The increasing demand for long-lived mobile computing devices has brought power conservation to the forefront of research. Techniques for optimizing the energy consumption of every component of a mobile device have been shown to produce dramatic improvements in device lifetime. Improving lifetime is particularly important for mobile ad hoc and sensor networks where devices are expected to be deployed for long periods of time without the potential for recharging their batteries. Various application-level techniques can be used to reduce the amount of data to send, and so the amount of energy consumed to send that data. However, once the application decides to send some data, it is up to the ad hoc network to try to deliver it in an energy-efficient manner. To support energy-efficient communication, it is necessary to consider energy consumption at multiple layers in the network protocol stack. At the network layer, intelligent routing protocols can minimize overhead and ensure the use of minimum energy routes. At the medium access control (MAC) layer, techniques can be used to reduce the energy consumed during data transmission and reception. Additionally, an intelligent MAC protocol can turn off the wireless communication device when the node is idle. While many of these techniques have been studied in isolation, any change to communication at one of the layers impacts the other and so may impact energy consumption and communication quality. The design and development of the Pulsar framework provides a hierarchical approach to energy conservation that focuses on the interrelationships between layers.
The hierarchical design of Pulsar focuses on node, routing and global adaptations to achieve energy-efficient communication. At the node layer, power control (i.e., dynamically changing transmission power levels) reduces the energy consumption of data transmissions. Additionally, power management (i.e., placing the device in a low-power sleep mode) reduces the energy consumed unnecessarily during idle periods in communication. At the routing layer, energy consumption is reduced by finding minimum energy routes, maximizing the number of nodes in low-power mode and reducing the overhead of the routing protocol. At the global layer, Pulsar uses topology control to reduce transmission energy consumption and alleviate contention in the network. Given the cooperative nature of communication in ad hoc networks, energy conservation at one node may impact communication in the entire network. Additionally, greedy energy conservation at individual nodes may increase total energy consumption across all nodes. These issues make it challenging to support energy-efficient communication without a comprehensive understanding of the interrelationships between the various energy-conserving techniques. The goal of our research is to capture these relationships in the adaptations of Pulsar, through the following architecture: