Node Activation Based on Link Distance (NA-BOLD) for Geographic Transmissions in Fading Channels

We consider a collection of battery-operated, low-power sensors randomly deployed within a geographic region for the purpose of sensing/monitoring the environment. In such a scenario, it is desirable to allow nodes to sleep (power off) whenever possible to conserve energy and increase the lifetime of the network. However, when the channel is subject to random variations, such as fading, there is an inherent trade-off between node activation and diversity. We consider a scenario in which a fixed number of nodes are allowed to turn on around a transmitter and the goal is to maximize the expected value of the distance that the message travels from the transmitter to the farthest receiver. We investigate the design of an algorithm to probabilistically determine whether a node should turn on based on its distance from the transmitter. This turns out to be a difficult probabilistic problem. We transform this problem into an analytical problem that provides a sub-optimal solution to the probabilistic problem. We compare the performance of this approach to a simpler protocol that turns on all the nodes within some radius of the transmitter. The results show that the link-distance based activation protocol provides significant gains in maximizing the expected value of the transmission distance to the farthest receiver, compared to the simpler protocol.