Free space optical sensor networking for underwater sensing applications

Free space optical (FSO) links for sensor networks can provide data rates that can range from bits/s to hundreds of Mb/s. In addition, FSO links using blue-green lasers or light emitting diodes can provide underwater communication over distances of tens of meters. Compared to acoustic technology, optical communication provides larger bandwidths, faster propagation speeds, and reduced multipath fading effects. These features make FSO an attractive medium for undersea communications, as compared to present day acoustic technology. In this paper the system design, implementation, and evaluation of a prototype FSO sensor network are presented. The system includes a network of small, low power (mW), integrated systems, or ¿motes,¿ that transmit data optically to a central ¿cluster head,¿ which controls the network traffic of all the motes and can relay data to another cluster head in a series of multi-hops to achieve data communication over longer distances. The devices are designed with multiple narrow-beam transmitters oriented in different directions to provide signal coverage over a wide field of view. This paper presents the system design and media access controls of our prototype FSO-based sensor network that can be tailored to fit underwater sensor networking applications.