LED CHARACTERISTICS
Over the past few years, growing insights have
been gained into the efficient implementation of
VLC data transmission using LEDs initiallydeveloped for illumination purposes. In general,
there are two main types of white-light LEDs
commonly used for lighting: phosphorescent and
multi-color (RGB). The phosphorescent type
consists of a blue LED chip plus a yellow phosphor
layer. The multi-color type, in contrast,
consists of three (or in some cases four) individual
chips, mostly red, green and blue (hence
RGB). While the phosphorescent type allows for
cost-efficient installations, mainly because of its
simpler driver design, it provides only narrow
modulation bandwidth, given the slow response
time of the phosphorescent material. However,
we were able to demonstrate that the bandwidth
can be enhanced by an order of magnitude of
about 20 MHz by suppressing the phosphorescent
portion of the optical spectrum with the aid
of a blue filter at the receiver end [6]. In contrast,
white-light RGB-type LEDs enable three
individual color channels, each providing approximately
15 MHz bandwidth. By using three
drivers in parallel, wavelength-division multiplexing
(WDM) can be realized. However, the
advantage of an increased aggregate data rate is
achieved at the expense of higher costs.
LED CHARACTERISTICS
Over the past few years, growing insights have
been gained into the efficient implementation of
VLC data transmission using LEDs initiallydeveloped for illumination purposes. In general,
there are two main types of white-light LEDs
commonly used for lighting: phosphorescent and
multi-color (RGB). The phosphorescent type
consists of a blue LED chip plus a yellow phosphor
layer. The multi-color type, in contrast,
consists of three (or in some cases four) individual
chips, mostly red, green and blue (hence
RGB). While the phosphorescent type allows for
cost-efficient installations, mainly because of its
simpler driver design, it provides only narrow
modulation bandwidth, given the slow response
time of the phosphorescent material. However,
we were able to demonstrate that the bandwidth
can be enhanced by an order of magnitude of
about 20 MHz by suppressing the phosphorescent
portion of the optical spectrum with the aid
of a blue filter at the receiver end [6]. In contrast,
white-light RGB-type LEDs enable three
individual color channels, each providing approximately
15 MHz bandwidth. By using three
drivers in parallel, wavelength-division multiplexing
(WDM) can be realized. However, the
advantage of an increased aggregate data rate is
achieved at the expense of higher costs.
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