Intellectual Merit: The objective of this research is to design a quickly deployable, reliable communication infrastructure for reestablishing communication following a disaster. Such a disaster area wireless network (DAWN) would provide much needed communication for coordinating relief and recovery efforts until normal communication channels can be reestablished. The DAWN infrastructure is based on network nodes deployed on balloons that are tethered to the ground. Each node utilizes free-space optical (FSO) and radio frequency (RF) links to construct a hybrid network between balloons and between balloons and the ground. To realize such a system, this research investigates: (i) viable mechanisms for physical layer connectivity between balloons using FSO links that consider link acquisition and maintenance; (ii) receiver access control (RAC) protocols to allow sharing of receivers among multiple FSO nodes; (iii) routing algorithms and methods for topology design to realize a self-configuring FSO ring topology with an RF link for inter-nodal communications and backup capacity when the FSO links are unavailable; (iv) aggregation of multiple wireless local area network signals into a single FSO signal and extraction of signals for transmission to ground; (v) techniques to balance power and weight to increase battery life and meet balloon payload requirements; and (vi) methods to provide ample coverage of ground-based nodes and reliable connectivity to existing terrestrial networks. A combination of experimental research and theoretical modeling will be utilized.
Broader Impacts: If successful, this research will lead to methods to realize rapidly deployable, cost-effective communication systems that facilitate coordination between law enforcement and public safety agencies responding to natural and manmade disasters. Additional applications include airborne internet access and battlefield communications. Experiments are planned for adoption in two ongoing engineering and science summer academies for middle and high school students and teachers. The investigators will engage undergraduates in research and will leverage existing relationships to recruit undergraduates from underrepresented groups to participate.
Project Outcomes and Findings Report - An innovative design for optical transmitter and receiver (bug eyes) has been developed. Fiber bundles, instead of a traditional single fiber, are carefully placed offthe focal length of a single lens. Unlike conventional technology that uses gimbals and fast steering mirrors, the newly introduced technique activating fibers at the transmitter to control beam steering atan optical speed. At the receiver each fiber is attached to a micro lens and judiciously placed to enhance receiver field of view. An optical combiner is then used to conjoin optical signals from all fibers and effectively increase received power. The novelbug eye design enhances any optical system towardrapidly establishing and consistently maintaining optical communication in mobile platforms exposed to limited vibration. Deployment on unmanned aerial vehicles could prove valuable. - A newly developed optical medium access control protocol allows multiple optical transmitters to share the medium with a single receiver. RTS/CTS are utilized for reservation and data frames to facilitate information packet transfer. When compared to the current infrared data association (IrDA) standard and its advanced version (AIr), the new protocol offers simplified medium sharing and enhanced network throughput. In fact, throughput increases from 50% to 90%. - This project investigated a simple, inexpensive, yet effective propelling system (hardware and software)to stabilize an aerial platform attached to a tethered,helium-filled balloon. Balloon directionality was maintained for optical communication 45% percent of the time at winds up to 10mph, When using an FSO system with optical data rates, this figure translates to i.e. a 500Mbps communication link. - A multipath routing protocol was developed to enable packet transfer in a networkcharacterized with hybrid free-space optics(FSO)/radio frequency (RF) nodes. Inhomogeneity of technologies is exploited by the new protocol to optimize connectivity wherein optical communication is maintained at high data rates. In the event that one or more optical links are severed, the protocol will adjust its tables and transfer information packets over RF links to sustain network connectivity. - A testbed was constructed to facilitate testing and evaluation of the newly introduced medium access control and routing protocols. Experimental results are evaluated against analytical and numerical assessments. - In addition to the hardware and software achievements, the project had several broader ranging impacts. A total of 28 scholarly articles were produced, including 2 articles in scientific journals and 26 articles presented and published at technical conferences. A total of 15 students were trained in scientific disciplines related to the project, including 3 doctoral students (1 graduated), 5 masters students (5 degrees granted), and 7 undergraduate students, three of which were supported through supplemental REU grants. Of these students, over 50% were from under-represented groups, with an especially large participation (six) from female students. Aspects of the program were modified to support activities within a summer academy for students in grades 8 through 11. While the project emphasis was on rapidly deployable communications systems for disaster recovery, the physical and software products developed are readily adaptable to a number of civilian and military applications, including airborne internet, the next generation air control system under development, and battlefield command and control systems.
