Indoor high-bandwidth optical wireless links for sensor networks

Emergence of sensor networks for data-procurement in wide-ranging applications, including defense, medical, environmental and structural health monitoring, has led to development of low-power miniature devices employing radio frequency (RF) communications. In contrast to RF, optical devices are smaller and consume less power; reflection, diffraction, and scattering from aerosols help distribute signal over large areas; and optical wireless provides freedom from interference and eavesdropping within an opaque enclosure. Optics can accommodate high-bandwidth transmission of multimedia in aircrafts, where RF is shunned due to interference with control signals. These motivate use of optical wireless as a mode of communication in sensor networks. We have set up and experimented on an infrared laser transceiver test-bed with ceiling used as reflector to establish an intensity-modulated/direct-detected (IM/DD) link. Frequency measurements are conducted to characterize the link up to 1 GHz, and are transformed to obtain impulse responses and eye diagrams. These experimental findings demonstrate the capability of indoor optical wireless links of delivering 1 gigabit per second and beyond, without intersymbol interference. Thus, a broadband infrastructure can be deployed allowing high-quality audio-visual data communication among sensor nodes.