimal policy.
Synchronous digital hierarchy byte pointer justification versus VC‐12 payload bit justification effects
Authors: Owen Henry L.
Published: September 2008

Four contributors to Synchronous Digital Hierarchy (SDH) network desynchronizer buffer fill variations are the justification bits in the VC‐12 payload, the irregular spacing of the data in the VC‐12 payload, the irregular spacing of the data in the SDH frame, and the pointer activity which contains byte activity as opposed to the bit activity in the VC‐12 itself. These phenomena result in a variation of the rate at which bits arrive at a desynchronizer in a SDH network. Modeling and understanding of these processes is required in order to be able to propose advanced pointer processor algorithms as well as advanced jitter reduction techniques in SDH de‐synchronizers. This paper examines the relative effects of bit justifications in VC‐12 payloads in conjunction with the corresponding byte justifications in SDH networks in order to determine the dynamics of SDH network plesiochronous desynchronizer buffers.
History of education of telecommunications engineers in italy
Authors: Stracca Giovanni B.
Published: September 2008

The paper analyzes the history of education of telecommunications engineers in Italian engineering, schools, the aim being to provide a stimulus to analyzing the parallel development of this education also in other European countries. It covers the time from the 19‐th century, when telegraphy and telephony were the first practical applications of scientific knowledge concerning electrical phenomena, to recent years, when a “laurea” (5 year degree course) and a “diploma universitario” or D.U. (3 year degree course) in telecommunications engineering were introduced into Italian universities. The evolution of the teaching of telecommunications engineering is compared with the parallel development of telecommunications services and of related scientific knowledge. Whereas the main Italian engineering schools introduced curricula for electrical engineering early in the 19‐th century, due to early recognition of the importance of electrical energy applications, there was some delay in the introduction of telecommunications disciplines into engineering curricula (though such applications were born before). The paper points out some reasons for this delay. Brief biographies of some important professors are given.
Performance of coherent and differential detection for trellis‐coded 8‐PSK over satellite flat rician fading channels
Authors: Gaudenzi Riccardo De , Vanghi Vieri
Published: September 2008

Trellis‐coded 8‐PSK (TC‐8‐PSK) modulation is a power and bandwidth efficient modulation scheme which is finding increasing applications in terrestrial and satellite systems. In particular, TC‐8‐PSK is demonstrating attractive performances over die satellite mobile fading channel where it provides considerable coding gain with respect to uncoded QPSK with no bandwidth efficiency loss. In this paper die capabilities of a decision‐directed maximum‐likelihood coherent phase tracker are investigated for flat Rician fading channel. Open loop and steady‐state performances of die digital phase tracker are analytically determined and verified by means of computer simulations. By optimizing phase loop parameters in presence of Rician fading with respect to the mean time to lose lock, it is shown that, for typical satellite fading channels, die coherent decision‐directed phase tracker performs poorly. This is also true for feed forward decision‐feedback phase estimator. In these cases, the additional power loss required by differential detection of TC‐8‐PSK respect to coherent detection has been evaluated by means of computer simulations.
A study on spectral optimisation in partial response CPM signals
Authors: Campanella Matteo , Garbo Giovanni , Mamola Giovanni , Randazzo Edoardo
Published: September 2008

An optimisation technique for the minimisation of the effective bandwidth in partial response CPM signals is described. The minimum Euclidean distance is used as optimisation constraint because the bit error probability is a function of this parameter for high values of signal to noise ratio. The procedure has been implemented for a correlation length corresponding to two signalling intervals. The optimisation problem leads to a system of two nonlinear differential equations for the pulse shape, together with some boundary conditions. Numerical solution of the differential equations has been performed; initial conditions have been adjusted, to satisfy the boundary conditions using an iteration method based on the Newton‐Raphson algorithm. The whole procedure is based on a particular assumption about the minimising difference sequence for the minimum Euclidean distance. This assumption has been tested and the limit value of the modulation index satisfying the test is also reported.
Applications of the kohonen algorithm in vector quantization
Authors: Poggi Giovanni
Published: September 2008

