bluuebunny/crossref_metadata_2025 huggingface dataset:
Pricing Framework for a Differential Services Internet
Authors: Borella Michael S. , Upadhyay Vandana , Sidhu Ikhlaq
Published: September 2008

A number of recent proposals and proposed standards have addressed adding differential services to the Internet. Although their details and tentative implementations differ, most are recommending what essentially amounts to multiple levels of best‐effort service. In this paper, we survey recent differential services and pricing proposals and introduce a pricing framework for a differentiated‐services network that focuses on simplicity, flexibility, and ease of implementation. In particular, our model can be used in the current heterogeneous Internet without major restructuring. We focus on flat‐rate, per‐time and usage‐based pricing, where users can change their service level on an ad‐hoc basis. We also show that a sender‐pays model with back‐charging is simple to implement and can be effective even in complicated transactions, such as multicasting. Our approach is different from many previous proposals and consciously integrates differential services and pricing with implementation as the immediate goal. Finally, we outline future areas of research including ISP support for pricing, the dynamics of service quality and pricing in a differentiated Internet, and the latest trends and directions of QoS deployment and standardization.
MC‐CDMA in the Context of General Multiuser/ Multisubchannel Transmission Methods
Authors: Lindner Jürgen
Published: September 2008

MC‐CDMA is considered in the context of more general multiuser/multisubchannel transmission systems. Those systems understand the transmission task for all users as an integrated whole and they allow an easy understanding of the advantages and disadvantages of MC‐CDMA in comparison with alternative methods. Multiple antennas are also included. An appropriate vector‐valued transmission model is explained and then special the cases OFDM‐OFDMA and MC‐CDMA are considered. Examples are discussed which demonstrate the advantages of spreading techniques in the context of OFDM‐OFDMA and the additional gain in power (or bandwidth) efficiency compared with pure OFDM‐OFDMA. Simulation results for an indoor scenario with 8 users are presented. Variants of MC‐CDMA, extensions and alternatives are also discussed.
Performance of OFDM‐CDMA with Simple Peak Power Reduction
Authors: Ochiai Hideki , Imai Hideki
Published: September 2008

In this paper we propose simple schemes which reduce the peak‐to‐average power ratio (PAPR) of the OFDM‐CDMA signals. The statistical behavior of the peak power in the OFDM‐CDMA signals is first examined by computer simulations, employing the two orthogonal sets of spreading sequences, namely, Walsh‐Hadamard sequences and Golay complementary sequences. It is shown that for small number of active users or uplink‐system, Golay complementary sequences yield much lower PAPR than Walsh‐Hadamard sequences, and for large number of active users, Walsh‐Hadamard sequences eventually becomes better. A simple scrambling scheme is introduced, which may result in considerable peak power reduction in the case of small number of the active users. For the downlink system, further reduction of the peak power can be achieved by a simple adaptive scheme based on the selection of the set of the spreading sequences.
Adaptive Reduced Complexity Multicarrier CDMA (MC‐CDMA) Structure for Downlink PCS
Authors: Visser Matthijs A. , Bar‐Ness Yeheskel
Published: September 2008

Conventional multiuser code division multiple access (CDMA) suffers from the well‐known near‐far problem. Both the conventional decorrelator and an adaptive separator termed bootstrap algorithm were used to mitigate this problem and obtain near‐far resistant receivers. These approaches still require the knowledge of which users are active and their respective codes. Eliminating this requirement is advantageous for downlink communication as only the desired user is of interest. Furthermore, in a multipath environment the use of the RAKE receiver adds to the complexity. A transmission method called multicarrier CDMA (MC‐CDMA) uses multiple narrowband subcarriers and, as a result, the channel is flat‐fading at each subcarrier. In this paper, a receiver for downlink MC‐CDMA is proposed that does not require the knowledge of which users are active. This is achieved by replacing the bank of matched filters of the full dimensional multiuser detector by 2 matched filters; one for the desired user and one representing all the interfering users combined in a specific way. Additionally, this significantly reduces the number of adaptively controlled weights. The performance of this system is analyzed and simulation results are obtained for the Rayleigh fading channel with and without correlation between the subcarriers.
Pseudo‐Noise Code Synchronization of Multicarrier DS‐CDMA Systems on Multipath Fading Channels Part II: Digital Code Tracking with Diversity
Authors: Sheen Wern‐Ho , Chang Ming‐Jou , Wu Cheng‐Shong
Published: September 2008

Pseudo‐noise code tracking with diversity reception is investigated for multi‐carrier direct‐sequence code division multiple access (DS‐CDMA) systems on multipath Rayleigh fading channels. The traditional noncoherent digital delay locked loop (DDLL) is analyzed under the effects of multipath fading and multiple access interference. A new decision‐directed tracking loop based on a differentially‐detected phase detector is proposed and analyzed. The new tracking loop significantly outperforms the traditional DDLL. Computer simulations have been conducted to verify our analytical results.
An Architectural Framework for Multimedia Integrated Wired‐Wireless Systems
Authors: Iera Antonio , Marano Salvatore , Molinaro Antonella
Published: September 2008

