Application of Low Cost Optical Communication Systems to Underwater Acoustic Networks

Acoustic communications are the dominant method for underwater information transmission in underwater environments where radio is heavily absorbed underwater. Due to the vast discrepancy in propagation delay between acoustic and optical communication, short range low cost optical systems have the potential to compliment the capabilities of underwater acoustic networks.In this paper we evaluate several applications in which ultralow cost, short range optical transmitter-receiver pairs can be applied to improve the performance and utility of underwater acoustic sensor networks. Applications evaluated include time synchronization between nodes and TCP communication.Next, Broadcast MAC, a prototypical media access control protocol which performs well underwater is simulated in Aquasim. Results of this simulation show that schemes which focus on using optical links to reduce the total amount of data sent over the acoustic network are more worthwhile those which focus on reducing the overhead associated with adding additional nodes.Finally a prototype, low cost IR transmitter/receiver pair is constructed from parts which can be purchased for a few dollars. A parts list, circuit diagram, and details on setting up the linux time synchronization server and establishing a TCP/IP link over the serial connection are included. While a blue-green LED would have provided much greater range underwater ( 100 ft vs 1 ft), the inherent simplicity of this device should help to save a great deal of time in the implementation of other more advanced underwater optical communication systems.