On the deployment of a hybrid free-space optic/radio frequency (FSO/RF) mobile ad-hoc network

The hybrid free-space optics/radio frequency (FSO/RF) network paradigm promises new levels of throughput for sensor and mobile ad-hoc networks. However, several challenges must be addressed before such a network model can be realized. These include a means by which deployed robots can autonomously establish optical links over sufficiently long distances as well as the formulation of a mobile network architecture that can exploit high throughput FSO channels. In this paper, we offer solutions to these problems in the form of hierarchical link acquisition and routing protocols. The heart of our link acquisition system (LAS) is a vision-based alignment phase for locating robot link partners via high zoom camera systems. Identification is accomplished in real-time using a multi-resolution image representation and normalized intensity distribution (NID) as a similarity metric. Our routing protocol relies upon the hierarchical state routing (HSR) model adapted to the FSO/RF paradigm. Experimental results from a large set of link acquisition trials as well as a small scale FSO/RF deployment are provided to support our approach.