The paper deals with the exploitation of the codebook‐ordering property of the Kohonen algorithm in vector quantization (VQ). First, the substantial equivalence between the Kohonen algorithm and the generalized‐Lloyd algorithm in terms of encoding performance for memo‐ryless VQ is established. Then, algorithms based on the use of Kohonen ordered codebooks are proposed to solve different problems in VQ such as rate reduction, progressive transmission, and channel‐error protection.
Wireless infrared factory network for hand‐held terminals
Authors: Roviras Daniel , Lescure Marc , Bensalah Rachid , Bosch Tthierry
Published: September 2008

An experimental wireless infrared network with ISDN compatibility is described. This factory network has been studied in a European project: “FCPN” (Factory Customer Premises Network). The architecture of the network is a cellular one. Infrared cells are connected together by a high‐speed optical fiber backbone. Hand‐held terminals communicate via an infrared (IR) channel based on a diffusion technique. The communication protocol on the infrared channel is based on the ISDN protocol with standard ISDN rate (2 x 64 kbits/s + 16 kbits/s)r Measurements of diffusion properties of standard construction materials are presented. These properties are in good agreement with the requirements of an indoor IR diffuse transmission. Architectural choices for the IR transceiver are discussed with special emphasis on consumption reduction for mobile‐terminals autonomy improvement. Key elements of the IR transceiver implementation are described. Experimental results for an IR diffuse channel are presented, showing the suitability of such a transmission technique for indoor hand‐held terminals. Performances of the system are described in term of Bit Error Rate measurements.
Fast texture segmentation for object‐oriented video coding
Authors: Lavagetto Fabio , Cocurullo Fabio
Published: September 2008

Object‐oriented approaches to still and moving picture coding, thanks to the extensive use of efficient algorithms for image segmentation and region coding, are expected to improve significantly the rate‐distortion performances of conventional block‐based methodologies. Recent results show that most of the chances to win this challenge depend on the efficiency in image segmentation: the precise aim of our investigation and the purpose of this paper is just to show the concrete possibility of employing fast adaptive algorithms for segmenting images and video frames and allowing high quality coding with very high compression. The segmentation algorithm we propose relies on the recursive computation of the Spatial Gray Level Dependence Matrix (SGLDM) and on a fast adaptive procedure for the statistics evaluation. Subsequent clustering of the image pixels in the 5‐dimensional statistical‐spatial space MVCXY, composed of local mean (M), local variance (V), local correlation (C) and spatial coordinates (XY) is encharged of providing final image segmentation. Target applications for videophone coding of color sequences at very low bitrate are foreseen.
Lossless hierarchical storage of images
Authors: Piscaglia Patrik , Macq Benoit
Published: September 2008

Nowadays, more and more images from every area need to be stored. If a lossless compression of the image is desired, the storage space requirements can still be enormous. The aim of this paper is to show how to store those images in such a way that a quick access AND a big storage capacity are available together. The tools used are a multi‐resolution entropy coding (the Haar transform and the Universal Variable Length Coder) combined with a hierarchical quantization (the slicing) of each resolution. The main idea is to have a small icon stored on a fast access media, instantly accessible, while the high resolution components are stored on mass media and are loaded only if needed. The total compression is lossless.
Combination of simple vision modules for robust real‐time motion tracking
Authors: Denzier Joachim , Niemann Heinrich
Published: September 2008

