bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal and sub‐optimal maximum a posteriori algorithms suitable for turbo decoding
Authors: Robertson Patrick , Hoeher Peter , Villebrun Emmanuelle
Published: September 2008

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

Methods for the evaluation of the outage probability in mobile radio systems have been widely investigated, but analytical results have been published only for Rayleigh fading radio channels. For the case of Rice fading, only approximated results have been found. In this paper, an exact expression of the outage probability for a subscriber of a CDMA cellular mobile radio system, with the radio channel impaired by Rice fading and log‐normal shadowing superimposed is given.
Letter: Low bit‐rate vector quantization with progressive transmission
Authors: Poggi Giovanni
Published: September 2008

This paper proposes a VQ‐based coding scheme to perform the fast progressive transmission of images. The basic idea is to exploit the inter‐block correlation by jointly encoding the indexes generated by the vector quantizer. The use of ordered codebooks for VQ guarantees that the indexes are highly correlated and therefore that the compression will be successful. In order to preserve the progressive transmission property, the compression is carried out at the bit‐plane level, by means of a classified‐predictive encoding scheme. Numerical experiments on well‐known test images show a rate reduction of about 30% in case of full‐transmission, and of over 60% in case of partial‐transmission, the latter being by far the most common situation in the applications.
Improving the performance of CDMA systems in a multipath delay and fading environment
Authors: Hu Lan , Burkley Cyril J.
Published: September 2008

In this paper, a new channel filter is proposed for a CDMA direct‐sequence spread‐spectrum system in a multi‐user and multipath delay and fading environment. In the proposed system, the channel filter is placed before the acquisition system to overcome the multipath delay and co‐channel interference effects. Monte Carlo simulation is used to evaluate and compare the performance of the system in terms of multi‐user interference and multipath delay both with and without the proposed channel filter. Results show that the proposed technique can significantly improve the overall system performance. Details of the system configuration, the design concept of the channel filter and the simulation techniques used are discussed.
Letter: Doppler optimised compression filters for both aperiodical and periodical sequences
Authors: Zejak Aleksa J. , Dukić Miroslav L.
Published: September 2008

The problem of designing Spread Spectrum (SS) radar detection filters that minimise sidelobe (SL) levels in both Doppler and range co‐ordinates is considered and a new algorithm for the Doppler optimised mismatched filter is presented. The Iterative Reweighted Least Square (IRLS) procedure for minimax filter coefficients calculation is applied. A special attention has been paid to the analysis of Code Division Multiple Access (CDMA) SS communication systems. The computer simulation results obtained show that SL levels rejection using a new algorithm is very high, both for aperiodical and periodical sequences.
Robust programmable‐rate wireless graphical correspondence
Authors: Hanzo Lajos , Yuen Andy H.
Published: September 2008

An adaptive fixed‐length differential chain coding (FL‐DCC) scheme is proposed for the transmission of line graphics, which canbe re‐configured as a lower rate, lower resolution or higher rate, higher resolution source codec. Compared to Differential Chain Coding (DCC), the proposed FL‐DCC codec has a lower coding rate in both of its lower‐ and higher‐rate operating modes, while maintaining a similar subjective graphical quality. The dual‐rate re‐configurable FL‐DCC codec is embedded in a voice, video multimedia communicator system, which allocates the FL‐DCC graphics packets to idle speech packets with the aid of the Packet Reservation Multiple Access (PRMA) multiplexer. In a bandwidth of 200 kHz, which is characteristic of the Pan‐European GSM system, nine speech, video and graphics multimedia users can be accommodated using bandwidth efficient 16‐level Quadrature Amplitude Modulation (16QAM) over benign microcellular channels. Under less favourable propagation conditions the more robust, but less bandwidth efficient 4QAM mode of operation can be invoked. In the diversity‐aided and automatic repeat request (ARQ) assisted 16QAM mode of operation the multimedia user bandwidth becomes 22.2 kHz and the minimum required channel signal to noise ratio (SNR) over AWGN and Rayleigh channels is about 11 and 15 dB, respectively. The most salient system features are summarised in Table 2.
A new software architecture for evolvable multimedia software
Authors: Itoh Jun‐Ichiro , Yokote Yasuhiko , Feret Michel
Published: September 2008

This paper describes the Micro Virtual Machine and the operating system (OS) interface that Sony has designed and implemented for Sony's future products such as set top boxes and servers for the delivery of on‐line multimedia services. This article is derived from a proposal document presented at the 11‐th meeting of the Digital Audio‐Visual Council (DAVIC) held in Berlin in December 1995. The technologies presented in this paper were first used at Telecom 95 in Geneva and later in the DAVIC inter‐operability trials which took place in Tokyo in the Fall of 1996.
Feedforward frequency estimation for PSK: A tutorial review
Authors: Morelli Michele , Mengali Umberto
Published: September 2008

