Light emitting diode designs and modulation schemes for dual illumination and visible light communication applications

Muralidharan, Sruthi
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Dutta, Partha S.
Karlicek, Robert F.
Connor, Kenneth A.
Wetzel, Christian
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Electrical engineering
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The 3 dB optical bandwidth in the range of 30-35 MHz has been observed using the blue emission from the GaInN HC and HV LEDs without the phosphor contribution. The bandwidths of these LEDs were also estimated from the measured values of series resistance and diode capacitance. The parasitic resistances and capacitances from the LED driver circuit, LED package in conjunction with the series resistance and junction capacitance of the LED result in an order of magnitude reduction in the bandwidth from the expected bandwidth of the LED alone. The design considerations of driver circuits for power conversion and high-speed switching make the HV LED configuration preferable for the dual-usage paradigm. To increase the aggregate bandwidth of visible light communication (VLC) systems in the 100 Mbps-multi-Gbps range, a coded inverse multiplexing architecture has been developed. The new scheme uses multiple channels of same frequency and different duty cycles with On-Off Keying (OOK). This system has been shown to deliver bandwidths as high as 50 MHz. It is capable of bandwidth up to 400 MHz using existing commercial LEDs and drivers with reduced circuit parasitics. Coded inverse multiplexing can also be deployed with color tunable red-green-blue-yellow (RGBY) light fixtures for a multi-channel VLC network. This scheme when implemented using Red-Green-Blue (RGB) LEDs for general lighting had minimal impact on correlated color temperature (~ 35 K) for communication at modulation rates ~ 50 MHz. Since this scheme is a multiple input, single output (MISO) scheme, compact receivers can be used and the scaling up of bandwidth can be done by adding more LED channels to the transmitter.
December 2013
School of Engineering
Dept. of Electrical, Computer, and Systems Engineering
Rensselaer Polytechnic Institute, Troy, NY
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