Fluid limits for networks with bandwidth sharing and general document size distributions

We consider a stochastic model of Internet congestion control, introduced by Massouli\'{e} and Roberts [Telecommunication Systems 15 (2000) 185--201], that represents the randomly varying number of flows in a network where bandwidth is shared among document transfers. In contrast to an earlier work by Kelly and Williams [Ann. Appl. Probab. 14 (2004) 1055--1083], the present paper allows interarrival times and document sizes to be generally distributed, rather than exponentially distributed. Furthermore, we allow a fairly general class of bandwidth sharing policies that includes the weighted $\alpha$-fair policies of Mo and Walrand [IEEE/ACM Transactions on Networking 8 (2000) 556--567], as well as certain other utility based scheduling policies. To describe the evolution of the system, measure valued processes are used to keep track of the residual document sizes of all flows through the network. We propose a fluid model (or formal functional law of large numbers approximation) associated with the stochastic flow level model. Under mild conditions, we show that the appropriately rescaled measure valued processes corresponding to a sequence of such models (with fixed network structure) are tight, and that any weak limit point of the sequence is almost surely a fluid model solution. For the special case of weighted $\alpha$-fair policies, we also characterize the invariant states of the fluid model.Comment: Published in at http://dx.doi.org/10.1214/08-AAP541 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Testing Embedded Memories in Telecommunication Systems

Extensive system testing is mandatory nowadays to achieve high product quality. Telecommunication systems are particularly sensitive to such a requirement; to maintain market competitiveness, manufacturers need to combine reduced costs, shorter life cycles, advanced technologies, and high quality. Moreover, strict reliability constraints usually impose very low fault latencies and a high degree of fault detection for both permanent and transient faults. This article analyzes major problems related to testing complex telecommunication systems, with particular emphasis on their memory modules, often so critical from the reliability point of view. In particular, advanced BIST-based solutions are analyzed, and two significant industrial case studies presente

Telecommunication Systems

This book is based on both industrial and academic research efforts in which a number of recent advancements and rare insights into telecommunication systems are well presented. The volume is organized into four parts: "Telecommunication Protocol, Optimization, and Security Frameworks", "Next-Generation Optical Access Technologies", "Convergence of Wireless-Optical Networks" and "Advanced Relay and Antenna Systems for Smart Networks." Chapters within these parts are self-contained and cross-referenced to facilitate further study

Telecommunications Division

Spacecraft telecommunication systems - coding methods for phase locked loops, absolute time determination by pulsar, communications elements researc

Data security for third generation telecommunication systems

This research work started as a humble, and yet ambitious attempt of enhancing the current security level in wireless data communication. Detailed analysis of the existing security protocols and wireless networks, together with their strengths and weaknesses, presented in the beginning of this thesis, indicates the need of employing human voice as an alternative security solution. Consequently the presentation of the state of the art biometric solutions and their applicability to the desired communication medium is more than necessary. However, the lack of previous involvement of human voice in an encryption method with successful results, constitute the core of this work. The majority of biometric applications aim to improve the confidence of the system to know whether a user is who he or she claims to be (authentication) and a few of them help the system in deciding his/her identity (identification). This novel method of encryption combines wireless communication (especially Third Generation mobile phones), data security, digital signal processing and smart cards. All these four different research areas have been covered theoretically in the beginning of this thesis. Thorough discussion of the fundamental principles governing each area results in identifying the strengths and weaknesses of these four core research elements and benefits the implementation stages of this work. Continuing with the thesis and proceeding to the second part, the theoretical analysis has been backed up by experimental development and testing. Every aspect of the novel research architecture has been transformed into a research algorithm. The performance of the algorithm, its cohesion and coupling has been closely investigated. The overall result of the research work accompanied with the algorithm’s strengths and weaknesses, future directions together with possible applicability of the research solution provide the epilogue of this scientific journey has been discussed

A nonlinear-coherence receiver

Mathematical analysis and detailed study of generic model for coherent receiver has demonstrated that nonlinear coherence between given biphase-modulated input signal and supplied reference signal can be used in receivers to improve telecommunication systems

Interference Calculation in Asynchronous Random Access Protocols using Diversity

The use of Aloha-based Random Access protocols is interesting when channel sensing is either not possible or not convenient and the traffic from terminals is unpredictable and sporadic. In this paper an analytic model for packet interference calculation in asynchronous Random Access protocols using diversity is presented. The aim is to provide a tool that avoids time-consuming simulations to evaluate packet loss and throughput in case decodability is still possible when a certain interference threshold is not exceeded. Moreover the same model represents the groundbase for further studies in which iterative Interference Cancellation is applied to received frames.Comment: This paper has been accepted for publication in the Springer's Telecommunication Systems journal. The final publication will be made available at Springer. Please refer to that version when citing this paper; Springer Telecommunication Systems, 201

Simulation program of nonlinearities applied to telecommunication systems

In any satellite communication system, the problems of distorsion created by nonlinear devices or systems must be considered. The subject of this paper is the use of the Fast Fourier Transform (F.F.T.) in the prediction of the intermodulation performance of amplifiers, mixers, filters. A nonlinear memory-less model is chosen to simulate amplitude and phase nonlinearities of the device in the simulation program written in FORTRAN 4. The experimentally observed nonlinearity parameters of a low noise 3.7-4.2 GHz amplifier are related to the gain and phase coefficients of Fourier Service Series. The measured results are compared with those calculated from the simulation in the cases where the input signal is composed of two, three carriers and noise power density