This paper considers feedforward carrier frequency estimation methods in burst‐mode digital transmission, with tutorial objectives foremost. Assuming PSK modulation, two scenarios are envisaged in which frequency estimates are derived either from a preamble appended to the data block, or directly from the modulated signal. Several estimation algorithms are considered with different and somewhat contrasting characteristics. The characteristics we focus on are: estimation accuracy, estimation range, minimum operating signal‐to‐noise ratio (threshold), and implementation complexity. They provide a framework within which current estimation methods can be evaluated. The paper reviews and compares some prominent algorithms proposed in literature, trying to single out the best ones for a given application.
Adaptive linear interference suppression for packet DS‐CDMA
Authors: Honig Michael L.
Published: September 2008

The performance of adaptive linear interference suppression is studied in the context of packet DS‐CDMA. A multi‐cell system is assumed with stochastic arrivals and departures of asynchronous users, and additive Gaussian noise as the only channel impairment. Interference suppression is achieved with a tapped‐delay line filter, where the filter spans a single symbol interval. Adaptive algorithms considered include the stochastic gradient (LMS), exponentially‐weighted Least Squares (LS), block LS, and a reduced‐rank LS algorithm. The reduced‐rank LS algorithm first projects the received signal onto a signal sub‐space spanned by eigenvectors of the averaged outer product matrix of received vectors. The purpose of the projection is to eliminate low‐level background interference and noise. Both decision‐directed and blind algorithms, which do not require a training sequence, are compared. Computer simulation is used to obtain error rates as a function of traffic load, and algorithm and system parameters (including timing offset). Results indicate that the adaptive algorithms offer a significant increase in capacity (nearly a factor of two at moderate error rates), and are insensitive to variations in received power over the user population.
Measurements and simulations of cell delays in ATM switches
Authors: Wittevrongel Sabine , De Vleeschauwer Danny , Bruneel Herwig , Brinkmann Axel , De Vries Rein
Published: September 2008

Within the RACE project EXPLOIT, traffic experiments are being performed on an ATM testbed, the EXPLOIT Testbed, which is situated in Basel. A subset of these experiments is described in this paper. Specifically, the network performance parameter cell delay, and especially the part due to queueing effects, is focused on. The aim of this paper is to compare the measurement results with the results of a generic simulation model based on renewal theory. It is shown that the simulation model predicts the delay histogram very well, but slightly underestimates the covariance over time of die delays.
Lettereffect of enhanced leaky bucket parameters on the maximum queue length: Worst‐case analysis
Authors: Wu Jung‐Shyr , Su Shyh‐Wen
Published: September 2008

In ATM networks, various usage parameter control (UPC) strategies are used to regulate incoming traffic according to the characteristics of the sources declared at call set‐up. Among these UPC schemes, the Leaky Bucket method is well‐known and has been discussed extensively. In this paper, we study the characteristics of the multiplexer in which cell arrivals are first policed by Enhanced Leaky‐Buckets (ELBs) before entering the system. In addition to both policing mean cell rate and peak cell rate, cell delay variation (CDV) are also taken into consideration for each ELB. We derive the upper and lower bounds on the maximum queue length expressed as a funtion of the ELB parameters and the number of sources. We also rigorously prove that these bounds occur with respect to a coincident token‐generating pattern and a perfectly interleaved token‐generating pattern, respectively.
Demodulation and decoding of trellis coded continuous phase modulations in an incoherent mobile radio environment
Authors: Abrardo Andrea , Mori Alessandro , Benelli Gluliano
Published: September 2008

Digital communication systems using Trellis Coded‐Continuous Phase Modulations (TC‐CPM) have been shown to be power efficient, both for coherent and incoherent detection. In this paper some techniques for the incoherent detection of TC‐CPM signals in a radio‐mobile environment are studied. Two different differential decoding algorithms for the detection of TC‐CPM are presented. The first one is a Viterbi algorithm characterised by a reduced number of states when compared with the classical coherent Viterbi detector. The second one is a modified SAN(B) algorithm for the incoherent detection of convoluttonally encoded CPM over a mobile radio environment. Comparisons with the coherent Viterbi decoder show that the proposed algorithms are quite attractive, especially in the case of frequency non‐selective radiomobile channels.
Analysis of the effect of phase noise in OFDM systems
Authors: Tomba Luciano
Published: September 2008

Multicarrier systems are gaining much attention for their possible application to the transmission of asynchronous transfer mode (ATM) data packets over indoor radio channels. Due to the high frequency selectivity of these channels, at data rate of some tens of Mbits/s multicarrier modulation appears a convenient technique to reduce the intersymbol interference produced by multipath propagation. However, multicarrier modulation exhibits a significant sensitivity to the phase noise of the oscillator used for frequency down‐conversion at the receiver. In order to give a quantitative measure of such impairment, in this paper we evaluate the impact of the oscillator phase noise on the system performance and, in particular, four modulation schemes are compared.
MACSE: A generic connection establishment protocol for multimedia communication residing at the OSI application layer
Authors: Orphanos George N. , Papadopoulos George D. , Koubias Stavros A.
Published: September 2008

