CPLD-PGPS scheduler in wireless OFDM systems

In this paper, we propose a new scheduler for orthogonal frequency-division multiplexing (OFDM) wireless communication systems, called Channel-Condition and Packet-Length Dependent Packet Generalized Processor Sharing (CPLD-PGPS) scheduler. Based on PGPS, the CPLD scheduler considers both the physical channel condition and the length of packets, and optimally allocates the sub-carriers to different users. The total transmit power is adaptively allocated to each subcarrier. With this scheduler, the system can achieve better system BER performance, and correspondingly superior PER performance. The system throughput is improved, the required bandwidth is guaranteed, and long term fairness for all traffic in the system is provided. In order to reduce the complexity, a simplified algorithm is proposed, which maintains the system throughput as in the original scheduler, and guarantees the system performance with properly set system parameters. The superior performance of the proposed schedulers is demonstrated by simulation with multimedia traffic. © 2006 IEEE.published_or_final_versio

A generalized processor sharing approach to flow control in integrated services networks : the single server case

Caption title.Includes bibliographical references (p. 47-48).Research supported by a Vinton Hayes Fellowship.Abhay K. Parekh and Robert G. Gallager

Geometric modeling and analysis of dynamic resource allocation mechanisms

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 159-163).The major contribution of this thesis is the investigation of a specific resource allocation optimization problem whose solution has both practical application as well as theoretical interest. It is presented as a specific case of a more general modeling framework we put forth. The underlying question asks how to partition a given resource into a fixed number of parts such that the elements of the resulting partition can be scheduled among a set of user requests to minimize the worst case difference between the schedule and the requests. This particular allocation problem has not been studied before. The general problem is difficult in part because the evaluation of the objective problem is a difficult task by itself. We present a novel algorithm for its exact solution in a constrained setting and discussion of the unconstrained setting in, followed by a number of practical applications of these solutions. The solution to the constrained optimization problem is shown to provide sizable benefits in allocation efficiency in a number of contexts at a minimal implementation cost. The specific contexts we look at include communication over a shared channel, allocation of many small channels to a few users and package delivery from a central office to a number of satellite offices. We also present a set of new fairness results for auction-based allocation mechanisms and show how these mechanisms also fall within our modeling framework. Specifically, we look at using auctions as mechanisms to allocate an indivisible shared resource fairly among a number of users. We establish that a straightforward approach as has been tried in the literature does not guarantee an fair allocation over a long time scale and provide a modified approach that does guarantee a fair allocation. We also show that by allowing users to strategize when bidding on the resource we can avoid the problem of unfairness, for some simple cases. This analysis has not been seen in existing literature. Finally, an analysis of the deterministic and stochastic stability of our class of models is presented that applies to a large subset of the models within our framework. The deterministic stability results presented establish the ultimate boundedness of the lag of deterministically stabilizable models in our framework under a wide variety of quantizer-based scheduling rules. This variety of available rules can be used to further control the behavior of the lag of a stable mechanism. We also discuss the application of existing stochastic stability theory to a large subset of the stochastic models in our framework. This is a straightforward usage of existing stability results based on verifying the satisfaction of a stochastic drift condition.by Matthew Secor.Ph.D

Optimal joint path computation and rate allocation for real-time traffic

Computing network paths under worst-case delay constraints has been the subject of abundant literature in the past two decades. Assuming Weighted Fair Queueing scheduling at the nodes, this translates to computing paths and reserving rates at each link. The problem is NP-hard in general, even for a single path; hence polynomial-time heuristics have been proposed in the past, that either assume equal rates at each node, or compute the path heuristically and then allocate the rates optimally on the given path. In this paper we show that the above heuristics, albeit finding optimal solutions quite often, can lead to failing of paths at very low loads, and that this could be avoided by solving the problem, i.e., path computation and rate allocation, jointly at optimality. This is possible by modeling the problem as a mixed-integer second-order cone program and solving it optimally in split-second times for relatively large networks on commodity hardware; this approach can also be easily turned into a heuristic one, trading a negligible increase in blocking probability for one order of magnitude of computation time. Extensive simulations show that these methods are feasible in today's ISPs networks and they significantly outperform the existing schemes in terms of blocking probability