In the perspective of global communications, new conception Wired‐Wireless systems aim at satisfying the user expectation of high performance services and the need for flexibility in the management of disparate categories of multimedia and multi‐requirement applications. This paper proposes an enhanced protocol architecture for the effective handling of multimedia tele services in an integrated wired‐wireless environment. The features of the proposed protocol framework are pointed out with special focus on control issues. Enhanced medium access algorithms, bandwidth allocation strategies, handover, and admission control procedures are embraced in the system functionality. These functions are mapped onto a layered architecture, covering the entire protocol stack proposed for a generic UMTS radio access system. The introduced functions are described in terms of their basic algorithms, signalling messages and control channels, and involved protocol entities, both on the user and control planes of the proposed protocol framework.
Network Performance and Fault Detection in a PSTN Using Non‐Intrusive Methods
Authors: Beritelli Francesco , Casale Salvatore , Cavallaro Alfredo , Montagna Roberto
Published: September 2008

The paper presents a new approach for managing QoS in telecommunication systems based on Non‐Intrusive Methods for performance evaluation of a Public Switched Telephone Network. These methods use devices called INMDs (In‐service Non‐intrusive Measurement Devices), which measure a series of significant parameters for the evaluation of network performance, analysing signals of telephone calls in progress; in this way measurements are continuously performed on the network without having to interrupt the service. Previous studies have shown the advantages and limits of this measurement method in relation to the diagnostic capabilities of single INMDs without considering the possibility of coordinating the measurement information collected by several INMDs, which would make malfunctioning detection more efficient. The method proposed by the authors is based on the presence in the management network of a mesh of INMDs that can be connected by means of data services (connections). The performance of the INMD mesh has been evaluated by means of a simulation tool called COQUE (Communication Quality Evaluation), which allows estimation of the performance obtainable and a reasonable guess of the trade‐off between the costs and benefits obtainable with INMD techniques. The results obtained in a case study are interesting, as in a high percentage of cases malfunctioning is not only detected but also located. Moreover, the proposed case study indicates the possibility of programmable techniques that can further improve the performance of the method.
Letter Throughput and Delay Analysis of the Ideal Window
Authors: Aloha Stabilized , Alcober Jesus , Casares Vicente
Published: September 2008

We consider the problem of random access communications over a time slotted channel with feedback of infinitely multiplicity at the beginning of each collision resolution interval (CRI), i.e., users know via instantaneous feedback the number of users involved in that collision. Once this is known, the resolution algorithm (CRA) operates with binary (successful / non successful, s/ns) feedback. The analysis of this simple full feedback sensing window random access algorithm, named ideal window stabilized ALOHA, (IWSA), algorithm, provides a throughput of 0.5052 packets/slot. Its delay is also analyzed and compared with similar algorithms.
Letter FFT Based Generation of Bandlimited Gaussian Noise Variates
Authors: Beaulieu Norman C. , Tan Christopher C.
Published: September 2008

Rapid generation of time series samples of stationary, zero‐mean, correlated Gaussian noise will accelerate digital communication system simulations. In this letter, we show that a fast Fourier transform (FFT) based method is well suited to rapidly generate such noise samples. The FFT method requiresO(N) memory elements andO(Nlog2N) floating‐point operations to generate each sequence ofNvariates. Sequences that are bandlimited incur an aliasing error in the correlation function of the sequence, but for practical simulations we show this error is negligible. We quantify this error for arbitrary sampling rates and correlation functions.
Feedforward Synchronization Schemes for MSK‐Type Signals
Authors: D'Amico Antonio , D'Andrea Aldo N. , Mengali Umberto
Published: September 2008

Feedforward algorithms are investigated for estimating carrier frequency, carrier phase and symbol timing in MSK‐type modulations. Their derivation is based on maximum likelihood criteria and leads to synchronization schemes that are suitable for full digital implementation. The operation of these algorithms is decoupled, meaning that the frequency parameter is measured first and independently of the others. Subsequently, phase and timing are computed through simple formulas. The performance of the proposed algorithms is investigated analytically and by simulation and the results are compared with Cramer‐Rao bounds. It turns out that the estimation accuracy is very close to the theoretical limits. The frequency estimation range is in the order of 20% of the symbol rate for MSK and 10% for GMSK. A frequency estimation threshold lower that 4 dB is achieved with fairly short observation windows.
An Introduction to Generalized Concatenated Codes
Authors: Zyablov Victor , Shavgulidze Sergo , Bossert Martin
Published: September 2008