The multiple association control service element (MACSE) described in this work is a new connection establishment protocol for the application layer of the OSI reference model (OSIRM). The objective of the protocol is efficient establishment and control of multimedia associations among multiple spatially dispersed users. MACSE defines a new OSI service to support the communication requirements of multimedia applications so as to shift the burden of setting‐up a complex call to a protocol entity, instead of the application developer. The MACSE protocol enhances the OSIRM by introducing careful service definition, service primitives and relevant parameters, as well as a non‐monolithic protocol specification. The protocol defines procedures for the negotiation and confirmation of quality of service (QoS) per association while it forms the core of a proposed architectural model which provides a coherent treatment of QoS across all layers of the OSIRM and reduces the complexity of it. Out‐of‐band, rather than in‐band, signalling at the application layer and multi‐target associations are introduced and analysed, in contrast to the structure of the well‐known OSI association control service element (ACSE) protocol. Moreover, ACSE can be considered a particular case of MACSE.
Coherent and noncoherent decoding metrics for the is‐95 reverse link
Authors: Frank Colin D. , Ling Fuyun , Scnaffner Terry M.
Published: September 2008

The IS‐95 [1] reverse link modulation chain consists of a rate 1/3 convolutional code, a bit‐level interleaver, and 64‐ary orthogonal modulator. The interleaver improves the performance of the convolutional code by intreducing time diversity. However, calculation of the log‐likelihood ratio for the combination of bil‐level interleaving and 64‐ary orthogonal modulation is difficult and may require detailed knowledge of the channel fading process. Several decoding metrics have teen published in me literature including the single‐ and dual‐max metrics [2, 3], This paper presents two decoding metrics, the weighted dual‐max and the coherent dual‐max, which are non‐parametric, reasonable in complexity, and which improve on die performance of the dual‐max by 0.3 dB and 1.5 dB respectively.
Joint intersymbol and multiple‐access interference suppression algorithms for CDMA systems
Authors: Beheshti Soosan , Wornell Gregory W. , Isabelle Steven H.
Published: September 2008

Two promising classes of techniques are developed for efficient multiuser detection in code‐division multiple‐access (CDMA) communication systems subject to fading due to time‐varying multipath propagation. Both are designed to jointly suppress both intersymbol and multiple‐access interference inherent in such systems, and exploit all available time and frequency diversity. The first is a family of linear receivers for time‐varying multiuser channels that generalize familiar linear equalizers designed for traditional single‐user linear time‐invariant channels. Minimum mean‐square error, zero‐forcing, and matched‐filter versions of such multiuser detectors are all developed within a common state‐space framework, and have convenient recursive implementations. Performance issues as well as natural decision‐feedback variants of the detector structure are both discussed. The second is a family of nonlinear receivers that are specifically designed for use with spread‐signature CDMA systems on time‐varying multipath channels. These multiuser detectors employ a batch‐iterative (multipass or “turbo” stayl) decoding algorithm based on a successive‐cancellation strategy. Several aspects of the performance of this algorithm are developed, including its monotonic convergence property. Collectively, these two classes of algorithmic structures for joint equalization, interference suppression, demodulation, and detection are representative of several emerging and interrelated approaches to receiver design for next‐generation CDMA systems.
Iterative detection in code‐division multiple‐access with error control coding
Authors: Alexander Paul D. , Grant Alex J. , Reed Mark C.
Published: September 2008

A code‐division multiple‐access system with channel coding may be viewed as a serially‐concatenated coded system. In this paper we propose a low complexity method for decoding the resulting inner code (due to the spreading sequence), which allows iterative (turbo) decoding of the serially‐concatenated code pair. The per‐bit complexity of the proposed decoder increases only linearly with the number of users. Performance within a fraction of a dB of the single user bound for heavily loaded asynchronous CDMA is shown both by simulation and analytically.
Probability of error for diversity combining in DS CDMA systems with synchronization errors
Authors: Sunay M. Oǧuz , McLane Peter J.
Published: September 2008

An efficient series that is used to calculate the probability of error for a BPSK modulated DS CDMA system with chip timing and carrier phase errors in a slowly fading, multipath channel is derived. The receiver is assumed to be a coherent RAKE receiver. Three types of diversity schemes are considered: selection diversity, equal gain diversity combining and maximal ratio diversity combining. The error probability derivation does not resort to the widely used Gaussian approximation for the intersymbol interference and multiple access interference and is very accurate. The derived series for probability of error calculations is used to assess the reduction in the system capacity due to different levels of synchronization errors. For all three diversity combining schemes considered, the degradation in the system performance is expressed as an effective reduction in the system processing gain. Systems of 1.25 MHz, 5 MHz and 10 MHz are considered for different number of diversity branches and it is shown that the percentage reduction in the system capacity due to synchronization errors is approximately the same for all these systems.
A hybrid‐ARQ system using rate‐compatible trellis codes designed for rayleigh fading
Authors: Eröz Mustafa , Fuja Tomas E.
Published: September 2008