In this paper we describe a real time object tracking system consisting of three modules (motion detection, object tracking, robot control), each working with a moderate accuracy, implemented in parallel on a workstation cluster, and therefore operating fast without any specialized hardware. The robustness and quality of the system is achieved by a combination of these vision modules with an additional attention module which recognizes errors during the tracking. For object tracking in image sequences we apply the method of active contour models (snakes) which can be used for contour description and extraction as well. We show how the snake is initialized automatically by the motion detection module, explain the tracking module, and demonstrate the detection of errors during the tracking by the attention module. Experiments show that this approach allows a robust real‐time object tracking over long image sequences. Using a formal error measurement presented in this paper it will be shown that the moving object is in the center of the image in 90 percent of all images.
A new suboptimum viterbi receiver structure for digital communication systems
Authors: Behm Wolfgang , Fliege Norbert J.
Published: September 2008

Minimization of the average symbol error probability is the central aim when designing a receiver structure of a digital communication system. It is well known that the maximum‐likelihood (ML) decision rule yields the best solution in this sense. In practical applications, the ML sequence estimation is realized by the computationally efficient Viterbi algorithm. As a drawback, however, the computational complexity of this algorithm depends exponentially on the length of the channel impulse response. In this paper, a new suboptimum receiver structure is presented containing a linear recursive equalizer for channel memory truncation and a Viterbi detector. The criterion for adjusting the equalizer and the remaining impulse response for the Viterbi detector is derived from the zeros of the channel transfer function. The proposed concept takes control of both the noise enhancement by the equalizer and the computational complexity of the Viterbi algorithm.
On the error burst properties of the “standard” K = 7, rate‐1/2 convolutional code with soft‐decision viterbi decoding
Authors: Franchi Antonio , Harris Robert A.
Published: September 2008

The error burst properties of the “standard” rate‐1/2, K = 7, convolutional code (generators 133,171) with soft‐decision Viterbi decoding are studied. The average burst length is determined by computer simulation as a function of Eb/N0. At low Eb/N0 it is shown to depend strongly on the criterion used to define a burst. The distribution of burst lengths is well modelled by a geometric distribution which depends only on the average burst length. At high Eb/No, the distribution is that of the code words at the minimum Hamming distance from any given code word. A simple heuristic model, valid at low Eb/Na, is developed for predicting the average number of errors in an error event of given length. This is validated by computer simulation. At high Eb/N0 the distribution is also determined by that of the minimum distance code words. For both models there is a smooth transition between the two extremes. The simple, low Eb/N0, models are combined to derive an estimate for the average error‐density for all bursts. Although neither model individually is a good fit at high Eb/N0, the composite model agrees well with computer simulations at all values of Eb/N0. This paper also serves to gather material from a number of widely spread sources into a single place, providing a coherent treatment. A number of useful empirical relationships are derived from the simulation results.
Capacity assignment for circuit‐switched reference networks with nonhierarchical routing
Authors: Hartmann Harro L. , He Hucang
Published: September 2008

Capacity assignment (CA) implies the minimization of network cost subject to several constraints, such as traffic demands, end‐to‐end Grade of Services (GOS) and the non negativity conservation of flows. Real asymmetric networks may be described by several statistical moments of different orders. Thus a reference network may be characterized by the mean distance between a given set of fully intermeshed nodes, the mean traffic offered per demand pair, and the mean GOS for all end‐to‐end blockings. At first, we present an exact theoretical solution of the CA‐problem for symmetric circuit‐ switched networks. We start with the formulation of the end‐to‐end blockinges with nonhierarchical two‐link path alternate routing for reversible and nonreversible scheme, respectively. Next, we derive the Kuhn‐Tucker conditions for the CA‐problem. The corresponding solution is verified to be unique and stable. Then, we proceed to approximate the relevant optimal parameters, such as the economic high link blocking, the optimal size of routing sequences and the minimum link size, by using least‐square fitting. The results form new rules of thumb for a wide range of traffic demand and GOS and may thus be used to support the initial dimensioning of asymmetric nonhierarchical networks. Finally an approximation for asymmetric networks is proposed and verified, which is based on an appropriate CA decomposition and relevant traffic parameters of both the symmetric reference and its asymmetric extension.
Codes and iterative decoding on general graphs
Authors: Wiberg Niclas , Loeliger Hans‐Andrea , Kotter Ralf
Published: September 2008

