Autonomous reconfiguration in free-space optical sensor networks

This research focuses on the physical and logical control and reconfigurability of network topologies through intelligent and dynamic rearrangement of nodes in an optical wireless sensor network. We address high data rate sensor networks (e.g., infrastructure monitoring; surveillance), which consist of gigabit per second, narrow beam, free-space optical links between fixed and/or mobile nodes. In our approach, the seamless operation of such networks requires maintenance of wireless link connectivity and quality and at all times, amidst, for example, changing atmospheric, and traffic and platform conditions. This is achieved by dynamic reconfiguration through topology control. We address the problem of dynamic formulation of topologies, which contain only two transceivers per communications node or switch. The task of reconfiguration requires the formation of a biconnected graph or a ring topology. The problem is similar to the traveling salesman problem and is NP complete. We address the mixed integer programming formulation of this problem, and show that it does not scale even for a small network. We then focus on heuristics for dynamic, autonomous reconfiguration. Using simulations, we investigate tradeoff between solution quality and computational time. We also investigate the effectiveness of these dynamic reconfiguration heuristics compared to fixed, degraded topologies.

I. Introduction

Our research has focused on the physical and logical control and reconfigurability of network topologies through intelligent and dynamic rearrangement of fixed and mobile backbone nodes in high data rate, optical wireless networks. These sensor networks can be used for infrastructure monitoring and surveillance, for example, and they typically consist of gigabit per second, narrow beam, free-space optical (FSO) links. The positioning of the nodes, either as part of a base-station-oriented infrastructure or mobile platform, allows for the use of available power (the laser diodes emit 10 mW; additional electronics use a few Watts). The main challenge for such networks is the dynamic, autonomous reconfiguration both in hardware and software in order to maximize communications availability and capacity in an Internet. The provision of new topologies is in response to degradation in one or more links in the network. We refer to this overall process as topolozy control [1].