Identification and functional characterization of an ABC transporter of Haemonchus contortus, the P-glycoprotein 13

Les lactones macrocycliques (LM) sont des anthelminthiques (AH) à effet paralysant très utilisés chez les animaux et les humains contre les nématodes parasites. Cependant, leur succès thérapeutique est compromis par la résistance croissante aux LM, qui pourrait être en partie dû aux ABC transporteurs P-glycoprotéines (Pgps) sélectionnés et surexprimés chez les nématodes résistants aux LM. Dans ce travail, nous avons étudié plus précisément la P-glycoprotéine 13 du parasite de petits ruminants, Haemonchus contortus. Son orthologue chez le modèle nématode C. elegans, Cel-Pgp-13, est exprimé dans les amphides, structures qui ont été associées à la sensibilité aux AH chez C. elegans et H. contortus. Pour prédire la capacité des Pgps de nematode à transporter des drogues, incluant des LM et autres AH, nous avons développé un modèle de docking in silico. Nous avons utilisé la structure cristallographique de C. elegans Pgp-1 (Cel-Pgp-1), et nous avons montré la liaison avec une forte affinité de plusieurs ligands décrits comme activateurs de sa fonction ATPasique. Nous avons aussi décrit une forte affinité des LM, et un site spécifique de liaison de ces composés à Cel-Pgp-1. Cette approche représente un outil important pour prédire les interactions entre AH, et pour concevoir rationnellement de nouveaux inhibiteurs compétitifs des Pgps de nématode, dans le but d'améliorer les stratégies thérapeutiques. Sur la base de cette approche, nous avons prédit la structure 3D de Hco-Pgp-13 à partir du cristal de Cel-Pgp-1 afin d'étudier son intéraction avec des substrats potentiels, en particulier les LM. Nous avons trouvé des affinités similaires pour différents composés précédemment testés sur Cel-Pgp-1. In vitro, la mesure de l'activité ATPasique montre que l'actinomycine D est un substrat de Hco-Pgp-13. Nos données démontrent la présence possible d'un domaine de reconnaissance multispécifique sur ce transporteur de parasite. La détermination par immunofluorescence de l'expression de Hco-Pgp-13 a montré une distribution tissulaire large indiquant que Hco-Pgp-13 pourrait jouer un role important dans le transport de substrats endogènes et/ou exogènes. En conclusion, ce travail permet de mieux comprendre le rôle des Pgps de nématodes dans le transport de médicaments AH, tant au niveau de l'organisme modèle C. elegans que du nématode parasite H. contortus. Cette étude suggère la conservation de la fonction de tranporteur ABC multidrogue dans ces espèces. La localisation de Hco-Pgp-13 sur les structures amphidiales, et son éventuelle implication dans la résistance aux médicaments et à la survie de H. contortus à l'exposition à des composés AH, restent à préciser.Macrocyclic lactones (ML) are paralyzing anthelmintics used in animals and humans against parasite nematodes. However, their therapeutic success is compromised by the spread of ML resistance. This might be at least partly due to P-glycoproteins (Pgps) ABC transporters that are selected and overexpressed in ML-resistant nematodes. Deciphering the role of the 10 Pgps expressed in the parasite of small ruminants Haemonchus contortus is thus of major importance to guaranty anthelmintic (AH) efficacy of various drugs. Here we focused on Hco-Pgp-13 due to the expression in the amphids of its closest ortholog in the model nematode C. elegans. Indeed, the amphids represent a putative entry route of drugs to reach AH targets in the nervous system and have been linked to AH susceptibility in C. elegans and H. contortus. In order to predict the capacity of nematode Pgps to transport drugs, including ML and otherAH, we have developed an in silico drug docking model. We have used C. elegans Pgp-1 (Cel-Pgp-1) crystal structure and have showed a high affinity binding of several ligands that have been shown to be activators of its ATPase function. ML were also found to bind with high affinity to Cel-Pgp-1, on a specific binding site. This approach provides a valuable tool to predict drug-drug interactions and to rationally design new competitive inhibitors of nematode Pgps, in order to improve anthelmintic therapeutics. We then predicted a putative 3D structure of Hco-Pgp-13 based on the recently released crystal of Cel-Pgp-1, with which it presented a high homology. This allowed the study of the interaction of Hco-Pgp-13 with potential substrates, in particular ML. We found similar affinities for various drugs previously tested on Cel-Pgp-1, supporting the good homology of these two proteins. Together with in vitro ATPase assay experiments that confirmed the substrate status of actinomycin D, this indicates a possible multispecifc recognition capacity of this parasitic transporter. The determination of Hco-Pgp-13 localization using immunohistochemistry showed a wide tissue expression consistent with a critical role for Hco-Pgp-13 in endogenous and/or exogenous substrate transport. In conclusion, this work provides insights into the role of nematode Pgps in transporting AH drugs, both at the level of the model organism C. elegans and of the parasitic nematode H. contortus. This suggests a high homology of function conserved between ABC tranporters in these species. The localization of such protein on amphidial structures and its possible involvement in drug resistance and survival of H. contortus to exposure to AH compounds remain to be precised