This paper presents classes of rate‐compatible trellis codes designed for channels with flat, slow Rayleigh fading. The codes are “multiple” TCM (MTCM) codes as proposed by Divsalar and Simon – i.e., codes in which multiple symbols are associated with each transition through the trellis; by applying appropriate puncturing tables to low‐rate MTCM codes we obtain families of MTCM codes, all of which can be decoded with (essentially) the same decoder. By means of computer search, several such families are obtained so that each family member is at least as good as any comparable code in the literature. (“Good” here is defined in terms of minimum time diversity and minimum squared product distance, the most important parameters for performance over Rayleigh fading channels). A protocol to implement these rate‐compatible trellis codes in a type‐II hybrid ARQ format is described. The proposed protocol selectively punctures symbols from the low‐rate code based on the observed fading values observed on each branch. Upper bounds on the resulting bit error rate are developed and the results are used to select the best adaptive code from several possibilities. Simulation results comparing the proposed scheme with fixed‐rate codes of the same throughput show substantial coding gain. Finally a protocol modification limiting the variability of the code rate over a frame is described; this modification eliminates the need for excessive buffering, with a very small effect on performance.
Orthogonal frequency‐division multiple access and its application to CATV networks
Authors: Sari Hikmet , Karam Georges
Published: September 2008

We introduce the concept of orthogonal frequency‐division multiple access (OFDMA) and investigate its application to send upstream information from subscriber premises to the cable head‐end in cable TV (CATV) networks. The carrier and timing synchronizations needed to ensure orthogonality between different subscriber signals are achieved by sending common pilot signals from the head‐end. WhereasNdemodulators are required to accommodateNsimultaneous users in conventional FDMA systems, OFDMA only requires a single demodulator followed by anN‐point discrete Fourier transform (DFT). We analyze the performance of this technique and compare it to time‐division multiple access (TDMA) which appears in several international standards. Our results indicate that OFDMA is an attractive multiple access technique which offers increased robustness to narrowband interference, impulse noise, and other signal impairments which characterize typical CATV networks.
Influence of dispersive waves on vector soliton propagation
Authors: Midrio Michele
Published: September 2008

A perturbation theory for the coupled nonlinear Schrödinger (NLS) equations is developed to investigate the effect of the background radiation on the soliton amplitude, frequency and polarization angle. By resorting to the theory of the inverse scattering transform, it is shown that the background radiation can be taken into account by evaluating the off diagonal terms of the scattering matrix associated with the coupled NLS equations. The theory is applied to the characterization of the soliton amplitude decrease observed in the propagation in the presence of loss and periodical amplification.
A feed‐forward technique for initial reference parameter estimation in burst mode PSK demodulation
Authors: Andronico Maurizio , Casale Salvatore , Corte Aurelio La
Published: September 2008

In burst mode communications, fast and efficient estimation of demodulator reference parameters is a key issue as receivers must be able to correctly synchronize on short bursts of data. To do so, it is possible to use a preamble in each data burst as long as the algorithms used require very short preambles and therefore do not degrade communication efficiency excessively. If a preamble is used, in fact, estimation performance is better than when a fully modulated carrier is used. In this paper the authors propose a novel feedforward technique for reference parameter recovery in PSK demodulation, the main characteristics of which are robustness to frequency offsets, short acquisition time and ease of implementation, even with low‐cost digital hardware. The technique is based on a very short special carrier preamble modulated by a known pattern, which allows the reference parameters to be estimated simultaneously and directly.
A Modified PRMA Protocol for Joint Voice Data Packet Wireless Networks
Authors: Capella Riccardo , Re Enrico Del , Fantacci Romano
Published: September 2008

This paper discusses the possibility of using the Packet Reservation Multiple Access (PRMA) protocol to provide spatially dispersed voice and data user terminals wireless access to a base station over a common short‐range radio channel. The case of ideal radio channel propagation conditions as well as that of non‐ideal and non‐stationary radio channel propagation conditions is considered. A modified PRMA (MPRMA) protocol is proposed in order to enhance system performance under heavy traffic load conditions. A technique to break off the possibility of accessing the common radio channel by a data user terminal is also discussed to avoid unsuccessful transmission of data packets during poor channel conditions. Performance comparisons with the standard PRMA protocol clearly point out a better behavior for the proposed MPRMA protocol.
Tight Upper Bounds for Cell Loss Probabilities and Required Bandwidth Estimation in ATM Multiplexers
Authors: Xiaoming Lru , Liming Liu , Bensaou Brahim , Tsang Danny H. K.
Published: September 2008

