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High Data Rate Acoustic Communication


OBJECTIVE: To develop an acoustic modem for sending information through ocean acoustic channels at extremely high bit rates (~ 500 Kbps) over ranges from 10 to 100 meters. DESCRIPTION: The key to many off board sensing designs is communication at high data rates with Low Probability of Detection and Low Probability of Interception (LPD/LPI) at relevant ranges. At longer ranges this is very challenging, but as the range requirements are reduced below 100 meters, much higher frequencies and much wider bandwidths are made available. Imaging sonars take advantage of this bandwidth to capture high quality images at ranges up to 80 meters. An Ultra high frequency (.5-1 MHz) modem has only to deal with a one way transmission and will be expected to meet if not exceed the range and information rate of the imaging sonars at similar frequencies. The proposed effort will require the development of sampling and processing hardware and systems that operate at more than order of magnitude higher rates than are found in common commercial practice. Innovative concepts will be required to meet the challenges, particularly in the areas of size, weight and power requirements. System performance will mirror optics in some aspects; mainly that high attenuation limits the useful range, but also the ultimate detectable range. PHASE I: Develop initial concept design and perform an analysis of the expected performance of a modem including the details of the carrier, modulation, and information coding strategy that will support bit rates in excess of 500 Kbps over ranges from 10 to 100 meters. Analysis should include a Low Probability of Detection and Low Probability of Interception (LPD/LPI) performance characterization with estimates of detection probability as a function of range and other considerations. PHASE II: Develop a prototype acoustic modem system and demonstrate capacity and other performance metrics using actual transmissions of acoustic data. Analysis should include both communication capacity and LPD/LPI performance characterization as a function of range and other considerations. Develop a production design, including size, weight, power, and costs estimates, as well as complete system performance predictions and evaluations to include capacity estimates under a variety of environmental conditions and ranges. PHASE III: Transition a successfully tested and functioning point to point communication system on components of the ONR Advanced Undersea Warfare System FNC and demonstrate sharing of both raw and processed information at short ranges. Determine the capabilities and limitations, and obtain end user feedback which can be used to improve the system under a spiral development strategy. SECRET clearance may be required for Phase III. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Direct system application of the modems will likely include users of UUVs in marine construction and oil/gas production, but the concepts developed may be leveraged to enhance other technologies that rely on sound propagation in the ocean for sensing and navigation. REFERENCES: 1."Unmanned Undersea Vehicles Master Plan,"2004. data/technology/uuvmp.pdf 2. D. B. Kilfoyle and A. B. Baggeroer,"The state of the art in underwater acoustic telemetry,"IEEE J. Oceanic Eng., vol. 25, pp. 4-27, 2000. 3. M. Stojanovic, Josko A. Catipovic, and John G. Proakis,"Phase-coherent digital communications for underwater acoustic channels,"IEEE Journal of Oceanic Engineering, vol. 19, pp. 100-111, 1994.
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