"Smart paint" containing fluorescent and phosphorescent pigments could extend the possibilities of proposed LiFi networks, report a team led by K S Narayan at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bengaluru, India. The researchers analysed the effect of nearby luminescent surfaces on the noise characteristics of visible light communication system (VLC) signals, and found that secondary emission could limit bandwidth locally by overwhelming receivers. The residual glow from phosphors could even be modulated to transmit a signal after the primary LED source has been turned off.
LiFi uses visible and near-visible light to connect electronic devices in much the same way as now nearly ubiquitous WiFi. Like its more familiar counterpart, LiFi technology is expected to play a role in connecting devices within the incipient internet of things. Unlike microwaves, however, visible-light signals cannot pass through walls, meaning that LiFi networks are, in principle, less vulnerable to eavesdropping from outside.
It has already been established that VLCs can operate without line-of-sight contact between transmitters and receivers, since sufficiently high signal-to-noise ratios can be retained in light reflected from surfaces in the local environment. Now, Narayan and his team have investigated the situation for more complex arrangements, in which a luminescent component is superimposed on the primary signal.
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