This paper presents an introduction to the theory of generalized concatenated codes. We consider the encoding and decoding procedures of both ordinary concatenated codes, and generalized concatenated codes where block codes are used as inner codes. We give the main parameters of these codes, and by means of examples, show that under the same conditions the latter outperforms the former with respect to minimum code distance. We also heuristically describe the generalized concatenated decoding procedure. Then we show how the generalized concatenated coding ideas can be applied to encoded memoryless modulation. Such construction is often referred to as a multilevel code in literature. We consider the multilevel codes from the standpoint of generalized concatenated codes and with the help of a simple example, show how encoding and decoding procedures can be carried out. Ordinary concatenated and generalized concatenated coding schemes are considered next, using inner convolutional codes or inner modulation with memory. With the help of examples, we analyze the distance properties of such constructions.
ATM‐Based Multimedia Communication via Satellite
Authors: Lutz Erich , Bischl Hermann , Bostič Janez , Delucchi Cecilia , Ernst Harald , Holzbock Matthias , Jahn Axel , Werner Markus
Published: September 2008

Within the next years, a large number of new satellite systems for broadband multimedia communications will be developed, mainly for fixed terminals, but to a lesser degree also for portable and mobile terminals. The most important systems will be based on low earth orbit (LEO) satellite constellations with inter satellite links (ISLs), and will be seamlessly integrated into the environment of terrestrial broadband networks. Since most of the terrestrial broadband networks will be based on the Asynchronous Transfer Mode ATM, it is advantageous for the satellite networks to adopt the ATM transmission scheme and implement ATM switches on board the satellites. However, compared to communication in fixed networks, satellite communication is characterised by special constraints (limited bandwidth, propagation delay, transmission errors, dynamic network topology) requiring the development of a new ATM‐based communication technology. In the paper, an ISL‐based LEO satellite network for multimedia communication will be considered. Several relevant aspects will be discussed, such as the system architecture, the system requirements, and the protocol architecture. Since the users access the satellite network via a radio interface, an error control scheme and a multiple access scheme suitable for multimedia communication must be implemented. The aspects of TDMA‐ and CDMA‐based medium access control are discussed. Further issues are ATM resource management, radio resource management, and ISL routing. Finally, methods for terminal antenna steering are addressed, and the demonstration of aeronautical multimedia communication via the ITALSAT satellite is described.
Evolution Towards Photonic Networks
Authors: Lagasse Paul , Demeester Piet , Ackaert Ann , Van Caenegem Bart , Van Parys Wim , O'Mahony Michael J. , Stubkjaer Kristian , Benoit Jacques
Published: September 2008

This paper is an edited version of “Roadmap towards the Optical Communication Age” published by the HORIZON project within the ACTS Photonic Domain. This paper summarises possible evolution scenarios leading to photonic access and transport networks.
Maximizing Multicast Throughput in WDM Networks with Tuning Latencies Using the Virtual Receiver Concept
Authors: Ortiz Zeydy , Rouskas George N. , Perros Harry G.
Published: September 2008

We consider the problem of supporting multipoint communication at the MAC layer of broadcast WDM networks. We first introduce themidticcut rhroughprrt asthe performance measure of interest and we show that it depends on two measures that have previously been considered in isolation, namely, the efficient use of channel bandwidth and wavelength throughput. We then present a new technique for the transmission of multicast packets based on the concept of aLzirninlreceiver, a set of physical receivers which behave identically in terms of tuning. We also demonstrate that the number of virtual receivers naturally captures the performance of the system in terms of multicast throughput. Consequently, we focus on the problem of optimally selecting the virtual receivers to maximize multicast throughput, and we prove that it is Ji'P‐complete. Finally, we present four heuristics of varying degree of complexity for obtaining a set of virtuat receivers that provide near‐optimal performance in terms of multicast throughput.
Single‐Layer Optical Platform Based on WDM/TDM Multiple Access for Large‐Scale “Switchless” Networks
Authors: Caponio Nunzio Paolo , Hill Alan Michael , Neri Fabio , Sabella Roberto
Published: September 2008

The European Union ACTS project SONATA will define and demonstrate a cswitchlessn all‐optical network to provide a future single‐layer, advanced transport architecture on a national scale. The single‐hop, shared‐access network employs time and wavelength agility (a WDMA/TDMA protocol), using fast tunable transmitters and receivers to route individual customer connections as well as bandwidth pipes through a single wavelength router (suitably replicated for resilience). No electronic switching nodes or cross‐connects (telephony, IP, ATM, SDH) are required within the transport network, nor optical cross‐connects (save the wavelength routing node), thus providing major transport architecture simplifications and hardware reductions. The network is scalable to 200 Tbit/s throughput over 1, 000 krn, connecting 20 million terminals operating at 622 Mbit/s over 50.000‐way split c<hyperPONss, by means of 800 WDM channels with 0.05 nm channel spacing (6.25 GHz). Details of network dimensioning, physical layer modeling and network control issues are presented.
All‐Optical WDM Cross‐Connect Meshed‐Ring Communications Networks
Authors: Rubin Izhak , Ling Jing
Published: September 2008