Estimating the cell loss probability in an ATM multiplexer is a key issue in network management and traffic control tasks such as call admission control and bandwidth allocation. In this paper, we derive a new approximation to estimate the total and individual cell loss probabilities in an ATM multiplexer fed by a superposition of heterogeneous on‐off sources. Based on this approximation, a simple algorithm is proposed to estimate accurately the aggregate required bandwidth to guarantee a given cell loss probability. Numerical results and comparisons to alternative approaches are also shown.
Array Codes Correcting Likely Burst Error Patterns
Authors: Breitbach Markus , Bossert Martin , Zyablov V. , Sidorenko V.
Published: September 2008

This contribution considers data transmission over channels which are corrupted by two‐dimensional bursts of errors. A code is constructed that allows to correct one rectangular burst. Its code rate is close to the generalized Singleton bound, and in the case of binary code symbols it can be implemented efficiently using only shift registers and XOR gates. Based on this code, constructions of codes are studied whose error correcting capabilities are restricted to a subset of rectangular bursts. When only likely error patterns can be corrected, the code rate can be raised while accepting only a small increase in error probability. In particular it will be shown that asymptotically these codes permit data transmission with arbitrarily low error probability at a rate beyond the Generalized Singleton bound.
Modeling of a Cost‐to‐Benefit Frequency Function for the Design of Wideband Wireless LANs
Authors: Ruggieri Marina
Published: September 2008

In the deployment of Wireless Local Area Networks for Wideband communications (WWLAN), a key and particularly critical role is played by the choice of the operation frequency range. In fact, different and conflicting aspects must be taken into account in order to perform an effective selection. In this perspective, the paper proposes a model of the various features which contribute to the selection of the frequency range in a WWLAN, through the introduction of a cost‐to‐benefit frequency function. The model, whose role in the design of WWLANs is also described in the paper, is adopted to explore several situations varying the model parameters. The frequency behavior of the modeled function is investigated, in order to select the optimal WWLAN operation frequencies in the range 10+60 GHz. The achieved results, which are reported and commented in the paper, indicate the 60 GHz range as a very attractive candidate for the design and development of future WWLANs.
Efficient Connection Admission Control Algorithms for Adaptive QoS Real‐Time Connections over ATM Networks
Authors: Jia Weijia , Zhao Wei
Published: September 2008

In this paper, we extend the traditional QoS model into one that is adaptive. We address how to admit real‐time connections under this new model. We investigate various search techniques in connection admission and assess their tradeoffs under different performance criteria. We show that our connection admission control algorithm with heuristic search techniques can increase the probability that a connection is admitted, and provide the best possible QoS to admitted connections while at the same time maintaining the execution time of the algorithm at a reasonable level. Many existing CAC algorithms for real‐time connections use direct testing techniques to determine if deadlines constraints can be satisfied. This is usually time consuming due to the extensive computation involved in obtaining delay bounds. We introduce an indirect testing method that can substantially reduce the execution time of CAC algorithms.
Accelerated Signalling for the Internet over ATM (ASIA)
Authors: Boyer Jacqueline , Boyer Pierre , Dugeon Olivier , Guillemin Fabrice , Mangin Christophe
Published: September 2008

To face up the rapid development of Internet services with even more growing needs in terms of quality of service and bandwidth, we introduce in this paper an accelerated signalling capability for the ATM network. As a preliminary, we draw attention to the fact that cell spacing can regulate the dynamics of TCP over ATM if the spacing period is adequately chosen. Then, we propose to associate with each Internet information flow (generated by TCP or UDP) a Deterministic Bit Rate (DBR) virtual channel connection within the ATM network. The cell spacing mechanism actually makes the cell stream of an Internet information flow compliant with a DBR connection, for which quality of service objectives in terms of negligible cell loss and bounded cell transfer delays can be guaranteed. To achieve this, we study a synchronization method between the two connection establishment procedures, namely that at the Internet protocol level and the signalling procedure for the ATM network. The ATM connection is established throughout the network via a light‐weight signalling procedure, which relies on the exchange of single cell messages consisting of Resource Management (RM) cells. The addressing system proposed for this accelerated signalling capability is that of classical IP, which is and will certainly be the predominant one in the near future.
Performance of a TCP/IP Backbone Based on Optical Packet Switching
Authors: Callegati Franco , Casoni Maurizio , Raffaelli Carla , Bostica Bruno , Burzio Marco , Masip‐Torné Jaume , Solé‐Pareta Josep
Published: September 2008

