In wireless multi-hop packet radio networks (MPRNs) that employ geographic transmissions, sleep schedules or node activation techniques may be used to power off some nodes to conserve energy. We consider the problem of selecting which nodes should power on to listen to a scheduled transmission when the channel suffers from random fading. We choose the objective of maximizing the expected value of the distance covered in a single transmission between a transmitter and the farthest receiver that successfully receives the packet, under a constraint on the expected number of receivers that turn on. Since there is a tradeoff between the distance of a node from the transmitter and the probability that the node receives the message correctly, we propose to use node-activation based on link-distance (NA-BOLD). We investigate optimal and sub-optimal NA-BOLD schemes and compare their performance with that of schemes that use a constant sleep schedule for every node within some radius of the transmitter. Our results show that the proposed NA-BOLD schemes achieve significantly larger transmission distances than conventional schemes.

In mobile ad hoc networks (MANETs), conventional packet forwarding schemes that pre-select the next-hop receivers for a packet may fail if the channel coherence time is on the order of the typical packet duration because the pre-selected node may often suffer a deep fade for the duration of the packet. An alternative approach is geographic transmission, in which the packet is transmitted in the direction of the destination, but the next-hop forwarding node is selected among those nodes that are in the direction of the destination and that correctly recover the message. This approach takes advantage of multi-user diversity to significantly improve the probability of the packet being correctly received by a forwarding agent. However, this approach places additional burden on the energies of the mobile nodes if the forwarding scheme requires all of the next-hop neighbors of the transmitter (that are in the direction of the destination) attempt to receive a transmitted message. In this paper, we consider the joint design of node-activation strategies and transmission rates to maximize the expected value of transport capacity over a Nakagami-m channel under a constraint on the expected number of nodes that attempt to receive a packet. We show that our approach offers better performance than other approaches.

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.