Distributed Algorithms

... 5, MAY 1994 345 Dependability Modeling and Analysis ... Higher performance and reliability can be ob-tained not only through fault-tolerant nodes and communica-tion links but also in the form of redundant distribution of programs and data files throughout the system. ...

ABSTRACT Tracking multiple navigating targets in a bounded region is a common problem that arises in many real-life applications, such as rescue operations, surveillance and reconnaissance. Placing a set of agents optimally to track targets, of interest is another problem associated with the tracking problem. This paper introduces a distributed stochastic approach to a well-defined agent placement problem, which can be shown to be NP-hard. First, a stochastic target motion model is introduced to enable agents to predict future target locations. Second, a model-based distributed algorithm is developed. Given the motion model, agents predict target location probabilities and compute their next best locations based on the predictions. The proposed approach involves coordination among mobile agents in order to achieve near-optimal global utilities. The approach has been evaluated through a set of simulation experiments. Simulation results reveal the superiority of the proposed model-based agent placement approach over existing approaches.

ABSTRACT The amplify-and-forward (AF) cooperative communication scheme is modeled using the Stackelberg market framework, where a relay is willing to sell its resources, power, and bandwidth to multiple users to maximize its revenue. The relay determines the prices for relaying the users' information, depending on its available resources and the users' demands. Subsequently, each user maximizes its own utility function by determining the optimum power and bandwidth to buy from the relay. The utility function of the user is formulated as a joint concave function in power and bandwidth. The existence and uniqueness of the Nash equilibrium (NE) are investigated using the concavity of the utility function and the exact potential game associated with the proposed utility function. The NE solution can be obtained in a centralized manner, which requires full knowledge of all channel gains of all users, which may be difficult to obtain in practice. In this sense, a distributed algorithm can be applied to obtain power and bandwidth allocations with minimum information exchange between the relay and the users. Similarly, the optimum prices for the power and bandwidth can also be obtained in a distributed manner. The convergence of the algorithms is investigated using the Jacobian matrix at the NE. Numerical simulations are used to verify the validation of the proposed framework.

The problem of computing bandwidth guaranteed paths for given flow requests in an ad-hoc network is complicated because neighboring links share the medium. We define the path width on top of the conflict-graph based interfer-ence model, and present the Ad-Hoc Shortest ...

The 26 papers in this special issue focus on game theory in communication systems. The papers are grouped in four clusters according to their topics: (1) Physical layer models in wireless communications, (2) higher layer and cross-layer issues in wireless communications, (3) wire-line communication networks, and (4) specific topics including peer-to-peer networking, network coding, and network security.

For many military and civilian large-scale, real-world systems of interest, data are first acquired asynchronously, ie at irregular intervals of time, at geographically-dispersed sites, processed utilizing decision-making algorithms, and the processed data then ...

... Mihail E. Tudoreanu a , Rong Wu 0 , Ashley Hamilton-Taylor 0 , and Eileen Kraemer 0 ... The tool would also provide a sim-ple customization mechanism to avoid requiring the user to ... We also want to thank Ritu Dhawan for her con-tribution in implementing the termination ...

ABSTRACT Data grids support distributed data-intensive applications that need to access massive datasets stored around the world. Ensuring efficient access to such datasets is hindered by the high latencies of wide-area networks. To speed up access, files can be replicated so a user can access a nearby replica. Much of the work on the replica placement problem in data grids has focused on average system performance and ignored quality assurance issues. In the existing work that considers QoS, a simplified replication model is often assumed, therefore, resulting solutions may not be applicable to real systems. In this paper, we introduce a more realistic model for replica placement in hierarchical Data Grids which determines the positions of a minimum number of replicas expected to satisfy certain quality requirements both from user and system perspectives. Our placement algorithm is based on a highly distributed and decentralized technique that exploits the data access history for popular data files and computes replica locations by minimizing overall replication cost (read and update) while maximizing QoS satisfaction for a given traffic pattern. The problem is formulated using dynamic programming. We assess our algorithm using OptorSim. Simulation results demonstrate the effectiveness of our replica placement technique considering various factors such as storage and workload constraints of replica servers, link capacity constraints, user QoS requirements, etc.

The Stable Matching problem was introduced by Gale and Shapley in 1962. The input for the stable matching problem is a complete bipartite K n, n graph together with a ranking for each node. Its output is a matching that does not contain a blocking pair, where a blocking ...

We pose a new and intriguing question motivated by distributed computing regarding random walks on graphs: How long does it take for several independent random walks, starting from the same vertex, to cover an entire graph? We study the cover time – the expected time required to visit every node in a graph at least once – and we show that for a large collection of interesting graphs, running many random walks in parallel yields a speed-up in the cover time that is linear in the number of parallel walks. We demonstrate that an exponential speed-up is sometimes possible, but that some natural graphs allow only a logarithmic speed-up. A problem related to ours (in which the walks start from some probabilistic distribution on vertices) was previously studied in the context of space efficient algorithms for undirected s–t connectivity and our results yield, in certain cases, an improvement upon some of the earlier bounds.

We present two space and time efficient asynchronous distributed self-stabilizing algorithms. The first sorts an oriented chain network and the second heapifies a rooted tree network. The time complexity of both solutions is linear - in terms of the nodes (for the chain) and height (for the tree). The chain sorting algorithm uses O(m) bits per process where m represents