A general framework, based on ideas of Tanner, for the description of codes and iterative decoding (“turbo coding”) is developed. Just like trellis‐based code descriptions are naturally matched to Viterbi decoding, code descriptions based on Tanner graphs (which may be viewed as generalized trellises) are naturally matched to iterative decoding. Two basic iterative decoding algorithms (which are versions of the algorithms of Berrou et al. and of Hagenauer, respectively) are shown to be natural generalizations of the forward‐backward algorithm (Bahl et al.) and the Viterbi algorithm, respectively, to arbitrary Tanner graphs. The careful derivation of these algorithms clarifies, in particular, which a priori probabilities are admissible and how they are properly dealt with. For cycle codes (a class of binary linear block codes), a complete characterization is given of the error patterns that are corrected by the generalized Viterbi algorithm after infinitely many iterations.
Separable concatenated convolutional codes: The structure and properties of a class of codes for iterative decoding
Authors: Lodge John H. , Young Richard J. , Guinand Paul S.
Published: September 2008

In this paper a brief overview of the concept of iterative processing is provided. Then a code construction for convolutional codes, that results in a signal structure amenable to iterative processing, is studied. This construction is analogous to product coding for block codes. It is shown that the construction shares a number of properties with die product coding construction, including the property that it is “commutative”. The relationship between the free distance and the interleaving factors is examined, and then exemplified with computer simulation results.
Weight distributions and bounds for turbo‐codes
Authors: Svirid Yuri V.
Published: September 2008

An optimal interleaving between two component encoders of a turbo‐code is proposed. The optimally criterion for any real constructable interleaver is given. For component codes with known weight distribution (WD), the WD of the turbo‐code with optimal interleaving is calculated. Furthermore, a method for approximate calculation of the WD of convolutional code with terminated feed‐forward and feed‐back encoders is proposed. Using this WD's and proposed interleaving, the union upper bounds on the bit error rate of the turbo‐code are given. It is shown that the often observed “break” in the performance curves of turbo‐codes is a result of their “broken” WD. For component codes lying on the Gilbert‐Varshamov bound, an upper bound on the ratio between the minimum distance of the turbo‐code and the component code is determined. The lower bounds on the signal‐to‐noise ratio needed to achieve error free decoding of turbo‐codes with random component coders are given. These bounds are compared with the Shannon limit and analogous bounds for random codes.
Effect of transmitter filter on the performance of FSK‐DPD and DPSK‐DPD in satellite mobile channel
Authors: Korn Israel
Published: September 2008

We study the effect of bandlimiting transmitter filter on the bit error probability (BEP) of M‐ary Frequency Shift Keying and Differential Phase Shift Keying with Differential Phase Detector in Satellite Mobile Channel. Numerical results are presented in the case when the transmitter and receiver filters are Butterworth filters of order NT = 4 and NR = 3 respectively. The BEP is reduced with increasing transmitter bandwidth with a minimum at infinite bandwidth, i.e. no transmitter filter. However finite values of this bandwidth can be used without significantly increasing the BEP. In the computation of the BEP we optimised various parameters, like the receiver bandwidth, sampling time, modulation index (for FSK only) and decision level.
Generalized cut‐off rate of DPSK noisy‐phase channels
Authors: Dallal Yeheskel E. , Shamai Shlomo
Published: September 2008

