7945895
Wireless sensor networks: leveraging the virtual infrastructure
Overlaying a virtual infrastructure over a physical network is a time-honored strategy for conquering scale. We design a general-purpose virtual architecture for wireless sensor networks and show that it can be leveraged by a number of different protocols.
44759030
Media access using dynamic bandwidth system to improve satellite network uplink performance
The paper describes a media access system for satellite network uplinks. The media access protocol is designed to support a range of low-level protocols using a dual-framing system, that is, there is a synchronous traffic subframe in which registered station requests are assigned fixed blocks or slots and an asynchronous traffic subframe for unregistered station random access on a contention basis. Slots for the registered stations are assigned through request to the satellite; the remaining frame time is assigned to unregistered stations. Capacity waste through contention resulting in collisions is minimized. The system uses dynamic bandwidth (bit rate) allocation for each channel, that is, the base frequency and bandwidth are changed for each channel at frame boundaries. The total bandwidth for the sum of all uplink channels is fixed. Channels that have low load based upon their request in a prior uplink frame are assigned lower bandwidth, while those with higher loading are provided larger bandwidth. By sharing bandwidth over channels at frame boundaries, overall network efficiency and fairness are significantly enhanced. Bandwidth allocation is decided in the satellite. It allocates sufficient bandwidth for all synchronous traffic and then commits the remaining bandwidth to asynchronous traffic. Here, the allocation for asynchronous traffic provides each channel with sufficient slots so that equal probability of success for stations sharing the channel can be expected. The combination of traffic assignment and bandwidth allocation provides significant improvement in overall network efficiency and fairness for all traffic types. The hardware implementation of media access for variable bandwidth sharing between channels use the concepts of Digital Software Radio. Copyright © 2003 John Wiley & Sons, Ltd.
2805859
A time-optimal solution for the path cover problem on cographs
We show that the notoriously difficult problem of finding and reporting the smallest number of vertex-disjoint paths that cover the vertices of a graph can be solved time- and work-optimally for cographs. Our result implies that for this class of graphs the task of finding a Hamiltonian path can be solved time- and work-optimally in parallel.It was open for more than 10 years to find a time- and work-optimal parallel solution for this important problem. Our contribution is to offer an optimal solution to this important problem. We begin by showing that any algorithm that solves an instance of size n of the problem must take ?(logn) time on the CREW, even if an infinite number of processors are available. We then go on to show that this time lower bound is tight by devising an EREW algorithm that, given an n-vertex cograph G represented by its cotree, finds and reports all the paths in a minimum path cover in O(logn) time using n/logn processors.
31459718
Sequential and Parallel Meta-Heuristics for Solving the Single Row Routing Problem
The design of multi-layer printed circuit boards is vital in the construction of complex electronic systems. Wire routing is a crucial step in the overall design process, which can be decomposed into a number of single row routing (SRR) problems. This paper proposes an approach to solve the SRR problem based on parallel meta-heuristics. The development of this technique involves the design of an encoding strategy that allows all possible routings to be uniquely represented and the derivation of cost functions that maximizes the quality of the developed solutions. Further, parallelization of the proposed approach is attempted to improve the computational efficiency. The different stages of the development are backed by experiments to show the pros and cons of the sequential and parallel implementations.
932666
Q-Win – A New Admission and Handoff Management Scheme for Multimedia LEO Satellite Networks
Low Earth Orbit (LEO) satellite networks are deployed as an enhancement to terrestrial wireless networks in order to provide broadband services to users regardless of their location. In addition to global coverage, these satellite systems support communications with hand-held devices and offer low cost-per-minute access cost, making them promising platform for Personal Communication Services (PCS). LEO satellites are expected to support multimedia traffic and to provide their users with the negotiated Quality of Service (QoS). However, the limited bandwidth of the satellite channel, satellite rotation around the Earth and mobility of end-users makes QoS provisioning and mobility management a challenging task. One important mobility problem is the intra-satellite handoff management. The main contribution of this work is to propose Q-Win, a novel call admission and handoff management scheme for LEO satellite networks. A key ingredient in our scheme is a companion predictive bandwidth allocation strategy that exploits the topology of the network and contributes to maintaining high bandwidth utilization. Our bandwidth allocation scheme is specifically tailored to meet the QoS needs of multimedia connections. The performance of Q-Win is compared to that of two recent schemes proposed in the literature. Simulation results show that our scheme offers low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, while maintaining bandwidth utilization high.
45508612
A unifying look at clustering in mobile ad hoc networks
In recent years, a significant number of clustering schemes have been proposed in the literature. Most of them treat cluster initialization and cluster maintenance differently as if they were two entirely different undertakings. The main contribution of this work is a unifying way of looking at clustering in MANET. We make an important point: there is no difference between cluster initialization and cluster maintenance, and one algorithm should gracefully blend into the other. To illustrate the feasibility of this concept, we propose a novel tree-based clustering algorithm for MANET based on a number of properties of diameter-2 graphs. The algorithm is cluster-centric and, unlike the vast majority of algorithms in the literature, works in the presence of node mobility. Extensive simulation results show the effectiveness of our algorithm when compared to other clustering schemes proposed in the recent literature. Copyright © 2004 John Wiley & Sons, Ltd.
29579371
A New Characterization of Unbreakable Graphs
A nonempty set C of vertices of a graph G is a star-cutset if G\C is disconnected and some vertex in C is adjacent to all the remaining vertices in C. A graph G is unbreakable if neither G nor its complement Ḡ contains a star-cutset. In this note we present a new characterization of unbreakable graphs.
9975325
On the Structure of Graphs with Few P4s
Abstract We present new classes of graphs for which the isomorphism problem can be solved in polynomial time. These graphs are characterized by containing — in some local sense — only a small number of induced paths of length three. As it turns out, every such graph has a unique tree representation: the internal nodes correspond to three types of graph operations, while the leaves are basic graphs with a simple structure. The paper extends and generalizes known results about cographs, P4-reducible graphs, and P4-sparse graphs.
41878962
On the p-connectedness of Graphs - A Survey
Abstract A graph is said to be p-connected if for every partition of its vertices into two non-empty, disjoint, sets some chordless path with three edges contains vertices from both sets in the partition. As it turns out, p-connectedness generalizes the usual connectedness of graphs and leads, in a natural way, to a unique tree representation for arbitrary graphs. This paper reviews old and new results, both structural and algorithmic, about p-connectedness along with applications to various graph decompositions.
204991386
Quasi-brittle graphs, a new class of perfectly orderable graphs
Abstract A graph G is quasi-brittle if every induced subgraph H of G contains a vertex which is incident to no edge extending symmetrically to a chordless path with three edges in either H or its complement H¯ . The quasi-brittle graphs turn out to be a natural generalization of the well-known class of brittle graphs. We propose to show that the quasi-brittle graphs are perfectly orderable in the sense of Chvatal: there exists a linear order a , b , c , d and edges ab , bc , cd has a b and d c .