We introduce a meshed ring communications network which employs cross‐connect switches. The crossconnect switches can be implemented as wavelength routers resulting in WDM networks, or as ATM Virtual Path (VP) switches leading to ATM compatible network systems. We show in the paper that this network architecture results in a significant increase in throughput performance in comparison with (SDHISONET) ring networks. For a certain class of meshed rings, under a uniform traffic matrix, we derive the optimal topology which achieves maximum throughput efficiency. Using such a topology, we obtain upper and lower bounds on the number of wavelengths required to achieve that efficiency level. The network is divided into (overlapping) communities of nodes. Each community is assigned a wavelength and a subnetwork (identified as a wavelength graph). Each pair of nodes in a community can communicate across the associated wavelength graph. Wavelength graphs (subnets) are constructed to demonstrate the implementation of the routing scheme using the number of wavelengths that is equal to the derived upper bound. For practical implementation reasons, we investigate the performance of networks which employ a reduced number of wavelengths. We show that by modifying the topological layout of the meshed ring network, we can reduce substantially the number of required wavelengths, while incurring just a modest reduction in throughput efficiency.
Performance of WDM Rings with Partial and Sparse Wavelength Conversion under General Dynamic Traffic
Authors: Maier Guido , Scappini Mauro , Martinelli Mario , Pattavina Achille
Published: September 2008

Dynamic wavelength assignment in a WDM all‐optical network with partial and sparse wavelength conversion is discussed in this paper. The performance of unidirectional and bidirectional ring networks in terms of blocking probability, conversion gain and fairness is evaluated under various types of offered traffic patterns. Smooth and peaked patterns have been considered in addition to the classical Poisson traffic type. We show how the partial use of wavelength converters having a limited conversion capability affects the blocking performance of connections and, more importantly in terms of network fairness, its dependence on the source‐destination distance.
Measuring the Survivability of a Network: Connectivity and Rest‐Connectivity
Authors: Duque‐Anton Manuel , Bruyaux Frederic , Semal Pierre
Published: September 2008

When evaluating the survivability performance of a communication network, it is important to detect whether the graph is connected, whether there are separation nodes and separation pairs. The algorithms [1] and [2] developed by Tar‐jan and Hopcroft are the adequate tools for this purpose. They are able to determine the bi‐ and triconnected components of a graph in o (N+E) where N is the number of nodes and E the number of edges of the graph. Practically however, the decomposition of the graph is a step only in the evaluation of the connectivity performance of a graph. Indeed, when a separation element (node or pair) has been detected, it is crucial to know what are the consequences if this element fails down. For example, which precise parts of the graph are disconnected or more simply how large are the parts which are separated by this element? The paper introduces the notion of rest‐connectivity. Basically, for each separation element, the rest‐connectivity value is defined as the number of node pairs which got disconnected by the failure of that separation element. In this paper, algorithms [1] and [2] are enhanced in order to determine the rest‐connectivity values for all separation nodes and pairs of a graph while keeping the complexity in o(N+E).
Analysis of a Dual‐Rate Transmission Scheme for Gaussian Broadcast Channels
Authors: Sajadieh Masoud , Kschischang Frank R. , Leon‐Garcia Alberto
Published: September 2008

In a broadcast channel, a single transmitter communicates to receivers with different channel capacities, a typical example of which is the over‐the‐air television broadcasting. A natural question that arises is evaluation of the optimal information transfer rate in such an environment. For the two‐receiver case, we examine various transmission scenarios in this environment and focus on the theoretically optimal superposition scheme, where the information intended for the better channel is superimposed on the portion of information common to both receivers. As a result, a basic grade of service is maintained throughout the entire coverage area in addition to a higher quality service offered to the receivers with better reception conditions. Using end‐to‐end distortion and coverage channel signal‐to‐noise ratio threshold measures, three specific embedded signaling modes are introduced. We demonstrate that a generalized embedding scheme provides a practical trade‐off between distortion and coverage radius. The scheme is also formulated in terms of an optimization problem, seeking the best embedding factor for a given application. To verify the theoretical results, we idealize a dual rate transmission system over a Gaussian broadcast channel, in which receivers are distributed according to a circularly symmetric exponential pdf. The numerical results indicate that this model offers a higher per capita data rate comparing to the conventional single rate transmission systems. Application of this multirate broadcast holds promise for multiresolution transmission of digital audio and high definition television.
Exact Error Probability for Slow Frequency Hopping
Authors: Györfi László , Jordán Árpád , Vajda István
Published: September 2008