Reconfiguration issues in a quasi-static packet switch.

by Man Wai-Hung.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.Includes bibliographical references (leaves 62-66).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- General Types of Switch Architecture --- p.2Chapter 1.1.1 --- Input-Buffered Switch --- p.2Chapter 1.1.2 --- Output-Buffered Switch --- p.4Chapter 1.1.3 --- Crossbar-Based Switch --- p.4Chapter 1.1.4 --- Shared Buffer Memory Switch --- p.5Chapter 1.2 --- From Clos Network to Cross-path Switch --- p.6Chapter 1.3 --- Motivation and Organization --- p.12Chapter 2 --- Route Reconfiguration in Clos Network --- p.14Chapter 2.1 --- Connection Matrix in Clos Network --- p.15Chapter 2.2 --- Rearranging Central Modules in Clos Network --- p.18Chapter 2.3 --- Changing the Connection Matrix --- p.20Chapter 2.4 --- One Step Route Reconfiguration --- p.21Chapter 2.5 --- Closing Remarks --- p.25Chapter 3. --- Frame-Based Reconfiguration Scheme in Cross-Path Switch --- p.26Chapter 3.1 --- Route Assignment in Cross-Path Switch --- p.27Chapter 3.1.1 --- Requirement Matrix and Capacity Matrix --- p.27Chapter 3.1.2 --- Allocation Vector --- p.29Chapter 3.2 --- Progress Tracing in Cross-Path Switch --- p.30Chapter 3.3 --- Implementing Frame-Based Reconfiguration --- p.32Chapter 3.3.1 --- Recognizing Receiver Virtual Path --- p.33Chapter 3.3.2 --- Finding Donor Virtual Path --- p.34Chapter 3.4 --- Simulation Results --- p.36Chapter 3.4.1 --- Fixed Requirement Matrix --- p.36Chapter 3.4.2 --- Time-Varying Requirement Matrix --- p.38Chapter 3.5 --- Unfavourable Reconfigurations --- p.39Chapter 3.6 --- Closing Remarks --- p.41Chapter 4. --- Performance and Delay Tradeoff in Frame-Based Reconfiguration Scheme --- p.43Chapter 4.1 --- Service Curve and Cross-Path Switch --- p.44Chapter 4.2 --- Service Curve of Cross-Path Switch under Reconfiguration --- p.45Chapter 4.3 --- Impact of Reconfiguration Algorithms to Maximum Delay Increase --- p.48Chapter 4.4 --- Numerical Example --- p.56Chapter 4.5 --- Closing Remarks --- p.57Chapter 5. --- Conclusions and Future Researches --- p.59Chapter 5.1 --- Suggestions for Future Researches --- p.60Bibliography --- p.6

