In recent years, there is an increased interest in the applications of underwater acoustic networks (UANs). Currently, floating nodes are used to interface the UAN through radio links to non-sea-based units and to correlate the position of underwater nodes to a global coordinate system. However, such an approach could be impractical for extended missions, ineffective for rapid response scenarios, and/or undesirable for covert operations. Moreover, little attention has been paid to mitigating frequent breaks in UAN connectivity due to node drifts and time varying property of the underwater environment. To address these issues, this research project promotes the development of innovative communication mechanisms for interfacing UANs directly to an aerial mobile unit (AMU) without the need of floating nodes. The outcome can boost the effectiveness of many civil and scientific applications of a national and international interest. Examples of these applications include search-and-rescue, coastal patrol, oceanographic data collection, environmental monitoring, assisted navigation, and security surveillance. Furthermore, the project will enrich the undergraduate and graduate curricula in computer networks, wireless communication, sensor networks, lasers, and embedded and distributed systems. Outreach to local community colleges and high schools is planned in order to publicize underwater researches and recruit students to STEM education. UMBC's the Meyerhoff Scholarship, and CWIT (Center for Women & Info. Tech.) programs will be exploited to actively recruit female and minority students.
The project opts to develop a suite of protocols enabling direct two-way communication between UANs and AMUs. These protocols are then leveraged to extend the global coordinate system in the underwater environment to aid in localization and topology management. The specific technical contributions are: (1) Develop protocols for reliable bidirectional communication between the UAN and an AMU. The optoacoustic effect will be utilized to create a downlink where encoded underwater acoustic signals are generated by directing airborne laser beams to the water surface. The uplink, on the other hand, is established by means of a laser Doppler vibrometer that will detect impinging and protrusion caused by an incident acoustic transmission from an underwater node onto the water surface; (2) Devise encoding and modulation schemes to suit transmission across the air-water interface. Fundamental limitations in terms of underwater reach, effective channel capacity, bit error rate, etc., will be studied; (3) Develop a network discovery and localization protocol that leverages communication with the AMU to enable the establishment of underwater global coordinate system. This is accomplished by utilizing the aerial vehicle in making encoded optoacoustic transmissions to generate reference points on the water surface linked to a terrestrial global coordinate system, e.g. GPS; (4) Develop topology management protocols that utilizes the AMUs in mitigating node drifts and re-establishing broken acoustic links with a node or an isolated block of nodes. Validation is planned through test-beds and field experiments.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