In this paper a frequency hopping multiple access packet communication network was considered. The channel was assumed to be slotted and frame synchronous. Reed‐Solomon codes were used both for protocol sequences and forward error correction. The exact probability of decoding error is given. A useful Gaussian approximation was computed, which led to a simple design of the system's parameters.
Experiences from the Implementation and Use of Multimedia Synchronization Mechanisms
Authors: Bozios Theodoros H. , Pronios Nikos B. , Georgiapis Panagiotis
Published: September 2008

This paper presents experiences from the implementation of Multimedia Synchronization Mechanisms related to the support of the many‐to‐one inter‐media synchronization and describes the proposed Synchronization Architecture and its Design Objectives. The main goal of the communication system in the proposed architecture is to maintain the asynchrony levels between the media streams belonging in a Synchronization Group between the levels specitied by the Multimcdia Application. This is achieved through appropriate Synchronization Primitives related to the management and monitoring of the synchronization. The pilper emphasizes on the implementation issues and problems, and the solutions adopted. concluding to the lirst experiences from the use of the synchronization.
On Union Bounds for Random Serially Concatenated Turbo Codes with Maximum Likelihood Decoding
Authors: Sason Igal , Shamai Shlomo
Published: September 2008

The input‐output weight enumeration (distribution) function of the ensemble of serially concatenated turbo codes is derived, where the ensemble is generated by a uniform choice over the interleaver and a uniform choice of the component codes from the set of time varying recursive systematic convolutional codes. The conventional union bound is employed to obtain an upper bound on the bit error probability of the ensemble of serially concatenated turbo codes for the binary‐input additive white Gaussian noise (AWGN) channel with coherent detection OF antipodal signals and maximum likelihood decoding. The influence of the interleaver lengthNand the memory length of the component codesinon the ensemble performance is investigated and compared with relevant results for parallel concatenated multiple‐turbo codes.
Performance Analysis and Estimation of Call Admission Control Parameters in Wireless Integrated Voice and Data Networks
Authors: El‐Hadidi Mahmoud T. , Elsayed Khaled M. , Abdallah Mohamed M.
Published: September 2008

We propose an admission control policy for wireless multimedia networks that is based on the well known threshold‐based guard channel method. The new scheme deals with two different types of traffic classes; namely: voice and data. We assume two different thresholds, one for each traffic class. In addition. we propose to buffer the handoff data calls if no free channels are available rather than rejecting them. For handoff voice calls, we propose two methods. namely: a blocking method and a preemptive method. For the blockins method, we reject the handoff voice calls it no channels are available. For the precmptive method, an ongoing data call can be buffered and its channel allocated to the handoff voice call. We study the effect of the thresholds. buffer size and the application of the proposed methods on call blocking probabilities. It is shown that the new call blocking probabilities are only affected by the threshold values. Meanwhile, the data handoff blocking probability exhibited grcat improvement. For handoff voice calls, when the blocking method is applied. the blocking probability value increases slightly with the increase of buffer size. Meanwhile. for the preemptive method, the handoff voice call blocking probability significantly decreases as the buffer size increases. Based on these results. we develop an algorithm that uses the proposed policy to estimate the appropriate thresholds and buffer six which meet the required call blocking probabilities for each traffic type.
Multicanier Modulation with Multistage Encoding/Decoding for a Nakagami Fading Channels
Authors: Goldfeld Lev , Wulich Dov
Published: September 2008

The Multi Carrier Modulation (MCM) system with a multistage encoding/decoding scheme based on repetition and erasures‐correcting decoding of block codes applied for a Nakagami fading channel is considered. Bit Error Rate (BER) as a function of Signal‐to‐Noise Ratio (SNR) has been found to agree well with the simulated results. It is shown that for low SNR the proposed system has a lower BER than both the MCM with Forward Error Correction (FEC) and MCM with optimal diversity reception and FEC.
Each Carrier Transmission Power Control with Antenna Carrier Diversity for OFDMDS‐CDMA System
Authors: Jarot Sigit Puspito Wigati , Nakagawa Masao
Published: September 2008

In OFDM‐DS/CDMA system, frequency distortion caused by multipath propagation occurs at different frequencies in the bandwidth and generally affects selected subcarriers within the larger bandwidth. It has been investigated that each carrier transmission power control is effective to compensate for subchannel variation due to multipath, by assigning different transmission power level to different subcarriers based on the attenuation level suffered by them. The effectiveness of power control is mainly affected by the accuracy of the transmission power adjustment at the transmitter. As a matter of fact, however, the dynamic range of transmission power is very limited, due to the restriction on power consumption of a mobile station (transmitter side of reverse link). When a subcarrier is subjected to strong fading, power control is not able to compensate for channel attenuation by transmitting signals with large power, and this condition is very potential to degrade system performance. In this paper, we propose to combine each carrier transmission power control with antenna‐carrier diversity reception to lighten the burden imposed on power control. This system allows the base station (receiver side) to select the best combination among the carriers and antennas after receiving signals from mobile station (transmitter side), thus power control only compensates for smaller attenuation level. System performance is evaluated in terms of Bit Error Rate (BER) performance as a function of Doppler frequency, number of users, number of branches, updating period and dynamic range. The result of computer simulations clearly show that the proposed system reduces significantly the burden imposed on power control.
Transformation Methods, Coding and Equalization for Time‐ and Frequency‐Selective Channels
Authors: Reinhardt Markus , Ecle Jochem , Lindner JÜRcen
Published: September 2008

