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Introduction
Underwater communication has the potential to benefit a myriad of fields. Oil companies are constantly looking to extract oil from offshore wells in deeper and deeper water. Scientists are attempting to study vast areas of water to extract information on the effects of global climate change and the health of the Earth's ecosystem. The Navy also has a vested interest for obvious tactical reasons.
The underwater environment presents numerous interesting challenges, however. The shear size of the ocean makes wired networking prohibitively expensive in most areas of interest, and the need for mobility in many applications makes wires too restrictive. The standard medium of communication in terrestrial wireless networks, RF, is inefficient and extremely limited in range underwater. Optical communications has also been found to be restricted in range and inefficient. Acoustic waves propagate well in water and are more efficient than either the RF or optical options. As such, acoustic communications are the best choice for underwater networks.
Challenges
Acoustic communications are characterized by extremely long propagation delays and large multipath interference. Frequency selective attenuation, variable sound speed, and Doppler spreading combine to result in a challenging medium. Accepted terrestrial networking technologies are not suited to the underwater environment. New models need to be developed that accurately portray the wide range of variables effecting acoustic communication, and new networking protocols must be developed from the ground up to account for the unique environment in which they will operate.
Current Projects
- MAC protocols for UAN
- UAN Simulation Module for NS 2
- Channel Modelling and Physical Layer Protocols
Common MAC protocols found in terrestrial networks do not react well to the low data rates and high propagation delays found in underwater networks. New MAC protocols must be developed that are directly designed to have low overhead, high energy efficiency, and that are robust to changing link conditions. We are currently working on developing MAC protocols that are energy efficient without degrading channel utilization.
The unique characteristics of the underwater medium often has unexpected or unintuitive results on the performance of network protocols. Accurate analysis of UAN protocols requires simulation models that accurately depict the underwater channel. The complex models that give accurate depictions, however, require computation time that make them unusable in network simulations. We hope to develop a module for NS 2 that will strike a middle ground providing reasonably accurate results in an acceptable running time.
The underwater channel exhibits characteristics which are not found in traditional terrestrial channels. These include high multipath delay and doppler sreading, acoustic propogation that is driven by the underwater sound speed profile, long propogation delays, and high attenuation. It is imperative in the design of underwater networking simulations and protocols that these limitations are captured. However, creating a simulation tool that both accurately models the underwater channel and is capable of performing in a reasonably short run-time is an ongoing area of research. At the University of Washington, we are interested in both creating accurate channel modeling tools for underwater networks and using these tools to create underwater physical layer protocols that perform with low probability of error, high data rate, and low energy.