Coded communication is examined for binary differential phase shift keying (DPSK) modulation where the communication channel consists of both a Brownian Motion phase noise and an additive white Gaussian noise (AWGN). Decoding utilizes a mismatched soft‐decision metric that accounts for the prefiltering of the phase‐noise‐impaired signals followed by differential demodulation. Binary Multiplexing of the equivalent channel results in a binary‐input, output‐symmetric, discrete‐time, coding channel, which is both stationary and memoryless. This multiplexing accounts as well for an underlying time‐diversity (repetition codes), providing an effective, yet simple, means of boosting the capabilities of less powerful codes to cope with high phase‐noise levels. The cut‐off rate of the considered channel is analytically too complicated to compute. The approach taken yields a coding channel characterization that further generalizes the concept of the generalized cut‐off rate for mismatched metrics to account as well for incomplete statistical characterization. The theoretical implication of this criterion for coded communication is examined. The Brownian Motion phase model is characterized by a finite set of the univariate moments admitted by certain exponential functional of the phase sample path, whose exact statistics seem intractable.
The effect of non‐ideal interpolation on symbol synchronizer performance
Authors: Bucket Katrien , Moeneclaey Marc
Published: September 2008

This contribution deals with the symbol synchronizer performance of a fully digitally implemented receiver, operating on a narrowband M‐PSK signal (one‐sided bandwidth not exceeding the symbol rate). The considered digital receiver operates on samples of the complex enveloper(t)of the received signal, taken by afixedclock which isnot synchronizedto the transmitter clock. The synchronized samples required for the symbol synchronization algorithm are computed byinterpolatingbetween the available non‐synchronized samples. Because of finite memory, interpolation is non‐ideal; hence, some amount of distortion is introduced, which affects the performance of the symbol synchronizer. By means oftheoretical analysis, we investigate the tracking performance of a specific decision‐directed feedback synchronizer, assuming interpolation of orders zero, one and two. We show that non‐ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that mainly occur near/= 0 when the number of samples per symbol is close to an integer. Unless a sufficiently small loop bandwidth is chosen, the contribution of these spectral lines could dominate the timing error variance, which then becomes much larger than for synchronized sampling.
Multilevel differential modulation techniques (64‐DAPSK) for multicarrier transmission systems
Authors: Engels Volker , Rohling Hermann
Published: September 2008

In Digital Video Broadcasting (DVB) applications the objective is to transmit a high data rate of 34.368 Mbit/s in a single channel. For terrestrial digital transmission the considered radio channel bandwidth is 7 or 8 MHz. In this paper we analyse the performance of a multicarrier transmission technique, the well‐known Orthogonal Frequency Division Multiplexing (OFDM) method, and consider the system parameters for this DVB application. For the OFDM transmission technique an absolute modulation scheme (64‐QAM) has been suggested. In this case and in frequency‐selective interference situations a channel estimation process and a channel equalization are necessary [4], The equalization process can be realized by a multiplier bank at the FFT output in the receiver, a so‐called frequency‐domain equalizer. Alternatively, a multilevel differential modulation technique, the so‐called Differential Amplitude and Phase Shift Keying (64‐DAPSK) is proposed in this paper, in which the phase and the amplitude are used simultaneously for differential modulation. A differential modulation technique does not require any explicit knowledge about the radio channel properties in the differential channel equalization process. In an OFDM/64‐DAPSK receiver it is therefore not necessary to implement a frequency‐domain equalizer, which reduces the computation complexity. The performance of both modulation techniques has been analysed in the uncoded case referring to Gaussian and frequency‐selective Rayleigh fading channels. The results are described in this paper.
256‐state trellis code with 12‐D rectangular constellation using an extended wei method
Authors: Sterian Corneliu‐Eugen D.
Published: September 2008

The Wei's method of constructing trellis codes with 2N‐D rectangular constellations is limited to N being an integer power of two. In the present letter to the editor, this limitation is removed and the example of a 256‐state, rate 4/5 linear trellis code with 12‐D rectangular signal set is given.
On information rates in fading channels with partial side information
Authors: Kaplan Gideon , Shamai Shlomo
Published: September 2008