A method to generate transmit signal sets is proposed which are especially suited for transmission over Rayleigh fading channels. It is shown that this method in combination with a suitable iterative receive algorithm allows the asymptotical transformation of a Rayleigh channel into a set of parallel additive white gaussian noise (AWGN) subchannels. Therefore, coding methods designed for the AWGN channel are now applicable also to Rayleigh channels resulting in a coding gain that is separable into the known AWGN coding gain and an additional diversity gain attributable to the orthonormal transform.

Starting from this result, the method is extended to a transmission over frequency and/or time‐selective channels. This leads to an extension of the recently introduced multicamer code division multiplexing (MC‐CDM) scheme. A unified transmission model is derived which allows the application of the iterative reception algorithm also in the latter case and to transform time‐ and frequency‐selective channels under certain assumptions asymptotically into a set of parallel AWGN subchannels. The performance of these transformation methods for an uncoded scheme and together with high rate trellis codes designed for the AWGN channel is investigated and compared to the matched filter bound (MFB). For the calculation of the MFB for channels with a separable time‐variant transfer function a method is introduced that significantly reduces the complexity of computation.
Randomized OFDM for Multi‐Cell Environments
Authors: Ping Li
Published: September 2008

This paper is concerned with a randomized OFDM (R‐OFDM) scheme. The basic principle is to apply a scrambling operation to several OFDM frames. With a proper design strategy, the scrambling operation will not affect intra‐cell orthogonality of OFDM (even considering multi‐path effect), For signals from different cells, mutually random scramblings are used to reduce their correlation. This alleviates the worst case inter‐cell interference problem. R‐OFDM combines some advantages of both OFDM and CDMA, namely, intra‐cell interference avoidance, cross‐cell interference mitigation as well as simple receiver structure.
Analysis of Doppler Spread Perturbations in OFDM(A) Systems
Authors: Robertson Patrick , Kaiser Stefan
Published: September 2008

We analyze the effects of Doppler spread in mobile channels on Orthogonal Frequency Division Multiplex (OFDM) systems. This is important, since channel variations during one OFDM symbol cause Inter Sub‐carrier Interference (ICI) in OFDM systems, which degrades the performance, since ICI can be seen as additional near‐Gaussian noise. The analysis is presented and closed‐form results are given for numerous important practical Doppler spread encountered in mobile channels and applications such as mobile reception of DVB‐T. We also show that for the case of asymmetrical Doppler spreads, the frequency correction of the receiver can be adjusted so as to minimize the ICI. To extend our work to OFDM(A) mobile radio systems where many users' contributions to the ICI overlap, we have introduced the concept of an equivalent single‐user which causes the total ICI, in order to use the same analytical framework, and compared the uplink and downlink cases. Simulation results confirm our analysis and show the importance of the analytical tool to perform realistic system analysis without having to resort to time consuming time‐domain simulations.
GSn: A new service type for integrated services on the internet
Authors: Gregori Enrico , Marcantonio Riccardo , Potorti Francesco
Published: September 2008

Network services with deterministic guarantees are based on a worst—case description of user—generated traffic. When designing a policing and scheduling algorithm for guaranteed services on the Internet, accuracy of description of the traffic profile has to be traded with simplicity of implementation. The result of this trade off is often expressed as the number of token buckets required by the service along with the choice of their parameters. The GS type of service proposed by the IETF uses two token buckets both for characterizing the traffic and for policing it. The choice of using only two token buckets is primarily driven by policing costs. In this paper we propose a method that allows the number of token buckets used for characterizing the traffic to be greater than what is actually needed to police it. This means we can obtain an accurate profile of the traffic while keeping policing simple. The method consists of computing a profile of the traffic which involves a number of token buckets of the order of ten, and then doing the policing using only the first token bucket, plus another one which is chosen depending on the delay requirements of the receivers. This paper shows that with this simple enhancement we obtain a guaranteed service whose performance closely approaches the theoretical limits of services with deterministic guarantees.
Hybrid ARQ and optimal signal—to—interference ratio assignment for high—quality data transmission in DS—CDMA
Authors: Sun Songsong , Krzymien Witold A.
Published: September 2008

