“Our approach increases the average amount of data that can be transmitted within the network by at least 20 percent for networks with randomly placed nodes – and up to 80 percent if the nodes are positioned in clusters within the network,” says Dr. Rudra Dutta, an associate professor of computer science at NC State and co-author of a paper on the research. The approach also makes the network more energy efficient, which can extend the lifetime of the network if the nodes are battery-powered.
Computer Communications - Centrality-based power control for hot-spot mitigation in multi-hop wireless networks
Multi-hop wireless networks utilize multiple wireless nodes to provide coverage to a large area by forwarding and receiving data wirelessly between the nodes. However, these networks have “hot spots” – places in the network where multiple wireless transmissions can interfere with each other. This limits how quickly the network can transfer data, because the nodes have to take turns transmitting data at these congested points.
Data can be transmitted at low power over short distances, which limits the degree of interference with other nodes. But this approach means that the data may have to be transmitted through many nodes before reaching its final destination. Or, data can be transmitted at high power, which means the data can be sent further and more quickly – but the powerful transmission may interfere with transmissions from many other nodes.
Dutta and Ph.D. student Parth Pathak developed an approach called centrality-based power control to address the problem. Their approach uses an algorithm that instructs each node in the network on how much power to use for each transmission depending on its final destination.
The algorithm optimizes system efficiency by determining when a powerful transmission is worth the added signal disruption, and when less powerful transmissions are needed.
When shortest path routing is employed in large scale multi-hop wireless networks such as sensor networks, nodes located near the center of the network have to perform disproportionate amount of relaying for others. Nodes in such traffic hot-spots deplete their batteries faster than others due to their high relay load. These traffic hot-spots also adversely affect the network capacity due to increased congestion in the regions. To solve the problem, various divergent routing schemes are used which route the data on center-avoiding divergent routing paths. Though they achieve better load balancing, overall relaying is increased significantly due to their longer routing paths. In this paper, we propose power control as a way for balancing relay load and mitigating hot-spots in wireless sensor networks. Using a heuristic based on the concept of centrality, we show that if we increase the power levels of only the nodes which are expected to relay more packets, significant relay load balancing can be achieved even with shortest path routing. Different from divergent routing schemes, such load balancing strategy is applicable to any arbitrary topology and traffic pattern. With extensive simulations, we show that centrality based power control can drastically increase the network lifetime of sensor networks. We compare its performance with other divergent routing schemes and multiple battery level assignment strategy. Also, it is shown that centrality based power control results into better throughput capacity in many different topologies.
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