A coded antipodal communication system operating over a Rayieigh fading channel is considered. A partial Side Information (SI) scheme is addressed, where the receiver has an access to the sum of received faded energies over several consecutive symbols. The generalized cut‐off rate is examined both for the independent and for the correlated fading models, and conclusions regarding the usefulness of this particular SI scheme are drawn.
About optimum slave clock bandwidth on SDH equipment
Authors: Ciammaichella Pietro , Ricchiuti Vittorio
Published: September 2008

In order to improve reliability, the modern telecommunication systems require hardware redundancy. In particular, many SDH devices include two timing units, locked to the same reference signal, that can provide each one in its turn a synchronization signal to the transmission units. Any switch between the two timing units produces a phase step on the input of the slave' clock linked to the synchronization signal. In this paper, with reference to a slave clock model based on Phase Locked Loop (PLL) system, it is derived the optimum PLL bandwidth that produces a good output short term stability in terms of MRTIE compliant with SDH Recommendations.
Stability requirements of oscillators used for synchronization loops in communication systems
Authors: Welti Arnold L. , Bernhard Urs P.
Published: September 2008

An imperfect clock timing recovery in receivers of modern communication systems degrades the performance of synchronization loops and, hence, the overall system reliability and data transmission quality. In this paper, the phase‐locked loop (PLL) for the carrier recovery and the delay‐locked loop (DLL) for the clock timing recovery of the pseudonoise (PN) code in direct‐sequence spread‐spectrum systems are analyzed regarding the impacts of imperfect oscillators (including phase noise and a frequency offset between transmitter and receiver) and channel noise on the mean exit time. The optimal design considerations to achieve a maximum mean exit time for second‐order synchronization loops can be used to find the required oscillator stability,Le., the maximum tolerable frequency offset and oscillator phase noise.
N‐branch diversity reception of mary DPSK signals in slow and nonselective nakagami fading
Authors: Fedele Gennaro
Published: September 2008

The problem of diversity reception of M‐ary differential phase shift keying modulated, signals in the presence of additive white Gaussian noise and Nakagami‐distributed slow and non‐selective fading is addressed. N‐branch selection diversity and maximal ratio combiners are considered. The average symbol error rate is analytically evaluated in terms of integral expressions, which can be easily computed via numerical integration routines. Numerical results are presented that allow one to point out those operational situations where diversity systems can operate successfully to mitigate the degrading effects of short‐term fading.
Improved performance of fast acquisition PLL synthesizer withN‐stage cycle swallower
Authors: Saba Takahiko , Park Duk‐Kyu , Mori Shinsaku
Published: September 2008

The PLL frequency synthesizer with anN‐stage cycle swallower (NSCS) is one of the fastest frequency switching synthesizers. The synthesizer, however, requires many stages in theNSCSto obtain accurate output frequencies. In this paper, to obtain both more accurate output frequencies with a few stages and a higher speed acquisition time, we propose two methods for improvingNSCSswitching operation. First, by allowing theNSCSoutput frequency to be variable a large range of choices in the division ratios becomes available in theNSCS. The proposed synthesizer has the output frequency of deviation within 0.0003 ppm when the 3‐stage cycle swallower is employed. Second, by temporarily increasing the expected amount of the variation in the output frequency, the acquisition time of theNSCSsynthesizer can be improved. Experimental results confirm that the proposed technique results in a shortened acquisition time.
A deterministic method for the derivation of a discrete WSSUS multipath fading channel model
Authors: Pätzold Matthias , Killat Ulrich , Shi Yu , Laue Frank
Published: September 2008