Combined error correction and detection techniques, or hybrid automatic—repeat—request (ARQ) schemes with negative acknowledgment are considered for highly reliable reverse link data transmission in direct sequence code division multiple access (DS—CDMA) personal communication systems. The proposed selective repeat hybrid ARQ scheme employs an inner convolutional code for error correction and an outer shortened BCH code for error detection. Each negative acknowledgment message contains all packet sequence numbers that have been detected in error, and it is both error—correction and error—detection encoded. Accepted packet error rate and throughput are derived as a function of the error correction encoded frame error rate. An optimum signal—to—interference ratio (SIR) assignment maximizing the system's capacity is also found. A comprehensive simulation is conducted to evaluate performance of the data transmission system. Analysis and simulations show that by applying the proposed type I hybrid ARQ scheme with properly selected system parameters, virtually error free and highly efficient data transmission in CDMA personal communication systems is possible.
hing reed—solomon codes with 4—DPSK block detectors
Authors: Guarco Gianni , Visintin Monica , Elia Michele
Published: September 2008

Transmission of 4—DPSK signals over an additive white Gaussian noise channel with an unknown phase rotation is considered, together with block detection [1] and Reed—Solomon encoding. The combination of the block detection's length and RS code parameters is analyzed.
Outage probability analysis for a nakagami signal in L nakagami interferers
Authors: Karagiannidis George , Georgopoulos Chris , Kotsopoulos Stavros
Published: September 2008

Outage analysis is one of the primary objectives in the design and operation of the 3rd Generation (3G) micro— and pico— cellular mobile radio systems in order to increase spectrum efficiency and to control the Quality of Service (QoS) and Grade of Service (GoS) demands. This paper presents an alternative direct formulation of the outage probability for Nakagami fading channels in the presence of multiple L Nakagami interferers with arbitrary parameters. This formulation can be used with and—without a constraint of a minimum signal power. Computer simulation results are also presented to illustrate the proposed formulation.
Error resilient transmission of H. 263 video for mobile communications
Authors: Abrardo Andrea , Barni Mauro , Garzelli Andrea , Marotta Domenico
Published: September 2008

Automatic Repeat Request (ARQ) strategies reduce error propagation in low bitrate video transmission. However, retransmission of corrupted data introduces delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission bit rate. In this paper, a strategy is proposed which instead of protecting the whole H. 263 video stream, uses all the redundancy to protect the most important parts of the bit stream, i. e. GOB start codes. More specifically, the 22—bit—long start code used in the H. 263 standard is replaced with longer Gold sequences which ensure a higher protection against noise. A different sequence is used for each GOB so that additional information can be obtained which can be used to improve the quality of the decoded sequence. The new technique is derived by assuming a slow—fading channel such as those encountered in pedestrian applications. Simulation results prove the effectiveness of the proposed technique with respect to classical FEC schemes in terms of PSNR and overall bit rate.
SMART: A rapid layer adaptation protocol for layered video multicast
Authors: Lee Jiwoong , Kim Jae‐Kyoon
Published: September 2008

This paper presents a new network layer traffic control protocol for rapid layer adaptation and prompt congestion recovery of a layered—video multicast session. The proposed protocol SMART, which stands for Scalable Multimedia Rapid Rate Control in Multicast Networks, defines a concept of dependency between multicast group addresses that are pertaining to the same layered—video session. The information on dependency is carried on an extended version of Internet Group Managenemt Protocol, which is called IGMP—DX (Dependency Extension). SMART router creates a database to manage the dependency information. With SMART, receivers can adapt their subscription level to the right level rapidly by the function of Fast Learning. Emergency Drop Request is sent by a host who detects intensive congestion, and the router blocks the associated traffic. In this manner network can recover from congestion rapidly while not impairing the minimal multicast service. SMART supports both IGMPv2 and IGMPv3, including sourcespecific multicast in Internet. It is shown by simulations that SMART provides a rapid rate control mechanism and good scalability with small amount of control signal.
Transport of MPEG—4 over IP/RTP
Authors: Basso Andrea , Varakliotis Socrates , Castagno Roberto , Lohan Florin
Published: September 2008

In this paper we review and discuss some of the current efforts and proposals in the standardization bodies IETF and MPEG for the delivery of MPEG—4 over IP. We address the issues of payload format and media control by describing two architectures that allow for MPEC—4 streaming. Finally, we describe some MPEG—4 over IP streaming experiments in which the RTP MPEG—4 payload format is used in conjunction with per—stream Forward Error Correction support, in presence of packet loss.
An end—to—end performance comparison methodology for ATM transport of CBR and VBR encoded digital video
Authors: Kurçeren Ragip , Modestino Jim W.
Published: September 2008

