When being deployed, ad-hoc and sensor networks are unstructured and lack an efficient and reliable communication scheme. Hence, the organization of a MAC layer is the primary goal during and immediately after the dep...
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In this paper we argue that achieving symmetric errors is the key to an improved understanding of clock synchronization. We present a clock synchronization algorithm with drift compensation that implements this symmet...
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ISBN:
(纸本)9781605581231
In this paper we argue that achieving symmetric errors is the key to an improved understanding of clock synchronization. We present a clock synchronization algorithm with drift compensation that implements this symmetric error paradigm. The performance of the algorithm is evaluated by measurements in an indoor testbed using the TinyNode hardware platform. We show that the remaining error is symmetric and in the range of the clock granularity. Copyright 2008 ACM.
In this paper, we initiate the study of the approximability of the facility location problem in a distributed setting. In particular, we explore a trade-off between the amount of communication and the resulting approx...
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ISBN:
(纸本)9781581139945
In this paper, we initiate the study of the approximability of the facility location problem in a distributed setting. In particular, we explore a trade-off between the amount of communication and the resulting approximation ratio. We give a distributed algorithm that, for every constant k, achieves an O(√k(mp)1/√klog (m + n)) approximation in O(k] communication rounds where message size is bounded to O(log n) bits. The number of facilities and clients are m and n, respectively, and ρ is a coefficient that depends on the cost values of the instance. Our technique is based on a distributed primal-dual approach for approximating a linear program, that does not form a covering or packing program. Copyright 2005 ACM.
Reducing interference is one of the main challenges in wireless communication, and particularly in ad hoc networks. The amount of interference experienced by a node v corresponds to the number of other nodes whose tra...
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ISBN:
(纸本)1595930922
Reducing interference is one of the main challenges in wireless communication, and particularly in ad hoc networks. The amount of interference experienced by a node v corresponds to the number of other nodes whose transmission range covers v. At the cost of communication links being dropped, interference can be reduced by decreasing the node's transmission power. In this paper, we study the problem of minimizing the average interference while still maintaining desired network properties, such as connectivity, point-to-point connections, or multicast trees. In particular, we present a greedy algorithm that computes an O(log n) approximation to the interference problem with connectivity requirement, where n is the number of nodes in the network. We then show the algorithm to be asymptotically optimal by proving a corresponding Ω(log n) lower bound that holds even in a more restricted interference model. Finally, we show how the algorithm can be generalized towards solving the interference problem for network properties that can be formulated as a 0-1 proper function. Copyright 2005 ACM.
We study the distributed complexity of computing a maximal independent set (MIS) in radio networks with completely unknown topology, asynchronous wake-up, and no collision detection mechanism available. Specifically, ...
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ISBN:
(纸本)9781581139945
We study the distributed complexity of computing a maximal independent set (MIS) in radio networks with completely unknown topology, asynchronous wake-up, and no collision detection mechanism available. Specifically, we propose a novel randomized algorithm that computes a MIS in time O(log2n) with high probability, where n is the number of nodes in the network. This significantly improving on the best previously known solutions. A lower bound of Ω(log2n/log log n) given in [11] implies that our algorithm's running time is close to optimal. Our result shows that the harsh radio network model imposes merely an additional O(log n) factor compared to Luby's MIS algorithm in the message passing model. This has important implications in the context of ad hoc and sensor networks whose characteristics are closely captured by the radio network model. Copyright 2005 ACM maximal independent sets, radio network,.
In this paper, we study bounds for the α-approximate effectiveness of non-decreasing (μ + λ)-archiving algorithms that optimize the hypervolume. A (μ + λ)-archiving algorithm defines how μ individuals are to be ...
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We study the problem of exploring all nodes of an unknown directed graph. A searcher has to construct a tour that visits all nodes, but only has information about the parts of the graph it already visited. The goal is...
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In this paper we study the NP-complete problem of finding small fc-dominating sets in general graphs, which allow κ - 1 nodes to fail and still dominate the graph. The classic minimum dominating set problem is a spec...
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Recently, a number of frameworks were proposed to extend interface theory to the domains of single-processor and distributed real-time systems. This paper unifies some of these approaches and proves properties like re...
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ISBN:
(纸本)1595935428
Recently, a number of frameworks were proposed to extend interface theory to the domains of single-processor and distributed real-time systems. This paper unifies some of these approaches and proves properties like refinement and independent implementability. We also explicitly state the requirements to a framework for these properties to be fulfilled. Further, a new notion of adaptive interfaces is introduced that supports the design by providing mechanisms for propagating system constraints, such as (end-to-end) delays, available computing and communication resources, buffer spaces, and energy. Guarantees and assumptions on interfaces are not any longer static but adapt according to the system environment. This can be used to answer synthesis questions at design time or to adapt system parameters to changing environment requirements at run-time. The applicability of the presented framework is proven by adapting it to a number of different real-time analysis models. Copyright 2006 ACM.
In this paper we look at the difficulty of fixing solutions of classic network problems. We study local changes in graphs (edge resp. node insertion resp. deletion), and network problems (e.g. maximal independent set,...
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