Abstract A suitable and often used stochastical model for the description of the fading behaviour of a time variant and frequency‐selective channel is the wide sense stationary uncorrelated scattering (WSSUS) model. Usually, the wide sense stationary process is assumed to be a zero mean Gaussian process. In such a case, the WSSUS model is completely determind by the so called scattering function. In order to approximate a desired scattering function of a WSSUS model by a simulation model, it is well known that Monte Carlo based methods cm be used for the computation of the simulation model parameters (discrete echo delays and discrete Doppler frequencies). In this paper, we present a new method, which results always in a better approximation of a prescribed scattering function of a WSSUS model than the Monte Carlo principle. We show that the statistical behaviour of the resulting fading channel model ‐ in particular the level‐crossing rate and the average duration of fades ‐ is not only independent of a random realization of the discrete echo delays and discrete Doppler frequencies, but is also extremely close to the statistical behaviour as it was to be expected from the theory.
Letter: Large families of polynomial phase sequences with low correlation
Authors: Luke Hans Dieter
Published: September 2008

Large families of ≈ pQ (p prime, Q = 2, 3, 4.,) polynomial phase sequences are presented. The p‐ary sequences are of length p. Their correlation magnitudes are upper bounded by ≈ Q √p. The families are suitable for application in asynchronous CDMA systems.
Letter: A method of spread spectrum radar polyphase code design by nonlinear programming
Authors: Dobrosavljevic Zoran S. , Dukic Miroslav L.
Published: September 2008

A method of spread spectrum radar polyphase code design based on the code elements' symmetry and nonlinear programming is presented. The main features of the synthesized code are the very low sidelobes in the compressed pulse and noncoherent processing. The comparison to the well‐known classes of polyphase codes is made.
Letter: Opportunistic channel for sending an extra 300 bit/s using a trellis coded modulation scheme which transmits 9.6 kbit/s on telephone lines
Authors: Sterian Corneliu‐Eugen D.
Published: September 2008

It is shown that the TCM scheme with 8‐D rectangular constellation designed by Tretter [1] based on a well known method invented by Wei [2] can support an opportunistic channel which can transmit 300 bits/s.
Bit error rate performances of M‐QAM orthogonal multicarrier modulation in presence of time‐selective multipath fading
Authors: Santella Giovanni
Published: September 2008

Orthogonal Frequency Division Multiplexing (OFDM) is considered as an effective technique in high speed digital transmission under multipath fading. In this paper we theoretically analyze the behaviour of a coherent pilot‐symbol aided M‐QAM‐OFDM system in presence of time selective multipath channel. In the analyzed scheme, pilot symbols are periodically inserted to monitor the channel characteristics. The fading process experienced by the pilot symbols is used to estimate the fade characteristics at symbol‐rate through interpolation. The estimated channel is used to compensate for the random phase variation caused by the Doppler spread, so that the signal can be coherently demodulated. The bit error rate (BER) performance of this coherent OFDM modulation scheme is derived. The obtained results show that, with a reasonable amount of redundancy (frequency of the pilot symbols) introduced, the system performance approaches that of the ideal coherent demodulation, as long as a suitable channel estimate procedure is adopted.
Performance evaluation of a continuous‐phase CDMA modem operating over the 60 GHz mobile radio channel
Authors: Giannetti Filippo , Luise Marco , Reggiannini Ruggero
Published: September 2008

This paper (1) describes the structure and the performance of a band‐limited spread‐spectrum transmission system suited for short‐range terrestrial inter‐vehicle or vehicle‐to‐beacon radio links that features Generalized MSK as modulation format and asynchronous direct‐sequence code‐division multiple access. The Bit Error Rate (BER) performance of such a system is evaluated over a recently proposed 60 GHz short‐range mobile radio channel model. In particular, the sensitivity to a number of relevant link parameters (such as the distance between transmit and receive antennas and the receiver speed) is investigated, and the impact of code tracking errors and of differential encoding/detection of the spreading code chips on system performance is also discussed.
Letter: Optimal echo path modelling using chaotic modulated speech
Authors: Milner Simon H. , Elmirghani Jaafar M. H. , Cryan R. A.
Published: September 2008