Compressed digital video can be transported on ATM networks using either a constant bit rate (CBR) or a variable bit rate (VBR) network transport service. The use of VBR transport is generally considered to offer some potentially attractive advantages over more traditional CBR transport. These potential advantages include the expectation of improved reconstructed video quality, shorter end—to—end delays and improved statistical multiplexing performance. Unfortunately, most evaluations of the relative end—to—end performance of VBR versus CBR transport of digital video fail to adequately take into account the effects of lost cells in transporting multiple VBR streams which compete for limited network resources. These effects can be avoided with CBR transport using appropriate call admission control (CAC) procedures. Furthermore, these relative performance evaluations are generally not provided under comparable levels of network resource utilizations. Indeed, no methodology presendy exists for fairly assessing the relative end—to—end performance of CBR and VBR encoded video at the same level of resource utilization. In this paper, we develop and illustrate a methodology for comparing the relative performance, in terms of the corresponding end—to—end distortion, of CBR and VBR encoded digital video transport for fixed network resources and at identical multiplexing levels. The approach is an extension of a previously developed joint source—channel coding approach for VBR digital video transport on ATM networks. Our objective in this paper is to provide a common comparison framework for CBR and VBR video streams.
On improving CBR service playback buffer mechanism in WATM networks
Authors: Beben Andrzej , Burakowski Wojciech
Published: September 2008

The commonly recommended approach to meet the Constant Bit Rate (CBR) service requirements in ATM networks is to use the playback buffer mechanism implemented at the AAL layer [1],[2],[3]. This solution was originally proposed for the fibre optics ATM networks, where cell loss ratio is negligible (e. g. 10—9). However, for the wireless ATM network concept the designers have to take into account the fact that an essential part of sending cells can be simply lost due to transmission errors and these losses can also occur in bursts (despite applying error protection mechanisms). Moreover, the variation of cell transfer delay is expected to be significantly larger and this is mainly due to radio access protocol behaviour. As a consequence, the above leads to a need to modify the playback buffer mechanism in order to improve its functionality in the wireless ATM network environment. The solution proposed in this paper is based on some enhancements of the dummy cell insertion (instead of lost cells) algorithm and on the K times extension of AAL1 PDU numbering range, by assigning the same number to K consecutive cells. The justification of the approach is provided in terms of theoretical considerations and simulation results.
The application of modified lapped transform domain median filter to narrow—band interference excision in DSSS systems
Authors: Guangruihu Chongni Li
Published: September 2008

A novel communication receiver which uses lapped transform (LT) incorporating modified median filter (MMF) algorithm is designed for narrow—band interference (NB1) excision. Comparing to traditional Fourier Transform, LT has longer basis vectors, less spectral leakage, thus better frequency resolution. The LT domain MMF algorithm takes full advantages of the direct sequence spread spectrum signal, as well as the characteristics of LT, performs the transform domain filtering twice. The first filtering locates the position of interference and mitigates most of them. The second filtering was performed in a small neighborhood of the located interference. So LT domain MMF algorithm can completely mitigate the interference without distorting the desired signal. Simulation results demonstrated the improved BER performance and increased robustness of our approach.
Feedforward joint phase and timing estimation for MSK—type signals
Authors: Morelli Michele , Vitetta Giorgio M.
Published: September 2008

Novel non data—aided (NDA) algorithms are proposed for joint estimation of timing and carrier phase in MSK—type modulations. They are based on maximum likelihood methods and have a feedforward structure which is suitable to fully digital implementation. Performance with MSK and Gaussian MSK. (GMSK) is assessed by computer simulations and compared with that of other existing estimation schemes.
Exploiting the short—term and long—term channel properties in space and time: Eigenbeamforming concepts for the BS in WCDMA
Authors: Brunner Christopher , Utschick Wolfgang , Nossek Josef A.
Published: September 2008

The deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space—time (ST) processing, processing may take place in reduced dimension, i. e., pre—filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long—term and short—term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short—term and long—term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well—known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte—Carlo simulations.

Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed—loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short—term channel properties. Even though the short—term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/—beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantageous feedback signalling.
MIMO vector channel sounder measurement for smart antenna system evaluation
Authors: Thomä R. S. , Hampicke D. , Richter A. , Sommerkorn G. , Trautwein U.
Published: September 2008

For the simulation and design of smart antenna transmission principles in mobile radio, precise knowledge of the time—variant directional multipath structure in various radio environments is required. In this paper, a new real—time multiple—input—multiple—output (MIMO) vector radio channel sounder is described, which uses multiple antennas at the transmitter as well as at the receiver position. The proposed MIMO measurement principle can be effectively exploited to estimate the propagation direction at both ends of the wireless link simultaneously, and thus, dramatically enhance overall resolution of the multiple path parameters. Applying a proper antenna architecture and the multidimensional unitary ESPRIT algorithm, joint superresolution estimation of the direction of departure (DOD), time—delay of arrival (TDOA), Doppler shift, and direction of arrival (DOA) of the propagating waves becomes possible. The measured results can also be used directly for the simulation of combined transmit—receive diversity (MIMO) transmission principles and space—time (ST) adaptive receivers in a multi—user scenario. Results based on measurements in different locations are referenced, including a complicated indoor environment as is typical for industrial WLAN applications.