When underwater acoustic nodes should sleep with one eye open: idle-time power management in underwater sensor networks

Abstract

The current interest in underwater sensor networks stems from the potential to use long term sensing devices to monitor the large mass of oceans on the planet (e.g., underwater seismic event monitoring or underwater oil rig monitoring). To accomplish this, the sensor nodes must have the ability to self-configure the communication network and provide energy-efficient data transmission. To this end, researchers have begun devising MAC-layer protocols that minimize energy consumption for data transmission. Acoustic modems typically present a number of modes of operation, similar to radio interfaces (e.g., transmit, receive, sleep, etc.), each of which consumes different levels of energy. In radio communications, the cost of keeping the interfaces idle is high; therefore, a number of idle-time power management solutions have been devised (e.g., GAF [1], STEM [2], TITAN [3]) to conserve energy during times of no communication. It is natural to attempt to use these same methods for energy conservation in underwater sensor networks. However, there are significant differences between acoustic modems and radios transceivers, making it doubtful whether previous conclusions will be valid for the underwater environment. The relative costs of various interface modes are significantly different for acoustic devices than for radios. Typical radio interfaces [4] have similar costs for transmitting, receiving and idling. On the other hand, acoustic modems have very high transmission costs with respect to receive costs, and have very low idle costs.