The application of the Optical Transparent Packet (OTP) network concept, as developed in the framework of the ACTS KEOPS project, in the evolving Information and Communication Network Technology is presented where users are IP traffic sources. In particular the OTP network is supposed to operate as an interconnection facility for high capacity backbone routers and to provide the high switching capability needed for border routers at Network Access Points. The network architecture is described and performance evaluation is carried on at network access and on end‐to‐end basis. The investigation of algorithms for managing packet flows with different quality of service requirements is also developed as a key issue for the future network scenarios.
A Framework for Dynamic Protocol Configuration
Authors: Plagemann Thomas
Published: September 2008

Traditional end‐system protocols are not able to support the wide range of Quality of Service (QoS) requirements of existing and emerging distributed multimedia applications on top of current networks. The aim of protocol configuration in Da CaPo (Dynamic Configuration of Protocols) is to combine fine granular software and hardware building blocks at runtime in such a manner that the resulting protocol configuration fulfills the application requirements and needs as less resources as possible. Main features of Da CaPo include a formal model, a new approach for specifying application requirements as objective functions, and a unified module interface that allows syntactically unconstrained configuration of software and hardware building blocks. The performance evaluation of the prototype implementation demonstrates that the overhead introduced by the flexible approach is marginal compared to modules that access multiple bytes in each packet. Thus, decreasing protocol complexity by configuring appropriate protocols distinctly increases protocol performance. Furthermore, the flexible approach is able to support the broad range of QoS requirements and is open for future developments.
Multicast Congestion Control for Active Network Services
Authors: Azcorra Arturo , Moreno Jose Ignacio , Calderón María , Sedano Marifeli
Published: September 2008

The growing interest in multicast applications for the Internet, that will increase with the introduction of active network technoiogy, brings out the need for providing effective congestion control mechanisms. This paper studies the problems and specific requirements for multicast congestion control. From this study, a general mechanism is proposed and its advantages and compliance with the requirements are described. The general mechanism is then applied in detail to the Reliable Multicast Active Network Protocol implementation. We conclude that active networks provide good support for congestion control mechanism and that the proposed approach satisfies the stated requirements. However, further work is needed to optimize the values of the system parameters.
Spread Spectrum‐Based Subcarrier Recovery Method for Multi‐Carrier Code Division Multiplexing System
Authors: Hara Shinsuke , Budsabathon Montree
Published: September 2008

A time domain Spread Spectrum (SS)‐based subcarrier recovery method is proposed for down‐link Multi‐Carrier Code Division Multiplexing (MC‐CDM) system, which periodically inserts SS pilot signals into data signal stream in a time division manner at the transmitter. Instantaneous channel impulse response is first estimated by correlating the received pilot signal at the receiver, and then corresponding instantaneous frequency response essential for subcarrier recovery is calculated from the Discrete Fourier Transform (DFT) of the estimated impulse response. The SS pilot‐assisted method is also applicable to Direct Sequence (DS)‐CDM system as a means to estimate instantaneous channel impulse response for Rake combining, and taking the same approach in both MC‐CDM and DS‐CDM systems, there is no large difference between them in terms of transmission efficiency and receiver complexity. The proposed MC‐CDM system must be a promising down‐link multiplexing protocol, because it can achieve better bit error rate (BER) performance than the DS‐CDM system with the same SS pilot‐assisted Rake combiner in frequency selective fast Rayleigh fading channel.
Performance Effects of the Uplink Asynchronism in a Spread Spectrum Multi‐Carrier Multiple Access System
Authors: Kaiser Stefan , Krzymien Witold A.
Published: September 2008

In this paper we investigate the effects of the asynchronism of user signals in the uplink of a spread spectrum multi‐carrier multiple access (SS‐MC‐MA) system. Different propagation delays due to different distances between the mobile transmitters and their base station cause asynchronous arrivals of the uplink signals in addition to multipath propagation. The proposed uplink SS‐MC‐MA scheme uses for synchronization only the frame structure received on the synchronous downlink and requires no additional synchronization measures. A guard interval that is smaller than the sum of the maximum time offset between the users and the maximum excess delay of the frequency selective multipath channel is used. It minimizes the loss in bandwidth efficiency by allowing residual interference. The residual interference is minimized by proper positioning of the detection interval in the receiver. It is shown that with this approach the guard interval can be reduced by about 50%. The performance of the proposed uplink scheme is compared to an uplink SS‐MC‐MA scheme with perfect synchronization.
A Fractionally Spaced Decision Feedback Joint Detection Proposal for Multi Carrier CDMA
Authors: Ikonomou Demosthenes , Vandendorpe Luc
Published: September 2008

Significant attention has been paid lately on Multiple Access (MA) schemes based on Code Division Multiple Access (CDMA) as well as Orthogonal Frequency Division Multiplexing (OFDM), especially in the context of the UMTS Terrestrial Radio Access (UTRA) selection process. The advantages and weaknesses of CDMA schemes are relatively well known as they provide high immunity against multipath, high flexibility and they are well suited for variable rate links. On the other hand, their performance and capacity is strongly dependent and limited by Multiple Access‐ and Self‐ Interference (MAI and SI respectively). The advances in DSP technology resulting in compact and relatively easy to implement digital modulators combined with the favourable characteristics of OFDM such as immunity to Inter Symbol Interference (ISI), bandwidth efficiency and frequency diversity have resulted over the last years in a number of different radio access scheme proposals for mobile channels that combine OFDM and CDMA. In the context of this paper, we focus in the system implementation known as Multi Carrier CDMA (MC‐CDMA). The use of equalising receiver structures versus the use of the Guard Time technique in MC transmission schemes is discussed and a Fractionally Spaced Decision Feedback Equaliser (FS/DFE) receiver structure for an MC‐CDMA system is proposed. Its performance is evaluated by means of computer simulations and compared to the use of the Guard Time technique. A FS Multiple Input Multiple Output (MIMO) DF equalising structure performing Joint Detection (JD) further improves the performance of the proposed equalising scheme in terms of MAI.
A Promising New Wideband Multiple‐Access Scheme for Future Mobile Communications Systems
Authors: Schnell Michael , De Broeck Isabella , Sorger Uli
Published: September 2008

Recently, “Interleaved Frequency‐Division Multiple‐Access” (IFDMA) has been introduced as a new spread‐spectrum multiple‐access scheme for mobile communications which is suitable for both downlink and uplink applications. IFDMA combines spread‐spectrum multicarrier transmission with frequency‐division multiple‐access and, therefore, is capable of achieving frequency diversity while multiple‐access interference is avoided. Moreover, compared to other wideband multiple‐access schemes IFDMA shows several additional advantages. The cost to achieve these advantages is to allow for intersymbol interference. However, the effects of intersymbol interference can be reduced significantly by applying an equalizer at the IFDMA receiver.

In this paper, the principle of IFDMA is reviewed and it is shown that IFDMA is a promising new wideband multiple‐access scheme suitable for future mobile communications systems. The frequency diversity achievable with IFDMA is determined as well as performance results for uncoded and coded transmission taking into account different equalization techniques. As a result, uncoded IFDMA applying optimum equalization performs even better than uncoded multicarrier code‐division multiple‐access applying maximum‐likelihood multi‐user detection. In the case of coded IFDMA transmission coding gains up to 6.8 dB at a bit‐error‐rate of 10−‐4are achieved using a standard convolutional code. An additional performance gain of up to 2.2 dB is possible if equalization and decoding are considered jointly.
The Sensitivity of MC‐CDMA to Synchronisation Errors
Authors: Steendam Heidi , Moeneclaey Marc
Published: September 2008

In this contribution, we investigate the sensitivity of MC‐CDMA systems to synchronisation errors. We show that the signal‐to‐noise ratio (SNR) of the MC‐CDMA system at the input of the decision device in the presence of a carrier frequency offset or a clock frequency offset is a rapidly decreasing function of the number of carriers. For a maximal load, carrier phase jitter and timing jitter give rise to a degradation that is independent of the spectral content of the jitter; moreover, the degradation caused by carrier phase jitter is independent of the number of carriers. A constant carrier phase offset and a constant timing offset cause no degradation of the MC‐CDMA system performance.
Pseudo‐Noise Code Synchronization of Multicarrier DS‐CDMA Systems on Multipath Fading Channels Part I: Analysis of the Serial Search Multiple‐Dwell Acquisition
Authors: Sheen Wern‐Ho , Chang Ming‐Jou , Wang Huan‐Chün , Wu Cheng‐Shong
Published: September 2008

Pseudo‐Noise (PN) code synchronization is investigated in this and an accompanied paper for multicarrier direct‐sequence code division multiple access (DS‐CDMA) systems on multipath Rayleigh fading channels. In this part, a new analysis is developed to evaluate accurately the mean acquisition time performance of serial search multiple‐dwell acquisition systems. The method is unique in that it can take the correlations due to fading into account, including the correlations among different dwells and carriers. In addition, the effects of system parameters on the acquisition performance such as carrier and user numbers, fading correlations, dwell number and times, and thresholds can be easily evaluated, as compared to computer simulations, and, therefore, facilitating the design of the acquisition subsystem. Our analytical results are verified by computer simulations.
A Multimode and Variable‐Rate Voice Communications System with Source‐Matched Error Protection for Mobile Communications
Authors: Babich Fulvio , Vatta Francesca
Published: September 2008

