An Energy Balanced Dynamic Topology Control Algorithm for Improved Network Lifetime

In wireless sensor networks, a few sensor nodes end up being vulnerable to potentially rapid depletion of the battery reserves due to either their central location or just the traffic patterns generated by the application. Traditional energy management strategies, such as those which use topology control algorithms, reduce the energy consumed at each node to the minimum necessary. In this paper, we use a different approach that balances the energy consumption at each of the nodes, thus increasing the functional lifetime of the network. We propose a new distributed dynamic topology control algorithm called Energy Balanced Topology Control (EBTC) which considers the actual energy consumed for each transmission and reception to achieve the goal of an increased functional lifetime. We analyze the algorithm's computational and communication complexity and show that it is equivalent or lower in complexity to other dynamic topology control algorithms. Using an empirical model of energy consumption, we show that the EBTC algorithm increases the lifetime of a wireless sensor network by over 40% compared to the best of previously known algorithms

Degree-sequenced matching algorithms for input-queued switches

Telecommunication Systems, 34(1-2): pp. 37-49.This paper presents a class of algorithms for scheduling packets in input-queued switches. As opposed to previously known algorithms that focus only on achieving high throughput, these algorithms seek to achieve low average delay without compromising the throughput achieved. Packet scheduling in input-queued switches based on the virtual-output-queued architecture is a bipartite graph matching problem wherein ports are represented by vertices and the traffic flows by the edges. The set of matched edges determine the packets that are to be transferred from the input ports to the output ports. Current matching algorithms implicitly prioritize high-degree vertices, i.e., ports with a large number of flows, causing longer delays at ports with a smaller number of flows. Motivated by this observation, we present three matching algorithms based on explicitly prioritizing low-degree vertices and the edges through them. Using both real gateway traffic traces as well as synthetically generated traffic, we present simulation results showing that this class of algorithms achieves a low average delay as compared to other scheduling algorithms of equivalent complexity while still achieving similar throughput. We also show that these algorithms determine the maximum size matching in almost all cases

A new protocol to mitigate the unheard RTS/CTS problem in networks with switched beam antennas

Paper presented at the 2007 2nd International Symposium on Wireless Pervasive Computing, San Juan, PR, US.Wireless networks with the capability for directional transmissions using switched beam antennas have increasingly been used to increase the coverage area of nodes as well as to improve spatial reuse. This paper is concerned with the unheard RTS/CTS problem that arises due to the use of directional transmissions. The problem occurs because a node, while beamformed in one direction, cannot hear the RTS/CTS messages that arrive on another direction with information pertaining to channel reservation. A node, therefore, transmits when it should defer, leading to unnecessary collisions and degraded performance. In this paper, we propose a new MAC protocol that uses a combination of three features to combat the problem: fragmentation of packets, the use of a tone signal to alert potential collision-causing nodes during ongoing transmission, and the use of a pause period when transmission is likely to lead to a collision. As opposed to other recent work on this problem, our protocol does not assume separate data and control channels. We present simulation results showing that our protocol can reduce the number of retransmissions of data packets due to the unheard RTS/CTS problem by as much as 86%, thus improving the delay and throughput characteristics of the network