A novel modulating scheme is presented that allows optimal echo path modelling using, real time least mean square (LMS) system identification techniques. The systems of interest are usually based on a class of digital adaptive filters (DAFs). The modelling convergence rate derived from the optimal Wiener weights defines the performance criterion. A novel chaotic based modulation regime utilising the logistic mapping is exploited to whiten the speech power spectral density (PSD) whilst preserving the signal bandwidth requirements. The whitened signal optimises the convergence rate and allows adaptation times to be calculated without a‐priori knowledge of the speech signal's second order statistics. Software simulations are reported for an ensemble of conversational speech realisations and it is shown that the described modulation scheme significantly improves the convergence rate and guarantees optimal modelling independent of the input speech signal statistics. Furthermore, the noise whitened input signal circumvents control supervisory problems usually associated with uncoded speech inputs.
PPM transmission over a photon counting channel: Comparison among various transmission formats
Authors: Cancellieri Giovanni , Chiaraluce Franco , Gambi Ennio
Published: September 2008

A detailed analysis for a variety of transmission formats suitable for photon communication systems is presented. More precisely, starting from the basic orthogonal pulse position modulation (PPM), here assumed as a reference, several alternative modulation schemes are discussed. They can be seen as extensions of the basic format or. equivalently, as particular cases of the most complete alphabet obtained by considering all the possible combinations of high and low levels in a transmission organized over slotted time intervals. The analysis is developed in comparative terms, looking at the three parameters which are usually invoked for performance evaluation, i.e. transmission capacity, cut‐off rate and bit error rate. Closed form expressions are given in all the examined cases, stressing the role, as figures of merit, of the transmission efficiency and the bandwidth expansion factor. At a parity of the latter parameter, it is shown that the performance of basic PPM can be improved, even significantly, by resorting to the alternative transmission formats. In particular, they maintain the spectral occupancy within acceptable limits, whereas the bit error rate can be lowered using alphabet puncturation or asymmetric error correcting codes.
Performance measurements and traffic characterization on the ATM pilot network
Authors: Louvion Jean‐Raymond , Piller Benoit
Published: September 2008

From mid‐94 to end‐95 the “Performance Working Group (PWG)” of the ATM PILOT has carried out a lot of measurements (in relationship to functions available on test equipments). The results obtained were mainly related to ATM layer performance measurements (availability and non time‐related performance parameters) and to traffic characterization. Performance measurements aimed at checking the validity of the set of proposed or standardized ATM layer performance parameters, at studying the sensitivity of the parameters definitions and at obtaining early results in order to propose performance objectives for the relevant recommendations. These results have shown that the ATM layer performance is very much dependent of the observation period of time and of the physical path of the connection under test. Furthermore it has been observed that the ATM layer performance is not so sensitive to the parameter definitions and the associated thresholds. Traffic characterisation is necessary to identify what is going on in the network (will the cells be equally spaced or will they come in bursts ?). The PWG had taken the opportunity to do field trials with real traffic coming from Pilot and has carried out a range of tests on both CBR sources (carrying voice or video applications) and VBR sources (multimedia application or LAN to LAN interconnection). Two main traffic types have been observed during the tests:

CBR sources carrying voice or video applications.

VBR sources with multimedia applications or LAN to LAN interconnection using the SMDS/‐CBDS service.
Performance of open loop digital frequency estimation techniques for burst‐mode transmission
Authors: Di Girolamo Rocco , Le‐Ngoc Tho
Published: September 2008

This paper presents the variance analysis, and performance comparison, of the least‐squares frequency estimator (LSFE), and a specific version of the nonlinear frequency estimator (NIX). The results are obtained for the case where the received signal contains both phase and frequency errors (ΔΘ and Δfrespectively). It is shown that under rather restrictive conditions, the LSFE is a low signal‐to‐noise ratio approximation to the ML estimate of ΔfAlso considered are the effects on the moments of this estimate, if any of these conditions are violated. The latter part of the paper deals with the various versions of the NFE. The problem of phase ambiguity associated with these nonlinear estimators is investigated, and a resolution technique is proposed.