This paper presents a performance evaluation of the multimode Fast Variable Rate CELP coder developed by CSELT S.p.A. in the UMTS Code Division Testbed (CODIT) Project [1] for applications involving channels with time‐varying error characteristics. The radio channel is statistically modelled by one Rician or Rayleigh‐distributed desired signal and several uncorrelated Rayleigh plus log‐normally shadowed interfering signals, propagating according to two different laws: a dual path loss law with a turning point (microcellular environment) and a single path loss law (macrocellular environment). For channels with these error characteristics, each mode of the Fast Variable Rate CELP coder has a particular allocation of bits between source and channel coding stages, leading to an unequal error protection code tailored to suit the different error sensitivities of the source bits. It is shown that, on the basis of the sensitivity evaluation of source bits to errors, according to two different error sensitivity measures. Forward Error Correction whose power is matched to the error sensitivity of the source bits can be used. Increased robustness of source bits to errors can thus be obtained while satisfying bandwidth requirements.
Routing and Wavelength Assignment in Optical Networks Using Genetic Algorithms
Authors: Beckmann Dirk , Killat Ulrich
Published: September 2008

In this paper we consider the wavelength requirement for all‐optical networks based on wavelength‐division multiplexing (WDM). Given a static channel demand, the problem of routing and wavelength assignment (RWA) in such networks has to be solved. Due to the restricted number of wavelengths available on each link it is desirable to get a solution of the RWA problem, in which the needed number of wavelengths is minimized. Unfortunately, this optimization problem belongs to the class of NP‐complete problems. Therefore in this paper we present a new powerful method for the approximative solution of the RWA problem. This new approach is based on the combination of a genetic algorithm and a quite simple heuristic. The efficiency of this combined algorithm is demonstrated by the application to some well known benchmark problems.
Capacity of Multi‐antenna Gaussian Channels
Authors: Telatar Emre
Published: September 2008

We investigate the use of multiple transmitting and/or receiving antennas for single user communications over the additive Gaussian channel with and without fading. We derive formulas for the capacities and error exponents of such channels, and describe computational procedures to evaluate such formulas. We show that the potential gains of such multi‐antenna systems over single‐antenna systems is rather large under independenceassumptions for the fades and noises at different receiving antennas.
A Radio Independent Network – the Enabler for Software Radio
Authors: Berruto Ermanno , Diaz Pilar , Fleming Gary
Published: September 2008

Software radio will likely have a significant role to play in third generation mobile systems. The first tentative steps towards identifying the impact of software radio on a mobile network have already been taken in the RAINBOW project. This paper will consider network issues related to the software radio concept. The requirements on the network to allow the use of software radio in future generation mobile systems will be presented. Significant attention will be given to the network design required to allow software radio to be exploited to its full potential.
Decoding and Equalization with Analog Non‐linear Networks
Authors: Hagenauer Joachim , Offer Elke , Méasson Cyril , Mörz Matthias
Published: September 2008

Using analog, non‐linear and highly parallel networks, we attempt to perform decoding of block and convolutional codes, equalization of certain frequency‐selective channels, decoding of multi‐level coded modulation and reconstruction of coded PCM signals. This is in contrast to common practice where these tasks are performed by sequentially operating processors. Our advantage is that we operate fully on soft values for input and output, similar to what is done in 'turbo' decoding. However, we do not have explicit iterations because the networks float freely in continuous time. The decoder has almost no latency in time because we are only restricted by the time constants from the parasitic RC values of integrated circuits. Simulation results for several simple examples are shown which, in some cases, achieve the performance of a conventional MAP detector. For more complicated codes we indicate promising solutions with more complex analog networks based on the simple ones. Furthermore, we discuss the principles of the analog VLSI implementation of these networks.
Letter Four “Firsts” in Telephony
Authors: Catania Basilio
Published: September 2008

At the beginning of telephony, it soon became evident that telephone lines required better conductors, with larger cross‐section, with respect to telegraph lines, as well as measures to counteract the skin effect. Moreover, inductive loading allowed doubling the range of the line. Call signaling systems, anti‐sidetone circuits and measures to insure the quietness of the environment must also be devised. This letter reminds the pioneering work of Antonio Meucci in all these areas.
A Distributed Control Protocol for Wavelength Routing with Fairness Improvement in WDM Networks
Authors: Mohan Curusamy , Murthy Chebiyyam Siva Ram
Published: September 2008

This paper considers the problem of distributed routing with fairness improvement in wavelength‐routed wavelength‐division multiplexed (WDM) networks with dynamic traffic conditions. The wavelength continuity constraint imposed by WDM networks causes increased blocking of connection requests. The performance loss is more for connections with longer hop counts, when compared to that for connections with shorter hop counts. This is further worsened when distributed routing is used due to the reservation conflicts. We propose a distributed control protocol to select a usable wavelength and route and to improve fairness among connections with different hop counts. The proposed dynamic priority based fairness improvement scheme(DPFS) improves fairness among connections by enforcing dynamically varying priority based control to the connection requests over access to a subset of the available wavelengths. while allowing a free access to the remaining wavelengths. We study the effectiveness of the proposed protocol through extensive simulation experiments. The results show that the proposed scheme improves fairness significantly with an acceptable level of degradation in the overall network performance.