Critical-Path Aware Scheduling for Latency Efficient Broadcast in Duty-Cycled Wireless Sensor Networks

Minimum latency scheduling has arisen as one of the most crucial problems for broadcasting in duty-cycled Wireless Sensor Networks (WSNs). Typical solutions for the broadcast scheduling iteratively search for nodes able to transmit a message simultaneously. Other nodes are prevented from transmissions to ensure that there is no collision in a network. Such collision-preventions result in extra delays for a broadcast and may increase overall latency if the delays occur along critical paths of the network. To facilitate the broadcast latency minimization, we propose a novel approach, critical-path aware scheduling (CAS), which schedules transmissions with a preference of nodes in critical paths of a duty-cycled WSN. This paper presents two schemes employing CAS which produce collision-free and collision-tolerant broadcast schedules, respectively. The collision-free CAS scheme guarantees an approximation ratio of in terms of latency, where denotes the maximum node degree in a network. By allowing collision at noncritical nodes, the collision-tolerant CAS scheme reduces up to 10.2 percent broadcast latency compared with the collision-free ones while requiring additional transmissions for the noncritical nodes experiencing collisions. Simulation results show that broadcast latencies of the two proposed schemes are significantly shorter than those of the existing methods

A provably tight delay-driven concurrently congestion mitigating global routing algorithm

Routing is a very important step in VLSI physical design. A set of nets are routed under delay and resource constraints in multi-net global routing. In this paper a delay-driven congestion-aware global routing algorithm is developed, which is a heuristic based method to solve a multi-objective NP-hard optimization problem. The proposed delay-driven Steiner tree construction method is of O(n(2) log n) complexity, where n is the number of terminal points and it provides n-approximation solution of the critical time minimization problem for a certain class of grid graphs. The existing timing-driven method (Hu and Sapatnekar, 2002) has a complexity O(n(4)) and is implemented on nets with small number of sinks. Next we propose a FPTAS Gradient algorithm for minimizing the total overflow. This is a concurrent approach considering all the nets simultaneously contrary to the existing approaches of sequential rip-up and reroute. The algorithms are implemented on ISPD98 derived benchmarks and the drastic reduction of overflow is observed. (C) 2014 Elsevier Inc. All rights reserved

Delay-sensitive flooding based on expected path quality in low duty-cycled wireless sensor networks

Flooding in low duty-cycled wireless sensor networks suffers from a large transmission delay because a sender has to wait until a receiver becomes active to forward a packet. With the presence of unreliable radio links, the delay performance is even more severely degraded. In this article, we aim to reduce the flooding delay in low duty-cycled wireless sensor networks in relation to link unreliability. The key idea is to build a delay-sensitive flooding tree in which a node receives packet through the shortest path in terms of the total expected number of transmissions. In addition, the algorithm allows multiple senders to send through links outside of the tree if they can provide earlier expected delivery time. To give priorities to potential senders, we employ an energy-balancing mechanism which dynamically distributes the sending role among them. The mechanism not only makes sure senders start to acquire the channel at different times to prevent collisions but also lets them alternatively take turns based on residual energy, in order to lengthen network lifetime. Compared with the best known schemes, the proposed algorithm achieves up to 8% improvement in terms of flooding delay, energy consumption, and network lifetime

Diffusion multiple par des cibles élastiques immergées (propagation d'ondes cohérentes et interactions résonantes)

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