Optical wireless sensor network in multi-scattering channel: Laboratory experiment

Networked sensors are an emerging technology with the purpose of gathering data, profiled in time and space, for monitoring and surveillance in medical, environmental, home security and other applications. Typically, a large number of miniature sensing and communicating nodes are distributed ad hoc at the location of interest, where they establish a network and wirelessly communicate sensed data to one another, or to a base station. The optical modality is a potential solution for the links, due to the small and lightweight hardware and low power consumption, despite the drawback of alignment limitations. We propose an experimental concept to investigate the multi user interference effects arising when a number of nodes operate in a multi-scattering environment simultaneously. The laboratory experiment simulates a single internode link and the multi-scattering environment is modeled by a fog chamber. Linear and angular perturbations of transmitter-receiver line-of-sight (LOS) simulate geometries wherein multiply scattered light from the transmitted beam may interfere with the desired signal at the receiver causing multi-access interference. The potential multi-access interference is evaluated at differing optical densities and wavelengths. Conversely, the possibility for communication in the absence of LOS is inferred. Lastly, interference due to side-scattering from a link in the proximity of a receiver is modeled and assessed. In conclusion, guidelines are outlined for future experimental validation.