Ensuring Service Level Agreements for Composite Services by Means of Request Scheduling

Building distributed systems according to the Service-Oriented Architecture (SOA) allows simplifying the integration process, reducing development costs and increasing scalability, interoperability and openness. SOA endorses the reusability of existing services and aggregating them into new service layers for future recycling. At the same time, the complexity of large service-oriented systems negatively reflects on their behavior in terms of the exhibited Quality of Service. To address this problem this thesis focuses on using request scheduling for meeting Service Level Agreements (SLAs). The special focus is given to composite services specified by means of workflow languages. The proposed solution suggests using two level scheduling: global and local. The global policies assign the response time requirements for component service invocations. The local scheduling policies are responsible for performing request scheduling in order to meet these requirements. The proposed scheduling approach can be deployed without altering the code of the scheduled services, does not require a central point of control and is platform independent. The experiments, conducted using a simulation, were used to study the effectiveness and the feasibility of the proposed scheduling schemes in respect to various deployment requirements. The validity of the simulation was confirmed by comparing its results to the results obtained in experiments with a real-world service. The proposed approach was shown to work well under different traffic conditions and with different types of SLAs

Network Calculus

Network Calculus is a collection of results based on Min-Plus algebra, which applies to deterministic queuing systems found in communication networks. It can be used for example to understand - the computations for delays used in the IETF guaranteed service - why re-shaping delays can be ignored in shapers or spacer-controllers - a common model for schedulers - deterministic effective bandwidth and much more

Parametric Design Synthesis of Distributed Embedded Systems

This paper presents a design synthesis method for distributed embedded systems. In such systems, computations can flow through long pipelines of interacting software components, hosted on a variety of resources, each of which is managed by a local scheduler. Our method automatically calibrates the local resource schedulers to achieve the system's global end-to-end performance requirements. A system is modeled as a set of distributed task chains (or pipelines), where each task represents an activity requiring nonzero load from some CPU or network resource. Task load requirements can vary stochastically, due to second-order effects like cache memory behavior, DMA interference, pipeline stalls, bus arbitration delays, transient head-of-line blocking, etc. We aggregate these effects -- along with a task's per-service load demand -- and model them via a single random variable, ranging over an arbitrary discrete probability distribution. Load models can be obtained via profiling tasks in isolation, or simply by using an engineer's hypothesis about the system's projected behavior. The end-to-end performance requirements are posited in terms of throughput and delay constraints. Specifically, a pipeline's delay constraint is an upper bound on the total latency a computatation can accumulate, from input to output. The corresponding throughput constraint mandates the pipeline's minimum acceptable output rate -- counting only outputs which meet their delay constraints. Since per-component loads can be generally distributed, and since resources host stages from multiple pipelines, meeting all of the system's end-to-end constraints is a nontrivial problem. Our approach involves solving two sub-problems in tandem: (A)~finding an optimal proportion of load to allocate each task and channel; and (B)~deriving the best combination of service intervals over which all load proportions can be guaranteed. The design algorithms use analytic approximations to quickly estimate output rates and propagation delays for candidate solutions. When all parameters are synthesized, the estimated end-to-end performance metrics are re-checked by simulation. The per-component load reservations can then be increased, with the synthesis algorithms re-run to improve performance. At that point the system can be configured according to the synthesized scheduling parameters -- and then re-validated via on-line profiling. In this paper we demonstrate our technique on an example system, and compare the estimated performance to its simulated on-line behavior. (Also cross-referenced as UMIACS-TR-98-18