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24 August 2010 Free space optical sensor network for short-range applications
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Free space optical (FSO) sensor networks using direct line of light (LOS) laser links can provide spatially efficient and physically secure connectivity. The data rates can range from bits/s to hundreds of Mb/s with the complete optical transceiver system consuming power in the tens of mW. These features are advantageous for low-power communication networks over short distances in environments where LOS is available, and where radio frequency connectivity must be avoided because of interference or security problems. The range of links in FSO networks is limited by power requirements and angular coverage. In order for FSO directional networks to provide viable short-range connectivity, the networks must provide signal coverage over a wide field of view and operate with efficient media access protocols to minimize random access times for the independent transmitting nodes within the network. In this paper, the system design of a FSO sensor network is presented. The system includes a network of small, low power (mW), integrated systems, or "motes," that transmit data optically to a central "cluster head," which controls the network traffic of all the motes and can relay data to another cluster head in a series of multi-hops to achieve data communication over longer distances. To provide wide field of view signal coverage, each cluster head is equipped with multiple vertical cavity surface emitting lasers oriented in different directions and controlled to diverge at 10°. To implement the proper media access controls, a properly designed master-slave network connecting multiple motes to a cluster head was developed and implemented. The network can handle multiple access from all motes within each cluster head's field of view, as well as set up a directional network backbone between multiple cluster heads, so that signals collected from a mote can be relayed through other cluster heads, until the signal is delivered to its destination. This paper presents the network architecture and optical communication system hardware of our FSO sensor network, and some experimental performance results of our multiple access protocol attempting to resolve channel contention between 10 motes and a cluster head.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Navik Agrawal, Stuart D. Milner, and Christopher C. Davis "Free space optical sensor network for short-range applications", Proc. SPIE 7814, Free-Space Laser Communications X, 78140E (24 August 2010);

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